How are distributions for tail risk measures estimated in practice?

Let's say you want to calculate a VaR for a portfolio of 1000 stocks. You're really only interested in the left tail, so do you use the whole set of returns to estimate mean, variance, skew, and shape (let's also assume a skewed generalized error distribution - SGED)? Or would you just use the left tail (let's say the bottom 10% of returns)? For some reason, using the whole set of returns seems more correct to me (by using only the left 10% or returns you'd really be approaching a non-parametric VaR). But using the whole set of returns would likely cause some distortion in the left tail in order to get a better fit elsewhere. How are the pros doing this? Thanks!

risk probability estimation value-at-risk expected-return

Perhaps you may want to consider article by D. Levine - Modeling Tail Behavior with Extreme Value Theory who gives practicale example on how EVT can be used to calculate probabilities on returns in tails with use of the Pickands-Balkema-de Haan Theorem and generalized Pareto distribution. It also contains some criterias and points on other methods that can be used to determine threshold value for PBH theorem: Contrary to this notion is the fact that the PBH theorem states a result based on the assumption of threshold values approaching the right endpoint of the distribution F. This implies that better...

Great question. We would expect 3rd party risk providers to have specialized expertise (robust regression techniques, factor research, data cleansing etc.). We might grant them these advantages but still find weakness in the product design. Let's start off with the different uses of risk models and the procedure or metric which is maximized to solve for that use case. What we will see is that solving for a particular objective diminishes our ability to achieve other objectives. Portfolio construction = If you want to construct a minimum variance portfolio, for example, then the key here is developing a covariance matrix...

One starts with the Black-Scholes equation $$\frac{\partial C}{\partial t}+\frac{1}{2}\sigma^2S^2\frac{\partial^2 C}{\partial S^2}+ rS\frac{\partial C}{\partial S}-rC=0,\qquad\qquad\qquad\qquad\qquad(1)$$ supplemented with the terminal and boundary conditions (in the case of a European call) $$C(S,T)=\max(S-K,0),\qquad\qquad\qquad\qquad\qquad\qquad\qquad\qquad(2)$$ $$C(0,t)=0,\qquad C(S,t)\sim S\ \mbox{ as } S\to\infty.\qquad\qquad\qquad\qquad\qquad\qquad$$ The option value $C(S,t)$ is defined over the domain $0 Step 1. The equation can be rewritten in the equivalent form $$\frac{\partial C}{\partial t}+\frac{1}{2}\sigma^2\left(S\frac{\partial }{\partial S}\right)^2C+\left(r-\frac{1}{2}\sigma^2\right)S\frac{\partial C}{\partial S}-rC=0.$$ The change of independent variables $$S=e^y,\qquad t=T-\tau$$ results in $$S\frac{\partial }{\partial S}\to\frac{\partial}{\partial y},\qquad \frac{\partial}{\partial t}\to - \frac{\partial}{\partial \tau},$$ so one gets the constant coefficient equation $$\frac{\partial C}{\partial \tau}-\frac{1}{2}\sigma^2\frac{\partial^2 C}{\partial y^2}-\left(r-\frac{1}{2}\sigma^2\right)\frac{\partial C}{\partial y}+rC=0.\qquad\qquad\qquad(3)$$ Step 2. If we...

Nick Higham's specialty is algorithms to find the nearest correlation matrix. His older work involved increased performance (in order-of-convergence terms) of techniques that successively projected a nearly-positive-semi-definite matrix onto the positive semidefinite space. Perhaps even more interesting, from the practitioner point of view, is his extension to the case of correlation matrices with factor model structures. The best place to look for this work is probably the PhD thesis paper by his doctoral student Ruediger Borsdorf. Higham's blog entry covers his work up to 2013 pretty well.


How come the nude protesters were not arrested?

I read today about the Anti-Censorship Activists in New York (Warning! NSFW pictures inside link) who protested against Facebook while being totally nude out in the street. I'm also pretty sure public nudity is not allowed in the USA. How come they were not arrested or at least warned by police? Is there some exception to the law?

Public nudity is illegal in New York as it is in almost every U.S. jurisdiction. And, if the police had arrested the nude protesters, the arrests probably would have been upheld in court, because a ban on nudity in public would probably be viewed as a time, place and manner restriction on the freedom of speech which is constitutionally valid. For example, the Ninth U.S. Circuit Court of Appeals recently upheld San Francisco’s public nudity ordinance in Taub v. City and County of San Francisco (2017). As the court in that case explains in a factually very similar case: Public...

No Parliament is sovereign : Parliamentary sovereignty is a principle of the UK constitution. It makes Parliament the supreme legal authority in the UK, which can create or end any law. Generally, the courts cannot overrule its legislation and no Parliament can pass laws that future Parliaments cannot change . Parliamentary sovereignty is the most important part of the UK constitution.

A "land contract" is not a way of renting property, it is a way of purchasing property on an installment basis without bank financing. It is Ohio's version of what in some other places is known as "contract for deed". See "What is a Land Contract in Ohio" and "How Land Contracts Work" The actual law is Section 5313 . In a land contract, the buyer has equitable but not legal title. The buyer normally pays all taxes and fees, and is responsible for maintaining the property, just as if s/he has bought the property. But if the buyer defaults,...

An essential component of your contract with them is that they will provide you with food free of animal stuff (the exact nature of "vegan approved" may be up for debate, but actual meat should not be included). So they breached their contract with you, and you might sue them for breach of contract. The case of Gupta v. Asha (orders were mixed up) could be useful in this matter. In this case, Hindus were served samosas containing beef, despite repeated assertions that they were vegetarian. Plaintiffs sued, the case was dismissed, and the appeals court deemed that the lower...


I have assembled a small DIY drip-irrigation system for my terrace garden. Please have a look at the attached image. I switch on a small pump to start the drip-irrigation system and then switch it off. But even after that, the water keeps flowing through the system and stops only when I physically lift the pump out of water. How can I stop this water flow without requiring any physical action? Please note that I plan to automate the switch-on/off of the pump using a timer so that it functions without requiring my physical presence. ======================================================================== I tried the suggestion of "Making a pinhole in the highest point of the pipe." It worked like a charm and solved the issue I was facing. Completely loved it, more so, because it does not involve procuring new stuff. I also like the option of using a solenoid-valve, but have not tried it yet. Will use it when I install such a system again where the tank is at a considerably higher place than the plants. Thank you everyone who took the effort to write an answer, and that too with detailed explanations.

As other have pointed out, the main utility is to allow easier cleaning of the tank cars from sediment (solid precipitates). Usually, there is a drain in the lowest point. The reason that it is in the middle is that in this way, you can allow double the incline compared to if you had the drain at one of the ends for the same height. For example, if the allowed height difference is about 15 cm, and about 15 m length, then if you had the drain in: the edge, the angle would be $\arctan\left(\frac{0.15}{15}\right)=0.57^\circ$ or 1%. the middle ,...

You want to let air into the pipe when you switch the pump off, without letting water out. Here's a few ways to do this. Make a pinhole in the highest point of the pipe. You will lose a bit of water this way, but if it is above the tank, the water will drip back in (provided it doesn't spray too far.) You could even put it just under the tank lid. Install a tee and riser at the highest point of the pipe. this will need to be high enough to avoid the pump pressure pumping water out...

Electricity production optimization is a very complex subject. It is also affected by many parameters , which I will try to outline below. TL;DR: Demand is constantly monitored and supply is constantly adjusted TL;DR 2: Lshaver's excellent post is a suggested reading after reading this, because it expands and explains what happens at timescales ranging from the micro-second to minutes timescales. Changes in energy demand during the day First of all, the energy demand during the day, week, month of year can change quite a lot. Below is a typical day in New England. Fluctuation in power energy consumption a...

I will expand on DKNguyen answer, because to my knowledge also the two reasons are: reduce contact/bearing stresses (having a significant effect on thin finishes live galvanisation) change the joint tightening characteristics (see joint diagram). reduce contact stresses on surfaces. The basic idea is that since contact stress is defined as: $$\sigma = \frac{F}{A}$$ Obviously the larger the area the less the stress. Also, like Nuclear Hoagie pointed out the area changes with a square law of the diameter. UPDATE 2 - Calculation for M6 bolt (thanks to BenC) *The question gathered enough interest for me to carry out a...


I've googled through internet, and all I found was "what expiration dates mean". I found nothing about the underlying mechanism of expiration. As drugs are chemicals, why do they expire? Are there chemical reactions that produce other chemicals?

Drug molecules, even when stored safely inside a tablet\capsule, inside a closed container, upon a high shelf (hopefully), are still exposed to the environment, and are thus exposed to all of the chemical processes and reactions that go about all around us (to name just a few - oxidation, hydrolysis, isomerization, polymerization, and more). Depending on the type of drug molecule and its functional groups, the molecule may undergo all kinds of chemical processes that may change its structure and\or properties. Therefore, drugs (and foodstuffs, as mentioned in the comment above) degrade and decompose over time, and are thus given...

In the blister shown, the likelihood of rupture is decreased because of the thickness of the epidermis on the palm of the hand, so you can leave it alone until the underlying area re-epithelializes. You'll know this is happening because of the decreased pain and the slow reabsorption of the fluid. Eventually you will just peal it off what's left of the blister, finding clean new skin underneath. But this is a great starting point for an answer about the treatment of blisters in general: is it better to leave them alone, drain the fluid, or de-roof them (take the...

In general, the benefit of flu shots is to the general population. Taking the cited value of 40%-60% from the CDC, we can say that it might be a coin toss for you personally to be protected from influenza by the shot. However, if many thousands of people take the flu shot, even if it only works on 40% of them, it helps protect the remaining population from the spread of the virus (AKA herd immunity). This is especially important to those within the population who cannot access the shot or cannot receive it due to a preexisting medical condition....

Your question contains a lot of misconceptions. A cure is definitely possible A cure could be found, proved, and proved safe, more quickly than a vaccine People and firms that could be working on cures are choosing to work on vaccines None of these are correct. Most virus-caused diseases have no cure: colds, Zika, Dengue, and so on. A tiny handful have treatments that can ease the course of the disease: you've heard of Tamiflu and so on. And some can be actually cured with medication. So the first assumption, that a cure exists to be found, is not a...


Machine Learning vs Regression and/or Why still use the latter?

I come from a different field (Machine learning/AI/data science), but aim to ask a philosophical question with the utmost respect: Why do quantitative financial analysts (analysts/traders/etc.) prefer (or at least seem) traditional statistical methods (traditional = frequentist/regression/normal correlation methods/ts analysis) over newer AI/machine learning methods? I've read a million models, but it seems biased? Background: I recently joined a 1B AUM (I know it's not a ton) asset management firm. I was asked to build a new model for a sector rotation strategy (basically predicting which SP 500 sector would do the best over 6 months-- chose to use forward rolling 6 month returns) they employ and my first inclination was to combine ARIMA (traditional) with random forest (feature selection) and a categorical (based on normal distribution standard deviation) gradient boosted classifier for ETFs in each sector. Not to be rude, but I beat the ValuLine timeliness for each sector. I used the above mentioned returns as my indicator and pretty much threw everthing at the wall for predictors initially (basically just combing FRED), then used randomForest to select features. I ended up combining EMA and percent change to create a pretty solid model that, like I said, beat ValuLine. I've read a lot of literature, and I haven't seen anyone do anything like this. Any help in terms of pointing me in the right direction for literature? Or any answers to the overarching idea of why isn't there more machine learning in equity markets (forgetting social/news analysis)? EDIT: For clarification, I'm really interested in long-term predictions (I think Shiller was right) based on macro predictors. Thanks PS- I've been lurking for a while. Thanks for all the awesome questions, answers, and discussions.

In order to answer your question (for you) you would need something to compare to . You would need numbers to know if it is slower/faster, how much, and if it will impact your system overall. Also knowing your performance goals could narrow down the options. My advice is to take a look at your overall architecture of the sytem you have or intend to build. To just look at QuickFIX is rather meaningless without the whole chain involved in processing information and reacting to it . As an example, say QuickFIX is 100 times faster than some part (in...

In general there are two basic ways to make money out of your option pricing models: Sell side (market maker, risk neutral): You use these models to calculate your greeks to hedge your portfolio, so that you live on the spread. Buy side (market/risk taker): You use your model to find mispriced options in the market and buy/sell accordingly. (A third possibility would be to write fancy books and papers about these models and get rich and/or tenure this way ;-)

Because of: The (extreme) dominance of noise over signal The prevalence of non-repeating patterns (many of which we know are not going to repeat) A pathetic sample size for cross-validation Regime changes due to exogenous events. These are typically in the cross-val window which makes it even worse. (GFC, financial integration, trade law changes, interest rate adjustments by central banks, some idiot in a bank was hiding trades and loses 5 billions dollars, etc). It is well known that non-linear relationships are generally just artefacts of the in sample dataset There is also the following: Much price changes are driven...

There are some cases where you can blend your portfolios using weights directly. One case involves corner portfolios . In this case a linear combination of weights is also efficient. Another case is where you can treat the two separate weights you have produced each as distinct portfolio under the assumption that the correlation between these portfolios is relatively stable. In this scenario, the problem reduces to a two-asset portfolio optimization problem (each asset is simply the linear combination of weights produced via your two methods). The other class of methods involves blending via the expected returns. If you arrived...


What are the rules on businesses that wish to only hire attractive females?

Many businesses feature beautiful female employees as part of their business plan and service offering. Examples include: Hooter's waitresses Sportclips stylists A small chain of drive-thru smoothies in my area that feature bikini clad hotties with whom you can purchase a photo Most all entertainment jobs I am considering buying a franchise that falls into one of these categories and I just wanted to understand the legality of hiring only attractive women. Is it sexual discrimination or just a legitimate hiring practice, since offering attractive female employees is part of the business strategy? I'm in Maryland, USA in case that matters, but I'm looking for kind of a high level, general answer that might apply to anyone in the US.

There is a good answer at the Skeptics StackExchange here . Its three most relevant references are: 42 U.S.C. Chapter 21 , especially Subchapter VI (applies only to employers with fifteen or more employees every day in at least 20 calendar weeks in a year) An example case, Wilson v. Southwest Airlines Co. 517 F. Supp. 292 (N.D. Tex. 1981) Katie Manley, The BFOQ Defense: Title VII’s Concession to Gender Discrimination , 16 Duke Journal of Gender Law & Policy 169-210 (2009) Wilson v Southwest held that being attractive and female is not a Bona Fide Occupational Qualification (BFOQ) for...

There isn't any rule which would prioritize the President, as far as I can tell. Generally, organ allocation is required to be based on medical criteria, not on factors such as the occupation or societal role of the patient. 42 USC 273 specifies that organ procurement shall be administered by "qualified organ procurement organizations" and sets up ground rules for their operation, one of which is: have a system to allocate donated organs equitably among transplant patients according to established medical criteria. Further regulations implementing this law are to be found at 42 CFR 121 . 121.8(a)(1) specifies that allocation...

The Plan For A Clearly Guilty Client Without Bargaining Power This question underestimates how much of a criminal defense lawyer's work involves sentencing rather than a determination of guilt or innocence. Suppose as the OP does that the prosecution can easily prove beyond a reasonable doubt that your client is guilty, you client has no plausible defenses, and the prosecutor won't budge on a plea. As a criminal defense lawyer, you may well advise your client that there is no percentage in fighting guilt on the charges, and have your client plea guilty. This prevents the prosecutor from spelling out...

This aspect (and many others) of contract law is applicable in the US and various countries of the EU. can they renege after the candidate has begun their journey, thus saddling the candidate with the travel cost? No. The company would incur breach of contract. There is no need for a formal contract. The candidate only needs to prove that the company agreed (in writing, orally or clearly through its conduct) to cover or reimburse those expenses and that this elicited a meeting of the minds . The agreement would be void if the candidate incurred the expenses despite knowing...


If a user refuses cookies on a website, then how can that website store that refusal? As far as I can tell, the GDPR requires you to store both consent to and refusal of personal data storage. But it seems to me that there is a catch 22 here: they specifically refused the storage of their data, and now the website is supposed to store that somehow. How can you store that information in a compliant way? My initial thought is to use a cookie, but would that be non-compliant? They did just refuse the storage of cookies on their device... And if I store it in a database somewhere, how am I supposed to associate that refusal with that user if I can't store personal information? According to the accepted answer to this question , you can use a userId or some such. But first of all that is in the context of consenting, not refusing, to cookies; secondly, if that identifier is associated with a user, then by definition it is personal data (right?) and therefore storing that information would be non-compliant. Regarding the storage of consent, is it enough to store that in a cookie on the user's device or do you really need to store it in a database somewhere? That really seems superfluous to me.

privacy gdpr european-union data-protection

Trump was an officer of the government, and Twitter wasn't. The First Amendment forbids the government and its agents from viewpoint discrimination, but private companies are not bound by it and can discriminate as much as they please. (There was a question as to whether such discrimination might affect whether the company enjoys a shield from liability under 47 USC 230 , but even so they have the right to block and censor as they wish if they are willing to risk that liability.)

What is the legality of someone putting a virtual hot spot on your property without permission? I know we are in uncharted territory but how would this compare to setting up a contest that would require going on your property without permission? The existence of a game does not authorise entrance to private property, barring some agreement with the owner. That is - if it is trespassing without Pokemon Go (or, for that matter Ingress), then it is trespassing while playing them. That being said, the creators of the game are free to place their in-game targets anywhere they please,...

Short Answer Applicants are required by military regulation to have a percentile score on a standardized test called the ASVAB that is 31 or more, which is roughly comparable to an IQ score on the Stanford-Binet scale of a little bit less than 92, for high school graduates seeking to enter the Army or Navy (other services have more strict requirements and applicants with only a GED or to the national guard must have an ASVAB score in the 50th percentile which is equivalent to an IQ of 100). But, U.S. law allows the Department of Defense to allow people...

The so-called 'cookie law' obliges you to inform the user about the site's cookies (or use of Storage or such on the user's computer) and ask for consent for those that are not "strictly necessary for the provision of an information society service requested by the subscriber or user". It does not require you to seek consent for the use of any cookie no matter what function it has. "Strictly necessary" cookies include those necessary for the website to comply with the law. Per guidance from the Information Commissioner's Office (ICO) in the UK (see the example box), a cookie...


"Diffie-Hellman Key Exchange" in plain English

Can someone explain what the Diffie-Hellman Key Exchange algorithm in plain English? I have read that Twitter has implemented this technology which allows two parties to exchange encrypted messages on top of a non-secured channel. How does that work?

cryptography key-exchange diffie-hellman asymmetric

Disclaimer: I am the author, creator, owner and maintainer of Have I Been Pwned and the linked Pwned Passwords service. Let me clarify all the points raised here: The original purpose of HIBP was to enable people to discover where their email address had been exposed in data breaches. That remains the primary use case for the service today and there's almost 5B records in there to help people do that. I added Pwned Passwords in August last year after NIST released a bunch of advice about how to strengthen authentication models. Part of that advice included the following :...

The short answer is yes. The long answer is also yes. /dev/urandom yields data which is indistinguishable from true randomness, given existing technology. Getting "better" randomness than what /dev/urandom provides is meaningless, unless you are using one of the few "information theoretic" cryptographic algorithm, which is not your case (you would know it). The man page for urandom is somewhat misleading, arguably downright wrong, when it suggests that /dev/urandom may "run out of entropy" and /dev/random should be preferred; the only instant where /dev/urandom might imply a security issue due to low entropy is during the first moments of a...

You can roll your own, but you probably will make a major security mistake if you are not an expert in security/cryptography or have had your scheme analyzed by multiple experts. I'm more willing to bet on an open-source publicly known encryption scheme that's out there for all to see and analyze. More eyes means more likely that the current version doesn't have major vulnerabilities, as opposed to something developed in-house by non-experts. From Phil Zimmermann's (PGP creator) Introduction to Cryptography (Page 54) : When I was in college in the early 70s, I devised what I believed was a...

Diffie-Hellman is a way of generating a shared secret between two people in such a way that the secret can't be seen by observing the communication. That's an important distinction: You're not sharing information during the key exchange, you're creating a key together. This is particularly useful because you can use this technique to create an encryption key with someone, and then start encrypting your traffic with that key. And even if the traffic is recorded and later analyzed, there's absolutely no way to figure out what the key was, even though the exchanges that created it may have been...


Do adult braces have a medical need beyond cosmetics?

While middle/upper-class American parents often have their children get braces as teenagers, an adult getting braces out of his/her own volition could be viewed as a sign of vanity, much like plastic surgery. While in most communities, braces are seen as more socially acceptable than plastic surgery, both involve modifying the body to improve outward appearance to gain the attraction and respect of others. Do adult braces have a medical needs, are are they purely to alter cosmetic appearance?

dentistry cosmetics dental-braces teeth-alignment

There are certain types of malocclusion that are have been shown to adversely affect quality of oral health and quality of life, but these are far, far fewer than the number of people sporting braces, adult or adolescent. The need for braces in the average teen, therefore, is no greater than the average adult. If you think of braces for teens as a necessity, it is no less a necessity for adults, that is, appearance is probably the only significant result for both average teens and adults. However, increased longevity has led to the need to keep healthy teeth for...

Let's get a few things out of the way... Sex is normal ( 1 ). Sexual desire and arousal are normal ( 2 ). Asexuality is normal ( 3 ). Masturbation is normal ( 4 ),( 5 ). There is no problem whatsoever with these three things, although everyone blushes when they talk about them. Is Masturbation healthy? Downsides : Masturbation is not risk free. It is about as dangerous as chewing or walking ( 6 ). Some side effects are irritated skin and ruptured penis, but only if you really, really, really overdo it (Once or twice a day...


Why will there be vaccines first before a cure for COVID-19?

I found this link on the internet: 70 vaccines are getting ready for coronavirus: 3 very promising Why is it that there will be vaccines before a cure? Shouldn't it be the other way around? What is the reason for the vaccine first then the cure?

Your question contains a lot of misconceptions. A cure is definitely possible A cure could be found, proved, and proved safe, more quickly than a vaccine People and firms that could be working on cures are choosing to work on vaccines None of these are correct. Most virus-caused diseases have no cure: colds, Zika, Dengue, and so on. A tiny handful have treatments that can ease the course of the disease: you've heard of Tamiflu and so on. And some can be actually cured with medication. So the first assumption, that a cure exists to be found, is not a...

Overall, there has been inconsistent data on the effects of using zinc lozenges to treat the common cold. Most studies have also been done on children, which may lead to more uncertainty about its effects on adults, but some of the studies I will mention have been tested on adults. One study showed the effects of using zinc to prevent the common cold in schoolchildren. They found that between the two groups they studied (one took zinc sulfate tablets, the other placebos) that the zinc-supplemented group had less of a chance of getting the cold. They concluded that zinc supplements...

Assuming the person is not taking anticoagulants, it's actually quite difficult to bleed to death from dismemberment of small members (hands, feet, penis, ears, nose, etc). Even large members such as arms and legs are often survivable because the body is very good at protecting itself from blood loss. For example, transected arteries will spasm and clamp off blood flow, and loss of blood will cause the body to divert blood flow away from the extremities and to the vital organs, thereby slowing the bleeding and allowing it to clot. In fact, the whole shock process can be viewed as...

One of the primary purposes of corticosteroids is to suppress immune activity and inflammation: that's exactly why they are used in asthma. Of course the immune system has an actual job besides causing nuisance inflammation: fighting infection. For some infections, the harm to the infected person caused by the immune reaction itself is worse than that of the pathogen itself, so steroids can help prevent damage or ease symptoms while the immune system continues to mount a response, without being hyper active. For others, immune suppression may be detrimental. Corticosteroids mediate the immune response by suppressing a variety of cytokines...


Could double jeopardy protect a murderer who bribed the judge and jury to be declared not guilty?

Assume the following hypothetical case: a well-known multi-billionaire is holding an event with lots of invitees, (so there is no doubt about his identity), then in front of many witnesses and live cameras takes out a gun and murders several people, while saying that he is of sane mind, and intended to do this because they annoyed him. It seems like a clear-cut case, his guilt is beyond all reasonable doubt. But at the trial, he is declared not guilty. Everyone is horrified, but he goes free. Much later it comes to evidence that the judge and jury received ludicrous sums of money, and disappeared in a country with no extradition treaty. Can someone be protected by double jeopardy in such a case?

The Plan For A Clearly Guilty Client Without Bargaining Power This question underestimates how much of a criminal defense lawyer's work involves sentencing rather than a determination of guilt or innocence. Suppose as the OP does that the prosecution can easily prove beyond a reasonable doubt that your client is guilty, you client has no plausible defenses, and the prosecutor won't budge on a plea. As a criminal defense lawyer, you may well advise your client that there is no percentage in fighting guilt on the charges, and have your client plea guilty. This prevents the prosecutor from spelling out...

There is precedent for the idea that double jeopardy need not apply when the initial trial was a sham because the judge and/or jury had been bribed. See Aleman v. Judges of Cook County Circuit Court , 138 F.3d 302 (7th Cir. 1998) . This case was very similar to your hypothetical: Aleman was initially acquitted of a murder, but years later it came to light that he had bribed the judge (in a bench trial). He was retried and convicted in state court. He appealed his conviction on the grounds of double jeopardy, but the Seventh Circuit denied his...

Technically anyone can sit on a jury. Lawyers are not automatically excluded from juries anymore, as being called for jury duty is a right and a duty that the law abhors automatically excluding people from. That is the official line on this. However, in reality, lawyers will always be stricken from serving by one of the lawyers trying the case. Each lawyer has a certain number of preemptory strikes (the ability to get rid of a juror for any reason, aside from those protected by law, such as race, religion, etc). They also have unlimited "for cause strikes," which are...

Public nudity is illegal in New York as it is in almost every U.S. jurisdiction. And, if the police had arrested the nude protesters, the arrests probably would have been upheld in court, because a ban on nudity in public would probably be viewed as a time, place and manner restriction on the freedom of speech which is constitutionally valid. For example, the Ninth U.S. Circuit Court of Appeals recently upheld San Francisco’s public nudity ordinance in Taub v. City and County of San Francisco (2017). As the court in that case explains in a factually very similar case: Public...


Why and when would an attorney be handcuffed to their client?

While reading about the trial of Hans Reiser I came across this peculiar sentence: On Monday, July 7, 2008, Reiser led police to Nina's shallow grave in the Oakland Hills. Reiser's attorney, William Du Bois, who was handcuffed to Reiser and accompanied by a heavy police guard to the site, said that the remains were found buried on the side of a hill […] (Originally reported by SFGate ) I find this very strange for multiple reasons: The attorney is not legally responsible for the defendant's safety or security. The attorney is free to leave at any time. The attorney is not required to be armed and can not be expected to defend himself from a violent defendant …nor can he be expected to physically restrain the defendant if necessary. If the heavy police guard has to intervene, having an innocent civilian chained to the target must make their job much more difficult in case the defendant has to be subdued by force. Why and when would this be standard practice, and who would order that? Is it something that the Judge would order, or would the attorney himself have to suggest it? † † Unfortunately we can not ask him personally since, while researching the question, I found that he recently passed away .

This is entirely possible in a number of different motions that could have been made. At this point, Vinny had destroyed the Prosecutor's eyewitnesses by showing they had issues that called their testimony into question (The first has a timeline that doesn't line up with events, the second has poor vision and her prescription glasses were not doing their job, and the third had many obstructions blocking his view of the scene). His first witness tears apart the "expert" witness, who was only there to testify that the tires were the same brand (albeit, a popular brand at the time......

Yes, their waiver has no legal basis and is invalid under the GDPR. They should have hired a better lawyer. GDPR rights cannot be waived ( mrllp.com ). The last bit should have been: Therefore, in consideration of my participation in any project, I understand that retaining my name and email address, as described above, does not require my consent and that the right of erasure, as spelled out in the GDRP Article 17 (1) b does not apply. The legal basis for our lawful processing of this personal data is Article 6 (1) f ("processing is necessary for the...

Virginia employer terminated employee and wants signing bonus returned Can the employer legally keep his last check and send the employee a bill for the remainder ? No, unless (1) the employee resigned and (2) his resignation does not amount to constructive termination . The employer may withhold the remaining $7,000 only if the employee did not meet the condition of " 30 days of employment with xxxxx ". Absent any language to the contrary, the requirement of " 1-year commitment " is to be construed as the consideration expected from the employee (namely, " not to quit ") in...

My impression, and the plausible explanation in the absence of the actual facts, is that this was something that the attorney agreed to, in order to allow a skittish client to reveal information pursuant to a favorable plea agreement. The police probably insisted that the client be handcuffed to someone while doing this to prevent the client from fleeing. The attorney probably offered to do the job instead of a police officer, to be able to provide advice to his client and keep his client calm enough to do it, which might not have happened (sacrificing the favorable plea deal...


Internet courtship: Why would a hacker buy me poker chips?

Believe me, I never expected to ever write a title like that on a Stack Exchange site either! Yesterday evening I got a call from my mother. She is quite tech savvy and generally knows her way around spam and viruses. However, yesterday she was startled: she got an email from Facebook thanking her for her purchase of 40 dollars worth of poker chips in the Facebook game TexasHoldEm. She was ultimately sure she had never done a purchase like that, but she was worried she had lost money one way or another. The email seemed genuine. Logo, text, sender, and links all pointed to genuine Facebook resources. I decided to take a look and followed the link to the 'receipt'. A payment overview at Facebook.com opened and everything was documented as the email had stated: her account had acquired 40 dollars worth of poker chips in the app (game) TexasHoldEm. Surprisingly, though, those chips were paid with a PayPal-account registered to an email address we have never heard of: givenName.LastNameNumber@web.de This is odd for two reasons: we live in Belgium, but have no relation, friends, family or otherwise, in Germany. Second we know no one by that name either. At first I thought it may have been an error on that person's side, or that it is simply possible to 'donate' chips to someone else's Facebook account. But this would allow app developers to spam people who had never used their app with free gifts, so this seemed unlikely. I then checked her account's recent activity, more specifically the 'recent sessions' tab. To my surprise there was indeed an active session in Düsseldorf, Germany. As a panic attack, I immediately ended that session. Unfortunately that also hid the information about that session. For me this meant only one thing: her account must have been hacked, as she hasn't been to Germany and there is no way there could be an active - poker-playing - Facebook instance there. In light of this, I urged her to immediately change her password. After that, Facebook seems smart enough to know you made the change because you thought something was wrong: it proposed to go through her recent app activity and post and possibly deleting strange behaviour. Indeed, the app TexasHoldEm had been used, and there had been four posts (of the app on her behalf) that she had been playing the game - going back one whole week. As a conclusion I would think that someone hacked my mother's account, played poker on it and paid for chips him/herself and ... That's it. Maybe I am getting old, but isn't this weird behaviour? Why would a hacker do this: hack some one's account, buy poker chips with their own PayPal account, and play the game? And how can I better protect myself against such 'attacks'? The poker chips were for Zynga's Poker game on Facebook. As has been mentioned in the comments , you cannot withdraw won money from this game. This is valuable - and intriguing - information which makes understanding the hacker's motives even harder.

I interpret your question as: What's the motivation for someone to use an alien Facebook account to play poker and stock it with chips? It's not that strange if you think about it this way: As poker is a game where knowledge about the dealt cards gives you a significant edge in the game, you'd like to use sock puppets at a table to know more about the card distribution. Thus, using sock puppets that are valid, active - real - Facebook accounts are the only way to gather more information without being spotted easily by heuristics. Düsseldorf is where...

By any measure, they're wrong: Seven random printable ASCII: 95 7 = 69 833 729 609 375 possible passwords. Ten random alphabetics: 52 10 = 144 555 105 949 057 024 possible passwords, or over 2000 times as many. Length counts. If you're generating your passwords randomly, it counts for far more than any other method of making them hard to guess.

It is the magic of public-key cryptography . Mathematics are involved. The asymmetric key exchange scheme which is easiest to understand is asymmetric encryption with RSA. Here is an oversimplified description: Let n be a big integer (say 300 digits); n is chosen such that it is a product of two prime numbers of similar sizes (let's call them p and q ). We will then compute things "modulo n ": this means that whenever we add or multiply together two integers, we divide the result by n and we keep the remainder (which is between 0 and n-1 ,...

Facebook is allowing you to make a handful of mistakes to ease the login process. A Facebook engineer explained the process at a conference . The gist of it is that Facebook will try various permutations of the input you submitted and see if they match the hash they have in their database. For example, if your password is "myRealPassword!" but you submit "MYrEALpASSWORD!" (capslock on, shift inverting capslock). The submitted password obviously doesn't match what they have stored in their database. Rather than reject you flat out, Facebook tries to up the user experience by trying to "correct" a...


Why shouldn't we create our own security schemes? I see a lot of questions around here about custom crypto and custom security mechanisms, especially around password hashing. With that in mind, I'm looking for a canonical answer, with the following properties: Easy for a newbie to understand. Clear and explicit in why rolling your own is a bad idea. Provides strong examples. Obligatory xkcd.

Yes, it is a security feature, and the purpose of the delay is to prevent attacks based around tricking the user into entering input to skip past the dialog by popping it up unexpectedly when the user is in the middle of inputting multiple key presses or mouse clicks in quick succession. The two examples that are given in this blog post explaining the feature are: A CAPTCHA that asks the user to type the word only . When they press n , a save dialog is popped up, and then the user will immediately press l and then y...

You should use the maximum number of rounds which is tolerable, performance-wise, in your application. The number of rounds is a slowdown factor, which you use on the basis that under normal usage conditions, such a slowdown has negligible impact for you (the user will not see it, the extra CPU cost does not imply buying a bigger server, and so on). This heavily depends on the operational context: what machines are involved, how many user authentications per second... so there is no one-size-fits-all response. The wide picture goes thus: The time to verify a single password is v on...

In some circumstances, peppers can be helpful. As a typical example, let's say you're building a web application. It consists of webapp code (running in some webapp framework, ASP.NET MVC, Pyramid on Python, doesn't matter) and a SQL Database for storage. The webapp and SQL DB run on different physical servers . The most common attack against the database is a successful SQL Injection Attack. This kind of attack does not necessarily gain access to your webapp code, because the webapp runs on a different server & user-ID. You need to store passwords securely in the database, and come up...


Why do color TVs make black and white snow?

If you let a color TV display something from an unplugged display port, it displays snow, right? Randomly varying black or white pixels on the whole screen. My guess was that the television was decoding the noise from the unplugged wires as a video signal. Assuming this, it makes sense that B&W TVs make B&W snow (they would decode the noise as being a B&W video signal). But then color TVs should make colored snow , right? Shouldn't they decode the noise as being a color video signal?

One of the problems that plagued older rechargeable batteries (e.g. Nickel Cadmium ($\text{NiCad}$) and Nickel Metal Hydride ($\text{NiMH}$)) was the memory effect . The memory effect occurs when a rechargeable battery is not fully discharged. It then "forgets" that it has a greater capacity than it thinks it has, and so in the future it discharges less. A good example is a water bottle. Initially, water bottles have a certain capacity for water. Let's say that I drink most of the water in a water bottle during one usage. If the memory effect affected water bottles, I would not be...

If the receiver does not detect the sub-carrier for the "colour burst" signal which is transmitted during the horizontal blanking period the receiver switches on the "colour-killer" circuit so the set reverts to black and white mode. The colour-burst signal - 8 to 10 cycles of 3.85 MHz - is unlikely to be generated by random noise. Figure 1. The colorburst signal is transmitted on the "back porch" between the horizontal blanking pulse and the start of that line's luminance signal. The colorburst signal is used to synchronise the QAM (quadrature amplitude modulation) oscillator which can hold its frequency accurately...

The current limit specification for a wire is limited by the heat that current will produce, and how much heat the wire can dissipate before getting too hot. "Too hot" depends on the circumstances. You will see higher current ratings for the same type of wire in chassis wiring applications than the electrical code allows for home installations, for example. This is mostly due to how hot too hot is. The ultimate limit for extreme applications is that the conductor not melt. Temperatures anywhere near that would be unsafe running along wooden supports inside a wall in a house. As...

It depends on how steep the hill is. On a slight hill, the energy added by gravity is still not enough to overcome rolling friction and air resistance, so the car still needs power to maintain speed. On a steeper hill, the two may balance out, so no power is used, and no power is generated. On a hill that's steep enough to require braking to control the speed, the car recovers energy. It's called regenerative braking. If the car is going too fast, applying the brakes turns the motor into a generator and charges the battery.


Why is Gbt3fC79ZmMEFUFJ a weak password?

On https://passwordsgenerator.net/ , it says Examples of weak passwords: qwert12345, Gbt3fC79ZmMEFUFJ, 1234567890, 987654321, nortonpassword The first, third, and fourth examples are obviously weak. I can't, however, see what's weak about the second one. Indeed, the only problem I see with it at the moment is that it doesn't have any special symbols. Is that enough for a password to be considered weak ?

I was curious about the same thing, so I put Gbt3fC79ZmMEFUFJ into Google, and lo! and behold it found something that wasn't just a paraphrase of "Don't use this password" advice — the password itself was embedded in example source code that showed how you could send a password to a server! ( link to page , and screenshot below) So I think the real goal of that advice is not that Gbt3fC79ZmMEFUFJ is a mysteriously weak password because of the keyboard layout or because of low entropy or because it doesn't include symbols or Unicode or emoji or whatever:...

"If lack of encryption allows FBI to catch terrorists, then lack of encryption allows criminals to loot your emails and plunder your bank account." The rational point here is that technology is morally neutral. Encryption does not work differently depending on whether the attacker is morally right and the defender morally wrong, or vice versa. It is all fear-driven rhetoric anyway, so don't use logic; talk about what most frightens people, personally. And people fear most for their money.

The reason password expiration policies exist, is to mitigate the problems that would occur if an attacker acquired the password hashes of your system and were to break them. These policies also help minimize some of the risk associated with losing older backups to an attacker. For example, if an attacker were to break in and acquire your shadow password file, they could then start brute forcing the passwords without further accessing the system. Once they know your password, they can access the system and install whatever back doors they want unless you happen to have changed your password in...

This is the simplest way of performing host discovery with nmap. nmap -sP 192.168.2.1/24 Why does it not work all the time ? When this command runs nmap tries to ping the given IP address range to check if the hosts are alive. If ping fails it tries to send syn packets to port 80 (SYN scan). This is not hundred percent reliable because modern host based firewalls block ping and port 80. Windows firewall blocks ping by default. The hosts you have on the network are blocking ping and the port 80 is not accepting connections. Hence nmap assumes...


How does a traffic light sense the proximity of vehicles?

Some traffic lights don't operate periodically but instead detect when a car is close by and then turns green. I have heard that they use a magnetic sensor embedded in the road to sense cars as they come near. Is this correct? Do they use other means as well?

I can understand your concern. This is going to be difficult for two reasons: Finding out the agency that is responsible for the maintenance may be next to impossible for a layperson. Note that I said "maintenance", because this might be a different entity than the owner due to agreements. Due to the number of complaints that the public agencies receive, it is very likely that your comment will get ignored. This often has nothing to do with whether or not your concern has merit. Public vs. Private Public agencies will be the easiest to contact. In a city, calling...

If you consider only the static forces then indeed the thickness might seem over-engineered. However, engine blocks are not statically loaded. They operate in the range of a few hundred to a few thousand rpm (Revolution Per Minute), so there are dynamic considerations here. Fatigue When materials are subjected to cyclic loading they exhibit a reduction in the allowable stresses. See below for an example: In general, BCC (body-centered cubic) materials (like steel) show a marked drop in strength (close to 50% or more depending on the steel). For these material there is stress (called the endurance limit), for which...

As others stated before, induction loops are the primary - most reliable method: the coils (usually just several loops of wire) embedded in the road; fed given frequency from a generator, in presence of metal the frequency of the LC circuit changes and the sensor circuitry detects the change of frequency, producing a presence signal. In some cases these may fail to detect bicycles, but they are by far most common as they aren't affected by weather (or more precisely, the detection circuit tunes in to slow changes of frequency caused by weather) and are immune to accidental false positives....

The current limit specification for a wire is limited by the heat that current will produce, and how much heat the wire can dissipate before getting too hot. "Too hot" depends on the circumstances. You will see higher current ratings for the same type of wire in chassis wiring applications than the electrical code allows for home installations, for example. This is mostly due to how hot too hot is. The ultimate limit for extreme applications is that the conductor not melt. Temperatures anywhere near that would be unsafe running along wooden supports inside a wall in a house. As...


Secure way of masking out sensitive information in screenshots?

As a guy working in security/pentest, I regularly take screenshots of exposed passwords/sensitive information. Whenever I report these, I mask parts or complete info as in the sample given below I often wonder, is it possible for someone to 'reverse engineer' these pics and recover the original information? If so, what should be the correct way of masking such kind of info? I am using shutter for taking screenshots and using accompanied edit tool to add the black stroke. EDIT: As pointed out by some of you, my question is different from this since: I am not asking about MS paint/black strokes. The image is just an example to better explain the question I have clearly asked for the correct/most secure way of producing photographic evidence.

It typically works like this: Say your password is "baseball". I could simply store it raw, but anyone who gets my database gets the password. So instead I do an SHA1 hash on it, and get this: $ echo -n baseball | sha1sum a2c901c8c6dea98958c219f6f2d038c44dc5d362 Theoretically it's impossible to reverse a SHA1 hash. But go do a google search on that exact string , and you will have no trouble recovering the original password. Plus, if two users in the database have the same password, then they'll have the same SHA1 hash. And if one of them has a password hint...

I was one of the implementers of JScript and on the ECMA committee in the mid to late 1990s, so I can provide some historical perspective here. The JavaScript Math.random() function is designed to return a floating point value between 0 and 1. It is widely known (or at least should be) that the output is not cryptographically secure First off: the design of many RNG APIs is horrible . The fact that the .NET Random class can trivially be misused in multiple ways to produce long sequences of the same number is awful. An API where the natural way...

Yes, it can be recovered. As long as shutter does not use layer (it almost certainly does not) and as long as the black is really all black (it must not be transparent), it is enough. The picture that you provided uses some amount of transparency, see here: All I had to do is use the Fill tool in MS Paint. If I used some algorithm that would take the jpg compression into account, I could probably get better results. Solution: Use an editor that does not make the block transparent. Make sure layers are not used. Make sure change...

As mentioned in the answers to a very similar question , scribbling over part of an image will destroy the original pixels, assuming that your editor doesn't store any layers or undo history in the saved image. (Paint doesn't.) There are some things to watch out for, though: The width of the blanked region places an upper bound on the length of the secret data The height of the region could tell attackers whether the text representation of the data has ascenders or descenders (like in the letters b and p ) Any spaces in the blanked region provide information...


What exactly does it mean when Chrome reports 'no certificate transparency information was supplied by the server?'

When visiting Gmail in Chrome, if I click on the lock icon in the address bar and go to the connection tab, I receive a message 'no certificate transparency information was supplied by the server' (before Chrome 45, the message was displayed as 'the identity of this website has been verified by Google Internet Authority G2 but does not have public audit records'). What exactly does it mean that the certificate does not have public audit records? Are their certain threats a site using a certificate without public audit records has that a site using a certificate with public audit records does not?

Chrome not only stores your password text, it will show it to you. Under settings -> advanced -> manage passwords you can find all your passwords for all your sites. Click show on any of them and it will appear in the clear. Hashed passwords work for the site authenticating you. They are not an option for password managers. Many will encrypt the data locally, but the key will also be stored locally unless you have a master password setup. Personally, I use the chrome password manager and I find it convenient. I also, however, have full disk encryption and...

Note : If you're here because your certificate isn't trusted by Chrome, this is not the reason. Chrome will still trust certificates without CT information. If your certificate isn't trusted, there is an additional factor that you may have missed. This has to do with the concept of Certificate Transparency . The Problem Browsers currently trust certificates if four conditions are met: (a) the certificate is signed by a trusted CA, (b) the current time is within the valid period of the certificate and signing certs (between the notBefore and notAfter times), (c) neither the certificate nor any signing certificate...

/** Dave's Home-brew Hash */ // user data $user = ''; $password = ''; // timestamp, "random" # $time = date('mdYHis'); // known to attackers - totally pointless // ^ also, as jdm pointed out in the comments, this changes daily. looks broken! // different hashes for different days? huh? or is this stored as a salt? $rand = mt_rand().'\n'; // mt_rand is not secure as a random number generator // ^ it's even less secure if you only ask for a single 31-bit number. and why the \n? // crypt is good if configured/salted correctly // ... except you've...


How do you ensure physical network interfaces always get the same interface name across reboots on an embedded Linux system?

For an embedded Linux system, if I have two or more network interfaces, how do I ensure that they always get the same interface names every boot In other words, I want, for example, eth0 to always map to one physical Ethernet port, eth1 to the next, etc. My Linux "distribution" is home-grown, and I use devtmpfs for populating /dev. I use busybox for init (and most everything else), along with custom init scripts for system startup and shutdown. I do not need hotplug facilities of mdev or udev -- I'm referring to "fixed" Ethernet ports.

It is more efficient to transmit DC using about the same infrastructure. This is because of several effects: Skin effect experienced with AC. There is no skin effect with DC. Higher voltage allowed with DC for the same transmission lines. The lines have to withstand the peak voltage. With AC, that is 1.4 times higher than the RMS. With DC, the RMS and peak voltages are the same. However, the power transmitted is the current times the RMS, not peak, voltage. No radiation loss with DC. Long transmission lines act as antennas and do radiate some power. That can only...

This works for me with Linux 3.9.0 on an x86_64 architecture. #!/bin/sh # This assumes the interfaces come up with default names of eth*. # The interface names may not be correct at this point, however. # This is just a way to get the PCI addresses of all the active # interfaces. PCIADDRLIST= for dir in /sys/class/net/eth* ; do [ -e $dir/device ] && { PCIADDRLIST="`readlink -f $dir/device` ${PCIADDRLIST}" } done # Now assign the interface names from an ordered list that maps # to the PCI addresses of each interface. # IFNAMES could come from some config file....

When a reactor is shut down the core produces much less heat, but they do still produce heat through a mechanism known as decay heat . The fact that the core is producing less heat means that the coolant temperature is going to drop, but how far that temperature drops depends on the decay heat generation rate. This in turn is based on operating history, or the power at which the plant was operating before shutdown. This can be large for commercial plants, because they typically operate at or very near capacity and the power companies bring coal or natural...

I will expand on DKNguyen answer, because to my knowledge also the two reasons are: reduce contact/bearing stresses (having a significant effect on thin finishes live galvanisation) change the joint tightening characteristics (see joint diagram). reduce contact stresses on surfaces. The basic idea is that since contact stress is defined as: $$\sigma = \frac{F}{A}$$ Obviously the larger the area the less the stress. Also, like Nuclear Hoagie pointed out the area changes with a square law of the diameter. UPDATE 2 - Calculation for M6 bolt (thanks to BenC) *The question gathered enough interest for me to carry out a...


Why are iron levels different in the left and right hands?

Yesterday I donated blood. When the nurse performed a finger prick test of iron using my left hand, she indicated that the level was too low. However, she then asked to perform the test again on my right hand. Surprisingly, the iron level was adequate. She said that this is a well known phenomenon, specifically that the dominant hand often has higher iron levels. (For references, I am right handed.) How can this be? I would have thought that, given blood circulates throughout the entire body, it would be uniform everywhere.

Great question! I think it's answerable as an overview, but please know this is only the tip of the iceberg.* Summary : Yes, we have deficits of certain blood products in certain locations at certain times that affect patient care. However, a small percentage of blood product does expire unused (because it wasn't the right product [see background] in the right place at the right time). A little background Donated blood is not usually transfused into a patient as whole blood. Instead, it's broken down into several components which are transfused in different clinical scenarios. The issues of storage and...

In general, the benefit of flu shots is to the general population. Taking the cited value of 40%-60% from the CDC, we can say that it might be a coin toss for you personally to be protected from influenza by the shot. However, if many thousands of people take the flu shot, even if it only works on 40% of them, it helps protect the remaining population from the spread of the virus (AKA herd immunity). This is especially important to those within the population who cannot access the shot or cannot receive it due to a preexisting medical condition....

I'm guessing the "iron" test was actually a hemoglobin test (though I'm certainly no expert in blood donation screens...). I suspect your nurse is reporting a folk tale rather than any true difference. Unfortunately, medical professionals are not always an excellent source of scientific knowledge. I looked for papers that have actually compared measurements in the two hands. Here's one: Patel, A. J., Wesley, R., Leitman, S. F., & Bryant, B. J. (2013). Capillary versus venous haemoglobin determination in the assessment of healthy blood donors. Vox sanguinis, 104(4), 317–323. https://doi.org/10.1111/vox.12006 Capillary fingerstick samples were assayed by HemoCue in 150 donors....

I believe that those lines are craze lines. "Craze lines are merely cracks in the enamel that do not extend into the dentin." They occur because of stress in your teeth, ie: grinding your teeth, biting your nails, and even routine use of your teeth. What you've said also matches up with craze lines in that you don't experience any pain. Those craze lines aren't nearly as bad as some other teeth. Craze lines rarely lead to tooth breakdown, so you almost definitely won't have to get them replaced. There are some studies that say that craze lines may be...


What is the best data structure/implementation for representing a time series?

I was wondering what is best practice for representing elements in a time series, especially with large amounts of data. The focus/context is in a back testing engine and comparing multiple series. It seems there are two options: 1) Using an integer index, or 2) Using a date-based index At the moment I am using dates, but this impacts on performance & memory usage in that I am using a hash table rather than an array, and it requires some overhead in iteration (either forward or backwards) as I have to determine the next/previous valid date before I can access it. However, it does let me aggregate data on the fly (e.g. building the ohlc for the previous week when looking at daily bars) and most importantly for me allows me to compare different series with certainty I am looking at the same date/time. If I am looking at an equity issue relative to a broader index, and say the broader index is missing a few bars for whatever reason, using an integer indexed array would mean I'm looking at future data for the broad index vs present data for the given security. I don't see how you could handle these situations unless you're using date/times. Using integer indexes would be a lot easier code wise, so I was just wondering what others are doing or if there is best practice with this.

Representing time series (esp. tick data) using elaborate data structures may be not the best idea. You may want to try to use two arrays of the same length to store your time series. The first array stores values (e.g. price) and the second array stores time. Note that the second series is monotonically increasing (or at least non-decreasing), i.e. it's sorted. This property enables you to search it using the binary search algorithm. Once you get an index of a time of interest in the second array you also have the index of the relevant entry in the first...

The risk-neutral measure $\mathbb{Q}$ is a mathematical construct which stems from the law of one price , also known as the principle of no riskless arbitrage and which you may already have heard of in the following terms: "there is no free lunch in financial markets". This law is at the heart of securities' relative valuation , see this very nice paper by Emmanuel Derman ("Metaphors, Models & Theories", 2011) and some part of this discussion. In what follows, assume for the sake of simplicity existence of a risk-free asset ; deterministic and constant rates, with risk-free rate $r$ ;...

1. Determine Factors Economically, the use of factor models can be either motivated using the ICAPM or the APT . Although there are some theoretical differences between the model, for empirical and practical work these differences are irrelevant. In the end, both models stipulate that returns and expected returns are linear functions of the factors: $$ r_{i,t} = \alpha_i + \sum_j \beta_{i,j} F_{j,t} + \epsilon_{i,t} \quad (1)$$ $$ \mathbb{E}[ r_{i,t}] = \lambda_o + \sum_j \beta_{i,j} \lambda_j \quad\quad\quad(2)$$ where $F_{j,t}$ is the factor surprise of factor $j$ at time $t$ and $\lambda_j $ is the factor risk premium of factor $j$....

One starts with the Black-Scholes equation $$\frac{\partial C}{\partial t}+\frac{1}{2}\sigma^2S^2\frac{\partial^2 C}{\partial S^2}+ rS\frac{\partial C}{\partial S}-rC=0,\qquad\qquad\qquad\qquad\qquad(1)$$ supplemented with the terminal and boundary conditions (in the case of a European call) $$C(S,T)=\max(S-K,0),\qquad\qquad\qquad\qquad\qquad\qquad\qquad\qquad(2)$$ $$C(0,t)=0,\qquad C(S,t)\sim S\ \mbox{ as } S\to\infty.\qquad\qquad\qquad\qquad\qquad\qquad$$ The option value $C(S,t)$ is defined over the domain $0 Step 1. The equation can be rewritten in the equivalent form $$\frac{\partial C}{\partial t}+\frac{1}{2}\sigma^2\left(S\frac{\partial }{\partial S}\right)^2C+\left(r-\frac{1}{2}\sigma^2\right)S\frac{\partial C}{\partial S}-rC=0.$$ The change of independent variables $$S=e^y,\qquad t=T-\tau$$ results in $$S\frac{\partial }{\partial S}\to\frac{\partial}{\partial y},\qquad \frac{\partial}{\partial t}\to - \frac{\partial}{\partial \tau},$$ so one gets the constant coefficient equation $$\frac{\partial C}{\partial \tau}-\frac{1}{2}\sigma^2\frac{\partial^2 C}{\partial y^2}-\left(r-\frac{1}{2}\sigma^2\right)\frac{\partial C}{\partial y}+rC=0.\qquad\qquad\qquad(3)$$ Step 2. If we...


Is it common to allow local desktop and/or active directory admin access and rights for developers in organizations?

I work at a company with a staff of about 1000+. We currently have programming development staff that work on web based projects (approx 50 people). Recently due to security concerns our IT and Security department implemented a restriction no longer allowing local admin access on machines . The entire company runs Windows OS for both workstations and servers. I completely agreed with the decision to remove admin, honestly I thought it was long overdue (as the company deals with patient data and requires HIPAA compliance). Unfortunately I believe they took the decision too far. I assumed a subgroup or AD group would be created for users that legitimately needed admin access to do their job (EX my programming team) something like a Tech group that would retain admin access. However this was not the case, the only group created a specific Admin group for Network and Help Desk staff. The main problem is, as web developers we run programs that require local admin access and unfortunately can't do our job without them running as admin. Example programs include Visual Studio for ASP.NET web development, MAMP for local development, composer, etc. I believe the main reason these programs need admin access is because they need to run and modify local IIS, command line, etc. Basically there was short notice of when the local admin access was removed. After about 2 days of the development team being dead in the water in terms of being able to work and me and other team leaders basically yelling and screaming at the IT staff to come up with a solution they finally conceded and found a third party program that works as a pass through allowing the administrators to create the ability for certain programs to run as admin even though we don't have local admin access. Unfortunately, this program we use for local admin access is incredibly buggy and unreliable and not from a reputable source and there doesn't seem to be much for alternatives out there. (I would prefer not to disclose the program we use.) My question is, is it typical to not allow Programmers/Developers local admin access at a company or corporation? And if it is common practice to do so, then how do developers run the programs they need as local admin? A little more information on our network environment (not that it really relates to the question I just thought I'd add this): We use AppBlocker to block programs not on an approved list We use an email security blocker that does things like scan and convert attachments to PDF, etc. We have at least 2 major antivirus programs on all workstations. The network and it's servers very segregated, users only have access to certain servers, folders, and databases that they legitimately need access to.

windows audit compliance programming windows-server

Diffie-Hellman is a way of generating a shared secret between two people in such a way that the secret can't be seen by observing the communication. That's an important distinction: You're not sharing information during the key exchange, you're creating a key together. This is particularly useful because you can use this technique to create an encryption key with someone, and then start encrypting your traffic with that key. And even if the traffic is recorded and later analyzed, there's absolutely no way to figure out what the key was, even though the exchanges that created it may have been...

There are a few issues with HTTP Basic Auth: The password is sent over the wire in base64 encoding (which can be easily converted to plaintext). The password is sent repeatedly, for each request. (Larger attack window) The password is cached by the webbrowser, at a minimum for the length of the window / process. (Can be silently reused by any other request to the server, e.g. CSRF). The password may be stored permanently in the browser, if the user requests. (Same as previous point, in addition might be stolen by another user on a shared machine). Of those, using...

This is actually an interesting new field in infosec— reputation management . Employers, Law Enforcement and other government agencies, legal professionals, the press, criminals and others with an interest in your reputation will be observing all online activity associated with your real name. These "interested parties" (snoops) are usually terrible at separating professional and personal life, so you could be made to suffer for unpopular opinions, political or religious convictions, associates or group affiliations they consider "unsavory", and any behavior that can be interpreted in the most uncharitable light. (Teachers have been forced to resign for drinking wine responsibly while...

Here's one data point from a software company that has an interest in security. I know this is common in similar organisations. There is a number of networks. They are physically separated and airgapped, run different colour-coded network cables. Each employee has an 'administration' machine, which can connect to the Internet (via a proxy) for doing email etc. All users are strictly locked down, and there's strict device and access control. In addition to this, each developer has an 'engineering' machine. This has full admin access, and the user can do whatever they like. However it is connected only to...


Are disclaimers of warranty, liability, and the like legally required to be in all-caps? For example, the "disclaimer of warranty" section from the GNU GPL : THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM “AS IS” WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU. SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR OR CORRECTION. On the other hand, Stack Exchange's disclaimer of warranty uses normal casing (well, normal for legal documents): Stack Exchange has no special relationship with or fiduciary duty to Subscriber. Subscriber acknowledges that Stack Exchange has no control over, and no duty to take any action regarding: which users gains access to the Network; which Content Subscriber accesses via the Network; what effects the Content may have on Subscriber; how...

Do they have to use all caps? Well, no. It's just that companies feel that's the easiest way to make the text "conspicuous" which is required by the Uniform Commercial Code explicitly in § 2-316. Exclusion or Modification of Warranties. (2)Subject to subsection (3), to exclude or modify the implied warranty of merchantability or any part of it the language must mention merchantability and in case of a writing must be conspicuous, and to exclude or modify any implied warranty of fitness the exclusion must be by a writing and conspicuous. Language to exclude all implied warranties of fitness is...

Think through the logical combinations of two questions: The government is tyrannical or just, the revolution is successful or not. Tyrannical government, revolution successful: The revolutionaries will congratulate each other, and of course they are not persecuted by the new government they install . Just government, revolution successful: The revolutionaries will congratulate each other, and of course they are not persecuted by the new government they install . Tyrannical government, revolution not successful: The legal system will find the justified attempt illegal (because they are the legal system defending a tyrannical government), the would-be revolutionaries are persecuted. Just government, revolution...

I believe you have just misunderstood what you paid for. Blizzard's End User License Agreement says: Your use of the Platform is licensed, not sold, to you, and you hereby acknowledge that no title or ownership with respect to the Platform or the Games is being transferred or assigned and this Agreement should not be construed as a sale of any rights. It also says: Blizzard may change, modify, suspend, or discontinue any aspect of the Platform or Accounts at any time, including removing items, or revising the effectiveness of items in an effort to balance a Game. Blizzard may...

There isn't any indication in that news story that the disabled son was anywhere nearby. I agree the situation you describe sounds like a legitimate use of the placard, but it seems in this situation, the placard was being used in a manner totally unrelated to the transport of a disabled person. My guess is that the cops cited her because the son wasn't in the car, and was not inside the establishment at which she parked. California code has this to say: A person to whom a disabled person placard has been issued may permit another person to use...


How to correctly size the blades for a small educational wind turbine?

I want to design a small wind turbine that can be easily carried out of the classroom into the sports field in relatively low-wind conditions (5-15km/h) that can power a small ultra-bright 5V LED - just enough to show that it works. How do I calculate the power I can get from different blade diameters in these wind conditions, and the power needed to drive a small DC motor/generator enough to light the LED?

electrical-engineering renewable-energy power-engineering wind-power

As it happens, I just recently went through that calculation myself for a different site. Given the following facts from a quick web search, it isn't difficult to work out the numbers. The maximum efficiency of a (large) windmill is about 40%. The density of air is 1.225 kg/m 3 You need about 50 mW (10 mA at 5V) to light up an LED First, we'll need about 50 mW / 0.40 = 125 mW of air power flowing through the windmill to create the electricity we need (ignoring other factors such as the actual efficiency of a small windmill...

Cross-interference between aircraft is a high unlikely event because all commercial aircraft designs have to pass DO-160 environmental testing requirements. Among the DO-160 testing specification is EMI/EMC Testing. These tests include Radiated Emission, Interference and Immunity Testing. Part of these tests are to answer " Two aircraft are very close together " and " The other aircraft accidentally receives the signal because it is so close. " Below is a picture of an anechoic chamber used to test aircraft. Fly-by-wire allows the aircraft control system to access and command monitoring and control systems. The monitoring and control systems have a...

Some ideas: Wheel Load Distribution : The load is greater on the rear wheels providing the power; more force on the front ones bring no benefit and would provide less traction. Better manoeuvrability from having a shorter wheelbase. Better Ground Clearance in some conditions, especially for bumps and or up a increasing slope for instance. Better Driving : The front wheels now turn around a point closer to the C.G. than with the rear wheels. Not good with vehicle dynamics but this appears better than the rear end 'trailing' behind. Structural : As some people have pointed out, it's better...

At the beginning of my career (1979) as a design engineer at HP, the mechanical engineer created the part design and then rendered it in pencil on paper, and then transferred it onto sheets of vellum paper held onto a huge flat tilting table called a drafting board which had a precision sliding arm on it with which parallel and right angle lines could be drawn anywhere on the sheet. Clever graphical rules were applied to the resulting drawings which permitted auxiliary views of the part to be generated so it could be viewed from any desired angle, as an...


Rapid Response COVID-19 Antigen Test: What can be assumed by the control bar?

Rapid COVID-19 antigen tests include a control line similar to this: From Case Western Reserve rapid testing instruction available here . What does the control bar/strip control for? All the chemicals required to test for COVID are present in acceptable concentrations. If there is COVID on the swab this test will show it. Other Indicators that should be present when the swab is correctly done have been identified. You have correctly swabbed and if you have COVID this test will show it. Both. This test is in good standing condition and you have properly swabbed. If you have COVID this will show it. Since this test was distributed to the general public and there was little to no information about what the control bar/strip meant or did in the included documentation I was under the impression that option 3 was the most probable. *All statements above assume no false positives or false negatives which I know can happen.

Your explanation numbered 1 is correct. The control line indicates that the antibodies required to detect the SARS-CoV-2 (the virus that causes COVID-19) particles have reached that location on the test strip. Each product is slightly different, but the Rapid Response package insert notes: Anti-SARS-CoV-2 antibodies are immobilized on the test region of the nitrocellulose membrane. Anti-SARS-CoV-2 antibodies conjugated to coloured particles are immobilized on the conjugated pad. A sample is added to the extraction buffer which is optimized to release the SARS-CoV-2 antigens from specimen. During testing, the extracted antigens bind to anti-SARS-CoV-2 antibodies conjugated to coloured particles. As...

It turns out the answer to this is fairly simple, and but not terribly easy to find. In the 1800s a Belgian named Adolphe Quetelet (1796–1874) performed some statistics on the weights and heights of people in Europe and Britain (chiefly France and Britain) and published his seminal work, Sur l'homme et le développement de ses facultés, ou Essai de physique sociale (Treatise on Man and the Development of his Faculties, or Essays on Social Physics) in 1835. The relevant section for this can be found as a PDF for free (I believe) at the Wiley Publishing journal Obesity Research...

I think a missing bit of information that might help you get a better sense of this practice is: steroids are miracle drugs. OK, that was in jest - no miracles here. Truth be told, though, if there is a single class of drugs that has added more quality-adjusted life-years to human history than any other, steroids must be competing with just a few antibiotic classes for that title. To make clear what we’re talking about, the term “steroid” as a label for drugs generally refers to glucocorticoids (GCs) - drugs that act like cortisol, an endogenous steroid hormone. Commonly...

This event occurred in the US. In the US, enzootic (dog-to-dog) canine rabies virus has been virtually eliminated through vaccination and stray control programs, making wild animals the primary concern. It is quite true, as @EMT_Jedi stated, that rabies is usually caused by an animal's saliva, usually introduced by a bite (e.g. rabid cats, raccoons, etc.) However, this is not true of bat-related rabies. There is reason to be vaccinated after any strange contact with a bat. The most dangerous and common route of rabies exposure is from the bite of a rabid mammal. An exposure to rabies also might...


Estimating whether the flow through a valve or nozzle cavitates

My understanding is that cavitation occurs in the flow of a liquid when the static pressure drops below the vapor pressure, even intermittently. So even if the time-averaged static pressure (what you might measure) is above the vapor pressure, the pressure fluctuations from turbulence or other unsteadiness could be large enough to cause cavitation locally. So comparing the time-averaged static pressure against the vapor pressure isn't enough; you need to add some extra cushion to account for the pressure fluctuations. (This is my interpretation, not having read too deeply into this.) So, in various books, websites, and journal articles I have seen two different types of dimensionless numbers for estimating whether the flow through a valve or nozzle cavitates. They are generally called the cavitation index or cavitation number. They take one of two forms: $$\sigma = \frac{p_\text{in} - p_\text{vapor}}{p_\text{in} - p_\text{out}}$$ or $$\sigma = \frac{p_\text{in} - p_\text{vapor}}{\tfrac{1}{2} \rho V^2}$$ where $p_\text{in}$ is the inlet pressure, $p_\text{out}$ is the outlet pressure, $p_\text{vapor}$ is the vapor pressure, $\rho$ is the liquid density, and $V$ is some characteristic velocity of the flow (say, in the nozzle case, the velocity at the outlet). Some forms of this number are inversions of the numbers above, but these aren't that different. What is the difference between these parameters? Based on energy conservation you can relate the pressure drop to the flow rate, but typically there is an empirical coefficient added in to account for non-idealities. Is there something else I am missing? Is one form preferred over the other? Best I can tell whether to use one or the other depends on what sort of data you have (so, for flow over a turbine blade, the velocity form is preferred), but I've seen both even for nozzles. Where can I get accurate data to predict cavitation based on these numbers? I've tried using some data on atomizer nozzles from various journal articles but generally they use different forms of the cavitation number. Some of the data suggests the flow through the nozzle will cavitate at the pressures I want, but other data for similar nozzles suggests it won't. I'm not sure what the source of the inconsistency is. My understanding could be faulty, the cavitation number model could be too simplistic, the data could be inaccurate, etc.

If you consider only the static forces then indeed the thickness might seem over-engineered. However, engine blocks are not statically loaded. They operate in the range of a few hundred to a few thousand rpm (Revolution Per Minute), so there are dynamic considerations here. Fatigue When materials are subjected to cyclic loading they exhibit a reduction in the allowable stresses. See below for an example: In general, BCC (body-centered cubic) materials (like steel) show a marked drop in strength (close to 50% or more depending on the steel). For these material there is stress (called the endurance limit), for which...

There are a few simple reasons why the speed of a vehicle (road conditions notwithstanding) may be limited: Gearing -- Production vehicles with conventional transmissions have a limited number of gears. For most modern cars, this is usually 5 or 6, whereas older vehicles may have as few as 2 or 3. If the gear ratio of the highest gear is too low ("lower" gears are expressed as larger numerical ratios), it's entirely possible that the engine will redline before air resistance becomes a factor at all. This ties into your first point about the red zone on the tachometer....

In the video you've linked to, the spheres are seen on both the leading and trailing edges of the propeller: I expect they are intentional - there are a number of ways to attach a propeller without having to disturb that surface, or using flush caps. Cavitation is caused by a drop in pressure. This would be seen on the trailing edges of the propeller, and is worse on the outer edge of the propeller which is moving faster through water than the inner area. I doubt these spheres have any effect on cavitation at all. It is either a...

The difference between the two equations The cavitation number is the ratio of the static pressure difference to the dynamic pressure difference. So, if you want to use the first equation, you would need to take the pressure using a Pitot tube to measure the total pressure, whereas if you want to use the second equation you will need to measure the freestream velocity, but I would recommend measuring it upstream rather than downstream because of possible effects of acceleration and boundary layer growth. Also, your $V$ should be $V_{in}$ such that it corresponds to the same location where $p_{in}$...


How is it possible that people observing an HTTPS connection being established wouldn't know how to decrypt it?

I've often heard it said that if you're logging in to a website - a bank, GMail, whatever - via HTTPS, that the information you transmit is safe from snooping by 3rd parties. I've always been a little confused as to how this could be possible. Sure, I understand fairly well (I think) the idea of encryption, and that without knowing the encryption key people would have a hard time breaking the encryption. However, my understanding is that when an HTTPS connection is established, the encryption key is "discussed" between the various computers involved before the encrypted connection is established. There may be many factors involved in choosing an encryption key, and I know it has to do with an SSL certificate which may come from some other server. I do not know the exact mechanism. However, it seems to me that if the encryption key must be negotiated between the server and the client before the encryption process can begin, then any attacker with access to the network traffic would also be able to monitor the negotiation for the key, and would therefore know the key used to establish the encryption. This would make the encryption useless if it were true. It's obvious that this isn't the case, because HTTPS would have no value if it were, and it's widely accepted that HTTPS is a fairly effective security measure. However, I don't get why it isn't true. In short: how is it possible for a client and server to establish an encrypted connection over HTTPS without revealing the encryption key to any observers?

encryption tls cryptography man-in-the-middle key-exchange

As a starting point, we will consider that each elementary operation implies a minimal expense of energy; Landauer's principle sets that limit at 0.0178 eV, which is 2.85×10 -21 J. On the other hand, the total mass of the Solar system, if converted in its entirety to energy, would yield about 1.8×10 47 J (actually that's what you would get from the mass of the Sun, according to this page , but the Sun takes the Lion's share of the total mass of the Solar system). This implies a hard limit of about 6.32×10 68 elementary computations, which is about...

It is the magic of public-key cryptography . Mathematics are involved. The asymmetric key exchange scheme which is easiest to understand is asymmetric encryption with RSA. Here is an oversimplified description: Let n be a big integer (say 300 digits); n is chosen such that it is a product of two prime numbers of similar sizes (let's call them p and q ). We will then compute things "modulo n ": this means that whenever we add or multiply together two integers, we divide the result by n and we keep the remainder (which is between 0 and n-1 ,...


What exactly is meant by "microstructure noise"?

I see that term tossed around a lot, in articles relating to HFT, and ultra high frequency data. It says at higher frequencies, smaller intervals, microstructure noise is very dominant. What is this microstructure noise that they refer to?

volatility statistics high-frequency market-microstructure high-frequency-estimators

The volatiltiy surface is just a representation of European option prices as a function of strike and maturity in a different "unit" - namely implied volatility (while the term implied volatility has to be made precise by the model used to convert prices (quotes) into implied volatilities - for example: we may consider log-normal vols and normal vols). Volatility is often preferred over prices, e.g., when considering interpolations of European option prices (although this may introduce difficulties like arbitrage violations, see, e.g., http://papers.ssrn.com/sol3/papers.cfm?abstract_id=1964634 ). A local volatility model can generate a perfect fit to the implied volatility surface via Dupire's...

Volatility is mean reverting if the underlying security doesn't drop to zero. If the security has some underlying "value" then its price is co-integrated with that "value". The volatility is the uncertainty of that price as it tracks the security's "value". Edit 12/03/2011 ================================================= @pteetor, I may have missed something, but the question was " Why is volatility mean-reverting?". I realize that the standard answer is that the VIX (I'm assuming he's asking about the VIX) is related to the historical volatility of the S&P. A simple version of that relationship provides a reasonable R^2 (see Fig. 1). It relates...

The term has a different meaning to different people. to econometricians, microstructure noise is a disturbance that makes high frequency estimates of some parameters (e.g. realized volatility) very unstable. Generally this strand of the literature professes agnosticism as to the its origin; to market microstructure researchers, microstructure noise is a deviation from fundamental value that is induced by the characteristics of the market under consideration, e.g. bid-ask bounce, the discreteness of price change, latency, and asymmetric information of traders. The last example is frequently cited but I don't think it is accurate. Asymmetric information does not have to be a...

The risk-neutral measure $\mathbb{Q}$ is a mathematical construct which stems from the law of one price , also known as the principle of no riskless arbitrage and which you may already have heard of in the following terms: "there is no free lunch in financial markets". This law is at the heart of securities' relative valuation , see this very nice paper by Emmanuel Derman ("Metaphors, Models & Theories", 2011) and some part of this discussion. In what follows, assume for the sake of simplicity existence of a risk-free asset ; deterministic and constant rates, with risk-free rate $r$ ;...


Things like gender and age and height and weight make perfect sense to me, but I don't really see why most doctors ask for your race. Is there a medical reason behind this or is it just for identification purposes?

epidemiology research genetic-predisposition race ethnicity

In general, the benefit of flu shots is to the general population. Taking the cited value of 40%-60% from the CDC, we can say that it might be a coin toss for you personally to be protected from influenza by the shot. However, if many thousands of people take the flu shot, even if it only works on 40% of them, it helps protect the remaining population from the spread of the virus (AKA herd immunity). This is especially important to those within the population who cannot access the shot or cannot receive it due to a preexisting medical condition....

Let's get a few things out of the way... Sex is normal ( 1 ). Sexual desire and arousal are normal ( 2 ). Asexuality is normal ( 3 ). Masturbation is normal ( 4 ),( 5 ). There is no problem whatsoever with these three things, although everyone blushes when they talk about them. Is Masturbation healthy? Downsides : Masturbation is not risk free. It is about as dangerous as chewing or walking ( 6 ). Some side effects are irritated skin and ruptured penis, but only if you really, really, really overdo it (Once or twice a day...

Race and ethnicity are risk factors in many diseases. Examples include, but are not limited to, cystic fibrosis and spinal muscular atrophy. There is also an epidemiological purpose of collecting this information. It is important to know if some disease is affecting some races or some ethnicities disproportionately. This is how it was found out that race or ethnicity is a risk factor in certain diseases in the first place. RFERENCES: Sheets L, Johnson J, Todd T, Perkins T, Gu C, Rau M. Unsupported labeling of race as a risk factor for certain diseases in a widely used medical textbook....


Why do cars turn by turning the front wheel?

Why do we design cars to turn by turning the front wheel? Wouldn't it better to keep all wheels straight and turn by rotating the wheels on one side of a car more then the wheels on the opposite side of the car, like tank tracks do? That way you can turn even if you are standing still. Why don't cars do this?

Note: This is specific to gasoline based engines. Assuming your car was produced after the ~1990's it is equipped with a Deceleration Fuel Cut-Off (DFCO) system which cuts the fuel flow to the engine when the gas pedal is not depressed and the car is in gear. In this case it is more fuel efficient to stay in gear because you are letting gravity run the engine instead of fuel. In addition, it saves wear on your brakes because the partial-vacuum created in the engine leads to engine-braking . In many states in the US it is actually required that...

If you were going to turn left 90 degrees, without turning the wheels, then you wind up dragging the wheels sideways while you turn. 16 seconds into this video shows exactly what I'm talking about . So every time you try to back out of your driveway, or a parking spot, or turn into a parking spot, or turn anywhere for any reason, you're going to lay down rubber because the tires are rotating quickly while remaining nearly stationary as you turn. Again, look at the wheel slip in the video I linked. You'd be hard pressed to find "four...

Please note : I'm not a building designer by trade, but I have had to investigate related questions for other reasons. I'll let you in on a dirty secret about sanitation lines within buildings - The biggest concern is not about how fast things are flying, it's about maintaining air pressure and providing adequate ventilation. This guide presents a bit of a historical background to tall building design with respect to sanitation system design. This presentation provides some more recent perspective and goes into some of the research that is refining current building standards. The traditional viewpoint is that waste...

After the 2014 ICCT report revealed that these light-duty passenger diesel vehicles were emitting too much NOx and US regulators confronted VW about the results, VW did some testing and proposed a voluntary software recall to recalibrate the various emissions control devices on the affected vehicles. From the California Air Resources Board's (CARB's) in-use compliance letter to Volkwagen AG, 2015-09-18 , following that recall: To have a more controlled evaluation of the high NOx observed over the road, CARB developed a special dynamometer cycle which consisted of driving the Phase 2 portion of the FTP repeatedly. This special cycle revealed...