{
 "body_sha256": "9fc77ca07928214342f44ade280e37f710d8b3a2e8f93a1569ffcab14431877b",
 "caveats": {
  "LV60A_crop": "Talabi's 0.377 porosity is not reachable on the released LV60A image: over all 3,442,951 possible 300^3 crops the porosity spans [0.3555, 0.3713]. The offset he used is not recorded in the thesis, and a central cube is what his other six samples' porosities support. That is the whole of LV60A's porosity gap, and it is not the walk.",
  "band": "This is a RELAXATION pack. Its 200 us save grid is 22x coarser than the #143 rule asks of a Connectom, deliberately: the acquisition it reproduces carries no gradient at all. What keeps that honest is the pack's own band -- 21.33 Hz over the walk at K = 128, small and stated -- and a consumer replaying a gradient beyond it is refused by waveform_band rather than served a wrong number.",
  "inversion": "The log-mean is the weakest link in this comparison, and every number here is on a 1 ms sampling of the decay. Measured on F42A, which still holds 3.3 % of its signal at 3 s: 674.4 ms at 1 ms sampling, 668.0 at 10 ms, 309.7 at 20 ms -- a truncated decay lets the regularised solve split amplitude between a short and a very long component. LV60A, down to 1.0 %, is 487.7 / 487.6 / 487.4 at the same three. Over lam in [0.003, 1] and five T2 grids the log-mean spans 3.1 % on LV60A and 4.2 % on Berea."
 },
 "crossref": {
  "agency": "crossref",
  "container": "Journal of Petroleum Science and Engineering",
  "doi": "10.1016/j.petrol.2009.05.013",
  "resolved": "2026-09-26T23:36:22Z",
  "title": "Pore-scale simulation of NMR response",
  "type": "journal-article"
 },
 "description": "Micro-CT sand packs and a sandstone walked on their own voxels through the label-volume producer: the surface-relaxation reference outside the brain, replayed as a CPMG decay. Relaxation is not in the walk -- one pack answers every relaxivity.",
 "doi": "10.1016/j.petrol.2009.05.013",
 "geometry_derivation": "the geometry is the released one when no free parameter marked 'ours' changes it; these do: crop",
 "geometry_parameters_ours": [
  "crop"
 ],
 "inputs_sha256": "b3f46f15ee36e386e2c73d3262f79b8b72f1b4e1afcca701849b3cf6acb986d6",
 "licence_note": "CC-BY-4.0 images; the thesis is CC-BY-ND and its numbers are cited, never redistributed; the packs are CC-BY-4.0",
 "parameters": [
  {
   "changes_geometry": false,
   "how": "fitted by him to his own LV60Y / F42Y CPMG; an effective value tied to his ~10 um voxel, because a segmentation's surface is the Manhattan area at that resolution, which is what both walks relax against",
   "name": "rho",
   "unit": "m/s",
   "value": 4.1e-05,
   "where": "thesis \u00a77.6.2",
   "whose": "theirs"
  },
  {
   "changes_geometry": false,
   "how": "the brine's self-diffusion at 308 K, stated",
   "name": "D0",
   "unit": "m^2/s",
   "value": 2.07e-09,
   "where": "thesis eq. 7.1",
   "whose": "theirs"
  },
  {
   "changes_geometry": false,
   "how": "the brine's bulk T2, stated; applied at replay, not in the walk",
   "name": "T2B",
   "unit": "s",
   "value": 3.1,
   "where": "thesis eq. 7.2",
   "whose": "theirs"
  },
  {
   "changes_geometry": true,
   "how": "a central cube: over all 3,442,951 possible 300^3 crops of LV60A the porosity spans [0.3555, 0.3713] and his 0.377 is not reachable, so the offset is ours",
   "name": "crop",
   "unit": "voxels",
   "value": "central 300^3",
   "where": "thesis App. A-1 states the size, not the offset",
   "whose": "ours"
  },
  {
   "changes_geometry": false,
   "how": "his is an unconstrained normal-equation solve with a fourth-derivative penalty on 100 points from 0.1 ms; ours is non-negative with a second-difference penalty on 60 points from 1 ms, so the log-mean is comparable to his Table 7-2 rather than computed the same way",
   "name": "T2 inversion",
   "unit": "-",
   "value": "non-negative least squares with a second-difference penalty, lam = 0.1 (t2_distribution)",
   "where": "thesis App. A-3 (after Chen et al. 1999)",
   "whose": "ours"
  },
  {
   "changes_geometry": false,
   "how": "he kills a walker at an attempted move into a grain voxel with probability 2 rho s / (3 D); this walk weights it per specular reflection. The two agree in the continuum limit",
   "name": "surface rule",
   "unit": "-",
   "value": "exp(-2 (rho/D) d_perp) per reflection",
   "where": "thesis \u00a73.5 for his",
   "whose": "ours"
  }
 ],
 "previous_sha256": "6de4bc05c509a8f61329eebb65d135e6c38c0c5a76c4a285cdc866b6cb18657c",
 "published_kind": "number",
 "quantities": [
  {
   "direct": {
    "grid": {
     "from_s": 0.001,
     "kind": "log",
     "n": 60,
     "sample_ms": 1.0,
     "solver": "non-negative least squares with a second-difference penalty, lam = 0.1 (t2_distribution)",
     "to_s": 10.0
    },
    "n_walkers": 200000,
    "se": 0.0019517411744048516,
    "se_derivation": "the delta method over walkers on the log-mean (talabi_micro_ct_rocks.log_mean_gradient), MEASURED here at record time on this family's own lv60a.rpk -- 0.004115 over 45,000 walkers at the same rho, channel and grid -- and scaled to the direct walk's 200,000 by 1/sqrt(N) (x 0.474342). The direct walk's own per-walker decays were not retained; the relative per-echo spread is a property of the substrate and the estimator, not of the pack.",
    "se_kind": "delta_method",
    "solver": "non-negative least squares with a second-difference penalty, lam = 0.1 (t2_distribution)",
    "source": "examples/validation/talabi_micro_ct_rocks.py (run_rock), asserted by tests/validation/test_talabi_rocks.py",
    "unit": "ms",
    "value": 487.6
   },
   "documents": {
    "10.25560/4261": {
     "agency": "datacite",
     "container": "Imperial College London",
     "doi": "10.25560/4261",
     "resolved": "2026-09-26T23:36:23Z",
     "title": "Pore Scale Simulation of NMR Response in Porous Media",
     "type": "Text"
    }
   },
   "name": "T2_log_mean",
   "published": {
    "data_sha256": null,
    "data_url": null,
    "document": "10.25560/4261",
    "locator": "Table 7-2, p. 63, the 'Micro-CT' column of Mean T2 (ms)",
    "printed_in": "Talabi O (2008), Pore Scale Simulation of NMR Response in Porous Media, Imperial College London PhD thesis",
    "uncertainty": 0.0,
    "uncertainty_is": "none stated: Table 7-2 prints one figure per sample with no error bar and the thesis quotes none, so the gate's budget rests on our own standard error alone",
    "unit": "ms",
    "value": 512.0,
    "verbatim": "LV60A             496        512       565              32.2      35.3     27.2       4.8        4.9        3.8"
   },
   "substrate": "LV60A"
  },
  {
   "direct": {
    "grid": {
     "from_s": 0.001,
     "kind": "log",
     "n": 60,
     "sample_ms": 1.0,
     "solver": "non-negative least squares with a second-difference penalty, lam = 0.1 (t2_distribution)",
     "to_s": 10.0
    },
    "n_walkers": 200000,
    "se": 0.0020167727296136247,
    "se_derivation": "the delta method over walkers on the log-mean (talabi_micro_ct_rocks.log_mean_gradient), MEASURED here at record time on this family's own f42a.rpk -- 0.004252 over 45,000 walkers at the same rho, channel and grid -- and scaled to the direct walk's 200,000 by 1/sqrt(N) (x 0.474342). The direct walk's own per-walker decays were not retained; the relative per-echo spread is a property of the substrate and the estimator, not of the pack.",
    "se_kind": "delta_method",
    "solver": "non-negative least squares with a second-difference penalty, lam = 0.1 (t2_distribution)",
    "source": "examples/validation/talabi_micro_ct_rocks.py (run_rock), asserted by tests/validation/test_talabi_rocks.py",
    "unit": "ms",
    "value": 679.0
   },
   "documents": {
    "10.25560/4261": {
     "agency": "datacite",
     "container": "Imperial College London",
     "doi": "10.25560/4261",
     "resolved": "2026-09-26T23:36:23Z",
     "title": "Pore Scale Simulation of NMR Response in Porous Media",
     "type": "Text"
    }
   },
   "name": "T2_log_mean",
   "published": {
    "data_sha256": null,
    "data_url": null,
    "document": "10.25560/4261",
    "locator": "Table 7-2, p. 63, the 'Micro-CT' column of Mean T2 (ms)",
    "printed_in": "Talabi O (2008), Pore Scale Simulation of NMR Response in Porous Media, Imperial College London PhD thesis",
    "uncertainty": 0.0,
    "uncertainty_is": "none stated: Table 7-2 prints one figure per sample with no error bar and the thesis quotes none, so the gate's budget rests on our own standard error alone",
    "unit": "ms",
    "value": 677.0,
    "verbatim": "F42A              668        677       756              42.0      59.0     61.5       5.2        5.8        3.6"
   },
   "substrate": "F42A"
  }
 ],
 "same_released_geometry": false,
 "sample": "the same released micro-CT images: his 'Micro-CT' column is a random walk on these very volumes, on the central 300^3 section (App. A-1), and his 'Experiment' column is a CPMG measured on the sand the images are of",
 "sample_relation": "the same object",
 "source_note": "Dong & Blunt 2009 (Phys Rev E 80:036307) images, Imperial College 2007 collection on Figshare; Talabi 2008 (Imperial College PhD thesis) for the reference random walk and the measured CPMG, published as Talabi et al., J. Pet. Sci. Eng. 2009.",
 "stage": "reference",
 "title": "Pore-scale simulation of NMR response",
 "title_matches": true
}