Changing the resonant nucleus by altering the static field, compensation of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si3.svg"><mml:mrow><mml:mi>γ</mml:mi></mml:mrow></mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si4.svg"><mml:mrow><mml:msub><mml:mi>B</mml:mi><mml:mn>0</mml:mn></mml:msub></mml:mrow></mml:math> effects in T2 and T2* measurements of porous media
Bibliographic record
Abstract
• Multinuclear MR study of 1 H, 13 C, and 23 Na at constant Larmor frequency of 33 MHz. • A variable field superconducting magnet was employed. • For a given f 0 = 33.71 MHz, the B 0 field for 1 H: 0.79 T; 23 Na: 2.99 T 13 C: 3.15 T. • Similar line widths & inhomogeneous broadening effects observed in T 2 * measurements. • Similar diffusion through internal field gradient effects observed between nuclei. Multinuclear 1 H, 13 C, and 23 Na magnetic resonance (MR) has many advantages for studying porous media systems containing hydrocarbons and brine. In recent work, we have explored changing the nucleus measured, keeping the Larmor frequency constant, by changing the static magnetic field B 0 . Increasing the static B 0 field distorts the field in the pore space due to susceptibility mismatch between the matrix and pore fluid. Distortion of the magnetic field in the pore space scales with the applied static field. The gradients that result from the spatial variation of the distorted field will also scale with B 0 . The equations that describe the inhomogeneous broadening in T 2 * show that the MR result depends on γ B 0 . The diffusion through internal field gradients effect on T 2 depends on the product of γ and G, with G depending on B 0 . Increasing the static field to bring a nucleus with lower γ into resonance at the same frequency will result in the products γ B 0 and γ G being constant, and therefore, inhomogeneous broadening and diffusion attenuation effects in porous media are predicted to be constant. We explore the T 2 * hypothesis with 23 Na and 1 H measurements of brine in porous reservoir core plugs. We explore the diffusion through internal field gradients effect hypothesis with 1 H and 13 C measurements of decane saturated glass beads. The nuclei chosen for study: 1 H, 13 C, and 23 Na are the three most important nuclei for studies of fluids (brine and hydrocarbons) in reservoir core plugs. These three nuclei have a common resonance frequency of 33.7 MHz at static fields of 0.79 T, 3.19 T, and 2.99 T, respectively. All three fields are readily achieved with our variable field superconducting magnet.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.018 | 0.004 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".