NMR measurement of the magnetic field correlation function in porous media

The structure factor provides a fundamental characterization of porous and granular materials as it is the key for solid crystals via measurements of x-ray and neutron scattering. Here, we demonstrate that the structure factor of the granular and porous media can be approximated by the pair correlation function of the inhomogeneous internal magnetic field, which arises from the susceptibility difference between the pore filling liquid and the solid matrix. In-depth understanding of the internal field is likely to contribute to further development of techniques to study porous and granular media.open9

Measurements of diffusion, T 1 and T 2 in one shot by MMME

In this paper, we demonstrate a rapid simultaneous measurement of diffusion constant D, T1 and T2 relaxation times in just two scans. Theoretical standard deviations of D, T1 T2 for a wide range of T1 and T2 were predicted for given sequences with a random experimental error of 3%. By carefully selecting of sequence parameters for samples with different relaxation times, the error propagators in T1, T2, and D can be modified to within 10%

A fast Monte Carlo sampler for NMR T2 inversion

The inversion of noisy NMR T2 echo data into a T2 spectrum is widely recognized as an inherently non-unique process [1]. One approach to quantifying this uncertainty is to use Monte Carlo sampling. Uncorrelated measurement noise combine with the non-negativity constraint on T2 spectral values to yield spectra following a non-negative normal distribution. There are two published samplers for truncated normal distributions [2], of which nonnegative normal samples are a subset, but we show that these converge too slowly to be practical for the T2 spectral inversion problem. This is because they are based on Gibbs’ samplers that update the spectral estimate just one T2 component at a time. When all of the spectral elements are fixed but one, that one has little room for change without violating the noise constraints on the data. Thus each spectral sample can only be slightly different from the preceding sample, indicating a high degree of statistical correlation and slow convergence. Our solution is to simultaneously update two neighboring spectral components at a time, allowing changes due to one spectral component to be offset by changes in its neighbor. Central to this improvement is a fast 2D slice sampler for non-negative normal distributions. This improves convergence by more than two orders of magnitude. Such speedup allows routine Monte Carlo inversion of 1D NMR spectra, and opens the door for the inversion of 2D NMR spectra

Exploring Boarding Strategies for High-Speed Railway

In light of the increasing demand for passenger transportation on high-speed railway (HSR), the pedestrian flow at HSR stations has become quite crowded in many countries, which has attracted researchers to study the HSR boarding behavior. In this paper, we propose three boarding strategies based on the features of the boarding behavior at an origin HSR station; we then use a cellular automaton (CA) model to study the impacts of boarding strategies on each passenger’s motion during the boarding process at HSR station. The simulation results indicate that some of the three strategies can optimize some passengers’ boarding time and relieve the congestion degree, and the positive impacts on the boarding process are the most prominent when the three strategies are used simultaneously. The results can help administrators to effectively organize the boarding process at the origin HSR station

Propagator Resolved Transverse Relaxation Exchange Spectroscopy

We use the propagator resolved transverse relaxation exchange technique to look at the movement of fluid in three different types of rock samples. The two pore model previously used to fit molecular exchange simulations to the experimental data is expanded to accommodate the three site exchange seen in two of the samples. Estimated values for pore space characteristics from the simulations were compared to values calculated from X‐Ray CT data of the samples. While discrepancies exist between the NMR and X‐Ray CT results, the molecular exchange behavior estimated from the three samples reflects well with their morphology