bluuebunny/crossref_metadata_2025 huggingface dataset:
Paychecks don’t tell all: Working towards gender pay equality through recruitment processes
Authors: Singh Anisha , Ngugi Stanley
Published: July 2024

At Busara we believe the pursuit of a diverse, equitable and inclusive workplace must start by looking within. We did some research to understand how we’re doing along the various aspects of diversity, including nationality, age, gender, ethnicity, parenthood, education, and mental health. Using this data, we will strengthen our DEI framework addressing internal inequities and considering our identity as a global organization. As part of our commitment to transparency and accountability, we have published our gender representation and pay gap statistics.
PENGARUH PENGGUNAAN MEDIA PEMBELAJARAN BAHASA INDONESIA DI SEKOLAH DASAR
Authors: Izza Roisyatul
Published: July 2024

The aim of this research is to determine the effect of using Indonesian language learning media in elementary schools. Indonesian has a very important position and function for the daily lives of elementary school students. Therefore, Indonesian language learning in elementary school needs to be optimized, one of which is the use of media. The use of Indonesian language learning media in elementary school makes it easier to achieve Indonesian language learning goals, especially in language skills. This research uses a qualitative approach with a literature review method. The data collected and analyzed all come from literature and other documentation materials, such as articles in journals, as well as other media that are relevant and are still being studied. So, by using a qualitative approach to this literature study method, it can be seen that there is an influence on the use of Indonesian language learning media used in elementary schools. The benefit of this research is that readers can find out the important role of media in learning Indonesian in elementary school
Oxygen diffusion through perovskite membranes
Authors: Wang Haihui , Yang Weishen , Tablet Cristina , Caro Jürgen
Published: July 2024

The oxygen permeation flux through the perovskite membrane made of Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) has been measured as a function of both the temperature and the oxygen pressure gradient across the membrane. A simple model for the surface exchange fluxes was used to understand the mechanism of the oxygen transport. The limiting step of the oxygen transport was found to be the bulk diffusion for the BSCF perovskite at temperatures above 700 oC. Furthermore, the oxygen vacancy diffusion coefficient (Dv) can be deduced from the dependence of the oxygen permeation flux on the oxygen pressure gradient. From permeation measurement on the BSCF membrane tube, Dv is between 2.82×10-9 m2/s at 900 oC and 0.82×10-9 m2/s at 700 oC.
Impact of multi-scale moisture transport on durability of hardened cement pastes
Authors: Chemmi Houria , Petit Dominique , Levitz Pierre , Korb Jean-Pierre , Bérard Mathieu
Published: July 2024

We report on proton NMR relaxation of hardened Grey CEM I paste with two controlled degree of relative humidity. The comparison between these two aged materials evidences that the moisture transport only occurs on the meso and capillary scales. The proton population distribution vs T1 follows power laws with a negative exponent in the nanopore-mesopore pore scale, and a positive exponent in the mesopore-capillary pore scale. This opposite exponent sign shows that the spatial hierarchical proton distribution behaves like a surface and volume distribution on short and large scales, respectively.
Low cost CE-NMR with microcoils for chemical detection
Authors: Adams Kristl L. , Klunder Greg , Demas Vasiliki , Malba Vince , Bernhardt Anthony , Evan Lee , Harvey Chris , Maxwell Robert , Herberg Julie L.
Published: July 2024

Understanding speciation in solids and solutions is important for environmental and toxicological purposes. Capillary electrophoresis (CE) is a simple rapid separation technique that can be used to identify species in solution. CE is particularly is well suited for rapid separations of metal containing samples. Direct on-capillary measurement of metal compound speciation can be obtained with nuclear magnetic resonance (NMR). The development of a low-cost microcoil CE-NMR system for in situ characterization of samples of interest is discussed. High precision laser lithography is used to produce copper sputtered microcoils that have comparable resistivity and quality factors to that of hand wound microcoils. A portable NMR system coupled with a CE system has the potential to identify chemical species in aqueous solutions. In addition, transient isotachophoresis can separate and pre-concentrate samples of interest to obtain separate chemical peaks for speciation by online NMR analysis. We are developing separation assays to determine the speciation of chemical complexes in solutions with minimal perturbation to the original sample equilibrium. On-line NMR measurements will be made downstream of the UV detector.
Measurements of diffusion, T1 and T2 in one shot by MMME
Authors: Ren Xiaohong , Song Yi-Qiao
Published: July 2024

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%.
Split 180° sequences
Authors: Freed Denise E. , Scheven Ulrich M. , Hürlimann Martin D.
Published: July 2024

In applications of NMR in inhomogeneous fields, sequences based on the Carr-Purcell-Meiboom-Gill (CPMG) sequence play a central role. The standard CPMG sequence consists of an initial 90° excitation pulse, followed by a long string of 180° refocusing pulses. This creates a series of echoes that decay with characteristic relaxation time T2eff. Here we present a modified sequence, the Split-180° sequence that specifically takes advantage of grossly inhomogeneous fields. In its simplest implementation, the 180° refocusing pulse of the CPMG sequence is split into two separate pulses. This sequence, which can be viewed as a modification of the CPMG sequence, simultaneously generates two types of signal that can be separately detected. One is a CPMG-like signal that decays with the expected relaxation time T2eff. In addition, a second type of signal builds up and approaches a steady-state. The amplitude of this dynamic equilibrium depends on the ratio of the longitudinal to the transverse relaxation times, T1/T2. We present experimental results and summarize the new theory that describes both signals in a unified manner.
Time-dependent diffusion coefficient of proton in polymer electrolyte membrane
Authors: Ohkubo Takahiro , Kidena Koh , Ohira Akihiro
Published: July 2024

We investigated the time-dependent self-diffusion coefficients of water, D(T eff), in polymer electrolyte membranes at 278 K. TheD(T eff) was measured from T eff=0.7 to 100 ms by field gradient NMR techniques. The results showed that the self-diffusion coefficients of water were dependent on T eff less than 2 ms due to restricted diffusion, and were constant beyond 3 ms. The tortuosity and surface-to-volume ratio related to water diffusion were also estimated from D(T eff). The obtained values revealed the existence of large-scale restricted geometry compared with well-known nanometer-sized domain in polymer electrolyte membranes.
Characterisation of pulsing flow in trickle-bed reactors using ultra-fast magnetic resonance imaging
Authors: Nguyen Thoa T. M. , Sederman Andrew J. , Gladden Lynn F.
Published: July 2024

We use ultra-fast Magnetic Resonance Imaging (MRI) to characterise hydrodynamics during pulsing flow in trickle-bed reactors. One-dimensional (1-D) liquid holdup profiles along the flow direction were acquired using Fast Low Angle SHot (FLASH) MRI at spatial and temporal resolutions of 352 μm pixel-1 and 3.3 ms, respectively. Liquid pulse properties such as pulse velocity, duration and frequency obtained with MRI are in good agreement with those measured using a well established technique called the conductance method. In addition, MRI gives local measurements and provides additional spatial information to track individual liquid pulses, which cannot be obtained with the conductance method approach.
Chemical resolution in T2-T1 correlations
Authors: Mitchell Jonathan , Chandrasekera Thusara C. , Fordham Edmund J. , Crawshaw John , Staniland John , Johns Mike L. , Gladden Lynn F.
Published: July 2024

Oil and water fractions have been identified in fluid saturated carbonate rock cores using a novel T2-T1-d pulse sequence. The inclusion of the chemical shift dimension d allows T2-T1 plots to be generated independently for the oil and water. The T2-T1-d pulse sequence utilises a “double-shot” T1 measurement that provides free induction decays (FIDs) as a function of both relaxation times for suitably broad line samples. The T2-T1-d data set is acquired in the same experimental time as a conventional T1-T2 measurement (without chemical resolution) of equivalent data density. Here we demonstrate that different behaviour can be observed between the oil and water fractions in water wet and preferentially oil wet cores, and that saturation states can be determined. This technique could provide a quantitative NMR measure of wettability.
Magnetic resonance spectral characterization of diffusion with chemical shift resolution
Authors: Lasič Samo , Åslund Ingrid , Topgaard Daniel
Published: July 2024

We present a modulated gradient spin-echo method (MGSE), which uses a train of sinusoidally shaped gradient pulses separated by 180-degree RF pulses. The RF pulses efficiently refocus chemical shifts and de-phasing due to susceptibility differences, resulting in undistorted, high-resolution diffusion weighted spectra. This allows for simultaneous spectral characterization of diffusion of several molecular components with different chemical shifts. Feasibility of the technique is demonstrated by following the diffusion of water, oil, and water-soluble salt in a highly concentrated water-in-oil emulsion.
Human mobility and spatial disease dynamics
Authors: Brockmann Dirk , David Vincent , Gallardo Alejandro Morales
Published: July 2024

The understanding of human mobility and the development of qualitative models as well as quantitative theories for it is of key importance to the research of human infectious disease dynamics on large geographical scales. In our globalized world, mobility and traffic have reached a complexity and volume of unprecedented degree. Long range human mobility is now responsible for the rapid geographical spread of emergent infectious diseases. Multiscale human mobility networks exhibit two prominent features: (1) Networks exhibit a strong heterogeneity, the distribution of weights, traffic fluxes and populations sizes of communities range over many orders of magnitude. (2) Although the interaction magnitude in terms of traffic intensities decreases with distance, the observed power-laws indicate that long range interactions play a significant role in spatial disease dynamics. We will review how the topological features of traffic networks can be incorporated in models for disease dynamics and show, that the way topology is translated into dynamics can have a profound impact on the overall disease dynamics. We will also introduce a class of spatially extended models in which the impact and interplay of both spatial heterogeneity as well as long range spatial interactions can be investigated in a systematic fashion. Our analysis of multiscale human mobility networks is based on a proxy network of dispersing US dollar bills, which we incorporated in a model to produce real-time epidemic forecasts that projected the spatial spread of the recent outbreak of Influenza A(H1N1).
NMR diffusion measurements of complex systems
Authors: Stait-Gardner Tim , Willis Scott A. , Yadav Nirbhay N. , Zheng, Gang , Price William S.
Published: July 2024

The pulsed gradient spin-echo nuclear magnetic resonance experiment is a powerful tool for studying the constitution and structure of complex systems (e.g., polydisperse systems and porous media). In applications to polydisperse systems, it is important to consider the effects of obstruction, exchange, entanglement, and diffusional averaging processes whereas in applications to porous samples, reliable structural information can only be extracted from the time-dependence of the apparent diffusion coefficient when the deleterious effects of spatially and/or temporally inhomogeneous background (magnetic field) gradients can be suppressed. These issues are considered in this review.
Recent progress in the simulation of diffusion associated with hollow and Bi-metallic nanoparticles
Authors: Murch Graeme E. , Evteev Alexander V. , Levchenko Elena V. , Belova Irina V.
Published: July 2024

In this paper, we review the recent understanding gained by kinetic Monte Carlo and molecular dynamics simulation and related theory of the diffusion processes involved in 1) the formation and later shrinkage of hollow nanoparticles and 2) the formation of segregated bi-metallic nanoparticles.
Mechanical stability: a construction principle for cells
Authors: Wolff Lars , Kroy Klaus
Published: July 2024

The glassy wormlike chain model is a highly successful phenomenological model recently introduced to describe anomalously slow subdiffusive dynamics in biopolymer networks and living cells. Here we extend this model by proposing a generic scheme how to include nonlinear plastic effects by introducing the possibility of force-dependent opening and closing of internal bonds. Further, we discuss physiological implications of this bond kinetics. Stability arguments lead us to the postulation of a “physiological sheet” in the parameter space. This sheet defines the set of parameters characterizing cells which are flexible enough to perform biological tasks while still being able to bear external perturbations characteristic of their surroundings and their internally generated prestress without damage. At the end of this contribution, we speculate about the connection between prestress and cell stiffness and about the mechanism by which the cell adapts to its mechanical environment.
simple mathematical proof of boltzmann's equal a priori probability hypothesis
Authors: Evans Denis J. , Searles Debra J. , Williams Stephen R.
Published: July 2024

Using the Fluctuation Theorem (FT), we give a first-principles derivation of Boltzmann’s postulate of equal a priori probability in phase space for the microcanonical ensemble. Using a corollary of the Fluctuation Theorem, namely the Second Law Inequality, we show that if the initial distribution differs from the uniform distribution over the energy hypersurface, then under very wide and commonly satisfied conditions, the initial distribution will relax to that uniform distribution. This result is somewhat analogous to the Boltzmann H-theorem but unlike that theorem, applies to dense fluids as well as dilute gases and also permits a nonmonotonic relaxation to equilibrium. We also prove that in ergodic systems the uniform (microcanonical) distribution is the only stationary, dissipationless distribution for the constant energy ensemble.
3D X-ray CT and diffusion measurements to assess tortuosity and constrictivity in a sedimentary rock
Authors: Takahashi Hiroaki , Seida Yoshimi , Yui Mikazu
Published: July 2024

A high-resolution, three-dimensional (3D) image of the interior of the sedimentary rock was obtained by means of nano-focus X-ray computer tomography (X-ray CT). Using computational methods to analyze the 3D microstructure of the rock, we presented the tortuosity and geometrical constrictivity. We also presented results on the tritiated water (HTO) diffusion tests and a mercury intrusion porosimetry (MIP) test performed on the rock. We have compared these results to understand the dominant parameters that control diffusion of HTO in the present system. These results suggest that the dominant parameters in the present system are not the constrictivity but the tortuosity and the diffusion-accessible porosity. The material considered in this study is the siliceous mudstones sampled from 500 m in depth at the Wakkanai formation around Horonobe underground research center in Hokkaido, Japan.
Influence of defect clusters on diffusion processes in UO2+x
Authors: Riahi Fatma , Mekki Djamel Eddine
Published: July 2024

Thermodynamic and transport properties of hyperstoichiometric uranium dioxide,UO2+x, constitute a key issue in the application of this material for nuclear fuel since they are closely related to many chemical and physical processes, e.g., diffusion or creep. Starting from a point defect model for UO2+x developed by the authors in a preceding work[1] and quantitatively consistent with some literature experimental measurements of deviation from stoichiometry [2] and electrical conductivity[3],the oxygen and uranium self diffusion processes have been studied in order to appreciate the influence of defects involved in the model and particularly, the two Willis complexes i.e., 2(Oi"Oi''Vȯ)" and 2(Oi"O1''Vȯ)4''. Such a result leads the way to a better understanding of the mechanisms involved in diffusion processes and also helps to define more accurately the nature, as well as the type of the preferential interactions between diffusing impurities and the defects responsible for these transport properties.
fractal based model of diffusion MRI in cortical grey matter
Authors: Hansen Brian , Østergaard Leif , Vestergaard-Poulsen Peter
Published: July 2024

Diffusion Weighted Magnetic Resonance (DWMR) Imaging is an important tool in diagnostic neuroimaging, but the biophysical basis of the DWMR signal from biological tissue is not entirely understood. Testable, theoretical models relating the DWMR signal to the tissue, therefore, are crucial. This work presents a toy version of such a model of water DWMR signals in brain grey matter. The model is based on biophysical characteristics and all model parameters are directly interpretable as biophysical properties such as diffusion coefficients and membrane permeability allowing comparison to known values. In the model, a computer generated Diffusion Limited Aggregation (DLA) cluster is used to describe the collected membrane morphology of the cells in cortical grey matter. Using credible values for all model parameters model output is compared to experimental DWMR data from normal human grey matter and it is found that this model does reproduce the observed signal. The model is then used for simulating the effect on the DWMR signal of cellular events known to occur in ischemia. These simulations show that a combination of effects is necessary to reproduce the signal changes observed in ischemic tissue and demonstrate that the model has potential for interpreting DWMR signal origins and tissue changes in ischemia. Further studies are required to validate these results and compare them with other modeling approaches. With such models, it is anticipated that sensitivity and specificity of DWMR in tissues can be improved, leading to better understanding of the origins of MR signals in biological tissues, and improved diagnostic capability.
Nuclear Magnetic Resonance Logging While Drilling (NMR-LWD)
Authors: Blanz Martin , Kruspe Thomas , Thern Holger Frank , Kurz Gerhard Alfons
Published: July 2024

NMR T2 distribution measurement is our chosen everyday method for NMR logging while drilling oil and gas wells. This method yields straightforward preparation and execution of the job as well as a normally easy interpretation of the measured data. For instance, gas and light oil discrimination against water is feasible by direct observation of the T2 distribution. A condition for this measurement method is a NMR logging tool that hardly moves while drilling and in addition uses a small static magnetic field gradient and short inter-echo time TE to be motion tolerant. Using data compression techniques, we can transmit by mud pulse telemetry the T2 distribution in real time from the borehole to the surface. This enables the drilling operator to use the NMR data for real-time decisions such as geosteering.
Dynamic correlations between susceptibility gradients and T2-relaxation as a probe for wettability properties of liquid saturated rock cores
Authors: Pavlin Tina , Seland John Georg
Published: July 2024

We explore the use of correlations between susceptibility gradients, G0, and T2-relaxation (G0-T2), and show how the difference in response for oil and water with respect to G0 can be used for improved characterization of wettability of the internal surface in porous rock cores.
spoiler recovery method for rapid diffusion measurements
Authors: Sørland Geir Humborstad , Anthonsen Henrik Walbye , Zick Klaus , Sjöblom Johan , Simon Sébastien
Published: July 2024

A method for rapid acquisition of multiple scans of NMR sequences is presented. The method initially applies two RF-pulses in combination with two magnetic field gradient pulses of opposite polarity, different strength and different duration. The basic idea is to spoil any magnetization in any direction before by letting the system recover to some degree of restoration of the thermal equilibrium magnetization. Thereafter any pulse sequence can be applied, and the next scan may be run immediately after the end of the pulse sequence. Thus one avoids the 5 times T1 delay between each scan. A set of PFG sequences are presented that apply the spoiler recovery method for significant reduction in acquisition time, and the method has been verified at 0.5 Tesla as well as at 11.7 Tesla.
Maxwell-Stefan diffusivities and velocity cross-correlations in dilute ternary systems
Authors: Liu Xin , Bardow André , Vlugt Thijs, J.H.
Published: July 2024

The Maxwell-Stefan (MS) approach is commonly used for describing mass transport by diffusion in gases and liquids since it correctly accounts for the chemical potential gradient as driving force. It is well known that MS diffusivities are concentration dependent which should be taken into account in practical applications. Unfortunately, it is difficult to obtain MS diffusivities both from experiments and molecular simulations. Therefore, there is a considerable interest in predictive models describing the concentration dependence of MS diffusivities. MS diffusivities can be expressed as functions of (1) easily obtainable self- diffusivities, and (2) the integrals of velocity cross-correlations. By assuming that the latter terms are small, we recently derived the multicomponent Darken equation. The objectives of the present study are twofold: First, we present a validation of the multicomponent Darken equation in ternary systems. Second, we investigate the dependence of velocity crosscorrelations on concentration and system size. A linear relation between the velocity cross-correlations and 1/N is found (“N” being the total number of molecules in the system). Two types of systems are studied: (1) Weeks-Chandler-Andersen (WCA) fluids in which only repulsive interactions are considered; (2) the ternary system water-DMSO-methanol in which atoms are interacting using both Lennard-Jones and electrostatic potentials.
Adsorption of organics on MSC5A in supercritical CO2: chromatographic measurements & stop & go simulation
Authors: Chihara Kazuyuki , Ito Shingo , Nagashima Hideo , Hikita Masayuki , Suzuki Ryosuke
Published: July 2024

Chromatographic measurements were made for the adsorption of benzene, toluene and m-xylene on molecular sieving carbon (MSC) in a supercritical fluid CO2 mixed with organics. A supercritical chromatograph packed with MSC was used to detect pulse responses of the organics. Adsorption equilibria and adsorption dynamic parameters for organics were obtained by moment analysis of the response peaks. Dependences of adsorption equilibrium constants, K*, and micropore diffusivity, D, on the amount adsorbed were examined. The dependencies of adsorption equilibrium constants, K*, and micropore diffusivities, D, for benzene, toluene and m-xylene, on the molarity of benzene over a range of temperature and pressure were obtained. Experimental results were simulated using the “Stop & Go” method as well as by molecular simulation.
Dynamics of Rouse polymers in Maxwell fluids
Authors: Tothova Jana , Lisy Vladimir
Published: July 2024

A generalization of the Rouse model of the dynamics of polymers in solution is proposed. The motion of long polymer chains is considered to be due to exponentially correlated random forces driving the polymer segments, which is a more realistic model than the approximation of white thermal noise in the standard theory. Due to the fluctuationdissipation theorem such a model is consistent with the assumption that the solvent has weakly viscoelastic properties, which corresponds to the theory, originally proposed by Maxwell and later substantiated coming from first principles. A consequence of such approach is the appearance of “memory” in the polymer dynamics. To obtain a correct description at short times, we also include inertial effects into the consideration. Discrete and continuum models of the universal dynamics of polymer chains are built. Exact solutions are obtained for the center of mass motion of the polymer coil in the discrete variant of the theory. The time correlation functions describing the dynamics of internal modes are calculated in the continuum approximation. The results significantly differ from those in the standard Rouse theory and its later generalizations valid at long times.
NMR study of the anisotropic transport properties of uniaxially stretched membranes for fuel cells
Authors: Klein Mathieu , Perrin Jean-Christophe , Leclerc Sébastien , Guendouz Laouès , Lottin Olivier , Dillet Jérôme
Published: July 2024

We used NMR techniques to probe the anisotropic properties of stretched Nafion®115membranes. The alignment of the polymeric structure under a uniaxial load is at the origin of a strong anisotropy of both the water self-diffusion coefficient and the proton conductivity. The determination of these two important membrane properties may lead to new fundamental information on the nature of the proton transport mechanisms in such oriented weaklycharged systems.
Water dynamics of LiCl solutions confined in nanopores
Authors: Beckert Steffen , Stallmach Frank
Published: July 2024

The self-diffusion of water in aqueous solutions of lithium chloride in bulk solutions and in these solutions confined to porous glass monoliths with bimodal pore structure has been studied by PFG NMR. The concentration dependent data for the bulk solutions are analyzed by the description of Sevrugin et al. [1], which yields information about the water dynamics within the ion’s hydration shell. For an application to confined diffusion, this description is extended by introducing a tortuosity factor. Whereas in the larger macropores no influence on the water dynamics within the hydration shell is detected, in the smaller mesopores, a significant increase of the mobility of the hydrating water molecules is observed.
Rapid characterization of emulsions by pulsed field gradient nuclear magnetic resonance
Authors: Sørland Geir Humborstad , Keleşoğlu Serkan , Simon Sébastien , Sjöblom Johan
Published: July 2024

A method for rapid characterization of emulsions is presented. From the proposed setup we are able to measure the droplet size distribution of brine or water droplets confined by an oil phase, even though there is complete overlap in relaxation times and/or molecular mobility between the water and the oil phases. A PFG-NMR sequence is presented that applies the spoiler recovery method for significant reduction in acquisition time, and the method is used for rapid characterization of emulsions.
NMR imaging as a tool for studying the diffusion and co-diffusion of gases in zeolite catalysts
Authors: Fraissard Jacques
Published: July 2024

1H NMR imaging is a powerful technique for studying the diffusion of pure hydrocarbons (for example benzene and n-hexane) during their adsorption in or desorption from a fixed bed of zeolite crystallites. This technique is used to visualize the progression of the diffusing molecules in the zeolite bed and to determine their intracrystallite diffusion coefficients. More importantly, NMR imaging is today the only technique able to give the time dependence of the distribution of two gases during their competitive diffusion.
Photon diffusion in biological tissues
Authors: Dudko Olga K. , Weiss George H.
Published: July 2024

The use of laser-based optical techniques for medical imaging is an attractive alternative to other methods that utilize ionizing radiation. Beside being non-carcinogenic, it is non-invasive, the equipment is transportable, and the methodology can be used to examine properties of soft tissue. However, unlike x-ray photons, optical photons generated in the near-infrared suffer significant amounts of scattering by heterogeneous bodies (e.g., organelles) found in biological tissue. Thus, theory is required to interpret experimental data which appear in the form o spatially or temporally varying light patterns on the skin surface. There is a wide range of parameters over which either diffusion theory or the theory of lattice random walks can be called on to translate optical data into medically significant information embodied in optical parameters of the tissue. We discuss several problems in diffusion theory arising in the analysis of optical measurements, for tissues modeled by a semi-infinite or slab geometry, having either isotropic or anisotropic optical parameters. The measured quantities are related to the intensity of light re-emitted on the tissue surface. A brief discussion is given related to the telegrapher’s equation, which has been suggested as a simple way of incorporating the effects of forward scattering. Mention is made of calculations related to layered media which frequently occur in tissues such as skull and esophagus. Finally, we briefly discuss discrete random walk models for photon migration. These have recently been used to provide parameters conveying information related to the region interrogated by photons constrained to reappear on skin surface.
Simulation of diffusion under pressure in bcc metals
Authors: Valikova Irina V. , Nazarov Andrei V.
Published: July 2024

This work is devoted to simulation of atom configurations in bcc metals near the point defect using the molecular static method. The values of migration and formation volumes are very sensitive to the atomic structure in the vicinity of a defect, which makes it necessary to consider a large number of atoms in the computation cell and to take into account an elastic matrix around the cell. We have developed the new model taking into the consideration these factors. It allows to define “fine structure” of displacement atoms near the point defect. The atoms of third zone were embedded in an elastic continuum. The displacement of each atom embedded in an elastic continuum was defined as the first and the second terms in solution of elastic equation. In the framework of this model we calculated the formation and migration volumes of defect. Also we take into the consideration that the energy of system (in particular the system with defect) depends on the outer pressure. This dependence gives an addition to the values of migration and formation volumes.
Projection of two-dimensional diffusion in a curved midline and narrow varying width channel embedded on a curved surface
Authors: Chacón-Acosta Guillermo , Pineda Inti , Dagdug Leonardo
Published: July 2024

This study focuses on the derivation of a general effective diffusion coefficient to describe the twodimensional (2D) diffusion in a narrow and smoothly asymmetric channel of varying width that lies on a curved surface, in the simple diffusional motion of noninteracting point-like particles under no external field. To this end we extend the generalization of the Kalinay-Percus’ projection method [J. Chem. Phys. 122, 204701 (2005); Phys. Rev. E 74, 041203 (2006)] for the asymmetric channels introduced in [J. Chem. Phys. 137, 024107 (2012)], to project the anisotropic 2D diffusion equation on a smooth curved manifold into an effective one-dimensional generalized Fick-Jacobs equation which is modified due to the curvature of the surface. The lowest order in the perturbation parameter, corresponding to the Fick-Jacobs equation, contains an extra term that accounts for the curvature of the surface. We found explicitly the first order correction for the invariant effective concentration, which is defined as the correct marginal concentration in one variable, and we obtain the first approximation to the effective diffusion coefficient analogous to Bradley’s coefficient [Phys. Rev. E 80, 061142 (2009)] as a function of metric elements of the surface. Straightforwardly we study the perturbation series up to the n-th order, and we derive the full effective diffusion coefficient for 2D diffusion in a narrow asymmetric channel, which have modifications due to the curved metric. Finally, as an example we show how to use our formula to calculate the effective diffusion coefficient considering the case of an asymmetric conical channel embedded on a torus.
Diffusion and polymers in fractal, disordered environments
Authors: Fricke Niklas , Bock Johannes , Janke Wolfhard
Published: July 2024

We numerically investigate random walks (RWs) and self-avoiding random walks (SAWs) on critical percolation clusters, basic models for diffusion and flexible polymers in disordered media. While this can be easily done for RWs using a simple enumeration method, it is difficult for long SAWs due to the long-range correlations. We employed a sophisticated algorithm that makes use of the self-similar structure of the critical clusters and allows exact enumeration of several thousand SAW steps. We also investigate a kinetic version of the SAW, the so-called kinetic growth (self-avoiding) walk (KGW), as well static averaging over all RW conformations, which describes the so-called ideal chain. For the KGW, we use a chain-growth Monte Carlo method which is inspired by the pruned-enriched Rosenbluth method. The four walk types are found to be affected in different ways by the fractal, disordered structure of the critical clusters. The simulations were carried out in two and three dimensions.
review on bulk diffusion in metallic solids
Authors: Ghorai Amitava
Published: July 2024

In this paper bulk diffusion techniques in case of metals and alloys will be reviewedwith a special emphasis on resistometric technique.  The experiment is restricted only to those metals, which can be made in the form of wire but has the advantage of applying to materials whose suitable radioactive isotopes are not available. A brief introduction along with different diffusion mechanisms with corresponding activation energies, diffusion coefficients, correlation factors, isotope effect, enhancement factor, etc. is also incorporated. Three models for bulk diffusion are also mentioned.
Determining the clog state of constructed wetlands using an embeddable Earth’s Field Nuclear Magnetic Resonance probe
Authors: Hill-Casey Fraser , Hughes-Riley Theodore , Bradley C. R. , Newton Michael Ian , Morris Robert H.
Published: July 2024

The recent rise in interest of green technologies has led to significant adoption of the constructed wetland as a waste water treatment technique. This increased popularity has only been mired by the decline in operational lifetime of wetland units, leading to the need for more regular, time consuming, and expensive rejuvenation techniques to be performed than initially anticipated. To extend operational lifetimes and increase efficiency of wetland units, it is crucial to have an accurate method to determine the internal state of the wetland system. The most important parameter to measure within the reed bed is the clog state of the system, which is representative of the overall system health. In previous work, magnetic resonance (MR) measurements, parameters of T1 and T2eff, have been demonstrated as extremely powerful tools to determine the internal clog state of a wetland [1, 2]. Measurements have been performed in a laboratory setting, using low field permanent magnet arrangements. This work presents an Earth’s Field Nuclear Magnetic Resonance (EFNMR) probe suitable for in situ measurements within constructed wetlands. We show T2eff and T1 measurements using the EFNMR probe. T1 values are shown to be sensitive to the change in the clog state with 1498 ms for the thickly clogged sample and 2728 ms for the thinly clogged sample. T2eff values are shown to be marginally more sensitive to clog state with 630 ms for a thickly clogged sample and 1212 ms for the thinly clogged sample. This gives distinguishable variation within both parameters suggesting that this probe is suitable for embedding into an operational constructed wetland. This work was conducted as part of an EU FP7 project to construct an Automated Reed Bed Installation, “ARBI”.
Miniature mobile NMR sensors for material testing and moisture-monitoring
Authors: Oligschläger Dirk , Kupferschläger Klaus , Poschadel Thomas , Watzlaw Jan , Blümich Bernhard
Published: July 2024

Miniaturization plays an essential role in modern life of the 21st century. It is encountered, e.g., in communication, personalized and portable computers and in medicine. Miniaturization also affects NMR, one of the most versatile analytical tools, leading to dedicated sensors and portable devices which lead to new applications of NMR in different disciplines. The miniaturization of two portable stray-field NMR sensor types, the NMR-MOUSE® and an inside-out sensor are reported in this work. The sensors are critically evaluated and compared to other standard probes. Applications in material testing and civil engineering are evaluated.
Competition between diffusion and advection may mediate self-repair of wax microstructures on plant surfaces
Authors: Konrad Wilfried , Neinhuis Christoph , Roth-Nebelsick Anita
Published: July 2024

Cuticles are extracellular membranes covering the primary aerial parts of vascular plants. They consist of a multifunctional polymeric material with embedded soluble components, called waxes and serve as the interface between plants and their atmospheric environment, first of all protecting them from desiccation. Waxes are produced within the epidermal cells, then transported to the leaf surface and finally integrated into the polymer or deposited upon the cuticle. Remarkably, damaged wax layers may become repaired within a few hours. Base on an earlier hypothesis we present a theoretical framework explaining how waxes are transported through the plant epidermis by a combination of advection and diffusion. This combination suggests also a self-regulating repair mechanism, based on the assumption that intact cuticles induce an antagonistic equilibrium between advection and diffusion: whenever a wax layer is damaged, the equilibrium is disturbed in favour of advection, starting a repair process, which is intrinsically coming to an end after the cuticle has gained its original thickness.
Grassmann variables and pseudoclassical Nuclear Magnetic Resonance
Authors: Damion Robin A.
Published: July 2024

The concept of a propagator is useful and is a well-known object in diffusion NMR experiments. Here, we investigate the related concept; the propagator for the magnetization or the Green’s function of the Torrey-Bloch equations. The magnetization propagator is constructed by defining functions such as the Hamiltonian and Lagrangian and using these to define a path integral. It is shown that the equations of motion derived from the Lagrangian produce complex-valued trajectories (classical paths) and it is conjectured that the end-points of these trajectories are real-valued. The complex nature of the trajectories also suggests that the spin degrees of freedom are also encoded into the trajectories and this idea is explored by explicitly modeling the spin or precessing magnetization by anticommuting Grassmann variables. A pseudoclassical Lagrangian is constructed by combining the diffusive (bosonic) Lagrangian with the Grassmann (fermionic) Lagrangian, and performing the path integral over the Grassmann variables recovers the original Lagrangian that was used in the construction of the propagator for the magnetization. The trajectories of the pseudoclassical model also provide some insight into the nature of the end-points.
Vacancy formation energy of simple metals using reliable model and ab initio pseudopotentials
Authors: Haldar S. , Ghorai A. , Sen D.
Published: July 2024

We present a self-consistent calculation of the mono vacancy formation energy for seven simple metals Li, Na, K, Rb, Cs (all bcc), Al (fcc) and Mg (hcp) using both model and ab initio pseudopotential used in earlier unified studies. The local model pseudopotential calculations show small variations with respect to different exchange-correlation functions and the results are in fair agreement with other similar calculations and the available experimental data. The comparisons show that reliable model (pseudo) potential for simple metals can indeed be obtained for explaining a host of properties. Also, considering the importance of third order term in ab initio calculations, the results of our second order calculation appear fairly reasonable and are comparable with other first principle calculations. The perturbation series being an oscillating one, we hope to improve the calculational results using suitable series convergence acceleration method in the next part of our study.
FID NMR Studies of Suspensions and Porous Media
Authors: Kishenkov Oleg , Menshikov Leonid , Maximychev Alexander
Published: July 2024

Nuclear Magnetic Resonance is used for the determination of the properties of porous media in Geophysics and oil exploration. As it stands, there is a challenge in understanding the connection between the times measured in Free Induction Decay Nuclear Magnetic Resonance experiments and the shape of samples. In this work, suspensions and watersaturated densely-packed porous media with the volume fraction of the glass solid phase in the range from 10–4 to ∼1 are found to exhibit FID decay rates proportional to the square root of the volume fraction of the solid phase of the samples. A model of spheres in liquid is proposed for the description of such behavior.
High Temperature Fast Field Cycling Study of Crude Oil
Authors: Lozovoi Artur , Hurlimann Martin , Kausik Ravinath , Stapf Siegfried , Mattea Carlos
Published: July 2024

A set of crude oil samples with different composition and characteristics is studied by means of Fast Field Cycling (FFC) 1H relaxometry, which probes the distribution of longitudinal relaxation times T1 as a function of the Larmor frequency. Investigation of T1 profiles at different temperatures is able to provide an insight into the dynamics and structural changes of oil components, with our particular interest being the high temperature behaviour of asphaltene. It is well-known that asphaltenes tend to form porous clusters in crude oils, which can cause severe problems for the process of oil extraction. Therefore, FFC experiments are conducted on Stelar Spinmaster FFC2000 in the temperature range 203K < T <443K, where the upper limit of 443K is aimed at approximating the typical maximal in-situ well temperatures. FFC relaxometry data of crude oils at such a high temperature are obtained for the first time with the use of a specially modified NMR probe. Inverse Laplace transformation is applied to the longitudinal agnetization decays, yielding T1 distributions at different frequencies. A comparative analysis of these distributions for different Larmor frequencies and temperatures showed that there is a systematic variation of the frequency dependence of T1 correlating with the asphaltene content in the samples, at temperatures similar to the well conditions.
Lateral diffusion of proteins in cell membrane
Authors: Lubelski Ariel , Klafter Joseph
Published: July 2024

We present a method describing the lateral movement of proteins in cell membranes as observed in FRAP experiments. We extend earlier results derived for normal diffusion [1] to account for the case of anomalous subdiffusion. Our analytic closed forms are compared to computer simulations of anomalous diffusion and both show excellent agreement. The approach sheds light on the behavior of proteins in such complex systems and provides a tool to analyze experimental results.
Spinodal decomposition of solutions during crystallization
Authors: Guskov Alex
Published: July 2024

The modern theory of phase transitions cannot explain the results of many experiments of interphase mass transfer. One reason for this is the assumption that during crystallization the solution is in the metastable state. The decomposition of the solution occurs by binodal scenario in this case. Crystallization nuclei form and grow in solution. The purpose of this study to show that in many cases the solution during crystallization is in an unstable state. The unstable condition leads to decomposition the solution by spinodal scenario.
PFG-NMR studies of ATP diffusion in PEG-DA hydrogels and aqueous solutions of PEG-DA polymers
Authors: Majer Günter , Southan Alexander
Published: July 2024

Adenosine triphosphate (ATP) is the major carrier of chemical energy in cells. The diffusion of ATP in hydrogels, which have a structural resemblance to the natural extracellular matrix, is therefore of great importance to understand many biological processes. In continuation of our recent studies of ATP diffusion in poly(ethylene glycol) diacrylate (PEG-DA) hydrogels by pulsed field gradient nuclear magnetic resonance (PFG-NMR), we present precise diffusion measurements of ATP in aqueous solutions of PEG-DA polymers, which are not cross-linked to a three-dimensional network. The dependence of the ATP diffusion on the polymer volume fraction in the hydrogels, φ, was found to be consistent with the predictions of a modified obstruction model or the free volume theory in combination with the sieving behavior of the polymer chains. The present measurements of ATP diffusion in aqueous solutions of the polymers revealed that the diffusion coefficient is determined by φ only, regardless of whether the polymers are cross-linked or not. These results seem to be inconsistent with the free volume model, according to which voids are formed by a statistical redistribution of surrounding molecules, which is expected to occur more frequently in the case of not cross-linked polymers. The present results indicate that ATP diffusion takes place only in the aqueous regions of the systems, with the volume fraction of the polymers, including a solvating water layer, being blocked for the ATP molecules. The solvating water layer increases the effective volume of the polymers by 66%. This modified obstruction model is most appropriate to correctly describe the ATP diffusion in PEG-DA hydrogels.