bluuebunny/crossref_metadata_2025 huggingface dataset:
Axon radius estimation with Oscillating Gradient Spin Echo (OGSE) diffusion MRI
Authors: Siow Bernard , Drobnjak Ivana , Ianus Andrada , Christie Isabel N. , Lythgoe Mark F. , Alexander Daniel C.
Published: July 2024

The estimation of axon radius provides insights into brain function [1] and could provide progression and classification biomarkers for a number of white matter diseases [2-4]. A recent in silico study [5] has shown that optimised gradient waveforms (GEN) and oscillating gradient waveform spin echo (OGSE) have increased sensitivity to small axon radius compared to pulsed gradient spin echo (PGSE) diffusion MR sequences. In a follow-up study [6], experiments with glass capillaries show the practical feasibility of GEN sequences and verify improved pore-size estimates. Here, we compare PGSE with sine, sine with arbitrary phase, and square wave OGSE (SNOGSE, SPOGSE, SWOGSE, respectively) for axon radius mapping in the corpus callosum of a rat, ex-vivo. Our results suggest improvements in pore size estimates from OGSE over PGSE, with greatest improvement from SWOGSE, supporting theoretical results from [5] and other studies [7-9].
Effect of goethite coating on the Nuclear Magnetic Resonance relaxation signal in sand
Authors: Duschl Markus , Pohlmeier Andreas , Vereecken Harry
Published: July 2024

Nuclear magnetic resonance relaxation is a fast and well-known method to get a measure of pore size distributions. To obtain reliable results, one needs to get information about influences like internal gradients evoked by paramagnetic impurities on the NMR relaxation signal. Therefore, we did a series of longitudinal and transverse relaxation experiments of samples with variable paramagnetic content. Missing echo time and magnetic field strength dependence leads us to the conclusion that we have no significant influence of internal gradients in our measurements.
Helium migration and precipitation in irradiated and annealed copper boron alloy
Authors: Tiwari Gyanendra P. , Mishra Ratikanta , Mehrotra Radhey Shyam
Published: July 2024

The paper analyses afresh the data of Russell and Hastings on the changes in lattice parameter during post-irradiation annealing of copper-boron alloy in the temperature range 823-923 K. The changes in lattice parameter are brought about by the generation of helium during irradiation through (n, α) reaction and its subsequent behavior during annealing. The new analytical procedure adopted here follows chemical kinetics route to determine the appropriate activation energies associated with the rate processes controlling the changes in lattice parameter. During the first stage of annealing, the lattice parameter decreases to a value which is below the equilibrium one. The second stage involves the recovery of lattice parameter to the equilibrium value. The diffusion of monovacancy and the jump of helium atom to vacancy on its nearest neighbor site are identified as the unit processes for the first and second stages of annealing respectively. Finally, it is suggested that a helium–monovacancy complex may act as nucleus for the formation of helium gas bubbles.
Hierarchical simulations of diffusion in zeolites
Authors: Papadopoulos George K. , Theodorou Doros N.
Published: July 2024

The work presented in this chapter involves comparison of simulation and experimental results for intracrystalline and long-range diffusion in zeolitic media in order to demonstrate the hierarchical character of the study of transport in microporous structures in response to the need to address sorption and diffusion phenomena in porous materials over broad scales of length and time.
Diffusion in nanocrystalline solids
Authors: Chadwick Alan V.
Published: July 2024

Enhanced atomic migration was an early observation from experimental studies into nanocrystalline solids. This contribution presents an overview of the available diffusion data for simple metals and ionic materials in nanocrystalline form. It will be shown that enhanced diffusion can be interpreted in terms of atomic transport along the interfaces, which are comparable to grain boundaries in coarse-grained analogues. However, the method of sample preparation is seen to play a major role in the experiments and there are still many gaps in understanding the detailed mechanisms of diffusion in these systems.
Oxygen diffusion in oxide crystals - tracing new routes to identify
the rate limiting step of oxygen permeation through perovskite
membranes
Authors: Wang Haihui , Yang Weishen , Tablet Cristina , Caro Jürgen
Published: July 2024

Perovskites are known as mixed electric conductors because they show both electronic (via electron holes) and ionic (via oxygen vacancies) conductivity. Since the electron conductivity is orders of magnitude higher than the ionic one, oxygen vacancy bulk diffusion is regarded as the rate limiting step in oxygen permeation through perovskites. However, for thin perovskite layer the rate of this bulk diffusion process starts to compete with the so called surface reaction which represents the dissociative adand desorption of the oxygen molecule and the incorporation/release of the oxygen ions from the perovskite framework. The oxygen permeation flux through the perovskite membrane made of Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3-δ (BSCF) has been measured as a function of both the temperature, membrane thickness and the oxygen pressure gradient across the membrane. A combined bulk diffusion/surface reaction model can be used to understand the mechanism of the oxygen transport. The limiting step of the oxygen transport was found to be the bulk oxygen ion diffusion coefficient (D i ) for the BSCF perovskite at temperatures above 700 ℃. Furthermore, the oxygen vacancy diffusion coefficient (D v) can be deduced from the dependence of the oxygen permeation flux on the oxygen pressure gradient provided that the oxygen vacancy δ are known. From permeation measurement on the BSCF membrane tube under study, is found to be between 2.82×10 -5 cm2/s at 900 ℃ and 0.82×10 -5 cm2/s at 700 ℃.
Molecular diffusion under confinement
Authors: Kärger Jörg
Published: July 2024

With reference to molecular transport in manifold media of porous structure, a survey is given on the ample spectrum of diffusion phenomena under confinement. The presentation is mainly based on the evidence provided by pulsed field gradient NMR and by interference and IR microscopy. These "microscopic" techniques of diffusion measurement are particularly powerful for exploring the diverse features of molecular propagation in complex systems. The presented data cover the peculiarities of molecular diffusion under the regime of "intracrystalline" zeolitic diffusion, refer to deviations from normal diffusion and deal with the practically particularly important case where the overall diffusion process includes molecular propagation in the gas phase. In many cases, the reported experimental studies have been performed in immediate response to theoretical issues including single-file diffusion and sorption hysteresis. Simultaneously, they have given rise to new challenges for basic research correlating equilibrium and non-equilibrium phenomena of molecular propagation.
Rock-typing of laminated sandstones by nuclear magnetic resonance in the presence of diffusion coupling
Authors: Alhwety Nader H. , Sayedakram Nawaf I. , Shikhov Igor , Arns Christoph H.
Published: July 2024

In this work, the aim is to assess the relative importance of the impact of diffusional coupling on NMR measurements of saturated laminated sandstone numerically at the layer scale to assess the feasibility of NMR rock-typing approaches. We use two 3D model structures based on a Boolean particle process, providing a range of structural to diffusion length ratios to explore the relationships between pore geometry, surface magnetic properties, and NMR transverse relaxation time. The influence of surface relaxivity and bulk susceptibility contrast on T2 relaxation responses is tested for layered structures to improve the rock-typing methodology. An escalation in pore coupling is observed with decreasing bed thickness as well as decreasing bulk susceptibility contrast and surface relaxivity the latter ones reducing the time available for pore coupling by reducing the effective relaxation rate. When pore coupling is strong, the T2 distribution clearly misrepresents the underlying bimodal distribution of the different morphologies. Consequently, the bimodal relaxation time becomes merged and the relative amplitude of the peaks fails to reflect the true morphologies of the models. Furthermore, we observed that in low noise conditions of numerical simulation the effect of diffusional coupling on transverse relaxation may be misinterpreted for the regularization effect on ILT solution. In such cases, careful selection of Laplace inversion method is essential for effective rock-typing by NMR.
Changes in specific surface as observed by NMR, caused by
saturation of chalk with porewater bearing divalent ions
Authors: Katika Konstantina , Adassi Mouadh , Alam Mohammad Monzurul , Fabricius Ida Lykke
Published: July 2024

Nuclear Magnetic Resonance (NMR) spectrometry has proved to be a good technique for determining the petrophysical properties of reservoir rocks; such as porosity and pore size distribution. We investigated how pore water rich in divalent ions affect the NMR signal from chalk with two different depositional textures. We compared two cases. The first experiments on outcrop chalk with high salinity brines showed that saturation with divalent ions (Mg2+, Ca2+ and SO42-) cause major shifts in the T2 distribution curve, probably due to precipitation in the pore space. In a second set of experiments, fluid samples where precipitation takes place were found to show shifts in the T2 relaxation curve due to the creation of crystals. We were able to identify how differences in the rock texture and precipitants within the pore space may affect the transverse relaxation time by altering the surface-to-volume ratio of the pore space. The results of this work could benefit the ongoing study on the optimization of the water composition for Enhanced Oil Recovery (EOR) methods and shed light on how it can affect the mechanical and physical properties of the rock.
Traveling Wave Magnetic Particle Imaging for determining the
iron-distribution in rock
Authors: Vogel Patrick , Rückert Martin Andreas , Klauer Peter , Kullmann Walter H. , Jakob Peter Michael , Behr Volker Christian
Published: July 2024

Determining the composition of solid materials is of high interest in areas such as material research or quality assurance. There are several modalities at disposal with which various parameters of the material can be observed, but of those only magnetic resonance imaging (MRI) or computer tomography (CT) offer anon-destructive determination of material distribution in 3D. A novel non-destructive imaging method is Magnetic Particle Imaging (MPI), which uses dynamic magnetic fields for a direct determination of the distribution of magnetic materials in 3D. With this approach, it is possible to determine and differentiate magnetic and non-magnetic behaviour. In this paper, the first proof-of-principle measurements of magnetic properties in solid environments are presented using a home-built traveling wave magnetic particle imaging scanner.
Electrophoresis and electroosmosis as determined on the level of a single isolated colloid by use of optical tweezers
Authors: Semenov Ilya , Kremer Friedrich
Published: July 2024

Experiments are described on the electrophoretic mobility of a single isolated colloid and the electro-osmotic response of the surrounding medium. For that optical tweezers are employed which enable one to trap a particle without any mechanical contact and to measure its position and the forces acting on it with high resolution (±2 nm, ±200 fN). In a custom-made microfluidic cell, the two effects are separated using the identical colloid. The electrophoretic response is found to be ~ 5 times stronger than the electroosmotic effect. It is phase-shifted with respect to the external electric field, hence giving rise to a complex electrophoretic mobility which can be theoretically described by a strongly damped driven harmonic oscillator model. The measured electrophoretic mobility in monovalent salt is found to be in agreement with computations combining primitive model molecular dynamics simulations of the ionic double layer with the standard electrokinetic model. Mobility reversal of a single colloid is observed for trivalent ionic solutions (LaCl3) at ionic strengths > 10−2 mol/l. The latter is in quantitative agreement with a numerical model in which ion specific attractive forces are taken into consideration.
Polymers in disordered environments
Authors: Fricke Niklas , Sturm Sebastian , Lämmel Marc , Schöbl Sebastian , Kroy Klaus , Janke Wolfhard
Published: July 2024

Using a combination of analytical theory and newly developed numerical algorithms, we analyze the most pertinent conformational characteristics of three paradigmatic types of polymers in disordered environments: (i) flexible polymers in quenched, self-similar disorder as represented by a self-avoiding random walk on a critical percolation cluster, (ii) semiflexible polymers in quenched, steric disorder as represented by an equilibrium hard-disk fluid and (iii) semiflexible polymers subject to the random energy landscape that emerges from a surrounding network of similar semiflexible polymers.
Testing the (time)1/4 diffusion law of rehydroxylation in fired
clays: evidence for single-file diffusion in porous media?
Authors: Hare Vincent J. , Kärger Jörg , Moinester Murray , Piasetzky Eli
Published: July 2024

Fired clay minerals rehydroxylate after firing, a phenomenon that causes the long-term mass gain and expansion seen in archaeological ceramics. During rehydroxylation, fired clay minerals react with H2O to form structural hydroxyl (OH). Recent models propose that rehydroxylation is described by a quartic root (t1/4) time dependence, which has led to a dating method based on the process (RHX, rehydroxylation dating). The time dependence has been interpreted as an indication of a transport process of single-file diffusion of H2O molecules along restricted pathways in clay mineral, as theory predicts that the associated root mean square displacement is proportional to t1/4. However, dating trials have led to alternative models, and the process is still poorly understood. Here we outline currently outstanding problems found in different experimental studies, and propose novel ways of investigating the phenomenon. These include (i) gravimetric analyses using pure clay ceramics which are free of calcite and other minerals, and reducing cooling effects by using thin samples; (ii) highresolution nuclear magnetic resonance (NMR) with aluminum and silicon as well as with protons (hydroxyls, water) for exploring structure and dynamics, and pulsed field gradient (PFG) NMR for exploring water/proton diffusivities; (iii) IR spectroscopy, and micro-IR imaging to explore the spatial-temporal dependence of rehydroxylation of fired clay and (iv) structural investigations by high-resolution electron microscopy and X-ray diffraction.
Theory for the Surface Induced Growth of Helium Gas Bubbles in Irradiated and Annealed Copper - Boron Alloys
Authors: Tiwari G. P. , Laghate M. , Mehrotra R. S.
Published: July 2024

Neutron irradiated copper-boron alloys are employed to study the mutual interaction between metallic crystalline lattices and inert gases. Inert gases precipitate to form gas bubbles and their growth induces dilation of the matrix. This dilation, technically designated as swelling, affects the structural integrity of nuclear fuels during their service. The estimated enthalpy of solution of helium in copper is 5.5 eV/atom. As a Consequence, its solubility in the copper matrix is extremely poor and it cannot enter a copper based matrix via any thermo-chemical route. Hence, recourse to a nuclear reaction is taken to impregnate copper with helium. Helium is produced in situ through neutron irradiation in copper-boron alloys as a result of (n, alpha) nuclear reaction between boron atoms and neutrons. The characteristic feature of the growth of helium gas bubbles driven by isothermal annealing of the metallic matrix is that their rate of growth is highly sensitive to the distance of the bubbles from the external surface of the specimen. The growth of gas bubbles as a function of time and temperature is modulated by the flow of vacancies from the free surface of the specimen. A theory for the surface induced growth of helium gas bubbles in the neutron irradiated copper-boron alloys is presented here.
Hardware and Software for Embedded Compact
Authors: Louis-Joseph Alain , Nauton Alexis , Coupvent-Desgravier Denis , Korb Jean-Pierre
Published: July 2024

Numerous compact NMR spectrometers have been designed for an easy measurement of proton NMR spectra. High sensitivity and resolution can be reached even with low field spectrometers (LFNMR) (i.e. 60 MHz), thanks to great improvements in electronic hardware, which open up a wide field of analytical quantification and relaxation applications. A specificity of Low field NMR spectrometer is the use of a permanent and cryogen free magnet technology, avoiding the need for weekly and expensive cryogenic services. Here we present and describe a low field NMR spectrometer fabricated in our laboratory. This spectrometer (ECBLFNMR) operates at basic resonant frequencies ranging from 1 to 60 MHz, with standard sample diameter (5-10 mm). All the embedded hardware is very compact and requires only a 24 V DC power supply, so this spectrometer is portable, easy to install and has a small footprint. This ECBFLNMR is dedicated to education and quantification, and enables low-field NMR research. It may be coupled with scientific experiments not requiring high magnetic fields.
Measurement of NMR flow propagators and local numerical analysis of dual scale porous media
Authors: Zheng Yong , Shikhov Igor , D'Eurydice Marcel N. , Arns Christoph
Published: July 2024

Flow propagators have been frequently used in characterisation of porous media and the study of fluid transport behaviour. Previous work considered the shape of measured flow propagators using Nuclear Magnetic Resonance (NMR) discussed the influence of pore geometry, dispersion, relaxation and internal gradients. In addition, numerically simulated flow propagators were also reported. However, a uantitative numerical analysis of local contributions to flow propagators has not been considered in the literature, yet may provide significant new insights into the flow behaviour through complex porous media. In this work we use two types of beads to realize a dual-scale bead pack consisting of micro- and macropore regions for the NMR experiments. A low-field NMR system (2 MHz) was used to measure flow propagators for this sample. We further generated a dual-scale Gaussian Random Field (GRF) image based on porosity, beads diameters and volume fraction of each type of bead for numerical simulations. A Lattice Boltzmann Method (LBM) and Random Walk (RW) technique were combined to derive the simulated flow propagators and validated against experiments. We carry out a local analysis of the flow propagators showing a significant difference in bandwidth of displacements in micro- and macro-pore regions. In addition, the local flow propagators indicate a linear relationship between mixing (the fluid exchange on regions' boundaries) and flow velocities as well as a non-linear correlation between mixing and evolution times.
N-body potentials in simulation of point defect properties
Authors: Chirkov Andrey , Nazarov Andrei
Published: July 2024

This work is devoted to simulation of the diffusion features of point defects in bcc metals. The properties of point defects have been investigated with the usage of many-body interatomic potentials. This approach, based on the density-functional theory, permitted us to derive more adequate diffusion features of solids. The investigation is carried out within the framework of the Finnis-Sinclair formalism, developed for an assembly of N atoms and represents the second-moment approximation of the tight-binding theory. We used a new model, based on the molecular static method for simulating the atomic structure near the defect and vacancy migration in pure metals. This approach gives the opportunity to simulate the formation and the migration volumes of the point defects, taking into consideration the influence of pressure on structure and consequently on energy. The diffusion characteristics of bcc α-Fe and anomalous β-Zr have been simulated. The preliminary results of this research were presented and taken for publishing on the international conference “Diffusion in solids” (DiSo-2005) in May 2005.
Apparent longitudinal relaxation of mobile spins in thin, periodically excited slices
Authors: Gädke Achim , Nestle Nikolaus
Published: July 2024

In this contribution, we present simulations and first experimental results on the apparent longitudinal relaxation behavior of mobile spins in thin periodically excited slices. This phenomenon is especially of interest in the context of NMR microimaging at extremely high spatial resolution and also for the development of mechanically detected NMR on biological samples under semiambient conditions. In the most simple case, the signal amplitude available in such an experiment is determined by the recovery of saturated in-slice magnetization during the time interval between two excitations. This magnetization recovery results both from relaxation and from diffusive exchange with magnetization outside the slice. We recently studied the combined effect of relaxation and diffusion in a simple saturation-recovery experiment on a fully relaxed sample. In the case of periodic excitation, the diffusion balance is complicated by the fact that there is also partially excited out-of-slice magnetization left over from earlier excitation cycles.
Diffusion of Environmental Awareness
Authors: Lösch Stefanie , Okhrin Ostap , Wiesmeth Hans
Published: July 2024

A high level of “environmental awareness” in the participating countries will likely raise the success of the Kyoto Protocol negotiated in Paris in 2015. In this context it is of interest to investigate the diffusion of environmental awareness, and also the (economic) factors, on which this diffusion depends. This paper addresses these questions for the regions of the Russian Federation, which are sufficiently diverse regarding cultural and economic issues. From a formal point of view, a “Multiple-Indicator-Multiple-Causes” (MIMIC) approach, based on a variety of “indicators” for environmental awareness, derived from search entries in c Yandex, and a variety of “causes”, economic and socio-economic factors, is applied. The empirical results point first to a strong dependence of environmental awareness on the level of GRP per capita. Moreover, the diffusion seems to spread from the eastern part of Russia towards the western regions.
Curvature effects on a simplified reaction-diffusion model of biodegradation
Authors: Chacón-Acosta Guillermo , Núnez-López Mayra , Santiago José A.
Published: July 2024

The biodegradation process of some types of polymers occurs due to many different factors including their morphology, structure and chemical composition. Although this is a complicated process, most of its important stages like the diffusion of monomers and the hydrolysis reactions have been modeled phenomenologically through reaction-diffusion equations, where the properties of the polymers were encompassed. Using a simplified reaction-diffusion model for the biodegradation of polymers, in this contribution we study the possible effects of the curvature of the system’s geometry in the degradation process, which is characterized by the interaction of the corresponding reaction rate and the diffusion coefficient. To illustrate the problem of diffusion on a curved surface we consider the surface of a cylinder and of the so-called Gaussian bump. We show how the degradation process is affected by the curvature of the system for the simplified model.
Kirkendall Effect on the Nanoscale
Authors: Cserháti C. , Langer G. , Parditka B. , Csik A. , Iguchi Y. , Czigány Zs. , Erdélyi Z.
Published: July 2024

Kirkendall effect has been studied experimentally as well as theoretically for decades already. There are theoretical indications, that the Kirkendall effect must operate from the beginning of the diffusion process but there are practically no measurements on this short time and length scale. For that reason, diffusion on the nanometer scale was investigated experimentally in different binary systems in thin film geometry. We followed the diffusion process as well as the Kirkendall effect by different methods (TEM, SNMS and synchrotron X-ray waveguide technique). Investigations were performed in systems with complete solubility (Bi-Sb, Cu-Ni, Bi-Sb) as well as in systems forming intermetallic phase (Fe-Sb, Fe-Pd). It was found that with these methods the Kirkendall shift can be well followed on the nano-scale. In Fe-Sb system even the bifurcation of the Kirkendall plane was observed.
Calculation of parameters of Heine and Abarenkov model potential for bcc crystals
Authors: Ghorai Amitava
Published: July 2024

Parameters of Heine and Abarenkov model potential (HAP) have been computed in this
Formation and Ripening of Nanobelts/Nanofibers under Stirring of aqueous Solution – alternative models
Authors: Korol Yaroslav , Gusak Andriy , Danielewski Marek , Gajewska Marta
Published: July 2024

Problem of V2O5 nanobelts production under intensive stirring of V2O5 powder in salted water is revisited. Method was initially proposed in 2016 but models and understanding were lacking. Here an independent attempt of the controlled V2O5 nanobelts formation and growth under stirring with various rotation frequencies is reported, as well as some alternative mechanisms and respective mathematical models of the nanobelts growth and ripening kinetics.
Diffusion in Nanoporous Materials: Challenges, Surprises and Tasks of the Day
Authors: Chmelik Christian , Hwang Seungtaik , Kärger Jörg
Published: July 2024

Diffusion is an omnipresent, most fundamental phenomenon in nature and thus critical for the performance of numerous technologies. This is in particular true for nanoporous materials with manifold applications for matter upgrading by separation, purification and conversion. The path lengths of molecular transportation within the industrial plants range from the elementary steps of diffusion within the micropores of the individual particles up to the matter flow over macroscopic distances. Each of them might be decisive in determining overall performance so that detailed knowledge of all modes of mass transfer is crucial for a knowledge-based optimization of the devices with reference to their transport properties. The rate of mass transfer is particularly complicated to be assessed within the individual (adsorbent) particles/crystallites with pore sizes of the order of molecular dimensions. We are going to present two powerful techniques exactly for this application, operating under both equilibrium (Pulsed Field Gradient (PFG) NMR) and non-equilibrium (Microimaging by interference microscopy and IR microscopy) conditions. The potentials of these techniques are demonstrated in a few showcases, notably including the options of transport enhancement in pore hierarchies. The contribution concludes with a survey on present activities within an IUPAC initiative aiming at the elaboration of “guidelines for measurements and reporting of diffusion properties of chemical compounds in nanoporous materials”
New Analytical Results and Numerical Schemes for Irregular Diffusion Processes
Authors: Kovács Endre , Saleh Mahmoud , Barna Ferenc , Mátyás László
Published: July 2024

We examine the transient diffusion equation with time- and space-dependent diffusion coefficients in 1D. Such transport equations can be easily derived from the Fokker-Planck equation and are essential to understand the diffusion mechanisms in general, e.g. in carbon nanotubes. With the help of the classical self-similar Ansatz we give new, nontrivial analytical solutions. Then we reproduce these by 16 explicit numerical time integration methods, 11 of which are recent and unconditionally stable. The results show that some of the algorithms, e.g. the leapfrog-hopscotch method, are very efficient and can outperform the standard FTCS method.
Diffusive and non-diffusive language shift: Why are language borders moving and language islands shrinking?
Authors: Prochazka Katharina , Vogl Gero
Published: July 2024

We compare two situations of language shift: When a language border exists, as e.g. between Slovenian and German in Carinthia, Austria before World War I or between Gaelic and English in Northwestern Scotland, then close to that border language shift is promoted by diffusive contact between different settlements. Such contact, however, was of no significant influence on language shift from German to Hungarian in Southern Hungary where no language border exists.
One and a Half Century of Diffusion: Fick, Einstein, Before and Beyond
Authors: Philibert Jean
Published: July 2024

The year 2005 gave us, through two anniversaries (1855 Fick and 1905 Einstein), the wish to go back to these authors’ seminal papers, whose aftermath had been (and still is) prodigious. This essay describes the contents of these articles: the macroscopic approach with Fick equations and the microscopic one with the Einstein-Smoluchowski random walk (Brownian motion) equation, while considering them in their historical context. Some further developments are briefly iscussed.
Transient behavior of a zeolite membrane under non-linear conditions
Authors: Ruthven Douglas M.
Published: July 2024

A simplified mathematical model is proposed to provide an analytic solution for the transient behavior of a Langmuirian zeolite membrane subjected to a step increase in sorbate pressure at the upstream surface at time zero. The concentration profiles derived from the simplified model agree with those calculated by numerical solution of the governing partial differential equation. The model is used to investigate the validity of the classical time-delay method of measuring diffusion in the adsorbed phase. Under non-linear conditions the time delay depends on the degree of non-linearity as well as on the diffusional time constant. Under highly non-linear conditions application of the classical linear model yields apparent diffusivity values that are about four times larger than the limiting value (Do). The new model is used to reanalyze experimental permeation diffusivity data for pxylene in a single crystal zeolite membrane. The resulting Do values are shown to be consistent with the values determined by other experimental techniques.
Effects of anisotropic optical parameters on the penetration of
photons into a turbid medium
Authors: Pajevic Sinisa , Weiss George H.
Published: July 2024

There are by now many applications of methods based on near- infrared radiation (NIR) used for optical imaging and  therapeutic purposes in medical settings. Such optical techniques are appealing in not requiring potentially harmful ionizing radiation, being non-invasive, and generally being easily implementable. Since photons are randomly scattered by cell components, successful use of NIR requires knowledge of the photon trajectories expressed in statistical terminology. Until now the necessary analysis has been based on diffusion theory assuming that the scattering coefficient is an isotropic material property. We analyze the properties of the penetration depth when this assumption is violated. By penetration depth will be meant the depth attained in the turbid medium, given its ultimate emission at the planar surface at a time T , as a function of the degree of anisotropy of the scattering coefficient. Our analysis will be based on a continuous-time random walk formalism. Properties of both time-gated and continuous-wave experiments will be derived.
DAMARIS – a flexible and open software platform for NMR
spectrometer control
Authors: Gädke Achim , Rosenstihl Markus , Schmitt Christopher , Stork Holger , Nestle Nikolaus
Published: July 2024

Home-built NMR spectrometers with self-written control software have a long tradition in porous media research. Advantages of such spectrometers are not just lower costs but also more flexibility in developing new experiments (while commercial NMR systems are typically optimized for standard applications such as spectroscopy, imaging or quality control applications). Increasing complexity of computer operating systems, higher expectations with respect to user-friendliness and graphical user interfaces as well as increasing complexity of the NMR experiments themselves have made spectrometer control software development a more complex task than it used to be some years ago. Like that, it becomes more and more complicated for an individual lab to maintain and develop an infrastructure of purely homebuilt NMR systems and software. Possible ways out are:
● commercial NMR hardware with full-blown proprietary software or
● semistandardied home-built equipment and common open-source software environment for spectrometer control.
Our present activities in Darmstadt aim at providing a nucleus for the second option:
DArmstadt MAgnetic Resonance Instrument Software (DAMARIS) [1]. Based on an ordinary PC, pulse control cards and ADC cards, we have developed an NMR spectrometer control platform that comes at a price tag of about 8000 Euro. The present functionalities of DAMARIS are mainly focused on TD-NMR: the software was successfully used in single-sided NMR [2], pulsed and static field gradient NMR diffusometry [3]. Further work with respect to multipulse/multitriggering experiments in the time domain [4] and solid state NMR spectroscopy multipulse experiments are under development.
Diffusion in hydrogeology
Authors: Barker John A.
Published: July 2024

The field of hydrogeology is primarily concerned with the flow of water below the ground surface and with transport, normally of solutes and heat, within that water. Many disciplines have contributed to this endeavor which requires skills from across the spectrum of science, engineering and beyond. The diffusion equation describes not only solute transport but also the flow of water, via Darcy’s law. Of particular interest is transport in fractured rock where most of the flow is through the fractures while most of the storage is in the rock pores: a ‘double-porosity’ system. Hydrogeology remains a field that welcomes those who bring techniques from other areas of science to address problems as varied as water supply, radioactive waste disposal and geothermal energy.
Diffusion: macroscale dwarf and nanoscale giant
Authors: Nestle Nikolaus
Published: July 2024

Diffusion processes of particles or energy exhibit a characteristic scaling behavior with space and time. In this contribution, the background of this scaling behavior will be shortly described and its consequences in physics, chemistry, biology and various areas of technology shall be explored. Furthermore, some demonstration experiments for different aspects of diffusion and its scaling behavior will be discussed in the course of the article.
Challenges in macroscopic measurement of diffusion in zeolites
Authors: Brandani Stefano
Published: July 2024

The paper presents a brief historical overview of the field of the measurement of diffusion in zeolites. The focus will be on macroscopic measurements, i.e. when diffusion through entire crystals is studied. While this may appear to be a simple task, we will see that there are difficulties in obtaining reliable results. Two case studies, the volumetric/piezometric experiment and the Transient Analysis of Products (TAP) apparatus are discussed and ways to improve either the experiments or the way in which the results are analyzed are presented. The author’s perspective into what are the current challenges in the field concludes the paper.
Relationship between ionic radius and pressure dependence of ionic conductivity in water
Authors: Kumar Parveen , Shukla Ashok Kumar , Yashonath Subramanian
Published: July 2024

Experimental measurements of ionic conductivity in water are analysed in order to obtain insight into the pressure dependence of limiting ionic conductivity of individual ions (λ0) for ions of differing sizes. Conductivities of individual ions, λ0 do not exhibit the same trend as a function of pressure for all ions. Our analysis suggests that the effect of pressure on ionic conductivity depends on the temperature. At low temperatures, the effect of pressure on relatively small ions such as Li+ exhibit an increase in conductivity with pressure. Intermediate sized ions exhibit an increase in conductivity with increase in pressure initially and then at still higher pressures, a decrease in ionic conductivity is observed. Although there are data at low temperatures for ions of large radius, the effect of increased pressure is expected to lower conductivity with increase in pressure over the whole range. At higher temperatures, the dependence of conductivity on pressure changes and these changes are discussed. Divalent ions such as SO2−4 exhibit different trends as a function of pressure at different temperatures. Both the divalent ions (Ca2+ and SO2−4 ) for which experimental data exists, exhibit an increase with pressure at lower temperatures. At slightly higher temperatures, a maximum in conductivity is seen as a function of pressure over the same range of pressure.
Interdiffusion in critical binary mixtures by molecular dynamics simulation
Authors: Binder Kurt , Das Subir K. , Fisher Michael E. , Horbach Jürgen , Sengers Jan V.
Published: July 2024

A simulation study of the static and dynamic critical behavior of a symmetric binary Lennard-Jones mixture is briefly reviewed. Using a combination of semi-grand-canonical Monte Carlo (SGMC) and molecular dynamics (MD) methods near the critical temperature of liquid-liquid unmixing, the correlation length and “susceptibility” related to the critical concentration fluctuations are estimated, as well as the self- and interdiffusion coefficients. While the self-diffusion coefficient does not show a detectable critical anomaly, the interdiffusion coefficient is found to vanish when one approaches the critical temperature at fixed critical concentration. It is shown that in the corresponding Onsager coefficient both a divergent singular part and a nonsingular background term need to be taken into account. With appropriate finite-size scaling analysis (the particle numbers studied for the dynamics lie only in the range from N = 400 to 6400), the critical behavior of the interdiffusion coefficient is found to be compatible both with the theoretically predicted behavior and with corresponding experimental evidence.
Hydrodynamic dispersion of pressure-induced and electroosmotic flow in porous glasses probed by Nuclear Magnetic Resonance
Authors: Li Yujie , Farrherr German , Kimmich Rainer
Published: July 2024

Fluid transport by flow in random porous media is subject to hydrodynamic dispersion. In a series of pulsed field-gradient NMR experiments, we have compared flow induced by pressure gradients on the one hand and by electroosmosis on the other. The media were porous glasses with pore dimensions from 1 to 100 μm. With increasing flow rates, a crossover from subdiffusive to superdiffusive mean-squared displacement laws was observed in both cases. This demonstrates the competition between molecular diffusion and convection, and is a typical example of anomalous transport.
Drift-diffusion of highly mobile dopants in CdTe
Authors: Wolf Herbert , Wagner Florian , Kronenberg Jörg , Wichert Thomas , Grill Roman , Belas Eduard
Published: July 2024

The diffusion of Ag in CdTe exhibits anomalous concentration profiles, which essentially reflect the profile of the deviation from stoichiometry. At a diffusion temperature of about 800 K, the Ag dopant atoms are present as charged interstitials. The deviation from stoichiometry at diffusion temperature substantially changes upon an external source of Cd atoms. Such an external source can be represented either by the vapor pressure from metallic Cd or by a Cd layer arising at the interface to an evaporated layer of Cu or Au. Also, the Co diffusion in CdZnTe is shown to be strongly affected by the presence of an external vapor pressure of Cd, but in a substantially different way compared to the Ag diffusion in CdTe.
Fast anion-conduction in oxynitrides: oxygen and nitrogen transport in (Y, Zr)-(O, N)
Authors: Kilo Martin , Taylor Marcela Andrea , Borchardt Günter , Kaiser-Bischoff Ines , Boysen Hans , Rödel Christoph , Lerch Martin
Published: July 2024

Cation doped zirconium oxynitrides (for example zirconium oxide doped with yttrium oxide and nitrogen, \''YZrON\''), having a fluorite-based structure, are suggested to have fairly high nitrogen diffusivity, besides their high oxygen mobility. In the present work, the tracer-diffusion of nitrogen and oxygen was measured in single crystalline \''YZrON\''. Results are compared to the migration pathways and migration enthalpies of nitrogen and oxygen ions as determined by elastic neutron diffraction studies. Excellent agreement of the measured activation enthalpies of nitrogen diffusion (about 2 eV) and oxygen diffusion (about 1 eV) determined by the two methods is found.
Growth of amorphous domains in precursor derived Si-C-N-Ceramics studied with small angle X-ray scattering
Authors: Gruber Wolfgang , Starykov Oleksiy , Oppermann Wilhelm , Schmidt Harald
Published: July 2024

Amorphous precursor derived ceramics with the composition Si26C41N33 were isothermally annealed at 1500 °C for 5 minutes up to 190 minutes. Two series of measurements were carried out: one at a nitrogen partial pressure of 1 bar and one at a nitrogen partial pressure of 1 mbar. Small angle X-ray scattering was used to determine the diameter of the amorphous domains. The Guinier radius was found to vary from 9.5 Å to 13 Å irrespective of the partial pressure of nitrogen. This finding is quite surprising since crystallization of this material strongly depends on the partial pressure of nitrogen.
Effect of compressive stress on Fe self-diffusion in nanocrystalline FeN(Zr) thin films
Authors: Chakravarty Sujoy , Gupta Mukul , Schmidt Harald , Gupta Ajay
Published: July 2024

In the present work the effect of compressive stress on self-diffusion of Fe in nanocrystalline FeN(Zr) alloys has been investigated. Two different types of Fe64N26Zr10 samples, one without applied stress and another with applied compressive stress of 42 GPa, were deposited under identical conditions using magnetron sputtering. The stress has been applied to the sample by bending the substrate during the deposition using a three point bending device. The self-diffusivities of Fe were determined by measuring the broadening of 57Fe marker layers by Secondary Ion Mass Spectrometry after annealing at 443 K, 483 K and 523 K for 1 hour. The activation energy and preexponential factor for Fe diffusion is comparatively higher in the stressed sample. The higher activation energy might be due to the fact that the system transforms into a more dense state when compressive stress is applied.
Suppression of the anomalous relationship between diffusivities of cations and anions by water in imidazolium-based ionic liquids
Authors: Menjoge Amrish , Vasenkov Sergey
Published: July 2024

Proton pulsed field gradient (PFG) NMR technique at high magnetic field (17.6 T) and high magnetic field gradients (up to 30 T/m) is applied to study diffusion of the anions and cations in the ionic liquid 1-ethyl-3-methylimidazolium ethylsulfate ([Emim][ETSO4]) with and without water. Excellent NMR spectral resolution attained by this technique allowed high-precision monitoring of the diffusivities of the anions, cations and water in a single experiment. The PFG NMR data show that the anomalous relationship between the ion diffusivities, i.e. larger self-diffusion coefficient of the bulkier [Emim] cation than that of the less bulky [ETSO4] anion, becomes much less pronounced due to addition of water into the ionic liquid. This observation is explained by the distortion of the local structure in the ionic liquid by water molecules leading to a possible loss of the diffusion anisotropy for the cation diffusion. The reported experimental data are in a qualitative agreement with the most recent results of molecular dynamics simulations (see references 9 and 10).
Multi-pulsed free-induction NMR signal from spins diffusing in a spatially restricted flow
Authors: Lisy Vladimir , Tothova Jana
Published: July 2024

A multi-pulsed free-induction NMR experiment is described theoretically for spins diffusing within a cylindrical capillary. The characteristic time for the particles to move on a distance of the capillary diameter is smaller or comparable to the time interval between the applied 90° rf pulses and the relaxation times entering the Bloch equations. In this case the spin diffusion is restricted and the classical solutions of these equations for unbounded media are not applicable. We have calculated the mean magnetization in the cross-section of the capillary after any of the rf pulses and found the induced NMR signal within the Bloch-Torrey-Stejskal theory for spins reflected at boundaries. The problem is extended by considering a possible macroscopic (plug and Poiseuille) flow of the fluid inside a capillary. It is found that with the increase of the rf pulse number, the maxima of the observed signals do not decay to zero but converge to a nonzero value. The proposed theory thus seems to be suitable for the description of experiments on systems rapidly relaxing due to diffusion and flow.
TRAINING ON DESIGNING INTERACTIVE LEARNING MEDIA-BASED AI (ARTIFICIAL INTELLIGENCE) AT SMPN 1 PLUMBON
Authors: Rahmatudin Jajang , Musyarofah Siti , Arrofilah Syifa Fijri , Widyawati Tiwi , Ahyani Hisyam , Atifah Shoimatul
Published: July 2024

Abstract: SMPN 1 Plumbon is one of the public schools in Cirebon Regency. Based on the results of observations, SMPN 1 Plumbon already has facilities that support digital-based learning. Technology can help teachers be more creative in developing learning in the classroom. One way to expand learning in the school is by utilizing creative learning media so students can be more active. Learning media can facilitate the achievement of specific learning goals. Based on this description, Community Service (PKM) was carried out on learning media in the form of a learning media workshop with the theme "AI-Based Learning Media Design Training (Artificial Intelligence)." This activity aims to train teachers in utilizing technology by creating AI-based interactive learning media (Artificial intelligence). The "AI-Based Learning Media Design Training (Artificial Intelligence)" was implemented on May 17, 2024, at SMPN 1 Plumbon with the resource person Mr. Jajang Rahmatudin, M.Pd. The training was carried out at 13.00, the training activity for AI-based interactive learning media design (Artificial intelligence). It began with the brief provision of material by the resource persons. After the provision of the material, the trainees were invited to try to design AI-based interactive learning media (Artificial intelligence) directly on the spot. The resource person explained the steps that must be taken, and then the participants followed the directions. Students help assist participants who have difficulties creating learning media. The implementation of the training went smoothly and well, and the trainees looked enthusiastic during the training activities.