Single Diffusion Research Articles

Surface Modification of the Improved Stainless Steel Alloy AISI-304 and the Use of Diffusion Coating and a Study of Its Efficiency in Resistivity Hot Corrosion in an Atmosphere of Sodium Chloride Vapor NaCL and Sodium SulfateNa_2 SO_4

This research aims to modify the components of stainless steel alloy by the method of surface engineering through the single diffusion coating technique in order to obtain new alloys with high efficiency in resisting harsh environmental conditions. Steam a mixture of sodium chloride ( ) and sodium sulfate ( ) at a temperature of 900 and then compare it with the base alloy. The results showed that the alloys produced in this way are very efficient. The results showed that the aluminum coating showed high efficiency in resisting oxidation and provided better protection for a longer time compared to the uncoated alloy due to the oxide crust layer formed with high adhesion as well as the aluminum-rich phases, whether the phases were nickel-aluminum or iron-aluminum. The results also showed that the thickness of the coating and the weight gain of the alloy is subject to the parabola relationship with time.

Microstructure Optimization and Coercivity Enhancement of Sintered NdFeB Magnet by Grain Boundary Diffusion of Multicomponent Tb60Pr10Cu10Al10Zn10 Films.

The use of magnetron sputtering film as a diffusion source was recently achieved in the industrial production of important grain-boundary-diffusion magnets. In this paper, the multicomponent diffusion source film is explored to optimize the microstructure of NdFeB magnets and improve their magnetic properties. Multicomponent Tb60Pr10Cu10Al10Zn10 films of 10 μm in thickness and single Tb films of 10 μm in thickness were deposited on commercial NdFeB magnets' surfaces by magnetron sputtering as diffusion sources for grain boundary diffusion. The effects of diffusion on the microstructure and magnetic properties of the magnets were investigated. The coercivity of multicomponent diffusion magnets and single Tb diffusion magnets increased from 11.54 kOe to 18.89 kOe and 17.80 kOe, respectively. The microstructure and element distribution of diffusion magnets were characterized by scanning electron microscope and transmission electron microscopy. The multicomponent diffusion facilitates the infiltration of Tb along grain boundaries, rather than entering the main phase, thereby improving the Tb diffusion utilization. Furthermore, compared to the Tb diffusion magnet, the thicker thin-grain boundary was observed in multicomponent diffusion magnets. This thicker thin-grain boundary can effectively serve as the impetus for the magnetic exchange/coupling between grains. Therefore, the multicomponent diffusion magnets have higher coercivity and remanence. The multicomponent diffusion source has an increased mixing entropy and decreased Gibbs free energy, and it therefore does not easily enter the main phase but is retained in the grain boundary, thus optimizing the microstructure of the diffusion magnet. Our results show that the multicomponent diffusion source is an effective route for fabricating diffusion magnets with high performance.

Hydrogen storage and mobility determined by NMR to various organically functionalized porous silica synthetized by using the post-grafting method

The results of this study will help in guiding the future design of low-cost and highly performing functionalized mesoporous silica using cationic surfactants as directing agents. Indeed, by properly tuning surface interactions and the textural characteristics, the overall efficiency of H2 capture processes could be improved. Among different synthetized samples, the experimental results show the better interaction with (3-Aminopropyl)triethoxysilane precursor. Furthermore, an NMR investigation aiming at clarifying the internal arrangement and diffusion properties of hydrogen molecules inside functionalized porous silica materials has been performed. The NMR spectral analysis and the T1 relaxation times indicated two different “populations” for H2 sorbate due to the molecules adsorbed in mesopores and in micropores. For the first time, the H2 self-diffusion coefficient in functionalized silica has been experimentally measured by pulsed field gradient NMR. The spin-echo decay revealed two different diffusion mechanisms coexist in the functionalized mesoporous silica, except for the material functionalized with iodopropyl groups, which shows a single diffusion coefficient.

Spectroscopic, thermal, electrical and magnetic characterization on gel grown nickel succinate tetrahydrate crystals

Crystallization of nickel succinate tetrahydrate was done by gel technique; employing single diffusion method and powder X ray diffraction analysis confirmed the monoclinic structure for the synthesized compound. Spectral characterization of grown crystals was done by Fourier transform infrared and Raman spectroscopy. Thermal stability of the crystal was investigated and the dehydration of the crystal and its thermal degradation at different temperatures are discussed. At different temperatures, the prepared sample was examined for its dielectric properties, as a function of frequency. The octahedral coordination in the crystal is confirmed by UV– Visible spectral studies and magnetic susceptibility data.

Syntheses and properties of imidazolium-based quaternary salts with D-π-A unit containing azobenzene groups

Several novel organic ionic salts containing azophenyl groups with d-π-A structural unit was synthesized through the quaternization of azophenyl imidazole derivatives and 2, 4-dinitro-chlorobenzene in refluxing xylene. The donor-acceptor structure of the new ionic salts was characterized by the UV–vis, IR, ESI-MS, and NMR spectra. And the structure of ionic salt 8 was also evidenced by its single crystal X-ray diffusion. The UV−visible absorption spectra of all compounds exhibited two major strong absorption bands about at 340 and 440 nm, attributed to the strong intra-molecular π-π* and n-π* charge transfer of the azophenyl group, respectively. The results on thermal properties of ionic salts showed that all ionic salts 7–12 with d-π-A structural unit have better thermal stabilities and higher decomposition temperatures, and ionic salt 10 has the lowest melting point at 114 °C, almost close in the temperature range of ionic liquids. The electronic effect of substituted group has a certainly effect on the absorption spectra of azophenyl group and thermal properties of ionic salt with d-π-A structural unit.

Reversible Live-Cell Labeling with Retro-engineered HaloTags Enables Long-Term High- and Super-Resolution Imaging.

Self-labeling enzymes (SLE) such as the HaloTag have emerged as powerful tools in high and super-resolution fluorescence microscopy. Newly developed fluorogenic SLE substrates enable imaging in the presence of excess dye. To exploit this feature for reversible labeling, we engineered two variants of HaloTag7 with restored dehalogenase activity. Kinetic studies in vitro showed different turnover kinetics for reHaloTagS (≈0.006 s-1 ) and reHaloTagF (≈0.055 s-1 ). Imaging by confocal and stimulated emission depletion microscopy yielded 3-5-time enhanced photostability of reHaloTag labeling. Prominently, single molecule imaging with reHaloTags enabled controlled and stable labeling density over extended time periods. By combination with structured illumination, simultaneous visualization of single molecule diffusion and organellar dynamics was achieved. These applications highlight the potential of reHaloTag labeling for pushing the limits of advanced fluorescence microscopy techniques.

English

The aim of this study is to phenotypically characterize Klebsiella isolates from rats. A survey  was  conducted on 100 swaps samples  obtained  from  captured  house  rats  in University of Abuja main campus from May to August 2021. Isolation and identification of the Klebsiella species was done using conventional cultural and biochemical techniques. Of the 100 samples analyzed, 20 (20%) were positive for Klebsiella, 12% of the isolates were identified as Klebsiella Pneumonia while 8% were identified as Klebsiella oxytoca. Isolates were further confirmed by Microbact 24E test kit identification system (Oxiod, UK). Klebsiella isolates encountered in this study were further subjected to antimicrobial susceptibility testing using modified single disk diffusion method. Result of the antimicrobial susceptibility testing showed that the Klebsiella species were resistant to chloramphenicol (80%), gentamycin (90%), augmentin (80%), Cotrimoxazole (70%) and amoxicillin (70%). However, the Isolates were susceptible to Pefloxacin (100%), Streptomycin (40%), Ofloxacin (100%), Ciprofloxacin (100%) and Sparfloxacin (80%). Conclusively, this study documented the occurrence and existence of multiple resistant strains of K. Pneumonia and K. Oxytoca in rats in our environment and it is therefore of public health concern.   Key words: Klebsiella species, household rat, Rattus rattus, antimicrobial susceptibility.

A novel thermal desalting process using a binary string-of-beads flow array

The large mass transfer spacing in conventional solar stills causes a large mass transfer resistance and low space utilization. Convection mass transfer in vertical diffusion stills is always inhibited at small spacing due to the commonly used planar wicks. This paper presents a binary string-of-beads flow array for solar desalination using fibers instead of planar wicks, thus solving those problems and enabling coupled diffusion-convection mass transfer at small spacing. A prototype of our novel distiller with 16 mm mass transfer spacing and its experimental system are set up. Salt contamination, likely caused by splashing, is found to be tolerable at feedwater flows less than 50 L/h. At a saline water inlet temperature of 80 °C, the maximum thermal-water conversion efficiency reaches 0.81, and the maximum water productivity per unit volume reaches 56.3 kg/h/m3. Higher energy and space utilization than conventional stills and single effect vertical diffusion stills is demonstrated. A calculation model for heat and mass transfer between cold and hot water column pairs is developed for the first time, and the deviation between the calculated and experimental water productivity is less than ± 20%. This research may provide new ideas for efficient freshwater production in remote off-grid areas.

Performance evaluation of thermal conductivity models for fission gases with application to [formula omitted]-zirconium dispersion fuel

In this paper, the modeling of fission gases, particularly xenon and krypton, and their effects on the thermal performance with application to UO2-zirconium dispersion fuel is investigated.To investigate the consequence of fission gas behavior in nuclear dispersion fuel, in the first step, our obtained single atom diffusion coefficient, Ds, of xenon in UO2 by implementing molecular dynamics is used and open source code SCIANTIX is improved and employed to obtain the density of bubbles through the fuel. A microstructure model of dispersed fuel has been used to treat fuel meat thermal conductivity by taking into account fission gas bubbles density. Furthermore, the results of other models are given to evaluate fission bubbles' evolution.To explore thermal conductivity models of dispersion fuel, a code called Kowsar-1 is developed by including fission gases generation.

Aspects of Cattaneo-Christov heat flux in nonlinear radiative ternary, hybrid, and single mass diffusion past stretching surface; A comparative study

The main aim of this study is to analyze the convective heat transport in hydromagnetic TiO2 water nanofluid (NF), TiO2−SWCNT water hybrid nanofluid (HNF) and TiO2−SWCNT−MWCNT water ternary hybrid nanofluid flow (THNF) under the influence of Cattaneo-Christov (CC) heat flux and nonlinear thermal radiation over a stretching sheet. This study will help in environmental purification, to decompose harmful substances and other applications that require cooling. Furthermore, consideration of CC heat flux is important for a finite speed heat flow to reduce system disorder. The system of governing partial differential (PDEs) equations for the heat transport within THNF flow is transformed into the system of ordinary differential equations (ODEs) and solved numerically via the shooting technique with Runge-Kutta-4 method. The flow behaviors for Lorentz force and volume fraction of TiO2(φ1), SWCNT(φ2) and MWCNT(φ3) nanomaterials are portrayed for both no slip (α=0) and velocity slip (α=0.5) conditions. It is concluded that the velocity is more significant in the case of no slip condition when one, two and three different nanomaterials are dispersed in the base fluid water. It is further observed that the heat and momentum transport is more significant in the case when we consider TiO2−SWCNT−MWCNT water THNF flow as compared to TiO2 water NF, TiO2−SWCNT water HNF flow over a stretching surface. Our results show that the present analysis on heat transport in the THNF is more significant as compared to the THNF taken in the study given by Majunatha et al. [14].

The role of iron in cement hydration process: From perspective of chemical admixture

The post-peak decelerating hydration progress plays a significant role for concrete technology to assure durability of concrete. The effect of chemical admixture on cement hydration, hydration products, pore structure and moisture diffusion process are conducted by various experiments and the controlling factor on deceleration period of cement hydration and the effect of iron ion on microstructure are revealed. When the chemical admixture is added into cement paste, more ferrite phase is consumed and the iron dissolved in the pore solution modifies the initial hydration product layer and accelerate the hydration process, causing more C-S-H gel generated and denser microstructure. In addition, it is also proved that single diffusion control factor occurs at 80 h for the later deceleration period of cement hydration.

Dynamic molecular ordering in multiphasic nanoconfined ionic liquids detected with time-resolved diffusion NMR

Molecular motion in nanosized channels can be highly complicated. For example, water molecules in ultranarrow hydrophobic nanopores move rapidly and coherently in a single file, whereas by increasing the pore size they organize into coaxial tubes, displaying stratified diffusion. Interestingly, an analogous complex motion is predicted in viscous charged fluids, such as room temperature ionic liquids (RTILs) confined in nanoporous carbon or silica; however, experimental evidence is still pending. Here, by combining 1H NMR diffusion experiments in different relaxation windows with molecular dynamics simulations, we show that the imidazolium-based RTIL [BMIM]+[TCM]−, entrapped in the MCM-41 silica nanopores, exhibits an intricate dynamic molecular ordering; adsorbed RTIL molecules form a fluctuating charged layer near the pore walls, while in the bulk pore space they diffuse discretely in coaxial tubular shells, with molecular mean square displacement following a nearly ∼τ0.5 time dependence, characteristic of single file diffusion.

Crystallization by single diffusion through agar gel.

Crystallization is an important process in nature, various biological systems, and in industrial processes ranging from pharmaceuticals to material synthesis. In the industrial crystallization processes, common methods of crystallization include evaporative and cooling crystallization, and less frequently varying pH and addition of anti-solvents. The crucial driving force in all these techniques involves bringing the concentration of solutions to supersaturation to trigger the initial nucleation and growth of crystals. These conventional modes may not be applicable in systems where localized nucleation is required as these methods cause supersaturation throughout the bulk of solution which makes it challenging to affect crystallization at a specific desired location. In addition, these modes of reaching supersaturation cannot be used to explain or influence the crystallization in certain scenarios e.g., biological systems and in cases where the scope of temperature and a systemic pH change is very minimal. Another existing mode of crystallization involves the separation of ions into two different chambers and double diffusion through gels which is also not widely practical. Here we propose a mechanism in which we place salts in different solubility conditions on two sides of a permeable gel medium held at a steady state. Our steady state diffusion calculations predict that in certain pairings of different solubility conditions, the concentration of ions in the gel will always be above saturation concentration despite the absolute concentration decreasing along the length of the medium. We perform experiments in systems with variable solubilities in two different scenarios (pH and solvent mixtures) and we observe that the crystallization takes place in the gel indicating the supersaturation of the ions. This method offers an alternative way to get supersaturated solutions without evaporating solvents, changing temperatures, or separating the constituent ions into two different chambers across the diffusive medium.

Nanoscopic lipid diffusion in the live cell plasma membrane revealed by ultrafast single-molecule tracking.

Membrane organization and dynamics underlie various molecular interactions required for membrane functions. Although the importance of investigating biological membranes at the nanoscale is well recognized, resolving nanoscopic structures and dynamics is technically challenging. In this work, we employ ultrafast single-particle tracking techniques to measure single phospholipid diffusion in the plasma membrane of live cells. We attach a monovalent gold nanoparticle to the headgroup of biotinylated phospholipid and record its diffusive motion on microsecond resolution and nanometer precision by advanced optical interference microscopy. We find that both saturated and unsaturated phospholipids (biotin-PEG-DSPE and biotin-PEG-DOPE, respectively) undergo anomalous subdiffusion in the length scale below 100 nm. The unsaturated lipid diffuses only slightly more freely than the saturated lipid. Moreover, the nanoscopic lipid diffusion is highly heterogeneous in space and time. With statistical analyses, we find that the apparent dual-mobility subdiffusion can describe measured diffusion. The subdiffusion agrees well with the hop diffusion model that describes a Brownian diffuser moving in periodic and partially permeable barriers created by the cytoskeleton. Inhibition of actin polymerization by the chemical drug CK-666 reduces confinement's effective size and strength. Furthermore, we examine the effect of cholesterol on lipid subdiffusion by manipulating the cholesterol concentration. Cholesterol depletion by methyl-b-cyclodextrin leads to a more restricted lipid diffusion. We attribute the more confined diffusion to the formation of solid-like gel-phase nanodomains that move slowly and act as diffusion obstacles. Lowing the system temperature shows similar effects on lipid diffusion, suggesting that the cholesterol-dependent lipid diffusion connects to the nanoscopic phase separation. Overall, this study provides experimental evidence that lipid diffusion in the cell membrane is heterogeneous at the nanoscale and regulated by the membrane cholesterol and actin cytoskeleton.

Submonolayer and Monolayer Sn Adsorption and Diffusion Behavior on Oxidized Nb(100)

Current efforts to produce brighter beams of charged particles are focused on developing Nb3Sn-coated superconducting radio frequency (SRF) cavities for use in superconducting accelerator facilities. The growth mechanisms driving the formation of Nb3Sn films on preexisting Nb SRF cavities are not, however, fully understood. In order to understand the complex interplay between metallic Sn and the oxidized Nb surface leading to Nb3Sn alloy formation, we have examined how the structural and chemical composition of an oxidized Nb(100) single crystal influences Sn adsorption and diffusion behavior at submonolayer and monolayer Sn coverages. Sn was deposited on an NbO surface and annealed at temperatures relevant to Nb3Sn growth procedures before analysis via in situ scanning tunneling microscopy (STM). Experimental data, along with supporting simulated STM and calculated binding energies obtained using density functional theory, revealed the influence of Sn coverage and annealing temperatures on thermodynamic and kinetically driven diffusion pathways, preferred binding sites, novel Sn adlayer structures, and how the underlying NbO substrate evolves to accommodate Sn diffusion. This newly realized understanding of the interfacial chemical interactions between adsorbed Sn and the Nb surface sites is essential to develop predictive growth models for Nb3Sn films for use in future SRF cavities.

Effect of Vacancy Defect Content on the Interdiffusion of Cubic and Hexagonal SiC/Al Interfaces: A Molecular Dynamics Study.

The mechanical properties of ceramic-metal nanocomposites are greatly affected by the equivalent properties of the interface of materials. In this study, the effect of vacancy in SiC on the interdiffusion of SiC/Al interfaces is investigated using the molecular dynamics method. The SiC reinforcements exist in the whisker and particulate forms. To this end, cubic and hexagonal SiC lattice polytypes with the Si- and C-terminated interfaces with Al are considered as two samples of metal matrix nanocomposites. The average main and cross-interdiffusion coefficients are determined using a single diffusion couple for each system. The interdiffusion coefficients of the defective SiC/Al are compared with the defect-free SiC/Al system. The effects of temperature, annealing time, and vacancy on the self- and interdiffusion coefficients are investigated. It is found that the interdiffusion of Al in SiC increases with the increase in temperature, annealing time, and vacancy.

Generation of cross-spectrally pure electromagnetic fields using a pair of moving diffusers.

In this paper, we demonstrate that the vector light field is cross-spectrally pure if it passes through two diffusers (having similar correlation properties) moving with identical linear speeds in opposite directions. To determine the spatio-temporal coherence function of cross-spectrally pure light, a double slit is placed just after the second diffuser. We show that the normalized space-time coherence Stokes parameters of emerging light can be described in the form of a reduction formula, whereas the absolute values of the normalized space-frequency coherence Stokes parameters are the same for every frequency component of the light field. These are the conditions of cross-spectral purity of Stokes parameters. We further prove that at zero time delay, the condition of strict cross-spectral purity is validated. Furthermore, we establish the conditions for cross-spectral purity for a vector light field passing through the aforesaid diffusers, when they rotate with identical angular speeds in opposite directions, offering a possibility to optimize the scheme using only a single diffuser. For the first time, to our knowledge, an additional condition for equality of the degree of cross-polarization in space-time and space-frequency domains for strict cross-spectrally pure light beams is also introduced.

Reliability and validity of DTI-based indirect disconnection measures

White matter connections enable the interaction within and between brain networks. Brain lesions can cause structural disconnections that disrupt networks and thereby cognitive functions supported by them. In recent years, novel methods have been developed to quantify the extent of structural disconnection after focal lesions, using tractography data from healthy controls. These methods, however, are indirect and their reliability and validity have yet to be fully established. In this study, we present our implementation of this approach, in a tool supplemented by uncertainty metrics for the predictions overall and at voxel-level. These metrics give an indication of the reliability and are used to compare predictions with direct measures from patients’ diffusion tensor imaging (DTI) data in a sample of 95 first-ever stroke patients. Results show that, except for small lesions, the tool can predict fiber loss with high reliability and compares well to direct patient DTI estimates. Clinical utility of the method was demonstrated using lesion data from a subset of patients suffering from hemianopia. Both tract-based measures outperformed lesion localization in mapping visual field defects and showed a network consistent with the known anatomy of the visual system. This study offers an important contribution to the validation of structural disconnection mapping. We show that indirect measures of structural disconnection can be a reliable and valid substitute for direct estimations of fiber loss after focal lesions. Moreover, based on these results, we argue that indirect structural disconnection measures may even be preferable to lower-quality single subject diffusion MRI when based on high-quality healthy control datasets.

Three mechanical relaxation modes associated with nanoscale structural heterogeneity in Pd42.5Ni7.5Cu30P20 fragile glass

The dynamic relaxation behavior of Pd42.5Ni7.5Cu30P20 metallic glass was studied at 173–563 K (∼0.98Tg) and at angular frequency 10−2 to 102 rad s−1. Master curves of 16-digit dynamic moduli at angular frequency 10−4 – 1012 rad s−1 were constructed and characterized by the stretched exponent relaxation function, which exhibits three discrete relaxation modes with different activation energies, i.e., α-relaxation (7.98 eV) associated with the cooperative motion of ∼5 atoms, slow β-relaxation (1.39 eV) associated with single atomic diffusion, and fast β-relaxation (0.25 eV) associated with rattling motion. These three modes were also detected as slope changes on the quasi-static creep compliance under an isochronal heating process, which was successfully reproduced by dynamic complex compliance using the dynamic moduli with fitting parameters related to the considerable inhomogeneous structural characteristics, elastic modulus and volume fraction, generated in the glass.

Self Supervised Denoising Diffusion Probabilistic Models for Abdominal DW-MRI.

Quantitative diffusion weighted MRI in the abdomen provides important markers of disease, however significant limitations exist for its accurate computation. One such limitation is the low signal-to-noise ratio, particularly at high diffusion b-values. To address this, multiple diffusion directional images can be collected at each b-value and geometrically averaged, which invariably leads to longer scan time, blurring due to motion and other artifacts. We propose a novel parameter estimation technique based on self supervised diffusion denoising probabilistic model that can effectively denoise diffusion weighted images and work on single diffusion gradient direction images. Our source code is made available at https://github.com/quin-med-harvard-edu/ssDDPM.