Slow Diffusion Research Articles

Active particle in one dimension subjected to resetting with memory.

The study of diffusion with preferential returns to places visited in the past has attracted increased attention in recent years. In these highly non-Markov processes, a standard diffusive particle intermittently resets at a given rate to previously visited positions. At each reset, a position to be revisited is randomly chosen with a probability proportional to the accumulated amount of time spent by the particle at that position. These preferential revisits typically generate a very slow diffusion, logarithmic in time, but still with a Gaussian position distribution at late times. Here we consider an active version of this model, where between resets the particle is self-propelled with constant speed and switches direction in one dimension according to a telegraphic noise. Hence there are two sources of non-Markovianity in the problem. We exactly derive the position distribution in Fourier space, as well as the variance of the position at all times. The crossover from the short-time ballistic regime, dominated by activity, to the long-time anomalous logarithmic growth induced by memory is studied. We also analytically derive a large deviation principle for the position, which exhibits a logarithmic time scaling instead of the usual algebraic form. Interestingly, at large distances, the large deviations become independent of time and match the nonequilibrium steady state of a particle under resetting to its starting position only.

A 2D Metallic KCu4S3 Anode for Fast‐Charging Sodium‐Ion Batteries

AbstractThe search for advanced electrode materials to solve slow ion diffusion and poor conductivity issues has spurred the development of fast‐charging sodium‐ion batteries (SIBs). Herein, a 2D metallic anode, KCu4S3, is reported expertly crafted using a KSCN molten salt approach, laying the foundation for fast‐charging SIBs. It is found that the mixed metal‐valence states within this compound provide substantial advantages, particularly in enhancing the high‐rate capability and ensuring long‐term durability. The mechanism that appears to facilitate these benefits can be traced to the formation of NaCu2S2 intermediate, which assist in electron transfer during Na+ (de)intercalation. In situ observations confirm the sodiation products of NaCu2S2 and sodium polysulfide can recover to the original phase upon desodiation. Such distinctive characteristics endow KCu4S3 with remarkable electrochemical performances, including an impressive capacity of 355 mAh g−1 at 20 A g−1 and 100% capacity retention within 3000 cycles. Moreover, the full cell exhibits a high energy density of 332 Wh kg−1 and retains 92% of its capacity across 150 cycles at 1 A g−1. This work opens new horizons in the field of fast‐charging materials, making a significant step forward in shaping the future of SIBs.

TbCu7-type Sm-Fe(-N) powder synthesized by low-temperature reduction-diffusion process using the Li–Ca reductant

It was predicted that TbCu7-type Sm-Fe powder prepared by the low-temperature reduction-diffusion (LTRD) process using a Li-Ca reductant would contain no residual ɑ-Fe because this reductant would not produce the absorbed water that hinders the reaction between Sm and Fe by forming oxychlorides when molten salt is used as the reductant. Contrary to this expectation, a detailed microstructure analysis revealed that a residual phase of unreacted ɑ-Fe existed in some TbCu7-type Sm-Fe particles rather than as separate Fe particles. This residual ɑ-Fe phase was not located in the center of the Sm-Fe particles and was not detected in some Sm-Fe particles, suggesting that the reason for the residual ɑ-Fe phase is inhomogeneous diffusion of Sm into the Fe due to slow diffusion at low temperatures. Although this TbCu7-type Sm-Fe powder contained a small amount of unreacted ɑ-Fe phase, the magnetic properties of the nitride TbCu7-type Sm-Fe were also estimated.

Evaluation of movability of shale oil in organic matter in depletion production by REV-scale simulations

The oil transfer in shale oil formations includes the oil flow in inorganic and organic pores, and the diffusion in the organic matter (OM). A novel triple-continuum model (OM matrix, organic pores, inorganic matrix) is proposed coupling the oil flow (in organic and inorganic pores) and diffusion (in OM matrix). The proposed model is further validated by three-dimensional (3D) numerical simulations. The simulation results show that the proportion of oil production of the absorbed oil from OM matrix in the total shale oil production is small due to the relatively slow diffusion process. However, the diffusion of oil from OM matrix to the organic pores can provide extra energy for the oil expansion in inorganic pores, and thus can greatly increase the oil production in the depletion process. The high OM content can prolong the timespan of oil production. More absorbed oil in OM provides more elastic energy for oil depletion in organic and inorganic pores, and thus leads to higher flow rate in the late period of shale oil production. Smaller size of OM means shorter distance for oil transfer from OM to inorganic matrix, and thus accounts for higher movability of oil in OM.

Fluorine-ion-regulated yolk–shell carbon-silicon anode material for high performance lithium ion batteries

Silicon is considered as the next-generation anode material for lithium-ion batteries due to its high theoretical specific capacity and abundant crustal abundance. However, its poor electrical conductivity results in slow diffusion of lithium ions during battery operation. Simultaneously, the alloying process of silicon undergoes a 300 % volume change, leading to structural fractures in silicon during the cycling process.As a result, it loses contact with the current collector, continuously exposing active sites, and forming a sustained solid electrolyte interface (SEI) membrane. This paper presents the design of a fluorine-ion-regulated yolk–shell carbon-silicon anode material, highlighting the following advantages: (a) Alleviating volume changes through the design of a yolk–shell structure, thereby maintaining material structural integrity during cycling. (b) Carbon shell prevents silicon from coming into contact with the electrolyte, simultaneously improving silicon's electrical conductivity and increasing ion/electron conductivity. (c) Utilizing fluorine-ion interface modification to obtain an SEI membrane rich in fluorine components (such as LiF), thereby enhancing its long cycling performance. The F-Si@Void@C exhibits outstanding electrochemical performance, with a reversible capacity of 1166 mAh/g after 900 cycles at a current density of 0.5 A/g.

Influence of coal rock on tight sandstone reservoirs in coal seam roofs: A case study of the lower jurassic in the Taibei sag, Turpan-Hami Basin, China

After shale gas, coalbed methane and gas hydrate, coal measure gas has become an important new unconventional resource, for which exploration to depths of >3000 m are taking place in China. However, owing to unusual geological conditions and as yet inadequate exploration technology the current level of exploration is low. The acidic water medium in coal-bearing strata affects the diagenesis of adjacent tight sandstone reservoirs, thereby influencing reservoir quality. However, the current understanding of the impact mechanism of coal seams on neighboring tight reservoirs is insufficient, constraining the further exploration of coal measure gas. In order to reveal the influence of coal rock on a tight sandstone reservoir in its roof, we study the coal-bearing strata of the Xishanyao Formation in the Taibei Sag of the Turpan-Hami Basin using cast thin sections, physical property tests, XRD analysis, carbon and oxygen isotopes, high-pressure mercury intrusion and low-temperature N2 adsorption. The carbonate cement in the sandstone reservoir of the coal seam roof was formed by the decarboxylation of organic acid. The organic acid, containing CO2 generated by coal rock hydrocarbon generation, has modified the tight sandstone reservoir of the coal seam roof via dissolution. This has improved the physical properties and pore throat structure of the tight sandstone reservoir close to the coal-sandstone interface. The amount of improvement extends to about 2 m into the sandstone. During the upward transport of fluid, the pre-existing carbonate cement dissolves and then precipitates, which causes the CO2 generated by the organic acid decarboxylation to exchange carbon with the carbon isotopes in the pre-existing carbonate cement. Due to the slow upward diffusion rate and limited diffusion distance of the CO2-bearing fluids, the carbonate cement exhibits gradually heavier δ13CPDB values with increasing distance from the coal-sandstone interface.

Enhanced asymmetric supercapacitor performance via facile construction of Cu-MOF@Co(OH)2 heterostructure

Integrating metal-organic frameworks (MOFs) with transition hydroxides has the potential to enhance the inadequate electronic conductivity and address the slow diffusion of MOF materials in electrochemical applications. Herein, we synthesized a 2D Cu-MOF and successfully prepared a Cu-MOF@Co(OH)2 heterostructure using a one-step hydrothermal method on a Co(OH)2/NF (nickel foam) substrate. The hybrid Cu-MOF@Co(OH)2 material exhibits high electrochemical reactivity, resulting in enhanced pseudocapacitor performance, with a specific capacitance of 2039.8 mF cm−2 at a current density of 1.0 mA cm−2. In addition, an asymmetric two-electrode cell was constructed using Cu-MOF@Co(OH)2/NF and activated carbon (AC)/NF, exhibiting a specific capacitance of 444.5 mF cm−2 at a current density of 1.0 mA cm−2, and demonstrating decent cycling durability with 90.1 % retention after 2000 cycles.

Design and Development of Sustainable Cu2 (II)- and Mn2 (III)-Embedded Bifunctional Electrocatalysts: Enhanced Hydrogen and Oxygen Generation.

Nowadays, environmentally friendly, low-cost-effective, and sustainable electrocatalysts used widely for hydrogen and oxygen evolution reactions have come into the limelight as a new research topic for scientists. This study highlights the preparation of two unique and symmetrical dinuclear Cu (II) and Mn (III) bifunctional catalysts by a facile simple slow evaporation and diffusion route. [C32H24Cu2F4N4O4] (1) and [C32H24Mn2F4N4O4] (2) both have monoclinic (C2/c (15)) crystal systems, with oxidation states +2 and +3, respectively. Prominent SPR peaks at 372 and 412 nm indicate an M-L charge transfer transition in both complexes. The synthesized electrocatalysts display exceptional catalytic activity for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Complex 1 exhibits enhanced hydrogen generation in 0.5 M H2SO4 with a small overpotential of 216 mV at -10 mA cm-2 along with a significantly lower Tafel value of 97 mV/dec compared to Complex 2. Moreover, Complex 1 is highly active for the OER in 1 M KOH with a small Tafel slope of 103 mV/dec and a low overpotential of 340 mV to acquire 10 mA cm-2 current density, compared to Complex 2. Complex 1 and Complex 2 remain stable up to 20 h in acidic electrolyte and up to 36 h and 20 h in the basic electrolyte, respectively.

The influence of in-situ induced and MnO2 polymorph-dependent structural changes to the energy storage and mechanism of supercapacitors

Due to its economic, environmental, and theoretical advantages, manganese dioxide (MnO2) is a promising cathode material for supercapacitors. However, the commercial application of MnO2 still faces challenges such as low intrinsic conductivity, slow ion diffusion, and structural instability. In this study, four crystalline forms of MnO2 powder electrodes (α-, β-, γ-, and δ-MnO2) were prepared, and results showed that with a specific capacitance of 218.2 F∙g−1, δ-MnO2 exhibited the best electrochemical performance. This was primarily due to the fact that δ-MnO2 possesses a high specific surface area, rich oxygen vacancy, and fast electron-ion transfer speed. A self-supported electrode (δ-MnO2/NF) without binder addition was further prepared using an in-situ-induced technique. The results revealed that the specific capacitance of δ-MnO2/NF was as high as 809.4 F∙g−1 and that the capacity retention rate and coulombic efficiency after 5000 cycles were 92.8 % and 99.2 %, respectively, which were superior to those of δ-MnO2 (80.3 % and 93.5 %). In-situ induction not only amplifies the structural advantages of δ-MnO2 but also generates more electrochemical active sites due to the intense interaction between NF and δ-MnO2. In addition, ultrathin nanosheet arrays formed on the NF provide a three-dimensional conductive network for the transport of ions and electrons. Density functional theory calculations were performed to verify the excellent electronic conductivity and ion diffusivity of δ-MnO2 and showed that transferring electrons from metal Ni to δ-MnO2 is the basis for producing numerous oxygen vacancies in δ-MnO2/NF.

Cross-cryptocurrency return predictability

Using data from Binance, we find strong evidence of cross-cryptocurrency return predictability. The lagged returns of other cryptocurrencies serve as significant predictors of focal cryptocurrencies. The results are robust across various methods, including the adaptive LASSO and principal component analysis. Furthermore, a long-short portfolio formed on the past returns of cryptocurrencies can generate a sizable return out-of-sample after accounting for transaction costs. Overall, our findings corroborate cross-cryptocurrency return predictability and are consistent with the spillover effect mechanism, where common shocks among cryptocurrencies coupled with the limited attention of investors lead to slow information diffusion across coins.

Interfacial Glucose to Regulate Hydrated Lipid Bilayer Properties: Influence of Concentrations.

A series of atomistic molecular dynamics (MD) simulations were carried out with a hydrated 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) bilayer with the variation of glucose concentrations from 0 to 30 wt % in the presence of 0.3 M NaCl. The study suggested that although the thickness of the lipid bilayer dropped significantly with the increase in glucose concentration, it expanded laterally at high glucose levels due to the intercalation of glucose between the headgroups of adjacent lipids. We adopted the surface assessment via the grid evaluation method to compute the deviation of the bilayer's key structural features for the different amounts of glucose present. This suggested that the accumulation of glucose molecules near the headgroups influences the local lipid bilayer undulation and crimping of the lipid tails. We find that the area compressibility modulus increases with the glucose level, causing enhanced bilayer rigidity arising from the slow lateral diffusion of lipids. The restricted lipid motion at high glucose concentrations controls the sustainability of the curved bilayer surface. Calculations revealed that certain orientations of of interfacial glucose with the of lipid headgroups are preferred, which helps the glucose to form direct hydrogen bonds (HBs) with the lipid headgroups. Such lipid-glucose (LG) HBs relax slowly at low glucose concentrations and exhibit a higher lifetime, whereas fast structural relaxation of LG HBs with a shorter lifetime was noticed at a higher glucose level. In contrast, lipid-water (LW) HBs exhibited a higher lifetime at a higher glucose level, which gradually decreased with the glucose level lowering. The study interprets that the glucose concentration-driven LW and LG interactions are mutually inclusive. Our detailed analysis will exemplify small saccharide concentration-driven membrane stabilizing efficiency, which is, in general, helpful for drug delivery study.

Irradiation-Hardening Model of TiZrHfNbMo0.1 Refractory High-Entropy Alloys.

In order to find more excellent structural materials resistant to radiation damage, high-entropy alloys (HEAs) have been developed due to their characteristics of limited point defect diffusion such as lattice distortion and slow diffusion. Specially, refractory high-entropy alloys (RHEAs) that can adapt to a high-temperature environment are badly needed. In this study, TiZrHfNbMo0.1 RHEAs are selected for irradiation and nanoindentation experiments. We combined the mechanistic model for the depth-dependent hardness of ion-irradiated metals and the introduction of the scale factor f to modify the irradiation-hardening model in order to better describe the nanoindentation indentation process in the irradiated layer. Finally, it can be found that, with the increase in irradiation dose, a more serious lattice distortion caused by a higher defect density limits the expansion of the plastic zone.

Nonlocal approximation of nonlinear diffusion equations

We show that degenerate nonlinear diffusion equations can be asymptotically obtained as a limit from a class of nonlocal partial differential equations. The nonlocal equations are obtained as gradient flows of interaction-like energies approximating the internal energy. We construct weak solutions as the limit of a (sub)sequence of weak measure solutions by using the Jordan-Kinderlehrer-Otto scheme from the context of 2-Wasserstein gradient flows. Our strategy allows to cover the porous medium equation, for the general slow diffusion case, extending previous results in the literature. As a byproduct of our analysis, we provide a qualitative particle approximation.

Influence of vanadium-carbide precipitation on the deformation behavior of Fe-30Mn-10Co-10Cr-2.5 V-1.5C multi-principal element alloy

Multi-principal element alloys represent a compelling avenue for the development of innovative alloys that have the potential to surpass conventional alloys in various applications, owing to the extensive compositional space they offer. For structural application though, this potential has not yet been realized, mostly because of hardly superior mechanical properties and elevated alloying costs. To overcome this hurdle, efforts have been made to increase mechanical properties using individual strengthening mechanisms, such as grain refinement, prior plastic deformation, precipitation hardening, and solid solution strengthening. In this study, we aim to combine multiple of these mechanisms into a singular alloy by adding V and C to the Fe30Mn10Co10Cr (at.-%) alloy. Using a custom calphad database, thermodynamic calculations were carried out to determine a suitable chemical composition which was subsequently cast and thermo-mechanically processed. Aging treatments above 700 °C for 4–24 h led to vanadium carbide precipitation, increasing the yield strength by up to 450 MPa to nearly 1GPa. Extensive aging times were necessary to facilitate precipitation, thereby indicating slow diffusion processes. A transition from twinning-induced to transformation-induced plasticity by vanadium carbide precipitation was observed and attributed to the reduction of C-content and stacking fault energy in the matrix as well as twin-precipitate interactions.

An unblocked Li transport pathway for all-solid-state batteries enabled by boosting bulk diffusion kinetic and interfacial ion conduction

The high interfacial resistance and dendrite growth associated with the high Li concentration gradient at the Li/solid-state electrolytes (SSEs) interface significantly hinder the cycle life of solid-state lithium metal batteries (SSLMBs). This limitation is primarily attributed to the slow diffusion of Li atoms in the bulk and the sluggish conduction of Li ions at the interface. Merely focusing on enhancing either aspect is typically not sufficient to fully address this challenge. Herein, we utilize AgNO3 molten salt to in-situ generate LixAg anode and nitrided interphase to simultaneously boost the bulk Li atom diffusion kinetics and the interfacial ion conduction, effectively constructing a fast-continuous ion/atom transport pathway and significantly reducing the concentration gradient of Li. The in-situ formed LixAg alloy, with a Li diffusion coefficient of approximately 10−8 cm2 s−1, demonstrates a diffusion rate three orders of magnitude higher than bulk Li (∼ 10−11 cm2 s−1), alleviating vacancy accumulation and contact loss at the anode/SSE interface. While the in-situ formed ionic conductive nitrided interphase promotes ion transport through the interface to reduce the Li concentration gradient and boost charge transfer kinetics. Benefiting from the high Li ion/atom transport rate in both bulk and interface, ultrahigh critical current density/areal capacity (1.2 mA cm−2;1.2 mAh cm−2) and cyclability (1.0 mA cm−2;0.5 mAh cm−2) are achieved for solid-state Li||Li symmetric cells. Impressively, an SSLMB assembled with a LiFePO4 electrode shows excellent cycling stability for as long as 1600 cycles at 0.5 C with a high capacity retention of 82.6 %.

Concentration-Gradient Structural LiFe0.5Mn0.5PO4/C Prepared via Co-precipitation Reaction for Advanced Lithium-Ion Batteries.

The intrinsically low electronic conductivity and slow ion diffusion kinetics limit further development of olivine LiFexMn1-xPO4 cathode materials. In this paper, with the aim of improving the performance of such materials and alleviating the Jahn-Taller effect of Mn3+ ion, a bimetallic oxalate precursor with gradient distribution of elemental concentration followed with an efficient process is applied to synthesize LiFe0.5Mn0.5PO4 nanocomposite. The results shown that with certain structural modulation of the precursor, the discharge capacity of synthesized LiFe0.5Mn0.5PO4 increased from 149 mAh g-1 to 156 mAh g-1 at 0.1 C, the cycling capacity was also remarkably improved. the Fe0.5Mn0.5C2O4 ⋅ 2H2O-1 precursor with gradient distribution of elemental concentration effectively restricts the reaction between electrode material and electrolyte, thereby alleviates the dissolution of Mn3+ ion, reduces the decay of capacity and improves the stability of the material.

Glacial-interglacial sedimentation control on gas seepage exemplified by Vestnesa Ridge off NW Svalbard margin

Vestnesa Ridge is built-up of thick contourites mainly deposited during the last ∼5 million years. Methane leaks from deep gas reservoirs creating pockmarks on its crest, and which have been the focus of numerous studies. Sedimentation patterns in relation to the pronounced changes in oceanography and climate of the last glacial-interglacial cycles and its possible impact of seepage of gas have rarely been studied. Here, we present a detailed history of contourite development covering the last ∼130,000 years with most details for the last 60,000 years. The study is based on 43 marine sediment cores and 1,430 km of shallow seismic lines covering the ridge including methane seep sites, with the purpose of reconstructing changes in depositional patterns in relation to paleoceanographical changes on glacial, interglacial, and millennial time scale in relation to activity of seepage of gas. The results show that thick Holocene deposits occurred below ∼1,250 m water depth in the western part of the ridge. Both in pockmarks at western and eastern Vestnesa Ridge, seepage decreased at ∼10–9 ka in the early Holocene. The fine Holocene mud likely reduced seepage to a slow diffusion of gas and microbial oxidation probably prevented escape from the seafloor. Results also showed that seepage of gas was highly variable during the glacial, and low to moderate during the cold Heinrich stadial H1 (19–15 ka) and Younger Dryas stadial (13–12 ka). Seepage reached a maximum during the deglaciation in the Bølling and Allerød interstadials 15–13 ka and early Holocene 12–10 ka. The deglaciation was a period of rapid climatic, oceanographic, and environmental changes. Seepage of gas varied closely with these events indicating that slower tectonic/isostatic movements probably played a minor role in these millennial scale rapid fluctuations in gas emission.

Quantifying H&E staining results, grading and predicting IDH mutation status of gliomas using hybrid multi-dimensional MRI.

To assess the performance of hybrid multi-dimensional magnetic resonance imaging (HM-MRI) in quantifying hematoxylin and eosin (H&E) staining results, grading and predicting isocitrate dehydrogenase (IDH) mutation status of gliomas. Included were 71 glioma patients (mean age, 50.17 ± 13.38years; 35 men). HM-MRI images were collected at five different echo times (80-200ms) with seven b-values (0-3000s/mm2). A modified three-compartment model with very-slow, slow and fast diffusion components was applied to calculate HM-MRI metrics, including fractions, diffusion coefficients and T2 values of each component. Pearson correlation analysis was performed between HM-MRI derived fractions and H&E staining derived percentages. HM-MRI metrics were compared between high-grade and low-grade gliomas, and between IDH-wild and IDH-mutant gliomas. Using receiver operational characteristic (ROC) analysis, the diagnostic performance of HM-MRI in grading and genotyping was compared with mono-exponential models. HM-MRI metrics FDvery-slow and FDslow demonstrated a significant correlation with the H&E staining results (p < .05). Besides, FDvery-slow showed the highest area under ROC curve (AUC = 0.854) for grading, while Dslow showed the highest AUC (0.845) for genotyping. Furthermore, a combination of HM-MRI metrics FDvery-slow and T2Dslow improved the diagnostic performance for grading (AUC = 0.876). HM-MRI can aid in non-invasive diagnosis of gliomas.

Configurational Sampling of All-Atom Solvated Membranes Using Hybrid Nonequilibrium Molecular Dynamics Monte Carlo Simulations.

All-atom simulations are a powerful approach to study the structure and dynamics of biological membranes. However, sampling the atomic configurations of inhomogeneous membranes can be challenging due to the slow lateral diffusion of the various constituents. To address this issue, a hybrid nonequilibrium molecular dynamics Monte Carlo (neMD/MC) simulation method is proposed in which randomly chosen lipid molecules are swapped to generate configurations that are subsequently accepted or rejected according to a Metropolis criterion based on the alchemical work for the attempted swap calculated via a short trajectory. A dual-topology framework constraining the common atoms of the exchanging molecules yields a good acceptance probability using switching trajectories as short as 10 ps. The performance of the hybrid neMD/MC algorithm and its ability to sample the distribution of lipids near a transmembrane helix carrying a net charge are illustrated for a binary mixture of charged and zwitterionic lipids.

Electrical anisotropy and its mitigation in conductive polymers printed by vat photopolymerization

In most additive manufacturing (AM) technologies, objects are realized layer by layer. This layer-by-layer construction leads to inherent anisotropic physical properties. Controlling, understanding and sometimes mitigating such anisotropy is a critical issue in the development of AM. Electrical anisotropy in conductive nanocomposites processed by Vat photopolymerization is demonstrated and quantified in the present work. In the used method, which enjoys high resolution and high speed, layers of an acrylate based resin, are successively cross-linked by UV irradiation of 2D patterns. Carbon nanotubes are used as conductive fillers for their low percolation threshold that allows realizing conductive and still sufficiently transparent materials for UV polymerization. Conductivity parallel to the layers of 3D objects is found to be much greater than conductivity perpendicular to the layers. This electrical anisotropy is explained by the high contact resistance between printed layers. High contact resistance results from the slow diffusion of carbon nanotubes from the uncured material towards the interface of the cured object. It is found that implementing a delay time before curing successive layers, or decreasing the matrix viscosity with temperature, to promote diffusion of the conductive particles allow substantial reduction of the contact resistance between layers. As a result, conductivity anisotropy can be reduced by almost two orders of magnitude. This control and mitigation of conductivity anisotropy allows reconciliation of the high resolution of the Vat photopolymerization technology with the possibility to realize uniform 3D materials.