Diffusion Mode Research Articles

Abstract Hollow cathodes are widely used for spacecraft electric propulsion, however improved understanding of the cathode plasma plume is required to improve performance and lifetime. The modular hollow cathode is developed to assist in cost effective ground testing by allowing simplified component replacement in the case of failure. In this work, a Langmuir probe is employed to characterise the plasma potential, electron temperature and electron density in the external cathode plume. Additionally, optical emission spectroscopy is used to qualitatively infer the relative plume composition. We examine the plume through independent tests using xenon and krypton, adjusting mass flow rates and other operating parameters. The modular hollow cathode exhibits different modes of operation including plume, spot, and diffuse modes. The experimental observations align with the theoretical predictions using various plasma mode transition criteria. In particular, the predator-prey criterion based on the ratio between the discharge current and the mass flow rate captures most of the mode transitions. Xenon operation results in a higher current collected at the anode in comparison to krypton where the total discharge power increases. Measurements collected determine the variation of the plasma properties at a fixed position from the keeper as a function of mass flow rate, keeper current and anode voltage in a triode configuration. The plasma potential and electron temperature downstream of the cathode orifice decrease with increased mass flow rate due to a more collisional plasma. As the flow rate rises, and with it the collisionality of the cathode plasma, the trends in electron temperature align well with qualitative Xe neutral/ion line ratios. The cathode is also coupled to a low-power wall-less (external discharge) hall thruster and operated on xenon to investigate the influence of the mode of operation on the discharge current and coupling voltage.

Understanding the dynamics of macromolecules adsorbed from extracellular fluids onto cell membranes is crucial for elucidating basic cellular processes and advancing applications in biotechnology, such as biosensing, therapeutics, and synthetic biology. However, this is complicated by the interplay between membrane heterogeneity, macromolecule conformation, and fluid hydrodynamics. We investigate the dynamics of linear polymers on binary lipid membranes using hydrodynamics simulations and single-molecule tracking experiments. We find that the preferential adsorption of nanosized polymer onto the raft-forming component of the membrane induces and stabilizes a single lipid raft that colocalizes with the polymer. This lipid raft, in turn, imposes dynamic confinement on the polymer, resulting in swollen yet restricted 2D conformations and Saffman-Delbrück-type diffusivity. These effects lead to an unusual scaling for polymer interfacial diffusion, [Formula: see text] with [Formula: see text]. Normal mode analysis further reveals that the relaxation time of the polymer's slowest mode surprisingly follows the prediction of Zimm model for a 3D chain in a good solvent, irrespective of whether the polymer's hydrodynamics are dominated by the 3D solvent or 2D fluid membrane. We also identify two diffusive modes: Saffman-Delbrück-type for polymer on heterogeneous membranes and Stokes-Einstein-like for polymer on homogeneous membranes, demonstrating the potential of polymer adsorbates as biosensors for membrane heterogeneity. Our study provides insights into polymer dynamics on biological membranes and suggests that polymer adsorbates can modulate lipid rafts, influencing raft-related cellular processes.

CO2 displacement is a very important oil displacement method, and the recovery rate of miscible displacement will be significantly improved. The miscibility of CO2 and oil involves diffusion, and studying its diffusion mechanism is beneficial for the efficient development of CO2 flooding. Pore scale flow simulation is a good method to study different oil displacement mechanisms, and micro-scale flow characterization can guide macro-development. Therefore, based on the N–S equation (Navier–Stokes equation) and convective diffusion model, this paper simulated and analyzed the influence of Pe number (Peclet number) to viscosity ratio on diffusion efficiency. When the viscosity ratio (R) is low (R < 3) and the Peclet number (Pe) is low (Pe < 300), the heterogeneous geometry of the porous media has a negligible influence on diffusion. However, with the increase in Pe number and viscosity ratio, diffusion efficiency became more sensitive to heterogeneity. The phase diagrams of Pe-viscosity ratios in different diffusion modes are also given. Considering the effect of the concentration-dependent diffusion coefficient on convective diffusion, four different diffusion coefficient cases, such as exponential and linear, are applied. It is found that exponential mode has the greatest influence on diffusion efficiency, and the influence of the concentration-dependent diffusion coefficient is only reflected at high viscosity ratios.

Gas drainage by boreholes is an important means to exploit coal seam gas. However, the high hydrostatic stress in deep in situ coal seams significantly limits the gas extraction efficiency. Gas drainage involves the problem of cross-scale gas emission under in situ stress. Nevertheless, the deformation response of the pore–fracture structure of coal under different hydrostatic stresses and its effect on the gas emission behavior have not been clarified. Therefore, gas seepage and emission experiments for four coal samples under different hydrostatic stresses were first carried out, and the evolutions of the fracture and matrix bulk modulus under different hydrostatic stresses were analyzed. Then, the control mechanism of the magnitude of hydrostatic stress on the gas emission behavior was analyzed through the changes in gas diffusion coefficients. In addition, a cross-scale gas emission model was developed to analyze the competitive effects of matrix pores and fractures on gas emission and the transformation behavior of gas diffusion modes. The main conclusions are as follows: The gas emission of coal with a small fracture bulk modulus is controlled by the fracture bulk modulus, while the gas emission of coal with a large fracture bulk modulus is controlled by the matrix bulk modulus. When the hydrostatic stress is small, the gas emission is mainly affected by the fracture closure effect. When the hydrostatic stress further increases, the change in the scale of the matrix pores becomes significant, causing the gas in the bulk diffusion state to transform into the surface diffusion state.

We predict that threshold detectors based on Al Josephson junctions with critical currents below 100 nA exhibiting a phase diffusion regime can be exploited for microwave photon detection at both 17 mK and 700 mK. We demonstrate the detection of two- and one-photon energies at 5 GHz with 90% and 15% efficiency and dark count times of about 0.1 s and 0.01 s, respectively. The weak temperature dependence of the detector’s performance observed in the sub-kelvin range fully confirms its phase diffusion mode of operation. On the other hand, these results show that inevitable thermal fluctuations are not the main source of detector noise. Consequently, there is still room to optimize the detector’s performance. These results are important for axion search experiments in the range of 5–25 GHz (20–100 μeV).

Abstract This paper examines the effects of NH3 dissociation on the physics driving low frequency dielectric barrier discharges operated in Penning Ar–NH3 gas mixtures. Optical emission and absorption diagnostics in combination with current–voltage characteristics are used to probe the global (averaged over the whole discharge zone) and local (at a given position along the gas flow lines) properties as a function of the gas flow rate. When the gas flow rate is sufficiently high, NH3 does not remain in the discharge zone long enough to be significantly dissociated and thus to have a significant impact on the discharge; hence, the characteristics are those of a typical glow discharge operated in a Penning mixture along the entire electrode length. When the gas flow rate decreases, the gas residence time in the discharge region increases such that NH3 becomes strongly converted to reaction products other than those leading to Penning ionization. This leads to a glow discharge only over a limited length of the electrode zone near the entrance, with no further breakdown towards the exit. The perceived effects on the discharge properties become significant if the overall behavior is considered, but on a local scale, the populations of Ar(1s5), Ar(2p), and H2(a) states deduced from optical diagnostics are only weakly modified. Using Ar(1s5) measurements and the predictions of a 1D fluid model, values of the degree of NH3 dissociation at two gas residence times are estimated. From such analysis, it is highlighted that the discharge can remain in a diffuse mode even when the quantity of NH3 is much lower than the one in the injected gas mixture.

Diffuse background illumination (DBI) diagnostics is applied to study spray instabilities in lean direct injection combustion systems for gas turbines. Experiments were performed in a reacting kerosene spray at atmospheric pressure using DBI, Mie Scattering, and OH* chemiluminescence (OH*-CL) imaging to delineate instability dynamics. Comparison of DBI and Mie scattering results shows that the Mie scattering is effective in illustrating the planar structure of the dispersed spray, but the line-of-sight DBI provided an improved visualization of the off-axis features of the spray to aid in understanding the spray dynamics. Measurements were postprocessed into phase-reconstructed data to illustrate the dynamic relationship between spray and OH*-CL oscillations and to demonstrate the effectiveness of DBI imaging for illustrating the influence of spray structure on the flame topology. Results show that DBI provides a clear illustration of how spray oscillations govern the switching between premixed (lean or rich) and diffusion modes of combustion over the course of the oscillation cycle.

Precise and convenient analytical methods are needed for the quantitative determination of calcium in water and food. Complexometric titration remains a reliable technique to determine calcium in milligram amounts. The titrations have been performed automatically by detecting color transitions with a webcam. Classical complexometric indicator calcein provided a sharp color transition. In diffuse reflection mode, the color appearance parameter (Hue) provides better precision and is more resistant to ambient light fluctuations compared to RGB primaries. In fluorescence mode with LED illumination, the fluorescence brightness of calcein is independent of ambient light, and the primary green color provides the sharpest endpoints. The color change during titration is better in the upper part of the acquired images due to the internal filter effect in calcein solutions. The automatic titration with a digital burette provides a standard deviation as low as 0.1 μmol. An example of its application is in the determination of calcium in commercial mineral waters. Based on the AGREE and ComplexMoGAPI rating scales, the semi-automatic titration showed better environmental assessment compared to the standard ASA method.

Biomolecular condensates formed through liquid-liquid phase separation are increasingly recognized as critical regulators of genome organization and gene expression. While the role of proteins in driving phase separation is well-established, how DNA modulates the structure and dynamics of protein-DNA condensates remains less well understood. Here, we employ a minimalist coarse-grained model to investigate the interplay between homotypic protein-protein and heterotypic protein-DNA interactions in governing condensate formation, composition, and internal dynamics. Our simulations reveal that DNA chain length and flexibility critically influence condensate morphology, leading to the emergence of multiphasic and core-shell organizations under strong heterotypic interactions. We find that DNA recruitment into the condensate significantly alters protein mobility, giving rise to differential dynamics of proteins within the condensate. By analyzing the distribution profiles of protein displacements, we identify up to five distinct diffusion modes, including proteins bound to DNA, confined within the dense phase, or freely diffusing. These results provide a mechanistic framework for interpreting spatially heterogeneous protein dynamics observed in chromatin condensates and emphasize the direct role of DNA in tuning condensate properties. Our findings provide new insights into how biophysical parameters may control the functional architecture of protein-DNA condensates in biological systems.

Real-time tracking of the kinetic binding processes of individual nanocargos on living cell membranes is essential for a better understanding of the cellular translocation mechanism and further optimization of the delivery functionality. In this work, we directly monitored the dynamic ligand-receptor interaction-modulated translational motions of two-dimensional (2D) nanocargos (gold nanodisks, Au NDs) on a living cell membrane. "Tango"-like diffusion is observed, where the nanocargos experience transitions between fast long-step searching and occasional restricted translational motion on the lipid membrane. From the single-particle tracking results, directional motion is involved in the long-range searching process, while tilted shaking dominates the restricted motion. Upon thoroughly analyzing the molecular binding free energy from the diffusion tracks, alternative bindings are clearly noted and closely associated with the transitions in different diffusion modes. These interesting observations provide deep insight into the translocation mechanism of 2D nanocargo in living cells.

Classification of urinary stones using near-infrared spectroscopy and chemometrics: A promising method for intraoperative application.

Large dataset on Fourier transform near infrared (FT-NIR) spectroscopy of green and roasted specialty coffee: Preprocessed infrared spectra and sensory scores for machine learning-based quality monitoring.

The formation offunctional nanoscopic domains is aninherent propertyof plasma membranes. Stimulated emission depletion combined with fluorescencecorrelation spectroscopy (STED-FCS) has been previously used to identifysuch domains; however, the information obtained by STED-FCS has beenlimited to the presence of such domains while crucial parameters havenot been accessible, such as size (Rd),the fraction of occupied membrane surface (f), in-membranelipid diffusion inside (Din) and outside(Dout) the nanodomains as well as theirself-diffusion (Dd). Here, we introducea quantitative approach based on a revised interpretation of the diffusionlaw. By analyzing experimentally recorded STED-FCS diffusion law plotsusing a comprehensive library of simulated diffusion law plots, weextract these five parameters from STED-FCS data. That approach isverified on ganglioside nanodomains in giant unilamellar vesicles,validating the Saffman-Delbrück assumption for Dd. STED-FCS data in both plasma membranes of living PtK2cells and giant plasma membrane vesicles are examined, and a quantitativeframework for molecular diffusion modes in biological membranes ispresented.

Baryonic black branes describe the quantum critical phase of the conformal conifold gauge theory at strong coupling. This phase extends to zero temperature at a finite baryonic chemical potential, represented by extremal black branes with AdS2×R3×T1,1 throat in asymptotic AdS5 × T1,1 geometry. We demonstrate here that this phase is dynamically unstable below some critical value of Tc/μ: the instability is represented by a diffusive mode in the hydrodynamic sound channel with a negative diffusion coefficient. We also identify a new (exotic) ordered phase of the conifold gauge theory: this phase originates at the same critical value of Tc/μ, but extends to arbitrary high temperatures, and is characterized by an expectation value of a dimension-2 operator, O2 ∝ T2, in the limit μT → 0.

Abstract Introduction Sleep spindles have been identified as key potential biomarkers for numerous neurological and psychiatric disorders, as well as for aging. Thus, studying spindle mechanisms provides valuable insight into the pathophysiology of various disorders. In addition to translatable human studies, animal model studies can more directly and invasively probe and systematically alter spindle networks. While various animal studies have shown distinct morphological differences between human and animal model spindles, the assumptions underlying approaches to spindle detection remain relatively unchanged across species. To assess the generalizability and validity of existing studies, it is crucial to understand how spindle activity and detection assumptions vary across species. Recently, new quantitative approaches have identified broader classes of human spindle-like transient events that are more informative than traditionally detected spindles. In this study, we extend these approaches to non-human primates and rodents to characterize spindle activity across species, validate signal processing assumptions, and understand implications for past and future studies. Methods We analyzed sleep period electroencephalogram (EEG) recordings of central electrodes from adult humans and mature macaques (N=5), rats (N=8), and mice (N=4) from baseline or control data from previously published studies. For each record, we used the DYNAM-O toolbox to quantify and visualize the dynamics of thousands of spindle-like transient oscillatory peaks across the night. Results We find distinct morphological and distributional differences in spindles between species. With increasingly lower-order species, spindles become markedly less morphologically distinct and more variable in their dynamics. In humans, fast spindles (12-16Hz) appear on spectrograms as distinct events in clear, narrow-band frequency. In primates, spindles are less separable and fall within a wider frequency range (8-14Hz). In rats, we observe one diffuse mode (6-16Hz) with little separability in events. Mice (6-20Hz) possess the least separable events and the most variability. Conclusion Given the diffuse morphology and high variability of spindles in animal models relative to humans, traditionally detected spindles likely represent a very small fraction of the underlying activity. Thus, caution should be taken, particularly in rodents, in the interpretation of studies focusing on individual spindles and their relationship to other waveforms. Support (if any) MJP: 1RF1AG079917-01A1, REB: I01 BX004673, FK: NIH K01 AG068366

Health equity is a fundamental concern within the broader health promotion aim of creating equal opportunities for health and bringing health differentials down to the lowest level possible. Cervical screening is just one example of a preventative health program where a health promotion lens is required to address entrenched health inequities. We draw on theorizations of policy ecologies to provide a framework for better understanding the processes involved in operationalizing policy with greater inclusivity in language in health promotion. Twenty-eight semi-structured interviews were conducted with 29 key informants between April and October 2022 to explore the operationalization of inclusive language in health promotion in the context of a national program to promote cervical screening to currently underscreening communities in Australia. Four thematic categories emphasize the balance required between demands and domains: (i) the need for clinical guidelines and flexibility in their translation and interpretation; (ii) organizational mandates, clinical practice, and patient-centred care; (iii) socio-cultural norms, behaviours, and attitudes amid politicized/ing milieus; and (iv) community preferences and the need for medical accuracy. As such, we identified how the operationalization of inclusive language in policy is influenced by and influences other domains where cervical screening is promoted. These findings hold wider implications for how the historical legacies of and contemporary need for 'women's health' can be maintained and respected amid demands for greater gender inclusion. At the same time, the failure to trace diverse and diffuse modes and contexts of operationalization may (re)produce health inequities in practice if left unexamined.

The use of a gas-diffusion carbon-graphite electrode for depolarizing the anode process in the sulfuric acid cycle of hydrogen production is promising. The sulfuric acid cycle is currently the most promising solution for addressing issues in atomic-hydrogen energy. The integration of large-scale electrochemical production and carbon-free electricity generation into a single system can solve the problem of "valley" and "peak" loads. The use of porous graphite-based anodes enables the process to be conducted in a gas- diffusion mode. A significant challenge is the high overpotential of the electrode process, which can be reduced by activating the surface of carbon materials. Porous graphite of the PG-50 grade was used as the base for the gas-diffusion electrode. To enhance catalytic activity and increase the specific surface area of the electrode, active carbon (AC) was deposited on the surface and in the pores of the graphite electrodes. Experimental results show that two impregnations of graphite with a polysaccharide solution followed by carbonization produce porous electrodes with an active carbon content of 82…85 % of the initial electrode weight. To establish the role of catalytically active carbon forms in the oxidation of SO2, cyclic voltammograms were obtained on glassy carbon (GC 12) in 1 mol·dm⁻ ³ sulfuric acid, both with and without the addition of sulfur(IV) oxide (0.24 mol·dm⁻ ³). GC 12 was chosen as a carbonaceous material with a low degree of surface development, whose actual surface area is close to its geometrically measured area. The experimental data indicate that sulfur(IV) oxide oxidation occurs on the glassy carbon surface. This oxidation process occurs at potentials where weakly bound oxygen forms on the graphite surface. Therefore, it can be assumed that the oxidation of sulfur(IV) oxide on graphite proceeds through weakly bound oxygen on the electrode surface. The activation of the carbon electrode surface to intensify SO2 oxidation was achieved by depositing catalytic additives in the form of active carbon onto the porous graphite surface. Multistage impregnation of the carbon-graphite base with a polysaccharide solution, followed by thermal decomposition and activation in nitric acid solution, regulated the amount of deposited AC. The amount of AC deposited per activation on a PG-50 sample was 9…12 mg·cm⁻ ². The AC content was increased by increasing the number of impregnation cycles with concentrated nitric acid, followed by thermal decomposition after each cycle. At an AC content of 33…39 mg·cm⁻ ², the majority of the electrode surface becomes available for free SO2 oxidation. Further increases in AC content lead to deteriorating electrode performance. With AC activation of the graphite base, the anodic current density reaches 3200…3300 A·m⁻ ², which is sufficient to recommend activated carbon-graphite materials for industrial application in the sulfuric acid cycle of hydrogen production.

The article presents the results of a numerical study of seepage water dynamics in the base of a municipal solid waste (MSW) landfill. The landfill is a complex engineering structure that receives, stores, and isolates waste in order to provide effective waste disposal management and ecological safety. During the life of a MSW landfill, contaminated runoff, or filtrate, is formed. The negative impact of the filtrate formed in the landfill body is associated with the possibility of its penetration into groundwater and, as a consequence, into surface water bodies. When organizing a landfill, a substrate in the form of an anti-seepage screen, which performs a barrier function, is laid. In numerical modeling of the filtering capacity of the screen, the filtrate layer is not considered. In this paper, the effect of the technogenic layer on the modes of diffusion and convective propagation of seepage waters in the base of municipal solid waste placement facilities was numerically investigated. To study the features of pollutant distribution and to determine migration parameters, archival data from a set of field and laboratory studies in the area of the operating landfill were used. A numerical model describing the hydrodynamics of substance migration in the soil layer was constructed. The process of pollutant movement is described in terms of dry residue dissolved in water. Factors that have a significant impact on the migration of MSW ingredients, such as convective transfer, diffusion and the geological composition of the landfill base, are taken into account in the mathematical formulation of the problem. It is shown that the instability lead.

Bioenergetic membranes of mitochondria, thylakoids, and chromatophores are primary sites of ATP production in living cells. These membranes contain an electron transport chain (ETC) in which electrons are shuttled between a series of redox proteins during the generation of ATP via oxidative phosphorylation. The phospholipid composition of these membranes, which often include negative lipids, plays a role in determining the electrostatics of their surface owing to the spatial distribution of their charged head groups. Cardiolipin (CDL) is a phospholipid commonly associated with bioenergetic membranes and is also a significant contributor to the negative surface charge. Interactions between cytochromes and phospholipid head groups in the membrane can in principle affect the rate of its travel between ETC components, hence influencing the rate of ATP turnover. Here, we use molecular dynamic (MD) simulations that feature an accelerated membrane model, termed highly mobile membrane mimetic (HMMM), to study protein-lipid interactions during the diffusion of cytochrome c2 between redox partners in a bioenergetic membrane. We observe a "skipping" mode of diffusion for cytochromes along with a bias for binding to anionic lipids, particularly with a strong preference for CDL. During diffusion, cytochrome c2 maintains a relatively fixed tilt with respect to the membrane normal with wider fluctuations in its angle with respect to the plane of the membrane. The obtained results describing the behavior of cytochrome c2 on a representative bioenergetic membrane have direct ramifications in shuttling motions of other similar electron-carrying elements in other bioenergetic membranes, which are composed of a significant amount of anionic lipids. The mode of surface-restricted diffusion reported here would modulate rapid electron transfer between the ETC complexes anchored in bioenergetic membranes by reducing the search space between them.

We introduce spatially-encoded dynamics tracking (SpeedyTrack), a strategy to enable direct microsecond wide-field single-molecule tracking/imaging on common microscopy setups. Capitalizing on the native sub-microsecond vertical charge shifting capability of popular electron-multiplying charge-coupled devices (EM-CCDs), SpeedyTrack staggers wide-field single-molecule images along the CCD chip at ~10-row spacings between consecutive timepoints, effectively projecting the time domain to the spatial domain. Wide-field tracking is thus achieved for freely diffusing molecules at down to 50 μs temporal resolutions for >30 timepoints, permitting trajectory analysis to quantify diffusion coefficients up to 1,000 μm2/s. Concurrent acquisition of single-molecule diffusion trajectories and Förster resonance energy transfer (FRET) time traces further elucidates conformational dynamics and binding states for diffusing molecules. Moreover, with a temporally patterned vertical shifting scheme, we deconvolve the spatial and temporal information to map long, fast single-molecule trajectories at the super-resolution level, thus resolving the diffusion mode of a fluorescent protein in live cells with nanoscale resolution. While these demonstrated capabilities substantially outperform existing approaches, SpeedyTrack further stands out for its simplicity by directly working off the built-in functionalities of EM-CCDs without the need to modify existing optics or electronics. We thus provide a facile solution to the microsecond tracking/imaging of single molecules and their super-resolution mapping in the wide field.