Concentration Jumps Research Articles

Photophoresis of a moderately large high-viscosity droplet in slip mode

Purpose of research. To obtain analytical expressions that allow calculating the strength and velocity of a moderately large, highly viscous droplet, taking into account the direct contribution of the evaporation coefficient, linear corrections by the Knudsen number and the reactive effect of a plane wave moving in the field of mono-chromatic radiationMethods. Methods of perturbation theory, gas kinetic methods, mathematical methods for solving linear partial differential equations with variable coefficients (the system of Stokes equations, Laplace and Poisson equations) were used.Results. In a quasi-stationary approximation, a theoretical description of the photophoretic motion of a moderately large evaporating highly viscous spherical droplet (there is no circulation of matter inside the droplet and interfacial surface tension forces) in a viscous binary gas mixture is carried out. A velocity-linearized system of Navi-Stokes equations and heat and mass transfer was solved. Expressions are obtained for the fields of mass velocity, pressure, temperature and the relative numerical concentration of the first component. The strength and speed of photophoresis of a highly viscous droplet was determined by integrating a stress tensor over the surface of the particle. Under boundary conditions on the surface of a highly viscous droplet, linear corrections in terms of the Knudsen number (isothermal, thermal and diffusion slips, temperature and concentration jumps, as well as sliding due to temperature inhomogeneity along the curved surface of the particle), the reactive effect and the contribution of the direct influence of the evaporation coefficient were taken into account. The contributions to the obtained formulas for the photophoresis of a moderately large highly viscous droplet are analyzed and the preliminary transitions to the results known in the literature (moderately large and large solid particles of spherical shape) are considered Conclusion. The obtained formulas based on the hydrodynamic method allow us to evaluate the effect of the direct contribution of the evaporation coefficient and linear corrections by the Knudsen number on the strength and speed of photophoresis of a moderately large evaporating highly viscous droplet in a binary gas mixture.

Southern Ocean drives multidecadal atmospheric CO2 rise during Heinrich Stadials

The last glacial period was punctuated by cold intervals in the North Atlantic region that culminated in extensive iceberg discharge events. These cold intervals, known as Heinrich Stadials, are associated with abrupt climate shifts worldwide. Here, we present CO2 measurements from the West Antarctic Ice Sheet Divide ice core across Heinrich Stadials 2 to 5 at decadal-scale resolution. Our results reveal multi-decadal-scale jumps in atmospheric CO2 concentrations within each Heinrich Stadial. The largest magnitude of change (14.0 ± 0.8 ppm within 55 ± 10 y) occurred during Heinrich Stadial 4. Abrupt rises in atmospheric CO2 are concurrent with jumps in atmospheric CH4 and abrupt changes in the water isotopologs in multiple Antarctic ice cores, the latter of which suggest rapid warming of both Antarctica and Southern Ocean vapor source regions. The synchroneity of these rapid shifts points to wind-driven upwelling of relatively warm, carbon-rich waters in the Southern Ocean, likely linked to a poleward intensification of the Southern Hemisphere westerly winds. Using an isotope-enabled atmospheric circulation model, we show that observed changes in Antarctic water isotopologs can be explained by abrupt and widespread Southern Ocean warming. Our work presents evidence for a multi-decadal- to century-scale response of the Southern Ocean to changes in atmospheric circulation, demonstrating the potential for dynamic changes in Southern Ocean biogeochemistry and circulation on human timescales. Furthermore, it suggests that anthropogenic CO2 uptake in the Southern Ocean may weaken with poleward strengthening westerlies today and into the future.

Double Diffusive Nonlinear Convective MHD Unsteady Slip-Flow Regime in a Rectangular Channel

In the paper, we numerically explored the combined impacts of non-linear thermal and mixed convective unsteady flow in a channel with slip conditions. The flow is caused by a moving flat parallel surface and is also electrically conductive. We analyse the mechanisms of heat, and mass transfer by incorporating temperature and concentration jumps. To simplify the model problem, we apply appropriate similarity transformations, reducing the prevailing problem to a nonlinear coupled ordinary boundary value problem. The transformed problem is solved using the Chebyshev Collocation Approach (CCA). We performed a comparative analysis by comparing the CCA with the literature to verify the accuracy of our approach, and a good agreement is found. In addition, we conducted a comprehensive parametric study to analyze the trends in the solutions obtained. The study reveals that the parameters M, α1, α3, Pr, and Sc have about 20% stronger impact on the nonlinear system compared to the linear system on both surfaces of the horizontal channel.

MHD chemical reactive flow with velocity slip temperature and concentration jump conditions

AbstractThe main purpose of this paper is to examine the effects of velocity slip on the magneto hydrodynamics (MHD) axi‐symmetric viscous fluid flow between two disks having different stretching ratio. The flow takes place in the presence of temperature and concentration jumps. In the presence of joule heating and viscous dissipation, the investigation is carried out. The MHD flows are of utmost importance in industrial and engineering sectors because such flows can control the fluid flows with the help of Lorentz force. MHD flows are also helpful in biological fields such as wound treatments, surgeries, cancer therapy and in diagnosing diseases. The resulting system of PDE's is converted into ODE's by suitable similarity transformation. The HAM is used to solve the resulting non‐linear governing equations. The behavior of velocity, temperature and concentration profiles are observed graphically. When the stretching rate of lower disk is greater than the upper disk then the velocity rises due to increase in stretching ratio. The radial and axial components of velocity increase when the value of magnetic field increases. The temperature profile enhances for Eckert number while converse behavior is seen for stretching ratio parameters. The concentration profile increases when the value of Schmidt number is enhanced.

Lattice Boltzmann modeling and simulation of velocity and concentration slip effects on the catalytic reaction rate of strongly nonequimolar reactions in microflows.

A lattice Boltzmann (LB) interfacial gas-solid three-dimensional model is developed for isothermal multicomponent flows with strongly nonequimolar catalytic reactions, further accounting for the presence of velocity slips and concentration jumps. The model includes diffusion coefficients of all reactive species in the calculation of the catalytic reaction rates as well as an updated velocity at the reactive boundary node. Lattice Boltzmann simulations are performed in a catalytic channel-flow geometry under a wide range of Knudsen (Kn) and surface Damköhler (Da_{s}) numbers. Comparisons with simulations from a computational fluid dynamics (CFD) Navier-Stokes solver show good agreement in the continuum regime (Kn<0.01) in terms of flow velocity and reactive species distributions, while comparisons with direct simulation Monte Carlo results from the literature attest to the model's applicability in capturing the correct slip velocity at Kn as high as 0.1, even with a significantly reduced number of grid points (N=10) in the cross-flow direction. Theoretical and numerical results demonstrate that the term Da_{s}×Kn×A_{2} (where A_{2} is a function of the mass accommodation coefficient) determines the significance of the concentration jump on the catalytic reaction rate. The developed model is applicable for many catalytic microflow systems with complex geometries (such as reactors with porous networks) and large velocity/concentration slips (such as catalytic microthrusters for space applications).

SSM-based electrophysiology, a label-free real-time method reveals sugar binding & transport events in SGLT1

Here, we present a solid-supported membrane (SSM)-based electrophysiological approach to study sugar binding and Na+/glucose cotransport by SGLT1 in membrane vesicles. SSM-based electrophysiology delivers a cumulative real-time current readout from numerous SGLT1 proteins simultaneously using a gold-coated sensor chip.In contrast to conventional techniques, which mainly operate with voltage steps, currents are triggered by sugar or sodium addition. Sugar concentration jumps in the presence of sodium lead to transport currents between 5 and 10 nA. Remarkably, in the absence of sodium (i.e. no transport), we observed fast pre-steady-state (PSS) currents with time constants between 3 and 10 ms. These PSS currents mainly originate from sugar binding. Sodium binding does not induce PSS currents. Due to high time resolution, PSS currents were distinguished from transport and eventually correlated with conformational transitions within the sugar translocation pathway.In addition, we analyzed the impact of driving forces on transport and binding currents, showing that membrane voltage and sodium concentration gradients lead to an increased transport rate without affecting sugar binding kinetics. We also compared Na+/sugar efflux with physiologically relevant influx and found similar transport rates, but lower affinity in efflux mode.SSM-based electrophysiology is a powerful technique, which overcomes bottlenecks for transport measurements observed in other techniques such as the requirement of labels or the lack of real-time data. Rapid solution exchange enables the observation of substrate-induced electrogenic events like conformational transitions, opening novel perspectives for in-depth functional studies of SGLT1 and other transporters.

Stimulation of Ca2+ -ATPase Transport Activity by a Small-Molecule Drug.

The sarco(endo)plasmic reticulum Ca2+−ATPase (SERCA) hydrolyzes ATP to transport Ca2+ from the cytoplasm to the sarcoplasmic reticulum (SR) lumen, thereby inducing muscle relaxation. Dysfunctional SERCA has been related to various diseases. The identification of small‐molecule drugs that can activate SERCA may offer a therapeutic approach to treat pathologies connected with SERCA malfunction. Herein, we propose a method to study the mechanism of interaction between SERCA and novel SERCA activators, i. e. CDN1163, using a solid supported membrane (SSM) biosensing approach. Native SR vesicles or reconstituted proteoliposomes containing SERCA were adsorbed on the SSM and activated by ATP concentration jumps. We observed that CDN1163 reversibly interacts with SERCA and enhances ATP‐dependent Ca2+ translocation. The concentration dependence of the CDN1163 effect provided an EC50=6.0±0.3 μM. CDN1163 was shown to act directly on SERCA and to exert its stimulatory effect under physiological Ca2+ concentrations. These results suggest that CDN1163 interaction with SERCA can promote a protein conformational state that favors Ca2+ release into the SR lumen.

Monitoring the Interaction of α-Synuclein with Calcium Ions through Exclusively Heteronuclear Nuclear Magnetic Resonance Experiments.

Many properties of intrinsically disordered proteins (IDPs), or protein regions (IDRs), are modulated by the nature of amino acid side chains as well as by local solvent exposure. We propose a set of exclusively heteronuclear NMR experiments to investigate these features in different experimental conditions that are relevant for physiological function. The proposed approach is generally applicable to many IDPs/IDRs whose assignment is available in the Biological Magnetic Resonance Bank (BMRB) to investigate how their properties are modulated by different, physiologically relevant conditions. The experiments, tested on α-synuclein, are then used to investigate how α-synuclein senses Ca2+ concentration jumps associated with the transmission of nerve signals. Novel modules in the primary sequence of α-synuclein optimized for calcium sensing in highly flexible, disordered protein segments are identified.

Monitoring the Interaction of α‐Synuclein with Calcium Ions through Exclusively Heteronuclear Nuclear Magnetic Resonance Experiments

AbstractMany properties of intrinsically disordered proteins (IDPs), or protein regions (IDRs), are modulated by the nature of amino acid side chains as well as by local solvent exposure. We propose a set of exclusively heteronuclear NMR experiments to investigate these features in different experimental conditions that are relevant for physiological function. The proposed approach is generally applicable to many IDPs/IDRs whose assignment is available in the Biological Magnetic Resonance Bank (BMRB) to investigate how their properties are modulated by different, physiologically relevant conditions. The experiments, tested on α‐synuclein, are then used to investigate how α‐synuclein senses Ca2+ concentration jumps associated with the transmission of nerve signals. Novel modules in the primary sequence of α‐synuclein optimized for calcium sensing in highly flexible, disordered protein segments are identified.

Simulation of 3D flow and solute transport in fractured rock at Äspö, Sweden

The code d3f++ developed under the leadership of GRS for simulating 3D flow and solute transport includes an advanced formulation for fracture flow and transport in lower-dimensional elements that has still been in need of qualification. A variety of in-situ experiments in the granitic rock at the Swedish Hard Rock Laboratory Aspo offers an excellent basis for this purpose. Particularly well suited is the work performed in the TRUE Block Scale Project where a hydrostructural model comprising 30 large-scale fractures in a cube-shaped domain with a side length of 200 m has been set up for simulating groundwater flow which in turn forms the basis for reproducing the results of the injection–extraction tracer test “C2”. The present paper deals with modelling 3D flow and solute transport with the code d3f++ as a qualification exercise. The modelling results reveal an excellent representation of the contrasts in flow velocity across the fractures. Also the jumps in tracer concentration along intersecting fractures where waters with different tracer concentrations mix are handled well by the code. Calibration has nevertheless been required in order to achieve a reasonable fit of measured and calculated breakthrough curves.

ТРАНСДЕРМАЛЬНАЯ ДОСТАВКА ЛЕКАРСТВЕННЫХ ВЕЩЕСТВ И ЕЕ РОЛЬ В ТЕРАПИИ СЕРДЕЧНО-СОСУДИСТОЙ ПАТОЛОГИИ

Introduction. Transdermal delivery of medicinal substances is based on the penetration of the active pharmaceutical ingredient through the intact skin, its further entry into the systemic bloodstream and, thereafter, to the target organ. Currently, gels, ointments, emulsions and transdermal therapeutic systems (transdermal patches) are used as transdermal agents. Transdermal patches are able to provide a target constant concentration of medicinal substances in blood plasma for a long time (from 1 to 7 days). Transdermal delivery has a number of advantages: increased bioavailability of medicinal substances due to the elimination of losses associated with metabolism in the gastrointestinal tract and in the liver; reducing the risk of adverse reactions which can be caused by leveling of concentration jumps of the medicinal substances in the blood; painlessness and convenience; possibility to change the dose by varying the area of the patch and the duration of use; possibility to stop the treatment at any time, etc. For patients with chronic diseases requiring constant repeated oral administration of drugs, suffering from dysphagia and diseases of the gastrointestinal tract, the transdermal route of administration is the most optimal. In some cases, when the patient is unconscious, suffers from sclerosis, or has impaired vital functions (for example, the ability to breathe and swallow independently), transdermal delivery is optimal and in some cases is the only alternative. Purpose. To analyze the current range of drugs for transdermal delivery, to assess the role and prospects of using transdermal delivery in the treatment of cardiovascular diseases. Methods. The search for literary data was carried out using the PubMed and Google search engines among Russian - and English-language original articles. The search of registered drugs in the form of transdermal patches was carried out using drugs registries of the United States and other countries. When searching, the terms «transdermal delivery», «transdermal patch», «bisoprolol», «clopidogrel», «transdermal delivery», «transdermal patch» were used. Conclusion. In the global pharmaceutical market, transdermal delivery is used for a limited number of medicinal substances of different pharmacotherapeutic groups, of which only three medicinal substances (nitroglycerin, clonidine, bisoprolol) are used in the treatment of cardiovascular diseases. Many attempts have been made to obtain and evaluate transdermal patches with angiotensin-converting enzyme inhibitors, angiotensin II receptor blockers, antiplatelet agents used in the treatment of cardiovascular diseases, but the volume of these studies is insufficient for registration and clinical use.

Numerical simulation of the effect of semipermeable properties of clay on the value of concentration jumps of contaminants in a thin geochemical barrier

Numerical simulation of the effect of semipermeable properties of clay on the value of concentration jumps of contaminants in a thin geochemical barrier

The problem of suspension injection into a porous medium within a two-velocity model of deep bed filtration

We consider flows of a suspension through a porous medium with account of the deposition of the suspended particles onto the internal surface of a porous matrix (deep bed filtration). The velocities of the suspended particles and the carrier fluid are plausibly supposed to differ by a known factor that depends on the suspension concentration. We present analytical and numerical solutions to the problem of suspension injection into a porous sample. The main qualitative result of the investigation is that — under certain circumstances — the smooth solutions (i.e., the ones that do not, in contrast to usual assumptions, involve concentration jumps) to the problem may exist. This feature may be of use for experimental data interpretation.

MHD Williamson Fluid Flow Over a Permeable Moving Wedge with Heat Source, Temperature and Concentration Jump

MHD Williamson Fluid Flow Over a Permeable Moving Wedge with Heat Source, Temperature and Concentration Jump

Efficient Solution of Washcoat Diffusion-Reaction Problem for Real-Time Simulations

As countries around the globe adapt more stringent emissions standards set by Real Driving Emissions (RDE) legislation, mathematical models are becoming ever more widely used as plant models for devising vehicle control strategies. It is important for the model to run on Hardware-in-Loop (HIL) and engine control unit (ECU) systems which have significantly less computational power and memory than modern personal computers. Washcoat diffusion limitations play a very important role in the efficient design of a catalytic converter. Numerical solution of aftertreatment models that include diffusion-reaction equations in the washcoat are computationally demanding. There are several simplified approaches proposed in the literature for the solution of diffusion-reaction equations in the washcoat to avoid the computational demand of the full numerical solution. In this paper, we use the recently proposed asymptotic solution and compare the results with that of the full numerical solution for the following aftertreatment reactor models with both single- and dual-layer washcoat configurations for the practical range of operating conditions; three-way catalyst (TWC), diesel oxidation catalyst (DOC), Selective Catalytic Reduction (SCR), and ammonia slip catalyst (ASC). These reactor models are constructed using published kinetic mechanisms and represent the global kinetics mechanisms (including non-linear reaction orders and inhibition functions) commonly used in the aftertreatment modeling community. We also discuss the importance of adaptive mesh, quasi-steady state assumption, and occurrence of concentration jumps in the simulation of aftertreatment reactors.

A New Concentration Jump Strategy Reveals the Lifetime of i-Motif at Physiological pH without Force.

Concentration jumps for kinetics measurement remain a challenge for single-molecule techniques, which have demonstrated superior signal-to-noise levels compared to ensemble average approaches. Currently, all concentration jumps use mixing strategies. Here, we report a simple and drastically different jump strategy by rapid transportation of molecules between two side-by-side laminar streams in 80 ms. This allowed us to measure the lifetime of bioactive DNA i-motif structures at physiological pH without force. We placed a human telomeric i-motif inside a DNA hairpin-based mechanical reporter. Since the folded or unfolded state of the hairpin correlates with that of the i-motif, by recording hairpin transitions, a half-life of ∼3 s was found for the DNA i-motif at neutral pH without force. Such a lifetime is sufficient for i-motif to interact with proteins to modulate cellular processes. We anticipate this concentration jump offers a generic platform to investigate single-molecule kinetics.

Conformational memory in the association of the transmembrane protein phospholamban with the sarcoplasmic reticulum calcium pump SERCA

The sarcoplasmic reticulum Ca2+-ATPase SERCA promotes muscle relaxation by pumping calcium ions from the cytoplasm into the sarcoplasmic reticulum. SERCA activity is regulated by a variety of small transmembrane peptides, most notably by phospholamban in cardiac muscle and sarcolipin in skeletal muscle. However, how phospholamban and sarcolipin regulate SERCA is not fully understood. In the present study, we evaluated the effects of phospholamban and sarcolipin on calcium translocation and ATP hydrolysis by SERCA under conditions that mimic environments in sarcoplasmic reticulum membranes. For pre-steady-state current measurements, proteoliposomes containing SERCA and phospholamban or sarcolipin were adsorbed to a solid-supported membrane and activated by substrate concentration jumps. We observed that phospholamban altered ATP-dependent calcium translocation by SERCA within the first transport cycle, whereas sarcolipin did not. Using pre-steady-state charge (calcium) translocation and steady-state ATPase activity under substrate conditions (various calcium and/or ATP concentrations) promoting particular conformational states of SERCA, we found that the effect of phospholamban on SERCA depends on substrate preincubation conditions. Our results also indicated that phospholamban can establish an inhibitory interaction with multiple SERCA conformational states with distinct effects on SERCA's kinetic properties. Moreover, we noted multiple modes of interaction between SERCA and phospholamban and observed that once a particular mode of association is engaged it persists throughout the SERCA transport cycle and multiple turnover events. These observations are consistent with conformational memory in the interaction between SERCA and phospholamban, thus providing insights into the physiological role of phospholamban and its regulatory effect on SERCA transport activity.

The “trapped fraction” and interfacial jumps of concentration in fission products release from coated fuel particles

The FP Kinetics computer code [1] designed for calculation of fission products release from HTGR coated fuel particles was modified to allow consideration of chemical bonding, effects of limited solubility and component concentration jumps at interfaces between coating layers. Curves of Cs release from coated particles calculated with the FP Kinetics and PARFUME [2] codes were compared. It has been found that the consideration of concentration jumps at silicon carbide layer interfaces allows giving an explanation of some experimental data on Cs release obtained from post-irradiation heating tests. The need to perform experiments for measurement of solubility limits in coating materials was noted.

Optogenetic Control of Ca2 + and Voltage-Dependent Large Conductance (BK) Potassium Channels

Ca2+ concentration jumps for the activation of Ca2+-dependent ion channels or transporters can be obtained either by fast solution exchange or by the use of caged Ca2+. Here, we report on an alternate optogenetic method for the activation of Ca2+ and voltage-dependent large conductance (BK) potassium channels. This was achieved through the use of the light-gated channelrhodopsin 2 variant, CatCh(Calcium translocating Channelrhodopsin) with enhanced Ca, which produces locally [Ca2+] in the μM range on the inner side of the membrane, without significant [Ca2+] increase in the cytosol. BK channel subunits α and β1 were expressed together with CatCh in HEK293 cells, and voltage and Ca2+ dependence were analyzed. Light activation of endogenous BK channels under native conditions in astrocytes and glioma cells was also investigated. Additionally, BK channels were used as sensors for the calibration of the [Ca2+] on the inner surface of the cell membrane.

Multistep Folding Kinetics of Group I Intron RNA Studied by Mg2+-Concentration Jump Simulations

RNA molecules can function as enzymes forming specific tertiary structures. Since they are highly charged molecules, mono- and divalent cations are essential for the folding reaction. Mg2+ ions are also often important at specific positions for their catalytic activities. Here, we study multistage folding kinetics of Azoarcus group I intron, which is mediated by Mg2+ cations, by Brownian dynamics simulations using a coarse-grained RNA model with explicit ions [1].