Force For Diffusion Research Articles

Thermodynamic and buoyancy force effects of Cu and TiO2 nanoparticles in engine oil flow over an inclined permeable surface

This study investigates the heat and mass transmission behavior in an unsteady magnetohydrodynamic (MHD) movement of nanofluids over an inclined permeable surface, with applications in enhancing thermal management systems such as automotive cooling and industrial heat exchangers. The model specifically examines the consequence of thermal diffusion (Soret effect) and buoyant forces on Cu and TiO2 nanoparticles dispersed in engine oil. The governing equations, comprising velocity, energy, and concentration equations, are recast into nonlinear ODEs manipulating similitude adaptations. These ODEs are then solved through a standard perturbation method under appropriate boundary conditions. The key findings indicate that enhancing thermal radiation diminishes the velocity and temperature profiles, while raising chemical reaction rates decrease concentration levels. Additionally, higher Soret parameter values are associated with increased velocity and concentration. Quantitatively, TiO2-engine oil nanofluids exhibit a 15% higher velocity compared to Cu-engine oil nanofluids, highlighting the superior performance of TiO2 in dynamic thermal systems. Furthermore, numerical outcomes for the local skin contention, Nusselt numeral, and Sherwood digit are tabulated to illustrate the consequence of material properties. The outcomes of this study are particularly beneficial in optimizing the design of heat exchangers, improving fuel efficiency in automotive engines, and enhancing industrial processes where precise thermal control is critical.

Rethinking Porosity-Based Diffusivity Estimates for Sorptive Gas Transport at Variable Temperatures.

The detection of noble gas radioisotopes following a suspected underground nuclear explosion is the surest indicator that nuclear detonation has occurred. However, the accurate interpretation and attribution of radioisotopic signatures is only possible with a complete understanding of transport processes occurring between the nuclear cavity and surface. In the far-field, diffusive forces contributing to gas transport are impacted by temperature gradients and subsurface lithology. In the current study, we investigate diffusive transport of xenon (Xe), krypton (Kr), and sulfur hexafluoride (SF6) through intact Bandelier tuff at elevated temperatures using a newly developed high temperature diffusion cell. Diffusion coefficients determined using Finite Element Heat and Mass transfer code simulations and the Parameter ESTimation tool range from 2.6-3.1 × 10-6 m2/s at 20 °C, 3.4-5.1 × 10-6 m2/s at 40 °C, and 4.3-7.0 × 10-6 m2/s at 70 °C. Sorption was found to be an important transport mechanism at ambient temperatures (20 °C). Most critically, our study shows that empirical porosity-based diffusion estimates for these gases through tuff captured neither the magnitude nor trends relative to a nonsorbing sandstone. These new insights highlight the importance of experimental transport investigations and will be used to improve models for subsurface gas propagation relevant to proliferation detection and environmental contamination.

A Modified of Fourth-Order Partial Differential Equations Model Based on Isophote Direction to Noise Image Removal

Image denoising is one of the initial stages of image processing. Many models based on the diffusion method have been used to smooth the image. One of the problems, we face in the model based on the diffusion method is its possible loss of edges. The diffusion force is known to be more effective in areas of high frequency. So This paper suggests combining the direction of isophote and fourth-order partial differential equations to reduce the problem of loss edges and preserve important details of the image. The direction of the isophote can regulate the direction of diffusion. Thus, we have a proposed model that can remove the noise in the area while preserving the important edges and details of the image. We have proven the efficiency and superiority of the proposed model by applying it to a set of images and solving it numerically using the finite difference method (FDM).

Revealing the coarsening behavior of precipitates and its effect on the thermal stability in Tʹ and ηʹ dual-phase strengthened Al-Zn-Mg-Cu alloys

High-strength Al-Zn-Mg-Cu alloys are widely utilized, but their strength deteriorates as strengthening precipitates coarsen rapidly at elevated temperatures, limiting their applications above 150°C. This study systematically investigates the microstructure evolution and its impact on the properties of peak-aged Al-Zn-Mg-Cu alloys with varying Zn/Mg ratios during thermal exposure at a series of temperatures from 150 to 300°C for 500 h. The results reveal that alloys A1 and A2 with an optimal Zn/Mg ratio (1.50−2.14) and relatively lower (Zn + Mg) content (7.0−8.8 wt.%), exhibit superior heat resistance properties compared to the other three alloys. Despite having lower strength relative to alloys with higher solute content, peak-aged alloys A1 and A2 retain the highest strength after thermal exposure. This performance is attributed to the high proportion (over 80%) of T′/T phases in the precipitates for alloys A1 and A2, which demonstrate better thermal stability in comparison to η′/η phases. Additionally, the lower solute content reduces the driving force for diffusion of Zn and Mg atoms, thus inhibiting the coarsening of precipitates. Moreover, the study elucidates that the coarsening mechanism of precipitates transitions from interfacial diffusion control at 150°C to matrix diffusion control at 200−300°C. These insights into the composition-dependent coarsening behavior of precipitates in dual-phase strengthened Al-Zn-Mg-Cu alloys offer valuable guidance for designing heat-resistant aluminum alloys with enhanced performance at elevated temperatures.

Pairwise balancing of forces in traveling granular waves

A survey is given of the forces at work inside traveling roll waves and monoclinal flood waves in dry granular matter. By numerically solving the generalized Saint-Venant equations for shallow granular flow, we find a hierarchy of pairwise near-balancing forces, which together are responsible for sustaining the shape of the nonlinear waves in question. The leading force pair is gravity vs. friction, followed by inertia vs. pressure, while the minor imbalance left by the aforementioned pairs is settled by a (small though essential) diffusive force.

Liberalizing the effects of Al and Cr in coatings for enhanced interface stability with Mo-rich Ni3Al-based superalloys

The interfacial behaviors between protective coatings and substrate single-crystal superalloys significantly impact their service performances. This work focuses on the elements interdiffusion and microstructural evolution at the interface between a NiCrAlY coating and a series of high-Mo Ni3Al-based single-crystal superalloys, through the coupled phase-field simulations and DICTRA kinetics calculations of their model systems. The critical roles of Al and Cr played in the microstructural evolution at coating/superalloy interface have been confirmed, which requires the appropriate content decreases of Al and Cr in the coating at 1100 °C. However, the addition of Mo reduces the driving force of element diffusion from coating to substrate by increasing the activities of Al and Cr in superalloy. Moreover, increasing the Mo content in superalloy from 8 wt% to 10 wt% could also counteract the promoting effect of Al on Ni mobility and mitigate the γ′ coarsening and detrimental TCP precipitation. Therefore, the effects of Mo enable the reasonable increase of Al content in coating to better balance the interfacial stability and oxidation resistance of coated superalloy, besides its advantage in reducing the anisotropy of TCP precipitate. The obtained interfacial evolution mechanisms resulting from the phase transformation thermodynamics and element interdiffusion kinetics are expected to aid the coating design for advanced single-crystal superalloys servicing at ultra-high temperature.

Multi-scale approach to hydrogen susceptibility based on pipe-forming deformation history

Hydrogen-induced-cracking initiates without external loading due to residual stresses. Pipe manufacturing process composed of crimping, U-ing, O-ing, and expansion has a major impact on local hydrogen concentration, as strain pattern evolves from one forming step to another, causing residual stresses that serve as driving force for hydrogen diffusion. The novelty of the presented work lies in the development of a multi-scale approach that links the residual stresses from the macroscopic pipe-forming process with locally dissolved hydrogen atoms in microstructure under the consideration of microstructural heterogeneities to identify areas susceptible to hydrogen-induced-cracking. First, a 3d-pipe-forming-model was built. Second, representative volume elements with lattice defects were generated to analyze hydrogen trapping in microstructure. Third, representative volume elements were placed in the pipe via sub-modeling, so that local loading history of the pipe was assigned to microstructure models. At the end of the pipe-forming process, representative volume elements were loaded with hydrogen on the surface and final hydrogen concentration was simulated based on residual stresses, considering microstructural effects such as grain size/shape, crystallographic texture and hydrogen traps, e.g. dislocations, voids and inclusions. On meso-/macroscale, a combined isotropic–kinematic hardening material model was implemented, while on microscale, a phenomenological crystal-plasticity-hydrogen-diffusion model was coded. According to the multi-scale simulations under the consideration of microstructural effects the bottom center position in the pipe was detected to be critical to hydrogen-induced-cracking as the maximum local hydrogen concentration was predicted at that location. Based on the loading history hydrogen-induced-cracking susceptibility increases from voids to hard and soft non-metallic inclusions.

Accelerating Battery Research through Atomistic and Multi-Scale Computational Chemistry

Computational screening and advanced insights from simulations will help you develop new and improved battery materials quicker and with less resources. We will discuss our efforts to help researchers to do that with the Amsterdam Modeling Suite (AMS). The AMS framework separates the atomistic engines (DFT, DFTB, ReaxFF, ML potentials) from the driver, which enables the exploration of potential energy surfaces (PESs), mechanical, and electronic properties at several levels of theory. The central AMS driver supports advanced PES explorations, molecular dynamics (MD) and Grand Canonical Monte Carlo (GCMC), based on energies and forces from the engines.With this driver-engine set up, you can calculate and predict relevant processes and properties for battery materials. We will discuss recent developments and examples using: DFT and GW with COSMO-RS for accurate electrode and redox potentials(e)ReaxFF for discharge processes including diffusion, discharge profiles, electrolyte degradation, and solid-electrolyte interface formationpolarizable force fields for accurate viscosities and charge mobilitiespre-parametrized and on-the-fly machine learning potentials for diffusion barriers, intercalation potentials, and reactive processeskinetic Monte Carlo to describe mesoscale processes such as dendrite formation We will also discuss where we envision future ML and multi-scale developments to accelerate materials discovery, particularly focusing on battery applications. Figure 1

Studying estrogen effects in an in vitro-model of traumatic brain injury (TBI)

In traumatic brain injury (TBI), mechanical forces trigger a series of detrimental processes in the affected brain, which eventually result in substantial neuronal death. TBI has thus become a leading cause of death and disability worldwide. Here we utilized organotypic hippocampal slice cultures from mice to simulate mild diffuse TBI, the most common type, in vitro. We specifically used this model to examine the potential of 17β-estradiol (E2), which is considered to be neuroprotective, to influence injury-induced events, such as astrocyte and microglia activation, and to reduce cell death, if applied acutely after TBI. We found that established consequences of mechanical brain injury are replicated in the model, as increased apoptosis was observed 8 h and PI-uptake was significantly enhanced 24 h after in vitro TBI in CA1 pyramidal layer. GFAP expression was not overall increased, but correlated with cell death, indicating a confined activation of astrocytes associated with cell injury. Similarly, no general increase of microglia was detected, but activated microglia was observed in the vicinity of dying cells. Notably, application of E2 (20 nM) increased GFAP expression after 48 h, but did not significantly reduce cell death at any of the studied time points. We conclude that the presented in vitro TBI model is generally suited to study processes triggered by diffuse mechanical forces acting on brain tissue. Our data further support a stimulating effect of E2 on GFAP expression in astrocytes, but they do not confirm a neuroprotective role of E2 in the early phase of TBI.

Experimental and theoretical study of multiple active site-functionalized Spirulina residue-based porous carbon as an economical adsorbent for NH3 and SO2 adsorption: Micro- and macro-mechanistic investigations

Here, we successfully synthesized a cost-effective (7.88 USD/kg) multi-active site (CuCl2, CuO and KCl) functionalized Spirulina residue-based porous carbon (MMBC). This innovative synthesis method utilizes Spirulina residue, a sustainable and low-cost biomass source, making the production of MMBC economically viable and environmentally friendly. Under ambient conditions, MMBC exhibits competitive adsorption capacities for NH3 and SO2 compared to other adsorbents, reaching 3.01 mmol/g (i.e., 51.26 mg/g) and 0.70 mmol/g (i.e., 44.85 mg/g), respectively, and tolerable recoverability. These values are significant improvements over many existing adsorbents, highlighting MMBC's efficiency in removing toxic industrial chemicals (TICs). Additionally, even at low molar fractions of NH3 or SO2, such as 0.001, MMBC demonstrates significant ideal adsorption solution theory (IAST) selectivity for NH3/N2 and SO2/N2, with values of 12.02 and 4.19, respectively. This high selectivity at low concentrations underscores MMBC's potential for applications in environments with trace amounts of pollutants. Furthermore, extensive research has been conducted in this study to elucidate the microscopic and macroscopic adsorption mechanisms of NH3 and SO2 on MMBC. Specifically, investigations in statistical physics models and statistical thermodynamics reveal that the adsorption of NH3 and SO2 on MMBC adhere to a non-aggregative, multilayer, multi-anchorage, and spontaneous exothermic physicochemical behavior. And the adsorption orientation occurs either horizontally or both horizontally and non-horizontally, contingent upon the system and temperature. These findings provide a deeper understanding of the adsorption processes and provide innovative insights into the adsorption mechanisms at the molecular level and at the macroscopic scale. Besides, the material characterization results reveal that the above adsorption process involves both physical interactions (pore diffusion and van der Waals forces) and chemical interactions (CuCl2 with NH3, CuO and KCl with SO2), indicating a physicochemical adsorption mechanism. This dual mechanism of adsorption offers a comprehensive explanation of the high performance of MMBC. In summary, this study developed a cost-effective Spirulina residue-based adsorbent, exhibiting high removal efficiency and selectivity for TICs, and providing deep insights into adsorption mechanisms. The innovative use of Spirulina residue addresses waste management issues and promotes the development of sustainable materials in the field of environmental remediation, contributing to cleaner production.

A robust and well-balanced finite volume solver for investigating the effects of tides on water renewal timescale in the Nador lagoon, Morocco

Coastal lagoons, particularly those not well-connected to the sea, are highly susceptible to continuous water retention, adversely affecting water quality and ecosystems. Understanding and quantifying the processes governing water renewal in such semi-enclosed regions is crucial. Using the principles of constituent-oriented age and residence time theory (www.climate.be/cart), we calculated timescales to explain the water renewal process in semi-enclosed areas. To improve our understanding and define the dynamics of the Nador lagoon, we use two distinct time scales: residence time and exposure time. Residence time indicates the length of time a parcel of water leaves the region of interest for the first time, while exposure time represents the overall length of time a parcel of water remains in that region, including any subsequent inflows. The modeling system adopts an Eulerian approach, including two interlinked model components: the shallow-water equations incorporating bottom friction, eddy viscosity, wind shear stresses, momentum diffusion, and Coriolis forces for modeling hydrodynamics, and a transport-diffusion equation utilized to simulate the advection and diffusion of the passive tracer concentration. The entire system is integrated into a high-order finite volume solver that employs unstructured meshes, upwind numerical fluxes, and slope limiters to achieve precise resolution of steep bathymetric gradients that may arise in the approximate solution. The scheme is non-oscillatory and preserves the conservation properties. In this research, we explore various situations related to the connection between the Mediterranean Sea and the Nador lagoon. Specifically, we suggest novel entry points that have the potential to significantly decrease the water residence within the lagoon.

Theoretical Understanding of Electromigration-Related Surface Diffusion and Current-Induced Force in Ag-Pd Systems.

Electromigration, as a common reason for interconnect failure, is becoming increasingly important in the ongoing decrease in the integrated circuit manufacturing process. A study is being carried out utilizing the ab initio calculational method to gain a deeper understanding of electromigration, with a focus on the atom diffusion process in the Ag-Pd alloy system, a commonly used interconnect material. We begin by establishing that the primary mechanism of diffusion is step-edge diffusion on the (111) surface. Following this, we examine the current-induced force exerted on the migrating Ag atom. The Pd substitutional defect reveals an effect that increases the energy barrier of diffusion and decreases the current-induced force that powers the directional migration.

On the kinetics of electrodeposition in a magnesium metal anode

Magnesium (Mg) metal batteries are promising for next-generation energy storage due to Mg’s abundance and potential for improved energy densities through two-electron redox in cathodes and thin film anodes supporting high current densities. However, reversible and uniform electrodeposition of Mg necessary for high-energy-density Mg batteries continues to be plagued by challenges traceable to energy barriers to desolvation in liquid electrolytes, the stabilization of passivation layers that impede Mg diffusion at electrified interfaces, and deleterious high-asperity electrodeposition morphologies. Thus, the specific impact and coupling of factors such as (i) composition of the salt solution, (ii) electrode overpotential, and (iii) reversible stripping/plating on the interfacial kinetics of electrodes remains an area of intense interest. This study investigates the effects of overpotential time-transients and electrolyte concentration using experimentally-guided phase-field methods and compares them with an electrochemical spherical cap model. Complex dynamics at the electrode/electrolyte interface involve transient changes in overpotential, influencing nucleation, diffusion, and crystallization, ultimately altering surface evolution. We find that the Damkohler number converges to approximately one for a symmetric Mg-Mg cell using 0.1 M Mg[TFSI]2 in 1:1 v/v diglyme/dimethoxyethane suggesting a subtle balance between reactive and diffusive forces. The results indicate the formation of dendritic structures is primarily driven by limitations in electrolyte transport. In addition, we determine the limiting current density of this cell under various electrolyte concentrations, which is an essential step in successful battery design and operation. Our findings underscore the critical role of overpotentials in underpinning reaction kinetics and non-equilibrium growth dynamics during metal electrodepositon.

Hydrocarbon expulsion mechanism of Lower Cambrian argillaceous source rocks in the Tarim Basin, China

The source of oil and gas in the Tarim Basin's platform has always been controversial. The Lower Cambrian Yurtusi Formation and the Xidashan Formation–Xishanbulak Formation argillaceous source rocks are an important set of oil source series in the basin. Based on the principle of conservation of matter, this paper calculates the hydrocarbon expulsion amount of the source rock. Using a phase state hydrocarbon expulsion amount characterization model, the paper reconstructs the evolution process of the hydrocarbon expulsion phase state of the source rock. According to the characterization model of hydrocarbon expulsion dynamics, the relative contribution of each force to hydrocarbon expulsion is evaluated. The hydrocarbon expulsion geologic model of argillaceous source rocks in the Lower Cambrian in the Tarim Basin is established. The results show that this set of source rocks can serve the main source rocks in the basin. The hydrocarbon expulsion of the Lower Cambrian argillaceous source rocks in the Tarim Basin can be divided into three stages. In the first stage, the hydrocarbon expulsion phase is dominated by the water‐soluble and diffusion phases. The conversion of clay minerals into dehydration and diffusion forces is the main driving force for the hydrocarbon expulsion. In the second stage, the oil and gas expulsion present the characteristics of multiphase and multidynamic coexistence. In the third stage, the phase state of oil and gas expulsion is mainly free phase. The capillary force difference and the thermal expansion force of the fluid rock are the main driving forces for oil and gas expulsion. The research results of this paper can deepen the understanding of the hydrocarbon expulsion mechanism of the set of source rocks, and then guide oil and gas exploration.

Insight into element segregation mechanisms during creep in γʹ-strengthened Co-based superalloy by elastoplastic phase-field simulation

The element segregation accompanying the creep process has been shown to significantly affect the deformation resistance of the superalloys. However, the processing and mechanism of element segregation are still unclear. This paper investigated the concentration evolution of a model Co–9Al–9W (at. %) alloy during 900 ​°C/275 ​MPa using developed ternary elastoplastic phase-field model coupled with CALPHAD method and crystal plasticity model. The results of simulation show that co-depletion of Al and W element occurs in γʹ precipitate and in γ side at γ/γʹ interface, and this depletion is gradually increasing with the accumulation of plastic strain. From the perspective of changes of driving force of element diffusion, it is found that these segregation phenomena are attributed to the high elastic potential caused by the large local plastic strain. In addition, the effects of these segregations on creep property are also predicted. The current research provides a new method for exploring the mechanism of element diffusion.

SIMMER code two-fluid model well-posedness and stability for simulating liquid metal (lead–lithium eutectic), water vapor, and non-condensable gases multi-component multi-phase flows

Liquid metals are employed as a coolant in liquid metal fast reactors (LMFR) and are considered breeders and coolants for future power-producing fusion reactors. The interaction of liquid metals with other coolants, such as air and water, is one of the possible occurrences in liquid metal-cooled reactors. Although the SIMMER-III computer code is currently in the validation and verification phase, it is a prospective candidate code for correctly investigating possible accidents. This study aims to determine the stability and well-posedness of the SIMMER-III code Eulerian-Eulerian two-fluid model (TFM) under any such accident scenario. This work also considers the influence of the virtual mass force and diffusion forces in momentum on TFM stability in accelerated liquid metal, steam, and non-condensable gaseous flows throughout all flow regimes. The characteristics method is used to assess the ill-posed nature of TFM for all types of accidents and accident scenarios in a hypothetical simplified system model with several components (Lead–Lithium, non-condensable gases, and water vapor). It has been discovered that the analysis findings vary from the air and water two-component two-phase flows (characteristics roots spectrum and error growth rate patterns) and are particularly sensitive to the diffusion and virtual mass coefficients. This is because liquid metals have a higher density than liquid water and steam, resulting in strong virtual mass forces and weak diffusion forces in liquid-metal and gas two-phase flows. Because of the extensive range of possible interactions between fluxes of different components, producing an accurate representation of diffusion in multi-component mixtures is difficult. Because of this, it is strongly suggested that the virtual mass coefficient and diffusion coefficients be handled more accurately for these kinds of flows. The values of these coefficients significantly affect how accurate proposed TFM predictions are, but there hasn't been much research on how to estimate them. The study also sheds light on the model's accuracy and highlights the areas where the model's predictions will be mathematically trustworthy.

Effect of thermodiffusion on compositional grading in hydrocarbon reservoirs: Insights from field cases and simulations

Heterogeneity of fluid composition in vertical and lateral directions is observed in many reservoirs, known as compositional grading. It is necessary to evaluate the diffusion forces for modeling this phenomenon. In addition to the chemical and gravity forces, the temperature gradient causes mass diffusion. In the present investigation, the accuracy and reliability of the Haase theory and the Shukla-Firoozabadi method in thermodiffusion modeling are studied comprehensively using field samples from light to heavy-oil reservoirs. On the one hand, the Shukla-Firoozabadi model results in compositional grading reduction by thermodiffusion; on the other hand, the Haase theory reveals enhancement and attenuation effects of thermodiffusion depending on reference enthalpy quantification. A new approach, which employs the reference enthalpies of pseudocomponents as tuning parameters, is proposed to improve the results of the Haase theory. The proposed procedure is also validated using field cases. In addition, the experimental field information compared with isothermal and nonisothermal models are studied to answer the question of "how" and to "what extent" thermodiffusion contributes to compositional grading. Results demonstrated the limited attenuation effect of thermodiffusion in light oils, while this phenomenon leads to severe enhancement of compositional grading in the medium and heavy-oil reservoirs. In heavy oils, the thermodiffusion effect is more pronounced on heavy pseudocomponents rather than light paraffinic species. Finally, the practice of compositional gradient model optimization, which is of particular interest to reduce the uncertainty in fluid initialization and to address reservoir compartmentalization, is presented.

Swelling kinetics of mixtures of soybean phosphatidylcholine and glycerol dioleate

Lipid-based drug delivery systems offer the potential to enhance bioavailability, reduce dosing frequency, and improve patient adherence. In aqueous environment, initially dry lipid depots take up water and form liquid crystalline phases. Variation of lipid composition, depot size and hydration-induced phase transitions will plausibly affect the diffusion in and out of the depot. Lipid depots of soybean phosphatidylcholine (SPC) and glycerol dioleate (GDO) mixtures were hydrated for varying time durations in a phosphate-buffered saline (PBS) buffer and then analyzed with Karl Fischer titration, magnetic resonance imaging (MRI) and gravimetrically. Mathematical modeling of the swelling process using diffusion equations, was used to estimate the parameters of diffusion. Both composition of lipid mixture and depot size affect swelling kinetics… The diffusion parameters obtained in Karl Fischer titration and MRI (with temporal and spatial resolution respectively) are in good agreement. Remarkably, the MRI results show a gradient of water content within the depot even after the end of diffusion process. Apparently contradicting the first Fick’s law in its classical form, these results find an explanation using the generalized Fick’s law that considers the gradient of chemical potential rather than concentration as the driving force of diffusion.

Numerical Study on the Formation Mechanism of Plume Bulge in the Pearl River Estuary under the Influence of River Discharge

Previous studies have investigated the characteristics and influencing factors of plume bulge in the Pearl River Estuary (PRE) using observations and numerical simulations. However, the understanding of how river discharge affects plume bulge is not consistent, and the response mechanism of plume bulge to changes in river discharge has not been revealed in detail. In this study, a three-dimensional hydrodynamic Finite-Volume Coastal Ocean Model (FVCOM) is constructed, and five experiments were set to characterize the horizontal and vertical distribution of the plume bulge outside the PRE under different river discharge conditions during spring tide. The physical mechanisms of plume bulge generation and its response mechanisms to river discharge were discussed through standardized analysis and momentum diagnostic analysis. The results indicate that the plume bulge is sensitive to changes in river discharge. When the river discharge is relatively low (e.g., less than 11,720 m3/s observed in the dry season), the bulge cannot be formed. Conversely, when the river discharge is relatively high (e.g., exceeding 23,440 m3/s observed in flood season), the bulge is more significant. The plume bulge is formed by the anticyclonic flow resulting from the action of the Coriolis force on the strongly mixed river plume. The bulge remains stable under the combined effects of barotropic force, baroclinic gradient force, and Coriolis force. The reduction of river discharge weakens the mixing of freshwater and seawater, resulting in the reduction of both the volume and momentum of the river plume, and the balance between advective diffusion and Coriolis forces are altered, resulting in the plume, which is originally flushed out from the Lantau Channel, not being able to maintain the anticyclonic structure and instead floating out along the coast of the western side of the PRE, with the disappearance of the plume bulge. Due to the significant influence of plume bulges on the physical and biogeochemical interactions between estuaries and terrestrial environments, studying the physical mechanisms behind the formation of plume bulges is crucial.

Skeletal muscle contractions attenuate the norepinephrine-related reduction in interstitial oxygen pressures in the rat spinotrapezius

Increased sympathetic nerve activity with exercise plays a key role in the control of arterial blood pressure and redistribution of blood flow. Within the microcirculation, elevated sympathetic outflow promotes the release of norepinephrine and smooth muscle contraction. Exercise-induced attenuation of sympathetic vasoconstriction (i.e., functional sympatholysis) is thus critical for active muscle oxygen delivery-utilization matching. However, the extent to which muscle contractions impact noradrenergic regulation of interstitial oxygen pressures (PO2is) is unknown. This is important because, as dictated by Fick’s law, PO2is provides the sole driving force for oxygen diffusion into the myocyte thereby supporting oxidative phosphorylation. PURPOSE: To determine the effects of norepinephrine administration on resting and contracting rat skeletal muscle PO2is. We tested the hypothesis that topical application (superfusion) of norepinephrine would result in blunted decreases in skeletal muscle PO2is during contractions compared to rest. METHODS: PO2is was determined via phosphorescence quenching in the exposed spinotrapezius muscle of anesthetized male Sprague-Dawley rats (n=7, 2-3 months old) at rest and during electrically-induced submaximal contractions (0.5 Hz, 3-6 V) for 6 minutes in response to norepinephrine superfusion (5x10−4 M). Functional sympatholysis was determined as the difference between the norepinephrine-induced changes in PO2is at rest and during the contraction steady-state (i.e., 2 min following the onset of muscle contractions) using (i) the absolute PO2is fall with norepinephrine (ΔPO2is), and (ii) the area under the PO2is curve plotted as a function of time (AUC). The tail (caudal) artery was cannulated for measurements of mean arterial pressure (MAP) and heart rate (HR). RESULTS: Consistent with our hypothesis, skeletal muscle contractions attenuated norepinephrine-evoked reductions in spinotrapezius interstitial oxygenation as evaluated by ΔPO2is (rest: -8.7±1.4, contractions: -4.3±1.1 mmHg, p<0.05) and AUC (rest: 2246±368, contractions: 1066±273 mmHg·s, p<0.05). Although MAP increased significantly with norepinephrine both at rest (+5±1%, p<0.05) and during contractions (+8±1%, p<0.05), this mild hypertensive response to norepinephrine was not different between conditions (p>0.05). Norepinephrine superfusion did not affect HR at rest or during contractions (p>0.05). CONCLUSIONS: That muscle contractions blunted the decrease in spinotrapezius PO2is with norepinephrine compared to the resting condition is consistent with functional sympatholysis. The latter serves to match active muscle O2 delivery-utilization in the face of elevated sympathetic nerve activity during exercise. The current results indicate that a novel combination of phosphorescence quenching (interstitial oxygenation, PO2is) and superfusion techniques may be used to evaluate functional sympatholysis in the intact rat spinotrapezius muscle. Showalter Research Trust, Purdue University. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.