Decrease In Potential Energy Research Articles

Multi-particle molecular dynamics simulation: shell thickness effects on sintering process of Cu-Ag core-shell nanoparticles

As a substitute for pure silver nanoparticles, Cu-Ag core-shell nanoparticles (CS NPs) have received significant attention in the fields of electronic packaging and conductive inks. Shell thickness is one of the important factors affecting the sintering performance of CS NPs. In this work, we conduct a multi-particle molecular dynamics simulation to investigate the shell thickness effects on the sintering process of Cu-Ag CS NPs at different temperatures. The results show that the less the shell thickness, the lower the potential energy decrease during sintering. This study mainly involves two sintering mechanisms, plastic deformation mechanism, and diffusion mechanism. During the sintering process, the contribution of the plastic deformation mechanism decrease with the layer thickness decreases. As for the diffusion mechanism, the self-diffusion coefficient at 500 K is much lower than that at higher temperatures. However, the slow diffusion can increase the densification by filling the pores generated in the initial stage of sintering. The self-diffusion coefficient of surface atoms increases as the shell thickness decreases. The decrease of shell thickness can produce more lattice mismatches at the core-shell interface, which hinders crystallization during the sintering process. And we found more amorphous Ag atoms at the sintering neck. A higher sintering temperature can induce the diffusion of Cu atom near the core-shell interface, especially for the particle with thinner shell thickness. Some diffused Cu atoms were found in the neck area of sintered CS NP of Ag5Cu3.5 and Ag5Cu4 at 700 K. Moreover, the sintered neck partly composed of Cu atoms was observed in sintered Ag5Cu4 CS NPs at 900 K.

Deforestation Impacts on Orographic Precipitation in the Tropical Andes

This study examines the implications of Tropical Montane Forests (TMFs) loss on orographic precipitation in the Eastern slopes of the Andes (EADS). The focus is on moist processes for synoptic regimes associated with significant EADS precipitation: (1) monsoon rainfall for weak and strong South America Low-Level Jet (LLJ) conditions and (2) heavy rainfall associated with cold air intrusions (CAI) in the dry season. High-resolution simulations using the Weather Research and Forecasting (WRF) model were conducted for realistic and modified land-cover resulting from the conversion of TMFs to savanna. The deforestation scenarios result in 50–100% decrease (up to ∼400 J kg–1) in Convective Available Potential Energy (CAPE) spatially organized by land-cover change along the EADS. Analysis of the differences in simulated frequency distributions of rainfall intensity shows robust daytime increases in light rainfall (<2 mm h–1) and decreases in moderate rainfall rates (2–10 mm h–1) in the altitudinal band 500–2,000 m where orographic enhancement is dominant. Whereas there are negligible changes in the spatial patterns of precipitation and hydrologic response for monsoon conditions, rainfall accumulations decrease for all cases, and the precipitation maxima shift downslope into the Amazon lowlands. Changes in rainfall amount and intensity result in runoff decreases of 5–10% at the event-scale for the CAI case. Sensitivity simulations for lower initial soil moisture conditions indicate a strong positive feedback of forest loss to hydrologic drought along the EADS foothills in the austral spring when CAIs play a key role in the tropical EADS dry season hydrometeorology.

Further inquiry into the interaction between the winter North Pacific storm track and the East Asian trough

Based on the daily ERA-Interim reanalysis, interactions between the winter North Pacific storm track (WNPST) and the East Asian trough (EAT) on the interannual scale are further explored from the perspective of energy conversion and the simplified quasi-geostrophic potential vorticity equation. There is a prominent out-of-phase relationship between the EAT and WNPST on the interannual scale. It is baroclinic energy conversion rather than barotropic energy conversion that is the main physical process that the EAT affects the WNPST. When the EAT is intensified, the energy conversion from mean available potential energy to eddy available potential energy decreases; further, the energy conversion from eddy available potential energy to eddy kinetic energy is attenuated, which leads directly to remarkable weakening in the strength of the WNPST in its peak area and the region west of the date line. In addition, when the WNPST is enhanced, the WNPST dynamic forcing contributes to lowering the geopotential height near the EAT and thus profits to recover the strength of the EAT, while the thermal forcing of WNPST is opposite. However, their joint effect is still to strengthen the EAT, indicating that the impact of WNPST dynamic forcing on the EAT is stronger than that of thermal forcing. The interaction between the WNPST and EAT may be a way for the WNPST to maintain itself.

Structural relaxation in amorphous materials under cyclic tension-compression loading

The process of structural relaxation in disordered solids subjected to repeated tension-compression loading is studied using molecular dynamics simulations. The binary glass is prepared by rapid cooling well below the glass transition temperature and then periodically strained at constant volume. We find that the amorphous system is relocated to progressively lower potential energy states during hundreds of cycles, and the energy levels become deeper upon approaching critical strain amplitude from below. The decrease in potential energy is associated with collective nonaffine rearrangements of atoms, and their rescaled probability distribution becomes independent of the cycle number at sufficiently large time intervals. It is also shown that yielding during startup shear deformation occurs at larger values of the stress overshoot in samples that were cyclically loaded at higher strain amplitudes. These results might be useful for mechanical processing of amorphous alloys in order to reduce their energy and increase chemical resistivity and resistance to crystallization.

Mathematical Representation of Clausius’ and Kelvin’s Statements of the Second Law and Irreversibility

We provide a stochastic mathematical representation for Clausius' and Kelvin-Planck's statements of the Second Law of Thermodynamics in terms of the entropy productions of a finite, compact driven Markov system and its lift. A surjective map is rigorously established through the lift when the state space is either a discrete graph or a continuous n-dimensional torus T^n. The corresponding lifted processes have detailed balance thus a natural potential function but no stationary probability. We show that in the long-time limit the entropy production of the finite driven system precisely equals the potential energy decrease in the lifted system. This theorem provides a dynamic foundation for the two equivalent statements of Second Law of Thermodynamics, a la Kelvin's and Clausius'. It suggests a modernized, combined statement: "A mesoscopic engine that works in completing irreversible internal cycles statistically has necessarily an external effect that lowering a weight accompanied by passing heat from a warmer to a colder body."

The Relativity of the Time with the Universal Density of Potential Energy at Different Stationary Reference Frames

This article is an analysis of current theory of the gravitational time dilatation in different stationary reference frames.This new approach leads us to a new vision of relativity because we find the time dependence relativeto the universal density of potential energy at placeand that density this varies from one reference frame to another reference frame. The time in each location varies in the inverse proportion of the square root of the respectiveuniversal density of potential energy. With the universal expansion the universal density of potential energy decreases and will cause the contraction of the time in the Earth reference.

A New Simplified Method for Calculating the Sliding Distance of the Rapid Long Run-out Loess Landslides

The area of loess in China is 640,000 km2, accounting for 6% of the total land area. Loess landslides occur frequently, causing economic losses of tens of millions of yuan per year. There is a close relationship between the hazard and the sliding distance of landslide. The study on the sliding distance of loess landslide can provide a scientific basis for the prediction of landslide risk. Based on the law of conservation of energy, a new simplified method for calculating the sliding distance of loess landslides is proposed in this paper. Based on the fact that the decrease of potential energy is equal to the energy consumed in the sliding process, the formula for calculating the sliding distance is obtained. Taking Dabuzi landslide in the Southern Jingyang Plateau (SJP) of Shaanxi Province as an example, considering the unsaturated property of soil, Morgenstern-Price method was used to calculate the slope stability of SJP and determine the most dangerous sliding surface and sliding body. According to the proposed formula, the calculated sliding distance is consistent with the actual one. The correctness of the proposed method is verified by case calculation.

Kinetic determination of sedimentation for GMZ bentonite colloids in aqueous solution: Effect of pH, temperature and electrolyte concentration

Bentonite colloids are readily generated by eroding the compacted bentonite blocks with flowing groundwater and facilitate the transport of radionuclides due to their high mobility. The geological fate of colloids is highly relevant to the aggregation and sedimentation of colloids in porous media. In the present work, the week-scale stability of bentonite colloids concerning sedimentation was determined by photon correlation spectroscopy (PCS) as a function of pH, temperature, and electrolyte concentration. The related mechanisms governing colloidal stability were elucidated by employing the DLVO model. The results showed that the alkaline condition was favorable for bentonite colloidal stability, while high temperature and high salinity destabilized colloids due to the decrease in repulsive potential energy. Ca2+ contributed more significantly to colloid sedimentation than Na+ because of the favorable replacement in the Stern layer. The critical coagulation concentration (CCC) values calculated theoretically from DLVO theory were applicable to predict the stability of bentonite colloids. Knowledge from the present work provides deep insight into the stability of bentonite colloids and has potential implication for understanding the detailed physico-chemical processes governing colloid migration under various subsurface environments.

How Does Latent Cooling Affect Baroclinic Development in an Idealized Framework?

Abstract Latent cooling by evaporating or melting hydrometeors has recently been shown to contribute to the positive low-level potential vorticity (PV) anomaly below the layer of latent heating in midlatitude cyclones. While the low-level PV anomaly might be intensified by latent cooling, the influence on the overall baroclinic development remains unclear. Including both latent heating and cooling in the Eady model, this study finds that latent cooling reduces baroclinic growth. While the PV anomaly between the layers of latent cooling and heating increases for realistic heating intensities, the PV anomaly at the top of the heating layer decreases, as latent heating is weakened because of reduced vertical motion within the cyclone. Consequently, the relative contribution from diabatic heating to the generation of eddy available potential energy decreases when latent cooling is included. Thus, despite the recently emphasized role of evaporation for the low-level PV anomaly in developing cyclones, the overall effect of latent cooling is detrimental to baroclinic growth.

The Effect of Froude Number on Flow Field of U-Shaped Channel Along a Side Weir in Supercritical Flow Regime

In this study, turbulence of the flow field as well as the flow free surface in a U-shaped channel located along a side weir under supercritical flow conditions are simulated using the RNG k-e turbulence model and VOF scheme. Comparison of the numerical and laboratory results shows that the numerical model simulates the free surface and characteristics of the flow field with acceptable accuracy. Then, the effects of the upstream Froude number of the side weir on the flow pattern of the main channel are investigated. For all Froude numbers, in the vicinity of the inner bank a free surface drop occurs at the beginning of the side weir upstream, and a surface jump is formed at the final quarter of the side weir length. Across the surface jump, the kinematic energy of water increases and the potential energy decreases. The dividing stream surface and the stagnation zone dimensions increase as the Froude number increases.

Influence of Black Carbon Aerosol on the Atmospheric Instability

AbstractTo date, influence of aerosols on the atmospheric stability and hence on the convection/precipitation is not well understood. From the detailed analysis carried out using high‐accuracy radiosonde and Aethalometer measurements, a significant decrease in the convective available potential energy has been noticed in association with the increase in surface concentration of black carbon (BC) for a restricted range of precipitable water vapor and under similar environmental background (wind speed, direction, and cloud cover) over Gadanki (13.5°N, 79.2°E), a tropical rural site in southern peninsular India. A number of case studies along with statistical analysis indicate a notable perturbation in the temperature profile associated with high‐surface BC concentration conditions compared to the regional mean concentration of the same. A discernible fall in the temperature lapse rate within and above the local boundary layer in association with the higher BC concentration has been observed, which in turn reduces the available potential energy for convection decreasing the positive buoyancy required for a rising moist air parcel. This observation has been noticed over a nonurban location, but the phenomenon is not location dependent and is more applicable to the urban regions where BC concentration is likely to be much higher.

An Analysis of Distributed Strike‐Slip Shear Deformation of the Qaidam Basin, Northern Tibetan Plateau

AbstractThe interior structure of the Qaidam Basin records kinematic information related to the regional deformation of the northern Tibetan Plateau. Based on balanced cross sections and depth structure maps covering two individual anticlines in the western Qaidam Basin, we calculate shortening and strike‐slip amounts on the structures. Strain analyses reveal a complex deformation mechanism for them, comprising ~7°–10° clockwise rotation and oblique convergence, with block rotation having contributed more to the sinistral slip than has oblique convergence. Considering the similarities in geometry, kinematics, and onset time of the pervasive northwest trending structures within the basin, we propose that they were developed during distributed dextral shear that has affected the Qaidam Basin since the early Miocene. The bulk shear strikes at ~N55°E, which is consistent with the northeastward decrease in gravitational potential energy away from the central Tibetan Plateau, and is facilitated by the movement on the Altyn Tagh and eastern Kunlun faults.

Hemodynamic Improvement with Application of Mechanical Circulatory Support in Heart Failure with Preserved Ejection Fraction in a Mock Circulation Loop

Purpose Mechanical circulatory support (MCS) is a non-obvious therapy for heart failure with preserved ejection fraction (HFpEF) because ventricular systolic function is not reduced. We hypothesize MCS of the left ventricle (LV) or left atrium (LA) can improve the hemodynamics in HFpEF including when pulmonary arterial hypertension (PH) is present. Methods Hemodynamic conditions of HFpEF ± PH were recreated on a mock circulation loop (MCL) with a tunable resistance, arterial compliance, peripheral resistance, inertance, venous compliance, and replication of the Frank-Starling mechanism. Hemodynamic parameters were recorded, including atrial and ventricular pressures, ventricular volumes, ejection fraction, and cardiac output. A HeartWare HVAD™ (Medtronic, MN) was used in two different support configurations: 1) LV to aorta (Ao) and 2) LA to Ao. The pump speed was titrated to achieve systemic flow (Qs) of 4.0 L/min and 4.5 L/min. Results Conditions typically seen in patients with HFpEF ± PH were created in the MCL with complete hemodynamic profiles including HVAD support seen in Table1. In both configurations and regardless of PH status, further Qs augmentation was associated with a reduction in LV end-diastolic pressure, LA pressure and mean pulmonary artery pressure. In the LV to Ao configuration, LV volumes decreased, and ejection fraction improved. In the LA to Ao configuration, LV volumes increased. In the LV to Ao configuration, pressure-volume loop (PVL) data show a reduction in pressure-volume area including a decrease in both stroke work and potential energy. In LA to Ao configuration, PVL data show a decrease in stroke work but an increase in potential energy. This study was not designed to evaluate for suction events. Conclusion In HFpEF ± PH, MCS can increase Qs and reduce LA pressure. As compared to LV decompression, LA decompression does not volume unload the LV. This study shows potential for MCS as a therapeutic alternative for HFpEF.

Variational Principles in the Mechanics of Conformational Motions of Macromolecules in a Viscous Medium

The mechanics of the conformational motions of macromolecules due to rotations around the valence bonds in a viscous medium have been considered. The variational principles for the energy-dissipation rate during conformational motions in a viscous medium and the rate of the potential energy decrease of a macromolecule during conformational relaxation have been analyzed. The seeming contradiction between this principle and the principle of the minimum energy-dissipation rate is resolved. It is shown that the energy-dissipation rate must be optimal and minimal in order to simultaneously satisfy the conservation laws and fulfill the deterministic nature of classical trajectories. The generalization and analysis of the influence of thermal fluctuations and external forces on the variational principles for the conformational relaxation of macromolecules is carried out. A visual graphical geometric depiction has been developed using hyperspheres in the space of the velocities of chain nodes to describe conformational movements along many degrees of freedom in a viscous medium. The equipartition of the energy-dissipation rates (and the rates of potential energy decrease) among the conformational degrees of freedom is discussed.

Ventricular Energetics in Pediatric Left Ventricular Assist Device Patients: A Retrospective Clinical Study.

The aim of this study is to estimate the trend of right and left energetic parameters in left ventricular assist device (LVAD) pediatric patients. Echocardiographic data were retrospectively collected at the baseline, in the acute phase after and at the monthly follow-ups till the LVAD explantation to estimate left and right ventricular energetic parameters. A significant relationship between the left and right ventricular energetic parameter trends was found along all the study period. Left ventricular end-systolic pressure-volume relationship improved till the follow-up of 2 months and then progressively decreases. Left arteroventricular coupling decreases after the LVAD, and right arteroventricular coupling decreases at the short-term follow-up. Left ventricular external work, potential energy, and pressure-volume area decrease at the short-term follow-up and then increase progressively. Right ventricular external work, potential energy, and pressure-volume area increase after the LVAD implantation. Left (right) cardiac mechanical efficiency is improved (worsened) by the LVAD. Energetic variables show that the LVAD benefits could decrease over time. A continuous and patient tailored LVAD setting could contribute to prolong LVAD benefits. The introduction of energetic parameters could lead to a more complete evaluation of LVAD patients' outcome which is a multiparametric process.

Weak temperature dependence of ageing of structural properties in atomistic model glassformers.

Ageing phenomena are investigated from a structural perspective in two binary Lennard-Jones glassformers, the Kob-Andersen and Wahnström mixtures. In both, the geometric motif assumed by the glassformer upon supercooling, the locally favoured structure (LFS), has been established. The Kob-Andersen mixture forms bicapped square antiprisms; the Wahnström model forms icosahedra. Upon ageing, we find that the structural relaxation time has a time-dependence consistent with a power law. However, the LFS population and potential energy increase and decrease, respectively, in a logarithmic fashion. Remarkably, over the time scales investigated, which correspond to a factor of 104 change in relaxation times, the rate at which these quantities age appears almost independent of temperature. Only at temperatures far below the Vogel-Fulcher-Tamman temperature do the ageing dynamics slow.

Influence of Open Water Bodies on the Modeling of Summertime Convection over the Canadian Prairies

Abstract There are numerous water features on the Canadian landscapes that are not monitored. Specifically, there are water bodies over the prairies and Canadian shield regions of North America that are ephemeral in nature and could have a significant influence on convective storm generation and local weather patterns through turbulent exchanges of sensible and latent heat between the land and the atmosphere. In this study a series of numerical experiments is performed with Environment and Climate Change Canada’s Global Environmental Multiscale (GEM) model at 2.5-km grid spacing to examine the sensitivity of the atmospheric boundary layer and the resulting precipitation to the presence of open water bodies. Operationally, the land–water fraction in GEM is specified by means of static geophysical databases that do not change with time. Uncertainty is introduced in this study into this land–water fraction and the sensitivity of the resulting precipitation is quantified for a convective precipitation event occurring over the Canadian Prairies in the summer of 2014. The results indicate that with an increase in open water bodies, accumulated precipitation, peak precipitation amounts, and intensities decrease. Moreover, shifts are seen in times of peak for both precipitation amounts and intensities, in the order of increasing wetness. Additionally, with an increase in open water bodies, convective available potential energy decreases and convective inhibition increases, indicating suppression of forcing for convective precipitation.

Interaction potential and friction of hydrogenated diamond surfaces at the atomic scale: first-principle calculation

Interaction potential plays a vital role on the friction. Potential energy of two contacts directly determines on the friction force. However, many mathematic models proposed, always abandon the instantaneous status during sliding to devote to a weighted average over lateral force, which might miss some information about friction behavior. In this work, the relation among potential energies, separation distances of two contracts, and positions in the sliding direction are studied to evaluate the instantaneous friction characteristics. Two hydrogenated diamond surfaces are used as the examined model. The results show that a watershed between positive and negative friction forces locates at the position with the minimum adsorption energy. A rapid decrease in potential energy occurs near the 2.5 nN external force, where the friction coefficient approaches zero at each position in the sliding direction. Therefore, a novel method may be developed to greatly reduce the friction coefficient between two surfaces by adjusting the contract pressure.

Effect of Ce-doped MnO2 catalyst on the lithium-air batteryperformance in the ambient atmosphere

MnO2 doped with Ce was hydrothermally synthesized and the as-made breathable waterproof membrane used outside the cathode was prepared for improving the lithium-air battery performance in air. The samples were characterized by scanning electron microscopy (SEM), energy dispersive spectrum analysis (EDS), charge–discharge cycle tests, charge–discharge cycle tests of limited capacity, and electrochemical impedance spectroscopy (EIS) tests. The result showed that Ce x Mn1-x O2 can effectively reduce the charge overpotential of the cathode. The charge and discharge electrical potential difference of Ce0.1Mn0.9O2 was only 700 mV while MnO2’s was 2100 mV. And Ce0.1Mn0.9O2 that exhibited high discharge capacity of 400 mAh g−1 in air had a stable discharge platform of 2.5 V and then the more obvious charge phenomenon appeared after 3.5 V. The excellent catalysis, the effect of cathode catalytic materials named Ce x Mn1-x O2, may attribute to the decrease of reaction potential energy of oxygen reduction reaction and oxygen evolution reaction.

Impact of aerosols on precipitation from deep convective clouds in eastern China

AbstractWe analyzed the impact of aerosols on precipitation based on 3 years of 3‐hourly observations made in heavily polluted eastern China. The probability of precipitation from different cloud types was calculated using International Satellite Cloud Climatology Project cloud data and gauge‐based hourly precipitation data. Because deep convective clouds have the largest precipitation probability, the influence of aerosols on the precipitation from such clouds was studied in particular. Aerosol properties were taken from the Modern‐Era Retrospective Analysis for Research and Applications Aerosol Reanalysis data set. As aerosol optical depth increased, rainfall amounts from deep convective clouds increased at first and then decreased. The descending part of the trend is likely due to the aerosol radiative effect. Downwelling solar radiative fluxes at the surface decreased as aerosol optical depth increased. The decrease in solar radiation led to a decrease in ground heat fluxes and convective available potential energy, which is unfavorable for development of convective clouds and precipitation. The tendencies for lower cloud top temperatures, lower cloud top pressures, and higher cloud optical depths as a response to larger aerosol optical depths suggest the invigoration effect. Vertical velocity, relative humidity, and air temperature from the National Centers for Environmental Prediction Climate Forecast System Reanalysis were sorted to help investigate if the trends are dependent on any environmental conditions. How dynamic and microphysical factors strengthen or mitigate the impact of aerosols on clouds and precipitation and more details about their interplay should be studied further using more observations and model simulations.