Local Distribution Function Research Articles

How Does Aqueous Choline- O-Sulfate Solution Nullify the Action of Urea in Protein Denaturation?

Choline- O-sulfate (COS) acts as a protecting osmolyte in several plants, fungal, and bacterial species. Classical molecular dynamics simulation is performed to examine the molecular mechanism by which COS molecules counteract urea-conferred denaturation of the S-peptide analogue. The calculations of root mean square deviation, the radius of gyration of the Cα atom, and the solvent accessible surface area of the peptide heavy atoms imply that the 4-12 residues of the peptide in pure water remain in helical conformation at 310 K temperature. But, in binary ∼8 M aqueous urea solution the peptide loses its native conformation. Interestingly, in the ternary peptide-urea-COS system with 0.30 M COS concentration, the native conformation of the peptide remains preserved. The estimation of the average number of hydrogen bonds between different solution species indicates that it is the preferential urea-COS interactions, which influence peptide-urea interactions significantly. This observation is further confirmed by the calculation of atomic density map of urea around the peptide heavy atoms and time-averaged relative local distribution functions involving peptide and urea. Moreover, the exclusion of COS molecules from the peptide surface is also confirmed by the determination of the number of COS molecules in the first solvation shell of the peptide as well as from the calculated time-averaged relative local distribution functions involving peptide and COS. A sharp drop in the diffusion coefficient values of all solution species is observed as COS is added. These findings suggest that it is the preferential solvation of urea molecule by COS, which makes the former (urea) less available for the peptide to show its deleterious effect and hence the native conformation of the peptide is retained.

Alfvén solitary waves with effect of arbitrary temperature degeneracy in spin quantum plasma

Nonlinear Alfvén waves are studied in a fluid model for nonrelativistic, magnetized spin-1/2 quantum plasmas with an arbitrary degeneracy effect. Following a local Fermi-Dirac distribution function, a modified equation of state is utilized which is applicable to both classical and degenerate limits. Using the fluid equations for Hall magnetohydrodynamics with quantum corrections due to statistical effects, Bohm potential, spin magnetization energy, and temperature degeneracy, a set of modified Zakharov equations are derived for circularly polarized nonlinear Alfvén waves. Ions are assumed to be cold, and the spin effects of electrons are incorporated through spin force along with spin magnetization current. A linear dispersion relation for finite amplitude Alfvén waves duly modified by spin magnetization and arbitrary temperature degeneracy effects is also obtained. Employing the Sagdeev potential approach, the properties of Alfvén solitary profiles in quantum plasmas with arbitrary degeneracy effects of electrons are analyzed. The amplitude of Sagdeev potential and of the associated soliton structure for both right and left-hand circularly polarized Alfvén waves is observed to decrease with the decrease in the value of the arbitrary temperature degeneracy factor G for the case of the nearly degenerate limit. Similarly, it is found that the amplitude of Sagdeev potential and of the related solitary profile increases for both kinds of circular polarized Alfvén waves with the increasing value of G in the case of the nearly non-degenerate limit.

A non-stationary geostatistical approach to multigaussian kriging for local reserve estimation

Multigaussian kriging technique has many applications in mining, soil science, environmental science and other fields. Particularly, in the local reserve estimation of a mineral deposit, multigaussian kriging is employed to derive panel-wise tonnages by predicting conditional probability of block grades. Additionally, integration of a suitable change of support model is also required to estimate the functions of the variables with larger support than that of the samples. However, under the assumption of strict stationarity, the grade distributions and important recovery functions are estimated by multigaussian kriging using samples within a supposedly spatial homogeneous domain. Conventionally, the underlying random function model is required to be stationary in order to carry out the inference on ore grade distribution and relevant statistics. In reality, conventional stationary model often fails to represent complicated geological structure. Traditionally, the simple stationary model neither considers the obvious changes in local means and variances, nor is it able to replicate spatial continuity of the deposit and hence produces unreliable outcomes. This study deals with the theoretical design of a non-stationary multigaussian kriging model allowing change of support and its application in the mineral reserve estimation scenario. Local multivariate distributions are assumed here to be strictly stationary in the neighborhood of the panels. The local cumulative distribution function and related statistics with respect to the panels are estimated using a distance kernel approach. A rigorous investigation through simulation experiments is performed to analyze the relevance of the developed model followed by a case study on a copper deposit.

A new combination active contour model for segmenting texture image with low contrast and high illumination variations

This paper presents a novel combined energy functional based on edge and region information for active contour model, which can be applied to segment textured images containing low contrast and high illumination variations. In the proposed method, the edge features are calculated based on the phase-based approaches derived from the monogenic signal, which are robust to illumination variations in the image. These feature values are used in an edge energy functional to assist the active contour evolving towards the true object boundaries. To extract the region features, at first, we compute the normalized accumulated short-term autocorrelation (NASTA) values for the image, which suppress background clutter and enhance dissimilarities between objects and background. Next, a local cumulative distribution function (LCDF) of NASTA is calculated for every pixel in a local window around it and is used as a region feature for that pixel. Then, the obtained features are employed to define a new localized region-based energy functional that can correctly segment regions with same intensity mean and variance. The proposed edge and region energy terms are integrated and a regularization term is added to them to form our combined active contour. Experimental results indicate remarkable advantages of proposed method comparing to existing combination models.

Kinetic features of collisionless sheaths around polarized cylindrical emitters from the orbital motion theory

The kinetic features of the sheath around a cylindrical emitter immersed in collisionless plasma at rest are analysed. After finding self-consistently the electric potential by applying the Orbital Motion Theory to the Vlasov-Poisson system, the local distribution functions are reconstructed and the radial profiles of important macroscopic quantities (plasma densities, currents, and temperatures) are then computed. It is found that there can only be three kinds of holes that are bound by three different boundaries—two related to the constraints from orbital effects and the other due to the electric potential barrier. The results are presented for three regimes: negative probe bias with monotonic and non-monotonic potential and positive probe bias with non-monotonic potential. To understand the variation of macroscopic-quantity radial profiles, three diagrams are presented for kinetic features: the ϵl-diagram for the integration domains of the two orbital invariants, the effective potential, and the local ...

A kinetic model for magnetogasdynamics

In this work the equations of ideal magnetogasdynamics are derived based on the introduced local complex Maxwellian distribution function. Using this kinetic model, we obtain the analog of a quasi-dynamic system of equations for magnetogasdynamics, including dissipative processes. The resulting model and the algorithm of its solution have been tested by applying them to a number of well-known problems. The given algorithm can be easily adapted to an architecture of high performance systems with extramassive parallelism.

Isotropic pressure model in the presence of coarse-graining scale Alfvén waves and its consequence for modulational instability

A scalar pressure model of solar wind plasma in the presence of Alfvén waves at the coarse-graining scale is discussed. Using a simple sub-grid-scale model, it is shown that the scalar pressure model can be applied to describe the background pressure, because the off-diagonal components of the sub-grid-scale stress tensor disappear in the presence of one-dimensional, sub-grid scale Alfvén waves. Local equilibrium velocity distribution functions corresponding to the scalar pressure including wave dynamics (apparent temperature) are also presented. The specific heat ratio of the apparent temperature is given by the Wentzel–Kramers–Brillouin approximation of the Alfvén waves. The consequence of the local equilibrium velocity distribution functions in the coarse-graining scale model is discussed by using a nonlinear equation set describing envelope-modulated nonlinear Alfvén waves. It is recognized that without sufficient separation between the scale of waves and the scale of integration, artificial changes of the growth rates appear in the solutions of linear growth rates owing to the finite length of the filter function.

Exact dynamics following an interaction quench in a one-dimensional anyonic gas

We study the nonequilibrium quench dynamics of a one-dimensional anyonic gas. We focus on the integrable anyonic Lieb-Liniger model and consider the quench from noninteracting to hard-core anyons. We study the dynamics of the local properties of the system. By means of integrability-based methods, we compute analytically the one-body density matrix and the density-density correlation function at all times after the quench and in particular at infinite time. Our results show that the system evolves from an initial state where the local momentum distribution function is nonsymmetric to a steady state where it becomes symmetric. Furthermore, while the initial momentum distribution functions (and the equilibrium ones) explicitly depend on the anyonic parameter, the final ones do not. This is reminiscent of the dynamical fermionization observed in the context of free expansions after release from a confining trap.

Observational Evidence for High Neutronization in Supernova Remnants: Implications for Type Ia Supernova Progenitors

Abstract The physical process whereby a carbon–oxygen white dwarf explodes as a Type Ia supernova (SN Ia) remains highly uncertain. The degree of neutronization in SN Ia ejecta holds clues to this process because it depends on the mass and the metallicity of the stellar progenitor, and on the thermodynamic history prior to the explosion. We report on a new method to determine ejecta neutronization using Ca and S lines in the X-ray spectra of Type Ia supernova remnants (SNRs). Applying this method to Suzaku data of Tycho, Kepler, 3C 397, and G337.2−0.7 in the Milky Way, and N103B in the Large Magellanic Cloud, we find that the neutronization of the ejecta in N103B is comparable to that of Tycho and Kepler, which suggests that progenitor metallicity is not the only source of neutronization in SNe Ia. We then use a grid of SN Ia explosion models to infer the metallicities of the stellar progenitors of our SNRs. The implied metallicities of 3C 397, G337.2−0.7, and N103B are major outliers compared to the local stellar metallicity distribution functions, indicating that progenitor metallicity can be ruled out as the origin of neutronization for these SNRs. Although the relationship between ejecta neutronization and equivalent progenitor metallicity is subject to uncertainties stemming from the 12C + 16O reaction rate, which affects the Ca/S mass ratio, our main results are not sensitive to these details.

Studies on radial and poloidal particle transport at the edge of SST-1 tokamak

The radial and poloidal particle fluxes occurring at the plasma edge are essential towards understanding the plasma confinement in the tokamak device. In tokamaks, the edge transport barriers play a critical role in the transitions from low confinement (L-mode) to high confinement (H-mode). Recently, the edge plasma profiles have been studied for steady-state superconducting tokamak-1 (SST-1) with the help of an array of Langmuir probes. The floating potential and ion saturation current fluctuations have been measured at different radial and poloidal distance at the edge of SST-1. Increases in magnetic fluctuations associated with enhanced magneto-hydrodynamic (MHD) activities have been found to increase the radial particle flux drastically. It indicates that the MHD activity leads to anomalous particle transport during the tokamak discharge at SST-1. It is found that the average poloidal velocity decreases from ∼4 km/s to ∼3.7 km/s whereas the average radial velocity decreases from ∼7.2 km/s to 4.7 km/s. Further, during MHD activity, it is found that as the magnetic island grows, the radial electric field changes from negative to positive. It is observed that the turbulent particle flux at SST-1 tokamak is predominantly positive and bursty. The local flux probability distribution function shows a clear non-Gaussian character, and it is skewed negatively.

Heat, temperature and Clausius inequality in a model for active Brownian particles

Methods of stochastic thermodynamics and hydrodynamics are applied to a recently introduced model of active particles. The model consists of an overdamped particle subject to Gaussian coloured noise. Inspired by stochastic thermodynamics, we derive from the system’s Fokker-Planck equation the average exchanges of heat and work with the active bath and the associated entropy production. We show that a Clausius inequality holds, with the local (non-uniform) temperature of the active bath replacing the uniform temperature usually encountered in equilibrium systems. Furthermore, by restricting the dynamical space to the first velocity moments of the local distribution function we derive a hydrodynamic description where local pressure, kinetic temperature and internal heat fluxes appear and are consistent with the previous thermodynamic analysis. The procedure also shows under which conditions one obtains the unified coloured noise approximation (UCNA): such an approximation neglects the fast relaxation to the active bath and therefore yields detailed balance and zero entropy production. In the last part, by using multiple time-scale analysis, we provide a constructive method (alternative to UCNA) to determine the solution of the Kramers equation and go beyond the detailed balance condition determining negative entropy production.

Fatigue analysis of spot-welded automobile components considering fatigue damage-induced stiffness degradation in time and frequency domains

In this study, fatigue analysis was performed on a multi-point spot-welded outrigger structure utilized in an automobile engine room, where stiffness degradation from accumulated fatigue damage were considered. The S-N curve was obtained through a fatigue test on a single-point tensile-shear spot-welded specimen under constant amplitude load and finite element analysis based on the Rupp/LBF model. Fatigue analyses were performed in the time and frequency domains on the spot-welded outrigger structure, where changes in the local stress distribution and transfer function due to accumulated fatigue damage to the welding points were considered. Based on these results, it can be stated that the fatigue life of multi-point spot-welded structure under random loading should be evaluated considering the stiffness changes due to accumulated fatigue damage under the frequency domain.

Local equations of state in nonequilibrium heterogeneous physicochemical systems

Equations describing local thermal and caloric equations of state in heterogeneous systems at any degree of their states’ deviation from equilibrium are derived. The state of a system is described by equations of the transfer of mixture components; these generalize the equations of classical non-equilibrium thermodynamics for strongly nonequilibrium processes. The contributions from reactions and external fields are taken into account. The equations are derived using the lattice gas model with discrete molecular distributions in space (on a scale comparable to molecular dimensions) and continuous molecular distributions (at short distances inside cells) during their translational and vibrational motions. For simplicity, it is assumed that distinctions between the sizes of mixture components are small. Contributions from potential functions of intermolecular interaction (of the Lennard-Jones type) to some coordination spheres are considered. The theory provides a unified description of the dynamics of distributions of concentrations and pair functions of mixture components in three aggregate states, and at their interfaces. Universal expressions for the local components of the pressure tensor and internal energy inside multicomponent bulk phases and at their interfaces are obtained. Local components of the pressure tensor and the internal energy are universally expressed through local unary and pair distribution functions (DFs) in any nonequilibrium state. The time evolution of the unary and pair DFs themselves is determined from the derived system of equations of mass, momentum, and energy transfer that ensure the transition of the system from a strongly nonequilibrium state to both the local equilibrium state described within traditional nonequilibrium thermodynamics and the complete thermodynamic equilibrium state postulated by classical thermodynamics.

Electrostatic thermal noise in a weakly ionized collisional plasma

AbstractQuasi‐thermal noise (QTN) spectroscopy is a plasma diagnostic technique which enables precise measurements of local electron velocity distribution function moments. This technique is based on measurements and analysis of voltage fluctuations at the antenna terminals, induced by thermal motion of charged particles. In this work, we accommodate, for the first time, this technique to weakly ionized collisional plasmas. It turns out that the QTN spectrum is modified both at low frequencies, increasing the level of power spectrum, and around the plasma frequency, where collisions damp the plasma oscillations and therefore broaden and reduce the amplitude of so called “plasma peak,” while the spectrum at high frequencies is nearly unmodified compared to the collisionless case. Based on these results, we show that QTN spectroscopy enables independent measurements of the collision frequency, electron density, and temperature, provided the ratio of collision frequency to plasma frequency is ν/ωp∼0.1. The method presented here can be used for precise estimation of plasma parameters in laboratory devices and unmagnetized ionospheres, while application in the ionosphere of Earth is possible but limited to small, low‐frequency range due to magnetic field influence.

Lattice Boltzmann methods for global linear instability analysis

Modal global linear instability analysis is performed using, for the first time ever, the lattice Boltzmann method (LBM) to analyze incompressible flows with two and three inhomogeneous spatial directions. Four linearization models have been implemented in order to recover the linearized Navier–Stokes equations in the incompressible limit. Two of those models employ the single relaxation time and have been proposed previously in the literature as linearization of the collision operator of the lattice Boltzmann equation. Two additional models are derived herein for the first time by linearizing the local equilibrium probability distribution function. Instability analysis results are obtained in three benchmark problems, two in closed geometries and one in open flow, namely the square and cubic lid-driven cavity flow and flow in the wake of the circular cylinder. Comparisons with results delivered by classic spectral element methods verify the accuracy of the proposed new methodologies and point potential limitations particular to the LBM approach. The known issue of appearance of numerical instabilities when the SRT model is used in direct numerical simulations employing the LBM is shown to be reflected in a spurious global eigenmode when the SRT model is used in the instability analysis. Although this mode is absent in the multiple relaxation times model, other spurious instabilities can also arise and are documented herein. Areas of potential improvements in order to make the proposed methodology competitive with established approaches for global instability analysis are discussed.

Phase stability, EXAFS investigation and correlation between nanostructure and extrinsic magnetic properties of nanocrystalline Pr2(Co,Fe)7

Nanocrystalline Pr2 Co7−x Fex (x⩽3.5) powder was synthesized by high energy milling and was subsequently annealed at 973 K for 30 min. Their crystalline structures were investigated by means of X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS) and transmission electron microscopy (TEM). Magnetic properties were also studied at room temperature and 10 K as a function of the iron composition.This compounds structure depends on the iron content; for x⩽ 1 they crystallize in the Ce2 Ni7-type hexagonal structure (space group: P63/mmc). For 1 <x⩽ 3, we observe a mixture of three phases, Pr2(Co,Fe)7, Pr(Co,Fe)3 and Pr2(Co,Fe)17 while for larger values of x the Pr2(Co,Fe)7 phase disappears completely. Since the substitution of cobalt by iron in a pure Pr2 Co7−x Fex phase is limited to x⩽ 1, a site preference can be suggested. Unfortunately standard XRD cannot be used unambiguously because Co and Fe have too close normal X-ray atomic scattering factors. Among the local and Fe selective available experimental methods, we have chosen to explore the P63/mmc space group Wyckoff positions for iron by EXAFS at the Fe edge. This study shows that the local iron radial distribution function is much larger than expected for all the specific sites, at least two Fe–Pr distances, except for 12k which gives the best fit. A preferential substitution of cobalt by iron in Ref. 12k site is coherent with (i) the EXAFS result (ii) the substitution rate x<1 (iii) the anisotropic increase of the crystal cell parameters. A mixture of 12k, 6h and 2a cannot be excluded. However, if we assume a unique preferential site, 12k is the only solution.For x⩽ 1, the magnetocryslalline anisotropy is observed in Pr2 Co7−x Fex alloys with fairly strong anisotropy fields at room temperature in range from 123 to 136 kOe for x = 0 and x = 1, respectively. For x>1, the magnetocrystalline anisotropy field of the 2:17 phase is lower than that of the 2:7 phase, which causes a further reduction in anisotropy and coercivity.

Convective-Diffusion Model of Transfer of a Sedimenting Low-Concentration Polydisperse Suspension of Stokesian Particles in a Plane Channel. Part I

With the analytical expression for the local particle size distribution function in the case of flow of a low-concentration polydisperse suspension whose dispersed phase moves in a turbulent regime simulated by the ideal-displacement model, the authors have quantitatively assessed the regularities of formation of the fields of mass concentration in the flow over the cross section and along the length of the channel, and also of thicknesses of sediments on the upper and lower "wetted" surfaces and their particle size distribution as functions of the intensity of mixing and the particle size distribution of the suspension.

Note on one-fluid modeling of low-frequency Alfvénic fluctuations in a solar wind plasma with multi-ion components

A simple point of view that non-zero Alfvén ratio (residual energy) appears as a consequence of one-fluid modeling of uni-directional Alfvén waves in a solar wind plasma is presented. Since relative speeds among ions are incorporated into the one-fluid model as a pressure anisotropy, the Alfvén ratio can be finite due to the decrease in the phase velocity. It is shown that a proton beam component typically found in the solar wind plasma can contribute to generating non-zero Alfvén ratio observed in the solar wind plasma. Local equilibrium velocity distribution functions of each ion component are also discussed by using maximum entropy principle.

Linear and nonlinear ion-acoustic waves in nonrelativistic quantum plasmas with arbitrary degeneracy.

Linear and nonlinear ion-acoustic waves are studied in a fluid model for nonrelativistic, unmagnetized quantum plasma with electrons with an arbitrary degeneracy degree. The equation of state for electrons follows from a local Fermi-Dirac distribution function and applies equally well both to fully degenerate and classical, nondegenerate limits. Ions are assumed to be cold. Quantum diffraction effects through the Bohm potential are also taken into account. A general coupling parameter valid for dilute and dense plasmas is proposed. The linear dispersion relation of the ion-acoustic waves is obtained and the ion-acoustic speed is discussed for the limiting cases of extremely dense or dilute systems. In the long-wavelength limit, the results agree with quantum kinetic theory. Using the reductive perturbation method, the appropriate Korteweg-de Vries equation for weakly nonlinear solutions is obtained and the corresponding soliton propagation is analyzed. It is found that soliton hump and dip structures are formed depending on the value of the quantum parameter for the degenerate electrons, which affect the phase velocities in the dispersive medium.

Incremental Hole Drilling for Residual Stress Analysis of Strongly Textured Material States – A New Calibration Approach

Technical components produced via sheet metal forming often obtain characteristic crystallographic textures and process induced residual stress distributions. Knowledge of the local residual stress states is essential for the proper components’ dimensioning. We report about the expansion of the incremental hole drilling technique for residual stress analysis to highly textured material states. A new evaluation approach using the differential evaluation algorithm is proposed, which bases on the calculation of multiple case specific calibration functions under consideration of the local orientation distribution function of the textured material. Systematic finite element (FE) simulations of incremental hole-drilling experiments are conducted regarding defined ideal nickel single crystal orientations (cube, Goss and brass). Multiple case-specific calibration functions, which consider the materials elastic anisotropy, are calculated and applied for stress calculation. In addition, the influence of a rosette misorientation between stress measurement and FE calibration is investigated. Using this new evaluation strategy a significant improvement of (residual) stress calculation on strongly textured materials is achieved. Finally, the capability of the proposed evaluation approach is experimentally validated for an uniaxially loaded CMSX-4 (nickel base super alloy) single crystal. The investigation clearly proved that in case of strongly anisotropic materials the evaluation using multiple case-specific calibration functions leads to a significant improvement in stress analysis compared to a conventional evaluation.