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https://www.readbyqxmd.com/read/29235990/the-fokker-planck-equation-for-coupled-brown-neel-rotation
#1
Juergen Weizenecker
Calculating the dynamic properties of magnetization of single-domain particles is of great importance for the tomographic imaging modality known as magnetic particle imaging (MPI). Although the assumption of instantaneous thermodynamic equilibrium (Langevin function) after application of time-dependent magnetic fields is sufficient for understanding the fundamental behavior, it is essential to consider the finite response times of magnetic particles for optimizing or analyzing various aspects, e.g., interpreting spectra, optimizing MPI sequences, developing new contrasts, and evaluating simplified models...
December 13, 2017: Physics in Medicine and Biology
https://www.readbyqxmd.com/read/29195652/from-artefacts-to-atoms-a-new-si-for-2018-to-be-based-on-fundamental-constants
#2
Terry Quinn
At the 26th General Conference on Weights and Measures (CGPM) in November 2018, it is planned to adopt a new definition of the International System of Units, SI, based on the fixed numerical values of seven defining constants, broadly the fundamental constants of physics. This will be the culmination of more than two hundred years of metrology, instantiating for the first time the original ideas of the creators of the metric system. The key is the replacement of the present definition of the unit of mass, the kilogram artefact of platinum-iridium, by one based on a fixed numerical value of the Planck constant...
October 2017: Studies in History and Philosophy of Science
https://www.readbyqxmd.com/read/29104300/anion-capture-and-exchange-by-functional-coatings-new-routes-to-mitigate-steel-corrosion-in-concrete-infrastructure
#3
Gabriel Falzone, Magdalena Balonis, Dale Bentz, Scott Jones, Gaurav Sant
Chloride-induced corrosion is a major cause of degradation of reinforced concrete infrastructure. While the binding of chloride ions (Cl(-)) by cementitious phases is known to delay corrosion, this approach has not been systematically exploited as a mechanism to increase structural service life. Recently, Falzone et al. [Cement and Concrete Research72, 54-68 (2015)] proposed calcium aluminate cement (CAC) formulations containing NO3-AFm to serve as anion exchange coatings that are capable of binding large quantities of Cl(-) ions, while simultaneously releasing corrosion-inhibiting NO3(-) species...
November 2017: Cement and Concrete Research
https://www.readbyqxmd.com/read/29083861/self-similar-interfacial-impedance-of-electrodes-in-high-conductivity-media
#4
Anil Koklu, Amin Mansoorifar, Ali Beskok
Electrode polarization (EP) happening due to accumulation of ions at the electrode/electrolyte interface is an inevitable phenomenon while measuring impedance spectrum in high conductivity buffers and at low RF spectrum. Well-characterized time scales elucidating the EP effect are important for the rational design of microfluidic devices and impedance sensors. In this Article, interfacial impedance at the electrode/electrolyte interface is investigated considering channel height and Debye length effects on characteristic time scale in a binary electrolyte solution using parallel plate electrode configuration...
November 7, 2017: Analytical Chemistry
https://www.readbyqxmd.com/read/29016604/novel-fine-scale-aerial-mapping-approach-quantifies-grassland-weed-cover-dynamics-and-response-to-management
#5
Carolyn M Malmstrom, H Scott Butterfield, Laura Planck, Christopher W Long, Valerie T Eviner
Invasive weeds threaten the biodiversity and forage productivity of grasslands worldwide. However, management of these weeds is constrained by the practical difficulty of detecting small-scale infestations across large landscapes and by limits in understanding of landscape-scale invasion dynamics, including mechanisms that enable patches to expand, contract, or remain stable. While high-end hyperspectral remote sensing systems can effectively map vegetation cover, these systems are currently too costly and limited in availability for most land managers...
2017: PloS One
https://www.readbyqxmd.com/read/28973890/fluctuation-enhanced-electric-conductivity-in-electrolyte-solutions
#6
Jean-Philippe Péraud, Andrew J Nonaka, John B Bell, Aleksandar Donev, Alejandro L Garcia
We analyze the effects of an externally applied electric field on thermal fluctuations for a binary electrolyte fluid. We show that the fluctuating Poisson-Nernst-Planck (PNP) equations for charged multispecies diffusion coupled with the fluctuating fluid momentum equation result in enhanced charge transport via a mechanism distinct from the well-known enhancement of mass transport that accompanies giant fluctuations. Although the mass and charge transport occurs by advection by thermal velocity fluctuations, it can macroscopically be represented as electrodiffusion with renormalized electric conductivity and a nonzero cation-anion diffusion coefficient...
October 10, 2017: Proceedings of the National Academy of Sciences of the United States of America
https://www.readbyqxmd.com/read/28957028/first-passage-time-memory-lifetimes-for-simple-multistate-synapses
#7
Terry Elliott
Memory models based on synapses with discrete and bounded strengths store new memories by forgetting old ones. Memory lifetimes in such memory systems may be defined in a variety of ways. A mean first passage time (MFPT) definition overcomes much of the arbitrariness and many of the problems associated with the more usual signal-to-noise ratio (SNR) definition. We have previously computed MFPT lifetimes for simple, binary-strength synapses that lack internal, plasticity-related states. In simulation we have also seen that for multistate synapses, optimality conditions based on SNR lifetimes are absent with MFPT lifetimes, suggesting that such conditions may be artifactual...
September 28, 2017: Neural Computation
https://www.readbyqxmd.com/read/28950646/regime-shifts-driven-by-dynamic-correlations-in-gene-expression-noise
#8
Yogita Sharma, Partha Sharathi Dutta
Gene expression is a noisy process that leads to regime shifts between alternative steady states among individual living cells, inducing phenotypic variability. The effects of white noise on the regime shift in bistable systems have been well characterized, however little is known about such effects of colored noise (noise with nonzero correlation time). Here, we show that noise correlation time, by considering a genetic circuit of autoactivation, can have a significant effect on the regime shift between distinct phenotypic states in gene expression...
August 2017: Physical Review. E
https://www.readbyqxmd.com/read/28950455/diffusive-transport-in-the-presence-of-stochastically-gated-absorption
#9
Paul C Bressloff, Bhargav R Karamched, Sean D Lawley, Ethan Levien
We analyze a population of Brownian particles moving in a spatially uniform environment with stochastically gated absorption. The state of the environment at time t is represented by a discrete stochastic variable k(t)∈{0,1} such that the rate of absorption is γ[1-k(t)], with γ a positive constant. The variable k(t) evolves according to a two-state Markov chain. We focus on how stochastic gating affects the attenuation of particle absorption with distance from a localized source in a one-dimensional domain...
August 2017: Physical Review. E
https://www.readbyqxmd.com/read/28950449/diffuse-charge-dynamics-in-ionic-thermoelectrochemical-systems
#10
Robert F Stout, Aditya S Khair
Thermoelectrics are increasingly being studied as promising electrical generators in the ongoing search for alternative energy sources. In particular, recent experimental work has examined thermoelectric materials containing ionic charge carriers; however, the majority of mathematical modeling has been focused on their steady-state behavior. Here, we determine the time scales over which the diffuse charge dynamics in ionic thermoelectrochemical systems occur by analyzing the simplest model thermoelectric cell: a binary electrolyte between two parallel, blocking electrodes...
August 2017: Physical Review. E
https://www.readbyqxmd.com/read/28949644/driven-anisotropic-diffusion-at-boundaries-noise-rectification-and-particle-sorting
#11
Stefano Bo, Ralf Eichhorn
We study the diffusive dynamics of a Brownian particle in the proximity of a flat surface under nonequilibrium conditions, which are created by an anisotropic thermal environment with different temperatures being active along distinct spatial directions. By presenting the exact time-dependent solution of the Fokker-Planck equation for this problem, we demonstrate that the interplay between anisotropic diffusion and hard-core interaction with the plain wall rectifies the thermal fluctuations and induces directed particle transport parallel to the surface, without any deterministic forces being applied in that direction...
August 11, 2017: Physical Review Letters
https://www.readbyqxmd.com/read/28940114/fractional-poisson-nernst-planck-model-for-ion-channels-i-basic-formulations-and-algorithms
#12
Duan Chen
In this work, we propose a fractional Poisson-Nernst-Planck model to describe ion permeation in gated ion channels. Due to the intrinsic conformational changes, crowdedness in narrow channel pores, binding and trapping introduced by functioning units of channel proteins, ionic transport in the channel exhibits a power-law-like anomalous diffusion dynamics. We start from continuous-time random walk model for a single ion and use a long-tailed density distribution function for the particle jump waiting time, to derive the fractional Fokker-Planck equation...
November 2017: Bulletin of Mathematical Biology
https://www.readbyqxmd.com/read/28863683/portable-double-sided-pulsed-laser-heating-system-for-time-resolved-geoscience-and-materials-science-applications
#13
G Aprilis, C Strohm, I Kupenko, S Linhardt, A Laskin, D M Vasiukov, V Cerantola, E G Koemets, C McCammon, A Kurnosov, A I Chumakov, R Rüffer, N Dubrovinskaia, L Dubrovinsky
A portable double-sided pulsed laser heating system for diamond anvil cells has been developed that is able to stably produce laser pulses as short as a few microseconds with repetition frequencies up to 100 kHz. In situ temperature determination is possible by collecting and fitting the thermal radiation spectrum for a specific wavelength range (particularly, between 650 nm and 850 nm) to the Planck radiation function. Surface temperature information can also be time-resolved by using a gated detector that is synchronized with the laser pulse modulation and space-resolved with the implementation of a multi-point thermal radiation collection technique...
August 2017: Review of Scientific Instruments
https://www.readbyqxmd.com/read/28835930/probing-topology-by-heating-quantized-circular-dichroism-in-ultracold-atoms
#14
Duc Thanh Tran, Alexandre Dauphin, Adolfo G Grushin, Peter Zoller, Nathan Goldman
We reveal an intriguing manifestation of topology, which appears in the depletion rate of topological states of matter in response to an external drive. This phenomenon is presented by analyzing the response of a generic two-dimensional (2D) Chern insulator subjected to a circular time-periodic perturbation. Because of the system's chiral nature, the depletion rate is shown to depend on the orientation of the circular shake; taking the difference between the rates obtained from two opposite orientations of the drive, and integrating over a proper drive-frequency range, provides a direct measure of the topological Chern number (ν) of the populated band: This "differential integrated rate" is directly related to the strength of the driving field through the quantized coefficient η0 = ν/ℏ(2), where h = 2π ℏ is Planck's constant...
August 2017: Science Advances
https://www.readbyqxmd.com/read/28810751/communication-on-the-diffusion-tensor-in-macroscopic-theory-of-cavitation
#15
Vitaly A Shneidman
The classical description of nucleation of cavities in a stretched fluid relies on a one-dimensional Fokker-Planck equation (FPE) in the space of their sizes r, with the diffusion coefficient D(r) constructed for all r from macroscopic hydrodynamics and thermodynamics, as shown by Zeldovich. When additional variables (e.g., vapor pressure) are required to describe the state of a bubble, a similar approach to construct a diffusion tensor D^ generally works only in the direct vicinity of the thermodynamic saddle point corresponding to the critical nucleus...
August 14, 2017: Journal of Chemical Physics
https://www.readbyqxmd.com/read/28752421/modeling-a-si-epidemic-with-stochastic-transmission-hyperbolic-incidence-rate
#16
Alejandra Christen, M Angélica Maulén-Yañez, Eduardo González-Olivares, Michel Curé
In this paper a stochastic susceptible-infectious (SI) epidemic model is analysed, which is based on the model proposed by Roberts and Saha (Appl Math Lett 12: 37-41, 1999), considering a hyperbolic type nonlinear incidence rate. Assuming the proportion of infected population varies with time, our new model is described by an ordinary differential equation, which is analogous to the equation that describes the double Allee effect. The limit of the solution of this equation (deterministic model) is found when time tends to infinity...
July 27, 2017: Journal of Mathematical Biology
https://www.readbyqxmd.com/read/28674453/on-noise-resolution-uncertainty-in-quantum-field-theory
#17
Timur E Gureyev, Alexander Kozlov, Yakov I Nesterets, David M Paganin, Harry M Quiney
An uncertainty inequality is presented that establishes a lower limit for the product of the variance of the time-averaged intensity of a mode of a quantized electromagnetic field and the degree of its spatial localization. The lower limit is determined by the vacuum fluctuations within the volume corresponding to the width of the mode. This result also leads to a generalized form of the Heisenberg uncertainty principle for boson fields in which the lower limit for the product of uncertainties in the spatial and momentum localization of a mode is equal to the product of Planck's constant and a dimensionless functional which reflects the joint signal-to-noise ratio of the position and momentum of vacuum fluctuations in the region of the phase space occupied by the mode...
July 3, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28618562/evolution-of-moments-and-correlations-in-nonrenewal-escape-time-processes
#18
Wilhelm Braun, Rüdiger Thul, André Longtin
The theoretical description of nonrenewal stochastic systems is a challenge. Analytical results are often not available or can be obtained only under strong conditions, limiting their applicability. Also, numerical results have mostly been obtained by ad hoc Monte Carlo simulations, which are usually computationally expensive when a high degree of accuracy is needed. To gain quantitative insight into these systems under general conditions, we here introduce a numerical iterated first-passage time approach based on solving the time-dependent Fokker-Planck equation (FPE) to describe the statistics of nonrenewal stochastic systems...
May 2017: Physical Review. E
https://www.readbyqxmd.com/read/28589413/single-particle-brownian-motion-with-solid-friction
#19
Prasenjit Das, Sanjay Puri, Moshe Schwartz
We study the Brownian dynamics of a solid particle on a vibrating solid surface. Phenomenologically, the interaction between the two solid surfaces is modeled by solid friction, and the Gaussian white noise models the vibration of the solid surface. The solid friction force is proportional to the sign of relative velocity. We derive the Fokker-Planck (FP) equation for the time-dependent probability distribution to find the particle at a given location. We calculate analytically the steady state velocity distribution function, mean-square velocity and diffusion coefficient in d-dimensions...
June 2017: European Physical Journal. E, Soft Matter
https://www.readbyqxmd.com/read/28571349/asymmetric-osmotic-water-permeation-through-a-vesicle-membrane
#20
Jiaye Su, Yunzhen Zhao, Chang Fang, Yue Shi
Understanding the water permeation through a cell membrane is of primary importance for biological activities and a key step to capture its shape transformation in salt solution. In this work, we reveal the dynamical behaviors of osmotically driven transport of water molecules across a vesicle membrane by molecular dynamics simulations. Of particular interest is that the water transport in and out of vesicles is highly distinguishable given the osmotic force are the same, suggesting an asymmetric osmotic transportation...
May 28, 2017: Journal of Chemical Physics
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