3,861 research outputs found
Mean first-passage times for an ac-driven magnetic moment of a nanoparticle
The two-dimensional backward Fokker-Planck equation is used to calculate the
mean first-passage times (MFPTs) of the magnetic moment of a nanoparticle
driven by a rotating magnetic field. It is shown that a magnetic field that is
rapidly rotating in the plane {\it perpendicular} to the easy axis of the
nanoparticle governs the MFPTs just in the same way as a static magnetic field
that is applied {\it along} the easy axis. Within this framework, the features
of the magnetic relaxation and net magnetization of systems composed of
ferromagnetic nanoparticles arising from the action of the rotating field are
revealed.Comment: 7 pages, 1 figur
Optimal discrete stopping times for reliability growth tests
Often, the duration of a reliability growth development test is specified in advance and the decision to terminate or continue testing is conducted at discrete time intervals. These features are normally not captured by reliability growth models. This paper adapts a standard reliability growth model to determine the optimal time for which to plan to terminate testing. The underlying stochastic process is developed from an Order Statistic argument with Bayesian inference used to estimate the number of faults within the design and classical inference procedures used to assess the rate of fault detection. Inference procedures within this framework are explored where it is shown the Maximum Likelihood Estimators possess a small bias and converges to the Minimum Variance Unbiased Estimator after few tests for designs with moderate number of faults. It is shown that the Likelihood function can be bimodal when there is conflict between the observed rate of fault detection and the prior distribution describing the number of faults in the design. An illustrative example is provided
Rapidly driven nanoparticles: Mean first-passage times and relaxation of the magnetic moment
We present an analytical method of calculating the mean first-passage times
(MFPTs) for the magnetic moment of a uniaxial nanoparticle which is driven by a
rapidly rotating, circularly polarized magnetic field and interacts with a heat
bath. The method is based on the solution of the equation for the MFPT derived
from the two-dimensional backward Fokker-Planck equation in the rotating frame.
We solve these equations in the high-frequency limit and perform precise,
numerical simulations which verify the analytical findings. The results are
used for the description of the rates of escape from the metastable domains
which in turn determine the magnetic relaxation dynamics. A main finding is
that the presence of a rotating field can cause a drastic decrease of the
relaxation time and a strong magnetization of the nanoparticle system. The
resulting stationary magnetization along the direction of the easy axis is
compared with the mean magnetization following from the stationary solution of
the Fokker-Planck equation.Comment: 24 pages, 4 figure
Strain induced electrochemical behaviors of ionic liquid electrolytes in an electrochemical double layer capacitor: Insights from molecular dynamics simulations.
Electrochemical Double Layer Capacitors (EDLCs) with ionic liquid electrolytes outperform conventional ones using aqueous and organic electrolytes in energy density and safety. However, understanding the electrochemical behaviors of ionic liquid electrolytes under compressive/tensile strain is essential for the design of flexible EDLCs as well as normal EDLCs, which are subject to external forces during assembly. Despite many experimental studies, the compression/stretching effects on the performance of ionic liquid EDLCs remain inconclusive and controversial. In addition, there is hardly any evidence of prior theoretical work done in this area, which makes the literature on this topic scarce. Herein, for the first time, we developed an atomistic model to study the processes underlying the electrochemical behaviors of ionic liquids in an EDLC under strain. Constant potential non-equilibrium molecular dynamics simulations are conducted for EMIM BF4 placed between two graphene walls as electrodes. Compared to zero strain, low compression of the EDLC resulted in compromised performance as the electrode charge density dropped by 29%, and the performance reduction deteriorated significantly with a further increase in compression. In contrast, stretching is found to enhance the performance by increasing the charge storage in the electrodes by 7%. The performance changes with compression and stretching are due to changes in the double-layer structure. In addition, an increase in the value of the applied potential during the application of strain leads to capacity retention with compression revealed by the newly performed simulations. [Abstract copyright: © 2023 Author(s). Published under an exclusive license by AIP Publishing.
Functional evaluation and testing of a newly developed Teleostâs Fish Otolith derived biocomposite coating for healthcare
Polymers such as polycaprolactone (PCL) possess biodegradability, biocompatibility and affinity with other organic media that makes them suitable for biomedical applications. In this work, a novel biocomposite coating was synthesised by mixing PCL with layers of calcium phosphate (hydroxyapatite, brushite and monetite) from a biomineral called otolith extracted from Teleost fish (Plagioscion Squamosissimus) and multiwalled carbon nanotubes in different concentrations (0.5, 1.0 and 1.5 g/L). The biocomposite coating was deposited on an osteosynthesis material Ti6Al4V by spin coating and various tests such as Fourier transformation infrared spectroscopy (FTIR), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), scratch tests, MTT reduction cytotoxicity, HOS cell bioactivity (human osteosarcoma) by alkaline phosphatase (ALP) and fluorescence microscopy were performed to comprehensively evaluate the newly developed biocoating. It was found that an increase in the concentration of carbon nanotube induced microstructural phase changes of calcium phosphate (CP) leading to the formation of brushite, monetite and hydroxyapatite. While we discovered that an increase in the concentration of carbon nanotube generally improves the adhesion of the coating with the substrate, a certain threshold exists such that the best deposition surfaces were obtained as PCL/CP/CNT 0.0 g/L and PCL/CP/CNT 0.5 g/L
Fractional diffusion modeling of ion channel gating
An anomalous diffusion model for ion channel gating is put forward. This
scheme is able to describe non-exponential, power-law like distributions of
residence time intervals in several types of ion channels. Our method presents
a generalization of the discrete diffusion model by Millhauser, Salpeter and
Oswald [Proc. Natl. Acad. Sci. USA 85, 1503 (1988)] to the case of a
continuous, anomalous slow conformational diffusion. The corresponding
generalization is derived from a continuous time random walk composed of
nearest neighbor jumps which in the scaling limit results in a fractional
diffusion equation. The studied model contains three parameters only: the mean
residence time, a characteristic time of conformational diffusion, and the
index of subdiffusion. A tractable analytical expression for the characteristic
function of the residence time distribution is obtained. In the limiting case
of normal diffusion, our prior findings [Proc. Natl. Acad. Sci. USA 99, 3552
(2002)] are reproduced. Depending on the chosen parameters, the fractional
diffusion model exhibits a very rich behavior of the residence time
distribution with different characteristic time-regimes. Moreover, the
corresponding autocorrelation function of conductance fluctuations displays
nontrivial features. Our theoretical model is in good agreement with
experimental data for large conductance potassium ion channels
Oscillatory behaviour in a lattice prey-predator system
Using Monte Carlo simulations we study a lattice model of a prey-predator
system. We show that in the three-dimensional model populations of preys and
predators exhibit coherent periodic oscillations but such a behaviour is absent
in lower-dimensional models. Finite-size analysis indicate that amplitude of
these oscillations is finite even in the thermodynamic limit. In our opinion,
this is the first example of a microscopic model with stochastic dynamics which
exhibits oscillatory behaviour without any external driving force. We suggest
that oscillations in our model are induced by some kind of stochastic
resonance.Comment: 7 pages, 10 figures, Phys.Rev.E (Nov. 1999
Universality of weak selection
Weak selection, which means a phenotype is slightly advantageous over
another, is an important limiting case in evolutionary biology. Recently it has
been introduced into evolutionary game theory. In evolutionary game dynamics,
the probability to be imitated or to reproduce depends on the performance in a
game. The influence of the game on the stochastic dynamics in finite
populations is governed by the intensity of selection. In many models of both
unstructured and structured populations, a key assumption allowing analytical
calculations is weak selection, which means that all individuals perform
approximately equally well. In the weak selection limit many different
microscopic evolutionary models have the same or similar properties. How
universal is weak selection for those microscopic evolutionary processes? We
answer this question by investigating the fixation probability and the average
fixation time not only up to linear, but also up to higher orders in selection
intensity. We find universal higher order expansions, which allow a rescaling
of the selection intensity. With this, we can identify specific models which
violate (linear) weak selection results, such as the one--third rule of
coordination games in finite but large populations.Comment: 12 pages, 3 figures, accepted for publication in Physical Review
- âŠ