1,103 research outputs found
An Quantum Kinetic Monte Carlo Method For Lindblad Equation
In this paper, we generalize the Quantum Kinetic Monte Carlo (QKMC) method of
the Schrodinger equation, which was first proposed by [Z. Cai and J. Lu. SIAM
J. Sci. Comput., 40(3):B706-B722, 2018] to the Lindblad equation. This
algorithm makes full use of the tensor product structure of the matrices in the
Lindblad equation, thus significantly reducing the storage cost, and can
calculate a more extensive system than the existing methods. We demonstrate the
method in the framework of the dissipative Ising model, and numerical
experiments verify the validity of the method and the error analysis
Development of molecular approaches in the study of lettuce downy mildew (Bremia lactucae) population biology
Downy mildew of lettuce caused by Bremia lactucae is a serious disease resulting in
yield loss. The population structure of the pathogen in the UK is poorly understood.
This PhD project concentrated on developing molecular markers to differentiate the
genotypic variation of B. lactucae populations, with the aim of improving methods to
investigate lettuce - Bremia interactions. Thirty-seven B. lactucae isolates (including
single-spore and new field isolates) were collected and characterized for virulence
using the conventional International Bremia Evaluation Board (IBEB) differential set.
Microsatellite markers (SSR, ISSR) were investigated for Bremia race specific
marker development. Three isolates of B. lactucae were characterized by ISSR (inter
simple sequence repeat) primers, although the polymorphic DNA could not be cloned
in this project due to the highly variable results of the ISSR process. Some
microsatellite repeats were found in B. lactucae isolates sequences that amplified by
Plasmopara viticola (grape downy mildew) SSR markers. The development of
Simple Sequence Repeat (SSR) markers from Bremia genomic DNA was not
successful, which might result from the primers used being unsuitable for Bremia
microsatellite enrichment. Bremia specific ITS primers were used for quantitative
PCR. RxLR primers obtained from UC Davis (USA) were tested using the collection
of B. lactucae isolates. RxLR1 primers distinguished between isolates BL801 and
BL806. Eight SNPs were identified in three isolates amplified by RxLR5. No
polymorphism was observed on the gel for the remaining RxLR primers on single
spore races. Unrefined field isolates showed more polymorphisms on the gel than
single spore isolates. The phenotypic differences between these two isolates have
been identified by the IBEB differential set. Microscopy and qPCR quantification
were used to investigate the compatible and incompatible interactions. The results
suggest that BL801 is more virulent than BL806, as more infection structures were
observed in IBEB resistant cultivars. Results of qPCR and spore count/unit weight of
cotyledons showed that BL801 and BL806 were significantly different. The qPCR
quantification results from 4 and 5 dpi were correlated with the spore count/unit
weight of cotyledons. Although further work is required to develop race specific
markers, the methods used in this project demonstrate the potential use of molecular
markers to investigate lettuce - Bremia interactions
Efficient Frozen Gaussian Sampling Algorithms for Nonadiabatic Quantum Dynamics at Metal Surfaces
In this article, we propose a Frozen Gaussian Sampling (FGS) algorithm for
simulating nonadiabatic quantum dynamics at metal surfaces with a continuous
spectrum. This method consists of a Monte-Carlo algorithm for sampling the
initial wave packets on the phase space and a surface-hopping type stochastic
time propagation scheme for the wave packets. We prove that to reach a certain
accuracy threshold, the sample size required is independent of both the
semiclassical parameter and the number of metal orbitals ,
which makes it one of the most promising methods to study the nonadiabatic
dynamics. The algorithm and its convergence properties are also validated
numerically. Furthermore, we carry out numerical experiments including
exploring the nuclei dynamics, electron transfer and finite-temperature
effects, and demonstrate that our method captures the physics which can not be
captured by classical surface hopping trajectories.Comment: 41 pages, 10 figure
An efficient iterative method for dynamical Ginzburg-Landau equations
In this paper, we propose a new finite element approach to simulate the
time-dependent Ginzburg-Landau equations under the temporal gauge, and design
an efficient preconditioner for the Newton iteration of the resulting discrete
system. The new approach solves the magnetic potential in H(curl) space by the
lowest order of the second kind Nedelec element. This approach offers a simple
way to deal with the boundary condition, and leads to a stable and reliable
performance when dealing with the superconductor with reentrant corners. The
comparison in numerical simulations verifies the efficiency of the proposed
preconditioner, which can significantly speed up the simulation in large-scale
computations
Theoretical and experimental evidence on stock market volatilities: a two-phase flow model
The volumeāvolatility relationship usually ignores possible effects
of stock shares. This article proposes a two-phase flow model
assuming that capital and stock flows determine stock price and
return volatility. Computational simulations suggest that monodirectional capital or stock flows and collective flows exert different
effects on stock return volatilities. Considering the impact of stock
flows, the positive relationship between capital and return volatility is no longer guaranteed. The inflow of capital and the outflow
of stock increase stock price similarly; but exhibit completely different effects on stock return volatilities. A persistent stock inflow
(outflow) reduces (intensifies) return volatilities, whereas a monodirectional persistent capital outflow has no such effect. When
capital and stock flowsā velocities satisfy critical values determined
by the initial state of the market, the market enlargement accompanied with increasing stock and capital shows no impact on
market stability because of stable return volatilities. Otherwise,
stock flows drive return volatilities with stronger effects than capital flows. Further experimental studies that simulate the real
stock market through a trading system provide strong evidence
supporting the two-phase flow model. Given similar driving forces
of capital and stock flows, the interaction of them should be considered in constructing investment strategies and setting polici
Short-term Traffic Flow Prediction Based on Genetic Artificial Neural Network and Exponential Smoothing
In order to improve the accuracy of short-term traffic flow prediction, a combined model composed of artificial neural network optimized by using Genetic Algorithm (GA) and Exponential Smoothing (ES) has been proposed. By using the metaheuristic optimal search ability of GA, the connection weight and threshold of the feedforward neural network trained by a backpropagation algorithm are optimized to avoid the feedforward neural network falling into local optimum, and the prediction model of Genetic Artificial Neural Network (GANN) is established. An ES prediction model is presented then. In order to take the advantages of the two models, the combined model is composed of a weighted average, while the weight of the combined model is determined according to the prediction mean square error of the single model. The road traffic flow data of Xuancheng, Anhui Province with an observation interval of 5 min are used for experimental verification. Additionally, the feedforward neural network model, GANN model, ES model and combined model are compared and analysed, respectively. The results show that the prediction accuracy of the optimized feedforward neural network is much higher than that before the optimization. The prediction accuracy of the combined model is higher than that of the two single models, which verifies the feasibility and effectiveness of the combined model
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