506 research outputs found
Algebraic structure of stochastic expansions and efficient simulation
We investigate the algebraic structure underlying the stochastic Taylor
solution expansion for stochastic differential systems.Our motivation is to
construct efficient integrators. These are approximations that generate strong
numerical integration schemes that are more accurate than the corresponding
stochastic Taylor approximation, independent of the governing vector fields and
to all orders. The sinhlog integrator introduced by Malham & Wiese (2009) is
one example. Herein we: show that the natural context to study stochastic
integrators and their properties is the convolution shuffle algebra of
endomorphisms; establish a new whole class of efficient integrators; and then
prove that, within this class, the sinhlog integrator generates the optimal
efficient stochastic integrator at all orders.Comment: 19 page
Large current noise in nanoelectromechanical systems close to continuous mechanical instabilities
We investigate the current noise of nanoelectromechanical systems close to a
continuous mechanical instability. In the vicinity of the latter, the
vibrational frequency of the nanomechanical system vanishes, rendering the
system very sensitive to charge fluctuations and, hence, resulting in very
large (super-Poissonian) current noise. Specifically, we consider a suspended
single-electron transistor close to the Euler buckling instability. We show
that such a system exhibits an exponential enhancement of the current noise
when approaching the Euler instability which we explain in terms of telegraph
noise.Comment: 11 pages, 12 figures; v2: minor changes, published versio
The governing bodies of Lutheran secondary schools in Australia : an exploratory study
The governing bodies of Lutheran secondary colleges and schools in Australia are comprised of a cross-section of community-minded people, who have accepted the invitation to serve as college council members. The council members bring a range of experiences and expertise to the task they have accepted. This paper profiles the membership of college councils. It reports, to a limited degree, the alignment or otherwise of the way councils operate against the expectation of the By-laws of the Lutheran Church of Australia in regard to the operation of college councils. The paper also explores the views of both council members and principals on some issues, and uncovers the degree of difference or similarity in these views. The research method used for the study is the survey technique. Questionnaires were sent to the principals, council members and council chairpersons of all the Lutheran secondary colleges in Australia, except one. The research reveals that there are a significant number of issues of organisation and behaviours of Councils on which there are quite differing views, both between Councils, between individual council members, and between councils and principals
Dynamic model of gene regulation for the lac operon
Gene regulatory network is a collection of DNA which interact with each other and with other matter in the cell. The lac operon is an example of a relatively simple genetic network and is one of the best-studied structures in the Escherichia coli bacteria. In this work we consider a deterministic model of the lac operon with a noise term, representing the stochastic nature of the regulation. The model is written in terms of a system of simultaneous first order differential equations with delays. We investigate an analytical and numerical solution and analyse the range of values for the parameters corresponding to a stable solution
Dimer diffusion in a washboard potential
The transport of a dimer, consisting of two Brownian particles bounded by a
harmonic potential, moving on a periodic substrate is investigated both
numerically and analytically. The mobility and diffusion of the dimer center of
mass present distinct properties when compared with those of a monomer under
the same transport conditions. Both the average current and the diffusion
coefficient are found to be complicated non-monotonic functions of the driving
force. The influence of dimer equilibrium length, coupling strength and damping
constant on the dimer transport properties are also examined in detail.Comment: Final revised version. 7 pages, 6 figure
Spatiotemporal Fluctuation Induced Transition in a Tumor Model with Immune Surveillance
We report on a simple model of spatial extend anti-tumor system with a
fluctuation in growth rate, which can undergo a nonequilibrium phase
transition. Three states as excited, sub-excited and non-excited states of a
tumor are defined to describe its growth. The multiplicative noise is found to
be double-face: The positive effect on a non-excited tumor and the negative
effect on an excited tumor.Comment: 8pages,5figure
Positive-P phase space method simulation in superradiant emission from a cascade atomic ensemble
The superradiant emission properties from an atomic ensemble with cascade
level configuration is numerically simulated. The correlated spontaneous
emissions (signal then idler fields) are purely stochastic processes which are
initiated by quantum fluctuations. We utilize the positive-P phase space method
to investigate the dynamics of the atoms and counter-propagating emissions. The
light field intensities are calculated, and the signal-idler correlation
function is studied for different optical depths of the atomic ensemble.
Shorter correlation time scale for a denser atomic ensemble implies a broader
spectral window needed to store or retrieve the idler pulse.Comment: To be published in Phys. Rev.
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