853 research outputs found
Micromagnetic understanding of stochastic resonance driven by spin-transfertorque
In this paper, we employ micromagnetic simulations to study non-adiabatic
stochastic resonance (NASR) excited by spin-transfer torque in a
super-paramagnetic free layer nanomagnet of a nanoscale spin valve. We find
that NASR dynamics involves thermally activated transitions among two static
states and a single dynamic state of the nanomagnet and can be well understood
in the framework of Markov chain rate theory. Our simulations show that a
direct voltage generated by the spin valve at the NASR frequency is at least
one order of magnitude greater than the dc voltage generated off the NASR
frequency. Our computations also reproduce the main experimentally observed
features of NASR such as the resonance frequency, the temperature dependence
and the current bias dependence of the resonance amplitude. We propose a simple
design of a microwave signal detector based on NASR driven by spin transfer
torque.Comment: 25 pages 8 figures, accepted for pubblication on Phys. Rev.
PCN13 COST-EFFECTIVENESS OF HEPATIC ARTERY INFUSION FOR METASTATIC COLORECTAL CANCER (CALGB 9481)
Random walks on the Apollonian network with a single trap
Explicit determination of the mean first-passage time (MFPT) for trapping
problem on complex media is a theoretical challenge. In this paper, we study
random walks on the Apollonian network with a trap fixed at a given hub node
(i.e. node with the highest degree), which are simultaneously scale-free and
small-world. We obtain the precise analytic expression for the MFPT that is
confirmed by direct numerical calculations. In the large system size limit, the
MFPT approximately grows as a power-law function of the number of nodes, with
the exponent much less than 1, which is significantly different from the
scaling for some regular networks or fractals, such as regular lattices,
Sierpinski fractals, T-graph, and complete graphs. The Apollonian network is
the most efficient configuration for transport by diffusion among all
previously studied structure.Comment: Definitive version accepted for publication in EPL (Europhysics
Letters
Stochastic B\"acklund transformations
How does one introduce randomness into a classical dynamical system in order
to produce something which is related to the `corresponding' quantum system? We
consider this question from a probabilistic point of view, in the context of
some integrable Hamiltonian systems
Projected single-spin flip dynamics in the Ising Model
We study transition matrices for projected dynamics in the
energy-magnetization space, magnetization space and energy space. Several
single spin flip dynamics are considered such as the Glauber and Metropolis
canonical ensemble dynamics and the Metropolis dynamics for three
multicanonical ensembles: the flat energy-magnetization histogram, the flat
energy histogram and the flat magnetization histogram. From the numerical
diagonalization of the matrices for the projected dynamics we obtain the
sub-dominant eigenvalue and the largest relaxation times for systems of varying
size. Although, the projected dynamics is an approximation to the full state
space dynamics comparison with some available results, obtained by other
authors, shows that projection in the magnetization space is a reasonably
accurate method to study the scaling of relaxation times with system size. The
transition matrices for arbitrary single-spin flip dynamics are obtained from a
single Monte-Carlo estimate of the infinite temperature transition-matrix, for
each system size, which makes the method an efficient tool to evaluate the
relative performance of any arbitrary local spin-flip dynamics. We also present
new results for appropriately defined average tunnelling times of magnetization
and compute their finite-size scaling exponents that we compare with results of
energy tunnelling exponents available for the flat energy histogram
multicanonical ensemble.Comment: 23 pages and 6 figure
Rate-Based Transition Systems for Stochastic Process Calculi
A variant of Rate Transition Systems (RTS), proposed by Klin and Sassone, is introduced and used as the basic model for defining stochastic behaviour of processes. The transition relation used in our variant associates to each process, for each action, the set of possible futures paired with a measure indicating their rates. We show how RTS can be used for providing the operational semantics of stochastic extensions of classical formalisms, namely CSP and CCS. We also show that our semantics for stochastic CCS guarantees associativity of parallel composition. Similarly, in contrast with the original definition by Priami, we argue that a semantics for stochastic π-calculus can be provided that guarantees associativity of parallel composition
Hemorrhage associated with hepatic artery pseudoaneurysms after regional chemotherapy with floxuridine: case report
Pseudoaneurysms of the hepatic artery are a rare complication in patients with primary or secondary liver tumors treated with intra-arterial chemotherapy. We present two patients who developed this complication after placement of a catheter system into the gastroduodenal artery and initiation of regional chemotherapy with floxuridine. Diagnosis was made after symptomatic bleeding occurred, necessitating emergency angiography with coil embolization. Pseudoaneurysms usually occur after mechanical damage of the vessel wall, but the chemical toxicity of floxuridine may add to the development of vascular impairment
Evolution Equation of Phenotype Distribution: General Formulation and Application to Error Catastrophe
An equation describing the evolution of phenotypic distribution is derived
using methods developed in statistical physics. The equation is solved by using
the singular perturbation method, and assuming that the number of bases in the
genetic sequence is large. Applying the equation to the mutation-selection
model by Eigen provides the critical mutation rate for the error catastrophe.
Phenotypic fluctuation of clones (individuals sharing the same gene) is
introduced into this evolution equation. With this formalism, it is found that
the critical mutation rate is sometimes increased by the phenotypic
fluctuations, i.e., noise can enhance robustness of a fitted state to mutation.
Our formalism is systematic and general, while approximations to derive more
tractable evolution equations are also discussed.Comment: 22 pages, 2 figure
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