22,884 research outputs found
On the dynamics of random neuronal networks
We study the mean-field limit and stationary distributions of a pulse-coupled
network modeling the dynamics of a large neuronal assemblies. Our model takes
into account explicitly the intrinsic randomness of firing times, contrasting
with the classical integrate-and-fire model. The ergodicity properties of the
Markov process associated to finite networks are investigated. We derive the
limit in distribution of the sample path of the state of a neuron of the
network when its size gets large. The invariant distributions of this limiting
stochastic process are analyzed as well as their stability properties. We show
that the system undergoes transitions as a function of the averaged
connectivity parameter, and can support trivial states (where the network
activity dies out, which is also the unique stationary state of finite networks
in some cases) and self-sustained activity when connectivity level is
sufficiently large, both being possibly stable.Comment: 37 pages, 3 figure
Magnetic Nernst effect
The thermodynamics of irreversible processes in continuous media predicts the
existence of a Magnetic Nernst effect that results from a magnetic analog to
the Seebeck effect in a ferromagnet and magnetophoresis occurring in a
paramagnetic electrode in contact with the ferromagnet. Thus, a voltage that
has DC and AC components is expected across a Pt electrode as a response to the
inhomogeneous magnetic induction field generated by magnetostatic waves of an
adjacent YIG slab subject to a temperature gradient. The voltage frequency and
dependence on the orientation of the applied magnetic induction field are quite
distinct from that of spin pumping.Comment: 4 pages, 1 figur
Nano-structures at martensite macrotwin interfaces in
The atomic configurations at macrotwin interfaces between microtwinned martensite plates in material are investigated using transmission electron microscopy. The observed structures are interpreted in view of possible formation mechanisms for these interfaces. A distinction is made between cases in which the microtwins, originating from mutually perpendicular \{110\} austenite planes, enclose a final angle larger or smaller than . Two different configurations, a crossing and a step type are described. Depending on the actual case, tapering, bending and tip splitting of the smaller microtwin variants are observed. The most reproducible deformations occur in a region of approximately 5-10nm width around the interface while a variety of structural defects are observed further away from the interface. These structures and deformations are interpreted in terms of the coalescence of two separately nucleated microtwinned martensite plates and the need to accommodate remaining stresses
A periodic microfluidic bubbling oscillator: insight into the stability of two-phase microflows
This letter describes a periodically oscillating microfoam flow. For constant
input parameters, both the produced bubble volume and the flow rate vary over a
factor two. We explicit the link between foam topology alternance and flow rate
changes, and construct a retroaction model where bubbles still present
downstream determine the volume of new bubbles, in agreement with experiment.
This gives insight into the various parameters important to maintain
monodispersity and at the same time shows a method to achieve controlled
polydispersity.Comment: 4 page
A rigorous proof of the Landau-Peierls formula and much more
We present a rigorous mathematical treatment of the zero-field orbital
magnetic susceptibility of a non-interacting Bloch electron gas, at fixed
temperature and density, for both metals and semiconductors/insulators. In
particular, we obtain the Landau-Peierls formula in the low temperature and
density limit as conjectured by T. Kjeldaas and W. Kohn in 1957.Comment: 30 pages - Accepted for publication in A.H.
Testing and tuning symplectic integrators for Hybrid Monte Carlo algorithm in lattice QCD
We examine a new 2nd order integrator recently found by Omelyan et al. The
integration error of the new integrator measured in the root mean square of the
energy difference, \bra\Delta H^2\ket^{1/2}, is about 10 times smaller than
that of the standard 2nd order leapfrog (2LF) integrator. As a result, the step
size of the new integrator can be made about three times larger. Taking into
account a factor 2 increase in cost, the new integrator is about 50% more
efficient than the 2LF integrator. Integrating over positions first, then
momenta, is slightly more advantageous than the reverse. Further parameter
tuning is possible. We find that the optimal parameter for the new integrator
is slightly different from the value obtained by Omelyan et al., and depends on
the simulation parameters. This integrator could also be advantageous for the
Trotter-Suzuki decomposition in Quantum Monte Carlo.Comment: 14 pages, 6 figure
Computation of maximal local (un)stable manifold patches by the parameterization method
In this work we develop some automatic procedures for computing high order
polynomial expansions of local (un)stable manifolds for equilibria of
differential equations. Our method incorporates validated truncation error
bounds, and maximizes the size of the image of the polynomial approximation
relative to some specified constraints. More precisely we use that the manifold
computations depend heavily on the scalings of the eigenvectors: indeed we
study the precise effects of these scalings on the estimates which determine
the validated error bounds. This relationship between the eigenvector scalings
and the error estimates plays a central role in our automatic procedures. In
order to illustrate the utility of these methods we present several
applications, including visualization of invariant manifolds in the Lorenz and
FitzHugh-Nagumo systems and an automatic continuation scheme for (un)stable
manifolds in a suspension bridge problem. In the present work we treat
explicitly the case where the eigenvalues satisfy a certain non-resonance
condition.Comment: Revised version, typos corrected, references adde
Auto-dual connected operators based on iterative merging algorithms
This paper proposes a new set of connected operators that are autodual. Classical connected operators are analyzed within the framework of merging algorithms. The discussion highlights three basic notions: merging order , merging criterion and region model. As a result a general merging algorithm is proposed. It can be used to create new connected operators and in particular autodual operators. Implementation issues are also discussed.Peer ReviewedPostprint (published version
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