11,737 research outputs found
Probability tilting of compensated fragmentations
Fragmentation processes are part of a broad class of models describing the
evolution of a system of particles which split apart at random. These models
are widely used in biology, materials science and nuclear physics, and their
asymptotic behaviour at large times is interesting both mathematically and
practically. The spine decomposition is a key tool in its study. In this work,
we consider the class of compensated fragmentations, or homogeneous
growth-fragmentations, recently defined by Bertoin. We give a complete spine
decomposition of these processes in terms of a L\'evy process with immigration,
and apply our result to study the asymptotic properties of the derivative
martingale.Comment: 41 pages, 1 figure. This revised version improves the conditions in
Theorem 6.
Convergent-divergent nozzle flows
Uniform two-zone perfect gas expansions in convergent-divergent nozzle
Rigorous Proof of Pseudospin Ferromagnetism in Two-Component Bosonic Systems with Component-Independent Interactions
For a two-component bosonic system, the components can be mapped onto a
pseudo-spin degree of freedom with spin quantum number S=1/2. We provide a
rigorous proof that for a wide-range of real Hamiltonians with component
independent mass and interaction, the ground state is a ferromagnetic state
with pseudospin fully polarized. The spin-wave excitations are studied and
found to have quadratic dispersion relations at long wave length.Comment: 4 pages, no figur
A mechanism to pin skyrmions in chiral magnets
We propose a mechanism to pin skyrmions in chiral magnets by introducing
local maximum of magnetic exchange strength, which can be realized in chiral
magnetic thin films by engineering the local density of itinerate electrons.
Thus we find a way to artificially control the position of a single skyrmion in
chiral magnetic thin films. The stationary properties and the dynamical pinning
and depinning processes of an isolated skyrmion around a pinning center are
studied. We do a series of simulations to show that the critical current to
depin a skyrmion has linearly dependence on the pinning strength. We also
estimate the critical current to have order of magnitude
10^{7}\sim10^{8}A/m^{2}
Axisymmetric reacting gas nonequilibrium performance program
Computer program calculates the inviscid one-dimensional equilibrium, frozen, and nonequilibrium nozzle expansion of propellant exhaust mixtures containing these six elements - carbon, hydrogen, oxygen, nitrogen, fluorine, and chlorine plus either aluminum, beryllium, boron or lithium. This program will perform calculations for contoured and conical nozzles
Space shuttle: Supersonic aerodynamic characteristics of the MSC 040A orbiter (M equals 2.0 to 4.0)
A wind tunnel test of the space shuttle orbiter configuration 040A was run in a 20 in. supersonic wind tunnel. Basic aerodynamic data for this vehicle were determined at Mach 2.0, 2.4, 3.0 and 4.0
Origin of Low Thermal Conductivity in Nuclear Fuels
Using a novel many-body approach, we report lattice dynamical properties of
UO2 and PuO2 and uncover various contributions to their thermal conductivities.
Via calculated Grueneisen constants, we show that only longitudinal acoustic
modes having large phonon group velocities are efficient heat carriers. Despite
the fact that some optical modes also show their velocities which are extremely
large, they do not participate in the heat transfer due to their unusual
anharmonicity. Ways to improve thermal conductivity in these materials are
discussed.Comment: 4 pages, 3 figures, 1 tabl
Numerical and Monte Carlo Bethe ansatz method: 1D Heisenberg model
In this paper we present two new numerical methods for studying thermodynamic
quantities of integrable models. As an example of the effectiveness of these
two approaches, results from numerical solutions of all sets of Bethe ansatz
equations, for small Heisenberg chains, and Monte Carlo simulations in
quasi-momentum space, for a relatively larger chains, are presented. Our
results agree with those obtained by thermodynamics Bethe ansatz (TBA) and
Quantum Transfer Matrix (QTM).Comment: 8 pages, 6 figure
The role of inter-well tunneling strength on coherence dynamics of two-species Bose-Einstein condensates
Coherence dynamics of two-species Bose-Einstein condensates in double wells
is investigated in mean field approximation. We show that the system can
exhibit decoherence phenomena even without the condensate-environment coupling
and the variation tendency of the degree of coherence depends on not only the
parameters of the system but also the initial states. We also investigate the
time evolution of the degree of coherence for a Rosen-Zener form of tunneling
strength, and propose a method to get a condensate system with certain degree
of coherence through a time-dependent tunneling strength
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