247,394 research outputs found
Dynamic Model and Phase Transitions for Liquid Helium
This article presents a phenomenological dynamic phase transition theory --
modeling and analysis -- for superfluids. As we know, although the
time-dependent Ginzburg-Landau model has been successfully used in
superconductivity, and the classical Ginzburg-Landau free energy is still
poorly applicable to liquid helium in a quantitative sense. The study in this
article is based on 1) a new dynamic classification scheme of phase
transitions, 2) new time-dependent Ginzburg-Landau models for general
equilibrium transitions, and 3) the general dynamic transition theory. The
results in this article predict the existence of a unstable region H, where
both solid and liquid He II states appear randomly depending on fluctuations
and the existence of a switch point M on the lambda-curve, where the
transitions changes types
Analysing and attacking the 4-way handshake of IEEE 802.11i standard
The IEEE 802.11i standard has been designed to enhance security in wireless networks. In the 4-way handshake the supplicant and the authenticator use the pairwise master key (PMK) to derive a fresh pairwise transient key (PTK). The PMK is not used directly for security while assuming the supplicant and authenticator have the same PMK before running 4-way handshake. In this paper, the 4-way handshake phase has been analysed using Isabelle tool to identify a new Denial-of-Service (DoS) attack. The attack prevents the authenticator from receiving message 4 after the supplicant sends it out. This attack forces the authenticator to re-send the message 3 until time out and subsequently to de-authenticate supplicant. This paper has proposed improvements to the 4-way handshake to avoid the Denial-of-Service attack
Digital numerically controlled oscillator
The frequency and phase of an output signal from an oscillator circuit are controlled with accuracy by a digital input word. Positive and negative alterations in output frequency are both provided for by translating all values of input words so that they are positive. The oscillator reference frequency is corrected only in one direction, by adding phase to the output frequency of the oscillator. The input control word is translated to a single algebraic sign and the digital 1 is added thereto. The translated input control word is then accumulated. A reference clock signal having a frequency at an integer multiple of the desired frequency of the output signal is generated. The accumulated control word is then compared with a threshold level. The output signal is adjusted in a single direction by dividing the frequency of the reference clock signal by a first integer or by an integer different from the first integer
Quantum Correction in Exact Quantization Rules
An exact quantization rule for the Schr\"{o}dinger equation is presented. In
the exact quantization rule, in addition to , there is an integral term,
called the quantum correction. For the exactly solvable systems we find that
the quantum correction is an invariant, independent of the number of nodes in
the wave function. In those systems, the energy levels of all the bound states
can be easily calculated from the exact quantization rule and the solution for
the ground state, which can be obtained by solving the Riccati equation. With
this new method, we re-calculate the energy levels for the one-dimensional
systems with a finite square well, with the Morse potential, with the symmetric
and asymmetric Rosen-Morse potentials, and with the first and the second
P\"{o}schl-Teller potentials, for the harmonic oscillators both in one
dimension and in three dimensions, and for the hydrogen atom.Comment: 10 pages, no figure, Revte
Tetramixing of vector and pseudoscalar mesons: A source of intrinsic quarks
The tetramixing of pseudoscalar mesons --- and
vector mesons --- are studied in the light-cone
constituent quark model, and such mixing of four mesons provides a natural
source for the intrinsic charm components of light mesons. By mixing
with the light mesons, the charmonium states and could decay
into light mesons more naturally, without introducing gluons or a virtual
photon as intermediate states. Thus, the introduction of light quark components
into is helpful to reproduce the new experimental data of
decays. The mixing matrices and the behaviors of the transition form
factors are also calculated and compared with experimental data.Comment: 20 pages, 10 figures. Version for publication in PR
High--Resolution 3D Simulations of Relativistic Jets
We have performed high-resolution 3D simulations of relativistic jets with
beam flow Lorentz factors up to 7, a spatial resolution of 8 cells per beam
radius, and for up to 75 normalized time units to study the morphology and
dynamics of 3D relativistic jets. Our simulations show that the coherent fast
backflows found in axisymmetric models are not present in 3D models. We further
find that when the jet is exposed to non-axisymmetric perturbations, (i) it
does not display the strong perturbations found for 3D classical hydrodynamic
and MHD jets (at least during the period of time covered by our simulations),
and (ii) it does propagate according to the 1D estimate. Small 3D effects in
the relativistic beam give rise to a lumpy distribution of apparent speeds like
that observed in M87. The beam is surrounded by a boundary layer of high
specific internal energy. The properties of this layer are briefly discussed.Comment: 15 pages, 4 figures. Accepted to be publish in the ApJ Letters.
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The first coefficients of the asymptotic expansion of the Bergman kernel of the spin^c Dirac operator
We establish the existence of the asymptotic expansion of the Bergman kernel
associated to the spin-c Dirac operators acting on high tensor powers of line
bundles with non-degenerate mixed curvature (negative and positive eigenvalues)
by extending the paper " On the asymptotic expansion of Bergman kernel "
(math.DG/0404494) of Dai-Liu-Ma. We compute the second coefficient b_1 in the
asymptotic expansion using the method of our paper "Generalized Bergman kernels
on symplectic manifolds" (math.DG/0411559).Comment: 21 pages, to appear in Internat. J. Math. Precisions added in the
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