17,885 research outputs found
Separability of a Low-Momentum Effective Nucleon-Nucleon Potential
A realistic nucleon-nucleon potential is transformed into a low-momentum
effective one (LMNN) using the Okubo theory. The separable potentials are
converted from the LMNN with a universal separable expansion method and a
simple Legendre expansion. Through the calculation of the triton binding
energies, the separability for the convergence of these ranks is evaluated. It
is found that there is a tendency for the lower momentum cutoff parameter
of LMNN to gain good separability.Comment: 6 pages, 1 tabl
Lepton asymmetry in the primordial gravitational wave spectrum
Effects of neutrino free streaming is evaluated on the primordial spectrum of
gravitational radiation taking both neutrino chemical potential and masses into
account. The former or the lepton asymmetry induces two competitive effects,
namely, to increase anisotropic pressure, which damps the gravitational wave
more, and to delay the matter-radiation equality time, which reduces the
damping. The latter effect is more prominent and a large lepton asymmetry would
reduce the damping. We may thereby be able to measure the magnitude of lepton
asymmetry from the primordial gravitational wave spectrum.Comment: 14 pages, 5 figure
New Universality of Lyapunov Spectra in Hamiltonian Systems
A new universality of Lyapunov spectra {\lambda_i} is shown for Hamiltonian
systems. The universality appears in middle energy regime and is different from
another universality which can be reproduced by random matrices in the
following two points. One is that the new universality appears in a limited
range of large i/N rather than the whole range, where N is degrees of freedom.
The other is Lyapunov spectra do not behave linearly while random matrices give
linear behavior even on 3D lattice. Quadratic terms with smaller nonlinear
terms of potential functions play an intrinsic role in the new universality.Comment: 19 pages, 16 Encapsulated Postscript figures, LaTeX (100 kb
Expectation values of chiral primary operators in holographic interface CFT
We consider the expectation values of chiral primary operators in the
presence of the interface in the 4 dimensional N=4 super Yang-Mills theory.
This interface is derived from D3-D5 system in type IIB string theory. These
expectation values are computed classically in the gauge theory side. On the
other hand, this interface is a holographic dual to type IIB string theory on
AdS_5 x S^5 spacetime with a probe D5-brane. The expectation values are
computed by GKPW prescription in the gravity side. We find non-trivial
agreement of these two results: the gauge theory side and the gravity side.Comment: 17pages, no figur
Density wave instability in a 2D dipolar Fermi gas
We consider a uniform dipolar Fermi gas in two-dimensions (2D) where the
dipole moments of fermions are aligned by an orientable external field. We
obtain the ground state of the gas in Hartree-Fock approximation and
investigate RPA stability against density fluctuations of finite momentum. It
is shown that the density wave instability takes place in a broad region where
the system is stable against collapse. We also find that the critical
temperature can be a significant fraction of Fermi temperature for a realistic
system of polar molecules.Comment: 10 figure
Security devices based on liquid crystals doped with a colour dye
Liquid crystal properties make them useful for the development of security devices in applications of authentication and detection of fakes. Induced orientation of liquid crystal molecules and birefringence are the two main properties used in security devices.
Employing liquid crystal and dichroic colorants, we have developed devices that show, with the aid of a polarizer, multiple images on each side of the device. Rubbed polyimide is used as alignment layer on each substrate of the LC cell. By rubbing the polyimide in different directions in each substrate it is possible to create any kind of symbols, drawings or motifs with a greyscale; the more complex the created device is, the more difficult is to fake it.
To identify the motifs it is necessary to use polarized light. Depending on whether the polarizer is located in front of the LC cell or behind it, different motifs from one or the other substrate are shown. The effect arises from the dopant colour dye added to the liquid crystal, the induced orientation and the twist structure. In practice, a grazing reflection on a dielectric surface is polarized enough to see the effect. Any LC flat panel display can obviously be used as backlight as well
Geometric Approach to Lyapunov Analysis in Hamiltonian Dynamics
As is widely recognized in Lyapunov analysis, linearized Hamilton's equations
of motion have two marginal directions for which the Lyapunov exponents vanish.
Those directions are the tangent one to a Hamiltonian flow and the gradient one
of the Hamiltonian function. To separate out these two directions and to apply
Lyapunov analysis effectively in directions for which Lyapunov exponents are
not trivial, a geometric method is proposed for natural Hamiltonian systems, in
particular. In this geometric method, Hamiltonian flows of a natural
Hamiltonian system are regarded as geodesic flows on the cotangent bundle of a
Riemannian manifold with a suitable metric. Stability/instability of the
geodesic flows is then analyzed by linearized equations of motion which are
related to the Jacobi equations on the Riemannian manifold. On some geometric
setting on the cotangent bundle, it is shown that along a geodesic flow in
question, there exist Lyapunov vectors such that two of them are in the two
marginal directions and the others orthogonal to the marginal directions. It is
also pointed out that Lyapunov vectors with such properties can not be obtained
in general by the usual method which uses linearized Hamilton's equations of
motion. Furthermore, it is observed from numerical calculation for a model
system that Lyapunov exponents calculated in both methods, geometric and usual,
coincide with each other, independently of the choice of the methods.Comment: 22 pages, 14 figures, REVTeX
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