511 research outputs found
Observation of two-wave structure in strongly nonlinear dissipative granular chains
In a strongly nonlinear viscous granular chain under conditions of loading
that exclude stationary waves (e.g., impact by a single grain) we observe a
pulse that consists of two interconnected but distinct parts. One is a leading
narrow "primary pulse" with properties similar to a solitary wave in a "sonic
vacuum." It arises from strong nonlinearity and discreteness in the absence of
dissipation, but now decays due to viscosity. The other is a broad, much more
persistent shock-like "secondary pulse" trailing the primary pulse and caused
by viscous dissipation. The medium behind the primary pulse is transformed from
a "sonic vacuum" to a medium with finite sound speed. When the rapidly decaying
primary pulse dies, the secondary pulse continues to propagate in the "sonic
vacuum," with an oscillatory front if the viscosity is relatively small, until
its eventual (but very slow) disintegration. Beyond a critical viscosity there
is no separation of the two pulses, and the dissipation and nonlinearity
dominate the shock-like attenuating pulse which now exhibits a nonoscillatory
front
Momentum distribution in heavy deformed nuclei: role of effective mass
The impact of nuclear deformation on the momentum distributions (MD) of
occupied proton states in U is studied with a phenomenological
Woods-Saxon (WS) shell model and the self-consistent Skyrme-Hartree-Fock (SHF)
scheme. Four Skyrme parameterizations (SkT6, SkM*, SLy6, SkI3) with different
effective masses are used. The calculations reveal significant deformation
effects in the low-momentum domain of states, mainly of
those lying near the Fermi surface. For other states, the deformation effect on
MD is rather small and may be neglected. The most remarkable result is that the
very different Skyrme parameterizations and the WS potential give about
identical MD. This means that the value of effective mass, being crucial for
the description of the spectra, is not important for the spatial shape of the
wave functions and thus for the MD. In general, it seems that, for the
description of MD at MeV/c, one may use any single-particle
scheme (phenomenological or self-consistent) fitted properly to the global
ground state properties.Comment: 14 pages, 6 figure
A thick shell Casimir effect
We consider the Casimir energy of a thick dielectric-diamagnetic shell under
a uniform velocity light condition, as a function of the radii and the
permeabilities. We show that there is a range of parameters in which the stress
on the outer shell is inward, and a range where the stress on the outer shell
is outward. We examine the possibility of obtaining an energetically stable
configuration of a thick shell made of a material with a fixed volume
Self-Consistent Separable Rpa Approach for Skyrme Forces: Axial Nuclei
The self-consistent separable RPA (random phase approximation) method is
formulated for Skyrme forces with pairing. The method is based on a general
self-consistent procedure for factorization of the two-body interaction. It is
relevant for various density- and current-dependent functionals. The
contributions of the time-even and time-odd Skyrme terms as well as of the
Coulomb and pairing terms to the residual interaction are taken
self-consistently into account. Most of the expression have a transparent
analytical form, which makes the method convenient for the treatment and
analysis. The separable character of the residual interaction allows to avoid
diagonalization of high-rank RPA matrices and thus to minimize the calculation
effort. The previous studies have demonstrated high numerical accuracy and
efficiency of the method for spherical nuclei. In this contribution, the method
is specified for axial nuclei. We provide systematic and detailed presentation
of formalism and discuss different aspects of the model.Comment: 42 page
Role of the rho meson in the description of pion electroproduction experiments at JLab
We study the p(e,e' pi+)n reaction in the framework of an effective
Lagrangian approach including nucleon, pi and rho meson degrees of freedom and
show the importance of the rho-meson t-pole contribution to sigmaT, the
transverse part of cross section. We test two different field representations
of the rho meson, vector and tensor, and find that the tensor representation of
the rho meson is more reliable in the description of the existing data. In
particular, we show that the rho-meson t-pole contribution, including the
interference with an effective non-local contact term, sufficiently improves
the description of the recent JLab data at invariant mass W less 2.2 GeV and Q2
less 2.5 GeV2/c2. A ``soft'' variant of the strong piNN and rhoNN form factors
is also found to be compatible with these data. On the basis of the successful
description of both the sigmaL and sigmaT parts of the cross section we discuss
the importance of taking into account the sigmaT data when extracting the
charge pion form factor Fpi from sigmaL.Comment: 23 pages, 6 figures, accepted for publication in Phys. Rev.
On the instability of classical dynamics in theories with higher derivatives
The development of instability in the dynamics of theories with higher
derivatives is traced in detail in the framework of the Pais-Uhlenbeck fourth
oder oscillator. For this aim the external friction force is introduced in the
model and the relevant solutions to equations of motion are investigated. As a
result, the physical implication of the energy unboundness from below in
theories under consideration is revealed.Comment: 9 pages, no figures and no tables, revtex4; a few misprints are
correcte
Effect of the anisotropy of monocrystalline silicon mechanical properties on the dynamic characteristics of a micromechanical gyroscope
The aim of the research was to determine the effect of temperature on mechanical properties of a micromechanical gyroscope with the sensing element mounted on a silicon wafer, with the crystallographic orientation of (100) (110) (111). The research is of current relevancy since the metrological characteristics that depend on the eigenfrequencies over the full temperature range are to be controlled. The temperature-modal analysis of the micromechanical gyroscope model was performed with ANSYS program. The temperature dependence for eigenfrequencies was obtained. The dependence of the scale factor on temperature for the most temperature-independent variant of sensor positioning on the wafer was determined. The developed mathematical model was used to find the forms of the output oscillations of the gyroscope
Two-Photon Excitation of Low-Lying Electronic Quadrupole States in Atomic Clusters
A simple scheme of population and detection of low-lying electronic
quadrupole modes in free small deformed metal clusters is proposed. The scheme
is analyzed in terms of the TDLDA (time-dependent local density approximation)
calculations. As test case, the deformed cluster is considered.
Long-living quadrupole oscillations are generated via resonant two-photon
(two-dipole) excitation and then detected through the appearance of satellites
in the photoelectron spectra generated by a probe pulse. Femtosecond pump and
probe pulses with intensities and
pulse duration fs are found to be optimal. The modes of
interest are dominated by a single electron-hole pair and so their energies,
being combined with the photoelectron data for hole states, allow to gather new
information about mean-field spectra of valence electrons in the HOMO-LUMO
region. Besides, the scheme allows to estimate the lifetime of electron-hole
pairs and hence the relaxation time of electronic energy into ionic heat.Comment: 4 pages, 4 figure
Quark mass correction to the string potential
A consistent method for calculating the interquark potential generated by the
relativistic string with massive ends is proposed. In this approach the
interquark potential in the model of the Nambu--Goto string with point--like
masses at its ends is calculated. At first the calculation is done in the
one--loop approximation and then the variational estimation is performed. The
quark mass correction results in decreasing the critical distance
(deconfinement radius). When quark mass decreases the critical distance also
decreases. For obtaining a finite result under summation over eigenfrequencies
of the Nambu--Goto string with massive ends a suitable mode--by--mode
subtraction is proposed. This renormalization procedure proves to be completely
unique. In the framework of the developed approach the one--loop interquark
potential in the model of the relativistic string with rigidity is also
calculated.Comment: 34 pages, LATE
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