339 research outputs found
Stochastic Resonance in Washboard Potentials
We study the mobility of an overdamped particle in a periodic potential
tilted by a constant force. The mobility exhibits a stochastic resonance in
inhomogeneous systems with space dependent friction coefficient. The result
indicates that the presence of oscillating external field is not essential for
the observability of stochastic resonance, at least in the inhomogenous medium.Comment: 10 pages, 3 figure
Direct neutron capture cross sections of 62Ni in the s-process energy range
Direct neutron capture on 62Ni is calculated in the DWBA and the cross
sections in the energy range relevant for s-process nucleosynthesis are given.
It is confirmed that the thermal value of the capture cross section contains a
subthreshold resonance contribution. Contrary to previous investigations it is
found that the capture at higher energies is dominated by p-waves, thus leading
to a considerably increased cross section at s-process energies and a modified
energy dependence.Comment: 10 pages, 1 figure, corrected typos in Eq. 6 and subsequent paragrap
Motion in a rocked ratchet with spatially periodic friction
We present a detailed study of the transport and energetics of a Brownian
particle moving in a periodic potential in the presence of an adiabatic
external periodic drive. The particle is considered to move in a medium with
periodic space dependent friction with the same periodicity as that of the
potential but with a phase lag. We obtain several results, most of them arising
due to the medium being inhomogeneous and are sensitive to the phase lag. When
the potential is symmetric we show that efficiency of energy transduction can
be maximised as a function of noise strength or temperature. However, in the
case of asymmtertic potential the temperature may or may not facilitate the
energy conversion but current reversals can be obtained as a function of
temperature and the amplitude of the periodic drive. The reentrant behaviour of
current can also be seen as a function of phase lag
Quantum state-dependent diffusion and multiplicative noise: a microscopic approach
The state-dependent diffusion, which concerns the Brownian motion of a
particle in inhomogeneous media has been described phenomenologically in a
number of ways. Based on a system-reservoir nonlinear coupling model we present
a microscopic approach to quantum state-dependent diffusion and multiplicative
noise in terms of a quantum Markovian Langevin description and an associated
Fokker-Planck equation in position space in the overdamped limit. We examine
the thermodynamic consistency and explore the possibility of observing a
quantum current, a generic quantum effect, as a consequence of this
state-dependent diffusion similar to one proposed by B\"{u}ttiker [Z. Phys. B
{\bf 68}, 161 (1987)] in a classical context several years ago.Comment: To be published in Journal of Statistical Physics 28 pages, 3 figure
Uranium on uranium collisions at relativistic energies
Deformation and orientation effects on compression, elliptic flow and
particle production in uranium on uranium collisions (UU) at relativistic
energies are studied within the transport model ART. The density compression in
tip-tip UU collisions is found to be about 30% higher and lasts approximately
50% longer than in body-body or spherical UU reactions. The body-body UU
collisions have the unique feature that the nucleon elliptic flow is the
highest in the most central collisions and remain a constant throughout the
reaction. We point out that the tip-tip UU collisions are more probable to
create the QGP at AGS and SPS energies while the body-body UU collisions are
more useful for studying properties of the QGP at higher energies.Comment: 8 pages + 4 figure
Infinitesimal and local convexity of a hypersurface in a semi-Riemannian manifold
Given a Riemannian manifold M and a hypersurface H in M, it is well known
that infinitesimal convexity on a neighborhood of a point in H implies local
convexity. We show in this note that the same result holds in a semi-Riemannian
manifold. We make some remarks for the case when only timelike, null or
spacelike geodesics are involved. The notion of geometric convexity is also
reviewed and some applications to geodesic connectedness of an open subset of a
Lorentzian manifold are given.Comment: 14 pages, AMSLaTex, 2 figures. v2: typos fixed, added one reference
and several comments, statement of last proposition correcte
Profiles of emission lines generated by rings orbiting braneworld Kerr black holes
In the framework of the braneworld models, rotating black holes can be
described by the Kerr metric with a tidal charge representing the influence of
the non-local gravitational (tidal) effects of the bulk space Weyl tensor onto
the black hole spacetime. We study the influence of the tidal charge onto
profiled spectral lines generated by radiating tori orbiting in vicinity of a
rotating black hole. We show that with lowering the negative tidal charge of
the black hole, the profiled line becomes to be flatter and wider keeping their
standard character with flux stronger at the blue edge of the profiled line.
The extension of the line grows with radius falling and inclination angle
growing. With growing inclination angle a small hump appears in the profiled
lines due to the strong lensing effect of photons coming from regions behind
the black hole. For positive tidal charge () and high inclination angles
two small humps appear in the profiled lines close to the red and blue edge of
the lines due to the strong lensing effect. We can conclude that for all values
of , the strongest effect on the profiled lines shape (extension) is caused
by the changes of the inclination angle.Comment: Accepted by General Relativity and Gravitatio
Structure and phase-composition of Ti-doped gas atomized Raney-type Ni catalyst precursor alloys
Raney-type Ni precursor alloys containing 75 at.% Al and doped with 0, 0.75, 1.5 and 3.0 at.% Ti have been produced by a gas atomization process. The resulting powders have been classified by size fraction with subsequent investigation by powder XRD, SEM and EDX analysis. The undoped powders contain, as expected, the phases Ni2Al3, NiAl3 and an Al-eutectic. The Ti-doped powders contain an additional phase with the TiAl3 DO22 crystal structure. However, quantitative analysis of the XRD results indicate a far greater fraction of the TiAl3 phase is present than could be accounted for by a simple mass balance on Ti. This appears to be a (TixNi1-x)Al3 phase in which higher cooling rates favour small x (low Ti-site occupancy by Ti atoms). SEM and EDX analysis reveal that virtually all the available Ti is contained within the TiAl3 phase, with negligible Ti dissolved in either the Ni2Al3 or NiAl3 phases
Differential Transverse Flow in Central C-Ne and C-Cu Collisions at 3.7 GeV/nucleon
Differential transverse flow of protons and pions in central C-Ne and C-Cu
collisions at a beam energy of 3.7 GeV/nucleon was measured as a function of
transverse momentum at the SKM-200-GIBS setup of JINR. In agreement with
predictions of a transversely moving thermal model, the strength of proton
differential transverse flow is found to first increase gradually and then
saturate with the increasing transverse momentum in both systems. While pions
are preferentially emitted in the same direction of the proton transverse flow
in the reaction of C-Ne, they exhibit an anti-flow to the opposote direction of
the proton transverse flow in the reaction of C-Cu due to stronger shadowing
effects of the heavier target in thr whole range of transverse momentum.Comment: 15 pages, 5 figure
Gravitational Lensing by Black Holes
We review the theoretical aspects of gravitational lensing by black holes,
and discuss the perspectives for realistic observations. We will first treat
lensing by spherically symmetric black holes, in which the formation of
infinite sequences of higher order images emerges in the clearest way. We will
then consider the effects of the spin of the black hole, with the formation of
giant higher order caustics and multiple images. Finally, we will consider the
perspectives for observations of black hole lensing, from the detection of
secondary images of stellar sources and spots on the accretion disk to the
interpretation of iron K-lines and direct imaging of the shadow of the black
hole.Comment: Invited article for the GRG special issue on lensing (P. Jetzer, Y.
Mellier and V. Perlick Eds.). 31 pages, 12 figure
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