2,145 research outputs found
Rigidity of minimal submanifolds in hyperbolic space
We prove that if an -dimensional complete minimal submanifold in
hyperbolic space has sufficiently small total scalar curvature then has
only one end. We also prove that for such there exist no nontrivial
harmonic 1-forms on
Non-Markovian entanglement dynamics in coupled superconducting qubit systems
We theoretically analyze the entanglement generation and dynamics by coupled
Josephson junction qubits. Considering a current-biased Josephson junction
(CBJJ), we generate maximally entangled states. In particular, the entanglement
dynamics is considered as a function of the decoherence parameters, such as the
temperature, the ratio between the reservoir cutoff
frequency and the system oscillator frequency , % between
the characteristic frequency of the %quantum system of interest, and
the cut-off frequency of %Ohmic reservoir and the energy levels
split of the superconducting circuits in the non-Markovian master equation. We
analyzed the entanglement sudden death (ESD) and entanglement sudden birth
(ESB) by the non-Markovian master equation. Furthermore, we find that the
larger the ratio and the thermal energy , the shorter the
decoherence. In this superconducting qubit system we find that the entanglement
can be controlled and the ESD time can be prolonged by adjusting the
temperature and the superconducting phases which split the energy
levels.Comment: 13 pages, 3 figure
Entanglement, quantum phase transition and scaling in XXZ chain
Motivated by recent development in quantum entanglement, we study relations
among concurrence , SU(2) algebra, quantum phase transition and
correlation length at the zero temperature for the XXZ chain. We find that at
the SU(2) point, the ground state possess the maximum concurrence. When the
anisotropic parameter is deformed, however, its value decreases. Its
dependence on scales as in the XY metallic
phase and near the critical point (i.e. ) of the Ising-like
insulating phase. We also study the dependence of on the correlation length
, and show that it satisfies near the critical point. For
different size of the system, we show that there exists a universal scaling
function of with respect to the correlation length .Comment: 4 pages, 3 figures. to appear in Phys. Rev.
Linear response conductance and magneto-resistance of ferromagnetic single-electron transistors
The current through ferromagnetic single-electron transistors (SET's) is
considered. Using path integrals the linear response conductance is formulated
as a function of the tunnel conductance vs. quantum conductance and the
temperature vs. Coulomb charging energy. The magneto-resistance of
ferromagnet-normal metal-ferromagnet (F-N-F) SET's is almost independent of the
Coulomb charging energy and is only reduced when the transport dwell time is
longer than the spin-flip relaxation time. In all-ferromagnetic (F-F-F) SET's
with negligible spin-flip relaxation time the magneto-resistance is calculated
analytically at high temperatures and numerically at low temperatures. The
F-F-F magneto-resistance is enhanced by higher order tunneling processes at low
temperatures in the 'off' state when the induced charges vanishes. In contrast,
in the 'on' state near resonance the magneto-resistance ratio is a
non-monotonic function of the inverse temperature.Comment: 10 pages, 6 figures. accepted for publication in Phys. Rev.
Scaling Behavior of Anomalous Hall Effect and Longitudinal Nonlinear Response in High-Tc Superconductors
Based on existing theoretical model and by considering our longitudinal
nonlinear response function, we derive a nonliear equation in which the mixed
state Hall resistivity can be expressed as an analytical function of magnetic
field, temperature and applied current. This equation enables one to compare
quantitatively the experimental data with theoretical model. We also find some
new scaling relations of the temperature and field dependency of Hall
resistivity. The comparison between our theoretical curves and experimental
data shows a fair agreement.Comment: 4 pages, 3 figure
Asymptotically hyperbolic manifolds with small mass
For asymptotically hyperbolic manifolds of dimension with scalar
curvature at least equal to the conjectured positive mass theorem
states that the mass is non-negative, and vanishes only if the manifold is
isometric to hyperbolic space. In this paper we study asymptotically hyperbolic
manifolds which are also conformally hyperbolic outside a ball of fixed radius,
and for which the positive mass theorem holds. For such manifolds we show that
the conformal factor tends to one as the mass tends to zero
High frequency magnetic behavior through the magnetoimpedance effect in CoFeB/(Ta, Ag, Cu) multilayered ferromagnetic thin films
We studied the dynamics of magnetization through an investigation of the
magnetoimpedance effect in CoFeB/(Ta, Ag, Cu) multilayered thin films grown by
magnetron sputtering. Impedance measurements were analyzed in terms of the
mechanisms responsible for their variations at different frequency intervals
and the magnetic and structural properties of the multilayers. Analysis of the
mechanisms responsible for magnetoimpedance according to frequency and external
magnetic field showed that for the CoFeB/Cu multilayer, ferromagnetic resonance
(FMR) contributes significantly to the magnetoimpedance effect at frequencies
close to 470 MHz. This frequency is low when compared to the results obtained
for CoFeB/Ta and CoFeB/Ag multilayers and is a result of the anisotropy
distribution and non-formation of regular bilayers in this sample. The MImax
values occurred at different frequencies according to the used non-magnetic
metal. Variations between 25% and 30% were seen for a localized frequency band,
as in the case of CoFeB/Ta and CoFeB/Ag, as well as for a wide frequency range,
in the case of CoFeB/Cu.Comment: 14 pages, 5 figure
The floor in the interplanetary magnetic field: Estimation on the basis of relative duration of ICME observations in solar wind during 1976-2000
To measure the floor in interplanetary magnetic field and estimate the time-
invariant open magnetic flux of Sun, it is necessary to know a part of magnetic
field of Sun carried away by CMEs. In contrast with previous papers, we did not
use global solar parameters: we identified different large-scale types of solar
wind for 1976-2000 interval, obtained a fraction of interplanetary CMEs (ICMEs)
and calculated magnitude of interplanetary magnetic field B averaged over 2
Carrington rotations. The floor of magnetic field is estimated as B value at
solar cycle minimum when the ICMEs were not observed and it was calculated to
be 4,65 \pm 6,0 nT. Obtained value is in a good agreement with previous
results.Comment: 10 pages, 2 figures, submitted in GR
Triangle for the entropic index q of non-extensive statistical mechanics observed by Voyager 1 in the distant heliosphere
Tsallis identified a set of numbers, the q-triplet, (qstat, qsen, qrel), for
a system described by nonextensive statistical mechanics. The deviation of the
q's from unity is a measure of the departure from thermodynamic equilibrium. We
present observations of the q-triplets derived from two sets of daily averages
of the magnetic field strength B observed by Voyager 1 in the solar wind near
40 A.U. during 1989 and near 85 A.U. during 2002, respectively. The results for
1989 do not differ significantly from those for 2002. We find qstat = 1.75,
qsen = -0.6, and qrel = 3.8
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A multispacecraft analysis of a small-scale transient entrained by solar wind streams
The images taken by the Heliospheric Imagers (HIs), part of the SECCHI imaging package onboard the pair of STEREO spacecraft, provide information on the radial and latitudinal evolution of the plasma compressed inside corotating interaction regions (CIRs). A plasma density wave imaged by the HI instrument onboard STEREO-B was found to propagate towards STEREO-A, enabling a comparison between simultaneous remotesensing and in situ observations of its structure to be performed. In situ measurements made by STEREO-A show that the plasma density wave is associated with the passage of a CIR. The magnetic field compressed after the CIR stream interface (SI) is found to have a planar distribution. Minimum variance analysis of the magnetic field vectors shows that the SI is inclined at 54° to the orbital plane of the STEREO-A spacecraft. This inclination of the CIR SI is comparable to the inclination of the associated plasma density wave observed by HI. A small-scale magnetic cloud with a flux rope topology and radial extent of 0.08 AU is also embedded prior to the SI. The pitch-angle distribution of suprathermal electrons measured by the STEREO-A SWEA instrument shows that an open magnetic field topology in the cloud replaced the heliospheric current sheet locally. These observations confirm that HI observes CIRs in difference images when a small-scale transient is caught up in the compression region
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