34,421 research outputs found
Nonlinear Dynamics of Nuclear-Electronic Spin Processes in Ferromagnets
Spin dynamics is considered in ferromagnets consisting of electron and
nuclear subsystems interacting with each other through hyperfine forces. In
addition, the ferromagnetic sample is coupled with a resonance electric
circuit. Under these conditions, spin relaxation from a strongly nonequilibrium
initial state displays several peculiarities absent for the standard set-up in
studying spin relaxation. The main feature of the nonlinear spin dynamics
considered in this communication is the appearance of ultrafast coherent
relaxation, with characteristic relaxation times several orders shorter than
the transverse relaxation time . This type of coherent spin relaxation can
be used for extracting additional information on the intrinsic properties of
ferromagnetic materials and also can be employed for different technical
applications.Comment: 1 file, 4 pages, RevTex, no figure
Report of epibiont Thecacineta calix (Ciliophora: Suctorea) on deep sea Desmodora (Nematoda) from the Andaman Sea, Indian Ocean
Suctorian epibionts Thecacineta calix attached on the cuticle of nematodes Desmodora sphaerica and
D. pontica are reported here from the deep sea hexactinellid sponge Pheronema sp. from the Andaman
Sea (Indian Ocean). The epibiont T. calix is reported here for first time from the Andaman Sea
Dynamics of quantum dot superradiance
The possibility of realizing the superradiant regime of electromagnetic
emission by the assembly of quantum dots is considered. The overall dynamical
process is analyzed in detail. It is shown that there can occur several
qualitatively different stages of evolution. The process starts with dipolar
waves triggering the spontaneous radiation of individual dots. This corresponds
to the fluctuation stage, when the dots are not yet noticeably correlated with
each other. The second is the quantum stage, when the dot interactions through
the common radiation field become more important, but the coherence is not yet
developed. The third is the coherent stage, when the dots radiate coherently,
emitting a superradiant pulse. After the superradiant pulse, the system of dots
relaxes to an incoherent state in the relaxation stage. If there is no external
permanent pumping, or the effective dot interactions are weak, the system tends
to a stationary state during the last stationary stage, when coherence dies out
to a low, practically negligible, level. In the case of permanent pumping,
there exists the sixth stage of pulsing superradiance, when the system of dots
emits separate coherent pulses.Comment: Latex file, 31 pages, 3 figure
Joint Probabilities Reproducing Three EPR Experiments On Two Qubits
An eight parameter family of the most general nonnegative quadruple
probabilities is constructed for EPR-Bohm-Aharonov experiments when only 3
pairs of analyser settings are used. It is a simultaneous representation of 3
Bohr-incompatible experimental configurations valid for arbitrary quantum
states.Comment: Typo corrected in abstrac
Optical Properties and Correlation Effects in NaxCoO2
We have calculated the optical spectra of NaCoO for =0.3, 0.5,
and 0.7 within the LDA. We compare our results to available experimental data
and show that the important features and trends are reproduced well, but there
is a nearly uniform shift of peak positions and poor agreement in intensities.
We show, through application of a simple model, that these differences can be
attributed to overhybridization between Co and O orbitals and spin fluctuations
which renormalize the bandwidth. Applying the LDA+U procedure shifts the
optical peaks further from their experimental locations, indicating that this
method of incorporating correlation effects is ill-suited for the case NaxCoO2
Second Line of Defense Virtual Private Network Guidance for Deployed and New CAS Systems
This paper discusses the importance of remote access via virtual private network (VPN) for the Second Line of Defense (SLD) Central Alarm System (CAS) sites, the requirements for maintaining secure channels while using VPN and implementation requirements for current and future sites
Lattice dynamics and reduced thermal conductivity of filled skutterudites
The great reduction in thermal conductivity of skutterudites upon filling the
``void'' sites with Rare Earth (RE) ions is key to their favorable
thermoelectric properties but remains to be understood. Using lattice dynamic
models based on first principles calculations, we address the most popular
microscopic mechanism, reduction via rattling ions. The model withstands
inelastic neutron scattering and specific heat measurements, and refutes
hypotheses of an anharmonic RE potential and of two distinct localized RE
vibrations of disparate frequencies. It does indicate a strong hybridization
between bare La vibrations and certain Sb-like phonon branches, suggesting
anharmonic scattering by harmonic RE motions as an important mechanism for
suppression of heat conductivity.Comment: modified version resubmitted to PRB. Results unchanged, text changed
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Doping effects on the electronic and structural properties of CoO2: An LSDA+U study
A systematic LSDA+U study of doping effects on the electronic and structural
properties of single layer CoO2 is presented. Undoped CoO2 is a charge transfer
insulator within LSDA+U and a metal with a high density of states (DOS) at the
Fermi level within LSDA. (CoO2), on the other hand, is a band
insulator with a gap of 2.2 eV. Systems with fractional doping are metals if no
charge orderings are present. Due to the strong interaction between the doped
electron and other correlated Co d electrons, the calculated electronic
structure of (CoO2) depends sensitively on the doping level x. Zone
center optical phonon energies are calculated under the frozen phonon
approximation and are in good agreement with measured values. Softening of the
phonon at doping x ~0.25 seems to indicate a strong electron-phonon
coupling in this system. Possible intemediate spin states of Co ions, Na
ordering, as well as magnetic and charge orderings in this system are also
discussed.Comment: 11 pages, 12 figure
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