4,652 research outputs found
Exchange bias effect and intragranular magnetoresistance in Nd$_{0.84}Sr_{0.16}CoO_3
Electrical transport properties as a function of magnetic field and time have
been investigated in polycrystalline, Nd_{0.84}Sr_{0.16}CoO_3. A strong
exchange bias (EB) effect is observed associated with the fairly large
intragranular magnetoresistance (MR). The EB effect observed in the MR curve is
compared with the EB effect manifested in magnetic hysteresis loop. Training
effect, described as the decrease of EB effect when the sample is successively
field-cycled at a particular temperature, has been observed in the shift of the
MR curve. Training effect could be analysed by the successful models. The EB
effect, MR and a considerable time dependence in MR are attributed to the
intrinsic nanostructure giving rise to the varieties of magnetic interfaces in
the grain interior
Frequency dependence of the photonic noise spectrum in an absorbing or amplifying diffusive medium
A theory is presented for the frequency dependence of the power spectrum of
photon current fluctuations originating from a disordered medium. Both the
cases of an absorbing medium (``grey body'') and of an amplifying medium
(``random laser'') are considered in a waveguide geometry. The semiclassical
approach (based on a Boltzmann-Langevin equation) is shown to be in complete
agreement with a fully quantum mechanical theory, provided that the effects of
wave localization can be neglected. The width of the peak in the power spectrum
around zero frequency is much smaller than the inverse coherence time,
characteristic for black-body radiation. Simple expressions for the shape of
this peak are obtained, in the absorbing case, for waveguide lengths large
compared to the absorption length, and, in the amplifying case, close to the
laser threshold.Comment: 17 pages, 6 figure
Decoherence-free quantum information in the presence of dynamical evolution
We analyze decoherence-free (DF) quantum information in the presence of an
arbitrary non-nearest-neighbor bath-induced system Hamiltonian using a
Markovian master equation. We show that the most appropriate encoding for N
qubits is probably contained within the ~(2/9) N excitation subspace. We give a
timescale over which one would expect to apply other methods to correct for the
system Hamiltonian. In order to remain applicable to experiment, we then focus
on small systems, and present examples of DF quantum information for three and
four qubits. We give an encoding for four qubits that, while quantum
information remains in the two-excitation subspace, protects against an
arbitrary bath-induced system Hamiltonian. Although our results are general to
any system of qubits that satisfies our assumptions, throughout the paper we
use dipole-coupled qubits as an example physical system.Comment: 8 pages, 4 figure
The Xenopus Suc1/Cks Protein Promotes the Phosphorylation of G2/M Regulators
The entry into mitosis is controlled by Cdc2/cyclin B, also known as maturation or M-phase promoting factor (MPF). In Xenopus egg extracts, the inhibitory phosphorylations of Cdc2 on Tyr-15 and Thr-14 are controlled by the phosphatase Cdc25 and the kinases Myt1 and Wee1. At mitosis, Cdc25 is activated and Myt1 and Wee1 are inactivated through phosphorylation by multiple kinases, including Cdc2 itself. The Cdc2-associated Suc1/Cks1 protein (p9) is also essential for entry of egg extracts into mitosis, but the molecular basis of this requirement has been unknown. We find that p9 strongly stimulates the regulatory phosphorylations of Cdc25, Myt1, and Wee1 that are carried out by the Cdc2/cyclin B complex. Overexpression of the prolyl isomerase Pin1, which binds to the hyperphosphorylated forms of Cdc25, Myt1, and Wee1 found at M-phase, is known to block the initiation of mitosis in egg extracts. We have observed that Pin1 specifically antagonizes the stimulatory effect of p9 on phosphorylation of Cdc25 by Cdc2/cyclin B. This observation could explain why overexpression of Pin1 inhibits mitotic initiation. These findings suggest that p9 promotes the entry into mitosis by facilitating phosphorylation of the key upstream regulators of Cdc2
A new microscopic nucleon-nucleon interaction derived from relativistic mean field theory
A new microscopic nucleon-nucleon (NN) interaction has been derived for the
first time from the popular relativistic mean field theory (RMFT) Lagrangian.
The NN interaction so obtained remarkably relate to the inbuilt fundamental
parameters of RMFT. Furthermore, by folding it with the RMFT-densities of
cluster and daughter nuclei to obtain the optical potential, it's application
is also examined to study the exotic cluster radioactive decays, and results
obtained found comparable with the successfully used M3Y phenomenological
effective NN interactions. The presently derived NN-interaction can also be
used to calculate a number of other nuclear observables.Comment: 4 Pages 2 Figure
Influence of Spatial Correlations on the Lasing Threshold of Random Lasers
The lasing threshold of a random laser is computed numerically from a generic
model. It is shown that spatial correlations of the disorder in the medium
(i.e., dielectric constant) lead to an increase of the decay rates of the
eigenmodes and of the lasing threshold. This is in conflict with predictions
that such correlations should lower the threshold. While all results are
derived for photonic systems, the computed decay rate distributions also apply
to electronic systems
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