255 research outputs found
Centipede ladder at quarter filling
We study the ground state and excitation spectrum of a quasi one-dimensional
nanostructure consisting of a pole and rungs oriented in the opposite
directions ("centipede ladder", CL) at quarter filling. The spin and charge
excitation spectra are found in the limits of small and large longitudinal
hopping compared to the on-rung hopping rate and exchange
coupling . At small the system with ferromagnetic on-rung
exchange demonstrates instability against dimerization. Coherent propagation of
charge transfer excitons is possible in this limit. At large CL behaves
like two-orbital Hubbard chain, but the gap opens in the charge excitation
spectrum thus reducing the symmetry from SU(4) to SU(2). The spin excitations
are always gapless and their dispersion changes from quadratic magnon-like for
ferromagnetic on-rung exchange to linear spinon-like for antiferromagnetic
on-rung exchange in weak longitudinal hopping limit.Comment: 10 pages, 7 eps figure
Contributions of spontaneous phase slippage to linear and non-linear conduction near the Peierls transition in thin samples of o-TaS_3
In the Peierls state very thin samples of TaS_3 (cross-section area \sim
10^{-3} mkm^2) are found to demonstrate smearing of the I-V curves near the
threshold field. With approaching the Peierls transition temperature, T_P, the
smearing evolves into smooth growth of conductance from zero voltage
interpreted by us as the contribution of fluctuations to the non--linear
conductance. We identify independently the fluctuation contribution to the
linear conductance near T_P. Both linear and non-linear contributions depend on
temperature with close activation energies \sim (2 - 4) x 10^3 K and apparently
reveal the same process. We reject creep of the {\it continuous} charge-density
waves (CDWs) as the origin of this effect and show that it is spontaneous phase
slippage that results in creep of the CDW. A model is proposed accounting for
both the linear and non-linear parts of the fluctuation conduction up to T_P.Comment: 6 pages, 5 Postscript figure, RevTeX, accepted for publication in PR
Influence mechanisms of mineralocorticoid receptor antagonist (spironolactone) among elderly patients with chronic heartfailure against ischemic disease
It was determined that a significant positive dynamics of TNF-synthesis suppression by 67.0% (p 0.0001) was established in the 4th group of patients taking combined therapy with the blocker of mineralocorticoid receptors with spironolacton
Coupling of the lattice and superlattice deformations and hysteresis in thermal expansion for the quasi one-dimensional conductor TaS
An original interferometer-based setup for measurements of length of
needle-like samples is developed, and thermal expansion of o-TaS crystals
is studied. Below the Peierls transition the temperature hysteresis of length
is observed, the width of the hysteresis loop being up to . The behavior of the loop is anomalous: the length changes so
that it is in front of its equilibrium value. The hysteresis loop couples with
that of conductivity. The sign and the value of the length hysteresis are
consistent with the strain dependence of the charge-density waves (CDW) wave
vector. With lowering temperature down to 100 K the CDW elastic modulus grows
achieving a value comparable with the lattice Young modulus. Our results could
be helpful in consideration of different systems with intrinsic
superstructures.Comment: 4 pages, 3 figures. Phys. Rev. Lett., accepted for publicatio
Parametric generation of second sound in superfluid helium: linear stability and nonlinear dynamics
We report the experimental studies of a parametric excitation of a second
sound (SS) by a first sound (FS) in a superfluid helium in a resonance cavity.
The results on several topics in this system are presented: (i) The linear
properties of the instability, namely, the threshold, its temperature and
geometrical dependencies, and the spectra of SS just above the onset were
measured. They were found to be in a good quantitative agreement with the
theory. (ii) It was shown that the mechanism of SS amplitude saturation is due
to the nonlinear attenuation of SS via three wave interactions between the SS
waves. Strong low frequency amplitude fluctuations of SS above the threshold
were observed. The spectra of these fluctuations had a universal shape with
exponentially decaying tails. Furthermore, the spectral width grew continuously
with the FS amplitude. The role of three and four wave interactions are
discussed with respect to the nonlinear SS behavior. The first evidence of
Gaussian statistics of the wave amplitudes for the parametrically generated
wave ensemble was obtained. (iii) The experiments on simultaneous pumping of
the FS and independent SS waves revealed new effects. Below the instability
threshold, the SS phase conjugation as a result of three-wave interactions
between the FS and SS waves was observed. Above the threshold two new effects
were found: a giant amplification of the SS wave intensity and strong resonance
oscillations of the SS wave amplitude as a function of the FS amplitude.
Qualitative explanations of these effects are suggested.Comment: 73 pages, 23 figures. to appear in Phys. Rev. B, July 1 st (2001
Parametric Generation of Second Sound by First Sound in Superfluid Helium
We report the first experimental observation of parametric generation of
second sound (SS) by first sound (FS) in superfluid helium in a narrow
temperature range in the vicinity of . The temperature dependence
of the threshold FS amplitude is found to be in a good quantitative agreement
with the theory suggested long time ago and corrected for a finite geometry.
Strong amplitude fluctuations and two types of the SS spectra are observed
above the bifurcation. The latter effect is quantitatively explained by the
discreteness of the wave vector space and the strong temperature dependence of
the SS dissipation length.Comment: 4 pages, 4 postscript figures, REVTE
Study of the selective phenolic inhibitors of arginase 2 acute toxicity
We have previously shown that the isolated arginase 2 inhibitors have a pronounced endothelioprotective level. A strategy is proposed for the targeted search for isolated arginase 2 inhibitors among compounds of a phenolic nature. Received 3 compounds, isolated arginase inhibitors 2. As a result of the study, the acute toxicity of the compounds obtained was studie
Magnetic susceptibility of EuTe/PbTe Heisenberg superlattices: experimental and theoretical studies
We report results on the temperature dependence of the susceptibilities of a
set of MBE-grown short-period EuTe/PbTe antiferromagnetic superlattices having
different EuTe layer thicknesses. In-plane and orthogonal susceptibilities have
been measured and display a strong anisotropy at low temperature, confirming
the occurrence of a magnetic phase transition in the thicker samples, as seen
also in neutron diffraction studies. We suggest that dipolar interactions
stabilize antiferromagnetic long-range order in an otherwise isotropic system
and we present numerical and analytical results for the low-temperature
orthogonal susceptibility.Comment: 30 pages, 8 ps figures, RevTe
Discretized rotation has infinitely many periodic orbits
For a fixed k in (-2,2), the discretized rotation on Z^2 is defined by
(x,y)->(y,-[x+ky]). We prove that this dynamics has infinitely many periodic
orbits.Comment: Revised after referee reports, and added a quantitative statemen
Fluorinated Derivatives of Benz[4,5]imidazo[1,2-b][1,3] thiazole - Inhibitors of Reproduction of Measles Virus
ACKNOWLEDGMENTS This study was supported by MNTTs (grant no. 1198), Russian Foundation for Basic Research (project no. 03-03-32254), the Ministry of Education of the Russian Federation, and the American Civil Research and Development Foundation (CDRF, grants REC-005 and EK-005-XI)
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