1,820 research outputs found
Possibility of local pair existence in optimally doped SmFeAsO(1-x) in pseudogap regime
We report the analysis of pseudogap Delta* derived from resistivity
experiments in FeAs-based superconductor SmFeAsO(0.85), having a critical
temperature T_c = 55 K. Rather specific dependence Delta*(T) with two
representative temperatures followed by a minimum at about 120 K was observed.
Below T_s = 147 K, corresponding to the structural transition in SmFeAsO,
Delta*(T) decreases linearly down to the temperature T_AFM = 133 K. This last
peculiarity can likely be attributed to the antiferromagnetic (AFM) ordering of
Fe spins. It is believed that the found behavior can be explained in terms of
Machida, Nokura, and Matsubara (MNM) theory developed for the AFM
superconductors.Comment: 5 pages, 2 figure
Invariant Sets and Explicit Solutions to a Third-Order Model for the Shearless Stratified Turbulent Flow
We study dynamics of the shearless stratified turbulent flows. Using the
method of differential constraints we find a class of explicit solutions to the
problem under consideration and establish that the differential constraint
obtained coincides with the well-known Zeman--Lumley model for stratified
flows.Comment: arxiv version is already officia
Golden gaskets: variations on the Sierpi\'nski sieve
We consider the iterated function systems (IFSs) that consist of three
general similitudes in the plane with centres at three non-collinear points,
and with a common contraction factor \la\in(0,1).
As is well known, for \la=1/2 the invariant set, \S_\la, is a fractal
called the Sierpi\'nski sieve, and for \la<1/2 it is also a fractal. Our goal
is to study \S_\la for this IFS for 1/2<\la<2/3, i.e., when there are
"overlaps" in \S_\la as well as "holes". In this introductory paper we show
that despite the overlaps (i.e., the Open Set Condition breaking down
completely), the attractor can still be a totally self-similar fractal,
although this happens only for a very special family of algebraic \la's
(so-called "multinacci numbers"). We evaluate \dim_H(\S_\la) for these
special values by showing that \S_\la is essentially the attractor for an
infinite IFS which does satisfy the Open Set Condition. We also show that the
set of points in the attractor with a unique ``address'' is self-similar, and
compute its dimension.
For ``non-multinacci'' values of \la we show that if \la is close to 2/3,
then \S_\la has a nonempty interior and that if \la<1/\sqrt{3} then \S_\la$
has zero Lebesgue measure. Finally we discuss higher-dimensional analogues of
the model in question.Comment: 27 pages, 10 figure
Invariant description of solutions of hydrodynamic type systems in hodograph space: hydrodynamic surfaces
Hydrodynamic surfaces are solutions of hydrodynamic type systems viewed as
non-parametrized submanifolds of the hodograph space. We propose an invariant
differential-geometric characterization of hydrodynamic surfaces by expressing
the curvature form of the characteristic web in terms of the reciprocal
invariants.Comment: 12 page
Update of the e^+e^-\to\pi^+\pi^- cross section measured by SND detector in the energy region 400<\sqrt{s}<1000 MeV
The corrected cross section of the e^+e^-\to\pi^+\pi^- process measured in
the SND experiment at the VEPP-2M e^+e^- collider is presented. The update is
necessary due to a flaw in the e^+e^-\to\pi^+\pi^- and e^+e^-\to\mu^+\mu^-
Monte Carlo events generators used previously in data analysis.Comment: 10 pages,7 figure
Evolution of Hall coefficient in two-dimensional heavy fermion CeCoIn
We report on the pressure dependence of the Hall coefficient in
quasi-2D heavy fermion CeCoIn. At ambient pressure, below a temperature
associated with the emergence of non-Fermi liquid properties, is
anomalously enhanced. We found that the restoration of the Fermi liquid state
with applied pressure leads to a gradual suppression of this dramatic
enhancement. Moreover, the enhancement in was found to be confined to an
intermediate temperature window, where inelastic electron-electron scattering
is dominant. Our results strongly support the presence of cold and hot spots on
the Fermi surface probably due to anisotropic scattering by antiferromagnetic
fluctuations, which may also prove relevant for the debate on the anomalous
normal-state properties of high- cuprates.Comment: 9 pages, 5 fiqures, to be published in J. Phys. Soc. Jp
Palladium nanoparticles by electrospinning from poly(acrylonitrile-co-acrylic acid)-PdCl2 solutions. Relations between preparation conditions, particle size, and catalytic activity
Catalytic palladium (Pd) nanoparticles on electrospun copolymers of acrylonitrile and acrylic acid (PAN-AA) mats were produced via reduction of PdCl2 with hydrazine. Fiber mats were electrospun from homogeneous solutions of PAN-AA and PdCl2 in dimethylformamide (DMF). Pd cations were reduced to Pd metals when fiber mats were treated in an aqueous hydrazine solution at room temperature. Pd atoms nucleate and form small crystallites whose sizes were estimated from the peak broadening of X-ray diffraction peaks. Two to four crystallites adhere together and form agglomerates. Agglomerate sizes and fiber diameters were determined by scanning and transmission electron microscopy. Spherical Pd nanoparticles were dispersed homogeneously on the electrospun nanofibers. The effects of copolymer composition and amount of PdCl2 on particle size were investigated. Pd particle size mainly depends on the amount of acrylic acid functional groups and PdCl2 concentration in the spinning solution. Increasing acrylic acid concentration on polymer chains leads to larger Pd nanoparticles. In addition, Pd particle size becomes larger with increasing PdCl2 concentration in the spinning solution. Hence, it is possible to tune the number density and the size of metal nanoparticles. The catalytic activity of the Pd nanoparticles in electrospun mats was determined by selective hydrogenation of dehydrolinalool (3,7-dimethyloct-6- ene-1-yne-3-ol, DHL) in toluene at 90 °C. Electrospun fibers with Pd particles have 4.5 times higher catalytic activity than the current Pd/Al2O3 catalyst
Study of the process with SND detector at the VEPP-2M collider
In experiment with the SND detector at VEPP-2M collider the
cross section was measured in the energy range
=0.60--1.38 GeV with the integrated luminosity of 27.8 pb. The
measured cross section is well described by the vector meson dominance model
with contributions from the , , ,
resonances and agrees with results of previous
measurements. The decay probabilities \BR(\phi\to\eta\gamma),
\BR(\omega\to\eta\gamma) and \BR(\rho\to\eta\gamma) were measured with the
accuracies better than or comparable to the world averages.Comment: 13 pages, 6 figures, 5 table
Summing Divergent Perturbative Series in a Strong Coupling Limit. The Gell-Mann - Low Function of the \phi^4 Theory
An algorithm is proposed for determining asymptotics of the sum of a
perturbative series in the strong coupling limit using given values of the
expansion coefficients. Operation of the algorithm is illustrated by test
examples, method for estimating errors is developed, and an optimization
procedure is described. Application of the algorithm to the theory
gives a behavior at large for its Gell-Mann
-- Low function. The fact that the exponent is close to unity can be
interpreted as a manifestation of the logarithmic branching of the type
(with ), which is
confirmed by independent evidence. In any case, the theory is
internally consistent. The procedure of summing perturbartive series with
arbitrary values of expansion parameter is discussed.Comment: 23 pages, PD
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