1,517 research outputs found
Cocliques of maximal size in the prime graph of a finite simple group
In this paper we continue our investgation of the prime graph of a finite
simple group started in http://arxiv.org/abs/math/0506294 (the printed version
appeared in [1]). We describe all cocliques of maximal size for all finite
simple groups and also we correct mistakes and misprints from our previous
paper. The list of correction is given in Appendix of the present paper.Comment: published version with correction
Magnetocaloric effect and magnetization in a Ni-Mn-Ga Heusler alloy in the vicinity of magnetostructural transition
The magnetic and thermodynamic properties of a Ni2.19Mn0.81Ga alloy with
coupled magnetic and structural (martensitic) phase transitions were studied
experimentally and theoretically. The magnetocaloric effect was measured by a
direct method in magnetic fields 0-26 kOe at temperatures close to the
magnetostructural transition temperature. For theoretical description of the
alloy properties near the magnetostructural transition a statistical model is
suggested, that takes into account the coexistence of martensite and austenite
domains in the vicinity of martensite transformation point.Comment: presented at ICM-2003, to appear in JMM
Coherent interaction of laser pulses in a resonant optically dense extended medium under the regime of strong field-matter coupling
Nonstationary pump-probe interaction between short laser pulses propagating
in a resonant optically dense coherent medium is considered. A special
attention is paid to the case, where the density of two-level particles is high
enough that a considerable part of the energy of relatively weak external
laser-fields can be coherently absorbed and reemitted by the medium. Thus, the
field of medium reaction plays a key role in the interaction processes, which
leads to the collective behavior of an atomic ensemble in the strongly coupled
light-matter system. Such behavior results in the fast excitation interchanges
between the field and a medium in the form of the optical ringing, which is
analogous to polariton beating in the solid-state optics. This collective
oscillating response, which can be treated as successive beats between light
wave-packets of different group velocities, is shown to significantly affect
propagation and amplification of the probe field under its nonlinear
interaction with a nearly copropagating pump pulse. Depending on the probe-pump
time delay, the probe transmission spectra show the appearance of either
specific doublet or coherent dip. The widths of these features are determined
by the density-dependent field-matter coupling coefficient and increase during
the propagation. Besides that, the widths of the coherent features, which
appear close to the resonance in the broadband probe-spectrum, exceed the
absorption-line width, since, under the strong-coupling regime, the frequency
of the optical ringing exceeds the rate of incoherent relaxation. Contrary to
the stationary strong-field effects, the density- and coordinate-dependent
transmission spectra of the probe manifest the importance of the collective
oscillations and cannot be obtained in the framework of the single-atom model.Comment: 10 pages, 8 figures, to be published in Phys. Rev.
A multiloop improvement of non-singlet QCD evolution equations
An approach is elaborated for calculation of "all loop" contributions to the
non-singlet evolution kernels from the diagrams with renormalon chain
insertions. Closed expressions are obtained for sums of contributions to
kernels for the DGLAP equation and for the "nonforward" ER-BL
equation from these diagrams that dominate for a large value of , the
first -function coefficient. Calculations are performed in the covariant
-gauge in a MS-like scheme. It is established that a special choice of the
gauge parameter generalizes the standard "naive nonabelianization"
approximation. The solutions are obtained to the ER-BL evolution equation
(taken at the "all loop" improved kernel), which are in form similar to
one-loop solutions. A consequence for QCD descriptions of hard processes and
the benefits and incompleteness of the approach are briefly discussed.Comment: 13 pages, revtex, 2 figures are enclosed as eps-file, the text style
and figures are corrected following version, accepted for publication to
Phys. Rev.
Leading infrared logarithms for sigma-model with fields on arbitrary Riemann manifold
We derive non-linear recursion equation for the leading infrared logarithms
(LL) in four dimensional sigma-model with fields on an arbitrary Riemann
manifold. The derived equation allows one to compute leading infrared
logarithms to essentially unlimited loop order in terms of geometric
characteristics of the Riemann manifold.
We reduce the solution of the SU(oo) principal chiral field in arbitrary
number of dimensions in the LL approximation to the solution of very simple
recursive equation. This result paves a way to the solution of the model in
arbitrary number of dimensions at N-->ooComment: Talk given by MVP at the conference devoted to memory of A.N.
Vasilie
Description of paramagnetic--spin glass transition in Edwards-Anderson model in terms of critical dynamics
Possibility of description of the glass transition in terms of critical
dynamics considering a hierarchy of the intermodal relaxation time is shown.
The generalized Vogel-Fulcher law for the system relaxation time is derived in
terms of this approach. It is shown that the system satisfies the
fluctuating--dissipative theorem in case of the absence of the intermodal
relaxation time hierarchy.Comment: 10 pages, 6 figure
Magnetic properties and magnetostructural phase transitions in Ni2+xMn1-xGa shape memory alloys
A systematic study of magnetic properties of Ni2+xMn1-xGa (0 \le x \le 0.19)
Heusler alloys undergoing structural martensite-austenite transformations while
in ferromagnetic state has been performed. From measurements of spontaneous
magnetization, Ms(T), jumps \Delta M at structural phase transitions were
determined. Virtual Curie temperatures of the martensite were estimated from
the comparison of magnetization in martensitic and austenitic phases. Both
saturation magnetic moments in ferromagnetic state and effective magnetic
moments in paramagnetic state of Mn and Ni atoms were estimated and the
influence of delocalization effects on magnetism in these alloys was discussed.
The experimental results obtained show that the shift of martensitic transition
temperature depends weakly on composition. The values of this shift are in good
correspondence with Clapeyron-Clausius formalism taking into account the
experimental data on latent heat at martensite-austenite transformations.Comment: 7 pages, 8 figure
Effects of Turbulent Mixing on the Critical Behavior
Effects of strongly anisotropic turbulent mixing on the critical behavior are
studied by means of the renormalization group. Two models are considered: the
equilibrium model A, which describes purely relaxational dynamics of a
nonconserved scalar order parameter, and the Gribov model, which describes the
nonequilibrium phase transition between the absorbing and fluctuating states in
a reaction-diffusion system. The velocity is modelled by the d-dimensional
generalization of the random shear flow introduced by Avellaneda and Majda
within the context of passive scalar advection. Existence of new nonequilibrium
types of critical regimes (universality classes) is established.Comment: Talk given in the International Bogolyubov Conference "Problems of
Theoretical and Mathematical Physics" (Moscow-Dubna, 21-27 August 2009
Self-consistent theory of turbulence
A new approach to the stochastic theory of turbulence is suggested. The
coloured noise that is present in the stochastic Navier-Stokes equation is
generated from the delta-correlated noise allowing us to avoid the nonlocal
field theory as it is the case in the conventional theory. A feed-back
mechanism is introduced in order to control the noise intensity.Comment: submitted to J.Tech. Phys.Letters (St. Petersburg
Causal signal transmission by quantum fields. IV: The causal Wick theorem
Wick's theorem in the Schwinger-Perel-Keldysh closed-time-loop formalism is
written in a form where the place of contractions is taken by the linear
response function of the field. This result demonstrates that the physical
information supplied by Wick's theorem for operators is propagation of the free
field in space and time.Comment: Final version, to appear in Phys Rev
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