988 research outputs found
Martensitic transformation and magnetotransport properties of Ni47Mn42In11 alloy
The structure, electrical and magnetic properties of the Ni47Mn42In11 alloy, in which the temperature of the martensitic transformation is close to room temperature and practically coincides with the Curie temperature of austenite, have been investigated. The martensitic transformation in the Ni47Mn42In11 alloy proceeds with the formation of modulated martensite type 14M. It has been established that the spontaneous transformation from martensite to austenite is accompanied by a decrease in the specific resistance of 45%. In the martensitic transformation induced by a magnetic field of 18 kOe, a negative magnetoresistance is observed, reaching ∼ 15%. © Published under licence by IOP Publishing Ltd.Ural Branch, Russian Academy of Sciences, UB RAS: 18-10-2-39Federal Agency for Scientific Organizations: AAAA-A18-118020190116-6This work was supported by the Federal Agency for Scientific Organizations (themes “Structure”, project no. AAAA-A18-118020190116-6) and partly supported by the Comprehensive Program of the Ural Branch of the Russian Academy of Sciences (project No. 18-10-2-39)
Effect of additions of zinc stearate on the properties of sintered Nd-Fe-B magnets
Zinc stearate additions have been used to increase the remanence of sintered Nd-Fe-B magnets produced by the powder metallurgy without powder pressing. Zinc stearate acts as an internal lubricant, i.e., it decreases the friction forces between the particles and favors an increase in the degree of texture of the powders, which is induced by the magnetic field. It is shown that the density and the magnetic hysteresis characteristics of sintered magnets produced using additions of 0.15 wt % zinc stearate exceeds the corresponding values obtained for magnets produced without this addition at a filling density of powders in containers of more than 2.9 and 3.0 g/cm3 in dry and wet states, respectively. Using additions of zinc stearate in the amount of 0.15% with respect to the weight of the powder, magnets with a density of 7.55 g/cm3, B r = 14.02 kG, H c = 7.91 kOe, and (BH)max = 46.1 MG Oe have been produced. © 2013 Pleiades Publishing, Ltd
Burkhardt-Cottingham sum rule and forward spin polarizabilities in Heavy Baryon Chiral Perturbation Theory
We study spin-dependent sum rules for forward virtual Compton
scattering(VVCS) off the nucleon in heavy baryon chiral perturbation theory at
order . We show how these sum rules can be evaluated from low energy
expansions (in the virtual photon energy) of the forward VVCS amplitudes. We
study in particular the Burkhardt -Cottingham sum rule in HBChPT and higher
terms in the low energy expansion, which can be related to the generalized
forward spin polarizabilities of the nucleon. The dependence of these
observables on the photon virtuality can be accessed, at small and
intermediate values, from existing and forthcoming data at Jefferson Lab.Comment: 16 pages,4 fig
The Lyapunov Spectrum of a Continuous Product of Random Matrices
We expose a functional integration method for the averaging of continuous
products of random matrices. As an application, we
compute exactly the statistics of the Lyapunov spectrum of . This
problem is relevant to the study of the statistical properties of various
disordered physical systems, and specifically to the computation of the
multipoint correlators of a passive scalar advected by a random velocity field.
Apart from these applications, our method provides a general setting for
computing statistical properties of linear evolutionary systems subjected to a
white noise force field.Comment: Latex, 9 page
Crossing the phantom divide with k-essence in brane-worlds
We study a flat 3-brane in presence of a linear field with nonzero
cosmological constant . In this model the crossing of the phantom
divide (PD) occurs when the -essence energy density becomes negative. We
show that in the high energy regime the effective equation of state has a
resemblance of a modified Chaplygin gas while in the low energy regime it
becomes linear. We find a scale factor that begins from a singularity and
evolves to a de Sitter stable stage while other solutions have a
super-accelerated regime and end with a big rip. We use the energy conditions
to show when the effective equation of state of the brane-universe crosses the
PD.Comment: 8 pages, 5 figures. The article was fully rewritten. References
added. Accepted for publication in MPLA (2010
Fermionic approach to the evaluation of integrals of rational symmetric functions
We use the fermionic construction of two-matrix model partition functions to
evaluate integrals over rational symmetric functions. This approach is
complementary to the one used in the paper ``Integrals of Rational Symmetric
Functions, Two-Matrix Models and Biorthogonal Polynomials'' \cite{paper2},
where these integrals were evaluated by a direct method.Comment: 34 page
Hidden sl(2,R) Symmetry in 2D CFTs and the Wave Function of 3D Quantum Gravity
We show that all two-dimensional conformal field theories possess a hidden
sl(2,R) affine symmetry. More precisely, we add appropriate ghost fields to an
arbitrary CFT, and we use them to construct the currents of sl(2,R). We then
define a BRST operator whose cohomology defines a physical subspace where the
extended theory coincides with the original CFT. We use the sl(2,R) algebra to
construct candidate wave functions for 3-d quantum gravity coupled to matter,
and we discuss their viability.Comment: Minor misprints corrected.Eight references added. To appear in
JHEP.34 pages, LaTe
Brane Decay and Death of Open Strings
We show how open strings cease to propagate when unstable D-branes decay. The
information on the propagation is encoded in BSFT two-point functions for
arbitrary profiles of open string excitations. We evaluate them in tachyon
condensation backgrounds corresponding to (i) static spatial tachyon kink (=
lower dimensional BPS D-brane) and (ii) homogeneous rolling tachyon. For (i)
the propagation is restricted to the directions along the tachyon kink, while
for (ii) all the open string excitations cease to propagate at late time and
are subject to a collapsed light cone characterized by Carrollian contraction
of Lorentz group.Comment: 19 pages, published version (typos corrected, a reference added
Classical A_n--W-Geometry
This is a detailed development for the case, of our previous article
entitled "W-Geometries" to be published in Phys. Lett. It is shown that the
--W-geometry corresponds to chiral surfaces in . This is comes out
by discussing 1) the extrinsic geometries of chiral surfaces (Frenet-Serret and
Gauss-Codazzi equations) 2) the KP coordinates (W-parametrizations) of the
target-manifold, and their fermionic (tau-function) description, 3) the
intrinsic geometries of the associated chiral surfaces in the Grassmannians,
and the associated higher instanton- numbers of W-surfaces. For regular points,
the Frenet-Serret equations for --W-surfaces are shown to give the
geometrical meaning of the -Toda Lax pair, and of the conformally-reduced
WZNW models, and Drinfeld-Sokolov equations. KP coordinates are used to show
that W-transformations may be extended as particular diffeomorphisms of the
target-space. This leads to higher-dimensional generalizations of the WZNW and
DS equations. These are related with the Zakharov- Shabat equations. For
singular points, global Pl\"ucker formulae are derived by combining the
-Toda equations with the Gauss-Bonnet theorem written for each of the
associated surfaces.Comment: (60 pages
Off-Shell Interactions for Closed-String Tachyons
Off-shell interactions for localized closed-string tachyons in C/Z_N
superstring backgrounds are analyzed and a conjecture for the effective height
of the tachyon potential is elaborated. At large N, some of the relevant
tachyons are nearly massless and their interactions can be deduced from the
S-matrix. The cubic interactions between these tachyons and the massless fields
are computed in a closed form using orbifold CFT techniques. The cubic
interaction between nearly-massless tachyons with different charges is shown to
vanish and thus condensation of one tachyon does not source the others. It is
shown that to leading order in N, the quartic contact interaction vanishes and
the massless exchanges completely account for the four point scattering
amplitude. This indicates that it is necessary to go beyond quartic
interactions or to include other fields to test the conjecture for the height
of the tachyon potential.Comment: 37 pages, 3 figures, LaTeX, JHEP class. Typos corrected, references
added, published versio
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