5,088 research outputs found
Influence of intermartensitic transitions on transport properties of Ni2.16Mn0.84Ga alloy
Magnetic, transport, and x-ray diffraction measurements of ferromagnetic
shape memory alloy NiMnGa revealed that this alloy undergoes
an intermartensitic transition upon cooling, whereas no such a transition is
observed upon subsequent heating. The difference in the modulation of the
martensite forming upon cooling from the high-temperature austenitic state
[5-layered (5M) martensite], and the martensite forming upon the
intermartensitic transition [7-layered (7M) martensite] strongly affects the
magnetic and transport properties of the alloy and results in a large thermal
hysteresis of the resistivity and magnetization . The
intermartensitic transition has an especially marked influence on the transport
properties, as is evident from a large difference in the resistivity of the 5M
and 7M martensite, , which is larger than the jump of resistivity at
the martensitic transition from the cubic austenitic phase to the monoclinic 5M
martensitic phase. We assume that this significant difference in between
the martensitic phases is accounted for by nesting features of the Fermi
surface. It is also suggested that the nesting hypothesis can explain the
uncommon behavior of the resistivity at the martensitic transition, observed in
stoichiometric and near-stoichiometric Ni-Mn-Ga alloys.Comment: 7 pages, 6 figures, REVTEX
Numerical Study of Length Spectra and Low-lying Eigenvalue Spectra of Compact Hyperbolic 3-manifolds
In this paper, we numerically investigate the length spectra and the
low-lying eigenvalue spectra of the Laplace-Beltrami operator for a large
number of small compact(closed) hyperbolic (CH) 3-manifolds. The first non-zero
eigenvalues have been successfully computed using the periodic orbit sum
method, which are compared with various geometric quantities such as volume,
diameter and length of the shortest periodic geodesic of the manifolds. The
deviation of low-lying eigenvalue spectra of manifolds converging to a cusped
hyperbolic manifold from the asymptotic distribution has been measured by
function and spectral distance.Comment: 19 pages, 18 EPS figures and 2 GIF figures (fig.10) Description of
cusped manifolds in section 2 is correcte
The matrix realization of affine Jacobi varieties and the extended Lotka-Volterra lattice
We study completely integrable Hamiltonian systems whose monodromy matrices
are related to the representatives for the set of gauge equivalence classes
of polynomial matrices. Let be the algebraic
curve given by the common characteristic equation for
. We construct the isomorphism from the set of
representatives to an affine part of the Jacobi variety of . This variety
corresponds to the invariant manifold of the system, where the Hamiltonian flow
is linearized. As the application, we discuss the algebraic completely
integrability of the extended Lotka-Volterra lattice with a periodic boundary
condition.Comment: Revised version, 26 page
Massive Spin 3/2 Electrodynamics
We study the general non-minimally coupled charged massive spin 3/2 model
both for its low energy phenomenological properties and for its unitarity,
causality and degrees of freedom behaviour. When the model is viewed as an
effective theory, its parameters (after ensuring the correct excitation count)
are related to physical characteristics, such as the magnetic moment g factor,
by means of low energy theorems. We also provide the corresponding higher spin
generalisation. Separately, we consider both low and high energy unitarity, as
well as the causality aspects of our models. None (including truncated N=2
supergravity) is free of the minimal model's acausality.Comment: 23 pages, 1 figure, LaTeX and axodraw.sty, novel Majorana-type term
included; results unaltere
Accelerating Cosmologies from Exponential Potentials
An exponential potential of the form arising from
the hyperbolic or flux compactification of higher-dimensional theories is of
interest for getting short periods of accelerated cosmological expansions.
Using a similar potential but derived for the combined case of hyperbolic-flux
compactification, we study the four-dimensional flat (and open) FLRW
cosmologies and give analytic (and numerical) solutions with exponential
behavior of scale factors. We show that, for the M-theory motivated potentials,
the cosmic acceleration of the universe can be eternal if the spatial curvature
of the 4d spacetime is negative, while the acceleration is only transient for a
spatially flat universe. We also comment on the size of the internal space and
its associated geometric bounds on massive Kaluza-Klein excitations.Comment: 17 pages, 6 figures; minor typos fixe
Caracterização de frutos de Morinda citrifolia L. (Rubiaceae) nas condições de Manaus - AM.
O objetivo deste estudo foi caracterizar os frutos de noni, nas condições de Manaus, AM
A New Model for Fermion Masses in Supersymmetric Grand Unified Theories
We present a simple model for fermion mass matrices and quark mixing in the
context of supersymmetric grand unified theories and show its agreement with
experiment. Our model realizes the GUT mass relations , , in a new way and is easily consistent with values of
suggested by MSSM fits to LEP data.Comment: Latex, 8 p., ITP-SB-93-37 (revised version contains minor changes in
some wording and citations; no changes in analytic or numerical results.
UV Dust Attenuation in Star-forming Galaxies: II Calibrating the A(UV) vs. L_TIR/L_UV relation
We investigate the dependence of the total-infrared (TIR) to UV luminosity
ratio method for calculating the UV dust attenuation A(UV) from the age of the
underlying stellar populations by using a library of spectral energy
distributions for galaxies with different star formation histories. Our
analysis confirms that the TIR/UV vs. A(UV) relation varies significantly with
the age of the underlying stellar population: i.e. for the same TIR/UV ratio,
systems with low specific star formation rate (SSFR) suffer a lower UV
attenuation than starbursts. Using a sample of nearby field and cluster spiral
galaxies we show that the use of a standard (i.e. age independent) TIR/UV vs.
A(UV) relation leads to a systematic overestimate up to 2 magnitudes of the
amount of UV dust attenuation suffered by objects with low SSFR and in
particular HI-deficient star forming cluster galaxies. This result points out
that the age independent vs. relation cannot be used to study
the UV properties of large samples of galaxies including low star-forming
systems and passive spirals. Therefore we give some simple empirical relations
from which the UV attenuation can be estimated taking into account its
dependence on the age of the stellar populations, providing a less biased view
of UV properties of galaxies.Comment: 16 pages, 10 figures, 6 tables. Accepted for publication on MNRAS
main journal. High resolution version and tables also available at
http://www.astro.cf.ac.uk/pub/Luca.Cortese/UVattenuation.htm
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