1,216 research outputs found
Relationship between resistivity and specific heat in a canonical non-magnetic heavy fermion alloy system: UPt_5-xAu_x
UPt_(5-x)Au_x alloys form in a single crystal structure, cubic AuBe_5-type,
over a wide range of concentrations from x = 0 to at least x = 2.5. All
investigated alloys, with an exception for x = 2.5, were non-magnetic. Their
electronic specific heat coefficient varies from about 60 (x = 2) to
about 700 mJ/mol K^2 (x = 1). The electrical resistivity for all alloys has a
Fermi-liquid-like temperature variation, \rho = \rho_o + AT^2, in the limit of
T -> 0 K. The coefficient A is strongly enhanced in the heavy-fermion regime in
comparison with normal and transition metals. It changes from about 0.01 (x =
0) to over 2 micro-ohm cm/K^2 (x = 1). A/\gamma^2, which has been postulated to
have a universal value for heavy-fermions, varies from about 10^-6 (x = 0, 0.5)
to 10^-5 micro-ohm cm (mol K/mJ)^2 (x > 1.1), thus from a value typical of
transition metals to that found for some other heavy-fermion metals. This ratio
is unaffected, or only weakly affected, by chemical or crystallographic
disorder. It correlates with the paramagnetic Curie-Weiss temperature of the
high temperature magnetic susceptibility.Comment: 5 pages, 5 eps figures, RevTe
Specific heat of Ce_{0.8}La_{0.2}Al_{3} in magnetic fields: a test of the anisotropic Kondo picture
The specific heat C of Ce_{0.8}La_{0.2}Al_{3} has been measured as a function
of temperature T in magnetic fields up to 14 T. A large peak in C at 2.3 K has
recently been ascribed to an anisotropic Kondo effect in this compound. A 14-T
field depresses the temperature of the peak by only 0.2 K, but strongly reduces
its height. The corresponding peak in C/T shifts from 2.1 K at zero field to
1.7 K at 14 T. The extrapolated specific heat coefficient C/T(T->0) increases
with field over the range studied. We show that these trends are inconsistent
with the anisotropic Kondo model.Comment: 4 pages, 5 figures, ReVTeX + eps
Radiation of Quantized Black Hole
The maximum entropy of a quantized surface is demonstrated to be proportional
to the surface area in the classical limit. The general structure of the
horizon spectrum and the value of the Barbero-Immirzi parameter are found. The
discrete spectrum of thermal radiation of a black hole fits naturally the Wien
profile. The natural widths of the lines are very small as compared to the
distances between them. The total intensity of the thermal radiation is
calculated.Comment: 11 pages; few comments and a reference added; one more reference and
a comment on it added; a note added that the natural widths of the lines are
very small as compared to the distances between the
On the Shear Instability in Relativistic Neutron Stars
We present new results on instabilities in rapidly and differentially
rotating neutron stars. We model the stars in full general relativity and
describe the stellar matter adopting a cold realistic equation of state based
on the unified SLy prescription. We provide evidence that rapidly and
differentially rotating stars that are below the expected threshold for the
dynamical bar-mode instability, beta_c = T/|W| ~ 0.25, do nevertheless develop
a shear instability on a dynamical timescale and for a wide range of values of
beta. This class of instability, which has so far been found only for small
values of beta and with very small growth rates, is therefore more generic than
previously found and potentially more effective in producing strong sources of
gravitational waves. Overall, our findings support the phenomenological
predictions made by Watts, Andersson and Jones on the nature of the low-T/|W|.Comment: 20 pages; accepted to the Classical and Quantum Gravity special issue
for MICRA200
A toy model of open membrane field theory in constant 3-form flux
Based on an explicit computation of the scattering amplitude of four open
membranes in a constant 3-form background, we construct a toy model of the
field theory for open membranes in the large C field limit. It is a
generalization of the noncommutative field theories which describe open strings
in a constant 2-form flux. The noncommutativity due to the B-field background
is now replaced by a nonassociative triplet product. The triplet product
satisfies the consistency conditions of lattice 3d gravity, which is inherent
in the world-volume theory of open membranes. We show the UV/IR mixing of the
toy model by computing some Feynman diagrams. Inclusion of the internal degree
of freedom is also possible through the idea of the cubic matrix.Comment: 31 pages, latex, 2 eps figure
Background independent quantizations: the scalar field II
We are concerned with the issue of quantization of a scalar field in a
diffeomorphism invariant manner. We apply the method used in Loop Quantum
Gravity. It relies on the specific choice of scalar field variables referred to
as the polymer variables. The quantization, in our formulation, amounts to
introducing the `quantum' polymer *-star algebra and looking for positive
linear functionals, called states. Assumed in our paper homeomorphism
invariance allows to derive the complete class of the states. They are
determined by the homeomorphism invariant states defined on the CW-complex
*-algebra. The corresponding GNS representations of the polymer *-algebra and
their self-adjoint extensions are derived, the equivalence classes are found
and invariant subspaces characterized. In the preceding letter (the part I) we
outlined those results. Here, we present the technical details.Comment: 51 pages, LaTeX, no figures, revised versio
Quantized Black Holes, Their Spectrum and Radiation
Under quite natural general assumptions, the following results are obtained.
The maximum entropy of a quantized surface is demonstrated to be proportional
to the surface area in the classical limit. The general structure of the
horizon spectrum is found. The discrete spectrum of thermal radiation of a
black hole Under quite natural general assumptions, the following results are
obtained. The maximum entropy of a quantized surface is demonstrated to be
proportional to the surface area in the classical limit. The general structure
of the horizon spectrum is found. The discrete spectrum of thermal radiation of
a black hole fits the Wien profile. The natural widths of the lines are much
smaller than the distances between them. The total intensity of the thermal
radiation is estimated.
In the special case of loop quantum gravity, the value of the Barbero --
Immirzi parameter is found. Different values for this parameter, obtained under
additional assumption that the horizon is described by a U(1) Chern -- Simons
theory, are demonstrated to be in conflict with the firmly established
holographic bound.Comment: 15 pages, content of few talks given at conferences this summe
Discovery and Cross-Section Measurement of Neutron-Rich Isotopes in the Element Range from Neodymium to Platinum at the FRS
With a new detector setup and the high-resolution performance of the fragment
separator FRS at GSI we discovered 57 new isotopes in the atomic number range
of 60: \nuc{159-161}{Nb}, \nuc{160-163}{Pm}, \nuc{163-166}Sm,
\nuc{167-168}{Eu}, \nuc{167-171}{Gd}, \nuc{169-171}{Tb}, \nuc{171-174}{Dy},
\nuc{173-176}{Ho}, \nuc{176-178}{Er}, \nuc{178-181}{Tm}, \nuc{183-185}{Yb},
\nuc{187-188}{Lu}, \nuc{191}{Hf}, \nuc{193-194}{Ta}, \nuc{196-197}{W},
\nuc{199-200}{Re}, \nuc{201-203}{Os}, \nuc{204-205}{Ir} and \nuc{206-209}{Pt}.
The new isotopes have been unambiguously identified in reactions with a
U beam impinging on a Be target at 1 GeV/u. The isotopic production
cross-section for the new isotopes have been measured and compared with
predictions of different model calculations. In general, the ABRABLA and COFRA
models agree better than a factor of two with the new data, whereas the
semiempirical EPAX model deviates much more. Projectile fragmentation is the
dominant reaction creating the new isotopes, whereas fission contributes
significantly only up to about the element holmium.Comment: 9 pages, 4 figure
Energy and directional signatures for plane quantized gravity waves
Solutions are constructed to the quantum constraints for planar gravity
(fields dependent on z and t only) in the Ashtekar complex connection
formalism. A number of operators are constructed and applied to the solutions.
These include the familiar ADM energy and area operators, as well as new
operators sensitive to directionality (z+ct vs. z-ct dependence). The
directionality operators are quantum analogs of the classical constraints
proposed for unidirectional plane waves by Bondi, Pirani, and Robinson (BPR).
It is argued that the quantum BPR constraints will predict unidirectionality
reliably only for solutions which are semiclassical in a certain sense. The ADM
energy and area operators are likely to have imaginary eigenvalues, unless one
either shifts to a real connection, or allows the connection to occur other
than in a holonomy. In classical theory, the area can evolve to zero. A quantum
mechanical mechanism is proposed which would prevent this collapse.Comment: 54 pages; LaTe
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