3,001 research outputs found
Large thermal Hall coefficient in bismuth
We present a systematical study of thermal Hall effect on a bismuth single
crystal by measuring resistivity, Hall coefficient, and thermal conductivity
under magnetic field, which shows a large thermal Hall coefficient comparable
to the largest one in a semiconductor HgSe. We discuss that this is mainly due
to a large mobility and a low thermal conductivity comparing theoretical
calculations, which will give a route for controlling heat current in
electronic devices.Comment: 4pages, 3 figure
Glassy dynamics in thin films of polystyrene
Glassy dynamics was investigated for thin films of atactic polystyrene by
complex electric capacitance measurements using dielectric relaxation
spectroscopy. During the isothermal aging process the real part of the electric
capacitance increased with time, whereas the imaginary part decreased with
time. It follows that the aging time dependences of real and imaginary parts of
the electric capacitance were primarily associated with change in volume (film
thickness) and dielectric permittivity, respectively. Further, dielectric
permittivity showed memory and rejuvenation effects in a similar manner to
those observed for poly(methyl methacrylate) thin films. On the other hand,
volume did not show a strong rejuvenation effect.Comment: 7 pages, 7 figures. Phys. Rev. E (in press
Relative Burial Depths of Nakhlites: An Update
Nakhlites are augite-rich cumulate rocks with variable amounts of olivine and groundmass plus minor Fe, Ti oxides [e.g., 1]. Our previous studies revealed that nakhlites showed correlated petrography and mineralogy that could be explained by different locations (burial depths) in a common cooling cumulate pile [e.g., 2]. We so far analyzed six of the seven currently known nakhlites, Nakhla (Nak), Governador Valadares (GV), Lafayette (Laf), NWA817, Y000593 (Y) and MIL03346 (MIL) [e.g., 2,3] and calculated cooling rates of four nakhlites (Nak, GV, Laf, and NWA817) by using chemical zoning of olivine [e.g., 4]. In this abstract, we complete our examination of petrographic and mineralogical variation of all currently known nakhlites by adding petrology and mineralogy of NWA998. We also report results of cooling calculations for Y, MIL and NWA998. Then, we update our model of the nakhlite igneous body in terms of relative burial depth of each sample
Role of Oxygen Electrons in the Metal-Insulator Transition in the Magnetoresistive Oxide LaSrMnO Probed by Compton Scattering
We have studied the [100]-[110] anisotropy of the Compton profile in the
bilayer manganite. Quantitative agreement is found between theory and
experiment with respect to the anisotropy in the two metallic phases (i.e. the
low temperature ferromagnetic and the colossal magnetoresistant phase under a
magnetic field of 7 T). Robust signatures of the metal-insulator transition are
identified in the momentum density for the paramagnetic phase above the Curie
temperature. We interpret our results as providing direct evidence for the
transition from the metallic-like to the admixed ionic-covalent bonding
accompanying the magnetic transition. The number of electrons involved in this
phase transition is estimated from the area enclosed by the Compton profile
anisotropy differences. Our study demonstrates the sensitivity of the Compton
scattering technique for identifying the number and type of electrons involved
in the metal-insulator transition.Comment: 4 pages, 4 figures, accepted for publication in Physical Review
Letter
Biodiversity and Spatial Heterogeneity in Semi-Natural Grasslands in a Mountain Area in Slovakia
The spatial pattern of vegetation in the following 3 semi-natural grasslands in Banska Bystrica, Slovakia, was observed in August, 1998: (1) a grassland sown with improved herbage plants after plowing in 1991, (2) a grassland oversown with improved herbage plants in 1991, and (3) a natural grassland without any treatment at the time of establishment. A new method of measuring vegetation was adopted: in each grassland, 50 quadrats 50 cm × 50 cm, composed of 4 smaller cells 25 cm × 25 cm, were set up, and all the species in each cell were recorded. The sown grassland displayed the highest species richness and diversity though its spatial heterogeneity was very high while in the natural grassland these characteristics were least pronounced. The highest species richness and diversity could be maintained on the average in the sown grasslands although their plot-to-plot variations were very large
``Flux'' state in double exchange model
We study the ground state properties of the double-exchange systems. The
phase factor of the hopping matrix elements arises from spin texture
in two or more dimensions. A novel ``flux'' state is stabilized against the
canted antiferromagnetic and spiral spin states. In a certain range of hole
doping, the phase separation occurs between the ``flux'' state and
antiferromagnetic states. Constructing a trial state which provides the
rigorous upper bound on the ground state, we show that the metallic canted
antiferromagnetic state is not stable in the double exchange model.Comment: REVTEX, 8 pages and 4 PS figure
Quantum corrections to static solutions of Nahm equation and Sin-Gordon models via generalized zeta-function
One-dimensional Yang-Mills Equations are considered from a point of view of a
class of nonlinear Klein-Gordon-Fock models. The case of self-dual Nahm
equations and non-self-dual models are discussed. A quasiclassical quantization
of the models is performed by means of generalized zeta-function and its
representation in terms of a Green function diagonal for a heat equation with
the correspondent potential. It is used to evaluate the functional integral and
quantum corrections to mass in the quasiclassical approximation.
Quantum corrections to a few periodic (and kink) solutions of the Nahm as a
particular case of the Ginzburg-Landau (phi-in-quadro) and and Sin-Gordon
models are evaluated in arbitrary dimensions. The Green function diagonal for
heat equation with a finite-gap potential is constructed by universal
description via solutions of Hermit equation. An alternative approach based on
Baker-Akhiezer functions for KP equation is proposed . The generalized
zeta-function and its derivative at zero point as the quantum corrections to
mass is expressed in terms of elliptic integrals.Comment: Workshop Nonlinear Physics and Experiment; Gallipoli, 200
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An Evolutionarily Threat-Relevant Odor Strengthens Human Fear Memory.
Olfaction is an evolutionary ancient sense, but it remains unclear to what extent it can influence routine human behavior. We examined whether a threat-relevant predator odor (2-methyl-2-thiazoline) would contextually enhance the formation of human fear memory associations. Participants who learned to associate visual stimuli with electric shock in this predator odor context later showed stronger fear responses to the visual stimuli than participants who learned in an aversiveness-matched control odor context. This effect generalized to testing in another odor context, even after extinction training. Results of a separate experiment indicate that a possible biological mechanism for this effect may be increased cortisol levels in a predator odor context. These results suggest that innate olfactory processes can play an important role in human fear learning. Modulatory influences of odor contexts may partly explain the sometimes maladaptive persistence of human fear memory, e.g., in post-traumatic stress disorders
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