165 research outputs found
Temperature dependent magnetic anisotropy in metallic magnets from an ab-initio electronic structure theory: L1_0-ordered FePt
On the basis of a first-principles, relativistic electronic structure theory
of finite temperature metallic magnetism, we investigate the variation of
magnetic anisotropy, K, with magnetisation, M, in metallic ferromagnets. We
apply the theory to the high magnetic anisotropy material, L1_0-ordered FePt,
and find its uniaxial K consistent with a magnetic easy axis perpendicular to
the Fe/Pt layering for all M and to be proportional to M^2 for a broad range of
values of M. For small M, near the Curie temperature, the calculations pick out
the easy axis for the onset of magnetic order. Our results are in good
agreement with recent experimental measurements on this important magnetic
material.Comment: 4 pages, 2 figure
Past distribution of Tilia-feeding Phyllonorycter micromoth (Lepidoptera: Gracillariidae) in the Russian Far East based on survey of historical herbarium
Distribution data of Tilia-feeding Phyllonorycter in the Russian Far East have been retrieved from a century-old Tilia herbarium stored in Vladivostok. Overall, 280 typical mines of Phyllonorycter, some with larvae and pupae, were found on 61 out of 799 herbarized specimens of Tilia spp. collected in Khabarovskii krai and Primorskii krai. For the
first time, the presence of Tilia-feeding Phyllonorycter has been documented in Amurskaya oblast and Jewish Autonomous oblast. High densities of the leafminer have been recorded on Tilia amurensis sampled in Khabarovskii krai and Primorskii krai between 1937 and 2005 suggesting a population dynamics with recurrent outbreaks. Our results confirm the importance of historical herbarium collections in studying trophic interactions and invasion ecology of folivore organisms
Comments on Supercurrent Multiplets, Supersymmetric Field Theories and Supergravity
We analyze various supersymmetry multiplets containing the supercurrent and
the energy-momentum tensor. The most widely known such multiplet, the
Ferrara-Zumino (FZ) multiplet, is not always well-defined. This can happen once
Fayet-Iliopoulos (FI) terms are present or when the Kahler form of the target
space is not exact. We present a new multiplet S which always exists. This
understanding of the supersymmetry current allows us to obtain new results
about the possible IR behavior of supersymmetric theories. Next, we discuss the
coupling of rigid supersymmetric theories to supergravity. When the theory has
an FZ-multiplet or it has a global R-symmetry the standard formalism can be
used. But when this is not the case such simple gauging is impossible. Then, we
must gauge the current S. The resulting theory has, in addition to the graviton
and the gravitino, another massless chiral superfield Phi which is essential
for the consistency of the theory. Some of the moduli of various string models
play the role of Phi. Our general considerations, which are based on the
consistency of supergravity, show that such moduli cannot be easily lifted thus
leading to constraints on gravity/string models.Comment: 27 pages. v2: references added and minor changes. v3: minor changes.
v4: minor clarification
New Super Calogero Models and OSp(4|2) Superconformal Mechanics
We report on the new approach to constructing superconformal extensions of
the Calogero-type systems with an arbitrary number of involved particles. It is
based upon the superfield gauging of non-abelian isometries of some
supersymmetric matrix models. Among its applications, we focus on the new N=4
superconformal system yielding the U(2) spin Calogero model in the bosonic
sector, and the one-particle case of this system, which is a new OSp(4|2)
superconformal mechanics with non-dynamical U(2) spin variables. The
characteristic feature of these models is that the strength of the conformal
inverse-square potential is quantized.Comment: 12 pages, talk presented by E.Ivanov at the XIII International
Conference "Symmetry Methods in Physics", Dubna, July 6-9, 200
Many-Body Superconformal Systems from Hamiltonian Reductions
We propose a new reduction mechanism which allows one to construct n-particle
(super)conformal theories with pairwise interaction starting from a composite
system involving n(n-1)/2+1 copies of the ordinary (super)conformal mechanics.
Applications of the scheme include an N=4 superconformal extension for a
complexification of the Calogero model and a D(2,1|\alpha)-invariant n-particle
system.Comment: 12 pages, no figures. v2: Title changed. New material and
acknowledgements adde
Generalized Conformal Quantum Mechanics of D0-brane
We study the generalized conformal quantum mechanics of the probe D0-brane in
the near horizon background of the bound state of source D0-branes. We
elaborate on the relationship of such model to the M theory in the light cone
frame.Comment: 14 pages, RevTeX, revised version with added references to appear in
Phys. Rev.
w_{\infty} Algebras, Conformal Mechanics, and Black Holes
We discuss BPS solitons in gauged , D=4 supergravity. The
solitons represent extremal black holes interpolating between different vacua
of anti-de Sitter spaces. The isometry superalgebras are determined and the
motion of a superparticle in the extremal black hole background is studied and
confronted with superconformal mechanics. We show that the Virasoro symmetry of
conformal mechanics, which describes the dynamics of the superparticle near the
horizon of the extremal black hole under consideration, extends to a symmetry
under the algebra of area-preserving diffeomorphisms. We find that
a Virasoro subalgebra of can be associated to the Virasoro algebra
of the asymptotic symmetries of . In this way spacetime diffeomorphisms
of translate into diffeomorphisms in phase space: our system offers an
explicit realization of the correspondence. Using the
dimensionally reduced action, the central charge is computed. Finally, we also
present generalizations of superconformal mechanics which are invariant under
and superextensions of .Comment: Latex, 23 pages, minor errors corrected, references added; final
version to appear in Class. Quant. Gra
Non-compact Groups, Coherent States, Relativistic Wave Equations and the Harmonic Oscillator II: Physical and Geometrical Considerations
The physical meaning of the particularly simple non-degenerate supermetric,
introduced in the previous part by the authors, is elucidated and the possible
connection with processes of topological origin in high energy physics is
analyzed and discussed. New possible mechanism of the localization of the
fields in a particular sector of the supermanifold is proposed and the
similarity and differences with a 5-dimensional warped model are shown. The
relation with gauge theories of supergravity based in the group is
explicitly given and the possible original action is presented. We also show
that in this non-degenerate super-model the physic states, in contrast with the
basic states, are observables and can be interpreted as tomographic projections
or generalized representations of operators belonging to the metaplectic group
. The advantage of geometrical formulations based on non-degenerate
super-manifolds over degenerate ones is pointed out and the description and the
analysis of some interesting aspects of the simplest Riemannian superspaces are
presented from the point of view of the possible vacuum solutions.Comment: Stile of the text improved in Journa
A New Class of Four-Dimensional N=1 Supergravity with Non-minimal Derivative Couplings
In the N=1 four-dimensional new-minimal supergravity framework, we
supersymmetrise the coupling of the scalar kinetic term to the Einstein tensor.
This coupling, although introduces a non-minimal derivative interaction of
curvature to matter, it does not introduce harmful higher-derivatives. For this
construction, we employ off-shell chiral and real linear multiplets. Physical
scalars are accommodated in the chiral multiplet whereas curvature resides in a
linear one.Comment: 18 pages, version published at JHE
Age-dependent action of reactive oxygen species on transmitter release in mammalian neuromuscular junctions
© 2016 Elsevier Inc.Reactive oxygen species (ROS) are implicated in aging, but the neurobiological mechanisms of ROS action are not fully understood. Using electrophysiological techniques and biochemical assays, we studied the age-dependent effect of hydrogen peroxide (H2O2) on acetylcholine release in rat diaphragm neuromuscular junctions. H2O2 significantly inhibited both spontaneous (measured as frequency of miniature end-plate potentials) and evoked (amplitude of end-plate potentials) transmitter release in adult rats. The inhibitory effect of H2O2 was much stronger in old rats, whereas in newborns tested during the first postnatal week, H2O2 did not affect spontaneous release from nerve endings and potentiated end-plate potentials. Proteinkinase C activation or intracellular Ca2+ elevation restored redox sensitivity of miniature end-plate potentials in newborns. The resistance of neonates to H2O2 inhibition was associated with higher catalase and glutathione peroxidase activities in skeletal muscle. In contrast, the activities of these enzymes were downregulated in old rats. Our data indicate that the vulnerability of transmitter release to oxidative damage strongly correlates with aging and might be used as an early indicator of senescence
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