3,024 research outputs found
AdS/CFT Correspondence, Poincar\'{e} Vacuum State and Greybody Factors in BTZ Black Holes
The greybody factors in BTZ black holes are evaluated from 2D CFT in the
spirit of AdS/CFT correspondence. The initial state of black holes in the
usual calculation of greybody factors by effective CFT is described as
Poincar\'{e} vacuum state in 2D CFT. The normalization factor which cannot be
fixed in the effective CFT without appealing to string theory is shown to be
determined by the normalized bulk-to-boundary Green function. The relation
among the greybody factors in different dimensional black holes is exhibited.
Two kinds of operators which couple with the boundary
value of massless scalar field are discussed.Comment: 13 pages, Latex, no figures, minor corrections, to appear in Phys.
Lett.
BRST invariant approach to quantum mechanical tunneling
A new approach with BRST invariance is suggested to cure the degeneracy
problem of ill defined path integrals in the path-integral calculationof
quantum mechanical tunneling effects in which the problem arises due to the
occurrence of zero modes. The Faddeev-Popov procedure is avoided and the
integral over the zero mode is transformed in a systematic way into a well
defined integral over instanton positions. No special procedure has to be
adopted as in the Faddeev-Popov method in calculating the Jacobian of the
transformation. The quantum mechanical tunneling for the Sine-Gordon potential
is used as a test of the method and the width of the lowest energy band is
obtained in exact agreement with that of WKB calculations.Comment: 9 pages, LaTe
Antikaon production in nucleon-nucleon reactions near threshold
The antikaon production cross section from nucleon-nucleon reactions near
threshold is studied in a meson exchange model. We include both pion and kaon
exchange, but neglect the interference between the amplitudes. In case of pion
exchange the antikaon production cross section can be expressed in terms of the
antikaon production cross section from a pion-nucleon interaction, which we
take from the experimental data if available. Otherwise, a -resonance
exchange model is introduced to relate the different reaction cross sections.
In case of kaon exchange the antikaon production cross section is related to
the elastic and cross sections, which are again taken from
experimental measurements. We find that the one-meson exchange model gives a
satisfactory fit to the available data for the cross section
at high energies. We compare our predictions for the cross section near
threshold with an earlier empirical parameterization and that from phase space
models.Comment: 16 pages, LaTeX, 5 postscript figures included, submitted to Z. Phys.
Polynomial Interrupt Timed Automata
Interrupt Timed Automata (ITA) form a subclass of stopwatch automata where
reachability and some variants of timed model checking are decidable even in
presence of parameters. They are well suited to model and analyze real-time
operating systems. Here we extend ITA with polynomial guards and updates,
leading to the class of polynomial ITA (PolITA). We prove the decidability of
the reachability and model checking of a timed version of CTL by an adaptation
of the cylindrical decomposition method for the first-order theory of reals.
Compared to previous approaches, our procedure handles parameters and clocks in
a unified way. Moreover, we show that PolITA are incomparable with stopwatch
automata. Finally additional features are introduced while preserving
decidability
Quantum Tunneling of Spin Particles in Periodic Potentials with Asymmetric Twin Barriers
The tunneling effect of a periodic potential with an asymmetric twin barrier
per period is calculated using the instanton method. The model is derived from
the Hamiltonian of a small ferromagnetic particle in an external magnetic field
using the spin-coherent-state path integral. The instantons in two neighbouring
barriers differ and lead to different level shifts . We derive with Bloch theory the energy spectrum which has
formally the structure of an energy band. The spectrum depends on both level
shifts. The removal of Kramer's degeneracy by an external magnetic field is
discussed. In addition we find a new kind of quenching of macroscopic quantum
coherence which is irrelevant to Kramer's degeneracy.Comment: 18 pages, LaTex, one figur
Naphthalene-2,6-dicarboxylic acid–1-methylpyrrolidin-2-one (1/2)
The asymmetric unit of the title compound, C12H8O4·2C5H9NO, contains one half-molecule of naphthalene-2,6-dicarboxylic acid (NDA) and one molecule of 1-methylpyrrolidin-2-one (NMP): the NDA molecules lie on the crystallographic twofold rotation axes. In the crystal, the components are linked by strong O—H⋯O hydrogen bonds and C—H⋯O interactions
2D quantum dilaton gravitational Hamiltonian, boundary terms and new definition for total energy
The ADM and Bondi mass for the RST model have been first discussed from
Hawking and Horowitz's argument. Expressing the localized RST action in terms
of the ADM formulation, the RST Hamiltonian can be derived, meanwhile keeping
track of all boundary terms. Then the total boundary terms can be taken as the
total energy for the RST model. It has been found that there is a new
contribution to the ADM and Bondi mass from the RST boundary due to the
existence of the hidden dynamical field. The ADM and Bondi mass have been
discussed respectively in detail, and some new properties have been found.Comment: 14 pages, Latex file, no figure, to appear in Phys. Lett.
Regularity for harmonic maps into certain Pseudo-Riemannian manifolds
In this article, we investigate the regularity for certain elliptic systems
without a -antisymmetric structure. As applications, we prove some
-regularity theorems for weakly harmonic maps from the unit ball into certain pseudo-Riemannian
manifolds: standard stationary Lorentzian manifolds, pseudospheres
and
pseudohyperbolic spaces
. Consequently, such maps are shown to be H\"{o}lder
continuous (and as smooth as the regularity of the targets permits) in
dimension . In particular, we prove that any weakly harmonic map from a
disc into the De-Sitter space or the Anti-de-Sitter space
is smooth. Also, we give an alternative proof of the
H\"{o}lder continuity of any weakly harmonic map from a disc into the
Hyperbolic space without using the fact that the target is
nonpositively curved. Moreover, we extend the notion of generalized (weakly)
harmonic maps from a disc into the standard sphere to the case
that the target is or
, and obtain some -regularity results for such
generalized (weakly) harmonic maps.Comment: to appear in J. Math. Pures App
Kinetics of maternal immunity against rabies in fox cubs (Vulpes vulpes)
BACKGROUND: In previous experiments, it was demonstrated that maternal antibodies (maAb) against rabies in foxes (Vulpes vulpes) were transferred from the vixen to her offspring. However, data was lacking from cubs during the first three weeks post partum. Therefore, this complementary study was initiated. METHODS: Blood samples (n = 281) were collected from 64 cubs (3 to 43 days old) whelped by 19 rabies-immune captive-bred vixens. Sera was collected up to six times from each cub. The samples were analysed by a fluorescence focus inhibition technique (RFFIT), and antibody titres (nAb) were expressed in IU/ml. The obtained data was pooled with previous data sets. Subsequently, a total of 499 serum samples from 249 cubs whelped by 54 rabies-immune vixens were fitted to a non-linear regression model. RESULTS: The disappearance rate of maAb was independent of the vixens' nAb-titre. The maAb-titre of the cubs decreased exponentially with age and the half-life of the maAb was estimated to be 9.34 days. However, maAb of offspring whelped by vixens with high nAb-titres can be detected for longer by RFFIT than that of offspring whelped by vixens with relatively low nAb-titres. At a mean critical age of about 23 days post partum, maAb could no longer be distinguished from unspecific reactions in RFFIT depending on the amount of maAb transferred by the mother. CONCLUSIONS: The amount of maAb cubs receive is directly proportional to the titre of the vixen and decreases exponentially with age below detectable levels in seroneutralisation tests at a relatively early age
Design principles of hair-like structures as biological machines
Hair-like structures are prevalent throughout biology and frequently act to sense or alter interactions with an organism's environment. The overall shape of a hair is simple: a long, filamentous object that protrudes from the surface of an organism. This basic design, however, can confer a wide range of functions, owing largely to the flexibility and large surface area that it usually possesses. From this simple structural basis, small changes in geometry, such as diameter, curvature and inter-hair spacing, can have considerable effects on mechanical properties, allowing functions such as mechanosensing, attachment, movement and protection. Here, we explore how passive features of hair-like structures, both individually and within arrays, enable diverse functions across biology. Understanding the relationships between form and function can provide biologists with an appreciation for the constraints and possibilities on hair-like structures. Additionally, such structures have already been used in biomimetic engineering with applications in sensing, water capture and adhesion. By examining hairs as a functional mechanical unit, geometry and arrangement can be rationally designed to generate new engineering devices and ideas
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