1,376 research outputs found
Particle Motion and Electromagnetic Fields of Rotating Compact Gravitating Objects with Gravitomagnetic Charge
The exact solution for the electromagnetic field occuring when the
Kerr-Taub-NUT compact object is immersed (i) in an originally uniform magnetic
field aligned along the axis of axial symmetry (ii) in dipolar magnetic field
generated by current loop has been investigated. Effective potential of motion
of charged test particle around Kerr-Taub-NUT gravitational source immersed in
magnetic field with different values of external magnetic field and NUT
parameter has been also investigated. In both cases presence of NUT parameter
and magnetic field shifts stable circular orbits in the direction of the
central gravitating object. Finally we find analytical solutions of Maxwell
equations in the external background spacetime of a slowly rotating magnetized
NUT star. The star is considered isolated and in vacuum, with monopolar
configuration model for the stellar magnetic field.Comment: 18 pages, 6 figures, new results in section 2 added, section 3 is
revised, 3 references are adde
An extended pair tunneling model: studies on bilayer splitting and some superconducting state properties
We consider an extended version of the pair tunneling model including
interlayer single particle hopping (ISPH) as a complementary process to pair
tunneling. The normal state gap, as found in cuprates, is taken to suppress the
effective ISPH in conformity with the experimental observations, and this in
turn enhances the pair tunneling process. The effective ISPH involves a
probability factor P for which we consider two choices and provide
phenomenological arguments in favour of them. We address the issue of bilayer
splitting by calculating the spectral density function and corresponding
photoemission intensity curves and show that our calculations conform with the
absence of bilayer splitting observed in ARPES experiments on Bi2212. We have
also studied the temperature variation of the superconducting gap and ratio of
the superconducting gap to T_c. Our results, obtained for both the choices of
P, are reasonably in good agreement with those from experiments on cuprate
superconductors. A linear T-dependent choice of P, however, yields a precise
match to the experimantal data of the temperature varying superconducting gap.Comment: Latex file, 17 pages, 5 figures (postscript files) include
Towards the Thermodynamics of Localization Processes
We study the entropy time evolution of a quantum mechanical model, which is
frequently used as a prototype for Anderson's localization. Recently Latora and
Baranger [V. Latora, M. Baranger, Phys. Rev.Lett. 82, 520(1999)] found that
there exist three entropy regimes, a transient regime of passage from dynamics
to thermodynamics, a linear in time regime of entropy increase, namely a
thermodynamic regime of Kolmogorov kind, and a saturation regime. We use the
non-extensive entropic indicator recently advocated by Tsallis [ C. Tsallis, J.
Stat. Phys. 52, 479 (1988)] with a mobile entropic index q, and we find that
with the adoption of the ``magic'' value q = Q = 1/2 the Kolmogorov regime
becomes more extended and more distinct than with the traditional entropic
index q = 1. We adopt a two-site model to explain these properties by means of
an analytical treatment and we argue that Q =1/2 might be a typical signature
of the occurrence of Anderson's localization.Comment: 13 pages, 8 figures submitted to Phys. Rev.
Gaussian multiplicative Chaos for symmetric isotropic matrices
Motivated by isotropic fully developed turbulence, we define a theory of
symmetric matrix valued isotropic Gaussian multiplicative chaos. Our
construction extends the scalar theory developed by J.P. Kahane in 1985
Retrospective evaluation of foot-and-mouth disease vaccineeffectiveness in Turkey
AbstractFoot-and-mouth disease (FMD) is present in much of Turkey and its control is largely based on vaccination. The arrival of the FMD Asia-1 serotype in Turkey in 2011 caused particular concern, spreading rapidly westwards across the country towards the FMD free European Union. With no prior natural immunity, control of spread would rely heavily on vaccination.Unlike human vaccines, field protection is rarely evaluated directly for FMD vaccines. Between September 2011 and July 2012 we performed four retrospective outbreak investigations to assess the vaccine effectiveness (VE) of FMD Asia-1 vaccines in Turkey. Vaccine effectiveness is defined as the reduction in risk in vaccinated compared to unvaccinated individuals with similar virus exposure in the field.The four investigations included 12 villages and 1230 cattle >4 months of age. One investigation assessed the FMD Asia-1 Shamir vaccine, the other three evaluated the recently introduced FMD Asia-1 TUR 11 vaccine made using a field isolate of the FMD Asia-1 Sindh-08 lineage that had recently entered Turkey.After adjustment for confounding, the TUR 11 vaccine provided moderate protection against both clinical disease VE=69% [95% CI: 50%â81%] and infection VE=63% [95% CI: 29%â81%]. However, protection was variable with some herds with high vaccine coverage still experiencing high disease incidence. Some of this variability will be the result of the variation in virus challenge and immunity that occurs under field conditions.In the outbreak investigated there was no evidence that the Asia-1 Shamir vaccine provided adequate protection against clinical FMD with an incidence of 89% in single vaccinated cattle and 69% in those vaccinated two to five times.Based on these effectiveness estimates, vaccination alone is unlikely to produce the high levels of herd immunity needed to control FMD without additional control measures
c-Axis Transport and Resistivity Anisotropy of Lightly- to Moderately-Doped La_{2-x}Sr_{x}CuO_{4} Single Crystals: Implications on the Charge Transport Mechanism
Both the in-plane and the out-of-plane resistivities (\rho_{ab} and \rho_{c})
are measured in high-quality La_{2-x}Sr_{x}CuO_{4} (LSCO) single crystals in
the lightly- to moderately-doped region, x = 0.01 to 0.10, and the resistivity
anisotropy is determined. In all the samples studied, the anisotropy ratio \rho
_{c}/\rho_{ab} quickly increases with decreasing temperature, although in
non-superconducting samples the strong localization effect causes \rho
_{c}/\rho_{ab} to decrease at low temperatures. Most notably, it is found that
\rho_{c}/\rho_{ab} at moderate temperatures (100 - 300 K) is almost completely
independent of doping in the non-superconducting regime (x = 0.01 to 0.05);
this indicates that the same charge confinement mechanism that renormalizes the
c-axis hopping rate is at work down to x = 0.01. It is discussed that this
striking x-independence of \rho_{c}/\rho_{ab} is consistent with the idea that
holes form a self-organized network of hole-rich regions, which also explains
the unusually metallic in-plane transport of the holes in the lightly-doped
region. Furthermore, the data for x > 0.05 suggest that the emergence of the
superconductivity is related to an increase in the c-axis coupling.Comment: 7 pages, 5 figures, submitted to Phys. Rev.
Asymmetric Gepner Models II. Heterotic Weight Lifting
A systematic study of "lifted" Gepner models is presented. Lifted Gepner
models are obtained from standard Gepner models by replacing one of the N=2
building blocks and the factor by a modular isomorphic model on the
bosonic side of the heterotic string. The main result is that after this change
three family models occur abundantly, in sharp contrast to ordinary Gepner
models. In particular, more than 250 new and unrelated moduli spaces of three
family models are identified. We discuss the occurrence of fractionally charged
particles in these spectra.Comment: 46 pages, 17 figure
Kolmogorov turbulence, Anderson localization and KAM integrability
The conditions for emergence of Kolmogorov turbulence, and related weak wave
turbulence, in finite size systems are analyzed by analytical methods and
numerical simulations of simple models. The analogy between Kolmogorov energy
flow from large to small spacial scales and conductivity in disordered solid
state systems is proposed. It is argued that the Anderson localization can stop
such an energy flow. The effects of nonlinear wave interactions on such a
localization are analyzed. The results obtained for finite size system models
show the existence of an effective chaos border between the
Kolmogorov-Arnold-Moser (KAM) integrability at weak nonlinearity, when energy
does not flow to small scales, and developed chaos regime emerging above this
border with the Kolmogorov turbulent energy flow from large to small scales.Comment: 8 pages, 6 figs, EPJB style
Cosmogenic nuclides constrain surface fluctuations of an East Antarctic outlet glacier since the Pliocene
Understanding past changes in the Antarctic ice sheets provides insight into how they might respond to future climate warming. During the Pliocene and Pleistocene, geological data show that the East Antarctic Ice Sheet responded to glacial and interglacial cycles by remaining relatively stable in its interior, but oscillating at its marine-based margin. It is currently not clear how outlet glaciers, which connect the ice sheet interior to its margin, responded to these orbitally-paced climate cycles. Here we report new ice surface constraints from Skelton Glacier, an outlet of the East Antarctic ice sheet, which drains into the Ross Ice Shelf. Our multiple-isotope (10Be and 26Al) cosmogenic nuclide data indicate that currently ice-free areas adjacent to the glacier underwent substantial periods of exposure and ice cover in the past. We use an exposure-burial model driven by orbitally-paced glacialâinterglacial cycles to determine the probable ice surface history implied by our data. This analysis shows that: 1) the glacier surface has likely fluctuated since at least the Pliocene; 2) the ice surface was >200 m higher than today during glacial periods, and the glacier has been thicker than present for âŒ75â90% of each glacialâinterglacial cycle; and 3) ice cover at higher elevations possibly occurred for a relatively shorter time per Pliocene cycle than Pleistocene cycle. Our multiple-nuclide approach demonstrates the magnitude of ice surface fluctuations during the Pliocene and Pleistocene that are linked to marine-based ice margin variability
Spin-resonance modes of the spin-gap magnet TlCuCl_3
Three kinds of magnetic resonance signals were detected in crystals of the
spin-gap magnet TlCuCl_3.
First, we have observed the microwave absorption due to the excitation of the
transitions between the singlet ground state and the excited triplet states.
This mode has the linear frequency-field dependence corresponding to the
previously known value of the zero-field spin-gap of 156 GHz and to the closing
of spin-gap at the magnetic field H_c of about 50 kOe.
Second, the thermally activated resonance absorption due to the transitions
between the spin sublevels of the triplet excitations was found. These
sublevels are split by the crystal field and external magnetic field.
Finally, we have observed antiferromagnetic resonance absorption in the
field-induced antiferromagnetic phase above the critical field H_c. This
resonance frequency is strongly anisotropic with respect to the direction of
the magnetic field.Comment: v.2: typo correction (one of the field directions was misprinted in
the v.1
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