17,142 research outputs found
Comparisons of monthly mean cosmic ray counting rates observes from worldwide network of neutron monitors
In order to examine the stability of neutron monitor observation, each of the monthly average counting rates of a neutron monitors is correlated to those of Kiel neutron monitor. The regression coefficients thus obtained are compared with the coupling coefficients of isotropic intensity radiation. The results of the comparisons for five year periods during 1963 to 1982, and for whole period are given. The variation spectrum with a single power law with an exponent of -0.75 up to 50 GV is not so unsatisfactory one. More than one half of the stations show correlations with the coefficient greater than 0.9. Some stations have shifted the level of mean counting rates by changing the instrumental characteristics which can be adjusted
Holographic Derivation of Entanglement Entropy from AdS/CFT
A holographic derivation of the entanglement entropy in quantum (conformal)
field theories is proposed from AdS/CFT correspondence. We argue that the
entanglement entropy in d+1 dimensional conformal field theories can be
obtained from the area of d dimensional minimal surfaces in AdS_{d+2},
analogous to the Bekenstein-Hawking formula for black hole entropy. We show
that our proposal perfectly reproduces the correct entanglement entropy in 2D
CFT when applied to AdS_3. We also compare the entropy computed in AdS_5 \times
S^5 with that of the free N=4 super Yang-Mills.Comment: 5 pages, 3 figures, Revtex, references adde
Nonmetallic Low-Temperature Normal State of K0.70Fe1.46Se1.85Te0.15
The normal-state in-plane resistivity below the zero-field superconducting
transition temperature and the upper critical field Hc2 were measured by
suppressing superconductivity in pulsed magnetic fields for
K0.70Fe1.46Se1.85Te0.15. The normal-state resistivity is found to
increase logarithmically with decrasing temperature as
. Similar to granular metals, our results suggest
that a superconductor - insulator transition below zero-field T may be
induced in high magnetic fields. This is related to the intrinsic real-space
phase-separated states common to all inhomogeneous superconductors.Comment: 6 pages, 4 figure
Field-driven topological glass transition in a model flux line lattice
We show that the flux line lattice in a model layered HTSC becomes unstable
above a critical magnetic field with respect to a plastic deformation via
penetration of pairs of point-like disclination defects. The instability is
characterized by the competition between the elastic and the pinning energies
and is essentially assisted by softening of the lattice induced by a
dimensional crossover of the fluctuations as field increases. We confirm
through a computer simulation that this indeed may lead to a phase transition
from crystalline order at low fields to a topologically disordered phase at
higher fields. We propose that this mechanism provides a model of the low
temperature field--driven disordering transition observed in neutron
diffraction experiments on single crystals.Comment: 11 pages, 4 figures available upon request via snail mail from
[email protected]
Wolf-Rayet and LBV Nebulae as the Result of Variable and Non-Spherical Stellar Winds
The physical basis for interpreting observations of nebular morphology around
massive stars in terms of the evolution of the central stars is reviewed, and
examples are discussed, including NGC 6888, OMC-1, and eta Carinae.Comment: To be published in the Proceedings of IAU Colloquium 169 on Variable
and Non-Spherical Stellar Winds in Luminous Hot Stars, ed. B. Wolf
(Springer-Verlag, Berlin, Heidelberg). 7 pages, including 5 figures. A
full-resolution version of fig 4 is available in the version at
http://www.mpia-hd.mpg.de/theory/preprints.html#maclo
Magnetic excitations in the spin-1/2 triangular-lattice antiferromagnet CsCuBr
We report on high-field electron spin resonance (ESR) studies of magnetic
excitations in the spin-1/2 triangular-lattice antiferromagnet CsCuBr.
Frequency-field diagrams of ESR excitations are measured for different
orientations of magnetic fields up to 25 T. We show that the substantial
zero-field energy gap, K, observed in the low-temperature
excitation spectrum of CsCuBr [Zvyagin , Phys. Rev. Lett. 112,
077206 (2014)], is present well above . Noticeably, the transition into
the long-range magnetically ordered phase does not significantly affect the
size of the gap, suggesting that even below the high-energy spin dynamics
in CsCuBr is determined by short-range-order spin correlations. The
experimental data are compared with results of model spin-wave-theory
calculations for spin-1/2 triangle-lattice antiferromagnet.Comment: 6 pages, 9 figure
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