7,323 research outputs found
Theory of Orbital Ordering, Fluctuation and Resonant X-ray Scattering in Manganites
A theory of resonant x-ray scattering in perovskite manganites is developed
by applying the group theory to the correlation functions of the pseudospin
operators for the orbital degree of freedom. It is shown that static and
dynamical informations of the orbital state are directly obtained from the
elastic, diffuse and inelastic scatterings due to the tensor character of the
scattering factor. We propose that the interaction and its anisotropy between
orbitals are directly identified by the intensity contour of the diffuse
scattering in the momentum space.Comment: 4 pages, 1 figur
Spin and orbital excitation spectrum in the Kugel-Khomskii model
We discuss spin and orbital ordering in the twofold orbital degenerate
superexchange model in three dimensions relevant to perovskite transition metal
oxides. We focus on the particular point on the classical phase diagram where
orbital degeneracy is lifted by quantum effects exclusively. Dispersion and
damping of the spin and orbital excitations are calculated at this point taking
into account their mutual interaction. Interaction corrections to the
mean-field order parameters are found to be small. We conclude that
quasi-one-dimensional Neel spin order accompanied by the uniform
d_{3z^2-r^2}-type orbital ordering is stable against quantum fluctuations.Comment: 4 pages with 3 PS figures, 1 table, RevTeX, accepted to Phys. Rev. B.
Rapid Communicatio
Constraints on the origin of the ultra-high energy cosmic-rays using cosmic diffuse neutrino flux limits: An analytical approach
Astrophysical neutrinos are expected to be produced in the interactions of
ultra-high energy cosmic-rays with surrounding photons. The fluxes of the
astrophysical neutrinos are highly dependent on the characteristics of the
cosmic-ray sources, such as their cosmological distributions. We study possible
constraints on the properties of cosmic-ray sources in a model-independent way
using experimentally obtained diffuse neutrino flux above 100 PeV. The
semi-analytic formula is derived to estimate the cosmogenic neutrino fluxes as
functions of source evolution parameter and source extension in redshift. The
obtained formula converts the upper-limits on the neutrino fluxes into the
constraints on the cosmic-ray sources. It is found that the recently obtained
upper-limit on the cosmogenic neutrinos by IceCube constrains the scenarios
with strongly evolving ultra-high energy cosmic-ray sources, and the future
limits from an 1 km^3 scale detector are able to further constrain the
ultra-high energy cosmic-rays sources with evolutions comparable to the cosmic
star formation rate.Comment: 9 pages, 3 figures and 1 table. Accepted by Phys. Rev.
Prospects of Measuring General Higgs Couplings at e^+e^- Linear Colliders
We examine how accurately the general HZV couplings, with V=Z,gamma, may be
determined by studying e^+e^- --> Hff-bar processes at future e^+e^- linear
colliders. By using the optimal-observable method, which makes use of all
available experimental information, we find out which combinations of the
various HZV coupling terms may be constrained most efficiently with high
luminosity. We also assess the benefits of measuring the tau-lepton helicities,
identifying the bottom-hadron charges, polarizing the electron beam and running
at two different collider energies. The HZZ couplings are generally found to be
well constrained, even without these options, while the HZ-gamma couplings are
not. The constraints on the latter may be significantly improved by beam
polarization.Comment: 28 pages (LaTeX), 5 figures (axodraw and eps
Rational tangle surgery and Xer recombination on catenanes
The protein recombinase can change the knot type of circular DNA. The action
of a recombinase converting one knot into another knot is normally
mathematically modeled by band surgery. Band surgeries on a 2-bridge knot
N((4mn-1)/(2m)) yielding a (2,2k)-torus link are characterized. We apply this
and other rational tangle surgery results to analyze Xer recombination on DNA
catenanes using the tangle model for protein-bound DNA.Comment: 20 pages, 23 figure
Poor Water Pressure Rises during Earthquakes
A set of piezometers were embedded in sand deposits on a reclaimed island in Tokyo Bay and a seismograph was placed on the ground surface nearby in order to monitor insitu pore water pressures simultaneously with the horizontal accelerations during earthquakes. During the September 25, 1980 earthquake, the instruments registered increases of pore water pressures corresponding to 19% and 16 % of the effective confining pressure at depths of 6.0 m and 14.0 m, respectively. At the same time, a maximum horizontal acceleration of 95 gal was registered at the ground surface
Measurements of lnsitu Pore Water Pressures during Earthquakes
By installing several sets of piezometers and a seismograph in a recently reclaimed sand deposit on Ohgishima Island near Tokyo, Japan, an attempt was made to monitor pore water pressures as well as horizontal accelerations during earthquakes. The limited data obtained thus far have indicated that virtually no pore water could build up in the loose sand deposit with a small scale shaking having a maximum horizontal acceleration of 45 gal on the ground surface
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