315 research outputs found
Hall effect in cobalt-doped TiO
We report Hall effect measurements on thin films of cobalt-doped
TiO. Films with low carrier concentrations (10 - 10)
yield a linear behavior in the Hall data while those having higher carrier
concentrations (10 - 10) display anomalous behavior near zero
field. In the entire range of carrier concentration, n-type conduction is
observed. The appearance of the anomalous behavior is accompanied by a possible
structural change from rutile TiO to Ti_[n}O Magneli phase(s)
Two temperature viscous accretion flows around rotating black holes: Description of under-fed systems to ultra-luminous X-ray sources
We discuss two temperature accretion disk flows around rotating black holes.
As we know that to explain observed hard X-rays the choice of Keplerian angular
momentum profile is not unique, we consider the sub-Keplerian regime of the
disk. Without any strict knowledge of the magnetic field structure, we assume
the cooling mechanism is dominated by bremsstrahlung process. We show that in a
range of Shakura-Sunyaev viscosity parameter 0.2\gsim\alpha\gsim0.0005, flow
behavior varies widely, particularly by means of the size of disk, efficiency
of cooling and corresponding temperatures of ions and electrons. We also show
that the disk around a rotating black hole is hotter compared to that around a
Schwarzschild black hole, rendering a larger difference between ion and
electron temperatures in the former case. With all the theoretical solutions in
hand, finally we reproduce the observed luminosities () of two extreme cases
-- the under-fed AGNs and quasars (e.g. Sgr ) with L\gsim 10^{33}
erg/sec to ultra-luminous X-ray sources with erg/sec, at
different combinations of mass accretion rate, ratio of specific heats,
Shakura-Sunyaev viscosity parameter and Kerr parameter, and conclude that Sgr
may be an intermediate spinning black hole.Comment: 21 pages including 5 figures; few typos corrected; to appear in New
Astronom
Bosonic sector of the two-dimensional Hubbard model studied within a two-pole approximation
The charge and spin dynamics of the two-dimensional Hubbard model in the
paramagnetic phase is first studied by means of the two-pole approximation
within the framework of the Composite Operator Method. The fully
self-consistent scheme requires: no decoupling, the fulfillment of both Pauli
principle and hydrodynamics constraints, the simultaneous solution of fermionic
and bosonic sectors and a very rich momentum dependence of the response
functions. The temperature and momentum dependencies, as well as the dependency
on the Coulomb repulsion strength and the filling, of the calculated charge and
spin susceptibilities and correlation functions are in very good agreement with
the numerical calculations present in the literature
Optical band edge shift of anatase cobalt-doped titanium dioxide
We report on the optical properties of magnetic cobalt-doped anatase phase
titanium dioxide Ti_{1-x}Co_{x}O_{2-d} films for low doping concentrations, 0
<= x <= 0.02, in the spectral range 0.2 to 5 eV. For well oxygenated films (d
<< 1) the optical conductivity is characterized by an absence of optical
absorption below an onset of interband transitions at 3.6 eV and a blue shift
of the optical band edge with increasing Co concentration. The absence of below
band gap absorption is inconsistent with theoretical models which contain
midgap magnetic impurity bands and suggests that strong on-site Coulomb
interactions shift the O-band to Co-level optical transitions to energies above
the gap.Comment: 5 pages, 4 figures, 1 table; Version 2 - major content revisio
Magnetization process for a quasi-one-dimensional S=1 antiferromagnet
We investigate the magnetization process for a quasi-one-dimensional S=1
antiferromagnet with bond alternation. By combining the density matrix
renormalization group method with the interchain mean-field theory, we discuss
how the interchain coupling affects the magnetization curve. It is found that
the width of the magnetization plateau is considerably reduced upon introducing
the interchain coupling. We obtain the phase diagram in a magnetic field. The
effect of single-ion anisotropy is also addressed.Comment: 6 pages, 7 eps figure
Self-adapting method for the localization of quantum critical points using Quantum Monte Carlo techniques
A generalization to the quantum case of a recently introduced algorithm (Y.
Tomita and Y. Okabe, Phys. Rev. Lett. {\bf 86}, 572 (2001)) for the
determination of the critical temperature of classical spin models is proposed.
We describe a simple method to automatically locate critical points in
(Quantum) Monte Carlo simulations. The algorithm assumes the existence of a
finite correlation length in at least one of the two phases surrounding the
quantum critical point. We illustrate these ideas on the example of the
critical inter-chain coupling for which coupled antiferromagnetic S=1 spin
chains order at T=0. Finite-size scaling relations are used to determine the
exponents, and in agreement with previous
estimates.Comment: 5 pages, 3 figures, published versio
Origins of the Ambient Solar Wind: Implications for Space Weather
The Sun's outer atmosphere is heated to temperatures of millions of degrees,
and solar plasma flows out into interplanetary space at supersonic speeds. This
paper reviews our current understanding of these interrelated problems: coronal
heating and the acceleration of the ambient solar wind. We also discuss where
the community stands in its ability to forecast how variations in the solar
wind (i.e., fast and slow wind streams) impact the Earth. Although the last few
decades have seen significant progress in observations and modeling, we still
do not have a complete understanding of the relevant physical processes, nor do
we have a quantitatively precise census of which coronal structures contribute
to specific types of solar wind. Fast streams are known to be connected to the
central regions of large coronal holes. Slow streams, however, appear to come
from a wide range of sources, including streamers, pseudostreamers, coronal
loops, active regions, and coronal hole boundaries. Complicating our
understanding even more is the fact that processes such as turbulence,
stream-stream interactions, and Coulomb collisions can make it difficult to
unambiguously map a parcel measured at 1 AU back down to its coronal source. We
also review recent progress -- in theoretical modeling, observational data
analysis, and forecasting techniques that sit at the interface between data and
theory -- that gives us hope that the above problems are indeed solvable.Comment: Accepted for publication in Space Science Reviews. Special issue
connected with a 2016 ISSI workshop on "The Scientific Foundations of Space
Weather." 44 pages, 9 figure
The ALPS project release 1.3: open source software for strongly correlated systems
We present release 1.3 of the ALPS (Algorithms and Libraries for Physics
Simulations) project, an international open source software project to develop
libraries and application programs for the simulation of strongly correlated
quantum lattice models such as quantum magnets, lattice bosons, and strongly
correlated fermion systems. Development is centered on common XML and binary
data formats, on libraries to simplify and speed up code development, and on
full-featured simulation programs. The programs enable non-experts to start
carrying out numerical simulations by providing basic implementations of the
important algorithms for quantum lattice models: classical and quantum Monte
Carlo (QMC) using non-local updates, extended ensemble simulations, exact and
full diagonalization (ED), as well as the density matrix renormalization group
(DMRG). Changes in the new release include a DMRG program for interacting
models, support for translation symmetries in the diagonalization programs, the
ability to define custom measurement operators, and support for inhomogeneous
systems, such as lattice models with traps. The software is available from our
web server at http://alps.comp-phys.org/
Nonlinear electrodynamics of p-wave superconductors
We consider the Maxwell-London electrodynamics of three dimensional
superconductors in p-wave pairing states with nodal points or lines in the
energy gap. The current-velocity relation is then nonlinear in the applied
field, cubic for point nodes and quadratic for lines. We obtain explicit
angular and depth dependent expressions for measurable quantities such as the
transverse magnetic moment, and associated torque. These dependences are
different for point and line nodes and can be used to distinguish between
different order parameters. We discuss the experimental feasibility of this
method, and bring forth its advantages, as well as limitations that might be
present.Comment: Fourteen pages RevTex plus four postscript figure
Pair production of the heavy leptons in future high energy linear e^{+}e^{-} colliders
The littlest Higgs model with T-parity predicts the existence of the T-odd
particles, which can only be produced in pair. We consider pair production of
the T-odd leptons in future high energy linear collider ().
Our numerical results show that, as long as the T-odd leptons are not too
heavy, they can be copiously produced and their possible signals might be
detected via the processes in future
experiments.Comment: Discussions added, typos and references correcte
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