385 research outputs found
PMH45 Caregivers’ preferences for treatment options in Attention Deficit Hyperactivity Disorder (ADHD): a latent class analysis
Fermi liquid theory for the Anderson model out of equilibrium
We study low-energy properties of the Anderson impurity under a finite bias
voltage using the perturbation theory in of Yamada and Yosida in the
nonequilibrium Keldysh diagrammatic formalism, and obtain the Ward identities
for the derivative of the self-energy with respect to . The self-energy is
calculated exactly up to terms of order , and , and the
coefficients are defined with respect to the equilibrium ground state. From
these results, the nonlinear response of the current through the impurity has
been deduced up to order .Comment: 8 pages, 1 figur
Anisotropy in the Antiferromagnetic Spin Fluctuations of Sr2RuO4
It has been proposed that Sr_2RuO_4 exhibits spin triplet superconductivity
mediated by ferromagnetic fluctuations. So far neutron scattering experiments
have failed to detect any clear evidence of ferromagnetic spin fluctuations
but, instead, this type of experiments has been successful in confirming the
existence of incommensurate spin fluctuations near q=(1/3 1/3 0). For this
reason there have been many efforts to associate the contributions of such
incommensurate fluctuations to the mechanism of its superconductivity. Our
unpolarized inelastic neutron scattering measurements revealed that these
incommensurate spin fluctuations possess c-axis anisotropy with an anisotropic
factor \chi''_{c}/\chi''_{a,b} of \sim 2.8. This result is consistent with some
theoretical ideas that the incommensurate spin fluctuations with a c-axis
anisotropy can be a origin of p-wave superconductivity of this material.Comment: 5 pages, 3 figures; accepted for publication in PR
Polynomial-Time Amoeba Neighborhood Membership and Faster Localized Solving
We derive efficient algorithms for coarse approximation of algebraic
hypersurfaces, useful for estimating the distance between an input polynomial
zero set and a given query point. Our methods work best on sparse polynomials
of high degree (in any number of variables) but are nevertheless completely
general. The underlying ideas, which we take the time to describe in an
elementary way, come from tropical geometry. We thus reduce a hard algebraic
problem to high-precision linear optimization, proving new upper and lower
complexity estimates along the way.Comment: 15 pages, 9 figures. Submitted to a conference proceeding
Finite-temperature Fermi-edge singularity in tunneling studied using random telegraph signals
We show that random telegraph signals in metal-oxide-silicon transistors at
millikelvin temperatures provide a powerful means of investigating tunneling
between a two-dimensional electron gas and a single defect state. The tunneling
rate shows a peak when the defect level lines up with the Fermi energy, in
excellent agreement with theory of the Fermi-edge singularity at finite
temperature. This theory also indicates that defect levels are the origin of
the dissipative two-state systems observed previously in similar devices.Comment: 5 pages, REVTEX, 3 postscript figures included with epsfi
Spin fluctuations in nearly magnetic metals from ab-initio dynamical spin susceptibility calculations:application to Pd and Cr95V5
We describe our theoretical formalism and computational scheme for making
ab-initio calculations of the dynamic paramagnetic spin susceptibilities of
metals and alloys at finite temperatures. Its basis is Time-Dependent Density
Functional Theory within an electronic multiple scattering, imaginary time
Green function formalism. Results receive a natural interpretation in terms of
overdamped oscillator systems making them suitable for incorporation into spin
fluctuation theories. For illustration we apply our method to the nearly
ferromagnetic metal Pd and the nearly antiferromagnetic chromium alloy Cr95V5.
We compare and contrast the spin dynamics of these two metals and in each case
identify those fluctuations with relaxation times much longer than typical
electronic `hopping times'Comment: 21 pages, 9 figures. To appear in Physical Review B (July 2000
Field dependence of the vortex structure in chiral p-wave superconductors
To investigate the different vortex structure between two chiral pairing p_x
+(-) i p_y, we calculate the pair potential, the internal field, the local
density of states, and free energy in the vortex lattice state based on the
quasiclassical Eilenberger theory, and analyze the magnetic field dependence.
The induced opposite chiral component of the pair potential plays an important
role in the vortex structure. It also produces H^{1/2}-behavior of the
zero-energy density of states at higher field. These results are helpful when
we understand the vortex states in Sr2RuO4.Comment: 11 pages, 10 figures, to be published in Phys. Rev.
Vortex structure in chiral p-wave superconductors
We investigate the vortex structure in chiral p-wave superconductors by the
Bogoliubov-de Gennes theory on a tight-binding model. We calculate the spatial
structure of the pair potential and electronic state around a vortex, including
the anisotropy of the Fermi surface and superconducting gap structure. The
differences of the vortex structure between -wave
and -wave superconductors are clarified in the
vortex lattice state. We also discuss the winding case of the
-wave superconductivity.Comment: 10 pages, 8 figure
An Extreme Solar Event of 20 January 2005: Properties of the Flare and the Origin of Energetic Particles
The extreme solar and SEP event of 20 January 2005 is analyzed from two
perspectives. Firstly, we study features of the main phase of the flare, when
the strongest emissions from microwaves up to 200 MeV gamma-rays were observed.
Secondly, we relate our results to a long-standing controversy on the origin of
SEPs arriving at Earth, i.e., acceleration in flares, or shocks ahead of CMEs.
All emissions from microwaves up to 2.22 MeV line gamma-rays during the main
flare phase originated within a compact structure located just above sunspot
umbrae. A huge radio burst with a frequency maximum at 30 GHz was observed,
indicating the presence of a large number of energetic electrons in strong
magnetic fields. Thus, protons and electrons responsible for flare emissions
during its main phase were accelerated within the magnetic field of the active
region. The leading, impulsive parts of the GLE, and highest-energy gamma-rays
identified with pi^0-decay emission, are similar and correspond in time. The
origin of the pi^0-decay gamma-rays is argued to be the same as that of lower
energy emissions. We estimate the sky-plane speed of the CME to be 2000-2600
km/s, i.e., high, but of the same order as preceding non-GLE-related CMEs from
the same active region. Hence, the flare itself rather than the CME appears to
determine the extreme nature of this event. We conclude that the acceleration,
at least, to sub-relativistic energies, of electrons and protons, responsible
for both the flare emissions and the leading spike of SEP/GLE by 07 UT, are
likely to have occurred simultaneously within the flare region. We do not rule
out a probable contribution from particles accelerated in the CME-driven shock
for the leading GLE spike, which seemed to dominate later on.Comment: 34 pages, 14 Postscript figures. Solar Physics, accepted. A typo
corrected. The original publication is available at
http://www.springerlink.co
Low temperature electronic properties of Sr_2RuO_4 I: Microscopic model and normal state properties
Starting from the quasi one-dimensional kinetic energy of the d_{yz} and
d_{zx} bands we derive a bosonized description of the correlated electron
system in Sr_2RuO_4. At intermediate coupling the magnetic correlations have a
quasi one-dimensional component along the diagonals of the basal plane of the
tetragonal unit cell that accounts for the observed neutron scattering results.
Together with two-dimensional correlations the model consistently accounts for
the normal phase specific heat, cyclotron mass enhancement, static
susceptibility, and Wilson ratio and implies an anomalous high temperature
resistivity.Comment: 12 pages REVTEX, 6 figure
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