16,091 research outputs found
Ion-Cyclotron Double Resonance
A charged particle in a uniform moving magnetic field H describes a circular orbit in a plance perpendicular to H with an angular frequency or "cyclotron frequency" omagae. When an alternating electric field E(t) is applied normal to H at omegae, the ions absorb energy from the alternating electric field, and are accelerated to larger velocities and orbital radii. [1] The absorption of energy from E(t) at the cyclotron resonance frequency can be conveniently detected using a marginal oscillator detector. When the ions accelerated by E(t) collide with other particles, they lose some of their excess energy. A mixture of ions and neutral molecules in the presence of H and E(t) then reaches a steady-state condition in which the energy gained by the ions from E(t) between collisions is lost to the neutral molecules in collisions
Real-time dynamics in Quantum Impurity Systems: A Time-dependent Numerical Renormalization Group Approach
We develop a general approach to the nonequilibrium dynamics of quantum
impurity systems for arbitrary coupling strength. The numerical renormalization
group is used to generate a complete basis set necessary for the correct
description of the time evolution. We benchmark our method with the exact
analytical solution for the resonant-level model. As a first application, we
investigate the equilibration of a quantum dot subject to a sudden change of
the gate voltage and external magnetic field. Two distinct relaxation times are
identified for the spin and charge dynamics.Comment: 5 pages, 5 figure
Chart audit of inpatient treatment of schizophrenic patients: implications for development of coordinated care paths.
This study offers important information regarding the standard of care provided to schizophrenic patients treated at one inpatient facility. The findings were particularly useful in the development of a care path for this specific population. Areas for improvement identified in this research include medical tests, master treatment planning, documentation of care, patient teaching, and discharge planning. Given the limited health care dollars and the lack of a cure for schizophrenia, this research emphasizes the fact that treatment guidelines need to be aggressively tested as to their relevance to practice
Properties of Resonating-Valence-Bond Spin Liquids and Critical Dimer Models
We use Monte Carlo simulations to study properties of Anderson's
resonating-valence-bond (RVB) spin-liquid state on the square lattice (i.e.,
the equal superposition of all pairing of spins into nearest-neighbor singlet
pairs) and compare with the classical dimer model (CDM). The latter system also
corresponds to the ground state of the Rokhsar-Kivelson quantum dimer model at
its critical point. We find that although spin-spin correlations decay
exponentially in the RVB, four-spin valence-bond-solid (VBS) correlations are
critical, qualitatively like the well-known dimer-dimer correlations of the
CDM, but decaying more slowly (as with , compared with
for the CDM). We also compute the distribution of monomer (defect) pair
separations, which decay by a larger exponent in the RVB than in the CDM. We
further study both models in their different winding number sectors and
evaluate the relative weights of different sectors. Like the CDM, all the
observed RVB behaviors can be understood in the framework of a mapping to a
"height" model characterized by a gradient-squared stiffness constant . Four
independent measurements consistently show a value , with the same kinds of numerical evaluations of give
results in agreement with the rigorously known value . The
background of a nonzero winding number gradient introduces spatial
anisotropies and an increase in the effective K, both of which can be
understood as a consequence of anharmonic terms in the height-model free
energy, which are of relevance to the recently proposed scenario of "Cantor
deconfinement" in extended quantum dimer models. We also study ensembles in
which fourth-neighbor (bipartite) bonds are allowed, at a density controlled by
a tunable fugacity, resulting (as expected) in a smooth reduction of K.Comment: 26 pages, 21 figures. v3: final versio
Edge Dynamics in a Quantum Spin Hall State: Effects from Rashba Spin-Orbit Interaction
We analyze the dynamics of the helical edge modes of a quantum spin Hall
state in the presence of a spatially non-uniform Rashba spin-orbit (SO)
interaction. A randomly fluctuating Rashba SO coupling is found to open a
scattering channel which causes localization of the edge modes for a weakly
screened electron-electron (e-e) interaction. A periodic modulation of the SO
coupling, with a wave number commensurate with the Fermi momentum, makes the
edge insulating already at intermediate strengths of the e-e interaction. We
discuss implications for experiments on edge state transport in a HgTe quantum
well.Comment: 4 pages, 2 figures; published versio
Topological Optimization of the Evaluation of Finite Element Matrices
We present a topological framework for finding low-flop algorithms for
evaluating element stiffness matrices associated with multilinear forms for
finite element methods posed over straight-sided affine domains. This framework
relies on phrasing the computation on each element as the contraction of each
collection of reference element tensors with an element-specific geometric
tensor. We then present a new concept of complexity-reducing relations that
serve as distance relations between these reference element tensors. This
notion sets up a graph-theoretic context in which we may find an optimized
algorithm by computing a minimum spanning tree. We present experimental results
for some common multilinear forms showing significant reductions in operation
count and also discuss some efficient algorithms for building the graph we use
for the optimization
ALFA & 3D: integral field spectroscopy with adaptive optics
One of the most important techniques for astrophysics with adaptive optics is
the ability to do spectroscopy at diffraction limited scales. The extreme
difficulty of positioning a faint target accurately on a very narrow slit can
be avoided by using an integral field unit, which provides the added benefit of
full spatial coverage. During 1998, working with ALFA and the 3D integral field
spectrometer, we demonstrated the validity of this technique by extracting and
distinguishing spectra from binary stars separated by only 0.26". The
combination of ALFA & 3D is also ideally suited to imaging distant galaxies or
the nuclei of nearby ones, as its field of view can be changed between
1.2"x1.2" and 4"x4", depending on the pixel scale chosen. In this contribution
we present new results both on galactic targets, namely young stellar objects,
as well as extra-galactic objects including a Seyfert and a starburst nucleus.Comment: SPIE meeting 4007 on Adaptive Optical Systems Technology, March 200
Zero-bias conductance in carbon nanotube quantum dots
We present numerical renormalization group calculations for the zero-bias
conductance of quantum dots made from semiconducting carbon nanotubes. These
explain and reproduce the thermal evolution of the conductance for different
groups of orbitals, as the dot-lead tunnel coupling is varied and the system
evolves from correlated Kondo behavior to more weakly correlated regimes. For
integer fillings of an SU(4) model, we find universal scaling
behavior of the conductance that is distinct from the standard SU(2) universal
conductance, and concurs quantitatively with experiment. Our results also agree
qualitatively with experimental differential conductance maps.Comment: 4 pages, 5 figure
The Geology of the Davis Ranch Oil Pool, Wabaunsee County, Kansas
The discovery of the Davis Ranch oil pool in Wabaunsee County, Kansas, in April 1949 started one of the most important leasing and wildcat drilling programs in Kansas in recent years. In the 21 months since the completion of the discovery well, 65 holes have been drilled in Wabaunsee County alone. Of this total 38 may be classed as wildcat or semiwildcat wells, three of which have opened additional new pools.
In view of the increased activity in Wabaunsee County and the Kansas part of the Forest City basin, a report showing our interpretations of the stratigraphy and structural relations of the Davis Ranch pool has been considered appropriate. All interpretations must be considered tentative until further information is received by the Survey.
On February 1, 1951, the Davis Ranch pool had 18 producing oil wells. Six dry holes have been drilled and one oil well, the Aladdin and Bakke No. 1 Schutter in the SW SW SW sec. 34, T. 13 S., R. 10 E. was abandoned in December 1950. This well was the only producing well in the Davis Ranch East pool.
The structure shown by the surface rocks is a north-northeast trending anticline with a closure of more than 20 feet. The Davis Ranch anticline is located on the northeast-trending subsurface Alma anticline which extends northward into Pottawatomie County and southward into Lyon County. The pre-Pennsylvanian structure is marked by a reverse fault which is not noticeable in the surface structure.
Seventeen wells produce from the Viola dolomite and one well from the "Hunton" dolomite in the Davis Ranch pool. The thickness of the oil-saturated porous zone in the Viola ranges from a featheredge to 20 feet. Initial productivity tests indicated little or no water present in the producing zone
Wilson chains are not thermal reservoirs
Wilson chains, based on a logarithmic discretization of a continuous
spectrum, are widely used to model an electronic (or bosonic) bath for Kondo
spins and other quantum impurities within the numerical renormalization group
method and other numerical approaches. In this short note we point out that
Wilson chains can not serve as thermal reservoirs as their temperature changes
by a number of order Delta E when a finite amount of energy Delta E is added.
This proves that for a large class of non-equilibrium problems they cannot be
used to predict the long-time behavior.Comment: 2 page
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