17,851 research outputs found
Multichannel visible spectroscopy diagnostic for particle transport studies in the H-1 heliac
A multichannel spectroscopy diagnostic has been developed to study cross-field particle transport in the radiation-dominated low-temperature plasmas (Te<100 eV) in the H-1 heliac. The optical setup covers the full plasma minor radius in the poloidal plane collecting light from ten parallel chords arranged tangentially to the flux surfaces. The light collected from the plasma is coupled into optical fibers and through interference filters into photomultipliers. Two such ten-fiber arrays are aligned parallel to one another to allow the simultaneous monitoring of two different spectral lines. The net radial electron particle flux is determined from the continuity equation by integrating over the ionization source term in the steady-state partially ionized plasma. The diagnostic measures the neutral line intensities and their ratios (in case of helium using the line ratio technique) and also measures excited neutral and ion spectral lines (in case of the argon plasma transport studies). A comparative analysis of the radial particle transport in the low- and high-confinement regimes is presented
Are Currency Crises Low-State Equilibria? An Empirical, Three-Interest-Rate Model
Suppose that the dynamics of the macroeconomy were given by (partly) random fluctuations between two equilibria: "good" and "bad." One would interpret currency crises (or recessions) as a shift from the good equilibrium to the bad. In this paper, the authors specify a dynamic investment-savings-aggregate-supply (IS-AS) model, determine its closed-form solution, and examine numerically its comparative statics. The authors estimate the model via maximum likelihood, using data for Argentina, Canada, and Turkey. Since the data show no support for the multiple-equilibrium explanation of fluctuations, the authors cast doubt on the third-generation models of currency crisis.Uncertainty and monetary policy
Chaotic diffusion of particles with finite mass in oscillating convection flows
Deterministic diffusion in temporally oscillating convection is studied for
particles with finite mass. The particles are assumed to obey a simple
dissipative dynamical system and the particle diffusion is induced by the
strange attractor. The diffusion constants are numerically calculated for
convection models with free and rigid boundary conditions.Comment: 5 figure
Spatial Coherence of a Polariton Condensate
We perform Young's double-slit experiment to study the spatial coherence
properties of a two-dimensional dynamic condensate of semiconductor microcavity
polaritons. The coherence length of the system is measured as a function of the
pump rate, which confirms a spontaneous buildup of macroscopic coherence in the
condensed phase. An independent measurement reveals that the position and
momentum uncertainty product of the condensate is close to the Heisenberg
limit. An experimental realization of such a minimum uncertainty wave packet of
the polariton condensate opens a door to coherent matter-wave phenomena such as
Josephson oscillation, superfluidity, and solitons in solid state condensate
systems
Decreasing Medical Complications for Total Knee Arthroplasty: Effect of Critical Pathways on Outcomes
BACKGROUND: Studies on critical pathway use have demonstrated decreased length of stay and cost without compromise in quality of care. However, pathway effectiveness is difficult to determine given methodological flaws, such as small or single center cohorts. We studied the effect of critical pathways on total knee replacement outcomes in a large population-based study. METHODS: We identified hospitals in four US states that performed total knee replacements. We sent a questionnaire to surgical administrators in these hospitals including items about critical pathway use and hospital characteristics potentially related to outcomes. Patient data were obtained from Medicare claims, including demographics, comorbidities, 90-day postoperative complications and length of hospital stay. The principal outcome measure was the risk of having one or more postoperative complications. RESULTS: Two hundred ninety five hospitals (73%) responded to the questionnaire, with 201 reporting the use of critical pathways. 9,157 Medicare beneficiaries underwent TKR in these hospitals with a mean age of 74 years (± 5.8). After adjusting for both patient and hospital related variables, patients in hospitals with pathways were 32% less likely to have a postoperative complication compared to patients in hospitals without pathways (OR 0.68, 95% CI 0.50-0.92). Patients managed on a critical pathway had an average length of stay 0.5 days (95% CI 0.3-0.6) shorter than patients not managed on a pathway. CONCLUSION: Medicare patients undergoing total knee replacement surgery in hospitals that used critical pathways had fewer postoperative complications than patients in hospitals without pathways, even after adjusting for patient and hospital related factors. This study has helped to establish that critical pathway use is associated with lower rates of postoperative mortality and complications following total knee replacement after adjusting for measured variables
Coherent pairing states for the Hubbard model
We consider the Hubbard model and its extensions on bipartite lattices. We
define a dynamical group based on the -pairing operators introduced by
C.N.Yang, and define coherent pairing states, which are combinations of
eigenfunctions of -operators. These states permit exact calculations of
numerous physical properties of the system, including energy, various
fluctuations and correlation functions, including pairing ODLRO to all orders.
This approach is complementary to BCS, in that these are superconducting
coherent states associated with the exact model, although they are not
eigenstates of the Hamiltonian.Comment: 5 pages, RevTe
The potential role of 'non-rheumatic’ therapies in rheumatic disease
The relationship between inflammation and insulin resistance is complex and not fully understood. Patients with rheumatoid arthritis are at increased risk of mortality from cardiovascular disease, which is known to be associated with insulin resistance. In the previous issue of Arthritis Research & Therapy, Ormseth and colleagues report the results of an 8-week trial of pioglitazone, an agent commonly used to treat type 2 diabetes mellitus, upon the DAS-28 (disease activity score using 28 joint counts). Modest improvements in the DAS-28 CRP (DAS-28 C-reactive protein) were shown, with no effect on DAS-28 ESR (DAS-28 erythrocyte sedimentation rate). Other variables that improved with pioglitazone were the CRP, IL-6, and patient-reported assessment of global health. The authors discuss the contribution of insulin resistance to the inflammation noted in rheumatoid arthritis
Measurements of poloidal rotation velocity using cross-correlation spectroscopy in the H-1 heliac
A correlation spectroscopy diagnostic [M.G. Shats and J. Howard, Fusion Eng. Des. 34–35, 271 (1997)] measures fluctuation spectra and local fluctuation intensities in a radiation-dominated plasma, such as the low-temperature plasma in the H-1 heliac (Te<50 eV, ne<2×10¹⁸ m⁻³). When the fluctuation coherence lengths in the poloidal and radial directions are shorter than the plasma radius, the cross-correlation function of the two crossed-sightline fluctuating intensities contains information about the fluctuations amplitude and their phase in the intersection volume. The optical setup on the H-1 heliac uses two nearly orthogonal views to image 20 optical fibers arranged into two linear arrays in the plasma poloidal cross section. A matrix of 10×10 cross-correlation functions is then analyzed to determine the poloidal phase velocity of the fluctuations, poloidal and radial correlation lengths, and the radial profiles of the fluctuations intensity. The results on the poloidal propagation velocity measured using the cross-correlation technique (time delay of the cross-correlation functions) are compared with the poloidal velocity measured using poloidally separated probes in the plasma. Both velocities are found to be in good agreement and also agree well with the E×B drift velocity in this plasma
Cluster Dynamics for Randomly Frustrated Systems with Finite Connectivity
In simulations of some infinite range spin glass systems with finite
connectivity, it is found that for any resonable computational time, the
saturatedenergy per spin that is achieved by a cluster algorithm is lowered in
comparison to that achieved by Metropolis dynamics.The gap between the average
energies obtained from these two dynamics is robust with respect to variations
of the annealing schedule. For some probability distribution of the
interactions the ground state energy is calculated analytically within the
replica symmetry assumptionand is found to be saturated by a cluster algorithm.Comment: Revtex, 4 pages with 3 figure
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