47,078 research outputs found
Rotational correlation and dynamic heterogeneity in a kinetically constrained lattice gas
We study dynamical heterogeneity and glassy dynamics in a kinetically
constrained lattice gas model which has both translational and rotational
degrees of freedom. We find that the rotational diffusion constant tracks the
structural relaxation time as density is increased whereas the translational
diffusion constant exhibits a strong decoupling. We investigate distributions
of exchange and persistence times for both the rotational and translational
degrees of freedom and compare our results on the distributions of rotational
exchange times to recent single molecule studies.Comment: 7 pages, 5 figure
Advanced tube-bundle rocket thrust chamber
An advanced rocket thrust chamber for future space application is described along with an improved method of fabrication. Potential benefits of the concept are improved cyclic life, reusability, and performance. Performance improvements are anticipated because of the enhanced heat transfer into the coolant which will enable higher chamber pressure in expander cycle engines. Cyclic life, reusability and reliability improvements are anticipated because of the enhanced structural compliance inherent in the construction. The method of construction involves the forming of the combustion chamber with a tube-bundle of high conductivity copper or copper alloy tubes, and the bonding of these tubes by an electroforming operation. Further, the method of fabrication reduces chamber complexity by incorporating manifolds, jackets, and structural stiffeners while having the potential for thrust chamber cost and weight reduction
Does algorithmic trading improve liquidity?
Algorithmic trading has sharply increased over the past decade. Equity market liquidity has improved as well. Are the two trends related? For a recent five-year panel of New York Stock Exchange (NYSE) stocks, we use a normalized measure of electronic message traffic (order submissions, cancellations, and executions) as a proxy for algorithmic trading, and we trace the associations between liquidity and message traffic. Based on within-stock variation, we find that algorithmic trading and liquidity are positively related. To sort out causality, we use the start of autoquoting on the NYSE as an exogenous instrument for algorithmic trading. Previously, specialists were responsible for manually disseminating the inside quote. As stocks were phased in gradually during early 2003, the manual quote was replaced by a new automated quote whenever there was a change to the NYSE limit order book. This market structure change provides quicker feedback to traders and algorithms and results in more message traffic. For large-cap stocks in particular, quoted and effective spreads narrow under autoquote and adverse selection declines, indicating that algorithmic trading does causally improve liquidity
Non-invasive vibrational mode spectroscopy of ion Coulomb crystals through resonant collective coupling to an optical cavity field
We report on a novel non-invasive method to determine the normal mode
frequencies of ion Coulomb crystals in traps based on the resonance enhanced
collective coupling between the electronic states of the ions and an optical
cavity field at the single photon level. Excitations of the normal modes are
observed through a Doppler broadening of the resonance. An excellent agreement
with the predictions of a zero-temperature uniformly charged liquid plasma
model is found. The technique opens up for investigations of the heating and
damping of cold plasma modes, as well as the coupling between them.Comment: 4 pages, 4 figure
FINANCIAL CHARACTERISTICS OF REFRIGERATED FOOD PRODUCTS TRUCKING FIRMS IN THE U.S.
This study provides an overview of the financial characteristics of U. S. refrigerated food products trucking firms as a group and by regions. The analytical tools used for evaluating the financial assessment of the industry were several commonly used liquidity, profitability, and solvency ratios. One of the results reveals that the pre-tax income-to-gross revenue ratio, a measure of profitability, for the firms as a group averaged 0.01. This value means that one-cent of every dollar earned in services ("sales") was available to pay taxes and distribute profits.Agribusiness,
Quantitative assessment of Earthâs radiation belt modeling
The âQuantitative Assessment of Radiation Belt Modelingâ focus group was in place at Geospace Environment Modeling from 2014 to 2018. The overarching goals of this focus group were to bring together the current stateâofâtheâart models for the acceleration, transport, and loss processes in Earth's radiation belts; develop eventâspecific and global inputs of wave, plasma, and magnetic field to drive these models; and combine all these components to achieve a quantitative assessment of radiation belt modeling by validating against contemporary radiation belt measurements. This article briefly reviews the current understanding of radiation belt dynamics and related modeling efforts, summarizes the activities and accomplishments of the focus group, and discusses future directions.Accepted manuscrip
Dipole Oscillations of a Bose-Einstein Condensate in Presence of Defects and Disorder
We consider dipole oscillations of a trapped dilute Bose-Einstein condensate
in the presence of a scattering potential consisting either in a localized
defect or in an extended disordered potential. In both cases the breaking of
superfluidity and the damping of the oscillations are shown to be related to
the appearance of a nonlinear dissipative flow. At supersonic velocities the
flow becomes asymptotically dissipationless.Comment: 4 pages, 4 figure
Irregular Turbo Codes in Block-Fading Channels
We study irregular binary turbo codes over non-ergodic block-fading channels.
We first propose an extension of channel multiplexers initially designed for
regular turbo codes. We then show that, using these multiplexers, irregular
turbo codes that exhibit a small decoding threshold over the ergodic
Gaussian-noise channel perform very close to the outage probability on
block-fading channels, from both density evolution and finite-length
perspectives.Comment: to be presented at the IEEE International Symposium on Information
Theory, 201
Quantitative assessment of radiation belt modeling
The âQuantitative Assessment of Radiation Belt Modelingâ focus group was in place at Geospace Environment Modeling from 2014 to 2018. The overarching goals of this focus group were to bring together the current stateâofâtheâart models for the acceleration, transport, and loss processes in Earth's radiation belts; develop eventâspecific and global inputs of wave, plasma, and magnetic field to drive these models; and combine all these components to achieve a quantitative assessment of radiation belt modeling by validating against contemporary radiation belt measurements. This article briefly reviews the current understanding of radiation belt dynamics and related modeling efforts, summarizes the activities and accomplishments of the focus group, and discusses future directions.Accepted manuscrip
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