4,207 research outputs found
Free Energy and Phase Transition of the Matrix Model on a Plane-Wave
It has recently been observed that the weakly coupled plane wave matrix model
has a density of states which grows exponentially at high energy. This implies
that the model has a phase transition. The transition appears to be of first
order. However, its exact nature is sensitive to interactions. In this paper,
we analyze the effect of interactions by computing the relevant parts of the
effective potential for the Polyakov loop operator in the finite temperature
plane-wave matrix model to three loop order. We show that the phase transition
is indeed of first order. We also compute the correction to the Hagedorn
temperature to order two loops.Comment: 24 page
Implementation of ILLIAC 4 algorithms for multispectral image interpretation
Research has focused on the design and partial implementation of a comprehensive ILLIAC software system for computer-assisted interpretation of multispectral earth resources data such as that now collected by the Earth Resources Technology Satellite. Research suggests generally that the ILLIAC 4 should be as much as two orders of magnitude more cost effective than serial processing computers for digital interpretation of ERTS imagery via multivariate statistical classification techniques. The potential of the ARPA Network as a mechanism for interfacing geographically-dispersed users to an ILLIAC 4 image processing facility is discussed
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Optimization of the neutron yield in fusion plasmas produced by Coulomb explosions of deuterium clusters irradiated by a petawatt laser
The kinetic energy of hot (multi-keV) ions from the laser-driven Coulomb explosion of deuterium clusters and the resulting fusion yield in plasmas formed from these exploding clusters has been investigated under a variety of conditions using the Texas Petawatt laser. An optimum laser intensity was found for producing neutrons in these cluster fusion plasmas with corresponding average ion energies of 14 keV. The substantial volume (1-10 mm(3)) of the laser-cluster interaction produced by the petawatt peak power laser pulse led to a fusion yield of 1.6x10(7) neutrons in a single shot with a 120 J, 170 fs laser pulse. Possible effects of prepulses are discussed. DOI: 10.1103/PhysRevE.87.023106Glenn Focht Memorial FellowshipNNSA DE-FC52-08NA28512DOE Office of Basic Energy SciencesPhysic
In-situ observation of ULF wave activities associated with substorm expansion phase onset and current disruption
In this paper we present two substorm events with coordinated ground-based and in-situ THEMIS observations, and focus our interest on the wave activities in Pi1 and Pi2 bands from minutes before the substorm expansion phase (EP) onset to minutes after the local current disruption (CD). We find that Pi2 band (40–100 s) wave appears 1–2 min before the substorm onset and last over the entire EP interval, while higher-frequency wave within Pi1 band (10–30 s) emerges within few tens of seconds after the EP onset, intensifies during the local CD, and fades afterwards. The pre-onset Pi2 waves are attributed to a ballooning mode which acts as the seed perturbation to the substorm EP onset process. The azimuthal wavenumber estimated from the Doppler shift nature of the ballooning mode is consistent with the longitudinal "wavelength" inferred from the onset auroral structures. The Pi1 waves appearing within few tens of seconds after the EP onset are interpreted as supportive of a two-fluid instability mode of thin current sheet investigated in an accompanying paper (Liu and Liang, 2009). During the local CD, broadband wave activities from Pi2 band to well above the ion gyrofrequency are observed, suggesting the coexistence of various plasma instabilities featuring different frequency ranges
A Statistical Analysis of STEVE
There has been an exciting recent development in auroral research associated with the discovery of a new subauroral phenomenon called STEVE (Strong Thermal Emission Velocity Enhancement). Although STEVE has been documented by amateur night sky watchers for decades, it is as yet an unidentified upper atmosphere phenomenon. Observed first by amateur auroral photographers, STEVE appears as a narrow luminous structure across the night sky over thousands of kilometers in the east‐west direction. In this paper, we present the first statistical analysis of the properties of 28 STEVE events identified using Time History of Events and Macroscale Interactions during Substorms (THEMIS) all‐sky imager and the Redline Emission Geospace Observatory (REGO) database. We find that STEVE occurs about 1 hr after substorm onset at the end of a prolonged expansion phase. On average, the AL index magnitude is larger and the expansion phase has a longer duration for STEVE events compared to subauroral ion drifts or substorms. The average duration for STEVE is about 1 hr, and its latitudinal width is ~20 km, which corresponds to ~¼ of the width of narrow auroral structures like streamers. STEVE typically has an equatorward displacement from its initial location of about 50 km and a longitudinal extent of 2,145 km
Tuning gastropod locomotion: Modeling the influence of mucus rheology on the cost of crawling
Common gastropods such as snails crawl on a solid substrate by propagating
muscular waves of shear stress on a viscoelastic mucus. Producing the mucus
accounts for the largest component in the gastropod's energy budget, more than
twenty times the amount of mechanical work used in crawling. Using a simple
mechanical model, we show that the shear-thinning properties of the mucus favor
a decrease in the amount of mucus necessary for crawling, thereby decreasing
the overall energetic cost of locomotion.Comment: Corrected typo
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The Texas Petawatt Laser And Current Experiments
The Texas Petawatt Laser is operational with experimental campaigns executed in both F/40 and F3 target chambers. Recent improvements have resulted in intensities of >2x10(21) W/cm(2) on target. Experimental highlights include, accelerated electron energies of >2 GeV, DD fusion ion temperatures >25 keV and isochorically heated solids to 10-50 eV.Physic
Robust Weak-lensing Mass Calibration of Planck Galaxy Clusters
In light of the tension in cosmological constraints reported by the Planck
team between their SZ-selected cluster counts and Cosmic Microwave Background
(CMB) temperature anisotropies, we compare the Planck cluster mass estimates
with robust, weak-lensing mass measurements from the Weighing the Giants (WtG)
project. For the 22 clusters in common between the Planck cosmology sample and
WtG, we find an overall mass ratio of \left =
0.688 \pm 0.072. Extending the sample to clusters not used in the Planck
cosmology analysis yields a consistent value of from 38 clusters in common. Identifying the
weak-lensing masses as proxies for the true cluster mass (on average), these
ratios are lower than the default mass bias of 0.8 assumed in
the Planck cluster analysis. Adopting the WtG weak-lensing-based mass
calibration would substantially reduce the tension found between the Planck
cluster count cosmology results and those from CMB temperature anisotropies,
thereby dispensing of the need for "new physics" such as uncomfortably large
neutrino masses (in the context of the measured Planck temperature anisotropies
and other data). We also find modest evidence (at 95 per cent confidence) for a
mass dependence of the calibration ratio and discuss its potential origin in
light of systematic uncertainties in the temperature calibration of the X-ray
measurements used to calibrate the Planck cluster masses. Our results exemplify
the critical role that robust absolute mass calibration plays in cluster
cosmology, and the invaluable role of accurate weak-lensing mass measurements
in this regard.Comment: 5 pages, 2 figure
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