GRB Spikes Could Resolve Stars

GRBs vary more rapidly than any other known cosmological phenomena. The lower limits of this variability have not yet been explored. Improvements in detectors would reveal or limit the actual rate of short GRBs. Were microsecond "spike" GRBs to exist and be detectable, they would time-resolve stellar mass objects throughout the universe by their gravitational microlensing effect. Analyzing the time structure of sufficient numbers of GRB spikes would reveal or limit $\Omega_{star}$, $\Omega_{MACHO}$, and/or $\Omega_{baryon}$.Comment: 18 pages, 2 figures, in press: ApJ (Letters

Gravitational Waves from Sub-lunar Mass Primordial Black Hole Binaries - A New Probe of Extradimensions

In many braneworld models, gravity is largely modified at the electro-weak scale ~ 1TeV. In such models, primordial black holes (PBHs) with lunar mass M ~ 10^{-7}M_sun might have been produced when the temperature of the universe was at ~ 1TeV. If a significant fraction of the dark halo of our galaxy consists of these lunar mass PBHs, a huge number of BH binaries will exist in our neighborhood. Third generation detectors such as EURO can detect gravitational waves from these binaries, and can also determine their chirp mass. With a new detector designed to be sensitive at high frequency bands greater than 1 kHz, the existence of extradimensions could be confirmed.Comment: 4 pages, 1 figure, typos correcte

Gravitationally Lensed Gamma-Ray Bursts as Probes of Dark Compact Objects

If dark matter in the form of compact objects comprises a large fraction of the mass of the universe, then gravitational lensing effects on gamma-ray bursts are expected. We utilize BATSE and Ulysses data to search for lenses of different mass ranges, which cause lensing in the milli, pico, and femto regimes. Null results are used to set weak limits on the cosmological abundance of compact objects in mass ranges from 10$^{-16}$ to 10$^{-9}$ $M_{\odot}$. A stronger limit is found for a much discussed $\Omega = 0.15$ universe dominated by black holes of masses $\sim 10^{6.5} M_{\odot}$, which is ruled out at the $\sim$ 90% confidence level.Comment: 14 pages, 4 figures, fixed minor corrections. Accepted for publication in ApJ(L

Optical and evaporative cooling of cesium atoms in the gravito-optical surface trap

We report on cooling of an atomic cesium gas closely above an evanescent-wave atom mirror. At high densitities, optical cooling based on inelastic reflections is found to be limited by a density-dependent excess temperature and trap loss due to ultracold collisions involving repulsive molecular states. Nevertheless, very good starting conditions for subsequent evaporative cooling are obtained. Our first evaporation experiments show a temperature reduction from 10muK down to 300nK along with a gain in phase-space density of almost two orders of magnitude.Comment: 8 pages, 6 figures, submitted to Journal of Modern Optics, special issue "Fundamentals of Quantum Optics V", edited by F. Ehlotzk

Limits on the cosmological abundance of supermassive compact objects from a millilensing search in gamma-ray burst data

A new search for the gravitational lens effects of a significant cosmological density of supermassive compact objects (SCOs) on gamma-ray bursts has yielded a null result. We inspected the timing data of 774 BATSE-triggered GRBs for evidence of millilensing: repeated peaks similar in light-curve shape and spectra. Our null detection leads us to conclude that, in all candidate universes simulated, $\Omega_{SCO} < 0.1$ is favored for $10^5 < M_{SCO}/M_{\odot} < 10^9$, while in some universes and mass ranges the density limits are as much as 10 times lower. Therefore, a cosmologically significant population of SCOs near globular cluster mass neither came out of the primordial universe, nor condensed at recombination.Comment: 14 pages including 3 figures, appeared 2001 January 2

3D printed barium titanate/poly-(vinylidene fluoride) nano-hybrid with anisotropic dielectric properties

“3D-printed” anisotropy BTNFs/PVDF nanohybrids are successfully fabricated by the FDM technique which is attractive for developing novel functionalities in dielectric devices.</p

Editors' Choice—Effects of Parasitic Elements of Interconnection Lines in CNT Embedded Integrated Circuits

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Human Gait Analysis in Neurodegenerative Diseases: a Review

This paper reviews the recent literature on technologies and methodologies for quantitative human gait analysis in the context of neurodegnerative diseases. The use of technological instruments can be of great support in both clinical diagnosis and severity assessment of these pathologies. In this paper, sensors, features and processing methodologies have been reviewed in order to provide a highly consistent work that explores the issues related to gait analysis. First, the phases of the human gait cycle are briefly explained, along with some non-normal gait patterns (gait abnormalities) typical of some neurodegenerative diseases. The work continues with a survey on the publicly available datasets principally used for comparing results. Then the paper reports the most common processing techniques for both feature selection and extraction and for classification and clustering. Finally, a conclusive discussion on current open problems and future directions is outlined