Severe New Limits on the Host Galaxies of Gamma Ray Bursts

The nature of Gamma Ray Bursts (GRBs) remains a complete mystery, despite the recent breakthrough discovery of low energy counterparts, although it is now generally believed that at least most GRBs are at cosmological distances. Virtually all proposed cosmological models require bursters to reside in ordinary galaxies. This can be tested by looking inside the smallest GRB error boxes to see if ordinary galaxies appear at the expected brightness levels. This letter reports on an analysis of the contents of 26 of the smallest regions, many from the brightest bursts. These events will have $z < 0.4$ and small uncertainties about luminosity functions, K corrections and galaxy evolutions; whereas the recent events with optical transients are much fainter and hence have high redshifts and grave difficulties in interpretation. This analysis strongly rejects the many models with peak luminosities of $10^{57} photons \cdot s^{-1}$ as deduced from the $LogN-LogP$ curve with no evolution. Indeed, the lower limit on acceptable luminosities is $6 \times 10^{58} photons \cdot s^{-1}$. The only possible solution is to either place GRBs at unexpectedly large distances (with $z > 5.9$ for the faint BATSE bursts) or to require bursters to be far outside any normal host galaxy.Comment: 17 pages, to be published by ApJ

Suffusion in compacted loessial silts. Interaction with granular filters

Loess soils, which occupies much of central Argentina, is characterized by its high sensitivity to change in moisture. This condition categorized loess structure as internally unstable soil. Despite this natural condition, silts derived from loess are frequently used as material in roads and hydraulics constructions. In filtration processes, the soil should be shielded from erosion phenomena. The filter must have a particle size consistent with the ground to protect. In particular, sandy silts can be affected by phenomena of suffusion, or internal instability of the soil structure. The filter must control the loss of material and ensure the stability of flow. The present study shows the experimental results of flow applied to loessial silts, with low compaction. Tests have been conducted using filtration columns that simulate the soil-filter-drain. The test methodology applied aims to follow the research lines of similar studies worldwide. Studies have focused on analyzing the influence of variables such as degree of compaction, hydraulic gradient and composition of the filter material. The results obtained allow recommendations with reference to construction systems to be applied and the composition of the filter in order to properly control the suffusion.Fil: Terzariol, R. E. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; Argentina.Fil: Rocca, R. J. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; Argentina.Fil: Zeballos, M. E. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; Argentina.Otras Ingeniería Civi

Anisotropic plasma-chemical etching by an electron-beam-generated plasma

Includes bibliographical references (page 2466).Anisotropic etching of SiO2 has been achieved with a plasma generated by a broad-area low-energy (150-300 eV) electron beam in a He + CF4 atmosphere. Etch rates of up to 330 Å/min for SiO2 and 220 Å/min for Si were obtained. Etching occurred with good uniformity over the entire area exposed to the electron-beam-generated plasma. The fluxes of energetic charged particles to the sample surface are discussed in relation to their possible contribution to the etching process

Generation of millijoule-level soft-x-ray laser pulses at a 4-Hz repetition rate in a highly saturated tabletop capillary discharge amplifier

Includes bibliographical references (page 1117).Laser pulses with energies of as much as 1 mJ were generated at a wavelength of 46.9 nm by single-pass amplification in a 34.5 cm-long Ne-like Ar capillary discharge plasma. The large gain-length product of this plasma column allows for soft-x-ray amplification in a highly saturated regime, resulting inefficient energy extraction. Average laser output pulse energy of 0.88 mJ and peak power of 0.6 MW were obtained at a repetition rate of 4 Hz. With an estimated peak spectral brightness of ≈1 × 1023 photons/s mm2 mrad2 0.01% bandwidth) this tabletop laser is one of the brightest soft-x-ray sources to date

The Effect of Neutral Atoms on Capillary Discharge Z-pinch

We study the effect of neutral atoms on the dynamics of a capillary discharge Z-pinch, in a regime for which a large soft-x-ray amplification has been demonstrated. We extended the commonly used one-fluid magneto-hydrodynamics (MHD) model by separating out the neutral atoms as a second fluid. Numerical calculations using this extended model yield new predictions for the dynamics of the pinch collapse, and better agreement with known measured data.Comment: 4 pages, 4 postscript figures, to be published in Phys. Rev. Let

Electron beam assisted CVD of silicon dioxide and silicon nitride films

Includes bibliographical references (page 84).A glow discharge electron beam has been used to deposit silicon dioxide (SiO2) and silicon nitride(Si3N4) films for microelectronic applications. Electron beam assisted CVD is a new technique in which the reaction volume is defined mainly by the geometry of the electron beam and offers the possibility of uniform deposition over large areas. The SiO2films were deposited in silane-nitrous oxide-nitrogen mixtures, and the Si3N4 films were deposited in silane ammonia-nitrogen mixtures. The films were deposited with a 2-4 kV electron beam parallel to the sample, at 0.1-1 Torr pressures, and at substrate temperatures from 50-400°C. The index of refraction, sthoichiometry, pinhole density, etch rate, conformal step coverage, and hydrogen bonding were measured

Broad-area electron-beam-assisted etching of silicon in sulfur hexafluoride

Includes bibliographical references (page 1583).Silicon etching rates up to 250 Å/min have been observed in an electron-beam-generated He plus SF6 plasma. The etch rate was found to increase linearly with electron beam current density and to be practically independent of the electron acceleration voltage in the range investigated (170-260 V). Profiles of the resulting features show that etching is anisotropic with a vertical-to-horizontal ratio of 2.5 to 3

Single photon ionization of van der Waals clusters with a soft x-ray laser: (CO2)n and (CO2n(H2O)m

Includes bibliographical references (pages 154316-7).Pure neutral (CO2)n clusters and mixed (CO2)n(H2O)m clusters are investigated employing time of flight mass spectroscopy and single photon ionization at 26.5 eV. The distribution of pure (CO2)n clusters decreases roughly exponentially with increasing cluster size. During the ionization process, neutral clusters suffer little fragmentation because almost all excess cluster energy above the vertical ionization energy is taken away by the photoelectron and only a small part of the photon energy is deposited into the (CO2)n cluster. Metastable dissociation rate constants of (CO2)n+ are measured in the range of (0.2-1.5) × 104 s−1 for cluster sizes of 5≤n≤16. Mixed CO2-H2O clusters are studied under different generation conditions (5% and 20% CO2 partial pressures and high and low expansion pressures). At high CO2 concentration, predominant signals in the mass spectrum are the (CO2)n+ cluster ions. The unprotonated cluster ion series (CO2)nH2O+ and (CO2)n(H2O)2+ are also observed under these conditions. At low CO2 concentration, protonated cluster ions (H2O)nH+ are the dominant signals, and the protonated CO2(H2O)nH+ and unprotonated (H2O)n+ and (CO2) × (H2O)n+ cluster ion series are also observed. The mechanisms and dynamics of the formation of these neutral and ionic clusters are discussed

Spatio-temporal dynamics in vertical cavity surface emitting lasers excited by fast electrical pulses

Includes bibliographical references (pages 320-321).We have measured the time average spatial intensity distribution and the spatio-temporal evolution of the spectrally resolved radiation emitted from broad-area vertical cavity surface emitting lasers (VCSEL) when pumped by a fast current pulse. We show that an intrinsic symmetry break exists due to geometrical asymmetry of the device structure and that the frequency separation between different modes allows the evaluation of the asymmetry factor. The space-time behavior shows the appearance of higher-order modes coexisting or alternating in time. The dynamical behavior shows a chirping infrequency

Dense plasma interferometry with a tabletop soft X-ray laser and an amplitude division interferometer based on diffraction gratings

Includes bibliographical references (page 486).We have demonstrated a novel Mach-Zehnder soft x-ray interferometer that uses diffraction gratings as beam splitters. The interferometer was used together with a 46.9nm tabletop soft x-ray laser, to map the evolution of the electron density distribution of a large-scale laser created plasma