1,512 research outputs found
FiberGLAST: a scintillating fiber approach to the GLAST mission
FiberGLAST is a scintillating fiber gamma-ray detector designed for the GLAST mission. The system described below provides superior effective area and field of view for modest cost and risk. An overview of the FiberGLAST instrument is presented, as well as a more detailed description of the principle elements of the primary detector volume. The triggering and readout electronics are described, and Monte Carlo Simulations of the instrument performance are presented
Beam test results for the FiberGLAST instrument
The FiberGLAST scintillating fiber telescope is a large-area instrument concept for NASA\u27s GLAST program. The detector is designed for high-energy gamma-ray astronomy, and uses plastic scintillating fibers to combine a photon pair tracking telescope and a calorimeter into a single instrument. A small prototype detector has been tested with high energy photons at the Thomas Jefferson National Accelerator Facility. We report on the result of this beam test, including scintillating fiber performance, photon track reconstruction, angular resolution, and detector efficiency
A bone grease processing station at the Mitchell Prehistoric Indian Village: archaeological evidence for the exploitation of bone fats
Š Association for Environmental Archaeology 2015. Author's accepted manuscript version deposited in accordance with SHERPA RoMEO guidelines. The definitive version is available at http://www.maneyonline.com/doi/abs/10.1179/1749631414Y.0000000035.Recent excavations at the Mitchell Prehistoric Indian Village, an Initial Middle Missouri site in Mitchell, South Dakota have revealed a large, clay-lined feature filled with fractured and fragmented bison bones. Fracture and fragmentation analysis, along with taphonomic evidence, suggests that the bones preserved within the feature represent evidence of prehistoric bone marrow and bone grease exploitation. Further, the character of the feature suggests that it served as a bone grease processing station. Bone fat exploitation is an activity that is frequently cited as a causal explanation for the nature of many fractured and fragmented bone assemblages in prehistory, and zooarchaeological assemblages have frequently been studied as evidence of bone fat exploitation. The Mitchell example provides some of the first direct, in-situ archaeological evidence of a bone grease processing feature, and this interpretation is sustained by substantial analytical evidence suggesting bone fat exploitation. This new evidence provides a clearer concept of the nature of bone fat exploitation in prehistory as well as an indication of the scale and degree to which bone grease exploitation occurred at the Mitchell site. Finally, this research demonstrates the importance of careful zooarchaeological and taphonomic analysis for the interpretation of both artifactual remains as well as archaeological features
Estimation of GRB detection by FiberGLAST
FiberGLAST is one of several instrument concepts being developed for possible inclusion as the primary Gamma-ray Large Area Space Telescope (GLAST) instrument. The predicted FiberGLAST effective area is more than 12,000 cm2 for energies between 30 MeV and 300 GeV, with a field of view that is essentially flat from 0°â80°. The detector will achieve a sensitivity more than 10 times that of EGRET. We present results of simulations that illustrate the sensitivity of FiberGLAST for the detection of gamma-ray bursts
Development and testing of a fiber/multianode photomultiplier system for use on FiberGLAST
A scintillating fiber detector is currently being studied for the NASA Gamma-Ray Large Area Space Telescope (GLAST) mission. This detector utilizes modules composed of a thin converter sheet followed by an x, y plane of scintillating fibers to examine the shower of particles created by high energy gamma-rays interacting in the converter material. The detector is composed of a tracker with 90 such modular planes and a calorimeter with 36 planes. The two major component of this detector are the scintillating fibers and their associated photodetectors. Here we present current status of development and test result of both of these. The Hamamatsu R5900-00-M64 multianode photomultiplier tube (MAPMT) is the baseline readout device. A characterization of this device has been performed including noise, cross- talk, gain variation, vibration, and thermal/vacuum test. A prototype fiber/MAPMT system has been tested at the Center for Advanced Microstructures and Devices at Louisiana State University with a photon beam and preliminary results are presented
Structure and Colors of Diffuse Emission in the Spitzer Galactic First Look Survey
We investigate the density structure of the interstellar medium using new
high-resolution maps of the 8 micron, 24 micron, and 70 micron surface
brightness towards a molecular cloud in the Gum Nebula, made as part of the
Spitzer Space Telescope Galactic First Look Survey. The maps are correlated
with 100 micron images measured with IRAS. At 24 and 70 micron, the spatial
power spectrum of surface brightness follows a power law with spectral index
-3.5. At 24 micron, the power law behavior is remarkably consistent from the
0.2 degree size of our maps down to the 5 arcsecond spatial resolution. Thus,
the structure of the 24 micron emission is self-similar even at milliparsec
scales. The combined power spectrum produced from Spitzer 24 micron and IRAS 25
micron images is consistent with a change in the power law exponent from -2.6
to -3.5. The decrease may be due to the transition from a two-dimensional to
three-dimensional structure. Under this hypothesis, we estimate the thickness
of the emitting medium to be 0.3 pc.Comment: 13 Pages, 3 Figures, to be published in Astrophysical Journal
Supplement Series (Spitzer Special Issue), volume 154. Uses aastex v5.
Simulations of energetic beam deposition: from picoseconds to seconds
We present a new method for simulating crystal growth by energetic beam
deposition. The method combines a Kinetic Monte-Carlo simulation for the
thermal surface diffusion with a small scale molecular dynamics simulation of
every single deposition event. We have implemented the method using the
effective medium theory as a model potential for the atomic interactions, and
present simulations for Ag/Ag(111) and Pt/Pt(111) for incoming energies up to
35 eV. The method is capable of following the growth of several monolayers at
realistic growth rates of 1 monolayer per second, correctly accounting for both
energy-induced atomic mobility and thermal surface diffusion. We find that the
energy influences island and step densities and can induce layer-by-layer
growth. We find an optimal energy for layer-by-layer growth (25 eV for Ag),
which correlates with where the net impact-induced downward interlayer
transport is at a maximum. A high step density is needed for energy induced
layer-by-layer growth, hence the effect dies away at increased temperatures,
where thermal surface diffusion reduces the step density. As part of the
development of the method, we present molecular dynamics simulations of single
atom-surface collisions on flat parts of the surface and near straight steps,
we identify microscopic mechanisms by which the energy influences the growth,
and we discuss the nature of the energy-induced atomic mobility
A Sino-German 6 cm polarization survey of the Galactic plane II. The region from 129 degree to 230 degree longitude
Linearly polarized Galactic synchrotron emission provides valuable
information about the properties of the Galactic magnetic field and the
interstellar magneto-ionic medium, when Faraday rotation along the line of
sight is properly taken into account. We aim to survey the Galactic plane at 6
cm including linear polarization. At such a short wavelength Faraday rotation
effects are in general small and the Galactic magnetic field properties can be
probed to larger distances than at long wavelengths. The Urumqi 25-m telescope
is used for a sensitive 6 cm survey in total and polarized intensities. WMAP
K-band (22.8 GHz) polarization data are used to restore the absolute zero-level
of the Urumqi U and Q maps by extrapolation. Total intensity and polarization
maps are presented for a Galactic plane region of 129 degree < l < 230 degree
and |b| < 5 degree in the anti-centre with an angular resolution of 9'5 and an
average sensitivity of 0.6 mK and 0.4 mK Tb in total and polarized intensity,
respectively. We briefly discuss the properties of some extended Faraday
Screens detected in the 6 cm polarization maps. The Sino-German 6 cm
polarization survey provides new information about the properties of the
magnetic ISM. The survey also adds valuable information for discrete Galactic
objects and is in particular suited to detect extended Faraday Screens with
large rotation measures hosting strong regular magnetic fields.Comment: 17 pages, 20 figures, accepted by A&A. Resolutions of the figures
have been significantly reduced. For version with full resolution, see
http://159.226.88.6/zmtt/6cm/papers/gao.paper2.pd
The galactic first-look survey with the Spitzer space telescope
The galactic first look survey (GFLS) of the Spitzer space telescope was executed during 1â11 December 2003 as one of the first science observations during nominal operations. The aim of the FLS is to provide a characteristic âfirst-lookâ at the mid-and far-infrared sky at sensitivities that allow the detection of point sources â100 times fainter than those in previous systematic large-area surveys. The whole program took 35.5 h to complete and consisted of the following elements:
â˘Galactic longitudinal strips of size 15Ⲡà 1° with IRAC and MIPS at l = 105.6° and 254.4° and various galactic latitudes.
â˘10Ⲡà 10ⲠIRAC maps at l = 97.5° and b = 0°, Âą4°, and +16°.
â˘Coverage of L1228 with 2° scan maps.
Even at these large distances from the galactic center, confusion sets a limit to the detection of point sources in the galactic plane for IRAC channel 1 (3.6 Îźm) at 100 ÎźJy â 16.1^m. As positive galactic latitudes were mainly sampled at l = 97.5° and 105.6° and negative latitudes at 254.4° galactic longitude, the observations are well suited to derive information on the warp of the galactic disk. In order to reproduce the source counts from the GFLS we had to assume an amplitude of the warp within 20% of that derived from 2MASS. The whole survey is included in the Spitzer science archive which opened in April 2004
Canopy bird assemblages are less influenced by habitat age and isolation than understory bird assemblages in Neotropical secondary forest
Secondary forest habitats are increasingly recognized for their potential to conserve biodiversity in the tropics. However, the development of faunal assemblages in secondary forest systems varies according to habitat quality and speciesâspecific traits. In this study, we predicted that the recovery of bird assemblages is dependent on secondary forest age and level of isolation, the forest stratum examined, and the speciesâ traits of feeding guild and body mass. This study was undertaken in secondary forests in central Panama; spanning a chronosequence of 60â, 90â, and 120âyearâold forests, and in neighboring oldâgrowth forest. To give equal attention to all forest strata, we employed a novel method that paired simultaneous surveys in canopy and understory. This survey method provides a more nuanced picture than groundâbased studies, which are biased toward understory assemblages. Bird reassembly varied according to both habitat age and isolation, although it was challenging to separate these effects, as the older sites were also more isolated than the younger sites. In combination, habitat age and isolation impacted understory birds more than canopyâdwelling birds. Proportions of dietary guilds did not vary with habitat age, but were significantly different between strata. Body mass distributions were similar across forest ages for smallâbodied birds, but older forest supported more largeâbodied birds, probably due to control of poaching at these sites. Canopy assemblages were characterized by higher species richness, and greater variation in both dietary breadth and body mass, relative to understory assemblages. The results highlight that secondary forests may offer critical refugia for many bird species, particularly specialist canopyâdwellers. However, understory bird species may be less able to adapt to novel and isolated habitats and should be the focus of conservation efforts encouraging bird colonization of secondary forests
- âŚ