769 research outputs found
Molecular gas freeze-out in the pre-stellar core L1689B
C17O (J=2-1) observations have been carried out towards the pre-stellar core
L1689B. By comparing the relative strengths of the hyperfine components of this
line, the emission is shown to be optically thin. This allows accurate CO
column densities to be determined and, for reference, this calculation is
described in detail. The hydrogen column densities that these measurements
imply are substantially smaller than those calculated from SCUBA dust emission
data. Furthermore, the C17O column densities are approximately constant across
L1689B whereas the SCUBA column densities are peaked towards the centre. The
most likely explanation is that CO is depleted from the central regions of
L1689B. Simple models of pre-stellar cores with an inner depleted region are
compared with the results. This enables the magnitude of the CO depletion to be
quantified and also allows the spatial extent of the freeze-out to be firmly
established. We estimate that within about 5000 AU of the centre of L1689B,
over 90% of the CO has frozen onto grains. This level of depletion can only be
achieved after a duration that is at least comparable to the free-fall
timescale.Comment: MNRAS letters. 5 pages, 5 figure
LoanSTAR Energy Auditing: Update and Changes
Annual savings identified by detailed LoanSTAR audits during the period January, 1989 -December, 1991 are 46.1 million. These savings represent retrofit projects in state-owned buildings, local government-owned facilities, and independent school districts, accounting for 80%, 16%, and 4% of the investment cost, respectively. A summary of retrofit projects by type is presented and modifications to chillers and chilled water systems account for 26% of the savings and 32% of the cost, followed by lighting retrofits which account for 24% of the savings and 24% of the cost. The Governor's Energy Office has implemented changes to simplify the audit process by eliminating some calculations. Independent calculations and maintenance and operating procedures calculations are no longer required, and some retrofit projects may depend on standard paybacks to identify cost savings
New Measurement of the Cosmic-Ray Positron Fraction from 5 to 15 GeV
We present a new measurement of the cosmic-ray positron fraction at energies
between 5 and 15 GeV with the balloon-borne HEAT-pbar instrument in the spring
of 2000. The data presented here are compatible with our previous measurements,
obtained with a different instrument. The combined data from the three HEAT
flights indicate a small positron flux of non-standard origin above 5 GeV. We
compare the new measurement with earlier data obtained with the HEAT-e+-
instrument, during the opposite epoch of the solar cycle, and conclude that our
measurements do not support predictions of charge sign dependent solar
modulation of the positron abundance at 5 GeV.Comment: accepted for publication in PR
Understanding the Needs of Arkansas School Districts Relative to Building Use and Control Utility Tracking Personnel and Facility Planning
Parametric tolerance study of Trojan Horse plasma wakefield acceleration scheme
A promising scheme for plasma wakefield acceleration is the hybrid plasma acceleration mechanism, which is experimentally connected to world-wide programs at various accelerator facilities. This scheme may lead to extremely high quality electron bunches, which can be used to drive ultrabright light sources such as free electron lasers. The big challenge for plasma acceleration is to produce electron bunches with high quality in terms of low emittance, energy spread and high brightness. To overcome this challenge, the Trojan Horse scheme [1,2,3,4,5] is used for production of designer electron beams. This work explores the Trojan Horse mechanism in a parametric study by variation of the injector laser pulse by intensity a0, spot size w0 and relative spatiotemporal synchronization and alignment. These parameters define output electron witness beam parameters and its quality. This sensitivity study shows a high robustness of the scheme, which is promising for a wider key prospect of the approach, namely the development of compact plasma accelerators to produce electron beams with unprecedented emittance and brightness in order to power free-electron lasers
Foliar Fungicides in Seed Corn Production
Since 1982, we have conducted a program to determine the fungicides that may be effective for controlling foliar diseases in inbred and hybrid com. For the past seven years we have limited our research to only inbreds or sister line hybrids. In 1990, we started a cooperative program with seed companies and have conducted our research in commercial seed production fields in five greatly different years in terms of weather patterns. Thirty experiments have been established in seed production fields and 25 fields have been harvested for yield. Five experiments were abandoned because of herbicide injury interactions (2,4-D) with the fungicides, excessive Stewarts disease (a bacterial disease that can not be controlled with fungicides and was devastating), or drought
Recommended from our members
Fall 1969
Massachusetts Lawn and Turf Grass CouncilBetter Turf Through Research and Education Artificial Turf Faces Credibility Gab by Dr. Gene C. Nutter (page 1) Nitrogen Facts and Fallacies by W.H. Garman (2) DDT Opponents by Charles Wurster, Jr. (10) DDT Defenders by Charles Wurster, Jr. (11) What Type 2,4-D to Use? by J.S. Coartney and A.H. Kates (21) Irrigation Circuit Break Pinpointed in One Hour (24
Proton and Helium Spectra from the CREAM-III Flight
Primary cosmic-ray elemental spectra have been measured with the
balloon-borne Cosmic Ray Energetics And Mass (CREAM) experiment since 2004. The
third CREAM payload (CREAM-III) flew for 29 days during the 2007-2008 Antarctic
season. Energies of incident particles above 1 TeV are measured with a
calorimeter. Individual elements are clearly separated with a charge resolution
of ~0.12 e (in charge units) and ~0.14 e for protons and helium nuclei,
respectively, using two layers of silicon charge detectors. The measured proton
and helium energy spectra at the top of the atmosphere are harder than other
existing measurements at a few tens of GeV. The relative abundance of protons
to helium nuclei is 9.53+-0.03 for the range of 1 TeV/n to 63 TeV/n. The ratio
is considerably smaller than other measurements at a few tens of GeV/n. The
spectra become softer above ~20 TeV. However, our statistical uncertainties are
large at these energies and more data are needed
The Energy Spectra and Relative Abundances of Electrons and Positrons in the Galactic Cosmic Radiation
Observations of cosmic-ray electrons and positrons have been made with a new
balloon-borne detector, HEAT (the "High-Energy Antimatter Telescope"), first
flown in 1994 May from Fort Sumner, NM. We describe the instrumental approach
and the data analysis procedures, and we present results from this flight. The
measurement has provided a new determination of the individual energy spectra
of electrons and positrons from 5 GeV to about 50 GeV, and of the combined
"all-electron" intensity (e+ + e-) up to about 100 GeV. The single power-law
spectral indices for electrons and positrons are alpha = 3.09 +/- 0.08 and 3.3
+/- 0.2, respectively. We find that a contribution from primary sources to the
positron intensity in this energy region, if it exists, must be quite small.Comment: latex2e file, 30 pages, 15 figures, aas2pp4.sty and epsf.tex needed.
To appear in May 10, 1998 issue of Ap.
Texas LoanSTAR Monitoring and Analysis Program Progress Report
Eleven audit reports have been accepted by the review staff at Texas A&M
University. These eleven reports cover 3.8 million square feet of building space and two
street-lighting projects. One engineer has been employed to work in the GEMC for the
purpose of assigning audits, approving screening reports and reviewing overall auditing
progress
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