12,803 research outputs found
Analysis of reentry into the White Sands Missile Range (WSMR) for the LifeSat mission
This study investigates the reentry of the LifeSat vehicles into the WSMR. The LifeSat mission consists of two reusable reentry satellites, each carrying a removable payload module, which scientists will use to study long-term effects of microgravity, Van Allen belt radiation, and galactic cosmic rays on living organisms. A series of missions is planned for both low-Earth circular orbits and highly elliptic orbits. To recover the payload module with the specimens intact, a soft parachute landing and recovery at the WSMR is planned. This analysis examines operational issues surrounding the reentry scenario to assess the feasibility of the reentry
Skeletal Muscle Sorbitol Levels in Diabetic Rats with and without Insulin Therapy and Endurance Exercise Training
Sorbitol accumulation
is postulated to play a role in skeletal muscle
dysfunction associated with diabetes. The
purpose of this study was to determine the
effects of insulin and of endurance exercise on
skeletal muscle sorbitol levels in
streptozotocin-induced diabetic rats. Rats were
assigned to one experimental group (control
sedentary, control exercise, diabetic sedentary,
diabetic exercise, diabetic sedentary
no-insulin). Diabetic rats received daily
subcutaneous insulin. The exercise-trained rats
ran on a treadmill (1 hour, 5X/wk, for
12 weeks). Skeletal muscle sorbitol levels
were the highest in the diabetic sedentary
no-insulin group. Diabetic sedentary rats
receiving insulin had similar sorbitol levels to
control sedentary rats. Endurance exercise did
not significantly affect sorbitol levels. These
results indicate that insulin treatment lowers
sorbitol in skeletal muscle; therefore sorbitol
accumulation is probably not related to muscle
dysfunction in insulin-treated diabetic
individuals. Endurance exercise did not
influence intramuscular sorbitol values as
strongly as insulin
Quantum Melting of the Charge Density Wave State in 1T-TiSe2
We report a Raman scattering study of low-temperature, pressure-induced
melting of the CDW phase of 1T-TiSe2. Our Raman scattering measurements reveal
that the collapse of the CDW state occurs in three stages: (i) For P<5 kbar,
the pressure dependence of the CDW amplitude mode energies and intensities are
indicative of a ``crystalline'' CDW regime; (ii) for 5 < P < 25 kbar, there is
a decrease in the CDW amplitude mode energies and intensities with increasing
pressure that suggests a regime in which the CDW softens, and may decouple from
the lattice; and (iii) for P>25 kbar, the absence of amplitude modes reveals a
melted CDW regime.Comment: 5 pages, 4 figure
Literature Review: Global Neonicotinoid Insecticide Occurrence in Aquatic Environments
Neonicotinoids have been the most commonly used insecticides since the early 1990s. Despite their efficacy in improving crop protection and management, these agrochemicals have gained recent attention for their negative impacts on non-target species such as honeybees and aquatic invertebrates. In recent years, neonicotinoids have been detected in rivers and streams across the world. Determining and predicting the exposure potential of neonicotinoids in surface water requires a thorough understanding of their fate and transport mechanisms. Therefore, our objective was to provide a comprehensive review of neonicotinoids with a focus on their fate and transport mechanisms to and within surface waters and their occurrence in waterways throughout the world. A better understanding of fate and transport mechanisms will enable researchers to accurately predict occurrence and persistence of insecticides entering surface waters and potential exposure to non-target organisms in agricultural intensive regions. This review has direct implications on how neonicotinoids are monitored and degraded in aquatic ecosystems. Further, an improved understanding of the fate and transport of neonicotinoids aide natural resource practitioners in the development and implementation of effective best management practices to reduce the potential impact and exposure of neonicotinoids in waterways and aquatic ecosystems
VLT/UVES Observations of Interstellar Molecules and Diffuse Bands in the Magellanic Clouds
We discuss the abundances of interstellar CH, CH+, and CN in the Magellanic
Clouds (MC), derived from spectra of 7 SMC and 13 LMC stars obtained (mostly)
with the VLT/UVES. CH and/or CH+ are detected toward 3 SMC and 9 LMC stars; CN
is detected toward 2 stars. In the MC, the CH/H2 ratio is comparable to that
found for diffuse Galactic molecular clouds in some sight lines, but is lower
by factors up to 10-15 in others. The abundance of CH in the MC thus appears to
depend on local physical conditions -- and not just on metallicity. The
observed relationships between the column density of CH and those of CN, CH+,
Na I, and K I in the MC are generally consistent with the trends observed in
our Galaxy. Using existing data for the rotational populations of H2, we
estimate temperatures, radiation field strengths, and local hydrogen densities
for the diffuse molecular gas. Densities estimated from N(CH), assuming that CH
is produced via steady-state gas-phase reactions, are considerably higher; much
better agreement is found by assuming that the CH is made via the (still
undetermined) process(es) responsible for the observed CH+. The UVES spectra
also reveal absorption from the diffuse interstellar bands at 5780, 5797, and
6284 A in the MC. On average, the three DIBs are weaker by factors of 7-9 (LMC)
and about 20 (SMC), compared to those observed in Galactic sight lines with
similar N(H I), and by factors of order 2-6, relative to E(B-V), N(Na I), and
N(K I). The detection of several of the ``C2 DIBs'', with strengths similar to
those in comparable Galactic sight lines, however, indicates that no single,
uniform scaling factor (e.g., one related to metallicity) applies to all DIBs
(or all sight lines) in the MC. (abstract abridged)Comment: 59 pages, 15 figures, 10 tables; aastex; accepted to ApJ
The Role of Polycyclic Aromatic Hydrocarbons in Ultraviolet Extinction. I. Probing small molecular PAHs
We have obtained new STIS/HST spectra to search for structure in the
ultraviolet interstellar extinction curve, with particular emphasis on a search
for absorption features produced by polycyclic aromatic hydrocarbons (PAHs).
The presence of these molecules in the interstellar medium has been postulated
to explain the infrared emission features seen in the 3-13 m spectra of
numerous sources. UV spectra are uniquely capable of identifying specific PAH
molecules. We obtained high S/N UV spectra of stars which are significantly
more reddened than those observed in previous studies. These data put limits on
the role of small (30-50 carbon atoms) PAHs in UV extinction and call for
further observations to probe the role of larger PAHs. PAHs are of importance
because of their ubiquity and high abundance inferred from the infrared data
and also because they may link the molecular and dust phases of the
interstellar medium. A presence or absence of ultraviolet absorption bands due
to PAHs could be a definitive test of this hypothesis. We should be able to
detect a 20 \AA wide feature down to a 3 limit of 0.02 A. No
such absorption features are seen other than the well-known 2175 \AA bump.Comment: 16 pages, 3 figure, ApJ in pres
Coupled evolution of BrOx-ClOx-HOx-NOx chemistry during bromine-catalyzed ozone depletion events in the arctic boundary layer
Extensive chemical characterization of ozone (O3) depletion events in the Arctic boundary layer during the TOPSE aircraft mission in March–May 2000 enables analysis of the coupled chemical evolution of bromine (BrOx), chlorine (ClOx), hydrogen oxide (HOx) and nitrogen oxide (NOx) radicals during these events. We project the TOPSE observations onto an O3 chemical coordinate to construct a chronology of radical chemistry during O3 depletion events, and we compare this chronology to results from a photochemical model simulation. Comparison of observed trends in ethyne (oxidized by Br) and ethane (oxidized by Cl) indicates that ClOxchemistry is only active during the early stage of O3 depletion (O3 \u3e 10 ppbv). We attribute this result to the suppression of BrCl regeneration as O3 decreases. Formaldehyde and peroxy radical concentrations decline by factors of 4 and 2 respectively during O3 depletion and we explain both trends on the basis of the reaction of CH2O with Br. Observed NOx concentrations decline abruptly in the early stages of O3 depletion and recover as O3 drops below 10 ppbv. We attribute the initial decline to BrNO3 hydrolysis in aerosol, and the subsequent recovery to suppression of BrNO3 formation as O3 drops. Under halogen-free conditions we find that HNO4 heterogeneous chemistry could provide a major NOx sink not included in standard models. Halogen radical chemistry in the model can produce under realistic conditions an oscillatory system with a period of 3 days, which we believe is the fastest oscillation ever reported for a chemical system in the atmosphere
A study of subsonic transport aircraft configurations using hydrogen (H2) and methane (CH4) as fuel
The acceptability of alternate fuels for future commercial transport aircraft are discussed. Using both liquid hydrogen and methane, several aircraft configurations are developed and energy consumption, aircraft weights, range and payload are determined and compared to a conventional Boeing 747-100 aircraft. The results show that liquid hydrogen can be used to reduce aircraft energy consumption and that methane offers no advantage over JP or hydrogen fuel
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