8,110 research outputs found
Prospects for an orbital determination and capture cell experiment
A dust experiment which combines measurements of the elemental and isotopic composition of individual particles with orbital information would contribute fundamental, new scientific information on the sources contributing to the micrometeoroid population. The general boundary conditions for such a system are: (1) it must be capable of measuring velocities in the range of 10 km/sec to 100 km/sec with several percent accuracy; (2) it must collect particles in such a way that the debris atoms are locally concentrated so that precise isotopic measurements are possible; (3) it should collect particles over a wide range of sizes starting with a lower limit of 10 microns; (4) it should incorporate materials that will not compromise the isotopic measurements; and (5) it should be large enough to obtain statistically meaningful results within a reasonable exposure time. Techniques which may satisfy these conditions are described
Radar cross calibration investigation TAMU radar polarimeter calibration measurements
A short pulse, 20 MHz bandwidth, three frequency radar polarimeter system (RPS) operates at center frequencies of 10.003 GHz, 4.75 GHz, and 1.6 GHz and utilizes dual polarized transmit and receive antennas for each frequency. The basic lay-out of the RPS is different from other truck mounted systems in that it uses a pulse compression IF section common to all three RF heads. Separate transmit and receive antennas are used to improve the cross-polarization isolation at each particular frequency. The receive is a digitally controlled gain modulated subsystem and is interfaced directly with a microprocesser computer for control and data manipulation. Antenna focusing distance, focusing each antenna pair, rf head stability, and polarization characteristics of RPS antennas are discussed. Platform and data acquisition procedures are described
Spitzer's mid-infrared view on an outer Galaxy Infrared Dark Cloud candidate toward NGC 7538
Infrared Dark Clouds (IRDCs) represent the earliest observed stages of
clustered star formation, characterized by large column densities of cold and
dense molecular material observed in silhouette against a bright background of
mid-IR emission. Up to now, IRDCs were predominantly known toward the inner
Galaxy where background infrared emission levels are high. We present Spitzer
observations with the Infrared Camera Array toward object G111.80+0.58 (G111)
in the outer Galactic Plane, located at a distance of ~3 kpc from us and ~10
kpc from the Galactic center. Earlier results show that G111 is a massive, cold
molecular clump very similar to IRDCs. The mid-IR Spitzer observations
unambiguously detect object G111 in absorption. We have identified for the
first time an IRDC in the outer Galaxy, which confirms the suggestion that
cluster-forming clumps are present throughout the Galactic Plane. However,
against a low mid-IR back ground such as the outer Galaxy it takes some effort
to find them.Comment: Accepted for publication in ApJL -- 11 pages, 2 figures (1 colour
Diet Shapes Mortality Response to Trauma in Old Tephritid Fruit Flies.
Despite the importance of trauma in healthspan and lifespan in humans as well as in non-human species, with one important exception the literature in both gerontology and ecology contains virtually no experimental demographic studies concerned with trauma in any species. We used dietary manipulation [full diet (F) versus sugar-only (S)] to produce four levels of frailty in 55-day old tephritid fruit flies (Anastrepha ludens) that were then subject to the trauma of cage transfer stress (n = 900/sex in each of the 4 treatments). The key results included the following: (1) there is a trauma effect caused by the transfer that depends on previous diet before transfer, new diet after transfer and gender of the fly; (2) males are more vulnerable than females; (3) if initial diet was F, flies are relatively immune against the trauma, and the subsequent diet (F or S) does not matter; (4) however if initial diet was S, then the effect of the trauma depends largely on the diet after the transfer; (5) flies transferred from S to F diets do very well in terms of remaining longevity (i.e. greatest remaining longevity), while flies transferred from S to S diet do poorly (i.e. shortest remaining longevity). We discuss both the strengths and weaknesses of this study and implications of the results
Searching for dark clouds in the outer galactic plane I -- A statistical approach for identifying extended red(dened) regions in 2MASS
[Abridged] Though the exact role of infrared dark clouds in the formation
process is still somewhat unclear, they seem to provide useful laboratories to
study the very early stages of clustered star formation. Infrared dark clouds
have been identified predominantly toward the bright inner parts of the
galactic plane. The low background emission makes it more difficult to identify
similar objects in mid-infrared absorption in the outer parts. This is
unfortunate, because the outer Galaxy represents the only nearby region where
we can study effects of different (external) conditions on the star formation
process. The aim of this paper is to identify extended red regions in the outer
galactic plane based on reddening of stars in the near-infrared. We argue that
these regions appear reddened mainly due to extinction caused by molecular
clouds and young stellar objects. The work presented here is used as a basis
for identifying star forming regions and in particular the very early stages.
We use the Mann-Whitney U-test, in combination with a friends-of-friends
algorithm, to identify extended reddened regions in the 2MASS all-sky JHK
survey. We process the data on a regular grid using two different resolutions,
60" and 90". The two resolutions have been chosen because the stellar surface
density varies between the crowded spiral arm regions and the sparsely
populated galactic anti-center region. We identify 1320 extended red regions at
the higher resolution and 1589 at the lower resolution run. The majority of
regions are associated with major molecular cloud complexes, supporting our
hypothesis that the reddening is mostly due to foreground clouds and embedded
objects.Comment: Accepted for publication in A&A -- 9 pages, 5 figures (+ on-line only
tables
Selective and Differential Feeding on Marine Prokaryotes by Mucous Mesh Feeders
Microbial mortality impacts the structure of food webs, carbon flow, and the interactions that create dynamic patterns of abundance across gradients in space and time in diverse ecosystems. In the oceans, estimates of microbial mortality by viruses, protists, and small zooplankton do not account fully for observations of loss, suggesting the existence of underappreciated mortality sources. We examined how ubiquitous mucous mesh feeders (i.e. gelatinous zooplankton) could contribute to microbial mortality in the open ocean. We coupled capture of live animals by blue-water diving to sequence-based approaches to measure the enrichment and selectivity of feeding by two coexisting mucous grazer taxa (pteropods and salps) on numerically dominant marine prokaryotes. We show that mucous mesh grazers consume a variety of marine prokaryotes and select between coexisting lineages and similar cell sizes. We show that Prochlorococcus may evade filtration more than other cells and that planktonic archaea are consumed by macrozooplanktonic grazers. Discovery of these feeding relationships identifies a new source of mortality for Earth\u27s dominant marine microbes and alters our understanding of how top-down processes shape microbial community and function
L^2 torsion without the determinant class condition and extended L^2 cohomology
We associate determinant lines to objects of the extended abelian category
built out of a von Neumann category with a trace. Using this we suggest
constructions of the combinatorial and the analytic L^2 torsions which, unlike
the work of the previous authors, requires no additional assumptions; in
particular we do not impose the determinant class condition. The resulting
torsions are elements of the determinant line of the extended L^2 cohomology.
Under the determinant class assumption the L^2 torsions of this paper
specialize to the invariants studied in our previous work. Applying a recent
theorem of D. Burghelea, L. Friedlander and T. Kappeler we obtain a Cheeger -
Muller type theorem stating the equality between the combinatorial and the
analytic L^2 torsions.Comment: 39 page
Senescence can play an essential role in modelling and estimation of vector based epidemiological indicators: demographical approach
In the paper basic epidemiological indicators, produced by an aging population of vectors, are calculated. In the study we follow two lines: calculations for demographically structured population and individual life-history approach. We discuss the advantages and limitations of these approaches and compare the results of our calculations with epidemiological indicators obtained for non-aging population of vectors.Gibraltar, age effect, disease control, gerontology
Parametrizations of Inclusive Cross Sections for Pion Production in Proton-Proton Collisions
Accurate knowledge of cross sections for pion production in proton-proton
collisions finds wide application in particle physics, astrophysics, cosmic ray
physics and space radiation problems, especially in situations where an
incident proton is transported through some medium, and one requires knowledge
of the output particle spectrum given the input spectrum. In such cases
accurate parametrizations of the cross sections are desired. In this paper we
review much of the experimental data and compare to a wide variety of different
cross section parametrizations. In so doing, we provide parametrizations of
neutral and charged pion cross sections which provide a very accurate
description of the experimental data. Lorentz invariant differential cross
sections, spectral distributions and total cross section parametrizations are
presented.Comment: 32 pages with 15 figures. Published in Physical Review D62, 094030.
File includes 6 tex files. The main file is paper.tex which has include
statements refering to the rest. figures are in graphs.di
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