8,144 research outputs found
Error analysis for Mariner Venus/Mercury 1973 conducted at the JPL Mesa west antenna range
Theoretical analysis and experimental data are combined to yield the errors to be used with antenna gain, antenna patterns, and RF cable insertion loss measurements for the Mariner Venus-Mercury 1973 Flight Project. These errors apply to measurements conducted at the JPL Mesa, West Antenna Range, on the high gain antenna, low gain antenna, and RF coaxial cables
Resonance effects in the 5σ photoionization of CO
We report vibrational branching ratios and vibrationally resolved photoelectron angular distributions for resonant photoionization of the 5sigma level of CO leading to X^2Σ+CO+. These results were obtained using frozen-core Hartree–Fock photoelectron continuum orbitals. These studies provide a clear quantitative picture of the role of the kσ shape resonance in the observed non-Franck–Condon behavior and useful insight into the interplay between this shape resonance and a valence-like autoionizing resonance around 23 eV
The power spectra of CMB and density fluctuations seeded by local cosmic strings
We compute the power spectra in the cosmic microwave background and cold dark
matter (CDM) fluctuations seeded by strings, using the largest string
simulations performed so far to evaluate the two-point functions of their
stress energy tensor. We find that local strings differ from global defects in
that the scalar components of the stress-energy tensor dominate over vector and
tensor components. This result has far reaching consequences. We find that
cosmic strings exhibit a single Doppler peak of acceptable height at high
. They also seem to have a less severe bias problem than global defects,
although the CDM power spectrum in the ``standard'' cosmology (flat geometry,
zero cosmological constant, 5% baryonic component) is the wrong shape to fit
large scale structure data
Coking of JP-4 fuels in electrically heated metal tubes
A limited exploratory investigation of the rate of coking of four JP-4 fuels in electrically heated metal tubes was conducted in order to provide design information for fuel prevaporizers for turbojet-engine combustors. The fuels tested included two production and two minimum-quality JP-4 type fuels. The heating tube was operated at fuel pressures of approximately 500, 400, and 50 pounds per square inch. The operating fuel temperature was varied between approximately 600 degrees and 1200 degrees F
Substitutions near the hemagglutinin receptor-binding site determine the antigenic evolution of influenza A H3N2 viruses in U.S. swine
Swine influenza A virus is an endemic and economically important pathogen in pigs, with the potential to infect other host species. The hemagglutinin (HA) protein is the primary target of protective immune responses and the major component in swine influenza A vaccines. However, as a result of antigenic drift, vaccine strains must be regularly updated to reflect currently circulating strains. Characterizing the cross-reactivity between strains in pigs and seasonal influenza virus strains in humans is also important in assessing the relative risk of interspecies transmission of viruses from one host population to the other. Hemagglutination inhibition (HI) assay data for swine and human H3N2 viruses were used with antigenic cartography to quantify the antigenic differences among H3N2 viruses isolated from pigs in the United States from 1998 to 2013 and the relative cross-reactivity between these viruses and current human seasonal influenza A virus strains. Two primary antigenic clusters were found circulating in the pig population, but with enough diversity within and between the clusters to suggest updates in vaccine strains are needed. We identified single amino acid substitutions that are likely responsible for antigenic differences between the two primary antigenic clusters and between each antigenic cluster and outliers. The antigenic distance between current seasonal influenza virus H3 strains in humans and those endemic in swine suggests that population immunity may not prevent the introduction of human viruses into pigs, and possibly vice versa, reinforcing the need to monitor and prepare for potential incursions
Ariel - Volume 9 Number 5
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Three very young HgMn stars in the Orion OB1 Association
We report the detection of three mercury-manganese stars in the Orion OB1
association. HD 37886 and BD-0 984 are in the approximately 1.7 million year
old Orion OB1b. HD 37492 is in the approximately 4.6 million year old Orion
OB1c. Orion OB1b is now the youngest cluster with known HgMn star members. This
places an observational upper limit on the time scale needed to produce the
chemical peculiarities seen in mercury-manganese stars, which should help in
the search for the cause or causes of the peculiar abundances in HgMn and other
chemically peculiar upper main sequence stars.Comment: 8 pages including 1 figure. To appear in Astrophysical Journal
Letter
The transcriptomic evolution of mammalian pregnancy:gene expression innovations in endometrial stromal fibroblasts
The endometrial stromal fibroblast (ESF) is a cell type present in the uterine lining of therian mammals. In the stem lineage of eutherian mammals, ESF acquired the ability to differentiate into decidual cells in order to allow embryo implantation. We call the latter cell type “neo-ESF” in contrast to “paleo-ESF” which is homologous to eutherian ESF but is not able to decidualize. In this study, we compare the transcriptomes of ESF from six therian species: Opossum (Monodelphis domestica; paleo-ESF), mink, rat, rabbit, human (all neo-ESF), and cow (secondarily nondecidualizing neo-ESF). We find evidence for strong stabilizing selection on transcriptome composition suggesting that the expression of approximately 5,600 genes is maintained by natural selection. The evolution of neo-ESF from paleo-ESF involved the following gene expression changes: Loss of expression of genes related to inflammation and immune response, lower expression of genes opposing tissue invasion, increased markers for proliferation as well as the recruitment of FOXM1, a key gene transiently expressed during decidualization. Signaling pathways also evolve rapidly and continue to evolve within eutherian lineages. In the bovine lineage, where invasiveness and decidualization were secondarily lost, we see a re-expression of genes found in opossum, most prominently WISP2, and a loss of gene expression related to angiogenesis. The data from this and previous studies support a scenario, where the proinflammatory paleo-ESF was reprogrammed to express anti-inflammatory genes in response to the inflammatory stimulus coming from the implanting conceptus and thus paving the way for extended, trans-cyclic gestation
Evolutionary history of mammalian sucking lice (Phthiraptera: Anoplura)
<p>Abstract</p> <p>Background</p> <p>Sucking lice (Phthiraptera: Anoplura) are obligate, permanent ectoparasites of eutherian mammals, parasitizing members of 12 of the 29 recognized mammalian orders and approximately 20% of all mammalian species. These host specific, blood-sucking insects are morphologically adapted for life on mammals: they are wingless, dorso-ventrally flattened, possess tibio-tarsal claws for clinging to host hair, and have piercing mouthparts for feeding. Although there are more than 540 described species of Anoplura and despite the potential economical and medical implications of sucking louse infestations, this study represents the first attempt to examine higher-level anopluran relationships using molecular data. In this study, we use molecular data to reconstruct the evolutionary history of 65 sucking louse taxa with phylogenetic analyses and compare the results to findings based on morphological data. We also estimate divergence times among anopluran taxa and compare our results to host (mammal) relationships.</p> <p>Results</p> <p>This study represents the first phylogenetic hypothesis of sucking louse relationships using molecular data and we find significant conflict between phylogenies constructed using molecular and morphological data. We also find that multiple families and genera of sucking lice are not monophyletic and that extensive taxonomic revision will be necessary for this group. Based on our divergence dating analyses, sucking lice diversified in the late Cretaceous, approximately 77 Ma, and soon after the Cretaceous-Paleogene boundary (ca. 65 Ma) these lice proliferated rapidly to parasitize multiple mammalian orders and families.</p> <p>Conclusions</p> <p>The diversification time of sucking lice approximately 77 Ma is in agreement with mammalian evolutionary history: all modern mammal orders are hypothesized to have diverged by 75 Ma thus providing suitable habitat for the colonization and radiation of sucking lice. Despite the concordant timing of diversification events early in the association between anoplurans and mammals, there is substantial conflict between the host and parasite phylogenies. This conflict is likely the result of a complex history of host switching and extinction events that occurred throughout the evolutionary association between sucking lice and their mammalian hosts. It is unlikely that there are any ectoparasite groups (including lice) that tracked the early and rapid radiation of eutherian mammals.</p
Subterranean Clover Response to Phosphorus and Boron Fertilization
Last updated: 6/9/200
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