3,340 research outputs found
Polarization studies of Rotating Radio Transients
We study the polarization properties of 22 known rotating radio transients
(RRATs) with the 64-m Parkes radio telescope and present the Faraday rotation
measures (RMs) for the 17 with linearly polarized flux exceeding the off-pulse
noise by 3. Each RM was estimated using a brute-force search over trial
RMs that spanned the maximum measurable range (in steps of 1 ), followed by an
iterative refinement algorithm. The measured RRAT RMs are in the range |RM|
to rad m with an average linear polarization
fraction of per cent. Individual single pulses are observed to be up
to 100 per cent linearly polarized. The RMs of the RRATs and the corresponding
inferred average magnetic fields (parallel to the line-of-sight and weighted by
the free electron density) are observed to be consistent with the Galactic
plane pulsar population. Faraday rotation analyses are typically performed on
accumulated pulsar data, for which hundreds to thousands of pulses have been
integrated, rather than on individual pulses. Therefore, we verified the
iterative refinement algorithm by performing Monte Carlo simulations of
artificial single pulses over a wide range of S/N and RM. At and above a S/N of
17 in linearly polarized flux, the iterative refinement recovers the simulated
RM value 100 per cent of the time with a typical mean uncertainty of
rad m. The method described and validated here has also been
successfully used to determine reliable RMs of several fast radio bursts (FRBs)
discovered at Parkes.Comment: Submitted to MNRAS, 10 pages, 6 figure
Putting into Question the Imaginary of Recovery: A Dialectical Reading of the Global Financial Crisis and its Aftermath
In this article we put into question the discourses that emerged during the Global Financial Crisis (GFC) and that coalesced around a particular socio-economic imaginary of ?recovery? over the period 2009-2012. Our reading of these discourses is very much guided by the notion of the dialectic as developed by Fredric Jameson, and as such this paper can be read as attempt to put his theoretical ideas to work. Through our dialectical reading we aim to create a certain estrangement effect that makes the imaginary of recovery seem very odd and unnatural. In order to achieve such an effect we postulate four theses which are deliberately antagonistic: first, that there has been no ?crisis of capitalism?; second, that we must change the valence of the GFC from negative to positive; third, that the relationship between finance capitalism and ?free markets? is deeply contradictory; and fourth, that we must resist the regulation discourse
Distributed leadership, trust and online communities
This paper analyses the role of distributed leadership and trust in online communities. The team-based informal ethos of online collaboration requires a different kind of leadership from that in formal positional hierarchies. Such leadership may be more flexible and sophisticated, capable of encompassing ambiguity and rapid change. Online leaders need to be partially invisible, delegating power and distributing tasks. Yet, simultaneously, online communities are facilitated by the high visibility and subtle control of expert leaders. This paradox: that leaders need to be both highly visible and invisible as appropriate, was derived from prior research and tested in the analysis of online community discussions using a pattern-matching process. It is argued that both leader visibility and invisibility are important for the facilitation of trusting collaboration via distributed leadership. Advanced leadership responses to complex situations in online communities foster positive group interaction and decision-making, facilitated through active distribution of specific tasks
Identification of a novel retroviral gene unique to human immunodeficiency virus type 2 and simian immunodeficiency virus SIVMAC
Human and simian immunodeficiency-associated retroviruses are extraordinarily complex, containing at least five genes, tat, art, sor, R, and 3' orf, in addition to the structural genes gag, pol, and env. Recently, nucleotide sequence analysis of human immunodeficiency virus type 2 (HIV-2) and simian immunodeficiency virus SIVMAC revealed the existence of still another open reading frame, termed X, which is highly conserved between these two viruses but absent from HIV-1. In this report, we demonstrate for the first time that the X open reading frame represents a functional retroviral gene in both HIV-2 and SIVMAC and that it encodes a virion-associated protein of 14 and 12 kilodaltons, respectively. We also describe the production of recombinant TrpE/X fusion proteins in Escherichia coli and show that sera from some HIV-2-infected individuals specifically recognize these proteins
Observations of Ultracool White Dwarfs
We present new spectroscopic and photometric measurements of the white dwarfs LHS 3250 and WD 0346+246. Along with F351-50, these white dwarfs are the coolest ones known, all with effective temperatures below 4000 K. Their membership in the Galactic halo population is discussed, and detailed comparisons of all three objects with new atmosphere models are presented. The new models consider the effects of mixed H/He atmospheres and indicate that WD 0346+246 and F351-50 have predominantly helium atmospheres with only traces of hydrogen. LHS 3250 may be a double degenerate whose average radiative temperature is between 2000 and 4000 K, but the new models fail to explain this object
Chemical contaminants, pathogen exposure and general health status of live and beach-cast Washington sea otters (Enhydra lutris kenyoni)
Analyses of blood and liver samples from live captured sea otters and liver samples from beachcast sea otter carcasses off the remote Washington coast indicate relatively low exposure to contaminants, but suggest that even at the low levels measured, exposure may be indicated by biomarker response. Evidence of pathogen exposure is noteworthy - infectious disease presents a potential risk to Washington sea otters, particularly due to their small population size and limited distribution. During 2001 and 2002, 32 sea otters were captured, of which 28 were implanted with transmitters to track their movements and liver and blood samples were collected to evaluate contaminant and pathogen exposure. In addition, liver samples from fifteen beachcast
animals that washed ashore between 1991 and 2002 were analyzed to provide historical information and a basis of reference for values obtained from live otters. The results indicate low levels of metals, butyltins, and organochlorine compounds in the blood samples, with many of
the organochlorines not detected except polychlorinated biphenyls (PCBs), and a few aromatic hydrocarbons detected in the liver of the live captured animals. Aliphatic hydrocarbons were measurable in the liver from the live captured animals; however, some of these are likely from
biogenic sources. A significant reduction of vitamin A storage in the liver was observed in relation to PCB, dibutyltin and octacosane concentration. A significant and strong positive correlation in vitamin A storage in the liver was observed for cadmium and several of the
aliphatic hydrocarbons. Peripheral blood mononuclear cell (PBMC) cytochrome P450 induction was elevated in two of 16 animals and may be potentially related to aliphatic and aromatic hydrocarbon exposure. Mean concentration of total butyltin in the liver of the Washington beach-cast otters was more than 15 times lower than the mean concentration reported by Kannan et al. (1998) for Southern sea otters in California. Organochlorine compounds were evident in the liver of beach-cast animals, despite the lack of large human population centers and development along the Washington coast. Concentrations of PCBs and chlordanes (e.g., transchlordane, cis-chlordane, trans-nonachlor, cis-nonachlor and oxychlordane) in liver of Washington beach-cast sea otters were similar to those measured in Aleutian and California sea otters, excluding those from Monterey Bay, which were higher. Mean concentrations of 1,1,1,-
trichloro-2,2-bis(p-chlorophyenyl)ethanes (DDTs) were lower, and mean concentrations of cyclohexanes (HCH, e.g., alpha BHC, beta BHC, delta BHC and gamma BHC) were slightly
higher in Washington beach-cast otters versus those from California and the Aleutians.
Epidemiologically, blood tests revealed that 80 percent of the otters tested positive for morbillivirus and 60 percent for Toxoplasma, the latter of which has been a significant cause of mortality in Southern sea otters in California. This is the first finding of positive morbillivirus titers in sea otters from the Northeast Pacific. Individual deaths may occur from these diseases, perhaps more so when animals are otherwise immuno-compromised or infected with multiple
diseases, but a population-threatening die-off from these diseases singly is unlikely while population immunity remains high. The high frequency of detection of morbillivirus and Toxoplasma in the live otters corresponds well with the cause of death of stranded Washington
sea otters reported herein, which has generally been attributable to infectious disease. Washingtonâs sea otter population continues to grow, with over 1100 animals currently inhabiting Washington waters; however, the rate of growth has slowed over recent years. The population has a limited distribution and has not yet reached its carrying capacity and as such, is still considered at high risk to catastrophic events. (PDF contains 189 pages
Dust emission at 8-mic and 24-mic as Diagnostics of HII Region Radiative Transfer
We use the Spitzer SAGE survey of the Magellanic Clouds to evaluate the
relationship between the 8-mic PAH emission, 24-mic hot dust emission, and HII
region radiative transfer. We confirm that in the higher-metallicity Large
Magellanic Cloud, PAH destruction is sensitive to optically thin conditions in
the nebular Lyman continuum: objects identified as optically thin candidates
based on nebular ionization structure show 6 times lower median 8-mic surface
brightness (0.18 mJy arcsec^-2) than their optically thick counterparts (1.2
mJy arcsec^-2). The 24-mic surface brightness also shows a factor of 3 offset
between the two classes of objects (0.13 vs 0.44 mJy arcsec^-2, respectively),
which is driven by the association between the very small dust grains and
higher density gas found at higher nebular optical depths. In contrast, PAH and
dust formation in the low-metallicity Small Magellanic Cloud is strongly
inhibited such that we find no variation in either 8-mic or 24-mic emission
between our optically thick and thin samples. This is attributable to extremely
low PAH and dust production together with high, corrosive UV photon fluxes in
this low-metallicity environment. The dust mass surface densities and
gas-to-dust ratios determined from dust maps using Herschel HERITAGE survey
data support this interpretation.Comment: Accepted to ApJ, May 15, 2017. 10 pages, 9 figure
A Coral Damage Index and its Application to Diving Sites in the Egyptian Red Sea
A coral damage index (CDI) is provided, to screen sites to obtain a perspective on the extent and severity of physical damage to coral. Sites are listed as âhot spotsâ if in any transect the percent of broken coral colonies (BCC) is greater than or equal to 4% or if the percent cover of coral rubble (CR) is greater than or equal to 3%. To demonstrate its utility, the CDI is applied to a real-life management situation off Hurghada and Safaga, Egypt in the Red Sea. The extent of coral damage covered all four diving sites. Forty percent of all the transects were âhot spotsâ that required management action. Thirty-one percent of the 16 âhot spotâ transects were identified by both broken coral and rubble criteria, 25% by only broken coral criterion and 44% by only coral rubble criterion of the CDI, suggesting that past breakage was responsible for most of the observed damage. Sixty-three percent of the âhot spotâ transects were at 4â
m depth versus 37% at 8â
m depth, suggesting that most of the damage was caused by anchors dragging across the reef in shallow water. The severity of coral damage, reflected by CR, was the greatest at Small Giftun in transect 5 at 4â
m depth (333% above the CDI). EI Fanous experienced the most severe degree of broken coral damage (325% above the CDI) at 8â
m depth along transect 2. Estimates of the number of dives per year show diving carrying capacities for El Fanous, Gotta Abu Ramada, Ras Abu Soma and Small Giftun being exceeded by large amounts. The CDI can be used globally to; gauge the severity and extent of damage, focus managers on areas that need mooring buoys and associated dive site management programs, and provide a starting point from which to focus more detailed coral reef assessments and restoration programs
Plasma Physics
Contains research objectives and reports on four research projects.U.S. Atomic Energy Commission (Contract AT(30- 1)- 1842)U.S. Air Force (Electronic Systems Division) under Contract AF 19(604)- 599
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