15,177 research outputs found
An evaluation of the utilization of remote sensing in resource and environmental management of the Chesapeake Bay region
A nine-month study was conducted to assess the effectiveness of the NASA Wallops Chesapeake Bay Ecological Program in remote sensing. The study consisted of a follow-up investigation and information analysis of actual cases in which remote sensing was utilized by management and research personnel in the Chesapeake Bay region. The study concludes that the NASA Wallops Chesapeake Bay Ecological Program is effective, both in terms of costs and performance
The late time evolution of Gamma-Ray Bursts: ending hyperaccretion and producing flares
We consider the properties of a hyperaccretion model for gamma-ray bursts
(GRBs) at the late time when the mass supply rate is expected to decrease with
time. We point out that the region in the vicinity of the accretor and the
accretor itself can play an important role in determining the rate and time
behavior of the accretion and ultimately the energy output. Motivated by
numerical simulations and theoretical results, we conjecture that the energy
release can be repeatedly stopped and then restarted by the magnetic flux
accumulated around the accretor. We propose that the episode or episodes when
the accretion resumes correspond to X-ray flares discovered recently in a
number of GRBs.Comment: to appear in MNRAS Letters, revised versio
Neutrinos in Cosmology and Astrophysics
We briefly review the recent developments in neutrino physics and
astrophysics which have import for frontline research in nuclear physics. These
developments, we argue, tie nuclear physics to exciting developments in
observational cosmology and astrophysics in new ways. Moreover, the behavior of
neutrinos in dense matter is itself a fundamental problem in many-body quantum
mechanics, in some ways akin to well-known issues in nuclear matter and nuclei,
and in some ways radically different, especially because of nonlinearity and
quantum de-coherence. The self-interacting neutrino gas is the only many body
system driven by the weak interactions.Comment: 7 pages, 1 figur
Guide for users of the National Transonic Facility
The National Transonic Facility (NTF) is a fan-driven, closed-circuit, continuous flow, pressurized wind tunnel. The test section is 2.5 m x 2.5 m and 7.62 m long with a slotted-wall configuration. The NTF will have a Mach number range from 0.2 to 1.2, with Reynolds number up to 120 10 to the sixth power at Mach 1 (based on a reference length of 0.25 m). The pressure range for the facility will be from 1 to about 9 bars (1 ban = 100 kPa), and the temperature can be varied from 340 to 78 K. This report provides potential users of the NTF with the information required for preliminary planning to test programs and for preliminary layout of models and model supports which may be used in such programs
Bearing detection in the presence of two sources of varying coherence using the complex cepstrum
The effect of the presence of two acoustic sources (one, the primary, whose location is to be detected) of varying coherence on a cepstral bearing finding procedure is experimentally studied. The coherence between the acoustic sources was altered by adding random noise of various SNR (signal-to-noise ratio) to the input signal of the primary source; the same base signal being fed to both sources. The results demonstrate that, when block liftering is used, the primary source bearing is reliably estimated for coherences as low as gamma sup 2 greater than or approx equal to 0.5. The results also imply that background noise (unreflected) of SNR greater than or approx equal to 10 dB will not markedly affect the accuracy of the bearing estimation algorithm
Theoretical calculation of the electromagnetic response of a radially layered model moon Technical report
Theoretical calculation of electromagnetic response of radially layered moon mode
New roles for Fc receptors in neurodegeneration-the impact on immunotherapy for Alzheimer's disease
There are an estimated 18 million Alzheimer's disease (AD) sufferers worldwide and with no disease modifying treatment currently available, development of new therapies represents an enormous unmet clinical need. AD is characterized by episodic memory loss followed by severe cognitive decline and is associated with many neuropathological changes. AD is characterized by deposits of amyloid beta (A?), neurofibrillary tangles, and neuroinflammation. Active immunization or passive immunization against A? leads to the clearance of deposits in transgenic mice expressing human A?. This clearance is associated with reversal of associated cognitive deficits, but these results have not translated to humans, with both active and passive immunotherapy failing to improve memory loss. One explanation for these observations is that certain anti-A? antibodies mediate damage to the cerebral vasculature limiting the top dose and potentially reducing efficacy. Fc gamma receptors (Fc?R) are a family of immunoglobulin-like receptors which bind to the Fc portion of IgG, and mediate the response of effector cells to immune complexes. Data from both mouse and human studies suggest that cross-linking Fc?R by therapeutic antibodies and the subsequent pro-inflammatory response mediates the vascular side effects seen following immunotherapy. Increasing evidence is emerging that Fc?R expression on CNS resident cells, including microglia and neurons, is increased during aging and functionally involved in the pathogenesis of age-related neurodegenerative diseases. Therefore, we propose that increased expression and ligation of Fc?R in the CNS, either by endogenous IgG or therapeutic antibodies, has the potential to induce vascular damage and exacerbate neurodegeneration. To produce safe and effective immunotherapies for AD and other neurodegenerative diseases it will be vital to understand the role of Fc?R in the healthy and diseased brain. Here we review the literature on Fc?R expression, function and proposed roles in multiple age-related neurological diseases. Lessons can be learnt from therapeutic antibodies used for the treatment of cancer where antibodies have been engineered for optimal efficacy
Modification of the Brink-Axel Hypothesis for High Temperature Nuclear Weak Interactions
We present shell model calculations of electron capture strength
distributions in A=28 nuclei and computations of the corresponding capture
rates in supernova core conditions. We find that in these nuclei the Brink-Axel
hypothesis for the distribution of Gamow-Teller strength fails at low and
moderate initial excitation energy, but may be a valid tool at high excitation.
The redistribution of GT strength at high initial excitation may affect capture
rates during collapse. If these trends which we have found in lighter nuclei
also apply for the heavier nuclei which provide the principal channels for
neutronization during stellar collapse, then there could be two implications
for supernova core electron capture physics. First, a modified Brink-Axel
hypothesis could be a valid approximation for use in collapse codes. Second,
the electron capture strength may be moved down significantly in transition
energy, which would likely have the effect of increasing the overall electron
capture rate during stellar collapse.Comment: 15 pages, 19 figure
Neutrino Pair Emission from Hot Nuclei During Stellar Collapse
We present shell-model calculations showing that residual interaction-induced
configuration mixing enhances the rate of neutral current de-excitation of
thermally excited nuclei into neutrino-antineutrino pairs. Though our
calculations reinforce the conclusions of previous studies that this process is
the dominant source of neutrino pairs near the onset of neutrino trapping
during stellar collapse, our shell-model result has the effect of increasing
the energy of these pairs, possibly altering their role in entropy transport in
supernovae.Comment: 9 pages, 8 figure
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