22,658 research outputs found
Preparation of Organometallic Complexed Sugars:ā Hetero DielsāAlder Reactivity of Tricarbonyl(formyltrimethylenemethane)- iron
Application of Finite Elastic Theory to the Deformation of Rubbery Materials
The purpose of this discussion, then, is to show how the nature of
the strain energy function can be deduced from experiments on rubbery materials
The Feasibility of Magnetic Reconnection Powered Blazar Flares from Synchrotron Self-Compton Emission
Order of magnitude variability has been observed in the blazar sub-class of
Active Galactic Nuclei on minute timescales. These high-energy flares are often
difficult to explain with shock acceleration models due to the small size of
the inferred emitting region, with recent particle-in-cell (PIC) simulations
showing that magnetic reconnection is a promising alternative mechanism. Here,
we present a macroscopic emission model physically motivated by PIC
simulations, where the energy for particle acceleration originates from the
reconnecting magnetic field. We track the radial growth and relative velocity
of a reconnecting plasmoid, modelling particle acceleration and radiative
losses from synchrotron and synchrotron self-Compton (SSC) emission. To test
the viability of magnetic reconnection as the mechanism behind rapid blazar
flares we simultaneously fit our model to the observed light-curve and SED from
the 2016 TeV flare of BL Lacertae. We find generally that, without considering
external photons, reconnecting plasmoids are unable to produce Compton-dominant
TeV flares and so cannot reproduce the observations due to overproduction of
synchrotron emission. Additionally, problematically large plasmoids, comparable
in size to the entire jet radius, are required to emit sufficient SSC
gamma-rays to be observable. However, our plasmoid model can reproduce the
rapid TeV lightcurve of the flare, demonstrating that reconnection is able to
produce rapid, powerful TeV flares on observed timescales. We conclude that
while reconnection can produce SSC flares on the correct timescales, the
primary source of TeV emission cannot be SSC and the size of plasmoids required
may be implausibly large.Comment: Replaced with accepted version. Contains additional figures and
considers the effect of a magnetic guide fiel
Observations of stratospheric temperature changes coincident with the recent Antarctic ozone depletions
A high degree of correlation between the recent decline in Antarctic total ozone and cooling of the stratosphere during Austral spring has been noted in several recent studies (e.g., Sekiguchi, 1986; Angel, 1986). This study analyzes the observed temperature trends in detail, focusing on the spatial and temporal aspects of the observed cooling. Ozone losses and stratospheric cooling can be correlated for several reasons: (1) ozone losses (from an unspecified cause) will directly reduce temperatures due to decreased solar ultraviolet absorption (Shine, 1986), and/or (2) changes in both ozone and temperature structure due to modification of stratospheric circulation patterns (Mahlman and Fels, 1986). In order to scrutinize various ozone depletion scenarios, detailed information on the observed temperature changes is necessary; the goal is to provide such data. The data used are National Meteorological Center (NMC) Climate Analysis Center (CAC) derived temperatures, covering 1000 to 1 mb (0 to 48 km), for the period 1979 to 1987. Discussions on data origin and quality (assessed by extensive comparisons with radiosonde observations), along with other details of these observations, can be found in Newman and Randel (1988)
Development of an RF IV waveform based stress test procedure for use on GaN HFETs
This paper reports on the development of an RF IV waveform based stress test procedure. DC and low-voltage RF characterisation was carried out before and after high power RF stress. RF waveform measurements showed that the exact change in the RF load line induced during RF degradation cannot be directly inferred from the DC or low power RF measurement. The RF degradation takes the form of a knee-walkout, a small pinch-off shift consistent with charge trapping and defect generation, and in addition gate leakage occurs once the RF voltage exceeds a critical voltage
Some consequences of intense electromagnetic wave injection into space plasmas
The future possibility of actively testing the current understanding of how energetic particles may be accelerated in space or dumped from the radiation belts using intense electromagnetic energy from ground based antennas is discussed. The ground source of radiation is merely a convenience. A space station source for radiation that does not have to pass through the atmosphere and lower ionosphere, is an attractive alternative. The text is divided into two main sections addressing the possibilities of: (1) accelerating electrons to fill selected flux tubes above the Kennel-Petscheck limit for stably trapped fluxes, and (2) using an Alfven maser to cause rapid depletion of energetic protons or electrons from the radiation belts
Aircraft and ground vehicle friction correlation test results obtained under winter runway conditions during joint FAA/NASA Runway Friction Program
Aircraft and ground vehicle friction data collected during the Joint FAA/NASA Runway Friction Program under winter runway conditions are discussed and test results are summarized. The relationship between the different ground vehicle friction measurements obtained on compacted snow- and ice-covered conditions is defined together with the correlation to aircraft tire friction performance under similar runway conditions
Management of Wolf-Livestock Conflicts of Minnesota
In 1975, the gray wolf (Canis lupus) population in Minnesota was protected by the federal Endangered Species Act (USA). At that time, there were 500-750 wolves. By 2004, the population had grown to an estimated 3,020 wolves. Over time, conflicts between wolves and livestock increased. Wolf depredation control programs have been conducted by the U.S. Fish and Wildlife Service (1975-1986) and by the U.S. Department of Agriculture\u27s Wildlife Services program (1986 to present). In 1978, Minnesota\u27s wolves were reclassified from endangered to threatened which allowed authorized federal agents to lethally remove wolves that had depredated on livestock or pets. A State funded wolf compensation program was also established in 1978. Wildlife Services\u27 wolf damage management approach utilizes both non-lethal and lethal methods of control. Currently, wolf depredations are verified at 60-85 farms annually and 125-175 wolves are taken each year. Wolf compensation payments to livestock producers have averaged $67,111 per year during the past five years. Most livestock losses occur during spring and summer. Selective removal of depredating wolves, coupled with improvements in animal husbandry practices, has potential for reducing wolf-livestock conflicts. Minnesota\u27s wolf population is currently considered to be fully recovered and federal delisting is expected to occur in the near future
Evaluation of two transport aircraft and several ground test vehicle friction measurements obtained for various runway surface types and conditions. A summary of test results from joint FAA/NASA Runway Friction Program
Tests with specially instrumented NASA Boeing 737 and 727 aircraft together with several different ground friction measuring devices were conducted for a variety of runway surface types and conditions. These tests are part of joint FAA/NASA Aircraft/Ground Vehicle Runway Friction Program aimed at obtaining a better understanding of aircraft ground handling performance under adverse weather conditions and defining relationships between aircraft and ground vehicle tire friction measurements. Aircraft braking performance on dry, wet, snow and ice-covered runway conditions is discussed as well as ground vehicle friction data obtained under similar runway conditions. For a given contaminated runway surface condition, the correlation between ground vehicles and aircraft friction data is identified. The influence of major test parameters on friction measurements such as speed, test tire characteristics, type and amount of surface contaminant, and ambient temperature are discussed. The effect of surface type on wet friction levels is also evaluated from comparative data collected on grooved and ungrooved concrete and asphalt surfaces
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