425 research outputs found
GRB-081029: A Step Towards Understanding Multiple Afterglow Components
We present an analysis of the unusual optical light curve of the gamma-ray burst-081029 at a redshift of z = 3.8474. We combine X-ray and optical observations from (Swift) with optical and infrared data from REM to obtain a detailed data set extending from approx 10(exp 2)s to approx 10(exp 5)s after the BAT trigger, and from approx.10 keV to 16,000 AA. The X-ray afterglow showed a shallow initial decay followed by u rapid decay after about 18,000 s. The optical afterglow, however, shows an uncharecteristic rise at about 5000 s that has no corresponding feature in the X-ray light curve. The data are not consistent with a single-component jet. It is possible that there are multiple physical components contributing to the afterglow of GRB-081029
Task Analysis of Shuttle Entry and Landing Activities
The Task Analysis of Shuttle Entry and Landing (E/L) Activities documents all tasks required to land the Orbiter following an STS mission. In addition to analysis of tasks performed, task conditions are described, including estimated time for completion, altitude, relative velocity, normal and lateral acceleration, location of controls operated or monitored, and level of g's experienced. This analysis precedes further investigations into potential effects of zero g on piloting capabilities for landing the Orbiter following long-duration missions. This includes, but is not limited to, researching the effects of extended duration missions on piloting capabilities. Four primary constraints of the analysis must be clarified: (1) the analysis depicts E/L in a static manner--the actual process is dynamic; (2) the task analysis was limited to a paper analysis, since it was not feasible to conduct research in the actual setting (i.e., observing or filming duration an actual E/L); (3) the tasks included are those required for E/L during nominal, daylight conditions; and (4) certain E/L tasks will vary according to the flying style of each commander
Should we ban gasoline cars?
As electric vehicles become commercially viable, they have the potential to yield dramatic reductions in air pollution. The UK plans to have no gasoline vehicles by 2030, Norway by 2025, and California by 2035. But what is the best policy to achieve that? Is banning an effective option? Stephen P. Holland, Erin T. Mansur, and Andrew J. Yates provide a framework for assessing costs and benefits, elucidating key unknown parameters, and designing effective policies to discourage the use of gasoline
What Do Emissions Markets Deliver and to Whom? Evidence from Southern California's NOx Trading Program
A perceived advantage of cap-and-trade programs over more prescriptive environmental regulation is that enhanced compliance flexibility and cost effectiveness can make more stringent emissions reductions politically feasible. However, increased compliance flexibility can also result in an inequitable distribution of pollution. We investigate these issues in the context of Southern California's RECLAIM program. We match facilities in RECLAIM with similar California facilities also located in non-attainment areas. Our results indicate that emissions fell approximately 24 percent, on average, at RECLAIM facilities relative to our counterfactual. Furthermore, we find that observed changes in emissions do not vary significantly with neighborhood demographic characteristics.
Swift UVOT Observations of Core-Collapse SNe
We review recent UV observations of core-collapse supernovae (SNe) with the
Swift Ultra-violet/Optical Telescope (UVOT) during its first two years.
Rest-frame UV photometry is useful for differentiating SN types by exploiting
the UV-optical spectral shape and more subtle UV features. This is useful for
the real-time classification of local and high-redshift SNe using only
photometry. Two remarkable SNe Ib/c were observed with UVOT -- SN2006jc was a
UV bright SN Ib. Swift observations of GRB060218/SN2006aj began shortly after
the explosion and show a UV-bright peak followed by a UV-faint SN bump. UV
observations are also useful for constraining the temperature and ionization
structure of SNe IIP. Rest-frame UV observations of all types are important for
understanding the extinction, temperature, and bolometric luminosity of SNe and
to interpret the observations of high redshift SNe observed at optical
wavelengths.Comment: Figures are enlarged and colorized from print versio
Are There Environmental Benefits from Driving Electric Vehicles? The Importance of Local Factors
We combine a theoretical discrete-choice model of vehicle purchases, an econometric analysis of electricity emissions, and the AP2 air pollution model to estimate the geographic variation in the environmental benefits from driving electric vehicles. The second-best electric vehicle purchase subsidy ranges from 4,964 in North Dakota, with a mean of -$1,095. Ninety percent of local environmental externalities from driving electric vehicles in one state are exported to others, implying they may be subsidized locally, even when the environmental benefits are negative overall. Geographically differentiated subsidies can reduce deadweight loss, but only modestly
The Optical Afterglow of GRB 011211
We present early-time optical photometry and spectroscopy of the optical
afterglow of the gamma-ray burst GRB 011211. The spectrum of the optical
afterglow contains several narrow metal lines which are consistent with the
burst occurring at a redshift of 2.140 +/- 0.001. The optical afterglow decays
as a power law with a slope of alpha = 0.83 +/- 0.04 for the first
approximately two days after the burst at which time there is evidence for a
break. The slope after the break is at least 1.4. There is evidence for rapid
variations in the R-band light approximately 0.5 days after the burst. These
variations suggest that there are density fluctuations near the gamma-ray burst
on spatial scales of approximately 40--125 AU. The magnitude of the break in
the light curve, the spectral slope, and the rate of decay in the optical,
suggest that the burst expanded into an ambient medium that is homogeneous on
large scales. We estimate that the local particle density is between
approximately 0.1 and 10 cm^{-3} and that the total gamma-ray energy in the
burst was 1.2--1.9 x 10^{50} erg. This energy is smaller than, but consistent
with, the ``standard'' value of (5 +/- 2) x 10^{50} erg. Comparing the observed
color of the optical afterglow with predictions of the standard beaming model
suggests that the rest-frame V-band extinction in the host galaxy is less than
approximately 0.03 mag.Comment: 17 pages, 4 figures, AASTeX 5.02, to appear in AJ Referee's report
incorporated, minor changes in the tex
Spectra and Light Curves of Failed Supernovae
Astronomers have proposed a number of mechanisms to produce supernova
explosions. Although many of these mechanisms are now not considered primary
engines behind supernovae, they do produce transients that will be observed by
upcoming ground-based surveys and NASA satellites. Here we present the first
radiation-hydrodynamics calculations of the spectra and light curves from three
of these "failed" supernovae: supernovae with considerable fallback, accretion
induced collapse of white dwarfs, and energetic helium flashes (also known as
type .Ia supernovae).Comment: 33 pages, 14 figure
Air-coupled, focused ultrasonic dispersion spectrum reconstruction in plates
This paper presents and demonstrates a noncontact method for measuring the Lamb wave dispersion spectrum of a plate. Noncontact air-coupled source and receive transducers are used with line-focus mirrors and 50–700 kHz broadband apparatus for simultaneous measurement over a broad spectrum of refractive angles and multiple guided modes. Broadband, wide-angle wave forms are measured as a function of position. The Fourier transform of these wave forms from the t – x domain to the v – k domain gives an approximate spectrum of the dispersion relation. We measure the dispersion spectra of Lucite™, aluminum, balsa wood, and a carbon fiber epoxy laminate, and show that the measured spectra agree well with the dispersion relation calculated from Lamb wave theory
Why electric cars aren’t always environmentally sound
For them to help solve our air pollution problems, we need to clean up the electricity grid, write Stephen P. Holland, Erin T. Mansur, Nicholas Z. Muller and Andrew J. Yate
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