8,688 research outputs found
Socioeconomic impact of photovoltaic power at Schuchuli, Arizona
The social and economic impact of photovoltaic power on a small, remote native American village is studied. Village history, group life, energy use in general, and the use of photovoltaic-powered appliances are discussed. No significant impacts due to the photovoltaic power system were observed
Values of H_0 from Models of the Gravitational Lens 0957+561
The lensed double QSO 0957+561 has a well-measured time delay and hence is
useful for a global determination of H0. Uncertainty in the mass distribution
of the lens is the largest source of uncertainty in the derived H0. We
investigate the range of \hn produced by a set of lens models intended to mimic
the full range of astrophysically plausible mass distributions, using as
constraints the numerous multiply-imaged sources which have been detected. We
obtain the first adequate fit to all the observations, but only if we include
effects from the galaxy cluster beyond a constant local magnification and
shear. Both the lens galaxy and the surrounding cluster must depart from
circular symmetry as well.
Lens models which are consistent with observations to 95% CL indicate
H0=104^{+31}_{-23}(1-\kthirty) km/s/Mpc. Previous weak lensing measurements
constrain the mean mass density within 30" of G1 to be kthirty=0.26+/-0.16 (95%
CL), implying H0=77^{+29}_{-24}km/s/Mpc (95% CL). The best-fitting models span
the range 65--80 km/s/Mpc. Further observations will shrink the confidence
interval for both the mass model and \kthirty.
The range of H0 allowed by the full gamut of our lens models is substantially
larger than that implied by limiting consideration to simple power law density
profiles. We therefore caution against use of simple isothermal or power-law
mass models in the derivation of H0 from other time-delay systems. High-S/N
imaging of multiple or extended lensed features will greatly reduce the H0
uncertainties when fitting complex models to time-delay lenses.Comment: AASTEX, 48 pages 4 figures, 2 tables. Also available at:
http://www.astro.lsa.umich.edu:80/users/philf/www/papers/list.htm
The development of an engineering computer graphics laboratory
Hardware and software systems developed to further research and education in interactive computer graphics were described, as well as several of the ongoing application-oriented projects, educational graphics programs, and graduate research projects. The software system consists of a FORTRAN 4 subroutine package, in conjunction with a PDP 11/40 minicomputer as the primary computation processor and the Imlac PDS-1 as an intelligent display processor. The package comprises a comprehensive set of graphics routines for dynamic, structured two-dimensional display manipulation, and numerous routines to handle a variety of input devices at the Imlac
Chandra Observations of the Gravitationally Lensed System 2016+112
An observation of the gravitationally lensed system 2016+112 with the Chandra
X-ray Observatory has resolved a mystery regarding the proposed presence of a
dark matter object in the lens plane of this system. The Chandra ACIS
observation has clearly detected the lensed images of 2016+112 with positions
in good agreement with those reported in the optical and also detects 13
additional X-ray sources within a radius of 3.5 arcmin. Previous X-ray
observations in the direction of 2016+112 with the ROSAT HRI and ASCA SIS have
interpreted the X-ray data as arising from extended emission from a dark
cluster. However, the present Chandra observation can account for all the X-ray
emission as originating from the lensed images and additional point X-ray
sources in the field. Thus cluster parameters based on previous X-ray
observations are unreliable. We estimate an upper limit on the mass-to-light
ratio within a radius of 800 h_(50)^(-1) kpc of M/L_(V) < 190 h_(50)
(M/L_(V))_Sun. The lensed object is quite unusual, with reported narrow
emission lines in the optical that suggest it may be a type-2 quasar (Yamada
et. al. 1999). Our modeling of the X-ray spectrum of the lensed object implies
that the column density of an intrinsic absorber must lie between 3 and 85 x
10^22 cm^-2 (3 sigma confidence level). The 2-10 keV luminosity of the lensed
object, corrected for the lens magnification effect and using the above range
of intrinsic absorption, is 3 x 10^43 - 1.4 x 10^44 erg/s.Comment: 9 pages, includes 2 figures, Accepted for publication in ApJ
Fall speed measurement and high-resolution multi-angle photography of hydrometeors in free fall
We describe here a new instrument for imaging hydrometeors in free fall. The Multi-Angle Snowflake Camera (MASC) captures high-resolution photographs of hydrometeors from three angles while simultaneously measuring their fall speed. Based on the stereoscopic photographs captured over the two months of continuous measurements obtained at a high altitude location within the Wasatch Front in Utah, we derive statistics for fall speed, hydrometeor size, shape, orientation and aspect ratio. From a selection of the photographed hydrometeors, an illustration is provided for how the instrument might be used for making improved microwave scattering calculations. Complex, aggregated snowflake shapes appear to be more strongly forward scattering, at the expense of reduced back-scatter, than heavily rimed graupel particles of similar size
Boosting jet power in black hole spacetimes
The extraction of rotational energy from a spinning black hole via the
Blandford-Znajek mechanism has long been understood as an important component
in models to explain energetic jets from compact astrophysical sources. Here we
show more generally that the kinetic energy of the black hole, both rotational
and translational, can be tapped, thereby producing even more luminous jets
powered by the interaction of the black hole with its surrounding plasma. We
study the resulting Poynting jet that arises from single boosted black holes
and binary black hole systems. In the latter case, we find that increasing the
orbital angular momenta of the system and/or the spins of the individual black
holes results in an enhanced Poynting flux.Comment: 7 pages, 5 figure
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