955 research outputs found
Solid Waste Management and the Need for Effective Public Participation
Recent changes in technical requirements for landfill design, mandated by the U.S. Environmental Protection Agency, have led to closing the majority of solid waste landfills in the United States. Efforts to site new landfills have elicited widespread opposition. Based on eight case studies in Alabama, we identify three themes behind this opposition: threats to quality of life, potentially harmful economic impacts, and frustration over representational issues in the process involved in selecting the proposed solid waste facility. These concerns mirror much of the literature on public opposition to landfills and other facilities which pose similar threats to the environment and public health. The incidence of public opposition raises the question of why, when the technical regulations affecting solid waste landfills were updated, no parallel modification of the permit process for such facilities was initiated. In light of concerns expressed in our case studies, we identify a set of suggested modifications that would allow for greater public participation in the siting and permitting process
Hot White Dwarf Donors in Ultracompact X-Ray Binaries
The discovery of two accreting millisecond X-ray pulsars in binaries with 43
minute orbital periods allows for a new probe of the donor's structure. For XTE
J1751-305, only a hot white dwarf (WD) can fill the Roche Lobe. A cold He WD is
a possible solution for XTE J0929-314, though I will show that evolutionary
arguments make a hot WD more likely. In addition to being larger than the T=0
models, these finite entropy, low-mass (<0.03 solar masses) WDs have a minimum
mass for a fixed core temperature. If they remain hot as they lose mass and
expand, they can ``evaporate'' to leave an isolated millisecond radio pulsar.
They also adiabatically expand upon mass loss at a rate faster than the growth
of the Roche radius if the angular momentum deposited in the disk is not
returned to the donor. If the timescale of the resulting runaway mass transfer
is shorter than the viscous timescale in the outer disk, then the mass transfer
instability of Ruderman and Shaham for He WDs would be realized. However, my
estimates of these timescales still makes the instability unlikely for
adiabatic responses. I close by noting the possible impact of finite T WDs on
our understanding of AM CVn binaries.Comment: to appear in Astrophysical Journal Letter
Abell 43: Longest period Planetary Nebula Nucleus variable
Based on 24h high speed photometry of the hybrid PG 1159 star Abell 43, we
have detected 6 sighificant pulsations with periods between 2380 s and 6075 s.
A short (4h) run on the almost spectroscopic twin NGC 7094 central star
resulted in detection of 3 low amplitude pulsations with periods between 2000 s
and 5000 s. The results are close to predictions for g-mode pulsations driven
by the kappa-mechanism induced by the partial ionization of carbon and oxygen.Comment: 5 pages, 5 figures, to be published in Astronomy and Astrophysic
First Attempt at Spectroscopic Detection of Gravity Modes in a Long-Period Pulsating Subdwarf B Star -- PG 1627+017
In the first spectroscopic campaign for a PG 1716 variable (or long-period
pulsating subdwarf B star), we succeeded in detecting velocity variations due
to g-mode pulsations at a level of 1.0-1.5 km/s.The observations were obtained
during 40 nights on 2-m class telescopes in Arizona, South Africa,and
Australia. The target,PG1627+017, is one of the brightest and largest amplitude
stars in its class.It is also the visible component of a post-common envelope
binary.Our final radial velocity data set includes 84 hours of time-series
spectroscopy over a time baseline of 53 days. Our derived radial velocity
amplitude spectrum, after subtracting the orbital motion, shows three potential
pulsational modes 3-4 sigma above the mean noise level, at 7201.0s,7014.6s and
7037.3s.Only one of the features is statistically likely to be real,but all
three are tantalizingly close to, or a one day alias of, the three strongest
periodicities found in the concurrent photometric campaign. We further
attempted to detect pulsational variations in the Balmer line amplitudes. The
single detected periodicity of 7209 s, although weak, is consistent with
theoretical expectations as a function of wavelength.Furthermore, it allows us
to rule out a degree index of l= 3 or l= 5 for that mode. Given the extreme
weakness of g-mode pulsations in these stars,we conclude that anything beyond
simply detecting their presence will require larger telescopes,higher
efficiency spectral monitoring over longer time baselines,improved longitude
coverage, and increased radial velocity precision.Comment: 39 pages, 9 figures, 4 tables, ApJ accepted. See postscript for full
abtrac
Clinical application of three-dimensional echocardiographic laser stereolithography: Effect of leaflet funnel geometry on the coefficient of orifice contraction, pressure loss and the Gorlin formula in aortic stenosis
International audienc
A time varying speed of light as a solution to cosmological puzzles
We consider the cosmological implications of light travelling faster in the
early Universe. We propose a prescription for deriving corrections to the
cosmological evolution equations while the speed of light is changing. We
then show how the horizon, flatness, and cosmological constant problems may be
solved. We also study cosmological perturbations in this scenario and show how
one may solve the homogeneity and isotropy problems. As it stands, our scenario
appears to most easily produce extreme homogeneity, requiring structure to be
produced in the Standard Big Bang epoch. Producing significant perturbations
during the earlier epoch would require a rather careful design of the function
. The large entropy inside the horizon nowadays can also be accounted for
in this scenario.Comment: To be published in Physical Review D. Note added referring to John
Moffat's early work on VSL theorie
A design framework for realizing multifunctional wings for flapping wing air vehicles using solar cells
Partial funding for Open Access provided by the UMD Libraries' Open Access Publishing Fund.Long flight durations are highly desirable to expand mission capabilities for unmanned air systems and autonomous
applications in particular. Flapping wing aerial vehicles are unmanned air system platforms offering several performance
advantages over fixed wing and rotorcraft platforms, but are unable to reach comparable flight times when powered by
batteries. One solution to this problem has been to integrate energy harvesting technologies in components, such as
wings. To this end, a framework for designing flapping wing aerial vehicle using multifunctional wings using solar cells is
described. This framework consists of: (1) modeling solar energy harvesting while flying, (2) determining the number of
solar cells that meet flight power requirements, and (3) determining appropriate locations to accommodate the desired
number of solar cells. A system model for flapping flight was also developed to predict payload capacity for carrying
batteries to provide energy only for power spikes and to enable time-to-land safely in an area where batteries can
recharge when the sun sets. The design framework was applied to a case study using flexible high-efficiency (>24%) solar
cells on a flapping wing aerial vehicle platform, known as Robo Raven IIIv5, with the caveat that a powertrain with 81%
efficiency is used in place of the current servos. A key finding was the fraction of solar flux incident on the wings during
flapping was 0.63 at the lowest solar altitude. Using a 1.25 safety factor, the lowest value for the purposes of design
will be 0.51. Wind tunnel measurements and aerodynamic modeling of the platform determined integrating solar cells
in the wings resulted in a loss of thrust and greater drag, but the resulting payload capacity was unaffected because of
a higher lift coefficient. A time-to-land of 2500 s was predicted, and the flight capability of the platform was validated
in a netted test facility
Ecosystem effects of thermal manipulation of a whole lake, Lake Breisjøen, southern Norway (THERMOS project)
International audienceWe conducted a 3-year artificial deepening of the thermocline in the dimictic Lake Breisjøen, southern Norway, by means of a large submerged propeller. An adjacent lake served as untreated reference. The manipulation increased thermocline depth from 6 to 20 m, caused a significant increase in the heat content, and delayed ice-on by about 20 days. There were only minor changes in water chemistry. Concentrations of sulphate declined, perhaps due to greater reduction of sulphate at the sediment-water interface. Concentrations of particulate carbon and nitrogen decreased, perhaps due to increased sedimentation velocity. Water transparency increased. There was no significant change in concentration of phosphorus, the growth-limiting nutrient. There were few significant changes in principal biological components. Phytoplankton biomass and productivity did not change, although the chlorophyll-a concentration showed a small decrease. Phytoplankton species richness increased, and the species composition shifted. Growth of periphyton increased. There was no change in the macrophyte community. The manipulation did not affect the zooplankton biodiversity, but caused a significant shift in the relative abundance (measured as biomass) in the two major copepod species. The manipulation did not affect the individual density, but appeared to have changed the vertical distribution of zoobenthos. Fish populations were not affected. The lake is oligotrophic and clearwater and the manipulation did not change the supply of phosphorus, and thus there were only minor changes in lake chemistry and biology. Effects might be larger in eutrophic and dystrophic lakes in which internal processes are stronger
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