1,792 research outputs found
OPserver: interactive online-computations of opacities and radiative accelerations
Codes to compute mean opacities and radiative accelerations for arbitrary
chemical mixtures using the Opacity Project recently revised data have been
restructured in a client--server architecture and transcribed as a subroutine
library. This implementation increases efficiency in stellar modelling where
element stratification due to diffusion processes is depth dependent, and thus
requires repeated fast opacity reestimates. Three user modes are provided to
fit different computing environments, namely a web browser, a local workstation
and a distributed grid.Comment: 5 pages, 1 figur
Integrating process and factor understanding of environmental innovation by water utilities
Innovations in technology and organisations are central to enabling the water sector to adapt to major environmental changes such as climate change, land degradation or drinking water pollution. While there are literatures on innovation as a process and on the factors that influence it, there is little research that integrates these. Development of such an integrated understanding of innovation is central to understanding how policy makers and organisations can stimulate and direct environmental innovation. In the research reported here a framework is developed that enables such an integrated analysis of innovation process and factors. From research interviews and the literature twenty factors were identified that affect the five stages of the environmental innovation process in English and Welsh water utilities. The environmental innovations investigated are measures taken by water utilities to reduce or prevent pollution in drinking water catchments rather than technical measures to treat water. These Source Control Interventions are similar to other environmental innovations, such as ecosystem and species conservation, in that they emphasise the mix of technology, management and engagement with multiple actors. Results show that in water utilities direct performance regulation and regulation that raises awareness of a ‘performance’ gap as a ‘problem’ can stimulate innovation, but only under particular organisational, natural physical and regulatory conditions. The integrated framework also suggests that while flexible or framework legislation (e.g. Water Framework Directive) does not stimulate innovation in itself, it has shaped the option spaces and characteristics of innovations selected towards source control instead of technical end-of-pipe solutions
A Low Upper Limit to the Lyman Continuum Emission of two galaxies at z 3
Long exposure, long-slit spectra have been obtained in the UV/optical bands
for two galaxies at z=2.96 and z=3.32 to investigate the fraction of ionizing
UV photons escaping from high redshifts galaxies. The two targets are among the
brightest galaxies discovered by Steidel and collaborators and they have
different properties in terms of Lyman-alpha emission and dust reddening. No
significant Lyman continuum emission has been detected. The noise level in the
spectra implies an upper limit of f_{rel,esc}\equiv 3 f(900)/f(1500)< 16% for
the relative escape fraction of ionizing photons, after correction for
absorption by the intervening intergalactic medium. This upper limit is 4 times
lower than the previous detection derived from a composite spectrum of 29 Lyman
break galaxies at z 3.4. If this value is typical of the escape fraction of the
z 3 galaxies, and is added to the expected contribution of the QSO population,
the derived UV background is in good agreement with the one derived by the
proximity effect.Comment: 16 pages, 2 figures, ApJ Letters in pres
Using Three-Body Recombination to Extract Electron Temperatures of Ultracold Plasmas
Three-body recombination, an important collisional process in plasmas,
increases dramatically at low electron temperatures, with an accepted scaling
of T_e^-9/2. We measure three-body recombination in an ultracold neutral xenon
plasma by detecting recombination-created Rydberg atoms using a
microwave-ionization technique. With the accepted theory (expected to be
applicable for weakly-coupled plasmas) and our measured rates we extract the
plasma temperatures, which are in reasonable agreement with previous
measurements early in the plasma lifetime. The resulting electron temperatures
indicate that the plasma continues to cool to temperatures below 1 K.Comment: 5 pages, 3 figure
Line emission from gamma-ray burst environments
The time and angle dependent line and continuum emission from a dense torus
around a cosmological gamma-ray burst source is simulated, taking into account
photoionization, collisional ionization, recombination, and electron heating
and cooling due to various processes. The importance of the hydrodynamical
interaction between the torus and the expanding blast wave is stressed. Due to
the rapid deceleration of the blast wave as it interacts with the dense torus,
the material in the torus will be illuminated by a drastically different photon
spectrum than observable through a low-column-density line of sight, and will
be heated by the hydrodynamical interaction between the blast wave and the
torus. A model calculation to reproduce the Fe K-alpha line emission observed
in the X-ray afterglow of GRB 970508 is presented. The results indicate that ~
10^{-4} solar masses of iron must be concentrated in a region of less than
10^{-3} pc. The illumination of the torus material due to the hydrodynamic
interaction of the blast wave with the torus is the dominant heating and
ionization mechanism leading to the formation of the iron line. These results
suggest that misaligned GRBs may be detectable as X-ray flashes with pronounced
iron emission line features.Comment: Accepted for publication in ApJ. Updated recombination rate data;
discussion on element abundances added; references update
Validation and clinical application of molecular methods for the identification of molds in tissue
Background. Invasive fungal infections due to less-common molds are an increasing problem, and accurate diagnosis is difficult.Methods. We used our previously established molecular method, which allows species identification of molds in histological tissue sections, to test sequential specimens from 56 patients with invasive fungal infections who were treated at our institution from 1982 to 2000.Results. The validity of the method was demonstrated with the establishment of a molecular diagnosis in 52 cases (93%). Confirmation of the causative organism was made in all cases in which a mold had been cultured from the tissue specimen. Less-common molds were identified in 7% of cases and appear to be an increasing problem.Conclusions. Our previously established method has proven to be of value in determining the incidence of invasive infection caused by less-common molds. Institutions should continue to pursue diagnosis of invasive fungal infections by means of tissue culture and microbiologic analysis
Ultraviolet Spectra of CV Accretion Disks with Non-Steady T(r) Laws
An extensive grid of synthetic mid- and far-ultraviolet spectra for accretion
disks in cataclysmic variables has been presented by Wade and Hubeny (1998). In
those models, the disk was assumed to be in steady-state, that is T_eff(r) is
specified completely by the mass M_WD and radius R_WD of the accreting white
dwarf star and the mass transfer rate M_dot which is constant throughout the
disk. In these models, T_eff(r) is proportional to r^{-3/4} except as modified
by a cutoff term near the white dwarf.
Actual disks may vary from the steady-state prescription for T_eff(r),
however, e.g. owing to outburst cycles in dwarf novae M_dot not constant with
radius) or irradiation (in which case T_eff in the outer disk is raised above
T_steady). To show how the spectra of such disks might differ from the steady
case, we present a study of the ultraviolet (UV) spectra of models in which
power-law temperature profiles T_eff(r) is proportional to r^{-gamma} with
gamma < 3/4 are specified. Otherwise, the construction of the models is the
same as in the Wade & Hubeny grid, to allow comparison. We discuss both the UV
spectral energy distributions and the appearance of the UV line spectra. We
also briefly discuss the eclipse light curves of the non-standard models.
Comparison of these models with UV observations of novalike variables suggests
that better agreement may be possible with such modified T_eff(r) profiles.Comment: 13 pages, 6 figures (one reduced quality), ApJ in pres
Recommended from our members
Trend Following and Momentum Strategies for Global REITs
In this study, we investi- gate whether the risk-Adjusted returns of a global REIT portfolio would be enhanced by adopting a trend following global strategy (which is an abso- lute concept sometimes known as absolute mo- mentum), a momentum-based strategy (which is a relative concept and requires individual country al- locations), or indeed a combination of the two. e examine the results in terms of both a dedicated global REIT exposure, and the impact on a multi- asset portfolio. We find that the main improve- ments arise when the broad index is replaced with one of the four trend following strategies. The port- folios deliver similar returns but volatility is re- duced by up to a quarter to the 8%-9% range, the Sharpe ratios increase by 0.1 to 0.5 with the main benefit being the reduction in the maximum draw- down to under 30% compared to 43% when the broad index was used. We thus find that a com- bined momentum and trend following a global REIT strategy can be beneficial for both a dedicated REIT portfolio and adding REITs to a multi-Asset portfolio
Recommended from our members
The Blended Approach to Real Estate Allocations: Performance Implications of Combining an Exposure to German Spezialfonds with Global Listed Real Estate Securities
- …