31,964 research outputs found
The nature of the red disk-like galaxies at high redshift: dust attenuation and intrinsically red stellar populations
We investigate which conditions of dust attenuation and stellar populations
allow models of dusty, continuously star-forming, bulge-less disk galaxies at
0.8<z<3.2 to meet the different colour selection criteria of high-z ``red''
galaxies (e.g. Rc-K>5.3, Ic-K>4, J-K>2.3). As a main novelty, we use stellar
population models that include the thermally pulsating Asymptotic Giant Branch
(TP-AGB) phase of stellar evolution. The star formation rate of the models
declines exponentially as a function of time, the e-folding time being longer
than 3 Gyr. In addition, we use calculations of radiative transfer of the
stellar and scattered radiation through different dusty interstellar media in
order to explore the wide parameter space of dust attenuation. We find that
synthetic disks can exhibit red optical/near-infrared colours because of
reddening by dust, but only if they have been forming stars for at least about
1 Gyr. Extremely few models barely exhibit Rc-K>5.3, if the inclination i=90
deg and if the opacity 2*tauV>6. Hence, Rc-K-selected galaxies at 1<z<2 most
probably are either systems with an old, passively evolving bulge or
starbursts. Synthetic disks at 1<z<2 exhibit 4<Ic-K<4.8, if they are seen edge
on (i.e. at i about 90 deg) and if 2*tauV>0.5. This explains the large fraction
of observed, edge-on disk-like galaxies with Ks4. Finally,
models with 2<z<3.2 exhibit 2.3<J-K<3, with no bias towards i about 90 deg and
for a large range in opacity (e.g. 2*tauV>1 for i about 70 deg). In conclusion,
red disk-like galaxies at 0.8<z<3.2 may not necessarily be dustier than nearby
disk galaxies (with 0.5<2*tauV<2) and/or much older than about 1 Gyr. This
result is due both to a realistic description of dust attenuation and to the
emission contribution by TP-AGB stars... (Abridged)Comment: 16 pages, 8 ps figures, accepted for publication in MNRA
Physiological Effects of Chronic Copper Exposure to Rainbow Trout (\u3cem\u3eOncorhynchus Mykiss\u3c/em\u3e) in Hard and Soft Water: Evaluation of Chronic Indicators
Effects of chronic copper exposure on a suite of indicators were examined: acute toxicity, acclimation, growth, sprint performance, whole-body electrolytes, tissue residues, and gill copper binding characteristics. Juvenile rainbow trout were exposed for 30 d to waterborne copper in hard water (hardness = 120 ÎĽg/L as CaCO3, pH = 8.0, Cu = 20 and 60 ÎĽg/L) and soft water (hardness = 20 ÎĽg/L as CaCO3, pH = 7.2, Cu = 1 and 2 ÎĽg/L). Significant acclimation to the metal occurred only in fish exposed to 60 mg/L, as seen by an approx. twofold increase in 96-h LC50 (153 vs 91 ÎĽg Cu/L). Chronic copper exposure had little or no effect on survival, growth, or swimming performance in either water hardness, nor was there any initial whole-body electrolyte loss (Na+ and Cl-). The present data suggest that the availability of food (3% wet body weight/day, distributed as three 1% meals) prevented growth inhibition and initial ion losses that usually result from Cu exposure. Elevated metal burdens in the gills and livers of exposed fish were measures of chronic copper exposure but not of effect. Initial gill binding experiments revealed the necessity of using radiolabeled Cu (64Cu) to detect newly accumulated Cu against gill background levels. Using this method, we verified the presence of saturable Cu-binding sites in the gills of juvenile rainbow trout and were able to make estimates of copperbinding affinity (log Kgill=Cu) and capacity (Bmax). Furthermore, we showed that both chronic exposure to Cu and to low water calcium had important effects on the Cu-binding characteristics of the gills
Cost effective flat plate photovoltaic modules using light trapping
Work in optical trapping in 'thick films' is described to form a design guide for photovoltaic engineers. A thick optical film can trap light by diffusive reflection and total internal reflection. Light can be propagated reasonably long distances compared with layer thicknesses by this technique. This makes it possible to conduct light from inter-cell and intra-cell areas now not used in photovoltaic modules onto active cell areas
Sustainable and Green Information Systems: Preparing the next generation of practitioners.
Sustainable development and green computing issues are increasingly important for computing professionals. Preparing the next generation of implementers and developers requires that Higher Education providers develop curriculum to reflect this. There are a number of drivers behind this – encompassing industry and professional body demands, policy makers’ directives, as well as institutional commitments to sustainability. Other reasons include the effectiveness of this topic as a way to address particular issues in engagement and recruitment to computing courses. When considering “sustainability" or ("green-ness") in teaching, we should consider the appropriateness and suitability of material, and target it at an appropriate level. There are also choices about how to present the material so as to match students’ motivation, which can reflect gender and other demographic issues. Institutions can adopt different approaches, such as specialised courses as components of wider programmes, or as specialised courses in their own right. Some approaches integrate the topic into undergraduate teaching, treating environmental impact as a design constraint within a solution. This paper reports on some of these variations and directs readers to an online resource to enable colleagues interested in this topic to share ideas and approaches. Whilst the focus is on computing, many of the issues are transferrable to other STEM disciplines
Sustainability Issues in the Computing Curriculum
"Sustainability" or ("green-ness") has a significant role to play in the teaching of information systems in higher education. There is considerable variation possible in breadth and depth of content, and raises the question of appropriateness, suitability of material and targeting at an appropriate level. There also exists considerable potential for variation of emphasis in presentation according to students’ motivations. Institutions have adopted different approaches, some utilising specialised courses as components of wider programmes, or in their own right. Others have integrated the topic into undergraduate teaching, perhaps as a component of systems analysis and design courses, treating environmental impact as a design constraint within a solution. Computer science programmes may use their computer architecture-themed modules to introduce the relationship between hardware design and energy use or the ethics and professionalism strand may be developed through consideration of electronic waste or the legal issues around the need for compliance with legislation. This paper reports our study of these variations, and introduces some of the teaching materials we have developed as part of a recent HEA ICS project, along with an introduction to a community site to enable colleagues interested in this topic to share ideas and resources
The Flux Ratio Method for Determining the Dust Attenuation of Starburst Galaxies
The presence of dust in starburst galaxies complicates the study of their
stellar populations as the dust's effects are similar to those associated with
changes in the galaxies' stellar age and metallicity. This degeneracy can be
overcome for starburst galaxies if UV/optical/near-infrared observations are
combined with far-infrared observations. We present the calibration of the flux
ratio method for calculating the dust attenuation at a particular wavelength,
Att(\lambda), based on the measurement of F(IR)/F(\lambda) flux ratio. Our
calibration is based on spectral energy distributions (SEDs) from the PEGASE
stellar evolutionary synthesis model and the effects of dust (absorption and
scattering) as calculated from our Monte Carlo radiative transfer model. We
tested the attenuations predicted from this method for the Balmer emission
lines of a sample starburst galaxies against those calculated using radio
observations and found good agreement. The UV attenuation curves for a handful
of starburst galaxies were calculated using the flux ratio method, and they
compare favorably with past work. The relationship between Att(\lambda) and
F(IR)/F(\lambda) is almost completely independent of the assumed dust
properties (grain type, distribution, and clumpiness). For the UV, the
relationship is also independent of the assumed stellar properties (age,
metallicity, etc) accept for the case of very old burst populations. However at
longer wavelengths, the relationship is dependent on the assumed stellar
properties.Comment: accepted by the ApJ, 18 pages, color figures, b/w version at
http://mips.as.arizona.edu/~kgordon/papers/fr_method.htm
Mapping the Kinematical Regimes of Semi-Inclusive Deep Inelastic Scattering
We construct a language for identifying kinematical regions of transversely
differential semi-inclusive deep inelastic scattering cross sections with
particular underlying partonic pictures, especially in regions of moderate to
low where sensitivity to kinematical effects outside the usual very high
energy limit becomes non-trivial. The partonic pictures map to power law
expansions whose leading contributions ultimately lead to well-known QCD
factorization theorems. We propose methods for estimating the consistency of
any particular region of overall hadronic kinematics with the kinematics of a
given underlying partonic picture. The basic setup of kinematics of
semi-inclusive deep inelastic scattering is also reviewed in some detail.Comment: 37 pages, 11 Figure
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