2,927 research outputs found
The environment and host haloes of the brightest z~6 Lyman-break galaxies
By studying the large-scale structure of the bright high-redshift Lyman-break
galaxy (LBG) population it is possible to gain an insight into the role of
environment in galaxy formation physics in the early Universe. We measure the
clustering of a sample of bright (-22.7<M_UV<-21.125) LBGs at z~6 and use a
halo occupation distribution (HOD) model to measure their typical halo masses.
We find that the clustering amplitude and corresponding HOD fits suggests that
these sources are highly biased (b~8) objects in the densest regions of the
high-redshift Universe. Coupled with the observed rapid evolution of the number
density of these objects, our results suggest that the shape of high luminosity
end of the luminosity function is related to feedback processes or dust
obscuration in the early Universe - as opposed to a scenario where these
sources are predominantly rare instances of the much more numerous M_UV ~ -19
population of galaxies caught in a particularly vigorous period of star
formation. There is a slight tension between the number densities and
clustering measurements, which we interpret this as a signal that a refinement
of the model halo bias relation at high redshifts or the incorporation of
quasi-linear effects may be needed for future attempts at modelling the
clustering and number counts. Finally, the difference in number density between
the fields (UltraVISTA has a surface density ~1.8 times greater than UDS) is
shown to be consistent with the cosmic variance implied by the clustering
measurements.Comment: 19 pages, 8 figures, accepted MNRAS 23rd March 201
Constraints on the Spin Evolution of Young Planetary-Mass Companions
Surveys of young star-forming regions have discovered a growing population of
planetary-mass (<13 M_Jup) companions around young stars. There is an ongoing
debate as to whether these companions formed like planets (that is, from the
circumstellar disk), or if they represent the low-mass tail of the star
formation process. In this study we utilize high-resolution spectroscopy to
measure rotation rates of three young (2-300 Myr) planetary-mass companions and
combine these measurements with published rotation rates for two additional
companions to provide a look at the spin distribution of these objects. We
compare this distribution to complementary rotation rate measurements for six
brown dwarfs with masses <20 M_Jup, and show that these distributions are
indistinguishable. This suggests that either that these two populations formed
via the same mechanism, or that processes regulating rotation rates are
independent of formation mechanism. We find that rotation rates for both
populations are well below their break-up velocities and do not evolve
significantly during the first few hundred million years after the end of
accretion. This suggests that rotation rates are set during late stages of
accretion, possibly by interactions with a circumplanetary disk. This result
has important implications for our understanding of the processes regulating
the angular momentum evolution of young planetary-mass objects, and of the
physics of gas accretion and disk coupling in the planetary-mass regime.Comment: 31 pages, 10 figures, published in Nature Astronomy,
DOI:10.1038/s41550-017-0325-
Intensity enhancement of O VI ultraviolet emission lines in solar spectra due to opacity
Opacity is a property of many plasmas, and it is normally expected that if an
emission line in a plasma becomes optically thick, its intensity ratio to that
of another transition that remains optically thin should decrease. However,
radiative transfer calculations undertaken both by ourselves and others predict
that under certain conditions the intensity ratio of an optically thick to thin
line can show an increase over the optically thin value, indicating an
enhancement in the former. These conditions include the geometry of the
emitting plasma and its orientation to the observer. A similar effect can take
place between lines of differing optical depth. Previous observational studies
have focused on stellar point sources, and here we investigate the
spatially-resolved solar atmosphere using measurements of the I(1032 A)/I(1038
A) intensity ratio of O VI in several regions obtained with the Solar
Ultraviolet Measurements of Emitted Radiation (SUMER) instrument on board the
Solar and Heliospheric Observatory (SoHO) satellite. We find several I(1032
A)/I(1038 A) ratios observed on the disk to be significantly larger than the
optically thin value of 2.0, providing the first detection (to our knowledge)
of intensity enhancement in the ratio arising from opacity effects in the solar
atmosphere. Agreement between observation and theory is excellent, and confirms
that the O VI emission originates from a slab-like geometry in the solar
atmosphere, rather than from cylindrical structures.Comment: 17 pages, 4 figures, ApJ Letters, in pres
Soliton effects in dangling-bond wires on Si(001)
Dangling bond wires on Si(001) are prototypical one dimensional wires, which
are expected to show polaronic and solitonic effects. We present electronic
structure calculations, using the tight binding model, of solitons in
dangling-bond wires, and demonstrate that these defects are stable in
even-length wires, although approximately 0.1 eV higher in energy than a
perfect wire. We also note that in contrast to conjugated polymer systems,
there are two types of soliton and that the type of soliton has strong effects
on the energetics of the bandgap edges, with formation of intra-gap states
between 0.1 eV and 0.2 eV from the band edges. These intra-gap states are
localised on the atoms comprising the soliton.Comment: 6 pages, 3 figures, 3 tables, submitted to Phys. Rev.
Recovery of Waste Thermal Energy in U.S. Residential Appliances
With the United States being the world’s second largest consumer of primary energy, research into areas of significant consumption can provide large impacts in terms of the global energy consumption. Buildings account for 41% of US total energy consumption with the residential sector making up a majority. Household appliances account for the second largest site energy consumption at 27%, after the HVAC system for the U.S. residential sector. By quantifying the expected energy available in the waste stream for five major appliances; household refrigerator, clothes dryer and washer, dishwasher, and cooking oven, a potential energy source is presented. A cold water cooling stream is applied to the waste stream of each appliance and an estimated amount of energy can be recovered. The household refrigerator is modeled having an increase in cooling capacity of about 12% and a reduction on compressor power consumption of about 26%. A sample operation of the clothes dryer has the exhaust air stream being cooled down to 30.5°C (86.9°F) or on the other side, is able to heat 19 liter (5 gal) of water up to about 54.5°C (130.1°F). Large volumes of water are available by the clothes washer, but due to typical operation characteristics, low wash and rinse temperatures, the waste stream was not high in temperature. While the dishwasher provided higher heat source temperatures, 40°C (104°F), than the clothes washer, 36°C (97°F), the opposite was true. The volume of waste water drained is very low compared to the clothes washer 11.7 liter (3.1 gal) to 155 liter (41 gal). Thus water temperatures in the storage tank did not reach above 30°C (86°F) even with low storage volumes. The cooking oven can generate very high water temperatures depending how small of a storage tank is connected. Further work in this area is recommended due to the potential of high water temperatures generated from residential waste energy streams not currently being captured, and thus can offset some site-energy usage
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ERP Correlates of Recognition Memory in Autism Spectrum Disorder
Recognition memory in autism spectrum disorder (ASD) tends to be undiminished compared to that of typically developing (TD) individuals (Bowler et al. 2007), but it is still unknown whether memory in ASD relies on qualitatively similar or different neurophysiology. We sought to explore the neural activity underlying recognition by employing the old/new word repetition event-related potential effect. Behavioural recognition performance was comparable across both groups, and demonstrated superior recognition for low frequency over high frequency words. However, the ASD group showed a parietal rather than anterior onset (300–500 ms), and diminished right frontal old/new effects (800–1500 ms) relative to TD individuals. This study shows that undiminished recognition performance results from a pattern of differing functional neurophysiology in ASD
Energy Simulation And Optimized Retrofit Practices Applied To A Real Dwelling
Energy simulation and optimized retrofit practices applied to a real dwelling Giulia Marinello(a), Stephen L. Caskey(a), Eric J. Bowler(b), and Eckhard A. Groll(a) (a) Purdue University, School of Mechanical Engineering, ?Ray W. Herrick Laboratories, West Lafayette, IN 47907, USA (b)Whirlpool Corporation, Benton Harbor, MI 49022, USA Abstract According to the US Environmental Protection Agency, residential housing units account for 20.9% of the total energy usage in the U.S., causing 20.8% of the nation’s total carbon dioxide emissions. The average age of a single family home in the US is 34 years. These aging dwellings were built in a time when energy was cheap and carbon dioxide emission was not considered pollution. Therefore, these houses typically do not contain many energy efficiency measures. The practice of house retrofitting represents a huge source of energy saving. Although there are some general fundamental rules on how to retrofit a house, many different improvements can be applied and the optimum solution is normally based on the previous conditions of the house and on the climate zone where the house is located. In the past few years, many, increasingly sophisticated, software solutions able to provide energy modeling of a residential building have been developed. In this paper, a typical 1950s vintage residential house located in West Lafayette, Indiana, is taken as a case study. The aim is to combine the results obtained from two different energy simulation engines and compare them with real time energy usage data before and after the retrofit. The software tools used are BEOpt and Ecotect. BEOpt was developed by the National Renewable Energy Laboratory and is able to run optimization analyses and provide an indication on the most cost-effective improvements that can be done. Ecotect is based on Autodesk and is able to provide a more accurate energy analysis based on a 3D model of the house developed in Revit. The aim is to run an optimization analysis with BEOpt to identify the best retrofit practices for the case study and use the results to run a more accurate energy analysis in Ecotect. The results of the energy simulation can then be compared with real data thanks to the instrumentation system installed in the aforementioned house. The parameters monitored are the electricity consumption of every circuit, gas consumption, water consumption, and water temperature after the usage. Data from the house will be stored for a year to create a baseline scenario. The suggestions given by the energy simulation will be used to inform actual retrofit actions, which will be put in place during the summer of 2014. This study is part of a larger research project called the NEWW House, a collaboration between Whirlpool Corporation and Purdue University. The overall goal is to retrofit the residential building in order to create a net-zero energy and water house
No difference in orbital parameters of RV-detected giant planets between 0.1 and 5 au in single vs multi-stellar systems
Our Keck/NIRC2 imaging survey searches for stellar companions around 144
systems with radial velocity (RV) detected giant planets to determine whether
stellar binaries influence the planets' orbital parameters. This survey, the
largest of its kind to date, finds eight confirmed binary systems and three
confirmed triple systems. These include three new multi-stellar systems (HD
30856, HD 86081, and HD 207832) and three multi-stellar systems with newly
confirmed common proper motion (HD 43691, HD 116029, and HD 164509). We combine
these systems with seven RV planet-hosting multi-stellar systems from the
literature in order to test for differences in the properties of planets with
semimajor axes ranging between 0.1-5 au in single vs multi-stellar systems. We
find no evidence that the presence or absence of stellar companions alters the
distribution of planet properties in these systems. Although the observed
stellar companions might influence the orbits of more distant planetary
companions in these systems, our RV observations currently provide only weak
constraints on the masses and orbital properties of planets beyond 5 au. In
order to aid future efforts to characterize long period RV companions in these
systems, we publish our contrast curves for all 144 targets. Using four years
of astrometry for six hierarchical triple star systems hosting giant planets,
we fit the orbits of the stellar companions in order to characterize the
orbital architecture in these systems. We find that the orbital plane of the
secondary and tertiary companions are inconsistent with an edge-on orbit in
four out of six cases.Comment: 34 pages, 10 figures, 16 tables, including 4 tables in machine
readable format and 7 tables with online supplemental dat
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