2,146 research outputs found
The Stellar Metallicity Distribution Function of the Galactic Halo from SDSS Photometry
We explore the stellar metallicity distribution function of the Galactic halo
based on SDSS ugriz photometry. A set of stellar isochrones is calibrated using
observations of several star clusters and validated by comparisons with
medium-resolution spectroscopic values over a wide range of metal abundance. We
estimate distances and metallicities for individual main-sequence stars in the
multiply scanned SDSS Stripe 82, at heliocentric distances in the range 5 - 8
kpc and |b| > 35 deg, and find that the in situ photometric metallicity
distribution has a shape that matches that of the kinematically-selected local
halo stars from Ryan & Norris. We also examine independent kinematic
information from proper-motion measurements for high Galactic latitude stars in
our sample. We find that stars with retrograde rotation in the rest frame of
the Galaxy are generally more metal poor than those exhibiting prograde
rotation, which is consistent with earlier arguments by Carollo et al. that the
halo system comprises at least two spatially overlapping components with
differing metallicity, kinematics, and spatial distributions. The observed
photometric metallicity distribution and that of Ryan & Norris can be described
by a simple chemical evolution model by Hartwick (or by a single Gaussian
distribution); however, the suggestive metallicity-kinematic correlation
contradicts the basic assumption in this model that the Milky Way halo consists
primarily of a single stellar population. When the observed metallicity
distribution is deconvolved using two Gaussian components with peaks at [Fe/H]
~ -1.7 and -2.3, the metal-poor component accounts for ~20% - 35% of the entire
halo population in this distance range.Comment: Accepted for publication in Ap
Vivid Motor Imagery as an Adaptation Method for Head Turns on a Short-Arm Centrifuge
Artificial gravity (AG) has been proposed as a potential countermeasure to the debilitating physiological effects of long duration space flight. The most economical means of implementing AG may be through the use of a short-radius (2m or less) centrifuge. For such a device to produce gravitational forces comparable to those on earth requires rotation rates in excess of 20 revolutions per minute (rpm). Head turns made out of the plane of rotation at these rates, as may be necessary if exercise is combined with AG, result in cross-coupled stimuli (CCS) that cause adverse side effects including motion sickness, illusory sensations of motion, and inappropriate eye movements. Recent studies indicate that people can adapt to CCS and reduce these side effects by making multiple head turns during centrifuge sessions conducted over consecutive days. However, about 25% of the volunteers for these studies have difficulty tolerating the CCS adaptation paradigm and often drop out due to motion sickness symptoms. The goal of this investigation was to determine whether vivid motor imagery could be used as a pseudostimulus for adapting subjects to this unique environment. Twenty four healthy human subjects (14 males, 10 females), ranging in age from 21 to 48 years (mean 33, sd 7 years) took part in this study. The experimental stimuli were produced using the NASA JSC short-arm centrifuge (SAC). Subjects were oriented supinely on this device with the nose pointed toward the ceiling and head centered on the axis of rotation. Thus, centrifuge rotation was in the body roll plane. After ramp-up the SAC rotated clockwise at a constant rate of 23 rpm, producing a centrifugal force of approximately 1 g at the feet. Semicircular canal CCS were produced by having subjects make yaw head turns from the nose up (NU) position to the right ear down (RED) position and from RED to NU. Each head turn was completed in about one second, and a 30 second recovery period separated consecutive head movements. Participants were randomly assigned to one of three groups (n=8 per group): physical adapters (PA), mental adapters (MA), or a control group (CG). Each subject participated in a one hour test session on each of three consecutive days. Each test session consisted of an initial (preadaptation) period during which the subject performed six CCS maneuvers in the dark, followed by an adaptation period with internal lighting on the centrifuge, and a final (postadaptation) period during which six more CCS maneuvers were performed in the dark. For the PA group, the adaptation period consisted of performing 30 additional CCS maneuvers in the light. For the MA and CG group the centrifuge was ramped down to 0 rpm after the pre-adaptation period and ramped back up to 23 rpm before the post-adaptation period. For the both of these groups, the adaptation period consisted of making 30 CCS maneuvers in the light with the centrifuge stationary (so no cross-coupling occurred). MA group subjects were instructed to vividly imagine the provocative sensations produced by the preadaptation CCS maneuvers in terms of magnitude, duration, and direction of illusory body tilt, as well as any accompanying levels of motion sickness. CG group subjects were asked to answer low imagery content questions (trivial pursuit) during each adaptation period head turn. During the 30 second recovery following each head turn, psychophysical data were collected including self reports of motion sickness, magnitude and direction estimates of illusory body tilt, and the overall duration of these sensations. A multilevel mixed effects linear regression analysis performed on all response variables indicated that all three groups experienced some psychophysical adaptation across the three test sessions. For illusory tilt magnitude, the PA group exhibited the most overall adaptation, followed by the MA group, and the CG group. The slopes of these adaptation trajectories by group over day were significantly diffent from one another. For the perceived duration of sensations, the CG group again exhibited the least amount of adaptation. However, the rates of adaptation of the PA and the MA groups were indistinguishable, suggesting that the imagined pseudostimulus appeared to be just as effective a means of adaptation as the actual stimulus. The MA group's rate of adaptation to motion sickness symptoms was also comparable to the PA group. The use of vivid motor imagery may be an effective method for adapting to the illusory sensations and motion sickness symptoms produced by cross-coupled stimuli. For space-based AG applications, this technique may prove quite useful in retaining astronauts considered highly susceptible to motion sickness as it reduces the number of actual CCS required to attain adaptation
Photoemission evidence for crossover from Peierls-like to Mott-like transition in highly strained VO
We present a spectroscopic study that reveals that the metal-insulator
transition of strained VO thin films may be driven towards a purely
electronic transition, which does not rely on the Peierls dimerization, by the
application of mechanical strain. Comparison with a moderately strained system,
which does involve the lattice, demonstrates the crossover from Peierls- to
Mott-like transitions
Maximum entropy deconvolution of resonant inelastic x-ray scattering spectra
Resonant inelastic x-ray scattering (RIXS) has become a powerful tool in the
study of the electronic structure of condensed matter. Although the linewidths
of many RIXS features are narrow, the experimental broadening can often hamper
the identification of spectral features. Here, we show that the Maximum Entropy
technique can successfully be applied in the deconvolution of RIXS spectra,
improving the interpretation of the loss features without a severe increase in
the noise ratio
Investigating relationships between and within entry pathways on a sport related programme and the degree outcome obtained
Research within Higher Education in the United Kingdom has reported conflicting findings when investigating the relationship between undergraduate entry routes and gender, with successful performances across the degree cycle. This paper adds to this body of knowledge and examines the relationship between entry routes and gender on student outcomes in a sport-related degree at an UK HE institution. Students’ demographic data, entry qualifications and grade point averages (GPAs) across the 3 year degree programme were retrospectively analysed. In relation to entry routes the findings of this study revealed that no significant difference existed between entry level qualifications and all outcomes measures. Indicating that although entry routes into HE may differ this did not impact on student success for those who completed the programme. Further findings revealed significant differences (p < 0.05) between genders, in that females outperformed their male counterparts at levels 5, 6 dissertation and final GPA. Additionally, females were also more likely to achieve a first degree qualification. This study adds further weight to findings which have shown gender differences but in contrast adds to the complexity of predicting successful performances from entry qualifications
Neutron-proton interaction in rare-earth nuclei: Role of tensor force
We investigate the role of the tensor force in the description of doubly odd
deformed nuclei within the framework of the particle-rotor model. We study the
rare-earth nuclei 174Lu, 180Ta, 182Ta, and 188Re using a finite-range
interaction, with and without tensor terms. Attention is focused on the lowest
K=0 and K=1 bands, where the effects of the residual neutron-proton interaction
are particularly evident. Comparison of the calculated results with
experimental data evidences the importance of the tensor-force effects.Comment: 8 pages, 5 figures, to be published on Physical Review
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CONCEPTUAL DESIGN AND ECONOMICS OF A NOMINAL 500 MWe SECOND-GENERATION PFB COMBUSTION PLANT
Research has been conducted under United States Department of Energy Contract DE-AC21-86MC21023 to develop a new type of coal-fired plant for electric power generation. This new type of plant, called a Second Generation Pressurized Fluidized Bed Combustion Plant (2nd Gen PFB), offers the promise of efficiencies greater than 48 percent, with both emissions and a cost of electricity that are significantly lower than those of conventional pulverized coal-fired (PC) plants with wet flue gas desulfurization. The 2nd Gen PFB plant incorporates the partial gasification of coal in a carbonizer, the combustion of carbonizer char in a pressurized circulating fluidized bed boiler, and the combustion of carbonizer syngas in a gas turbine combustor to achieve gas turbine inlet temperatures of 2300 F and higher. A conceptual design and an economic analysis was previously prepared for this plant. When operating with a Siemens Westinghouse W501F gas turbine, a 2400psig/1000 F/1000 F/2-1/2 in. Hg. steam turbine, and projected carbonizer, PCFB, and topping combustor performance data, the plant generated 496 MWe of power with an efficiency of 44.9 percent (coal higher heating value basis) and a cost of electricity 22 percent less than a comparable PC plant. The key components of this new type of plant have been successfully tested at the pilot plant stage and their performance has been found to be better than previously assumed. As a result, the referenced conceptual design has been updated herein to reflect more accurate performance predictions together with the use of the more advanced Siemens Westinghouse W501G gas turbine. The use of this advanced gas turbine, together with a conventional 2400 psig/1050 F/1050 F/2-1/2 in. Hg. steam turbine increases the plant efficiency to 48.2 percent and yields a total plant cost of $1,079/KW (January 2002 dollars). The cost of electricity is 40.7 mills/kWh, a value 12 percent less than a comparable PC plant
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Pressurized Fluidized Bed Combustion Second-Generation System Research and Development
Research is being conducted under United States Department of Energy (DOE) Contract DE-AC21-86MC21023 to develop a new type of coal-fired plant for electric power generation. This new type of plant--called a Second-Generation or Advanced Pressurized Circulating Fluidized Bed Combustion (APCFB) plant--offers the promise of efficiencies greater than 45% (HHV), with both emissions and a cost of electricity that are significantly lower than conventional pulverized-coal-fired plants with scrubbers. The APCFB plant incorporates the partial gasification of coal in a carbonizer, the combustion of carbonizer char in a pressurized circulating fluidized bed boiler (PCFB), and the combustion of carbonizer syngas in a topping combustor to achieve gas turbine inlet temperatures of 2300 F and higher. A conceptual design was previously prepared for this new type of plant and an economic analysis presented, all based on the use of a Siemens Westinghouse W501F gas turbine with projected carbonizer, PCFB, and topping combustor performance data. Having tested these components at the pilot plant stage, the referenced conceptual design is being updated to reflect more accurate performance predictions together with the use of the more advanced Siemens Westinghouse W501G gas turbine and a conventional 2400 psig/1050 F/1050 F/2-1/2 in. steam turbine. This report describes the updated plant which is projected to have an HHV efficiency of 48% and identifies work completed for the October 2001 through September 2002 time period
Patterns and determinants of antenatal care utilization:analysis of national survey data in seven countdown countries
Antenatal care (ANC) is critical for improving maternal and newborn health. WHO recommends that pregnant women complete at least four ANC visits. Countdown and other global monitoring efforts track the proportions of women who receive one or more visits by a skilled provider (ANC1+) and four or more visits by any provider (ANC4+). This study investigates patterns of drop–off in use between ANC1+ and ANC4+, and explores inequalities in women’s use of ANC
services. It also identifies determinants of utilization and describes countries’ ANC–related policies, and programs
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