Now showing items 1-20 of 6486

(2019-01)

(2019-01)
• #### Research Practices of Indigenous Studies Scholars at the University of Arizona: An Ithaka S+R Report

(The University of Arizona., 2019-01)
Introduction: This report was completed at the invitation of Ithaka S+R, as part of a multi‐university qualitative study on the research practices of Indigenous Studies scholars. The University of Arizona Libraries (UAL) joined 11 other participating academic libraries in conducting interviews with scholars at their own institutions. The results of the local study are synthesized here as well as compiled, along with the other institutions’ findings, into the final Ithaka S+R report. The University of Arizona is a large public research university and land‐grant institution, founded in 1885, and situated on the lands of the Tohono O’odham Nation. Its American Indian Studies program was the first of its kind in the country to offer a Master’s degree and Ph.D. degree, in 1982 and 1997, respectively. It is home to the renowned American Indian Language Development Institute, the Native Nations Institute, and the Native American Research Training Center.
• #### Using GRACE to Estitmate Snowfall Accumulation and Assess Gauge Undercatch Corrections in High Latitudes

(AMER METEOROLOGICAL SOC, 2018-11)
Ten years of terrestrial water storage anomalies from the Gravity Recovery and Climate Experiment (GRACE) were used to estimate high-latitude snowfall accumulation using a mass balance approach. The estimates were used to assess two common gauge-undercatch correction factors (CFs): the Legates climatology (CF-L) utilized in the Global Precipitation Climatology Project (GPCP) and the Fuchs dynamic correction model (CF-F) used in the Global Precipitation Climatology Centre (GPCC) monitoring product. The two CFs can be different by more than 50%. CF-L tended to exceed CF-F over northern Asia and Eurasia, while the opposite was observed over North America. Estimates of snowfall from GPCP, GPCC-L (GPCC corrected by CF-L), and GPCC-F (GPCC corrected by CF-F) were 62%, 64%, and 46% more than GPCC over northern Asia and Eurasia. The GRACE-based estimate (49% more than GPCC) was the closest to GPCC-F. We found that as near-surface air temperature decreased, the products increasingly underestimated the GRACE-based snowfall accumulation. Overall, GRACE showed that CFs are effective in improving GPCC estimates. Furthermore, our case studies and overall statistics suggest that CF-F is likely more effective than CF-L in most of the high-latitude regions studied here. GPCP showed generally better skill than GPCC-L, which might be related to the use of satellite data or additional quality controls on gauge inputs to GPCP. This study suggests that GPCP can be improved if it employs CF-L instead of CF-F to correct for gauge undercatch. However, this implementation requires further studies, region-specific analysis, and operational considerations.
• #### Dynamical Constraints on the HR 8799 Planets with GPI

(IOP PUBLISHING LTD, 2018-11)
The HR 8799 system uniquely harbors four young super-Jupiters whose orbits can provide insights into the system's dynamical history and constrain the masses of the planets themselves. Using the Gemini Planet Imager, we obtained down to one milliarcsecond precision on the astrometry of these planets. We assessed four-planet orbit models with different levels of constraints and found that assuming the planets are near 1:2:4:8 period commensurabilities, or are coplanar, does not worsen the fit. We added the prior that the planets must have been stable for the age of the system (40 Myr) by running orbit configurations from our posteriors through N-body simulations and varying the masses of the planets. We found that only assuming the planets are both coplanar and near 1:2:4:8 period commensurabilities produces dynamically stable orbits in large quantities. Our posterior of stable coplanar orbits tightly constrains the planets' orbits, and we discuss implications for the outermost planet b shaping the debris disk. A four-planet resonance lock is not necessary for stability up to now. However, planet pairs d and e, and c and d, are each likely locked in two-body resonances for stability if their component masses are above 6 M-Jup and 7 M-Jup, respectively. Combining the dynamical and luminosity constraints on the masses using hot-start evolutionary models and a system age of 42 +/- 5 Myr, we found the mass of planet b to be 5.8 +/- 0.5 M-Jup, and the masses of planets c, d, and e to be 7.2(-0.7)(+0.6) M-Jup each.
• #### Atypical Flowers Can Be as Profitable as Typical Hummingbird Flowers

(UNIV CHICAGO PRESS, 2018-11)
In western North America, hummingbirds can be observed systematically visiting flowers that lack the typical reddish color, tubular morphology, and dilute nectar of hummingbird flowers. Curious about this behavior, we asked whether these atypical flowers are energetically profitable for hummingbirds. Our field measurements of nectar content and hummingbird foraging speeds, taken over four decades at multiple localities, show that atypical flowers can be as profitable as typical ones and suggest that the profit can support 24-h metabolic requirements of the birds. Thus, atypical flowers may contribute to successful migration of hummingbirds, enhance their population densities, and allow them to occupy areas seemingly depauperate in suitable resources. These results illustrate what can be gained by attending to the unexpected.
• #### The Gemini/Hubble Space Telescope Galaxy Cluster Project: Stellar Populations in the Low-redshift Reference Cluster Galaxies

(IOP PUBLISHING LTD, 2018-11)
In order to study stellar populations and galaxy structures at intermediate and high redshift (z = 0.2-2.0) and link these properties to those of low-redshift galaxies, there is a need for well-defined local reference samples. Especially for galaxies in massive clusters, such samples are often limited to the Coma cluster galaxies. We present consistently calibrated velocity dispersions and absorption-line indices for galaxies in the central 2 R-500 x 2 R-500 of four massive clusters at z < 0.1: Abell 426/Perseus, Abell 1656/Coma, Abell 2029, and Abell 2142. The measurements are based on data from the Gemini Observatory, McDonald Observatory, and Sloan Digital Sky Survey. For bulge-dominated galaxies, the samples are 95% complete in Perseus and Coma and 74% complete in A2029 and A2142, to a limit of M-B,M-abs <= -18.5 mag. The data serve as the local reference for our studies of galaxy populations in the higher-redshift clusters that are part of the Gemini/HST Galaxy Cluster Project (GCP). We establish the scaling relations between line indices and velocity dispersions as a reference for the GCP. We derive stellar population parameters, ages, metallicities [M/H], and abundance ratios from line indices, both averaged in bins of velocity dispersion and from individual measurements for galaxies in Perseus and Coma. The zero points of relations between the stellar population parameters and the velocity dispersions limit the allowed cluster-to-cluster variation of the four clusters to +/- 0.08 dex in age, +/- 0.06 dex in [M/H], +/- 0.07 dex in [CN/Fe], and +/- 0.03 dex in [Mg/Fe].
• #### AKARI mid-infrared slitless spectroscopic survey of star-forming galaxies at z ≲ 0.5

(EDP SCIENCES S A, 2018-10-18)
Context. Deep mid-infrared (MIR) surveys have revealed numerous strongly star-forming galaxies at redshift z less than or similar to 2. Their MIR fluxes are produced by a combination of continuum and polycyclic aromatic hydrocarbon (PAH) emission features. The PAH features can dominate the total MIR flux, but are difficult to measure without spectroscopy. Aims. We aim to study star-forming galaxies by using a blind spectroscopic survey at MIR wavelengths to understand evolution of their star formation rate (SFR) and specific SFR (SFR per stellar mass) up to z similar or equal to 0.5, by paying particular attention to their PAH properties. Methods. We conducted a low-resolution (R similar or equal to 50) slitless spectroscopic survey at 5-13 mu m of 9 mu m flux-selected sources (> 0.3 mJy) around the north ecliptic pole with the infrared camera (IRC) onboard AKARI. After removing 11 AGN candidates by using the IRC photometry, we identify 48 PAH galaxies with PAH 6.2, 7.7, and 8.6 mu m features at z < 0.5. The rest-frame optical-MIR spectral energy distributions (SEDs) based on CFHT and IRC imaging covering 0.37-18 mu m were produced, and analysed in conjunction with the PAH spectroscopy. We defined the PAH enhancement by using the luminosity ratio of the 7.7 mu m PAH feature over the 3.5 mu m stellar component of the SEDs. Results. The rest-frame SEDs of all PAH galaxies have a universal shape with stellar and 7.7 mu m bumps, except that the PAH enhancement significantly varies as a function of the PAH luminosities. We identify a PAH-enhanced population at z greater than or similar to 0.35, whose SEDs and luminosities are typical of luminous infrared galaxies. They show particularly larger PAH enhancement at high luminosity, implying that they are vigorous star-forming galaxies with elevated specific SFR. Our composite starburst model that combines a very young and optically very thick starburst with a very old population can successfully reproduce most of their SED characteristics, although we cannot confirm this optically think component from our spectral analysis.
• #### Computed stabilization for a giant fullerene endohedral: Y2C2@C1(1660)-C108

(Elsevier, 2018-10-16)
• #### Model-independent Test of the Cosmic Distance Duality Relation

(IOP PUBLISHING LTD, 2018-10-08)
A validation of the cosmic distance duality (CDD) relation, h() ( ) () () z zdz dz º+ = 1 A L 1 2 , coupling the luminosity (dL) and angular-diameter (dA) distances, is crucial because its violation would require exotic new physics. We present a model-independent test of the CDD, based on strong lensing and a reconstruction of the H II galaxy Hubble diagram using Gaussian processes, to confirm the validity of the CDD at a very high level of confidence. Using parameterizations h( )z z = +1 h0 and h( )z zz =+ + 1 h h 1 2 2, our best-fit results are h = - + 0.0147 0 0.066 0.056, and h = - + 0.1091 1 0.1568 0.1680 and h = - - + 0.0603 2 0.0988 0.0999, respectively. In spite of these strong constraints, however, we also point out that the analysis of strong lensing using a simplified single isothermal sphere (SIS) model for the lens produces some irreducible scatter in the inferred CDD data. The use of an extended SIS approximation, with a power-law density structure, yields very similar results, but does not lessen the scatter due to its larger number of free parameters, which weakens the best-fit constraints. Future work with these strong lenses should therefore be based on more detailed ray-tracing calculations to determine the mass distribution more precisely
• #### Interfacial energy band and phonon scattering effect in Bi2Te3-polypyrrole hybrid thermoelectric material

(AMER INST PHYSICS, 2018-10-08)
We hybridized n-type Bi2Te3 with an inexpensive and abundantly available conducting polymer, polypyrrole, to obtain a bulk-structured hybrid material in which the interfacial energy band and the phonon scattering effects should occur at the interface of the two components. The obtained hybrid material inevitably exhibited a lower electrical conductivity than pristine Bi2Te3, which may be attributable to carrier scattering at the interfacial energy barrier. However, the hybrid material completely compensated for this loss in electrical conductivity with a significant increase in the Seebeck coefficient, and thus it retained the power factor with no loss. In addition, the hybrid material displayed a much lower thermal conductivity than pristine Bi2Te3 owing to the phonon scattering effect. The hybrid material exhibited significant decoupling of the electrical and thermal properties, thus affording state-of-the-art figures of merit (ZT similar to 0.98 at 25 degrees C, ZT(max) similar to 1.21 at 100 degrees C, and ZT(ave) similar to 1.18 at 50-150 degrees C) that exceed those of most of the previously reported n-type Bi2Te3 or Bi-2(Te,Se)(3) materials. Published by AIP Publishing.
• #### Cosmological tests with the joint lightcurve analysis

(EPL ASSOCIATION, 2018-10-05)
We examine whether a comparison between wCDM and $R_{\textrm{h}}=ct$ using merged Type-Ia SN catalogs produces results consistent with those based on a single homogeneous sample. Using the Betoule et al. (Astron. Astrophys., 568 (2014) 22). Joint Lightcurve Analysis (JLA) of a combined sample of 613 events from SNLS and SDSS-II, we estimate the parameters of the two models and compare them. We find that the improved statistics can alter the model selection in some cases, but not others. In addition, based on the model fits, we find that there appears to be a lingering systematic offset of ~0.04–0.08 mag between the SNLS and SDSS-II sources, in spite of the cross-calibration in the JLA. Treating wCDM, ΛCDM and $R_{\textrm{h}}=ct$ as separate models, we find in an unbiased pairwise statistical comparison that the Bayes Information Criterion (BIC) favors the $R_{\textrm{h}}=ct$ Universe with a likelihood of $82.8\%$ vs. $17.2\%$ for wCDM, but the ratio of likelihoods is reversed ($16.2\%$ vs. $83.8\%$ ) when $w_{\textrm{de}}=-1$ (i.e., ΛCDM) and strongly reversed ($1.0\%$ vs. $99.0\%$ ) if in addition k = 0 (i.e., flat ΛCDM). We point out, however, that the value of k is a measure of the net energy (kinetic plus gravitational) in the Universe and is not constrained theoretically, though some models of inflation would drive $k\rightarrow 0$ due to an expansion-enforced dilution. Since we here consider only the basic ΛCDM model, the value of k needs to be measured and, therefore, the pre-assumption of flatness introduces a significant bias into the BIC.
• #### Constrained vs unconstrained labor supply: the economics of dual job holding

(SPRINGER, 2018-10)
This paper develops a unified model of dual and unitary job holding based on a Stone-Geary utility function. The model incorporates both constrained and unconstrained labor supply. Panel data methods are adapted to accommodate unobserved heterogeneity and multinomial selection into six mutually exclusive labor supply regimes. We estimate the wage and income elasticities arising from selection and unobserved heterogeneity as well as from the Stone-Geary Slutsky equations. The labor supply model is estimated with data from the British Household Panel Survey 1991-2008. Among dual job holders, our study finds that the Stone-Geary income and wage elasticities are much larger for labor supply to the second job compared with the main job. When the effects of selection and unobserved heterogeneity are taken account of, the magnitudes of these elasticities on the second job tend to be significantly reduced.
• #### Highly porous defective carbons derived from seaweed biomass as efficient electrocatalysts for oxygen reduction in both alkaline and acidic media

(PERGAMON-ELSEVIER SCIENCE LTD, 2018-10)
In this work, we report a series of defective carbon catalysts prepared through a facile and scalable "-Ndoping-removal" process using seaweed biomass sodium alginate (SA) as precursor. Our systematic studies reveal that the defect content, porosity characteristic and conductivity of defective carbons can be finely tuned by manipulating the pyrolysis temperature and viscosity of precursor polymer SA, which significantly affect the ORR performance. The optimized defective porous carbon catalyst (i.e., D-PC-1( 900)) that was revealed to possess abundant ORR-active defects, large surface area of 1377 m(2)g(-1), abundant hierarchical porosity and good conductivity, exhibited very nice ORR activity and selectivity in 0.1M KOH, comparable to the commercial Pt/C catalyst. In 0.5MH(2)SO(4), considerable ORR activity was also observed for D-PC-1(900), which is among the highest reported for defective carbons and comparable to many of N-doped carbons. Density functional theory calculations indicate that the carbon defect can create the active sites for ORR in acidic media. More importantly, in both alkaline and acidic media, D-PC-1(900) shows much better stability and methanol tolerance than those of the Pt/C catalyst. All these results demonstrate that the seaweed biomass derived defective carbon is an excellent candidate for non-precious-metal ORR catalyst in various fuel cells. (c) 2018 Elsevier Ltd. All rights reserved.
• #### Revisiting the Utility of Retrospective Pre-Post Designs: The Need for Mixed-Method Pilot Data

(Elsevier, 2018-10)
The retrospective pre-post design affords many benefits to program staff and, accordingly, has piqued renewed interest among applied program evaluators. In particular, the field has witnessed increasing application of a post-program-only data collection strategy in which only posttest and retrospective pretest data are collected. A post-program-only assessment strategy takes considerably less time than is required for collecting pre-program data and presumably has the added benefit of eliminating the impact of response-shift bias. Response-shift bias occurs when the knowledge, skills, or experiences participants gain through program participation leads them to interpret questionnaire items in a qualitatively different manner at pretest versus posttest. In this article, we discuss the strengths and weaknesses associated with administering retrospective pretest assessments and underscore the importance of thoroughly evaluating any application of a retrospective measurement strategy prior to its broader implementation. We provide a practical illustration of this evaluation process using a mixed-method study that assesses one measure of parenting education program effectiveness—the Parenting Skills Ladder.
• #### Feasibility of the debris ring transit method for the solar-like star HD 107146 by an occulted galaxy

(OXFORD UNIV PRESS, 2018-10)
Occulting galaxy pairs have been used to determine the transmission and dust composition within the foreground galaxy. Observations of the nearly face-on ring-like debris disc around the solar-like star HD 107146 by HST/ACS in 2004 and HST/STIS in 2011 reveal that the debris ring is occulting an extended background galaxy over the subsequent decades. Our aim is to use 2004 Hubble Space Telescope (HST) observations of this system to model the galaxy and apply this to the 2011 observation in order to measure the transmission of the galaxy through the outer regions of the debris disc. We model the galaxy with an exponential disc and a Sersic pseudo-bulge in the V and I bands, but irregularities due to small-scale structure from star-forming regions limits accurate determination of the foreground dust distribution. We show that debris ring transit photometry is feasible for optical depth increases of Delta tau >= 0.04 (1 sigma) on tens of au scales - the width of the background galaxy - when the 2011 STIS data are compared directly with new HST/STIS observations, instead of the use of a smoothed model as a reference.
• #### Measurements of Speckle Lifetimes in Near-infrared Extreme Adaptive Optics Images for Optimizing Focal Plane Wavefront Control

(IOP PUBLISHING LTD, 2018-10)
Although extreme adaptive optics (ExAO) systems can greatly reduce the effects of atmospheric turbulence and deliver diffraction-limited images, our ability to observe faint objects such as extrasolar planets or debris disks at small angular separations is greatly limited by the presence of a speckle halo caused by imperfect wavefront corrections. These speckles change with a variety of timescales, from milliseconds to many hours, and various techniques have been developed to mitigate them during observations and during data reduction. Detection limits improve with increased speckle reduction, so an understanding of how speckles evolve (particularly at near-infrared wavelengths, which is where most adaptive optics science instruments operate) is of distinct interest. We used a SAPHIRA detector behind Subaru Telescope's SCExAO instrument to collect H-band images of the ExAO-corrected point-spread function (PSF) at a frame rate of 1.68 kHz. We analyzed these images using two techniques to measure the timescales over which the speckles evolved. In the first technique, we analyzed the images in a manner applicable to predicting performance of real-time speckle-nulling loops. We repeated this analysis using data from several nights to account for varying weather and AO conditions. In our second analysis, which follows the techniques employed by Milli et al. (2016) but using data with three orders of magnitude better temporal resolution, we identified a new regime of speckle behavior that occurs at timescales of milliseconds. It is not purely an instrument effect and likely is an atmospheric timescale filtered by the ExAO response. We also observed an exponential decay in the Pearson's correlation coefficients (which we employed to quantify the change in speckles) on timescales of seconds and a linear decay on timescales of minutes, which is in agreement with the behavior observed by Milli et al. For both of our analyses, we also collected similar data sets using SCExAO's internal light source to separate atmospheric effects from instrumental effects.