24 research outputs found
Probing Shock Breakout with Serendipitous GALEX Detections of Two SNLS Type II-P Supernovae
We report the serendipitous detection by GALEX of fast (1
mag) UV emission from two Type II plateau (II-P) supernovae (SNe) at z=0.185
and 0.324 discovered by the Supernova Legacy Survey. Optical photometry and VLT
spectroscopy 2 weeks after the GALEX detections link the onset of UV emission
to the time of shock breakout. Using radiation hydrodynamics and non-LTE
radiative transfer simulations, and starting from a standard red supergiant
(RSG; Type II-P SN progenitor) star evolved self-consistently from the main
sequence to iron core collapse, we model the shock breakout phase and the 55 hr
that follow. The small scale height of our RSG atmosphere model suggests that
the breakout signature is a thermal soft X-ray burst (lambda_peak ~ 90\AA) with
a duration of <~ 2000 s. Longer durations are possible but require either an
extended and tenuous non-standard envelope, or an unusually dense RSG wind with
\dot{M} ~ 10^(-3) Msun yr^(-1). The GALEX observations miss the peak of the
luminous (M_FUV ~ -20) UV burst but unambiguously capture the rise of the
emission and a subsequent 2 day long plateau. The postbreakout, UV-bright
plateau is a prediction of our model in which the shift of the peak of the
spectral energy distribution (SED) from ~100 to ~1000\AA and the ejecta
expansion both counteract the decrease in bolometric luminosity from ~10^11 to
~10^9 L_sun over that period. Based on the observed detection efficiency of our
study we make predictions for the breakout detection rate of the GALEX Time
Domain Survey.Comment: 4 pages, 3 color figures, accepted to ApJ Letters, emulateapj,
corrections from proofs adde
The structure and evolution of M51-type galaxies
We discuss the integrated kinematic parameters of 20 M51-type binary
galaxies. A comparison of the orbital masses of the galaxies with the sum of
the individual masses suggests that moderately massive dark halos surround
bright spiral galaxies. The relative velocities of the galaxies in binary
systems were found to decrease with increasing relative luminosity of the
satellite. We obtained evidence that the Tully-Fisher relation for binary
members could be flatter than that for local field galaxies. An enhanced star
formation rate in the binary members may be responsible for this effect. In
most binary systems, the direction of orbital motion of the satellite coincides
with the direction of rotation of the main galaxy. Seven candidates for distant
M51-type objects were found in the Northern and Southern Hubble Deep Fields. A
comparison of this number with the statistics of nearby galaxies provides
evidence for the rapid evolution of the space density of M51-type galaxies with
redshift Z. We assume that M51-type binary systems could be formed through the
capture of a satellite by a massive spiral galaxy. It is also possible that the
main galaxy and its satellite in some of the systems have a common cosmological
origin.Comment: 8 pages, 4 figures, to be published in Astronomy Letter
Completed SDSS-IV extended Baryon Oscillation Spectroscopic Survey: Cosmological implications from two decades of spectroscopic surveys at the Apache Point Observatory
We present the cosmological implications from final measurements of clustering using galaxies, quasars, and Ly α forests from the completed Sloan Digital Sky Survey (SDSS) lineage of experiments in large-scale structure. These experiments, composed of data from SDSS, SDSS-II, BOSS, and eBOSS, offer independent measurements of baryon acoustic oscillation (BAO) measurements of angular-diameter distances and Hubble distances relative to the sound horizon, r_{d}, from eight different samples and six measurements of the growth rate parameter, fσ_{8}, from redshift-space distortions (RSD). This composite sample is the most constraining of its kind and allows us to perform a comprehensive assessment of the cosmological model after two decades of dedicated spectroscopic observation. We show that the BAO data alone are able to rule out dark-energy-free models at more than eight standard deviations in an extension to the flat, Λ CDM model that allows for curvature. When combined with Planck Cosmic Microwave Background (CMB) measurements of temperature and polarization, under the same model, the BAO data provide nearly an order of magnitude improvement on curvature constraints relative to primary CMB constraints alone. Independent of distance measurements, the SDSS RSD data complement weak lensing measurements from the Dark Energy Survey (DES) in demonstrating a preference for a flat Λ CDM cosmological model when combined with Planck measurements. The combined BAO and RSD measurements indicate σ_{8} = 0.85 ± 0.03, implying a growth rate that is consistent with predictions from Planck temperature and polarization data and with General Relativity. When combining the results of SDSS BAO and RSD, Planck, Pantheon Type Ia supernovae (SNe Ia), and DES weak lensing and clustering measurements, all multiple-parameter extensions remain consistent with a
Λ CDM model. Regardless of cosmological model, the precision on each of the three parameters, Ω_{Λ}, H_{0}, and σ_{8}, remains at roughly 1%, showing changes of less than 0.6% in the central values between models. In a model that allows for free curvature and a time-evolving equation of state for dark energy, the combined samples produce a constraint Ω_{k} = −0.0022 ± 0.0022. The dark energy constraints lead to w_{0} = −0.909 ± 0.081 and w_{a} = −0.49^{+0.35}_{-0.30}, corresponding to an equation of state of w_{p} = 1.018 ± 0.032 at a pivot redshift z_{p} = 0.29 and a Dark Energy Task Force Figure of Merit of 94. The inverse distance ladder measurement under this model yields H_{0} = 68.18 ± 0.79 km s^{-1} Mpc^{-1}, remaining in tension with several direct determination methods; the BAO data allow Hubble constant estimates that are robust against the assumption of the cosmological model. In addition, the BAO data allow estimates of H_{0} that are independent of the CMB data, with similar central values and precision under a Λ CDM model. Our most constraining combination of data gives the upper limit on the sum of neutrino masses at ∑m_{v} < 0.115 eV (95% confidence). Finally, we consider the improvements in cosmology constraints over the last decade by comparing our results to a sample representative of the period 2000–2010. We compute the relative gain across the five dimensions spanned by w, Ω_{k}, ∑m_{v}, H_{0}, H_{0}, and σ_{8} and find that the SDSS BAO and RSD data reduce the total posterior volume by a factor of 40 relative to the previous generation. Adding again the Planck, DES, and Pantheon SN Ia samples leads to an overall contraction in the five-dimensional posterior volume of 3 orders of magnitude
Toward a Comprehensive Approach to the Collection and Analysis of Pica Substances, with Emphasis on Geophagic Materials
Pica, the craving and subsequent consumption of non-food substances such as earth, charcoal, and raw starch, has been an enigma for more than 2000 years. Currently, there are little available data for testing major hypotheses about pica because of methodological limitations and lack of attention to the problem.In this paper we critically review procedures and guidelines for interviews and sample collection that are appropriate for a wide variety of pica substances. In addition, we outline methodologies for the physical, mineralogical, and chemical characterization of these substances, with particular focus on geophagic soils and clays. Many of these methods are standard procedures in anthropological, soil, or nutritional sciences, but have rarely or never been applied to the study of pica.Physical properties of geophagic materials including color, particle size distribution, consistency and dispersion/flocculation (coagulation) should be assessed by appropriate methods. Quantitative mineralogical analyses by X-ray diffraction should be made on bulk material as well as on separated clay fractions, and the various clay minerals should be characterized by a variety of supplementary tests. Concentrations of minerals should be determined using X-ray fluorescence for non-food substances and inductively coupled plasma-atomic emission spectroscopy for food-like substances. pH, salt content, cation exchange capacity, organic carbon content and labile forms of iron oxide should also be determined. Finally, analyses relating to biological interactions are recommended, including determination of the bioavailability of nutrients and other bioactive components from pica substances, as well as their detoxification capacities and parasitological profiles.This is the first review of appropriate methodologies for the study of human pica. The comprehensive and multi-disciplinary approach to the collection and analysis of pica substances detailed here is a necessary preliminary step to understanding the nutritional enigma of non-food consumption
Thermokinetic parameter determination of methacrylates radical polymerization by using real-time reaction calorimetry
Determination of the Concentration of Deep Levels in Semi-insulating CdS Single Crystals by Photoinduced-Current Transient Spectroscopy
Intellectual Property Rights, Globalization and Growth
I present a model that combines the key features of a Schumpeterian growth model without scale effects and a North - South model of trade.All open economies converge to parallel growth paths because of costly technological transfer.I study the e¤ects of intellectual property rights (IPR) regimes and trade policies on the growth rate, as well as on a given country's economic performance.The requirement that trade be balanced neutralizes all potential effects of the tariff policy on the world's growth rate, and on the performance of a single country.By contrast, an improvement of a given country's IPR regime is growth neutral but improves a country's position in the world's productivity rank.These findings are shown te be consistent with observedempirical relationships.