2,536 research outputs found
Beat Cepheids as Probes of Stellar and Galactic Metallicity
The mere location of a Beat Cepheid model in a Period Ratio vs. Period
diagram (Petersen diagram) puts very tight constraints on its metallicity Z.
The Beat Cepheid Peterson diagrams are revisited with linear nonadiabatic
turbulent convective models, and their accuracy as a probe for stellar
metallicity is evaluated. They are shown to be largely independent of the
helium content Y, and they are also only weakly dependent on the
mass-luminosity relation that is used in their construction. However, they are
found to show sensitivity to the relative abundances of the elements that are
lumped into the metallicity parameter Z. Rotation is estimated to have but a
small effect on the 'pulsation metallicities'. A composite Petersen diagram is
presented that allows one to read off upper and lower limits on the metallicity
Z from the measured period P0 and period ratio P1/P0.Comment: 9 pages, 12 color figures (black and white version available from 1st
author's website). With minor revisions. to appear in Ap
Taking a Dip in the Supreme Court Clerk Pool: Gender-Based Discrepancies in Clerk Selection
Former U.S. Supreme Court clerks are heavily recruited by select law firms, and many eventually find their way to policy “elite” positions in the government or in the legal academy. A number of former clerks have returned to the Court as litigators, and a subset has returned to the Court as Justices. We are interested in clerk selection for two reasons. First, clerks influence key aspects of the judicial process while serving in their clerkship capacity, and second, many seem to be in a good position to influence legal policy well after their clerkships have ended. With this in mind, it is natural to ask about the selection of such individuals to these posts. There are larger questions of diversity, however, that have permeated discussions of the Court’s clerkship selection practices. In this Article, we explore one critical dimension—the relative imbalance between men and women serving as High Court clerks. We analyze the U.S. Supreme Court directly, but also supply comparison points in assessing clerkship diversity in Canada and Brazil
A Bayesian approach to the modelling of alpha Cen A
Determining the physical characteristics of a star is an inverse problem
consisting in estimating the parameters of models for the stellar structure and
evolution, knowing certain observable quantities. We use a Bayesian approach to
solve this problem for alpha Cen A, which allows us to incorporate prior
information on the parameters to be estimated, in order to better constrain the
problem. Our strategy is based on the use of a Markov Chain Monte Carlo (MCMC)
algorithm to estimate the posterior probability densities of the stellar
parameters: mass, age, initial chemical composition,... We use the stellar
evolutionary code ASTEC to model the star. To constrain this model both seismic
and non-seismic observations were considered. Several different strategies were
tested to fit these values, either using two or five free parameters in ASTEC.
We are thus able to show evidence that MCMC methods become efficient with
respect to more classical grid-based strategies when the number of parameters
increases. The results of our MCMC algorithm allow us to derive estimates for
the stellar parameters and robust uncertainties thanks to the statistical
analysis of the posterior probability densities. We are also able to compute
odds for the presence of a convective core in alpha Cen A. When using
core-sensitive seismic observational constraints, these can raise above ~40%.
The comparison of results to previous studies also indicates that these seismic
constraints are of critical importance for our knowledge of the structure of
this star.Comment: 21 pages, 6 figures, to be published in MNRA
Analysis of Total and Segmental Body Composition Relative to Fitness Performance Measures in Law Enforcement Recruits
International Journal of Exercise Science 15(4): 245-260, 2022. Law enforcement agencies often test the fitness performance and body composition of incoming recruits. This study investigated the relationships between whole and segmental body composition, and fitness tests in law enforcement recruits. A retrospective analysis of 72 male and 11 female recruits was performed. Bioelectrical impedance analysis (BIA) variables were: lean mass (LM), upper-extremity lean mass (UELM), trunk LM, lower-extremity lean mass (LELM), fat mass (FM), upper-extremity fat mass (UEFM), trunk FM, and lower-extremity fat mass (LEFM). Fitness tests included: vertical jump (VJ), peak anaerobic power (PAPw), 75-yard pursuit run (75PR), push-ups, sit-ups, 2-kg medicine ball throw (MBT), and the multi-stage fitness test (MSFT). Partial correlations and ANCOVAs between quartiles assessed relationships between body composition and performance. Significant moderate-to-large relationships were found; LM, UELM, trunk LM, LELM all related to PAPw (r = 0.500-0.558) and MBT (r = 0.494-0.526). FM, UEFM, trunk FM, LEFM all related to VJ (r = -0.481 to -0.493), 75PR (r = 0.533-0.557), push-ups (r = -0.484 to -0.503), sit-ups (r = -0.435 to -0.449), and MSFT (r = -0.371 to -0.423). The highest LM quartile (4) had superior PAPw and MBT than LM quartiles 1-3. Higher FM quartiles performed poorer in VJ, push-ups, and sit-ups. The 75PR quartiles 2, 3, and 4 were slower than quartile 1, and MSFT quartile 4 completed less shuttles. Total and segmental measures of LM and FM shared the same relationships; lower FM and higher LM related to better performance. Monitoring body composition could help guide training to optimize performance
NuSTAR Observations of the Magnetar 1E 2259+586
We report on new broad band spectral and temporal observations of the
magnetar 1E 2259+586, which is located in the supernova remnant CTB 109. Our
data were obtained simultaneously with the Nuclear Spectroscopic Telescope
Array (NuSTAR) and Swift, and cover the energy range from 0.5-79 keV. We
present pulse profiles in various energy bands and compare them to previous
RXTE results. The NuSTAR data show pulsations above 20 keV for the first time
and we report evidence that one of the pulses in the double-peaked pulse
profile shifts position with energy. The pulsed fraction of the magnetar is
shown to increase strongly with energy. Our spectral analysis reveals that the
soft X-ray spectrum is well characterized by an absorbed double-blackbody or
blackbody plus power-law model in agreement with previous reports. Our new hard
X-ray data, however, suggests that an additional component, such as a
power-law, is needed to describe the NuSTAR and Swift spectrum. We also fit the
data with the recently developed coronal outflow model by Beloborodov for hard
X-ray emission from magnetars. The outflow from a ring on the magnetar surface
is statistically preferred over outflow from a polar cap.Comment: 37 pages, 9 figures, corresponding author, [email protected]
αβ,α'β'-Diepoxyketones are mechanism-based inhibitors of nucleophilic cysteine enzymes
Epoxides are an established class of electrophilic alkylating agents that react with nucleophilic protein residues. We report αβ,α′β′-diepoxyketones (DEKs) as a new type of mechanism-based inhibitors of nucleophilic cysteine enzymes. Studies with the L,D-transpeptidase LdtMt2 from Mycobacterium tuberculosis and the main protease from SARS-CoV-2 (Mpro) reveal that following epoxide ring opening by a nucleophilic cysteine, further reactions can occur, leading to irreversible alkylation
NuSTAR observations of X-ray bursts from the magnetar 1E 1048.1-5937
We report the detection of eight bright X-ray bursts from the 6.5-s magnetar
1E 1048.1-5937, during a 2013 July observation campaign with the Nuclear
Spectroscopic Telescope Array (NuSTAR). We study the morphological and spectral
properties of these bursts and their evolution with time. The bursts resulted
in count rate increases by orders of magnitude, sometimes limited by the
detector dead time, and showed blackbody spectra with kT=6-8 keV in the T90
duration of 1-4 s, similar to earlier bursts detected from the source. We find
that the spectra during the tail of the bursts can be modeled with an absorbed
blackbody with temperature decreasing with flux. The bursts flux decays
followed a power-law of index 0.8-0.9. In the burst tail spectra, we detect a
~13 keV emission feature, similar to those reported in previous bursts from
this source as well as from other magnetars observed with the Rossi X-ray
Timing Explorer (RXTE). We explore possible origins of the spectral feature
such as proton cyclotron emission, which implies a magnetic field strength of
B~2X10^15 G in the emission region. However, the consistency of the energy of
the feature in different objects requires further explanation.Comment: 10 pages, 6 figures, accepted for publication in Ap
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