Populating the Galaxy with low-mass X-ray binaries

We perform binary population synthesis calculations to investigate the incidence of low-mass X-ray binaries and their birth rate in the Galaxy. We use a binary evolution algorithm that models all the relevant processes including tidal circularization and synchronization. Parameters in the evolution algorithm that are uncertain and may affect X-ray binary formation are allowed to vary during the investigation. We agree with previous studies that under standard assumptions of binary evolution the formation rate and number of black-hole low-mass X-ray binaries predicted by the model are more than an order of magnitude less than what is indicated by observations. We find that the common-envelope process cannot be manipulated to produce significant numbers of black-hole low-mass X-ray binaries. However, by simply reducing the mass-loss rate from helium stars adopted in the standard model, to a rate that agrees with the latest data, we produce a good match to the observations. Including low-mass X-ray binaries that evolve from intermediate-mass systems also leads to favourable results. We stress that constraints on the X-ray binary population provided by observations are used here merely as a guide as surveys suffer from incompleteness and much uncertainty is involved in the interpretation of results.Comment: 17 pages and 9 figures; accepted by MNRA

The long and the short of it: modelling double neutron star and collapsar Galactic dynamics

The work presented here examines populations of double compact binary systems and tidally enhanced collapsars. We make use of BINPOP and BINKIN, two components of a recently developed population synthesis package. Results focus on correlations of both binary and spatial evolutionary population characteristics. Pulsar and long duration gamma-ray burst observations are used in concert with our models to draw the conclusions that: double neutron star binaries can merge rapidly on timescales of a few million years (much less than that found for the observed double neutron star population), common envelope evolution within these models is a very important phase in double neutron star formation, and observations of long gamma-ray burst projected distances are more centrally concentrated than our simulated coalescing double neutron star and collapsar Galactic populations. Better agreement is found with dwarf galaxy models although the outcome is strongly linked to the assumed birth radial distribution. The birth rate of the double neutron star population in our models range from 4-160 Myr^-1 and the merger rate ranges from 3-150 Myr^-1. The upper and lower limits of the rates results from including electron capture supernova kicks to neutron stars and decreasing the common envelope efficiency respectively. Our double black hole merger rates suggest that black holes should receive an asymmetric kick at birth.Comment: Accepted by MNRAS, 18 pages, 12 figures, 5 table

Statutes and Democratic Self-Authorship

In this Article, we argue that both sides of the usual debate over statutory interpretation—text versus purpose—rest on a common, but flawed, premise. Judges and scholars have assumed that legislative bodies are the authors of statutes. We disagree; instead, we argue that the people are the authors of statutes. Legislative bodies play an indispensable role in the process: they draft statutes. And courts play a similarly indispensable role: they interpret statutes. But ultimately, it is the polity—we, the people—that is responsible, as authors, for the content of the law. This shift yields dramatic consequences. To date, no theory of statutory interpretation has been able to explain the actual labor of interpreting statutes—either with respect to “super” statutes or with respect to regular statutes. Canons of statutory construction, though familiar to any practitioner, are a source of puzzlement for theorists. Our theory attempts to answer the challenge. It both offers an explanation of existing interpretive practices and supplies a normatively compelling view of what statutory construction involves. In this effort, we reach back to the origins of modern political theory—to the work of Thomas Hobbes—to demonstrate that “self-authorship” has long been integral to the ideal of democracy. Ultimately, the problem is very simple. Commentators have long been sympathetic to the notion of self-authorship as applied to “fundamental” law—especially constitutional law. But they have failed to notice that the exact same issues are at stake in the construction of “ordinary” laws. That is the connection we make here

Furnishing the Galaxy with Pulsars

The majority of pulsar population synthesis studies performed to date have focused on isolated pulsar evolution. Those that have incorporated pulsar evolution within binary systems have tended to either treat binary evolution poorly of evolve the pulsar population in an ad-hoc manner. Here we present the first model of the Galactic field pulsar population that includes a comprehensive treatment of both binary and pulsar evolution. Synthetic observational surveys mimicking a variety of radio telescopes are then performed on this population. As such, a complete and direct comparison of model data with observations of the pulsar population within the Galactic disk is now possible. The tool used for completing this work is a code comprised of three components: stellar/binary evolution, Galactic kinematics and survey selection effects. Here we give a brief overview of the method and assumptions involved with each component. Some preliminary results are also presented as well as plans for future applications of the code.Comment: 3 pages, 3 figures, Conference: "40 years of pulsars: Millisecond pulsars, magnetars and more", McGill University, Montreal, Canada, ed. A.Cumming et al., AI

Do screening parameters predict response to desmopressin in a primary nocturnal enuresis population?

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How bias correction goes wrong: measurement of X_(CO_2) affected by erroneous surface pressure estimates

All measurements of X_(CO_2) from space have systematic errors. To reduce a large fraction of these errors, a bias correction is applied to X_(CO_2) retrieved from GOSAT and OCO-2 spectra using the ACOS retrieval algorithm. The bias correction uses, among other parameters, the surface pressure difference between the retrieval and the meteorological reanalysis. Relative errors in the surface pressure estimates, however, propagate nearly 1:1 into relative errors in bias-corrected X_(CO_2). For OCO-2, small errors in the knowledge of the pointing of the observatory (up to ∼130 arcsec) introduce a bias in X_(CO_2) in regions with rough topography. Erroneous surface pressure estimates are also caused by a coding error in ACOS version 8, sampling meteorological analyses at wrong times (up to 3 h after the overpass time). Here, we derive new geolocations for OCO-2's eight footprints and show how using improved knowledge of surface pressure estimates in the bias correction reduces errors in OCO-2's v9 X_(CO_2) data

Production of functionally active Penicillium chrysogenum isopenicillin N synthase in the yeast Hansenula polymorpha

<p>Abstract</p> <p>Background</p> <p>β-Lactams like penicillin and cephalosporin are among the oldest known antibiotics used against bacterial infections. Industrially, penicillin is produced by the filamentous fungus <it>Penicillium chrysogenum</it>. Our goal is to introduce the entire penicillin biosynthesis pathway into the methylotrophic yeast <it>Hansenula polymorpha</it>. Yeast species have the advantage of being versatile, easy to handle and cultivate, and possess superior fermentation properties relative to filamentous fungi. One of the fundamental challenges is to produce functionally active enzyme in <it>H. polymorpha</it>.</p> <p>Results</p> <p>The <it>P. chrysogenum pcbC </it>gene encoding isopenicillin N synthase (IPNS) was successfully expressed in <it>H. polymorpha</it>, but the protein produced was unstable and inactive when the host was grown at its optimal growth temperature (37°C). Heterologously produced IPNS protein levels were enhanced when the cultivation temperature was lowered to either 25°C or 30°C. Furthermore, IPNS produced at these lower cultivation temperatures was functionally active. Localization experiments demonstrated that, like in <it>P. chrysogenum</it>, in <it>H. polymorpha </it>IPNS is located in the cytosol.</p> <p>Conclusion</p> <p>In <it>P. chrysogenum</it>, the enzymes involved in penicillin production are compartmentalized in the cytosol and in microbodies. In this study, we focus on the cytosolic enzyme IPNS. Our data show that high amounts of functionally active IPNS enzyme can be produced in the heterologous host during cultivation at 25°C, the optimal growth temperature for <it>P. chrysogenum</it>. This is a new step forward in the metabolic reprogramming of <it>H. polymorpha </it>to produce penicillin.</p

How bias correction goes wrong: measurement of X_(CO_2) affected by erroneous surface pressure estimates

All measurements of X_(CO_2) from space have systematic errors. To reduce a large fraction of these errors, a bias correction is applied to X_(CO_2) retrieved from GOSAT and OCO-2 spectra using the ACOS retrieval algorithm. The bias correction uses, among other parameters, the surface pressure difference between the retrieval and the meteorological reanalysis. Relative errors in the surface pressure estimates, however, propagate nearly 1:1 into relative errors in bias-corrected X_(CO_2). For OCO-2, small errors in the knowledge of the pointing of the observatory (up to ∼130 arcsec) introduce a bias in X_(CO_2) in regions with rough topography. Erroneous surface pressure estimates are also caused by a coding error in ACOS version 8, sampling meteorological analyses at wrong times (up to 3 h after the overpass time). Here, we derive new geolocations for OCO-2's eight footprints and show how using improved knowledge of surface pressure estimates in the bias correction reduces errors in OCO-2's v9 X_(CO_2) data

Red-Emitting Manganese-doped Aluminum Nitride Phosphor

We report high efficiency luminescence with a manganese-doped aluminum nitride red-emitting phosphor under 254 nm excitation, as well as its excellent lumen maintenance in fluorescent lamp conditions, making it a candidate replacement for the widely deployed europium-doped yttria red phosphor. Solid-state reaction of aluminum nitride powders with manganese metal at 1900 °C, 10 atm N2 in a reducing environment results in nitrogen deficiency, as revealed diffuse reflectance spectra. When these powders are subsequently annealed in flowing nitrogen at 1650 °C, higher nitrogen content is recovered, resulting in white powders. Silicon was added to samples as an oxygen getter to improve emission efficiency. NEXAFS spectra and DFT calculations indicate that the Mn dopant is divalent. From DFT calculations, the UV absorption band is proposed to be due to an aluminum vacancy coupled with oxygen impurity dopants, and Mn2+ is assumed to be closely associated with this site. In contrast with some previous reports, we find that the highest quantum efficiency with 254 nm excitation (Q.E. = 0.86 ± 0.14) is obtained in aluminum nitride with a low manganese doping level of 0.06 mol.%. The principal Mn2+ decay of 1.25 ms is assigned to non-interacting Mn sites, while additional components in the microsecond range appear with higher Mn doping, consistent with Mn clustering and resultant exchange coupling. Slower components are present in samples with low Mn doping, as well as strong afterglow, assigned to trapping on shallow traps followed by detrapping and subsequent trapping on Mn