401 research outputs found
Absolute dimensions of the unevolved B-type eclipsing binary GG Orionis
We present photometric observations in B and V as well as spectroscopic
observations of the detached, eccentric 6.6-day double-lined eclipsing binary
GG Ori, a member of the Orion OB1 association. Absolute dimensions of the
components, which are virtually identical, are determined to high accuracy
(better than 1% in the masses and better than 2% in the radii) for the purpose
of testing various aspects of theoretical modeling. We obtain M(A) = 2.342 +/-
0.016 solar masses and R(A) = 1.852 +/- 0.025 solar radii for the primary, and
M(B) = 2.338 +/- 0.017 solar masses and R(B) = 1.830 +/- 0.025 solar radii for
the secondary. The effective temperature of both stars is 9950 +/- 200 K,
corresponding to a spectral type of B9.5. GG Ori is very close to the ZAMS, and
comparison with current stellar evolution models gives ages of 65-82 Myr or 7.7
Myr depending on whether the system is considered to be burning hydrogen on the
main sequence or still in the final stages of pre-main sequence contraction. We
have detected apsidal motion in the binary at a rate of dw/dt = 0.00061 +/-
0.00025 degrees per cycle, corresponding to an apsidal period of U = 10700 +/-
4500 yr. A substantial fraction of this (approximately 70%) is due to the
contribution from General Relativity.Comment: To appear in The Astronomical Journal, December 200
Four-colour photometry of eclipsing binaries. XLI uvby light curves for AD Bootis, HW Canis Majoris, SW Canis Majoris, V636 Centauri, VZ Hydrae, and WZ Ophiuchi
CONTEXT: Accurate mass, radius, and abundance determinations from binaries
provide important information on stellar evolution, fundamental to central
fields in modern astrophysics and cosmology.
AIMS: Within the long-term Copenhagen Binary Project, we aim to obtain
high-quality light curves and standard photometry for double-lined detached
eclipsing binaries with late A, F, and G type main-sequence components, needed
for the determination of accurate absolute dimensions and abundances, and for
detailed comparisons with results from recent stellar evolutionary models.
METHODS: Between March 1985 and July 2007, we carried out photometric
observations of AD Boo, HW CMA, SW CMa, V636 Cen, VZ Hya, and WZ Oph at the
Str"omgren Automatic Telescope at ESO, La Silla.
RESULTS: We obtained complete uvby light curves, ephemerides, and standard
uvby\beta indices for all six systems.For V636 Cen and HW CMa, we present the
first modern light curves, whereas for AD Boo, SW CMa, VZ Hya, and WZ Oph, they
are both more accurate and more complete than earlier data. Due to a high
orbital eccentricity (e = 0.50), combined with a low orbital inclination (i =
84.7), only one eclipse, close to periastron, occurs for HW CMa. For the two
other eccentric systems, V636 Cen (e = 0.134) and SW CMa (e = 0.316), apsidal
motion has been detected with periods of 5270 +/- 335 and 14900 +/- 3600 years,
respectively.Comment: Only change is: Bottom lines (hopefully) not truncated anymore.
Accepted for publication in Astonomy & Astrophysic
Exceptional Laguerre and Jacobi polynomials and the corresponding potentials through Darboux-Crum Transformations
Simple derivation is presented of the four families of infinitely many shape
invariant Hamiltonians corresponding to the exceptional Laguerre and Jacobi
polynomials. Darboux-Crum transformations are applied to connect the well-known
shape invariant Hamiltonians of the radial oscillator and the
Darboux-P\"oschl-Teller potential to the shape invariant potentials of
Odake-Sasaki. Dutta and Roy derived the two lowest members of the exceptional
Laguerre polynomials by this method. The method is expanded to its full
generality and many other ramifications, including the aspects of generalised
Bochner problem and the bispectral property of the exceptional orthogonal
polynomials, are discussed.Comment: LaTeX2e with amsmath, amssymb, amscd 26 pages, no figure
The tobacco industryâs past role in weight control related to smoking
Background: Smoking is thought to produce an appetite-suppressing effect by many smokers. Thus, the fear of body weight gain often outweighs the perception of health benefits associated with smoking cessation, particularly in adolescents. We examined whether the tobacco industry played a role in appetite and body weight control related to smoking and smoking cessation. Methods: We performed a systematic search within the archives of six major US and UK tobacco companies (American Tobacco, Philip Morris, RJ Reynolds, Lorillard, Brown & Williamson and British American Tobacco) that were Defendants in tobacco litigation settled in 1998. Findings are dated from 1949 to 1999. Results: The documents revealed the strategies planned and used by the industry to enhance effects of smoking on weight and appetite, mostly by chemical modifications of cigarettes contents. Appetite-suppressant molecules, such as tartaric acid and 2-acetylpyridine were added to some cigarettes. Conclusion: These tobacco companies played an active and not disclaimed role in the anti-appetite effects of smoking, at least in the past, by adding appetite-suppressant molecules into their cigarettes
The Chemical Compositions of the Type II Cepheids -- The BL Her and W Vir Variables
Abundance analyses from high-resolution optical spectra are presented for 19
Type II Cepheids in the Galactic field. The sample includes both short-period
(BL Her) and long-period (W Vir) stars. This is the first extensive abundance
analysis of these variables. The C, N, and O abundances with similar spreads
for the BL Her and W Vir show evidence for an atmosphere contaminated with
-process and CN-cycling products. A notable anomaly of the BL Her
stars is an overabundance of Na by a factor of about five relative to their
presumed initial abundances. This overabundance is not seen in the W Vir stars.
The abundance anomalies running from mild to extreme in W Vir stars but not
seen in the BL Her stars are attributed to dust-gas separation that provides an
atmosphere deficient in elements of high condensation temperature, notably Al,
Ca, Sc, Ti, and -process elements. Such anomalies have previously been seen
among RV Tau stars which represent a long-period extension of the variability
enjoyed by the Type II Cepheids. Comments are offered on how the contrasting
abundance anomalies of BL Her and W Vir stars may be explained in terms of the
stars' evolution from the blue horizontal branch.Comment: 41 pages including 11 figures and 4 tables; Accepted for publication
in Ap
Clinical aspects of Mayer-Rokitansky-Kuester-Hauser syndrome: recommendations for clinical diagnosis and staging
BACKGROUND: The Mayer-Rokitansky-Kuester-Hauser (MRKH) syndrome is a malformation of the female genitals (occurring in one in 4000 female live births) as a result of interrupted embryonic development of the MĂŒllerian (paramesonephric) ducts. This retrospective study examined the issue of associated malformations, subtyping, and the frequency distribution of subtypes in MRKH syndrome. METHODS: Fifty-three MRKH patients were investigated using a newly developed standardized questionnaire. Together with the results of clinical and diagnostic examinations, the patients were classified into the three recognized subtypes [typical, atypical and MURCS (MĂŒllerian duct aplasia, renal aplasia, and cervicothoracic somite dysplasia)]. RESULTS: The typical form was diagnosed in 25 patients (47%), the atypical form in 11 patients (21%), and the most marked formâthe MURCS typeâin 17 patients (32%). Associated malformations were notably frequent among the patients. Malformations of the renal system were the most frequent type of accompanying malformation, with 23 different malformations in 19 patients, followed by 18 different skeletal changes in 15 patients. CONCLUSIONS: In accordance with the literature, this study shows that associated malformations are present in more than a third of cases. Therefore, new basic guidelines for standard diagnostic classification involving patients with suspected MRKH are presente
Retarding Sub- and Accelerating Super-Diffusion Governed by Distributed Order Fractional Diffusion Equations
We propose diffusion-like equations with time and space fractional
derivatives of the distributed order for the kinetic description of anomalous
diffusion and relaxation phenomena, whose diffusion exponent varies with time
and which, correspondingly, can not be viewed as self-affine random processes
possessing a unique Hurst exponent. We prove the positivity of the solutions of
the proposed equations and establish the relation to the Continuous Time Random
Walk theory. We show that the distributed order time fractional diffusion
equation describes the sub-diffusion random process which is subordinated to
the Wiener process and whose diffusion exponent diminishes in time (retarding
sub-diffusion) leading to superslow diffusion, for which the square
displacement grows logarithmically in time. We also demonstrate that the
distributed order space fractional diffusion equation describes super-diffusion
phenomena when the diffusion exponent grows in time (accelerating
super-diffusion).Comment: 11 pages, LaTe
Biosynthesis of coral settlement cue tetrabromopyrrole in marine bacteria by a uniquely adapted brominase-thioesterase enzyme pair
Author Posting. © The Author(s), 2016. This is the author's version of the work. It is posted here by permission of National Academy of Sciences for personal use, not for redistribution. The definitive version was published in Proceedings of the National Academy of Sciences of United States of America 113 (2016): 3797-3802, doi: 10.1073/pnas.1519695113.Halogenated pyrroles (halopyrroles) are common chemical moieties found in bioactive bacterial natural products. The halopyrrole moieties of mono- and di- halopyrrole-containing compounds arise from a conserved mechanism in which a proline-derived pyrrolyl group bound to a carrier protein is first halogenated then elaborated by peptidic or polyketide extensions. This paradigm is broken during the marine pseudoalteromonad bacterial biosynthesis of the coral larval settlement cue tetrabromopyrrole (1), which arises from the substitution of the proline-derived carboxylate by a bromine atom. To understand the molecular basis for decarboxylative bromination in the biosynthesis of 1, we sequenced two Pseudoalteromonas genomes and identified a conserved four-gene locus encoding the enzymes involved its complete biosynthesis. Through total in vitro reconstitution of the biosynthesis of 1 using purified enzymes and biochemical interrogation of individual biochemical steps, we show that all four bromine atoms in 1 are installed by the action of a single flavin-dependent halogenase- Bmp2. Tetrabromination of the pyrrole induces a thioesterase-mediated offloading reaction from the carrier protein and activates the biosynthetic intermediate for decarboxylation. Insights into the tetrabrominating activity of Bmp2 were obtained from the high-resolution crystal structure of the halogenase contrasted against structurally homologous halogenase Mpy16 that forms only a dihalogenated pyrrole in marinopyrrole biosynthesis. Structure-guided mutagenesis of the proposed substrate-binding pocket of Bmp2 led to a reduction in the degree of halogenation catalyzed. Our study provides a biogenetic basis for the biosynthesis of 1, and sets a firm foundation for querying the biosynthetic potential for the production of 1 in marine (meta)genomes.This work was jointly supported by the US National Science Foundation (OCE-1313747) and the US National Institute of Environmental Health Sciences (P01-ES021921) through the Ocean and Human Health Program to B.S.M., and the US National Institute of Allergy and Infectious Disease R01-AI47818 to B.S.M. and R21-
AI119311 to K.E.W. and T.J.M., the Mote Protect Our Reef Grant Program (POR-2012-3), the Dart Foundation, the Smithsonian Competitive Grants Program for Science to V.J.P., the Howard Hughes Medical Institute to J.P.N., the US National Institutes of Health (NIH) Marine Biotechnology Training Grant predoctoral fellowship to A.E. (T32-GM067550), the Helen Hay Whitney Foundation postdoctoral fellowship to V.A., and a Swiss National Science Foundation (SNF) postdoctoral Fellowship to S.D.2016-09-2
Cometary dust analogues for physics experiments
The CoPhyLab (Cometary Physics Laboratory) project is designed to study the
physics of comets through a series of earth-based experiments. For these
experiments, a dust analogue was created with physical properties comparable to
those of the non-volatile dust found on comets. This "CoPhyLab dust" is planned
to be mixed with water and CO ice and placed under cometary conditions in
vacuum chambers to study the physical processes taking place on the nuclei of
comets. In order to develop this dust analogue, we mixed two components
representative for the non-volatile materials present in cometary nuclei. We
chose silica dust as representative for the mineral phase and charcoal for the
organic phase, which also acts as a darkening agent. In this paper, we provide
an overview of known cometary analogues before presenting measurements of eight
physical properties of different mixtures of the two materials and a comparison
of these measurements with known cometary values. The physical properties of
interest are: particle size, density, gas permeability, spectrophotometry,
mechanical, thermal and electrical properties. We found that the analogue dust
that matches the highest number of physical properties of cometary materials
consists of a mixture of either 60\%/40\% or 70\%/30\% of silica dust/charcoal
by mass. These best-fit dust analogue will be used in future CoPhyLab
experiments
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