Lyman-alpha wing absorption in cool white dwarf stars

Kowalski & Saumon (2006) identified the missing absorption mechanism in the observed spectra of cool white dwarf stars as the Ly-alpha red wing formed by the collisions between atomic and molecular hydrogen and successfully explained entire spectra of many cool DA-type white dwarfs. Owing to the important astrophysical implications of this issue, we present here an independent assessment of the process. For this purpose, we compute free-free quasi-molecular absorption in Lyman-alpha due to collisions with H and H2 within the one-perturber, quasi-static approximation. Line cross-sections are obtained using theoretical molecular potentials to describe the interaction between the radiating atom and the perturber. The variation of the electric-dipole transition moment with the interparticle distance is also considered. Six and two allowed electric dipole transitions due to H-H and H-H2 collisions, respectively, are taken into account. The new theoretical Lyman-alpha line profiles are then incorporated in our stellar atmosphere program for the computation of synthetic spectra and colours of DA-type white dwarfs. Illustrative model atmospheres and spectral energy distributions are computed, which show that Ly-alpha broadening by atoms and molecules has a significant effect on the white dwarf atmosphere models. The inclusion of this collision-induced opacity significantly reddens spectral energy distributions and affects the broadband colour indices for model atmospheres with Teff<5000 K. These results confirm those previously obtained by Kowalski & Saumon (2006). Our study points out the need for reliable evaluations of H3 potential energy surfaces covering a large region of nuclear configurations, in order to obtain a better description of H-H2 collisions and a more accurate evaluation of their influence on the spectrum of cool white dwarfs.Comment: 11 pages, 12 figures, 1 table, to be published in MNRA

Multicomponent fluids of hard hyperspheres in odd dimensions

Mixtures of hard hyperspheres in odd space dimensionalities are studied with an analytical approximation method. This technique is based on the so-called Rational Function Approximation and provides a procedure for evaluating equations of state, structure factors, radial distribution functions, and direct correlations functions of additive mixtures of hard hyperspheres with any number of components and in arbitrary odd-dimension space. The method gives the exact solution of the Ornstein--Zernike equation coupled with the Percus--Yevick closure, thus extending to arbitrary odd dimension the solution for hard-sphere mixtures [J. L. Lebowitz, Phys.\ Rev.\ \textbf{133}, 895 (1964)]. Explicit evaluations for binary mixtures in five dimensions are performed. The results are compared with computer simulations and a good agreement is found.Comment: 16 pages, 8 figures; v2: slight change of notatio

Binding of the baculovirus very late expression factor 1 (VLF-1) to different DNA structures

BACKGROUND: Baculovirus genomes encode a gene called very late expression factor 1 (VLF-1) that is a member of the integrase (Int) family of proteins. In this report we describe the binding properties of purified Autographa californica multiple capsid nucleopolyhedrovirus (AcMNPV) VLF-1 to a number of different DNA structures including homologous regions. In addition, its enzymatic activity was examined. RESULTS: VLF-1 was expressed in a recombinant baculovirus as a fusion with both HA and HIS(6) tags and its binding activity to different DNA structures was tested. No binding was evident to single and double strand structures, very low binding was observed to Y-forks, more binding was observed to three-way junctions, whereas cruciform structures showed high levels of binding. VLF-1 binding was affected by divalent cations; optimal binding to three-way junctions and cruciforms was 2 and 0 mM MgCl(2), respectively. Homologous region (hr) sequences was also examined including oligomers designed to expose the hr palindrome as a hairpin, linear double strand, or H-shaped structure. Efficient binding was observed to the hairpin and H-shaped structure. No topoisomerase or endonuclease activity was detected. Sedimentation analysis indicated that *VLF-1 is present as a monomer. CONCLUSIONS: An HA- and HIS-tagged version of AcMNPV VLF-1 showed structure-dependent binding to DNA substrates with the highest binding affinity to cruciform DNA. These results are consistent with the involvement of VLF-1 in the processing of branched DNA molecules at the late stages of viral genome replication. We were unable to detect enzymatic activity associated with these complexes

Lyman α wing absorption in cool white dwarf stars

Kowalski & Saumon identified the missing absorption mechanism in the observed spectra of cool white dwarf stars as the Lyman α red wing formed by the collisions between atomic and molecular hydrogen and successfully explained entire spectra of many cool DA-type white dwarfs. Owing to the important astrophysical implications of this issue, we present here an independent assessment of the process. For this purpose, we compute free-free quasi-molecular absorption in Lyman α due to collisions with H and H2 within the one-perturber, quasi-static approximation. Line cross-sections are obtained using theoretical molecular potentials to describe the interaction between the radiating atom and the perturber. The variation in the electric dipole transition moment with the interparticle distance is also considered. Six and two allowed electric dipole transitions due to H-H and H-H2 collisions, respectively, are taken into account. The new theoretical Lyman α line profiles are then incorporated in our stellar atmosphere program for the computation of synthetic spectra and colours of DA-type white dwarfs. Illustrative model atmospheres and spectral energy distributions are computed, which show that Lyman α broadening by atoms and molecules has a significant effect on the white dwarf atmosphere models. The inclusion of this collision-induced opacity significantly reddens spectral energy distributions and affects the broad-band colour indices for model atmospheres with Teff 3 potential energy surfaces covering a large region of nuclear configurations, in order to obtain a better description of H-H2 collisions and a more accurate evaluation of their influence on the spectrum of cool white dwarfs.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat

Lyman α wing absorption in cool white dwarf stars

Kowalski & Saumon identified the missing absorption mechanism in the observed spectra of cool white dwarf stars as the Lyman α red wing formed by the collisions between atomic and molecular hydrogen and successfully explained entire spectra of many cool DA-type white dwarfs. Owing to the important astrophysical implications of this issue, we present here an independent assessment of the process. For this purpose, we compute free-free quasi-molecular absorption in Lyman α due to collisions with H and H2 within the one-perturber, quasi-static approximation. Line cross-sections are obtained using theoretical molecular potentials to describe the interaction between the radiating atom and the perturber. The variation in the electric dipole transition moment with the interparticle distance is also considered. Six and two allowed electric dipole transitions due to H-H and H-H2 collisions, respectively, are taken into account. The new theoretical Lyman α line profiles are then incorporated in our stellar atmosphere program for the computation of synthetic spectra and colours of DA-type white dwarfs. Illustrative model atmospheres and spectral energy distributions are computed, which show that Lyman α broadening by atoms and molecules has a significant effect on the white dwarf atmosphere models. The inclusion of this collision-induced opacity significantly reddens spectral energy distributions and affects the broad-band colour indices for model atmospheres with Teff 3 potential energy surfaces covering a large region of nuclear configurations, in order to obtain a better description of H-H2 collisions and a more accurate evaluation of their influence on the spectrum of cool white dwarfs.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat

Structural and functional analysis of the baculovirus single-stranded DNA-binding protein LEF-3

AbstractThe single-stranded DNA-binding protein LEF-3 of Autographa californica multinucleocapsid nucleopolyhedrovirus consists of 385 amino acid residues, forms oligomers, and promotes Mg2+-independent unwinding of DNA duplexes and annealing of complementary DNA strands. Partial proteolysis revealed that the DNA-binding domain of LEF-3 is located within a central region (residues 28 to 326) that is relatively resistant to proteolysis. In contrast, the N-terminus (27 residues) and C-terminal portion (59 residues) are not involved in interaction with DNA and are readily accessible to proteolytic digestion. Circular dichroism analyses showed that LEF-3 is a folded protein with an estimated α-helix content of more than 40%, but it is structurally unstable and undergoes unfolding in aqueous solutions at temperatures near 50 °C. Unfolding eliminated the LEF-3 domains that are resistant to proteolysis and randomized the digestion pattern by trypsin. The structural transition was irreversible and was accompanied by the generation of high molecular weight (MW) complexes. The thermal treatment inhibited DNA-binding and unwinding activity of LEF-3 but markedly stimulated its annealing activity. We propose that the shift in LEF-3 activities resulted from the generation of the high MW protein complexes, that specifically stimulate the annealing of complementary DNA strands by providing multiple DNA-binding sites and bringing into close proximity the interacting strands. The unfolded LEF-3 was active in a strand exchange reaction suggesting that it could be involved in the production of recombination intermediates

Intake of heterocyclic aromatic amines and the risk of prostate cancer in the EPIC-Heidelberg cohort

BACKGROUND: Heterocyclic amines (HCA) are positively associated with prostate cancer risk in animal models. Because of mostly inconsistent results of epidemiological studies, we examined the association between intake of HCA and prostate cancer risk. METHODS: In the EPIC-Heidelberg cohort, detailed information on diet, anthropometry, and lifestyle was assessed between 1994 and 1998. Dietary HCA intake was estimated using information on meat consumption, cooking methods, and preferred degree of browning. During 104,195 person-years of follow-up, 337 incident cases of prostate cancer (123 advanced cases) were identified among 9,578 men with valid dietary information. Multivariate Cox proportional hazards regression was used to examine the association between intake of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), and 2-amino-3,4,8-dimethylimidazo[4,5-f]quinoxaline (DiMeIQx) and prostate cancer. RESULTS: Men in the highest quartiles of PhIP, MeIQx, and DiMeIQx intake, respectively, had no increased risk of prostate cancer compared with men in the lowest quartiles (HR = 0.89, 95% CI 0.66-1.22 [PhIP]; 1.06, 0.77-1.45 [MeIQx]; 0.98, 0.72-1.34 [DiMeIQx]). There were no associations between HCA intake and advanced prostate cancer or between high consumption of strongly browned meat and prostate cancer. DISCUSSION: Our data do not support the hypothesis that HCA intake as consumed in a regular diet is a risk factor for prostate cancer

Associations between fruit and vegetable consumption and psychological distress: results from a population-based study.

BACKGROUND: Several studies observed associations of various aspects of diet with mental health, but little is known about the relationship between following the 5-a-day recommendation for fruit and vegetables consumption and mental health. Thus, we examined the associations of the Swiss daily recommended fruit and vegetable intake with psychological distress. METHODS: Data from 20,220 individuals aged 15+ years from the 2012 Swiss Health Survey were analyzed. The recommended portions of fruit and vegetables per day were defined as 5-a-day (at least 2 portions of fruit and 3 of vegetables). The outcome was perceived psychological distress over the previous 4 weeks (measured by the 5-item mental health index [MHI-5]). High distress (MHI-5 score ≤ 52), moderate distress (MHI-5 &gt; 52 and ≤ 72) and low distress (MHI-5 &gt; 72 and ≤ 100) were differentiated and multinomial logistic regression analyses adjusted for known confounding factors were performed. RESULTS: The 5-a-day recommendation was met by 11.6 % of the participants with low distress, 9.3 % of those with moderate distress, and 6.2 % of those with high distress. Consumers fulfilling the 5-a-day recommendation had lower odds of being highly or moderately distressed than individuals consuming less fruit and vegetables (moderate vs. low distress: OR = 0.82, 95 % confidence interval [CI] 0.69-0.97; high vs. low distress: OR = 0.55, 95 % CI 0.41-0.75). CONCLUSIONS: Daily intake of 5 servings of fruit and vegetable was associated with lower psychological distress. Longitudinal studies are needed to further determine the causal nature of this relationship

Structure of hard-hypersphere fluids in odd dimensions

The structural properties of single component fluids of hard hyperspheres in odd space dimensionalities $d$ are studied with an analytical approximation method that generalizes the Rational Function Approximation earlier introduced in the study of hard-sphere fluids [S. B. Yuste and A. Santos, Phys. Rev. A {\bf 43}, 5418 (1991)]. The theory makes use of the exact form of the radial distribution function to first order in density and extends it to finite density by assuming a rational form for a function defined in Laplace space, the coefficients being determined by simple physical requirements. Fourier transform in terms of reverse Bessel polynomials constitute the mathematical framework of this approximation, from which an analytical expression for the static structure factor is obtained. In its most elementary form, the method recovers the solution of the Percus-Yevick closure to the Ornstein-Zernike equation for hyperspheres at odd dimension. The present formalism allows one to go beyond by yielding solutions with thermodynamic consistency between the virial and compressibility routes to any desired equation of state. Excellent agreement with available computer simulation data at $d=5$ and $d=7$ is obtained. As a byproduct of this study, an exact and explicit polynomial expression for the intersection volume of two identical hyperspheres in arbitrary odd dimensions is given.Comment: 18 pages, 7 figures; v2: new references added plus minor changes; to be published in PR