Gas dynamics in Massive Dense Cores in Cygnus-X

We study the kinematic properties of dense gas surrounding massive protostars recognized by Bontemps et a. (2010) in a sample of five Massive Dense Cores in Cygnus-X. We investigate whether turbulent support plays a major role in stabilizing the core against fragmentation into Jeans-mass objects or alternatively, the observed kinematics could indicate a high level of dynamics. We present IRAM 30m single-dish (HCO+ and H13CO+) and IRAM PdBI high angular-resolution observations of dense gas tracers (H13CO+ and H13CN) to reveal the kinematics of molecular gas at scales from 0.03 to 0.1 pc. Radiative transfer modeling shows that H13CO+ is depleted within the envelopes of massive protostars and traces the bulk of material surrounding the protostars rather than their inner envelopes. H13CN shows a better correspondence with the peak of the continuum emission, possibly due to abundance anomalies and specific chemistry in the close vicinity of massive protostars. Analyzing the line-widths we show that the observed line-dispersion of H13CO+ at the scale of MDCs is smaller than expected from the quasi-static, turbulent-core model. At large-scales, global organized bulk motions are identified for 3 of the MDCs. At small-scales, several spectral components are identified in all MDCs showing filamentary structures and intrinsic velocity gradients towards the continuum peaks. The dynamics of these flows show diversity among the sample and we link this to the specific fragmentation properties of the MDCs. No clear evidence is found for a turbulence regulated, equilibrium scenario within the sample of MDCs. We propose a picture in which MDCs are not in equilibrium and their dynamics is governed by small-scale converging flows, which may initiate star-formation via their shears

Coplanar waveguide discontinuities for P-I-N diode switches and filter applications

A full wave space domain integral equation (SDIE) analysis of coplanar waveguide (CPW) two port discontinuities is presented. An experimental setup to measure the S-parameters of such discontinuities is described. Experimental and theoretical results for CPW realizations of pass-band and stop-band filters are presented. The S-parameters of such structures are plotted in the frequency range 5 to 25 GHz

Probing Majorana neutrinos in rare K and D, D_s, B, B_c meson decays

We study lepton number violating decays of charged K, D, D_s, B and B_c mesons of the form M^+\to {M'}^-\ell^+\ell^+, induced by the existence of Majorana neutrinos. These processes provide information complementary to neutrinoless double nuclear beta decays, and are sensitive to neutrino masses and lepton mixing. We explore neutrino mass ranges m_N from below 1 eV to several hundred GeV. We find that in many cases the branching ratios are prohibitively small, however in the intermediate range m_\pi < m_N < m_{B_c}, in specific channels and for specific neutrino masses, the branching ratios can be at the reach of high luminosity experiments like those at the LHC-b and future Super flavor-factories, and can provide bounds on the lepton mixing parameters.Comment: 25 page

A generalized mechanistic codon model.

Models of codon evolution have attracted particular interest because of their unique capabilities to detect selection forces and their high fit when applied to sequence evolution. We described here a novel approach for modeling codon evolution, which is based on Kronecker product of matrices. The 61 × 61 codon substitution rate matrix is created using Kronecker product of three 4 × 4 nucleotide substitution matrices, the equilibrium frequency of codons, and the selection rate parameter. The entities of the nucleotide substitution matrices and selection rate are considered as parameters of the model, which are optimized by maximum likelihood. Our fully mechanistic model allows the instantaneous substitution matrix between codons to be fully estimated with only 19 parameters instead of 3,721, by using the biological interdependence existing between positions within codons. We illustrate the properties of our models using computer simulations and assessed its relevance by comparing the AICc measures of our model and other models of codon evolution on simulations and a large range of empirical data sets. We show that our model fits most biological data better compared with the current codon models. Furthermore, the parameters in our model can be interpreted in a similar way as the exchangeability rates found in empirical codon models

RANDOM MAGNETIC FIELD EFFECTS ON ELECTRONIC PROPERTIES IN SUBSTITUTIONALLY AND TOPOLOGICALLY DISORDERED ALLOYS

We numerically investigate the effects of the random static magnetic field on a variety of electronic properties (localization of electron wavefunctions, spectral correlations and electrical conductance) in substitutionally and topologically disordered alloys. For this, we generate two-dimensional substitutionally disordered alloys and simulate three-dimensional amorphous structures by a molecular dynamics algorithm. As Hamiltonian models, we use the usual Anderson tight-binding model for the  substitutional  disorder and  a  tight-binding model with a set of explicit s-type orbitals for the topological disorder. We particularly focus on the effect of the random magnetic field on the localization of electron wavefunctions. In the presence of the substitutional disorder, we establish that the random magnetic field tends to delocalize the electron wavefunctions at the band center less than does the uniform magnetic field and it enhances the localization at the band edges. But, in the presence of the topological disorder, we observe the opposite effect. We show that the random magnetic field tends to delocalize the electron wavefunctions more than does the uniform magnetic field. In this respect, we demonstrate that the effect of the random magnetic field on the electron wavefunctions depends on the nature of the disorder.We numerically investigate the effects of the random static magnetic field on a variety of electronic properties (localization of electron wavefunctions, spectral correlations and electrical conductance) in substitutionally and topologically disordered alloys. For this, we generate two-dimensional substitutionally disordered alloys and simulate three-dimensional amorphous structures by a molecular dynamics algorithm. As Hamiltonian models, we use the usual Anderson tight-binding model for the  substitutional  disorder and  a  tight-binding model with a set of explicit s-type orbitals for the topological disorder. We particularly focus on the effect of the random magnetic field on the localization of electron wavefunctions. In the presence of the substitutional disorder, we establish that the random magnetic field tends to delocalize the electron wavefunctions at the band center less than does the uniform magnetic field and it enhances the localization at the band edges. But, in the presence of the topological disorder, we observe the opposite effect. We show that the random magnetic field tends to delocalize the electron wavefunctions more than does the uniform magnetic field. In this respect, we demonstrate that the effect of the random magnetic field on the electron wavefunctions depends on the nature of the disorder

Influence of the C/O ratio on titanium and vanadium oxides in protoplanetary disks

Context. The observation of carbon-rich disks have motivated several studies questioning the influence of the C/O ratio on their gas phase composition in order to establish the connection between the metallicity of hot-Jupiters and that of their parent stars. Aims. We to propose a method that allows the characterization of the adopted C/O ratio in protoplanetary disks independently from the determination of the host star composition. Titanium and vanadium chemistries are investigated because they are strong optical absorbers and also because their oxides are known to be sensitive to the C/O ratio in some exoplanet atmospheres. Methods. We use a commercial package based on the Gibbs energy minimization technique to compute the titanium and vanadium equilibrium chemistries in protoplanetary disks for C/O ratios ranging from 0.05 to 10. Our calculations are performed for pressures ranging from 1e-6 to 1e-2 bar, and for temperatures ranging from 50 to 2000 K. Results. We find that the vanadium nitride/vanadium oxide and titanium hydride/titanium oxide gas phase ratios strongly depend on the C/O ratio in the hot parts of disks (T > 1000 K). Our calculations suggest that, in these regions, these ratios can be used as tracers of the C/O value in protoplanetary disks.Comment: Accepted for publication in A&

Vector Meson Exchanges and CP Asymmetry in K±→π±π0K^{\pm}\rightarrow\pi^{\pm}\pi^0

Using a current algebra framework, we discuss the contribution of vector meson exchanges to the CP violating asymmetry in the decay $K^{\pm}\rightarrow\pi^{\pm}\pi^0$, resulting from the interference of the $K\rightarrow\pi\pi$ amplitude with the radiative correction $K\rightarrow\pi\pi\gamma$.Comment: 9 pages (plain-TEX), IC/93/186, UTS-DFT-93-18, (two figures not included

The impermanent fate of massive stars in AGN disks

Stars are likely to form or to be captured in AGN disks. Their mass reaches an equilibrium when their rate of accretion is balanced by that of wind. If the exchanged gas is well mixed with the stellar core, this metabolic process would indefinitely sustain an "immortal" state on the main sequence (MS) and pollute the disk with He byproducts. This theoretical extrapolation is inconsistent with the super-solar {\alpha} element and Fe abundances inferred from the broad emission lines in active AGNs with modest He concentration. We show this paradox can be resolved with a highly-efficient retention of the He ashes or the suppression of chemical blending. The latter mechanism is robust in the geometrically-thin, dense, sub-pc regions of the disk where the embedded-stars' mass is limited by the gap-formation condition. These stars contain a radiative zone between their mass-exchange stellar surface and the nuclear-burning core. Insulation of the core lead to the gradual decrease of its H fuel and the stars' equilibrium masses. These stars transition to their post-main-sequence (PostMS) tracks on a chemical evolution time scale of a few Myr. Subsequently, the triple-{\alpha} and {\alpha}-chain reactions generate {\alpha} and Fe byproducts which are released into their natal disks. These PostMS stars also undergo core collapse, set off type II supernova, and leave behind a few solar-mass residual black holes or neutron starsComment: 17 pages, 7 figures, Accepted for publication in MNRA

New insights on Saturn's formation from its nitrogen isotopic composition

The recent derivation of a lower limit for the $^{14}$N/$^{15}$N ratio in Saturn's ammonia, which is found to be consistent with the Jovian value, prompted us to revise models of Saturn's formation using as constraints the supersolar abundances of heavy elements measured in its atmosphere. Here we find that it is possible to account for both Saturn's chemical and isotopic compositions if one assumes the formation of its building blocks at $\sim$45 K in the protosolar nebula, provided that the O abundance was $\sim$2.6 times protosolar in its feeding zone. To do so, we used a statistical thermodynamic model to investigate the composition of the clathrate phase that formed during the cooling of the protosolar nebula and from which the building blocks of Saturn were agglomerated. We find that Saturn's O/H is at least $\sim$34.9 times protosolar and that the corresponding mass of heavy elements ($\sim$43.1 \Mearth) is within the range predicted by semi-convective interior models.Comment: Accepted for publication in Astrophysical Journal Letter

Maladie de kimura: À propos d’un cas

Introduction :  Mots-clés : Maladie de Kimura, parotide, chirurgie.La maladie de Kimura ou lymphogranulome éosinophile est une pathologie inflammatoire chronique très rare, d’étiologie inconnue. Nous rapportons un cas de maladie de Kimura à localisation parotidienne et à travers une revue de la littérature, rappelons les principales caractéristiques cliniques, paracliniques, thérapeutiques et évolutives de cette pathologie. Matériel et méthodes : Patient de 17 ans qui a consulté devant l’apparition d’une tuméfaction de la région parotidienne gauche évoluant depuis un an et sans paralysie faciale. Résultats : L’échographie cervico-parotidienne a révélé une parotide gauche hypertrophiée siège de multiples nodules hypoéchogènes. La tomodensitométrie cervico-faciale a mis en évidence une glande parotide gauche augmentée de taille et de structure hétérogène nodulaire sans adénopathies cervicales. La cytopontion était non concluante. Le patient a bénéficié d’une parotidectomie exofaciale gauche et l’étude anatomopathologique de la pièce opératoire revenue en faveur de la maladie de Kimura. Les suites opératoires étaient simples. Le recul est d’un an sans récidive. Discussion : La Maladie de Kimura se caractérise cliniquement par des nodules sous cutanés de localisation cervicofaciale, une augmentation du volume des glandes salivaires et des adénopathies satellites. Son diagnostic est histologique reposant sur l’identification d’une hyperplasie follicullaire avec des abcès à polynucléaires éosinophiles. Le traitement est chirurgical le plus souvent mais dans certains cas la corticothérapie est proposée. Ce diagnostic doit cependant rester à l’esprit devant toute masse cervico-faciale