Thermal buoyancy on Venus: Preliminary results of finite element modeling

Enhanced surface temperatures and a thinner lithosphere on Venus relative to Earth have been cited as leading to increased lithospheric buoyancy. This would limit or prevent subduction on Venus and favor the construction of thickened crust through underthrusting. In order to evaluate the conditions distinguishing between underthrusting and subduction, we have modeled the thermal and buoyancy consequences of the subduction end member. This study considers the fate of a slab from the time it starts to subduct, but bypasses the question of subduction initiation. Thermal changes in slabs subducting into a mantle having a range of initial geotherms are used to predict density changes and thus their overall buoyancy. Finite element modeling is then applied in a first approximation of the assessment of the relative rates of subduction as compared to the buoyant rise of the slab through a viscous mantle

Fabrication techniques developed for small- diameter, thin-wall tungsten and tungsten alloy tubing

Report describes methods for the fabrication of tungsten and tungsten alloys into small-diameter, thin-wall tubing of nuclear quality. The tungsten, or tungsten alloy tube blanks are produced by double extrusion. Plug-drawing has emerged as an excellent secondary fabrication technique for the reduction of the overall tube dimensions

Identification of a non-mammalian leptin-like gene:characterization and expression in the tiger salamander (Ambystoma tigrinum)

Leptin is well established as a multifunctional cytokine in mammals. However, little is known about the evolution of the leptin gene in other vertebrates. A recently published set of ESTs from the tiger salamander (Ambystoma tigrinum) contains a sequence sharing 56% nucleotide sequence identity with the human leptin cDNA. To confirm that the EST is naturally expressed in the salamander, a 409 bp cDNA was amplified by RT-PCR of salamander testis and stomach mRNAs. The coding sequence of the cDNA is predicted to encode 169 amino acids, and the mature peptide to consist of 146 residues, as in mammals. Although the overall amino acid identity with mammalian leptins is only 29%, the salamander and mammalian peptides share common structural features. An intron was identified between coding exons providing evidence that the sequence is present in the salamander genome. Phylogenetic analysis showed a rate of molecular divergence consistent with the accepted view of vertebrate evolution. The pattern of tissue expression of the leptin-like cDNA differed between metamorphosed adult individuals of different sizes suggesting possible developmental regulation. Expression was most prominent in the skin and testis, but was also detected in tissues in which leptin mRNA is present in mammals, including the fat body, stomach, and muscle. The characterization of a salamander leptin-like gene provides a basis for understanding how the structure and functions of leptin have altered during the evolution of tetrapod vertebrates

Molecular immunophenotyping of lungs and spleens in naive and vaccinated chickens early after pulmonary avian influenza A (H9N2) virus infection

In a respiratory-infection-model with the avian influenza A H9N2 virus we studied lung and splenic immune reactions in chickens using a recently developed 5K chicken immuno-microarray. Groups of chickens were either mock-immunized (referred to as non-immune), vaccinated with inactivated viral antigen only (immune) or with viral antigen in a water-in-oil (W/O) immunopotentiator (immune potentiated). Three weeks after vaccination all animals were given a respiratory infection. Immune potentiated birds developed inhibitory antiviral antibodies, showed minimal lung histopathology and no detectable viral sequences, while non-immune animals showed microscopic immunopathology and detectable virus. Immune birds, receiving antigen in saline only, showed minimal microscopic histopathology, and intermediate levels of virus detection. These classical features in the different groups were mirrored by overlapping or specific mRNA gene expression profiles in lungs and spleen using microarray analysis. To our knowledge this is the first study demonstrating pneumonia-associated lung pathology of the low pathogenic avian influenza H9N2 virus. Our data provide insights into the molecular interaction of this virus with its natural host when naive or primed by vaccination

Animal genomics and infectious disease resistance in poultry

Avian pathogens are responsible for major costs to society, both in terms of huge economic losses to the poultry industry and their implications for human health. The health and welfare of millions of birds is under continued threat from many infectious diseases, some of which are increasing in virulence and thus becoming harder to control, such as Marek's disease virus and avian influenza viruses. The current era in animal genomics has seen huge developments in both technologies and resources, which means that researchers have never been in a better position to investigate the genetics of disease resistance and determine the underlying genes/mutations which make birds susceptible or resistant to infection. Avian genomics has reached a point where the biological mechanisms of infectious diseases can be investigated and understood in poultry and other avian species. Knowledge of genes conferring disease resistance can be used in selective breeding programmes or to develop vaccines which help to control the effects of these pathogens, which have such a major impact on birds and humans alike

Supersymmetric Galileons

Galileon theories are of considerable interest since they allow for stable violations of the null energy condition. Since such violations could have occurred during a high-energy regime in the history of our universe, we are motivated to study supersymmetric extensions of these theories. This is carried out in this paper, where we construct generic classes of N=1 supersymmetric Galileon Lagrangians. They are shown to admit non-equivalent stress-energy tensors and, hence, vacua manifesting differing conditions for violating the null energy condition. The temporal and spatial fluctuations of all component fields of the supermultiplet are analyzed and shown to be stable on a large number of such backgrounds. In the process, we uncover a surprising connection between conformal Galileon and ghost condensate theories, allowing for a deeper understanding of both types of theories.Comment: 41 pages, v2: added a referenc

Time-Varying Potassium in High-Resolution Spectra of the Type Ia Supernova 2014J

We present a time series of the highest resolution spectra yet published for the nearby Type Ia supernova (SN) 2014J in M82. They were obtained at 11 epochs over 33 days around peak brightness with the Levy Spectrograph (resolution R~110,000) on the 2.4m Automated Planet Finder telescope at Lick Observatory. We identify multiple Na I D and K I absorption features, as well as absorption by Ca I H & K and several of the more common diffuse interstellar bands (DIBs). We see no evolution in any component of Na I D, Ca I, or in the DIBs, but do establish the dissipation/weakening of the two most blueshifted components of K I. We present several potential physical explanations, finding the most plausible to be photoionization of circumstellar material, and discuss the implications of our results with respect to the progenitor scenario of SN 2014J.Comment: 11 pages, 8 figures, 3 tables, submitted to Ap

An ion ring in a linear multipole trap for optical frequency metrology

A ring crystal of ions trapped in a linear multipole trap is studied as a basis for an optical frequency standard. The equilibrium conditions and cooling possibilities are discussed through an analytical model and molecular dynamics simulations. A configuration which reduces the frequency sensitivity to the fluctuations of the number of trapped ions is proposed. The systematic shifts for the electric quadrupole transition of calcium ions are evaluated for this ring configuration. This study shows that a ring of 10 or 20 ions allows to reach a short term stability better than for a single ion without introducing limiting long term fluctuations

Electrorotation of a pair of spherical particles

We present a theoretical study of electrorotation (ER) of two spherical particles under the action of a rotating electric field. When the two particles approach and finally touch, the mutual polarization interaction between the particles leads to a change in the dipole moment of the individual particle and hence the ER spectrum, as compared to that of the well-separated particles. The mutual polarization effects are captured by the method of multiple images. From the theoretical analysis, we find that the mutual polarization effects can change the characteristic frequency at which the maximum angular velocity of electrorotation occurs. The numerical results can be understood in the spectral representation theory.Comment: Minor revisions; accepted by Phys. Rev.

A 4-Planet System Orbiting the K0V Star HD 141399

We present precision radial velocity (RV) data sets from Keck-HIRES and from Lick Observatory's new Automated Planet Finder Telescope and Levy Spectrometer on Mt. Hamilton that reveal a multiple-planet system orbiting the nearby, slightly evolved, K-type star HD 141399. Our 91 observations over 10.5 years suggest the presence of four planets with orbital periods of 94.35, 202.08, 1070.35, and 3717.35 days and minimum masses of 0.46, 1.36, 1.22, and 0.69 Jupiter masses respectively. The orbital eccentricities of the three inner planets are small, and the phase curves are well sampled. The inner two planets lie just outside the 2:1 resonance, suggesting that the system may have experienced dissipative evolution during the protoplanetary disk phase. The fourth companion is a Jupiter-like planet with a Jupiter-like orbital period. Its orbital eccentricity is consistent with zero, but more data will be required for an accurate eccentricity determination.Comment: 11 pages, 13 figures, To appear in the Astrophysical Journa