The thermal power of aluminum nitride at temperatures between 1350 and 1650 deg C in argon and nitrogen atmospheres

The test apparatus for measuring the thermal voltage of aluminum nitride for temperature differences of up to + or - 60 C between 1350 and 1650 C is described. The thermal power and its homogeneous proportion are determined and the heat transfer of the migration ions resulting from the homogeneous thermal power is calculated. The conduction mechanism in aluminum nitride is discussed

Herschel-PACS imaging of protostars in the HH 1–2 outflow complex

We present 70 and 160 μm Herschel science demonstration images of a field in the Orion A molecular cloud that contains the prototypical Herbig-Haro objects HH 1 and 2, obtained with the Photodetector Array Camera and Spectrometer (PACS). These observations demonstrate Herschel’s unprecedented ability to study the rich population of protostars in the Orion molecular clouds at the wavelengths where they emit most of their luminosity. The four protostars previously identified by Spitzer 3.6–40 μm imaging and spectroscopy are detected in the 70 μm band, and three are clearly detected at 160 μm. We measure photometry of the protostars in the PACS bands and assemble their spectral energy distributions (SEDs) from 1 to 870 μm with these data, Spitzer spectra and photometry, 2MASS data, and APEX sub-mm data. The SEDs are fit to models generated with radiative transfer codes. From these fits we can constrain the fundamental properties of the protostars. We find luminosities in the range 12–84 L_⊙ and envelope densities spanning over two orders of magnitude. This implies that the four protostars have a wide range of envelope infall rates and evolutionary states: two have dense, infalling envelopes, while the other two have only residual envelopes. We also show the highly irregular and filamentary structure of the cold dust and gas surrounding the protostars as traced at 160 μm

Small-Angle Excess Scattering: Glassy Freezing or Local Orientational Ordering?

We present Monte Carlo simulations of a dense polymer melt which shows glass-transition-like slowing-down upon cooling, as well as a build up of nematic order. At small wave vectors q this model system shows excess scattering similar to that recently reported for light-scattering experiments on some polymeric and molecular glass-forming liquids. For our model system we can provide clear evidence that this excess scattering is due to the onset of short-range nematic order and not directly related to the glass transition.Comment: 3 Pages of Latex + 4 Figure

A Third Planet Orbiting HIP 14810

We present new precision radial velocities and a three-planet Keplerian orbit fit for the V = 8.5, G5 V star HIP 14810. We began observing this star at Keck Observatory as part of the N2K Planet Search Project. Wright et al. (2007) announced the inner two planets to this system, and subsequent observations have revealed the outer planet planet and the proper orbital solution for the middle planet. The planets have minimum masses of 3.9, 1.3, and 0.6 M_Jup and orbital periods of 6.67, 147.7, and 952 d, respectively. We have numerically integrated the family of orbital solutions consistent with the data and find that they are stable for at least 10^6 yr. Our photometric search shows that the inner planet does not transit.Comment: ApJL, accepte

Greenalite Nanoparticles in Alkaline Vent Plumes as Templates for the Origin of Life

Mineral templates are thought to have played keys roles in the emergence of life. Drawing on recent findings from 3.45–2.45 billion-year-old iron-rich hydrothermal sedimentary rocks, we hypothesize that greenalite (Fe₃Si₂O₅ (OH)₄) was a readily available mineral in hydrothermal environments, where it may have acted as a template and catalyst in polymerization, vesicle formation and encapsulation, and protocell replication. We argue that venting of dissolved Fe²⁺ and SiO₂ (aq) into the anoxic Hadean ocean favored the precipitation of nanometer-sized particles of greenalite in hydrothermal plumes, producing a continuous flow of free-floating clay templates that traversed the ocean. The mixing of acidic, metal-bearing hydrothermal plumes from volcanic ridge systems with more alkaline, organic-bearing plumes generated by serpentinization of ultramafic rocks brought together essential building blocks for life in solutions conducive to greenalite precipitation. We suggest that the extreme disorder in the greenalite crystal lattice, producing structural modulations resembling parallel corrugations (∼22 Å wide) on particle edges, promoted the assembly and alignment of linear RNA-type molecules (∼20 Å diameter). In alkaline solutions, greenalite nanoparticles could have accelerated the growth of membrane vesicles, while their encapsulation allowed RNA-type molecules to continue to form on the mineral templates, potentially enhancing the growth and division of primitive cell membranes. Once self-replicating RNA evolved, the mineral template became redundant, and protocells were free to replicate and roam the ocean realm

Greenalite Nanoparticles in Alkaline Vent Plumes as Templates for the Origin of Life

Mineral templates are thought to have played keys roles in the emergence of life. Drawing on recent findings from 3.45–2.45 billion-year-old iron-rich hydrothermal sedimentary rocks, we hypothesize that greenalite (Fe₃Si₂O₅ (OH)₄) was a readily available mineral in hydrothermal environments, where it may have acted as a template and catalyst in polymerization, vesicle formation and encapsulation, and protocell replication. We argue that venting of dissolved Fe²⁺ and SiO₂ (aq) into the anoxic Hadean ocean favored the precipitation of nanometer-sized particles of greenalite in hydrothermal plumes, producing a continuous flow of free-floating clay templates that traversed the ocean. The mixing of acidic, metal-bearing hydrothermal plumes from volcanic ridge systems with more alkaline, organic-bearing plumes generated by serpentinization of ultramafic rocks brought together essential building blocks for life in solutions conducive to greenalite precipitation. We suggest that the extreme disorder in the greenalite crystal lattice, producing structural modulations resembling parallel corrugations (∼22 Å wide) on particle edges, promoted the assembly and alignment of linear RNA-type molecules (∼20 Å diameter). In alkaline solutions, greenalite nanoparticles could have accelerated the growth of membrane vesicles, while their encapsulation allowed RNA-type molecules to continue to form on the mineral templates, potentially enhancing the growth and division of primitive cell membranes. Once self-replicating RNA evolved, the mineral template became redundant, and protocells were free to replicate and roam the ocean realm

Low-Temperature Excitations of Dilute Lattice Spin Glasses

A new approach to exploring low-temperature excitations in finite-dimensional lattice spin glasses is proposed. By focusing on bond-diluted lattices just above the percolation threshold, large system sizes $L$ can be obtained which lead to enhanced scaling regimes and more accurate exponents. Furthermore, this method in principle remains practical for any dimension, yielding exponents that so far have been elusive. This approach is demonstrated by determining the stiffness exponent for dimensions $d=3$, $d=6$ (the upper critical dimension), and $d=7$. Key is the application of an exact reduction algorithm, which eliminates a large fraction of spins, so that the reduced lattices never exceed $\sim10^3$ variables for sizes as large as L=30 in $d=3$, L=9 in $d=6$, or L=8 in $d=7$. Finite size scaling analysis gives $y_3=0.24(1)$ for $d=3$, significantly improving on previous work. The results for $d=6$ and $d=7$, $y_6=1.1(1)$ and $y_7=1.24(5)$, are entirely new and are compared with mean-field predictions made for d>=6.Comment: 7 pages, LaTex, 7 ps-figures included, added result for stiffness in d=7, as to appear in Europhysics Letters (see http://www.physics.emory.edu/faculty/boettcher/ for related information

Summer Distribution of Marine Birds in the Western Beaufort Sea

Proposed expansion of oil and gas development into offshore waters of the Beaufort Sea has raised concerns that marine birds could be affected by disturbance and oil spills. We conducted aerial surveys to determine the composition and distribution of avian species in the western Beaufort Sea. We sampled marine waters up to 100 km from shore, between Cape Halkett and Brownlow Point in June, July, and August of 1999 and 2000 and between Point Barrow and Demarcation Point in July 2001. Approximately 90% of the birds we observed were sea ducks, predominantly long-tailed ducks (Clangula hyemalis), king eiders (Somateria spectabilis), and scoters (Melanitta spp.). Densities of most species decreased with distance from shore, although king eider densities were higher in deeper, offshore waters. Densities of long-tailed ducks increased in nearshore coastal lagoons at the onset of post-breeding moult, and densities of eiders increased offshore during their peak moult migration. In general, bird densities were highest in areas with less than 30% ice cover, although high densities of king eiders occurred in areas with 30%-60% ice cover. Our results suggest species-specific uses of the Beaufort Sea in summer for moulting, migration, brood rearing, and foraging. The vulnerability of marine birds to potential oil spills and disturbance will depend on the location of facilities, timing of events, and ice conditions.Un projet d'expansion de l'exploitation pétrolière et gazière dans les eaux du large de la mer de Beaufort a soulevé des questions au sujet des retombées éventuelles pour les oiseaux marins suite aux perturbations et à des déversements d'hydrocarbures. On a effectué des relevés aériens pour analyser la composition et la répartition des espèces aviaires dans la mer de Beaufort occidentale. On a échantillonné les eaux marines jusqu'à une distance de 100 km du rivage, en juin, juillet et août de 1999 et de 2000, entre Cape Halkett et Brownlow Point et, en juillet 2001, entre Point Barrow et Demarcation Point. Environ 90% des oiseaux observés étaient des canards de mer, surtout des hareldes kakawis (Clangula hyemalis), des eiders à tête grise (Somateria spectabilis) et des macreuses (Melanitta spp). Les densités de la plupart des espèces diminuaient en s'éloignant du rivage, encore que celles de l'eider à tête grise étaient plus élevées dans les eaux plus profondes du large. Les densités de la harelde kakawi augmentaient dans les lagunes côtières à proximité du rivage au début de la mue post-reproductrice, et celles de l'eider augmentaient au large au plus fort de la migration de mue. En général, les densités d'oiseaux étaient plus fortes dans les zones où il y avait moins de 30% de manteau glaciel, encore que de fortes densités de l'eider à tête grise se trouvaient dans les zones ayant de 30 à 60% de manteau glaciel. Nos résultats suggèrent qu'en été les espèces utilisent la mer de Beaufort d'une façon qui leur est propre pour la mue, la migration, l'élevage des couvées et le nourrissage. La vulnérabilité des oiseaux marins face à d'éventuels déversements d'hydrocarbures et perturbations va dépendre de l'emplacement des installations, du moment où se produiront les événements et de l'état des glaces