Search For Oxygen in Cool DQ White Dwarf Atmospheres

We report new infrared spectroscopic observations of cool DQ white dwarfs by using Coolspec on the 2.7m Harlan-Smith Telescope. DQs have helium-rich atmospheres with traces of molecular carbon thought to be the result of convective dredge-up from their C/O interiors. Recent model calculations predict that oxygen should also be present in DQ atmospheres in detectable amounts. Our synthetic spectra calculations for He-rich white dwarfs with traces of C and O indicate that CO should be easily detected in the cool DQ atmospheres if present in the expected amounts. Determination of the oxygen abundance in the atmosphere will reveal the C/O ratio at the core/envelope boundary, constraining the important and uncertain ^{12}C(alpha,gamma)^{16}O reaction rate.Comment: 2 pages, 2 figures, to appear in proceedings of the 13th European Workshop on White Dwarf

Sonic levitation apparatus

A sonic levitation apparatus is disclosed which includes a sonic transducer which generates acoustical energy responsive to the level of an electrical amplifier. A duct communicates with an acoustical chamber to deliver an oscillatory motion of air to a plenum section which contains a collimated hole structure having a plurality of parallel orifices. The collimated hole structure converts the motion of the air to a pulsed. Unidirectional stream providing enough force to levitate a material specimen. Particular application to the production of microballoons in low gravity environment is discussed

Atlantic water on the Chukchi Shelf

An anomalously warm saline layer in the bottom of the shallow Chukchi Sea in August 1975 is believed due to a surge which drove water from the Atlantic Layer of the Arctic Ocean up onto the shelf. Two earlier occurrences of this kind of water in the Chukchi Sea have been identified in historical data.Submitted to: Director, Arctic Submarine Laboratory Naval Undersea Center, San Diego, CA.http://archive.org/details/atlanticwateronc00bourProject Order No. 00010N

Observations on the coastal current of Arctic Alaska

This paper describes characteristics of the warm coastal current in the vicinity of the ice margin in the Chukchi and Beaufort seas. The warm current originates in Bering Strait and is traced around Pt. Barrow to longitude 152°W in the Beaufort Sea. In the Chukchi Sea it is concentrated near the surface, overlying dense relict bottom water trapped by the shallow depths. Eastward, as the bottom deepens, the warm water descends to mid-depth, eventually becoming warmest near bottom in depths of 30 to 50 m. Mechanisms for cooling and dilution of the warm water are discussed

USNS BARTLETT Cruise to the Greenland Sea in September 1989: Data Report

As a component of the Greenland Sea Project, a hydrographic cruise was conducted on board the USNS BARTLETT during September 1989 in the southern Greenland Sea to characterize the water mass structure and circulation features of the Jan Mayen Current (JMC). A total of 48 high-quality CTD stations were occupied to depths of 1000 m; five stations extended to 3000 m or more. Five north-south tending transects permitted tracking of the JMC by its low temperature (< 0°C) , low salinity near-surface core. The JMC could also be well defined from its warm, saline intermediate water properties. Deep stations made in the trough of the Jan Mayen Fracture Zone suggest that the interchange of deep and bottom water from the Greenland and Norwegian Seas via this trough is a slow diffusive process and not an active advective feature as previously thought.Arctic Submarine Laboratory, Naval Ocean Systems Center, San Diego, CA.http://archive.org/details/usnsbartlettcrui00bourO&MN, Direct Fundin

Dual Fronts Propagating into an Unstable State

The interface between an unstable state and a stable state usually develops a single confined front travelling with constant velocity into the unstable state. Recently, the splitting of such an interface into {\em two} fronts propagating with {\em different} velocities was observed numerically in a magnetic system. The intermediate state is unstable and grows linearly in time. We first establish rigorously the existence of this phenomenon, called ``dual front,'' for a class of structurally unstable one-component models. Then we use this insight to explain dual fronts for a generic two-component reaction-diffusion system, and for the magnetic system.Comment: 19 pages, Postscript, A

Systematic derivation of a rotationally covariant extension of the 2-dimensional Newell-Whitehead-Segel equation

An extension of the Newell-Whitehead-Segel amplitude equation covariant under abritrary rotations is derived systematically by the renormalization group method.Comment: 8 pages, to appear in Phys. Rev. Letters, March 18, 199

Front propagation into unstable and metastable states in Smectic C* liquid crystals: linear and nonlinear marginal stability analysis

We discuss the front propagation in ferroelectric chiral smectics (SmC*) subjected to electric and magnetic fields applied parallel to smectic layers. The reversal of the electric field induces the motion of domain walls or fronts that propagate into either an unstable or a metastable state. In both regimes, the front velocity is calculated exactly. Depending on the field, the speed of a front propagating into the unstable state is given either by the so-called linear marginal stability velocity or by the nonlinear marginal stability expression. The cross-over between these two regimes can be tuned by a magnetic field. The influence of initial conditions on the velocity selection problem can also be studied in such experiments. SmC$^*$ therefore offers a unique opportunity to study different aspects of front propagation in an experimental system

New exact fronts for the nonlinear diffusion equation with quintic nonlinearities

We consider travelling wave solutions of the reaction diffusion equation with quintic nonlinearities $u_t = u_{xx} + \mu u (1 -u ) ( 1 +\alpha u + \beta u^2 +\gamma u^3)$. If the parameters $\alpha , \beta$ and $\gamma$ obey a special relation, then the criterion for the existence of a strong heteroclinic connection can be expressed in terms of two of these parameters. If an additional restriction is imposed, explicit front solutions can be obtained. The approach used can be extended to polynomials whose highest degree is odd.Comment: Revtex, 5 page