Metallic oxide switches using thick film technology

Metallic oxide thick film switches were processed on alumina substrates using thick film technology. Vanadium pentoxide in powder form was mixed with other oxides e.g., barium, strontium copper and glass frit, ground to a fine powder. Pastes and screen printable inks were made using commercial conductive vehicles and appropriate thinners. Some switching devices were processed by conventional screen printing and firing of the inks and commercial cermet conductor terminals on 96% alumina substrates while others were made by applying small beads or dots of the pastes between platinum wires. Static, and dynamic volt-ampere, and pulse tests indicate that the switching and self-oscillatory characteristics of these devices could make them useful in memory element, oscillator, and automatic control applications

Theory of Feshbach molecule formation in a dilute gas during a magnetic field ramp

Starting with coupled atom-molecule Boltzmann equations, we develop a simplified model to understand molecule formation observed in recent experiments. Our theory predicts several key features: (1) the effective adiabatic rate constant is proportional to density; (2) in an adiabatic ramp, the dependence of molecular fraction on magnetic field resembles an error function whose width and centroid are related to the temperature; (3) the molecular production efficiency is a universal function of the initial phase space density, the specific form of which we derive for a classical gas. Our predictions show qualitative agreement with the data from [Hodby et al, Phys. Rev. Lett. {\bf{94}}, 120402 (2005)] without the use of adjustable parameters

Distinguishing step relaxation mechanisms via pair correlation functions

Theoretical predictions of coupled step motion are tested by direct STM measurement of the fluctuations of near-neighbor pairs of steps on Si(111)-root3 x root3 R30 - Al at 970K. The average magnitude of the pair-correlation function is within one standard deviation of zero, consistent with uncorrelated near-neighbor step fluctuations. The time dependence of the pair-correlation function shows no statistically significant agreement with the predicted t^1/2 growth of pair correlations via rate-limiting atomic diffusion between adjacent steps. The physical considerations governing uncorrelated step fluctuations occurring via random attachment/detachment events at the step edge are discussed.Comment: 17 pages, 4 figure

Evidence for Differential Rotation on a T Tauri Star

Five years of photometric monitoring of the T Tauri star HBC 338 in NGC 1333 has revealed that it is a periodic variable, but the period has changed significantly with time. From 2000-2003, a period near 5.6 days was observed, while in the last two seasons, the dominant period is near 4.6 days. No other T Tauri star has been seen to change its period by such a large percentage. We propose a model in which a differentially rotating star is seen nearly equator-on and a high latitude spot has gradually been replaced by a low latitude spot. We show that this model provides an excellent fit to the observed shapes of the light curves at each epoch. The amplitude and sense of the inferred differential rotation is similar to what is seen on the Sun. This may be surprising given the likely high degree of magnetic surface activity on the star relative to the Sun but we note that HBC 338 is clearly an exceptional T Tauri star.Comment: Acepted for publication in PAS

Angular Distribution of Gamma-ray Bursts and Weak Lensing

We investigate whether Gamma-Ray Bursts (GRBs) from the Current BATSE Catalog have been affected by weak lensing by the nearby large scale structure. The redshift distribution of GRBs is believed to be broad, extending to z~5, so most events can be assumed to be at large redshifts, and hence subject to weak lensing, which would betray itself as projected (anti-)correlations between GRB events and galaxies or clusters that trace the intervening mass. Given the observed distribution of GRBs in fluence, and statistical positional error, e, we predict that most subsets drawn from BATSE Catalog will be anti-correlated with the foreground structure due to weak lensing, i.e. will show negative magnification bias. We find that GRBs are indeed anti-correlated with the APM galaxies (z~0.2-0.3) in the sense that galaxy density in circles of radii 1-1.5 deg (15-20 Mpc at z~0.3) centered on e<1 GRBs is about 10% lower than expected from a random distribution; the significance of GRB-APM anti-correlations reaches 99.7%. Cross-correlation between GRBs and distant rich Abell-Corwin-Olowin clusters is also negative. Standard cosmological models with Omega_matter ~ 0.3, Omega_Lambda ~ 0.7, and matter distribution on large scales following observed APM galaxy distribution with the biasing parameter of around 1 are not able to reproduce our GRB-APM anti-correlations. We propose a speculative model that does account for these anti-correlations as well as positive correlations found previously, between QSOs and APM galaxies. We briefly discuss if the proposed scheme is in conflict with observations of cosmic microwave background, galaxy surveys, cosmic velocity flows, and weak shear lensing

An Unusual Hydrogen Migration/C−H Activation Reaction with Group 3 Metals

A novel hydrogen migration from the phenyl ring to the pyridine ring of an yttrium pyridyl complex supported by a 1,1′-ferrocene diamide ligand is reported. Density functional theory calculations were instrumental in probing the mechanism for this transformation

The ground state of a spin-1/2 neutral particle with anomalous magnetic moment in a Aharonov-Casher configuration

We determine the (bound) ground state of a spin 1/2 chargless particle with anomalous magnetic moment in certain Aharonov-Casher configurations. We recast the description of the system in a supersymmetric form. Then the basic physical requirements for unbroken supersymmetry are established. We comment on the possibility of neutron trapping in these systems

Accurate fundamental parameters and distance to a massive early-type eclipsing binary in the Danks 2 cluster

We present a study of the properties of the O-type, massive eclipsing binary 2MASS J13130841-6239275 located in the outskirts of the Danks 2 cluster in the G305 star-forming complex, using near-infrared spectroscopy from VLT/ISAAC. We derive the masses and radii to be 24.5$\pm$0.9 M$_{\odot}$ and 9.2$\pm$0.1 R$_{\odot}$ for the primary and 21.7$\pm$0.8 M$_{\odot}$ and 8.7$\pm$0.1 R$_{\odot}$ for the secondary component. In addition, we evaluate the sensitivity of our parameters to the choice of the spectral features used to determine the radial velocities. Both components appear to be main-sequence O6.5$-$O7 type stars at an age of $\sim$5 Myr, which is in agreement with the age of the cluster. A high visual extinction of A$_{5495}$=11.9$\pm$0.1 mag is reported, which is likely attributed to the cold molecular gas contaminating the north-east region of the cluster. By fitting the spectral energy distribution of the system to the available $BVI_{c}JHK_{s}$ photometry, we determine a distance to the system of 3.52$\pm$0.08 kpc with a precision of 2$\%$, which is the most well-determined distance to the Danks 2 cluster and the host complex reported in the literature.Comment: 13 pages, 9 figures, 6 tables. Accepted for publication in A&