Epitaxial Ferromagnetic Nanoislands of Cubic GdN in Hexagonal GaN

Periodic structures of GdN particles encapsulated in a single crystalline GaN matrix were prepared by plasma assisted molecular beam epitaxy. High resolution X-ray diffractometery shows that GdN islands, with rock salt structure are epitaxially oriented to the wurtzite GaN matrix. Scanning transmission electron microscopy combined with in-situ reflection high energy electron diffraction allows for the study of island formation dynamics, which occurs after 1.2 monolayers of GdN coverage. Magnetometry reveals two ferromagnetic phases, one due to GdN particles with Curie temperature of 70K and a second, anomalous room temperature phase.Comment: 4 pages, 3 figure

Carbon nanotube: a low-loss spin-current waveguide

We demonstrate with a quantum-mechanical approach that carbon nanotubes are excellent spin-current waveguides and are able to carry information stored in a precessing magnetic moment for long distances with very little dispersion and with tunable degrees of attenuation. Pulsed magnetic excitations are predicted to travel with the nanotube Fermi velocity and are able to induce similar excitations in remote locations. Such an efficient way of transporting magnetic information suggests that nanotubes are promising candidates for memory devices with fast magnetization switchings

Life Stage Simulation Analysis: Estimating Vital-Rate Effects on Population Growth for Conservation

We developed a simulation method, known as life-stage simulation analysis (LSA) to measure potential effects of uncertainty and variation in vital rates on population growth (lambda) for purposes of species conservation planning. Under LSA, we specify plausible or hypothesized levels of uncertainty, variation, and covariation in vital rates fur a given population. We use these data under resampling simulations to establish random combinations of vital rates for a large number of matrix replicates and finally summarize results from the matrix replicates to estimate potential effects of each vital rate on lambda in a probability-based context. Estimates of potential effects are based on a variety of summary statistics, such as frequency of replicates having the same vital rate of highest elasticity, difference in elasticity values calculated under simulated conditions vs, elasticities calculated using mean invariant vital rates, percentage of replicates having positive population growth, and variation in lambda explained by variation in each vital rate. To illustrate, we applied LSA to viral rates for two vertebrates: desert tortoise (Gopherus agassizii) and Greater prairie Chicken (Tympanuchus cupido). Results fur the prairie chicken indicated that a single vital rate consistently had greatest effect on population growth. Results for desert tortoise, however, suggested that a variety of life stages could have strong effects on population growth. Additional simulations for the Greater Prairie Chicken under a hypothetical conservation plan also demonstrated that a variety of vital rates could be manipulated to achieve desired population growth. To improve the reliability of inference, we recommend that potential effects of vital rates on lambda be evaluated using a probability-based approach like LSA. LSA is an important complement to other methods that evaluate vital-rate effects on lambda, including classical elasticity analysis, retrospective methods of variance decomposition, and simulation of the effects of environmental stochasticity

Screw dislocation in zirconium: An ab initio study

Plasticity in zirconium is controlled by 1/3 screw dislocations gliding in the prism planes of the hexagonal close-packed structure. This prismatic and not basal glide is observed for a given set of transition metals like zirconium and is known to be related to the number of valence electrons in the d band. We use ab initio calculations based on the density functional theory to study the core structure of screw dislocations in zirconium. Dislocations are found to dissociate in the prism plane in two partial dislocations, each with a pure screw character. Ab initio calculations also show that the dissociation in the basal plane is unstable. We calculate then the Peierls barrier for a screw dislocation gliding in the prism plane and obtain a small barrier. The Peierls stress deduced from this barrier is lower than 21 MPa, which is in agreement with experimental data. The ability of an empirical potential relying on the embedded atom method (EAM) to model dislocations in zirconium is also tested against these ab initio calculations

The structure of Io's thermal corona and implications for atmospheric escape

We investigate the escape of species from Io's atmosphere using a steady-state model of Io's exospheric corona and its interaction with the Io plasma torus. The corona is assumed to be spherically symmetric with the radial density and compositional structure determined by the gas kinetic temperature, critical level radius, and mixing ratios of the component species. Thermal and nonthermal escape rates are calculated and the results compared with previously estimated torus and neutral cloud supply rates for O, S, Na, and K. Both oxygen- and sulfur-dominated exospheres are considered. Atmospheric sputtering is found to be the major escape mechanism for models in which the plasma flow reaches the critical level. However, such models produce total mass-loading rates an order of magnitude larger than inferred values suggesting that either (1) the structure of the thermal corona is significantly modified by the nonthermal interaction, or (2) substantial plasma flow modification and deflection occurs in the corona at or above the critical level. Assuming that the thermal model is a correct description of the corona, a comparison of these results with the observed near-Io distribution of neutral Na and estimated source rates for the neutral Na "jets" suggests an extended Na coronal component. Assuming that this component is part of the thermal exosphere, we find that the observations are consistent with an O-dominated corona, an exospheric temperature ~1000 K, a 0.001 critical level mixing ratio of Na, and a critical level radius ~1.5 R_(Io)

A Structural Investigation of Heteroleptic Lanthanide Substituted Cyclopentadienyl Complexes

The synthesis and structural authentication of novel heteroleptic lanthanide complexes supported by bulky cyclopentadienyl ligands is herein presented. Steric effects play a fundamental role in the coordination motifs.</p

G328.4+0.2 : A large and luminous Crab-like supernova remnant

We report on radio continuum and HI observations of the radio source G328.4+0.2 using the Australia Telescope Compact Array. Our results confirm G328.4+0.2 to be a filled-center nebula with no surrounding shell, showing significant linear polarization and an almost flat spectral index. These results lead us to conclude that G328.4+0.2 is a Crab-like, or ``plerionic'', supernova remnant (SNR), presumably powered by an unseen central pulsar. HI absorption towards G328.4+0.2 puts a lower limit on its distance of 17.4 +/- 0.9 kpc, making it the largest (D=25 pc) and most luminous (L_R = 3e35 erg/s) Crab-like SNR in the Galaxy. We infer G328.4+0.2 to be significantly older than the Crab Nebula, but powered by a pulsar which is fast spinning (P<20 ms) and which has a comparatively low magnetic field (B<1e12 G). We propose G328.4+0.2, G74.9+1.2 and N157B as a distinct group of large-diameter, high-luminosity Crab-like SNRs, all powered by fast-spinning low-field pulsars.Comment: 7 pages, 3 embedded EPS figures, uses emulateapj.sty. Accepted to ApJ. Abstract corrected so that distance is now in kpc, not pc

p63 is the molecular switch for initiation of an epithelial stratification program

Development of stratified epithelia, such as the epidermis, requires p63 expression. The p63 gene encodes isoforms that contain (TA) or lack (DeltaN) a transactivation domain. We demonstrate that TAp63 isoforms are the first to be expressed during embryogenesis and are required for initiation of epithelial stratification. In addition, TAp63 isoforms inhibit terminal differentiation, suggesting that TAp63 isoforms must be counterbalanced by DeltaNp63 isoforms to allow cells to respond to signals required for maturation of embryonic epidermis. Our data demonstrate that p63 plays a dual role: initiating epithelial stratification during development and maintaining proliferative potential of basal keratino-cytes in mature epidermis

Surfaces roughness effects on the transmission of Gaussian beams by anisotropic parallel plates

Influence of the plate surfaces roughness in precise ellipsometry experiments is studied. The realistic case of a Gaussian laser beam crossing a uniaxial platelet is considered. Expression for the transmittance is determined using the first order perturbation theory. In this frame, it is shown that interference takes place between the specular transmitted beam and the scattered field. This effect is due to the angular distribution of the Gaussian beam and is of first order in the roughness over wavelength ratio. As an application, a numerical simulation of the effects of quartz roughness surfaces at normal incidence is provided. The interference term is found to be strongly connected to the random nature of the surface roughness.Comment: 18 pages, Journal of Physics D: Applied Physics, volume 36, issue 21, pages 2697 - 270

Rheophysics of dense granular materials : Discrete simulation of plane shear flows

We study the steady plane shear flow of a dense assembly of frictional, inelastic disks using discrete simulation and prescribing the pressure and the shear rate. We show that, in the limit of rigid grains, the shear state is determined by a single dimensionless number, called inertial number I, which describes the ratio of inertial to pressure forces. Small values of I correspond to the quasi-static regime of soil mechanics, while large values of I correspond to the collisional regime of the kinetic theory. Those shear states are homogeneous, and become intermittent in the quasi-static regime. When I increases in the intermediate regime, we measure an approximately linear decrease of the solid fraction from the maximum packing value, and an approximately linear increase of the effective friction coefficient from the static internal friction value. From those dilatancy and friction laws, we deduce the constitutive law for dense granular flows, with a plastic Coulomb term and a viscous Bagnold term. We also show that the relative velocity fluctuations follow a scaling law as a function of I. The mechanical characteristics of the grains (restitution, friction and elasticity) have a very small influence in this intermediate regime. Then, we explain how the friction law is related to the angular distribution of contact forces, and why the local frictional forces have a small contribution to the macroscopic friction. At the end, as an example of heterogeneous stress distribution, we describe the shear localization when gravity is added.Comment: 24 pages, 19 figure