Direct observation of nuclear spin diffusion in real space

Images directly visualizing the spatial spin-diffusion process are reported. The measurements were performed using a magnetic resonance force microscope. The field gradient associated with the force-detection experiment is large enough to affect the spin dynamics and a modified kinetics of the spin-diffusion process is observed. The effects of the gradient were compensated for by a pulse scheme and a pure Zeeman diffusion rate constant of D=(6.2+/-0.7)x10{-12} cm{2}/s in CaF2 was observed.     

Noise-Induced Drift in Stochastic Differential Equations with Arbitrary Friction and Diffusion in the Smoluchowski-Kramers Limit

We consider the dynamics of systems with arbitrary friction and diffusion. These include, as a special case, systems for which friction and diffusion are connected by Einstein fluctuation-dissipation relation, e.g. Brownian motion. We study the limit where friction effects dominate the inertia, i.e. where the mass goes to zero (Smoluchowski-Kramers limit). Using the Itô stochastic integral convention, we show that the limiting effective Langevin equations has different drift fields depending on the relation between friction and diffusion. Alternatively, our results can be cast as different interpretations of stochastic integration in the limiting equation, which can be parametrized by α∈?. Interestingly, in addition to the classical Itô (α=0), Stratonovich (α=0.5) and anti-Itô (α=1) integrals, we show that position-dependent α=α(x), and even stochastic integrals with α?[0,1] arise. Our findings are supported by numerical simulations.     

The surface layers dual to hydrodynamic boundaries

The AdS/hydrodynamics correspondence provides a 1–1 map between large wavelength features of AdS black branes and conformal fluid flows. In this note we consider boundaries between nonrelativistic flows, applying the usual boundary conditions for viscous fluids. We find that a naive application of the correspondence to these boundaries yields a surface layer in the gravity theory whose stress tensor is not equal to that given by the Israel matching conditions. In particular, while neither stress tensor satisfies the null energy condition and both have nonvanishing momentum, only Israel's tensor has stress. The disagreement arises entirely from corrections to the metric due to multiple derivatives of the flow velocity, which violate Israel's finiteness assumption in the thin wall limit.     

Real time ellipsometry for monitoring plasma-assisted epitaxial growth of GaN

GaN is grown on Si-face 4H-SiC(0 0 0 1) substrates using remote plasma-assisted methods including metalorganic chemical vapour deposition (RP-MOCVD) and molecular beam epitaxy (MBE). Real time spectroscopic ellipsometry is used for monitoring all the steps of substrate pre-treatments and the heteroepitaxial growth of GaN on SiC. Our characterization emphasis is on understanding the nucleation mechanism and the GaN growth mode, which depend on the SiC surface preparation.     

Dirac equation in metric-affine gravitation theories and superpotentials

We consider a metric-affine gravitational framework in which the dynamical fields are the spin structures, the general linear connections, and the Dirac fermion fields. Using a spin structure and a linear connection on the world manifold, we construct a principal connection on the spinor bundle. By applying general ideas concerning the conservation laws in the Lagrangian approach to field theory, we examine the corresponding conserved currents. The main result is that the currents associated with infinitesimal vertical (internal) transformations of the covariance group are shown to vanish identically. It follows that to every vector field on the world manifold there corresponds a well-defined current, the stress-energymomentum of the fields. It turns out that the fermion fields do not contribute at all to the superpotential terms. Actually the expression we get for the superpotential generalizes the well-known expression obtained by Komar.     

Synthesis and properties of As<Subscript>x</Subscript>Te<Subscript>100−x</Subscript> films prepared by plasma deposition via elemental As and Te

As_xTe_100?x chalcogenide films (where x = 30–80 at.%) were synthesized via direct interaction of arsenic and tellurium vapors into low-temperature non-equilibrium RF (40 MHz) plasma discharge at reduced pressure. Phase and structural evolution of As_xTe_100?x films were implemented by gradual changing of the ratio of the initial substances in the gas phase. The dependence of the films structure, surface morphology and optical properties on phase and chemical content has been studied.     

Liquid-liquid phase separation of a surfactant-solubilized membrane protein

Solubilization of membrane proteins requires surfactants, whose structural properties play a crucial role in determining the protein phase behavior. We show that ionization of a pH-sensitive surfactant, lauryldymethylamino-N-oxide, bound to the bacterial photosynthetic Reaction Center, induces protein phase segregation in micrometric "droplets." Liquid-liquid phase separation takes place in a narrow pH range, is promoted by increasing temperature, and vanishes by adding salt. After a fast initial droplet growth, the nearly arrested kinetics at a later stage leaves the system in a finely divided, long-lasting emulsified state.