Magneto-resistance in a lithography defined single constrained domain wall spin valve

We have measured domain wall magnetoresistance in a single lithographically constrained domain wall. An H-shaped Ni nano-bridge was fabricated by e-beam lithography with the two sides being single magnetic do- mains showing independent magnetic switching. The connection between the sides constraining the domain wall when the sides line up anti-parallel. The magneto-resistance curve clearly identifies the magnetic con- figurations that are expected from a spin valve-like structure. The value of the magneto-resistance at room temperature is around 0.1% or 0.4 ­. This value is shown to be in agreement with a theoretical formulation based on spin accumulation. Micromagnetic simulations show it is possible to reduce the size of the domain wall further by shortening the length of the bridge

Gaussian noise and time-reversal symmetry in non-equilibrium Langevin models

We show that in driven systems the Gaussian nature of the fluctuating force and time-reversibility are equivalent properties. This result together with the potential condition of the external force drastically restricts the form of the probability distribution function, which can be shown to satisfy time-independent relations. We have corroborated this feature by explicitly analyzing a model for the stretching of a polymer and a model for a suspension of non-interacting Brownian particles in steady flow.Comment: 6 pages, submitted to PR

Nonpolar resistive switching in Cu/SiC/Au non-volatile resistive memory devices

Amorphous silicon carbide (a-SiC) based resistive memory (RM) Cu/a-SiC/Au devices were fabricated and their resistive switching characteristics investigated. All four possible modes of nonpolar resistive switching were achieved with ON/OFF ratio in the range 10 6-10 8. Detailed current-voltage I-V characteristics analysis suggests that the conduction mechanism in low resistance state is due to the formation of metallic filaments. Schottky emission is proven to be the dominant conduction mechanism in high resistance state which results from the Schottky contacts between the metal electrodes and SiC. ON/OFF ratios exceeding 10 7 over 10 years were also predicted from state retention characterizations. These results suggest promising application potentials for Cu/a-SiC/Au RM

Bose-stimulated scattering off a cold atom trap

The angle and temperature dependence of the photon scattering rate for Bose-stimulated atom recoil transitions between occupied states is compared to diffraction and incoherent Rayleigh scattering near the Bose-Einstein transition for an optically thin trap in the limit of large particle number, N. Each of these processes has a range of angles and temperatures for which it dominates over the others by a divergent factor as N->oo.Comment: 18 pages (REVTeX), no figure

Analysis of cyt0kine gene expression in stimulated T cells of small children by semi-quantitative PCR

Only limited amounts of peripheral blood samples can be obtained from small children. Therefore, a polymerase chain reaction (PCR) aided analysis of cytokine gene expression by PBMC or T cells is a valuable tool. We present a combination of procedures to obtain an accurate estimation of the expression of the cytokines IL-4 and IFN-γ. This can be performed on T cells purified from blood samples of up to 5 ml in volume from children aged 0–4 years with allergic asthma and atopic dermatitis. This procedure includes multiple sampling of PCR products to determine the linear phase of the PCR; inter-experiment correction using a helper T-cell clone, expressing both IL-4 and IFN-γ; interpatient correction by comparing the expression of a housekeeping gene (HPRT); and finally the development of specific software to analyse densitometric data obtained by scanning photographs of agarose gels, separating PCR products. In this way it is possible to study cytokine gene expression from a very small amount of material

Kinetics of Particles Adsorption Processes Driven by Diffusion

The kinetics of the deposition of colloidal particles onto a solid surface is analytically studied. We take into account both the diffusion of particles from the bulk as well as the geometrical aspects of the layer of adsorbed particles. We derive the first kinetic equation for the coverage of the surface (a generalized Langmuir equation) whose predictions are in agreement with recent simulation results where diffusion of particles from the bulk is explicitly considered.Comment: 4 page

Divergence-type 2+1 dissipative hydrodynamics applied to heavy-ion collisions

We apply divergence-type theory (DTT) dissipative hydrodynamics to study the 2+1 space-time evolution of the fireball created in Au+Au relativistic heavy-ion collisions at $\sqrt{s_{NN}}=$200 GeV. DTTs are exact hydrodynamic theories that do no rely on velocity gradient expansions and therefore go beyond second-order theories. We numerically solve the equations of motion of the DTT for Glauber initial conditions and compare the results with those of second-order theory based on conformal invariants (BRSS) and with data. We find that the charged-hadron minumum-bias elliptic flow reaches its maximum value at lower $p_T$ in the DTT, and that the DTT allows for a value of $\eta/s$ slightly larger than that of the BRSS. Our results show that the differences between viscous hydrodynamic formalisms are a significant source of uncertainty in the precise extraction of $\eta/s$ from experiments.Comment: v4: 29 pages, 12 figures, minor changes. Final version as published in Phys. Rev.

Momentum of an electromagnetic wave in dielectric media

Almost a hundred years ago, two different expressions were proposed for the energy--momentum tensor of an electromagnetic wave in a dielectric. Minkowski's tensor predicted an increase in the linear momentum of the wave on entering a dielectric medium, whereas Abraham's tensor predicted its decrease. Theoretical arguments were advanced in favour of both sides, and experiments proved incapable of distinguishing between the two. Yet more forms were proposed, each with their advocates who considered the form that they were proposing to be the one true tensor. This paper reviews the debate and its eventual conclusion: that no electromagnetic wave energy--momentum tensor is complete on its own. When the appropriate accompanying energy--momentum tensor for the material medium is also considered, experimental predictions of all the various proposed tensors will always be the same, and the preferred form is therefore effectively a matter of personal choice.Comment: 23 pages, 3 figures, RevTeX 4. Removed erroneous factor of mu/mu_0 from Eq.(44

Spin-orbit induced mixed-spin ground state in RRNiO3_3 perovskites probed by XAS: new insight into the metal to insulator transition

We report on a Ni L$_{2,3}$ edges x-ray absorption spectroscopy (XAS) study in $R$NiO$_3$ perovskites. These compounds exhibit a metal to insulator ($MI$) transition as temperature decreases. The L$_{3}$ edge presents a clear splitting in the insulating state, associated to a less hybridized ground state. Using charge transfer multiplet calculations, we establish the importance of the crystal field and 3d spin-orbit coupling to create a mixed-spin ground state. We explain the $MI$ transition in $R$NiO$_3$ perovskites in terms of modifications in the Ni$^{3+}$ crystal field splitting that induces a spin transition from an essentially low-spin (LS) to a mixed-spin state.Comment: 4 pages, 4 figures, accepted as PRB - Rapid Comm. Dez. 200