Amplitude-equation formalism for four-wave-mixing geometry with transmission gratings

An amplitude equation is derived for a four-wave-mixing geometry with nearly counterpropagating, mutually incoherent, nondiffracting pump beams, spatially overlapping in a photorefractive material with a nonlocal response. This equation extends the earlier linear two-dimensional theory to the weakly nonlinear regime. The analysis also starts from a more complete equation for the photorefractive effect, which leads to the prediction of novel effects especially apparent in the nonlinear regime. Precise predictions for the spatiotemporal behavior of the grating amplitude in the nonlinear regime are presented. The range of validity of the amplitude equation is studied. The characteristics of the instability in the nonlinear regime are analyzed through a front-selection analysis

A vapor barrier for cold testing printed circuit cards

Cold testing method prevents formation of frost on printed circuit boards and part holders during testing at sub-zero temperatures. Freon permits rapid attainment of the required testing temperature

Dual pathway spindle assembly increases both the speed and the fidelity of mitosis

Roughly half of all animal somatic cell spindles assemble by the classical prophase pathway, in which the centrosomes separate ahead of nuclear envelope breakdown (NEBD). The remainder assemble by the prometaphase pathway, in which the centrosomes separate following NEBD. Why cells use dual pathway spindle assembly is unclear. Here, by examining the timing of NEBD relative to the onset of Eg5-mEGFP loading to centrosomes, we show that a time window of 9.2 ± 2.9 min is available for Eg5-driven prophase centrosome separation ahead of NEBD, and that those cells that succeed in separating their centrosomes within this window subsequently show .3-fold fewer chromosome segregation errors and a somewhat faster mitosis. A longer time window would allow more cells to complete prophase centrosome separation and further reduce segregation errors, but at the expense of a slower mitosis. Our data reveal dual pathway mitosis in a new light, as a substantive strategy that increases both the speed and the fidelity of mitosis

Transition to an oscillator for double phase-conjugate mirror

Summary form only given. Some of the novel quantified characteristics for double phase conjugate mirrors are analysed including the effects of the nonlinearity on the critical dynamics (approach to saturation) and on the spatial distribution of the grating (large scale distortion of the beams and conjugation fidelity) and sensitivity to noise (seeding). The approach used also clarifies the question of linear instability and predicts a new transition to an oscillatory regime

The Influence of ZnO Layer Thickness on the Performance and Electrical Bias Stress Instality in ZnO Thin Film Transistors

University of Buea supported the first author during the writing of this manuscript Open access articleThin Film Transistors (TFTs) are the active elements for future large area electronic applications, in which low cost, low temperature processes and optical transparency are required. Zinc oxide (ZnO) thin film transistors (TFTs) on SiO2/n+-Si substrate are fabricated with the channel thicknesses ranging from 20 nm to 60 nm. It is found that both the performance and gate bias stress related instabilities of the ZnO TFTs fabricated were influenced by the thickness of ZnO active channel layer. The effective mobility was found to improve with increasing ZnO thickness by up to an order in magnitude within the thickness range investigated (20 – 60 nm). However, thinner films were found to exhibit greater stability in threshold voltage and turn-on voltage shifts with respect to both positive and negative gate bias stress. It was also observed that both the turn on voltage (Von) and the threshold voltage (VT) decrease with increasing channel thickness. Moreover, the variations in subthreshold slope (S) with ZnO thickness as well as variations in VT and Von suggest a possible dependence of trap states in the ZnO on the ZnO thickness. This is further correlated by the dependence of VT and Von instabilities with gate bias stress

Orientation and solvatochromism of dyes in liquid crystals.

The orientation and solvatochromism of some dye molecules in a liquid crystal have been investigated. Interactions with the host and the structure of the dye molecule affect the macroscopic alignment of dichroic dye molecules in a liquid crystal: It was observed that some dye molecules show a large bathochromic shift of their absorption maxima in the liquid crystal host relative to the situation in isotropic solvents. It is suggested that this is due to the occurrence of a much weaker reaction field in the anisotropic, rigid host. These dye molecules show little or no apparent order in the anisotropic host despite the observation of a reduction in the electro optic switching time when the dye is present. The highest degree of macroscopic alignment was observed for a merocyanine compound, which showed the smallest solvatochromic shift in the liquid crystal host. These results are discussed in terms of the steric, dipolar and hydrogen bond interactions between the guest and the host

Domain Coarsening in Systems Far from Equilibrium

The growth of domains of stripes evolving from random initial conditions is studied in numerical simulations of models of systems far from equilibrium such as Rayleigh-Benard convection. The scaling of the size of the domains deduced from the inverse width of the Fourier spectrum is studied for both potential and nonpotential models. The morphology of the domains and the defect structures are however quite different in the two cases, and evidence is presented for a second length scale in the nonpotential case.Comment: 11 pages, RevTeX; 3 uufiles encoded postscript figures appende

Full scale visualization of the wing tip vortices generated by a typical agricultural aircraft

The trajectories of the wing tip vortices of a typical agricultural aircraft were experimentally determined by flight test. A flow visualization method, similar to the vapor screen method used in wind tunnels, was used to obtain trajectory data for a range of flight speeds, airplane configurations, and wing loadings. Detailed measurements of the spanwise surface pressure distribution were made for all test points. Further, a powered 1/8 scale model of the aircraft was designed, built, and used to obtain tip vortex trajectory data under conditions similar to that of the full scale test. The effects of light wind on the vortices were demonstrated, and the interaction of the flap vortex and the tip vortex was clearly shown in photographs and plotted trajectory data

Effect of phonon scattering by surface roughness on the universal thermal conductance

The effect of phonon scattering by surface roughness on the thermal conductance in mesoscopic systems at low temperatures is calculated using full elasticity theory. The low frequency behavior of the scattering shows novel power law dependences arising from the unusual properties of the elastic modes. This leads to new predictions for the low temperature depression of the thermal conductance below the ideal universal value. Comparison with the data of Schwab et al. [Nature 404, 974 (2000)] suggests that surface roughness on a scale of the width of the thermal pathway is important in the experiment.Comment: 6 pages, 3 figure

Probing the Upper Scorpius mass function in the planetary-mass regime

We present the results of a deep ZYJ near-infrared survey of 13.5 square degrees in the Upper Scorpius (USco) OB association. We photometrically selected ~100 cluster member candidates with masses in the range 30-5 Jupiters, according to state-of-the-art evolutionary models. We identified 67 ZYJ candidates as bona-fide members, based on complementary photometry and astrometry. We also extracted five candidates detected with VISTA at YJ-only. One is excluded using deep optical z-band imaging, while two are likely non-members, and three remain as potential members. We conclude that the USco mass function is more likely decreasing in the planetary-mass regime (although a flat mass function cannot yet be discarded), consistent with surveys in other regions.Comment: Accepted by MNRAS, 10 pages, 4 figures, 4 tables (2 electronic tables). New version with updated figure3 where the (Z-J,Z) colour-magnitude diagram is include