Talbot effect of a high-density grating under femtosecond laser illumination

The Talbot effect of a high-density grating under femtosecond laser illumination is analyzed with rigorous electromagnetic theory which is based on the Fourier decomposition and the rigorous coupled-wave analysis (RCWA). Numerical simulations show that the contrast of the Talbot images steadily decreases as the transmitted femtosecond laser pulses propagate forward and with wider spectrum width of the femtosecond laser pulses. The Talbot images of high-density gratings have much higher sensitivity of the spectrum widths of the incident laser pulses than those of the traditional low-density gratings. In experiments, the spectrums and the pulse widths of the incident pulses are measured with a frequency-resolved optical grating (FROG) apparatus. The Talbot images are detected by using a Talbot scanning near-field optical microscopy (Talbot-SNOM) technique, which are in coincidence with the numerical simulations. This effect should be useful for developing new femtosecond laser techniques and devices. (C) 2008 Elsevier B.V. All rights reserved.

Magnetic field modulated direct overwrite with pulsed laser irradiation for TbFeCo magneto-optical disks

WE have designed a dual-beam magneto-optical (MO) storage system to test the dynamic storage properties of MO disks. The characteristics of this dual-beam system are demonstrated. Magnetic field modulated direct overwrite, which is a promising technique for highspeed MO storage, is realized on TbFeCo MO disks with this dual-beam MO system. The effect of light intensity, magnetic field intensity, and linear velocity of the disk and the modulating frequency variation on carrier-to-noise ratio is investigated. (C) 1997 Society of Photo-Optical Instrumentation Engineers.

Effect of surface plasmon resonance in TiO2/Au thin films on the fluorescence of self-assembled CdTe QDs structure

23rd Congress of the International Comission for Optics (ICO 23)

The effect of timing of tagging on streamer-tag recapture rates for American lobster (Homarus americanus)

Streamer tags are commonly used to study the ecology and population biology of the American lobster (Homarus americanus). Aquarium observations suggest that streamer tag loss, either through tag-induced mortality or tag shedding, is related to the molt stage of the lobster at the time of tagging, and the molting event itself. Tag-induced mortality, where lobsters did not molt, occurred within eleven and sixteen days following tagging for lobsters tagged in postmolt (4%) and late premolt (10%) stages, respectively; whereas no lobsters tagged in early premolt or intermolt stages died. Taginduced mortality at time of molting was observed for lobsters tagged in late premolt stage (11%), and tag shedding was observed for lobsters tagged both in early (25%) and late premolt (11%) stages, but was significantly higher (P=0.014) for lobsters tagged in early premolt stages. Autopsies revealed that lobsters died mainly of organ perforations (hepato-pancreas and pericardial sac) following the tagging process, and rupture of the dorsal thoraco-abdominal membrane during the molting process. The total tag loss was estimated at 4% for lobsters tagged after molting, and 27% and 31% for lobsters tagged in early and late premolt stages, respectively. There was no tag loss for lobsters tagged in the intermolt stage during four months of laboratory observations (July−October). To minimize streamer tag loss, lobsters should be tagged during the intermolt or postmolt stage. Based on field studies, recapture rates for lobsters tagged in premolt stage are always lower than those of lobsters tagged in postmolt stage. Furthermore, recapture rates during the second year, for lobsters that molt in the year following tagging, were drastically reduced, and no lobster was recaptured after four years at large. Finally, to account for tag loss during the first year at large, a minimal adjustment of 24.9% (SD 2.9%) and 4.4% (SD 1.6%) for the recapture rate of lobsters tagged immediately before and after the molting season, respectively, is recommended. Adjustments beyond one year at large are not recommended for the American lobster at this time.

Effect of blade tip geometry on the tip leakage flow in axial turbine cascades

The phenomenon of tip leakage has been studied in two linear cascades of turbine blades. The investigation includes an examination of the performance of the cascades with a variety of tip geometries. The effects of using plain tips, suction side squealers, and pressure side squealers are reported. Traverses of the exit flow field were made in order to determine the overall performance. A method of calculating the tip discharge coefficients for squealer geometries is put forward. In linking the tip discharge coefficient and cascade losses, a procedure for predicting the relative performance of tip geometries is developed. The model is used to examine the results obtained using the different tip treatments and to highlight the important aspects of the loss generation process.

Field emission from tetrahedrally bonded amorphous carbon

The field emission behaviour of a series of Tetrahedrally Bonded Amorphous Carbon (ta-C) films has been measured. The films were produced using a Filtered Cathodic Vacuum Arc System. The threshold field for emission and current densities achievable have been investigated as a function of sp3/sp2 bonding ratio and nitrogen content. Typical as-grown undoped ta-C films have a threshold field of order 10-15 V/μm and optimally nitrogen-doped films exhibit fields as low as 5 V/μm. The emission as a function of back contact and front surface condition has also been considered and shows that the back contact has only a minor effect on emission efficiency. However, after etching in either an oxygen or hydrogen plasma, the films show a marked reduction in threshold field, down to as low as 2-3 V/μm, and a marked improvement in emission site density.

Low field electron emission from nanoclustered carbon grown by cathodic arc

Nanocluster carbon films grown using a cathodic arc process at room temperature in the presence of background gases such as helium are found to be good electron emitters. The variation in the surface morphology and the corresponding emission characteristics of the films with change in helium partial pressure (5×10-4 to 50 Torr) during film growth are reported. The effect of helium partial pressure on clustering was studied for films grown at nitrogen partial pressures of 10-4 and 10-3 Torr. The surface morphology of the films varied from smooth through clusters (with sizes 50-200 nm) to fibrous films. The threshold field varied from 1 to 10 V/μm for an emission current density 1 μA/cm2.

Analytical model for the 3D-RESURF effect

This paper presents an analytical model for the determination of the basic breakdown properties of three-dimensional (3D)-RESURF/CoolMOS/super junction type structures. To account for the two-dimensional (2D) effect of the 3D-RESURF action, 2D models of the electric field distribution are developed. Based on these, expressions are derived for the breakdown voltage as a function of doping concentration and physical dimensions. In addition to cases where the drift regions are fully depleted, the model developed is also applicable to situations involving drift regions which are almost depleted. Accuracy of the analytical approach is verified by comparison with numerical results obtained from the MEDICI device simulator.

Physical properties of some novel nematic bimesogens for the flexoelectric effect

In a chiral nematic liquid crystal, the flexoelectric effect consists of a fast and linear coupling with an applied electric field. One difficulty to overcome is the unwinding of the helix that occurs at higher fields due to dielectric coupling. The use of bimesogens, which possess very low molecular dielectric anisotropy can improve flexoelectric characteristics. New bimesogen compounds have recently been synthesised that exhibit switching angles of 45° for applied fields of about 9 V.μm-1. In this paper, results from dielectric, electro-optic and dynamic light scattering measurements are reported for the new bimesogenic mixture. The dielectric anisotropy Δε changes sign with temperature and its values range between -0.2 and 0.3 for the temperature range studied. For Δε weakly positive, no electric field Freedericksz transition could be induced but Williams domains are observed instead. The large decrease in the bend elastic constant to viscosity coefficient ratio is attributed to a large increase in the bend viscosity coefficient. © 2001 OPA (Overseas Publishers Association) N.V. Published by license under the Gordon and Breach Science Publishers imprint, a member of the Taylor & Francis Group.

Secondary flow near an undulatory surface induced by wall blocking effect

Prandtl's secondary mean motions of the second kind near an undulating surface were explained in terms of turbulent blocking effect and kinematic boundary conditions at the surface, and its order of magnitude was estimated. Isotropic turbulence is distorted by the undulating surface of wavelength λ and amplitude h with a low slope, so that h « λ. The prime mechanism for generating the mean flow is that the far-field Isotropic turbulence is distorted by the non-local blocking effect of the surface to become anisotropic axisymmetric turbulence near the surface with principal axis that is not aligned with the local curvature of the undulation. Then the local analysis can be applied and the mechanism is similar to the mean flow generation mechanism for homogeneous axisymmetric turbulence over a planer surface, i.e. gradients of the Reynolds stress caused by the turbulent blocking effect generate the mean motions. The results from this simple analysis are consistent with previous exact analysis in which the effects of curvature are strictly taken into account. The results also qualitatively agree with flow visualization over an undulating surface in a mixing-box.

Simulated superior performance of superjuction bipolar transistors

This paper presents for the first time an investigation and comparison of the superjunction IGBT (SJBT) as proposed in [1,2] and the current state of art Field Stop IGBT [3,4]. Simulation results indicate the superior performance of the superjunction IGBT under switching conditions. For the same conditions, at a collector current density of 100A/cm2 and on-state voltage 1.6 V the switching off losses for a SJBT and Field-Stop IGBT are 1 and 4.5 mJ/cm 2 respectively. © 2006 IEEE.

Effect of electric stimulation on heart beat and body muscle in fish

The effect of AC and DC electric stimulations on the heart-rate and the entire body of Heteropneustis fossillis, Tilapia mossambica and Macrobrachium rosenbergii were studied and presented in kymograph tracings. The reaction of spinal cord in Puntius ticto, Heteropneustis fossilis and Tilapia mossambica to D. C. field was observed to find out its role in electric shocks. A test-check of the electrical resistance of a few species was also conducted. The effect of D. C. and A.C. on the body muscle was found to be the same as that in the case of frog. Different degrees of cardiac slowing were observed in AC and DC. Unbalanced galvanotropic movements were also noticed in spinal fishes.

On the behaviour of marine crustaceans in an electrical field of alternating current

The minimum flow of current essential to produce electro-narcosis and fixation in marine crustaceans, Metapenaeus affinis, Parapenaeopsis stylifera, Panulirus ornatus and Neptunus sanguinofentus in an AC field of specific strength varied with the lengths of animals tested, except in case of the last one where the increase in size of animals showed no significant effect on the effective period for different reactions. M. affinis in interrupted AC required threshold pulses for narcosis and fixation, which varied inversely with the length of the organism. Animals subjected to current of higher effective period required longer time for recovery in interrupted AC of 50 c/s. The period for narcosis and recovery of M. affinis did not vary significantly with repeated stimulations on the same organism.

On the selection of effective impulse frequencies for specific movements of fish in an electrical field

In order to determine effective pulse limits for Salmo irideus, Cyprinus carpio, Gasterosteus aculeatus, Tinca tinca, Salmo fario and ldus melanotus in impulse D. C. for galvanotaxis and galvanonarcosis, studies were carried out with rectangular and square impulses. The narcotizing pulse limits remained constant for each variety in an impulse D. C. of specific wave form. The anodic effect of fishes was better in square wave form and varied with the variation of temperature of surrounding medium. S. fario reacted better when placed parallel to the lines of electrical force. Transversal escape movement occured when the axis of fish body was at right angles to the direction of current.

Reaction of fishes to the underwater A.C. field

A comparative study on the effect of A.C. field on Puntius ticto, Heteropneustis fossilis and Tilapta mossambica was carried out using a slowly rising field intensity. Well defined reactions appeared in the species of fish with slight specific variations, depending on their orientation in the electrical field, on reaching the field intensity to specific value. These reactions can be distinguished as first reaction, when the fish perceive the surrounding field, jerky swimming when parallel to the current lines (longitudinal oscillotaxis), the static position finally adopted by the fish sooner or latter depending on the potential gradient (transverse oscillotaxis), and a state of muscular rigidity (tetanus). After switching off the current, a hypnotic condition prevailed in the treated fishes before returning to their normal swimming condition. The orientation of fish body in the field had an important bearing on the behaviour reactions and current thresholds necessary for those reactions. Initial reaction, jerky swimming between electrodes and hypnosis after stoppage of current appeared in fishes earlier when the fish body was in parallel to the current lines, whereas fishes responded to transverse oscillotaxis quickly when perpendicular to current lines.