Effect of Surface Condition of Electrode on the Surface Melting of Material by Laser-Guided Micro-Arc Discharge

This paper studies the surface melting in the atmosphere by YAG laser-guided micro-arc discharge. In three kinds of surface conditions (free, oiled, and polyethylene covered), we try to control the diameter and the power density of discharge pit. It is found that the power density of 3 x 10(6) W/cm(2) of discharge pit on the oiled surface is moderate to form the melted layer thicker than that of the others, adapting to strengthen the surface of material, and the power density of 1.07 x 10(7) W/cm(2) of discharge pit on the polyethylene-covered surface is highest to form the deepest discharge pit among them, adapting to remove the material.

A note on the heat-transfer to nonspherical particles from plasma

Heat transfer from plasma to a nonspherical partical in the free-molecular regime is studied in the present paper under thin plasma sheath condition. Analytical expressions for the floating potential charge and heat fluxes of an ellipsoid particle of revolution are derived and curves are given for key parameters for arbitrary plasma flow direction. On the basis of these results, an equivalent sphere with the same surface area as the nonspherical particle is suggested to be used for calculating the total heat flux of nonspherical particle in engineering application with acceptable accuracy. Furthermore, the effects of particle rotation, which occurs in most aerosol systems, on the heat transfer are also discussed.

Metal-semiconductor-metal ultraviolet photodetector based on GaN

A metal-semiconductor-metal (MSM) ultraviolet photodetector has been fabricated using unintentionally doped n-GaN films grown on sapphire substrates. Its dark current, photocurrent under the illumination with lambda = 360 nm light, responsivity, and the dependence of responsivity on bias voltage were measured at room temperature. The dark current of the photodetector is 1.03 nA under 5 V bias, and is 15.3 nA under 10 V bias. A maximum responsivity of 0.166 A/W has been achieved under the illumination with lambda = 366 nm light and 15 V bias. It exhibits a typical sharp band-edge cutoff at the wavelength of 366 nm, and a high responsivity at the wavelength from 320 nm to 366 nm. Its responsivity under the illumination with lambda = 360 nm light increases when the bias voltage increases.

Investigation on acceleration response of fiber optic mandrel hydrophone

The acceleration response of fiber optic mandrel hydrophone is studied based on the theory of elastic dynamics in this paper. For the first time the influence of the optical fiber on the acceleration response is taken into consideration. And the derivation of the radial deformation of the mandrel is presented in details. The acceleration response is evaluated both theoretically and experimentally and the results are in good agreement.

Design of spectrometer based on volume phase grating for near infrared range

In order to design and fabricate a spectrometer for the infrared range widely used in the different applications, Volume Phase Grating (VPG) with. low Polarization Dependence Loss (PDL) and high efficiency has been adopted as the dispersion element. VPG is constructed by coating an optical substrate with a thin film of dichromated. gelatin and exposing the film to two mutually coherent laser beams to form index modulation. The diffraction efficiency for a VPG is governed by Bragg effects. The depth (d) and index modulation contrast of the grating structure control the efficiency at which the light is diffracted when the Bragg condition is satisfied. Gradient index lens with high performance and low aberration are used as collimating system instead of standard lens. The spot diagrams and MTF curve of the collimating lens are shown in the paper. The receive system is InCaAs photodiode (PD) array including 512 pixels with 25 mum pitch. The spectrum resolution of the spectrometer reaches to 0.2nm and wavelength accuracy is 40pm.

Research on storing raster metadata in spatial database

Storage of raster metadata is a key topic in spatial database. Although there are a few of abstract standards on raster metadata, there is not implement standard about it. This paper concludes three storage models implemented in current spatial databases and discusses their advantages and disadvantages. After that analyzing, the paper proposes a mixed storage method which is used the relational table to store structured metadata and used XML to store non-structured metadata, and gives its implementation solution. © 2010 IEEE.