Self-Cleaning Transparent Dust Shields for Protecting Solar Panels and Other Devices

The development of transparent flexible dust shields using both single- and three-phase electrodynamic shields is reported here for possible application on Mars and Earth to minimize obscuration of solar panels from the deposition of dust. The electrodynamic screens (EDS) are made of transparent plastic sheets, such as polyethylene terephthalate (PET) for its UV radiation resistance, and a set of parallel conducting electrodes made of transparent indium tin oxide (ITO) embedded under a thin transparent film. The basic principle of EDS operation, a simplified mathematical model of particle trajectories, the experimental setup used for testing the screens, and their dust removal efficiencies (DRE) are described. Results of our measurements on dust removal efficiency of EDS as a function of the particle size and electrostatic charge distributions of Mars simulant dust are reported. The results show that the EDS technology has a strong potential for protecting solar panels against dust hazards with DRE higher than 80% for dust. The power requirements will be approximately 10 watts per square meter of the panels when cleaning is needed.     

The effect of fluid inertia on the film pressure between two axially oscillating parallel circular plates with a viscoelastic lubricant

A viscoelastic incompressible fluid between two parallel circular plates separated by a small distance with sinusoidal axial vibration of the top plate including fluid inertia terms was considered. Flow phenomena were characterized by non-dimensional parameters such as the Reynolds number Re and the elastic number S. An iteration method was used to solve the non-linear equations. The effects of Re and S on the fluid pressure were studied.     

Dispersion in unsteady Couette–Poiseuille flows

The paper presents the longitudinal dispersion of passive contaminant released in an incompressible viscous fluid flowing between two infinite parallel flat walls, in which the flow is driven by the application of both periodic pressure gradient and the oscillation of upper plate in its own plane with a constant velocity. A finite difference implicit scheme has been adopted to solve the unsteady convection-diffusion equation for all time period based on Aris method of moments. The dispersion coefficients are obtained for three different flow situations: steady, periodic and the combined effect of steady and periodic Couette–Poiseuille flows, separately. The results show that oscillation of upper plate produces more dispersion than the pulsation of pressure gradient and their combined action leads to a further increase of dispersion. Also plate oscillation has stronger effect on velocity distribution and on dispersion coefficient than the pressure pulsation. There is a remarkable difference in the behaviour of dispersion coefficient depending on whether the ratio of two frequencies arising from the oscillations of pressure gradient and the upper plate possesses a proper fraction or not.     

Effects of Powder Velocity and Contact Materials on Tribocharging of Polymer Powders for Powder Coating Applications

Electrostatic powder deposition using corona charging is widely used in a plethora of industrial applications. Disadvantages of this technique are back corona onset and the Faraday penetration limitation. Another method to charge powders is to use tribochargers. Tribocharging depends upon the work function difference between the contacting materials and generates bipolarly charged particles. In this study, acrylic and epoxy powders were fluidized and charged by passing through stainless steel, copper, aluminum, and polycarbonate static mixers, respectively. The particle velocity and powder flow rate were varied to determine their effect on the net charge-to-mass ratio (Q/M) acquired by the powders. The Q/M increased rapidly with velocities between 1.5 to 2.5 m/s and stabilized for higher velocities but decreased with increasing powder flow rate at a constant velocity. The net positive or negative charge on each powder was determined to be dependant on the charger material. The use of an aluminum charger (net negative charge) in combination with a PTFE finger nozzle (net positive charge) resulted in a net powder Q/M of - 0.05 μC/g. The generation of an ion-free powder cloud with high bipolar charge but overall charge density of almost zero is anticipated to provide a better coverage of recessed areas.     

Small-angle neutron scattering investigations on sintering behavior of combustion synthesized La0.8Sr0.2CrO3

Pore morphology of La0.8Sr0.2CrO3 (LSC) powder compacts, sintered between 1200 degrees C and 1450 degrees C for a fixed time, has been characterized by small-angle neutron scattering (SANS) in the scattering wave vector 'q' range, 0.003-0.17 nm(-1) of a double crystal based instrument. Scattering profile of green compact exhibits fractal scaling at two regions of 'q' with magnitudes of fractal dimensionality 1.8 and 2.36. Scattering profiles of sintered pellets have been modeled assuming a random distribution of near spherical pores in the solid matrix. Estimated pore size distributions of sintered pellets indicate decrease in pore volume has taken place by progressive elimination of smallest pores and growth of relatively larger pores with increasing sintering temperature. SANS results are supplemented by light scattering measurement and TEM image of powder and SEM image of the fracture surface of sintered pellet.     

Characterization of Cenospheres Collected from Ash-pond of a Super Thermal Power Plant

Abstract

As received cenospheres obtained from Rihand Super Thermal Power Plant, Uttar Pradesh,India, were processed using sink float method. The solvent system consisted of 1% TEALS (Triethanolamine lauryl sulphate) in acetone. Further flotation of the float with the same solvent system led to another float. Various fractions thus obtained were characterized in respect of their chemical, mineralogical, and morphological properties. The float obtained from second flotation was richer in cenospheres, which are round and within a small size range. The residues obtained were broken spheres. Phase-mineralogical analysis has revealed mullite enrichment in the floats. Chemical composition of the various fractions does not indicate high concentration of harmful elements. SEM analysis leads to the conclusion that the cenospheres are essentially open-pore type. Based on such experimental observations, various potential uses have been suggested.     

Prospects of β-SiC Based IMPATT Oscillator for Application in THz Communication and Growth of β-SiC p-n Junction on Ge Modified Si <100> Substrate to Realize THz IMPATTs

The prospects of p+ n n+ cubic Silicon Carbide (3C-SiC/ß-SiC) based IMPATT diode as a potential solid-state Terahertz source is studied for the first time through a modified generalized simulation scheme. The simulation predicts that the device is capable of generating a RF power output of 63.0 W at 0.33 THz with an efficiency of 13%. The effects of parasitic series resistance on the device performance and exploitable RF power level are further simulated. The studies clearly establish the potential of 3C-SiC as a base semiconductor material for high-power THz IMPATT device. Based on the simulation results an attempt has been made to fabricate β- SiC based IMPATT devices in THz region. Single crystalline, epitaxial 3C-SiC films are deposited on silicon (Si) <100> substrates by Rapid Thermal Chemical Vapour Deposition (RTPCVD) at a temperature as low as 800 0C using a single precursor methylsilane, which contains Si and C atoms in the same molecule. No initial surface carbonization step is required in this method. A p-n junction with n-type doping conc. of 4 x 10^24 m-3 (which is similar to the simulated design data) has been grown successfully and the characterization of the grown 3C-SiC film is reported in this paper. It is found that the inclusion of Ge improves the crystal quality and reduces the surface roughness.     

Prospects of aβ-SiC based IMPATT oscillator for application in THz communication and growth of a β-SiC p-n junction on a Ge modified Si 《100》 substrate to realize THz IMPATTs

The prospects ofa p<'+>nn<'+> cubic silicon carbide (3C-SiC/β-SiC)based IMPATT diode as a potential solidstate terahertz source is studied for the first time through a modified generalized simulation scheme.The simulation predicts that the device is capable of generating an RF power output of 63.0 W at 0.33 THz with an efficiency of 13%.The effects of parasitic series resistance on the device performance and exploitable RF power level are further simulated.The studies clearly establish the potential of 3C-SiC as a base semiconductor material for a high-power THz IMPATT device.Based on the simulation results,an attempt has been made to fabricate β-SiC based IMPATT devices in the THz region.Single crystalline,epitaxial 3C-SiC films are deposited on silicon (Si)(100)substrates by rapid thermal chemical vapour deposition (RTPCVD)at a temperature as low as 800℃ using a single precursor methylsilane,which contains Si and C atoms in the same molecule.No initial surface carbonization step is required in this method.A p-n junction with an n-type doping concentration of 4×10<'24> m<'-3> (which is similar to the simulated design data)has been grown successfully and the characterization of the grown 3C-SiC film is reported in this paper.It is found that the inclusion of Go improves the crystal quality and reduces the surface roughness.     

Theoretical and experimental investigation of the fast- andslow-scale instabilities of a DC-DC converter

We use an exact formulation based on nonlinear maps to investigate both the fast-scale and slow-scale instabilities of a voltage-mode buck converter operating in the continuous conduction mode and its interaction with a filter. Comparing the results of the exact model with those of the averaged model shows the shortcomings of the latter in predicting fast-scale instabilities. We show the impact of parasitics on the onset of chaos using a high-frequency model. The experimentally validated theoretical results of this paper provide an improved understanding of the dynamics of the converter beyond the linear regime and this may lead to less conservative control design and newer applications