MULTIDISCIPLINARY FLOW/THERMAL AND INDUCED STRESSES IN CONVECTIVELY COOLED STRUCTURES

A multidisciplinary finite element methodology with stabilizing features to prevent undue oscillatory solution behavior for the velocities, pressure, and temperature fields and which subsequently permits computations of the resulting thermal loads for the associated stress analysis is described for convectively cooled structures subjected to high-intensity localized heating. Of particular interest are the influences of coolants that serve to cool the structure whose exposed skin is permitted to radiate to outer space. Of the three coolants investigated - namely, liquid hydrogen, water, and liquid sodium - it is observed that the liquid sodium serves as an effective coolant that is consistent with past related studies. The resulting thermally induced stresses arising from the assumption of elastic and a materially nonlinear elastoplastic model are also evaluated. The nonlinear model seems more realistic because of the situations encountered at high temperatures and as expected yields lower values of the stresses. Illustrative examples of a flat skin structure and a curved skin geometry representing the cowl leading edge are analyzed for the flow/thermal and induced stresses.     

Intermittent Water Supply under Water Scarcity Situations

Abstract

This paper describes the recently developed ‘Guidelines for the design and control of intermittent water distribution systems’. These guidelines outline a new approach to the design of urban water distribution systems for developing countries in order to maintain adequate and equitable supplies under the common conditions of water resource shortage. The guidelines are novel in that they recognise the reality of intermittent supply and hence provide new methods of analysis and design, appropriate for such systems. Design objectives specifically tailored to intermittent systems are developed and drive the design process. These objectives are expressed in terms of equity in supply, adequate pressure at water connections and duration or time of supply that are convenient to the consumers. The modifications required to model such systems have been incorporated into a new network analysis simulation tool coupled with an optimal design tool.     

Robust contour tracking of nonholonomic mobile robots via adaptive velocity field motion planning scheme

This paper aims at designing a contour tracking scheme based on an adaptive velocity field formulation, for the case of uncertain nonholonomic (differential drive) mobile robots, with its dynamic controller. First, to handle kinematic uncertainties that deviate the map of the velocity field into wheel velocities, a linear parameterization of the uncertain Jacobian operator is proposed to synthesize an adaptive kinematic controller that shapes correctly the velocity field. Then, a robust model‐free dynamic controller is proposed to compensate in finite time for uncertain dynamics and disturbances, enforcing the kinematic reference. Finally, a representative simulation study is discussed to show the reliability of the proposed scheme.     

Practical compact modeling approaches and options for sub-0.1 μm CMOS technologies

This paper attempts to provide a general overview and guideline to develop a practical model for CMOS devices in the sub-0.1μm generations. It starts by giving an overview of the different modeling options including the charge-based approach, the surface potential based approach, and the conductance-based approach. Their relative advantages and weaknesses will be discussed. The evolution of the BSIM models from its first generation to the most recent release will be used as an example for the development of a practical device model. It will be followed by a discussion on how the accelerated technology development may impact the traditional modeling methodologies. A new paradigm to incorporate modern software engineering methodology to shorten model development cycle will be presented.     

Mechanism of charge recombination and IPCE in ZnO dye‐sensitized solar cells having I−/I and Br−/Br redox couple

The influence of intensity and wavelength variation on the solar cell parameters of two different ZnO‐based liquid state DSSCs named as Cell (A) ZnO/EosinY/LiI and Cell (B) ZnO/EosinY/LiBr was studied. It was found that V_oc and I_sc depend logarithmically and linearly on light flux, respectively, which indicates that light absorption and carrier diffusion do not limit the solar cell efficiency. The data was analyzed to ascertain the charge recombination mechanism between conduction band electrons and the electrolytes. The regeneration of dye due to I⁻/I₃ and Br⁻/Br redox couple was examined by studying the wavelength dependence of IPCE. An estimation of series and shunt resistance is made using two methods: (i) different illumination method (ii) single I–V curve, for the two cells in order to understand the role of the electrolyte in controlling the solar cell parameters. Copyright © 2010 John Wiley & Sons, Ltd.     

Grounded capacitor based grounded and floating inductancesimulation using current conveyors

Grounded and floating inductance simulation using current conveyors and needing grounded capacitors has been considered. Some grounded and floating inductance schemes are extracted from recently published current mode biquads. A new realisation using two dual output current conveyors, a grounded capacitor and two resistors is presented     

Monolithic Perovskite/Silicon Tandems with >28% Efficiency: Role of Silicon-Surface Texture on Perovskite Properties

Textured silicon wafers used in silicon solar cell manufacturing offer superior light trapping, which is a critical enabler for high-performance photovoltaics. A similar optical benefit can be obtained in monolithic perovskite/silicon tandem solar cells, enhancing the current output of the silicon bottom cell. Yet, such complex silicon surfaces may affect the structural and optoelectronic properties of the overlying perovskite films. Here, through extensive characterization based on optical and microstructural spectroscopy, it is found that the main effect of such substrate morphology lies in an altering of the photoluminescence response of the perovskite, which is associated with thickness variations of the perovskite, rather than lattice strain or compositional changes. With this understanding, the design of high-performance perovskite/silicon tandems is rationalized, yielding certified power conversion efficiencies of >28%.     

Iodization of antimony thin films: XRD, SEM and optical studies of nanostructured SbI3

Antimony films of thicknesses of 25, 40 and 80 nm deposited using thermal evaporation technique were annealed at 200 °C for 6 h. Programmed iodization was carried out at room temperature for periods ranging from 5 min to 9 h on both as-deposited and annealed films. X-ray diffraction studies on iodized films reveal that antimony tri-iodide nanoparticles grow only on annealed antimony films. Surface morphology as revealed through SEM consists of antimony and antimony tri-iodide nanoparticles are 25 nm and 1 μm, respectively. Optical absorption of Sb and SbI₃ nanoparticles carried out at room temperature. As-deposited antimony film of thickness 25 nm exhibits a sharp rise in the absorption near ultraviolet region while post-deposition annealed films were characterized by red shifted absorption. Interestingly 45 nm thick Sb films exhibit a broad volume plasmon resonance peak around 500 nm with a width of 200 nm. Progressive iodization of 25 nm thick film reveals two absorption bands at 381.7 nm (A₂) and 458.3 nm (B₃) with photon energies 3.25 and 2.70 eV, respectively, due to the development of SbI₃ valence band structure. Last members of hydrogen-like series of absorption levels A₂ and B₃ due to halogen doublet (3/2, 1/2) splitting have been observed at room temperature.