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We describe the effect of a radio-frequency (rf) power application on the performance of a magnetohydrodynamic (MHD) electrical power generator, as determined through shock-tunnel-based experiments and quasi-three-dimensional numerical simulations. The temporal plasma-fluid behavior, the one-dimensional plasma-fluid structure, the enthalpy-entropy diagram, the quality of the energy conversion efficiency, and the energy flow in the power-generating system are investigated. Preionization assistance by a small amount of rf power drastically changes the entire MHD power-generating system; the MHD extraction length is considerably extended and the isentropic efficiency is significantly improved. [ABSTRACT FROM AUTHOR]

The effect of localized microwave absorption in conducting thin films had been simulated using a heat diffusion model to quantitatively evaluate the electrical voltage maps obtained recently using a near-field scanning microwave microprobe (NSMM) in combination with the I-V characterization. In the experiment, the focused microwave emitted from the NSMM at a sample spot of dimension comparable to the NSMM tip dimension changes the local resistivity of the sample via microwave heating. By measuring the voltage response while scanning the NSMM, nonuniformity in the electrical current distribution in the sample can be resolved. To quantitatively assess the effect of various parameters, a theoretical simulation of the temperature profile has been made and related to the voltage response profile obtained experimentally. The variation of the induced voltage due to microwave absorption with time, microwave input power, and the thickness of the film has also been studied and the simulation compares well with experiment. Discussions on discrepancies between simulation and experiment will also be presented. [ABSTRACT FROM AUTHOR]

An ion-gel-based transistor was fabricated using an electrohydrodynamic (EHD) jet printing process. In general, EHD jet printing is operated in four jetting modes: dripping, micro-dripping, cone-jet and multi-jet ones. Both poly(3-hexylthiophene-2,5-diyl) (P3HT) and poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS), as a semiconductor and a gate electrode, respectively, enable successful printing in cone-jet mode and the resulting pattern widths are about 10 μm (P3HT) and 200 μm (PEDOT:PSS). On the other hand, the ion-gel electrolyte cannot be printed in cone-jet mode because of the excessive number of ions in the ink that perturb the fluidic behavior. Therefore, dripping mode was used to produce an ion-gel pattern under the application of a very low voltage, which is referred to as electrostatic-force-assisted dispensing printing. This method could make good patterns of an ion-gel and allow the fabrication of an ion-gel-based transistor. The EHD jet-printed transistor exhibited an average mobility ( μ ), threshold voltage ( V th ), on/off current ratio ( I on / I off ) and subthreshold swing ( SS ) of 0.12 ± 0.05 cm2/Vs, −0.83 ± 0.1 V, ∼10 5 and 73 ± 11 mV/decade, respectively. [ABSTRACT FROM AUTHOR]

For permanent-magnet linear motors (PMLMs), high-temperature rise can deteriorate their electromagnetic performance and limit their thrust output. A water-cooling system can be employed to reduce the temperature rise and to improve the thrust density. In order to study the thermal performance of a water-cooled, 14-pole, and 12-slot PMLM, a finite-element model and thermal network model are developed. Under continuous duty, the temperature distribution of this PMLM is investigated based on the two developed models, which are validated by experimental results. The effect of the water-cooling system and the impact of its parameters on the temperature rise are investigated. Then, the influence of the temperature rise on the motor thrust force and efficiency is studied. Finally, based on the finite-element model, thermal characteristics of this PMLM under short-time duty and intermittent duty are studied, and the relationship is obtained between the operation duration and the maximum allowed short-time current, as well as the impact of load sustained rate. [ABSTRACT FROM AUTHOR]

The prediction of the thermal behavior of an electrical machine in the design process basically depends on the used boundary conditions such as the convective heat transfer coefficient. Due to the complicated shape of the end windings, the heat transfer coefficient has to be identified empirically by using thermopiles as heat flux sensors placed at certain positions on the end windings, because an analytical derivation is not feasible. This paper presents the results of the measured values of the heat transfer on the end windings of an electrical machine. The gained coefficients are compared to the results obtained by numerical simulations using commercial software for computational fluid dynamics. The simulation results are discussed according to the validity of the gained heat transfer coefficient. The configuration of the simulation has been tested on a cylindrical shape in a cross-flow. [ABSTRACT FROM PUBLISHER]

Abstract: As dehumidification is one of the most important tasks of environment control of the building, it is necessary to know the energy efficiency of dehumidification processes. The energy efficiency can give the energy cost of drawing moisture from indoor air to the outside environment. This paper presents analysis of the ideal cost of dehumidification process by a liquid desiccant cycle. Formulas to calculate ideal efficiency of dehumidification process are obtained, which is determined by indoor temperature, outdoor temperature, and the temperature of the intersection point of the iso-relative humidity line of indoor air and the iso-humidity ratio line of outdoor air. The ideal efficiency of the condensing dehumidification method is lower than the ideal dehumidification process, due to the fact that condensing dehumidification method must dehumidify the air at the temperature of dew point. Results from this paper can be used as theoretical foundation for the further analysis of various dehumidification methods and the development of new dehumidification processes. [ABSTRACT FROM AUTHOR]

The generation of thermal stresses is a major cause for mechanical failure in encapsulated electronic components. In this study numerical modeling is employed to analyze thermal stresses in a high-voltage transformer encapsulated with filled epoxy. The transformer assembly consists of materials with an extremely disparate range of thermomechanical properties. The thermal histories considered mimic those in the operational condition. It is found that, upon thermal cooling from elevated temperature, the ceramic core can be under local tensile stress although it is entirely surrounded by materials with much greater coefficients of thermal expansion. The unique aspect of this paper originates from the fact that the volume shrinkage of the viscoelastic encapsulant during physical aging contributes to an increase in stress over time, thus increasing the tendency of fracture. This counter intuitive result (stress increase due to nonlinear viscoelastic physical aging) can now be predicted using constitutive models recently developed at Sandia National Laboratories. When a silicone coating between the core and the encapsulation is included, the stress is significantly reduced. The modeling result is shown to corroborate with the actual performance of the transformer. [ABSTRACT FROM AUTHOR]

Abstract: We analyze a minimal model of a population of identical oscillators with a nonlinear coupling—a generalization of the popular Kuramoto model. In addition to well-known for the Kuramoto model regimes of full synchrony, full asynchrony, and integrable neutral quasiperiodic states, ensembles of nonlinearly coupled oscillators demonstrate two novel nontrivial types of partially synchronized dynamics: self-organized bunch states and self-organized quasiperiodic dynamics. The analysis based on the Watanabe–Strogatz ansatz allows us to describe the self-organized bunch states in any finite ensemble as a set of equilibria, and the self-organized quasiperiodicity as a two-frequency quasiperiodic regime. An analytic solution in the thermodynamic limit of infinitely many oscillators is also discussed. [Copyright &y& Elsevier]

The MHD interaction around a conical test body in a hypersonic argon flow was experimentally investigated. The aim of the experiment was to produce a database to be used for the validation of numerical codes for the analysis and simulation of the magnetofluiddynamics in hypersonic flows. In these experiments, the flow was obtained in the High-Enthalpy Arc-heated hypersonic wind Tunnel of Alta, Pisa, Italy. Speeds at Mach 6 were reached. In this experiment, the flow and plasma characteristics have been determined. The MHD interaction was obtained in the shock layer of a conical test body placed at the exit of the hypersonic nozzle. The realized electrical configuration allowed the enhancement of the effect of the MHD interaction on the plasma parameters. This was done by utilizing the Hall field to generate the MHD interaction and by short-circuiting the Faraday current inside the plasma of the shock layer. The magnetic-flux density was produced by an array of three magnets located in the test body. Test runs were performed at three different stagnation pressures. Fluid-dynamic, electrical, and optical observations have been done. The experiment showed a large effect of the MHD interaction on the values of the measured quantities. In order to have a test body that is entirely contained in the region where a uniform hypersonic flow has been measured, a test body of smaller size has been constructed and tested. The results obtained in this case confirm the results of the tests with the larger body. [ABSTRACT FROM AUTHOR]

The paper deals with electric models applied in the investigation of complex systems, such as transport, economic, and neuron systems. The increasing interest in such systems can be explained by the fact that they are characterized by parallel (collective) means of complex calculation processes, under the influence of inner information processes. Electric models can also be looked upon as original structures for neuron-like systems. The paper puts emphasis on comparison between the electric models suggested by the authors, on the one hand, and the mechanical and thermal models, on the other hand. It has been shown that entropy phenomena, typical for the latter, can be closely compared to those of electric models, which are distinguished by pure electric values. Also, it has been shown that irreversible processes of energy dissipation, e.g., entropy processes in mechanical models, are corresponded to processes of energy concentration, energy transfer, and/or energy exchange in electric models. This enables us to shed a new light on processes in electric circuit, especially those concerning with structural improvements of electric circuitry and their self-organization, meaning a neg-entropic information character of these processes. Models of two economic tasks have been considered, wherein the calculation process is characterized under the influence of these processes. Assumption on the importance of reactive elements such as carriers of neg-entropy in electric circuits was made as well. [ABSTRACT FROM AUTHOR]

We investigate the heat generation in a nanoscale system coupled to normal leads and find that it is maximal when the average occupation of the electrons in the nanoscale system is 0.5, no matter what mechanism induces the heat generation. [ABSTRACT FROM AUTHOR]