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Electrical breakdown measurements were performed on polypropylene films impregnated with benzyltoluene and aged for different electric field values (100 V-ms mu m(-1) < E-a < 300 V-ms mu m(-1)). Two films of 13.6 mu m thickness were sandwiched between two plane electrodes and immersed in the liquid at 80 degrees C and with substantial O-2 concentrations. For this arrangement, the threshold voltage discharge (V-th) was ca 6-7 kVrms. The results show that for a given ageing time the films breakdown strength dependence on the ageing voltage V-a is different for V-a < V-th and V-a > V-th. This result is a confirmation of the occurrence of elect...
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Electrical breakdown measurements were performed on polypropylene films impregnated with benzyltoluene and aged for different electric field values (100 V-ms mu m(-1) < E-a < 300 V-ms mu m(-1)). Two films of 13.6 mu m thickness were sandwiched between two plane electrodes and immersed in the liquid at 80 degrees C and with substantial O-2 concentrations. For this arrangement, the threshold voltage discharge (V-th) was ca 6-7 kVrms. The results show that for a given ageing time the films breakdown strength dependence on the ageing voltage V-a is different for V-a < V-th and V-a > V-th. This result is a confirmation of the occurrence of electrical discharges in the capacitor for V-a > V-th. The area of degradated film is also different in both cases. For V-a < V-th the region with lower breakdown strength is restricted to the part of the film sandwiched between the electrodes. For V-a > V-th the region with lower breakdown voltage is larger (about 1 mm) than the electrode diameter (8 mm). This is the result of the radial propagation of discharges or streamers. The influence of an epoxy additive which is an effective stabiliser of impregnated PP films was also investigated. (C) 1997 Published by Elsevier Science Ltd.
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A new sensitive type of magnetron gauge has been developed in order to obtain a linear response of ion current, I_i, to pressure, P, with a high sensitivity over a wide range. The gauge is equipped with two ion collectors. The rat...
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A new sensitive type of magnetron gauge has been developed in order to obtain a linear response of ion current, I_i, to pressure, P, with a high sensitivity over a wide range. The gauge is equipped with two ion collectors. The ratio of the ion currents of the two ion collectors is measured and kept constant by controlling the filament voltage, in order to keep the electric field constant within the anode over a wide range of pressure measurement. When a divergent-magnetic field is applied to this hot-cathode magnetron gauge, the slope of the plot of the filament voltage vs the ratio of the ion current of the two separate two ion collectors is improved from -0.28 to + 1.1- + 3.9 (V~(-1)). When the diameters of the ion collectors were investigated, it was found that the current ratio η = 1 was attained when the outer diameters of the ion collectors were identical, and their inner diameters were 2 and 8 mm respectively. With this configuration, ion current was directly proportional to pressure in the range of 1 x 10~(-8)-1 x 10~(-4) Pa.
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A linear and nonlinear analysis is presented of coupled ion-acoustic and drift waves in a plasma consisting of electrons and ions that is penetrated by a mono-energetic stream of ions of another kind. All the plasma species (elect...
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A linear and nonlinear analysis is presented of coupled ion-acoustic and drift waves in a plasma consisting of electrons and ions that is penetrated by a mono-energetic stream of ions of another kind. All the plasma species (electrons and two ion fluids) are allowed to have density gradients in the direction perpendicular to the external magnetic field lines. In the linear domain the standard streaming instability of the acoustic modes and their interaction with drift modes is demonstrated. The threshold values of the stream velocity and the parallel wave number are calculated and discussed. In the nonlinear limit stationary coherent solutions are found which can represent the saturated state of the linearly unstable modes. (C) 2004 Elsevier B.V. All rights reserved.
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Abstract Drying of moist porous media, such as food or pulp and paper, is an energy-intensive process. Traditional drying technologies have disadvantages, including high energy consumption, thermal degradation of the samples, as w...
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Abstract Drying of moist porous media, such as food or pulp and paper, is an energy-intensive process. Traditional drying technologies have disadvantages, including high energy consumption, thermal degradation of the samples, as well as high capital cost. In this work, a new technology, making use of the Dielectrophoresis (DEP) mechanism, is introduced, to enhance the drying process of a moist porous medium. DEP is a translational motion of neutral matter caused by polarization effects in a non-uniform electric field. In a typical drying process, due to the existence of an electric permittivity gradient between liquid and vapor interfaces, the DEP force can act as an external force to effectively extract the vapor phase away from the product. This in turn enhances the evaporation rate. This article experimentally investigates the influence of the DEP force on the drying of moist hand-sheet paper samples. Specifically, the temperature profile and sample weight are monitored under various applied electric potentials. The non-uniform electric field is generated from a unique electrode design. The experimental results show a significant impact of the DEP force on the temperature profile and drying rate. In addition, the results also show extremely low energy consumption and high energy efficiency associated with the application of the DEP force for drying. With the application of the electric field, up to 10?°C drop in surface temperature and a 33.6% reduction in drying time have been achieved. The experimental work provides a basic understanding of this novel technology that could enhance the drying process in various industry sectors such as forest products, foods, pharmaceuticals, and chemicals.
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The paper presents two contributions in the context of the numerical simulation of magnetized fluid dynamics. First, we show how to extend the ideal magnetohydrodynamics (MHD) equations with an inbuilt magnetic field divergence cl...
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The paper presents two contributions in the context of the numerical simulation of magnetized fluid dynamics. First, we show how to extend the ideal magnetohydrodynamics (MHD) equations with an inbuilt magnetic field divergence cleaning mechanism in such a way that the resulting model is consistent with the second law of thermodynamics. As a byproduct of these derivations, we show that not all of the commonly used divergence cleaning extensions of the ideal MHD equations are thermodynamically consistent. Secondly, we present a numerical scheme obtained by constructing a specific finite volume discretization that is consistent with the discrete thermodynamic entropy. It includes a mechanism to control the discrete divergence error of the magnetic field by construction and is Galilean invariant. We implement the new high-order MHD solver in the adaptive mesh refinement code FLASH where we compare the divergence cleaning efficiency to the constrained transport solver available in FLASH (unsplit staggered mesh scheme). (C) 2018 Elsevier Inc. All rights reserved.
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Yee's classic algorithm was proved to be divergence-free in source-free regions. However, the divergence properties of the nonstandard finite difference (NSFD) methods have not been addressed. In this letter, we investigate the di...
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Yee's classic algorithm was proved to be divergence-free in source-free regions. However, the divergence properties of the nonstandard finite difference (NSFD) methods have not been addressed. In this letter, we investigate the divergence nature of the NSFD (2,2) and (2,4) algorithms. Both the differential and integral forms of Gauss's Law are examined
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This paper presents a methodology that employs the electrostatic field variations caused by thundercloud formation or displacement to generate lightning warnings over a region of interest in Southeastern Brazil. These warnings can...
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This paper presents a methodology that employs the electrostatic field variations caused by thundercloud formation or displacement to generate lightning warnings over a region of interest in Southeastern Brazil. These warnings can be used to prevent accidents during hazardous operations, such as the manufacturing, loading, and test of motor-rockets. In these cases, certain equipment may be moved into covered facilities and personnel are required to take shelter. It is also possible to avoid the threat of natural and triggered lightning to launches. The atmospheric electric field database, including the summer seasons of 2007/2008 and 2008/2009 (from November to February), and, for the same period and region, the cloud-to-ground lightning data provided by the Brazilian lightning detection network – BrasilDAT – were used in order to perform a comparative analysis between the lightning warnings and the cloud-to- ground lightning strikes that effectively occurred inside the area of concern. The analysis was done for three areas surrounding the sensor installation defined as circles with 5, 10 and 15 km of radius to determine the most effective detection range. For each area it was done using several critical electric field thresholds: +/- 0.5; +/- 0.8; +/- 0.9; +/- 1.0; +/- 1.2; and +/- 1.5 kV/m. As a result of the reduction of atmospheric electric field data provided by the sensor installed in area of concern and lightning provided by BrasilDAT, it was possible, for each of the areas of alert proposals, to obtain the following parameters: the number of effective alarms; the number of false alarms; and the number of failure to warning. From the analysis of these parameters, it was possible to conclude that, apparently, the most interesting critical electric field threshold to be used is the level of 0.9 kV/m in association with a distance range of 10 km around the point where the sensor is installed.
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We compute the one loop vacuum polarization from massless, minimally coupled scalar QED in a locally de Sitter background. Gauge invariance is maintained through the use of dimensional regularization, whereas conformal invariance ...
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We compute the one loop vacuum polarization from massless, minimally coupled scalar QED in a locally de Sitter background. Gauge invariance is maintained through the use of dimensional regularization, whereas conformal invariance is explicitly broken by the scalar kinetic term as well as through the conformal anomaly. A fully renormalized result is obtained. The one loop corrections to the linearized, effective field equations do not vanish when evaluated on-shell. In fact the on-shell one loop correction depends quadratically on the inflationary scale factor, similar to a photon mass. The contribution from the conformal anomaly is insignificant by comparison. (C) 2003 Elsevier Science (USA). All rights reserved. [References: 21]
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We derive a simple formula for one-loop logarithmic divergences on the background of a two-dimensional curved space-time for theories in which the second variation of the action is a nonminimal second-order operator with small non...
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We derive a simple formula for one-loop logarithmic divergences on the background of a two-dimensional curved space-time for theories in which the second variation of the action is a nonminimal second-order operator with small nonminimal terms. In particular, this formula allows calculating terms that are integrals of total derivatives. As an application of the result, we obtain one-loop divergences for higher-spin fields on a constant-curvature background in a nonminimal gauge that depends on two parameters. By an explicit calculation, we demonstrate that with the considered accuracy, the result is gauge independent and, moreover, spin independent for spins s >= 3.
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It is pointed out that the usual theta-algebra assumed for non-commuting coordinates is not P- and T-invariant unless one formally transforms the non-commutativity parameter theta(munu) in an appropriate way. By contrast, the Lore...
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It is pointed out that the usual theta-algebra assumed for non-commuting coordinates is not P- and T-invariant unless one formally transforms the non-commutativity parameter theta(munu) in an appropriate way. By contrast, the Lorentz-covariant DFR algebra, which 'relativitizes' the theta-algebra by replacing theta(munu) with a second-rank antisymmetric tensor operator (θ) over cap (munu), is P- and T-invariant. It is then proved that C, P and T are separately conserved in Lorentz-invariant non-commutative QED. [References: 44]
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