Validation of the hybrid quasi-static/full-wave method forcapacitively loaded thin-wire antennas

A hybrid method in which quasi-static and full-wave integral equations are combined was developed by R.G. Olson et al. (see ibid., vol.36, p.1180-1184, Aug. 1988). Using point colocation, the method is implemented here for axially symmetric problems containing thin wires in the full-wave region and conductors and/or dielectrics in electrically small regions. The method is validated by comparing the predicted input admittances with measured results for capacitor-loaded antennas. The method is shown to be a significant improvement over thin-wire codes in which the electrically small region is replaced with an equivalent lumped load. The improvement is especially apparent in cases for which a detailed knowledge of the field in the electrically small region is needed     

A moving-actuator type electromechanical total artificial heart.II. Circular type and animal experiment

A new type of electromechanical total artificial heart (TAH) based on circular rolling-cylinder mechanism was developed to overcome critical problems in motor-driven artificial hearts such as large size and difficulties in fitting the heart to atrial remnants and arterial vessels. Its performance and reliability were evaluated in mock circulation and in an animal implant experiment. The total weight and volume of the pump is 650 g and 600 mL, respectively. This new pump was implanted in a calf for total heart replacement and 96 h of survival was achieved. The whole system, including pump, controller, and control algorithm performed well enough to improve the prospect of eventual clinical application of our TAH system.     

A two-element antenna for suppression in multipath environments

The design of a two-element antenna for portable transceivers is considered. The antenna consists of a dipole terminated with a parallel loop-capacitor combination. The antenna has a single feed at a point on the loop opposite the junction and does not require external combining circuitry. The capacitor creates a phase shift between the dipole and loop currents, thereby greatly reducing the probability of deep s in the received signal when the antenna is deployed in free-space or in the vicinity of a fixed reflector, where standing wave patterns occur. Theoretical and simulation studies based on multiple incident/reflected plane wave fields typical of multipath environments are used to quantify the reduction in probability. Simulation results are presented for three antenna types: a dipole antenna, a loop-dipole antenna without a capacitor, and the loop-dipole antenna with capacitor. The results are verified by field measurements on an automated outdoor test range, where the incidence angle and distance from the reflector are varied. With a single incident plane wave, the loop-dipole-capacitor (LDC) design reduces the probability of deep s in the received signal by up to two orders of magnitude at low signal-to-noise ratios (SNRs) when compared with the standard dipole antenna and the loop-dipole antenna without the capacitor. The performance advantage of the new design decreases as the number of incident waves increases; however, it performs at least as well as the dipole antenna in all cases studied.     

PowerNap: an efficient power management scheme for mobile devices

We present PowerNap, an OS power management scheme, which can significantly improve the battery life of mobile devices. The key feature of PowerNap is the skipping of the periodic system timer ticks associated with the operating system. On an idle device, this modification increases the time between successive timer interrupts and enables us to put the processor/system into a more efficient low power state. This saves the energy consumed by workless timer interrupts and the excess energy consumed by the processor in less efficient low power states. PowerNap is tightly integrated with the kernel and is designed for optimal control of the latency and energy associated with transitioning in and out of the low power states. We describe an implementation of PowerNap and its impact on system software. Experiments with IBM's WatchPad verify the ability of PowerNap to extend battery life. An analytical model that quantifies the ability of the scheme to reduce power is also presented. The model is in good agreement with experimental results. We apply the model to small form-factor devices which use processors that have a PowerDown state. In such devices, PowerNap may extend battery life by more than 42 percent for small processor workloads and for background power levels below 10 mW.     

Radiation due to a convex curvature discontinuity of adielectric-coated perfect conductor

Surface waves radiate energy at discontinuities in the curvature of the guiding structure. By reciprocity, surface waves will be excited by plane waves incident upon such a discontinuity. Here, the problem of the radiation of a surface wave on a flat dielectric-coated perfect conductor incident upon an abrupt change to a dielectric-coated cylindrical conductor with a large radius of curvature is considered. The problem is formulated as an integral equation over the aperture of the discontinuity. Since the change in curvature is modest, an approximate perturbation solution to the integral equation is derived and the radiated field due to the discontinuity is found. This radiated field reduces to published results for an impedance surface approximation when that approximation is valid. The problem of mode conversion and associated radiation near higher mode cutoffs is also studied. It is found that near mode cutoffs, the higher order mode dominates the radiation pattern and causes the overall radiation pattern due to the discontinuity in curvature to be narrow and end fire. Away from cutoff, when all of the propagating bound modes are more tightly bound to the surface, the radiation pattern is less narrow and less end fire. For very tightly bound modes the pattern is nearly uniform. For dielectrics characterized by small permitivities, the changes in radiation pattern should be measurable     

Inactivating microorganisms using a pulsed electric fieldcontinuous treatment system

High-voltage pulsed electric fields (PEFs) can be used to inactivate microorganisms in liquids. Applying PEF technology to food pasteurization is a promising nonthermal method, which may radically change food preservation processes and provide consumers with microbiologically safe, minimally processed, fresh-like products. A continuous-flow system in a laboratory-size prototype was constructed for the nonthermal pasteurization of liquid foods with PEF technology. Major components in the prototype include a high-voltage repetitive pulse generator, a coaxial liquid food treatment chamber, a fiber-optic temperature sensing instrument and a data acquisition system. Microbial inactivation tests were conducted in the continuous PEF treatment system. Repetitive high-voltage pulses with an exponential decaying waveshape were applied to the liquid food which was pumped through the treatment chamber. Test microorganisms selected for inactivation were Escherichia coli, Staphylococcus aureus and Saccharomyces cerevisiae. Over 6-order-of-magnitude reductions in the viability of selected microorganisms were achieved while the food temperature was maintained below 40°C     

Heat conduction in microbes exposed to pulsed electric fields

Nonthermal pasteurization of liquid foods by intense pulsed electric fields results in advantages over conventional heat pasteurization. Thermal damage to liquid foods can adversely affect the flavor and taste and result in loss of nutrients. Numerical modeling of heating parameters near the microbe during exposure to these intense electric fields is described. Boundary conditions at membrane interfaces included the continuity of temperature and continuity of heat flow. Temperature, heat flow vector, and heat source were included in the one-dimensional model. Two simulations are reported here. Simulation 1 consisted of a 0.5 μm wide microbe suspended in liquid with conductivity of 0.01 S/m and was treated with an applied electric field of 40 kV/cm for 375 ns. Simulation 2 contained a 1.0 μm wide microbe suspended in liquid with conductivity of 0.1 S/m and was treated with an applied electric field of 40 kV/cm for 1 μs. Comparison is made with a uniform conductivity model (ohmic), and it is shown that significant differences exist in the heating parameters between the two models. For the parameters used in these one-dimensional simulations, conditions for electroporation were found to exist without a significant temperature rise in the microbe     

High-frequency scattering by a conducting circular cylinder coatedwith a lossy dielectric of nonuniform thickness

A closed-form expression for the field produced by a plane wave incident on an infinitely long conducting cylinder, coated with a lossy dielectric of nonuniform thickness, is obtained using perturbation theory. This approximate series solution is later evaluated asymptotically for electrically large cylinder sizes. The scattered fields are interpreted using geometric optics and creeping waves. The fields are calculated using the exact series, the approximate perturbation series, and the high-frequency asymptotic solutions, and compared for different angles of incidence     

Statistics of differential rain attenuation on adjacent earth-space propagation paths

Forty hours of observations of the three-dimensional radar reflectivity structure of rain in the Montreal area were used to simulate the centimetre-wavelength attenuations occurring simultaneously over a multitude of earth-space propagation paths. The same data base had been used in a previous study which confirmed that the radar estimates of attenuation statistics are in good agreement with attenuation distributions measured independently by passive radiometers. Differences between the attenuations occurring simultaneously over pairs of paths to a common point at the ground were tabulated as a function of angular path separation, viewing direction, radio frequency, and system margin. These data are required for evaluating the possibility of interference at an earth station caused by a signal from an adjacent satellite. In this study, values of angular separation from 2 to 9 degrees, radio frequencies from 11 to 30 GHz, elevation angles from 5 to 30 degrees, and system margins from 2 to 10 dB were considered. It was found that the cumulative distributions of differential attenuation could be characterized effectively by the attenuation difference occurring during 1 % of the time that the carrier signal suffered some attenuation, but not an attenuation exceeding the system margin. It was also found that this characteristic differential attenuation could be expressed to good approximation as a simple analytical function of the system parameters.     

Orientierende holztechnologische Untersuchungen an Pinus radiata D. Don aus Neuseeland

Informative tests according to German standards (DIN) have been made with 3 clear logs of Pinus radiata to compare the results with European softwoods. Modulus of rupture and compression strengths (density between 0.35 and 0.66 g/cm³, mean value 0.53 g/cm³) as wells as the modulus of elasticity for small, elear specimen of Radiata pine. European pine, Spruce and Silver fire were nearly the same. Swelling and shrinkage values were not worse than those of European softwoods. The length of tracheidal ray cells in specimen of heart wood were 3.4 mm in the average. Extraction for several hours with Cyclohexan showed very different resin contents over the cross section between 0.27 and 15%. The concentration of preservative in sapwood of Pinus radiata was lower than expected. Phenol resorcind adhesive bonds of non-treated and preservative treated wood showed shear strengths parallel to the grain in the range of solid wood strengths.