This review paper focuses on interdigital electrodes-a geometric structure encountered in a wide variety of sensor and transducer designs. Physical and chemical principles behind the operation of these devices vary so much across different fields of science and technology that the common features present in all devices are often overlooked. This paper attempts to bring under one umbrella capacitive, inductive, dielectric, piezoacoustic, chemical, biological, and microelectromechanical interdigital sensors and transducers. The paper also provides historical perspective, discusses fabrication techniques, modeling of sensor parameters, application examples, and directions of future research.

The paper describes Rthreads (Remote threads), a software distributed shared memory system that supports sharing of global variables on clusters of computers with physically distributed memory. Other DSM systems either use virtual memory to implement coherence on networks of workstations or require programmers to adopt a special programming model. Rthreads uses primitives to read and write remote data and to synchronize remote accesses similar to the DSM systems that are based on special programming models. Unique aspects of Rthreads are: the primitives are syntactically and semantically closely related to the POSIX thread model (Pthreads). A precompiler automatically transforms Pthreads (source) programs into Rthreads (source) programs. After the transformation the programmer is still able to alter the Rthreads code for optimizing run time. Moreover Pthreads and Rthreads can be mixed within a single program. We support heterogeneous workstation clusters by implementing the Rthreads system on top of PVM, MPI and DCE. We demonstrate that programmer based optimizations may reach a significant performance increase. Our performance results show that the Rthreads system introduces few overhead compared to equivalent programs in the baseline system PVM, and a superior performance compared to the DSM systems, Adsmith and CVM.

One class of modern pulse power generators use deionized water as an energy storage, switching and transmission dielectric. Water is chosen for its high dielectric constant and relatively high resistivity, which allows reasonably sized and efficient low-impedance high-voltage pulse lines where pulse durations are less than 100 µs. Water/ethylene glycol mixtures are being researched, so that rotating machinery, rather than the usual Marx generator, can be used as the primary energy store. The high resistivity and high dielectric constant of these mixtures at low temperature permit low-loss operation on millisecond time scales. Simple design criteria linking load parameters and charging circuit characteristics to the liquid dielectric are developed which show that the dielectric constant, breakdown strength, and relaxation time are the primary properties of interest to the pulse power engineer. On time scales greater than 100 µs, injection of space charge, with density q and mobility µ, affects the charging and discharging circuit characteristics, introduces the time constant of the time of flight for injected charge to migrate between electrodes, and increases the effective ohmic conductivity σ to σ + qµ. A drift-dominated conduction model is used to describe measured space-charge effects. Kerr electrooptic field mapping measurements show strong space-charge effects with significant distortions in the electric field distribution a few hundred microseconds after high voltage is applied. The injected charge magnitude and sign depends on the electrode material. Thus by appropriate choice of electrode material combinations and voltage polarity, it is possible to have uncharged liquid, unipolar-charged negative or positive, or bipolar-charged liquid. An important case is that of bipolar injection, which has allowed up to a 40 percent higher applied voltage without breakdown than with no charge injection, and thus a doubling of stored energy due to the space-charge shielding which lowers the electric field strengths at both electrodes. Although injected space charge increases the stored electric energy over the capacitive space-charge-free energy, (1/2)CV2, more energy is required from a source during charging and the energy delivered to a resistive load is reduced because of internal dissipation in the capacitor as the charge is conducted to the electrodes. However, it appears that this extra dissipation due to injected charge can be made negligibly small and well worth the price if the space charge allows higher voltage operation for long charging time or repetitively operated machines.