A frequency domain ultrasonic model for the pulse-echo transducer response of an arbitrary scatterer in a fluid

A very general model formulation is presented in the frequency domain for the pulse-echo ultrasonic response of an arbitrary scatterer in a fluid. The transducer is modeled as a piston source and the scatterer can be located anywhere in the transducer wavefield. The model is computationally efficient and is shown to agree well with initial experiments.     

An overview of fault monitoring and diagnosis in mining equipment

Proper detection and diagnosis of failing system components is crucial to efficient mining operations. However, the harsh mining environment offers special challenges to these types of actions. The atmosphere is damp, dirty, and potentially explosive, and equipment is located in confined areas far from shop facilities. These conditions, coupled with the increasing cost of downtime and complexity of mining equipment, have forced researchers and operators to investigate alternatives for improving equipment maintainability. This paper surveys monitoring and diagnosis technologies that offer opportunities for improving equipment availability in mining. Expert systems, model-based approaches, and neural nets are each discussed in the context of fault detection and diagnosis. The paper concludes with a comparative discussion summarizing the advantages and disadvantages of each     

Best structures for deep submicrometer (0.1-0.3 μm) MOS devices

Summary form only given. The LDD-type structure has begun to encounter difficulties in satisfying transistor requirements in manufacturing due to a basic conflict between the need to have a graded drain profile for hot carrier suppression and the requirements for manufacturability and performance which place emphasis on a shallow, steeply profiled drain. One approach for overcoming this conflict and limitation is a MOS transistor structure called the hot-carrier suppressed (HCS) MOSFET. In this approach, a lower doped drain region is placed behind, or above, the shallow, heavier doped drain region rather than being placed adjacent to the channel region. This structure is described in detail, and its simulated performance compared with that of the LDD and conventional MOSFET structures     

Rainbow Net analysis of VAXcluster system availability

A system modeling technique, Rainbow Nets, is used to evaluate the availability and mean-time-to-interrupt of the VAXcluster. These results are compared to the exact analytic results showing that reasonable accuracy is achieved through simulation. The complexity of the Rainbow Net implemented for the VAXcluster does not increase as the number of processors increases, but remains constant. This is unlike a Markov model which increases in size exponentially. The constancy is achieved by using tokens with identity attributes (items) that can have additional attributes associated with them (features) which can exist in multiple states. The time to perform the simulation increases, but this is a polynomial increase rather than exponential. With Rainbow Nets, there is no restriction on distributions used for transition firing times. This freedom allows real situations to be modeled more accurately by choosing the distribution which best fits the system performance. This eliminates the need to make the many simplifying assumptions that are typically required to keep analytic calculations from becoming intractable     

Clock frequency and latency in synchronous digital systems

The tradeoffs in the design of synchronous digital systems between clock frequency and latency in terms of the circuit characteristics of a pipelined data path are described. A design paradigm relating latency and clock frequency as a function of the level of pipelining is developed for studying the performance of a synchronous system. This perspective permits the development of design equations for constrained and unconstrained design problems which describe these performance parameters in terms of the delays of the logic, interconnect, registers, clock skew, and the number of logic states. These results provide an approach to the design of those synchronous digital systems in which latency and clock frequency are of primary importance. From the behavioral specifications for the proposed system, the designer can use these results to select the best logic architecture and the best available device technology to determine if the performance specifications can be satisfied, and, if so, what design options are available for optimization of other system attributes, such as area     

The relationship between optical guiding and the relative phase infree-electron lasers

The relative phase in this case is defined as the shift in the wavenumber from the vacuum value integrated over the interaction length. The relative phase is studied from the standpoint of the linear stability analysis in both the high- and low-gain regimes, and the qualitative implications in each of these regimes of the relative phase on the refractive guiding of the signal are identical. Specifically, the relative phase is found to be negative at the low-frequency end of the gain band. The relative phase increases with increasing frequency over this band until it turns positive at a frequency approximately 10% below the frequency of peak gain. Thus optical guiding is indicated over a large portion, but not all, of the gain band. The specific example of interest involves the low-gain regime prior to saturation. In this case, it is shown that the analytic result is in substantial agreement with the calculation of the relative phase     

Computer-aided analysis of free-running microwave oscillators

The authors present a newly developed free-running steady-state oscillator analysis algorithm suited to large-signal oscillator analysis. Kurokawa's oscillation condition is coupled with the modified nodal admittance form of the circuit equations to avoid degenerate solutions. The algorithm was implemented by using both harmonic balance and frequency-domain spectral balance techniques. It was used in the simulation of monolithically integrated varactor-tuned MESFET oscillator. Good agreement between simulated power and oscillation frequency results was obtained     

On the capacity of a cellular CDMA system

It is shown that, particularly for terrestrial cellular telephony, the interference-suppression feature of CDMA (code division multiple access) can result in a many-fold increase in capacity over analog and even over competing digital techniques. A single-cell system, such as a hubbed satellite network, is addressed, and the basic expression for capacity is developed. The corresponding expressions for a multiple-cell system are derived. and the distribution on the number of users supportable per cell is determined. It is concluded that properly augmented and power-controlled multiple-cell CDMA promises a quantum increase in current cellular capacity     

A device to measure the cross-sectional area of soft connectivetissues

A device has been designed and fabricated to measure the cross-sectional area of soft connective tissues ex vivo. It consists of two displacement transducers; one sensing tissue thickness and the other sensing width. Outputs are recorded (via an analog to digital interface) using a personal computer. Numerical integration of a thickness versus width plot computes cross-sectional area. This plot also provides a quality check of acquired data. This device has been successfully used in biomechanical studies of rabbit patellar tendons, rat medial collateral ligaments, and dissected specimens of human fascia.     

Electrical and optical feedback in an InGaAs/InP light-amplifyingoptical switch (LAOS)

A circuit model for optical and electrical feedback has been developed to investigate the cause of negative differential resistance (NDR) switching in a series connected heterojunction phototransistor (HPT) light-emitting diode (LED) device. The model considers optical feedback from the light generated in the LED, electrical feedback from the holes thermally emitted over the LED cladding layer, nonlinear gain of the HPT, the Early effect, and leakage resistance. The analysis shows that either electrical or optical feedback can be the dominant cause for the NDR, depending upon their relative strengths. The NDR observed in the devices was caused primarily by electrical feedback since the optical feedback is weak. For low input power, avalanche breakdown appears to initiate the NDR in the devices although avalanching alone cannot cause NDR