An experimental investigation of thick-sample effects in the measurement of directional-hemispherical transmittance of advanced glazing materials

Samples that are thick with respect to the measuring apparatus can pose problems in the measurement of directional-hemispherical transmittance. Due to the lateral displacement of light that these samples induce, traditional small-beam techniques are often no longer applicable. Broad-area irradiation offers a solution to these problems, but, in practice, imperfections in the extent and the uniformity of the irradiation can create errors. This paper reports measurement of the “detector-integrated inscattering function”, which describes the lateral displacement of light, for a number of thick samples over a range of incidence angles. This function is used to determine the minimum area that must be irradiated for an accurate broad-area irradiation transmittance measurement. The errors caused by transverse non-uniformities in the irradiance distributions produced by a state-of-the-art broad-area irradiation spectrophotometer are also reported. Errors caused by transverse irradiation non-uniformities are estimated, and transmittance measurements made with small-area and broad-area irradiation are compared. It is shown that in most cases small-area irradiation transmittance measurements underestimate the transmittance of thick samples due to outscattering, and that broad-area irradiation measurements using state-of-the-art irradiation optics can contain large errors of up to 20%, due to irradiance non-uniformities, particularly at large angles of incidence.     

Magnetic circuit modelling of the field regulated reluctancemachine. Part I: model development

A transient magnetic circuit model of a field regulated reluctance machine is presented. The model is based on flux loop equations rather than node equations as have previously been employed. A key feature of this approach is that magnetic circuit models based on loop equations permit an entire machine to be represented by only one equivalent pole     

Acoustic resonance spectroscopy (ARS)

The basics of acoustic resonance spectroscopy (ARS), which provides data about an object's physical structure and composition, are explained. In ARS, one actively excites a large number of resonances (normal modes) in an object that has no internal vibrations by slowly sweeping the excitation frequency to obtain an acoustic spectrum of the object. The instrumentation for this nondestructive evaluation technique is described, and some applications are briefly discussed     

10 Gbit/s NRZ global transmission using optically amplifiedelectronic regeneration

10 Gbit/s NRZ error-free fibre transmission over distances exceeding 400000 km is demonstrated using an optically amplified regenerator with a 160 km span. Direct modulation of a DFB laser raises the stimulated Brillouin scattering power threshold while maintaining system simplicity and robustness     

High-speed InGaP/GaAs HBTs with a strained InxGa1-xAs base

A self-aligned InGaP/GaAs heterojunction bipolar transistor with a compositionally graded In_xGa_1-xAs base has been demonstrated with f_T=83 GHz and f_max=197 GHz. To our knowledge, these results are the highest reported for both parameters in InGaP/GaAs HBT's. The graded base, which improves electron transport through the base, results in a DC current gain and a cutoff frequency which are 100% and 20% higher, respectively, than that achieved by an identical device with a nongraded base. The high f_max results from a heavily doped base, self-aligned base contacts, and a self-aligned collector etch. These results demonstrate the applicability of InGaP/GaAs HBT's in high-speed microwave applications     

Transient characteristics of small salient-pole alternators

The use of small alternators, other than for standby purposes, is increasing and this has focused attention on the reliability and utility of the parameters normally quoted for such machines. Test procedures are described and methods used for parameter estimation discussed, with particular emphasis on the difficulties presented by small brushless machines     

Performance analysis of concurrency control using locking withdeferred blocking

The concurrency control (CC) method employed can be critical to the performance of transaction processing systems. Conventional locking suffers from the blocking phenomenon, where waiting transactions continue to hold locks and block other transactions from progressing. In a high data contention environment, as an increasing number of transactions wait, a larger number of lock requests get blocked and fewer lock requests can get through. The proposed scheme reduces the blocking probability by deferring the blocking behavior of transactions to the later stages of their execution. By properly balancing the blocking and abort effects, the proposed scheme can lead to better performance than either the conventional locking or the optimistic concurrency control (OCC) schemes at all data and resource contention levels. We consider both static and dynamic approaches to determine when to switch from the nonblocking phase to the blocking phase. An analytical model is developed to estimate the performance of this scheme and determine the optimal operating or switching point. The accuracy of the analytic model is validated through a detailed simulation