Point of utilization power quality study results

A wide variety of electromagnetic phenomena occurring on AC power lines has been held responsible for literally billions of dollars per year in lost revenue. Information related to actual probability of occurrence of these power line deviations is presently limited. This paper describes the results of four years of point of utilization power quality monitoring at 112 North American locations. A quantity of 1057 site months of data collected between 1990 and 1994 was used in this assessment. The data indicate that the numbers of events occurring at typical locations may range from almost none, to thousands per month. The analysis results characterize several aspects of power quality related to the occurrence of low RMS events, high RMS events, transient events, and power interruptions (outages)     

Study of Desorption and Adsorption During Grain Aeration

One requirement in designing and operating and operating system is to minimize the moisture change in stored grain. Moisture transfer during the aeration process is generally believed to be caused by the partial pressure difference between water in grain and water in air (P₃-P₄). A mathematical model was developed for rough rice, which predicts the partial pressure difference under various grain and ambient conditions. Observations of moisture change over 10 aeration tests confirmed the good correlation between sorption phenomena and partial pressure differences. Studies indicated that air relative humidity, air temperature, grain temperature and grain moisture are significant factors influencing the partial pressure differences and, thus, affecting     

Structured genetic algorithm for robust H∞ controlsystems design

A structured genetic algorithm (SGA) approach is developed for robust controller design based on the concept of an H^∞ loop-shaping technique and the method of inequalities. Such an SGA is capable of simultaneously searching the orders and coefficients of the precompensator and postcompensator for the weighted plant. It is, therefore, not necessary to predefine the order of compensators as in usual practice. A multiple objective ranking approach is also incorporated so that the design criteria of extreme plants can be easily achieved. The effectiveness of such a technique is illustrated by a high-purity distillation column design example     

High speed p-type SiGe modulation-doped field-effect transistors

We report on the fabrication and characterization of high-speed p-type modulation-doped field-effect transistors (MODFETs) with 0.7-μm and 1-μm gate-lengths having unity current-gain cut-off frequencies (f_T) of 9.5 GHz and 5.3 GHz, respectively. The devices were fabricated on a high hole mobility SiGe heterostructure grown by ultra-high-vacuum chemical vapor deposition (UHV-CVD). The dc maximum extrinsic transconductance (g_m) is 105 mS/mm (205 mS/mm) at room temperature (77 K) for the 0.7-μm gate length devices. The fabricated devices show good pinch-off characteristics and have a very low gate leakage current of a few μA/mm at room temperature and a few nA/mm at 77 K     

Genetic algorithms: concepts and applications [in engineeringdesign]

This paper introduces genetic algorithms (GA) as a complete entity, in which knowledge of this emerging technology can be integrated together to form the framework of a design tool for industrial engineers. An attempt has also been made to explain “why” and “when” GA should be used as an optimization tool     

Analysis of thin walled structures using the boundary element method

In this article the direct boundary element formulations of stretching and bending plate problems are combined together to solve thin walled structures and other similar frames. The final system is obtained by assuming each individual plane structural element as a subregion. After the necessary transforms of these equations they can be combined together taking into account the displacement compatibility and equilibrium conditions.     

A comparison of leaf-spring with aircushion trailer suspensions in the transport environment

Packaging engineers need to be able to accurately determine the forces present in the shipping environment in order to protect packaged goods. The purpose of this study was to determine the vertical vibration levels measured in three separate truck-trailer suspension systems; conventional leaf-spring, conventional air-ride and damaged air-ride. The main conclusion reached in this study is that the air-ride suspension when maintained gives lower power density (PD) levels on all road surfaces studied. A damaged air-ride suspension and leaf-spring suspension are very similar in response frequencies, although the damaged air-ride produces higher vibration levels at lower frequencies.     

Entfestigungsverhalten des Stahls 50 CrV4 bei der thermomechanischen Behandlung

Softening behaviour of 50 CrV4 steel on thermomechanical treatment Determination of static softening of austenite on thermomechanical treatment of steel by rolling. Analysed was the development of the austenite structure and influencing the work softening processes depending on the deformation-temperature-time mode. The static softening processes were modelled mathematically by using Avrami's relationships.     

Wigner-space synthesis of discrete-time periodic signals

A procedure that facilitates at least-squares synthesis of periodic, discrete-time signals from Wigner quasi-distributions is proposed. The scheme is based on expanding the desired time sequence on a generally nonorthogonal, Gabor-type basis whose associated biorthogonal function presumably exists. The specific basis selection may crucially affect the efficiency and quality of the ensuing synthesis procedure. The cited basis type constitutes a considerable generalization over the standardly used orthogonal variety, thus creating previously unavailable degrees of freedom. Of primary significance is the acquired capability of generating time-frequency basis functions that are well localized. Localization is a highly desirable property that can advantageously serve in various applications. It is shown and numerically demonstrated that benefits of localization as well as the fact that achieving effective time-frequency basis localization renders a certain degree of oversampling unavoidable