Performance analysis and its impact on design

Methods for designing new computer systems have changed rapidly. Consider general purpose microprocessors: gone are the days when one or two expert architects would use hunches, experience, and rules of thumb to determine a processor's features. Marketplace competition has long since forced companies to replace this ad hoc process with a targeted and highly systematic process that focuses new designs on specific workloads. Although the process differs from company to company, there are common elements. The main advantage of a systematic process is that it produces a finely tuned design targeted at a particular market. At its core are models of the processor's performance and its workloads. Developing and verifying these models is the domain now called performance analysis. We cover some of the advances in dealing with modern problems in performance analysis. Our focus is on architectural performance, typically measured in cycles per instruction     

Alternating current impedance studies on oxide films in metal/oxide/electrolyte systems: a modified approach

The accurate determination of the impedance of oxide films in metal/oxide/electrolyte systems is shown to be possible through a modified procedure. The film impedance thus determined is found to be quite different from the measured cell impedance for anodic aluminium oxide formed on pure aluminium. The computed values of tan and conductivity are found to be in agreement with the values reported earlier for anodic and thermal oxides.     

Studies on oxychlorination of MoS2 in a fluid bed reactor

Studies on the chlorination kinetics of molybdenum sulfide in the presence of a mixture of oxygen, chlorine, and nitrogen gases have been carried out in a fluidized bed reactor at temperatures of 250 to 350 ° and particle size range of 75 to 200 μm. The reaction rate with respect to surface area of MoS₂ particles as well as the composition of reactant gases has been determined and the specific rate constants evaluated. The oxychlorination of MoS₂ has been determined to be of first order with respect to surface area of particles and the overall reaction is found to be controlled by chemical reaction.     

Dissociation constants of long chain fatty acids in methanol-water and ethanol-water mixtures

The pK_a values of lauric acid, myristic acid, palmitic acid and stearic acid in methanol-water and ethanol-water mixtures of different compositions at 303 K and ionic strength, I=0.1M(KNO₃) have been determined. The pK_a values of the fatty acids have been found to increase with the alcohol content of the solvent. It has also been found that, in general, the pK_a values in the ethanolic solvent are greater than those in the methanolic solvent. In a given solvent mixture the observed pK_a value decreases in the order of stearic acid > palmitic acid > myristic acid > lauric acid. Departure from the predicted linearity of the plots of pK_a against the inverse of the dielectric constant, 1/D indicates that the electrostatic effects taken into account by the Born theory are not adequate enough to represent the total medium effects on pK_a.     

Neural network design using Voronoi diagrams

A novel approach is proposed which determines the number of layers, the number of neurons in each layer, and their connection weights for a particular implementation of a neural network, with the multilayer feedforward topology, designed to classify patterns in the multidimensional feature space. The approach is based on construction of a Voronoi diagram over the set of points representing patterns in feature space and this finds added usefulness in deriving alternate neural network structures for realizing the desired pattern classification.     

Gravity and configurational energy induced microstructural changes in liquid phase sintering

Liquid phase sintered materials consist of interconnected crystalline grains in a homogeneous matrix phase that forms the liquid at high temperatures. The dihedral angle, grain size, and volume fraction of solid determine the energy of the system. Energy minimization is possible by the separation of phases due to density differences. This explains why some materials exhibit settling or distortion due to gravity during liquid phase sintering. Experiments performed with W-Ni-Fe heavy alloys are used to measure the microstructural changesvs position that occur in liquid phase sintering under normal gravity. The experimentally observed segregation is less than the calculated equilibrium seg-regation due to the retarding effect from the rigid solid skeleton formed during sintering. These re-sults improve our understanding of microstructure, mechanical properties, component shape, and dimensional stability benefits that may be realized from low gravity sintering. This paper is based on a presentation made in the symposium “Experimental Methods for Microgravity Materials Science Research” presented at the 1988 TMS-AIME Annual Meeting in Phoenix, Arizona, January 25-29, 1988, under the auspices of the ASM/MSD Thermo-dynamic Data Committee and the Material Processing Committee.     

A hybrid method through faradaic rectification and a.c. impedance measurements for the corrosion rate determination of metal/oxide/electrolyte systems. I. Theory

The interference of the oxide film in corrosion rate measurements of oxide covered metals is confirmed, and is found to limit the accuracy of measurements in all d.c. and a.c. polarization methods including impedance techniques. A new method is proposed to measure the corrosion rate in metal/oxide/electrolyte systems. It involves the use of faradaic rectification measurements in the absence of concentration polarization. The contribution of the oxide film to the measured currents and potentials are appropriately compensated and this represents a unique feature of the proposed method. Alternating current impedance values of the oxide film measured at the same frequency as that of faradaic rectification are used for this purpose.     

A note on universal matrices for triangular finite elements for the quasi-harmonic equation

An algorithm to generate universal matrices for plane triangular finite elements for the general ‘quasi-harmonic’ equation is presented. For every member of the triangle family three numerical universal matrices are obtained which are independent of the size, shape and ‘material’ properties of the element. Of these, two are basic and the third can be generated from one of these two. The element ‘stiffness’ matrix is conveniently generated by manipulating these two basic matrices taking into account the size, shape and material properties of the element in a simple manner.