A theoretical design basis for minimizing CMOS fixed taper bufferarea

This paper develops a theoretical basis for the minimization of chip area required for fixed taper buffer design. It modifies the well-known procedure for minimizing delay time in such circuits to derive a minimum number of required stages. Rather than minimize delay time, the procedure realizes a specified buffer delay time using a stage-area scale factor that minimizes the total area of the buffer. Since an integer number of tapered stages must be used while the calculations lead to noninteger results, the effects of roundoff errors are included     

Cortical implants for the blind

Arrays of stimulating electrodes can be placed in the brain itself, in the visual cortex, to bring vision to the profoundly blind. However, when designing such devices one needs to take into consideration the fact that the visual pathway maps images onto cortical structures in a complex and unpredictable way     

On the measurement of SSB noise figure using sideband cancellation

A new method for determining the single-sideband noise figure of a device from double-sideband measurements is proposed which eliminates the need for tunable filters and hence greatly reduces the complexity and cost of performing accurate noise figure measurements. This paper compares results obtained to those obtained using a traditional single-sideband measurement system with a tuneable filter and provides a full error analysis of the new technique. The method also offers considerable possibilities for future use at higher (microwave) frequencies where YIG filters and image reject mixers are not readily available     

Silicon carbide-toughened zirconia ceramics

Tetragonal zirconia polycrystalline (TZP) ceramics containing SiC reinforcement in the form of fine particles (nano-scale), particles (micro-scale), whiskers and platelets were synthesized by hot-pressing. The effects of morphology and grain size of SiC reinforcement on the strength and fracture toughness at room temperature were investigated. The addition of SiC (in whatever form) caused decreases in strength and toughness at room temperature with the exception of whisker-reinforced materials. Toughness fell off with increasing temperature, but nevertheless retained about one-half of the room-temperature value for that particular SiC reinforcement. However, the whisker- and particle-reinforced materials had higher K _lc values at high temperature than fine particle- or platelet-reinforced materials, with values in excess of 7 MPa m^1/2 at 1000 °C. The microstructure was examined for SiC whisker-reinforced/TZP materials by TEM and HREM, to examine the nature of the whisker/zirconia interface.     

Finite twist and extension of a cylindrical elastic membrane

Summary We consider a circular cylindrical membrane subjected to longitudinal extension and twist. The associated equilibrium deformation is considered to be axisymmetric and the analysis is based on a direct two-dimensional formulation. Wrinkling of the membrane is taken into account in an approximate way by introducing arelaxed strain energy function derived from the neo-Hookean strain energy for isotropic elastic solids. Analytical formulae for wrinkled parts of the membrane are used to corroborate the results of a numerical treatment of the full boundary value problem.Dedicated to the memory of A. C. Pipkin     

The controlling effect of 0.05% hydrogen sulfide gaseous atmosphere on the accelerated fatigue failure of coated MM-002 nickel-base superalloy at 650 °C

A systematic study was carried out aimed at evaluating the environmental effects of H₂S containing environment on the creep-fatigue failure of coated undirectionally solidified MM-002 nickel-base superalloy at high temperature. The cyclic loading conditions were constant and consisted of creep tension and plastic compression following the CP-mode of the strain range partitioning method. The results obtained have shown that although the pack cementation coating used showed adequate resistance under the combination of cyclic loading and oxidizing environments, this resistance was not evident under the H₂S containing atmosphere. In fact, it was found that even an amount as little as 0.05% H₂S had an extremely detrimental effect on the creep-fatigue life of the coated superalloy at 650 °C. The crack initiation and propagation in the H₂S environment was controlled by an aggressive sulphidation attack ahead of the crack tip. This was demonstrated by the formation of low melting eutectic sulfides at the plastic zone ahead of the crack tip, causing an accelerated transdendritic cracking and premature failure.     

Evaluation of a Conical Mill for Screening of Direct Compression Formulations

Suitability of a Quadro Comil^TM for screening of direct compression tablet masses was evaluated with respect to alteration of particle size distribution and blending efficiency. Air jet sieving was qualijied for determination of a particle size of spraydried lactose and microcrystalline cellulose. Using a full 3¹ × 2³ factorial design not only effects of single processing parameters (output screen size, impeller shape, velocity of the mill, and type of powder), but also their respective combinations were investigated in terms of impact on particle size and flow properties (angle of repose, bulk and tapped densities). Particle sizes before and after passing the Comil were found to be normally distributed. The results indicate that the process does not allow any of the powder characteristics studied beyond normal batch-to batch variability. This refers in particular to the proportion of fines. For evaluation of the deagglomeration effectiveness, a 2³ design was implemented with iron oxide as a model drug. Homogeneity of the blends was determined optically, and after screening twice it was found to be acceptable even with this substance, which has a particularly high agglomeration tendency, high density, and small particle size. The Quadro Comil is therefore regarded as fully suitable for deagglomeration of powders in a gentle and effective manner     

Effect of superconducting fluctuations on the nmr relaxation rate of high-T c superconductors

The effect of superconducting order parameter fluctuations on the nuclear-spin relaxation rate, 1/T ₁, is studied for clean two-dimensional systems by calculating the three Maki-Thomson-type diagrams which represent the lowest-order fluctuation contributions to the transverse susceptibility. For Gaussian fluctuations and for temperatures near the mean field transition temperature,T _c0, we employ a weak-coupling theory in which the pair-fluctuation propagator can also include pair-breaking effects. We also go beyond the Gaussian theory and take into account the interactions between Cooper-pair fluctuations corresponding to the fourth-order Ginzburg-Landau fluctuation terms. We compare our results with previous results in the dirty limit and in 3D. We obtain a pronounced peak in 1/T₁ atT _c and briefly discuss possible reasons why this peak is not observed.