Direct extraction of an empirical temperature-dependent InGaP/GaAs HBT large-signal model

A new empirical InGaP/GaAs heterojunction bipolar transistor (HBT) large-signal model including self-heating effects is presented. The model accounts for the inherent temperature dependence of the device characteristics due to ambient-temperature variation as well as self-heating. The model is accompanied by a simple extraction process, which requires only dc current-voltage (I-V) and multibias-point small-signal S-parameter measurements. All the current-source model parameters, including the self-heating parameters, are directly extracted from measured forward I-V data at different ambient temperatures. The distributed base-collector capacitance and base resistance are extracted from measured S-parameters using a new technique. The extraction procedure is fast, accurate, and inherently minimizes the average squared-error between measured and modeled data, thereby eliminating the need for further optimization following parameter extraction. This modeling methodology is successfully applied to predict the dc, small-signal S-parameter, and output fundamental and harmonic power characteristics of an InGaP/GaAs HBT, over a wide range of temperatures.     

Extraction error modeling and automated model debugging in high-performance custom designs

In the design cycle of high-performance integrated circuits, it is common that certain components are designed directly at the transistor level. This level of design representation may not be appropriate for test generation tools that usually require a model expressed at the gate level. Logic extraction is a key step in test model generation to produce a gate-level netlist from the transistor-level representation. This is a semi-automated process which is error-prone. Once a test model is found to be erroneous, manual debugging is required, which is a resource-intensive and time-consuming process. This paper presents an in-depth analysis of typical sets of extraction errors found in the test model representations of the pipelines in high-performance designs today. It also develops an automated debugging solution for single extraction errors for pipelines with no state equivalence information. A suite of experiments on circuits with similar architecture to that found in the industry confirms the fitness and practicality of the solution.     

Terminal slider control of robot systems

Many robotic systems would, in the future, be required to operate in environments that are highly unstructured (with varying dynamical properties) and active (possessing means of self-actuation). Although a significant volume of results exist in model-based, robust and adaptive control literature, many issues pertinent to the stabilization of contact interactions with unpredictable environments remain unresolved, especially in dealing with large magnitude and high frequency parametric uncertainties. The primary intent of this paper is nonlinear control synthesis for robotic operations in unstructured environments. We introduce the notion oftime constrained terminal convergence for controlled systems, and propose an approach to nonlinear control synthesis based upon a new class of sliding modes, denotedterminal sliders. Terminal controllers that enforce finite convergence to equilibrium are synthesized for an example nonlinear system (with and without parametric uncertainties). Improved performance is demonstrated through the elimination of high frequency control switching, employed previously for robustness to parametric uncertainties [2]. The dependence of terminal slider stability upon the rate of change of uncertainties over the sliding surface, rather than the magnitude of the uncertainty itself, results in improved control robustness. Improved reliability is demonstrated through the elimination ofinterpolation regions [2]. Finally, improved (guaranteed) precision is argued for through an analysis of steady state behavior.A preliminary version of this paper appeared as a JPL Engineering Memorandum # 347-90-284, Jet Propulsion Laboratory, Pasadena, CA, December 1990.     

CD72-mediated B cell activation involves recruitment of CD19 and activation of phosphatidylinositol 3-kinase

Occupancy of the B cell glycoprotein, CD72 results in syk-independent activation of phospholipase-C gamma and calcium mobilization. The cytoplasmic tail of CD72 does not contain an immunoreceptor tyrosine-based activation motif to directly transduce signals into the B lymphocyte. Hence, we investigated whether other coreceptors such as CD19 and its associated phosphatidylinositol 3-kinase (PI 3-K) were involved in CD72 signaling. Two specific inhibitors of PI 3-K inhibited CD72-stimulated B cell proliferation in a dose-dependent manner. Activation of B lymphocytes via CD72 resulted in recruitment and activation of PI 3-K, which was mediated by CD19. Accordingly, CD72 ligation induced CD19 tyrosine phosphorylation. Thus, lipid products generated as a result of PI 3-K activation may have an important function in CD72-mediated B lymphocyte activation. The kinetics of CD19 tyrosine phosphorylation induced by CD72 ligation were strikingly different from those seen following B cell antigen receptor (BCR) stimulation. A transient increase in the tyrosine phosphorylation of the complement receptors, CD21 and CD35 was observed in BCR- but not CD72-stimulated cells. Co-cross-linking of CD72 and CD19 failed to induce syk tyrosine phosphorylation suggesting that even under these conditions, CD72 signaling was independent of syk activation. A transient and stimulation-dependent physical association between CD19 and CD72 was observed in CD72-ligated cells. These observations suggest a mechanism by which CD72 can recruit CD19 and influence activation of CD19-associated PI 3-K, which appears to be critical for CD72-mediated B cell activation.     

Soft modes and structural phase transitions

This paper presents a survey of soft modes and their relationship to structural phase transitions. After introducing the concept of a soft mode, the origin of softening is considered from a lattice-dynamical point. The Landau theory approach to structural transitions is then discussed, followed by a generalisation of the soft-mode concept through the use of the dynamic order-parameter susceptibility. The relationship of soft modes to broken symmetry is also examined. Experimental results for several classes of crystals are next presented, bringing out various features such as the co-operative Jahn-Tellev effect. The survey concludes with a discussion of the central peak, touching upon both the experimental results and the theoretical speculations. Survey presented at the discussion meeting on phase transitions arra nged by the Indian Academy of Sciences at Bangalore in June 1978.     

The Gabriel-Colman rearrangement in biological systems: design, synthesis and biological evaluation of phthalimide and saccharin derivatives as potential mechanism-based inhibitors of human leukocyte elastase, cathepsin G and proteinase 3

Metal ion-promoted binding of Saccharomyces cerevisiae alcohol dehydrogenase to Cibacron Blue 3GA was used for its isolation by affinity precipitation with Eudragit-bound dye. The yeast cells were broken and the cell debris was separated by flocculation with poly(ethylene imine). The supernatant containing the enzyme activity was mixed with Eudragit--Cibacron Blue in the presence of zinc ions. The precipitation of the affinity complex was induced by the addition of 50 mM CaCl2 and a subsequent increase in temperature to 40 degrees C. The enzyme was desorbed by treating the precipitate with iminodiacetic acid solution. The procedure resulted in about 66% recovery of enzyme activity with more than 20-fold purification. Recycling of Eudragit--dye for enzyme purification was also shown to be possible.     

A view of computability on term algebras

A framework of definitions for, and questions about, notions of computability, complexity, and logic for term algebras is built around known results in the literature and the current work. The term algebra for finite binary trees and various classes of programs for computing on them, a class similar to LISP being the most powerful, serve as a focus. Several interesting classes of programs less powerful than LISP are obtained by varying the functions and predicates available in the programming language. It is shown how they relate to one another and then some of their properties are explored. For example, there is a class powerful enough to compute all the partial recursive functions on the natural numbers that is neither sufficiently powerful to code the binary trees into the natural numbers nor to recognize any set that is both infinite and coinfinite. A simple logic sufficient to talk about trees and LISP-like computations is given and it is suggested that certain pebble games provide very reasonable measures of complexity of trees. It is also indicated how various particular results give further insight into such fundamental notions as Turing computable and recursively enumerable.     

Microstructure and microhardness in alumina gel monoliths

Alumina gel monoliths prepared from aluminium isopropoxide through hydrolysis and chemical polymerization are porous, transparent, and consist of ultrafine particles. The monolithic xerogels exhibit lamellar, cellular and fractal microstructures which are found to arise due to instabilities during drying. Phase separation can occur during ageing and drying and influence the microstructure. The Vickers indentation hardness shows a power-law dependence on relative density.     

Phase equilibra of polystyrene/polybutadiene/tetrahydrofuran using gel permeation chromatography

Gel permeation chromatography using sequential differential refractive index and ultraviolet detectors has been successfully used to give the compositional analysis of conjugate phases in the incompatible system of polystyrene and polybutadiene with tetrahydrofuran as solvent. Application of this method to equilibrated samples yields tie lines, binodal curves, and plait points. The effects of molecular weights and molecular weight ratios on the slopes of the tie lines, the location of the binodal curve, and the depletion of second polymers from phases are discussed.