GaInP/GaAs HBTs for high-speed integrated circuit applications

The use of GaInP/GaAs heterojunction bipolar transistors (HBTs) for integrated circuit applications is demonstrated. The discrete devices fabricated showed excellent DC characteristics with low V_ce offset voltage and very low temperature sensitivity of the current gain. For a non-self-aligned device with a 3-μm×1.4-μm emitter area, f_T was extrapolated to 45 GHz and f_max was extrapolated to 70 GHz. The measured 1/f noise level was 20 dB better than that of AlGaAs HBTs and comparable to that of low-noise silicon bipolar junction transistors, and the noise bump (Lorentzian component) was not observed. The fabricated gain block circuits showed 8.5 dB gain with a 3-dB bandwidth of 12 GHz, and static frequency dividers (divide by 4) were operable up to 8 GHz     

Cold forming processes: some examples of predictions and design optimization using numerical simulations

Predicting the behaviour of steel during a deformation process, and then under service conditions, is one of the main challenges in cold forming. The design of optimized forging schedules, by means of classical trial+errors procedures, has become increasingly heavy in terms of time and cost in a competitive environment. Simultaneously, the improvement of steel qualities requires the microstructure, constitutive behaviour and deformability to be known a priori regarding a targeted application. During the last few years, numerical simulations have become a very efficient tool to reach these goals.

In this paper, we give examples of innovating forging sequences developed by numerical simulations, including the investigation of damage in tools and forged parts. In case of specific processes with very determined geometry — such as wire drawing — we show how systematic numerical studies may lead to predictive models of force, local strains and residual stress…

However, reliable predictions from numerical simulations require reliable input data, including constitutive laws, friction conditions and propensity to ductile damage. These data must be characterized under realistic sollicitations. Typical cold forging loadings are indeed very severe: local strains up to 600%, strain rates locally greater than 1000 s⁻¹, and subsequently, plastic heating over 500°C.

To characterize the constitutive behaviour, the standard upset test between grooved dies is used along with an original methodology to derive the strain hardening curve from the experimental force-displacement recording. Tool elastic deformations, specimen strain heterogeneity… are taken into account. This enables a precise determination of the strain hardening curve up to about 100% of strain. The extrapolation of the flow stress to greater deformations is then very easy and reliable. Such a test can be performed under quasi-static and isothermal conditions (0.1 s⁻¹ but also adiabatic and rapid conditions (up to 10 s⁻¹). This procedure was adapted to a Pellini hammer, which enables very simple characterization at 800 s⁻¹. The comparison of all these flow curves lead to the formulation of an original constitutive model, which accounts for the effects of plastic heating, strain rate, dynamic aging…

In order to predict ductile fracture during the forging process, the most classical criteria were tested over a wide range of experimental loading conditions. None of them were general enough to solve all the cold forming problems. On the other hand, mesoscopic models describing the deformation of the metal matrix around inclusions or second phases have proved to be in good agreement with the various experimental observations. An original plasticity criterium, based on the recent works in porous plasticity theory, has been developed and already displays promising capabilities. Simple experimental procedures enable a reliable classification of steel qualities, heat treatments… in term of forgeability.

Finally, the friction problem is treated using different methodologies based on the forming process considered. For forging operations, a fine analysis of the force-displacement curves in direct extrusion stages may lead to a precise measurement of the friction coefficient under pressures from about 200 MPa up to 1000 MPa and for sliding rates between 1 and 100 mm/s. For wire drawing process, a model relying on an analytical approach using a significantly improved slice method has been developed: the comparison of the experimental drawing force and the predicted one gives the friction coefficient in industrial processing conditions (speed up to 5 m/s).     

Relationship between the attenuation of downwelling irradiance at 490 nm with the attenuation of PAR (400 nm-700 nm) in the Baltic Sea

The vertical attenuation coefficient of diffuse downwelling irradiance at 490 nm (K_d 490) is a parameter that we routinely derive from SeaWiFS images of the Baltic Sea. Here, through model simulations, we examine the relationship between K_d(490), and the vertical attenuation coefficient of PAR (K_d PAR), as this later coefficient determines the light available for aquatic photosynthesis. A simple semi-analytical model is used to predict K_d(490) and K_d(PAR), as a function of the concentrations of chlorophyll, colored dissolved organic material (CDOM), suspended inorganic, and suspended organic particulate material. A series of model simulations based on variations in these optically significant constituents over a range realistic for the Baltic Sea, are used to define the relationship between the two attenuation coefficients.

Kd(PAR)=0.6677Kd^0.6763(490).     

Multidisciplinary Simulation of the Maneuvering of an Aircraft

A computational methodology for the simulation of the transient aeroelastic response of an unrestrained and flexible aircraft during high-G maneuvers is presented. The key components of this methodology are: (a) a three-field formulation for coupled fluid/structure interaction problems; (b) a second-order time-accurate and geometrically conservative flow solver for CFD computations on unstructured dynamic meshes; (c) a corotational finite element method for the solution of geometrically nonlinear and unrestrained structural dynamics problems; (d) a robust method for updating an unrestrained and unstructured moving fluid mesh; and (e) a second-order time-accurate staggered algorithm for time-integrating the coupled fluid/structure semi-discrete equations of motion. This computational methodology is illustrated with the simulation on a parallel processor of several three-dimensional high-G pullup maneuvers of the Langley Fighter in the transonic regime, using a detailed finite element aeroelastic model.     

Seismic response of a 40‐storey buckling‐restrained braced frame designed for the Los Angeles region

This study utilized nonlinear response history analysis to compare the seismic demand on three variations of a 40‐storey buckling‐restrained braced frame designed for high seismic hazard in the Los Angeles region. The three designs were referred to as a ‘code‐based design’, based on the 2006 International Building Code, a ‘performance‐based design’, based on criteria published by the Los Angeles Tall Building Design Council (LATBSDC) and a ‘performance‐based design plus’, based on newly developed criteria from The Pacific Earthquake Engineering Research Center (PEER). The response history analysis utilized spectrum‐matched ground motions as well as simulated ground motions for the Puente Hills fault. The spectrum‐matched motions were selected from the Next Generation Attenuation of Ground Motions (NGA) database, which is largely composed of recorded motions and scaled to five hazard levels. The simulated ground motions were broadband signals generated from a moment magnitude (M_w) 7.15 scenario rupture of the Puente Hills fault for two near fault regions and exhibit long period energy content that significantly exceeds the uniform hazard spectrum. Structural performance was assessed in terms of exceedance of a safe inter‐storey drift ratio (IDR). It was seen that the simulated ground motions impose higher IDR demands on the structures than the spectrum‐matched NGA ground motions. Furthermore, the number of instances of exceedance of a safe IDR, considered for this study as IDR = 0.03, is substantially higher for the simulated ground motions, pointing to the importance of considering such motions in the collapse prevention of tall buildings on a site‐specific basis. Copyright © 2010 John Wiley & Sons, Ltd.     

Results of transplantation for acute and chronic hepatic allograft rejection

B-chronic lymphocytic leukemia (CLL) is characterized by an accumulation of long-lived, resting B cells expressing the Bcl-2 protein. However, less than 10% of the CLL patients shows bcl-2 gene rearrangement in blood cells, using traditional Southern blotting analysis. In the present study, rearrangement of the bcl-2 gene in CLL cells was studied by pulsed-field gel electrophoresis (PFGE). With this method, large DNA fragments (> 50-10,000 kb) could be analyzed. Blood CLL cells from 9 of 9 patients and 2 of 2 CLL cell lines showed rearranged bcl-2 gene. In comparison, healthy blood B cells and lymphoblastoid cell lines (LCLs) established from normal peripheral blood lymphocytes of the patients showed only germ line configuration. Thus, the possibility of restriction fragment length polymorphisms (RFLPs) in this gene could be excluded. The primary cell involved in CLL might be a progenitor B cell that has accidentally rearranged the bcl-2 gene. As a consequence, such cells express stable amount of Bcl-2 protein and do not enter apoptosis. During prolonged survival, such cells may acquire secondary changes including chromosomal translocations and mutations.     

Thick boride coatings by chemical vapor deposition

In this paper we describe an experimental study of the chemical vapor deposition (CVD) of TiB₂ by the hydrogen reduction of TiCl₄ and BCl₃ with the purpose of obtaining very thick (more than 100 μm) and uniform coatings. The optimum deposition conditions were as follows: temperature, 900–950 °C; source gas ratios, $\text{[}\text{Ti}\text{]/[}\text{B}\text{] =}\text{1}\text{2}$ and $\text{[}\text{H}\text{]/[}\text{Cl}\text{] =}\text{6}\text{1}$. With these conditions, deposition rates greater than 25 μm h^-1 were obtained. The composition was very uniform with an excess of boron over stoichiometry (probably in the form of free boron). A small amount of chlorine remained incorporated in the deposit probably as TiCl₂ (0.05 wt.% at 950 °C). The coatings were very hard (about 3700 kgf mm^-2) and hardness was uniform through the thickness. With careful control of the deposition parameters, the CVD of uniform coatings with thickness of 1 mm or more appears feasible.     

Magnetic resonance diffusion imaging of ovarian masses: a first experience with 12 cases

Objective: The objective of the study was to determine the feasibility of using apparent diffusion coefficient (ADC) measurement for the differential diagnosis of malignancy in ovarian masses. Materials and methods: Twelve cases involving ovarian masses were imaged using spin echo diffusion magnetic resonance imaging (MRI). Five cases involved malignant ovarian masses, on the basis of postoperative histologic examination, and the rest involved benign masses. The ovarian masses were imaged in vivo (10 cases) before surgery and ex vivo (8 cases) after surgical resection. Diffusion-weighted data were corrected for motion using the phase data from unweighted data in nine cases. Multifactorial analysis of variance was used to evaluate the effects of malignancy, location (in vivo versus ex vivo), and motion correction on the measurement of ADC intensity and texture. Results: Motion correction caused an undesirable spatial smoothing of the ADC maps and a significant interaction ( ) was found between location and motion correction. ADC value ( ) and texture ( ) differences were found between malignant and nonmalignant ovarian masses. Conclusion: Measurement of ADC intensity and texture has the potential to differentially diagnose malignancy in individual ovarian masses if the problem of image motion artifact can be eliminated through the use of faster imaging sequences.Acknowledgements. The cooperation of Dr. Vance Chow in the acquisition of the in vivo diffusion MRI data is gratefully acknowledged. Thanks to Ron Borowsky for discussions on the statistical data analysis. Data management, final data analysis, and figure preparation was completed by Jennifer Hadley. This work was supported by the Canadian Institutes for Health Research (CIHR) and the Saskatchewan Health Services Utilization and Research Commission (HSURC).     

On finding minimal-length test sets for diagnosing faults in combinational circuits

A fault-detection matrix contains sufficient information for finding minimal-length, fault-diagnosis test sets. The necessary and sufficient condition is that the submatrix of the fault-detection matrix must not contain equal rows. Cited examples demonstrate that characteristics in the fault-detection matrix can be used to facilitate the search for tests.     

Legume-based fermented foods: their preparation and nutritional quality

Legume-based fermented foods are very popular in the Southeast Asia, the Near East, and parts of Africa. They form an appreciable part of daily diet of people as a main source of protein, calories, and certain vitamins. Preparation of legume-based fermented foods has remained to some extent an art, and their nutritional quality has been of interest to both professionals and layman. The fermentation process helps not only in improving the organoleptic quality of legumes but also enhances nutritional quality. This review examines the production of various legume-based fermented foods and critically assesses their nutritional quality.