Low dark current quasi-Schottky barrier MSM-photodiode structures on n-Ga/sub 0.47/In/sub 0.53/As with p/sup +/-Ga/sub 0.47/In/sub 0.53/As cap layer

The p/sup +/-cap layer was used to fabricate a metal-semiconductor-metal (MSM) interdigitated photodetector on Ga/sub 0.47/In/sub 0.53/As. The measured barrier height was Phi /sub Bn=/0.52 V, the ideality factor n=1.1 and average dark current density 2 mA/cm/sup 2/. A rise time of 45 ps at lambda =1.3 mu m under 2 V bias was measured for an MSM photodiode with 3 mu m finger width and finger gaps and an active area of 100*100 mu m/sup 2/.<>     

Product Focused Software Process Improvement: Concepts and Experiences from Industry

Management problems in the development of software have been addressed over the last years by a strong focus on the improvement of the development processes. Software process improvement (SPI) activities are characterized by an internal focus on a software development department and its procedures. However, the quality of the product is hardly addressed in software process improvement programs. This paper presents the application of a model for product focused SPI (P-SPI) and describes experiences with this model in practice. The main conclusions are that P-SPI puts products to be developed in a central position in improvement programs, results in fulfilling specific quality goals of a company and project, and industrial experiments show interesting benefits. Applying the approach in industrial projects showed that P-SPI is relatively cheap and gives fast results and high benefits.     

Quality through Managed Improvement and Measurement (QMIM): Towards a Phased Development and Implementation of a Quality Management System for a Software Company

The paper describes results of a longitudinal study of developments in the area of software product and process quality improvement within a Hungarian software company, IQSOFT Ltd. This company has been active in this area since 1993, trying to build, introduce and maintain an efficiently working quality management system which, e.g., fulfils the ISO 9001 requirements, allows steady software process improvement and, at the same time, conforms to company's own needs. Over the last eight years five phases could be distinguished. Each phase is described shortly, following the same structure, namely: basic starting points, key problem areas, literature consulted, activities and design executed, reflections on what happened and why. The lessons resulting from the analysis of this case have been formulated in terms of guidelines. We feel that these are applicable to any low maturity software development organisation embarking on a product or process quality improvement endeavour. These guidelines are developed around a framework containing the basic issues of software production (project management, technical processes and products). The guidelines advocate a careful step-by-step development of definitions, quality characteristics, and metrics related to these objects while at the same time developing and introducing the associated process.     

The W-Process for Software Product Evaluation: A Method for Goal-Oriented Implementation of the ISO 14598 Standard

The importance of software product evaluations will grow with the awareness of the need for better software quality. The process to conduct such evaluations is crucial to get evaluation results that can be applied and meet customers' expectations. This paper reviews a well-known evaluation process: the ISO 14598 standard. The review focuses on the difficulties in selecting and evaluating the appropriate evaluation techniques. The review shows that the standard has problems in applying evaluation processes in practice due to insufficient attention to goal definition and to relationships between activities being implicit. Also, the standard ignores the trade-off between goals and resources and pays insufficient attention to feedback. To address these deficiencies, the W-process is proposed. It extends the standard through an improved process structure and additional guidelines.     

Glucose and sucrose fermenting capacity of homofermentative lactic acid bacteria used as starters in fermented salads.

Salads, i.e., vegetables and/or meat in an oil-in-water emulsion with a low pH due to the addition of acids, are popular in western countries. The shelf life of these salads is influenced mainly by storage temperature and the use of preservatives, i.e., sorbic and benzoic acid. Lactic acid fermentation could be an interesting novel approach to salad preparation. As part of an investigation on fermented salads, lactic acid bacteria from the genera Lactobacillus, Pediococcus and Streptococcus were screened for their capacity to ferment glucose and sucrose in a model system and in a standard salad. The temperature optimum of these strains was in the range of 34-48 degrees C. Most of these strains produced about equal amounts of L(+)- and D(-)-lactic acid. To determine the specific sugar fermenting capacity (mmol lactic acid produced per min per g dry weight) of non-growing cells of lactic acid bacteria, a semi-automated model system was used, based on monitoring the pH decrease in a phosphate buffer during conversion of sugars to lactic acid. The strains tested showed acid production rates on glucose varying between 0.03 and 0.39 mmol of acid produced per min per g dry weight (average 0.23). These glucose-grown cells showed varying, but lower fermentation rates on sucrose (0-0.25 mmol/min/g d.w., average 0.04) than sucrose-grown cells (0-0.33 mmol/min/g d.w., average 0.19). Results obtained with the model system were in good agreement with those of fermentation tests, carried out with a standard salad. Inhibition of spoilage bacteria in the standard salad could be achieved by using starter cultures with high fermenting capacity.     

At least four percent of the Salmonella typhimurium genome is required for fatal infection of mice

Salmonella typhimurium infection of mice is an established model system for studying typhoid fever in humans. Using this model, we identified S. typhimurium genes which are absolutely required to cause fatal murine infection by testing independently derived transposon insertion mutants for loss of virulence in vivo. Of the 330 mutants tested intraperitoneally and the 197 mutants tested intragastrically, 12 mutants with 50% lethal doses greater than 1, 000 times that of the parental strain were identified. These attenuated mutants were characterized by in vitro assays which correlate with known virulence functions. In addition, the corresponding transposon insertions were mapped within the S. typhimurium genome and the nucleotide sequence of the transposon-flanking DNA was obtained. Salmonella spp. and related bacteria were probed with flanking DNA for the presence of these genes. All 12 attenuated mutants had insertions in known genes, although the attenuating effects of only two of these were previously described. Furthermore, the proportion of attenuated mutants obtained in this study suggests that mutations in about 4% of the Salmonella genome lead to 1,000-fold or greater attenuation in the mouse typhoid model of infection. Most of these genes appear to be required during the early stages of a natural infection.     

Molecular characterization of a heme-binding protein of Bacteroides fragilis BE1

An iron-repressible 44-kDa outer membrane protein plays a crucial role in the acquisition of heme by the anaerobic bacterium Bacteroides fragilis. The DNA sequence of the gene encoding the 44-kDa protein (hupA) was determined. The hupA gene encodes a protein of 431 amino acid residues with a calculated molecular mass of 48,189 Da. The hupA gene is preceded by an open reading frame of 480 bp that probably encodes a protein with a calculated molecular mass of 18,073 Da. hupA and this open reading frame are likely organized in an operon, and a sequence homologous to the Escherichia coli consensus Fur box was present in the putative promoter region of the operon. Heme-binding studies showed that HupA binds heme. Analysis of the deduced amino acid sequence revealed signature heme-binding consensus motifs, characteristic of heme lyases. Subcellular localization studies in E. coli revealed that HupA was mainly found in the cytoplasmic membrane but not in the outer membrane of E. coli. This suggested that B. fragilis uses another strategy for the translocation of this outer membrane protein across its cell envelope than E. coli does. HupA did not have significant homology with other putative bacterial heme receptors.     

Hysteresis in quartz resonators-a review

The literature on the frequency versus temperature characteristics of quartz crystal resonators is reviewed. Three papers that deal with frequency versus pressure hysteresis are included, as these may possibly have relevance to frequency versus temperature hysteresis. It is seen that the causes of hysteresis are not well understood. The evidence to date is inconclusive. The mechanisms that can cause hysteresis include: strain changes changes in the quartz, contamination redistribution, oscillator circuitry hysteresis, and apparent hysteresis due to thermal gradients. The results to date seem to indicate that lattice defects are somehow related to thermal hysteresis. Stress relief in the mounting structure can also produce significant hysteresis. As crystal processing techniques have improved. contamination has become less of a problem.