PCAAD—an object-oriented expert system for assembly of printed circuit boards

Abstract: Electronics manufacturing is the fastest growing segment of the manufacturing domain today. The rapid change in printed circuit board manufacturing has been possible with the induction of surface-mounted components and robotic assembly. The high density packaging capability of surface-mounted technology has contributed enormously to the development of new trends in printed circuit board manufacturing.
PCAAD—Printed Circuit Board Assembly Advisor—is an expert system developed to capture this new technology and its interaction with the existing through-hole-mounting technology. In building the system, rules and guidelines pertaining to assembly are formulated and incorporated into the knowledge-base. The system is built on an object-oriented paradigm. The object-oriented approach, Smalltalk-80, the object-oriented language and the hierarchical rule structure paradigm are briefly discussed. A rating system is also introduced to rank various assembly designs. PCAAD can advise whether or not to proceed with assembly with a particular assembly design, and suggests assembly modification at the early stage of design to eliminate the assembly problems in the later phase of board production.     

Chemical activation of the SHS process in the Nb−C system

The phenomenon of chemical activation is investigated using combustion of the Nb–C system in the presence of an activating additive, namely, polytetrafluoroethylene, as an example. Regions of the parameters of the process are found where the interaction occurs by two different mechanisms. The characteristic features of the process are established and the role of the activating additive in each region is determined.Institute of Chemical Physics, Academy of Sciences of Armenia, Yerevan. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 65, No.5, pp.590–593, November, 1993.     

Green laser sources optimized for highly efficient microdisplay‐based field‐sequential mobile projectors

Abstract— A novel green laser source, based on a monolithic cavity microchip laser platform, has been developed. The laser is designed to be a part of a miniature and efficient RGB light source for microdisplay‐based mobile projector devices. The use of highly efficient, periodically poled MgO‐doped lithium niobate as the non‐linear frequency doubler allows for a significant increase in the overall efficiency of the green microchip laser. Specifically, a 50–150‐mW green output with a wall‐plug efficiency exceeding 10% in the temperature range of greater than 40°C has been demonstrated. A compact package for this laser source with a volume less than 0.33 cm³ is discussed and results of performance tests are presented.     

Composite W–Cu powders by joint reduction of oxides in combustion mode

Composite powders W–Cu were prepared via joint reduction of WO₃ and CuO oxides with Mg?C combined reducer in a combustion mode by using the method of coupled reactions. Combustion phenomenology and the processes of phase and microstructure formation were investigated by thermocouple and copper- wedge techniques combined with XRD, SEM, and EDS analyses. Thermal conditions of combustion and phase composition and microstructure of products were found to depend on a Mg/C ratio in green mixtures. It was established that the magnesiothermic reaction was preceded by the stage of low-caloric carbothermal reduction. Slow propagation of combustion wave was found to favor the complete reduction of oxides and formation of target W–Cu composite nanopowder.     

Biomass production and small-scale testing of freeze-dried lactic acid bacteria starter strains for cassava fermentations

Based on their predominance in Gari fermentations, as well as suitable technological properties, Lactobacillus plantarum, Lactobacillus fermentum, Weissella paramesenteroides and Leuconostoc mesenteroides strains were investigated for their suitability for development as starter strains for this African traditional fermented cassava product. The strains were grown in optimized growth media in 2 L fermenters, harvested and freeze dried, and then tested in lab-scale cassava mash fermentation trials for their ability to ferment the cassava. The strains performed well and rapidly increased the titratable acidity from 1.1 to 1.3% at 24 h to 1.3–1.6% at 48 h. The benefit of including starter cultures was that it lowered the pH of the product much faster and to lower levels than in the uninoculated control fermentation. The results furthermore indicated that especially the L. plantarum-group strains could be produced as starter strains at low cost. Overall, the results of this study showed that starter strains could be easily and economically produced, and thus represent a feasible possibility for further development for application in the field.     

WC-based catalyst for isopropyl alcohol dehydration as prepared by combustion synthesis

WC-based catalyst was prepared by SHS method using highly exothermic WO₃ + Mg + C mixtures. Two kinds of tungsten oxide—commercially available and obtained by decomposition of the peroxo complex of tungsten oxide—were used as tungsten sources. To soften violent conditions of combustion, the well-known salt dilution method was applied. Tuning the reaction temperature by added NaCl and carbon afforded to regulate the composition of products. As a result, a submicron-sized WC/C material with an 11 m²/g specific surface area was produced. The latter was tested for the catalytic activity in isopropyl alcohol conversion. An 83% alcohol conversion into propylene and water with 100% selectivity was observed at ≈200°C.     

Features of combustion in the system niobium-carbon in the presence of an activating addition

Combustion processes are considered for stoichiometric mixtures of niobium with carbon with substitution of some of the carbon black by an activating addition, i.e. fluoroplastic. It is shown that in the presence of a small amouni (0.1–1.0 wt.%) of fluoroplastic the mixture acquires the capacity to burn without using any additional procedures.Erevan. Translated from Fizika Goreniya i Vzryva, Vol. 27, No. 6, pp. 72–77, November–December, 1991.     

Synthesis of WSi2 -SiC composite under the thermally activated combustion mode

Opportunities on combustion synthesizing the WSi2-SiC ceramic composites in a wide range of compositions under the thermal activated mode were studied. Tungsten, silicon powders and carbon black were used as initial reagents, and Magnesium–Teflon mixture was used as an activating additive. The stepwise character of the combustion process evolution, being characterized by low- and high-temperature regimes, was revealed. The end-products were subjected to SEM, XRD and DTA/TG analyses.     

Applicability of X-ray reflectometry to studies of polymer solar cell degradation

Although degradation of polymer solar cells is widely acknowledged, the cause, physical or chemical, has not been identified. The purpose of this work is to determine the applicability of X-ray reflectometry for in situ observation of physical degradation mechanisms. We find that the rough interfaces of the polymer solar cell constituent layers seriously obstruct the sensitivity of the technique, rendering it impossible to elucidate changes in the layer/interface structure at the sub-nanometer level.