The evolution of the WPI Advance Space Design Program-an evolvingprogram of technical and social analysis using the NASA Space Shuttlefor engineering education

In December of 1982, Worcester Polytechnic Institute, with the cooperation and support of the Mitre Corporation, initiated a primarily undergraduate educational program to develop experiments to be flown onboard a NASA Space Shuttle. Christened the MITRE WPI Space Shuttle Program, it sponsored the development of five educationally meritorious experiments over a period of four years. Although the experiments were ready to fly in early 1986, the Challenger disaster delayed their flight until the Spring of 1991. The delay notwithstanding, the benefits of the first program were sufficient to justify the development of a second set of experiments. More comprehensive in scope, this new venture, named the Advanced Space Design Program, addresses both technical and social areas of interested related to space flight. The authors present a general historical overview and self-assessment of WPI's space design programs     

Thermochemical investigation of binary liquid mixtures in glass-forming oxide systems

Methods and equipment successfully employed in high- temperature calorimetry to measure partial and integral enthalpies of mixing in liquid oxide systems are reviewed with special attention given to the drop-mixing method. This technique has been used to measure enthalpies of mixing in binary liq-uid mixtures composed of network forming oxides (e.g. SiO₂) and network modifying oxides (e.g. Na₂O). Results for the systems Na₂O-SiO₂ and Na₂O- B₂O₃ are presented graphically. Entropies of mixing were estimated by combining enthalpies with available data on Gibbs energies of mixing. Prominent thermochemical features of glass-forming oxide melts are pointed out. The observed thermodynamic behavior is discussed in relation to its structural basis.     

Recovery of residual oil using the alkali/surfactant/polymer process: effect of alkali concentration

An experimental study was conducted to examine the effectiveness of sodium carbonate in alkali, surfactant and polymer combined slugs in recovering waterflood residual oil. The effects of sodium carbonate concentration on the slug viscosity, interfacial tension, and phase behavior were first examined. Core flood experiments were conducted with unfired linear Berea sandstone cores. The incremental oil recovery, oil cut, residual resistance factor, and chemical propagation were measured for each flood.A significant oil bank was formed for all combined slugs having sodium carbonate concentration ≥1 wt%. The incremental oil recovery, oil cut and the injectivity of the combined slugs greatly improved as sodium carbonate concentration was increased. The effect of sodium carbonate concentration on chemical propagation was dramatic for the synthetic surfactant; a slight delay in surfactant breakthrough and a much slower rate of surfactant propagation were observed at high sodium carbonate concentrations.The results obtained in the present study indicate that the residual oil was recovered by two mechanisms: low interfacial tension and wettability reversal. The former mechanism is dominant at sodium carbonate concentrations ≤1 wt%, whereas the latter plays an important role only at high sodium carbonate concentrations.     

Assessment of melt cleanliness in A356.2 aluminium casting alloy using the porous disc filtration apparatus technique: Part II Inclusion analysis

The data obtained on inclusion types and concentrations has been analysed in the present part in terms of their effect on filtration time and fluidity (measured by the length of solidified metal in quartz tubes). The dross, i.e., the oxide layer that formed on the surface of the molten metal, was carefully collected and its mass determined; then it was examined in a scanning electron microscope equipped with an energy-dispersive X-ray system. The results show that inclusions are not the only parameter to be considered. More importantly, it is Al2O3 (films or particles), which seems to be the deciding factor. It is found, however, that it is quite difficult to separate the individual role of each parameter using the porous disc filtration apparatus (PoDFA) technique, i.e., sampling, without disturbing the molten metal. Sampling would introduce undesirable oxides into the PoDFA crucible, resulting in an artificial increase in the filtration time. Increasing the holding periods of the molten metal increases the quantity of dross. In all cases, the skimmed dross is wet, i.e., it contains an appreciable amount of molten metal. The main types of oxides in the dross are MgO, MgAl2O4, Al4C3 and Al2O3. This revised version was published online in November 2006 with corrections to the Cover Date.     

The GS algorithm for exact linearization to Brunovsky normal form

An algorithm utilizing the minimal number of integrations for the exact linearization of nonlinear systems to Brunovsky normal form under nonlinear feedback is presented. The tools which are involved are based on classical constructions appearing in the theory of exterior differential systems     

Gain recovery of bulk semiconductor optical amplifiers

The gain recovery time of 1.55-μm bulk semiconductor optical amplifiers (SOA's) with lengths from 500 to 1500 μm has been measured with a continuous-wave (CW) probe in the time domain. It is shown to decrease with increasing length down to 60 ps for the longest SOA. This behavior is theoretically explained. A lower limit for the recovery time is observed and explained     

Mesa-isolated GaAs Schottky-barrier photodiodes

The design, fabrication and characterisation of GaAs Schottky-barrier photodiodes with evaporated, free-standing-metal airbridges is reported. The photodiodes were fabricated using all dry-etching techniques. Anisotropic chemically assisted ion beam etching was used to etch vertical sidewall mesas, and isotropic reactive ion etching was used to etch a lateral tunnel. A free-standing-metal airbridge created by the lateral tunnel etch results in isolation of the active area at the same time providing free-standing-metal interconnection to the contact pad.<>     

论网络升级方式与光纤选择的关系

在重点说明影响传输光纤设计的主要问题的同时，简要介绍了各种升级方式所面临的主要技术挑战，并详细说明这些挑战对传输光纤提出的技术要求。     

Mechanism of current transfer in oxidized iron ore minerals

Mining Institute, Krivoi Rog. Translated from Fiziko-Technicheskie Problemy Razrabotki Poleznykh Iskopaemykh, No. 2, pp. 107-116, March-April, 1992.     

High-reliability GaAs-AlGaAs HBTs by MBE with Be base doping andInGaAs emitter contacts

The authors have developed a modified MBE growth process to produce high-gain n-p-n GaAs-AlGaAs heterojunction bipolar transistors (HBTs) with a mean time to failure (MTTF) of 1.5×10⁸ h at 125°C. Beryllium incorporation and diffusion are controlled through a combination of reduced substrate temperature and increased As/Ga flux ratio during MBE growth, resulting in extremely stable HBT profiles. The authors also demonstrate graded InGaAs surface layers with nonalloyed refractory metal contacts that significantly improve ohmic reliability compared to alloyed AuGe contacts. The ability to produce robust HBTs by MBE is critically important to this technology