Monolithically integrated HgCdTe focal plane arrays

The cost and performance of hybrid HgCdTe infrared (IR) focal plane arrays are constrained by the necessity of fabricating the detector arrays on a CdZnTe substrate. These substrates are expensive, fragile, available only in small rectangular formats, and are not a good thermal expansion match to the silicon readout integrated circuit. We discuss in this paper an IR sensor technology based on monolithically integrated IR focal plane arrays that could replace the conventional hybrid focal plane array technology. We have investigated the critical issues related to the growth of HgCdTe on Si read-out integrated circuits and the fabrication of monolithic focal plane arrays: (1) the design of Si read-out integrated circuits and focal plane array layouts; (2) the low-temperature cleaning of Si(001) wafers; (3) the growth of CdTe and HgCdTe layers on read-out integrated circuits; (4) diode creation, delineation, electrical, and interconnection; and (4) demonstration of high yield photovoltaic operation without limitation from earlier preprocessing such as substrate cleaning, molecular beam epitaxy (MBE) growth, and device fabrication. Crystallographic, optical, and electrical properties of the grown layers will be presented. Electrical properties for diodes fabricated on misoriented Si and readout integrated circuit (ROIC) substrates will be discussed. The fabrication of arrays with demonstrated I–V properties show that monolithic integration of HgCdTe-based IR focal plane arrays on Si read-out integrated circuits is feasible and could be implemented in the third generation of IR systems.     

Structural and magnetic investigations of some new boron containing rare earth intermetallic compounds

By alloying boron with RPd₃ (R=rare earth) compounds, new ternary alloys of the formula RPd₃B _x (0 ≤x ≤ 1) have been prepared. The parent RPd₃ compounds crystallise in the cubic AuCu₃ type structure. The addition of boron does not change the structure but results in an expansion of the lattice. Therefore, it is likely that the small boron atoms occupy the vacant body centred position in AuCu₃ type structure. It is also observed that compounds of the composition RRh₃B can be formed in the cubic structure for all rare earths R though the parent RRh₃ compounds exist only for R=Ce (AuCu₃ type) and La, Sm, Nd and Gd (all hexagonal CeNi₃ type). This points out the role of boron in stabilising new crystallographic phases. The results of susceptibility measurements on some of the RPd₃B and RRh₃B compounds are presented. In particular, it is noted that while GdPd₃ orders antiferromagnetically withT _N=6 K, GdPd₃B does not order magnetically down to 4.2 K.     

Dependence directed reasoning and learning in systems maintenancesupport

The maintenance of large information systems involves continuous modifications in response to evolving business conditions or changing user requirements. Based on evidence from a case study, it is shown that the system maintenance activity would benefit greatly if the process knowledge reflecting the teleology of a design could be captured and used in order to reason about he consequences of changing conditions or requirements, A formalism called REMAP (representation and maintenance of process knowledge) that accumulates design process knowledge to manage systems evolution is described. To accomplish this, REMAP acquires and maintains dependencies among the design decisions made during a prototyping process, and is able to learn general domain-specific design rules on which such dependencies are based. This knowledge cannot only be applied to prototype refinement and systems maintenance, but can also support the reuse of existing design or software fragments to construct similar ones using analogical reasoning techniques     

An investigation into the use of R12, R12 mixtures in air conditionersRecherches sur l'utilisation de mélanges de R12 et de R13 dans les conditioneurs d'air

An appraisal of the use of mixed refrigerants is presented following an investigation on the performance of a window air conditioner. This system was chosen because the temperature changes are comparatively large. The important results of the study and proposals to reduce power consumption and achieve optimum performance are described.     

Studies on the enzymatic synthesis of cholesterol: Use of a liver acetone powder

We have defined special conditions for the preparation of an acetone powder of rat liver microsomes which is capable of converting squalene to cholesterol in high yield. This preparation is also useful for the demonstration of cofactor requirements for certain reactions in sterol biosynthesis. Buffer washed acetone powders are virtually completely dependent upon the 105,000 ×g supernatant of rat liver (S₁₀₅) for activity, yet S₁₀₅ by itself is inert in sterol synthesis. The ability of S₁₀₅ to stimulate sterol synthesis is heat liable, nondialyzable, trypsin sensitive, and has been partially purified by ammonium sulfate precipitation and chromatography on Sephadex G-200. These results plus other experiments support the following hypothesis: the 105,000 ×g supernatant of rat liver (S₁₀₅) contains a noncatalytic carrier protein (Sterol Carrier Protein or SCP) which originates from the endoplasmic reticulum, binds the substrate, and makes the substrate reactive to the sterol synthesizing enzymes present in the acetone powder of liver microsomes. The participation of SCP may be an important general mechanism in the biological synthesis of cholesterol. One of 12 papers to be published from the Sterol Symposium presented at the AOCS Meeting, New Orleans, April, 1970.     

Fracture Toughness and Microcracks on Natural Apophyllite Crystals

Results on fracture toughness of natural apophyllite crystals when subjected to impact are presented. The morphology of the cracks and fracture has been studied. It is found that the crack formation does not show any anisotropic property and remains the same whatever may be the orientation of the crystal. The average values of the fracture toughness KC and brittleness index, as determined from measurements of crack length, are estimated to be 0.107 gμm-3/2and 4.19μm-1/2 respectively for the a(100) plane. The yield strength forα(100), p(111) and c(001) planes of apophyllite crystals for lower loads is 2250. 2160 and 1840 MPa and for higher loads is 1510, 1600 and 1430 MPa respectively