Materials technology for aerospace applications

Modern helicopter design depends on the successful combination of materials to fulfil a very wide range of critical functions. In the past few years demands from the aerospace industry have caused considerable enhancement in the favourable properties of both polymer based materials and metals. These are discussed in connection with the progressive technical evolution of helicopters and other advanced technological products from the Westland Group.     

Optical imaging of anatomical maps derived from magnetic resonanceimages using time-independent optical sources

Presents a model suitable for computing images of absorption cross sections of thick tissue structures illuminated at near infrared (NIR) wavelengths from tomographic projection data. Image reconstruction is accomplished by solving a system of linear equations derived from transport theory. Reconstruction results using different algebraic solvers are shown for anatomical maps of the breast, derived from magnetic resonance imaging data, containing two simulated pathologies, in which case qualitatively good reconstructions were obtained. Evaluation of magnetic resonance (MR) data to optimize NIR optical tomographic imaging methods and to assess the feasibility of a combined MR-optical measurement scheme is discussed     

The influence of trigger configurations and laminate lay-up on the failure mode of composite crush cylinders

In this paper the results are presented of a test program on the energy absorption of composite cylinders loaded in compression. The influence of the laminate lay-up and of the trigger configuration were determined. Two different failure modes for the different laminates and triggers were observed: a splaying mode and a fragmentation mode. The splaying mode is more efficient in absorbing energy. The failure mode did not change during the crushing process.     

Ankle performance after ankle fracture: a randomized study of early mobilization

Low concentrations of some neutral dipeptides, such as L-Ala-L-Ala, rapidly disrupt rat liver lysosomes. The phenomenon has been attributed to an osmotic imbalance generated by the production of amino acids in the lysosome by lysosomal dipeptidase activity. This hypothesis is challenged by testing several pairs of dipeptides available in both D- and L-forms and a range of dipeptides whose susceptibility to lysosomal dipeptidase activity is known. A good correlation was found between the lytic ability of dipeptides and their capacity to cross the lysosome membrane and be hydrolysed by lysosomal dipeptidase. The osmotic-imbalance hypothesis is critically evaluated in the light of the results and of recent information concerning the carrier-mediated transport of amino acids and dipeptides across the lysosome membrane. It is concluded that intralysosomal generation of amino acids remains the most plausible explanation of the lytic activity of dipeptides, and that the dipeptide porter(s) in the lysosome membrane must have higher Km than the amino acid porters.     

Enhanced electron emission from phosphorus-doped diamond-cladsilicon field emitter arrays

Undoped and phosphorus (P)-doped diamond-clad Si field emitter arrays have been successfully fabricated using microwave plasma chemical vapor deposition (MPCVD) technology. The electron emission from the blunt diamond-clad microtips are much higher than those for the pure Si tips with sharp curvature due to a lower work function. Furthermore, the characteristics of emission current against applied voltage for the P-doped diamond-clad tips show superior emission at lower field to the undoped ones. After the examination of Auger electron spectroscopy (AES) and electrical characteristics of as-grown diamond, such a significant enhancement of the electron emission from the P-doped diamond-clad tips is attributed to a higher electron conductivity and defect densities     

Studies on the in vitro Release of Ibuprofen from Polyethylene Glycol-Polyvinyl Acetate Mixtures Liquid Filled into Hard Gelatin Capsules

The release of ibuprofen from mixtures of polyethylene glycol (PEG) with polyvinyl acetate (PVAc) has been studied in vitro and complemented by x-ray diffraction measurements, differential scanning calorimetry (DSC), and melting point determinations via hot-stage microscopy (HSM). Results indicate that ibuprofen release can be affected markedly by alteration of the PVAc concentration. The molecular weight of the PEG and the pH of the dissolution medium are also shown to affect the release profile. Visual observation during the drug release process revealed a complex behavior which included emission of liquidlike droplets, formation of a crust around the releasing mass, and/or production of flakes of solid material. This behavior appeared to have a disadvantageous effect on the reproducibility of drug release. Construction of a phase diagram from results of thermal analysis using DSC and HSM indicated the formation of an eutectic mixture with a composition of 35% ibuprofen and 65% PEG 1500 and a melting point of 36°C. The complex behavior of the drug-releasing mass is discussed in terms of this phase diagram. Only the release data for systems containing 4% w/w or more of PVAc could be linearized by plotting against the square root of time whereas data for all of the systems studied could be linearized by first-order plots.     

Highly reliable testing of ULSI memories with on-chip voltage-downconverters

Two testing techniques for ultra-large-scale integrated (ULSI) memories containing on-chip voltage downconverters (VDCs) are described. The first in an on-chip VDC tuning technique that adjusts internal V_CC to compensate for the monitored characteristics of the process parameters during repair analysis testing. The second is an operating-voltage margin test, performed at various internal V_CC levels during the water sort test (WT) and the final shipping test (FT)     

Computer analysis,design and simulation of horizontal ground heat exchangers

This paper presents a new computerized procedure for dealing with the design of horizontal ground heat exchangers (HGHE). The computer program is based on the transient model of coupled nonlinear partial differential equations governing heat and mass flow in soils. The model is two-dimensional and delineates the operation of ground heat storage with the HGHE and such phenomena as freezing/thawing and drying/rewetting of soil moisture. Comprehensive climatological data, such as ambient temperature, solar radiation, wind velocity, rainfall, snowfall, snow characterstics, and water vapour pressure is used to simulate conditions at the ground surface over any required length of time. The package can be applied to any geographical location by changing climatic and soil data input. The designer has the possibility of selecting any of 12 types of soils from sand to clay, 12 commercial heat pumps, nine different configurations of the HGHE, 16 plastic pipes for ground coils, and 13 ground coil fluids. The program, however, does not calculate the length of the HGHE but it evaluates the thermodynamic performance of a ground heat pump system and provides comprehensive data on thermal and hydraulic conditions in ground heat storage. The length of the ground heat exchanger is obtained from a line source theory model or from site dimensions and pipe spacing. Computed results for ground heat exchanger operation correlate fairly well with experimental data. Simulation of temperature and moisture content in the ground for natural conditions (no heat extraction/deposition) showed a fair agreement with field data. The entire computer program is user-friendly, interactive, menu-driven, and written in FORTRAN 77.