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     

Mobile robot path planning based on hierarchical hexagonal decomposition and artificial potential fields

In this article, a new algorithm based on an artificial potential field and hierarchical cell decomposition technique is developed to solve the find-path problem for a mobile robot. The complete map of the workspace including obstacle locations is assumed to be known a priori. The basic cell structure used for decomposition is a hexagon. The artificial potential field is based on an attractive force from the goal position and repelling forces from the obstacles. Computer simulations of the algorithm for various obstacle scenarios are also presented. © 1994 John Wiley & Sons, Inc.     

Evidence for superantigen involvement in insulin-dependent diabetes mellitus aetiology

Insulin-dependent diabetes mellitus (IDDM) is a T-cell-mediated autoimmune disease whose onset is believed to be triggered by unknown environmental factors acting on a predisposing genetic background. Islet-infiltrating T (IIT) cells from two IDDM patients, who had died at the onset of the disease from brain swelling as a complication of ketoacidosis, were analysed. The results provided evidence for the involvement of a pancreatic islet cell membrane-bound superantigen as a diabetes aetiopathogenetic factor. There was a selective expansion of a T-cell receptor (TCR) variable segment of the beta-chain (V beta 7) in these IIT cells in association with unselected V alpha-chain segments; extensive junctional diversity of the TCR V beta 7 chains; and evidence of positive selection, after exposure to diabetic islet cell membrane preparations, of V beta 7+ T-cell clones among peripheral blood lymphocytes from non-diabetic individuals.     

Chronic herpes simplex encephalitis initially presenting with persistent myoclonus

A 59-year-old female patient with atypical chronic herpes simplex encephalitis was reported. Initial symptom was persistent myoclonus involving the trunk and limb muscles, and later lateral gaze palsy to the left side, cerebellar ataxia, consciousness disturbance and other brainstem symptoms including absence of corneal and gag reflex and vocal cord palsy developed. The patient was successfully treated with high dose of acyclovir. Electroencephalogram was normal in the initial stage but later showed diffuse slow waves. Although CT scan and MRI showed no abnormal finding in the cerebral cortex, brainstem lesion was observed on PD weighted image of MRI. Lumbar puncture yielded a clear cerebrospinal fluid, with slightly elevated protein, increased lymphocytes, and elevated titer of herpes simplex virus type I. The serological data, albumin ratio (10.3), antibody index (12.3) and antibody ratio (7.1) were consistent with herpes simplex encephalitis. Ten days' administration of acyclovir, 1,200 mg a day and repeated three times, was prominently effective for the myoclonus and consciousness disturbance. A diagnosis of chronic herpes simplex encephalitis initially presenting with brainstem encephalitis was made. Judging from the clinical and EEG findings, the brainstem lesion was initially thought to be a cause of myoclonus in this case. However, somatosensory evoked potential (SPE) of both upper and lower extremities revealed enlarged amplitude (giant SEP), and long loop reflex was enhanced (C-reflex) on the left. Giant SEP and C-reflex imply cerebral cortex as the origin of the myoclonus. Brainstem inflammatory lesion might have involved the ascending inhibitory system, thus disinhibiting the cortical sensorimotor area and causing cortical myoclonus.     

Cooperation of Ito cells and hepatocytes in the deposition of an extracellular matrix in vitro

Cellular and molecular mechanisms involved in the deposition of extracellular matrix components in both normal and fibrotic liver are still poorly understood. We have investigated the influence of cooperation between Ito cells and hepatocytes in matrix deposition in vitro. Immunoprecipitation of radiolabeled proteins from media of 5-day-old Ito cell primary cultures showed that these cells secreted high levels of the major basement membrane components, ie, collagen IV, laminin, and entactin/nidogen. By immunocytochemistry, precursors of basement membrane components were found intracellularly, but only scarce deposits were seen around the cells. When hepatocytes were added to 2-day-old Ito cell primary cultures, they established close contacts with Ito cells in less than 24 hours and expressed ZO-1, a tight junction-associated protein not detectable in standard hepatocyte culture. Cytochemistry analysis revealed an abundant extracellular matrix deposited over hepatocyte cords and between hepatocytes and Ito cells. Immunocytochemistry studies showed that this matrix contained laminin, fibronectin, and collagens proIII and IV. These data indicate that a high level of matrix protein synthesis by liver cells in vitro is not sufficient to induce extracellular matrix deposition, and that cell-cell interactions are strongly involved in this process. Hepatocyte/Ito cell co-culture, which may reflect the actual situation in vivo, represents a useful tool for studying liver fibrogenesis.     

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.