Broadband CPN demonstrator using wavelength and time divisionmultiplexing

RACE Project 1036 is developing the technology for a broadband customer premises network (CPN) using wavelength and time division multiplexing (WTDM). Features include close wavelength spacing (4 nm in the 1500 nm band), high-speed time multiplexing (2.5 Gbit/s, STM-16), and a layered control protocol. An initial demonstrator with two wavelengths carrying TV signals at 155 Mbit/s was exhibited in the autumn of 1990 and is now evolving into the final demonstrator due at the end of 1992 which will show 16 wavelengths and a 2.5 Gbit/s multiplex of HDTV, TV, and sound. The authors describe the devices made in the Project, the demonstrators, and the performance results achieved so far     

Factors affecting the enzymic susceptibility of alkali and acid pretreated sugar-cane bagasse

Acid and alkali pretreatments were studied to identify those factors which are critical in determining the susceptibility of a lignocellulosic substrate (bagasse) to enzymic hydrolysis. The different effects of each treatment on the structure of the bagasse affected the subsequent susceptibility to enzymic attack in different ways. The acid treatments appeared to act by disrupting the lignin structure, probably by hydrolysing the carbohydrate chains attached to the lignin, as well as the lignin itself. The attack on the carbohydrate content removed outlying material in the cell wall (i.e. hemicellulose and amorphous cellulose) to expose a ‘core’ of more resistant regions. The alkali treatments appeared to produce a more open structure by penetrating the inner layers and selectively removing hemicellulose molecules as well as breaking some lignin—carbohydrate bonds. The different treatments resulted in structural changes which were found to affect the hydrolysis mechanism.     

An explanation of the discrepancy between the results of h.p.l.c. and DNS assays in the analysis of lignocellulosic hydrolysates

The concentration of polymerised sugars in enzymic hydrolysates from lignocellulosic materials was determined by high pressure liquid chromatography (h.p.l.c.) of hydrolysates before and after dilute acid hydrolysis: significant quantities of polymerised glucose and xylose were found in lignocellulosic hydrolysates, and these accounted for the discrepancy between the dinitrosalicyclic acid (DNS) and h.p.l.c. assay methods.     

Compliant layer acetabular cups: friction testing of a range of materials and designs for a new generation of prosthesis that mimics the natural joint

Total joint replacements (TJRs) have a limited lifetime, but the introduction of components that exhibit good lubricating properties with low friction and low wear could extend the life of TJRs. A novel acetabular cup design using polyurethane (PU) as a compliant layer (to mimic the natural joint) has been developed. This study describes a series of friction tests that have been used to select the most appropriate material, optimize the design parameters, and fine-tune the manufacturing processes of these joints. To determine accurately the mode of lubrication under which these joints operate, a synthetic lubricant was used in all these tests. Friction tests were carried out to assess the lubrication of four PU bearing materials. Corethane 80A was the preferred material and was subjected to subsequent testing. Friction tests conducted on acetabular cups, manufactured using Corethane 80A articulating against standard, commercially available femoral heads, demonstrated friction factors approaching those for full-fluid-film lubrication with only approximately 1 per cent asperity contact. As the joint produces these low friction factors within less than half a walking cycle after prolonged periods of loading, start-up friction was not considered to be a critical factor. Cups performed well across the full range of femoral head sizes, but a number of samples manufactured with reduced radial clearances performed with higher than expected friction. This was caused by the femoral head being gripped around the equator by the low clearance cup. To avoid this, the cup design was modified by increasing the flare at the rim. In addition to this the radial clearance was increased. As the material is incompressible, a radial clearance of 0.08 mm was too small for a cup diameter of 32 mm. A clearance of between 0.10 and 0.25 mm produced a performance approaching full-fluid-film lubrication. This series of tests acted as a step towards the optimization of the design of these joints, which has now led to an in vivo ovine model.     

The history and future of Lake Champlain's fishes and fisheries

In the last two centuries, physical, chemical, and biological alterations of Lake Champlain have resulted in the loss of two species, addition of 15 fish species, and listing of 16 species as endangered, threatened or of special concern. The lake currently supports 72 native fish species; lake trout (Salvelinus namaycush) and Atlantic salmon (Salmo salar) were extirpated by 1900, American eel (Anguilla rostrata) and lake sturgeon (Acipenser fulvescens) populations are extremely low, and walleye (Sander vitreum) are declining. Dams on several rivers, and ten causeways constructed in the mid 1800s to early 1900s, cut off access to critical spawning areas and may have limited fish movements. Siltation and sediment loading from agricultural activity and urban growth have degraded substrates and led to noxious algal blooms in some bays. A commercial fishery targeting spawning grounds of lake whitefish (Coregonus clupeaformis), lake trout, and walleye probably reduced numbers of these species prior to its closure in 1912. Non-native species introductions have had ecosystem-wide impacts. Sea lamprey (Petromyzon marinus) populations were very high prior to successful control, possibly as a consequence of ecological imbalance and habitat changes. A paucity of historic survey data or accurate species accounts limits our understanding of the causes of current fish population trends and status; in particular, the effects of habitat fragmentation within the lake and between the lake and its watershed are poorly understood. Holistic, ecosystem management, including pollution reduction and examination of habitat impacts, is necessary to restore the general structure of native biological assemblages.     

Constrained optimization of an idealized Y-shaped baffle for the Fontan surgery at rest and exercise

Coupling shape optimization to three-dimensional unsteady cardiovascular simulations poses several key challenges, including high computational cost, a need to handle constraints, and a need for automatic generation of parameterized vessel geometry. In this work we extend our previous framework for cardiovascular optimization to include constraints, pulsatile flow under both rest and exercise conditions, and multiple geometric parameters. Optimization is performed using a derivative-free algorithm called the surrogate management framework, with constraints enforced using a filter method. In this work, we examine a specific surgery called the Fontan, which is performed to treat single-ventricle heart patients. These patients typically undergo a series of three surgeries, the last of which connects the inferior vena cava to the pulmonary arteries. Our group and others have recently proposed and evaluated a new Y-graft modification of the Fontan operation that replaces the current tube shaped baffle. Preliminary simulations have shown that the Y-graft modification is a promising design that increases energy efficiency and improves flow distribution to the pulmonary arteries. In this work, we perform optimization on a model Y-graft design problem. This work represents the first use of formal design optimization methods for the Fontan surgery, and also demonstrates the applicability of the optimization framework on a pulsatile flow problem with multiple design parameters and constraints. The idealized Y-graft model was parameterized with six geometric parameters including graft diameter and anastomosis locations, and the optimization procedure, including model construction, meshing, and simulation, was executed automatically. Energy efficiency was chosen as the objective function. A constraint on the wall shear stress (WSS), a presumed correlate to thrombosis risk, was added to the problem using a filter method, which allowed for exploration of the trade-offs between WSS and energy efficiency. Optimization was performed at two exercise levels with effects of respiration incorporated, and differences in optimal solutions were examined. It was shown that optimal shapes differed between rest and exercise, as well as steady and pulsatile flow conditions, with wide-span branches and decreasing graft branch size favored with increasing exercise level. The optimization method was found to be robust for different polling strategies, and computationally efficient both with and without constraints.