Physical model fitting - the choice of criterion of goodness of fit

Developments in numerical methods and the improved accessibility of corresponding software have greatly simplified the fitting of parametric physical models to observations. In particular, this applies to fitting in the sense of the (until recently intractable) non-differentiable criteria of goodness of fit as the sum of absolute deviations criterion and the minimax criterion. More than before, these methods and software enable one to investigate which criterion is best for a particular purpose: for example, the precision of the produced parameter estimates, the resolution of closely spaced parameters or robustness with respect to outliers.     

Failure of hypertrophy in revascularised fibula grafts due to stress protection

Three cases of long bone reconstruction with vascularised fibula grafts are described. Hypertrophy of the graft did not occur after a follow-up of 3-5 years. Three different kinds of stress shielding appeared to prevent transformation of the graft.     

Activation of the small GTPase rap1 in human neutrophils

A multicopy plasmid carrying the PDC1 gene (encoding pyruvate decarboxylase; Pdc) was introduced in Saccharomyces cerevisiae CEN. PK113-5D. The physiology of the resulting prototrophic strain was compared with that of the isogenic prototrophic strain CEN.PK113-7D and an empty-vector reference strain. In glucose-grown shake-flask cultures, the introduction of the PDC1 plasmid caused a threefold increase in the Pdc level. In aerobic glucose-limited chemostat cultures growing at a dilution rate of 0.10 h-1, Pdc levels in the overproducing strain were 14-fold higher than those in the reference strains. Levels of glycolytic enzymes decreased by ca. 15%, probably due to dilution by the overproduced Pdc protein. In chemostat cultures, the extent of Pdc overproduction decreased with increasing dilution rate. The high degree of overproduction of Pdc at low dilution rates did not affect the biomass yield. The dilution rate at which aerobic fermentation set in decreased from 0.30 h-1 in the reference strains to 0.23 h-1 in the Pdc-overproducing strain. In the latter strain, the specific respiration rate reached a maximum above the dilution rate at which aerobic fermentation first occurred. This result indicates that a limited respiratory capacity was not responsible for the onset of aerobic fermentation in the Pdc-overproducing strain. Rather, the results indicate that Pdc overproduction affected flux distribution at the pyruvate branch point by influencing competition for pyruvate between Pdc and the mitochondrial pyruvate dehydrogenase complex. In respiratory cultures (dilution rate, <0.23 h-1), Pdc overproduction did not affect the maximum glycolytic capacity, as determined in anaerobic glucose-pulse experiments.     

Perspectives on utility central station photovoltaic applications

This report develops nominal cost and performance goals for solar photovoltaic conversion devices intended for large-scale electric utility applications. The objective is to provide an improved basis for establishing research and development priorities for photovoltaic devices and conversion concepts. Comparisons are made among a number of generic power plant conceptual designs, with the aid of an array design parameter that is defined to include array-area-related costs, overall power plant efficiency, and average available insolation. The analysis indicates that flat plate approaches without concentration or tracking have good prospects for commercial viability if device conversion efficiencies near 10 per cent can be combined with installed device costs under $20/m² ($2/ft²) and device lifetimes in excess of 20 years. Thin-film approaches have potential for achieving these cost and performance goals because of low material content and potentially low fabrication costs. Very high efficiency devices coupled with concentrations in excess of about 100:1 represent a viable alternative if sufficiently high conversion efficiencies (25% or more) can be achieved. Such devices are likely to be expensive, but high concentration may make their costs acceptable. Several device types and converter approaches exist or have been proposed that have potential for reaching these efficiencies. In contrast to flat plate approaches, however, high-concentration approaches may have the disadvantage of requiring active cooling. Approaches employing low-to-medium concentration appear to have limited potential for large-scale applications. Required effieciencies are likely to be comparable to those needed for high-concentration approaches, but the concentration ratios are not likely to be high enough to make the photovoltaic device costs tolerable.     

Stressed liquid-crystal optical phased array for fast tip-tilt wavefront correction

A liquid-crystal optical phased-array technology that uses stressed liquid crystals provides a new type of tip-tilt wavefront corrector. It demonstrates a very fast time response (10 kHz) and high beam-steering efficiency (approximately 91%). The new technology presented here will allow for a nonmechanical, high-speed correction with simple device construction.     

Short-term <Emphasis Type="Italic">in vitro</Emphasis> and <Emphasis Type="Italic">in vivo</Emphasis> biocompatibility of a biodegradable polyurethane foam based on 1,4-butanediisocyanate

In this study short-term in vitro and in vivo biocompatibility apects of a biodegradable polyurethane (PU) foam were evaluated. The PU consists of hard urethane segments and amorphous soft segments based on a copolyester of dl-lactide and -caprolactone. The urethane segments are of uniform length and synthesized with 1,4-butanediisocyanate. The foam has good mechanical properties and will be used for tissue regeneration applications. Degradation tests were carried out in a buffer solution for twelve weeks. Cytotoxicity was determined using extract and direct contact test methods with incubation periods varying form 24 to 72 h. The foam was implanted subcutaneously for one, four and twelve weeks and the tissue response to the material was histologically evaluated.In vitro, the mass loss was 3.4% after twelve weeks. In the cytotoxicity tests the PU caused no abnormal growth behaviour, nor morphological changes or inhibition in metabolic activity. The in vivo studies showed no toxic tissue response to the PU. Connective tissue ingrowth, accompanied by vascular ingrowth was complete at twelve weeks. In vivo degradation had started within four to twelve weeks.In conclusion, the PU shows a good in vitro and in vivo biocompatibility in these short-term experiments.     

Finite-difference time-domain simulation of a liquid-crystal optical phased array

Accurate modeling of a high-resolution, liquid-crystal-based, optical phased array (OPA) is demonstrated. The modeling method is extendable to cases where the array element size is close to the wavelength of light. This is accomplished through calculating an equilibrium liquid-crystal (LC) director field that takes into account the fringing electric fields in LC OPAs with small array elements and by calculating the light transmission with a finite-difference time-domain method that has been extended for use in birefringent materials. The diffraction efficiency for a test device is calculated and compared with the simulation.