Dual-Priority versus Background Scheduling: A Path-Wise Comparison

In this paper, two well-known scheduling policies for real-time systems, namely background scheduling (BS) and dual-priority (DP) are compared in terms of response times for soft real-time traffic (SRT). It is proved in the preemptive as well as in the non-preemptive case that, when the SRT traffic is FIFO, the DP policy always outperforms BS for all instances of SRT tasks. When the SRT traffic is not FIFO but if all tasks are of equal size then, in the non-preemptive case, the average response times is shown to be always better under DP than under BS. As a complementary result, some non-FIFO examples where BS behaves better than DP for some SRT tasks but also on the average of the SRT response times, are given. The proofs are based on a trajectorial method that may be used for comparing other scheduling policies.     

Synthesis of Novel Niobium Aluminide-Based Composites

A reactive sintering process has been used to produce almost fully dense composites with interpenetrating networks of NbAl₃ and Al₂O₃. The process involves the reaction synthesis of niobium aluminides and Al₂O₃ from compacts of intensively milled aluminum and Nb₂O₅ powder mixtures. During carefully controlled heating under an inert atmosphere, the oxide reduction by aluminum to form niobium aluminides and Al₂O₃ proceeds at temperatures below the melting point of aluminum. At temperatures of >1000°C, the reaction-formed niobium aluminides and Al₂O₃ sinter. The present paper discusses processing parameters, such as attrition milling, the heating cycle, and the metal:ceramic ratio in the starting mixture, that control microstructure development and mechanical properties.     

Dominant Mechanisms that Shape the Airborne Particle Size and Composition Distribution in Central California

The size and composition of ambient airborne particulate matter is reported for winter conditions at five locations in (or near) the San Joaquin Valley in central California. Two distinct types of airborne particles were identified based on diurnal patterns and size distribution similarity: hygroscopic sulfate/ammonium/nitrate particles and less hygroscopic particles composed of mostly organic carbon with smaller amounts of elemental carbon. Daytime PM₁₀ concentrations for sulfate/ammonium/nitrate particles were measured to be 10.1 μ g m^?3, 28.3 μ g m^?3, and 52.8 μ g m^?3 at Sacramento, Modesto and Bakersfield, California, respectively. Nighttime concentrations were 10–30% lower, suggesting that these particles are dominated by secondary production. Simulation of the data with a box model suggests that these particles were formed by the condensation of ammonia and nitric acid onto background or primary sulfate particles. These hygroscopic particles had a mass distribution peak in the accumulation mode (0.56–1.0 μ m) at all times. Daytime PM₁₀ carbon particle concentrations were measured to be 9.5 μ g m^?3, 15.1 μ g m^?3, and 16.2 μ g m^?3 at Sacramento, Modesto, and Bakersfield, respectively. Corresponding nighttime concentrations were 200–300% higher, suggesting that these particles are dominated by primary emissions. The peak in the carbon particle mass distribution varied between 0.2–1.0 μ m. Carbon particles emitted directly from combustion sources typically have a mass distribution peak diameter between 0.1–0.32 μ m. Box model calculations suggest that the formation of secondary organic aerosol is negligible under cool winter conditions, and that the observed shift in the carbon particle mass distribution results from coagulation in the heavily polluted concentrations experienced during the current study. The analysis suggests that carbon particles and sulfate/ammonium/nitrate particles exist separately in the atmosphere of the San Joaquin Valley until coagulation mixes them in the accumulation mode.     

The hybrid-adjoint method: a semi-analytic gradient evaluation technique applied to composite cure cycle optimization

A method is presented for determining the optimal autoclave temperature history for pre-impregnated thermoset composites based on their failure performance. A coupled finite-element model that incorporates a thermochemical and incremental elastic analysis is used to predict the residual stress distribution at the edge of a thick composite beam. The optimal autoclave temperature is sought using a gradient-based optimization algorithm. The objective is designed to maximize the minimum failure load of the manufactured beam amongst a set of load cases, while the constraints are imposed to ensure that the composite is uniformly cured and does not sustain temperature damage during the manufacturing process. The hybrid-adjoint, a novel semi-analytic gradient evaluation technique is developed, that incorporates elements of both the adjoint and direct sensitivity methods. Results demonstrate that the method is highly accurate and competitive with a full adjoint approach for a moderate number of design variables.     

About the existing discrepancy in the determinations of theAvogadro constant

The values for the Avogadro constant N_A, derived from lattice spacing, density, and molar mass of silicon single crystals at several metrological institutes, show significant differences. To illuminate this discrepancy, comparison measurements of lattice spacing and density were performed. Positron annihilation measurements were used to estimate the vacancy concentration in Si samples. All crystals lead to nearly the same lattice spacing after correction for the influence of carbon and oxygen impurities. It is proved that the discrepancy in the determinations of the Avogadro constant cannot be explained by vacancies or interstitials. Also indications for macroscopic bubbles or cavities could not be found     

A wrinkle in flight: the role of elastin fibres in the mechanical behaviour of bat wing membranes

Bats fly using a thin wing membrane composed of compliant, anisotropic skin. Wing membrane skin deforms dramatically as bats fly, and its three-dimensional configurations depend, in large part, on the mechanical behaviour of the tissue. Large, macroscopic elastin fibres are an unusual mechanical element found in the skin of bat wings. We characterize the fibre orientation and demonstrate that elastin fibres are responsible for the distinctive wrinkles in the surrounding membrane matrix. Uniaxial mechanical testing of the wing membrane, both parallel and perpendicular to elastin fibres, is used to distinguish the contribution of elastin and the surrounding matrix to the overall membrane mechanical behaviour. We find that the matrix is isotropic within the plane of the membrane and responsible for bearing load at high stress; elastin fibres are responsible for membrane anisotropy and only contribute substantially to load bearing at very low stress. The architecture of elastin fibres provides the extreme extensibility and self-folding/self-packing of the wing membrane skin. We relate these findings to flight with membrane wings and discuss the aeromechanical significance of elastin fibre pre-stress, membrane excess length, and how these parameters may aid bats in resisting gusts and preventing membrane flutter.     

Congenital ball-and-socket anomaly of the ankle

We present the clinical and radiographic appearance of 11 patients with a ball-and-socket ankle joint with an average follow-up of 13.7 years. Ten patients demonstrated parallel symptoms of the femur-fibula-ulna syndrome (FFU) associated with a mean leg-length discrepancy of 4.3 cm (range, 2-20). In six patients, an annual follow-up of talar development was possible. Radiographically the patients showed an additional tarsal coalition at a mean age of 4.8 years (range, 3.2-5.9). This earlier fusion could be detected by an arthrographic examination. All patients had no clinical complaints except a slight reduction of hindfoot mobility. The ball-and-socket ankle joint is presumably not congenital itself but secondary to congenital conditions in the peritalar region.     

Urban design analysis by computer

In recent years we have seen a widespread concern among the general public about the architectural qualities of our cities. To urban designers, this means that a greater part of their work will be dedicated to the problems of urban architectural quality. The urban designer already uses the computer to manage all sorts of information such as drawings, word processing, land use data, statistics etc; this raises the possibility of using computers for other types of work. The analysis and evaluation of urban design are to a very large extent based on visual data. Powerful computers are needed to manipulate visual data; the new and more powerful machines which are now being manufactured make it possible to handle such data quickly and efficiently.