Analysis of Restart Mechanisms in Software Systems

Restarts or retries are a common phenomenon in computing systems, for instance, in preventive maintenance, software rejuvenation, or when a failure is suspected. Typically, one sets a time-out to trigger the restart. We analyze and optimize time-out strategies for scenarios in which the expected required remaining time of a task is not always decreasing with the time invested in it. Examples of such tasks include the download of Web pages, randomized algorithms, distributed queries, and jobs subject to network or other failures. Assuming the independence of the completion time of successive tries, we derive computationally attractive expressions for the moments of the completion time, as well as for the probability that a task is able to meet a deadline. These expressions facilitate efficient algorithms to compute optimal restart strategies and are promising candidates for pragmatic online optimization of restart timers     

Impoverishment of YOY‐fish assemblages by intense commercial navigation in a large Lowland river

Navigation‐induced physical forces have been suggested to modify the structure of riverine fish assemblages by impeding especially the recruitment of littoral bound species. To investigate the effect of vessel frequency on fish, we compared the composition and seasonal succession of young‐of‐the‐year (YOY) fish assemblages in three similarly degraded river reaches differing in average vessel passages (2, 6 and 41 per day). Fish were caught by electrofishing biweekly between May and September. Multivariate tests were used to analyse differences between YOY‐fish assemblages and hurdle regression models applied to determine abiotic factors predicting fish occurrence and abundance. Roach (Rutilus rutilus) and perch (Perca fluviatilis) densities were compared. Roach larvae remain in the littoral zone while perch larvae shift to the pelagic zone immediately after hatch. YOY‐fish assemblage structure substantially changed along the traffic intensity gradient. In the high traffic intensity reach, species number and total fish density were markedly reduced compared to the other reaches. Roach densities were lowest in the high traffic intensity reach whereas perch densities did not decline along the gradient. Hurdle regressions confirmed a stronger effect of commercial navigation traffic intensity on roach than on perch. The total zooplankton biomass was highest in the high traffic intensity reach. Our results provide empirical evidence that intensive commercial navigation impoverishes fish assemblages in width‐restricted waterways. They underlined that in particular those species that have their first nursery habitats in shoreline areas were more affected by intensive commercial navigation than species whose larvae live predominantly pelagic. The results indicate that the negative effect of intensive navigation on riverine fish results primarily from the navigation‐induced hydraulic disturbances along the banks. Therefore, mitigation of navigation‐induced hydraulic forces is required to prevent degradation of fish communities in waterways. Copyright © 2010 John Wiley & Sons, Ltd.     

Haptic two-finger contact with textiles

Real-time cloth simulation involves many computational challenges to be solved, particularly in the context of haptic applications, where high frame rates are necessary for obtaining a satisfying experience. In this paper, we present an interactive cloth simulation system that offers a compromise between a realistic physics-based simulation of fabrics and a haptic application meeting high requirements in terms of computation speed. Our system allows the user to interact with the fabric using two fingers. The required performance of the system is achieved by introducing an intermediate layer responsible for the simulation of the small part of the surface being in contact with the fingers. Additionally we separate the possible contact situations into different cases, each being individually handled by a specialised contact algorithm.

A Time Model for Time-Varying Visualization

The analysis of unsteady phenomena is an important topic for scientific visualization. Several time-dependent visualization techniques exist, as well as solutions for dealing with the enormous size of time-varying data in interactive visualization. Many current visualization toolkits support displaying time-varying data sets. However, for the interactive exploration of time-varying data in scientific visualization, no common time model that describes the temporal properties which occur in the visualization process has been established. In this work, we propose a general time model which classifies the time frames of simulation phenomena and the connections between different time scales in the analysis process. This model is designed for intuitive interaction with time in visualization applications for the domain expert as well as for the developer of visualization tools. We demonstrate the benefits of our model by applying it to two use cases with different temporal properties.     

Picosecond time-resolved bleaching dynamics of self-assembled quantum dots

Picosecond bleaching dynamics of vertically stacked self-assembled quantum dots (QDs) is investigated by means of time-resolved pump-probe differential reflection spectroscopy (TRDR) at room temperature (RT). We observe that the absorption spectrum, which represents the QD density of states at RT, is strongly shifted with respect to the photoluminescence spectrum. This shift can not be interpreted by carrier emission and re-trapping alone. TRDR allows us to study the dynamics of the pump generated carriers within the QDs. From the time-resolved measurements, we detect that the bleaching decay time has a strong energy dependence and is dominated by radiative and nonradiative recombination at low energy and by carrier emission at high energy.     

Biocompatibility study of three distinct carbon pastes for application as electrode material in neural stimulations and recordings

Neural interfaces hold great promise for research and treatment of a wide variety of neurological diseases. Medical electrodes are designed to interface with the nervous system and provide control signals for neural prostheses. We fabricated previously a hook-up neural electrode. Here we investigate the in vitro cytotoxicity of three commercial carbon pastes used for printing the conductor tracks of this electrode. At first, the carbon pastes were characterized with respect to their microstructure and chemical composition. SEM images showed a grainy texture that is associated to the carbon/graphite microparticles dispersed by the polymeric binder. All the three pastes contained in major proportions carbon and in different proportions other elements. The surface roughness analysis evidenced differences in the smoothness of the carbon paste surfaces. Sterilization procedures did not alter the microstructure or surface morphology of the pastes. Finally, cell viability based on -(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) test and fluorescence staining experiments proved non-cytotoxicity and suitability of the studied carbon pastes as electrode material for measuring neural activity during surgeries (up to a certain time period).     

Credit Constraints and Price Expectations of Homeowners

This paper examines the effect of credit constraints on the sale price expectations of homeowners. We extend the results of Genesove and Mayer (1997) by using a sample of mover and non-mover families living in the Netherlands—a country without formal down-payment requirements. We find that homeowners who are more credit constrained expect to sell their house for a higher price. Homeowners already seem to compensate for credit constraints at the very first stages of the transaction process. These results imply that the findings of Genesove and Mayer (1997) are much more generally applicable than previously considered.     

Connecting geodesics on smooth surfaces

In this paper, we present a novel method for computing multiple geodesic connections between two arbitrary points on a smooth surface. Our method is based on a homotopy approach that is able to capture the ambiguity of geodesic connections in the presence of positive Gaussian curvature that generates focal curves. Contrary to previous approaches, we exploit focal curves to gain theoretical insights on the number of connecting geodesics and a practical algorithm for collecting these. We consider our method as a contribution to the contemporary debate regarding the calculation of distances in general situations, applying continuous concepts of classical differential geometry which are not immediately transferable in purely discrete settings.     

Structure–Property Relationships in Aligned Electrospun Barium Titanate Nanofibers

Barium titanate nanofibers were uniaxially aligned by electrospinning onto a rotating copper wire drum and alignment was maintained during calcination of the fibers. Two methods for maintaining alignment during calcination were tested, by either using carbon tape or a peeling off method to remove the aligned fibers from the mandrel followed by calcination. The carbon tape removal method led to the formation of shorter aligned nanowires while the peeling off method resulted in longer nanofibers. Additionally, the effects of calcination temperature and time on crystal structure were also examined. The degree of tetragonality in the barium titanate nanofibers increased at higher calcination temperatures and times. Piezoelectricity was confirmed in the nanofibers calcined using piezoeresponse force microscopy, yielding a d₃₃ value of 15.5 pm/V. Using the methods presented here, large quantities of aligned piezoelectric barium titanate and other ceramic fibers or wires can be produced to fulfill their demand in novel microelectronics.