ALLSTEPS: Curriculum-driven Learning of Stepping Stone Skills

Humans are highly adept at walking in environments with foot placement constraints, including stepping-stone scenarios where footstep locations are fully constrained. Finding good solutions to stepping-stone locomotion is a longstanding and fundamental challenge for animation and robotics. We present fully learned solutions to this difficult problem using reinforcement learning. We demonstrate the importance of a curriculum for efficient learning and evaluate four possible curriculum choices compared to a non-curriculum baseline. Results are presented for a simulated humanoid, a realistic bipedal robot simulation and a monster character, in each case producing robust, plausible motions for challenging stepping stone sequences and terrains.     

Covid-19 pandemic and the unprecedented mobilisation of scholarly efforts prompted by a health crisis: Scientometric comparisons across SARS,MERS and 2019-nCoV literature

Scientometrics - During the current century, each major coronavirus outbreak has triggered a quick and immediate surge of academic publications on its respective topic. The spike in research...     

Grafting kinetics of poly(methyl methacrylate) on microparticulate silica

Grafting of poly(methyl methacrylate) (PMMA) on microparticulate silica was achieved by initiating the polymerization of MMA by 4,4′-azobis(4-cyanopentanoic acid) that was covalently bound to the silica surface. The initiator seems to be destabilized upon binding it to the silica surface. The kinetics of the graft polymerization are described and are largely affected by the Trommsdorff effect, which makes it possible to graft a high amount of PMMA on silica.     

Living in highly dynamic polluted river floodplains, do contaminants contribute to population and community effects?

The aim of this paper was to collect evidence for the effects of contaminants on biota in a highly dynamic river Rhine floodplain. To this purpose we reviewed the results of circa 10 studies performed in this floodplain. The floodplain was contaminated with elevated levels of cadmium, copper, PAHs, and PCBs and high levels of zinc which were at some sites above legislative values. The results showed that the present contaminants were accumulated by the floodplain inhabiting organisms, but meanwhile population and community effects were ambiguous. Only for the mayfly Ephoron virgo clear effects were detected at the level of the single floodplain. The absence of clear population and community effects is puzzling since at lower contaminant concentrations adverse effects were detected in other environments. Factors that may mask toxic effects include flooding and food quality and quantity. We conclude that given the site specific conditions, being an open, eutrophic system with a highly dynamic flooding pattern, assessment of the contribution of toxicants to observed population density or biomass and community composition requires 1] an increase in number of replicates; 2] a larger scale of investigation and 3] comparison to stable systems with comparable contamination levels.     

Higher Tool Productivity due to New Generation of PVD Coatings

PVD coating technology has seen many new developments in the past few years. HIPIMS⁺ is an example of these developments with excellent results on tool productivity and lifespan. The technology combines the advantages of arc evaporation with those of magnetron sputtering and results in a dense and defect‐free coating with tuneable residual stress. The coatings have been tested successfully by international tool manufacturers. Additional developments can be seen in DLC coatings and the hydrogen‐free variety ta‐C. These coatings are suitable for low temperature deposition and machining of special materials.     

In situ synchrotron tomography estimation of toughening effect by semi-ductile fibre reinforcement in a tungsten-fibre-reinforced tungsten composite system

Tungsten-fibre-reinforced tungsten composites (W_f/W) are supposed to enable enhanced toughness owing to extrinsic energy dissipation mechanisms such as interface debonding and plastic deformation of fibre. In particular, the latter is an effective source of toughening, since ductile tungsten fibres can absorb a considerable amount of plastic work. For a precise evaluation of the toughening capability, the energy dissipation mechanisms need to be analysed in detail. To this end, single-fibre tungsten composite specimens are fabricated and the stress–strain behaviour of the tungsten fibre bridging a matrix crack is measured by means of in situ high-energy synchrotron microtomography during a uniaxial tensile test. Despite the high X-ray attenuation in tungsten, a sufficiently high resolution is achieved and clear images of crack extension and deformation are obtained. The amount of absorbed energy due to plastic deformation of the tungsten fibre is determined and compared with values obtained conventionally from single-fibre tensile tests.     

Lead time anticipation in Supply Chain Operations Planning

Linear programming (LP) models for Supply Chain Operations Planning are widely used in Advanced Planning Systems. The solution to the LP model is a proposal for order releases to the various production units (PU) in the supply network. There is a non-linear relationship between the work-in-process in the PU and the lead time that is difficult to capture in the LP model formulation. We propose a two-step lead time anticipation (LTA) procedure where the LP model is first solved irrespective of the available production capacity and is subsequently updated with aggregate order release targets. The order release targets are generated by a local smoothing algorithm that accounts for the evolution of the stochastic workload in the PU. A solution that is both feasible with respect to the planned lead time and meets the material requirements may not exist. By means of discrete event simulation, we compare a conservative strategy where the production quantities are reduced to an optimistic strategy where the planned lead time constraint is allowed to be violated.     

Spatially oversampled TDC with digital resolution enhancement

A digital resolution enhancement technique for time-to-digital converters (TDC) is proposed. This involves a simultaneous multi-channel measurement of a time interval with low complexity TDC of varying low resolutions. The coarse outputs of each converter are digitally post-processed to obtain an output whose precision is much better than that of the individual converters. Three post-processing algorithms are proposed and their limitations in presence of converter non-idealities are analyzed. A prototype system with 8 channels is implemented in 90 nm CMOS. 40MS/s output of each channel is algorithmically combined to obtain over 2.2–3X measured improvement in the resolution in 4/6/8 channel modes, validating the system principle. The chip occupies 0.3 mm² and draws up to a maximum of 4 mA from a 1.2 V supply.