Passive compensation of nonlinear robot dynamics

In this paper, we derive a coordinate-free formulation of a passive controller that makes a mechanical system track reference curves in a potential field. Contrary to conventional reference tracking, we do not specify a single time-varying trajectory that the system has to track. Instead, we specify a whole curve that the system has to stay on at all times. Using tools from differential geometry, we first derive a controller that makes the system move along arbitrary (smooth enough) reference curves while keeping the kinetic energy constant. We then apply the results to the case of movement in an artificial potential field, in which case, the reference curves are completely determined by the potential field and cannot be chosen arbitrarily. Simulation then shows the performance of the controller on a benchmark robot with two degrees of freedom

Mapping the potential energy surfaces for ring-closing metathesis reactions of prototypical dienes by electronic structure calculations

The potential energy surfaces for ring-closing metathesis reactions of a series of simple alpha,omega-dienes which lead to 5-10 membered ring products, have been explored using density functional theory methods. We have investigated both the conformational aspects of the hydrocarbon chain during the course of the reactions, as well as the stationary structures on the corresponding potential energy surfaces. Extensive conformational searches reveal that the reaction proceeds via the conformation that would be expected for the cycloalkene product, though most unexpectedly, cyclohexene forms via complexes in boat-like conformations. The M06-L density functional has been used to map out the potential energy surfaces, and has identified metallocyclobutane fragmentation as being generally the highest barrier along the pathway. The structural variations along the pathway have been discussed for the reactant hydrocarbons of differing chain length to identify points at which cyclisation events may begin to affect reaction rates. Our study provides an excellent starting point from which to begin to learn about the way RCM reaction outcomes are controlled by diene structur

A surprising steric effect on a tandem cycloaddition/ring-opening reaction : rapid syntheses of difluorinated analogues of (hydroxymethyl)conduritols

Difluorinated analogues of (hydroxymethyl)conduritols can be synthesised from selected furans and a difluorinated dienophile in two reaction steps

L'alimentation de Brycinus leuciscus (Teleostei : Characidae) au Mali : aspects qualitatifs, quantitatifs et comportementaux

L'alimentation de #Brycinus leuciscus$ a été étudiée dans une mare alimentée par le fleuve Niger près de Bamako. Dans cet habitat, cette espèce possède un régime omnivore dans lequel la quantité de proies allochtones augmente en saison des pluies. Elle se nourrit surtout durant la photophase. Des observations en aquarium montrent que la détection des proies est essentiellement visuelle. Le rythme alimentaire nycthéméral semble modulé par la lunaison, la réplétion stomacale étant plus faible durant la pleine lune. Cela pourrait être lié à la formation de bancs à cette période, et donc à un antagonisme entre l'activité alimentaire individuelle et le grégarisme social. (Résumé d'auteur

Diagram techniques for confluence

AbstractWe develop diagram techniques for proving confluence in abstract reductions systems. The underlying theory gives a systematic and uniform framework in which a number of known results, widely scattered throughout the literature, can be understood. These results include Newman's lemma, Lemma 3.1 of Winkler and Buchberger, the Hindley–Rosen lemma, the Request lemmas of Staples, the Strong Confluence lemma of Huet, the lemma of De Bruijn

Mutation in NSUN2, which Encodes an RNA Methyltransferase, Causes Autosomal-Recessive Intellectual Disability

Causes of autosomal-recessive intellectual disability (ID) have, until very recently, been under researched because of the high degree of genetic heterogeneity. However, now that genome-wide approaches can be applied to single multiplex consanguineous families, the identification of genes harboring disease-causing mutations by autozygosity mapping is expanding rapidly. Here, we have mapped a disease locus in a consanguineous Pakistani family affected by ID and distal myopathy. We genotyped family members on genome-wide SNP microarrays and used the data to determine a single 2.5 Mb homozygosity-by-descent (HBD) locus in region 5p15.32–p15.31; we identified the missense change c.2035G>A (p.Gly679Arg) at a conserved residue within NSUN2. This gene encodes a methyltransferase that catalyzes formation of 5-methylcytosine at C34 of tRNA-leu(CAA) and plays a role in spindle assembly during mitosis as well as chromosome segregation. In mouse brains, we show that NSUN2 localizes to the nucleolus of Purkinje cells in the cerebellum. The effects of the mutation were confirmed by the transfection of wild-type and mutant constructs into cells and subsequent immunohistochemistry. We show that mutation to arginine at this residue causes NSUN2 to fail to localize within the nucleolus. The ID combined with a unique profile of comorbid features presented here makes this an important genetic discovery, and the involvement of NSUN2 highlights the role of RNA methyltransferase in human neurocognitive development

Research Report: A Preliminary Analysis of Medical Futility Decisionmaking: Law and Professional Attitudes

The debate in medical futility decisionmaking centers on the conflict between a patient insisting treatment and a doctor refusing to furnish it. Courts have taken two disparate approaches to the legal status of medical futility. Believing that such legal ambiguity may reflect ambiguity in the medical profession itself, this research report sought to identify any emerging consensus among professionals handling medical futility issues. The report explains the results of the Life Sustaining Treatment Survey, a nationwide survey of health care professionals at hospitals. Presented with a list of criteria, respondents assigned important ratings to the factors used in recent futility decisions at their institutions. The resulting data suggests that there is no consensus among professionals in medical futility decisionmaking. The data supports at least three distinct approaches for making futility decisions: emphasis on the patients’ preferences; providing for the patient and family; and adhering to objective medical and social norms. It is unlikely that the law will realize its full potential to regulate futility judgments until explicitly articulated professional standards emerge. This article advocates continued empirical research to document and test professional judgment principles. Such research may ultimately help identify factors that will form the basis for a consensus in medical futility decisionmaking

Towards an engineering model for curve squeal

Curve squeal is a strong tonal noise that may arise when a railway vehicle negotiates a curve. The wheel/rail contact model is the central part of prediction models, describing the frictional instability occurring in the contact during squeal. A previously developed time-domain squeal model considers the wheel and rail dynamics, and the wheel/rail contact is solved using Kalker’s nonlinear transient CONTACT algorithm with Coulomb friction. In this paper, contact models with different degree of simplification are compared to CONTACT within the previously developed squeal model in order to determine a suitable contact algorithm for an engineering curve squeal model. Kalker’s steady-state FASTSIM is evaluated, and, without further modification, shows unsatisfying results. An alternative transient single-point contact algorithm named SPOINT is formulated with the friction model derived from CONTACT. Comparing with the original model results, the SPOINT implementation results are promising and similar to results from CONTACT

Mosquitoes and malaria transmission in irrigated rice-fields in the Benoue valley of northern Cameroon

International audienc

A study of the osmotic membrane bioreactor process using a sodium chloride solution and an industrial effluent as draw solutions

[EN] Osmotic membrane bioreactor (OMBR) is an emerging membrane process which has gained interest in the recent years because of the low energy consumption and the high effluent quality. The osmotic membrane bioreactor combines a forward osmosis (FO) membrane and a biological treatment. However, salt reverse flux is the main problem because of the negative effect of the salt concentration increase in the reactor on the microbial activity. This is the reason why the study of a suitable draw solution (DS) is very important in the overall performance of the reactor. This study compares the process performance using two draw solutions: a 53 g L-1 NaCI solution and a real waste water solution (waste water from an absorption column consisting mainly of SO42- and NH4-N with concentrations of 153 g L-1 and 19 g L-1, respectively). The comparison is focused on the salt reverse flux during the reactor operation, the mixed liquor characteristics, the membrane fouling and the overall performance. The results indicated that the industrial wastewater showed a higher salt reverse flux, but also a less severe fouling and a higher the osmotic pressure difference in comparison with the NaCl solution. In terms of chemical oxygen demand (COD) removal efficiencies, both draw solutions attained values higher than 80%, though the efficiency was slightly lower when the industrial effluent was used as DS. This was related to the higher conductivity reached in the bioreactor when the industrial effluent was used as draw solution. In spite of it, the use of this industrial effluent as draw solution is strongly recommended because of the high permeate fluxes yielded, the low membrane fouling and the lack of necessity of regenerating the draw solution. (C) 2017 Elsevier B.V. All rights reserved.This study was supported by the Spanish Ministry of Economy and Competitiveness (Spain) through the project RTC-2015-3582-5-AR.Lujan Facundo, MJ.; Soler Cabezas, JL.; Mendoza Roca, JA.; Vincent Vela, MC.; Bes-Piá, M.; Doñate Hernández, S. (2017). A study of the osmotic membrane bioreactor process using a sodium chloride solution and an industrial effluent as draw solutions. Chemical Engineering Journal. 322:603-610. doi:10.1016/j.cej.2017.04.062S60361032