Interactions between earthworms and arsenic in the soil environment:a review

Chemical pollution of the environment has become a major source of concern. In particular, many studies have investigated the impact of pollution on biota in the environment. Studies on metalliferous contaminated mine spoil wastes have shown that some soil organisms have the capability to become resistant to metal/metalloid toxicity. Earthworms are known to inhabit arsenic-rich metalliferous soils and, due to their intimate contact with the soil, in both the solid and aqueous phases, are likely to accumulate contaminants present in mine spoil. Earthworms that inhabit metalliferous contaminated soils must have developed mechanisms of resistance to the toxins found in these soils. The mechanisms of resistance are not fully understood; they may involve physiological adaptation (acclimation) or be genetic. This review discusses the relationships between earthworms and arsenic-rich mine spoil wastes, looking critically at resistance and possible mechanisms of resistance, in relation to soil edaphic factors and possible trophic transfer routes.

Human parietal and primary motor cortical interactions are selectively modulated during the transport and grip formation of goal-directed hand actions

Posterior parietal cortex (PPC) constitutes a critical cortical node in the sensorimotor system in which goal-directed actions are computed. This information then must be transferred into commands suitable for hand movements to the primary motor cortex (M1). Complexity arises because reach-to-grasp actions not only require directing the hand towards the object (transport component), but also preshaping the hand according to the features of the object (grip component). Yet, the functional influence that specific PPC regions exert over ipsilateral M1 during the planning of different hand movements remains unclear in humans. Here we manipulated transport and grip components of goal-directed hand movements and exploited paired-pulse transcranial magnetic stimulation (ppTMS) to probe the functional interactions between M1 and two different PPC regions, namely superior parieto-occipital cortex (SPOC) and the anterior region of the intraparietal sulcus (aIPS), in the left hemisphere. We show that when the extension of the arm is required to contact a target object, SPOC selectively facilitates motor evoked potentials, suggesting that SPOC-M1 interactions are functionally specific to arm transport. In contrast, a different pathway, linking the aIPS and ipsilateral M1, shows enhanced functional connections during the sensorimotor planning of grip. These results support recent human neuroimaging findings arguing for specialized human parietal regions for the planning of arm transport and hand grip during goal-directed actions. Importantly, they provide new insight into the causal influences these different parietal regions exert over ipsilateral motor cortex for specific types of planned hand movements

Using extended contact to improve physiological responses and behavior toward people with schizophrenia

Extended contact has been shown to improve explicit and implicit attitudes toward a number of outgroups, but not yet toward people with mental health conditions. Using people with schizophrenia as the target group, this experiment is the first to demonstrate that extended contact can reduce explicit prejudice, buffer stress responses to future interactions, improve non-verbal behavior, and improve the quality of interactions in a manner detectable by the target group member. Participants watched a video of a brief, positive interaction between two strangers, one of whom they were led to believe had schizophrenia. Control participants watched the same video without being told that the person had schizophrenia. They then participated in a social interaction with a confederate whom they were led to believe had the disorder. Participants' cardiovascular and electrodermal activity were monitored immediately before the interaction. The interaction was also secretly recorded to allow independent judges to assess the participants' non-verbal behaviors. The confederate also rated the positivity of each interaction. Participants in the extended contact condition reported more positive attitudes toward people with schizophrenia, displayed more positive non-verbal behaviors, and had a more positive interaction with the confederate. Moreover, just prior to the interaction, participants in the extended contact condition displayed smaller anticipatory stress responses, as reflected in smaller changes in interbeat interval and non-specific skin conductance responses during this phase. Together, these findings support the use of the extended contact as an intervention that could lead to genuine changes in attitudes toward and treatment of people with severe mental health disorders.

Sound Synthesis for Contact-Driven Musical Instruments via Discretisation of Hamilton's Equations

Physical modelling of musical instruments involves studying nonlinear interactions between parts of the instrument. These can pose several difficulties concerning the accuracy and stability of numerical algorithms. In particular, when the underlying forces are non-analytic functions of the phase-space variables, a stability proof can only be obtained in limited cases. An approach has been recently presented by the authors, leading to unconditionally stable simulations for lumped collision models. In that study, discretisation of Hamilton’s equations instead of the usual Newton’s equation of motion yields a numerical scheme that can be proven to be energy conserving. In this paper, the above approach is extended to collisions of distributed objects. Namely, the interaction of an ideal string with a flat barrier is considered. The problem is formulated within the Hamiltonian framework and subsequently discretised. The resulting nonlinearmatrix equation can be shown to possess a unique solution, that enables the update of the algorithm. Energy conservation and thus numerical stability follows in a way similar to the lumped collision model. The existence of an analytic description of this interaction allows the validation of the model’s accuracy. The proposed methodology can be used in sound synthesis applications involving musical instruments where collisions occur either in a confined (e.g. hammer-string interaction, mallet impact) or in a distributed region (e.g. string-bridge or reed-mouthpiece interaction).

‘A picture of who we are as a family’: conceptualizing post-adoption contact as practices of family display

Social work has a central role in negotiating and supporting birth family contact following adoption from care. This paper argues that family display (Finch) offers a useful conceptual resource for understanding relationships in the adoptive kinship network as they are enacted through contact. It reports on an interpretative phenomenological analysis of adoptive parents' accounts of open adoption from care that revealed direct and indirect contact to be contexts in which they and birth relatives performed family display practices: communicating the meaning of their respective relationships with the adopted child and seeking recognition that this was a legitimate family relationship. The analysis explores how family display was performed, and the impact of validating or invalidating responses. It aims to illuminate these social and interpretive processes involved in adoptive kinship in order to inform social work support for contact. The findings suggest that successful contact may be promoted by helping adoptive and birth relatives validate the legitimacy of the other's kin connection with the child, and through arrangements that facilitate family-like interactions.

Confidence in Contact: A New Perspective on Promoting Cross-Group Friendship Among Children and Adolescents

Intergroup contact theory proposes that positive interactions between members of different social groups can improve intergroup relations. Contact should be especially effective in schools, where opportunities may exist to engage cooperatively with peers from different backgrounds and develop cross-group friendships. In turn, these friendships have numerous benefits for intergroup relations. However, there is evidence that children do not always engage in cross-group friendships, often choosing to spend time with same-group peers, even in diverse settings. We argue that in order to capitalize on the potential impact of contact in schools for promoting harmonious intergroup relations, a new model is needed that places confidence in contact at its heart. We present an empirically driven theoretical model of intergroup contact that outlines the conditions that help to make young people contact ready, preparing them for successful, sustained intergroup relationships by giving them the confidence that they can engage in contact successfully. After evaluating the traditional approach to intergroup contact in schools, we present our theoretical model which outlines predictors of cross-group friendships that enhance confidence in and readiness for contact. We then discuss theory-driven, empirically tested interventions that could potentially promote confidence in contact. Finally, we make specific recommendations for practitioners and policy makers striving to promote harmonious intergroup relations in the classroom.

Permanent stallion contact hastens onset of mares' cyclicity after winter anoestrus

The species Equus caballus is characterized as a seasonal polyoestrous herd mammal, providing continuous interactions between stallions and mares in feral herds throughout the year. Under domesticated conditions mares and stallions are stabled and kept separated mostly due to hygienic and safety concerns. Managing mares through the spring transitional phase until they show fertile cycles represents a high multifactorial challenge for horse breeders and veterinarians. The goal of this study was to examine the influence of a permanent stallion contact on the onset of cyclicity in anoestrous mares in the transition period.

Etudes structurales et fonctionnelles des interactions de SUMO avec des proteines d'echafaudage modeles: TIF1beta, PIAS1 et PML

L’adaptation des cellules à leur environnement externe repose sur la transduction adéquate de signaux régulés par une pléthore d'événements moléculaires. Parmi ces événements moléculaires, les modifications post-traductionnelles (MPT) de protéines aident à intégrer, à traduire et à organiser de façon spatiotemporelle ces signaux pour que les cellules puissent réagir aux stimuli externes. Parmi les modifications post-traductionnelles, les petites protéines de la famille de l’Ubiquitine (Ublps, Ubiquitin-like proteins) jouent un rôle majeur dans presque toutes les voies de signalisation. Cette thèse rapporte des études fonctionnelles et structurales des interactions covalentes et non covalentes entre SUMO (Small Ubiquitin related MOdifier), un membre de la famille des Ublps, et trois protéines d'échafaudage, TIF1beta, le corépresseur universel des protéines KRAB-multidoigt de zinc, PIAS1, une ligase E3 pour SUMO et PML, un suppresseur de tumeur. La première étude rapporte l'identification et la caractérisation biochimique des sites de SUMOylation de TIF1beta. Nous avons déterminé que la modification covalente de six résidus lysine par SUMO est essentielle à l’activité de répression de la transcription induit par TIF1beta. En outre, nous présentons des évidences indiquant que la SUMOylation de TIF1 exige non seulement sa capacité à homo-oligomériser, mais est aussi positivement régulée par son interaction avec le domaine KRAB des protéines à doigts de zinc. Partant de ce constat, nous postulons que les protéines KRAB-multidoigt de zinc recrutent leur corépresseur TIF1betaà des gènes cibles, mais aussi accentuent son activité répressive grâce à l'augmentation de sa SUMOylation. Notre seconde étude révèle qu’en plus de réprimer la transcription en tant que MPT covalente, SUMO joue aussi un rôle important dans la répression en tant que partenaire non covalent d’interactions protéine-protéine. Nous avons montré que SUMO interagit simultanément avec deux enzymes de la machinerie de SUMOylation, l’unique enzyme de conjugaison E2, UBC9, et la ligase E3 PIAS1 au sein d’un complexe ternaire répresseur. En outre, nous révélons que la formation du complexe ternaire PIAS1:SUMO:UBC9 est modulée par le niveau de phosphorylation de résidus sérine juxtaposés à un motif d’interaction avec SUMO (SIM) dans PIAS1. Ainsi, SUMO agit comme un adaptateur spécifique qui stabilise les interactions UBC9 E2: E3 PIAS1. Partant de ce constat, nous proposons que les enzymes E2 et E3 des autres systèmes Ublps exploitent des mécanismes similaires dans le cadre de leur fonction Enfin, notre troisième étude explore la régulation des interactions non covalentes de SUMO par la phosphorylation. En utilisant une combinaison d'études in vivo et in vitro, nous démontrons que l'interaction entre SUMO1 et PML est régi par la phosphorylation dépendant de CK2 sur quatre résidus sérine de PML. Les structures cristallographiques des complexes PML-SIM:SUMO1 révèlent que les phospho-sérines de PML contactent des résidus de la région basique de SUMO1. Sachant que la kinase CK2 peut être induite par des kinases activables par le stress, ces résultats suggèrent que les interactions non-covalentes avec SUMO sont modulées par le stress cellulaire. Sur la base de cette constatation, nous postulons que des événements analogues affectent des protéines contenant des séquences SIM ciblées par CK2. En résumé, cette étude révèle qu’en plus de son rôle de MPT, SUMO peut fonctionner comme un adaptateur permettant des interactions spécifiques entre protéines tel que pour les enzymes E3 et E2.

Structural rules for the formation of backbone-backbone interactions between closely packed RNA double helices

Les interactions entre les squelettes sucre-phosphate de nucléotides jouent un rôle important dans la stabilisation des structures tertiaires de larges molécules d’ARN. Elles sont régies par des règles particulières qui gouverne leur formation mais qui jusque là demeure quasiment inconnues. Un élément structural d’ARN pour lequel les interactions sucre-phosphate sont importantes est le motif d’empaquetage de deux doubles hélices d’ARN le long du sillon mineur. Ce motif se trouve à divers endroits dans la structure du ribosome. Il consiste en deux doubles hélices interagissant de manière à ce que le squelette sucre-phosphate de l’une se niche dans le sillon mineur de l’autre et vice versa. La surface de contact entre les deux hélices est majoritairement formée par les riboses et implique au total douze nucléotides. La présente thèse a pour but d’analyser la structure interne de ce motif et sa dépendance de stabilité résultant de l’association optimale ou non des hélices, selon leurs séquences nucléotidiques. Il est démontré dans cette thèse qu’un positionnement approprié des riboses leur permet de former des contacts inter-hélices, par l’entremise d’un choix particulier de l’identité des pairs de bases impliquées. Pour différentes pairs de bases participant à ce contact inter-hélices, l’identité optimale peut être du type Watson-Crick, GC/CG, or certaines pairs de bases non Watson-Crick. Le choix adéquat de paires de bases fournit une interaction inter-hélice stable. Dans quelques cas du motif, l’identité de certaines paires de bases ne correspond pas à la structure la plus stable, ce qui pourrait refléter le fait que ces motifs devraient avoir une liberté de formation et de déformation lors du fonctionnement du ribosome.

Le contact des policiers avec les citoyens : les perceptions de jeunes hommes noirs de la ville de Montréal

Les relations entre les policiers et les citoyens issus des communautés culturelles représentent un enjeu de taille pour le Service de Police de la Ville de Montréal (SPVM). En effet, les relations entre les policiers et les minorités ethniques sont au centre de débats et de consultations depuis plusieurs décennies. Force est de constater qu’encore aujourd’hui des tensions demeurent. Plusieurs recherches se sont penchées sur les perceptions des citoyens de leur service de police, mais peu se sont intéressées aux perceptions détaillées des jeunes hommes noirs. Il est pourtant démontré que ce groupe entretient les perceptions les moins favorables envers les policiers et que, par ailleurs, ils sont plus susceptibles d’avoir des contacts avec les policiers. Les perceptions pouvant avoir une réelle influence sur la réponse au contact policier, il appert qu'il est primordial de comprendre l’origine de ces perceptions. Ainsi, ce mémoire vise à identifier les éléments formateurs des perceptions de jeunes hommes noirs de la ville de Montréal âgés de 18 à 25 ans. Pour ce faire, l’approche qualitative a été retenue et des entretiens de type semi-directifs ont été effectués. L’analyse du discours des participants révèle principalement que les interactions personnelles avec les policiers forment les perceptions et/ou renforcent des perceptions déjà existantes. De plus, l’approche de l’agent de police lors de ce contact est mainte fois soulignée par les jeunes lors des entretiens réalisés démontrant que les premiers instants d’une interaction suffisent à l’instauration d’une perception positive ou négative. Il ressort aussi de l’étude que les expériences indirectes ont un impact certain dans la formation des perceptions surtout lorsque ces expériences ont été vécues par un proche. Ces expériences indirectes s’inscrivent d’ailleurs dans un contexte où l’appartenance culturelle du jeune et une certaine culture de quartier tendent à dicter ce que les jeunes se doivent de penser de l’organisation policière. De plus, une méconnaissance des enjeux sous-jacents aux perceptions de ces jeunes hommes par les corps policiers paraît être un obstacle à la mise en place d’interventions efficaces et significatives auprès de cette population.

Semiclassical theory of shot noise in ballistic n+in+ semiconductor structures: relevance of Pauli and long range Coulomb interactions

We work out a semiclassical theory of shot noise in ballistic n+-i-n+ semiconductor structures aiming at studying two fundamental physical correlations coming from Pauli exclusion principle and long-range Coulomb interaction. The theory provides a unifying scheme which, in addition to the current-voltage characteristics, describes the suppression of shot noise due to Pauli and Coulomb correlations in the whole range of system parameters and applied bias. The whole scenario is summarized by a phase diagram in the plane of two dimensionless variables related to the sample length and contact chemical potential. Here different regions of physical interest can be identified where only Coulomb or only Pauli correlations are active, or where both are present with different relevance. The predictions of the theory are proven to be fully corroborated by Monte Carlo simulations.

Interactions between earthworms and arsenic in the soil environment: a review

Chemical pollution of the environment has become a major source of concern. In particular, many studies have investigated the impact of pollution on biota in the environment. Studies on metalliferous contaminated mine spoil wastes have shown that some soil organisms have the capability to become resistant to metal/metalloid toxicity. Earthworms are known to inhabit arsenic-rich metalliferous soils and, due to their intimate contact with the soil, in both the solid and aqueous phases, are likely to accumulate contaminants present in mine spoil. Earthworms that inhabit metalliferous contaminated soils must have developed mechanisms of resistance to the toxins found in these soils. The mechanisms of resistance are not fully understood; they may involve physiological adaptation (acclimation) or be genetic. This review discusses the relationships between earthworms and arsenic-rich mine spoil wastes, looking critically at resistance and possible mechanisms of resistance, in relation to soil edaphic factors and possible trophic transfer routes. (C) 2003 Elsevier Science Ltd. All rights reserved.

Estimating root–soil contact from 3D X-ray microtomographs

Adequate contact with the soil is essential for water and nutrient adsorption by plant roots, but the determination of root–soil contact is a challenging task because it is difficult to visualize roots in situ and quantify their interactions with the soil at the scale of micrometres. A method to determine root–soil contact using X-ray microtomography was developed. Contact areas were determined from 3D volumetric images using segmentation and iso-surface determination tools. The accuracy of the method was tested with physical model systems of contact between two objects (phantoms). Volumes, surface areas and contact areas calculated from the measured phantoms were compared with those estimated from image analysis. The volume was accurate to within 0.3%, the surface area to within 2–4%, and the contact area to within 2.5%. Maize and lupin roots were grown in soil (<2 mm) and vermiculite at matric potentials of −0.03 and −1.6 MPa and in aggregate fractions of 4–2, 2–1, 1–0.5 and < 0.5 mm at a matric potential of −0.03 MPa. The contact of the roots with their growth medium was determined from 3D volumetric images. Macroporosity (>70 µm) of the soil sieved to different aggregate fractions was calculated from binarized data. Root-soil contact was greater in soil than in vermiculite and increased with decreasing aggregate or particle size. The differences in root–soil contact could not be explained solely by the decrease in porosity with decreasing aggregate size but may also result from changes in particle and aggregate packing around the root.

Classical simulation of deposition of thiophene oligomers on TiO(2)-anatase: Relevance of long-range electrostatic interactions

We performed classical molecular dynamics simulations of the vapor-deposition of alpha-T4 oligomers on the TiO(2)-anatase (101) surface, comparing different sets of charges associated with the atoms of the model. The potential energy surfaces for alpha-T4 and TiO(2) were described by re-parametrizations of the Universal force field with charges given by the charge equilibration (QEq) scheme, or with fixed charges obtained by an ab initio method using the Hirshfeld partition. The two sets of charges lead to completely different results for the interface formation, and for the characteristics of the organic film, with a clearly defined alpha-T4 contact layer in the QEq case, and a more homogeneous molecular distribution when using Hirshfeld charges. The main reason for the discrepancy was found to be the incorrect charge assignment given by QEq to the sulfur and alpha-carbon atoms in thiophenes, and highlight the relevance of long-range interactions in the organization of molecular films. (C) 2009 Elsevier B.V. All rights reserved.

The role of oomycete effectors in plant–pathogen interactions

Plants constantly come into contact with a diverse range of microorganisms that are potential pathogens, and they have evolved multi-faceted physical and hemical strategies to inhibit pathogen ingress and establishment of disease. Microbes, however, have developed their own strategies to counteract plant defence responses. Recent research on plant–microbe interactions has revealed that an important part of the infection strategies of a diverse range of plant pathogens, including bacteria, fungi and oomycetes, is the production of effector proteins that are secreted by the pathogen and that promote successful infection by manipulating plant structure and metabolism, including interference in plant defence mechanisms. Pathogen effector proteins may function either in the extracellular spaces within plant tissues or within the plant cell cytoplasm. Extracellular effectors include cell wall degrading enzymes and inhibitors of plant enzymes that attack invading pathogens. Intracellular effectors move into the plant cell cytoplasm by as yet unknown mechanisms where, in incompatible interactions, they may be recognised by plant resistance proteins but where, in compatible interactions, they may suppress the plant’s immune response. This article presents a brief overview of our current understanding of the nature and function of effectors produced by oomycete plant pathogens.