Phase segregation in supramolecular polymers based on telechelics synthesized via multicomponent reactions

The properties of supramolecular polymers in the solid state are strongly dependent on the binding strength of the supramolecular motifs used; however, It has been previously shown that the nanostructure of supramolecular polymers plays an equally important role. Supramolecular polymers are commonly synthesized via end-group functionalization of low-glass transition telechelics with supramolecular units. In these systems, the binding motifs segregate from the soft telechelic backbone and form a hydrogen bonded crystalline hard phase that provides physical cross-links. To date, the reported synthetic approaches do not permit the introduction of a wide variety of supramolecular units with low synthetic effort, which would facilitate studying the structure-property relationships. The use of the Passerini and Ugi multicomponent reactions to synthesize various poly(ethylene-co-butylene) telechelics with diverse amide end-groups is reported. The thermal properties of the supramolecular polymers obtained through their solid-state assembly are investigated and their nanophase- segregation is studied, which is dictated by the end-group volume fraction and the amide–amide hydrogen bonding

Abelian Higgs Hair for Black Holes

We find evidence for the existence of solutions of the Einstein and Abelian Higgs field equations describing a black hole pierced by a Nielsen-Olesen vortex. This situation falls outside the scope of the usual no-hair arguments due to the non-trivial topology of the vortex configuration and the special properties of its energy-momentum tensor. By a combination of numerical and perturbative techniques we conclude that the black hole horizon has no difficulty in supporting the long range fields of the Nielsen Olesen string. Moreover, the effect of the vortex can in principle be measured from infinity, thus justifying its characterization as black hole ``hair".Comment: 31 pages, plain tex, 7 figures included. minor corrections and references adde

Black holes on thick branes

The interplay between topological defects (branes) and black holes has been a subject of recent study, motivated in part by interest in brane-world scenarios. In this paper we analyze in detail the description of a black hole bound to a domain wall (a two-brane in four dimensions), for which an exact description in the limit of zero wall thickness has been given recently. We show how to smooth this singular solution with a thick domain wall. We also show that charged extremal black holes of a size (roughly) smaller than the brane thickness expel the wall, thereby extending the phenomenon of flux expulsion. Finally, we analyze the process of black hole nucleation {\it on} a domain wall, and argue that it is preferred over a previously studied mechanism of black hole nucleation {\it away} from the wall.Comment: 22 pages revtex, 4 figures, comments adde

Mapping medical careers: Questionnaire assessment of career preferences in medical school applicants and final-year students

BACKGROUND: The medical specialities chosen by doctors for their careers play an important part in the workforce planning of health-care services. However, there is little theoretical understanding of how different medical specialities are perceived or how choices are made, despite there being much work in general on this topic in occupational psychology, which is influenced by Holland's RIASEC (Realistic-Investigative-Artistic-Social-Enterprising-Conventional) typology of careers, and Gottfredson's model of circumscription and compromise. In this study, we use three large-scale cohorts of medical students to produce maps of medical careers. METHODS: Information on between 24 and 28 specialities was collected in three UK cohorts of medical students (1981, 1986 and 1991 entry), in applicants (1981 and 1986 cohorts, N = 1135 and 2032) or entrants (1991 cohort, N = 2973) and in final-year students (N = 330, 376, and 1437). Mapping used Individual Differences Scaling (INDSCAL) on sub-groups broken down by age and sex. The method was validated in a population sample using a full range of careers, and demonstrating that the RIASEC structure could be extracted. RESULTS: Medical specialities in each cohort, at application and in the final-year, were well represented by a two-dimensional space. The representations showed a close similarity to Holland's RIASEC typology, with the main orthogonal dimensions appearing similar to Prediger's derived orthogonal dimensions of 'Things-People' and 'Data-Ideas'. CONCLUSIONS: There are close parallels between Holland's general typology of careers, and the structure we have found in medical careers. Medical specialities typical of Holland's six RIASEC categories are Surgery (Realistic), Hospital Medicine (Investigative), Psychiatry (Artistic), Public Health (Social), Administrative Medicine (Enterprising), and Laboratory Medicine (Conventional). The homology between medical careers and RIASEC may mean that the map can be used as the basis for understanding career choice, and for providing career counselling

An Osmotic Model of the Growing Pollen Tube

Pollen tube growth is central to the sexual reproduction of plants and is a longstanding model for cellular tip growth. For rapid tip growth, cell wall deposition and hardening must balance the rate of osmotic water uptake, and this involves the control of turgor pressure. Pressure contributes directly to both the driving force for water entry and tip expansion causing thinning of wall material. Understanding tip growth requires an analysis of the coordination of these processes and their regulation. Here we develop a quantitative physiological model which includes water entry by osmosis, the incorporation of cell wall material and the spreading of that material as a film at the tip. Parameters of the model have been determined from the literature and from measurements, by light, confocal and electron microscopy, together with results from experiments made on dye entry and plasmolysis in Lilium longiflorum. The model yields values of variables such as osmotic and turgor pressure, growth rates and wall thickness. The model and its predictive capacity were tested by comparing programmed simulations with experimental observations following perturbations of the growth medium. The model explains the role of turgor pressure and its observed constancy during oscillations; the stability of wall thickness under different conditions, without which the cell would burst; and some surprising properties such as the need for restricting osmotic permeability to a constant area near the tip, which was experimentally confirmed. To achieve both constancy of pressure and wall thickness under the range of conditions observed in steady-state growth the model reveals the need for a sensor that detects the driving potential for water entry and controls the deposition rate of wall material at the tip

ARTICLE Variation in cougar (Puma concolor) predation habits during wolf (Canis lupus) recovery in the southern Greater Yellowstone Ecosystem

Abstract: We examined predation habits of cougars (Puma concolor (L., 1771)) following the recent recovery of gray wolves (Canis lupus L., 1758) in the southern Greater Yellowstone Ecosystem. With the extirpation of wolves in the early 20th century, cougars likely expanded their niche space to include space vacated by wolves, and increased use of habitat better suited to the foraging of a coursing predator, like wolves. We predicted that as wolves recolonized their former range, competitive exclusion would compel cougars to cede portions of niche space occupied in the absence of wolves. To examine this hypothesis, we radio-tracked cougars and examined their predation sites from winter 2000-2001 through summer 2009. Variation in foraging by cougars was associated with increasing wolf presence. As wolf numbers increased and the mean distance between wolf pack activity centers and cougar predation sites decreased, cougars made kills at higher elevations on more north-facing slopes during summer and in more rugged areas during winter. In addition, cougars preyed on a higher proportion of mule deer (Odocoileus hemionus (Rafinesque, 1817)), consistent with predictions of exploitative competition with wolves. Observed changes in predation characteristics reflect differences in predation strategy between cougars and wolves, given that wolves are coursing predators and cougars are ambush predators. These possible predation effects should be considered when developing management strategies in systems where the recolonization of wolves may occur. Key words: Canis lupus, cougars, competition, predation, Puma concolor, radio telemetry, recolonization, wolves, Wyoming. Résumé : Nous avons examiné les habitudes de prédation des pumas (Puma concolor (L., 1771)) dans la foulée de la découverte récente de loups gris (Canis lupus L., 1758) dans la partie sud de l'écosystème du Grand Yellowstone. La disparition des loups au début du 20 e siècle a vraisemblablement permis aux pumas d'élargir leur niche pour y inclure des aires laissées libres par les loups et d'accroître leur utilisation d'habitats mieux adaptés à un prédateur privilégiant la poursuite, comme le loup. Nous avons prédit que, à mesure que les loups se rétablissent dans leur aire de répartition antérieure, l'exclusion concurrentielle obligerait les pumas à céder des parties de leur niche occupées en l'absence des loups. Pour évaluer cette hypothèse, nous avons suivi des pumas par radiotélémétrie et examiné leurs lieux de prédation de l'hiver 2000-2001 à l'été 2009. Des variations sur le plan de la quête de nourriture par les pumas sont associées à la présence croissante des loups. À mesure que le nombre de ces derniers augmente et que la distance moyenne entre les centres d'activité de meutes de loups et les lieux de prédation des pumas diminue, ces derniers tuent leurs proies à plus grande élévation, sur des pentes d'orientation plus septentrionale durant l'été et dans des secteurs plus accidentés en hiver. En outre, les cerfs mulets (Odocoileus hemionus (Rafinesque, 1817)) représentent une proportion croissante des proies des pumas, ce qui concorde avec la prédiction d'une concurrence avec les loups pour l'exploitation des ressources. Les changements des caractéristiques de prédation observés reflètent les différentes stratégies de prédation des pumas et des loups, ces derniers étant des prédateurs qui poursuivent leurs proies alors que les pumas chassent par embuscade. Ces effets possibles de la prédation devraient être pris en considération dans l'élaboration de stratégies de gestion dans les systèmes où un rétablissement des loups pourrait avoir lieu. [Traduit par la Rédaction

Statistical mechanics where Newton’s third law is broken

There is a variety of situations in which Newton’s third law is violated. Generally, the action-reaction symmetry can be broken for mesoscopic particles, when their effective interactions are mediated by a nonequilibrium environment. Here, we investigate different classes of nonreciprocal interactions relevant to real experimental situations and present their basic statistical mechanics analysis.We show that in mixtures of particles with such interactions, distinct species acquire distinct kinetic temperatures. In certain cases, the nonreciprocal systems are exactly characterized by a pseudo-Hamiltonian; i.e., being intrinsically nonequilibrium, they can nevertheless be described in terms of equilibrium statistical mechanics. Our results have profound implications, in particular, demonstrating the possibility to generate extreme temperature gradients on the particle scale. We verify the principal theoretical predictions in experimental tests performed with two-dimensional binary complex plasmas