3,560 research outputs found

    Frustrated Polyelectrolyte Bundles and T=0 Josephson-Junction Arrays

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    We establish a one-to-one mapping between a model for hexagonal polyelectrolyte bundles and a model for two-dimensional, frustrated Josephson-junction arrays. We find that the T=0 insulator-to-superconductor transition of the {\it quantum} system corresponds to a continuous liquid-to-solid transition of the condensed charge in the finite temperature {\it classical} system. We find that the role of the vector potential in the quantum system is played by elastic strain in the classical system. Exploiting this correspondence we show that the transition is accompanied by a spontaneous breaking of chiral symmetry and that at the transition the polyelectrolyte bundle adopts a universal response to shear.Comment: 4 pages, 2 figures, 1 table minor changes to text, reference adde

    Differential effects of jasmonic acid treatment of Brassica nigra on the attraction of pollinators, parasitoids, and butterflies

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    Herbivore-induced plant defences influence the behaviour of herbivores as well as that of their natural enemies. Jasmonic acid is one of the key hormones involved in both these direct and indirect induced defences. Jasmonic acid treatment of plants changes the composition of defence chemicals in the plants, induces volatile emission, and increases the production of extrafloral nectar. However, few studies have addressed the potential influence of induced defences on flower nectar chemistry and pollinator behaviour. These have shown that herbivore damage can affect pollination rates and plant fitness. Here, we have investigated the effect of jasmonic acid treatment on floral nectar production and the attraction of pollinators, as well as the effect on the behaviour of an herbivore and its natural enemy. The study system consisted of black mustard plants, Brassica nigra L. (Brassicaceae), pollinators of Brassica nigra (i.e., honeybees and syrphid flies), a specialist herbivore, Pieris rapae L. (Lepidoptera: Pieridae), and a parasitoid wasp that uses Pieris larvae as hosts, Cotesia glomerata L. (Hymenoptera: Braconidae). We show that different trophic levels are differentially affected by jasmonic acid-induced changes. While the herbivore prefers control leaves over jasmonic acid-treated leaves for oviposition, the parasitoid C. glomerata is more attracted to jasmonic acid-treated plants than to control plants. We did not observe differences in pollinator preference, the rates of flower visitation by honeybees and syrphid flies were similar for control and jasmonic acid-treated plants. Plants treated with jasmonic acid secreted less nectar than control plants and the concentrations of glucose and fructose tended to be lower than in nectar from control plants. Jasmonic acid treatment resulted in a lower nectar production than actual feeding damage by P. rapae caterpillars

    Infochemical use in Brassica-insect interactions : a phenotypic manipulation approach to induced plant defences

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    Plants have developed a range of strategies to defend themselves against herbivore attack. Defences can be constitutive, i.e. always present independent of attack, or induced, i.e. only elicited when the plant is under attack. In this thesis, I focused on induced chemical defence responses of plants and the response of associated insects to these phenotypic changes in plants. Herbivore attack is known to induce chemical defences in Brassicaceous plants. Using several elicitors and inhibitors of different steps of the signalling pathways underlying herbivore-induced plant responses, I studied how induced infochemicals affect interactions with associated insects. Jasmonic acid (JA) is a key plant hormone in the octadecanoid signalling pathway known to be involved in herbivore-induced plant defences. Application of JA can induce plant responses that are similar, although not identical, to herbivore feeding. Two specialist herbivores of Brassicaceous plants, the butterflies Pieris rapae and P. brassicae, preferred to oviposit on non-induced plants over JA-induced plants. Development of P. rapae caterpillars was shown to be reduced, suggesting that oviposition avoidance on JA-induced plants is adaptive. The levels of glucosinolates, secondary metabolites of Brassicaceous plants that are used by Pieris butterflies as oviposition stimulants, could not explain the observed oviposition preference of the butterflies. JA-induced changes in the plants also affected members of the third trophic level. Volatile emission of JA-induced plants attracted parasitoid wasps to the plants. Parasitoid attraction to JA-induced plants was shown to depend on dose and induction time. However, using JA to induce phenotypic changes had effects different from those induced by herbivores, both chemically and ecologically. Volatile emission of JA-induced and herbivore-induced plants differed; whereas JA-induced plants emitted larger amounts of volatiles, the parasitoids preferred herbivore-induced plants over JA-treated ones. Early events in plant defence responses, involved in attacker recognition, are damage-induced modulations of ion channel activities resulting in ion imbalances. The fungal elicitor alamethicin, an ion channel-forming peptide mixture, was used to mimic early steps in defence responses. Alamethicin treatment increased attractiveness of plants to parasitoid wasps. Although volatile emission of alamethicin-treated plants was much lower, they were equally attractive as JA-treated plants. This indicates that quality rather than quantity of induced plant volatile blends is important to parasitoids. Besides chemical elicitation of herbivore-induced responses, which is a widely applied approach, plant defence responses can also be chemically inhibited. This provides the opportunity to inhibit the rate of specific enzymatic steps in a signal-transduction pathway. Furthermore, visual cues associated with feeding damage can be present (and similar) in control- and inhibitor-treated plants. Phenidone is a compound that inhibits lipoxygenase, an enzyme catalyzing an early step in the octadecanoid pathway. Parasitoid attraction was reduced when the plants were treated with phenidone before infestation. Also herbivore oviposition preference was shown to be affected by inhibition of this signalling pathway. Herbivores can differ in their oviposition preferences. I studied two specialist herbivores with different oviposition preferences: Pieris brassicae avoids oviposition on herbivore-induced plants, whereas Plutella xylostella prefers to oviposit on Pieris-infested plants. I showed that these preferences have a chemical basis and are dependent on octadecanoid signalling, since treatment with the lipoxygenase inhibitor phenidone eliminated herbivore-induced oviposition avoidance or preference. Thus far, most of the studies on induced plant defences have been done with vegetative plants. However, since reproduction and defence are both processes that require energy and nutrients, this could result in a trade-off. Herbivore feeding on leaves, flowers or roots is known to affect pollinator visitation, but the mechanisms mediating this change have not been addressed. Effects of induction with JA on nectar secretion and pollinator visitation to flowers were investigated. JA-induced plants secreted less nectar, but the sugar concentrations did not change. Also visitation of honeybees and syrphid flies did not change upon JA induction. These results show the complexity of induced plant defence responses and the variety of behavioural responses of insects on different trophic levels. Combining the phenotypic manipulation approach to induced plant defences, as used in this thesis, with molecular genetic techniques and building on recent developments in plant biochemistry provides a promising way forward towards enhanced understanding of the intricate interactions between plants and insects. <br/

    Implementation of Assistive Technology in the Classroom

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    Assistive technology (AT) can be defined as “any piece of equipment or device that may be used by a person with a disability to perform specific tasks, improve functional capabilities, and become more independent” (Netherton & Deal, 2006, p. 11). Assistive technology can be used in the classroom to help assist students become successful in tasks otherwise not possible. A review of the literature shows that many teachers have difficulties implementing technology seamlessly into the curriculum because of a lack of funding and training. This research focused on teachers‟ perspectives of assistive technology in the classroom and the training they have received to be successful in implementing a variety of technology into the classroom curriculum. A study was conducted at several suburban school districts located in Western New York consisting of teachers in a variety of subjects and grade levels. Each of the participants answered an anonymous survey to see how much training they have received for using assistive technology and if they felt the training was beneficial and what types of training would be most beneficial to teachers according to their perspective

    Regulatory T cells and immune tolerance after allogeneic hematopoietic stem cell transplantation

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    The story of allogeneic hematopoietic stem cell transplantation (allo-SCT) begins after the atomic bombings of Hiroshima and Nagasaki in 1945. It was observed that fallout radiation caused dose-dependent depression of hematopoiesis 1. Research first focused on how to protect the hematopoietic system from irradiation injury and it was discovered that infusion of spleen or marrow cells from a healthy donor restored hematopoiesis through the establishment of hematopoietic donor chimerism in an irradiated recipient 2. This finding led to the realization that it might also be applied to treat hematological malignancies. In 1957, a new approach to human cancer treatment was reported: radiation and chemotherapy followed by the intravenous infusion of healthy donor bone marrow 3,4. However, all the early clini

    Viral self-assembly as a thermodynamic process

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    The protein shells, or capsids, of all sphere-like viruses adopt icosahedral symmetry. In the present paper we propose a statistical thermodynamic model for viral self-assembly. We find that icosahedral symmetry is not expected for viral capsids constructed from structurally identical protein subunits and that this symmetry requires (at least) two internal "switching" configurations of the protein. Our results indicate that icosahedral symmetry is not a generic consequence of free energy minimization but requires optimization of internal structural parameters of the capsid proteins.Comment: pdf file, 13 pages, three figure
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