2,463 research outputs found

    Positron Fraction in the CMSSM

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    A fit to the present data on the cosmic ray positron fraction can be considerably improved,if in addition to the positron production by nuclear interactions in the universe the possible contribution from supersymmetric dark matter annihilation is taken into account. We scan over the complete SUSY parameter space of the Constrained Minimal Supersymmetric Model (CMSSM) and find that in the acceptable regions the neutralino annihilation into b-bbar quark pairs is the dominant channel with hard positrons emerging from the semileptonic decays of the B-mesons.Comment: 6 pages, Latex, Proceedings of the 4th International Workshop on Identification of Dark Matter (idm2002), York, England, 2-6 September, 200

    Development and BiomechanicalInvestigation of a New Compound Palatal Arch

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    Abstract. : Background and Aim: : There are many advantages in using a transpalatal arch in orthodontic treatment. In addition to the active movement of individual teeth, such an arch can be used to provide additional anchorage. The aim of this study was to further develop and improve both the clinical and the biomechanical properties of the conventional transpalatal arch. Material and Methods: : Currently available compound material components form an established part of orthodontic therapy. The Compound palatal arch® broadens the scope of this treatment system. The biomechanical effects of the newly developed Compound palatal arch® were verified by comparing them with those of commercially available conventional transpalatal arches. The recently developed Compound palatal arch® is made of one compound element: nickel-titanium/stainless steel. The specific dimensions and design of the nickel-titanium element are aimed at exploiting its superelasticity, even during active molar movement. The biomechanical investigation was carried out using sixcomponent measuring sensors to register the forces and moments in the three spatial dimensions (x, y and z) at 37 °C. The following appliances were investigated: Goshgarian transpalatal arch, quad-helix appliance, Arndt memory expander®, and Compound palatal arch®. Results: : Transpalatal arches could not be inserted without the arch being under tension. This is particularly important when the arch is being used for anchorage purposes. The Goshgarian arch had to be classified as problematic for the movement of single teeth as the load/deflection rate was high. However, this can be utilized for anchorage purposes. The clinical advantage of a quad-helix appliance is the option for asymmetric tooth movement. Conclusions: : This study showed that the quad-helix was effective for both unilateral and bilateral derotation as well as for transversal tooth movement. However, expansions should be confined to ≤ 4 mm, and derotations to < 10°, as forces and moments are otherwise not within the physiologic range. The Arndt memory expander® displayed no advantages over either the quad-helix appliance or the Goshgarian transpalatal arch. Nor did it display any superelastic properties. The linear relationship, the relatively high forces and moments, and the lack of clinical adjustability cast doubts on the benefits of this appliance. The newly developed Compound palatal arch® showed substantial advantages in molar derotation compared with conventional transpalatal arches. Superelastic properties were achieved through the design and positioning of the nickel-titanium element. Expansion with the Compound palatal arch® was comparable with that with conventional transpalatal arches. The clinical advantage is in the fact that this appliance can be reactivated and that dental asymmetries can be treate

    Localized ultraviolet laser microbeam irradiation of early Drosophila embryos: Fate maps based on location and frequency of adult defects

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    Drosophila embryos were locally irradiated with a 257-nm laser microbeam during blastoderm and germ band stages. Depending on stage and beam diameter (10–30 μm), from 0 to 45 nuclei were exposed to the uv radiation. The doses used, 5 or 10 erg, did not eliminate nuclei or cells at once, but up to 50% of the adult survivors from irradiated eggs carried defects in the thorax. These were scored with reference to the imaginal discs from which the affected structures derive. For each thoracic disc a “target center” was calculated as the weighted mean value of all beam locations affecting the respective adult derivatives. The target centers for the germ band stage map within the respective germ band segments. The pattern of target centers for the blastoderm stage is comparable to the thoracic region of published fate maps, and the distances between adjacent leg centers (approximately three cell diameters) agree with recent evidence based on mosaic flies. We discuss the question whether the target centers mark the position of the respective disc progenitor cells at the stages of irradiation and conclude that these positions are rendered rather correctly at least with reference to the longitudinal egg axis
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