418 research outputs found
The timing and location of glial cell line-derived neurotrophic factor expression determine enteric nervous system structure and function
Ret signaling is critical for formation of the enteric nervous system (ENS) because Ret activation promotes ENS precursor survival, proliferation, and migration and provides trophic support for mature enteric neurons. While these roles are well established, we now provide evidence that increasing levels of the Ret ligand GDNF in mice causes alterations in ENS structure and function that are critically dependent on the time and location of increased GDNF availability. This is demonstrated using two different strains of transgenic mice and by injecting newborn mice with GDNF. Furthermore, because different subclasses of ENS precursors withdraw from the cell cycle at different times during development, increases in GDNF at specific times alter the ratio of neuronal subclasses in the mature ENS. In addition, we confirm that esophageal neurons are GDNF responsive and demonstrate that the location of GDNF production influences neuronal process projection for NADPH diaphorase expressing, but not acetylcholinesterase, choline acetyltransferase, or tryptophan hydroxylase expressing small bowel myenteric neurons. We further demonstrate that changes in GDNF availability influence intestinal function in vitro and in vivo. Thus, changes in GDNF expression can create a wide variety of alterations in ENS structure and function and may in part contribute to human motility disorders
Triangle-generation in topological D-brane categories
Tachyon condensation in topological Landau-Ginzburg models can generally be
studied using methods of commutative algebra and properties of triangulated
categories. The efficiency of this approach is demonstrated by explicitly
proving that every D-brane system in all minimal models of type ADE can be
generated from only one or two fundamental branes.Comment: 34 page
Obstructions and lines of marginal stability from the world-sheet
The behaviour of supersymmetric D-branes under deformations of the closed
string background is studied using world-sheet methods. We explain how lines of
marginal stability and obstructions arise from this point of view. We also show
why N=2 B-type branes may be obstructed against (cc) perturbations, but why
such obstructions do not occur for N=4 superconformal branes at c=6, i.e. for
half-supersymmetric D-branes on K3. Our analysis is based on a field theory
approach in superspace, as well as on techniques from perturbed conformal field
theory.Comment: 32 page
Basal body stability and ciliogenesis requires the conserved component Poc1
Centrioles are the foundation for centrosome and cilia formation. The biogenesis of centrioles is initiated by an assembly mechanism that first synthesizes the ninefold symmetrical cartwheel and subsequently leads to a stable cylindrical microtubule scaffold that is capable of withstanding microtubule-based forces generated by centrosomes and cilia. We report that the conserved WD40 repeat domain–containing cartwheel protein Poc1 is required for the structural maintenance of centrioles in Tetrahymena thermophila. Furthermore, human Poc1B is required for primary ciliogenesis, and in zebrafish, DrPoc1B knockdown causes ciliary defects and morphological phenotypes consistent with human ciliopathies. T. thermophila Poc1 exhibits a protein incorporation profile commonly associated with structural centriole components in which the majority of Poc1 is stably incorporated during new centriole assembly. A second dynamic population assembles throughout the cell cycle. Our experiments identify novel roles for Poc1 in centriole stability and ciliogenesis
Experimental properties of Bose-Einstein condensates in 1D optical lattices: Bloch oscillations, Landau-Zener tunneling and mean-field effects
We report experimental results on the properties of Bose-Einstein condensates
in 1D optical lattices. By accelerating the lattice, we observed Bloch
oscillations of the condensate in the lowest band, as well as Landau-Zener
(L-Z) tunneling into higher bands when the lattice depth was reduced and/or the
acceleration of the lattice was increased. The dependence of the L-Z tunneling
rate on the condensate density was then related to mean-field effects modifying
the effective potential acting on the condensate, yielding good agreement with
recent theoretical work. We also present several methods for measuring the
lattice depth and discuss the effects of the micromotion in the TOP-trap on our
experimental results.Comment: 11 pages, 14 figure
Matrix factorisations and D-branes on K3
D-branes on K3 are analysed from three different points of view. For
deformations of hypersurfaces in weighted projected space we use geometrical
methods as well as matrix factorisation techniques. Furthermore, we study the
D-branes on the T^4/\Z_4 orbifold line in conformal field theory. The behaviour
of the D-branes under deformations of the bulk theory are studied in detail,
and good agreement between the different descriptions is found.Comment: 35 pages, no figure
Astroparticle Physics with a Customized Low-Background Broad Energy Germanium Detector
The MAJORANA Collaboration is building the MAJORANA DEMONSTRATOR, a 60 kg
array of high purity germanium detectors housed in an ultra-low background
shield at the Sanford Underground Laboratory in Lead, SD. The MAJORANA
DEMONSTRATOR will search for neutrinoless double-beta decay of 76Ge while
demonstrating the feasibility of a tonne-scale experiment. It may also carry
out a dark matter search in the 1-10 GeV/c^2 mass range. We have found that
customized Broad Energy Germanium (BEGe) detectors produced by Canberra have
several desirable features for a neutrinoless double-beta decay experiment,
including low electronic noise, excellent pulse shape analysis capabilities,
and simple fabrication. We have deployed a customized BEGe, the MAJORANA
Low-Background BEGe at Kimballton (MALBEK), in a low-background cryostat and
shield at the Kimballton Underground Research Facility in Virginia. This paper
will focus on the detector characteristics and measurements that can be
performed with such a radiation detector in a low-background environment.Comment: Submitted to NIMA Proceedings, SORMA XII. 9 pages, 4 figure
Defects and Bulk Perturbations of Boundary Landau-Ginzburg Orbifolds
We propose defect lines as a useful tool to study bulk perturbations of
conformal field theories, in particular to analyse the induced renormalisation
group flows of boundary conditions. As a concrete example we investigate bulk
perturbations of N=2 supersymmetric minimal models. To these perturbations we
associate a special class of defects between the respective UV and IR theories,
whose fusion with boundary conditions indeed reproduces the behaviour of the
latter under the corresponding RG flows. v2: Some explanations added in section
4, minor changes.Comment: 37 pages, 6 figure
Global CO2 emissions from dry inland waters share common drivers across ecosystems
Many inland waters exhibit complete or partial desiccation, or have vanished due to global change, exposing sediments to the atmosphere. Yet, data on carbon dioxide (CO2) emissions from these sediments are too scarce to upscale emissions for global estimates or to understand their fundamental drivers. Here, we present the results of a global survey covering 196 dry inland waters across diverse ecosystem types and climate zones. We show that their CO2 emissions share fundamental drivers and constitute a substantial fraction of the carbon cycled by inland waters. CO2 emissions were consistent across ecosystem types and climate zones, with local characteristics explaining much of the variability. Accounting for such emissions increases global estimates of carbon emissions from inland waters by 6% (~0.12 Pg C y−1). Our results indicate that emissions from dry inland waters represent a significant and likely increasing component of the inland waters carbon cycle
Search for direct production of charginos and neutralinos in events with three leptons and missing transverse momentum in √s = 7 TeV pp collisions with the ATLAS detector
A search for the direct production of charginos and neutralinos in final states with three electrons or muons and missing transverse momentum is presented. The analysis is based on 4.7 fb−1 of proton–proton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with Standard Model expectations in three signal regions that are either depleted or enriched in Z-boson decays. Upper limits at 95% confidence level are set in R-parity conserving phenomenological minimal supersymmetric models and in simplified models, significantly extending previous results
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