Automatic guiding of the primary image of solar Gregory telescopes

The primary image reflected from the field-stop of solar Gregory telescopes is used for automatic guiding. This new system avoids temporal varying influences from the bending of the telescope tube by the main mirror's gravity and from offsets between the telescope and a separate guiding refractor. The required stiffness of the guider mechanics and the small areas of the sensors demand small f-numbers for the guider optics, which cause problems with the image quality and with heat. Problems also arise from the imaging of the pinhole in the telescope's field stop. The corresponding lack of image information at that location can be reduced numerically by Fourier methods much more effectively than with profile centering methods. Several types of such guiders are tested, a final equipment, now installed at the Gregory telescopes at Tenerife and at Locarno, is described

Electromagnetic Calorimeter for HADES

We propose to build the Electromagnetic calorimeter for the HADES di-lepton spectrometer. It will enable to measure the data on neutral meson production from nucleus-nucleus collisions, which are essential for interpretation of dilepton data, but are unknown in the energy range of planned experiments (2-10 GeV per nucleon). The calorimeter will improve the electron-hadron separation, and will be used for detection of photons from strange resonances in elementary and HI reactions. Detailed description of the detector layout, the support structure, the electronic readout and its performance studied via Monte Carlo simulations and series of dedicated test experiments is presented. The device will cover the total area of about 8 m^2 at polar angles between 12 and 45 degrees with almost full azimuthal coverage. The photon and electron energy resolution achieved in test experiments amounts to 5-6%/sqrt(E[GeV]) which is sufficient for the eta meson reconstruction with S/B ratio of 0.4% in Ni+Ni collisions at 8 AGeV. A purity of the identified leptons after the hadron rejection, resulting from simulations based on the test measurements, is better than 80% at momenta above 500 MeV/c, where time-of-flight cannot be used.Comment: 40 pages, 38 figures version2 - the time schedule added, information about PMTs in Sec.III update

String Loop Corrections to Kahler Potentials in Orientifolds

We determine one-loop string corrections to Kahler potentials in type IIB orientifold compactifications with either N=1 or N=2 supersymmetry, including D-brane moduli, by evaluating string scattering amplitudes.Comment: 80 pages, 4 figure

Brane Induced Gravity, its Ghost and the Cosmological Constant Problem

"Brane Induced Gravity" is regarded as a promising framework for addressing the cosmological constant problem, but it also suffers from a ghost instability for parameter values that make it phenomenologically viable. We carry out a detailed analysis of codimension > 2 models employing gauge invariant variables in a flat background approximation. It is argued that using instead a curved background sourced by the brane would not resolve the ghost issue, unless a very specific condition is satisfied (if satisfiable at all). As for other properties of the model, from an explicit analysis of the 4-dimensional graviton propagator we extract a mass, a decay width and a momentum dependent modification of the gravitational coupling for the spin 2 mode. In the flat space approximation, the mass of the problematic spin 0 ghost is instrumental in filtering out a brane cosmological constant. The mass replaces a background curvature that would have had the same function. The optical theorem is used to demonstrate the suppression of graviton leakage into the uncompactified bulk. Then, we derive the 4-dimensional effective action for gravity and show that general covariance is spontaneously broken by the bulk-brane setup. This provides a natural realization of the gravitational Higgs mechanism. We also show that the addition of extrinsic curvature dependent terms has no bearing on linearized brane gravity.Comment: v2: LaTeX, JHEP style, 41 pages, 3 eps figures. Partly rewritten to improve presentation, results unchanged, published versio

Noncommutativity from the string perspective: modification of gravity at a mm without mm sized extra dimensions

We explore how the IR pathologies of noncommutative field theory are resolved when the theory is realized as open strings in background B-fields: essentially, since the IR singularities are induced by UV/IR mixing, string theory brings them under control in much the same way as it does the UV singularities. We show that at intermediate scales (where the Seiberg-Witten limit is a good approximation) the theory reproduces the noncommutative field theory with all the (un)usual features such as UV/IR mixing, but that outside this regime, in the deep infra-red, the theory flows continuously to the commutative theory and normal Wilsonian behaviour is restored. The resulting low energy physics resembles normal commutative physics, but with additional suppressed Lorentz violating operators. We also show that the phenomenon of UV/IR mixing occurs for the graviton as well, with the result that, in configurations where Planck's constant receives a significant one-loop correction (for example brane-induced gravity), the distance scale below which gravity becomes non-Newtonian can be much greater than any compact dimensions.Comment: 30 pages. Slight revision: clarified some points and added a referenc

Induced Gravity on Intersecting Branes

We establish Einstein-Hilbert gravity couplings in the effective action for Intersecting Brane Worlds. The four-dimensional induced Planck mass is determined by calculating graviton scattering amplitudes at one-loop in the string perturbation expansion. We derive a general formula linking the induced Planck mass for N=1 supersymmetric backgrounds directly to the string partition function. We carry out the computation explicitly for simple examples, obtaining analytic expressions.Comment: references added, minor changes to discussion of path integral normalization on page

Calcium phosphate crystals induce cell death in human vascular smooth muscle cells: a potential mechanism in atherosclerotic plaque destabilization

Vascular calcification is associated with an increased risk of myocardial infarction; however, the mechanisms linking these 2 processes are unknown. Studies in macrophages have suggested that calcium phosphate crystals induce the release of proinflammatory cytokines; however, no studies have been performed on the effects of calcium phosphate crystals on vascular smooth muscle cell function. In the present study, we found that calcium phosphate crystals induced cell death in human aortic vascular smooth muscle cells with their potency depending on their size and composition. Calcium phosphate crystals of approximately 1 microm or less in diameter caused rapid rises in intracellular calcium concentration, an effect that was inhibited by the lysosomal proton pump inhibitor, bafilomycin A1. Bafilomycin A1 also blocked vascular smooth muscle cell death suggesting that crystal dissolution in lysosomes leads to an increase in intracellular calcium levels and subsequent cell death. These studies give novel insights into the bioactivity of calcified deposits and suggest that small calcium phosphate crystals could destabilize atherosclerotic plaques by initiating inflammation and by causing vascular smooth muscle cell death