17574926
Elasticity and conformal tension via the Kaluza-Klein mechanism
The principle of symmetric criticality allows one to reduce the search of symmetric critical points for the conformal total tension functional in a Kaluza‐Klein conformal universe, to the search of closed curves in its gravitatory component which are critical points for certain r-elastic energy functionals. The constancy of the mean curvature is preserved in this reduction of symmetry. In this framework we study ther-elasticity of fibres in a semi-Riemannian warped tube. We obtain a wide class of tubes which are foliated by r-elastic circles and give some applications including a characterization of the photon sphere in a Schwarzschild spacetime from the point of view of the r-elasticity. © 2000 Elsevier Science B.V. All rights reserved.
121953438
Bosonic string theory in Lorentzian principal circle bundles over anti-de-Sitter space AdS3
Abstract In this note we show a bosonic conformal string theory on U (1)-bundles over AdS 3 . To this end, we first look for r -elastic helices in the space AdS 3 , because they generate solutions of the motion equation on backgrounds P which are principal circle-bundles over AdS 3 endowed with the standard metric or generalized Kaluza–Klein metrics. In fact, we reduce the search of U (1)-symmetric string configurations on P to the search of r -elastic curves in the orbit space AdS 3 .
55465692
Isotropy and Marginally Trapped Surfaces in a Spacetime
In this paper we shall study the notions of an isotropic and marginally trapped surface in a spacetime by using a differential geometric approach. We first consider spacelike isotropic surfaces in a Lorentzian manifold and, in particular, in a four-dimensional spacetime, where the isotropy function appears to be determined by the mean curvature vector field of the surface. Explicit examples of isotropic marginally outer trapped surfaces are given in the standard four-dimensional space forms: Minkowski, de Sitter and anti-de Sitter spaces. Then we prove rigidity theorems for complete spacelike 0-isotropic surfaces without flat points in these standard space forms. As a consequence, we also obtain characterizations of complete spacelike isotropic marginally trapped surfaces in these backgrounds.
120425236
Effect of neutron and gamma-ray irradiation on the transmittance power of glasses and glues
Abstract LHC, working at the expected nominal luminosity, will induce an extremely high irradiation in the CMS experiment. The CMS alignment system uses optical elements to build the laser beams paths. Optical properties of basic components such as glasses and glues may result affected and their transmission power may degrade significantly. We have proceeded to a first test of various glasses and glues and identified some of them that can stand up to 150 kGy of gamma-rays plus 5×10 14 neutrons / cm 2 .
117452043
A direct imaging search for wide (sub)stellar companions around rad-vel planet host stars
We present an overview of our ongoing systematic search for wide (sub)stellar companions around the stars known to host rad-vel planets. By using a relatively large field of view and going very deep our survey can find all directly detectable stellar and brown dwarf companions (m>40 Mjup) within a 1000 AU orbit.
118040393
A Search for Wide (Sub)Stellar Companions Around Extrasolar Planet Host Stars
We present an overview of our ongoing systematic search for wide (sub)stellar companions around the stars known to host rad‐vel planets. By using a relatively large field of view and going very deep, our survey can find all directly detectable stellar and massive brown dwarf companions (m>40 MJup) within a 1000 AU orbit.
17464041
The T Tauri star RX J1608.6-3922 -not an eclipsing binary but a spotted single star
High-resolution spectroscopy and photometric monitoring of the pre-main sequence star RX J1608.6-3922 shows that it is not an eclipsing binary, as previously claimed. Radial velocity measurements covering suitable time spans in order to detect a spectroscopic binary with the claimed period of about 7 days have been performed. The scatter of the radial velocity does not exceed 2.4 km s -1 , defining an upper mass limit of 24 $M_{{\tiny Jupiter}}$ for any eclipsing companion orbiting this star with the claimed period. Photometric observations of RX J1608.6-3922 in 7 consecutive nights (i.e. as long as the claimed orbital period) reveal brightness variations of the order of 0.2 mag with a period of 3.6 days. The shape of the detected light curve differs from a light curve of the star recorded in 1996. The small variations of the radial velocity, the variable shape of the light curve, as well as ($B-V$) color variations suggest that the flux of RX J1608.6-3922 is modulated by spots on the stellar surface with a rotational period of 3.6 days. The stellar activity of this star seems to be highly variable, taking into account the variable shape of the light curve, with an amplitude varying from 0.5 to 0.2 mag in a few years, as well as hints for a variable H α equivalent width.
120520890
Silicon microstrip detectors for future tracker alignment systems
Abstract The next experiments at particles colliders will demand stability of the tracking systems to the level of few microns. The available technology cannot provide a supporting structure able to guarantee this degree of stability in working condition, when environmental changes will misalign the detectors out of their nominal position. Based on the successful experience of AMS and CMS tracker systems, we propose to use infrared laser beams traversing consecutive layers of silicon detectors to align them with respect to the beams. For such a laser track to reach the last sensor, high transmittance of microstrip sensors to infrared (IR) light is needed. We simulated the passage of a coherent beam of light through a microstrips detector and we identified the minimum set of changes to the design and technology that boost its transmittance while still respecting its tracking capabilities. The first prototypes are in process at IMB-CNM clean room facilities. We held the fabrication process at an intermediate step and we performed the first measurements of transmittance and reflectance on the sensors.