Large magnetoresistance effect due to spin-injection into a non-magnetic semiconductor

A novel magnetoresistance effect, due to the injection of a spin-polarized electron current from a dilute magnetic into a non-magnetic semiconductor, is presented. The effect results from the suppression of a spin channel in the non-magnetic semiconductor and can theoretically yield a positive magnetoresistance of 100%, when the spin flip length in the non-magnetic semiconductor is sufficiently large. Experimentally, our devices exhibit up to 25% magnetoresistance.Comment: 3 figures, submitted for publicatio

Antiferromagnetic ordering of energy levels for spin ladder with four-spin cyclic exchange: Generalization of the Lieb-Mattis theorem

The Lieb-Mattis theorem is generalized to an antiferromagnetic spin-ladder model with four-spin cyclic exchange interaction. We prove that for J>2K, the antiferromagnetic ordering of energy levels takes place separately in two sectors, which remain symmetric and antisymmetric under the reflection with respect to the longitudinal axis of the ladder. We prove also that at the self-dual point J=2K, the Lieb-Mattis rule holds in the sectors with fixed number of rung singlets. In both cases, it agrees with the similar rule for Haldane chain with appropriate spin number.Comment: 4 pages, some references updated and added, typos corrected, to appear in Phys. Rev.

Design and fabrication of a low-specific-weight parabolic dish solar concentrator

A segmented design and fabrication and assembly techniques were developed for a 1.8 m (6 ft) diameter parabolic concentrator for space application. This design and these techniques were adaptable to a low cost, mass-produced concentrator. Minimal machining was required. Concentrator segments of formed magnesium were used. The concentrator weighed only 1.6 kg sq m (0.32 lbm/sq ft)

The Laser Astrometric Test of Relativity: Science, Technology, and Mission Design

The Laser Astrometric Test of Relativity (LATOR) experiment is designed to explore general theory of relativity in the close proximity to the Sun -- the most intense gravitational environment in the solar system. Using independent time-series of highly accurate measurements of the Shapiro time-delay (interplanetary laser ranging accurate to 3 mm at 2 AU) and interferometric astrometry (accurate to 0.01 picoradian), LATOR will measure gravitational deflection of light by the solar gravity with accuracy of 1 part in a billion -- a factor ~30,000 better than currently available. LATOR will perform series of highly-accurate tests in its search for cosmological remnants of scalar field in the solar system. We present science, technology and mission design for the LATOR mission.Comment: 12 pages, 4 figures. To appear in the proceedings of the International Workshop "From Quantum to Cosmos: Fundamental Physics Research in Space", 21-24 May 2006, Warrenton, Virginia, USA http://physics.jpl.nasa.gov/quantum-to-cosmos

Polynucleotide Phosphorylase from a Cyanobacterium (Synechococcus sp.): Subunit Composition and Properties

Polynucleotide phosphorylase from cells of the cyanobacterium Synechococcus sp. has been purified 1400-fold by an improved procedure. The enzyme purified to homogeneity and lacking nuclease, phosphatase and protease contaminations reveals a single band of ADP polymerizing activity upon polyacrylamide gel electrophoresis under nondenaturing conditions which corresponds to a molecular mass of about 275 000. The enzyme migrates as a single polypeptide of Mr≈70 000 when subjected to gel electrophoresis in the presence of dodecyl sulfate indicating a composition of α4 for the native enzyme molecule. The isoelectric point of the purified enzyme as determined by isoelectric focusing was found to be at 4.2±0.1. Polynucleotide phosphorylase of Synechococcus is preferentially activated by Mg2+; Kcl has a significant stimulatory effect. © 1982, Walter de Gruyter. All rights reserved

Double facades a more sustainable solution than a optimal single facade

Facade parameters influence the energy flows coming through the facade, in order to optimize the indoor environment for the comfort of the individual building occupant with minimal energy use. How can the facade make optimal use of the free incoming energy flows to maximize the comfort level of the individual building occupant at minimal energy use? The type of façade described as a second skin façade is characterised by a single glass layer on the outside and an isolated façade layer on the inside, which often includes an insulated glass layer. The application of the single glass layer as a second skin around the insulated layer results in an air cavity between these two layers. The property that distinguishes a second skin façade from other DSF is that it relies on natural ventilation of the cavity, in comparison to other facades which use mechanical systems to induce the airflow. The advantage of merely using natural ventilation in the façade cavity is the lower energy consumption. However, it also results in some unresolved issues which require further attention. This project is concerned with the behaviour of a highly complex shaped second skin facade on a Dutch office building, and the thermal comfort impact on the building user. During 3 weeks different measurements were done to determine the main characteristics of the glass and the facade. These measurements were related to earlier measurements done by other buildings with a second skin facade. A key difference between a second skin facade, as well as other climate facades, and more traditional opaque facades is its dynamic behaviour

Local Group dSph radio survey with ATCA (III): Constraints on Particle Dark Matter

We performed a deep search for radio synchrotron emissions induced by weakly interacting massive particles (WIMPs) annihilation or decay in six dwarf spheroidal (dSph) galaxies of the Local Group. Observations were conducted with the Australia Telescope Compact Array (ATCA) at 16 cm wavelength, with an rms sensitivity better than 0.05 mJy/beam in each field. In this work, we first discuss the uncertainties associated with the modeling of the expected signal, such as the shape of the dark matter (DM) profile and the dSph magnetic properties. We then investigate the possibility that point-sources detected in the proximity of the dSph optical center might be due to the emission from a DM cuspy profile. No evidence for an extended emission over a size of few arcmin (which is the DM halo size) has been detected. We present the associated bounds on the WIMP parameter space for different annihilation/decay final states and for different astrophysical assumptions. If the confinement of electrons and positrons in the dSph is such that the majority of their power is radiated within the dSph region, we obtain constraints on the WIMP annihilation rate which are well below the thermal value for masses up to few TeV. On the other hand, for conservative assumptions on the dSph magnetic properties, the bounds can be dramatically relaxed. We show however that, within the next 10 years and regardless of the astrophysical assumptions, it will be possible to progressively close in on the full parameter space of WIMPs by searching for radio signals in dSphs with SKA and its precursors.Comment: 17 pages, 6 figure panels. Companion papers: arXiv:1407.5479 and arXiv:1407.5482. v3: minor revision, matches published versio

Double facades a more sustainable solution than a optimal single facade

Facade parameters influence the energy flows coming through the facade, in order to optimize the indoor environment for the comfort of the individual building occupant with minimal energy use. How can the facade make optimal use of the free incoming energy flows to maximize the comfort level of the individual building occupant at minimal energy use? The type of façade described as a second skin façade is characterised by a single glass layer on the outside and an isolated façade layer on the inside, which often includes an insulated glass layer. The application of the single glass layer as a second skin around the insulated layer results in an air cavity between these two layers. The property that distinguishes a second skin façade from other DSF is that it relies on natural ventilation of the cavity, in comparison to other facades which use mechanical systems to induce the airflow. The advantage of merely using natural ventilation in the façade cavity is the lower energy consumption. However, it also results in some unresolved issues which require further attention. This project is concerned with the behaviour of a highly complex shaped second skin facade on a Dutch office building, and the thermal comfort impact on the building user. During 3 weeks different measurements were done to determine the main characteristics of the glass and the facade. These measurements were related to earlier measurements done by other buildings with a second skin facade. A key difference between a second skin facade, as well as other climate facades, and more traditional opaque facades is its dynamic behaviour