2,082 research outputs found
Shuttle antenna radome technology test program. Volume 2: Development of S-band antenna interface design
The effects of the Thermal Protection Subsystem (TPS) contamination on the space shuttle orbiter S band quad antenna due to multiple mission buildup are discussed. A test fixture was designed, fabricated and exposed to ten cycles of simulated ground and flight environments. Radiation pattern and impedance tests were performed to measure the effects of the contaminates. The degradation in antenna performance was attributed to the silicone waterproofing in the TPS tiles rather than exposure to the contaminating sources used in the test program. Validation of the accuracy of an analytical thermal model is discussed. Thermal vacuum tests with a test fixture and a representative S band quad antenna were conducted to evaluate the predictions of the analytical thermal model for two orbital heating conditions and entry from each orbit. The results show that the accuracy of predicting the test fixture thermal responses is largely dependent on the ability to define the boundary and ambient conditions. When the test conditions were accurately included in the analytical model, the predictions were in excellent agreement with measurements
MapReduce Operations with WS-VLAM Workflow Management System
AbstractWorkflow management systems are widely used to solve scientific problems as they enable orchestration of remote and lo- cal services such as database queries, job submission and running an application. To extend the role that workflow systems play in data-intensive science, we propose a solution that integrates WMS and MapReduce model. In this paper, we discuss possible solution of combining MapReduce and workflow applications, we describe the implementation of chosen solution based on metaprogramming approach in Ruby programming language and evaluate it with an example of word count application
Perspective on the physics of two-dimensional perovskites in high magnetic field
Two-dimensional (2D) metal halide perovskites consist of atomically thin layers composed of low bandgap metal-halide slabs, surrounded by high bandgap organic ligands, which behave as barriers. In this Perspective, we highlight how the use of large magnetic fields has been an extremely insightful tool to unravel some of the fundamental electronic properties of 2D perovskites. We focus on the combination of magnetoabsorption measurements and theoretical modeling to extract the carrier effective mass, on the use of magnetic field to clarify the fine structure of the exciton manifold, and on how magnetic fields can be helpful to correctly assign side peaks in the complex absorption or photoluminescence spectra displayed by 2D perovskites. We finally point out some challenges which might be successfully addressed by magneto-optical experimental techniques
A Time-Orbiting Potential Trap for Bose-Einstein Condensate Interferometry
We describe a novel atom trap for Bose-Einstein condensates of 87Rb to be
used in atom interferometry experiments. The trap is based on a time-orbiting
potential waveguide. It supports the atoms against gravity while providing weak
confinement to minimize interaction effects. We observe harmonic oscillation
frequencies omega_x, omega_y, omega_z as low as 2 pi times (6.0,1.2,3.3) Hz. Up
to 2 times 10^4 condensate atoms have been loaded into the trap, at estimated
temperatures as low as 850 pK. We anticipate that interferometer measurement
times of 1 s or more should be achievable in this device.Comment: 9 pages, 3 figure
Non equilibrium anisotropic excitons in atomically thin ReS
We present a systematic investigation of the electronic properties of bulk
and few layer ReS van der Waals crystals using low temperature optical
spectroscopy. Weak photoluminescence emission is observed from two
non-degenerate band edge excitonic transitions separated by 20 meV. The
comparable emission intensity of both excitonic transitions is incompatible
with a fully thermalized (Boltzmann) distribution of excitons, indicating the
hot nature of the emission. While DFT calculations predict bilayer ReS to
have a direct fundamental band gap, our optical data suggests that the
fundamental gap is indirect in all cases
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