Thermal Characterization of a Hall Effect Thruster

The thermal characteristics of a Hall thruster directly influence thruster and spacecraft design. High temperatures affect the magnetic coil capabilities and cause higher insulator erosion rates, influencing both thruster performance and lifetime. The Hall thruster transfers heat through both radiation and conduction, and the spacecraft must handle this additional thermal energy. An infrared camera provides a non-intrusive method to analyze the thermal characteristics of an operational Hall thruster. This thesis contains the thermal analysis of a Busek Co. Inc. 200 W Hall thruster, using a FLIR ThermaCAM SC640 infrared camera. The Space Propulsion Analysis and System Simulator Laboratory at the Air Force Institute of Technology on Wright-Patterson Air Force Base provided the location for thruster set up and operation. The infrared camera furnishes the surface temperatures for the entire thruster, and approximates the transient heating behavior during start up, steady state, and shut down. Thermocouples verify and correct the camera data. Experimentally determined emissivities characterize the materials of the thruster. In addition, a view factor analysis between the camera pixels and the alumina sprayed portion of the cathode determines the exchange of radiation between the pixels and cathode surface. This process develops a technique to map surface temperatures of complex geometries with confidence in the actual values. Accurately mapping the surface temperatures of a Hall Effect thruster will improve both thruster efficiency and lifetime, and predict the thruster\u27s thermal load on a satellite

Elastic scaling of cloud application performance based on Western Electric rules by injection of aspect-oriented code

The main benefit of cloud computing lies in the elasticity of virtual resources that are provided to end users. Cloud users do not have to pay fixed hardware costs and are charged for consumption of computing resources only. While this might be an improvement for software developers who use the cloud, application users and consumers might rather be interested in paying for application performance than resource consumption. However there is little effort on providing elasticity based on performance goals instead of resource consumption. In this paper an autoscaling method is presented which aims at providing increased application performance as it is demanded by consumers. Elastic scaling is based on “statistical process monitoring and control” and “Western Electric rules”. By demonstrating the architecture of the autoscaling method and providing performance measurements gathered in an OpenStack cloud environment, we show how the injection of aspect-oriented code into cloud applications allows for improving application performance by automatically adapting the underlying virtual environment to pre-defined performance goals. The effectiveness of the autoscaling method is verified by an experiment with a test program which shows that the program executes in only half of the time which is required if no autoscaling capabilities are provided

Response to Aubin et al. (2017)

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/138910/1/add13937.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/138910/2/add13937_am.pd

Optimum Detection Location-Based Cooperative Spectrum Sensing in Cognitive Radio

Cognitive radio arises as a hot research issue in wireless communications recently, attributed to its capability of enhancing spectral efficiency and catering for the growing demand for bandwidth. As a good embodiment of cognitive radio’s unique feature, i.e. making use of every bit spectral resource, spectrum sensing plays a vital role in the implementation of cognitive radio. To alleviate negative effect on cooperative spectrum sensing brought by bit errors, we introduce a novel concept, i.e. Optimum Detection Location (ODL) and present two algorithms of different computational complexity for locating ODL, together with an ODL-Based cooperative spectrum sensing scheme, with the motivation to exploit the gain derived from geographic advantages and multiuser diversity. Numerical and simulation results both demonstrate that our proposed spectrum sensing scheme can significantly improve the sensing performance in the case of reporting channel with bit errors

Attitude Determination from Single-Antenna Carrier-Phase Measurements

A model of carrier phase measurement (as carried out by a satellite navigation receiver) is formulated based on electromagnetic theory. The model shows that the phase of the open-circuit voltage induced in the receiver antenna with respect to a local oscillator (in the receiver) depends on the relative orientation of the receiving and transmitting antennas. The model shows that using a {\it single} receiving antenna, and making carrier phase measurements to seven satellites, the 3-axis attitude of a user platform (in addition to its position and time) can be computed relative to an initial point. This measurement model can also be used to create high-fidelity satellite signal simulators that take into account the effect of platform rotation as well as translation.Comment: 12 pages, and one figure. Published in J. Appl. Phys. vol. 91, No. 7, April 1, 200

Crystalline Bi4Ge3O12 fibers fabricated by micro-pulling down technique for optical high voltage sensing

AbstractCommonly optical high voltage sensors employ the Pockels effect in a bulk electro-optic crystal such as Bi4Ge3O12 (BGO). Typically, the maximum crystal length is 100-200mm and determined by the limits of the conventional growth technique (Czochralski). In this paper we report on the growth by a micro-pulling down technique of long single crystalline BGO fibers as an alternative to bulk crystals and their characterization for voltage sensing. The fiber thickness may range from a few 100μm to a few mm. The parameters needed for stable growth over the entire length of the crystal were analyzed and optimized. Thin rods with a length of up to 850mm were grown. Samples were characterized with respect to homogeneity of growth, residual birefringence (BGO is free of natural birefringence), crystal orientation, and performance under voltage

Life at the extreme: Lessons from the genome

© 2012 BioMed Central Ltd. Extremophile plants thrive in places where most plant species cannot survive. Recent developments in high-throughput technologies and comparative genomics are shedding light on the evolutionary mechanisms leading to their adaptation

From genome to function: the Arabidopsis aquaporins

BACKGROUND: In the post-genomic era newly sequenced genomes can be used to deduce organismal functions from our knowledge of other systems. Here we apply this approach to analyzing the aquaporin gene family in Arabidopsis thaliana. The aquaporins are intrinsic membrane proteins that have been characterized as facilitators of water flux. Originally termed major intrinsic proteins (MIPs), they are now also known as water channels, glycerol facilitators and aqua-glyceroporins, yet recent data suggest that they facilitate the movement of other low-molecular-weight metabolites as well. RESULTS: The Arabidopsis genome contains 38 sequences with homology to aquaporin in four subfamilies, termed PIP, TIP, NIP and SIP. We have analyzed aquaporin family structure and expression using the A. thaliana genome sequence, and introduce a new NMR approach for the purpose of analyzing water movement in plant roots in vivo. CONCLUSIONS: Our preliminary data indicate a strongly transcellular component for the flux of water in roots