Stathopoulos A.,College of William and Mary |
McCombs J.R.,Cobham Inc.
ACM Transactions on Mathematical Software | Year: 2010
This article describes the PRIMME software package for solving large, sparse Hermitian standard eigenvalue problems. The difficulty and importance of these problems have increased over the years, necessitating the use of preconditioning and near optimally converging iterative methods. However, the complexity of tuning or even using such methods has kept them outside the reach of many users. Responding to this problem, we have developed PRIMME, a comprehensive package that brings state-of-the-art methods from bleeding edge to production, with the best possible robustness, efficiency, and a flexible, yet highly usable interface that requires minimal or no tuning. We describe (1) the PRIMME multimethod framework that implements a variety of algorithms, including the near optimal methods GD+k and JDQMR; (2) a host of algorithmic innovations and implementation techniques that endow the software with its robustness and efficiency; (3) a multilayer interface that captures our experience and addresses the needs of both expert and end users. © 2010 ACM.
Youmans D.G.,Cobham Inc. |
Williams G.,Voxtel Inc. |
Huntington A.,Voxtel Inc.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2011
The optoelectronic gain of a linear mode Avalanche photo-diode (APD) results from the cascade of electron and hole impact ionizations that take place in the high-field intrinsic multiplication layer of the APD. Due to the uncertainty associated with the stochastic nature of the APD's gain, the shot noise present in the resulting photo-generated electrical signal is accentuated and degrades the detection of single photon initiated Avalanche signals. Recent advances in linearmode InGaAs APD detectors have been demonstrated that have reduced excess noise, along with the high gain necessary for detecting single photons. In these devices the Avalanche buildup is characterized with a temporally varying noise. At low incident photon / photo-electron levels, the stochastic nature of the impulse response function of these APDs offers the potential of increased probability that the output exceeds a threshold level resulting in a "detection" and, hence, a better receiver-operating- characteristic (ROC). In this paper we examine the ROC (Pdetection vs PFalseAlarm) statistics of these single photon APDs as a function of the quasi-deterministic mean gain and standard deviation for an rms ROIC (readout integrated circuit) noise level of 25e-. Single photo-electron and multiple photo-electron detection statistics are also examined for predicting a ROC. Measured linear-mode APD data are also presented. © 2011 SPIE.
Dick B.N.,Boeing Company |
Griffin T.E.,Cobham Inc.
42nd International Conference on Environmental Systems 2012, ICES 2012 | Year: 2012
This paper will discuss the design and development of the system which will be used to resupply the International Space Station (ISS) with Oxygen and Nitrogen for its current and future needs. The on-going operation of the ISS requires a continuous supply of oxygen and nitrogen. This supply is used for metabolic, medical, system, and payload purposes. Due to Shuttle retirement, and based on a trade study to evaluate the best method to resupply ISS with O2/N2, NASA is developing a new system called the Nitrogen Oxygen Recharge System or NORS. The system architecture and preliminary design of NORS has been presented in two prior papers, Nitrogen Oxygen Recharge System for the ISS and Current Status of the NORS. The paper addresses significant changes to the design of the system, the current status of the development and manufacture of the system, and an operational outline for the system. The NORS provides pressurized gas to the ISS through the use of portable high pressure tanks, designed to be transportable to the available launch vehicles while fully pressurized. The system also includes a set of valve assemblies and other interfacing hardware that facilitate the delivery of the gas on the ISS to the various users on the ISS. The NORS project is nearing the Critical Design Review (CDR) phase. Majorities of the components of the system have passed through the development test phase and are beginning qualification testing. The manufacture of selected long lead item has begun. Operational procedures for the system are being developed. This paper will discuss the significant results of the development phase and initial results of qualification testing. Additionally, the paper will discuss the challenges of manufacturing and assembling precision components for use in the high pressure Oxygen application of the NORS. Finally, the preliminary operational concepts for NORS will be outlined. © 2012 by Boeing. All rights reserved.
Youmans D.G.,Cobham Inc.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2010
Several multiple-hypothesis range-rate algorithms are investigated to determine initial target acquisition capabilities of a direct detection ladar operating under low photo-electron return conditions. During initial acquisition of an object, the location of the object is not known, therefore the ladar returns cannot be simply summed in order to improve detection statistics. Analogous to classical radar multiple hypothesis algorithm approaches a "shift and sum," a "shift and accumulate," and a "numerically shift and histogram" algorithm are investigated. The probability density function for the maximum of the multiple-hypothesis range-rate algorithm matrix output is developed so that a threshold crossing probability can be determined and a "detection" declared (receiver-operating-characteristic). This is expressed as a function of false alarm rate which is a function of the number of ladar returns processed in the acquisition process and the length of the acquisition window. © 2010 SPIE.
Cobham Inc. | Date: 2015-03-04
A rotationally-stabilizing tracking antenna system includes a three-axis pedestal, a drive assembly rotating a vertical support assembly relative to a base assembly, a cross-level driver pivoting a cross-level frame assembly relative to the vertical support assembly, and an elevation driver pivoting an elevation frame assembly relative to the cross-level frame assembly, a motion platform assembly affixed to the elevation frame assembly, three orthogonally mounted angular rate sensors disposed on the motion platform assembly sensing motion about X, Y and Z axes, a three-axis gravity accelerometer mounted on the motion platform assembly to determine a true-gravity zero reference, and a control unit determining the actual position of elevation frame assembly based upon sensed motion about X, Y, and Z axes and the true-gravity zero reference, and controlling the azimuth, cross-level and elevation drivers to position the elevation frame assembly in a desired position.