Low thrust orbit determination program

Logical flow and guidelines are provided for the construction of a low thrust orbit determination computer program. The program, tentatively called FRACAS (filter response analysis for continuously accelerating spacecraft), is capable of generating a reference low thrust trajectory, performing a linear covariance analysis of guidance and navigation processes, and analyzing trajectory nonlinearities in Monte Carlo fashion. The choice of trajectory, guidance and navigation models has been made after extensive literature surveys and investigation of previous software. A key part of program design relied upon experience gained in developing and using Martin Marietta Aerospace programs: TOPSEP (Targeting/Optimization for Solar Electric Propulsion), GODSEP (Guidance and Orbit Determination for SEP) and SIMSEP (Simulation of SEP)

Investigation of upwind, multigrid, multiblock numerical schemes for three dimensional flows. Volume 1: Runge-Kutta methods for a thin layer Navier-Stokes solver

A state-of-the-art computer code has been developed that incorporates a modified Runge-Kutta time integration scheme, upwind numerical techniques, multigrid acceleration, and multi-block capabilities (RUMM). A three-dimensional thin-layer formulation of the Navier-Stokes equations is employed. For turbulent flow cases, the Baldwin-Lomax algebraic turbulence model is used. Two different upwind techniques are available: van Leer's flux-vector splitting and Roe's flux-difference splitting. Full approximation multi-grid plus implicit residual and corrector smoothing were implemented to enhance the rate of convergence. Multi-block capabilities were developed to provide geometric flexibility. This feature allows the developed computer code to accommodate any grid topology or grid configuration with multiple topologies. The results shown in this dissertation were chosen to validate the computer code and display its geometric flexibility, which is provided by the multi-block structure

The Effect of Location Based Tax Incentives on Establishment Location and Employment Across Industry Sectors

This article examines the potential for location-based employment tax incentives to have a differential effect on establishment location and employment across industry sectors. The authors model the differential effect of the location-based federal Empowerment Zone (EZ) wage tax credit on equilibrium labor and total cost savings across industry sectors. The model guides the empirical work, as the authors test the effect of the program across industry sectors. The empirical analysis shows that location-based tax incentives have a positive effect on firm location in some of the industries their model predicts and a negative effect in industries that could be crowded out

Computational Fluid Dynamic Studies of Vortex Amplifier Design for the Nuclear Industry—I. Steady-State Conditions

In this study the effects of changes to the geometry of a vortex amplifier are investigated using computational fluid dynamics (CFD) techniques, in the context of glovebox operations for the nuclear industry. These investigations were required because of anomalous behavior identified when, for operational reasons, a long-established vortex amplifier design was reduced in scale. The aims were (i) to simulate both the anomalous back-flow into the glovebox through the vortex amplifier supply ports, and the precessing vortex core in the amplifier outlet, then (ii) to determine which of the various simulated geometries would best alleviate the supply port back-flow anomaly. Various changes to the geometry of the vortex amplifier were proposed; smoke and air tests were then used to identify a subset of these geometries for subsequent simulation using CFD techniques. Having verified the mesh resolution was sufficient to reproduce the required effects, the code was then validated by comparing the results of the steady-state simulations with the experimental data. The problem is challenging in terms of the range of geometrical and dynamic scales encountered, with consequent impact on mesh quality and turbulence modeling. The anomalous nonaxisymmetric reverse flow in the supply ports of the vortex amplifier has been captured and the mixing in both the chamber and the precessing vortex core has also been successfully reproduced. Finally, by simulating changes to the supply ports that could not be reproduced experimentally at an equivalent cost, the geometry most likely to alleviate the back-flow anomaly has been identified

Efficient Change Management of XML Documents

XML-based documents play a major role in modern information architectures and their corresponding work-flows. In this context, the ability to identify and represent differences between two versions of a document is essential. A second important aspect is the merging of document versions, which becomes crucial in parallel editing processes. Many different approaches exist that meet these challenges. Most rely on operational transformation or document annotation. In both approaches, the operations leading to changes are tracked, which requires corresponding editing applications. In the context of software development, however, a state-based approach is common. Here, document versions are compared and merged using external tools, called diff and patch. This allows users for freely editing documents without being tightened to special tools. Approaches exist that are able to compare XML documents. A corresponding merge capability is still not available. In this thesis, I present a comprehensive framework that allows for comparing and merging of XML documents using a state-based approach. Its design is based on an analysis of XML documents and their modification patterns. The heart of the framework is a context-oriented delta model. I present a diff algorithm that appears to be highly efficient in terms of speed and delta quality. The patch algorithm is able to merge document versions efficiently and reliably. The efficiency and the reliability of my approach are verified using a competitive test scenario

Design, development and verification of the 30 and 44 GHz front-end modules for the Planck Low Frequency Instrument

We give a description of the design, construction and testing of the 30 and 44 GHz Front End Modules (FEMs) for the Low Frequency Instrument (LFI) of the Planck mission to be launched in 2009. The scientific requirements of the mission determine the performance parameters to be met by the FEMs, including their linear polarization characteristics. The FEM design is that of a differential pseudo-correlation radiometer in which the signal from the sky is compared with a 4-K blackbody load. The Low Noise Amplifier (LNA) at the heart of the FEM is based on indium phosphide High Electron Mobility Transistors (HEMTs). The radiometer incorporates a novel phase-switch design which gives excellent amplitude and phase match across the band. The noise temperature requirements are met within the measurement errors at the two frequencies. For the most sensitive LNAs, the noise temperature at the band centre is 3 and 5 times the quantum limit at 30 and 44 GHz respectively. For some of the FEMs, the noise temperature is still falling as the ambient temperature is reduced to 20 K. Stability tests of the FEMs, including a measurement of the 1/f knee frequency, also meet mission requirements. The 30 and 44 GHz FEMs have met or bettered the mission requirements in all critical aspects. The most sensitive LNAs have reached new limits of noise temperature for HEMTs at their band centres. The FEMs have well-defined linear polarization characteristcs.Comment: 39 pages, 33 figures (33 EPS files), 12 tables. Planck LFI technical papers published by JINST: http://www.iop.org/EJ/journal/-page=extra.proc5/1748-022

Forecasting Inflation in Developing Nations: The Case of Pakistan

This study attempts to outline the practical steps which need to be undertaken to use autoregressive integrated moving average (ARIMA) time series models for forecasting Pakistan’s inflation. A framework for ARIMA forecasting is drawn up. On the basis of insample and out-of-sample forecast it can be concluded that the model has sufficient predictive powers and the findings are well in line with those of other studies. Further, in this study, the main focus is to forecast the monthly inflation on short-term basis, for this purpose, different ARIMA models are used and the candid model is proposed. On the basis of various diagnostic and selection & evaluation criteria the best and accurate model is selected for the short term forecasting of inflation.Forecasting inflation; ARIMA

The Robinson Gravitational Wave Background Telescope (BICEP): a bolometric large angular scale CMB polarimeter

The Robinson Telescope (BICEP) is a ground-based millimeter-wave bolometric array designed to study the polarization of the cosmic microwave background radiation (CMB) and galactic foreground emission. Such measurements probe the energy scale of the inflationary epoch, tighten constraints on cosmological parameters, and verify our current understanding of CMB physics. Robinson consists of a 250-mm aperture refractive telescope that provides an instantaneous field-of-view of 17 degrees with angular resolution of 55 and 37 arcminutes at 100 GHz and 150 GHz, respectively. Forty-nine pair of polarization-sensitive bolometers are cooled to 250 mK using a 4He/3He/3He sorption fridge system, and coupled to incoming radiation via corrugated feed horns. The all-refractive optics is cooled to 4 K to minimize polarization systematics and instrument loading. The fully steerable 3-axis mount is capable of continuous boresight rotation or azimuth scanning at speeds up to 5 deg/s. Robinson has begun its first season of observation at the South Pole. Given the measured performance of the instrument along with the excellent observing environment, Robinson will measure the E-mode polarization with high sensitivity, and probe for the B-modes to unprecedented depths. In this paper we discuss aspects of the instrument design and their scientific motivations, scanning and operational strategies, and the results of initial testing and observations.Comment: 18 pages, 11 figures. To appear in Millimeter and Submillimeter Detectors and Instrumentation for Astronomy III, Proceedings of SPIE, 6275, 200