Preliminary Orbit Determination System (PODS) for Tracking and Data Relay Satellite System (TDRSS)-tracked target Spacecraft using the homotopy continuation method

The Preliminary Orbit Determination System (PODS) provides early orbit determination capability in the Trajectory Computation and Orbital Products System (TCOPS) for a Tracking and Data Relay Satellite System (TDRSS)-tracked spacecraft. PODS computes a set of orbit states from an a priori estimate and six tracking measurements, consisting of any combination of TDRSS range and Doppler tracking measurements. PODS uses the homotopy continuation method to solve a set of nonlinear equations, and it is particularly effective for the case when the a priori estimate is not well known. Since range and Doppler measurements produce multiple states in PODS, a screening technique selects the desired state. PODS is executed in the TCOPS environment and can directly access all operational data sets. At the completion of the preliminary orbit determination, the PODS-generated state, along with additional tracking measurements, can be directly input to the differential correction (DC) process to generate an improved state. To validate the computational and operational capabilities of PODS, tests were performed using simulated TDRSS tracking measurements for the Cosmic Background Explorer (COBE) satellite and using real TDRSS measurements for the Earth Radiation Budget Satellite (ERBS) and the Solar Mesosphere Explorer (SME) spacecraft. The effects of various measurement combinations, varying arc lengths, and levels of degradation of the a priori state vector on the PODS solutions were considered

High speed motion in water with supercavitation for sub-, trans-, supersonic Mach Numbers

The results of research for supercavitating motion in water at very high speeds comparable with sonic speed ~1500m/s are presented. At such speeds the water is a compressible fluid and the basic compressible hydrodynamics of supercavitating flows together with practical approaches and experimental data are considered. The theory of ballistic projectiles motion is developed with emphasis on the problems of maximal range, lateral motion prediction and problems of minimal declination, hydro-elastic effects, and resonant oscillation frequencies. One main purpose of the article is an attempt to advance the level of understanding of the problem of very high-speed underwater launch by a comprehensive review of previous research on this topic.http://deepblue.lib.umich.edu/bitstream/2027.42/84267/1/CAV2009-final72.pd

Second and foreign language teachers’ problem-solving schemata development through informal problem-solving:the relationship between experience and expertise

Purpose: Second and foreign language (SL/FL) teachers’ informal problem-solving has received little explicit research attention while it is widely acknowledged that problem-solving is crucial to expertise development in any complex knowledge domain. To develop a clearer understanding of the role of informal problem-solving in SL/FL teachers’ expertise development, this study investigated how experience (i.e. time on the job) affects the level of problem-solving schemata development. Design/methodology/approach: This situational analysis of teaching practices was conducted with 15 SL/FL teachers divided into three experience groups. Through qualitative coding of verbal reflections on teachers’ own lessons, the structural components of problem-solving schemata development were explored at two levels. The first or basic level represents the broader knowledge base which problem-solving utilizes in understanding and recognizing classroom situations. The second is the expert-level problem-solving knowledge level. Qualitative codes were quantified to enable descriptive statistics and t-tests for the analysis regarding the basic level. A descriptive analysis was performed to uncover expert-level knowledge. Findings and Originality/value: The results show that experience affects problem-solving schemata development in qualitatively different ways at different levels. At the first or basic level, most teachers develop extensive and numerous domain-specific problem-solving schemata with experience. Few experienced teachers develop expert-level schemata. At this level, experience mostly affects the type of domain-specific knowledge and quality of feedback on effective strategies incorporated in these schemata. The findings suggest that future studies need to adopt a multi-level analysis of problem-solving schemata development.</p

Resummation of double logarithms in electroweak high energy processes

At future linear $e^+e^-$ collider experiments in the TeV range, Sudakov double logarithms originating from massive boson exchange can lead to significant corrections to the cross sections of the observable processes. These effects are important for the high precision objectives of the Next Linear Collider. We use the infrared evolution equation, based on a gauge invariant dispersive method, to obtain double logarithmic asymptotics of scattering amplitudes and discuss how it can be applied, in the case of broken gauge symmetry, to the Standard Model of electroweak processes. We discuss the double logarithmic effects to both non-radiative processes and to processes accompanied by soft gauge boson emission. In all cases the Sudakov double logarithms are found to exponentiate. We also discuss double logarithmic effects of a non-Sudakov type which appear in Regge-like processes.Comment: 26 pages, 3 figures, Latex2

What is Double Parton Scattering?

Processes such as double Drell-Yan and same-sign WW production have contributions from double parton scattering, which are not well-defined because of a delta(z_\perp=0) singularity that is generated by QCD evolution. We study the single and double parton contributions to these processes, and show how to handle the singularity using factorization and operator renormalization. We compute the QCD evolution of double parton distribution functions (PDFs) due to mixing with single PDFs. The modified evolution of dPDFs at z_\perp=0, including generalized dPDFs for the non-forward case, is given in the appendix. We include a brief discussion of the experimental interpretation of dPDFs and how they can probe flavor, spin and color correlations of partons in hadrons.Comment: 7 pages, 12 figures; v2: appendix fixed and extended, journal versio

The BFKL Pomeron in 2+1 Dimensional QCD

We investigate the high-energy scattering in the spontaneously broken Yang - Mills gauge theory in 2+1 space--time dimensions and present the exact solution of the leading $\ln s$ BFKL equation. The solution is constructed in terms of special functions using the earlier results of two of us (L.N.L. and L.S.). The analytic properties of the $t$-channel partial wave as functions of the angular momentum and momentum transfer have been studied. We find in the angular momentum plane: (i) a Regge pole whose trajectory has an intercept larger than 1 and (ii) a fixed cut with the rightmost singularity located at $j=1$. The massive Yang - Mills theory can be considered as a theoretical model for the (non-perturbative) Pomeron. We study the main structure and property of the solution including the Pomeron trajectory at momentum transfer different from zero. The relation to the results of M. Li and C-I. Tan for the massless case is discussed.Comment: 28 pages LATEX, 3 EPS figures include

Symmetry Properties of the Effective Action for High-Energy Scattering in QCD

We study the effective action describing high-energy scattering processes in the multi-Regge limit of QCD, which should provide the starting point for a new attempt to overcome the limitations of the leading logarithmic and the eikonal approximations. The action can be obtained via simple graphical rules or by integrating in the QCD functional integral over momentum modes of gluon and quark fields that do not appear explicitely as scattering or exchanged particles in the considered processes. The supersymmetry is used to obtain the terms in the action involving quarks fields from the pure gluonic ones. We observe a Weizs\"acker - Williams type relations between terms describing scattering and production of particles.Comment: 37 pages LATEX, 1 Table and 7 figures using package FEYNMA