The study of satellite relative motion has been of great historic interest, primarily due to its application to rendezvous, intercept, and docking maneuvers, between spacecraft in orbit about gravitational bodies, such as the Earth. Recent interest in the problem of satellite formation flight has also led to renewed effort in understanding the dynamics of relative motion. Satellite formations have been proposed for various tasks, such as deep-space interferometry, and terrestrial observation, among others. Oftentimes, the rich natural dynamics of the relative motion problem near a gravitational body are exploited to design formations of a specific geometry. Traditional analysis models relative motion under the assumptions of a circular reference orbit, linearized differential gravity field (small relative distance), and without environmental perturbations such as oblateness effects of the attracting body, and atmospheric drag. In this dissertation, the dynamics of the relative motion problem are studied when these assumptions are relaxed collectively. Consequently, the combined effects of nonlinearity, eccentricity, and Earth oblateness effects on relative motion, are studied. To this end, coupling effects between the various environmental perturbations are also accounted for. Five key problems are addressed - the development of a state transition matrix that accounts for eccentricity, nonlinearity, and oblateness effects; oblateness effects on averaged relative motion; eccentricity effects on formation design and planning; new analytical expressions for periodic relative motion that account for nonlinearity and eccentricity effects; and a solution to the optimal rendezvous problem near an eccentric orbit. The most notable feature of this dissertation, is that the solutions to the stated problems are completely analytical, and closed-form in nature. Use has been made of a generalized reversion of vector series, and several integral forms of Kepler’s equations, without any assumptions on the magnitude of the eccentricity of the reference orbit.

The study is concerned with the problem of how to improve the teaching of Arabic as a foreign or a second language. It lays down some of the essential foundation-work necessary for bringing about systematic and constructive improvements in the teaching of Arabic as a foreign language (TAFL) by investigating the contributions of modern linguistic sciences (such as applied linguistics, educational linguistics, psycholinguistics and sociolinguistics) to the development of foreign language (FL) teaching and learning. A survey of the literature indicates that a 'revolution' is currently taking place in FL teaching and that a new approach, known as the Communicative Approach (CA), has begun to emerge and influence the teaching of FLs in general, over the last decade or so. Since the CA is currently being adopted to the teaching of most major FLs and since this revolution has not yet had much impact on TAPL, the study explores the possibility of the application of the CA to the teaching of Arabic as a living language. The thesis is divided into 7 chapters. Chapter 1 introduces the importance of viewing the nature of language and FL teaching from a multidimensional point of view. Chapter 2 outlines the general nature and importance of the subject matter (i.e. the Arabic language) in a wide context. In order to understand what has directly or indirectly influenced the teaching practices of TAFL, Chapter 3 provides an overview of the development of views of FL teaching approaches and methods in recent times, from formalism (teacher-centred learning) to functionalism (student -centred learning). Chapter 4 concentrates on providing an interpretation of the current 'state of the art' of TPPL in Britain. A theoretical outline of the CA is presented in Chapter 5. This chapter provides a working hypothesis of a proposed integrative model for communicative competence that can be used as a practical reference tool in the relevant areas of communicative language development In TAPL. Chapter 6 focuses on one of these areas; communicative syllabus design, in which the stages in Arabic language programme development and types of communicative syllabuses are discussed. The last chapter concludes with a suggetion of specific further research needs in TAFL: communicative teaching methodology, communicative materials development, communicative testing techniques and communicative tea cher training.

This article investigates the determinants of entry and exit in the Austrian manufacturing sector based on 1981 to 1994 data. We study the response of entry, exit and other indicators of firm dynamics to changes in average plant size, size heterogeneity, concentration, incentives and vertical integration. By applying Bayesian simulation methods we estimate random coefficient models and study the symmetry of the determinants of entry and exit. Our empirical analysis shows that entry and exit rates are driven by the same determinants. The impacts of these determinants are nearly homogeneous for both, entry rates and exits rates, respectively. Moreover, we find (i) that changes in average plant size, size heterogeneity and concentration are not symmetric with respect to entry and exit, (ii) that changes in the growth of sales is weakly symmetric and (iii) that the growth rate of employment is strongly asymmetric across industries in Austrian manufacturing. Furthermore, we infer from the data that the turnover of firms influences the changes in the number of competitors. Low entry rates go hand in hand with low net entry rates and a low turnover. (author's abstract) / Series: Working Papers Series "Growth and Employment in Europe: Sustainability and Competitiveness"

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal.

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal

In recent years there have been a major developments in the computational mechanics community when it comes to modelling of fracture mechanics. There are now several well established numerical methods that are implemented in commercial programs such as: Phase Field Modelling, Enhanced Assumed Strain (EAS), Smeared Crack Methods, Extended Finite Element Method (XFEM) and Partition of Unity Finite Element Method (PUFEM). This work has been based on PUFEM and it has been of interest to investigate if this numerical method can be combined with plastic deformation. The reason for this is that it has been known that complex structural and material phenomenon such as embrittlement of steels or composites show a variation of fracture toughness. Thus more advanced approaches are required to capture the response of such structures and materials. The analysis was split in to three parts. First, a benchmark analysis was done with linear tetrahedral elements and, which has been implemented in previous applications. Thereafter the same analysis was done for quadratic tetrahedral elements. Finally, the interface between plasticity and PUFEM was implemented and was analysed with the same geometries as in the benchmark case. The analysis show that it is possible to combine plasticity in PUFEM setting and that it has a possibility to be used in future applications. / Under dem senaste åren har det skett en massiv utveckling inom beräkningsmekaniken när det kommer till att modellera brottmekaniska fenomen. Det finns nu ett flertal väletablerade numeriska metoder som är implementerade i kommersiella program såsom: Phase Field Modelling, Enhanced Assumed Strain (EAS), Smeared Crack Methods, Extended Finite Element Method (XFEM) and Partition of Unity Finite Element Method (PUFEM). Detta arbete har fokuserat på (PUFEM) och det har varit av intresse att se om denna metod kan kombineras tillsammans med plastisk deformation. Anledningen till att detta har varit av intresse är på grund av att det finns ett flertal komplexa struktur - och materialfenomen såsom försprödning av stål och kompositer som uppvisar en variation i sin duktilitet. Detta medför att mer avancerade metoder behöver tillämpas för att fånga responsen av dessa strukturer och material. Analysen som har genomförts var uppdelad i tre delar. Först analyserades ett problem med linjär tetrahedriska element som ett riktmärke, detta har implementerats i tidigare applikationer. Därefter analyserades samma problem fast med tethraderiska element med kvadratisk interpolation. Slutligen så integrerades plasticitet med PUFEM, där samma geometrier analyserades som riktmärke. Den analysen som har genomfört visar att det går att kombinera plastiska deformation tillsammans med PUFEM och att denna metod har potentialen att användas i framtida applikationer.

Achieving low unemployment in an environment of weak growth is a major policy challenge; a more egalitarian distribution of hours worked could be the key to solving it. Whether worksharing actually increases employment, however, has been debated controversially. In this article we present stylized facts on the distribution of hours worked and discuss the role of work-sharing for a sustainable economy. Building on recent developments in labor market theory we review the determinants of working long hours and its effect on well-being. Finally, we survey work-sharing reforms in the past. While there seems to be a consensus that worksharing in the Great Depression in the U.S. and in the Great Recession in Europe was successful in reducing employment losses, perceptions of the work-sharing reforms implemented between the 1980s and early 2000s are more ambivalent. However, even the most critical evaluations of these reforms provide no credible evidence of negative employment effects; instead, the overall success of the policy seems to depend on the economic and institutional setting, as well as the specific details of its implementation. (authors' abstract) / Series: Ecological Economic Papers

A mission architecture consisting of two NASA LONESTAR-2 satellites in Low Earth Orbit is considered. The craft are equipped with cross-communication radios and GPS units. Analyses are conducted for ejection, thruster and attitude maneuvers to achieve objectives of the mission, including sustained communications between the craft. Simulations are conducted to determine the duration of the communication window following the initial separation of the two craft. Recommendations are made to maximize this window while accounting for attitude constraints and the effects of atmospheric drag. Orbital mechanics and control theory are employed to form an algorithm for filtering GPS position fixes. The orbit-determination algorithm accounts for the effects of drag and Earth’s oblateness. Procedures are formed for verifying the initial separation velocities of two spacecraft and for measuring the velocity imparted by impulsive thruster maneuvers. An algorithm is also created to plan the timing and magnitude of corrective thruster maneuvers to align the orbital planes of the two craft. When the craft pass out of communication range, a ground station is used to relay data and commands to conduct state rendezvous procedures. A plan for coordinated attitude maneuvers is developed to strategically utilize the cumulative effects of drag and orbit decay to align the craft over long time periods. The methodologies developed here extend prior research into close proximity operations, forming the foundation for autonomous on-orbit rendezvous under a broader set of initial conditions. / text

El presente trabajo analiza la estructura de los costos de ajuste del capital para el caso de la industria manufacturera argentina. Haciendo uso de un modelo estructural de demanda por inversión intertemporal de la firma, se estiman los costos de ajuste del capital para un panel de plantas manufactureras argentinas. Los parámetros estimados son utilizados luego en experimentos contrafácticos con el objetivo de evaluar los efectos de shocks sobre la demanda de factores. Los resultados obtenidos sugieren la existencia de convexidades, no-convexidades e irreversibilidades en la forma funcional de los costos de ajuste. En particular, se estiman altos costos fijos y de transacción. Asimismo, los ejercicios de simulación contrafácticos resaltan la importancia de considerar la movilidad del capital y sus fricciones a fines de evaluar los efectos de shocks sobre los mercados de factores. Tanto la velocidad como la magnitud del ajuste de los mercados dependen directamente de la movilidad del capital y de los costos de ajuste de este.

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