The recent addition of autonomous formation flying spacecraft to the world's satellite fleet provides new motivation to study feedback control techniques. In this thesis, we develop nonlinear orbit control laws for use in spacecraft orbital maneuvers, and spacecraft formation flying. We apply these new control laws to a number of sample maneuvers, including formation stablishment and formation keeping maneuvers for NASA-Goddard's Leonardo-BRDF formation, and coupled orbit, and attitude maneuvers for HokieSat, a spacecraft designed, and built by students at Virginia Tech to fly in the Ionospheric Observation Nanosatellite Formation (ION-F). To provide target orbit states for feedback control, we develop and apply an algorithm to calculate a formation master orbit representing the geometric center of the formation. We also define a new technique for choosing orbital element feedback gains which appropriately scales the gains for orbit maintenance, and provides an excellent starting point for gain optimization. The orbital element feedback control law, augmented by mean motion control, and applied with appropriate gains, forces asymptotic convergence to a spacecraft target orbit, for a large variety of spacecraft maneuvers. / Master of Science

International Telemetering Conference Proceedings / October 21, 2002 / Town & Country Hotel and Conference Center, San Diego, California / Simplification of the analog front end of a signal conditioning circuit can be accomplished by over-quantizing the input signal and using DSP for gain and offset. In this case, a much higher precision A/D converter is used than required by the desired output accuracy. The excess bits are then used to allow the DSP math to give an effective gain to the signal. By a similar function, offset of over 100% can be mathematically removed as long as the input signal does not exceed the A/D input voltage range.

International Telemetering Conference Proceedings / October 26-29, 1998 / Town & Country Resort Hotel and Convention Center, San Diego, California / A simplex or ‘passive’ continuous wave and monopulse seeker tracks specific attributes of a target’s radio frequency (RF) radar return in some coordinate frame. In particular, a return carries dynamic information in amplitude (ω) and frequency (ω) at some point in azimuth (r,θ) and elevation (r,θ) planes. A passive seeker requires an illuminator beam, I(ω,φ,θ), and may require a frequency modulation on the illuminator. To model a simplex target return, we have based the dynamics on a point source radar cross section (RCS) along a line of sight (LoS) radial. The Az and El angles are equivalent to antenna placement, the attenuation and frequency dynamics are modeled in commercial off-the-shelf (COTS) software.

No description available.

No description available.

Prior studies of immigrants to the United States show significant weight gain after 10 years of US residence. Pediatric refugees are a vulnerable population whose post-immigration weight trajectory has not been studied. We examined the longitudinal weight trajectory of 1067 pediatric refugees seen in a single university based refugee health program between the dates of September 3, 2012 and September 3, 2014 to determine how quickly significant weight gain occurs post-arrival. The most recent BMI was abstracted from the electronic health record and charts reviewed to obtain serial BMI measurements in 3 year increments after the date of US arrival. The mean arrival BMI percentile for all refugees was 47th percentile. This increased significantly to the 63rd percentile within 3 years of US arrival (p < 0.01). This rapid increase was largely attributable to African and South and Southeast Asian refugees. The overall prevalence of age and sex adjusted obesity rose from 7.4 % at arrival to 18.3 % within 9 years of US immigration exceeding the pediatric US national obesity prevalence of 16.9 %. Pediatric refugees are at increased risk of rapid weight gain after US immigration. Targeted interventions focused on prevention of weight gain in specific populations are warranted.

La dynamique du geste reste peu exploitée dans le domaine de l’interaction hommemachinealors qu’elle permet de définir des critères simples d’analyse de l’intention desutilisateurs. Sa principale utilisation porte sur les fonctions de transfert des périphériquesisotoniques. Ces fonctions permettent d’établir une relation entre le geste de l’utilisateureffectué dans l’espace moteur avec le périphérique de pointage (i.e. souris) et le mouvementdu pointeur dans l’espace visuel. Les fonctions de transfert utilisées par les systèmesd’exploitation modernes restent cependant fortement méconnues même si des études ontmontré qu’elles ont un impact sur les performances des utilisateurs. Pour caractériser cesfonctions, nous avons développé un périphérique électronique qui simule une souris réelleet qui permet d’obtenir les fonctions de transfert de tout système. Nous avons ainsi puobtenir les fonctions des systèmes Windows, Linux et Mac et nous avons observé des différencesnotables entre ces fonctions. Nous avons ensuite cherché à optimiser ces fonctionsen réduisant au maximum le nombre de leurs degrés de liberté. En faisant varier de manièreexhaustive ces paramètres, nous avons ainsi pu observé des différences significativesqui montrent qu’il existe une famille de fonctions pour lesquelles les performances sontoptimales. Enfin, nous nous sommes intéressés à l’utilisation de la dynamique du gestedans un autre contexte, celui de la génération d’événements discrets, pertinent dans lecadre des interfaces sans contact de type Kinect. Nous avons ainsi montré qu’il est possiblede distinguer la sélection du déplacement dans une tâche d’interaction 3D. La techniquedéveloppée est ensuite améliorée dans le cas des cibles de petites tailles et son applicationdans un contexte d’interaction 2D est évaluée. / The dynamic of the gesture is not used a lot in the domain of human-computer interaction,while it can help to define some simple heuristics to analyze the intents of users.Its first use is related to transfer functions for isotonic devices. Those functions establisha relationship between the gesture of the user, executed in motor space with the pointingdevice (i.e. a mouse), and the movement of the pointer in the visual space. The transferfunctions used by modern operating systems are still not well known, even if somestudies have shown they have an impact on user’s performance. To characterize thosefunctions, we have developed an electronic device which simulates a real mouse, and thatcan retrieve the transfer functions of any system. We have then exposed the functions ofthe Windows, Linux and Mac systems, and we observed some visible differences betweenthose functions. We have then tried to optimize those functions by reducing their numberof degrees of freedom. By varying those parameters in an exhaustive way, we have thenobserved some significant differences that show there is a family of functions for whichperformances are optimal. Finally, we were interested in the use of the dynamic of thegesture in another context : the generation of discrete events, useful when dealing withcontact-less interfaces, like the Kinect. We have shown that it is possible to distinguishbetween picking and drag’n’drop in a 3D interaction task. The technique is then improvedin the case of small size targets, and its application in a 2D interaction context isevaluated.

Background: Since inmates in Canada are excluded from household statistics, very little information is known about obesity prevalence or associated risks in this vulnerable population. This is a problem since obesity rates are high in Canada, and obesity is considered a public health crisis. Furthermore, the burden of obesity is disproportionately carried by low-income, vulnerable and marginalized populations (such as inmates). The goal of this study was to determine weight changes during incarceration in Canadian federal penitentiaries, and to determine which factors were influential at the socio-demographic, behavioral, institutional and policy level. Methods: This study was a retrospective cohort study that used a quantitative approach. The setting for this study was 12 correctional institutions in Ontario, New Brunswick and Nova Scotia (or the “Atlantic region”). Administrative data were collected from 1420 inmates, with 754 of these participants also participating in a face to face interview to gather additional data on self-reported behavioral determinants and measured anthropometric data. Eligibility criteria for inmates to participate were: a recorded admission weight in their medical chart, housed in their current institution for at least 6 months, not acutely or terminally ill (and requiring hospitalization), and not pregnant or in a wheelchair. Results: We found that almost three quarters of inmates (73%) gained weight during incarceration. Obesity rates increased by 71%, going from 26.6% to 45.4%. The observed weight gain was associated with the tobacco ban (macrosystem level), the use of commissary store (or “canteen”) (at the microsystem level), and many determinants at the individual level (physical activity, diet, smoking status). The observed weight gain was also significantly associated with age, ethnicity, length of incarceration, duration of total sentence and region. It was however not associated with the national menu, food service/feeding system, sleep, screen time, mental health status or psychotropic medication use. Some inmates who gained excessive weight also developed obesity related illnesses. Interpretation: The observed weight gain was deemed to be unhealthy, since obesity rates increased significantly (and the proportion of inmates with normal weight decreased). These findings have potential repercussions on inmate health, since the observed weight gain was associated with the development of obesity related illnesses. Lastly, many of the factors associated with the observed weight gain were modifiable, which means it is possible to intervene to manage weight gain during incarceration.

The contribution of this thesis is on the temporal adjustment of the consensus weights, as applied to spacecraft formation control. Such an objective is attained by dynamically enforcing attitude synchronization via coupling terms included in each spacecraft controller. It is assumed that each spacecraft has identical dynamics but with unknown inertia parameters and external disturbances. By augmenting a standard adaptive controller that accounts for the unknown parameters, made feasible via an assumption on parameterization, with adaptation of the consensus weights, one opts to improve spacecraft synchronization. The coupling terms, responsible for enforcing synchronization amongst spacecraft, are weighted dynamically in proportion to the disagreement between the states of the spacecraft. The time adjustment of edge-dependent gains as well as the special cases of node-dependent and agent-independent constant gains are derived using Lyapunov redesign methods. The proposed adaptive control architectures which allow for adaptation of both parameter uncertainties and consensus penalty terms are demonstrated via extensive numerical studies of spacecraft networks with limited connectivity. By considering the sum of deviation-from-the-mean and rotational kinetic energy as appropriate metrics for synchronization and controller performance, the numerical studies also provide insights on the choice of optimal consensus gains.

Le germanium dopé n et contraint en tension est un candidat potentiel pour démontrer un laser sur silicium compatible avec un environnement CMOS. Dans ce travail de thèse, j’ai d’abord développé un formalisme qui permet de calculer le gain optique en fonction de la déformation en tension, du dopage n et de l’injection des porteurs. Une technique de transfert de déformation via le dépôt de couche contrainte de SiN a été optimisée. J’ai réalisé plusieurs types de cavités germanium contraintes sous forme de guides d’onde et de microdisques. Le transfert de déformation a été optimisé par sous-gravure et par une méthode de bi-encapsulation qui a permis d’aboutir à une déformation biaxiale homogène et élevée de l’ordre de 1.5%. L’évaluation des déformations a été confrontée à des simulations par éléments finis, photoluminescence et spectroscopie Raman. L’étude expérimentale et théorique des guides d’onde a montré l’avantage de la direction <100> par rapport à la direction <110> permettant une injection plus efficace de porteurs en centre de zone. L’étude expérimentale des microdisques a permis d’observer des modes de galerie avec un facteur de qualité Q = 1540 à λ = 1940 nm. D’autre part, j’ai mis en évidence par photoluminescence la présence d’un fort dopage de 4×10¹⁹ cm⁻³ dans des couches germanium sur silicium épitaxiées par épitaxie par jets moléculaires utilisant une technique de co-dopage. Une modélisation du gain modal a permis de mettre en exergue l’effet du gradient de déformation dans le volume de la cavité. L’élargissement homogène a été introduit dans la modélisation du gain optique afin de prendre en compte l’impact d’un dopage élevé. / Tensile strained and n-doped germanium is a potential candidate to demonstrate a laser on silicon in a CMOS-compatible environment. In this thesis, I developed a formalism to calculate the optical gain as a function of tensile strain, n-doping and carrier injection. A tensile strain transfer technique via strained SiN layer deposition has been optimized. I realized several types of strained germanium cavities. Tensile strain transfer was optimized by under-etching and a bi-encapsulation technique which allowed to achieve a high and uniform biaxial strain up to 1.5%. The evaluation of strain level was faced with finite elements modeling, photoluminescence and Raman spectroscopy. The experimental and theoretical study of the waveguides showed the advantage of the <100> direction as compared with the <110> direction for more efficient carrier injection at zone center. The experimental study of microdisks allowed us to observe gallery modes with quality factor up to Q = 1540 at λ= 1940 nm. On the other hand, photoluminescence enhancement has shown the presence of a heavy doping of 4×10¹⁹ cm⁻³ in germanium on silicon layers grown by molecular beam epitaxy and using a co-doping technique. Modeling the modal gain helped to emphasize the effect of the strain gradient in the cavity volume. The homogeneous broadening was introduced in the optical gain modeling to take into account the impact of a high doping.