<p>  </p> <p>Some of the variability found in measures of mental workload (see e.g. Singleton et al. 1973; Wierwille and Connor 1983; Steelman-Allen et al. 2011; Casner and Gore 2010) may be due to the effort applied to the task by participants, rather than by the independent variable of interest. If true, capturing and removing the variation due to ‘applied effort’ could improve the ability of studies to detect effects of interest. </p> <p>While introducing participants to two sub-tasks derived from Multi-Attribute Task Battery II (Santiago-Espada et al. 2011), the study investigated the influence of applied effort on MATB-II performance measures of mental workload while holding other effects constant. Two groups of participants each completed easy and hard trials of MATB-II-derived sub-tasks. Treatment group of participants was offered an additional reward if they achieved a sufficiently high performance.</p> <p>The treatment group performed better by just under 4% in both easy and hard trials which provides a suggestion about the size of the effect of applied effort in this study. </p> <p>Additionally pilot error analysis was performed using Tracking task results. Error probability distributions did not fit known distributions and did not show consistent difference between treatment and control groups. Novel method of distribution “tails” comparison showed significant difference in extreme error durations, extents and delays between treatment and control groups.</p> <p>Measuring or controlling for applied effort can improve the ability of researchers to determine the effects of interventions on workload measures by reducing the amount of variability that is captured as error. Also, “tails” method seems to be a viable tool in comparing probability  </p>

No description available.

Using a hydrodynamical smoothed particle hydrodynamics (SPH) zoom-in simu lation of a galaxy group, we present a set of tail identification methods, and study the statistical properties of galaxy tails and their correlations with their expected formation mechanisms. We have a sample of 4548 M > 108 M⊙ galaxies across 58 snapshots from z = 0.67 to z = 0. For each galaxy, we apply a series of velocity and density cuts to identify the tail. We observed no significant correlations between galaxy tail mass and ram pressure, though we note some issues with our sampling. Tracking four visually identified jellyfish galaxies over time showed some evidence of increased ram pressure driving ISM mass loss, as well as spikes in tail mass pre ceding spikes in ram pressure with temporal offsets ranging from 500 Myr to 2 Gyr. No correlation was found between ISM mass and tail mass. We track the tail gas of a particularly well defined jellyfish galaxy 3.2 Gyrs back in time. We find that a lower bound of 30% of the tail gas was never in the ISM. Distinguishing between former ISM tail material and never ISM-accreted tail material, we see evidence of temperature mixing with the IGM in the former. Velocity and radial trajectory maps show a sharp impulse of ∆v ≈ 50 km s−1 over 4 snapshots, affecting both the never ISM-accreted tail material and CGM material, with the former showing evidence of momentum mixing onto the former ISM material. Combined with ob servations of CGM stripping, we propose that a significant portion of galaxy tails consists of stripped CGM that got swept up into the stripped ISM / Thesis / Master of Science (MSc)

In pursuit of producing robots capable of achieving the dexterity exhibited by animals in nature, roboticists have begun to explore the application of robotic tails. This thesis will explore the design, optimization, construction, and implementation of an articulated serpentine robotic tail. Numerous serpentine tail prototypes have been designed and tested; however, they have not yet been integrated with a mobile base. The main challenges preventing the incorporation of serpentine tails with mobile bases include: (1) the large size and inflexible packaging associated with the actuation unit for the tail, (2) the relatively low power to weight ratios of the existing serpentine tail systems, and (3) the complexity of optimizing the tails physical parameters. Therefore, to address these issues, a novel layout for a serpentine robotic tail actuation unit along with a design optimization methodology for the tail are proposed. The actuation unit will feature a power dense and modular design which allows for flexibility in packaging. Simulation results along with experimental data gathered using a prototype of the design will be reviewed in order to quantify the performance of the actuation unit. Following, a design optimization methodology which uses a modified direct collocation technique will be presented. The optimization allows for the simultaneous optimization of both a trajectory and the physical structure of a tail. Representative results of this technique will be presented and compared against more traditional methods for design optimization. To conclude the on-going and future work for both the actuation unit and optimization methodology will be stated. / Master of Science / Robotic tails largely fall into two categories based on their construction. These two categories are pendulum and serpentine structure. Pendulum structure tails consist of a long rigid rod with a weight attached to the end of it which can be swung to assist in controlling the orientation of the base which it is attached to. Serpentine tails are characterized by their ability to articulate and move in three dimensions similar to cat or monkey tails. The non-rigid structure of the tail opens up many new possibilities for their use. However, these possibilities come at the cost of design complexity. To date this complexity has led to designs for serpentine tails which are too heavy or unwieldy to be easily added to a mobile base. Additionally, the complexity of the tail structure itself make it difficult to optimize the design as has been done previously with pendulum designs. In an effort to overcome these challenges this thesis presents a novel design for a tail actuation unit and design optimization methodology. The actuation unit design is more power dense and provides greater flexibility in its layout than previous designs. This makes it much easier to adapt to and integrate with a mobile base. This will be demonstrated through the creation of a prototype tailed quadruped featuring the new actuation unit. The optimization methodology will use a technique known as direct collocation which has previously been developed for optimal path planning. This technique accommodates the complexities of serpentine tail designs and allows for the parameters such as length and weight of the tail to be optimized. The conclusion of the thesis will present the on-going and future work for both the actuation unit and optimization technique.

This dissertation explores the design, and implementation of articulated robotic tail mechanisms onboard reduced degree-of-freedom (DOF) legged robots to augment performance in terms of stability and maneuverability. Fundamentally, this research is motivated by the question of how to improve the stability and maneuverability of legged robots. The conventional approach to address these challenges is to utilize leg mechanisms that are composed of three or more active DOFs that are controlled simultaneously to provide propulsion, maneuvering, and stabilization. However, animals such as lizards and cheetahs have been observed to utilize their tails to aid in these functionalities. It is hypothesized that by using an articulated tail mechanism to aid in these functionalities onboard a legged robot, the burden on the robot's legs to simultaneously maneuver and stabilize the robot may be reduced. This could allow for simplification of the leg's design and control algorithms. In recent years, significant progress has been accomplished in the field of robotic tail implementation onboard mobile robots. However, the main limitation of this work stems from the proposed tail designs, the majority of which are composed of rigid single-body pendulums that provide a constrained workspace for center-of-mass positioning, an important characteristics for inertial adjustment applications. Inspired by lizards and cheetahs that adjust their body orientation using flexible tail motions, two novel articulated, cable driven, serpentine-like tail mechanisms are proposed. The first is the Roll-Revolute-Revolute Tail which is a 3-DOF mechanism, designed for implementation onboard a quadruped robot, that is capable of forming two mechanically decoupled tail curvatures via an s-shaped cable routing scheme and gear train system. The second is a the Discrete Modular Serpentine Tail, designed for implementation onboard a biped robot, which is a modular two-DOF mechanism that distributes motion amongst links via a multi-diameter pulley. Both tail designs utilize a cable transmission system where cables are routed about circular contoured links that maintain equal antagonistic cable displacements that can produce controlled articulated tail curvatures using a single active-DOF. Furthermore, analysis and experimental results have been presented to demonstrate the effectiveness of an articulated tail's ability to: 1) increase the manifold for center-of-mass positioning, and 2) generate enhanced inertial loading relative to conventionally implemented pendulum-like tails. In order to test the tails ability to augment the performance of legged robots, a novel Robotic Modular Leg (RML) is proposed to construct both a reduced-DOF quadrupedal and bipedal experimental platform. The RML is a modular two-DOF leg mechanism composed of two serially connected four-bar mechanisms that utilizes kinematic constraints to maintain a parallel orientation between it's flat foot and body without the use of an actuated ankle. A passive suspension system integrated into the foot enables the dissipation of impact energy and maintains a stable four point-of-contact support polygon on both flat and uneven terrain. Modeling of the combined legged robotic systems and attached articulated tails has led to the derivation of dynamic formulations that were analyzed to scale articulated tails onboard legged robots to maximize inertial adjustment capabilities resulting from tail motions and design a control scheme for tail-aided maneuvering. The tail prototypes, in conjunction with virtual simulations of the quadruped and biped robot, were used in experiments and simulations to implement and analyze the methods for maneuvering and stabilizing the proposed legged robots. Results successfully demonstrate the tails' ability to augment the performance of reduced-DOF legged robots by enabling comparable walking criteria with respect to conventional legged robots. This research provides a firm foundation for future work involving design and implementation of articulated tails onboard legged robots for enhanced inertial adjustment applications. / Ph. D. / In nature, animals commonly use their tails to assist propulsion, stabilization, and maneuvering. However, in legged robotic systems, the dominant research paradigm has been to focus on the design and control of the legs as a means to simultaneously provide propulsion, maneuvering, and stabilization. Fundamentally, this research is motivated by the question of how to improve the stability and maneuverability of legged robots utilizing an articulated tail mechanism. It is hypothesized that by using an articulated tail mechanism to aid in these functionalities onboard a legged robots, the burden on the robot’s legs to simultaneously maneuver and stabilize the robot may be reduced. This could allow for simplification of the leg’s design and control algorithms. This doctoral dissertation addresses this problem statement and hypothesis by proposing two articulated tail mechanisms, R3-RT and DMST, that are uniquely designed to be practically implemented on a reduced DOF quadruped and biped robot, respectively, for tail-aided stabilization and maneuverability. Through analysis and experimentation, it is demonstrated that articulated tails enable enhanced workspace and inertial loading capabilities relative to previously implemented pendulum-like tails while the proposed leg mechanism enables the construction of legged robots with simplified design and control. However, these legged robots cannot effectively walk as standalone machines which justifies the implementation of articulated tails for augmented performance. The dynamics of the combined robotic system consisting of reduced DOF legged robots with implemented tails are derived to scale and optimize articulated tails to maximize inertial adjustment capabilities and derive control schemes for enhanced maneuvering and stabilization using tail-aided motion. Using experiments and simulations, the combined robotic systems consisting of a reduced DOF quadruped and biped robots augmented via articulated tails demonstrate walking criteria that is comparable to conventional legged robots.

La cicatrisation cornéenne représente un processus de réparation complexe qui vise à restaurer l'intégrité, la structure et la transparence de la cornée. Cependant, dans un certain nombre de cas, ce processus peut évoluer de façon anormale et se stabiliser en entraînant la formation d'une opacité cornéenne installée. Les mécanismes impliqués dans la formation de ces cicatrices persistantes ne sont pas encore complètement élucidés, mais il est établi que la composition et l'organisation de la matrice extracellulaire du stroma jouent un rôle majeur dans la restauration de la transparence de la cornée. Ce projet s’est concentré sur la métalloprotéase extracellulaire BMP-1 (Bone Morphogenetic Protein 1), déjà connue pour son rôle dans l'assemblage de la matrice extracellulaire et l'activation du TGF-bêta. Afin d’identifier les processus contrôlés par BMP-1 dans la cornée, nous avons d’abord effectué une comparaison systématique des inhibiteurs de BMP-1 connus ou potentiels, de différentes origines, pour caractériser leurs propriétés à la fois in vitro et dans des cultures cellulaires. Ensuite, nous avons mené une étude approfondie du sécrétome des cellules stromales de la cornée humaine (kératocytes), et des conséquences de la différenciation de ces cellules en myofibroblastes. Enfin, nous avons analysé les événements protéolytiques médiés par BMP-1 dans le sécrétome des kératocytes en utilisant principalement une approche de protéomique quantitative basée sur le marquage iTRAQ des protéines entières (technique TAILS). La comparaison des inhibiteurs disponibles de BMP-1 a permis de mettre en évidence différents profils d’efficacité, de spécificité et de toxicité et a conduit à l’identification d’un inhibiteur hydroxamate et d’un inhibiteur protéique efficaces, peu toxiques et très spécifiques de BMP-1. Le sécrétome des kératocytes s’est avéré être un modèle adéquat pour l’étude des activités de BMP-1 dans le contexte cornéen. Plus de 2022 protéines ont été identifiées, dont la métalloprotéase BMP-1 et 16 de ses 33 substrats connus jusqu’à présent. Enfin, 76 protéines modifiées par l’activité de BMP-1 ont été identifiées dans le sécrétome des kératocytes. Ces résultats confirment les liens forts entre BMP-1, l'assemblage de la matrice extracellulaire et le TGF-bêta, mais suggèrent également de nouveaux rôles pour la protéase dans l'inflammation. Certains des substrats nouvellement identifiés (TGFBI, HSP47 et collagène VI) sont très pertinents dans le contexte de la cicatrisation de la cornée et ont été validés d’un point de vue biochimique. En conclusion, BMP-1 est confirmée comme une cible potentielle intéressante pour traiter ou prévenir la formation des opacités cornéennes et la caractérisation des inhibiteurs disponibles ouvre des perspectives importantes pour des études précliniques chez l’animal / When the cornea is injured, a complex multi-step healing process is triggered which aims at restoring corneal integrity, structure and transparency. However, in some cases, corneal healing results in the formation of a stable scar associated with a prolonged loss of corneal transparency and with functional blindness. The mechanisms involved in the formation of these persistent scars are still not fully understood but it is known that the composition and organization of the extracellular matrix significantly contributes to the maintenance of corneal transparency. This work focused on the extracellular metalloproteinase called BMP-1 (Bone Morphogenetic Protein 1), a major player in the control of extracellular matrix assembly and TGF-beta activation, which was previously shown to be up-regulated in corneal healing and scarring. In order to further probe BMP-1 functions in corneal healing, we first performed a systematic comparison of known or potential BMP-1 inhibitors from different origins to characterize their properties both in vitro and in cell cultures. We then carried out an in-depth study of the secretome of human corneal stromal cells (keratocytes) and of the consequences of the differentiation of these cells into myofibroblasts. Finally, we analyzed BMP-1-mediated proteolytic events in keratocyte secretomes, mainly using a quantitative proteomic approach based on iTRAQ labeling of proteins (TAILS technique). The comparison of BMP-1 available inhibitors revealed different profiles of efficacy, specificity and toxicity and led to the identification of one hydroxamate inhibitor and one protein inhibitor, which were very efficient, non-toxic and very specific of BMP-1. The keratocyte secretome was shown to be a suitable model for the study of BMP-1 activities in the corneal context. More than 2022 proteins were identified, including the BMP-1 metalloprotease and 16 of its 33 already known substrates. Finally, 76 proteins modified by BMP-1 activity were identified in the keratocyte secretome. These results confirm the strong links between BMP-1, extracellular matrix assembly and TGF-beta, but also suggest new roles for this protease in cell proliferation and inflammation. Some of the newly identified substrates (TGFBI, HSP47 and collagen VI) are highly relevant in the context of corneal healing and were validated at the biochemical standpoint. In conclusion, BMP-1 is confirmed as a potential target to treat or prevent the formation of corneal opacities and the characterization of available inhibitors opens up important perspectives for preclinical studies in animals

This thesis' topic is stochastic programming, in particular with regard to portfolio optimization and heavy tailed data. The first part of the thesis mentions the most common types of problems associated with stochastic programming. The second part focuses on solving the stochastic programming problems via the SAA method, especially on the condition of data with heavy tailed distributions. In the final part, the theory is applied to the portfolio optimization problem and the thesis concludes with a numerical study programmed in R based on data collected from Google Finance.

<p>The main goal of this work is to explore the effects of time-varying extreme jump tail dependencies in asset markets. Consequently, a lot of attention has been devoted to understand the extremal tail dependencies between of assets. As pointed by Hansen (2013), the estimation of tail risks dependence is a challenging task and their implications in several sectors of the economy are of great importance. One of the principal challenges is to provide a measure systemic risks that is, in principle, statistically tractable and has an economic meaning. Therefore, there is a need of a standardize dependence measures or at least to provide a methodology that can capture the complexity behind global distress in the economy. These measures should be able to explain not only the dynamics of the most recent financial crisis but also the prior events of distress in the world economy, which is the motivation of this paper. In order to explore the tail dependencies I exploit the information embedded in option prices and intra-daily high frequency data. </p><p>The first chapter, a co-authored work with Andrew Patton, proposes a new class of dynamic copula models for daily asset returns that exploits information from high frequency (intra-daily) data. We augment the generalized autoregressive score (GAS) model of Creal, et al. (2013) with high frequency measures such as realized correlation to obtain a "GRAS" model. We find that the inclusion of realized measures significantly improves the in-sample fit of dynamic copula models across a range of U.S. equity returns. Moreover, we find that out-of-sample density forecasts from our GRAS models are superior to those from simpler models. Finally, we consider a simple portfolio choice problem to illustrate the economic gains from exploiting high frequency data for modeling dynamic dependence.</p><p>In the second chapter using information from option prices I construct two new measures of dependence between assets and industries, the Jump Tail Implied Correlation and the Tail Correlation Risk Premia. The main contribution in this chapter is the construction of a systemic risk factor from daily financial measures using a quantile-regression-based methodology. In this direction, I fill the existing gap between downturns in the financial sector and the real economy. I find that this new index performs well to forecast in-sample and out-of-sample quarterly macroeconomic shocks. In addition, I analyze whether the tail risk of the correlation may be priced. I find that for the S&P500 and its sectors there is an ex ante premium to hedge against systemic risks and changes in the aggregate market correlation. Moreover, I provide evidence that the tails of the implied correlation have remarkable predictive power for future stock market returns.</p> / Dissertation

This article aims at the statistical assessment of time series with large fluctuations in short time, which are assumed to stem from a continuous process perturbed by a Lévy process exhibiting a heavy tail behavior. We propose an easily implementable procedure to estimate efficiently the statistical difference between the noisy behavior of the data and a given reference jump measure in terms of so-called coupling distances. After a short introduction to Lévy processes and coupling distances we recall basic statistical approximation results and derive rates of convergence. In the sequel the procedure is elaborated in detail in an abstract setting and eventually applied in a case study to simulated and paleoclimate data. It indicates the dominant presence of a non-stable heavy-tailed jump Lévy component for some tail index greater than 2.

Enhancing the ability to predict airflow around the Vertical Tail Plane (VTP) of an aircraft is vital in the aviation industry. The size of the VTP is driven by a particular flight condition - loss of an engine during take-off and low speed climb. Nowadays, Computational Fluid Dynamics (CFD) is the main tool used by engineers to assess VTP flows. However, due to uncertainties in the prediction of VTP effectiveness, aircraft designers keep to a conservative approach, which risks oversizing of the tail plane, adding more drag. Uncertainties emerge from difficulties in predicting the massive separation that occurs on the swept tail when it is approached by a flow at high incidence. Furthermore, the deployment of the control surface (the rudder) over the tail plane and the skewed flow along the span increase the CFD challenges. Improved predictive capabilities of the flow around VTPs would enable a more optimal design approach with potential drag saving. The correct prediction of flow separation is the essence of this study. Currently, the industry uses steady Reynolds-Averaged Navier-Stokes (RANS) simulations to analyse VTPs flow. In order to assess RANS performance, the study of airflow detaching from a backward rounded ramp is performed and the results are compared to Large-Eddy Simulations (LES). The analysis shows that, even though RANS may predict the onset of flow separation correctly, they completely miss the location of flow reattachment over the ramp, and this affects the whole flow solution. Moreover, the flow features a strong anisotropy at the onset of separation, difficult to be captured by RANS. The analysis shows that RANS cannot predict production of turbulent kinetic energy in the detached flow region correctly, discouraging flow mixing, and delaying flow reattachment. A hybrid RANS/LES carried out on the same test case shows the benefits of using eddy-resolving simulations for detached flows. The prediction of the locations of the separation and reattachment points differs by only 1% from the highly-resolved simulation. The VTP investigation carried out in this thesis uses a wind tunnel model tested at Airbus. The study starts with steady RANS approaches for different turbulence models. RANS simulations produce acceptable results for the flow at low incidence levels. On the contrary, at high incidence, when flow separation occurs, RANS methods fail. The second step of the research consists of using unsteady RANS (URANS) simulations for VTP flows at high sideslip angles. The introduction of time-accuracy brings important benefits. Nevertheless, the results still show some inaccuracies (around 20% error). Finally, restarting from the flow solutions obtained by URANS simulations, higher fidelity hybrid RANS/LES techniques in the form of Delayed Detached-Eddy Simulations (DDES) are used to assess the characteristics of the separated flow around the tail plane. Results show a remarkable improvement of the flow solution. The pressure distribution matches experimental results favourably, and this translates into an improved prediction of the aerodynamic loads over the VTP. This leads towards a new strategy for the assessment of the flow over aircraft VTPs, amounting to an important contribution to the design of future aircraft.