Discrete Mechanics and Optimal Control Applied to the Compass Gait Biped

This paper presents a methodology for generating locally optimal control policies for simple hybrid mechanical systems, and illustrates the method on the compass gait biped. Principles from discrete mechanics are utilized to generate optimal control policies as solutions of constrained nonlinear optimization problems. In the context of bipedal walking, this procedure provides a comparative measure of the suboptimality of existing control policies. Furthermore, our methodology can be used as a control design tool; to demonstrate this, we minimize the specific cost of transport of periodic orbits for the compass gait biped, both in the fully actuated and underactuated case

POPULATION AGING AND ECONOMIC DEPENDENCY RATIO: COMPARATIVE STUDY OF THE CZECH REPUBLIC AND SLOVAKIA

The article examines the effects of population aging on economic dependency ratio. The results are estimated using broader definition of economic dependency allowing for variability in employment rates of age- and gender-specific groups. The Czech Republic and Slovakia are used as case study countries with similar starting point to assess their comparative population dynamics. The results suggest a significant growth of dependent share of population. Dependency ratios are predicted to increase from 110 % in 2016 to 161 % in 2060 and from 120 % to 181 % for Czech and Slovak economy respectively. Decomposition of the indicator shows substantial old-age cohort contribution, which indicates increased pressure on fiscal stability due to population aging. In second stage, the sensitivity of economic dependency on employment rates is tested to model three policy reforms to tackle the increased dependency – increase in exit age from workforce, gender equalizing labour market reform and mobilization of young-age workers. The evidence suggests that a cumulative effect of simulated reforms has the ability to decrease predicted dependency ratios back to current levels

Development of Nanomaterial Supports for the Study of Affinity-Based Analytes Using Ultra-Thin Layer Chromatography

Ultra-thin layer chromatography (UTLC) is a growing field in analytical separations. UTLC is a branch of planar and liquid chromatography that is related to thin layer chromatography. The main advantage of UTLC compared to other techniques is it uses much less material, allowing for faster and more sensitive separations to take place. The UTLC devices fabricated in this project used either silicon oxide or silicon nanopillars deposited on a glass slide using glancing angle deposition (GLAD). Even a thin layer of these nanopillars deposited on a glass slide provide a large surface area for the analyte to be separated. GLAD is a physical vapor deposition technique that allows, in this case, silicon oxide or silicon to be vaporized by an ion source and deposited in slanted pillar structures onto a glass substrate. The overall goal of this thesis is to develop and optimize a nanomaterial support/stationary phase for a UTLC device that can be utilized for affinity chromatography. The studies performed in this thesis provide proof-of-concept that SiO2 nanopillars can perform efficient separations and that protein can also be immobilized onto the surface of the nanopillars. With further studies, protein immobilization can be fully optimized and affinity separations performed on these UTLC devices. Advisor: David Hag

Geometry of unsteady fluid transport during fluid–structure interactions

We describe the application of tools from dynamical systems to define and quantify the unsteady fluid transport that occurs during fluid–structure interactions and in unsteady recirculating flows. The properties of Lagrangian coherent structures (LCS) are used to enable analysis of flows with arbitrary time-dependence, thereby extending previous analytical results for steady and time-periodic flows. The LCS kinematics are used to formulate a unique, physically motivated definition for fluid exchange surfaces and transport lobes in the flow. The methods are applied to numerical simulations of two-dimensional flow past a circular cylinder at a Reynolds number of 200; and to measurements of a freely swimming organism, the Aurelia aurita jellyfish. The former flow provides a canonical system in which to compare the present geometrical analysis with classical, Eulerian (e.g. vortex shedding) perspectives of fluid–structure interactions. The latter flow is used to deduce the physical coupling that exists between mass and momentum transport during self-propulsion. In both cases, the present methods reveal a well-defined, unsteady recirculation zone that is not apparent in the corresponding velocity or vorticity fields. Transport rates between the ambient flow and the recirculation zone are computed for both flows. Comparison of fluid transport geometry for the cylinder crossflow and the self-propelled swimmer within the context of existing theory for two-dimensional lobe dynamics enables qualitative localization of flow three-dimensionality based on the planar measurements. Benefits and limitations of the implemented methods are discussed, and some potential applications for flow control, unsteady propulsion, and biological fluid dynamics are proposed

Hallo! Voulez vous luncher avec moi hüt? Le "code switching" dans la communication par SMS

Within the last two decades, text messaging by means of SMS has become a central tool of communication around the globe. The use of more than one language for composing a message is wide spread, but, to this day, is relatively underrepresented in research. This paper presents an analysis of the plurilingual nature of SMS communication in Switzerland with the limelight on the forms and functions of code-switching within a set of 345 messages, base language of which is French. Results show that SMS users regularly exhibit code-switching even if they are not members of a bilingual speech community. Code-switching most frequently consists of inserts, i.e. embeddings of single items or combinations of items within a message composed in another language, and this typically involves (only) a limited range of routinized expressions. While English is the most frequently used language for code-switching, German, Swiss German, Spanish and Italian are also recurrent, the latter two being particularly associated with terms of endearment. Code-switching regularly highlights the expression of actions that have a strong interpersonal (phatic) focus, such as greetings, good-byes or thanks. It elucidates the expressive character of the messages, and is also associated with the expression of affection. The specificity of the plurilingual SMS repertoire is discussed in the paper's conclusion