Speed control with low armature loss for very small sensorless brushed DC motors

A method for speed control of brushed dc motors is presented. It is particularly applicable to motors with armatures of less than 1 cm3. Motors with very small armatures are difficult to control using the usual pulsewidth-modulation (PWM) approach and are apt to overheat if so driven. The technique regulates speed via the back electromotive force but does not require current-discontinuous drives. Armature heating in small motors under PWM drive is explained and quantified. The method is verified through simulation and measurement. Control is improved, and armature losses are minimized. The method can expect to find application in miniature mechatronic equipment

When Technology Is Too Hot, Too Cold Or Just Right

Many instructors acknowledge the importance of quantitative literacy in non-STEM fields and may themselves use advanced tools for data analysis, statistics and visualization. But how, if at all, does an instructor introduce quantitative methods into the classroom without overwhelming and disengaging students who may have been drawn to the field precisely because it has not traditionally required any skill or interest in science, technology, engineering or math? I present a model of iterative assignment design illustrated by the evolution of a phonetic exercise in which students are asked to measure vowels from their own speech and to plot their measurements on a graph in order to re-create the standard organization of vowel sounds found in linguistics textbooks. The different iterations involved varying degrees of technology (from low-tech pencil-and-paper to high-tech computing environment) and technological support and are evaluated with respect to NICHE best practices. The most recent iteration finds a compromise in a simple web app driven by the powerful R statistical computing environment

Naming and sharing resources across administrative boundaries

I tackle the problem of naming and sharing resources across administrative boundaries. Conventional systems manifest the hierarchy of typical administrative structure in the structure of their own mechanism. While natural for communication that follows hierarchical patterns, such systems interfere with naming and sharing that cross administrative boundaries, and therefore cause headaches for both users and administrators. I propose to organize resource naming and security, not around administrative domains, but around the sharing patterns of users. The dissertation is organized into four main parts. First, I discuss the challenges and tradeoffs involved in naming resources and consider a variety of existing approaches to naming. Second, I consider the architectural requirements for user-centric sharing. I evaluate existing systems with respect to these requirements. Third, to support the sharing architecture, I develop a formal logic of sharing that captures the notion of restricted delegation. Restricted delegation ensures that users can use the same mechanisms to share resources consistently, regardless of the origin of the resource, or with whom the user wishes to share the resource next. A formal semantics gives unambiguous meaning to the logic. I apply the formalism to the Simple Public Key Infrastructure and discuss how the formalism either supports or discourages potential extensions to such a system. Finally, I use the formalism to drive a user-centric sharing implementation for distributed systems. I show how this implementation enables end-to-end authorization, a feature that makes heterogeneous distributed systems more secure and easier to audit. Conventionally, gateway services that bridge administrative domains, add abstraction, or translate protocols typically impede the flow of authorization information from client to server. In contrast, end-to-end authorization enables us to build gateway services that preserve authorization information, hence we reduce the size of the trusted computing base and enable more effective auditing. I demonstrate my implementation and show how it enables end-to-end authorization across various boundaries. I measure my implementation and argue that its performance tracks that of similar authorization mechanisms without end-to-end structure. I conclude that my user-centric philosophy of naming and sharing benefits both users and administrators

Biotic and Abiotic Characteristics Influencing Nest Location and Trophic Relationships of the Fungus-Growing Ant \u3ci\u3eTrachymyrmex septentrionalis\u3c/i\u3e (Formicidae: \u3ci\u3eAttini)\u3c/i\u3e

Trachymyrmex septentrionalis represents the only species of fungus-growing ant in the southeastern United States. T. septentrionalis cultivates a symbiotic fungus on which the ants feed. Worker ants collect plant and animal debris to feed the fungus. These ants are common in Florida, but increasingly scarce as they near the northern extent of their range in New Jersey. Colonies of T. septentrionalis occur in patches throughout Blackwater Ecological Preserve, a longleaf pine forest in southeastern Virginia. Blackwater Ecologic Preserve is a 129 hectare tract of land, located in Isle of Wight county, that is undergoing a regimen of controlled burning to increase the population of longleaf pines ( Pinus palustris). Over an 8 year period, multiple abiotic and biotic factors were studied to better understand what conditions determine the distribution of T. septentrionaliscolonies within an ecosystem and how those factors may affect the ability of individual colonies to collect sufficient substrate to sustain the fungal symbiont and feed the colony. Soil temperature (23.5 vs. 25.1°C), air temperature (22.3 vs. 26.4°C), and light intensity (302.8 vs. 595.2 lumens) were all found to be significantly higher around inactive nests. Plant cover, which would affect light intensity around the nests, was significantly higher above active nests (71.1%) than over inactive nests (57.9%). Soil samples from T. septentrionalis populated and adjacent, unpopulated sites resulted in soil moisture being significantly lower in the upper 60 cm of soil in populated versus unpopulated areas. No consistent differences were found for soil organic matter, cation exchange capacity, or pH between populated and unpopulated sites. Colony densities, calculated for each nesting site, ranged from 0.072 to 0.145 nests/m 2, and these densities can be correlated to soil and air temperatures, light intensity, and vegetation cover. In an attempt to understand the patchy distribution of T. septentrionalis in Blackwater Ecologic Preserve, the composition of ant and plant communities in areas with and without T. septentrionalis nests were analyzed. A total of 34 ant species was collected, with 27 species from sites with T. septentrionalis and 30 from those without. Only Aphaenogaster treatae displayed significantly different numbers between sites, but there were numerous species that occurred only in one or the other. A total of 15 plant species were identified in areas populated by T. septentrionalis, but 22 were identified in unpopulated areas. As with the ant community, numerous species could be located in one site but not the other. Just as air temperatures affect the overall activity of T. septentrionalis colonies, they also influence foraging rates. Field preference of forage falls into four categories (Berry, Pteridium aquilinum, Quercus sp., Unknown Materials). Carbon and nitrogen concentrations increase as the elements are tracked from the substrate to the fungus then to the ants themselves. During a season of activity, a nest of 356 workers, alates, and pupae is expected to capture approximately 29.58 kcal/m 2 of energy through substrate collection. From this total, the T. septentrionalis/fungus symbiont is estimated to assimilate between 11.1 and 12.79 kcal/nest/yr. T. septentrionalis appears to be highly sensitive to environmental conditions such as temperatue and light intensity both for daily activities and the foundation of new colonies. Soil moisture may also be considered as an important factor, either directly as it influences chamber excavation and stability or indirectly by determining vegetative cover. Overall, ant and plant communities did not affect the presence or absence of T. septentrionalis. T. septentrionalis acquires limited nutrients and energy from the surrounding ecosystem, this may be due to an inability to exploit the environment or the higher energetic demands required to acquire richer sources of nutrients and energy by leaf cutting

A corpus search methodology for focus realization

Poster presentation, 157th Meeting of the Acoustical Society of America. Abstract appears in J. Acoust. Soc. Am. Volume 125, Issue 4, pp. 2573-2573.We describe a methodology for investigating the semantic-grammatical conditioning and phonetic realization of contrastive intonation using a web harvest of particular word strings followed by grammatical and acoustic analysis. A commercial audio web search engine using speech recognition retrieved 179 MP3 files purportedly containing a token of the string 'than I did.' In this comparative clause fragment, contrastive focus commonly falls on the subject 'she did more than I_F did' , on 'did', 'I wish I had done more than I did_F', or following 'I said more now than I did before_F' . The 96 true tokens of 'than I did' were classified into the categories 'subject', 'did', and 'following' by grammatical and semantic criteria. For each token, 5 segment intervals were hand-annotated and more than 300 acoustic parameters extracted using a Praat script. SVM machine learning classifiers were trained that identify focus classes by acoustic criteria. On a 10-fold crossvalidation test, the classifier achieves 90.2% accuracy in discriminating the dominant 'subject' and 'following' classes. In a listening task, human subjects achieved comparable accuracy of 90.3 given only the acoustic target 'than I did'. Stepwise logistic regression revealed measures of duration, f0, intensity, formants, and formant bandwidths among the significant factors

Wind tunnel and numerical study of a small vertical axis wind turbine

This paper presents a combined experimental and computational study into the aerodynamics and performance of a small scale vertical axis wind turbine (VAWT). Wind tunnel tests were carried out to ascertain overall performance of the turbine and two- and three-dimensional unsteady computational fluid dynamics (CFD) models were generated to help understand the aerodynamics of this performance. Wind tunnel performance results are presented for cases of different wind velocity, tip-speed ratio and solidity as well as rotor blade surface finish. It is shown experimentally that the surface toughness on the turbine rotor blades has a significant effect on performance. Below a critical wind speed (Reynolds number of 30,000) the performance of the turbine is degraded by a smooth rotor surface finish but above the turbine performance is enhanced by a smooth surface finish. Both two bladed and three bladed it, rotors were tested and a significant increase in performance coefficient is observed for the higher solidity rotors (three bladed rotors) over most of the operating range. Dynamic stalling behaviour and the resulting large and rapid changes in force coefficients and the rotor torque are shown to be the likely cause of changes to rotor pitch angle that occurred during early testing. This small change in pitch angle caused significant decreases in performance. The performance coefficient predicted by the two dimensional computational model is significantly higher than that of the experimental and the three-dimensional CFD model. The predictions show that the presence of the over tip vortices in the 3D simulations is responsible for producing the large difference in efficiency compared to the 2D predictions. The dynamic behaviour of the over tip vortex as a rotor blade rotates through each revolution is also explored in the paper. (C) 2009 Elsevier Ltd. All rights reserved

Physical and numerical analysis of fracture in flat plates arising from translating loads

Previous work with moving loads showed a significant decrease in structural capacity of samples subjected to moving loads that caused plastic damages, however did not investigate loads which incited fracture. The state of the art in material science for ductile metals indicates that fracture can be predicted by a locus of triaxiality, Lode Angle Parameter and effective plastic strain. However, in the case of stationary loads, effective fracture strain has been used to accurately predict fracture. Collision analysis for loads which incite fracture is more frequently being completed using non-linear finite element analysis, commonly using the effective plastic strain to fracture method. However, real collisions are often oblique, and as such, it can be assumed that some horizontal translation is realistic and should be modelled as a moving load. This thesis explores the effects of moving loads which incite fracture in plate samples using experiments and corresponding numerical models. The results of this thesis found a significant loss in ability to resist fracture during the horizontal translation of a load along a plate sample as well as a clear inability to accurately characterize a moving load numerically using the effective plastic strain to fracture method. In particular, this thesis presents: the results of laboratory experiments using the Moving Load Apparatus involving two distinct indenters (cutting and rolling wheel) designed to induce different stress states; a discussion of calibrated numerical models as well as triaxiality and Lode Angle Parameter for the point of fracture of these models

On Modal Interpretations of the French Conditionnel !

Introduction The first goal of this paper is to pursue a uniform formal semantic analysis of different modal uses of the French conditionnel morphology, so named for its use in the main clause of counterfactual (aka remote or subjunctive) conditionals. (1) S'il n'était pas linguiste, il serait comédien. 'If he were not an actor, he would be an actor. ' It is possible to analyze the morphology as composed of future and perfective morphology (e.g. Iatridou 2000); however for the purpose of analyzing its interaction with certain modals and attitude predicates, I will treat it as a unit. I will also assume differences in person and number (je mangerais 'I would eat'; ils mangeraient 'they would eat') to be orthogonal. The second goal is be an analysis of the related phenomena in English, including the morphologically preterite forms of modals (should, ought to, might and could) and the attitude verb wish. Section 2 argues that the core shared meaning of the conditionnel is its possible counterfactuality. In the analysis proposed, should, for example, is a necessity modal embedded under a counterfactual operator like would. Section 3 proposes an account of the difference in meaning between, for example, should and would have to, based on certain characteristic discourse properties. 2. (Possible) Counterfactuality 2.1 Epistemic doit and devrai

Curvature suppresses the Rayleigh-Taylor instability

The dynamics of a thin liquid film on the underside of a curved cylindrical substrate is studied. The evolution of the liquid layer is investigated as the film thickness and the radius of curvature of the substrate are varied. A dimensionless parameter (a modified Bond number) that incorporates both geometric parameters, gravity, and surface tension is identified, and allows the observations to be classified according to three different flow regimes: stable films, films with transient growth of perturbations followed by decay, and unstable films. Experiments and theory confirm that, below a critical value of the Bond number, curvature of the substrate suppresses the Rayleigh-Taylor instability

Design of 3D-Printed Titanium Compliant Mechanisms

This paper describes 3D-printed titanium compliant mechanisms for aerospace applications. It is meant as a primer to help engineers design compliant, multi-axis, printed parts that exhibit high performance. Topics covered include brief introductions to both compliant mechanism design and 3D printing in titanium, material and geometry considerations for 3D printing, modeling techniques, and case studies of both successful and unsuccessful part geometries. Key findings include recommended flexure geometries, minimum thicknesses, and general design guidelines for compliant printed parts that may not be obvious to the first time designer