1,378 research outputs found
Hyperbolic outer billiards : a first example
We present the first example of a hyperbolic outer billiard. More precisely
we construct a one parameter family of examples which in some sense correspond
to the Bunimovich billiards.Comment: 11 pages, 8 figures, to appear in Nonlinearit
A conceptual model for building design coordination using open source tools
Building Design Coordination is the process of communicating and integrating multidisciplinary designs into a single, coherent set of information that can be used for construction,
to anticipate problems that would otherwise only be raised on the construction site. As
projects grow in complexity and size, digital communication tools and other technological
improvements have made it possible for physically distant design teams to collaborate in novel
ways. More recently, BIM (Building Information Modelling), has opened even greater
possibilities, although the design process nevertheless is often one of trial and error,
demanding on each small change multiple possibilities to be considered, with decisions
requiring to be validated among designers and other project stakeholders. Regardless of all the
advantages that BIM has brought to the industry, testing for design changes in BIM models
often requires a big effort and is a time-consuming activity that should be avoided whenever
simpler processes can be used.
Further developments on this study will propose a framework for building design coordination,
using a non-relational graph database. The system can track design issues between unlimited users, organized into teams, handling formal project documents and keeping an historical
record of the design development timeline. Since all the information regarding the design
development process is stored in the form of Nodes and Relationships these can be intuitively
be manipulated making it easier for teams to provide input on design decisions in real time
with least cost impact to the project, providing at the same time access to pertinent
information on the status of design issues and how the various stakeholders are contributing
to the project. Through the use of reliable open source tools, a prototype can be implemented
and made available to the industry professionals for testing, providing guidelines for modelling
a Building Design Coordination system.info:eu-repo/semantics/publishedVersio
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Comparison of Structure and Properties of Femtosecond and Nanosecond Laser-Structured Silicon
We compare the optical properties, chemical composition, and crystallinity of silicon microstructures formed in the presence of SF6 by femtosecond laser irradiation and by nanosecond laser irradiation. In spite of very different morphology and crystallinity, the optical properties and chemical composition of the two types of microstructures are very similar. The structures formed with femtosecond (fs) pulses are covered with a disordered nanocrystalline surface layer less than 1 um thick, while those formed with nanosecond (ns) pulses have very little disorder. Both ns-laser-formed and fs-laser-formed structures absorb near-infrared (1.1 – 2.5 um) radiation strongly and have roughly 0.5% sulfur impurities.Engineering and Applied Science
Performance of a thermally deformable mirror for correction of low-order aberrations in laser beams
The thermally deformable mirror is a device aiming at correcting beam-wavefront distortions for applications where classical mechanical methods are precluded by noise considerations, as in advanced gravitational wave interferometric detectors. This moderately low-cost technology can be easily implemented and controlled thanks to the good reproducibility of the actuation. By using a flexible printed circuit board technology, we demonstrate experimentally that a device of 61 actuators in thermal contact with the back surface of a high-reflective mirror is able to correct the low-order aberrations of a laser beam at 1064 nm and could be used to optimize the mode matching into Fabry-Perot cavities
Contact complete integrability
Complete integrability in a symplectic setting means the existence of a
Lagrangian foliation leaf-wise preserved by the dynamics. In the paper we
describe complete integrability in a contact set-up as a more subtle structure:
a flag of two foliations, Legendrian and co-Legendrian, and a
holonomy-invariant transverse measure of the former in the latter. This turns
out to be equivalent to the existence of a canonical
structure on the leaves of the co-Legendrian foliation. Further, the above
structure implies the existence of contact fields preserving a special
contact 1-form, thus providing the geometric framework and establishing
equivalence with previously known definitions of contact integrability. We also
show that contact completely integrable systems are solvable in quadratures. We
present an example of contact complete integrability: the billiard system
inside an ellipsoid in pseudo-Euclidean space, restricted to the space of
oriented null geodesics. We describe a surprising acceleration mechanism for
closed light-like billiard trajectories
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Growth of laser-induced damage during repetitive illumination of HfO2-SiO2 multilayer mirror and polarizer coatings
As peak fluence of high power lasers is increased, it becomes necessary to tolerate damage on mirrors, polarizers. To study how different types of damage morphologies initiate and grow during repetitive illumination, hafnia-silica multilayer mirror and polarizer coatings were laser damage tested. The coatings were prepared by e-beam evaporation and irradiated with a 3-ns pulse at 1064 nm. The damage morphology was recorded after each shot to determine the types of damage that cause massive unstable failure and lower the optic`s functional damage threshold. Results were summarized on damage stability maps plotting the average damage size vs number of shots for fluences ranging from 10 to 40 J/cm{sup 2}. The maps indicate that the commonly observed damage morphologies (pits, flat bottom pits, scalds, outer layer delamination) have distinct growth behaviors and influence the value of the functional damage threshold differently. While pits are stable up to fluences as high as 40 J/cm{sup 2}, flat bottom pits can grow during repetitive illumination above a critical fluence of about 35 J/cm{sup 2}. Scalds are formed in the first shot and never grow at fluences below 40 J/cm{sup 2}. Finally, delaminates are highly unstable and have the potential for damaging the coating catastrophically above 15 J/cm{sup 2}. Results show that delaminate damage should be prevented; this knowledge has allowed coatings development efforts to focus on eliminating the origin of such damage morphology
Virtual blebbistatin: A robust and rapid software approach to motion artifact removal in optical mapping of cardiomyocytes
Fluorescent reporters of cardiac electrophysiology provide valuable information on heart cell and tissue function. However, motion artifacts caused by cardiac muscle contraction interfere with accurate measurement of fluorescence signals. Although drugs such as blebbistatin can be applied to stop cardiac tissue from contracting by uncoupling calcium-contraction, their usage prevents the study of excitation-contraction coupling and, as we show, impacts cellular structure. We therefore developed a robust method to remove motion computationally from images of contracting cardiac muscle and to map fluorescent reporters of cardiac electrophysiological activity onto images of undeformed tissue. When validated on cardiomyocytes derived from human induced pluripotent stem cells (iPSCs), in both monolayers and engineered tissues, the method enabled efficient and robust reduction of motion artifact. As with pharmacologic approaches using blebbistatin for motion removal, our algorithm improved the accuracy of optical mapping, as demonstrated by spatial maps of calcium transient decay. However, unlike pharmacologic motion removal, our computational approach allowed direct analysis of calcium-contraction coupling. Results revealed calcium-contraction coupling to be more uniform across cells within engineered tissues than across cells in monolayer culture. The algorithm shows promise as a robust and accurate tool for optical mapping studies of excitation-contraction coupling in heart tissue
Influence of carbon and nitrogen on electronic structure and hyperfine interactions in fcc iron-based alloys
Carbon and nitrogen austenites, modeled by Fe8N and Fe8C superstructures are
studied by full-potential LAPW method. Structure parameters, electronic and
magnetic properties as well as hyperfine interaction parameters are obtained.
Calculations prove that Fe-C austenite can be successfully modeled by ordered
Fe8C superstructure. The results show that chemical Fe-C bond in Fe8C has
higher covalent part than in Fe8N. Detailed analysis of electric field gradient
formation for both systems is performed. The calculation of electric field
gradient allow us to carry out a good interpretation of Moessbauer spectra for
Fe-C and Fe-N systems.Comment: 8 pages, 3 figures, IOP-style LaTeX, submitted to J. Phys. Condens.
Matte
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Evolving microstructure: Mechanisms of electromigration in stressed aluminum-copper and copper films
We report on a collective body of work wherein we have studied the mass transport phenomena which are likely to be operative during stress driven changes in microstructure arising from electromigration and stress voiding. Our goal is to understand such microstructural evolution leading to failure of the metal lines or interconnects associated with integrated electronic circuits or chips. This work, when complete, will lead to improved electronics performance and reliability and faster product development arising from accurate and predictive models of wearout phenomena. We report on the role of thermal induced strain leading to hole and hillock formation, the influence of grains structure on the reliability of Al- based interconnects, and the observation of counter-current electromigration of Ua in Al grain boundaries
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