15,221 research outputs found
Desde la geometría hasta la representación generativa. La búsqueda de una solución optimizada en el proyecto del Club Táchira (Caracas, 1955)
No full text<p>La construcción de formas de la geometría compleja procede, a menudo, de la búsqueda de una solución “optimizada” con referencia a un determinado parámetro elegido. Ese método es perfectamente reconocible en el proyecto del Club Táchira.</p><p>A través del análisis de la génesis geométrica del proyecto y de la reconstrucción del modelo utilizando instrumentos de representación paramétrica, la investigación quiere demostrar cómo el empleo de estos instrumentos puede hacer visible un proceso al alcance sólo de algunos, también a diseñadores no especializados, que puedan controlar la complejidad sin ignorar los principios de eficiencia.</p></jats:p
Aspects of Holography beyond AdS BMS superrotations in higher dimensions
No full textA crucial role in the problem of four-dimensional asymptotically flat spacetime holographyis long believed to be played by the Bondi-Metzner-(van der Burg)-Sachs (BMS) asymptotic symmetry group. The discovery of deep relationships between such symmetries andgravitational infrared effects - pertrubative soft theorems and gravitational wave memories - has sparkled new interest in the problem. In this context, superrotations extendthe standard general relativistic definition of BMS group. While there has been somedebate on the extension of BMS to higher dimensions (d > 4), very little has been saidabout superrotations. In this thesis we initiate a systematic study of such structures. We provide evidence that consistency of superrotation Killing fields with a fully non-lineard > 4 gravitational configuration space requires different boundary conditions than thoseconsidered in literature. The first such evidence comes from cosmic (d − 3)-branes, whichare conjectured to be related to superrotations in d > 4 as a natural generalization ofthe relationship between cosmic strings in d = 4 and d = 4 superrotations. The generalboundary conditions may be taken to define asymptotically locally Minkowski spacetimes.The first part of the thesis recaps fundamentals of AdS/CFT - the most well known example of holographic duality - and the second moves to asymptotically flat spacetimes. Thereview material marks the conceptual and technical differences between AdS holographyand the attempts at flat holography. A recurring theme is that of variational principlesand asymptotic charges. Their mutual consistency is pivotal in dynamically realisingAdS/CFT. We take this requirement as the basis of asymptotically flat holography andthe analysis of the configuration space is fundamental to the construction of well-defined variational principles and the phase space
General null asymptotics and superrotation-compatible configuration spaces in d≥4
No full textWe address the problem of consistent Campiglia-Laddha superrotations in d > 4 by solving Bondi-Sachs gauge vacuum Einstein equations at the non-linear level with the most general boundary conditions preserving the null nature of infinity. We discuss how to generalise the boundary structure to make the configuration space compatible with supertanslation-like and superrotation-like transformations. One possibility requires the time-independent boundary metric on the cuts of to be non-Einstein, while the other sticks to Einstein but time-dependent metrics. Both are novel features with respect to the four-dimensional case, where time-dependence of the two-dimensional cross-sectional metric is not required and the Einstein condition is trivially satisfied. Other cases are also discussed. These conditions imply that the configuration spaces are not asymptotically flat in the standard sense. We discuss the implications on the construction of the phase space and the relationship with soft scattering theorems. We show that in even spacetime dimensions, the initial data compatible with such asymptotic symmetries produce maximally polyhomogeneous expansions of the metric and we advance a potential interpretation of this structure in terms of AdS/CFT and realizations of Ricci-flat holography
Cosmic branes and asymptotic structure
No full textSuperrotations of asymptotically flat spacetimes in four dimensions can be interpreted in terms of including cosmic strings within the phase space of allowed solutions. In this paper we explore the implications of the inclusion of cosmic branes on the asymptotic structure of vacuum spacetimes in dimension d > 4. We first show that only cosmic (d-3)-branes are Riemann flat in the neighbourhood of the brane, and therefore only branes of such dimension passing through the celestial sphere can respect asymptotic local flatness. We derive the asymptotically locally flat boundary conditions associated with including cosmic branes in the phase space of solutions. We find the asymptotic expansion of vacuum spacetimes in d=5 with such boundary conditions; the expansion is polyhomogenous, with logarithmic terms arising at subleading orders in the expansion. The asymptotically locally flat boundary conditions identified here are associated with an extended asymptotic symmetry group, which may be relevant to soft scattering theorems and memory effects
Preliminary aerothermal design of axial compressors
No full textThis dissertation documents a compressor preliminary design study conducted by the author
in fulfilment of his MSc thesis requirements. The compressor is intended for a new
development engine within the 20Klbf thrust category, planned to be used on a short-haul
aircraft, namely the ERJ-190.
A market research suggests that there exists a definite opportunity for a commercially
profitable engine within this thrust class. Furthermore, the proposed new engine is projected
to outperform current production engines on critical issues such as fuel efficiency and
operability.
By and large, the objectives of this work have been achieved and a compressor design and
layout is suggested, which matched or exceeded all the initial requirements. The quality of
the results from this study are thought to be of sufficient detail to allow a further, more
detailed development study to resolve some subtle pending issues. It is expected that, some
compressor stages may have to be altered slightly during detailed design to augment their
performance and ease of manufacture and assembly.
Throughout this study, the importance of the compressor design figure of merits, pertaining
to a short haul engine, has been outlined and their interaction on the design process is well
documented. Furthermore, some rather unorthodox objectives such as compressor
performance retention and reliability have been discussed. The author approached these
subjects in an innovative way due to the limited non-proprietary knowledge available on
these issues, especially considering their implications within preliminary design.
Furthermore, the author developed and tested a new preliminary turbomachinery design code,
named Turbodev, which can be used as an aid in future compressor design endeveours.
Turbodev can handle most types of compressor layouts and generates an overall aerodynamic
assessment of the turbomachinery performance.
In conclusion; this documentation and the associated literature review aim to provide the
reader with an overview of the work done and yield a better understanding of the decisions
that face any design bureau when developing a new or modified engine component.The research work disclosed in this publication is partially funded by the
Strategic Educational Pathways Scholarship Scheme (Malta). The
scholarship is part-financed by the European Union – European Social
Fund under Programme II – Cohesion Policy 2007-2013
Surgical treatment of acetabular fractures in the elderly: a systematic review of the results
No full textWe performed a systematic review of the literature involving a number of databases to identify studies that included outcomes of surgical treatment of acetabular fractures in patients aged > 55 year
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No full textXML wordt in veel situaties gebruikt, en voor dat gebruik worden talloze tools gebouwd. Er zijn verschillende manieren om XML-tools te ontwikkelen, en dit artikel behandelt de voor- en nadelen van de verschillende alternatieven. XML en XML-tools De uitgever Kluwer biedt verschillende soorten informatie aan, zoals wetteksten en belastinggidsen. Deze informatie heeft vaak een vaste structuur: een wet heeft bijvoorbeeld altijd een nummer, en een belastinggids beschrijft componenten die voorkomen op het inkomstenbelastingformulier. De structuur verschilt echter van informatiesoort tot informatiesoort. Voor de beschrijving van een document van dit soort structuren gebruikt Kluwer de Extensible Markup Language (XML) [6], en voor de beschrijving van een structuur zelf een Document Type Definitions (DTD) of een Schema. Een manier om de populariteit van een onderwerp te bepalen is Google te vragen hoe vaak een term voorkomt op het Web, of eigenlijk, in de databases van Google. Zo komen de Beatles bijna 3 miljoen keer voor, en ABBA honderdduizend keer. XML komt ongeveer 20 miljoen keer voor, en verslaat daarmee alle programmeertalen behalve Java. Een andere populariteitsmaat is het aantal vierkante meters boekenplank dat in beslag wordt genomen door boeken over het onderwerp in een academische boekhandel. In mijn lokale boekhandel verslaat XML menig andere nieuwe technologie. Maar wat is XML? XML is een eenvoudig, flexibel tekstformaat, dat veel gebruikt wordt voor het uitwisselen van data op het internet, maar ook tussen bedrijven onderling, en tussen bedrijven en hun klanten. Hier is een voorbeeld van een XML document
ClueS Collusive Stealing Framework
No full text<p>Please check the code here for now (anonymous git repository): </p><p>https://anonymous.4open.science/r/federated-stealing-D782/README.md</p>
Fabrication of Nanoslits with <111> Etching TSWE Method
No full textIn this paper, we report a modified three step anisotropic wet etching (TSWE) method to fabricate solid-state silicon nanoslits. The slit-opening process is performed by <111> crystal plane etching. The etching rate of the <111> crystal plane is reasonably slow as it is only 1/45 of the <100> etching rate, thus allowing and therefore good slits-opening controllability. By slowly etching the <111> crystal plane, the over-etching was effectively reduced. Perfectly rectangular nanoslits with different dimensions were successfully obtained. The smallest achieved feature size of the nanoslit is 8.3 nm.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Electronic Components, Technology and Material
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