Fragile Spaces

This book consists of a range of essays covering the complex crises, tensions and dilemmas but also the positive potential in the meeting of Jews with Western culture. In numerous contexts and through the work of fascinating individuals and thinkers, the work examines some of the consequences of political, cultural and personal rupture, as well as the manifold ways in which various Jewish intellectuals, politicians (and occasionally spies!) sought to respond to these ruptures and carve out new, sometimes profound, sometimes fanciful, options of thought and action. It also delves critically into the attacks on liberal and Enlightenment humanism. In almost all the essays the fragility of things is palpably present and the book touches on some of the ironies, problematics and functions of responses to that condition. The work mirrors the author's ongoing fascination with the always fraught, fragile and creatively fecund confrontation of Jews (and others) with European modernity, its history, politics, culture and self-definition. In a time of increasing anxiety and feelings of fragility, this work may be helpful in understanding how people at an earlier (and sometimes contemporary) period sought to come to terms with a similar predicament

A magic approach to octonionic Rosenfeld spaces

In his study on the geometry of Lie groups, Rosenfeld postulated a strict relation between all real forms of exceptional Lie groups and the isometries of projective and hyperbolic spaces over the (rank-2) tensor product of Hurwitz algebras taken with appropriate conjugations. Unfortunately, the procedure carried out by Rosenfeld was not rigorous, since many of the theorems he had been using do not actually hold true in the case of algebras that are not alternative nor power-associative. A more rigorous approach to the definition of all the planes presented more than thirty years ago by Rosenfeld in terms of their isometry group, can be considered within the theory of coset manifolds, which we exploit in this work, by making use of all real forms of Magic Squares of order three and two over Hurwitz normed division algebras and their split versions. Within our analysis, we find 7 pseudo-Riemannian symmetric coset manifolds which seemingly cannot have any interpretation within Rosenfeld's framework. We carry out a similar analysis for Rosenfeld lines, obtaining that there are a number of pseudo-Riemannian symmetric cosets which do not have any interpretation \`a la Rosenfeld.Comment: 28 pages, 3 figure

Un sistema de construcción para climas tropicales basado en pórticos arriostrados de bambú

A low-cost housing system was developed for use in tropical countries, specifically Haiti, with the aims of minimizing environmental impact (including carbon emissions), maximizing use of local and preferably recycled materials, and using local labor. The housing system integrates low-strength concrete blocks (made using recycled concrete aggregate), an innovative seismically-resistant bamboo frame, earthen plasters, bamboo trusses, and metal deck roofs. The bamboo frame relies on flexural yielding of a short rebar dowel to provide ductile performance at a controlled strength level. The plinth walls below the frame and short rebar dowel protects the bamboo from moisture. The top of a plastic soda bottle is used to protect the rebar from moisture and to seal the base of the bamboo culm, allowing mortar to be introduced into the culm above. This paper focuses on the experimental and analytical results of the flexural yielding of the rebar dowel to establish the structural design of this critical component of the system for resisting wind and seismic loads.En este artículo se presenta un sistema de construcción de viviendas de bajo coste para países tropicales en los cuales existe riesgo sísmico. Los objetivos de este trabajo son generar bajo impacto medioambiental (incluyendo las emisiones de carbono), empleo de materiales locales, preferiblemente reciclados, y mano de obra local. Para esta construcción se han empleado bloques de hormigón de baja resistencia (con agregado reciclado) junto con un innovador sistema de pórticos de bambú, botellas de plástico, vigas de bambú y cubiertas de chapa. El comportamiento dúctil de la estructura se garantiza introduciendo una barra de acero en la base del pórtico de bambú. Para proteger el bambú de la humedad, el pórtico se monta sobre un zócalo. Los resultados experimentales y analíticos obtenidos se utilizan para el diseño estructural del sistema frente a cargas de viento y sísmicas

Evaluation of the marginal fit of three margin designs of resin composite crowns using CAD/CAM

OBJECTIVES: To examine the marginal fit of resin composite crowns manufactured with the CEREC 3 system employing three different margin designs; bevel, chamfer and shoulder, by means of a replica technique and a luting agent. METHODS: Three master casts were fabricated from an impression of a typodont molar tooth and a full-coverage crown prepared with a marginal finish of a bevel, a chamfer and a shoulder. Each cast was replicated 10 times (n = 10). Scanning of the replicas and crown designing was performed using the CEREC ScanTM system. The crowns were milled from Paradigm MZ100TM composite resin blocks. The marginal fit of the crowns was evaluated with a replica technique (AquasilTM LV, Dentsply), and with a resin composite cement (RelyXTM Unicem, AplicapTM) and measured with a travelling microscope. Statistical analysis was performed using two-way ANOVA. RESULTS: For the replica technique the average marginal gaps recorded were: Bevel Group 105±34 mm, Chamfer Group 94±27 mm and Shoulder Group 91±22 mm. For the resin composite cement the average marginal gaps were: Bevel Group 102±28 mm, Chamfer Group 91±11 mm and Shoulder Group 77±8 mm. Two-way ANOVA analysis showed that there was no statistically significant difference between the three groups of finishing lines regardless of the cementation technique used. CONCLUSIONS: The marginal gap of resin composite crowns manufactured with the CEREC 3 system is within the range of clinical acceptance, regardless of the finishing line prepared or the cementation technique used

Peak Displacements and Interstory Drifts on Nonlinear Multi Degree of Freedom Systems Using Principal Component Analysis.

Principal Components Analysis (PCA) is a method to extract the principal components (or modes) of response from recorded or computed response data, of systems exhibiting linear and/or nonlinear response. For linear systems, the PCA mode shapes coincide with the elastic mode shapes, if the nodal mass is uniformly distributed. For nonuniform mass distributions, the PCA modes are related to the elastic modes. The PCA technique is particularly valuable when applied to systems responding nonlinearly, because it identifies the 'predominant mode' of response and the degree to which the response is in this mode. This paper illustrates the use of the PCA technique for estimating floor and interstory drifts for a 12-story moment-resistant frame responding to earthquake ground motions. Linear and nonlinear responses are considered, and the observed mode shapes and the accuracy of drift estimates are discussed. The interaction of modal amplitudes in time is considered in detail. The peak roof drift and interstory drifts are expressed as linear combinations of the PCA modes, and are represented graphically, together with the observed interaction response. A technique is described to determine peak values of these quantities by maximizing the drift functions relative to the observed modal interactions

An Estimate of the Yield Displacement of Coupled Walls for Seismic Design

A formula to estimate the yield displacement observed in the pushover analysis of coupled wall lateral force-resisting systems is presented. The estimate is based on the results of an analytical study of coupled walls ranging from 8 to 20 stories in height, with varied amounts of reinforcement in the reinforced concrete coupling beams and walls, subjected to first-mode pushover analysis. An example illustrates the application of these estimates to the performance-based seismic design of coupled walls