Speeding up liquid crystal SLMs using overdrive with phase change reduction

Nematic liquid crystal spatial light modulators (SLMs) with fast switching times and high diffraction efficiency are important to various applications ranging from optical beam steering and adaptive optics to optical tweezers. Here we demonstrate the great benefits that can be derived in terms of speed enhancement without loss of diffraction efficiency from two mutually compatible approaches. The first technique involves the idea of overdrive, that is the calculation of intermediate patterns to speed up the transition to the target phase pattern. The second concerns optimization of the target pattern to reduce the required phase change applied to each pixel, which in addition leads to a substantial reduction of variations in the intensity of the diffracted light during the transition. When these methods are applied together, we observe transition times for the diffracted light fields of about 1 ms, which represents up to a tenfold improvement over current approaches. We experimentally demonstrate the improvements of the approach for applications such as holographic image projection, beam steering and switching, and real-time control loops

La Habana: apuntes sobre la evolución de un asentamiento urbano en el siglo XIX

Roberto Marte (biografía): Roberto Marte es historiador egresado de la Universidad Autónoma de Santo Domingo y de la Universidad Complutense de Madrid, donde se doctoró. Es especialista en historia latinoamericana y ha sido profesor de historia en diversas universidades. Su libro "Estadísticas y documentos históricos sobre Santo Domingo (1805-1890)" le hizo merecedor del Premio Nacional de Historia de República Dominicana. Otros libros y artículos suyos son: "Santo Domingo en los manuscritos de Juan Bautista Muñoz: transcripción y glosas" (1981), "Escritos autobiográficos sobre Santo Domingo" (en coautoría con Hilde Domin) (1999), "La oralidad sobre el pasado insular y el concepto de nación en el mundo rural dominicano del siglo XIX" (2009) y "El testimonio autobiográfico en la historia dominicana: un análisis crítico" (2014). ----------------/---------------------- Gustavo Moré G. (biografía): Nació en Santo Domingo el 3 de mayo de 1956. Es de nacionalidad dominicana e italiana. Se graduó de arquitecto en la Universidad Pedro Henríquez Ureña (UNPHU). Luego obtuvo una beca de las Naciones Unidas que le permitió realizar una maestría en restauración de monumentos y centros históricos en la Universidad de los Estudios de Florencia, Italia. Ganó la beca Cátedra Antoni Gaudí para el curso de paisajismo y jardinería que ofrece el gobierno español, y después realizó el curso "Techniques of Traditional Town Planning" en la Universidad de Harvard. Es uno de los ganadores de la prestigiosa beca Fullbright. Parte de su tiempo lo ha dedicado a la enseñanza, tanto en universidades dominicanas (la UNPHU, Universidad Iberoamericana, UNIBE) como en instituciones extranjeras. Entre sus principales obras arquitectónicas están los edificios de la Embajada de Italia en Santo Domingo, Rosario Dominicana, Procuraduría General de la República, Parque Central de Santiago, Suprema Corte de Justicia (junto a Juan Caro), la Fundación Global, Democracia y Desarrollo y el proyecto de desarrollo urbano y arquitectónico Cap Cana. En cuanto a libros, ha publicado los siguientes: "Los tiempos de la libertad 1961-1978", "Modernidad y contradicción en la arquitectura de la República Dominicana", "Atlas cartográfico de la arquitectura en los centros históricos del gran Caribe", "Historia para la construcción de la arquitectura dominicana (1492-2008)" (editor). Es editor de la revista "Archivos de Arquitectura Antillana". Ha ganado premios en distintas bienales de arquitectura en Iberoamérica y ha recibido varios homenajes y reconocimientos por su trayectoria.El auge económico-productivo que vivió La Habana a partir de la segunda mitad del siglo XVIII y sus efectos en la fisonomía urbanística y arquitectónica de la ciudad en el siglo XIX es el tema que se desarrolla en el presente trabajo. Gracias a que esa ciudad fue punto de abastecimiento de la flota española de la Carrera de Indias, su actividad económica había sido ya eminente, pero creció y se intensificó aún más debido a diversos factores. Primero fueron las inversiones en las grandes construcciones defensivas del Morro y los castillos de la Cabaña y Atarés, las cuales promovieron el empleo masivo de mano de obra esclava y fomentaron a su alrededor el incremento del comercio y el crédito. Luego estuvieron las medidas para intensificar la producción azucarera, cultivo que se vio altamente favorecido por la disminución de los gravámenes, la libertad en la trata de esclavos, la revolución de Saint-Domingue (Haití) y la progresiva apertura comercial de la colonia a los mercados internacionales, lo que llegó a su culmen con el establecimiento formal del libre comercio en 1818. De forma paralela al auge económico, la población de la ciudad creció: de unas 50,000 almas, en 1774, se pasó a unas 94,023 en 1827 y a 250,000 a fines del siglo XIX. El crecimiento físico de la ciudad (a lo largo del noroeste costero y hacia el suroeste) es acompañado por una serie de reglamentaciones que norman las dimensiones de las nuevas cuadrículas y calles, la jerarquización de las vías, el tránsito vehicular e incluso los parámetros y atributos arquitectónicos que deben tener las edificaciones según la zona en que se encuentren. Grandes proyectos urbanos surgen a partir de la colaboración de la oficialidad española y la aristocracia criolla. Al terminar el siglo XIX, La Habana es una ciudad plenamente moderna en la que predominan los componentes arquitectónicos barrocos y neoclásicos

Avalanches in a Bose-Einstein condensate

Collisional avalanches are identified to be responsible for an 8-fold increase of the initial loss rate of a large 87-Rb condensate. We show that the collisional opacity of an ultra-cold gas exhibits a critical value. When exceeded, losses due to inelastic collisions are substantially enhanced. Under these circumstances, reaching the hydrodynamic regime in conventional BEC experiments is highly questionable.Comment: 4 pages, 2 figures, 1 tabl

Dyadic existential rules

In the field of ontology-based query answering, existential rules (a.k.a. tuple-generating dependencies) form an expressive Datalog-based language to specify implicit knowledge. The presence of existential quantification in rule-heads, however, makes the main reasoning tasks undecidable. To overcome this limitation, in the last two decades, a number of classes of existential rules guaranteeing the decidability of query answering have been proposed. Unfortunately, such classes are typically based on different syntactic conditions imposing the development of different ad hoc reasoners. This paper introduces a novel general condition that allows to define, systematically, from any decidable class C of existential rules, a new class called Dyadic-C that enjoys the following properties: (i) it is decidable; (ii) it generalizes C; (iii) it keeps the same data complexity as C; and (iv) it can exploit any reasoner for query answering over C. Additionally, the paper proposes a simple and elegant syntactic condition that gives rise to the class Ward+ generalizing the well-known decidable classes Shy and Ward, and being included in Dyadic-Shy

Wind Field and Trajectory Models for Tornado-Propelled Objects

A mathematical model to predict the trajectory of tornado born objects postulated to be in the vicinity of nuclear power plants is developed. An improved tornado wind field model satisfied the no slip ground boundary condition of fluid mechanics and includes the functional dependence of eddy viscosity with altitude. Subscale wind tunnel data are obtained for all of the missiles currently specified for nuclear plant design. Confirmatory full-scale data are obtained for a 12 inch pipe and automobile. The original six degree of freedom trajectory model is modified to include the improved wind field and increased capability as to body shapes and inertial characteristics that can be handled. The improved trajectory model is used to calculate maximum credible speeds, which for all of the heavy missiles are considerably less than those currently specified for design. Equivalent coefficients for use in three degree of freedom models are developed and the sensitivity of range and speed to various trajectory parameters for the 12 inch diameter pipe are examined

Explaining the environmentally sustainable consumer behavior: a social capital perspective

Purpose - The purpose of this study is to examine the effects of social capital within a community on the adoption of consumer eco-behaviour or environmentally sustainable behaviour of consumers. The authors draw on the behavioural perspective model (BPM) of consumer behaviour and social capital theory in arguing that social capital shapes a consumer\u27s knowledge of environmental issues and pro-environmental attitudes, which in turn influence a consumer\u27s perceived capability to engage in eco-behaviour. Design/methodology/approach - This study uses partial least squares approach to structural equation modelling of survey data involving 1,044 consumers in the Philippines. It involves testing of a measurement model to examine the validity and reliability of the constructs used in the study. This is followed by testing of the structural models to test the hypothesised relationships of the constructs. Findings - The results suggest the substantive influence of social capital on environmental knowledge, pro-environmental attitudes and eco-capability. Both knowledge and attitudes have positive effects on eco-capability, which in turn positively shapes eco-behaviour. Research limitations/implications - Future studies can examine how social capital as a multi-dimensional construct impacts context-specific consumer behaviour. Practical implications - Social and environmental marketing may focus on social network activation to encourage eco-behaviours of consumers. Social implications - Findings highlight the role of social capital within one\u27s community as a resource channel to encourage environmentally responsible consumer behaviour. Originality/value - The study extends the BPM by offering a social capital view as a more nuanced explanation of consumer eco-behaviour

Optomechanical deformation and strain in elastic dielectrics

Light forces induced by scattering and absorption in elastic dielectrics lead to local density modulations and deformations. These perturbations in turn modify light propagation in the medium and generate an intricate nonlinear response. We generalise an analytic approach where light propagation in one-dimensional media of inhomogeneous density is modelled as a result of multiple scattering between polarizable slices. Using the Maxwell stress tensor formalism we compute the local optical forces and iteratively approach self-consistent density distributions where the elastic back-action balances gradient- and scattering forces. For an optically trapped dielectric we derive the nonlinear dependence of trap position, stiffness and total deformation on the object's size and field configuration. Generally trapping is enhanced by deformation, which exhibits a periodic change between stretching and compression. This strongly deviates from qualitative expectations based on the change of photon momentum of light crossing the surface of a dielectric. We conclude that optical forces have to be treated as volumetric forces and that a description using the change of photon momentum at the surface of a medium is inappropriate

Orbital angular momentum exchange in an optical parametric oscillator

We present a study of orbital angular momentum transfer from pump to down-converted beams in a type-II Optical Parametric Oscillator. Cavity and anisotropy effects are investigated and demostrated to play a central role in the transverse mode dynamics. While the idler beam can oscillate in a Laguerre-Gauss mode, the crystal birefringence induces an astigmatic effect in the signal beam that prevents the resonance of such mode.Comment: 10 pages, 8 figures, regular articl

Wave Packet Echoes in the Motion of Trapped Atoms

We experimentally demonstrate and systematically study the stimulated revival (echo) of motional wave packet oscillations. For this purpose, we prepare wave packets in an optical lattice by non-adiabatically shifting the potential and stimulate their reoccurence by a second shift after a variable time delay. This technique, analogous to spin echoes, enables one even in the presence of strong dephasing to determine the coherence time of the wave packets. We find that for strongly bound atoms it is comparable to the cooling time and much longer than the inverse of the photon scattering rate

Critical collisional opacity in a Bose-Einstein condensate

Summary form only given. In a Bose-Einstein condensate, due to the very low temperature, the s-wave scattering length can be used as a measure for the strength of the atom-atom interaction. Under typical experimental conditions, this interaction is weak and hence can be treated in terms of a mean field. However, when scattering length is large or the density is high, the mean field approximation breaks down. In this collisional (hydrodynamic) regime, effects of the interactions such as quantum depletion or shifts in the frequencies of the elementary excitations become large. It is therefore of great interest to study condensates close to or in the collisional regime. It has been demonstrated in recent experiments that the scattering length and thus the interactions among the atoms can be tuned by means of a Feshbach resonance (Inouye et al, 1998; Courteille et al., 1998; Vuleti et al., 1999; Cornish et al., 2000). In the vicinity of Feshbach resonances, however, the increase of the cross-section for elastic collisions is accompanied by a dramatic increase of particle losses. In this paper we report on the observation of anomalous losses from a 87Rb condensate with a high column density in the absence of an inelastic scattering resonance