Modeling truncated pixel values of faint reflections in MicroED images.

The weak pixel counts surrounding the Bragg spots in a diffraction image are important for establishing a model of the background underneath the peak and estimating the reliability of the integrated intensities. Under certain circumstances, particularly with equipment not optimized for low-intensity measurements, these pixel values may be corrupted by corrections applied to the raw image. This can lead to truncation of low pixel counts, resulting in anomalies in the integrated Bragg intensities, such as systematically higher signal-to-noise ratios. A correction for this effect can be approximated by a three-parameter lognormal distribution fitted to the weakly positive-valued pixels at similar scattering angles. The procedure is validated by the improved refinement of an atomic model against structure factor amplitudes derived from corrected micro-electron diffraction (MicroED) images

MicroED data collection and processing.

MicroED, a method at the intersection of X-ray crystallography and electron cryo-microscopy, has rapidly progressed by exploiting advances in both fields and has already been successfully employed to determine the atomic structures of several proteins from sub-micron-sized, three-dimensional crystals. A major limiting factor in X-ray crystallography is the requirement for large and well ordered crystals. By permitting electron diffraction patterns to be collected from much smaller crystals, or even single well ordered domains of large crystals composed of several small mosaic blocks, MicroED has the potential to overcome the limiting size requirement and enable structural studies on difficult-to-crystallize samples. This communication details the steps for sample preparation, data collection and reduction necessary to obtain refined, high-resolution, three-dimensional models by MicroED, and presents some of its unique challenges

Wormholes in String Theory

A wormhole is constructed by cutting and joining two spacetimes satisfying the low energy string equations with a dilaton field. In spacetimes described by the "string metric" the dilaton energy-momentum tensor need not satisfy the weak or dominant energy conditions. In the cases considered here the dilaton field violates these energy conditions and is the source of the exotic matter required to maintain the wormhole. There is also a surface stress-energy, that must be produced by additional matter, where the spacetimes are joined. It is shown that wormholes can be constructed for which this additional matter satisfies the weak and dominant energy conditions, so that it could be a form of "normal" matter. Charged dilaton wormholes with a coupling between the dilaton and the electromagnetic field that is more general than in string theory are also briefly discussed.Comment: 9 pages, LaTex, submitted to Phys. Rev.

Lifetime multi-objective optimization of maintenance of existing steel structures

In this paper, the lifetime performance of deteriorating structures, defined by their time dependent condition index and reliability index, is analyzed. The effect of preventive and essential maintenance actions on performance and cost in predicted, and the optimal times of application of preventive and essential maintenance actions are found. Due to significant uncertainty in the initial performance, effects of deterioration and of maintenance actions, as well as, times of application and cost of maintenance actions, the analysis is performed in a probabilistic framework. The reduction in performance due to deterioration is simulated using an extension of the model proposed by Frangopol (1998). The probabilistic condition index, reliability index, and cumulative cost profiles are computed using Latin Hypercube simulation. Optimization of times of application is performed using genetic algorithms. Results show the significant importance of preventive maintenance actions in reducing the lifetime cost of existing structures, but also their fundamental role of essential maintenance action in keeping structures safe and serviceable during the entire lifetime

Multi-objective probabilistic optimization of bridge lifetime maintenance : novel approach

Due to the increase in deterioration of the existing civil infrastructure, in particular bridge networks, governments and highway agencies are trying to find methods that allow a consistent and rational management of existing bridges. In this paper, a novel approach is presented. This approach uses multi-objective probabilistic optimization over time and defines performance of existing bridges in terms of lifetime condition, safety, and cost. The proposed approach aims at providing a tool for optimal maintenance management policy definition of a large group of similar structures. Consequently, emphasis is put on the use of limited information and low computational cost. Applications to real cases are presented showing the applicability of the method as well as its advantages in terms of reduction of costs and improvements in performance.(undefined

Evaluación de la presión de fallo del edificio de contención de una central nuclear tipo PWR-W tres lazos. Parte II: Simulación numérica

En este articulo se presentan los resultados de la simulación numérica efectuada para evaluar la presión de fallo debida a un accidente del edificio de contención de una central nuclear PWR- W tres lazos. El modelo computacional tridimensional de elementos finitos utilizado ha sido descrito en la primera parte del artículo1. En esta segunda parte se analiza la influencia que tiene sobre la presión de fallo de la contención tanto la inclusión en el modelo estructural de la losa de cimentación como los efectos térmicos. El estudio numérico demuestra que puede llevarse a cabo la simulación del proceso de fallo utilizando un modelo estructural que no incluya la losa de cimentación y la carga de temperatura. Finalmente, se presentan y se discuten los resultados de un estudio probabilista de simulación de la presión de fallo y se resumen las conclusiones.Peer Reviewe

Evaluación de la presión de fallo del edificio de contención de una central nuclear tipo PWR-W tres lazos. Parte 1: Metodología

Se presenta en este artículo la metodología seguida para la evaluación de la presión de fallo del edificio de contención de una central nuclear PWR-W tres lazos. El análisis debe ser totalmente tridimensional para permitir la consideración de los elementos estructurales más significativos, tener en cuenta el comportamiento no lineal de los materiales y estudiar la sensibilidad de los resultados ante ciertas incertidumbres asociadas a algunos parámetros. El modelo computacional incluye las ecuaciones constitutivas para el hormigón y las armaduras de acero, la discretización espacial (elementos isoparamétricos con armado) y la resolución del problema estructural no lineal mediante algoritmos incrementales-iterativos con aceleradores de convergencia. Se describen los modelos estructurales utilizados y los análisis llevados a cabo para su calibración.Peer Reviewe

Assessment of algorithms for mitosis detection in breast cancer histopathology images

The proliferative activity of breast tumors, which is routinely estimated by counting of mitotic figures in hematoxylin and eosin stained histology sections, is considered to be one of the most important prognostic markers. However, mitosis counting is laborious, subjective and may suffer from low inter-observer agreement. With the wider acceptance of whole slide images in pathology labs, automatic image analysis has been proposed as a potential solution for these issues. In this paper, the results from the Assessment of Mitosis Detection Algorithms 2013 (AMIDA13) challenge are described. The challenge was based on a data set consisting of 12 training and 11 testing subjects, with more than one thousand annotated mitotic figures by multiple observers. Short descriptions and results from the evaluation of eleven methods are presented. The top performing method has an error rate that is comparable to the inter-observer agreement among pathologists