Optimizing signal-to-error ratio in standing wave ultrasonic measurements

Standing wave ultrasonic techniques for the measurement of very small changes in acoustic attenuation and phase velocity are discussed. Enhanced sensitivity to these small changes was achieved by making the specimen part of a composite ultrasonic resonator. It was found that a point of maximum sensitivity on the response of such an ultrasonic resonator need not coincide with a point of maximum signal-to-error ratio. A model is presented and analyzed which takes into account error due to long term (low frequency) noise effects such as gain drifts and dc level shifts. This model yields a quantitative value for the signal-to-error ratio in which the signal is defined as the ideal change in the monitored response and the error as the difference between the experimentally measured change and the signal. The specific frequency dependent forms for the ultrasonic response and the sensitivity enhancement factor were used to predict the operating point on a mechanical resonance corresponding to maximum signal-to-error ratio

Control dynamics analysis of the Centaur stage propellant utilization control system

Stability properties of Centaur propellant utilization control syste

Formation of viable cell fragments by treatment with colchicine

Time-lapse cinematography of human fibroblasts revealed that mitotic cells separated into numerous cell fragments containing varying amounts of chromatin and cytoplasm when treated with colchicine. As cell fragments were very loosely attached to the surface of the culture vessel during their formation, they could be easily detached like mitotic cells by gently shaking the vessel and thus separated from normal interphase cells. Fragments obtained by this procedure were able to exclude trypan blue indicating, therefore, an intact cell membrane. When placed into Petri dishes many of them attached to and even spread out on the surface. Five hours later the majority of the attached fragments incorporated [3H]leucine. Time-lapse films showed that fragments were able to extend and retract pseudopodia at least for several hours after their formation. Although the fragments degenerated within a few days, in the present experiments the possibility was not excluded that fragments which had lost only a very small amount of chromatin and cytoplasm survived for longer periods of time. The observations clearly indicate viability of many newly formed fragments

UV micro-irradiation of the Chinese hamster cell nucleus and caffeine post-treatment immunocytochemical localization of DNA photolesions in cells with partial and generalized chromosome shattering

UV micro-irradiation of a small part of the Chinese hamster nucleus and caffeine post-incubation often results in shattered chromosomes at the first post-irradiation mitosis. In some of these mitotic cells, chromosome shattering is restricted to a few chromosomes spatially related in a small area of the metaphase spread; in others, shattering includes the whole chromosome complement. These 2 types of damage have been called partial and generalized chromosome shattering (PCS and GCS). Using antisera that specifically react with UV-irradiated DNA, we identified micro-irradiated chromatin in interphase nuclei and in mitotic cells with PCS or GCS by indirect immunofluorescence microscopy. In PCS, immunofluorescence staining was found in the damaged area, while the surrounding intact chromosomes were not stained. In GCS, staining was also restricted to a small region of the shattered chromosome complement. In other experiments, cells synchronized in G1 were micro-irradiated in the nucleus, pulse-labelled with [3H]thymidine and post-incubated with caffeine. Autoradiographs of cells with GCS showed unscheduled DNA synthesis restricted to a small chromatin region. Our data present direct evidence that the distribution of DNA photolesions does not coincide with the sites of chromosomal damage in GCS. As a working hypothesis, we propose that an indirect mechanism is involved in the induction of GCS by which DNA photolesions in a small nuclear segment induce shattering of both micro-irradiated and non-irradiated chromosomes

Promoviendo la justicia social a través del aprendizaje-servicio en la formación de maestros de Educación Infantil

As early childhood teacher education programs have begun to place greater emphasis on standards and accountability, there has been less focus on working with the community, and especially working on important social justice issues (Kroll, 2013). In this paper we argue that integrating service-learning and teacher education is a strategy for increasing awareness of social justice issues for young children, age three to grade three. Through the use of questionnaires and interviews to collect our data, we found that implementing a cascading service-learning model in teacher education programs has a positive transformative effect on Pre-Service Teachers. Additionally, we examined the effects of social justice service-learning projects on young children. The results from the data indicated that implementing a social justice service-learning project with these participants had a great impact or transformation on them.Como en los programas de formación del profesorado para la primera infancia han empezado a poner mayor énfasis en los estándares y la rendición de cuentas, se está haciendo menos hincapié en el trabajo con la comunidad, y especialmente en trabajos centrados en temas relevantes de justicia social (Kroll, 2013). En este artículo se argumenta que la integración del aprendizaje-servicio y la formación del profesorado es una estrategia para aumentar la conciencia sobre temas de justicia social con los niños pequeños, desde los tres años hasta tercer grado. A través del uso de cuestionarios y entrevistas para la recolección de datos, se encontró que la implementación de un modelo de aprendizaje-servicio en cascada en los programas de formación del profesorado tiene un efecto transformador positivo en profesores en formación. Además, se examinaron los efectos de los proyectos de aprendizaje-servicio de justicia social con niños pequeños. Los resultados de los datos indican que la implementación de un proyecto de aprendizaje-servicio de justicia social con estos participantes tiene un gran impacto o transformación en ellos.Os programas de formação do professorado para a primeira infância começaram a pôr maior ênfase nos padrões e a prestação de contas, dando-se menos ênfase ao trabalho com a comunidade, e especialmente em trabalhos centrados em temas relevantes de justiça social (Kroll, 2013). Neste artigo se argumenta que a integração do aprendizagem-serviço e a formação do professorado é uma estratégia para aumentar a consciência sobre temas de justiça social com as crianças pequenas, desde os três anos até o terceiro grau. Através do uso de questionário e entrevistas para a coleta de dados, encontrou-se que a implementação de um modelo de aprendizagem-serviço em cascata nos programas de formação de professores tem um efeito transformador positivo em professores em formação. Ademais, examinaramse os efeitos dos projetos de aprendizagem-serviço de justiça social com crianças pequenas. Os resultados dos dados indicam que a implantação de um projeto de aprendizagem-serviço de justiça social com estes participantes causa neles um grande impacto ou transformação

Multifold node authentication in mobile ad hoc networks

An ad hoc network is a collection of nodes that do not need to rely on a predefined infrastructure to keep the network connected. Nodes communicate amongst each other using wireless radios and operate by following a peer-to-peer network model. In this article we propose a multifold node authentication approach for protecting mobile ad hoc networks. The security requirements for protecting data link and network layers are identified and the design criteria for creating secure ad hoc networks using multiple authentication protocols are analysed. Such protocols, which are based on zero knowledge and challenge response techniques, are presented through proofs and simulation results