A Fixpoint Semantics of Event Systems with and without Fairness Assumptions

We present a fixpoint semantics of event systems. The semantics is presented in a general framework without concerns of fairness. Soundness and completeness of rules for deriving "leads-to" properties are proved in this general framework. The general framework is instantiated to minimal progress and weak fairness assumptions and similar results are obtained. We show the power of these results by deriving sufficient conditions for "leads-to" under minimal progress proving soundness of proof obligations without reasoning over state-traces

Diseño y construcción de programas mediante CSP

En este artículo presentamos, a través de un caso de estudio, el desarrollo de programas paralelos mediante métodos formales. El caso de estudio es el núcleo básico de un sistema operativo multitarea, y el método formal utilizado es la teoría de procesos secuenciales comunicantes, CSP. CSP es una teoría de programación que permite modelar sistemas mediante procesos comunicantes. Los procesos se modelan mediante un conjunto de eventos observables del sistema a implantar. CSP dispone de un lenguaje de especificación que permite describir el comportamiento de los procesos a través de sus eventos observables. La especificación inicial de un sistema debe ser lo suficientemente abstracta para indicar lo que el sistema debe hacer, sin dar detalles de cómo lo hace. Para dar tales detalles, una especificación debe refinarse de manera paulatina; esto se hace a través de pasos de refinamiento. En cada paso de refinamiento se debe probar que el refinamiento satisface los criterios de la especificación original; para dar tal garantía, CSP dispone de un conjunto de leyes algebraicas. El diseño y construcción del núcleo básico de un sistema operativo inicia con la especificación del entrelazamiento de acciones que modela nuestra intuición del paralelismo de un monitor multitareas. Esta especificación es refinada para itroducir los mecanismos necesarios para implantar la conmutación entre tareas del monitor. Se da la prueba formal de ciertos refinamientos y en otros, donde la complejidad aumenta, utilizamos FDR, un sistema que de manera automática, verifica la corrección de los refinamientos.Eje: Ingeniería de software. Bases de datosRed de Universidades con Carreras en Informática (RedUNCI

Interannual variability of the Tropical Atlantic independent of and associated with ENSO: Part II. The South Tropical Atlantic

Two dominant ocean-atmosphere modes of variability on interannual timescales were defined in Part I of this work, namely, the North Tropical Atlantic (NTA) and South Tropical Atlantic (STA) modes. In this paper we focus on the STA mode that covers the equatorial and sub-tropical South Atlantic. We show that STA events occurring in conjunction with ENSO have a preference for the southern summer season and seem to be forced by an atmospheric wave train emanating from the central tropical Pacific and travelling via South America, in addition to the more direct ENSO-induced change in the Walker circulation. They are lagged by one season from the peak of ENSO. These events show little evidence for other-than-localised coupled ocean-atmosphere interaction. In contrast, STA events occurring in the absence of ENSO favour the southern winter season. They appear to be triggered by a Southern Hemisphere wave train emanating from the Pacific sector, and then exhibit features of a self-sustaining climate mode in the tropical Atlantic. The southward shift of the inter tropical convergence zone that occurs during the warm phase of such an event triggers an extra tropical wave train that propagates downstream in the Southern Hemisphere. We present a unified view of the NTA and STA modes through our observational analysis of the interannnual tropical Atlantic variability

Interannual variability of the tropical Atlantic independent of and associated with ENSO: Part I. The North Tropical Atlantic

The interannual variability of the tropical Atlantic ocean-atmosphere system is examined using 50 years of sea-surface temperature (SST) and re-analysis data, and satellite data when available. A singular value decomposition analysis of 12- to 72-month bandpass filtered SST and zonal wind stress reveals two dominant modes of interannual variability. The SST anomalies are confined to the North Tropical Atlantic (NTA) in the first mode and extend over the equatorial and South Tropical Atlantic in the second mode. No evidence is found for an Atlantic SST dipole. The structure of the first (NTA) mode is examined in detail here, while the second mode has been described in a companion paper. In particular, the relationship of the NTA mode with El Nino-Southern Oscillation (ENSO) is investigated. There are 12 NTA events (seven warm and five cold) that are associated with ENSO, and 18 NTA events (seven warm and 11 cold) that are independent of ENSO. The ENSO-associated NTA events appear to be a passive response to remote ENSO forcing, mainly via a Pacific-North America (PNA)-like wave train that induces SST anomalies over the NTA through changes in the surface wind and latent heat flux. The NTA anomalies peak four months after ENSO. There does not appear to be an atmospheric response to the NTA SST anomalies as convection over the Atlantic is suppressed by the anomalous Walker circulation due to ENSO. The ENSO-independent NTA events also appear to be induced by an extratropical wave train from the Pacific sector (but one that is independent of Pacific SST), and forcing by the North Atlantic Oscillation (NAO) also contributes. As the event matures, the atmosphere does respond to the NTA SST anomalies, with enhanced convection over the Caribbean and a wave train that propagates northeastward to Europe

Surto de malária induzida entre usuários de drogas injetáveis

Five cases of malaria were detected among cocaine users by the local health service in Bauru, a city with a population of 260,000, located 324 km from S. Paulo, Brazil, during the first three weeks of July 1990. Autochthonous malaria had not occurred in Bauru since 1978, and all the five cases denied having recently traveled to endemic areas. An extensive epidemiologic survey conducted from July 19 to September 13 revealed that the 5 cases were in fact part of a malaria outbreak among endovenous drug users. Moreover, at least 114 other people, who had in the last three months shared syringes and needles with one or more proved cases, were also involved in the outbreak. One hundred and two people were identified and interviewed orally. The examination of thick smears made from samples collected from 99 of them confirmed 21 cases of vivax malaria. Three people with negative blood smears had an indirect imunofluorescent assay positive to P. vivax antigen. Although the index case could not be discovered, the investigation suggested that one or more people who had recently traveled to the Amazon region might have introduced the disease. The control of the outbreak was achieved after offering treatment with chloroquine (10 tablets) to confirmed cases and contacts, followed by weekly suppresive chloroquine (2 tablets) until the last contact was detected. Malaria examination of 91 blood samples also revealed a high prevalence of hepatitis B virus infection (40%) and HIV infection (58%) among those involved in the outbreak. The strategy used to identify the cases and the contacts and the difficulties overcome in carrying it through are described. It is also suggested that malaria might become an endemic disease among endovenous drug users in the State of S. Paulo.Em julho de 1990, foi registrado na cidade de Bauru, Estado de São Paulo, Brasil, um surto de malária envolvendo usuários de cocaína injetável. Uma ampla investigação epidemiológica, conduzida de 19 de julho a 13 de setembro, revelou que pelo menos 119 pessoas estavam envolvidas no surto, uma vez que haviam compartilhado seringas e agulhas com um ou mais casos confirmados nos 3 meses anteriores à ocorrência. Cento e duas dessas pessoas foram localizadas e entrevistadas, e destas, 99 foram submetidas a exame de gota espessa e 91 a exames sorológicos para malária. Foram confirmados por exame hemoscópico 21 casos de malária por P. vivax, e 3 outros tiveram exame sorológico positivo para P. vivax. O controle da transmissão foi obtido fornecendo-se cloroquina aos envolvidos no surto, numa dose inicial de 10 comprimidos, seguida de doses supressivas semanais de 2 comprimidos até que fosse identificado o último comunicante. Amostras de soro coletadas na ocasião revelaram, ao lado da malária, uma alta prevalência de infecções pelo HIV (58%) e pelo vírus da hepatite B (40%). Foram discutidas as dificuldades para o controle do surto e a possibilidade da malária vir a se tornar uma doença endêmica entre usuários de drogas injetáveis, no Estado de São Paulo

Bonding structure and hydrogen content in silicon nitride thin films deposited by the electron cyclotron resonance plasma method

The bonding structure and hydrogen content of amorphous hydrogenated silicon nitride (a-SiNx:H) thin films have been investigated by infrared spectroscopy and ion beam techniques. Electron cyclotron resonance plasma enhanced chemical vapor deposition was used to produce these films under different values of gas flow ratio, deposition temperature, and microwave power. The amount of bonded hydrogen was calculated from the N-H and Si-H infrared absorption bands. An increase of the SiH4 partial pressure during deposition was found to have the same effect on the H content as an increase of the substrate temperature: both cause a decrease of the N-H bond density and an increase in the number of Si-H bonds. This is explained by a competitive process in the formation of N-H and Si-H bonds during the growth of the film, whereby Si-H bonds are favored at the expense of N-H bonds when either the SiH4 flow or the substrate temperature are increased. Such tendency to chemical order is compared with previous results in which the same behavior was induced by thermal annealing or ion beam bombardment

On the Inconsistent Relationship between Pacific and Atlantic Niños

The tropical Atlantic wind response to El Niño forcing is robust, with weakened northeast trade winds north of the equator and strengthened southeast trade winds along and south of the equator. However, the relationship between sea surface temperature (SST) anomalies in the eastern equatorial Pacific and Atlantic is inconsistent, with El Niño events followed sometimes by warm and other times by cold boreal summer anomalies in the Atlantic cold tongue region. Using observational data and a hindcast simulation of the Nucleus for European Modeling of the Ocean (NEMO) global model at 0.5° resolution (NEMO-ORCA05), this inconsistent SST relationship is shown to be at least partly attributable to a delayed negative feedback in the tropical Atlantic that is active in years with a warm or neutral response in the eastern equatorial Atlantic. In these years, the boreal spring warming in the northern tropical Atlantic that is a typical response to El Niño is pronounced, setting up a strong meridional SST gradient. This leads to a negative wind stress curl anomaly to the north of the equator that generates downwelling Rossby waves. When these waves reach the western boundary, they are reflected into downwelling equatorial Kelvin waves that reach the cold tongue region in late boreal summer to counteract the initial cooling that is due to the boreal winter wind stress response to El Niño. In contrast, this initial cooling persists or is amplified in years in which the boreal spring northern tropical Atlantic warming is weak or absent either because of a positive North Atlantic Oscillation (NAO) phase or an early termination of the Pacific El Niño event

Understanding equatorial Atlantic interannual variability

An observational-based analysis of coupled variability in the equatorial Atlantic and its seasonality is presented. Regression analysis shows that the three elements of the Bjerknes positive feedback exist in the Atlantic and are spatially similar to those of the Pacific. The cross-correlation functions of the elements of the Bjerknes feedback are also similar and consistent with an ocean–atmosphere coupled mode. However, the growth rate in the Atlantic is up to 50% weaker, and explained variance is significantly lower. The Bjerknes feedback in the Atlantic is strong in boreal spring and summer, and weak in other seasons, which explains why the largest sea surface temperature anomalies (SSTAs) occur in boreal summer. Its seasonality is determined by seasonal variations in both atmospheric sensitivity to SSTA and SSTA sensitivity to subsurface temperature anomalies