970 resultados para Sigma Xi, the Scientific Research Society of North America


Relevância:

100.00% 100.00%

Publicador:

Resumo:

Este trabajo tiene como objetivo describir la experiencia de implementación y desarrollo del Portal de revistas de la Facultad de Humanidades y Ciencias de Educación de la Universidad Nacional de La Plata a fin de que pueda ser aprovechada por todos aquellos que emprendan iniciativas de características similares. Para ello, se realiza en primer lugar un repaso por la trayectoria de la Facultad respecto a la edición de revistas científicas y la labor bibliotecaria para contribuir a su visualización. En segundo orden, se exponen las tareas llevadas adelante por la Prosecretaría de Gestión Editorial y Difusión (PGEyD) de la Facultad para concretar la puesta en marcha del portal. Se hace especial referencia a la personalización del software, a la metodología utilizada para la carga masiva de información en el sistema (usuarios y números retrospectivos) y a los procedimientos que permiten la inclusión en repositorio institucional y en el catálogo web de todos los contenidos del portal de manera semi-automática. Luego, se hace alusión al trabajo que se está realizando en relación al soporte y a la capacitación de los editores. Se exponen, después, los resultados conseguidos hasta el momento en un año de trabajo: creación de 10 revistas, migración de 4 títulos completos e inclusión del 25de las contribuciones publicadas en las revistas editadas por la FaHCE. A modo de cierre se enuncian una serie de desafíos que la Prosecretaría se ha propuesto para mejorar el Portal y optimizar los flujos de trabajo intra e interinstitucionales

Relevância:

100.00% 100.00%

Publicador:

Resumo:

Mode of access: Internet.

Relevância:

100.00% 100.00%

Publicador:

Resumo:

Chemical abstracts

Relevância:

100.00% 100.00%

Publicador:

Resumo:

List of officers and members for 1909, 1914, 1919, 1931, separately paged are included in v. 2, 8, 13, 25, respectively.

Relevância:

100.00% 100.00%

Publicador:

Resumo:

Mode of access: Internet.

Relevância:

100.00% 100.00%

Publicador:

Resumo:

Mode of access: Internet.

Relevância:

100.00% 100.00%

Publicador:

Resumo:

The drawings by Mr. Faxon have been engraved (v. 1-5 by Philibert and Eugène Picart) under the direction of A. Riocreux.

Relevância:

100.00% 100.00%

Publicador:

Resumo:

"Published by order of the International Lodge of North America."

Relevância:

100.00% 100.00%

Publicador:

Resumo:

Better understanding of seed-bank dynamics of Echinochloa colona, Urochloa panicoides and Hibiscus trionum, major crop weeds in sub-tropical Australia, was needed to improve weed control. Emergence patterns and seed persistence were investigated, with viable seeds sown at different depths in large in-ground pots. Seedlings of all species emerged between October and March when mean soil temperatures were 21-23C. However, E. colona emerged as a series of flushes predominantly in the first year, with most seedlings emerging from 0-2 cm. Urochloa panicoides emerged mostly as a single large flush in the first two years, with most seedlings emerging from 5 cm. Hibiscus trionum emerged as a series of flushes over three seasons, initially with majority from 5 cm and then 0-2 cm in the later seasons. Longevity of the grass seed was short, with <5% remaining after burial at 0-2 cm for 24 months. In contrast, 38% of H. trionum seeds remained viable after the same period. Persistence of all species increased significantly with burial depth. These data highlight that management strategies need to be tailored for each species, particularly relating to the need for monitoring, application times for control tactics, impact of tillage, and time needed to reduce the seed-bank to low numbers.

Relevância:

100.00% 100.00%

Publicador:

Resumo:

Covers the history of the study of boring sponges, taxonomy and distributions. Also includes identification of species, descriptions, key, references and plates. (PDF contains 30 pages)

Relevância:

100.00% 100.00%

Publicador:

Resumo:

This thesis consists of two separate parts. Part I (Chapter 1) is concerned with seismotectonics of the Middle America subduction zone. In this chapter, stress distribution and Benioff zone geometry are investigated along almost 2000 km of this subduction zone, from the Rivera Fracture Zone in the north to Guatemala in the south. Particular emphasis is placed on the effects on stress distribution of two aseismic ridges, the Tehuantepec Ridge and the Orozco Fracture Zone, which subduct at seismic gaps. Stress distribution is determined by studying seismicity distribution, and by analysis of 190 focal mechanisms, both new and previously published, which are collected here. In addition, two recent large earthquakes that have occurred near the Tehuantepec Ridge and the Orozco Fracture Zone are discussed in more detail. A consistent stress release pattern is found along most of the Middle America subduction zone: thrust events at shallow depths, followed down-dip by an area of low seismic activity, followed by a zone of normal events at over 175 km from the trench and 60 km depth. The zone of low activity is interpreted as showing decoupling of the plates, and the zone of normal activity as showing the breakup of the descending plate. The portion of subducted lithosphere containing the Orozco Fracture Zone does not differ significantly, in Benioff zone geometry or in stress distribution, from adjoining segments. The Playa Azul earthquake of October 25, 1981, Ms=7.3, occurred in this area. Body and surface wave analysis of this event shows a simple source with a shallow thrust mechanism and gives Mo=1.3x1027 dyne-cm. A stress drop of about 45 bars is calculated; this is slightly higher than that of other thrust events in this subduction zone. In the Tehuantepec Ridge area, only minor differences in stress distribution are seen relative to adjoining segments. For both ridges, the only major difference from adjoining areas is the infrequency or lack of occurrence of large interplate thrust events.

Part II involves upper mantle P wave structure studies, for the Canadian shield and eastern North America. In Chapter 2, the P wave structure of the Canadian shield is determined through forward waveform modeling of the phases Pnl, P, and PP. Effects of lateral heterogeneity are kept to a minimum by using earthquakes just outside the shield as sources, with propagation paths largely within the shield. Previous mantle structure studies have used recordings of P waves in the upper mantle triplication range of 15-30°; however, the lack of large earthquakes in the shield region makes compilation of a complete P wave dataset difficult. By using the phase PP, which undergoes triplications at 30-60°, much more information becomes available. The WKBJ technique is used to calculate synthetic seismograms for PP, and these records are modeled almost as well as the P. A new velocity model, designated S25, is proposed for the Canadian shield. This model contains a thick, high-Q, high-velocity lid to 165 km and a deep low-velocity zone. These features combine to produce seismograms that are markedly different from those generated by other shield structure models. The upper mantle discontinuities in S25 are placed at 405 and 660 km, with a simple linear gradient in velocity between them. Details of the shape of the discontinuities are not well constrained. Below 405 km, this model is not very different from many proposed P wave models for both shield and tectonic regions.

Chapter 3 looks in more detail at recordings of Pnl in eastern North America. First, seismograms from four eastern North American earthquakes are analyzed, and seismic moments for the events are calculated. These earthquakes are important in that they are among the largest to have occurred in eastern North America in the last thirty years, yet in some cases were not large enough to produce many good long-period teleseismic records. A simple layer-over-a-halfspace model is used for the initial modeling, and is found to provide an excellent fit for many features of the observed waveforms. The effects on Pnl of varying lid structure are then investigated. A thick lid with a positive gradient in velocity, such as that proposed for the Canadian shield in Chapter 2, will have a pronounced effect on the waveforms, beginning at distances of 800 or 900 km. Pnl records from the same eastern North American events are recalculated for several lid structure models, to survey what kinds of variations might be seen. For several records it is possible to see likely effects of lid structure in the data. However, the dataset is too sparse to make any general observations about variations in lid structure. This type of modeling is expected to be important in the future, as the analysis is extended to more recent eastern North American events, and as broadband instruments make more high-quality regional recordings available.

Relevância:

100.00% 100.00%

Publicador:

Resumo:

A review of the relative productivity and value of the shad fisheries of North America as reflected in recorded commercial catches. A review of reasons for the decline that are biological and socioeconomic. Factors that have been held responsible are: pollution; destruction or impairment of spawning and nursery areas; overfishing; hydroelectric and canal dams; natural fluctuations in abundance. Natural catastrophes, parasites, and predators are not considered important in causing the decrease in commercial production. Attempts to rehabilitate the fisheries by various means of stocking artificially-reared fry and pond-reared fingerling shad, appear to have failed in every instance. Introduction of shad fry on the Pacific Coast has resulted in a major fishery. The most significant program is a controlled catch management plan, operating at this time [1953] only in Maryland.

Relevância:

100.00% 100.00%

Publicador:

Resumo:

EXTRACT (SEE PDF FOR FULL ABSTRACT): The seasonal cycles of coastal wind stress, adjusted sea level height (ASL), shelf currents and water temperatures off the west coast of North America (35°N to 48°N) were estimated by fitting annual and semiannual harmonics to data from 1981-1983. Longer records of monthly ASL indicate that these two harmonics adequately represent the long-term monthly average seasonal cycle, and that the current measurement period is long enough to define the seasonal cycles, with relatively small errors in magnitude and phase.