Dynamics of the North American continent

The forces that cause deformation of western North America have been debated for decades. Recent studies, primarily based on analysis of crustal stresses in the western United States, have suggested that the deformation of the region is mainly controlled by gravitational potential energy (GPE) variations and boundary loads, with basal tractions due to mantle flow playing a relatively minor role. We address these issues by modelling the deviatoric stress field over western North America from a 3-D finite element mantle circulation model with lateral viscosity variations. Our approach takes into account the contribution from both topography and shallow lithosphere structure (GPE) as well as that from deeper mantle flow in one single model, as opposed to separate lithosphere and circulation models, as has been done so far. In addition to predicting the deviatoric stresses we also jointly fit the constraints of geoid, dynamic topography and plate motion both globally and over North America, in order to ensure that the forces that arise in our models are dynamically consistent. We examine the sensitivity of the dynamic models to different lateral viscosity variations. We find that circulation models that include upper mantle slabs yield a better fit to observed plate velocities. Our results indicate that a model of GPE variations coupled with mantle convection gives the best fit to the observational constraints. We argue that although GPE variations control a large part of the deformation of the western United States, deeper mantle tractions also play a significant role. The average deviatoric stress magnitudes in the western United States range 30-40 MPa. The cratonic region exhibits higher coupling to mantle flow than the rest of the continent. We find that a relatively strong San Andreas fault gives a better fit to the observational constraints, especially that of plate velocity in western North America.

Assessing resilience and state-transition models with historical records of cheatgrass Bromus tectorum invasion in North American sagebrush-steppe

1. Resilience-based approaches are increasingly being called upon to inform ecosystem management, particularly in arid and semi-arid regions. This requires management frameworks that can assess ecosystem dynamics, both within and between alternative states, at relevant time scales. 2. We analysed long-term vegetation records from two representative sites in the North American sagebrush-steppe ecosystem, spanning nine decades, to determine if empirical patterns were consistent with resilience theory, and to determine if cheatgrass Bromus tectorum invasion led to thresholds as currently envisioned by expert-based state-and-transition models (STM). These data span the entire history of cheatgrass invasion at these sites and provide a unique opportunity to assess the impacts of biotic invasion on ecosystem resilience. 3. We used univariate and multivariate statistical tools to identify unique plant communities and document the magnitude, frequency and directionality of community transitions through time. Community transitions were characterized by 37-47% dissimilarity in species composition, they were not evenly distributed through time, their frequency was not correlated with precipitation, and they could not be readily attributed to fire or grazing. Instead, at both sites, the majority of community transitions occurred within an 8-10year period of increasing cheatgrass density, became infrequent after cheatgrass density peaked, and thereafter transition frequency declined. 4. Greater cheatgrass density, replacement of native species and indication of asymmetry in community transitions suggest that thresholds may have been exceeded in response to cheatgrass invasion at one site (more arid), but not at the other site (less arid). Asymmetry in the direction of community transitions also identified communities that were at-risk' of cheatgrass invasion, as well as potential restoration pathways for recovery of pre-invasion states. 5. Synthesis and applications. These results illustrate the complexities associated with threshold identification, and indicate that criteria describing the frequency, magnitude, directionality and temporal scale of community transitions may provide greater insight into resilience theory and its application for ecosystem management. These criteria are likely to vary across biogeographic regions that are susceptible to cheatgrass invasion, and necessitate more in-depth assessments of thresholds and alternative states, than currently available.

Fatores de risco de perda de documentos eletrônicos de caráter arquivístico em uma instituição pública : um estudo de caso na Câmara dos Deputados

Identifica os riscos de perda de documentos eletrônicos de caráter arquivístico em uma organização, tomando por base um estudo de caso na Câmara dos Deputados. Analisa as diversas origens desses riscos na instituição : visão estratégica do problema, monitoração e auditoria, treinamento, conservação e obsolescência tecnológica, políticas e responsabilidades, aspectos técnicos, administrativos e culturais, sistemas eletrônicos de gestão arquivística de documentos, conhecimento de normas e padrões.

O lado invisível da participação política : gestão da informação dos mecanismos digitais de participação política nos parlamentos da América Latina, com uma análise do caso da Câmara dos Deputados do Brasil

Examina uma das dimensões dos mecanismos digitais de interação e participação política oferecidos por parlamentos para a sociedade - a gestão da informação. São mapeadas as formas de participação política empregadas nos portais legislativos da América Latina, com o objetivo de conhecer as informações que cercam as iniciativas e contextualizar o estudo de caso da Câmara dos Deputados do Brasil. Procura-se entender como a Câmara dos Deputados do Brasil realiza a coleta, a organização, a distribuição, o armazenamento e o uso da informação concernente aos mecanismos de interação e participação política, de caráter multilateral, empregados em seu Portal. Conclui-se que os parlamentos latino-americanos colocam à disposição da sociedade dezenas de canais digitais de interação e participação, como uma tendência irreversível das democracias modernas, mas a gestão da informação inerente às experiências ainda é um desafio a ser alcançado.

Soundings: the Newsletter of the Monterey Bay Chapter of the American Cetacean Society. 1980

(PDF contains 39 pages.)

Soundings: the Newsletter of the Monterey Bay Chapter of the American Cetacean Society. 1981

Missing the April issue. (PDF has 26 pages.)

Soundings: the Newsletter of the Monterey Bay Chapter of the American Cetacean Society. 1982

(PDF contains 34 pages.)

Soundings: the Newsletter of the Monterey Bay Chapter of the American Cetacean Society. 1983

(PDF contains 112 pages.)

Soundings: the Newsletter of the Monterey Bay Chapter of the American Cetacean Society. 1984

(PDF contains 96 pages.)

Soundings: the Newsletter of the Monterey Bay Chapter of the American Cetacean Society. 1985

(PDF contains 84 pages.)

Soundings: the Newsletter of the Monterey Bay Chapter of the American Cetacean Society. 1986

(PDF contains 62 pages.)

Soundings: the Newsletter of the Monterey Bay Chapter of the American Cetacean Society. 1987

Missing November issue. (PDF contains 62 pages.)

Soundings: the Newsletter of the Monterey Bay Chapter of the American Cetacean Society. 1988

Missing July, August, October issues. (PDF contains 56 pages.)

Soundings: the Newsletter of the Monterey Bay Chapter of the American Cetacean Society. 1989

Missing June issue. (PDF contains 50 pages.)

Soundings: the Newsletter of the Monterey Bay Chapter of the American Cetacean Society. 1990

(PDF contains 118 pages.)