The Effect Of Roughness On Bottom Loss From Elastic Ocean Bottoms

Acoustic interaction with the ocean bottom profoundly affects propagation in shallow waters. However, most forward ocean bottom interactions are modeled as if the bottom were a flat interface or use a simple model to quantify the additional loss. These assumptions either neglect or over-estimate the enhancement of ocean bottom loss due to scattering into the bottom. Scattering from and into elastic bottoms is particularly interesting since it can induce the production of an interface wave. In this study, finite element analysis is used to calculate acoustic scattering from elastic ocean bottoms with varying degrees of roughness. The forward scattering loss from these bottoms is calculated as a function of angle and then compared with the flat bottom reflection coefficient in order to gain insight on the conditions under which enhancement of bottom loss by rough interface scattering is significant.Applied Research Laboratorie

Wave Propagation In Water-Saturated Sand And Grain Contact Physics

Measurements in sandy ocean sediments over a broad range of frequencies show that the sound speed dispersion is significantly greater than that predicted by the Biot-Stoll model with constant coefficients, and the observed sound attenuation does not seem to follow a consistent power law. The observations may be explained in terms of the Biot-Stoll model with frequency-dependent complex frame bulk and shear moduli that are governed by the grain-grain contact physics, and random motion at the grain level. In the case of water-saturated sands, the contact stiffness is dominated by squirt flow and viscous drag of a thin fluid film that permeates the contact area. Using this approach, the observed sound and shear wave speeds and attenuations may be modeled over a broad band of frequencies.Applied Research Laboratorie

The Evolution Of Sediment Acoustic Models

Sediment acoustic models contain two connected components, the geo-physical description of the sediment and the model of acoustic processes. Geo-physical descriptors are used in the classification of sediments, and they are based on grain size, density and other physical descriptors. Acoustic sediment models were initially fluid approximations that were simple to implement. As the need for accuracy increased, the fluid model was extended to stratified fluid and visco-elastic models. The latter, with five frequency-independent parameters, appeared to be consistent with sediment acoustic data up to the 1980s. More recent experimental data have revealed discrepancies in the frequency-dependence of attenuation and sound speed, particularly in the case of sandy sediments, which cover a large fraction of the continental shelves. Broad-band acoustic measurements of wave speeds and attenuations are more consistent with a poro-elastic model, consisting of Biot's theory with extensions to account for the physics of granular media. Aside from terminology, there is a fundamental difference between viscoelastic and poro-elastic theories. The former is based on two types of waves, a compressional wave and a shear wave, while the latter has an additional compressional wave, often called the Biot wave. There are currently two approaches to the development of sediment acoustic models: (a) visco-elastic models with frequency dependent parameters that mimic the observed behavior, and (b) poro-elastic models that reflect the physical processes. It is shown that (a) would be a significant improvement over existing models, but (b) is the preferred solution.Applied Research Laboratorie

Towards Understanding the Politics of Flex Crops and Commodities: Implications for Research and Policy Advocacy

This discussion paper offers a preliminary exploration of the concept and phenomenon of “flex crops and commodities”, building on an earlier and initial analysis and abbreviated idea put forward by some of the authors of this paper. We discuss the dual concepts of the “multiple-ness” and “flexible-ness” of crops and commodities as two distinct but intertwined dimensions of some key crops and commodities. These key crops and commodities are shaped by the changing global context that is itself (re)moulded in large part by the convergence of multiple crises and the various responses to those crises. Building on these dual concepts, we will identify and explain the minimum requirements for crop and commodity flexing. We will also try to typologize the various types of crop and commodity flexing, namely, “real flexing”, “anticipated/speculated flexing”, and “imagined flexing”—to allow for a deeper examination of these interrelated processes. The boundaries between these categories (multiple/flexible, real, anticipated and imagined) are not always clearly demarcated, requiring us to examine the issue of flex crops and commodities in a more interlinked manner. We will focus our initial exploration on the political dynamics of such interactions and intersections, looking into the factors that encourage or discourage, facilitate or hinder maximization of the “multiple-ness” and/or “flexible-ness” of particular crops and commodities. Finally, and as a way of closing, we will outline the implications of these dynamics for how we think of engaged research, public actions and policy advocacy, including a brief discussion of what we call “flex policy narratives” by governments and corporations.

Espectrofotometría fotoeléctrica de los planetas Marte, Júpiter y Saturno

Se compararon las curvas de magnitudes relativas de los planetas mencionados con las curvas respectivas de estrellas de tipo espectral cercano al Sol, en el rango comprendido entre 3.000 y 6.000 Å.Asociación Argentina de Astronomí

Espectrofotometría fotoeléctrica de los planetas Marte, Júpiter y Saturno

Se compararon las curvas de magnitudes relativas de los planetas mencionados con las curvas respectivas de estrellas de tipo espectral cercano al Sol, en el rango comprendido entre 3.000 y 6.000 Å.Asociación Argentina de Astronomí

Espectrofotometría fotoeléctrica de los planetas Marte, Júpiter y Saturno

Se compararon las curvas de magnitudes relativas de los planetas mencionados con las curvas respectivas de estrellas de tipo espectral cercano al Sol, en el rango comprendido entre 3.000 y 6.000 Å.Asociación Argentina de Astronomí

Interaction between nitric oxide signaling and gap junctions: Effects on vascular function

Nitric oxide signaling, through eNOS (or possibly nNOS), and gap junction communication are essential for normal vascular function. While each component controls specific aspects of vascular function, there is substantial evidence for cross-talk between nitric oxide signaling and the gap junction proteins (connexins), and more recently, protein protein association between eNOS and connexins. This review will examine the evidence for interaction between these pathways in normal and diseased arteries, highlight the questions that remain about the mechanisms of their interaction, and explore the possible interaction between nitric oxide signaling and the newly discovered pannexin channels. This article is part of a Special Issue entitled: The Communicating junctions, composition, structure and characteristics. (C) 2011 Elsevier B.V. All rights reserved

Influence of Coolant Flow Rate on Tool Life and Wear Development in Cryogenic and Wet Milling of Ti-6Al-4V

AbstractThe use of cryogenic coolants has emerged as a way to improve productivity in machining Ti-alloys. In this study, liquid carbon dioxide is used as coolant in face milling of Ti-6Al-4V with PVD coated inserts. The influence of coolant flow rate on tool life is studied by means of controlled experiments. Tool life is shown to improve with higher flow rates of coolant, the effect being stronger in cryogenic compared to wet milling due to the fact that the cryogenic coolant delays the wear development. The tool life is determined by notch wear irrespective of coolant nature in titanium milling. Different analyses were used to understand the mechanism behind the delay of notch wear development when using carbon dioxide coolant