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 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

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.

MAPK phosphorylation of connexin 43 promotes binding of cyclin E and smooth muscle cell proliferation

<p>Rationale: Dedifferentiation of vascular smooth muscle cells (VSMC) leading to a proliferative cell phenotype significantly contributes to the development of atherosclerosis. Mitogen-activated protein kinase (MAPK) phosphorylation of proteins including connexin 43 (Cx43) has been associated with VSMC proliferation in atherosclerosis.</p> <p>Objective: To investigate whether MAPK phosphorylation of Cx43 is directly involved in VSMC proliferation.</p> <p>Methods and Results: We show in vivo that MAPK-phosphorylated Cx43 forms complexes with the cell cycle control proteins cyclin E and cyclin-dependent kinase 2 (CDK2) in carotids of apolipoprotein-E receptor null (ApoE−/−) mice and in C57Bl/6 mice treated with platelet-derived growth factor–BB (PDGF). We tested the involvement of Cx43 MAPK phosphorylation in vitro using constructs for full-length Cx43 (Cx43) or the Cx43 C-terminus (Cx43CT) and produced null phosphorylation Ser>Ala (Cx43MK4A/Cx43CTMK4A) and phospho-mimetic Ser>Asp (Cx43MK4D/Cx43CTMK4D) mutations. Coimmunoprecipitation studies in primary VSMC isolated from Cx43 wild-type (Cx43+/+) and Cx43 null (Cx43−/−) mice and analytic size exclusion studies of purified proteins identify that interactions between cyclin E and Cx43 requires Cx43 MAPK phosphorylation. We further demonstrate that Cx43 MAPK phosphorylation is required for PDGF-mediated VSMC proliferation. Finally, using a novel knock-in mouse containing Cx43-MK4A mutation, we show in vivo that interactions between Cx43 and cyclin E are lost and VSMC proliferation does not occur after treatment of carotids with PDGF and that neointima formation is significantly reduced in carotids after injury.</p> <p>Conclusions: We identify MAPK-phosphorylated Cx43 as a novel interacting partner of cyclin E in VSMC and show that this interaction is critical for VSMC proliferation. This novel interaction may be important in the development of atherosclerotic lesions.</p&gt

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

A Robust Age Model for the Cryogenian Pocatello Formation of Southeastern Idaho (Northwestern USA) from Tandem in situ and Isotope Dilution U-Pb Dating of Volcanic Tuffs and Epiclastic Detrital Zircons

Tandem in situ and isotope dilution U-Pb analysis of zircons from pyroclastic volcanic rocks and both glacial and non-glacial sedimentary strata of the Pocatello Formation (Idaho, northwestern USA) provides new age constraints on Cryogenian glaciation in the North American Cordillera. Two dacitic tuffs sampled within glacigenic strata of the lower diamictite interval of the Scout Mountain Member yield high-precision chemical abrasion isotope dilution U-Pb zircon eruption and depositional ages of 696.43 ± 0.21 and 695.17 ± 0.20 Ma. When supplemented by a new high-precision detrital zircon maximum depositional age of ≤ 670 Ma for shoreface and offshore sandstones unconformably overlying the lower diamictite, these data are consistent with correlation of the lower diamictite to the early Cryogenian (ca. 717–660 Ma) Sturtian glaciation. These 670–675 Ma zircons persist in beds above the upper diamictite and cap dolostone units, up to and including a purported “reworked fallout tuff,” which we instead conclude provides only a maximum depositional age of ≤ 673 Ma from epiclastic volcanic detritus. Rare detrital zircons as young as 658 Ma provide a maximum depositional age for the upper diamictite and overlying cap dolostone units. This new geochronological framework supports litho- and chemostratigraphic correlations of the lower and upper diamictite intervals of the Scout Mountain Member of the Pocatello Formation with the Sturtian (716–660 Ma) and Marinoan (≤ 650–635 Ma) low-latitude glaciations, respectively. The Pocatello Formation thus contains a more complete record of Cryogenian glaciations than previously postulated