Dynamics analysis of a system of hinge-connected flexible bodies

The subject of this work is the dynamics of flexible space vehicles modelled by a chain of rigid and elastic bodies with tree structure. The aim of this investigation is to obtained an impedance matrix giving in frequency domain the response of the structure to external forces. We show that it is possible to obtain an expansion of this impedance matrix in terms of an infinite set of modal frequencies termed constrained modes and an expansion of the inverse of this impedance matrix in terms of an other set of modes. The work is a generalization of the theory made by Hugues [3] and others for systems with star structure.     

Tidal frequency dynamics of a Southern Brazil coastal lagoon: Choking and short period forced oscillations

The Patos Lagoon is a choked, microtidal coastal laggon situated in southern Brazil between 30°S and 32°S. The response of the lagoon to tidal oscillations is studied through data analysis and numerical modeling experiments. Two types of high frequency oscillations are observed in the tidal frequency band: mixed tides, predominantly diurnal; and forced oscillations having a period of 24 h occurring in the inner lagoon. In the southern portion of the lagoon, tides are selectively filtered by the entrance channel. The main diurnal constituent O₁ is linearly attenuated as it progresses landwards. In the inner parts of the lagoon, 24-h oscillations are mainly forced by the combined effect of diurnal tides and sea breeze action. They are tied with a natural period of oscillation of 24 h. Results also indicate that these are not inertial frequency oscillations, despite the lagoon being placed in a critical 30°S area. The interaction between astronomical tides and meteorological effects produces a complicated picture for tidal forecasting derived from data collected inside the lagoon.     

Impactites of the Haughton impact structure,Devon Island,Canadian High Arctic

Abstract— Contrary to the previous interpretation of a single allochthonous impactite lithology, combined field, optical, and analytical scanning electron microscopy (SEM) studies have revealed the presence of a series of impactites at the Haughton impact structure. In the crater interior, there is a consistent upward sequence from parautochthonous target rocks overlain by parautochthonous lithic (monomict) breccias, through allochthonous lithic (polymict) breccia, into pale grey allochthonous impact melt breccias. The groundmass of the pale grey impact melt breccias consists of microcrystalline calcite, silicate impact melt glass, and anhydrite. Analytical data and microtextures indicate that these phases represent a series of impact‐generated melts that were molten at the time of, and following, deposition. Impact melt glass clasts are present in approximately half of the samples studied. Consideration of the groundmass phases and impact glass clasts reveal that impactites of the crater interior contain shock‐melted sedimentary material from depths of >920 to <1880 m in the pre‐impact target sequence. Two principal impactites have been recognized in the near‐surface crater rim region of Haughton. Pale yellow‐brown allochthonous impact melt breccias and megablocks are overlain by pale grey allochthonous impact melt breccias. The former are derived from depths of >200 to <760 m and are interpreted as remnants of the continuous ejecta blanket. The pale grey impact melt breccias, although similar to the impact melt breccias of the crater interior, are more carbonate‐rich and do not appear to have incorporated clasts from the crystalline basement. Thus, the spatial distribution of the crater‐fill impactites at Haughton, the stratigraphic succession from target rocks to allochthonous impactites, the recognition of large volumes of impact melt breccias, and their probable original volume are all analogous to characteristics of coherent impact melt layers in comparatively sized structures formed in crystalline targets.     

Winners and Losers in Marine Conservation: Fishers' Displacement and Livelihood Benefits from Marine Reserves

Marine reserves can create both benefits and costs to fishers. This article explores the perceptions of fishers in Kenya and Seychelles about displacement, spillover, and overall impacts of local marine reserves on their livelihoods. We test whether these perceptions are different among fishers from different geographic and socioeconomic conditions. Sixty-six percent of fishers had been displaced from marine reserves or coastal development and 90% believed they had caught fishes that spilled over from marine reserves. Poorer fishers in Kenya were both displaced from, and also felt like they benefited from, marine reserves. This highlights how people's experiences with marine reserves, both positive and negative, are affected by a range of social considerations that may not be incorporated in typical evaluations of ecological and economic marine reserve success.     

The impact of internal waves on upper continental slopes: insights from the Mozambican margin (southwest Indian Ocean)

Evidences of sedimentation affected by oceanic circulation, such as nepheloid layers and contourites are often observed along continental slopes. However, the oceanographic processes controlling sedimentation along continental margins remain poorly understood. Multibeam bathymetry and high-resolution seismic reflection data revealed a contourite depositional system in the Mozambican upper continental slope composed of a contourite terrace (a surface with a gentle seaward slope dominated by erosion) and a plastered drift (a convex-shape sedimentary deposit). A continuous alongslope channel and a field of sand dunes (mainly migrating upslope), formed during Holocene, were identified in the contourite terrace at the present seafloor. Seismic reflection data of the water column show internal waves and boluses propagating in the pycnocline near the upper slope. The channel and the dunes are probably the result of the interaction of the observed internal waves with the seafloor under two different conditions. The alongslope channel is located in a zone where intense barotropic tidal currents may arrest internal solitary waves, generating a hydraulic jump and focused erosion. However, upslope migrating dunes may be formed by bottom currents induced by internal solitary waves of elevation propagating landwards in the pycnocline. These small-scale sedimentary features generated by internal waves are superimposed on large-scale contouritic deposits, such as plastered drifts and contourite terraces, which are related to geostrophic currents. These findings provide new insights into the oceanographic processes that control sedimentation along continental margins that will help interpretation of palaeoceanographic conditions from the sedimentary record. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd