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Pereira, Felipe Augusto Cardoso; Colli, Eduardo; Sartorelli, Jose Carlos
Fonte: AMER INST PHYSICS; MELVILLE Publicador: AMER INST PHYSICS; MELVILLE
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
455.90867%
Period adding cascades have been observed experimentally/numerically in the dynamics of neurons and pancreatic cells, lasers, electric circuits, chemical reactions, oceanic internal waves, and also in air bubbling. We show that the period adding cascades appearing in bubbling from a nozzle submerged in a viscous liquid can be reproduced by a simple model, based on some hydrodynamical principles, dealing with the time evolution of two variables, bubble position and pressure of the air chamber, through a system of differential equations with a rule of detachment based on force balance. The model further reduces to an iterating one-dimensional map giving the pressures at the detachments, where time between bubbles come out as an observable of the dynamics. The model has not only good agreement with experimental data, but is also able to predict the influence of the main parameters involved, like the length of the hose connecting the air supplier with the needle, the needle radius and the needle length. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3695345]

## On the photosynthetic potential in the very Early Archean oceans

Avila, Daile; Cardenas, Rolando; Martin, Osmel
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
352.93074%
In this work we apply a mathematical model of photosynthesis to quantify the potential for photosynthetic life in the very Early Archean oceans. We assume the presence of oceanic blockers of ultraviolet radiation, specifically ferrous ions. For this scenario, our results suggest a potential for photosynthetic life greater than or similar to that in later eras/eons, such as the Late Archean and the current Phanerozoic eon.; Comment: Accepted for publication in Origins of Life and Evolution of Biospheres

## Horizontal subduction zones, convergence velocity and the building of the Andes

Martinod, Joseph; Husson, Laurent; Roperch, Pierrick; Guillaume, Benjamin; Espurt, Nicolas
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
360.89133%
We discuss the relationships between Andean shortening, plate velocities at the trench, and slab geometry beneath South America. Although some correlation exists between the convergence velocity and the westward motion of South America on the one hand, and the shortening of the continental plate on the other hand, plate kinematics neither gives a satisfactory explanation to the Andean segmentation in general, nor explains the development of the Bolivian orocline in Paleogene times. We discuss the Cenozoic history of horizontal slab segments below South America, arguing that they result from the subduction of oceanic plateaus whose effect is to switch the buoyancy of the young subducting plate to positive. We argue that the existence of horizontal slab segments, below the Central Andes during Eocene-Oligocene times, and below Peru and North-Central Chile since Pliocene, resulted (1) in the shortening of the continental plate interiors at a large distance from the trench, (2) in stronger interplate coupling and ultimately, (3) in a decrease of the trenchward velocity of the oceanic plate. Present-day horizontal slab segments may thus explain the diminution of the convergence velocity between the Nazca and South American plates since Late Miocene.

## Geo-neutrinos

Bellini, G.; Ianni, A.; Ludhova, L.; Mantovani, F.; McDonough, W. F.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
353.75152%
We review a new interdisciplinary field between Geology and Physics: the study of the Earth's geo-neutrino flux. We describe competing models for the composition of the Earth, present geological insights into the make up of the continental and oceanic crust, those parts of the Earth that concentrate Th and U, the heat producing elements, and provide details of the regional settings in the continents and oceans where operating and planned detectors are sited. Details are presented for the only two operating detectors that are capable of measuring the Earth's geo-neutrinos flux: Borexino and KamLAND; results achieved to date are presented, along with their impacts on geophysical and geochemical models of the Earth. Finally, future planned experiments are highlighted.

## Statistical mechanics of Fofonoff flows in an oceanic basin

Naso, A.; Chavanis, P. H.; Dubrulle, B.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
370.95625%
We study the minimization of potential enstrophy at fixed circulation and energy in an oceanic basin with arbitrary topography. For illustration, we consider a rectangular basin and a linear topography h=by which represents either a real bottom topography or the beta-effect appropriate to oceanic situations. Our minimum enstrophy principle is motivated by different arguments of statistical mechanics reviewed in the article. It leads to steady states of the quasigeostrophic (QG) equations characterized by a linear relationship between potential vorticity q and stream function psi. For low values of the energy, we recover Fofonoff flows [J. Mar. Res. 13, 254 (1954)] that display a strong westward jet. For large values of the energy, we obtain geometry induced phase transitions between monopoles and dipoles similar to those found by Chavanis and Sommeria [J. Fluid Mech. 314, 267 (1996)] in the absence of topography. In the presence of topography, we recover and confirm the results obtained by Venaille and Bouchet [Phys. Rev. Lett. 102, 104501 (2009)] using a different formalism. In addition, we introduce relaxation equations towards minimum potential enstrophy states and perform numerical simulations to illustrate the phase transitions in a rectangular oceanic basin with linear topography (or beta-effect).; Comment: 26 pages...

## Vesicularity, bubble formation and noble gas fractionation during MORB degassing

Aubry, G.; Sator, N.; Guillot, B.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
356.5402%
The objective of this study is to use molecular dynamics simulation (MD) to evaluate the vesicularity and noble gas fractionation, and to shed light on bubble formation during MORB degassing. A previous simulation study (Guillot and Sator (2011) GCA 75, 1829-1857) has shown that the solubility of CO2 in basaltic melts increases steadily with the pressure and deviates significantly from Henry's law at high pressures (e.g. 9.5 wt% CO2 at 50 kbar as compared with 2.5 wt% from Henry's law). From the CO2 solubility curve and the equations of state of the two coexisting phases (silicate melt and supercritical CO2), deduced from the MD simulation, we have evaluated the evolution of the vesicularity of a MORB melt at depth as function of its initial CO2 contents. An excellent agreement is obtained between calculations and data on MORB samples collected at oceanic ridges. Moreover, by implementing the test particle method (Guillot and Sator (2012) GCA 80, 51-69), the solubility of noble gases in the two coexisting phases (supercritical CO2 and CO2-saturated melt), the partitioning and the fractionation of noble gases between melt and vesicles have been evaluated as function of the pressure. We show that the melt/CO2 partition coefficients of noble gases increase significantly with the pressure whereas the large distribution of the 4He/40Ar* ratio reported in the literature is explained if the magma experiences a suite of vesiculation and vesicle loss during ascent. By applying a pressure drop to a volatile bearing melt...

## Applying Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) spectral indices for geological mapping and mineral identification on the Tibetan Plateau

Corrie, Robert; Ninomiya, Yoshiki; Aitchison, Jonathan
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
361.18926%
The Tibetan Plateau holds clues to understanding the dynamics and mechanisms associated with continental growth. Part of the region is characterized by zones of ophiolitic melange believed to represent the remnants of ancient oceanic crust and underlying upper mantle emplaced during oceanic closures. However, due to the remoteness of the region and the inhospitable terrain many areas have not received detailed investigation. Increased spatial and spectral resolution of satellite sensors have made it possible to map in greater detail the mineralogy and lithology than in the past. Recent work by Yoshiki Ninomiya of the Geological Survey of Japan has pioneered the use of several spectral indices for the mapping of quartzose, carbonate, and silicate rocks using Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) thermal infrared (TIR) data. In this study, ASTER TIR indices have been applied to a region in western-central Tibet for the purposes of assessing their effectiveness for differentiating ophiolites and other lithologies. The results agree well with existing geological maps and other published data. The study area was chosen due to its diverse range of rock types, including an ophiolitic melange, associated with the Bangong-Nujiang suture (BNS) that crops out on the northern shores of Lagkor Tso and Dong Tso ("Tso" is Tibetan for lake). The techniques highlighted in this paper could be applied to other geographical regions where similar geological questions need to be resolved. The results of this study aim to show the utility of ASTER TIR imagery for geological mapping in semi-arid and sparsely vegetated areas on the Tibetan Plateau.; Comment: 6 pages...

## Plate Tectonic Consequences of competing models for the origin and history of the Banda Sea subducted oceanic lithosphere

Heine, Christian; Quevedo, Leonardo; McKay, Hamish; Müller, R. Dietmar
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
367.29152%
The Banda Arc, situated west of Irian Jaya and in the easternmost extension of the Sunda subduction zone system, reveals a characteristic bowl-shaped geometry in seismic tomographic images. This indicates that the oceanic lithosphere still remains attached to the surrounding continental margins of northern Australia and the Bird's Head microcontinent. Major controversies exist between authors proposing an allochthonous or autochthonous origin of the Bird's Head block. Either scenario has important implications for plate kinematic models aiming to reconstruct the tectonic evolution of the region and the late Jurassic seaoor spreading geometry of this now subducted Argo-Tanimbar-Seram (ATS) ocean basin. Wider implications affect the tectonic conguration of the Tethyan-Pacic realm, the distribution of plate boundaries as well as the shape and size of continental blocks which have been rifted off the northeastern Gondwana margin during the Late Jurassic and are now accreted to the SE Asia margin. We apply structural geology restoration techniques to unfold the subducted oceanic lithosphere of the Banda Slab. Our slab unfolding results help to discriminate between the different hypotheses concerning the origin and kinematic history of the Bird's Head tectonic block. According to our preferred model...

## Predicting rogue waves in random oceanic sea states

Schober, Constance; Islas, Alvaro
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
364.35367%
Using the inverse spectral theory of the nonlinear Schrodinger (NLS) equation we correlate the development of rogue waves in oceanic sea states characterized by the JONSWAP spectrum with the proximity to homoclinic solutions of the NLS equation. We find in numerical simulations of the NLS equation that rogue waves develop for JONSWAP initial data that is near'' NLS homoclinic data, while rogue waves do not occur for JONSWAP data that is far'' from NLS homoclinic data. We show the nonlinear spectral decomposition provides a simple criterium for predicting the occurrence and strength of rogue waves (PACS: 92.10.Hm, 47.20.Ky, 47.35+i).; Comment: 7 pages, 6 figures submitted to Physics of Fluids, October 25, 2004 Revised version submitted to Physics of Fluids, December 12, 2004

## Solvable phase diagrams and ensemble inequivalence for two-dimensional and geophysical turbulent flows

Venaille, Antoine; Bouchet, Freddy
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
353.56%
Using explicit analytical computations, generic occurrence of inequivalence between two or more statistical ensembles is obtained for a large class of equilibrium states of two-dimensional and geophysical turbulent flows. The occurrence of statistical ensemble inequivalence is shown to be related to previously observed phase transitions in the equilibrium flow topology. We find in these turbulent flow equilibria, two mechanisms for the appearance of ensemble equivalences, that were not observed in any physical systems before. These mechanisms are associated respectively with second-order azeotropy (simultaneous appearance of two second-order phase transitions), and with bicritical points (bifurcation from a first-order to two second-order phase transition lines). The important roles of domain geometry, of topography, and of a screening length scale (the Rossby radius of deformation) are discussed. It is found that decreasing the screening length scale (making interactions more local) surprisingly widens the range of parameters associated with ensemble inequivalence. These results are then generalized to a larger class of models, and applied to a complete description of an academic model for inertial oceanic circulation, the Fofonoff flow.; Comment: 41 pages...

## Protoplanetary Earth Formation: Further Evidence and Geophysical Implications

Herndon, J. Marvin
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
360.6998%
Recently, I showed that the "standard model" of solar system formation is wrong,yielding the contradiction of terrestrial planets having insufficiently massive cores, and showed instead the consistency of Eucken's 1944 concept of planets raining out in the central regions of hot, gaseous protoplanets. Planets generally consist of concentric shells of matter, but there has been no adequate geophysical explanation to account for the Earth's non-contiguous crustal continental rock layer, except by assuming that the Earth in the distant past was smaller and subsequently expanded. Here, I show that formation of Earth, from within a Jupiter-like protoplanet, will account for the compression of the rocky Earth to about 64 percent of its current radius, yielding a closed, contiguous continental shell with concomitant Earth expansion commencing upon the subsequent removal of its protoplanetary gaseous shell. I now propose that Earth expansion progresses, not from spreading at mid-oceanic ridges as usually assumed, but primarily by the formation of expansion cracks (often near continental margins) and the in-filling of those cracks with basalt (produced from volume expansion in the mantle), which is extruded mainly at mid-oceanic ridges, solidifies and traverses the ocean floor by gravitational creep to regions of lower gravitational potential energy...

## Laboratory Investigation of Entrainment and Mixing in Oceanic Overflows

Philippe, Odier; Jun, Chen; Ecke, Robert E.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
360.9589%
We present experimental measurements of a wall-bounded gravity current, motivated by characterizing natural gravity currents such as oceanic overflows. We use particle image velocimetry and planar laser-induced fluorescence to simultaneously measure the velocity and density fields as they evolve downstream of the initial injection from a turbulent channel flow onto a plane inclined at 10$^\circ$ with respect to horizontal. The turbulence level of the input flow is controlled by injecting velocity fluctuations upstream of the output nozzle. The initial Reynolds number based on Taylor microscale of the flow, R$_\lambda$, is varied between 40 and 120, and the effects of the initial turbulence level are assessed. The bulk Richardson number $Ri$ for the flow is about 0.3 whereas the gradient Richardson number $Ri_g$ varies between 0.04 and 0.25, indicating that shear dominates the stabilizing effect of stratification. Kelvin-Helmholtz instability results in vigorous vertical transport of mass and momentum. We present baseline characterization of standard turbulence quantities and calculate, in several different ways, the fluid entrainment coefficient $E$, a quantity of considerable interest in mixing parameterization for ocean circulation models. We also determine properties of mixing as represented by the flux Richardson number $Ri_f$ as a function of $Ri_g$ and diapycnal mixing parameter $K_\rho$ versus buoyancy Reynolds number $Re_b$. We find reasonable agreement with results from natural flows.; Comment: 36 pages...

## Turbulence and fossil turbulence lead to life in the universe

Gibson, Carl H.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
353.87465%
Turbulence is defined as an eddy-like state of fluid motion where the inertial-vortex forces of the eddies are larger than all the other forces that tend to damp the eddies out. Fossil turbulence is a perturbation produced by turbulence that persists after the fluid ceases to be turbulent at the scale of the perturbation. Because vorticity is produced at small scales, turbulence must cascade from small scales to large, providing a consistent physical basis for Kolmogorovian universal similarity laws. Oceanic and astrophysical mixing and diffusion are dominated by fossil turbulence and fossil turbulent waves. Observations from space telescopes show turbulence and vorticity existed in the beginning of the universe and that their fossils persist. Fossils of big bang turbulence include spin and the dark matter of galaxies: clumps of ~ 10^12 frozen hydrogen planets that make globular star clusters as seen by infrared and microwave space telescopes. When the planets were hot gas, they hosted the formation of life in a cosmic soup of hot-water oceans as they merged to form the first stars and chemicals. Because spontaneous life formation according to the standard cosmological model is virtually impossible, the existence of life falsifies the standard cosmological model.; Comment: 12 pages...

## Origin and evolution of marginal basins of the NW Pacific: Diffuse-plate tectonic reconstructions

Xu, Junyuan; Kelty, Tom; Ben-Avraham, Zvi; Yu, Ho-Shing
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
449.16594%
Formation of the gigantic linked dextral pull-apart basin system in the NW Pacific is due to NNE- to ENE-ward motion of east Eurasia. This mainly was a response to the Indo-Asia collision which started about 50 Ma ago. The displacement of east Eurasia can be estimated using three aspects: (1) the magnitude of pull-apart of the dextral pull-apart basin system, (2) paleomagnetic data from eastern Eurasia and the region around the Arctic, and (3) the shortening deficits in the Large Tibetan Plateau. All the three aspects indicate that there was a large amount (about 1200 km) of northward motion of the South China block and compatible movements of other blocks in eastern Eurasia during the rifting period of the basin system. Such large motion of the eastern Eurasia region contradicts any traditional rigid plate tectonic reconstruction, but agrees with the more recent concepts of non-rigidity of both continental and oceanic lithosphere over geological times. Based on these estimates, the method developed for restoration of background diffuse deformation of the Eurasian plate and the region around the Arctic, and the related kinematics of the marginal basins, we present plate tectonic reconstruction of these marginal basins in global plate tectonic settings at the four key times: 50...

## Temporal variations of the gravity field and Earth precession-nutation

Bourda, G.; Capitaine, N.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
353.4179%
Due to the accuracy now reached by space geodetic techniques, and also considering some modelisations, the temporal variations of some Earth Gravity Field coefficients can be determined. They are due to Earth oceanic and solid tides, as well as geophysical reservoirs masses displacements. They can be related to the variations in the Earth's orientation parameters (through the inertia tensor). Then, we can try to improve our knowledge of the Earth Rotation with those space measurements of the Gravity variations. We have undertaken such a study, using data obtained with the combination of space geodetic techniques. In particular, we use CHAMP data that are more sensitive to such variations and that complete the ones already accumulated (for example with Starlette and LAGEOS I). In this first approach, we focus on the Earth precession nutation, trying to refine it by taking into account the temporal variations of the Earth dynamical flattening. The goal is mainly to understand how Geodesy can influence this field of science. Like this, we will be able to compare our computation with up to date determinations of precession nutation.

## A Magma Accretion Model for the Formation of Oceanic Lithosphere: Implications for Global Heat Loss

Hamza, V. M.; Cardoso, R. R.; Alexandrino, C. H.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
366.7884%
A simple magma accretion model of the oceanic lithosphere is proposed and its implications for understanding the thermal field of oceanic lithosphere examined. The new model (designated VBA) assumes existence of lateral variations in magma accretion rates and temperatures at the boundary zone between the lithosphere and the asthenosphere. Heat flow and bathymetry variations calculated on the basis of the VBA model provide vastly improved fits to respective observational datasets. The improved fits have been achieved for the entire age range and without the need to invoke the ad-hoc hypothesis of large-scale hydrothermal circulation in stable ocean crust. The results suggest that estimates of global heat loss need to be downsized by at least 25%.; Comment: 45 pages, 11 figures

## Subterranean production of neutrons, $^{39}$Ar and $^{21}$Ne: Rates and uncertainties

Šrámek, Ondřej; Stevens, Lauren; McDonough, William F.; Mukhopadhyay, Sujoy; Peterson, R. J.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
358.09574%
Accurate understanding of the subsurface production of radionuclide $^{39}$Ar rate is necessary for argon dating techniques and noble gas geochemistry of the shallow and the deep Earth, and is also of interest to the WIMP dark matter experimental particle physics community. Our new calculations of subsurface production of neutrons, $^{21}$Ne, and $^{39}$Ar take advantage of the best available tools of nuclear physics to obtain reaction cross sections and spectra (TALYS) and to evaluate neutron propagation in rock (MCNP6). We discuss our method and results in relation to previous studies and show the relative importance of various neutron, $^{21}$Ne, and $^{39}$Ar nucleogenic production channels. Uncertainty in nuclear reaction cross sections, which is the major contributor to overall calculation uncertainty, is estimated from variability in existing experimental and library data. Depending on selected rock composition, on the order of $10^7$-$10^{10}$ {\alpha} particles are produced in one kilogram of rock per year (order of 1-$10^3$ kg$^{-1}$ s$^{-1}$), the number of produced neutrons is lower by $\sim6$ orders of magnitude, $^{21}$Ne production rate drops by an additional factor of 15-20, and another at least one order of magnitude is dropped in production of $^{39}$Ar. Our calculation yields a nucleogenic $^{21}$Ne/$^4$He production ratio of $(4.6\pm0.6) \times 10^{-8}$ in Continental Crust and $(4.2\pm0.5) \times 10^{-8}$ in Oceanic Crust and Depleted Mantle. Calculated $^{39}$Ar production rates span a range from $29\pm9$ atoms kg-rock$^{-1}$ yr$^{-1}$ in the K-Th-U-enriched Upper Continental Crust to $(2.6\pm0.8) \times 10^{-4}$ atoms kg-rock$^{-1}$ yr$^{-1}$ in Depleted Upper Mantle.; Comment: 6 figures...

## Detecting coherent structures using braids

Allshouse, Michael R.; Thiffeault, Jean-Luc
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
352.4588%
The detection of coherent structures is an important problem in fluid dynamics, particularly in geophysical applications. For instance, knowledge of how regions of fluid are isolated from each other allows prediction of the ultimate fate of oil spills. Existing methods detect Lagrangian coherent structures, which are barriers to transport, by examining the stretching field as given by finite-time Lyapunov exponents. These methods are very effective when the velocity field is well-determined, but in many applications only a small number of flow trajectories are known, for example when dealing with oceanic float data. We introduce a topological method for detecting invariant regions based on a small set of trajectories. In the method we regard the two-dimensional trajectory data as a braid in three dimensions, with time being the third coordinate. Invariant regions then correspond to trajectories that travel together and do not entangle other trajectories. We detect these regions by examining the growth of hypothetical loops surrounding sets of trajectories, and searching for loops that show negligible growth.; Comment: 23 pages, 22 figures. PDFLaTeX with RevTeX4-1 format. Minor corrections to the text

## The rotation and translation of non-spherical particles in homogeneous isotropic turbulence

Byron, Margaret L.
Tipo: Artigo de Revista Científica