Composite microbialites: Thrombolite, dendrolite, and stromatolite associations in a modern environment, Pozo Bravo lake, Salar de Antofalla, Catamarca Puna, Argentina

2021 ◽  
Vol 91 (12) ◽  
pp. 1305-1330
Author(s):  
Agustina I. Lencina ◽  
Mariana N. Soria ◽  
Fernando J. Gomez ◽  
Emmanuelle Gérard ◽  
M. Eugenia Farias
Keyword(s):  
Bottom Topography ◽  
Water Level Fluctuations ◽  
Gradual Transition ◽  
Gradual Change ◽  
Active System ◽  
Wide Range ◽  
Gradient Based ◽  
Strong Winds ◽  
Textural Changes ◽  
Narrow Belt

ABSTRACT Pozo Bravo is a high-altitude Andean lake that harbors modern microbialites thriving in hypersaline conditions in the Salar de Antofalla, one of the driest sites on Earth and located in the Puna region of Catamarca, northwest Argentine. Due to the lake physiography, microbialites are restricted to a narrow belt following Pozo Bravo lake variations. Microbialites exhibit a wide range of external morphologies including domal, discoidal, tabular, and horseshoe-like bioherms which vary considerably in size, as well as large biostromal terraces. As documented by other studies on modern microbialites, external morphology appears to be mainly the product of the environmental setting. In Pozo Bravo lake, high evaporation rates and hypersalinity (driven by high temperature and strong winds), water-level fluctuations, and lake-bottom topography are major controlling factors. The distinctive feature of Pozo Bravo microbialites is their internal structure, showing a gradual transition from a thrombolitic core to dendrolitic structures and to a sharply overlying stromatolitic layer within a single microbialite. We suggest that these various microbialite textures represent a gradual change within an environmental gradient based on lake-level variations, and the influence of these environmental factors on biological activity, mainly by cyanobacteria and diatoms. The study of this site is particularly relevant given that it represents an active system where progressive changes in microbialite type (from thrombolites to dendrolites and stromatolites) are recorded, providing an excellent natural laboratory to study these textural changes from a mechanistic perspective, and it may provide insights for better understanding of the microbialite geological record. In addition, given that these systems are threatened by human activities (mining of lithium-rich brines), its study and preservation are necessary.

Calculation of the primary trajectories of seeds and other particles in strong winds

1983 ◽  
Vol 219 (1215) ◽  
pp. 217-217
Keyword(s):  
Equations Of Motion ◽  
Aerodynamic Resistance ◽  
Reynolds Numbers ◽  
Spherical Particles ◽  
Spores And Pollen ◽  
General Terms ◽  
Wide Range ◽  
Strong Winds ◽  
Dispersal Distances ◽  
Enormous Number

The movement of variously dense spherical particles representing a variety of seeds, fruits, spores and pollen, and released from rest into arbitrary winds and a gravitational field is discussed in general terms that account in detail for changes in the quasi-static aerodynamic resistance to motion experienced by such particles during aerial flight. A hybrid analytical-empirical law is established which describes this resistance fairly accurately for particle Reynolds numbers in the range 0—60 000 and that allows for the numerical integration of the equations of motion so as to cover a very wide range of flight conditions. This makes possible the provision of a set of four-parameter universal range tables from which the dispersal distances for an enormous number of practical cases may be estimated. One particular case of particle movement in a region of pseudo-thermal convection is also discussed and this shows how a marked degree of deposition concentration may be induced in some circumstances by such a flow. Botanists and ecologists concerned with seed and particle dispersal in the environment may find the universal range tables of particular interest and use. This is because the tables obviate the need for the integration of the equations of motion when dealing with individual cases and permit an estimation of range purely on the basis of the specified quantities of particle size, density and altitude of release, atmospheric wind speed, density and viscosity, and the acceleration due to gravity.

scholarly journals Stellar Winds in Massive X-ray Binaries

2016 ◽  
Vol 12 (S329) ◽  
pp. 355-358
Author(s):  
Peter Kretschmar ◽  
Silvia Martínez-Núñez ◽  
Enrico Bozzo ◽  
Lidia M. Oskinova ◽  
Joachim Puls ◽  
...  
Keyword(s):  
Compact Object ◽  
High Mass ◽  
Stellar Winds ◽  
X Rays ◽  
X Ray ◽  
Current State ◽  
Wide Range ◽  
Strong Winds ◽  
The One ◽  
X Ray Binaries

AbstractStrong winds from massive stars are a topic of interest to a wide range of astrophysical fields. In High-Mass X-ray Binaries the presence of an accreting compact object on the one side allows to infer wind parameters from studies of the varying properties of the emitted X-rays; but on the other side the accretor’s gravity and ionizing radiation can strongly influence the wind flow. Based on a collaborative effort of astronomers both from the stellar wind and the X-ray community, this presentation attempts to review our current state of knowledge and indicate avenues for future progress.

Design Optimization of Solenoid Actuated Butterfly Valves Dynamically Coupled in Series

2015 ◽  
Author(s):  
Peiman Naseradinmousavi ◽  
C. Nataraj
Keyword(s):  
Intelligent Design ◽  
Nonlinear Modeling ◽  
Nonlinear Flow ◽  
Efficient Operation ◽  
Smart Systems ◽  
Critical Design ◽  
Highly Nonlinear ◽  
Wide Range ◽  
In Series ◽  
Gradient Based

In this effort, we present novel nonlinear modeling of two solenoid actuated butterfly valves operating in series and then develop an optimal configuration in the presence of highly coupled nonlinear dynamics. The valves are used in the so-called “Smart Systems” to be employed in a wide range of applications including bioengineering, medicine, and engineering fields. Typically, tens of the actuated valves are instantaneously operating to regulate the amount of flow and also to avoid probable catastrophic disasters which have been observed in the practice. We focus on minimizing the amount of energy used in the system as one of the most critical design criteria to yield an efficient operation. We optimize the actuation subsystems interacting with the highly nonlinear flow loads in order to minimize a lumped amount of energy consumed. The contribution of this work is to include coupled nonlinearities of electromechanical valve systems to optimize the actuation units. Stochastic, heuristic, and gradient based algorithms are utilized in seeking the optimal design of two sets. The results indicate that substantial amount of energy can be saved by an intelligent design that helps select parameters carefully but also uses flow torques to augment the closing efforts.

scholarly journals The Role of Closed Gyres in Setting the Zonal Transport of the Antarctic Circumpolar Current

2015 ◽  
Vol 45 (6) ◽  
pp. 1491-1509 ◽  
Author(s):  
Louis-Philippe Nadeau ◽  
Raffaele Ferrari
Keyword(s):  
Wind Stress ◽  
Large Scale ◽  
Bottom Topography ◽  
Channel Length ◽  
Horizontal Resolution ◽  
Wind Stress Curl ◽  
Barotropic Flow ◽  
Wide Range ◽  
Circumpolar Current ◽  
Baroclinic Transport

AbstractEddy-permitting simulations are used to show that basinlike gyres can be observed in the large-scale barotropic flow of a wind-driven channel with a meridional topographic ridge. This is confirmed using both two-layer quasigeostrophic and 25-level primitive equation models at high horizontal resolution. Comparing results from simulations with and without the topographic ridge, it is shown that the zonal baroclinic transport in the channel increases with increasing wind stress when the bottom topography is flat but not when there is a meridional ridge. The saturation of transport for increasing wind occurs in conjunction with the development of recirculating gyres in the large-scale barotropic streamfunction. This suggests that the total circulation can be thought of as a superposition of a gyre mode (which has zero circumpolar transport) and a free circumpolar mode (which contains all of the transport). Basinlike gyres arise in the channel because the topography steers the barotropic streamlines and supports a frictional boundary layer similar to the more familiar ones observed along western boundaries. The gyre mode is thus closely linked with the bottom form stress exerted by the along-ridge flow and provides the sink for the wind momentum input. In this framework, any increase in wind forcing spins a stronger gyre as opposed to feeding the circumpolar transport. This hypothesis is supported with a suite of experiments where key parameters are carried over a wide range: wind stress, wind stress curl, ridge height, channel length, and bottom friction.

Forecasting for a Remote Island: A Class Exercise

2003 ◽  
Vol 84 (6) ◽  
pp. 777-784 ◽  
Author(s):  
Allen J. Riordan
Keyword(s):  
Research Team ◽  
Weather Conditions ◽  
State University ◽  
Current Output ◽  
North Carolina State University ◽  
Wind Speeds ◽  
Wide Range ◽  
Remote Island ◽  
Satellite Meteorology ◽  
Strong Winds

Students enrolled in a satellite meteorology course at North Carolina State University, Raleigh, recently had an unusual opportunity to apply their forecast skills to predict wind and weather conditions for a remote site in the Southern Hemisphere. For about 40 days starting in early February 2001, students used satellite and model guidance to develop forecasts to support a research team stationed on Bouvet Island (54°26′S, 3°24′E). Internet products together with current output from NCEP's Aviation (AVN) model supported the activity. Wind forecasts were of particular interest to the Bouvet team because violent winds often developed unexpectedly and posed a safety hazard. Results were encouraging in that 24-h wind speed forecasts showed reasonable reliability over a wide range of wind speeds. Forecasts for 48 h showed only marginal skill, however. Two critical events were well forecasted—the major February storm with wind speeds of over 120 kt and a brief calm period following several days of strong winds in early March. The latter forecast proved instrumental in recovering the research team.

scholarly journals Internal Tide Generation Using Green Function Analysis: To WKB or Not to WKB?

2016 ◽  
Vol 46 (7) ◽  
pp. 2157-2168 ◽  
Author(s):  
Manikandan Mathur ◽  
Glenn S. Carter ◽  
Thomas Peacock
Keyword(s):  
Green Function ◽  
Numerical Simulations ◽  
Function Analysis ◽  
Bottom Topography ◽  
Internal Tide ◽  
Function Approach ◽  
Wkb Approximation ◽  
Analytical Technique ◽  
Wide Range ◽  
Green Function Approach

AbstractAn established analytical technique for modeling internal tide generation by barotropic flow over bottom topography in the ocean is the Green function–based approach. To date, however, for realistic ocean studies this method has relied on the WKB approximation. In this paper, the complete Green function method, without the WKB approximation, is developed and tested, and in the process, the accuracy of the WKB approximation for realistic ridge geometries and ocean stratifications is considered. For isolated Gaussian topography, the complete Green function approach is shown to be accurate via close agreement with the results of numerical simulations for a wide range of height ratios and criticality; in contrast, the WKB approach is found to be inaccurate for small height ratios in the subcritical regime and all tall topography that impinges on the pycnocline. Two ocean systems are studied, the Kaena and Wyville Thomson Ridges, for which there is again excellent agreement between the complete Green function approach and numerical simulations, and the WKB approximate solutions have substantial errors. This study concludes that the complete Green function approach, which is typically only modestly more computationally expensive than the WKB approach, should be the go-to analytical method to model internal tide generation for realistic ocean ridge scenarios.

Family continuity in England and Japan

2007 ◽  
Vol 22 (2) ◽  
pp. 193-214 ◽  
Author(s):  
MOTOYASU TAKAHASHI
Keyword(s):  
Religious Faith ◽  
Continuous Series ◽  
Gradual Change ◽  
Wide Range ◽  
Male Line ◽  
Household Labour ◽  
Kinship Ties ◽  
The Village ◽  
Generational Continuity ◽  
Almost Continuous

ABSTRACTThis article examines generational continuity and kinship patterns in Willingham (England) between the sixteenth and eighteenth centuries and in Kami-shiojiri (Japan) in the late eighteenth and early nineteenth centuries. In Willingham few families continued to survive in a given locality for more than a couple of generations in the male line. Yet at the same time local testators left bequests to a wide range of kin in their wills, indicating that, despite the mobility of the population, kinship ties remained important and were acknowledged. For Kami-shiojiri, the almost continuous series of Shumon Aratame-cho (religious faith registers) reveals a gradual change towards smaller and simpler household structures (Ie). In addition, occasional abrupt increases in the numbers of households and in the numbers of messuages (dwelling units) imply that the community as a whole and/or the local overlord did sometimes intervene to reconstruct sections of the village economy and the use of household labour. Households in Kami-shiojiri were larger and more complex than those in England and the population was much more stable, with the mobility rate about half that reported for England. The extent of variation in inheritance patterns within both populations is also discussed, showing that some families persisted for several generations in Willingham and that in Kami-shiojiri more than a third of cases of change of headship of the household, involved a successor who was not the eldest son of the previous head.

Cell wall disassembly in ripening fruit

2006 ◽  
Vol 33 (2) ◽  
pp. 103 ◽  
Author(s):  
David A. Brummell
Keyword(s):  
Cell Wall ◽  
Middle Lamella ◽  
Primary Cell Wall ◽  
Side Chains ◽  
Fruit Softening ◽  
Structure Degradation ◽  
Wide Range ◽  
Textural Changes ◽  
Cell Wall Disassembly ◽  
Pectin Solubilisation

Fruit softening during ripening involves a coordinated series of modifications to the polysaccharide components of the primary cell wall and middle lamella, resulting in a weakening of the structure. Degradation of polysaccharides and alterations in the bonding between polymers cause an increase in cell separation and a softening and swelling of the wall, which, combined with alterations in turgor, bring about fruit softening and textural changes. A wide range in the extent of cell wall pectic modifications has been observed between species, whereas the depolymerisation of xyloglucan is relatively limited and more consistent. The earliest events to be initiated are usually a loss of pectic galactan side chains and the depolymerisation of matrix glycans, which may begin before ripening, followed by a loss of pectic arabinan side chains and pectin solubilisation. The depolymerisation of pectins may begin during early to mid-ripening, but is usually most pronounced late in ripening. However, some of these events may be absent or occur at very low levels in some species. Cell wall swelling may be related to a loosening of the xyloglucan–cellulose network and to pectin solubilisation, and these processes combined with the loss of pectic side chains increase wall porosity. An increase in wall porosity later in ripening may allow increased access of degradative enzymes to their substrates.

The Surficial Sediments of Lake Huron

1973 ◽  
Vol 10 (2) ◽  
pp. 226-271 ◽  
Author(s):  
R. L. Thomas ◽  
A. L. Kemp ◽  
C. F. M. Lewis
Keyword(s):  
Organic Carbon ◽  
Clay Minerals ◽  
Bottom Topography ◽  
Northern Region ◽  
Glacial Till ◽  
Lake Huron ◽  
Surficial Sediments ◽  
Thunder Bay ◽  
Wide Range ◽  
Lake Bottom

On the basis of extensive sampling and echo sounding, three major lithological units are recognized in the main basin of Lake Huron: (1) glacial till and bedrock; (2) glaciolacustrine clay; and (3) postglacial mud. Sand is a lesser unit in the Huron surficial sediments. Owing to the wide range in bathymetric complexity, postglacial muds occur in basins of three distinct types:Type A. Regular basins in which mud forms a continuous cover.Type B. Irregular basins with undulating bottom topography. Glaciolacustrine clays outcrop in the crests and mud fill occurs in the hollows. Mud cover is greater than 50%.Type C. As for type B but with mud cover less than 50%.The sediment distribution pattern is essentially simple with a natural superposition of sediment units reflecting the glacial and postglacial history of the lake. A bedrock escarpment from Point Clark to Thunder Bay divides Lake Huron into two distinct morphological regions. To the south of the escarpment, the lake has a gentle topography. A second low amplitude escarpment, trending northeast from Ipperwash, divides the southern region of the lake into two large depositional basins. To the north of the major escarpment, the lake is much deeper and has a complex bottom topography. The northern region is separated into two large basins of discontinuous sediment deposition by a rise of glacial sediments trending north from Thunder Bay. The inshore region of Lake Huron and the two escarpments are composed of glacial till and bedrock. The till is overstepped in the deeper water by glaciolacustrine clays which are themselves overstepped by postglacial muds. Postglacial mud accumulation is continuous in the southern basins due to the gentle relief of the lake bottom. In the northern region of the lake, mud accumulation is discontinuous due to the undulating nature of the lake bottom. Mud fills the hollows leaving glaciolacustrine clay exposed at the top of the undulations in this region.The surficial sediments contain variable amounts of quartz, clay minerals, organic carbon, and carbonates. Quartz content is greatest in the coarser inshore sediments while clay minerals and organic carbon are greatest in the liner offshore sediments. Carbonate is low throughout the lake, except along the eastern edge. Blite is the dominant clay mineral with lesser amounts of chlorite and kaolinite.Amphipods, oligochaetes, and chironomids are the major benthic organisms in the Huron sediments. Amphipods are most numerous at a water depth of 70 m, oligochaetes at 140 m, and chironomids in the shallowest depths.The textural characteristics of the sediments, defined by moment measures, can be interpreted as resulting from variable mixing of a clay and a sand end member population.Both end member populations are leptokurtic and asymmetrically skewed due to the introduction of a silt size mode predominantly in the form of a carbonate. The sand end member population is positively skewed and occurs in the inshore zone comprising the coastal nearshore region and the shallow mid-lake regions. The clay end member is negatively skewed and occurs in the depositional basins. Between these two extremes there is a gradual prograding from sand to clay related to a progressive mixing of the two populations. This mixing is believed to be a direct function of declining energy with increasing water depth.Sediment composition reflects both the source materials and the textural properties. The sediments of the southern basin are derived predominantly from glacial tills whereas the composition of the sediments of the northern basin has been substantially modified by dilution with reworked glaciolacustrine clays.

scholarly journals Influences of InGaP Conical Frustum Nanostructures on the Characteristics of GaAs Solar Cells

2013 ◽  
Vol 2013 ◽  
pp. 1-6 ◽  
Author(s):  
Nguyen Dinh Lam ◽  
Youngjo Kim ◽  
Kangho Kim ◽  
Jaejin Lee
Keyword(s):  
Refractive Index ◽  
Solar Cells ◽  
Power Conversion Efficiency ◽  
Power Conversion ◽  
Window Layer ◽  
Gradual Change ◽  
Single Junction ◽  
Wide Range ◽  
Photovoltaic Characteristics ◽  
Lithography Technique

Conical frustums with quasihexagonal nanostructures are fabricated on an InGaP window layer of single junction GaAs solar cells using a polystyrene nanosphere lithography technique followed by anisotropic etching processes. The optical and photovoltaic characteristics of the conical frustum nanostructured solar cells are investigated. Reflectance of the conical frustum nanostructured solar cells is significantly reduced in a wide range of wavelengths compared to that of the planar sample. The measured reflectance reduction is attributed to the gradual change in the refractive index of the InGaP conical frustum window layer. An increase of 15.2% in the power conversion efficiency has been achieved in the fabricated cell with an optimized conical frustum nanostructure compared to that of the planar cell.

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