scholarly journals The downward spiral: eco-evolutionary feedback loops lead to the emergence of ‘elastic’ ranges

2014 ◽  
Author(s):  
Alexander Kubisch ◽  
Anna-Marie Winter ◽  
Emanuel A. Fronhofer
Keyword(s):  
Environmental Changes ◽  
Elastic Behavior ◽  
Elastic Behaviour ◽  
Necessary Condition ◽  
Habitat Isolation ◽  
Extinction Rate ◽  
Allee Effects ◽  
Species Ranges ◽  
Range Contraction ◽  
Patch Isolation

In times of severe environmental changes and resulting shifts in the geographical distribution of animal and plant species it is crucial to unravel the mechanisms responsible for the dynamics of species' ranges. Without such a mechanistic understanding, reliable projections of future species distributions are difficult to derive. Species' ranges may be highly dynamic. One particularly interesting phenomenon is range contraction following a period of expansion, referred to as `elastic' behaviour. It has been proposed that this phenomenon occurs in habitat gradients, which are characterized by a negative cline in selection for dispersal from the range core towards the margin, as one may find, for example, with increasing patch isolation. Using individual-based simulations and numerical analyses we show that Allee effects are an important determinant of range border elasticity. If only intra-specific processes are considered, Allee effects are even a necessary condition for ranges to exhibit elastic behavior. The eco-evolutionary interplay between dispersal evolution, Allee effects and habitat isolation leads to lower colonization probability and higher local extinction risk after range expansions, which result in an increasing amount of marginal sink patches and consequently, range contraction. We also demonstrate that the nature of the gradient is crucial for range elasticity. Gradients which do not select for lower dispersal at the margin than in the core (especially gradients in patch size, demographic stochasticity and extinction rate) do not lead to elastic range behavior. Thus, we predict that range contractions are likely to occur after periods of expansion for species living in gradients of increasing patch isolation, which suffer from Allee effects.

Sensitivity Investigation of Specimen Shape on Elastic Behaviour of Perforated Plate

2009 ◽  
Author(s):  
Chang-Hoon Ha ◽  
Tae-Jung Park ◽  
Moo-Yong Kim ◽  
Kwang-Sang Seon ◽  
Jae-Mean Koo ◽  
...  
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Perforated Plate ◽  
Type Specimen ◽  
Elastic Behavior ◽  
Elastic Behaviour ◽  
Element Analysis ◽  
Bending Tests ◽  
The Finite Element Analysis ◽  
Specimen Shape

There are various types of tube support plates installed in a steam generator according to the component designer’s preference. Most widely used types of tube support plates are BTSP (broached tube support plate), ATSG (advanced tube support grid), and the eggcrate. In this study, trefoil BTSP specimens made of ASME stainless steel are analyzed and tested. This study is to investigate the effect of specimen shape on an elastic behavior of trefoil BTSP through the compression and bending tests. Prior to the compression and bending tests of BTSP specimens, the equivalent elastic properties of BTSP unit cell are analyzed by the finite element analysis according to the different loading orientation as well as size of the model. Autodesk® Inventor™ software was used to make an analytical model and ANSYS® software was used for the finite element analysis and post-processing. Five and three different shapes of trefoil BTSP specimens are machined and utilized for the compression and bending (4-point and 3-point side bending) tests, respectively. Through the finite element analyses, compression, and bending tests, the equivalent elastic modulus of trefoil BTSP specimen is suggested to be 6,254MPa (907ksi) and the equivalent Poisson’s ratio as 0.64. Specifically the CS5 type specimen which has a ratio of one-fourth (= width/length) was revealed as an appropriate shape of specimen to show those elastic behavior.

New Approach for Engineering Design of Bolted Joints Using Over-Elastic Behaviour

2005 ◽  
Author(s):  
C. Friedrich ◽  
J. Panthel ◽  
T. Bohlender
Keyword(s):  
Engineering Design ◽  
Contact Pressure ◽  
Bolted Joints ◽  
High Loading ◽  
Elastic Behavior ◽  
Elastic Behaviour ◽  
New Approach ◽  
Loading Level ◽  
Component Systems ◽  
Critical Materials

The behavior of bolted joints in component systems with relatively small fastening systems, critical materials or with high loading level often shows significant yielding effects with reduction of preload. Thus, poor reliability or even failures are possible. This problem requires an adaptation of the established analytical engineering design methods. A new approach with consideration of over-elastic behavior and preload history is proposed. Examples refer to magnesium components, contact pressure and tightening with angular control.

Parallel Singularities for the Design of Softening Springs Using Compliant Mechanisms

2015 ◽  
Author(s):  
Quentin Boehler ◽  
Marc Vedrines ◽  
Salih Abdelaziz ◽  
Philippe Poignet ◽  
Pierre Renaud
Keyword(s):  
Additive Manufacturing ◽  
Material Properties ◽  
Compliant Mechanisms ◽  
Elastic Behavior ◽  
Necessary Condition ◽  
Hyper Elastic

In this paper, the design of nonlinear softening springs using compliant mechanisms is investigated. The use of compliant structures is of great interest, because of the resulting absence of backlash and friction. We demonstrate that the existence of parallel singularities is a necessary condition for the architecture of a compliant softening spring. From this result, two original arrangements of softening springs are derived, with the introduction of traction and torsion softening springs. A synthesis is performed and the traction spring is numerically and experimentally assessed. As nonlinearity can also be obtained from material properties, the interest of using additive manufacturing with multi-material capability is investigated. Rubber-like materials exhibit a hyper-elastic behavior. Their integration in the proposed compliant architecture is shown to be of interest to customize the geometry of a softening spring according to the designer requirements.

Elastic Behavior of the Plain Journal Bearing Coated With a Textured Surface and a Non-Textured Surface

2020 ◽  
Vol 8 (1) ◽  
pp. 55-77
Author(s):  
Mehala Kadda ◽  
Bendaoud Nadia
Keyword(s):  
Journal Bearing ◽  
Surface Effect ◽  
Rotational Velocity ◽  
Surface Texturing ◽  
Pressure Profile ◽  
Operating Conditions ◽  
Elastic Behavior ◽  
Elastic Behaviour ◽  
Shear Stresses ◽  
Textured Surface

Surface texturing technology has been newly explored technique in the tribological domain, and this method is carried out to improve the displacement and performance of the Babbitt plain journal bearing with a textured surface. The numerical analysis is carried out to study the textured surface effect on the elastic behaviour of the journal bearing. First, the bearing is tested without texture; second, it is examined completely textured, by varying the operating parameters of the bearing. The performance is observed in a pressure profile, displacement, and shear stress, generated for each combination of radial loads, and rotational velocity of the shaft. The numerical modelling is used by solving the displacement equations by the finite element method to analyses bearing displacement for severe operating conditions. The results show that the elastic deformations for textured bearing, are important and preponderant for higher rotational speeds, and shear stresses are important for higher hydrodynamic pressures.

Effects of the early Toarcian Oceanic Anoxic Event on ichthyosaur body size and faunal composition in the Southwest German Basin

Paleobiology ◽  
2015 ◽  
Vol 42 (1) ◽  
pp. 117-126 ◽  
Author(s):  
Erin E. Maxwell ◽  
Peggy Vincent
Keyword(s):  
Body Size ◽  
Environmental Changes ◽  
Marine Invertebrates ◽  
Abundant Species ◽  
Extinction Rate ◽  
Oceanic Anoxic Event ◽  
Environmental Perturbations ◽  
Anoxic Event ◽  
Posidonia Shale ◽  
German Basin

AbstractThe Early Jurassic Toarcian Oceanic Anoxic Event is considered one of the most dramatic environmental perturbations of the Mesozoic. An elevated extinction rate among marine invertebrates accompanied rapid environmental changes, but effects on large vertebrates are less understood. We examined changes in ichthyosaur body size in the Posidonia Shale of the Southwest German Basin spanning the extinction interval to assess how environmental changes and biotic crisis among prey species affected large reptiles. We report no species-level extinction among the ichthyosaurs coinciding with peak invertebrate extinction. Large ichthyosaurs were absent from the fauna during the extinction interval, but became more abundant in the immediate aftermath.Stenopterygius quadriscissus, the most abundant species during the extinction interval, increased in body size after the biotic event. Rapid invasion by large taxa occurred immediately following the extinction event at the end of the first ammonite zone of the early Toarcian. Greater mobility permitting exploitation of ephemeral resources and opportunistic feeding behavior may minimize the impacts of environmental change on large vertebrates.

Diversity dynamics of Early Jurassic ostracods of the Cordillera Ibérica (Spain) and the re-evaluation of the Pliensbachian–Toarcian mass extinction

2007 ◽  
Vol 44 (10) ◽  
pp. 1397-1411 ◽  
Author(s):  
Carmen Arias
Keyword(s):  
Mass Extinction ◽  
Environmental Changes ◽  
Marine Invertebrates ◽  
Marine Species ◽  
Extinction Time ◽  
Extinction Rate ◽  
Extinction Rates ◽  
Cordillera Ibérica ◽  
Global Extinction ◽  
Ultimate Cause

The extinction and recovery of Ostracoda at the Pliensbachian–Toarcian (P–T) boundary are analyzed based on a database of taxonomically revised Pliensbachian to Toarcian transition ostracod assemblages. In contrast to earlier assertions, the results of this study indicate that ostracod extinction rates were significant in comparison with other marine invertebrates. An extinction rate of 54% has been calculated for upper Pliensbachian ostracod species occurring in more than one section. Diversification took place in the latest Pliensbachian (Spinatum Zone) and early Toarcian (Tenuicostatum Zone), whereas diversity decrease occurred in the middle early Toarcian (Strangewaysi Subzone, Serpentinus Zone). This notable diversity decline in the early Toarcian corresponds to a global mass extinction time, whose peak has been documented in the Tenuicostatum Zone. Meanwhile, the ostracod mass extinction occurred within the Serpentinus Zone and was followed by radiation and recovery in the succeeding Bifrons Zone. Similar diversity changes of ostracods are observed in other European areas, although in the Cordillera Ibérica, the demise began later. Many aspects of this event are still debated, and there is no common cause or single set of climatic or environmental changes common to this event. The supposed extinction-causing environmental changes resulting from anoxia episodes are unclear and are unlikely to have been of sufficient intensity or geographic extent to cause this global extinction. In this paper, the decrease in marine species diversity is explained by a new palaeoceanographic scenario, in which a rapid global cooling episode is regarded as the ultimate cause.

scholarly journals A Theoretical and Methodological Analysis of the Scholars’ Views on Defining the Concept of «Competitiveness»

2020 ◽  
Vol 11 (514) ◽  
pp. 13-17
Author(s):  
T. V. Shtal ◽  
◽  
D. A. Shulha ◽  
D. A. Torkut ◽  
◽  
...  
Keyword(s):  
Life Support ◽  
Environmental Changes ◽  
International Competitiveness ◽  
Machine Building ◽  
Necessary Condition ◽  
Modern World ◽  
Competitive Advantages ◽  
Economic Relations ◽  
State Of Affairs ◽  
Definition Of

The article is aimed at analyzing the interpretation of the concept of «competitiveness» and defining the importance of attracting the attention of enterprises to this topic. The relevance of the problem of increasing the competitiveness of enterprises is determined not only by the needs of domestic development and life support of the country, but also by those profound changes that are taking place in the modern system of international economic relations, directed towards forming a new international division of labor and a new mechanism for the distribution of the global incomes. Never before in the history of international relations has the phenomenon of competitiveness acquired such actual importance as it does nowadays. Ukraine faces the issue of sustainable economic development, characterized by increased adaptability to environmental changes, as well as the availability of favorable conditions for functioning with a constant increase of competitive advantages. The line between the competitiveness of firms, industries and the competitiveness of the country is extremely conditional. One of the most globalized markets today is the market of machine-building products, which often determines the international competitiveness of the country and its role on the world stage. In this aspect, the issues of formation of competitive advantages of domestic enterprises on international markets as the basis of their long-term presence in these markets become particularly relevant. Having analyzed the theoretical principles of the concept of international competitiveness, it was determined that there is currently no generally accepted definition of the content and understanding of this category. Enterprises should understand that the concepts of «competition» and «competitiveness» are not interchangeable. Companies need to assess the level of international competitiveness in order to understand the state of affairs and take adequate measures if the level of international competitiveness is unsatisfactory. Thus, finding points of growth of the level of international competitiveness and influencing them is a critically necessary condition for the effective activity of an enterprise in the modern world.

scholarly journals A STUDY OF THE ELASTIC BEHAVIOUR PRESENTED BY DIFFERENT TYPES OF SEDIMENTARY ROCKS

2015 ◽  
Vol 33 (2) ◽  
Author(s):  
Ana Paula O. Castro ◽  
Eliane Da Costa Alves ◽  
Guilherme F. Vasquez
Keyword(s):  
Wave Propagation ◽  
Sedimentary Rocks ◽  
Theoretical Models ◽  
The United States ◽  
Elastic Behavior ◽  
Elastic Behaviour ◽  
Seismic Velocities ◽  
Behavior Understanding ◽  
Middle West ◽  
Indiana Limestone

ABSTRACT. The purpose of this paper is to study the elastic behavior of the different kinds of sedimentary rocks from outcrops of the Middle-West region of the United States of America, among those, Berea sandstone from Bedford formation (Ohio), Indiana limestone from Salem formation (Indiana) and Silurian dolomite from Thornton formation (Illinois). To do so, it has been made in the Laboratório de Física de Rochas from Cenpes (Centro de Pesquisas e Desenvolvimento da Petrobras ), measurements of porosity, density and elastic wave propagation velocity presented by each type of studied rock. The wave propagation velocities were estimated by measuring the transit time ultrasonic pulses transmitted through the samples. From the results obtained, it was possible to compare the measured velocities with predictions from theoretical models, as well as to observe correlations between the petrophysical properties of rocks and its seismic behavior. Understanding these correlations helps to improve the interpretation of geophysical measurements and to improve the seismic method, which in turn has a direct impact on exploration and development activities reservoirs.Keywords: seismic velocities, elastic properties, sedimentary rocks.RESUMO. O objetivo deste trabalho é estudar o comportamento elástico de diferentes tipos de rochas sedimentares provenientes de afloramentos da região Centro-Oeste dos Estados Unidos da América, entres estas, o arenito Berea da formação Bedford (Ohio), o calcário Indiana da formação Salem (Indiana) e o dolomito Silurian da formação Thornton (Illinois). Para tanto, foram realizadas, no Laboratório de Física de Rochas do Cenpes (Centro de Pesquisas e Desenvolvimento da Petrobras), medidas de porosidade, densidade e de velocidades de propagação das ondas elásticas apresentadas por tipo de rocha estudada. As velocidades de propagação das ondas foram determinadas medindo-se o tempo de trânsito de um pulso ultrassônico de alta frequência transmitido através das amostras. A partir dos resultados obtidos, foi possível comparar as velocidades medidas com as previsões feitas a partir de modelos teóricos, assim como foi possível observar correlações existentes entre as propriedades petrofísicas das rochas e o seu comportamento sísmico. O entendimento dessas correlações contribui para a melhoria da interpretação de medidas geofísicas e para o aprimoramento do método sísmico, que por sua vez, tem impacto direto nas atividades de exploração e desenvolvimento de reservatórios.Palavras-chave: velocidades sísmicas, propriedades elásticas, rochas sedimentares.

The Infancy of Solar-Type Stars and its Relevance for the Origin of Life

1997 ◽  
Vol 161 ◽  
pp. 267-282 ◽  
Author(s):  
Thierry Montmerle
Keyword(s):  
Main Sequence ◽  
Solar Nebula ◽  
Circumstellar Disks ◽  
T Tauri Stars ◽  
Necessary Condition ◽  
Sequence Evolution ◽  
T Tauri ◽  
Solar Type ◽  
Optical Domain ◽  
The Origin Of Life

AbstractFor life to develop, planets are a necessary condition. Likewise, for planets to form, stars must be surrounded by circumstellar disks, at least some time during their pre-main sequence evolution. Much progress has been made recently in the study of young solar-like stars. In the optical domain, these stars are known as «T Tauri stars». A significant number show IR excess, and other phenomena indirectly suggesting the presence of circumstellar disks. The current wisdom is that there is an evolutionary sequence from protostars to T Tauri stars. This sequence is characterized by the initial presence of disks, with lifetimes ~ 1-10 Myr after the intial collapse of a dense envelope having given birth to a star. While they are present, about 30% of the disks have masses larger than the minimum solar nebula. Their disappearance may correspond to the growth of dust grains, followed by planetesimal and planet formation, but this is not yet demonstrated.

Electron Microscopy of Metal-Matrix Composites

1970 ◽  
Vol 28 ◽  
pp. 404-405
Author(s):  
A. Lawley ◽  
M. R. Pinnel ◽  
A. Pattnaik
Keyword(s):  
Electron Microscopy ◽  
Metal Matrix Composites ◽  
Metal Matrix ◽  
Critical Evaluation ◽  
Elastic Behavior ◽  
Matrix Composites ◽  
Directionally Solidified ◽  
Fracture Characteristics ◽  
Broad Program

As part of a broad program on composite materials, the role of the interface on the micromechanics of deformation of metal-matrix composites is being studied. The approach is to correlate elastic behavior, micro and macroyielding, flow, and fracture behavior with associated structural detail (dislocation substructure, fracture characteristics) and stress-state. This provides an understanding of the mode of deformation from an atomistic viewpoint; a critical evaluation can then be made of existing models of composite behavior based on continuum mechanics. This paper covers the electron microscopy (transmission, fractography, scanning microscopy) of two distinct forms of composite material: conventional fiber-reinforced (aluminum-stainless steel) and directionally solidified eutectic alloys (aluminum-copper). In the former, the interface is in the form of a compound and/or solid solution whereas in directionally solidified alloys, the interface consists of a precise crystallographic boundary between the two constituents of the eutectic.

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