scholarly journals Adaptive metabolic strategies in consumer-resource models

2018 ◽  
Author(s):  
Leonardo Pacciani-Mori ◽  
Andrea Giometto ◽  
Samir Suweis ◽  
Amos Maritan
Keyword(s):  
Molecular Mechanisms ◽  
Growth Curves ◽  
Point Of View ◽  
Exclusion Principle ◽  
Relative Fitness ◽  
Metabolic Adaptation ◽  
Theoretical Point ◽  
Set Up ◽  
Metabolic Strategies ◽  
Consumer Resource

AbstractBacteria are able to adapt to different environments by changing their “metabolic strategies”, i.e. the ways in which they uptake available resources from the environment. For example, in a celebrated experiment Jacques Monod showed that bacteria cultured in media containing two different sugars consume them sequentially, resulting in bi-phasic growth curves called “diauxic shifts”. From the theoretical point of view, microbial communities are commonly described using MacArthur’s consumer-resource model, which describes the population dynamics of species competing for a given set of resources. In this model, however, metabolic strategies are treated as constant parameters. Here, we introduce adaptive metabolic strategies in the framework of consumer-resource models, allowing the strategies to evolve to maximize each species’ relative fitness. By doing so, we are able to describe quantitatively, and without invoking any specific molecular mechanisms for the metabolism of the microbial species, growth curves of the baker’s yeastSaccharomyces cerevisiaemeasured in a controlled experimental set-up, with galactose as the primary carbon source. We also show that metabolic adaptation enables the community to self-organize, allowing species to coexist even in the presence of few resources, and to respond optimally to a time-dependent environment. A connection between the Competitive Exclusion Principle and the metabolic theory of ecology is also discussed.

Recent progress in prominence seismology

2005 ◽  
Vol 364 (1839) ◽  
pp. 405-415 ◽  
Author(s):  
José Luis Ballester
Keyword(s):  
Small Amplitude ◽  
Point Of View ◽  
Future Research ◽  
Theoretical Point ◽  
Structure And Properties ◽  
Research Topics ◽  
Solar Prominences ◽  
Different Types ◽  
Set Up ◽  
Local Nature

Prominence seismology is a rapidly developing topic which seeks to infer the internal structure and properties of solar prominences from the study of their oscillations. An extense observational background about oscillations in quiescent solar prominences has been gathered during the last 70 years. These observations point out the existence of two different types of oscillations: flare-induced oscillations (winking filaments) which affect the whole prominence and are of large amplitude and small amplitude oscillations which seem to be of local nature. From the theoretical point of view, few models have been set up to explain the phenomenon of winking filaments while, on the contrary, for small amplitude oscillations a large number of models trying to explain the observed features have been proposed. Here, recent theoretical and observational developments on both types of oscillations are reviewed, and suggestions about future research topics which should provide us with a more in-depth knowledge of solar prominences are made.

scholarly journals Theoretical Evaluation of Graphene Membrane Performance for Hydrogen Separation Using Molecular Dynamic Simulation

Membranes ◽  
2019 ◽  
Vol 9 (9) ◽  
pp. 110 ◽  
Author(s):  
Mahdi Nouri ◽  
Kamran Ghasemzadeh ◽  
Adolfo Iulianelli
Keyword(s):  
Pressure Gradient ◽  
Molecular Dynamic ◽  
Molecular Mechanisms ◽  
Gas Diffusion ◽  
Point Of View ◽  
Theoretical Point ◽  
Pore Density ◽  
Theoretical Evaluation ◽  
Membrane Performance ◽  
Graphene Membranes

The main purposes of this study are to evaluate the performance of graphene membranes in the separation/purification of hydrogen from nitrogen from a theoretical point of view using the molecular dynamic (MD) simulation method, and to present details about molecular mechanisms of selective gas diffusion through nanoscale pores of graphene membranes at the simulated set conditions. On the other hand, permeance and perm-selectivity are two significant parameters of such a membrane that can be controlled by several variables such as pressure gradient, pore density, pore layer angles etc. Hence, in this work, the hydrogen and nitrogen permeating fluxes as well as the H2/N2 ideal perm-selectivity are investigated from a theoretical point of view in a two-layer nanoporous graphene (NPG) membrane through classical MD simulations, wherein the effects of pressure gradient, pore density, and pore angle on the NPG membrane performance are evaluated and discussed. Simulation outcomes suggest that hydrogen and nitrogen permeating fluxes increase as a consequence of an increment of pressure gradient across the membrane and pore density.

scholarly journals Evolution of diversity in metabolic strategies

2020 ◽  
Author(s):  
R. A. Caetano ◽  
Y. Ispolatov ◽  
M. Doebeli
Keyword(s):  
Evolutionary Dynamics ◽  
Fundamental Problem ◽  
Exclusion Principle ◽  
Ecological Interactions ◽  
Competitive Exclusion Principle ◽  
Theoretical Approaches ◽  
Coexisting Species ◽  
Metabolic Strategies ◽  
Very High ◽  
Consumer Resource

Understanding the origin and maintenance of biodiversity is a fundamental problem. Many theoretical approaches have been investigating ecological interactions, such as competition, as potential drivers of diversification. Classical consumer-resource models predict that the number of coexisting species should not exceed the number of distinct resources, a phenomenon known as the competitive exclusion principle. It has recently been argued that including physiological tradeoffs in consumer-resource models can lead to violations of this principle and to ecological coexistence of very high numbers of species. Here we show that these results crucially depend on the functional form of the tradeoff. We investigate the evolutionary dynamics of resource use constrained by tradeoffs and show that if the tradeoffs are non-linear, the system either does not diversify, or diversifies into a number of coexisting species that does not exceed the number of resources. In particular, very high diversity can only be observed for linear tradeoffs.

scholarly journals On broadband jet–ring interaction noise and aerofoil turbulence-interaction noise predictions

2010 ◽  
Vol 653 ◽  
pp. 337-364 ◽  
Author(s):  
MICHEL ROGER
Keyword(s):  
Transfer Function ◽  
Mixing Layer ◽  
Point Of View ◽  
Turbulent Velocity ◽  
Aerodynamic Noise ◽  
Experimental Point ◽  
Far Field ◽  
Theoretical Point ◽  
Parallel Side ◽  
Set Up

The aerodynamic noise of a thin rigid annulus (referred to as the ring here) placed in the mixing layer of a subsonic circular jet is investigated in the paper, both theoretically and experimentally. From the experimental point of view, the jet–ring configuration is understood as an axisymmetric alternative to more usual ones involving a rectangular aerofoil held between parallel side plates, dedicated to the study of the noise due to the impingement of upstream turbulence. The main advantages of the circular geometry are a minimum background noise, the absence of tip effects and more specifically the account for all radiation angles from the surface in the far-field acoustic signature. The circular set-up is well suited for the study of pure broadband interaction noise only if the flow remains free of self-sustained oscillations. This is ensured by keeping a sufficient interaction distance between the nozzle and the ring, and by shaping serrations on the nozzle lip. From the theoretical point of view, an analytical model is derived as a straightforward extension of existing formulations. The induced unsteady lift forces on the ring are first inferred from a linearized unsteady aerodynamic theory and the far field is calculated in a second step by a radiation integral. This relates the far-field acoustic pressure power spectral density (PSD) to the two-wavenumber spectrum of the radial turbulent velocity at the ring location, by means of an aeroacoustic transfer function. The latter is shown asymptotically identical to the one detailed in the Appendix for a rectangular aerofoil, in the limit of relatively high frequencies. The analytical acoustic predictions are found to agree well with the measurements over an extended frequency range, provided that the model is fed with turbulent velocity input data measured by a hot-wire probe. Indirectly, this agreement validates the transfer function for a rectangular aerofoil at oblique radiation angles, which is not achievable in a set-up involving side plates and a rectangular nozzle.

scholarly journals Diffusion Cooling of Electrons in an A.C. Field

1997 ◽  
Vol 50 (3) ◽  
pp. 577 ◽  
Author(s):  
R. E. Robson
Keyword(s):  
Velocity Distribution Function ◽  
Field Studies ◽  
Mean Free Path ◽  
Point Of View ◽  
Zero Field ◽  
Theoretical Point ◽  
Cooling Effects ◽  
Set Up ◽  
Gas Chamber ◽  
Harmonic Representation

Boundaries affect the measured values of transport coeffcients in all drift tube experiments, to a greater or lesser extent, and nowhere is this more apparent than in the experiment first devised by Cavalleri (1969) and subsequently adapted by Crompton and coworkers in the 1970s. The phenomenon of ‘diffusion cooling’ is particularly striking and arises essentially from a penetration of the ‘boundary layer’ (of thickness of the order of the mean free path for energy exchange) throughout a significant portion of the gas chamber. Although this is something of an obstacle to extracting the classical diffusion coefficient from experimental data, it is of great interest in its own right from a theoretical point of view, and the Crompton et al. experiments motivated several theoretical treatments which successfully explained diffusion cooling, albeit for zero applied field and on the basis of the ‘two-term’ spherical harmonic representation of the velocity distribution function. The present paper puts these theories in the context of the modern, generalised eigenvalue theory, which may be used as a basis for describing all swarm experiments. In addition, the earlier zero-field studies are generalised to the extent that an a.c. heating field is included, as was the case for the original Cavalleri experimental set-up. This field is found to enhance diffusion cooling effects for a simple model cross section.

Investigations on a Base Excited Rotor

2005 ◽  
Author(s):  
N. Driot ◽  
C. H. Lamarque ◽  
A. Berlioz
Keyword(s):  
Dynamic Behavior ◽  
Ritz Method ◽  
Multiple Scale ◽  
Point Of View ◽  
Theoretical Point ◽  
Coupled Equations ◽  
Lateral Displacements ◽  
Support Excitation ◽  
Set Up ◽  
Form Approach

In this study, the dynamic behavior of a flexible rotor system under support excitation (imposed displacements of its base) is analyzed. The effect of an excitation on lateral displacements is investigated from an experimental and a theoretical point of view. The study focuses on the behavior in bending. An experimental set-up is developed to observe the dynamic behavior that permits to measure the lateral displacements when the support of the system is submitted to a sinusoidal rotation. A mathematical model with two gyroscopic coupled equations is then derived using Rayleigh-Ritz method. The theoretical study is based on both the multiple scale method and the normal form approach. The experimental results are favorably compared with the analytical and numerical results.

scholarly journals Evolution of diversity in metabolic strategies

eLife ◽  
2021 ◽  
Vol 10 ◽  
Author(s):  
Rodrigo Caetano ◽  
Yaroslav Ispolatov ◽  
Michael Doebeli
Keyword(s):  
Evolutionary Dynamics ◽  
Fundamental Problem ◽  
Exclusion Principle ◽  
Ecological Interactions ◽  
Competitive Exclusion Principle ◽  
Theoretical Approaches ◽  
Coexisting Species ◽  
Metabolic Strategies ◽  
Very High ◽  
Consumer Resource

Understanding the origin and maintenance of biodiversity is a fundamental problem. Many theoretical approaches have been investigating ecological interactions, such as competition, as potential drivers of diversification. Classical consumer-resource models predict that the number of coexisting species should not exceed the number of distinct resources, a phenomenon known as the competitive exclusion principle. It has recently been argued that including physiological tradeoffs in consumer-resource models can lead to violations of this principle and to ecological coexistence of very high numbers of species. Here we show that these results crucially depend on the functional form of the tradeoff. We investigate the evolutionary dynamics of resource use constrained by tradeoffs and show that if the tradeoffs are non-linear, the system either does not diversify, or diversifies into a number of coexisting species that does not exceed the number of resources. In particular, very high diversity can only be observed for linear tradeoffs.

Timber Auctions in the Context of the Modern Auction Theory

2007 ◽  
pp. 86-94
Author(s):  
A. Manakov
Keyword(s):  
Theoretical Analysis ◽  
Auction Theory ◽  
Point Of View ◽  
Theoretical Point ◽  
English Auction ◽  
Analysis And Evaluation

The article provides theoretical analysis and evaluation of the timber auctions reforms in Russia. The author shows that the mechanism of the "combined auctions", which functioned until recently, is more appropriate from the theoretical point of view (and from the point of view of the Russian practice) as compared to the officially approved format of the English auction.

A novel cryptosystem based on abstract automata and Latin cubes

2015 ◽  
Vol 52 (2) ◽  
pp. 221-232
Author(s):  
Pál Dömösi ◽  
Géza Horváth
Keyword(s):  
Block Cipher ◽  
Finite Automata ◽  
Theoretical Background ◽  
Point Of View ◽  
Theoretical Point ◽  
Transition Matrices ◽  
Encryption And Decryption ◽  
Secret Keys ◽  
Automata Network ◽  
Fully Functioning

In this paper we introduce a novel block cipher based on the composition of abstract finite automata and Latin cubes. For information encryption and decryption the apparatus uses the same secret keys, which consist of key-automata based on composition of abstract finite automata such that the transition matrices of the component automata form Latin cubes. The aim of the paper is to show the essence of our algorithms not only for specialists working in compositions of abstract automata but also for all researchers interested in cryptosystems. Therefore, automata theoretical background of our results is not emphasized. The introduced cryptosystem is important also from a theoretical point of view, because it is the first fully functioning block cipher based on automata network.

The Revolutionizing of the Revolution

2017 ◽  
Author(s):  
R. R. Palmer
Keyword(s):  
French Revolution ◽  
Point Of View ◽  
Strict Sense ◽  
French Government ◽  
Thing In Itself ◽  
Set Up ◽  
The Moment ◽  
The French Revolution ◽  
The Revolution

In 1792, the French Revolution became a thing in itself, an uncontrollable force that might eventually spend itself but which no one could direct or guide. The governments set up in Paris in the following years all faced the problem of holding together against forces more revolutionary than themselves. This chapter distinguishes two such forces for analytical purposes. There was a popular upheaval, an upsurge from below, sans-culottisme, which occurred only in France. Second, there was the “international” revolutionary agitation, which was not international in any strict sense, but only concurrent within the boundaries of various states as then organized. From the French point of view these were the “foreign” revolutionaries or sympathizers. The most radical of the “foreign” revolutionaries were seldom more than advanced political democrats. Repeatedly, however, from 1792 to 1799, these two forces tended to converge into one force in opposition to the French government of the moment.

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