scholarly journals Genomic divergence landscape in recurrently hybridizing Chironomus sister taxa suggests stable steady state between mutual gene flow and isolation

2020 ◽  
Author(s):  
Dennis Schreiber ◽  
Markus Pfenninger
Keyword(s):  
Steady State ◽  
Gene Flow ◽  
Stable Steady State ◽  
Genomic Divergence

scholarly journals Results of the Marine Ice Sheet Model Intercomparison Project, MISMIP

2012 ◽  
Vol 6 (3) ◽  
pp. 573-588 ◽  
Author(s):  
F. Pattyn ◽  
C. Schoof ◽  
L. Perichon ◽  
R. C. A. Hindmarsh ◽  
E. Bueler ◽  
...  
Keyword(s):  
Steady State ◽  
Adaptive Mesh Refinement ◽  
Ice Sheet ◽  
Adaptive Mesh ◽  
Stable Steady State ◽  
Fixed Grid ◽  
Approximate Analytical Solutions ◽  
Grounding Line ◽  
Intercomparison Project ◽  
Line Positions

Abstract. Predictions of marine ice-sheet behaviour require models that are able to robustly simulate grounding line migration. We present results of an intercomparison exercise for marine ice-sheet models. Verification is effected by comparison with approximate analytical solutions for flux across the grounding line using simplified geometrical configurations (no lateral variations, no effects of lateral buttressing). Unique steady state grounding line positions exist for ice sheets on a downward sloping bed, while hysteresis occurs across an overdeepened bed, and stable steady state grounding line positions only occur on the downward-sloping sections. Models based on the shallow ice approximation, which does not resolve extensional stresses, do not reproduce the approximate analytical results unless appropriate parameterizations for ice flux are imposed at the grounding line. For extensional-stress resolving "shelfy stream" models, differences between model results were mainly due to the choice of spatial discretization. Moving grid methods were found to be the most accurate at capturing grounding line evolution, since they track the grounding line explicitly. Adaptive mesh refinement can further improve accuracy, including fixed grid models that generally perform poorly at coarse resolution. Fixed grid models, with nested grid representations of the grounding line, are able to generate accurate steady state positions, but can be inaccurate over transients. Only one full-Stokes model was included in the intercomparison, and consequently the accuracy of shelfy stream models as approximations of full-Stokes models remains to be determined in detail, especially during transients.

scholarly journals Suppression of marine ice sheet instability

2018 ◽  
Vol 857 ◽  
pp. 648-680 ◽  
Author(s):  
Samuel S. Pegler
Keyword(s):  
Steady State ◽  
Rapid Assessment ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Stable Steady State ◽  
Ice Shelf ◽  
West Antarctic Ice Sheet ◽  
West Antarctic ◽  
Grounding Line ◽  
The Stability

A long-standing open question in glaciology concerns the propensity for ice sheets that lie predominantly submerged in the ocean (marine ice sheets) to destabilise under buoyancy. This paper addresses the processes by which a buoyancy-driven mechanism for the retreat and ultimate collapse of such ice sheets – the marine ice sheet instability – is suppressed by lateral stresses acting on its floating component (the ice shelf). The key results are to demonstrate the transition between a mode of stable (easily reversible) retreat along a stable steady-state branch created by ice-shelf buttressing to tipped (almost irreversible) retreat across a critical parametric threshold. The conditions for triggering tipped retreat can be controlled by the calving position and other properties of the ice-shelf profile and can be largely independent of basal stress, in contrast to principles established from studies of unbuttressed grounding-line dynamics. The stability and recovery conditions introduced by lateral stresses are analysed by developing a method of constructing grounding-line stability (bifurcation) diagrams, which provide a rapid assessment of the steady-state positions, their natures and the conditions for secondary grounding, giving clear visualisations of global stabilisation conditions. A further result is to reveal the possibility of a third structural component of a marine ice sheet that lies intermediate to the fully grounded and floating components. The region forms an extended grounding area in which the ice sheet lies very close to flotation, and there is no clearly distinguished grounding line. The formation of this region generates an upsurge in buttressing that provides the most feasible mechanism for reversal of a tipped grounding line. The results of this paper provide conceptual insight into the phenomena controlling the stability of the West Antarctic Ice Sheet, the collapse of which has the potential to dominate future contributions to global sea-level rise.

scholarly journals System Approach from Biomass Combustion in Packed Bed Reactor

2007 ◽  
Vol 7 (1 & 2) ◽  
pp. 16 ◽  
Author(s):  
Anhkien Le ◽  
Le Xuan Hai ◽  
V. N. Sharifi ◽  
J. Swithenbank
Keyword(s):  
Steady State ◽  
Transition Period ◽  
Computing Time ◽  
Substrate Inhibition ◽  
Simple Algorithm ◽  
Packed Bed ◽  
Packed Bed Reactor ◽  
Biomass Combustion ◽  
Stable Steady State ◽  
State Tests

A simple algorithm originally proposed by Choong, Paterson and Scott (2002) was tested on a model of an isothermal controlled-cycled stirred tank reactor with substrate inhibition kinetics, (r = 1 ~c). In previous work, this reacting system had been shown to exhibit steady-state multiplicity. The transition period of this system to the stable steady state is sometimes characterized by very slow change followed by a very rapid convergence to the stable steady state. Tests of the Choong-Paterson-Scott algorithm showed that the feature, which prevents premature termination of the calculations prior to reaching the true steady state, is very useful for this system. However, tests of the stopping criterion showed that the other feature of reducing the computing time was not realized in this system.

Heuristic control of bipedal running: steady-state and accelerated

Robotica ◽  
2011 ◽  
Vol 29 (6) ◽  
pp. 939-947
Author(s):  
A. D. Perkins ◽  
K. J. Waldron ◽  
P. J. Csonka
Keyword(s):  
Steady State ◽  
Experimental System ◽  
Legged Robots ◽  
Stable Steady State ◽  
Control Laws ◽  
Mechanical Coupling ◽  
Ankle Joints

SUMMARYThe design, control, and actuation of legged robots that walk is well established, but there remain unsolved problems for legged robots that run. In this work, dynamic principles are used to develop a set of heuristics for controlling bipedal running and acceleration. These heuristics are then converted into control laws for two very different bipedal systems: one with a high-inertia torso and prismatic knees and one with a low-inertia torso, articulated knees, and mechanical coupling between the knee and ankle joints. These control laws are implemented in simulation to achieve stable steady-state running, accelerating, and decelerating. Stable steady-state running is also achieved in a planar experimental system with a semiconstrained torso.

Analysis of chemical kinetic systems over the entire parameter space - I. The Sal’nikov thermokinetic oscillator

1988 ◽  
Vol 416 (1851) ◽  
pp. 391-402 ◽  
Keyword(s):  
Steady State ◽  
Parameter Space ◽  
Limit Cycles ◽  
Stable Limit Cycle ◽  
Chemical Kinetic ◽  
Phase Portraits ◽  
Stable Steady State ◽  
Stable Limit ◽  
Unstable Steady State ◽  
Undamped Oscillations

In this series of papers we re-examine, using recently developed techniques, some chemical kinetic models that have appeared in the literature with a view to obtaining a complete description of all the qualitatively distinct behaviour that the system can exhibit. Each of the schemes is describable by two coupled ordinary differential equations and contain at most three independent parameters. We find that even with these relatively simple chemical schemes there are regions of parameter space in which the systems display behaviour not previously found. Quite often these regions are small and it seems unlikely that they would be found via classical methods. In part I of the series we consider one of the thermally coupled kinetic oscillator models studied by Sal’nikov. He showed that there is a region in parameter space in which the system would be in a state of undamped oscillations because the relevant phase portrait consists of an unstable steady state surrounded by a stable limit cycle. Our analysis has revealed two further regions in which the phase portraits contain, respectively, two limit cycles of opposite stability enclosing a stable steady state and three limit cycles of alternating stability surrounding an unstable steady state. This latter region is extremely small, so much so that it could be reasonably neglected in any predictions made from the model.

scholarly journals Energy Requirement for Maintenance of Adenylate Energy Charge and Metabolic ATP in Platelets During Starvation

1977 ◽  
Author(s):  
J.W.N. Akkerman ◽  
G. Gorter ◽  
J.J. Sixma
Keyword(s):  
Steady State ◽  
Adenine Nucleotides ◽  
Energy Requirement ◽  
Energy Charge ◽  
Lactate Production ◽  
Stable Steady State ◽  
Adenylate Energy Charge ◽  
Consumption Energy ◽  
Steady State Levels ◽  
Lactate Formation

Energy requirements for maintenance of stable adenylate energy charge (AEC) and metabolic ATP(ATP-m)level were studied in gel filtered platelets at various degrees of starvation. Platelets gel filtered and subsequently incubated during 40 min.at 37°C with 1mM CN- and without glucose consumed their glycogen at a rate of 0.79 ± 0.23(± SD, n=6)/μmol glycosyl residues .min-1 10-11 cells. During this period AEC and ATP-m decreased linearly with time at rates of 5-6.10-3 and 0.75-1.05% of total radioactive adenine nucleotides .min-1.10-11 cells respectively. Addition of 25–1000μM glucose increased lactate production and decreased the fall of AEC and ATP-m proportional to the amounts of glucose added. Glycogenolysis remained active below 100μM glucose but ceased at higher glucose concentrations. From these data ATP-m production from glycogenolysis and glycolysis was calculated and compared with the decrease of steady state levels of AEC and ATP-m. A production of 3μmol ATP-m.min-1.10-11 cells was required to maintain initial AEC and ATP-m level. At lower rates of ATP-m production these values fell without reaching stable steady state levels in a lower range. After 40-50 min variations in AEC and ATP-m ceased and lactate formation stopped leaving the cells in a state of hybernation. Subsequent addition of glucoserestored lactate accumulation, AEC and ATP-m. On the basis of formation and steady state levels of ATP-m its consumption was calculated. A lowering production was not completely met by a lowering consumption. Energy consumption in resting platelets is therefore partly independent from energy production.

Development of a Carbon Nanotube-Based Electromechanical Resonator: Device Modeling

2008 ◽  
Author(s):  
Changhong Ke
Keyword(s):  
Steady State ◽  
Carbon Nanotube ◽  
Parallel Plate ◽  
Force Sensing ◽  
Stable Steady State ◽  
Device Modeling ◽  
Complex Relationship ◽  
Novel Device ◽  
Close Form ◽  
Electromechanical Dynamics

We present an electromechanical analysis of a novel double-sided driven carbon nanotube-based electromechanical resonator. The device comprises a cantilevered carbon nanotube actuated by two parallel-plate electrodes. Close-form analytical solutions capable of predicting the steady-state resonation of the device and its resonant pull-in conditions are derived using an energy-based method. Our close-form formulas clearly reveal the complex relationship among the device geometry, the driving voltages, and the device’s electromechanical dynamics. Our theoretical modeling shows that the stable steady-state spanning range of the resonating cantilever substantially exceeds the previously reported quasi-static pull-in limit for single-sided driven cantilevered nanotube-based NEMS, while the resonant pull-in voltage is only a small fraction of the quasi-static pull-in voltage. The unique behaviors of this novel device are expected to significantly enhance the applications of electromechanical resonators in the fields of signal processing, mass and force sensing, and chemical and molecule detection.

scholarly journals Neutral equilibrium and forcing feedbacks in marine ice sheet modelling

2018 ◽  
Vol 12 (11) ◽  
pp. 3605-3615 ◽  
Author(s):  
Rupert M. Gladstone ◽  
Yuwei Xia ◽  
John Moore
Keyword(s):  
Steady State ◽  
False Positive ◽  
Ice Sheet ◽  
Stable Steady State ◽  
Model Configuration ◽  
Grounding Line ◽  
Neutral Equilibrium ◽  
Poor Convergence ◽  
Line Positions ◽  
Additional Constraints

Abstract. Poor convergence with resolution of ice sheet models when simulating grounding line migration has been known about for over a decade. However, some of the associated numerical artefacts remain absent from the published literature. In the current study we apply a Stokes-flow finite-element marine ice sheet model to idealised grounding line evolution experiments. We show that with insufficiently fine model resolution, a region containing multiple steady-state grounding line positions exists, with one steady state per node of the model mesh. This has important implications for the design of perturbation experiments used to test convergence of grounding line behaviour with resolution. Specifically, the design of perturbation experiments can be under-constrained, potentially leading to a “false positive” result. In this context a false positive is an experiment that appears to achieve convergence when in fact the model configuration is not close to its converged state. We demonstrate a false positive: an apparently successful perturbation experiment (i.e. reversibility is shown) for a model configuration that is not close to a converged solution. If perturbation experiments are to be used in the future, experiment design should be modified to provide additional constraints to the initialisation and spin-up requirements. This region of multiple locally stable steady-state grounding line positions has previously been mistakenly described as neutral equilibrium. This distinction has important implications for understanding the impacts of discretising a forcing feedback involving grounding line position and basal friction. This forcing feedback cannot, in general, exist in a region of neutral equilibrium and could be the main cause of poor convergence in grounding line modelling.

PREDATION AND STEADY STATES IN HIGH-TC SUPERCONDUCTORS

1993 ◽  
Vol 07 (12) ◽  
pp. 829-833
Author(s):  
RONALDO MOTA
Keyword(s):  
Steady State ◽  
Steady States ◽  
Dynamical Model ◽  
Stable Steady State ◽  
Spin Polaron ◽  
High Tc Superconductors ◽  
High Tc ◽  
Practical Model

A study of the role played by predation in a population dynamical model previously considered for spin-polaron-pairs in high-Tc superconductors is presented. A practical model which exhibits two positive linearly stable steady state populations is considered. A discussion of various aspects and implications of the model is given.

Pre-Stall Instability Distribution Over a Transonic Compressor Rotor

2008 ◽  
Author(s):  
A. J. Gannon ◽  
G. V. Hobson
Keyword(s):  
Steady State ◽  
Low Frequency ◽  
Tip Vortex ◽  
Stable Steady State ◽  
Complex Flow ◽  
Suction Surface ◽  
Steady State Condition ◽  
Transonic Compressor ◽  
Compressor Rotor ◽  
Area Of Interest

An investigation of the behavior of a transonic compressor rotor when operating close to stall is presented. The specific area of interest is the behavior and location of low-frequency instabilities when operating close to stall. When running close to stall compressors begin to exhibit non-periodic flow between the blade passages even when appearing to be operating in a stable steady-state condition. These frequencies are not geometrically fixed to the rotor and typically appear at 0.3–0.8 of the rotor speed. The presence of these low-frequency instabilities are known and detection are reasonably commonplace, however attempts to quantify the location and strength of these instabilities as stall is approached have proved difficult. In the test rotor probes were positioned in the case-wall upstream, downstream and over the rotor blade tips. Simultaneous data from all the probes was taken at successive steady-state settings each operating closer to stall. The simultaneous data is presented to show the development and distribution of the instabilities over the rotor as stall was approached. Initially the instabilities appeared within the rotor row and extended downstream. At operation closer to stall they protruded upstream and downstream. The greatest amplitude of the instabilities was within the blade row in the complex flow region that contained the tip-vortex interacting with the shock and the shock impinging on the blade suction surface. In the current rotor the data shows that the instabilities were present during steady-state operation when stall was approached even when stall was not imminent. In addition they do not behave in a linear manner as stall was approached.

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