scholarly journals Time-dependent fitness effects can drive bet-hedging populations extinct

2016 ◽  
Author(s):  
Eric Libby ◽  
William Ratcliff
Keyword(s):  
Resource Competition ◽  
Bet Hedging ◽  
Short Term ◽  
Time Intervals ◽  
Hedging Strategies ◽  
Diversification Strategies ◽  
Environmental Fluctuations ◽  
Long Time ◽  
Temporally Correlated

AbstractTo survive unpredictable environmental change, many organisms adopt bet-hedging strategies that trade short-term population growth for long-term fitness benefits. Because the benefits of bet-hedging may manifest over long time intervals, bet-hedging strategies may be out-competed by strategies maximizing short-term fitness. Here, we investigate the interplay between two drivers of selection, environmental fluctuations and competition for limited resources, on different bet-hedging strategies. We consider an environment with frequent disasters that switch between which phenotypes they affect in a temporally-correlated fashion. We determine how organisms that stochastically switch between phenotypes at different rates fare in both competition and survival. When disasters are correlated in time, the best strategy for competition is among the worst for survival. Since the time scales over which the two agents of selection act are significantly different, environmental fluctuations and resource competition act in opposition and lead populations to evolve diversification strategies that ultimately drive them extinct.

scholarly journals Short‐term insurance versus long‐term bet‐hedging strategies as adaptations to variable environments

Evolution ◽  
2018 ◽  
Vol 73 (2) ◽  
pp. 145-157 ◽  
Author(s):  
Thomas Ray Haaland ◽  
Jonathan Wright ◽  
Jarle Tufto ◽  
Irja Ida Ratikainen
Keyword(s):  
Bet Hedging ◽  
Short Term ◽  
Hedging Strategies ◽  
Variable Environments ◽  
Term Insurance

scholarly journals Methods of long-term and short-term adaptation for biometric image of keystroke dynamics

2021 ◽  
Vol 7 (3D) ◽  
pp. 450-457
Author(s):  
Dmitry V. Pashchenko ◽  
Dmitry A. Trokoz ◽  
Alexey I. Martyshkin ◽  
Elena A. Balzannikova
Keyword(s):  
Working Capacity ◽  
Keystroke Dynamics ◽  
Short Term ◽  
User Identification ◽  
New Device ◽  
Short Term Adaptation ◽  
Long Time

This article discusses one of the main problems of user identification by keyboard handwriting - short-term changes in the keystroke dynamics of users in connection with its psychophysical state, as well as changes over a long time associated with the formation of keystroke dynamics by a new user or when switching to a new device. A method for determining the phase of working capacity by the time characteristics of the keystroke dynamics is proposed.

Metaheuristic Search with Inequalities and Target Objectives for Mixed Binary Optimization – Part II

2010 ◽  
Vol 1 (2) ◽  
pp. 1-17 ◽  
Author(s):  
Fred Glover ◽  
Saïd Hanafi
Keyword(s):  
Linear Programming ◽  
Programming Models ◽  
Mixed Integer ◽  
Embedded Memory ◽  
Short Term ◽  
Solution Strategies ◽  
Diversification Strategies ◽  
Metaheuristic Search ◽  
New Inequalities

Recent metaheuristics for mixed integer programming have included proposals for introducing inequalities and target objectives to guide this search. These guidance approaches are useful in intensification and diversification strategies related to fixing subsets of variables at particular values. The authors’ preceding Part I study demonstrated how to improve such approaches by new inequalities that dominate those previously proposed. In Part II, the authors review the fundamental concepts underlying weighted pseudo cuts for generating guiding inequalities, including the use of target objective strategies. Building on these foundations, this paper develops a more advanced approach for generating the target objective based on exploiting the mutually reinforcing notions of reaction and resistance. The authors demonstrate how to produce new inequalities by “mining” reference sets of elite solutions to extract characteristics these solutions exhibit in common. Additionally, a model embedded memory is integrated to provide a range of recency and frequency memory structures for achieving goals associated with short term and long term solution strategies. Finally, supplementary linear programming models that exploit the new inequalities for intensification and diversification are proposed.

scholarly journals Modes of response to environmental change and the elusive empirical evidence for bet hedging

2011 ◽  
Vol 278 (1712) ◽  
pp. 1601-1609 ◽  
Author(s):  
Andrew M. Simons
Keyword(s):  
Environmental Change ◽  
Empirical Evidence ◽  
Natural Environments ◽  
Bet Hedging ◽  
Fluctuating Selection ◽  
Hedging Strategies ◽  
Evolutionary Response ◽  
Human Decision ◽  
Response To Environmental Change

Uncertainty is a problem not only in human decision-making, but is a prevalent quality of natural environments and thus requires evolutionary response. Unpredictable natural selection is expected to result in the evolution of bet-hedging strategies, which are adaptations to long-term fluctuating selection. Despite a recent surge of interest in bet hedging, its study remains mired in conceptual and practical difficulties, compounded by confusion over what constitutes evidence for its existence. Here, I attempt to resolve misunderstandings about bet hedging and its relationship with other modes of response to environmental change, identify the challenges inherent to its study and assess the state of existing empirical evidence. The variety and distribution of plausible bet-hedging traits found across 16 phyla in over 100 studies suggest their ubiquity. Thus, bet hedging should be considered a specific mode of response to environmental change. However, the distribution of bet-hedging studies across evidence categories—defined according to potential strength—is heavily skewed towards weaker categories, underscoring the need for direct appraisals of the adaptive significance of putative bet-hedging traits in nature.

Simulation of Hydrogen Distribution due to In-Vessel Severe Accident in WWER-1000 NPP Containment: A Comparison of CONTAIN and MELCOR Codes Results

2018 ◽  
Author(s):  
Omid Noorikalkhoran ◽  
Massimiliano Gei
Keyword(s):  
Severe Accident ◽  
Second Step ◽  
Hydrogen Distribution ◽  
Short Term ◽  
Long Time ◽  
Design Basis Accident ◽  
Safety Features ◽  
Design Pressure ◽  
Good Agreement

During a severe accident or Beyond Design Basis Accident (BDBA), the reaction of water with zirconium alloy as fuel clad, radiolysis of water, molten corium-concrete interaction (MCCI) and post-accident corrosion can generate a source of hydrogen. In the present work, hydrogen distribution due to in-vessel reaction (between zircaloy and steam) has been simulated inside a WWER-1000 reactor containment. In the first step, the thermal hydraulic parameters of containment have been simulated for a DECL (Double Ended Cold Leg) accident (DBA phase) in both short and long time and the effects of spray as Engineering Safety Features (ESFs) on mitigating the parameters have been studied. In the second step, it has been assumed that the accident developed into an in-vessel core melting accident. While in pre-phase of core melting (severe accident phase), hydrogen will be produced as a result of zircaloy and steam reaction (BDBA phase), the hydrogen distribution has been simulated for 23 cells inside the reactor containment by using CONTAIN 2.0 (Best estimate code) and MELCOR 1.8.6 codes. Finally, the results have been compared to FSAR results. As it can be seen from the comparisons, both CONTAIN and MELCOR codes can predict the results in good agreement with FSAR (ANGAR code) results. CONTAIN shows peak pressure around 0.36 MPa in short-term and this amount is about 0.38 and 0.4 MPa for MELCOR and ANGAR (FSAR) results respectively. All these values are under design pressure that is around 0.46 MPa. Cell 20 has the maximum mole fraction of hydrogen in long-term about 9.5% while the maximum amount of hydrogen takes place in cell 22. The differences between the results of codes are because of different equations, Models, Numerical methods and assumptions that have been considered by the codes. The simulated Hydrogen Distribution Map (HDM) can be used for upgrading the location of HCAV systems and Hydrogen Mitigator features (like the recombiners and ignitors) inside the containment to reduce the risk of hydrogen explosion.

Photometry of Variable Stars, and System Transformability Over Long Time Intervals

2003 ◽  
Vol 12 (4) ◽  
Author(s):  
C. Sterken
Keyword(s):  
Fundamental Problem ◽  
Variable Stars ◽  
Time Intervals ◽  
Multi Wavelength ◽  
Long Time ◽  
Photometric Monitoring ◽  
Made In

AbstractThe fundamental problem of long-term photometric monitoring of variable stars and of multi-wavelength photometric campaigns is the problem of bringing the data to a common standard. Such homogenization can be achieved only when the measurements are made in photometric systems that are truly transformable. This fundamental problem is of a technical nature, and photometric observers, sometimes, are not aware of the problems. This frequently leads to over-interpretation of the data.

A Canonical Microfunction for Learning Perceptual Invariances

Perception ◽  
1996 ◽  
Vol 25 (2) ◽  
pp. 207-220 ◽  
Author(s):  
James V Stone
Keyword(s):  
Model Neuron ◽  
Learning Rule ◽  
Image Sequences ◽  
Weight Changes ◽  
Short Term ◽  
Stereo Disparity ◽  
Random Dot Stereograms ◽  
Long Time ◽  
Generic Strategy

An unsupervised method is presented which permits a set of model neurons, or a microcircuit, to learn low-level vision tasks, such as the extraction of surface depth. Each microcircuit implements a simple, generic strategy which is based on a key assumption: perceptually salient visual invariances, such as surface depth, vary smoothly over time. In the process of learning to extract smoothly varying invariances, each microcircuit maximises a microfunction. This is achieved by means of a learning rule which maximises the long-term variance of the state of a model neuron and simultaneously minimises its short-term variance. The learning rule involves a linear combination of anti-Hebbian and Hebbian weight changes, over short and long time scales, respectively. The method is demonstrated on a hyperacuity task: estimating subpixel stereo disparity from a temporal sequence of random-dot stereograms. After learning, the microcircuit generalises, without additional learning, to previously unseen image sequences. It is proposed that the approach adopted here may be used to define a canonical microfunction, which can be used to learn many perceptually salient invariances.

Influence of Whipping on Long-term Vertical Bending Moment

2004 ◽  
Vol 48 (04) ◽  
pp. 261-272
Author(s):  
Gro Sagli Baarholm ◽  
Jørgen Juncher Jensen
Keyword(s):  
Nonlinear Response ◽  
Extreme Values ◽  
Bending Moment ◽  
Sea Waves ◽  
Short Term ◽  
Strip Theory ◽  
Long Time ◽  
Wave Induced ◽  
Vertical Bending Moment

This paper is concerned with estimating the response value corresponding to a long return period, say 20 years. Time domain simulation is required to obtain the nonlinear response, and long time series are required to limit the statistical uncertainty in the simulations. It is crucial to introduce ways to improve the efficiency in the calculation. A method to determine the long-term extremes by considering only a few short-term sea states is applied. Long-term extreme values are estimated using a set of sea states that have a certain probability of occurrence, known as the contour line approach. Effect of whipping is included by assuming that the whipping and wave-induced responses are independent, but the effect of correlation of the long-term extreme value is also studied. Numerical calculations are performed using a nonlinear, hydroelastic strip theory as suggested by Xia et al (1998). Results are presented for the S-175 containership (ITTC 1983) in head sea waves. The analysis shows that whipping increases the vertical bending moment and that the correlation is significant.

Short-term stress for long-lasting otolith morphology — brief embryological stress disturbance can reorient otolith ontogenetic trajectory

2018 ◽  
Vol 75 (10) ◽  
pp. 1713-1722 ◽  
Author(s):  
Matthias Vignon
Keyword(s):  
Environmental Conditions ◽  
Salmo Trutta ◽  
Short Term ◽  
Otolith Shape ◽  
Fisheries Resources ◽  
Otolith Morphology ◽  
Ontogenetic Trajectory ◽  
Brown Trout Salmo Trutta ◽  
Long Time

Long-term plasticity of otolith shape has become a unifying principle to use morphological differences as indicator of environmental conditions. Contrary to the longstanding paradigmatic view that otolith shape can only reflect residency in particular environmental conditions over long time periods, data emphasize that otolith ontogenetic trajectory may be reoriented in case of short-term episodes of environmental disturbance during early lifetime. Using geometric morphometrics, discrimination was posible in absence of growth-related differences between control and brown trout (Salmo trutta Linnaeus, 1758) that have experienced brief thermal stress prior to their emergence but have grown in similar conditions (i.e., cohabiting within the same aquarium) during 6 months. Data emphasize that brief stress during key developmental periods can durably influence ontogenetic trajectories, subsequent otolith development, and can consequently change otolith morphology in juveniles. Therefore, differences in shape between groups of fish may not be exclusively indicative of long-time residency in contrasted and (or) separated habitats as it is generally assumed. Moving beyond long-term assumptions is fundamental if otolith shape is to be used as an effective tool for management of fisheries resources in the future.

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