Waveform Invariance in Nonlinear Periodic Systems Using Higher-Order Multiple Scales

2016 ◽  
Author(s):  
Matthew Fronk ◽  
Michael J. Leamy
Keyword(s):  
Perturbation Analysis ◽  
Multiple Scales ◽  
Initial Conditions ◽  
Higher Order ◽  
Linear Quadratic ◽  
Numerical Studies ◽  
Specific Order ◽  
Spectral Variance ◽  
Force Displacement

This paper carries-out a higher-order, multiple scales perturbation analysis on nonlinear monoatomic and diatomic chains with the intent of predicting invariant waveforms. The chains incorporate linear, quadratic, and cubic force-displacement relationships, and linear dampers. Multi-harmonic results for 1st and 2nd order expansions are reported in closed form, while results for the 3rd order are computed numerically on a case-by-case basis, thus avoiding difficulties associated with large symbolic expressions. Dimensionless parameters are introduced which characterize the amplitude-dependent nonlinear nature of a given chain. Interpretation of the perturbation solutions suggests that the nonlinear chains support certain waveforms which propagate invariantly; i.e., the spectral content does not change significantly over time and space. Numerical simulations confirm this finding using initial conditions corresponding to a specific order of the perturbation solution, and subsequent FFT’s of the response track the growth (or decay) of spatial harmonic content. A variance parameter computes mean fluctuation of the harmonics about their initial values. For a variety of parameter sets, the numerical studies confirm that spectral variance reduces when waves receive 2nd order initial conditions as compared to 1st order ones. Furthermore, chains given 3rd order initial conditions exhibit smaller variance when compared to those given 1st and 2nd order ones. The studies’ results suggest that introducing higher-order multiple scales perturbation analysis captures long-term, non-localized invariant waves (or cnoidal waves), which have the potential for propagating coherent information over long distances.

scholarly journals Aircraft Maintenance Check Scheduling Using Reinforcement Learning

Aerospace ◽  
2021 ◽  
Vol 8 (4) ◽  
pp. 113
Author(s):  
Pedro Andrade ◽  
Catarina Silva ◽  
Bernardete Ribeiro ◽  
Bruno F. Santos
Keyword(s):  
Reinforcement Learning ◽  
Time Horizon ◽  
Learning Algorithm ◽  
Initial Conditions ◽  
Q Learning ◽  
Scheduling Policy ◽  
Real Scenario ◽  
Maintenance Plan ◽  
Small Disturbances

This paper presents a Reinforcement Learning (RL) approach to optimize the long-term scheduling of maintenance for an aircraft fleet. The problem considers fleet status, maintenance capacity, and other maintenance constraints to schedule hangar checks for a specified time horizon. The checks are scheduled within an interval, and the goal is to, schedule them as close as possible to their due date. In doing so, the number of checks is reduced, and the fleet availability increases. A Deep Q-learning algorithm is used to optimize the scheduling policy. The model is validated in a real scenario using maintenance data from 45 aircraft. The maintenance plan that is generated with our approach is compared with a previous study, which presented a Dynamic Programming (DP) based approach and airline estimations for the same period. The results show a reduction in the number of checks scheduled, which indicates the potential of RL in solving this problem. The adaptability of RL is also tested by introducing small disturbances in the initial conditions. After training the model with these simulated scenarios, the results show the robustness of the RL approach and its ability to generate efficient maintenance plans in only a few seconds.

scholarly journals “Is It Overtraining or Just Work Ethic?”: Coaches’ Perceptions of Overtraining in High-Performance Strength Sports

Sports ◽  
2021 ◽  
Vol 9 (6) ◽  
pp. 85
Author(s):  
Lee Bell ◽  
Alan Ruddock ◽  
Tom Maden-Wilkinson ◽  
Dave Hembrough ◽  
David Rogerson
Keyword(s):  
Physical Performance ◽  
Thematic Analysis ◽  
High Performance ◽  
Higher Order ◽  
Short Term ◽  
Semistructured Interviews ◽  
Diagnostic Symptoms ◽  
Careful Manipulation ◽  
Sport Coaches

Optimal physical performance is achieved through the careful manipulation of training and recovery. Short-term increases in training demand can induce functional overreaching (FOR) that can lead to improved physical capabilities, whereas nonfunctional overreaching (NFOR) or the overtraining syndrome (OTS) occur when high training-demand is applied for extensive periods with limited recovery. To date, little is known about the OTS in strength sports, particularly from the perspective of the strength sport coach. Fourteen high-performance strength sport coaches from a range of strength sports (weightlifting; n = 5, powerlifting; n = 4, sprinting; n = 2, throws; n = 2, jumps; n = 1) participated in semistructured interviews (mean duration 57; SD = 10 min) to discuss their experiences of the OTS. Reflexive thematic analysis resulted in the identification of four higher order themes: definitions, symptoms, recovery and experiences and observations. Additional subthemes were created to facilitate organisation and presentation of data, and to aid both cohesiveness of reporting and publicising of results. Participants provided varied and sometimes dichotomous perceptions of the OTS and proposed a multifactorial profile of diagnostic symptoms. Prevalence of OTS within strength sports was considered low, with the majority of participants not observing or experiencing long-term reductions in performance with their athletes.

scholarly journals Simulation of MASPn Experiments in MISTRA Test Facility with COCOSYS Code

2008 ◽  
Vol 2008 ◽  
pp. 1-7 ◽  
Author(s):  
Mantas Povilaitis ◽  
Egidijus Urbonavičius
Keyword(s):  
Boundary Conditions ◽  
Nuclear Power ◽  
Power Plants ◽  
Volume Fraction ◽  
Characteristic Length ◽  
Initial Conditions ◽  
Test Facility ◽  
Work Package ◽  
Acceptable Agreement

An issue of the stratified atmospheres in the containments of nuclear power plants is still unresolved; different experiments are performed in the test facilities like TOSQAN and MISTRA. MASPn experiments belong to the spray benchmark, initiated in the containment atmosphere mixing work package of the SARNET network. The benchmark consisted of MASP0, MASP1 and MASP2 experiments. Only the measured depressurisation rates during MASPn were available for the comparison with calculations. When the analysis was performed, the boundary conditions were not clearly defined therefore most of the attention was concentrated on MASP0 simulation in order to develop the nodalisation scheme and define the initial and boundary conditions. After achieving acceptable agreement with measured depressurisation rate, simulations of MASP1 and MASP2 experiments were performed to check the influence of sprays. The paper presents developed nodalisation scheme of MISTRA for the COCOSYS code and the results of analyses. In the performed analyses, several parameters were considered: initial conditions, loss coefficient of the junctions, initial gradients of temperature and steam volume fraction, and characteristic length of structures. Parametric analysis shows that in the simulation the heat losses through the external walls behind the lower condenser installed in the MISTRA facility determine the long-term depressurisation rate.

Homework questions designed to require higher-order cognitive skills in an undergraduate animal physiology course did not produce desirable difficulties, testing effects, or improvements in information retention

2021 ◽  
Author(s):  
Caitlin N Cadaret ◽  
Dustin T Yates
Keyword(s):  
Undergraduate Students ◽  
Cognitive Skills ◽  
Higher Order ◽  
Information Retention ◽  
Desirable Difficulties ◽  
Animal Physiology ◽  
Initial Learning ◽  
Retention Of Knowledge ◽  
Practical Exam

Abstract Studies show that retrieval practices such as homework assignments that are completed during the encoding phase of learning benefit knowledge acquisition and retention. In addition, desirable difficulties, which are strategies that intentionally create a greater challenge during initial learning to enhance encoding and retrieval pathways, also benefit learning long term. Our objective was to determine whether weekly homework questions intended to create desirable difficulties by requiring higher-order cognitive skills (HOCS) benefited students’ long-term retention of physiology concepts compared to questions designed to require lower-order cognitive skills (LOCS). Undergraduate students in a junior-level animal physiology course were presented information during weekly laboratory periods, and then required to complete retrieval practices in the form of online homework assignments 5 d after each lab. Homework questions were formatted per Bloom’s Taxonomy to require HOCS (i.e. level 4 or 5) or LOCS (i.e. level 1 or 2). Information retention was assessed the next week via performance on an in-class quiz and again at semesters’ end via performance on a final practical exam. We observed no differences in performance on the in-class quiz or final practical exam between students randomly assigned to complete homework with HOCS questions compared to LOCS questions. However, students that received homework with HOCS questions had decreased (P < 0.05) performance scores on 9 out of the 11 homework assignments compared to those receiving homework with LOCS questions. These findings indicate that desirable difficulties were not created by our HOCS homework questions because students receiving these more difficult retrieval practices did not achieve equal success on them. As a result, this attempt to create variations in cognitive demand did not enhance retention of knowledge in this study.

The role of service fairness in the service quality – relationship quality – customer loyalty chain

2015 ◽  
Vol 25 (6) ◽  
pp. 744-776 ◽  
Author(s):  
Apostolos Giovanis ◽  
Pinelopi Athanasopoulou ◽  
Evangelos Tsoukatos
Keyword(s):  
Service Quality ◽  
Relationship Quality ◽  
Customer Loyalty ◽  
Higher Order ◽  
Equation Modeling ◽  
Content Type ◽  
Order Construct ◽  
Service Fairness

Purpose – The purpose of this paper is to extend the well-established nomological network of service quality-relationship quality-customer loyalty by introducing service fairness – a distinct service evaluation concept. Specifically, the study aims to investigate the impact of service fairness on relationship quality as a complementary to service quality driver, and the direct and indirect effect of service fairness on customer loyalty in the presence of service quality and relationship quality in a no failure/recovery effort service context. Design/methodology/approach – A telephone survey of a random sample of 408 customers of auto repair and maintenance services was implemented using a structured questionnaire with established scales. Data were analyzed with partial least squares path methodology, a structural equation modeling methodology. Findings – Interactional fairness is the most important formative determinant of customers’ overall fairness perception, followed by procedural and distributive fairness. Relationship quality measured as a higher order construct, made of satisfaction; trust; affective and calculative commitment, is the main determinant of customer loyalty. Also, it partially mediates, along with service quality, the relationship between service fairness and customer loyalty and fully mediates the effect of service quality on customer loyalty. Finally, service fairness has the highest overall effect on customer loyalty. Research limitations/implications – The sample is industry-specific and this may affect generalizability of findings. Also, the cross-sectional design adopted does not reflect temporal changes. Practical implications – Interactional fairness is of utmost importance to customers of the investigated industry. So, customers should be fairly treated at every point of contact. Also, service quality is heavily affected by service fairness. Thus, fair service leads to high-perceived service quality. Third, service quality affects customer loyalty only through relationship quality. Only when service quality is coupled by long-term quality relationships, signs of customer loyalty appear. Finally, service fairness influences customer loyalty mainly through service and relationship quality and has the highest overall effect on customer loyalty. So, fairly treating customers is crucial for developing long-term relationships that lead to customer loyalty. Originality/value – The role of service fairness in the service quality-relationship quality-customer loyalty chain is investigated and using a higher order construct for relationship quality.

scholarly journals Soft-wired long-term memory in a natural recurrent neuronal network

2020 ◽  
Author(s):  
Miguel A. Casal ◽  
Santiago Galella ◽  
Oscar Vilarroya ◽  
Jordi Garcia-Ojalvo
Keyword(s):  
Neuronal Network ◽  
Neuronal Networks ◽  
Initial Conditions ◽  
Permutation Entropy ◽  
Long Term Memory ◽  
Term Memory ◽  
C Elegans ◽  
Living Organisms ◽  
Recurrent Connections

Neuronal networks provide living organisms with the ability to process information. They are also characterized by abundant recurrent connections, which give rise to strong feed-back that dictates their dynamics and endows them with fading (short-term) memory. The role of recurrence in long-term memory, on the other hand, is still unclear. Here we use the neuronal network of the roundworm C. elegans to show that recurrent architectures in living organisms can exhibit long-term memory without relying on specific hard-wired modules. A genetic algorithm reveals that the experimentally observed dynamics of the worm’s neuronal network exhibits maximal complexity (as measured by permutation entropy). In that complex regime, the response of the system to repeated presentations of a time-varying stimulus reveals a consistent behavior that can be interpreted as soft-wired long-term memory.A common manifestation of our ability to remember the past is the consistence of our responses to repeated presentations of stimuli across time. Complex chaotic dynamics is known to produce such reliable responses in spite of its characteristic sensitive dependence on initial conditions. In neuronal networks, complex behavior is known to result from a combination of (i) recurrent connections and (ii) a balance between excitation and inhibition. Here we show that those features concur in the neuronal network of a living organism, namely C. elegans. This enables long-term memory to arise in an on-line manner, without having to be hard-wired in the brain.

scholarly journals Complexity In Psychological Self-Ratings: Implications for research and practice

2020 ◽  
Author(s):  
Merlijn Olthof ◽  
Fred Hasselman ◽  
Anna Lichtwarck-Aschoff
Keyword(s):  
Complex Systems ◽  
Systems Approach ◽  
Complex Dynamics ◽  
Initial Conditions ◽  
Regime Shifts ◽  
Fundamental Aspect ◽  
Time Varying ◽  
Term Prediction ◽  
Sensitive Dependence

Background: Psychopathology research is changing focus from group-based ‘disease models’ to a personalized approach inspired by complex systems theories. This approach, which has already produced novel and valuable insights into the complex nature of psychopathology, often relies on repeated self-ratings of individual patients. So far it has been unknown whether such self-ratings, the presumed observables of the individual patient as a complex system, actually display complex dynamics. We examine this basic assumption of a complex systems approach to psychopathology by testing repeated self-ratings for three markers of complexity: memory, the presence of (time-varying) short- and long-range temporal correlations, regime shifts, transitions between different dynamic regimes, and, sensitive dependence on initial conditions, also known as the ‘butterfly effect’, the divergence of initially similar trajectories.Methods: We analysed repeated self-ratings (1476 time points) from a single patient for the three markers of complexity using Bartels rank test, (partial) autocorrelation functions, time-varying autoregression, a non-stationarity test, change point analysis and the Sugihara-May algorithm.Results: Self-ratings concerning psychological states (e.g., the item ‘I feel down’) exhibited all complexity markers: time-varying short- and long-term memory, multiple regime shifts and sensitive dependence on initial conditions. Unexpectedly, self-ratings concerning physical sensations (e.g., the item ‘I am hungry’) exhibited less complex dynamics and their behaviour was more similar to random variables. Conclusions: Psychological self-ratings display complex dynamics. The presence of complexity in repeated self-ratings means that we have to acknowledge that (1) repeated self-ratings yield a complex pattern of data and not a set of (nearly) independent data points, (2) humans are ‘moving targets’ whose self-ratings display non-stationary change processes including regime shifts, and (3) long-term prediction of individual trajectories may be fundamentally impossible. These findings point to a limitation of popular statistical time series models whose assumptions are violated by the presence of these complexity markers. We conclude that a complex systems approach to mental health should appreciate complexity as a fundamental aspect of psychopathology research by adopting the models and methods of complexity science. Promising first steps in this direction, such as research on real-time process-monitoring, short-term prediction, and just-in-time interventions, are discussed.

Visualising the invisible: performing chaos theory

Leonardo ◽  
2020 ◽  
pp. 1-8
Author(s):  
Emma Weitkamp
Keyword(s):  
Complex Systems ◽  
Chaos Theory ◽  
Initial Conditions ◽  
Starting Point ◽  
Weather And Climate ◽  
Butterfly Effect ◽  
Long Term Behavior ◽  
The Invisible

Edward Lorenz, the pioneering figure in the field of chaos theory coined the phrase “butterfly effect” and posed the famous question “Does the flap of a butterfly's wings in Brazil set off a tornado in Texas?” In posing the question, Lorenz sought to highlight the intrinsic difficulty of predicting the long term behavior of complex systems that are sensitive to initial conditions, like, for example, the weather and climate; these systems are often referred to as chaotic. Taking Lorenz' butterfly as a starting point, Chaos Cabaret sought to explore the nuances of chaos theory through performance and music.

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