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Theory of constraints

Hyacinth O Ukuhor, Janet Hirst, S José Closs, William J Montelpare
Objective. The aim of this research was to explore the influence of service organisation and delivery on providers and users' interactions and decision-making in the context of Down's syndrome screening. Methods. A qualitative descriptive study involving online interviews conducted with a purposive sample of 34 community midwives, 35 pregnant women, and 15 partners from two maternity services in different health districts in England. Data were analysed using a combination of grounded theory principles and content analysis and a framework was developed...
2017: Journal of Pregnancy
Julian Barreiro-Gomez, Carlos Ocampo-Martinez, Nicanor Quijano
Model predictive control (MPC) is a suitable strategy for the control of large-scale systems that have multiple design requirements, e.g., multiple physical and operational constraints. Besides, an MPC controller is able to deal with multiple control objectives considering them within the cost function, which implies to determine a proper prioritization for each of the objectives. Furthermore, when the system has time-varying parameters and/or disturbances, the appropriate prioritization might vary along the time as well...
April 15, 2017: ISA Transactions
A M S Macêdo, Iván R Roa González, D S P Salazar, G L Vasconcelos
A unified approach is proposed to describe the statistics of the short-time dynamics of multiscale complex systems. The probability density function of the relevant time series (signal) is represented as a statistical superposition of a large time-scale distribution weighted by the distribution of certain internal variables that characterize the slowly changing background. The dynamics of the background is formulated as a hierarchical stochastic model whose form is derived from simple physical constraints, which in turn restrict the dynamics to only two possible classes...
March 2017: Physical Review. E
Esther Sebastián-González
The mutualistic interaction between frugivore birds and the fruiting plants they disperse presents an asymmetric interaction pattern, with some species having a more important role (i.e. being essential) for maintaining the structure and functioning of the interaction network. The identification of the biological characteristics of these species is of major importance for the understanding and conservation of seed-dispersal interactions. In this study, I use a network approach and avian seed-dispersal networks from 23 different geographical areas to test 5 hypotheses about species characteristics determining the structure of the assemblage...
April 17, 2017: Journal of Animal Ecology
Hanlin Deng, Weihua Li, Feng Qiu, An-Chang Shi
Monolayers of linear and miktoarm star ABC triblock copolymers with equal A and C blocks were investigated using self-consistent field theory. Monolayers of ABC triblock copolymers were formed between two parallel surfaces that were attractive to the A and C blocks. The repulsive interaction parameter χACN between the A and C blocks was chosen to be weaker than the A/B and B/C interactions, quantified by χABN and χBCN, respectively, such that the B blocks were confined at the A/C interface, resulting in various B domains with different geometries and arrangements...
April 20, 2017: Journal of Physical Chemistry. B
Dennis McKenna, Jordi Riba
New World indigenous peoples are noted for their sophisticated use of psychedelic plants in shamanic and ethnomedical practices. The use of psychedelic plant preparations among New World tribes is far more prevalent than in the Old World. Yet, although these preparations are botanically diverse, almost all are chemically similar in that their active principles are tryptamine derivatives, either DMT or related constituents. Part 1 of this paper provides an ethnopharmacological overview of the major tryptamine-containing New World hallucinogens...
April 2, 2017: Current Topics in Behavioral Neurosciences
René F Kizilcec, Geoffrey L Cohen
Academic credentials open up a wealth of opportunities. However, many people drop out of educational programs, such as community college and online courses. Prior research found that a brief self-regulation strategy can improve self-discipline and academic outcomes. Could this strategy support learners at large scale? Mental contrasting with implementation intentions (MCII) involves writing about positive outcomes associated with a goal, the obstacles to achieving it, and concrete if-then plans to overcome them...
April 10, 2017: Proceedings of the National Academy of Sciences of the United States of America
Filip Šebesta, Jaroslav V Burda
Two possible pathways of the substitution reaction within the reduction process of the PtIV(DACH)Cl4 by dGMP are compared: associative reaction course and autocatalytic Basolo-Pearson mechanisms. Since two forms: single-protonated and fully-deprotonated phosphate group of dGMP are in equilibrium at neutral and mildly acidic solutions, consideration of a side reactions scheme with acido-basic equilibrium-constraint is a very important model for obtaining reliable results. The examined complexes are optimized at the B3LYP-D3/6-31G(d) level with the COSMO implicit solvation model and Klamt's radii used for cavity construction...
April 10, 2017: Journal of Physical Chemistry. B
Zachary E Dell, Kenneth S Schweizer
We develop a segment-scale, force-based theory for the breakdown of the unentangled Rouse model and subsequent emergence of isotropic mesoscopic localization and entropic elasticity in chain polymer liquids in the absence of ergodicity-restoring anisotropic reptation or activated hopping motion. The theory is formulated in terms of a conformational N-dynamic-order-parameter generalized Langevin equation approach. It is implemented using a universal field-theoretic Gaussian thread model of polymer structure and closed at the level of the chain dynamic second moment matrix...
April 7, 2017: Journal of Chemical Physics
Jing Chen, Robert W Proctor
Procedure invariance is a basic assumption of rational theories of choice, however, it has been shown to be violated: Different response modes, or task frames, sometimes reveal opposite preferences. The current study focused on selection and rejection task frames, involving a unique type of problem with enriched and impoverished options, which has previously led to conflicting findings and theoretical explanations: the compatibility hypothesis (Shafir, 1993) and the accentuation hypothesis (Wedell, 1997). We examined the role of task frame by distinguishing these 2 hypotheses and evaluating the information-processing basis of the choices...
April 2017: Journal of Experimental Psychology. General
Urška Jelerčič
Tubular vesicles represent abundant structural motifs which are observed both in experiments and in nature. We analyse them within the theory of bending elasticity and determine the equilibrium solutions at fixed volume, surface area, and segment length without imposing any specific symmetry or periodicity. We identify four different non-periodic equilibrium shapes. Depending on the precise value of the constraints or the corresponding Lagrange multipliers, these four shapes include: (i) snake-like and (ii) helical structures, (iii) tubes with a spherical body, and (iv) tubes with a discoidal body...
April 19, 2017: Soft Matter
Liangfu Ni, Jicheng Jin, Chao Peng, Zhengbin Li
We extend the coupled-wave-theory (CWT) framework to a supercell lattice photonic crystal (PC) structure to model the radiation of high-Q resonances under structural fluctuations since they are inevitable in realistic devices. The comparison of CWT results and the finite-element-method (FEM) simulations confirm the validity of CWT. It is proved that the supercell model approaches a realistic finite-size PC device when the supercell size is large enough. The Q factors within fluctuated structures are constraint owing to the appearance of fractional orders of radiative waves, which are induced by structural fluctuations...
March 6, 2017: Optics Express
Romain Gallet, Cyrille Violle, Nathalie Fromin, Roula Jabbour-Zahab, Brian J Enquist, Thomas Lenormand
Size is one of the most important biological traits influencing organismal ecology and evolution. However, we know little about the drivers of body size evolution in unicellulars. A long-term evolution experiment (Lenski's LTEE) in which Escherichia coli adapts to a simple glucose medium has shown that not only the growth rate and the fitness of the bacterium increase over time but also its cell size. This increase in size contradicts prominent 'external diffusion' theory (EDC) predicting that cell size should have evolved toward smaller cells...
April 4, 2017: ISME Journal
Emily Lancsar, Denzil G Fiebig, Arne Risa Hole
We provide a user guide on the analysis of data (including best-worst and best-best data) generated from discrete-choice experiments (DCEs), comprising a theoretical review of the main choice models followed by practical advice on estimation and post-estimation. We also provide a review of standard software. In providing this guide, we endeavour to not only provide guidance on choice modelling but to do so in a way that provides a 'way in' for researchers to the practicalities of data analysis. We argue that choice of modelling approach depends on the research questions, study design and constraints in terms of quality/quantity of data and that decisions made in relation to analysis of choice data are often interdependent rather than sequential...
April 3, 2017: PharmacoEconomics
Dan Zhang, Qing-Guo Wang, Dipti Srinivasan, Hongyi Li, Li Yu
This paper is concerned with the asynchronous state estimation for a class of discrete-time switched complex networks with communication constraints. An asynchronous estimator is designed to overcome the difficulty that each node cannot access to the topology/coupling information. Also, the event-based communication, signal quantization, and the random packet dropout problems are studied due to the limited communication resource. With the help of switched system theory and by resorting to some stochastic system analysis method, a sufficient condition is proposed to guarantee the exponential stability of estimation error system in the mean-square sense and a prescribed $H∞ performance level is also ensured...
March 29, 2017: IEEE Transactions on Neural Networks and Learning Systems
Grant S Shields, Matthew A Sazma, Andrew M McCullough, Andrew P Yonelinas
A growing body of research has indicated that acute stress can critically impact memory. However, there are a number of inconsistencies in the literature, and important questions remain regarding the conditions under which stress effects emerge as well as basic questions about how stress impacts different phases of memory. In this meta-analysis, we examined 113 independent studies in humans with 6,216 participants that explored effects of stress on encoding, postencoding, retrieval, or postreactivation phases of episodic memory...
April 3, 2017: Psychological Bulletin
Daniel W Heck, Edgar Erdfelder
When making inferences about pairs of objects, one of which is recognized and the other is not, the recognition heuristic states that participants choose the recognized object in a noncompensatory way without considering any further knowledge. In contrast, information-integration theories such as parallel constraint satisfaction (PCS) assume that recognition is merely one of many cues that is integrated with further knowledge in a compensatory way. To test both process models against each other without manipulating recognition or further knowledge, we include response times into the r-model, a popular multinomial processing tree model for memory-based decisions...
April 3, 2017: Psychological Review
Nan Hou, Hongli Dong, Zidong Wang, Weijian Ren, Fuad E Alsaadi
In this paper, the H∞ state estimation problem is investigated for a class of uncertain discrete-time neural networks subject to infinitely distributed delays and fading channels. Randomly occurring uncertainties (ROUs) are introduced to reflect the random nature of the network condition fluctuations, and the channel fading phenomenon is considered to account for the possibly unreliable network medium on which the measurement signal is transmitted. A set of Bernoulli-distributed white sequences are employed to govern the ROUs and the L-th Rice fading model is utilized where channel coefficients are mutually independent random variables with certain probability density function on [0,1]...
May 2017: Neural Networks: the Official Journal of the International Neural Network Society
Huaguang Zhang, Xiaohong Cui, Yanhong Luo, He Jiang
In this paper, a neural network (NN)-based online model-free integral reinforcement learning algorithm is developed to solve the finite-horizon H∞ optimal tracking control problem for completely unknown nonlinear continuous-time systems with disturbance and saturating actuators (constrained control input). An augmented system is constructed with the tracking error system and the command generator system. A time-varying Hamilton-Jacobi-Isaacs (HJI) equation is formulated for the augmented problem, which is extremely difficult or impossible to solve due to its time-dependent property and nonlinearity...
March 1, 2017: IEEE Transactions on Neural Networks and Learning Systems
Wei He, Yiting Dong
This paper investigates adaptive fuzzy neural network (NN) control using impedance learning for a constrained robot, subject to unknown system dynamics, the effect of state constraints, and the uncertain compliant environment with which the robot comes into contact. A fuzzy NN learning algorithm is developed to identify the uncertain plant model. The prominent feature of the fuzzy NN is that there is no need to get the prior knowledge about the uncertainty and a sufficient amount of observed data. Also, impedance learning is introduced to tackle the interaction between the robot and its environment, so that the robot follows a desired destination generated by impedance learning...
March 1, 2017: IEEE Transactions on Neural Networks and Learning Systems
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