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Initial Position (initial + position)
Selected AbstractsEnvironmental power analysis , a new perspectiveENVIRONMETRICS, Issue 5 2001David R. Fox Abstract Power analysis and sample-size determination are related tools that have recently gained popularity in the environmental sciences. Their indiscriminate application, however, can lead to wildly misleading results. This is particularly true in environmental monitoring and assessment, where the quality and nature of data is such that the implicit assumptions underpinning power and sample-size calculations are difficult to justify. When the assumptions are reasonably met these statistical techniques provide researchers with an important capability for the allocation of scarce and expensive resources to detect putative impact or change. Conventional analyses are predicated on a general linear model and normal distribution theory with statistical tests of environmental impact couched in terms of changes in a population mean. While these are ,optimal' statistical tests (uniformly most powerful), they nevertheless pose considerable practical difficulties for the researcher. Compounding this difficulty is the subsequent analysis of the data and the impost of a decision framework that commences with an assumption of ,no effect'. This assumption is only discarded when the sample data indicate demonstrable evidence to the contrary. The alternative (,green') view is that any anthropogenic activity has an impact on the environment and therefore a more realistic initial position is to assume that the environment is already impacted. In this article we examine these issues and provide a re-formulation of conventional mean-based hypotheses in terms of population percentiles. Prior information or belief concerning the probability of exceeding a criterion is incorporated into the power analysis using a Bayesian approach. Finally, a new statistic is introduced which attempts to balance the overall power regardless of the decision framework adopted. Copyright © 2001 John Wiley & Sons, Ltd. [source] THE PRICE OF METAPHORHISTORY AND THEORY, Issue 1 2005JOSEPH FRACCHIA ABSTRACT In his critical response to our skeptical inquiry, "Does Culture Evolve?" (History and Theory, Theme Issue 38 [December 1999], 52,78), W. G. Runciman affirms that "Culture Does Evolve." However, we find nothing in his essay that convinces us to alter our initial position. And we must confess that in composing an answer to Runciman, our first temptation was simply to urge those interested to read our original article,both as a basis for evaluating Runciman's attempted refutation of it and as a framework for reading this essay, which addresses in greater detail issues we have already raised. Runciman views the "selectionist paradigm" as a "scientific""puzzle-solving device" now validated by an "expanding literature" that has successfully modeled social and cultural change as "evolutionary." All paradigms, however, including scientific ones, give rise to self-validating "normal science." The real issue, accordingly, is not whether explanations can be successfully manufactured on the basis of paradigmatic assumptions, but whether the paradigmatic assumptions are appropriate to the object of analysis. The selectionist paradigm requires the reduction of society and culture to inheritance systems that consist of randomly varying, individual units, some of which are selected, and some not; and with society and culture thus reduced to inheritance systems, history can be reduced to "evolution." But these reductions, which are required by the selectionist paradigm, exclude much that is essential to a satisfactory historical explanation,particularly the systemic properties of society and culture and the combination of systemic logic and contingency. Now as before, therefore, we conclude that while historical phenomena can always be modeled selectionistically, selectionist explanations do no work, nor do they contribute anything new except a misleading vocabulary that anesthetizes history. [source] Portfolio management using value at risk: A comparison between genetic algorithms and particle swarm optimizationINTERNATIONAL JOURNAL OF INTELLIGENT SYSTEMS, Issue 7 2009V. A. F. Dallagnol In this paper, it is shown a comparison of the application of particle swarm optimization and genetic algorithms to portfolio management, in a constrained portfolio optimization problem where no short sales are allowed. The objective function to be minimized is the value at risk calculated using historical simulation where several strategies for handling the constraints of the problem were implemented. The results of the experiments performed show that, generally speaking, the methods are capable of consistently finding good solutions quite close to the best solution found in a reasonable amount of time. In addition, it is demonstrated statistically that the algorithms, on average, do not all consistently achieve the same best solution. PSO turned out to be faster than GA, both in terms of number of iterations and in terms of total running time. However, PSO appears to be much more sensitive to the initial position of the particles than GA. Tests were also made regarding the number of particles needed to solve the problem, and 50 particles/chromosomes seem to be enough for problems up to 20 assets. © 2009 Wiley Periodicals, Inc. [source] Improving Decision Making by Means of Dissent,JOURNAL OF APPLIED SOCIAL PSYCHOLOGY, Issue 1 2001Charlan Jeanne Nemeth Antidotes to problems associated with uniformity of viewpoints have generally involved dissent in one form or another (Katzenstein, 1996), one being "devil's advocate." Research on authentic dissent has documented additional advantages in that it stimulates divergent and original thought (Nemeth, 1995). In this study, authentic disscnt was compared with devil's advocate and with no dissent. Findings indicate that authentic dissent was superior in (a) stimulating a greater proportion of original thoughts, (b) considering the opposite position, and (c) direct attitude change. Devil's advocate was found to stimulate cognitive boistcring of the initial position, thus raising concerns about the unintended consequences of techniques such as devil's advocate and the subtle task facing attempts to foster original thought and yet maintain cohesion. [source] THE COST OF ILLIQUIDITY AND ITS EFFECTS ON HEDGINGMATHEMATICAL FINANCE, Issue 4 2010L. C. G. Rogers Though liquidity is commonly believed to be a major effect in financial markets, there appears to be no consensus definition of what it is or how it is to be measured. In this paper, we understand liquidity as a nonlinear transaction cost incurred as a function of rate of change of portfolio. Using this definition, we obtain the optimal hedging policy for the hedging of a call option in a Black-Scholes model. This is a more challenging question than the more common studies of optimal strategy for liquidating an initial position, because our goal requires us to match a random final value. The solution we obtain reduces in the case of quadratic loss to the solution of three partial differential equations of Black-Scholes type, one of them nonlinear. [source] Trajectory optimization involving sloshing mediaOPTIMAL CONTROL APPLICATIONS AND METHODS, Issue 1 2002Harald Leonpacher Abstract This paper is concerned with the optimization of the transport motion of an open topped fluid filled container within a warehouse environment. In particular, optimal trajectories of the motion of the driver,container system in two-dimensional space will be investigated via numerical solutions of the model equations using sequential quadratic programming. The fluid and the mechanical facility that moves the container are subject to several constraints. The objective of the optimization is the time to transport the container from an initial position to its final destination within the warehouse. Optimization criteria are investigated to control the movement of the fluid within the container. The systems of ordinary and partial differential equations, representing the dynamics of the models are solved numerically using a direct shooting method. The resulting non-linear programming problem is solved using sequential quadratic programming (SQP). Copyright © 2002 John Wiley & Sons, Ltd. [source] Signal transduction in Mimosa pudica: biologically closed electrical circuitsPLANT CELL & ENVIRONMENT, Issue 5 2010ALEXANDER G. VOLKOV ABSTRACT Biologically closed electrical circuits operate over large distances in biological tissues. The activation of such circuits can lead to various physiological and biophysical responses. Here, we analyse the biologically closed electrical circuits of the sensitive plant Mimosa pudica Linn. using electrostimulation of a petiole or pulvinus by the charged capacitor method, and evaluate the equivalent electrical scheme of electrical signal transduction inside the plant. The discharge of a 100 µF capacitor in the pulvinus resulted in the downward fall of the petiole in a few seconds, if the capacitor was charged beforehand by a 1.5 V power supply. Upon disconnection of the capacitor from Ag/AgCl electrodes, the petiole slowly relaxed to the initial position. The electrical properties of the M. pudica were investigated, and an equivalent electrical circuit was proposed that explains the experimental data. [source] Stabilization of the inverted spherical pendulum via Lyapunov approach,ASIAN JOURNAL OF CONTROL, Issue 6 2009O. Octavio Gutiérrez F. Abstract In this paper a nonlinear controller is presented for the stabilization of the spherical inverted pendulum system. The control strategy is based on the Lyapunov approach in conjunction with LaSalle's invariance principle. The proposed controller is able to bring the pendulum to the unstable upright equilibrium point with the position of the movable base at the origin. The obtained closed-loop system has a very large domain of attraction, that can be as large as desired, for any initial position of the pendulum which lies above the horizontal plane. Copyright © 2009 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society [source] Analysis and experiment on simultaneous swing-up of a parallel cart-type double inverted pendulum,ASIAN JOURNAL OF CONTROL, Issue 1 2008Mingcong Deng Abstract This paper considers experimental study and analysis on simultaneous swing-up control of a parallel cart-type double inverted pendulum. The proposed controller includes both a swing-up controller based on weighted energy related function and a cart travel controller designed by a pole assignment control scheme. The cart travel controller can restrict cart travel during the swing-up. When the two pendulums are swung up, the controller will be switched to a stabilizing controller, and the controller can take the cart to the initial position. Control simulation and experiment were successfully conducted. Copyright © 2008 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society [source] Prospective real-time correction for arbitrary head motion using active markersMAGNETIC RESONANCE IN MEDICINE, Issue 4 2009Melvyn B. Ooi Abstract Patient motion during an MRI exam can result in major degradation of image quality, and is of increasing concern due to the aging population and its associated diseases. This work presents a general strategy for real-time, intraimage compensation of rigid-body motion that is compatible with multiple imaging sequences. Image quality improvements are established for structural brain MRI acquired during volunteer motion. A headband integrated with three active markers is secured to the forehead. Prospective correction is achieved by interleaving a rapid track-and-update module into the imaging sequence. For every repetition of this module, a short tracking pulse-sequence remeasures the marker positions; during head motion, the rigid-body transformation that realigns the markers to their initial positions is fed back to adaptively update the image-plane,maintaining it at a fixed orientation relative to the head,before the next imaging segment of k -space is acquired. In cases of extreme motion, corrupted lines of k -space are rejected and reacquired with the updated geometry. High-precision tracking measurements (0.01 mm) and corrections are accomplished in a temporal resolution (37 ms) suitable for real-time application. The correction package requires minimal additional hardware and is fully integrated into the standard user interface, promoting transferability to clinical practice. Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc. [source] | ||||||||||