Presence Of Local Maxima Research Articles

Межа максимальної ефективності роботи вітроелектричних установок із заданими типорозмірами у конкретних вітрокліматичних умовах

In the paper, the parameters of 115 types of existing wind turbines (WT) were analyzed and their power curves were modeled by using the Weibull cumulative distribution function (CDF). On the basis of these data, regression equations were obtained for the CDF parameters for the power curves of WT due to their main sizes: the nameplate capacity of the generator P and the rotor D. Based on the analysis of the obtained 115 WT CDF parameters and main sizes, the regression model of the WT average used power (AUP) in specific wind conditions has been built. The area of existence of possible values of main sizes P and D is defined. The presence of local maxima in the distribution of AUP by nameplate capacity at fixed values of the rotor diameters has been revealed. An analytical relationship was found between the optimal values of WT main sizes in different wind conditions. Certain restrictions were obtained for the maximum rotor diameter depending on the values of the nameplate capacity. The average starting wind speed of 3.37 m per s, at which the wind turbine starts working, has been determined theoretically.

Simulations of Pump Absorption in Tandem-Pumped Octagon Double-Clad Fibers

The cladding pumping within a double-clad fiber structure is an effective technique to convert high-power multimode beam into high-power, almost diffraction limited beam. Since the pump efficiency is limited by the presence of higher skew-ray modes, geometrical perturbations are used to scramble the modes and to achieve a higher overlap of the electromagnetic field with the doped core. In this paper, the combined effect of fiber coiling and twisting is investigated in the double-clad fiber structure with the octagonal shape of an inner cladding. Electromagnetic field propagation through fibers with different cross-section areas, bending radii and twisting rates is numerically simulated using finite element beam propagation method. Holmium-doped double-clad fiber pumped in tandem configuration at wavelength 1950 nm is selected as an example. Nontrivial dependence of pump absorption on bending radius with the presence of local maxima is revealed. The observed impact of fiber coiling and twisting increases with the size of the cross-section area of the inner cladding.

Mean Shift Cluster Recognition Method Implementation in the Nested Sampling Algorithm.

Nested sampling is an efficient algorithm for the calculation of the Bayesian evidence and posterior parameter probability distributions. It is based on the step-by-step exploration of the parameter space by Monte Carlo sampling with a series of values sets called live points that evolve towards the region of interest, i.e., where the likelihood function is maximal. In presence of several local likelihood maxima, the algorithm converges with difficulty. Some systematic errors can also be introduced by unexplored parameter volume regions. In order to avoid this, different methods are proposed in the literature for an efficient search of new live points, even in presence of local maxima. Here we present a new solution based on the mean shift cluster recognition method implemented in a random walk search algorithm. The clustering recognition is integrated within the Bayesian analysis program NestedFit. It is tested with the analysis of some difficult cases. Compared to the analysis results without cluster recognition, the computation time is considerably reduced. At the same time, the entire parameter space is efficiently explored, which translates into a smaller uncertainty of the extracted value of the Bayesian evidence.

An Approval of MPPT Based on PV Cell’s Simplified Equivalent Circuit During Fast-Shading Conditions

The partial shading conditions significantly affect the functionality of solar power plants despite the presence of multiple maximum power point tracking systems. The primary cause of this problem is the presence of local maxima in the power–current and/or power–voltage characteristic curves that restrict the functionality of the conventional maximum power point tracking systems. The present article proposes a modified algorithm based on the simplified equivalent circuit of solar cells to improve the functionality of traditional maximum power point tracking systems. This algorithm provides a method for regularly monitoring the photo-current of each solar module. The upper and lower boundaries of the regulating parameter such as current or voltage are decided very precisely, which is helpful to find the location of the global maximum. During a sequential search, the control system accurately determines the lower and upper boundaries of the global maximum. Simultaneously, the maximum power point tracking system increases the photovoltaic current up to one of these boundaries and applies one of the conventional algorithms. Additionally, the control system regularly monitors the photovoltaic characteristics and changes the limits of regulating parameter concerning any change in global maximum location. This proposed method is fast and precise to locate the global maximum boundaries and to track global maximum even under fast-changing partial shading conditions. The improved performance and overall efficiency are validated by simulation study for variable solar irradiance.

A scale space approach for exploring structure in spherical data

A novel scale space approach, SphereSiZer, is proposed for exploring structure in spherical data, that is, directional data on the unit sphere of the three-dimensional Euclidean space. The method finds statistically significant gradients of the smooths of the probability density function underlying the observed data. Bootstrap is used to establish significance and inference is summarized with planar maps of contour plots of smooths of the data, overlaid with arrows that indicate the directions and magnitudes of the significant gradients. An effective way to explore such maps is a movie where each frame corresponds to a fixed level of smoothing, that is, a particular spatial scale on the sphere. The SphereSiZer is demonstrated using simulated data as well as two real-data examples. The first example examines the distribution of infant head normal vector directions. The presence of local maxima in the normal vector distribution may indicate head deformity, such as severe flatness or asymmetry. The second example considers the distribution of earthquakes in the Northern Hemisphere.

PML solution of longitudinal wave propagation in heterogeneous media

This paper describes the development of a model for unbounded heterogeneous domains with radiation damping produced by an unphysical wave absorbing layer. The Perfectly Matched Layer (PML) approach is used along with a displacement-based finite element. The heterogeneous model is validated using the closed-form solution of a benchmark problem: a free rod with two-part modulus subjected to a specified time history. Both elastically supported and unsupported semi-infinite rods with different degrees of inhomogeneity and loading are considered. Numerical results illustrate the effects of inhomogeneity on the response and are compared with those for equivalent homogeneous domains. The effects of characteristic features of the inhomogeneous problem, presence of local maxima and cut-off frequency are determined. A degenerate case of a homogeneous semi-infinite rod on elastic foundations is produced by tending the magnitude of the foundation stiffness to zero. The response of the latter is compared with that of a free rod. The importance of proper selection of the PML parameters to highly accurate and efficient results is demonstrated by example problems.

Identifying tree crown delineation shapes and need for remediation on high resolution imagery using an evidence based approach

In order to fully realize the benefits of automated individual tree mapping for tree species, health, forest inventory attribution and forest management decision making, the tree delineations should be as good as possible. The concept of identifying poorly delineated tree crowns and suggesting likely types of remediation was investigated. Delineations (isolations or isols) were classified into shape types reflecting whether they were realistic tree shapes and the likely kind of remediation needed. Shape type was classified by an evidence based rules approach using primitives based on isol size, shape indices, morphology, the presence of local maxima, and matches with template models representing trees of different sizes.A test set containing 50,000 isols based on an automated tree delineation of 40cm multispectral airborne imagery of a diverse temperate-boreal forest site was used. Isolations representing single trees or several trees were the focus, as opposed to cases where a tree is split into several isols. For eight shape classes from regular through to convolute, shape classification accuracy was in the order of 62%; simplifying to six classes accuracy was 83%. Shape type did give an indication of the type of remediation and there were 6% false alarms (i.e., isols classed as needing remediation but did not). Alternately, there were 5% omissions (i.e., isols of regular shape and not earmarked for remediation that did need remediation).The usefulness of the concept of identifying poor delineations in need of remediation was demonstrated and one suite of methods developed and shown to be effective.

Automated focusing in bright‐field microscopy for tuberculosis detection

Automated microscopy to detect Mycobacterium tuberculosis in sputum smear slides would enable laboratories in countries with a high tuberculosis burden to cope efficiently with large numbers of smears. Focusing is a core component of automated microscopy, and successful autofocusing depends on selection of an appropriate focus algorithm for a specific task. We examined autofocusing algorithms for bright-field microscopy of Ziehl-Neelsen stained sputum smears. Six focus measures, defined in the spatial domain, were examined with respect to accuracy, execution time, range, full width at half maximum of the peak and the presence of local maxima. Curve fitting around an estimate of the focal plane was found to produce good results and is therefore an acceptable strategy to reduce the number of images captured for focusing and the processing time. Vollath's F₄ measure performed best for full z-stacks, with a mean difference of 0.27 μm between manually and automatically determined focal positions, whereas it is jointly ranked best with the Brenner gradient for curve fitting.

Silicone Rubber Tack II: The Time-Dependent Autohesion for Symmetric Rubber–Rubber Contacts

The autohesion data are gathered for poly(dimethyl siloxane) (PDMS) with different molecular weights. The influence of molecular weight of the polymer is very pronounced. The data are interpreted on basis of the Wool-deGennes reptation theory; the application of first order kinetics of wetting is also tested. PDMS with a molecular weight only partially permitting the formation of entanglements exhibits a remarkably different and unusual behavior compared with the high molecular weight polymers. The latter develop tack in the form of logarithmic type curves, while the former show the presence of local maxima in the tack-time curves.

An Evolutionary Algorithm With Applications to Statistics

Evolutionary algorithms are used to find maxima of functions. Their claim to fame is an ability to find a global maximum in the presence of local maxima. The computations do not require derivatives or convexity, but still may be fairly computationally intensive in larger dimensions. This article presents a new type of evolutionary algorithm that works well in many dimensions, with the added advantage that linear equality constraints are implemented in a natural way. Bounds on the coordinates of the solution are also easy to implement. Several examples are presented and the new algorithm is compared with standard versions of evolutionary algorithms. The first group consists of functions in one or two dimensions, chosen to be difficult to maximize by gradient or simplex-based methods. The second set of examples are from statistics problems that are known to be computationally difficult. The first is least absolute deviations nonlinear regression with bootstrapped confidence bounds on the mean response, the second is smoothed nonparametric unimodal density estimation requiring both a linear equality constraint and linear inequality constraints. The Fortran subroutine is available for the user.

Vertical vibration of a circular footing on a linear-wave-velocity half-space

An exact treatment is presented for the problem of a rigid surface foundation vibrating vertically on an elastic half-space with a linear wave velocity profile. By means of a displacement-potential representation and integral transforms, the dynamic problem is formulated as a set of dual integral equations which are reducible to a Fredholm integral equation of the second kind. Numerical results are presented to illustrate the effects of the in situ inhomogeneity on the static and dynamic foundation responses. Characteristic features of the inhomogeneous half-space problem, such as the presence of local maxima in the dynamic foundation compliance functions and the existence of cut-off frequencies, are demonstrated. Les auteurs abordent le problème de la vibration verticale de fondations à surface rigide surune masse é1astique semi-infinie à vitesse de propagation d'onde linéaire. A l'aide d'une représentation du potentiel de déplacement et de transformations intégrales, ils formulent le problème dynamique sous la forme d'un ensemble de doubles équations intégrales que l'on pent réduire à une équation intégrale de Fredholm du deuxième ordre. Les résultats numériques présentés illustrent les effets de l'inhomogénéité en place sur les réactions statiques et dynamiques des fondations. Les auteurs démontrent les caractéristiques du problème des masses inhomo-gènes semi-infinies comme la présence de maxima locales dans les fonctions de conformitéde fondations dynamiques et l'existence de fréquences de transition.

Ozone profiles over a suburban neighborhood

The development of ozone (O 3) air quality models and the measurement of O 3 dry deposition over built-up areas requires assumptions concerning the vertical distribution of O 3. However, few [O 3] profiles have been measured over urban and suburban areas. A 150 m thick layer of air over a suburban neighborhood in Lafayette, Indiana, U.S.A. was profiled for potential temperature, moisture mixing ratio, and oxidant concentrations during 38 soundings made between mid-day and early evening in late summer and early fall 1994. The residential neighborhood had 17% of the area covered by trees, with a mean vegetation canopy height of 9 m. Although some [O 3] and oxidant concentration ([oxidant]) profiles showed a monotonic decrease or increase in concentration with height, many profiles (63%) exhibited a distinct local maximum in the profile. The local [oxidant] maxima were typically observed near the top of a relatively stable layer of air, and occurred more frequently when the local surface winds were from the agricultural rural regions to the north of the neighborhood and the air had resided within the Lafayette–Indianapolis region since the prior day. The magnitude of the local [oxidant] maximum was directly related to the 155 m [oxidant] during the mid-day and early-afternoon profiles. The presence of local maxima in many of the [O 3] profiles indicate that one cannot safely assume that [O 3] profiles monotonically decrease with decreasing height above all suburban areas. As a result, the estimation of O 3 fluxes should always include profile measurements to assure the representativeness of the calculated flux at the measurement height to surface deposition. Correlations between measures of local traffic activity, above-canopy air temperatures, the magnitude of local [O 3] maxima, and [O 3] above the canopy indicate that a change in the dominant processes producing the maxima appeared to occur around the time of plant senescence.

Frequency response of magnetic flux sheaths

When a sound wave is incident on a magnetic flux sheath, it causes fluctuations in the mean magnetic field of the sheath. We have calculated the space-average of the longitudinal component of these fluctuations and plotted this against the frequency of the incident sound wave. The main result is the presence of local maxima and minima in the response curve. If such maxima and minima could be detected in any actual observation then these would provide an estimate of the thickness of these magnetic structures.