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Centroid
Terms modified by Centroid Selected AbstractsSeasonality of the northern hemisphere circumpolar vortexINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 6 2007Kalyn M. Wrona Abstract In previous research, Rohli et al. (2005) identified long-term features of the northern hemispheric circumpolar vortex (NHCPV) in January. This research provides a seasonal analysis using December and February to augment the previously analyzed January data in representing winter, along with April, July, and October data to represent spring, summer, and autumn, respectively. A representative 500 hPa geopotential height contour was selected to delineate the NHCPV in each of the five months. The area, shape, and centroid of the monthly December, February, April, July, and October NHCPV are computed for 1959,2001 to supplement the previously identified January properties. These geometrical features of the NHCPV reveal relationships between hemispheric-scale circulation and temperature anomalies throughout the year. A circularity ratio (Rohli et al., 2005) is used to characterize the shape of the hemispheric-scale circulation. Results suggest that only October exhibit long-term trends in either area or circularity, with July being the most variable month in area and October being the most variable month in circularity. Centroids tend to be skewed toward the Pacific basin, except in spring, but few systematic temporal shifts in centroid position were noted for any month. The NHCPV is correlated with atmospheric teleconnection patterns in several months. For example, as was the case for January (Rohli et al., 2005), the Arctic Oscillation (AO) is associated with the area of the December, February, and April NHCPV, while in December the circularity is positively correlated to the AO Index. Also, the Pacific-North American index is correlated with the area of the December and February NHCPV and with the shape of the December and October NHCPV. Copyright © 2006 Royal Meteorological Society [source] Non-Covalent Interactions of Organic Halogen Compounds with Aromatic Systems , Analyses of Crystal Structure DataEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 6 2005Dariusz Swierczynski Abstract The Cambridge Structural Database showed in mid 2002 about 20.000 structures containing halogen atoms and aryl rests with distances d between the aryl center and the halogen atom, which would allow both hydrogen bonds with the aromatic hydrogens and/or van der Waalsinteractions with the ,-cloud. The latter are characterized by short distances d and by small angles , between the vector along the aryl centroid,halogen line and the perpendicular vector originating in the aryl center (the plane normal). The cases with d < 3.0 Å for F; and d < 3.5 Å for Cl, Br or I (outliers neglected), and , , 10 ± 5°, indicating predominating van der Waals forces, amount to several hundreds. The majority of fragments exhibit larger d and , values, in line with avoidance of electrostatic repulsion between the negative partial charges of the halogens and the ,-cloud center, and with an increasing electrostatic attraction with the aromatic hydrogen atoms. The corresponding hydrogen bonds are characterized by longer distances d and by angle values of , > 60° (about 40 % of the fragments), with only very few cases close to linear hydrogen bonds (then with , = 90°). Compounds containing metal,halogen bonds were omitted in view of possible strong orientational interferences. The structures were screened with four different halogen binding modes, all of them containing the halogen attached to a carbon atom, but with different hybrizations at the connecting carbon centers. The results show only small differences in the distance distributions, with a slight preference for smaller , values for sp2 frameworks. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Analytical formulas for the geometric and inertia quantities of the largest removable blocks around tunnelsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 11 2007Fulvio Tonon Abstract This paper presents algorithms for determining the vertices of the maximum removable block (MB) created by a joint pyramid (JP) around a tunnel when discontinuities are fully persistent. It is shown that an MB cannot be formed by more than 4 discontinuities and this drastically limits the proliferation of rock blocks that need to be analysed. The non-convex block obtained after the MB is tunnelled through (real maximum block, RMB) is partitioned into a set of tetrahedra, and procedures are given for determining the vertices of these tetrahedra. Geometric and inertia quantities needed for stability analysis and support/reinforcement design are determined as functions of the calculated vertices' co-ordinates. These quantities are: RMB's volume, face areas, perimeter of the excavated surface, centroid and inertia tensor. The algorithms for their calculation are at least two times faster than other algorithms previously proposed in other applications. It is shown that the formulations presented by Goodman and Shi for translational analysis and by Tonon for rotatability analysis can be used to analyse the RMBs using the geometric quantities presented. A numerical example is presented among those used to verify these analytical procedures and their implementation. Copyright © 2006 John Wiley & Sons, Ltd. [source] The moment-of-fluid method in actionINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 10 2009Hyung Taek Ahn Abstract The moment-of-fluid (MOF) method is a new volume-tracking method that accurately treats evolving material interfaces. The MOF method uses moment data, namely the material volume fraction, as well as the centroid, for a more accurate representation of the material configuration, interfaces and concomitant volume advection. In contrast, the volume-of-fluid method uses only volume fraction data for interface reconstruction and advection. Based on the moment data for each material, the material interfaces are reconstructed with second-order spatial accuracy in a strictly conservative manner. The MOF method is coupled with a stabilized finite element incompressible Navier,Stokes solver for two materials. The effectiveness of the MOF method is demonstrated with a free-surface dam-break and a two-material Rayleigh,Taylor problem. Copyright © 2008 John Wiley & Sons, Ltd. [source] A two-grid fictitious domain method for direct simulation of flows involving non-interacting particles of a very small sizeINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 11 2010A. Dechaume Abstract The full resolution of flows involving particles whose scale is hundreds or thousands of times smaller than the size of the flow domain is a challenging problem. A naive approach would require a tremendous number of degrees of freedom in order to bridge the gap between the two spatial scales involved. The approach used in the present study employs two grids whose grid size fits the two different scales involved, one of them (the micro-scale grid) being embedded into the other (the macro-scale grid). Then resolving first the larger scale on the macro-scale grid, we transfer the so obtained data to the boundary of the micro-scale grid and solve the smaller size problem. Since the particle is moving throughout the macro-scale domain, the micro-scale grid is fixed at the centroid of the moving particle and therefore moves with it. In this study we combine such an approach with a fictitious domain formulation of the problem resulting in a very efficient algorithm that is also easy to implement in an existing CFD code. We validate the method against existing experimental data for a sedimenting sphere, as well as analytical results for motion of an inertia-less ellipsoid in a shear flow. Finally, we apply the method to the flow of a high aspect ratio ellipsoid in a model of a human lung airway bifurcation. Copyright © 2009 John Wiley & Sons, Ltd. [source] Fringe element reconstruction for front tracking for three-dimensional incompressible flow analysisINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 6 2005Du-Soon Choi Abstract Fringe element reconstruction technique for tracking the free surface in three-dimensional incompressible flow analysis was developed. The flow field was calculated by the mixed formulation based on a four-node tetrahedral element with a bubble function at the centroid (P1+/P1). Since an Eulerian approach was employed in this study, the flow front interface was advected by the flow through a fixed mesh. For accurate modelling of interfacial movement, a fringe element reconstruction method developed can provide not only an accurate treatment of material discontinuity but also surface tension across the interface. The effect of surface tension was modelled by imposing tensile stress directly on the constructed surface elements at the flow front interface. To verify the numerical approach developed, the developed algorithm was applied to two examples whose solutions are available in references. Good agreement was obtained between the simulation results and these solutions. Copyright © 2005 John Wiley & Sons, Ltd. [source] Seasonality of the northern hemisphere circumpolar vortexINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 6 2007Kalyn M. Wrona Abstract In previous research, Rohli et al. (2005) identified long-term features of the northern hemispheric circumpolar vortex (NHCPV) in January. This research provides a seasonal analysis using December and February to augment the previously analyzed January data in representing winter, along with April, July, and October data to represent spring, summer, and autumn, respectively. A representative 500 hPa geopotential height contour was selected to delineate the NHCPV in each of the five months. The area, shape, and centroid of the monthly December, February, April, July, and October NHCPV are computed for 1959,2001 to supplement the previously identified January properties. These geometrical features of the NHCPV reveal relationships between hemispheric-scale circulation and temperature anomalies throughout the year. A circularity ratio (Rohli et al., 2005) is used to characterize the shape of the hemispheric-scale circulation. Results suggest that only October exhibit long-term trends in either area or circularity, with July being the most variable month in area and October being the most variable month in circularity. Centroids tend to be skewed toward the Pacific basin, except in spring, but few systematic temporal shifts in centroid position were noted for any month. The NHCPV is correlated with atmospheric teleconnection patterns in several months. For example, as was the case for January (Rohli et al., 2005), the Arctic Oscillation (AO) is associated with the area of the December, February, and April NHCPV, while in December the circularity is positively correlated to the AO Index. Also, the Pacific-North American index is correlated with the area of the December and February NHCPV and with the shape of the December and October NHCPV. Copyright © 2006 Royal Meteorological Society [source] January northern hemisphere circumpolar vortex variability and its relationship with hemispheric temperature and regional teleconnectionsINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 11 2005Robert V. Rohli Abstract Variability in the hemispheric-scale atmospheric circulation can be directly linked to variations in surface environmental features, such as temperature, precipitation, salinity of water bodies, and pollutant transport. One indicator of the behavior of the hemispheric-scale circulation is the circumpolar vortex (CPV). This research utilizes a geographic information system approach to characterize variability in the Northern Hemispheric (NH) CPV. Specifically, the area, shape, and centroid of the January NHCPV are analyzed for 1959,2001 because it may provide insight about relationships between hemispheric-scale circulation and global temperature change. We also use a new means of characterizing the hemispheric-scale circulation using a ,circularity ratio' (Rc). Results suggest that the January NHCPV has exhibited no long-term trends in area or shape, and that the mean centroid is positioned at approximately 85.3°N, 178.0°W. Regional patterns emerge, which suggest that the area and circularity are associated with variability in surface temperature and moist static energy. Furthermore, the area of the January NHCPV is associated with variability in the Arctic Oscillation, while the shape is tied to variability in the Pacific-North American teleconnection pattern. These results will facilitate understanding of the relationship between hemispheric-scale circulation, regional circulation, and local temperatures. Copyright © 2005 Royal Meteorological Society. [source] Classification of leaf imagesINTERNATIONAL JOURNAL OF IMAGING SYSTEMS AND TECHNOLOGY, Issue 1 2006Chia-Ling Lee Abstract There are tremendous content-based retrieval systems. Most of them are applied to general image databases. Some were proposed for specified databases such as texture databases, ancient paintings, document image databases, digital mammography, face image databases, etc. However, there are fewer for plant databases. Plants are used in various fields such as in foodstuff, medicine, and industry. Recently, plant is important for environment protection. On the other hand, the problem of plant destruction becomes worse in the few years. We should train people to know about plants, in turn, to treasure and protect them. In addition to the limited number of expert botanists, the convenient content-based retrieval system for plant is necessary and useful, since it can retrieve related information and knowledge from plant database for the query leaf so as to facilitate fast learning of plants. In this study, a leaf database is constructed and a classification method for leaves is proposed. Most approaches for leaf classification in literature used contour-based features. The proposed method tries to use region-based features. The reasons are that region-based features are more robust than contour-based features since significant curvature points are hard to find. Those features adopted include aspect ratio, compactness, centroid, and horizontal/vertical projections. The effectiveness of the proposed method has been demonstrated by various experiments. On the average, our method has the classification accuracy for 1-NN rule as 82.33% and the recall rate for 10 returned images as 48.2%, while the contour-based method has 37.6% and 21.7%, respectively. © 2006 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 16, 15,23, 2006 [source] Winter selection of landscapes by woodland caribou: behavioural response to geographical gradients in habitat attributesJOURNAL OF APPLIED ECOLOGY, Issue 5 2008Daniel Fortin Summary 1Understanding animal,habitat relationships is central to the development of strategies for wildlife management and conservation. The availability of habitat attributes often changes along latitudinal and longitudinal axes, and animals may respond to those changes by adjusting their selection. We evaluated whether landscape selection by forest-dwelling woodland caribou Rangifer tarandus caribou varied along geographical gradients in habitat attributes. 2Centroids (n = 422) of track networks made by caribou in winter were recorded during aerial surveys conducted over 161 920 km2 of boreal forest in Québec, Canada. Autologistic models were estimated by comparing the characteristics of landscapes (201 km2) centred on each centroid to an equal number of randomly located landscapes, with an autocovariate controlling for the non-independence among caribou locations. 3The availability of habitat attributes varied along longitudinal and latitudinal gradients, and caribou altered their landscape selection with respect to those gradients. 4Information Theory provided substantial support for only one model. The model revealed that the probability of occurrence of caribou increased with the abundance of conifer forests over most of the study region, but this positive response gradually became negative towards the southern portion of the region. The association between caribou and lichens changed from being negative west of the study region to being positive in the eastern part. Availability of landscapes dominated by lichen decreased from west to east. Finally, caribou generally displayed an aversion to areas with high road density, a negative association that became positive in the southern part of the study region. 5Synthesis and applications. Under current legislation in Canada, the critical habitat of woodland caribou must be defined, and then protected. Our autoregressive models can help to identify landscapes to prioritize conservation efforts. The probability of occurrence of caribou was related to different landscape characteristics across their range, which implies that the typical habitat of woodland caribou differs spatially. Such behavioural plasticity could be problematic for defining critical habitat, but we showed that spatial variation in landscape selection was organized along geographical gradients. Our study illustrates how geographical trends in habitat selection can guide management and conservation decisions. [source] A centroid-based sampling strategy for kriging global modeling and optimizationAICHE JOURNAL, Issue 1 2010Eddie Davis Abstract A new sampling strategy is presented for kriging-based global modeling. The strategy is used within a kriging/response surface (RSM) algorithm for solving NLP containing black-box models. Black-box models describe systems lacking the closed-form equations necessary for conventional gradient-based optimization. System optima can be alternatively found by building iteratively updated kriging models, and then refining local solutions using RSM. The application of the new sampling strategy results in accurate global model generation at lower sampling expense relative to a strategy using randomized and heuristic-based sampling for initial and subsequent model construction, respectively. The new strategy relies on construction of an initial kriging model built using sampling data obtained at the feasible region's convex polytope vertices and centroid. Updated models are constructed using additional sampling information obtained at Delaunay triangulation centroids. The new sampling algorithm is applied within the kriging-RSM framework to several numerical examples and case studies to demonstrate proof of concept. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Effects of distal radius malunion on distal radioulnar joint mechanics,an in vivo studyJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 4 2007Joseph J. Crisco Abstract Patients with a malunited distal radius often have painful and limited forearm rotation, and may progress to arthritis of the distal radioulnar joint (DRUJ). The purpose of this study was to determine if DRUJ congruency and mechanics were altered in patients with malunited distal radius fractures. In nine subjects with unilateral malunions, interbone distances and dorsal and palmar radioulnar ligament lengths were computed from tomographic images of both forearms in multiple forearm positions using markerless bone registration (MBR) techniques. The significance of the changes were assessed using a generalized linear model, which controlled for forearm rotation angle (,60° to 60°). In the malunited forearm, compared to the contralateral uninjured arm, we found that ulnar joint space area significantly decreased by approximately 25%, the centroid of this area moved an average of 1.3 mm proximally, and the dorsal radioulnar ligament elongated. Despite our previous findings of insignificant changes in the pattern of radioulnar kinematics in patients with malunited fractures, we found significant changes in DRUJ joint area and ligament lengthening. These findings suggest that alterations in joint mechanics and soft tissues may play an important role in the dysfunction associated with these injuries. © 2007 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 25:547,555, 2007 [source] A Cooperative Game Theory of Noncontiguous AlliesJOURNAL OF PUBLIC ECONOMIC THEORY, Issue 4 2001Daniel G. Arce M. This paper develops a cooperative game-theoretic representation of alliances with noncontiguous members that is based on cost savings from reducing overlapping responsibilities and sequestering borders. For various scenarios, three solutions (the Shapley value, nucleolus, and core's centroid) are found and compared. Even though their underlying ethical norm varies, the solutions are often identical for cases involving contiguous allies and for rectangular arrays of noncontiguous allies. When transaction costs and/or alternative spatial configurations are investigated, they may then differ. In all cases the cooperative approach leads to a distribution of alliance costs that need not necessarily coincide with the traditional emphasis on gross domestic product size as a proxy for deterrence value (the exploitation hypothesis). Instead, burdens can now be defined based upon a country's spatial and strategic location within the alliance. [source] A New Video Image Analysis System to Study Red Blood Cell Dynamics and Oxygenation in Capillary NetworksMICROCIRCULATION, Issue 6 2005SHRUTI A. JAPEE ABSTRACT Objective: The authors present a Measurement and Analysis System for Capillary Oxygen Transport (MASCOT) to study red blood cell (RBC) dynamics and oxygenation in capillary networks. The system enables analysis of capillaries to study geometry and morphology and provides values for capillary parameters such as diameter and segment length. It also serves as an analysis tool for capillary RBC flow characteristics, including RBC velocity, lineal density, and supply rate. Furthermore, the system provides a means of determining the oxygen saturation of hemoglobin contained within RBCs, by analysis of synchronized videotapes containing images at two wavelengths, enabling the quantification of the oxygen content of individual RBCs. Methods: Video recordings of RBC flow at two wavelengths, 420 nm (isosbestic) and 436 nm (oxygen sensitive), are made using a dual camera video microscopy system. The 420-nm recording is used to generate images based on the variance of light intensity fluctuations that help to identify capillaries in a given field of view that are in sharp focus and exhibit flow of individual RBCs separated by plasma gaps. A region of interest enclosing the desired capillary is defined and a fixed number of successive video frames at the two wavelengths are captured. Next a difference image is created, which delineates the RBC column, whose width is used to estimate the internal diameter of the capillary. The 420-nm images are also used to identify the location and centroid of each RBC within the capillary. A space,time image is generated to compute the average RBC velocity. Lineal density is calculated as the number of RBCs per unit length of a capillary segment. The mean optical density (OD) of each RBC is calculated at both wavelengths, and the average SO2 for each cell is determined from OD436/OD420. Results and Conclusions: MASCOT is a robust and flexible system that requires simple hardware, including a SGI workstation fitted with an audio-visual module, a VCR, and an oscilloscope. Since the new system provides information on an individual cell basis from entire capillary segments, the authors believe that results obtained using MASCOT will be more accurate than those obtained from previous systems. Due to its flexibility and ease of extension to other applications, MASCOT has the potential to be applied widely as an analysis tool for capillary oxygen transport measurements. [source] Accreting millisecond pulsar SAX J1808.4,3658 during its 2002 outburst: evidence for a receding discMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2009Askar Ibragimov ABSTRACT An outburst of the accreting X-ray millisecond pulsar SAX J1808.4,3658 in 2002 October,November was followed by the Rossi X-ray Timing Explorer for more than a month. A detailed analysis of this unprecedented data set is presented. For the first time, we demonstrate how the area covered by the hotspot at the neutron star surface is decreasing in the course of the outburst together with the reflection amplitude. These trends are in agreement with the natural scenario, where the disc inner edge is receding from the neutron star as the mass accretion rate drops. These findings are further supported by the variations of the pulse profiles, which clearly show the presence of the secondary maximum at the late stages of the outburst after October 29. This fact can be interpreted as the disc receding sufficiently far from the neutron star to open the view of the lower magnetic pole. In that case, the disc inner radius can be estimated. Assuming that disc is truncated at the Alfvén radius, we constrain the stellar magnetic moment to ,= (9 ± 5) × 1025 G cm3, which corresponds to the surface field of about 108 G. On the other hand, using the magnetic moment recently obtained from the observed pulsar spin-down rate we show that the disc edge has to be within factor of 2 of the Alfvén radius, putting interesting constraints on the models of the disc,magnetosphere interaction. We also demonstrate that the sharp changes in the phase of the fundamental are intimately related to the variations of the pulse profile, which we associate with the varying obscuration of the antipodal spot. Using the phase-resolved spectra, we further argue that the strong dependence of the pulse profiles on photon energy and the observed soft time lags result from the different phase dependence of the normalizations of the two spectral components, the blackbody and the Comptonized tail, being consistent with the model, where these components have significantly different angular emission patterns. The pulse profile amplitude allows us to estimate the colatitude of the hotspot centroid to be ,4°,10°. [source] The effect of a binary source companion on the astrometric microlensing behaviourMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2001Cheongho Han If gravitational microlensing occurs in a binary source system, both source components are magnified, and the resulting light curve deviates from the standard one of a single source event. However, in most cases only one source component is highly magnified and the other component (the companion) can be treated as a simple blending source: this is a blending approximation. In this paper we show that, unlike the light curves, the astrometric curves, representing the trajectories of the source image centroid, of an important fraction of binary source events will not be sufficiently well-modelled by the blending effect alone. This is because the centroid shift induced by the source companion endures to considerable distances from the lens. Therefore, in determining the lens parameters from astrometric curves to be measured by future high-precision astrometric instruments, it will be important to take the full effect of the source companion into consideration. [source] Design of Self Compensating Soft Loading HoodPARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 4-5 2007William McBride Abstract This paper presents a design, and a design method, sufficient to engineer a passive solution to the problem of discharge bias resulting from tonnage fluctuation with soft loading transfer chutes. This is achieved by considering the momentum change inherent in the bulk material stream through the hood section of a soft loading transfer point. This momentum change is utilised to move the hood in a predefined path to ensure the discharge centroid remains consistent. The majority of soft loading transfer points are between conveyor belts that include a plan view change in the material direction which immediately impacts on the design of the transfer point. This impact is, the designer must optimise the transfer for a narrow bandwidth of throughput to achieve optimal outcomes or else accept the potential for mis tracking on the receiving belt. This is due to variations in throughput tonnage altering the location of the discharged materials centroid from a fixed hood section, resulting in a tendency for the receiving belt to mistrack due to biased loading. [source] First principles simulations of F centers in cubic SrTiO3PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2005J. Carrasco Abstract Atomic and electronic structure of regular and O-deficient SrTiO3 have been studied. Several types of first principles atomistic simulations: Hartree-Fock method, Density Functional Theory, and hybrid HF-DFT functionals, have been applied to periodic models that consider supercells of different sizes (ranging between 40 and 240 atoms). We confirm the ionic character of the Sr-O bonds and the high covalency of the Ti-O2 substructure. For the stoichiometric cubic crystal; the lattice constant and bulk modulus correctly reproduce the experimental data whereas the band gap is only properly obtained by the B3PW functional. The relaxed geometry around the F center shows a large expansion of the two nearest Ti ions. Moreover, the vacancy formation energy is extremely sensitive to the size and the shape of the supercell as well as the calculation method. The electronic density map indicates the redistribution of two electrons of the missing O atom between the vacancy and 3d atomic orbitals of the two nearest Ti ions, in contrast to the F centers in ionic oxides where the charge centroid does not change. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] What the honeybee sees: a review of the recognition system of Apis melliferaPHYSIOLOGICAL ENTOMOLOGY, Issue 1 2005Adrian Horridge Abstract., For many years, two opposing theories have dominated our ideas of what honeybees see. The earliest proposal based on training experiments was that bees detected only simple attributes or features, irrespective of the actual pattern. The features demonstrated experimentally before 1940 were the disruption of the pattern (related to spatial frequency), the area of black or colour, the length of edge, and the angle of orientation of a bar or grating. Cues discovered recently are the range, and radial and tangential edges, and symmetry, relative to the fixation point, which is usually the reward hole. This theory could not explain why recognition failed when the pattern was moved. In the second theory, proposed in 1969, the bee detected the retinotopic directions of black or coloured areas, and estimated the areas of overlap and nonoverlap on each test pattern with the corresponding positions in the training pattern. This proposal explained the progressive loss of recognition as a test pattern was moved or reduced in size, but required that the bees saw and remembered the layout of every learned pattern and calculated the mismatch with each test image. Even so, the same measure of the mismatch was given by many test patterns and could not detect a pattern uniquely. Moreover, this theory could not explain the abundant evidence of simple feature detectors. Recent work has shown that bees learn one or more of a limited number of simple cues. A newly discovered cue is the position, mainly in the vertical direction, of the common centre (centroid) of black areas combined together. Significantly, however, the trained bees look for the cues mentioned above only in the range of places where they had occurred during the training. These two observations made possible a synthesis of both theories. There is no experimental evidence that the bees detect or re-assemble the layout of patterns in space; instead, they look for a cue in the expected place. With an array of detectors of the known cues, together with their directions, this mechanism would enable bees to recognize each familiar place from the coincidences of cues in different directions around the head. [source] A list of organic kryptoracematesACTA CRYSTALLOGRAPHICA SECTION B, Issue 1 2010László Fábián A list of 181 organic kryptoracemates has been compiled. This class of crystallographic oddities is made up of racemic compounds (i.e. pairs of resolvable enantiomers) that happen to crystallize in Sohnke space groups (i.e. groups that include only proper symmetry operations). Most (151) of the 181 structures could have crystallized as ordered structures in non-Sohnke groups. The remaining 30 structures do not fully meet this criterion but would have been classified as kryptoracemates by previous authors. Examples were found and checked with the aid of available software for searching the Cambridge Structural Database, for generating and comparing InChI strings, and for validating crystal structures. The pairs of enantiomers in the true kryptoracemates usually have very similar conformations; often the match is near-perfect. There is a pseudosymmetric relationship of the enantiomers in about 60% of the kryptoracemate structures, but the deviations from inversion or glide symmetry are usually quite easy to spot. Kryptoracemates were found to account for 0.1% of all organic structures containing either a racemic compound, a meso molecule, or some other achiral molecule. The centroid of a pair of enantiomers is more likely (99.9% versus 99% probability) to be located on an inversion center than is the centroid of a potentially centrosymmetric molecule. [source] (Acetato-,O)aqua(1H -imidazole-,N3)(picolinato-,2N,O)copper(II) 0.87-hydrate: a Z,> 1 structureACTA CRYSTALLOGRAPHICA SECTION C, Issue 8 2009Anne-Christine Chamayou The crystal structure of the title compound, [Cu(C6H4NO2)(C2H3O2)(C3H4N2)(H2O)]·0.87H2O, has a square-pyramidal-coordinated CuII centre (the imidazole is trans to the picolinate N atom, the acetate is trans to the picolinate ,CO2 group and the aqua ligand is in a Jahn,Teller-elongated apical position) and has two symmetry-independent molecules in the unit cell (Z, = 2), which are connected through complementary imidazole,picolinate N,H...O hydrogen bonding. The two partially occupied solvent water molecules are each disordered over two positions. The disordered solvent water molecules, together with pseudosymmetry elements, support the notion that a crystal structure with multiple identical chemical formula units in the structural asymmetric unit (Z, > 1) can represent a crystal `on the way', that is, a kinetic intermediate form which has not yet reached its thermodynamic minimum. Neighbouring molecules form ,,, stacks between their imidazole and picolinate N-heterocycles, with centroid,centroid distances in the range 3.582,(2),3.764,(2),Å. [source] The host,guest complex between cone-25,26:27,28-bis(methylenedioxy)calix[4]arene and dichloromethaneACTA CRYSTALLOGRAPHICA SECTION C, Issue 5 2003Cedric Dielemann The title compound, 25,26:27,28-bis(methylenedioxy)pentacyclo[19.3.1.13,7.19,13.115,19]octacosa-1(25)3,5,7(28),9,11,13(27),15,17,19(26),21,23-dodecaene dichloromethane solvate, C30H24O4·CH2Cl2, possesses crystallographic twofold symmetry in both components. The calixarene shows a pinched cone conformation with an elliptical cavity, in which the guest dichloromethane solvent molecule is accommodated. The contact distance between guest and host (H,ring centroid = 2.44,Å) is extremely short. [source] ansa -[(tert -Butylamino)(isodicyclopentadienyl)dimethylsilane]Zr(NMe2)2 prepared by an amine-elimination reactionACTA CRYSTALLOGRAPHICA SECTION C, Issue 4 2003Judith C. Gallucci An amine-elimination reaction was used to obtain the title compound, i.e. (N - tert -butyl- N -{[(1,2,3,3a,7a-,)-4,5,6,7-tetrahydro-4,7-methano-1H -inden-2-yl]dimethylsilyl}amido-,N)bis(N -methylmethanaminato-,N)zirconium(IV) or [isodiCpSiMe2N- tert -butyl]Zr(NMe2)2 (Cp is cyclopentadienyl), [Zr(C16H25NSi)(C2H6N)2], in very good yield. Treatment of isodiCpHSiMe2NH- tert -butyl with Zr(NMe2)4 leads to the formation of a yellow solid that can be purified by sublimation. The single-crystal structure of the product shows the exo complexation of the isodicyclopentadienyl ligand to the Zr atom. The Cp portion of this ligand is bonded to the Zr atom in a ,5 manner, with a Zr,Cg (Cg is the ring centroid) distance of 2.2352,(10),Å. The isodiCpSiMe2N- tert -butyl ligand has a constrained geometry, which is exhibited by the small angle of 95.55,(10)° for N,Si,CCp. [source] On the distance to the Ophiuchus star-forming regionASTRONOMISCHE NACHRICHTEN, Issue 1 2008E.E. Mamajek Abstract The Ophiuchus molecular cloud complex has produced in Lynds 1688 the richest known embedded cluster within ,300 pc of the Sun. Unfortunately, distance estimates to the Oph complex vary by nearly ,40% (,120,165 pc). Here I calculate a new independent distance estimate of 135±8 pc to this benchmark star-forming region based on Hipparcos trigonometric parallaxes to stars illuminating reflection nebulosity in close proximity to Lynds 1688. Combining this value with recent distance estimates from reddening studies suggests a consensus distance of 139±6 pc (4% error), situating it within ,11 pc of the centroid of the ,5 Myr old Upper Sco OB subgroup of Sco OB2 (145 pc). The velocity vectors for Oph and Upper Sco are statistically indistinguishable within ,1 km s,1 in each vector component. Both Oph and Upper Sco have negligible motion (<1 km s,1) in the Galactic vertical direction with respect to the Local Standard of Rest, which is inconsistent with the young stellar groups having formed via the high velocity cloud impact scenario. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The geography of melanoma in South AustraliaAUSTRALIAN AND NEW ZEALAND JOURNAL OF PUBLIC HEALTH, Issue 2 2009Adrian R. Heard Abstract Objective: We sought to determine the distribution of melanoma in South Australia with respect to the relative incidence and mortality in coastal/river versus inland areas and metropolitan versus regional/remote areas, and to outline the public health implications of this distribution. Methods: All melanoma cases and deaths for the period 1985-2004 for Adelaide and 11 regional centres were geo-coded and then allocated to ABS collection districts. Collection districts with a centroid within 2 km of the coast or River Murray were determined using mapping software. Results: Melanoma incidence is higher in coastal South Australia (OR=1.19) and near the River Murray (OR=1.25) than in inland South Australia. This geographical effect remains after adjustment for age and socio-economic status. Incidence is also higher in metropolitan Adelaide than in regional areas (OR=1.10). For melanoma mortality there is no significant effect of living near the coast or river, and no effect of living in regional areas. Conclusion: Living near the coast or River Murray in South Australia is associated with an increased risk of being diagnosed with melanoma. Implications: Melanoma prevention and acute care programs can be usefully targeted at persons living in coastal and riverine areas, where there is a significant excess of melanoma incidence. This target population is older than inland populations and will require interventions appropriate for aged communities. [source] Topographic pharmaco-EEG mapping of the effects of the South American psychoactive beverage ayahuasca in healthy volunteersBRITISH JOURNAL OF CLINICAL PHARMACOLOGY, Issue 6 2002Jordi Riba Aims,Ayahuasca is a traditional South American psychoactive beverage used in Amazonian shamanism, and in the religious ceremonies of Brazilian-based syncretic religious groups with followers in the US and several European countries. This tea contains measurable amounts of the psychotropic indole N,N -dimethyltryptamine (DMT), and ,-carboline alkaloids with MAO-inhibiting properties. In a previous report we described a profile of stimulant and psychedelic effects for ayahuasca as measured by subjective report self-assessment instruments. In the present study the cerebral bioavailability and time-course of effects of ayahuasca were assessed in humans by means of topographic quantitative-electroencephalography (q-EEG), a noninvasive method measuring drug-induced variations in brain electrical activity. Methods, Two doses (one low and one high) of encapsulated freeze-dried ayahuasca, equivalent to 0.6 and 0.85 mg DMT kg,1 body weight, were administered to 18 healthy volunteers with previous experience in psychedelic drug use in a double-blind crossover placebo-controlled clinical trial. Nineteen-lead recordings were undertaken from baseline to 8 h after administration. Subjective effects were measured by means of the Hallucinogen Rating Scale (HRS). Results,Ayahuasca induced a pattern of psychoactive effects which resulted in significant dose-dependent increases in all subscales of the HRS, and in significant and dose-dependent modifications of brain electrical activity. Absolute power decreased in all frequency bands, most prominently in the theta band. Mean absolute power decreases (95% CI) at a representative lead (P3) 90 min after the high dose were ,20.20±15.23 µV2 and ,2.70±2.21 µV2 for total power and theta power, respectively. Relative power decreased in the delta (,1.20±1.31% after 120 min at P3) and theta (,3.30±2.59% after 120 min at P3) bands, and increased in the beta band, most prominently in the faster beta-3 (1.00±0.88% after 90 min at P3) and beta-4 (0.30±0.24% after 90 min at P3) subbands. Finally, an increase was also seen for the centroid of the total activity and its deviation. EEG modifications began as early as 15,30 min, reached a peak between 45 and 120 min and decreased thereafter to return to baseline levels at 4,6 h after administration. Conclusions, The central effects of ayahuasca could be objectively measured by means of q-EEG, showing a time pattern which closely paralleled that of previously reported subjective effects. The modifications seen for the individual q-EEG variables were in line with those previously described for other serotonergic psychedelics and share some features with the profile of effects shown by pro-serotonergic and pro-dopaminergic drugs. The q-EEG profile supports the role of 5-HT2 and dopamine D2 -receptor agonism in mediating the effects of ayahuasca on the central nervous system. [source] Measuring Similarity Among Various Shapes Based on Geometric MatchingGEOGRAPHICAL ANALYSIS, Issue 4 2005Zuoquan Zhao The purpose of this article is to examine how to measure the degree of similarity among various shapes, including for the first time those that are fragmented and perforated, by the overlap-based elongation index. It is argued that complete removal of the effects of position, size, and orientation on shape, which is essential for the calibration of shape similarity, can be achieved by a shape similarity index that varies continuously with changes in shape. After examining the characteristics of shape change, it is demonstrated that the elongation index is sensitive to changes in the shape of two spatial objects only when the centroids of the two objects are coincident. Two related rules of shape similarity are then presented. The applicability of the elongation index is evaluated by comparing several simple and complex shapes. The principal contribution of this article is that for the first time similarity among various shapes, fragmented or perforated, can be identified using the elongation index. [source] Traffic flow continuum modeling by hypersingular boundary integral equationsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 1 2010Luis M. Romero Abstract The quantity of data necessary in order to study traffic in dense urban areas through a traffic network, and the large volume of information that is provided as a result, causes managerial difficulties for the said model. A study of this kind is expensive and complex, with many sources of error connected to each step carried out. A simplification like the continuous medium is a reasonable approximation and, for certain dimensions of the actual problem, may be an alternative to be kept in mind. The hypotheses of the continuous model introduce errors comparable to those associated with geometric inaccuracies in the transport network, with the grouping of hundreds of streets in one same type of link and therefore having the same functional characteristics, with the centralization of all journey departure points and destinations in discrete centroids and with the uncertainty produced by a huge origin/destination matrix that is quickly phased out, etc. In the course of this work, a new model for characterizing traffic in dense network cities as a continuous medium, the diffusion,advection model, is put forward. The model is approached by means of the boundary element method, which has the fundamental characteristic of only requiring the contour of the problem to be discretized, thereby reducing the complexity and need for information into one order versus other more widespread methods, such as finite differences and the finite element method. On the other hand, the boundary elements method tends to give a more complex mathematical formulation. In order to validate the proposed technique, three examples in their fullest form are resolved with a known analytic solution. Copyright © 2009 John Wiley & Sons, Ltd. [source] A rational elasto-plastic spatially curved thin-walled beam elementINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 3 2007Yong-Lin Pi Abstract Torsion is one of the primary actions in members curved in space, and so an accurate spatially curved-beam element needs to be able to predict the elasto-plastic torsional behaviour of such members correctly. However, there are two major difficulties in most existing finite thin-walled beam elements, such as in ABAQUS and ANSYS, which may lead to incorrect predictions of the elasto-plastic behaviour of members curved in space. Firstly, the integration sample point scheme cannot capture the shear strain and stress information resulting from uniform torsion. Secondly, the higher-order twists are ignored which leads to loss of the significant effects of Wagner moments on the large twist torsional behaviour. In addition, the initial geometric imperfections and residual stresses are significant for the elasto-plastic behaviour of members curved in space. Many existing finite thin-walled beam element models do not provide facilities to deal with initial geometric imperfections. Although ABAQUS and ANSYS have facilities for the input of residual stresses as initial stresses, they cannot describe the complicated distribution patterns of residual stresses in thin-walled members. Furthermore, external loads and elastic restraints may be applied remote from shear centres or centroids. The effects of the load (and restraint) positions are important, but are not considered in many beam elements. This paper presents an elasto-plastic spatially curved element with arbitrary thin-walled cross-sections that can correctly capture the uniform shear strain and stress information for integration, and includes initial geometric imperfections, residual stresses and the effects of the load and restraint positions. The element also includes elastic restraints and supports, which have to be modelled separately as spring elements in some other finite thin-walled beam elements. Comparisons with existing experimental and analytical results show that the elasto-plastic spatially curved-beam element is accurate and efficient. Copyright © 2006 John Wiley & Sons, Ltd. [source] A preconditioned semi-staggered dilation-free finite volume method for the incompressible Navier,Stokes equations on all-hexahedral elementsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 9 2005Mehmet Sahin Abstract A new semi-staggered finite volume method is presented for the solution of the incompressible Navier,Stokes equations on all-quadrilateral (2D)/hexahedral (3D) meshes. The velocity components are defined at element node points while the pressure term is defined at element centroids. The continuity equation is satisfied exactly within each elements. The checkerboard pressure oscillations are prevented using a special filtering matrix as a preconditioner for the saddle-point problem resulting from second-order discretization of the incompressible Navier,Stokes equations. The preconditioned saddle-point problem is solved using block preconditioners with GMRES solver. In order to achieve higher performance FORTRAN source code is based on highly efficient PETSc and HYPRE libraries. As test cases the 2D/3D lid-driven cavity flow problem and the 3D flow past array of circular cylinders are solved in order to verify the accuracy of the proposed method. Copyright © 2005 John Wiley & Sons, Ltd. [source] | |||||||||||||||||||||||||||||||