The Impact of Global Clustering on Spatial Database Systems

Global clustering has rarely been investigated in the area of spatial database systems although dramatic performance improvements can be achieved by using suitable techniques. In this paper, we propose a simple approach to global clustering called cluster organization. We will demonstrate that this cluster organization leads to considerable performance improvements without any algorithmic overhead. Based on real geographic data, we perform a detailed empirical performance evaluation and compare the cluster organization to other organization models not using global clustering. We will show that global clustering speeds up the processing of window queries as well as spatial joins without decreasing the performance of the insertion of new objects and of selective queries such as point queries. The spatial join is sped up by a factor of about 4, whereas non-selective window queries are accelerated by even higher speed up factors

Collision induced spatial organization of microtubules

The dynamic behavior of microtubules in solution can be strongly modified by interactions with walls or other structures. We examine here a microtubule growth model where the increase in size of the plus-end is perturbed by collisions with other microtubules. We show that such a simple mechanism of constrained growth can induce ordered structures and patterns from an initially isotropic and homogeneous suspension. First, microtubules self-organize locally in randomly oriented domains that grow and compete with each other. By imposing even a weak orientation bias, external forces like gravity or cellular boundaries may bias the domain distribution eventually leading to a macroscopic sample orientation.Comment: Submitted to Biophysical Journa

A Network for Learning Kinematics with Application to Human Reaching Models

A model for self-organization of the coordinate transformations required for spatial reaching is presented. During a motor babbling phase, a mapping from spatial coordinate directions to joint motion directions is learned. After learning, the model is able to produce straight-line spatial velocity trajectories with characteristic bell-shaped spatial velocity profiles, as observed in human reaches. Simulation results are presented for transverse plane reaching using a two degree-of-freedom arm.Office of Naval Research (N00014-92-J-1309

Fine-Scale Spatial Organization of Face and Object Selectivity in the Temporal Lobe: Do Functional Magnetic Resonance Imaging, Optical Imaging, and Electrophysiology Agree?

The spatial organization of the brain's object and face representations in the temporal lobe is critical for understanding high-level vision and cognition but is poorly understood. Recently, exciting progress has been made using advanced imaging and physiology methods in humans and nonhuman primates, and the combination of such methods may be particularly powerful. Studies applying these methods help us to understand how neuronal activity, optical imaging, and functional magnetic resonance imaging signals are related within the temporal lobe, and to uncover the fine-grained and large-scale spatial organization of object and face representations in the primate brain

Origin of spatial organization of DNA-polymer in bacterial chromosomes

In-vivo DNA organization at large length scales ($\sim 100nm$) is highly debated and polymer models have proved useful to understand the principle of DNA-organization. Here, we show that $<2$% cross-links at specific points in a ring polymer can lead to a distinct spatial organization of the polymer. The specific pairs of cross-linked monomers were extracted from contact maps of bacterial DNA. We are able to predict the structure of 2 DNAs using Monte Carlo simulations of the bead-spring polymer with cross-links at these special positions. Simulations with cross-links at random positions along the chain show that the organization of the polymer is different in nature from the previous case.Comment: arXiv admin note: text overlap with arXiv:1701.0506

Spatial organization of individuals and ecosystems services in tropical agroecosystems : COS 18-9

Background/Question/Methods Agroecology involves the optimization of ecological processes in agroecosystems. It has been identified as a sustainable alternative to the negative environmental impact of modern agriculture. A challenge in agricultural research is to design innovative "agroecological" systems: allowing to maintain an acceptable level of productivity; but also fostering on other ecosystem services. We worked on ecological concepts influencing the dynamics and ecological performances in ecosystems, and studied its application on agroecosystems. The spatial organization of individuals is fundamental in ecological theories. It is an important structural characteristics that influence ecosystem functioning and productivity. In agroecosystems, the spatial organization of individuals may influence key aspects influencing ecosystem services sought-after in sustainable agriculture. Our aim was to analyze the spatial organization of plant individuals in complex agroecosystems; and to highlight the links between spatial organization of plant individuals and selected ecosystems services: provisioning services (crop productivity), biodiversity conservation (trees species richness) and regulating services (pest and disease regulation). We used the Ripley function to analyze the spatial organization of shade and cacao trees in cacao agroforests in Costa Rica. We also assessed the species richness of shade trees; and cacao productivity and damages by Frosty Pod Rot, an important disease in Costa Rica. Results/Conclusions Three types of stands were identified: the first characterised by significant clustering of shade trees. The second type was characterised by random spatial organisation of shade trees. The third types showed a trend towards regular organisation. The clustered structure of shade trees appears to be a trade-off between biodiversity and productivity. Even if the damaged production (estimated by the number of damaged pods in the plots) was significantly higher in the clustered type, the potential (total number of pods) also tended to be higher, leading to an healthy (number of healthy pods) productions equivalent to the regular and the random spatial types. However, the clustered type had the highest shade tree species richness. The clustered type were located in remote places, closer to natural forest systems, and are managed for years by farmers who are very respectful of nature, and do not wish to disturb the natural process of tree regeneration. Manipulating spatial structure in complex agroecosystems appears as a lever for the ecological intensification of these agroecosystems. Indeed, the clustered spatial structure appears to favour a synergy between biodiversity conservation (tree species richness), and provisioning services (cacao production), taking into account a regulation services (pest and disease regulation). (Résumé d'auteur

Hierarchical Spatial Organization of Geographical Networks

In this work we propose the use of a hirarchical extension of the polygonality index as a means to characterize and model geographical networks: each node is associated with the spatial position of the nodes, while the edges of the network are defined by progressive connectivity adjacencies. Through the analysis of such networks, while relating its topological and geometrical properties, it is possible to obtain important indications about the development dynamics of the networks under analysis. The potential of the methodology is illustrated with respect to synthetic geographical networks.Comment: 3 page, 3 figures. A wokring manuscript: suggestions welcome