Incremental and Decremental Maintenance of Planar Width

We present an algorithm for maintaining the width of a planar point set dynamically, as points are inserted or deleted. Our algorithm takes time O(kn^epsilon) per update, where k is the amount of change the update causes in the convex hull, n is the number of points in the set, and epsilon is any arbitrarily small constant. For incremental or decremental update sequences, the amortized time per update is O(n^epsilon).Comment: 7 pages; 2 figures. A preliminary version of this paper was presented at the 10th ACM/SIAM Symp. Discrete Algorithms (SODA '99); this is the journal version, and will appear in J. Algorithm

Cloud base height estimates from sky imagery and a network of pyranometers

Cloud base height (CBH) is an important parameter for physics-based high resolution solar radiation modeling. In sky imager-based forecasts, a ceilometer or stereographic setup is needed to derive the CBH; otherwise erroneous CBHs lead to incorrect physical cloud velocity and incorrect projection of cloud shadows, causing solar power forecast errors due to incorrect shadow positions and timing of shadowing events. In this paper, two methods to estimate cloud base height from a single sky imager and distributed ground solar irradiance measurements are proposed. The first method (Time Series Correlation, denoted as “TSC”) is based upon the correlation between ground-observed global horizontal irradiance (GHI) time series and a modeled GHI time series generated from a sequence of sky images geo-rectified to a candidate set of CBH. The estimated CBH is taken as the candidate that produces the highest correlation coefficient. The second method (Geometric Cloud Shadow Edge, denoted as “GCSE”) integrates a numerical ramp detection method for ground-observed GHI time series with solar and cloud geometry applied to cloud edges in a sky image. CBH are benchmarked against a collocated ceilometer and stereographically estimated CBH from two sky imagers for 15 min median-filtered CBHs. Over 30 days covering all seasons, the TSC method performs similarly to the GCSE method with nRMSD of 18.9% versus 20.8%. A key limitation of both proposed methods is the requirement of sufficient variation in GHI to enable reliable correlation and ramp detection. The advantage of the two proposed methods is that they can be applied when measurements from only a single sky imager and pyranometers are available

Fast Hierarchical Clustering and Other Applications of Dynamic Closest Pairs

We develop data structures for dynamic closest pair problems with arbitrary distance functions, that do not necessarily come from any geometric structure on the objects. Based on a technique previously used by the author for Euclidean closest pairs, we show how to insert and delete objects from an n-object set, maintaining the closest pair, in O(n log^2 n) time per update and O(n) space. With quadratic space, we can instead use a quadtree-like structure to achieve an optimal time bound, O(n) per update. We apply these data structures to hierarchical clustering, greedy matching, and TSP heuristics, and discuss other potential applications in machine learning, Groebner bases, and local improvement algorithms for partition and placement problems. Experiments show our new methods to be faster in practice than previously used heuristics.Comment: 20 pages, 9 figures. A preliminary version of this paper appeared at the 9th ACM-SIAM Symp. on Discrete Algorithms, San Francisco, 1998, pp. 619-628. For source code and experimental results, see http://www.ics.uci.edu/~eppstein/projects/pairs

Turbulent-laminar patterns in shear flows without walls

Turbulent-laminar intermittency, typically in the form of bands and spots, is a ubiquitous feature of the route to turbulence in wall-bounded shear flows. Here we study the idealised shear between stress-free boundaries driven by a sinusoidal body force and demonstrate quantitative agreement between turbulence in this flow and that found in the interior of plane Couette flow -- the region excluding the boundary layers. Exploiting the absence of boundary layers, we construct a model flow that uses only four Fourier modes in the shear direction and yet robustly captures the range of spatiotemporal phenomena observed in transition, from spot growth to turbulent bands and uniform turbulence. The model substantially reduces the cost of simulating intermittent turbulent structures while maintaining the essential physics and a direct connection to the Navier-Stokes equations. We demonstrate the generic nature of this process by introducing stress-free equivalent flows for plane Poiseuille and pipe flows which again capture the turbulent-laminar structures seen in transition.Comment: 13 pages, 9 figure

Dynamic similarity promotes interpersonal coordination in joint-action

Human movement has been studied for decades and dynamic laws of motion that are common to all humans have been derived. Yet, every individual moves differently from everyone else (faster/slower, harder/smoother etc). We propose here an index of such variability, namely an individual motor signature (IMS) able to capture the subtle differences in the way each of us moves. We show that the IMS of a person is time-invariant and that it significantly differs from those of other individuals. This allows us to quantify the dynamic similarity, a measure of rapport between dynamics of different individuals' movements, and demonstrate that it facilitates coordination during interaction. We use our measure to confirm a key prediction of the theory of similarity that coordination between two individuals performing a joint-action task is higher if their motions share similar dynamic features. Furthermore, we use a virtual avatar driven by an interactive cognitive architecture based on feedback control theory to explore the effects of different kinematic features of the avatar motion on the coordination with human players

Complex Remanence vs. Simple Persistence: Are Hysteresis and Unit-Root Processes observationally equivalent?

The hysteresis terminology has mainly been used in two fields of economics, unemplyment and international trade, with a different meaning however, involving either linear autoregressive macro behaviour or non- linear heterogenous mico behaviour. There may nonetheless be observational equivalence between the 'persistence' characterising unit- root processes and the 'remanence' created by the aggregation of non- linear dynamics. Stochastic simulations are employed to analyse the properties of the output of an hysteretic system, subject to white noise and random walk inputs. Non-linear hysteretic systems are found to generate a sizeable proportion - two-thirds - of stationary output from stationary input, and to possibly generate an output cointegrated with the corresponding input. Such processes therefore appear significantly different from an integrated process. This stresses the specific relevance of a non-linear approach to hysteresis.hysteresis, non-linearity, aggregation, heterogeneity, experimental economics

Testigos de piedra: estelas armadas entre el Tajo internacional y el Duero, Península Ibérica

Pocos territorios en Europa reúnen la concentración de estelas en piedra que se documentan entre el Tajo y el Duero. La arqueología asegura amplias posibilidades extractivas, con un claro centro neurálgico en el actual distrito de Castelo Branco. Desde los primeros descubrimientos de piezas tan singulares como las de São Martinho, hasta el registro actual, la variedad y diacronía de estelas y menhires en piedra resulta excepcional en el contexto ibérico y europeo. La tradicional lectura, que alejaba los viejos menhires de las estelas del Bronce Final, queda muy matizada ante el uso de referencias temáticas y técnicas semejantes. En este texto aportamos otro argumento a sumar a esas similitudes, con la reutilización de los antiguos soportes como base material para la generación de las estelas del Bronce Final. Las imágenes humanas que se grabaron en estas memorias en piedra expresan narrativas sociales elaboradas. Las secuencias gráficas que argumentamos aseguran el papel político de estas piezas como justificaciones materiales de pasados ancestrales. Indudablemente albergan relatos orales sobre la relación entre los viejos ancestros y los nuevos líderes, justificando el orden del entramado económico asociado al control de la extracción y comercio del metal.Few places in Europe concentrate as many stone stelae as the area between the Tagus and the Douro. Archaeology has shown the ample possibilities for metal mining, the modern region of Castelo Branco being the epicentre in the area. From the first discoveries of such unique objects as the São Martinho stelae to the current record, the variety and diachronicity of stone stelae and menhirs is exceptional on the Iberian and European scales. The traditional interpretation that differentiated between the old menhirs and Late Bronze Age stelae has been nuanced by the evidence of similar themes and techniques. Another argument presented here is the use of the old stones as the basic material to produce the Late Bronze Age stelae. Human images carved on these memorial stones express elaborate social narratives. The graphic sequences described here demonstrate the ‘political’ role of these stones and material justification of ancestral pasts. They were undoubtedly imbued with oral tales about old ancestors and new leaders, to justify the order of the economic system associated with mining and metal trade.Ministerio de Ciencia, Innovación y Universidades 2018-099405-BI0