Anytime Hierarchical Clustering

We propose a new anytime hierarchical clustering method that iteratively transforms an arbitrary initial hierarchy on the configuration of measurements along a sequence of trees we prove for a fixed data set must terminate in a chain of nested partitions that satisfies a natural homogeneity requirement. Each recursive step re-edits the tree so as to improve a local measure of cluster homogeneity that is compatible with a number of commonly used (e.g., single, average, complete) linkage functions. As an alternative to the standard batch algorithms, we present numerical evidence to suggest that appropriate adaptations of this method can yield decentralized, scalable algorithms suitable for distributed/parallel computation of clustering hierarchies and online tracking of clustering trees applicable to large, dynamically changing databases and anomaly detection.Comment: 13 pages, 6 figures, 5 tables, in preparation for submission to a conferenc

Coordinated Robot Navigation via Hierarchical Clustering

We introduce the use of hierarchical clustering for relaxed, deterministic coordination and control of multiple robots. Traditionally an unsupervised learning method, hierarchical clustering offers a formalism for identifying and representing spatially cohesive and segregated robot groups at different resolutions by relating the continuous space of configurations to the combinatorial space of trees. We formalize and exploit this relation, developing computationally effective reactive algorithms for navigating through the combinatorial space in concert with geometric realizations for a particular choice of hierarchical clustering method. These constructions yield computationally effective vector field planners for both hierarchically invariant as well as transitional navigation in the configuration space. We apply these methods to the centralized coordination and control of $n$ perfectly sensed and actuated Euclidean spheres in a $d$-dimensional ambient space (for arbitrary $n$ and $d$). Given a desired configuration supporting a desired hierarchy, we construct a hybrid controller which is quadratic in $n$ and algebraic in $d$ and prove that its execution brings all but a measure zero set of initial configurations to the desired goal with the guarantee of no collisions along the way.Comment: 29 pages, 13 figures, 8 tables, extended version of a paper in preparation for submission to a journa

Leakage current by Frenkel-Poole emission in Ni/Au Schottky contacts on Al0.83In0.17N/AlN/GaN heterostructures

Cataloged from PDF version of article.In order to determine the reverse-bias leakage current mechanisms in Schottky diodes on Al0.83In0.17N/AlN/GaN heterostructures, the temperature-dependent current-voltage measurements were performed in the temperature range of 250-375 K. In this temperature range, the leakage current was found to be in agreement with the predicted characteristics, which is based on the Frenkel-Poole emission model. The analysis of the reverse current-voltage characteristics dictates that the main process in leakage current flow is the emission of electrons from a trapped state near the metal-semiconductor interface into a continuum of states which associated with each conductive dislocation

Forward tunneling current in Pt/p-InGaN and Pt/n-InGaN Schottky barriers in a wide temperature range

Cataloged from PDF version of article.The current-transport mechanisms of the Pt contacts on p-InGaN and n-InGaN were investigated in a wide temperature range (80-360 K) and in the forward bias regime. It was found that the ideality factor (n) values and Schottky barrier heights (SBHs), as determined by thermionic emission (TE), were a strong function of temperature and Phi(b0) show the unusual behavior of increasing linearly with an increase in temperature from 80 to 360 K for both Schottky contacts. The tunneling saturation (J(TU)(0)) and tunneling parameters (E-0) were calculated for both Schottky contacts. We observed a weak temperature dependence of the saturation current and a fairly small dependence on the temperature of the tunneling parameters in this temperature range. The results indicate that the dominant mechanism of the charge transport across the Pt/p-InGaN and Pt/n-InGaN Schottky contacts are electron tunneling to deep levels in the vicinity of mixed/screw dislocations in the temperature range of 80-360 K. (c) 2012 Elsevier B.V. All rights reserved

Interference Localization for Uplink OFDMA Systems in Presence of CFOs

Multiple carrier frequency offsets (CFOs) present in the uplink of orthogonal frequency division multiple access (OFDMA) systems adversely affect subcarrier orthogonality and impose a serious performance loss. In this paper, we propose the application of time domain receiver windowing to concentrate the leakage caused by CFOs to a few adjacent subcarriers with almost no additional computational complexity. This allows us to approximate the interference matrix with a quasi-banded matrix by neglecting small elements outside a certain band which enables robust and computationally efficient signal detection. The proposed CFO compensation technique is applicable to all types of subcarrier assignment techniques. Simulation results show that the quasi-banded approximation of the interference matrix is accurate enough to provide almost the same bit error rate performance as that of the optimal solution. The excellent performance of our proposed method is also proven through running an experiment using our FPGA-based system setup.Comment: Accepted in IEEE WCNC 201

Energy Relaxation Rates in AlInN/AlN/GaN Heterostructures

Cataloged from PDF version of article.The two-dimensional (2D) electron energy relaxation in Al0.83In0.17N/AlN/GaN heterostructures has been investigated experimentally. Shubnikov-de Haas (SdH) effect measurements were employed in the investigations. The electron temperature (T (e)) of hot electrons was obtained from the lattice temperature (T (L)) and the applied electric field dependencies of the amplitude of SdH oscillations. The experimental results for the electron temperature dependence of power loss are also compared with current theoretical models for power loss in 2D semiconductors. The power loss from the electrons was found to be proportional to (T (e) (3) - T (L) (3) ) for electron temperatures in the range 1.8 K < T (e) < 14 K, indicating that the energy relaxation of electrons is due to acoustic phonon emission via unscreened piezoelectric interaction. The effective mass and quantum lifetime of the 2D electrons have been determined from the temperature and magnetic field dependencies of the amplitude of SdH oscillations, respectively. The values obtained for quantum lifetime suggest that remote ionized impurity scattering is the dominant scattering mechanism in Al0.83In0.17N/AlN/GaN heterostructures

Development of Building Damage Functions for Big Earthquakes in Turkey

AbstractThe current work is an attempt to predict building reactions to big earthquakes using real data collected from surveys carried out after the occurrence of earthquakes. With the development of building damage functions for big earthquakes in Turkey one can predict the damage levels as a function of earthquakes’ intensity and the building parameters. Our model is based on neural networks techniques which allow for the non-linear correlations to be taken into account. We analyse data collected for damaged buildings after the following three big earthquakes: Afyon (2002; Mw = 6.0), Bingöl (2003; Mw = 6.4) and Düzce (1999; Mw = 7.2). The current model includes some of the main important factors affecting the health of any structure, namely, age, number of stories, floor areas, and the column areas. Our method of damage prediction is based on several earthquakes and buildings with different damage levels. The obtained results show that there is a strong correlation between the strength of the earthquake, the basic building parameters and the damage level. The obtained building damage function is essential for future plans and regulations for new constructions and can be considered as an essential module for hazards mitigation systems

Cost and emission impacts of virtual power plant formation in plug-in hybrid electric vehicle penetrated networks

Cataloged from PDF version of article.With increasing interest in alternative energy resources and technologies, mass penetration of PHEVs (plug-in hybrid vehicles) into the electricity grid and widespread utilization of DERs (distributed energy resources) are anticipated in the near future. As an aggregation unit, the VPP (virtual power plant) is introduced for load management and resource scheduling. In this article, we develop an energy management model for VPPs and analyze the cost and emission impacts of VPP formation and PHEV penetration. We conduct a case study for the state of California using real-world data from official resources. An average of 29.5% cost reduction and 79% CO2 and 83% NOx emission reductions are attained as shared benefits of consumers in the case study. Results are illustrative of opportunities that VPP formation can provide for the community. Sensitivity of the results to the DER costs and capacities, battery and gasoline prices are also analyzed. In addition, we prove that charging and discharging do not simultaneously occur in the solutions, which leads to a simplification in traditional energy management models. 2013 Elsevier Ltd. All rights reserved