Rigid vs compliant contact: an experimental study on biped walking

Multibody System Dynamics - Contact modeling plays a central role in motion planning, simulation and control of legged robots, as legged locomotion is realized through contact. The two prevailing...     

Utilizing Voronoi Cells of Location Data Streams for Accurate Computation of Aggregate Functions in Sensor Networks

Sensor networks are unattended deeply distributed systems whose database schema can be conceptualized using the relational model. Aggregation queries on the data sampled at each sensor node are the main means to extract the abstract characteristics of the surrounding environment. However, the non-uniform distribution of the sensor nodes in the environment leads to inaccurate results generated by the aggregation queries. In this paper, we introduce “spatial aggregations” that take into consideration the spatial location of each measurement generated by the sensor nodes. We propose the use of spatial interpolation methods derived from the fields of spatial statistics and computational geometry to answer spatial aggregations. In particular, we study Spatial Moving Average (SMA), Voronoi Diagram and Triangulated Irregular Network (TIN). Investigating these methods for answering spatial average queries, we show that the average value on the data samples weighted by the area of the Voronoi cell of the corresponding sensor node, provides the best precision. Consequently, we introduce an algorithms to compute and maintain the accurate Voronoi cell at each sensor node while the location of the others arrive on data stream. We also propose AVC-SW, a novel algorithm to approximate this Voronoi cell over a sliding window that supports dynamism in the sensor network. To demonstrate the performance of in-network implementation of our aggregation operators, we have developed prototypes of two different approaches to distributed spatial aggregate processing. Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. To copy otherwise, to republish, to post on servers or to redistribute to lists, requires prior specific permission and/or a fee. GIS'04, November 12–13, 2004, Washington DC, USA. Copyright 2004 ACM 1-58113-979-9/04/0011...$5.00.     

Processing Optimal Sequenced Route Queries Using Voronoi Diagrams

The Optimal Sequenced Route (OSR) query strives to find a route of minimum length starting from a given source location and passing through a number of typed locations in a specific sequence imposed on the types of the locations. In this paper, we propose a pre-computation approach to OSR query in both vector and metric spaces. We exploit the geometric properties of the solution space and theoretically prove its relation to additively weighted Voronoi diagrams. Our approach recursively accesses these diagrams to incrementally build the OSR. Introducing the analogous diagrams for the space of road networks, we show that our approach is also efficiently applicable to this metric space. Our experimental results verify that our pre-computation approach outperforms the previous index-based approaches in terms of query response time. This research has been funded in part by NSF grants EEC-9529152 (IMSC ERC), IIS-0238560 (PECASE), IIS-0324955 (ITR), IIS-0534761, and unrestricted cash gifts from Google and Microsoft. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the NSF.

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Evaluation of air blast parameters in block cave mining using particle flow code

Air blast, a sudden mass movement of air, can occur in underground mining system where caving develops an extensive mass of unsupported rock spanning a large void. Air blast can result in injury to mine personnel, damage to equipment or disrupts mine operation. Evaluation of air blast parameters is, therefore, an essential part to develop strategies to mitigate the hazard. The properties of a muckpile or a caved zone are significant factors affecting the magnitude of air blast in particular on the undercut and extraction levels. This research investigates the effect of muckpile properties on air flow using the numerical code, PFC2D. The critical parameters such as thickness, block size and porosity (swell factor) of the muckpile have been studied to quantify how much they could change the magnitude of air pressures and velocities while the air flows through the muckpile. It was found that the porosity of the muckpile is the most effective parameter on the magnitude of air blast and by designing a thick layer of blasted rock with low porosity in the caved zone, the intensity of the air blast can be significantly reduced. The findings of this study can be used to design air blast plugs or bulkheads in order to isolate any potential air blast from the active workings, or to quantify the minimum thickness of the muckpile above extraction levels to manage air blast hazards.     

Two-phase flow component fraction measurement using gamma-ray attenuation technique

Multiphase flow meters as the potential alternatives to separation and metering techniques have been in rapid development since 1980 s.Before its field operation,the instrument should be calibrated in a standard test-facility.In spite of the known medium and large scale facilities all over the world,we developed a laboratory scale instrument for component fraction measurements.It has a two-phase flow homogenizer loop with the clamp-on potential of the meters to provide a regime independent measurement.It is capable of delivering a complete homogenization by γ-ray densitometer.With an error of±5%in component fraction measurements,this instrument is appropriate for testing and calibrating other meters.     

Using anisotropic diffusion equations in pixon domain for image de-noising

Image enhancement is an essential phase in many image processing algorithms. In any image de-noising algorithm, it is a major concern to keep the interesting structures of the image. Such interesting structures in an image often correspond to the discontinuities in the image (edges). In this paper, we propose a new algorithm for image de-noising using anisotropic diffusion equations in pixon domain. In this approach, diffusion equations are applied on the pixonal model of the image. The algorithm has been examined on a variety of standard images and the performance has been compared with algorithms known from the literature. The experimental results show that in comparison with the other existing methods, the proposed algorithm has a better performance in de-noising and preserving image edges.     

Using simulators to model transmitted variability in ICmanufacturing

The authors describe a response surface design methodology based on process and device simulations to estimate device variations due to changes in process input parameters from their designed values. The gradient of the simulated device characteristics is estimated directly and used to compute device sensitivities. This methodology was applied to Stanford's 2-μm CMOS fabrication process. Threshold voltage, subthreshold slope, linear transconductance, and saturation current were picked as the target device characteristics for optimization. Five process parameters were examined: boron concentration in the wafer, phosphorous n-well implant dose, boron threshold adjust dose, gate oxidation temperature, and gate length. The methodology was shown to be successful for the exploration of device characteristic values as a function of process parameters, but success for the transmitted variability, because it depends on derivatives which tend to be less like polynomials than the functions themselves, is more limited. In the absence of a direct assessment of the derivative, response surface models fit to the simulator values can give a very misleading picture of the transmitted variability. Models used were quadratic models for Box-Cox transformed device characteristics     

Synthesis of Janus/non-Janus hollow graphene oxide micro- and nanoparticles and the effects of their localization on the thermal conductivity of blend-based polymer composites

Journal of Materials Science - In this study, the effects of Janus, hydrophilic and hydrophobic hollow graphene oxide (HO) particles on the thermal conductivity of binary polymer blends were...