Direct measurement of the spectral transfer function of a laser based anemometer

The effect of a continuous-wave (cw) laser based anemometer's probe volume on the measurement of wind turbulence is studied in this paper. Wind speed time series acquired by both a remote sensing cw laser anemometer, whose line-of-sight was aligned with the wind direction, and by a reference sensor (sonic anemometer) located in the same direction, were used. The spectral transfer function, which describes the attenuation of the power spectral density of the wind speed turbulence, was calculated and found to be in good agreement with the theoretical exponential function, which is based on the properties of the probe volume of a focused Gaussian laser beam. Parameters such as fluctuations of the wind direction, as well as the overestimation of the laser Doppler spectrum threshold, were found to affect the calculation of the spectral transfer function by introducing high frequency noise.     

An Object Oriented Architectural Library for the Design and Implementation of Network Protocols

The society of telecommunication and computer networks encompasses a wide variety of organizations, forums and industry companies that specify, standardize, evaluate, implement and deploy network infrastructures. These infrastructures are well defined and deployed in order to offer high quality end-user services and meet the need for interconnectivity, expandability and upgradeability. What users see and experience is the tip of the iceberg. Great amount of time and money is spent in specification, standardization, design, debugging, testing (both conformance and stress) and finally evaluating network components or subsystems before the deployment takes place. The framework, proposed in the current paper and implemented in open source software library, provides an object oriented methodology for the implementation of network protocols and the software realization of network components. The method is formed in respect to: (a) operating system architecture (b) network architecture and (c) Object Oriented (OO) methodology.     

Signaling Performance Trials and Evaluation Results on a GPRS Platform

Generic Packet Radio Service (GPRS) enhances data transfers up to occasional transmission of large amounts of user data. Signaling procedures are specified for the provision of connection oriented services and the establishment of data channels between mobile subscribers. The time-overhead introduced with the performance of end-to-end signaling operations is a crucial performance factor that determines the provided Quality of Service (QoS). A significant time-overhead associated with the high rate establishment and release of many short-lived data channels, required during hand-over or for Internet access, would result in network performance degradation.Nevertheless, despite its main significance, there is a lack of papers in the Internet community that either investigate the issue of GPRS signaling performance or present GPRS trials and measurements. This lack becomes even more obvious and gets more importance from the moment that the deployment of GPRS, at least in the first phase, revealed significant performance delays in the connection setup times.To this respect, this paper presents the experiments conducted at a GPRS testing platform focusing on the performance assessment of signaling functionality. The trials focus on the performance evaluation of the GPRS signaling operations related to the establishment and release of user data channels through the Gn and Gi interfaces. Timing results that quantify the overall delay under diverse conditions of signaling load, rate and subscribers are presented.     

Transport properties of porous media from the microgeometry of a three-dimensional voronoi network

In this work a way of calculating effective transport coefficients from the microgeometry of a porous medium is presented. The model material consists of a random packing of uniform spheres, and by applying the Voronoi—Delaunay tessellation technique the void between the spheres is simulated as a network of cylindrical pores. The tessellation yields all the necessary information for the structural characterization, such as the pore diameter, pore angle and pore length distribution functions and the topological interconnection. The effective transport coefficients of ordinary diffusion, Knudsen flow and viscous flow are calculated numerically by mass balancing at each network node and over all nodes of the system. The results obtained agree very well with the experimental ones, especially for ordinary diffusion. For Knudsen and viscous flow, inaccuracies in the estimation of the pore overlapping volume cause a relative error between the numerical and experimental results of the order of 16%–33%.     

Etude des propriétés des films préparés par evaporation des solutions d'un polymére dans différents solvants

Films of a plasticized random terpolymer were prepared by evaporation of solutions in several solvents. The glass transition temperatures of the films were determined and were found to follow the Fox's equation. Their tensile modulus, measured just below the glass transition temperature, was found to depend on the residual solvent content of the films.     

Iterative sound synthesis by means of cross-coupled digital oscillators

Abstract

Musicians have long been interested in using iterative processes to aid the composition of musical forms (macrostructure) and to synthesize sounds (microstructure). This paper introduces a new sound synthesis method exploring the non-linear behaviour of two iterative cross-coupled digital oscillators. It begins with a brief introduction to iterative systems followed by background information on previous attempts at using them for synthesizing sounds (e.g. feedback frequency and amplitude modulations). Next, it introduces our synthesis method and briefly explains how it has been implemented in a system for real-time composition and performance. The paper concludes with a discussion on how the system has been put into practice to compose and perform a number of works.     

Comparative assessment of neural networks and regression models for forecasting summertime ozone in Athens

A comparison study has been performed with neural networks (NNs) and multiple linear regression models to forecast the next day's maximum hourly ozone concentration in the Athens basin at four representative monitoring stations that show very different behavior. All models use 11 predictors (eight meteorological and three persistence variables) and are developed and validated between April and October from 1992 to 1999. Performance results based on a wide set of forecast quality measures indicate that the NNs provide better estimates of ozone concentrations at the monitoring sites, whilst the more often used linear models are less efficient at accurately forecasting high ozone concentrations. The violation of the European information threshold of 180 microg/m(3) is successfully predicted by the NN in 72% of the cases on average. Results at all stations are consistent with similar ozone forecast studies using NNs in other European cities.     

Optimized capacitive active ripple compensation topology for a 3.7 kW single-phase high power density on-board charger of electric vehicles

Electrical Engineering - In this paper, a comprehensive investigation of the capacitive active ripple compensation (ARC) techniques is made to conclude which one is optimal to be used in on-board...     

A real-time vision module for interactive perceptual agents

Abstract. Interactive robotics demands real-time visual information about the environment. Real-time vision processing, however, places a heavy load on the robot's limited resources, which must accommodate multiple other processes running simultaneously. This paper describes a vision module capable of providing real-time information from ten or more operators while maintaining at least a 20-Hz frame rate and leaving sufficient processor time for a robot's other capabilities. The vision module uses a probabilistic scheduling algorithm to ensure both timely information flow and a fast frame capture. In addition, it tightly integrates the vision operators with control of a pan-tilt-zoom camera. The vision module makes its information available to other modules in the robot architecture through a shared memory structure. The information provided by the vision module includes the operator information along with a time stamp indicating information relevance. Because of this design, our robots are able to react in a timely manner to a wide variety of visual events.     

Digital watermarking robust to geometric distortions.

In this paper, we present two watermarking approaches that are robust to geometric distortions. The first approach is based on image normalization, in which both watermark embedding and extraction are carried out with respect to an image normalized to meet a set of predefined moment criteria. We propose a new normalization procedure, which is invariant to affine transform attacks. The resulting watermarking scheme is suitable for public watermarking applications, where the original image is not available for watermark extraction. The second approach is based on a watermark resynchronization scheme aimed to alleviate the effects of random bending attacks. In this scheme, a deformable mesh is used to correct the distortion caused by the attack. The watermark is then extracted from the corrected image. In contrast to the first scheme, the latter is suitable for private watermarking applications, where the original image is necessary for watermark detection. In both schemes, we employ a direct-sequence code division multiple access approach to embed a multibit watermark in the discrete cosine transform domain of the image. Numerical experiments demonstrate that the proposed watermarking schemes are robust to a wide range of geometric attacks.