Search results for "aves"
showing 10 items of 2443 documents
A method for reducing the influence of quarter-wave plate errors in phase stepping photoelasticity
1998
The phase stepping technique has recently been applied to the automated analysis of photoelastic fringes to determine the isoclinic parameter and the relative retardation. Generally, in these methods the error of quarter-wave plates, due to common manufacturing tolerances, influences the determination of the isoclinic parameter and the fringe order. In this paper a new phase stepping method in which the influence of quarter-wave plate error is null on the isoclinic parameter and negligible on the fringe order is proposed. The theoretical results have been confirmed by experimental tests.
Computer aided photoelasticity by an optimum phase stepping method
2002
In this paper an automated photoelastic method based on the phase stepping technique is described. It provides full-field maps of the isoclinic parameter and the relative retardation. The technique is based on processing six images of a photoelastic specimen acquired using plane and circularly polarized light. The number of acquisitions and the type of polariscope used in this approach have been chosen with the aim at reducing the influence of quarter wave plate errors and obtaining raw photoelastic data in a periodic form suitable for easy applications of automatic unwrapping routines.
Adapting available finite element structural programs to solve three-dimensional high frequency electromagnetic problems
1991
The adaptation of available structural mechanics software to solve microwave problems is possible by the analogy between the differential equations. A brief review of the analogy between transverse or shear waves in elasticity and electromagnetic waves is presented, followed by a more detailed discussion of the adaptation of a program to obtain the resonant frequencies of a rectangular resonant cavity, doing a three-dimensional analysis. The geometry of the electric field is also obtained for the resonant modes.
Control of an open-end winding induction machine via a two-output indirect matrix converter
2014
In this paper an Indirect Matrix Converter (IMC) with two output stages feeding an open-end winding induction machine is presented. The IMC has the advantage of having nobulky energy storage elements and with the two output stages up to 1.5 times the input phase voltage can be obtained across the windings of the machine, without overmodulation. A vector control scheme for the machine currents is used along with a modulation strategy for the converter two-output stages to reduce the common mode voltage and compensate the phase zero sequence currents. Simulation results showing the performance of the controlscheme and the reduction of zero sequence and common mode voltages are presented and d…
A computer‐aided instrument for pattern recognition of partial discharges
1998
In this paper a new computer‐aided digital system for partial discharge (PD) measurements is presented. The system is able to collect a great number of data, up to a pulse repetition rate of 100kHz, during the acquisition phase, thus allowing an off‐line analysis of PD data. After a description of the instrument, some experimental tests performed on epoxy specimens are here presented in terms of amplitude, phase and energy resolved histograms. Finally, emphasis is given to the very interesting use of the instrument for pattern recognition techniques in the discrimination and classification of discharges in HV components.
Fiber laser mode locked through an evolutionary algorithm
2015
Mode locking of fiber lasers generally involves adjusting several control parameters, in connection with a wide range of accessible short-pulse dynamics. In this Letter, we experimentally demonstrate the ability of an evolutionary algorithm to prescribe a set of cavity parameters entailing specific self-starting mode locking. The prescribed parameters are applied to electrically driven polarization controllers, thus shaping the effective nonlinear transfer function at play within the fiber cavity. According to the specifications of the objective function used for the optimization procedure, various short-pulse regimes are obtained. Our versatile method represents an effective novel avenue f…
Phase Margin Degradation of a Peak Current Controlled Converter at Reduced Duty Cycle
2010
An inner current loop is frequently used in many switching power supplies to achieve higher stability and a good current sharing. Nevertheless, some problems derived from its practical implementation can be encountered. One problem is related to the need of filtering of the sensed current and was discovered by the authors in the implementation of a 500 W converter, when peak current control was applied by sensing the switch current. This paper will demonstrate mathematically that an RC filter not only filters out the noise but also can cause a degradation of the phase margin, especially, if the needed duty cycle is close to zero. The main reason for it is the severe distortion of the curren…
Algorithmic method of design and analysis of fractional-slot windings of AC machines
1998
The paper presents a new algorithmic method of designing fractional-slot windings for AC machines of the double and single layer type. The method allows to design windings with a small number of slots per pole and phase, and then to analyse their MMF harmonic spectra in a simple systematic way and to optimise the construction. The presented method comprises not only 3-phase, but alsom-phase windings, which in the case of compact converter-motor units are quite applicable.
Visual Behaviour Based Bio-Inspired Polarization Techniques in Computer Vision and Robotics
2012
For long time, it was thought that the sensing of polarization by animals is invariably related to their behavior, such as navigation and orientation. Recently, it was found that polarization can be part of a high-level visual perception, permitting a wide area of vision applications. Polarization vision can be used for most tasks of color vision including object recognition, contrast enhancement, camouflage breaking, and signal detection and discrimination. The polarization based visual behavior found in the animal kingdom is briefly covered. Then, the authors go in depth with the bio-inspired applications based on polarization in computer vision and robotics. The aim is to have a comprehe…
Rare earths and trace elements contents in leaves: A new indicator of the composition of atmospheric dust
2017
The relationship between the trace element distribution in atmospheric particles and leaves of some exposed plants in the environment was recently demonstrated. This indication would suggest that the trace element analysis of leaves in these plants could provide information about the composition, nature and origin of the atmospheric dust dispersed in the environment. In order to corroborate this hypothesis, the distribution of trace elements and Rare Earths were studied in leaves of some endemic plants, in the atmospheric fallout and in soils of rural, urban and industrial ecosystems in Sicily. These elements have been chosen to discriminate the source and nature of different source on atmo…