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Showing papers in "Measurement Science and Technology in 1999"


Journal ArticleDOI
TL;DR: In this paper, a modified Landweber iteration method is proposed to enhance the quality of the image when two distinct phases are present, and a simple constraint is used as a regularization for computing a stabilized solution, with better immunity to noise and faster convergence.
Abstract: Electrical capacitance tomography (ECT) is a so-called `soft-field' tomography technique. The linear back-projection (LBP) method is used widely for image reconstruction in ECT systems. It is numerically simple and computationally fast because it involves only a single matrix-vector multiplication. However, the images produced by the LBP algorithm are generally qualitative rather than quantitative. This paper presents an image-reconstruction algorithm based on a modified Landweber iteration method that can greatly enhance the quality of the image when two distinct phases are present. In this algorithm a simple constraint is used as a regularization for computing a stabilized solution, with a better immunity to noise and faster convergence. Experimental results are presented.

507 citations


Journal ArticleDOI
TL;DR: In this article, a simple method of determining the melting point, heat of fusion, specific heat and thermal conductivity of phase-change materials (PCMs) is presented, which is especially useful for the selection of lots of candidate PCMs used for the purpose of engineering and for preparing new PCMs.
Abstract: A simple method of determining the melting point, heat of fusion, specific heat and thermal conductivity of phase-change materials (PCMs) is presented. Compared with other methods, such as conventional calorimetric methods, differential thermal analysis and differential scanning calorimetry methods, it has the following salient features: the experimental unit is simple, able to measure the heat of fusion, specific heat and thermal conductivity of several samples of PCMs simultaneously and allows one to observe the phase-change process of each PCM sample. Using the method, the thermophysical properties of various salt hydrates, paraffin and some PCMs developed by us were measured. For the PCMs whose thermophysical properties are available in the literature, our results gave fairly good agreement. The method is especially useful for the selection of lots of candidate PCMs used for the purpose of engineering and for preparing new PCMs.

409 citations


Journal ArticleDOI
TL;DR: In this article, whispering gallery modes were used for very accurate permittivity and dielectric loss measurements of ultralow loss isotropic and uniaxially anisotropic single crystals.
Abstract: Whispering gallery modes were used for very accurate permittivity and dielectric loss measurements of ultralow loss isotropic and uniaxially anisotropic single crystals. Several materials including sapphire, YAG, quartz, and SrLaAlO4 were measured. The total absolute uncertainty in the real part of permittivity tensor components was estimated to be ±0.1%, limited principally by the uncertainty in sample dimensions. Imaginary parts of permittivities were measured with uncertainties of about 10%, limited by the accuracy of Q-factor measurements of whispering gallery modes. It has been observed that, for most crystals, dielectric losses can be approximated by a power function of absolute temperature only in limited temperature ranges. At temperatures between 4-50 K, losses are often affected by impurities, which are always present in real crystals.

319 citations


Journal ArticleDOI
TL;DR: The hypervelocity impact facilities of the University of Kent as discussed by the authors include a 2 MV Van de Graaff accelerator for the electrostatic acceleration of dust particles (mass and velocities) and a two-stage light gas gun firing millimetre-sized particles at.
Abstract: The hypervelocity impact facilities of the University of Kent are described. They comprise a 2 MV Van de Graaff accelerator for the electrostatic acceleration of dust particles (mass and velocities ) and a two-stage light gas gun firing millimetre-sized particles at . Results for impact ionization studies using iron dust accelerated in the Van de Graaff and hitting a variety of metal targets (gold, silver, indium, iron, rhodium and molybdenum) are presented. Over the range , the ionization yields are found to be similar to within a factor of 20 at low velocity and converge to within a factor of five at high velocity. The light gas gun is used to investigate the volumes of craters in metal targets for impacts of 1 mm diameter stainless steel spheres on aluminium at velocities in the range . For normal incidence the crater volume scales with the square of the impact velocity. For oblique impacts at a fixed velocity it is found that the crater volume scales with the cosine of the impact angle.

244 citations


Journal ArticleDOI
TL;DR: In this article, the results of beam bending and direct tension testing of microelectromechanical systems (MEMS) have been summarized, and the efforts to integrate the sample and loading system on the microscopic scale are also explained.
Abstract: The microscopic mechanical devices in microelectromechanical systems (MEMS) use materials such as silicon and many other thin films, which had not previously been considered mechanical materials and thus are not well characterized regarding their mechanical properties. However, as the field matures, sustained research and commercial development in the coming years will demand better understanding of mechanical properties such as Young's modulus and the fracture strength. Uniaxial tension testing is generally considered the most reliable way to measure the mechanical properties. However, the problems associated with the microscopic size of the test specimen for MEMS, such as sample handling and sample alignment, led to such alternative ways as membrane-bulge testing and natural frequency testing at the beginning of MEMS. In this paper, recent methods for testing microscale mechanical properties and their results are summarized. Many reports, based on two distinct types of test, beam bending and direct tension, are introduced. The efforts to integrate the sample and loading system on the microscopic scale are also explained. Studies of fatigue, the most recent development in microscale measurement of mechanical properties, are discussed. The results from the testing methods described are listed for comparison.

199 citations


Journal ArticleDOI
TL;DR: In this paper, a range of optical techniques are presented, including optical self-mixing, phase modulators and photorefraction-based interferometers for remote detection of ultrasound.
Abstract: During the last decade, significant advances in the field of remote detection of ultrasound have taken place Optical systems with increasing sensitivity for monitoring ultrasound on samples with optically rough surfaces have been developed, so that some designs are now moving from the research laboratory into industrial environments In this review, a range of optical techniques is presented These techniques are analysed regarding their use for the measurement of ultrasonic waves They include the use of optical self-mixing, phase modulators and photorefraction-based interferometers For the case of established instruments such as two-beam interferometers and Fabry-Perot interferometers, various newly developed configurations with associated ultrasonic transfer functions are described Many interferometers have broadband frequency responses that extend up to several hundred megahertz Some systems offer in-plane ultrasonic measurement, whilst most offer out-of-plane measurements Emphasis is placed on their potential for industrial applications, taking into account the likely sample-surface roughness and environmental vibration

170 citations


Journal ArticleDOI
TL;DR: The phase-evaluation methods as discussed by the authors use a combination of phase-shifted intensity values, provided by the modulation of one or several fringe patterns, to calculate the principal value of the optical phase.
Abstract: Many optical measurement techniques provide fringe patterns as their results. The decodification processes that employ one or several fringe patterns to automatically retrieve the phase are generally designated as phase-evaluation methods. In this work, an overview of these methods will be schematically presented. Their particular performances will be compared, stressing their main advantages and drawbacks. An important group of these methods employs the well-known phase-shifting algorithms as a tool for calculating the phase. In the general form of these algorithms, the principal value of the optical phase is computed by an inverse trigonometric function whose argument is a combination of phase-shifted intensity values, provided by the modulation of one or several fringe patterns. These algorithms will be also studied in the general context of the phase-evaluation methods.

163 citations


Journal ArticleDOI
TL;DR: In this article, the authors focus on the use of MEMS for the diagnosis of turbulent shear flows and survey the status and outlook of microsensors as used for measurements of fluctuating wall pressure and wall shear stress, two quantities which are particularly difficult to measure with conventional probes.
Abstract: From a fluid dynamics perspective, the introduction of microelectromechanical systems (MEMS) has considerably broadened the spectrum of workable experiments. A typical MEMS sensor is at least one order of magnitude smaller than traditional sensors used to measure instantaneous flow quantities such as pressure and velocity. The microsensors can resolve all relevant scales even in high-Reynolds-number turbulent flows, and arrays of microsensors make it feasible, for the first time, to achieve complete information on the effective small-scale coherent structures in turbulent wall-bounded flows. In this paper we focus on the use of MEMS for the diagnosis of turbulent shear flows and survey the status and outlook of microsensors as used for measurements of fluctuating wall pressure and wall shear stress, two quantities which we deem particularly difficult to measure with conventional probes. For both wall pressure and wall shear stress sensors, we give general background, design criteria and calibration procedure. Examples of measurements conducted with MEMS-based sensors are provided and the minute devices are compared to their larger cousins.

163 citations


Journal ArticleDOI
TL;DR: Examples of the use of both linear and non-linear optics in pursuit of DOFS development are presented, together with details of a range of systems which have been investigated for particular applications.
Abstract: The ability to understand and monitor the distributed behaviour of extended, critical structures is recognized as a matter of increasing importance. Optical fibres offer unique advantages for spatially distributed measurement. This article reviews the field of distributed optical-fibre sensing (DOFS), tracing its origins and its evolution, and discussing the present and future positions. Examples of the use of both linear and non-linear optics in pursuit of DOFS development are presented, together with details of a range of systems which have been investigated for particular applications.

155 citations


Journal ArticleDOI
TL;DR: In this paper, the authors reviewed the relationship between the sensor characteristics and the associated data and explained how the sensor design influences the data and why a realistic appreciation of clinical findings requires a preliminary understanding of the chosen sensor.
Abstract: The sole of the foot acts as the interface between the ground and the body and is subjected to changing patterns of stress. These stresses will be accompanied by temporary or permanent strains within the tissues and may therefore be linked with those foot conditions which involve some degree of structural failure. One method of investigating the stresses is to measure the pressure distribution at the sole; an apparently simple task that continues to test scientific ingenuity and technological progress. Recent attempts to quantify shear stresses show that this extra goal may be even more challenging. Previous reviews describe the technology but not the relationship between the sensor characteristics and the associated data. The apparent lack of understanding of this relationship is reflected in some published reports and has meant that clinical findings can be misinterpreted. This report reviews those sensor characteristics that have been recorded in the literature. It also shows how the sensor design influences the data and explains why a realistic appreciation of clinical findings requires a preliminary understanding of the chosen sensor.

151 citations


Journal ArticleDOI
TL;DR: It is shown that the Fuzzy ARTMAP classifier, unlike LVQ and MLP, is able to perform efficient on-line learning in this application without forgetting previously learnt knowledge.
Abstract: An electronic nose based system, which employs an array of inexpensive commercial tin-oxide odour sensors, has been used to analyse the state of ripeness of bananas. Readings were taken from the headspace of three sets of bananas during ripening over a period of 8-14 days. A principal-components analysis and investigatory techniques were used to define seven distinct regions in multisensor space according to the state of ripeness of the bananas, predicted from a classification of banana-skin colours. Then three supervised classifiers, namely Fuzzy ARTMAP, LVQ and MLP, were used to classify the samples into the observed seven states of ripeness. It was found that the Fuzzy ARTMAP and LVQ classifiers outperformed the MLP classifier, with accuracies of 90.3% and 92%, respectively, compared with 83.4%. Furthermore, these methods were able to predict accurately the state of ripeness of unknown sets of bananas with almost the same accuracy, i.e. 90%. Finally, it is shown that the Fuzzy ARTMAP classifier, unlike LVQ and MLP, is able to perform efficient on-line learning in this application without forgetting previously learnt knowledge. All of these characteristics make the Fuzzy-ARTMAP-based electronic nose a very attractive instrument with which to determine non-destructively the state of ripeness of fruit.

Journal ArticleDOI
TL;DR: In this article, a method to determine the optimal step length for an iterative algorithm is proposed for electrical capacitance tomography, and the efficiency of the method has been demonstrated experimentally.
Abstract: Due to the 'soft-field' nature of electrical capacitance tomography, it is necessary to employ an iterative approach for image reconstruction in order to obtain good-quality images. In an iterative algorithm it is important to determine the gain factor, i.e., the step length approaching the converging point, because it may either cause divergence or slow down the iterative process. Usually the step length is fixed. In this communication, a method to determine the optimal step length is derived for an iterative algorithm. The efficiency of the method has been demonstrated experimentally.

Journal ArticleDOI
TL;DR: In this article, the authors investigated methods for cleaning dc-etched polycrystalline tungsten tips for scanning tunnelling microscopy (STM), including Ar-ion sputtering, heating, chemical treatments and Ne-ion self-sputtering.
Abstract: We have investigated methods for cleaning dc-etched polycrystalline tungsten tips for scanning tunnelling microscopy (STM). The cleaning methods include Ar-ion sputtering, heating, chemical treatments and Ne-ion self-sputtering. We correlate transmission electron microscopy images of the tip, field-emission data from the tip and images of a clean Cu(111) surface to find an optimum procedure for STM imaging. Clean and sharp tips are made by sputtering, combined with careful heating by electron bombardment. We found that optimum sputtering was obtained either by use of a 4 keV Ar-ion gun for a few seconds or by self-sputtering with Ne ions for a few seconds or until decapitation occurs.

Journal ArticleDOI
TL;DR: A submersible holography system for in situ recordings of the spatial distribution of plankton has been developed and deployed in the Strait of Georgia as discussed by the authors, which utilizes a ruby laser with an in-line recording configuration and has a sample volume of 732 ml.
Abstract: A submersible holography system for in situ recordings of the spatial distribution of plankton has been developed and deployed The system utilizes a ruby laser with an in-line recording configuration and has a sample volume of 732 ml The reconstructed images have a resolution ranging from 10-20 µm for spherical particles and 3 µm for linear particles that lie within 100 mm from the film Reconstructed volumes from holograms recorded during two recent deployments in the Strait of Georgia are scanned to obtain focused images of the particles, their position, size and orientation The particles are also classified to several groups based on their morphological characteristics The holograms include a set recorded during a 15 min vertical transect of the top 30 m of the water column Along with the holograms, the data include records of depth, temperature, salinity, dissolved oxygen and optical transmissivity The results show substantial variations in population makeup between layers spaced a short distance apart, particle concentration maxima at and near a pycnocline and evidence of zooplankton migration A predominant horizontal diatom orientation is indicated in the region of peak diatom concentration Individual holograms show clustering within different classes of plankton

Journal ArticleDOI
TL;DR: In this paper, a system consisting of a high-speed CCD camera, a frame grabber and associated image processing software was developed for on-line continuous flicker measurements of combustion flames.
Abstract: The flicker of a flame is an important physical parameter associated with the characteristics of a combustion process. This paper presents a novel instrumentation system developed for on-line continuous flicker measurements of combustion flames. The system comprises a high-speed CCD camera, a frame grabber and associated image processing software. The flicker signal was obtained by processing the radiation intensity of individual pixels within the luminous region of a flame image. Power spectral density analysis was performed to obtain the frequency components of the flicker signal. The quantitative flicker of a flame is defined in terms of weighted spectral components in the frequency domain and this definition has been proven to be well suited to quantification of the flickering characteristics of a flame. A tungsten lamp driven by a frequency-varying power supply was employed to calibrate the measurement system. The calibration results show that the system is capable of measung the flicker of an unknown light source with a relative error no greater than 3% . The system developed has been utilized to investigate the relationship between the flicker of a diffusion flame and the burner diameter, and to study the effect of the equivalence ratio on the flicker of a premixed flame under a range of combustion conditions. The experimental results obtained by both motion image analysis and spectral analysis have demonstrated that the flicker of a diffusion flame depends predominantly on the burner diameter. It has also been found that the flicker of a premixed flame varies with the equivalence ratio and a peak flicker exists for a given air flow rate.

Journal ArticleDOI
TL;DR: In this paper, a gravimetric experimental device allowing the measurement of pure gas adsorption isotherms is presented, where mass measurement is performed by a Rubotherm magnetic suspension balance instrumented in such a way to allow completely automated gas adotherm measurements for pressures ranging from 0 to 10 000 kPa and for temperatures from 303 to 423 K.
Abstract: A gravimetric experimental device allowing the measurement of pure gas adsorption isotherms is presented. The mass measurement is performed by a Rubotherm magnetic suspension balance instrumented in such a way to allow completely automated adsorption isotherm measurements for pressures ranging from 0 to 10 000 kPa and for temperatures from 303 to 423 K. Its main originality is that, although it works at high temperature, all the components in contact with the adsorbate are at the experimental temperature so that it is possible to study adsorbates which condensate at high-pressure and ambient temperature. This paper provides a detailed experimental procedure, the measurement accuracy and some comments on the advantages and drawbacks of the method. As examples of experimental results, adsorption isotherms of nitrogen and butane on activated carbon (F30-470, Chemviron Carbon) at five temperatures (303, 323, 343, 363 and 383 K) are presented. As a first step of a general study devoted to the comparison of high-pressure adsorption measurement techniques, the 303 K nitrogen adsorption isotherm is compared to data obtained for the same system but with a volumetric apparatus working in narrower ranges of temperature and pressure.

Journal ArticleDOI
TL;DR: In this paper, the first achievements towards the development of mid-infrared fiber-optic evanescent wave sensors operating in the spectral range 3-20 µm in seawater are summarized.
Abstract: The sustained health of the marine ecosystems can be seen as a research task of substantial importance, since increasing pollution of the oceans poses a serious threat to the global water resources. Hence, understanding of the physical, chemical and biological parameters determining the condition of the oceans demands persistent monitoring of the aquatic environment. This requires the development of advanced screening instrumentation capable of continuous in situ and real-time monitoring of hazardous pollutants. Remotely operated optical sensor systems able to withstand harsh measurement conditions represent a promising alternative to conventional methods involving extensive sampling procedures. Thus, interest in emerging novel sensor techniques has substantially increased during the last decade. This paper summarizes first achievements towards the development of mid-infrared fibre-optic evanescent wave sensors operating in the spectral range 3-20 µm in seawater. This wavelength region is particularly attractive for optical sensing, since molecule-specific information due to the stimulation of ground vibrational modes of organic substances is provided. First results focusing on the detection of chlorinated hydrocarbons reveal the feasibility of this approach, with detection limits in the low ppb concentration range in artificial seawater. As well as the design of a miniaturized subsea sensor module based on Fourier transform infrared spectroscopy, possibly interfering parameters such as salinity and turbidity are investigated under laboratory conditions.

Journal ArticleDOI
TL;DR: In this paper, the authors describe an experimental facility to measure the low velocity impact behavior of spherical particles with high accuracy, and the results are accurate enough to be used for quantitative comparison to theoretical studies.
Abstract: The aim of this paper is to describe an experimental facility to measure the low velocity impact behaviour of spherical particles with high accuracy. Measurements have been made of particle rotation, normal restitution coefficient to within of glancing incidence, and tangential restitution coefficient to within of normal impact, with very low scatter. The results are accurate enough to be used for quantitative comparison to theoretical studies. Achievement of a high level of precision and reproducibility has involved detailed attention to all aspects of the experiment design, construction, control and computer-based image measurement.

Journal ArticleDOI
TL;DR: In this article, the authors used a neural network to convert multi-beam gamma-ray spectra into a classification of the flow regime and void fraction, as well as to determine which detector positions best serve this purpose.
Abstract: This paper describes low-energy gamma-ray densitometry using a 241Am source for the determination of void fraction and flow regime in oil/gas pipes. Due to the reduced shielding requirements of this method compared to traditional gamma-ray densitometers using 137Cs sources, the low-energy source offers a compact design and the advantage of multi-beam configuration. One of the aims of this investigation was to demonstrate the use of a neural network to convert multi-beam gamma-ray spectra into a classification of the flow regime and void fraction, as well as to determine which detector positions best serve this purpose. In addition to spectra obtained from measurements on a set of phantom arrangements, simulated gamma-ray spectra were used. Simulations were performed using the EGS4 software package. Detector responses were simulated for void fractions covering the range from 0 - 100%, and the simulations were performed with homogeneous, annular and stratified flows. Neural networks were trained on the simulated gamma-ray data and then used to analyse the measured spectra. This analysis allowed determination of the void fraction with an error of 3% for all of the flow regimes, and the three types of flow regime were always correctly distinguished. It has thus been shown that multi-beam gamma-ray densitometers with detector responses examined by neural networks can analyse a two-phase flow with high accuracy.

Journal ArticleDOI
TL;DR: In this paper, the development of diode laser-based sensors for gas detection in microgravity is presented, detailing measurements of molecular oxygen and future application possibilities for these methods on the International Space Station.
Abstract: Diode laser absorption spectroscopy provides a direct method of determinating species concentration and local gas temperature in combustion flames. Under microgravity conditions, diode lasers are particularly suitable, given their compact size, low mass and low power requirements. The development of diode laser-based sensors for gas detection in microgravity is presented, detailing measurements of molecular oxygen. Current progress of this work and future application possibilities for these methods on the International Space Station are discussed.

Journal ArticleDOI
TL;DR: In this paper, a high-luminosity-light-collection system for highly spatial detection of chemiluminescence of radical species in flames has been developed, which employs only reflective components (in combination with an optical fibre for light collection).
Abstract: A high-luminosity-light-collection system for highly spatial detection of chemiluminescence of radical species in flames has been developed. The system, multi-colour integrated Cassegrain receiving optics (MICRO) is based upon a Cassegrain-type configuration, which implies that it employs only reflective components (in combination with an optical fibre for light collection). It provides therefore spherical- and chromatic-aberration-free detection, which is of importance for high-spatial-resolution measurements and for the simultaneous monitoring of signals in different wavelength regions from a given spatial volume. The effective light-collection volume has been estimated to be only 1.6 mm × 0.2 mm × 0.2 mm by ray-tracing techniques, which is more than three orders of magnitude smaller than that provided by a corresponding simple single-lens system and comparable to that of laser-based techniques, e.g. Doppler anemometry. The system is also easily aligned since the active probe volume can be visualized by sending in visible light through the system in the reverse direction. In order to demonstrate the performance of the system, OH-radical chemiluminescence in a Bunsen flame was monitored using MICRO and compared with the ion-current signal from a Langmuir probe with a minute sensor tip. A good correlation between the fluctuations in the two signals could be obtained, proving the high spatial and temporal resolution of the MICRO system.

Journal ArticleDOI
TL;DR: A spherical cat's-eye retroreflector made from a glass material having a refractive index of two was developed and the geometrical sphericity of the cat's eye and theSphericity examined optically were approximately 100 nm and 500 nm respectively.
Abstract: A spherical cat's-eye retroreflector made from a glass material having a refractive index of two was developed. The geometrical sphericity of the cat's eye and the sphericity examined optically were approximately 100 nm and 500 nm respectively. The discrepancy between these two values is discussed. This optical device is very versatile in terms of applications since it is free from viewing angle restrictions.

Journal ArticleDOI
TL;DR: In this paper, the variation of the water interaction on the thermal coupling versus the probe temperature was investigated. And the results have important implications for any quantitative interpretation of thermal images made in air.
Abstract: The Scanning Thermal Microscopic (SThM) probe, a thin Pt resistance wire, is used in the constant force mode of an Atomic Force Microscope (AFM). Thermal signal-distance curves for differing degrees of relative humidity and different surrounding gases demonstrate how heat is transferred from the heated probe to the sample. It is known that water affects atomic force microscopy and thermal measurements; we report here on the variation of the water interaction on the thermal coupling versus the probe temperature. Measurements were taken for several solid materials and show that the predominant heat transfer mechanisms taking part in thermal coupling are dependent on the thermal conductivity of the sample. The results have important implications for any quantitative interpretation of thermal images made in air.

Journal ArticleDOI
TL;DR: In this paper, a mass is made to collide with a force transducer and the impulse, i.e., the time integration of the impact force, is measured highly accurately as a change in momentum of the mass.
Abstract: A method for evaluating the dynamic characteristics of force transducers in impact detection is proposed. In this method a mass is made to collide with a force transducer and the impulse, i.e. the time integration of the impact force, is measured highly accurately as a change in momentum of the mass. To realize linear motion with a sufficiently low friction acting on the mass, the pneumatic linear bearing `Air-Slide' is used, and the velocity of the mass, the moving part of the bearing, is measured using an optical interferometer. This method will be effective for evaluating the dynamic characteristics and the uncertainties of force transducers in impact detection, and evaluating the uncertainty in applying the results of other conventional dynamic calibration methods to impact detection. The relative combined standard uncertainty in the measurement of the impulse acting on a force transducer by this method is estimated to be less than .

Journal ArticleDOI
TL;DR: In this article, a temperature measurement using an ultrasonic sensor consisting of a piezoelectric transducer and a waveguide is presented, and the temperature measured ultrasonically is in good agreement with that obtained by using a commercial thermocouple.
Abstract: Temperature measurement using an ultrasonic sensor consisting of a piezoelectric transducer and an ultrasonic waveguide is presented. The waveguide is a clad rod consisting of a steel core and a stainless steel cladding together with two discontinuities created near the probing end. The temperature information is obtained from information about the time delay between the ultrasonic echoes reflected from these discontinuities and the probing end surface as a function of the temperature. The temperature measured ultrasonically is in good agreement with that obtained by using a commercial thermocouple.

Journal ArticleDOI
TL;DR: It is shown that the number of measurement points for the current-voltage characteristic can have an important effect on the accuracy of the parameters extracted, and the Marquardt-Levenberg algorithm using a least squares error criterion and a hybrid algorithm employing an area criterion outperform other choices of fitting algorithm.
Abstract: This article concerns the influence of measurement conditions on the extraction of a solar cell's equivalent circuit parameters. Influences previously not investigated are considered, thus helping to define suitable measurement strategies. The influences of measurement environments are investigated, as is the influence of the fitting algorithm chosen. It is shown that the number of measurement points for the current-voltage characteristic can have an important effect on the accuracy of the parameters extracted. The stability of the system is of minor importance, as long as the variations in the measurement conditions are monitored. We also show that the Marquardt-Levenberg algorithm using a least squares error criterion and a hybrid algorithm employing an area criterion outperform other choices of fitting algorithm.

Journal ArticleDOI
TL;DR: In this paper, an experimental arrangement for the measurement of the velocity field of glycerol suspensions, in the diametric plane, inside glass capillaries with internal diameter of the order of 200 µm.
Abstract: We assembled an experimental arrangement for the measurement of the velocity field of glycerol suspensions, in the diametric plane, inside glass capillaries with internal diameter of the order of 200 µm. Glass spheres of mean diameter of 10 µm were used to seed the flow. The velocity fields were determined by the particle image velocimetry (PIV) method, whereby, in contrast to the usual implementations of this method based on light-sheet imaging, a forwards-scattering technique with the entire volume flow illuminated was used and the plane of interest was determined by the objective lens of a microscope. Statistical analysis of acquired experimental results was performed and possible limitations of the proposed technique were investigated. The method, with its present implementation, was used to measure velocities up to 4 mm s-1 and seems to be promising for similar measurements in glass capillaries or in microcirculation.

Journal ArticleDOI
TL;DR: It proved possible to merge these approaches and the resulting algorithm produced correlation coefficients with a lower variance than either of the individual algorithms, which can then be capitalized upon in order to produce better estimates of the turbulence power spectrum.
Abstract: The estimation of turbulence power spectra from randomly sampled laser Doppler anemometer (LDA) data can be done via the autocorrelation function (ACF) approach, whereby the slotting technique has the advantage that the ACF can be estimated at any data rate. Two improvements on Mayo's slotting technique for estimating the ACF, `local normalization' and the `fuzzy slotting technique', were proposed and compared in a benchmark test. However, it proved possible to merge these approaches and the resulting algorithm produced correlation coefficients with a lower variance than either of the individual algorithms. This lower variance in the ACF estimates can then be capitalized upon in order to produce better estimates of the turbulence power spectrum.

Journal ArticleDOI
TL;DR: In this article, the first deployable version consists of a membrane introduction interface coupled with a linear quadrupole mass filter for in situ detection and quantification of dissolved gases and volatile organic compounds.
Abstract: Progress in the design, construction and packaging of small portable mass spectrometers for operation on autonomous underwater vehicles (AUVs) is described. Our first deployable version consists of a membrane introduction interface coupled with a linear quadrupole mass filter for in situ detection and quantification of dissolved gases and volatile organic compounds. We present laboratory results which demonstrate that sub-parts-per-billion detection limits have been achieved for toluene. The mass-spectrometer system is compatible with AUV constraints and operates on 24 V dc, consuming of the order of 100 W of power. Technical challenges of performing underwater mass spectrometry are addressed, in particular sample introduction from the water column and the maintenance of a vacuum system. Initial operation will be in shallow water of 30 m depth or less. Alternative versions of interfaces and mass spectrometers are also discussed. We anticipate that providing the capability of performing in situ underwater mass-spectrometric analysis will have a significant impact in the areas of marine science and environmental monitoring.

Journal ArticleDOI
TL;DR: In this article, the microwave permittivity of polycrystalline yttrium iron garnet (YIG) was measured at frequencies between 5.5 and 12.5 GHz using split post dielectric resonators and ferrite disc resonators.
Abstract: Two techniques are evaluated for the accurate measurement of the microwave permittivity of polycrystalline yttrium iron garnet (YIG) at frequencies between 5.5 and 12.5 GHz: split post dielectric resonator (SPDR) and ferrite disc resonator (Courtney). Both techniques separate YIG permittivity from that of YIG permeability by applying a magnetic induction bias to the YIG sample under test. The SPDR method needs no special sample preparation in the case of YIG substrates, whereas the Courtney method requires the grinding of rods from bulk YIG. The Courtney measurements of the YIG real permittivity are found to be higher on average than SPDR measurements. Agreement between the two techniques improves with increasing magnetic induction bias.