Alternative Calibration Method Research Articles

LS-SVM: uma nova ferramenta quimiométrica para regressão multivariada. Comparação de modelos de regressão LS-SVM e PLS na quantificação de adulterantes em leite em pó empregando NIR

Least-squares support vector machines (LS-SVM) were used as an alternative multivariate calibration method for the simultaneous quantification of some common adulterants found in powdered milk samples, using near-infrared spectroscopy. Excellent models were built using LS-SVM for determining R2, RMSECV and RMSEP values. LS-SVMs show superior performance for quantifying starch, whey and sucrose in powdered milk samples in relation to PLSR. This study shows that it is possible to determine precisely the amount of one and two common adulterants simultaneously in powdered milk samples using LS-SVM and NIR spectra.

New Thomson scattering diagnostic on RFX-mod

This article describes the completely renovated Thomson scattering (TS) diagnostic employed in the modified Reversed Field eXperiment (RFX-mod) since it restarted operation in 2005. The system measures plasma electron temperature and density profiles along an equatorial diameter, measuring in 84 positions with 7 mm spatial resolution. The custom built Nd:YLF laser produces a burst of 10 pulses at 50 Hz with energy of 3 J, providing ten profile measurements in a plasma discharge of about 300 ms duration. An optical delay system accommodates three scattering volumes in each of the 28 interference filter spectrometers. Avalanche photodiodes detect the Thomson scattering signals and allow them to be recorded by means of waveform digitizers. Electron temperature is obtained using an alternative relative calibration method, based on the use of a supercontinuum light source. Rotational Raman scattering in nitrogen has supplied the absolute calibration for the electron density measurements. During RFX-mod experimental campaigns in 2005, the TS diagnostic has demonstrated its performance, routinely providing reliable high resolution profiles.

Temperature measurement on series resistance and devices in power packs based on on-state voltage drop monitoring at high current

Based on the on-state voltage drop monitoring at high current, an alternative method for thermo-sensitive parameters calibration is reported. The main goal is that it allows the simultaneous calibration of the series resistance and power devices voltage drop on temperature. Thereby, the average temperature over all power devices and the temperature difference in average inside the pack can be measured in real applications.

Least-squares support vector machines and near infrared spectroscopy for quantification of common adulterants in powdered milk

This paper proposes the use of the least-squares support vector machine (LS-SVM) as an alternative multivariate calibration method for the simultaneous quantification of some common adulterants (starch, whey or sucrose) found in powdered milk samples, using near-infrared spectroscopy with direct measurements by diffuse reflectance. Due to the spectral differences of the three adulterants a nonlinear behavior is present when all groups of adulterants are in the same data set, making the use of linear methods such as partial least squares regression (PLSR) difficult. Excellent models were built using LS-SVM, with low prediction errors and superior performance in relation to PLSR. These results show it possible to built robust models to quantify some common adulterants in powdered milk using near-infrared spectroscopy and LS-SVM as a nonlinear multivariate calibration procedure.

Calibration and characterization of UV sensors for water disinfection

The National Institute of Standards and Technology (NIST), USA is participating in a project with the American Water Works Association Research Foundation (AwwaRF) to develop new guidelines for ultraviolet (UV) sensor characteristics to monitor the performance of UV water disinfection plants. The current UV water disinfection standards, ÖNORM M5873-1 and M5873-2 (Austria) and DVGW W294 3 (Germany), on the requirements for UV sensors for low-pressure mercury (LPM) and medium-pressure mercury (MPM) lamp systems have been studied. Additionally, the characteristics of various types of UV sensors from several different commercial vendors have been measured and analysed. This information will aid in the development of new guidelines to address issues such as sensor requirements, calibration methods, uncertainty and traceability. Practical problems were found in the calibration methods and evaluation of spectral responsivity requirements for sensors designed for MPM lamp systems. To solve the problems, NIST is proposing an alternative sensor calibration method for MPM lamp systems. A future calibration service is described for UV sensors intended for low- and medium-pressure mercury lamp systems used in water disinfection applications.

A photon pressure calibrator for the GEO 600 gravitational wave detector

Interferometer mirror displacement induced by radiation pressure is used to demonstrate an alternative calibration method for the GEO 600 detector. The photon calibrator utilizes an amplitude modulated laser diode with up to 1.4 W output power at a wavelength of 1035 nm. The achieved accuracy of the strain amplitude calibration is dominated by the laser power calibration error, which is in the range of ±4% for the measurements presented in this Letter.

A mathematical description of orthotropy in sheet metals

The plane stress description of orthotropy presented by Hill [1990. Constitutive modelling of orthotropic plasticity in sheet metals. J. Mech. Phys. Solids 38(3), 405–417] is revisited. In particular, the calibration methods are analysed in an alternative form. The alternative calibration methods are used to develop the mathematical form of the orthotropic representation. The new seven parameter yield criterion is shown to be more flexible than the current model without the need for additional test data. The usefulness of the model in describing aluminium, titanium and steel is also illustrated.

Bestimmung der Inhaltsstoffe bei der Ernte mit dem Feldhäcksler

Near-infrared spectroscopy (NIRS) can be used to assess forage quality. Rugged NIRS sensors make it possible to use them on agricultural machines. Until now the calibration of these sensors was specifically designed for the respective machines and operating conditions. For use in agriculture alternative calibration methods are needed. One possibility is to gather a wide variance of content concentrations through experimental cultivation with specific variety selection and fertiliser application. The calibrations would then be determined in the laboratory. In order to transfer the calibrations from the laboratory to various choppers, the effects of the different samples were investigated.

Quantitative measurements of dielectric spectra with microdielectric fringe-effect sensors.

The parallel-plate method is a gold standard for measuring dielectric properties of materials. However, it requires sampling of the material under testing (MUT), which makes it less suitable for real time, dynamic, and in situ measurements. The alternative to the parallel-plate method is to use the microdielectric fringe-effect (FE) sensors, which can be placed inside the process or laboratory equipment to provide rapid, on-line, and noninvasive characterization of the dielectric properties. An additional potential advantage of the FE measurements is the ability to obtain spatially localized and interfacial measurements, which may be important in some applications. Unfortunately, interpretation of the FE sensor measurements is difficult because of the spatial nonuniformity of the electrical excitation field created by the FE sensor and the extraneous contributions from the sensor substrate and unknown stray elements. The objective of this study is to summarize the theoretical basis of the dielectric measurements using planar interdigitated sensors and to use it in the development of a new method for obtaining quantitative measurements with FE sensors. As the first step, the basic correlation between the impedance measurements obtained with the FE sensor and the dielectric properties of the MUT is elucidated. The theoretical results are then used to analyze the contribution of the sensor substrate and unknown stray components to the overall measurements. A novel calibration method to eliminate extraneous contributions is then proposed. The application example demonstrates the application of the developed method to the measurement of the dielectric permittivities of a polydispersed cis-polyisoprene samples. The results are compared with those obtained using the parallel-plate measurements and show excellent agreement. Experimental comparison with the alternative calibration methods is also performed, indicating significant improvement in accuracy of dielectric measurements over a broad range of frequencies.

Manipulation of intracellular pH by electroporation: an alternative method for fast calibration of pH in living cells

Manipulation of intracellular pH by electroporation: an alternative method for fast calibration of pH in living cells

Redundant space calibration of hexagonal and Y-shaped beamforming radars and interferometric radiometers

The calibration of large antenna arrays in the absence of a beamforming point source is a common problem in beamforming radars and interferometric radiometers. In this paper the fundamentals of the redundant space calibration (RSC) method for phase and amplitude are reviewed, pointing out the parallelism between the active and passive cases, the technique is then applied in a general and systematic way to two cases of interest: hexagonal planar and Y-shaped arrays, which are known to be the optimum periodic twodimensional configurations. In both cases, the system of equations is determined taking into account the available redundancies and symmetries of these structures. The performance of the RSC method is analysed in terms of the propagation of errors in reference phaselamplitude. The technique is then considered for two hexagonal array systems: the Turbulent Eddy Profiler (TEP), a volume-imaging radar of the lower atmosphere developed at the University of Massachusetts, and the Microwave Imaging Radiometer by Aperture Synthesis (MIRAS), an L-band interferometric radiometer to be launched in 2005 in the Earth Explorer Opportunity Mission-Soil Moisture and Ocean Salinity Mission (SMOS) of the European Space Agency (ESA). In the TEP case the proposed scheme stabilizes an otherwise ill-posed inversion problem, and in the MIRAS case it presents an alternative calibration method to the noise-injection one, without any additional hardware required.

Hollow-Fiber flow field-flow fractionation of synthetic polymers in organic solvents.

A modified polyacrylonitrile (PAN) hollow-fiber membrane from a commercial source has been applied as the separation channel in flow field-flow fractionation (FFF). With the PAN membrane fiber, the application range of flow FFF could be extended to synthetic polymers that are soluble in a variety of organic solvents. The PAN membrane was shown to be resistant to hydrophobic solvents, such as dichloromethane (DCM), tetrahydrofuran (THF), ethyl acetate, and methyl ethyl ketone (MEK), as was illustrated by the successful fractionation of different polymer standards in these solvents. The system performance was assessed using polystyrene (PS) standards with ethyl acetate as the solvent. For a 100 kDa PS standard, the average recoverywas 57%, but for standards with a molar mass of 400 kDa and higher, 100% recovery was obtained. A linear relationship between peak area and injected mass was found. The run-to-run and fiber-to-fiber repeatability was determined using 100- and 400 kDa PS standards. The repeatability appeared to be satisfactory, with relative standard deviations < 2% for the retention times and < 5% for the recoveries of the standards. Plate numbers for the 400 kDa standard on different fibers were in the order of 110. From measurements on the fractionation of ferritin aggregates, it is concluded that the instrumental band-broadening is negligible. For an accurate determination of diffusion coefficients and molecular sizes based on retention times, calibration of the channel with standards appeared to be necessary. However, it was shown that the FFF system could be coupled to a multiangle light scattering (MALS) detector, thus providing an alternative on-line method for calibration. Expressions for the maximum obtainable plate number per unit of time have been derived for a hollow-fiber flow FFF system. It is shown that an increase in the system performance can be expected from a scaling down of the fiber diameter.

Ionization chambers for measuring air kerma integrated over beam area. Deviations in calibration values using simplified calibration methods

Calibrations of kerma-area product meters (KAP meters) are often performed using simplified methods. The accuracy thus obtained can be insufficient, especially when the KAP meters are used for optimizing radiological procedures. The deviations between the best available calibration factor (k) and the simplified calibration factor were measured at different clinical x-ray installations. Depending on the type of x-ray installation and calibration method, the quotient ranged from 0.83 to 1.19, reflecting the error made in practice using these methods. A simple alternative calibration method based on comparison with a KAP meter calibrated by the best available method is described. Depending on tube potential and the stability of the electrometers, the uncertainty in the calibration factor derived with this method was between 3.8% and 5.6% (at 95% confidence level).

Standardization of 234Th by Cerenkov counting

We take advantage of the secular equilibrium between the first two descendants of 238U to calibrate 234Th in a conventional liquid scintillation spectrometer by Cerenkov counting. The dependence of the Cerenkov counting efficiency on the conditions of the medium other than the refractive index is studied. In particular, we show that the decrease of the counting efficiency observed for samples in HNO 3 is generated by light absorption. We compare the Cerenkov counting standardization method with other alternative calibration methods (i.e. liquid scintillation or gamma spectrometry) obtaining discrepancies less than 2%.

Line network network (LNN): an alternative in-fixture calibration procedure

An alternative method for a network analyzer calibration is evaluated. This line network network (LNN) method avoids de-embedding of the device under test (DUT) and it allows the characterization of an unknown two-port inserted between an arbitrary number of cascaded unknown two-ports. An unknown obstacle must be moved on a transmission line into three positions. The LNN calibration technique delivers the electrical wavelength or the relative dielectric constant of the transmission line and the scattering parameters of the obstacle. Since the connectors do not have to be exchanged, nonreproducibilities of the connectors are only a minor problem. Additionally, a double-calibration technique is presented. The double-calibration technique is used to employ the LNN method on both sides of the two-port DUT in order to perform an error-corrected measurement. Experimental results compare the LNN method with the tru-reflect-line (TRL) method particularly for an in-fixture calibration.

Calibrating screens for continuous colour displays.

This paper focuses on two issues that are important to those who use colour monitors for research in vision. One is concerned with the measurement and calibration of colour screens. To this end the luminance and chromaticity readings of a tri-filter colorimeter and a spectroradiometer are compared (both commonly used to calibrate screens). The second is concerned with screen interactions, whereby colours can be distorted from their expected or calculated values by the colours displayed in neighbouring areas. This issue is crucial for those who use measurements of the light emitted from the red, green and blue phosphors of a monitor in isolation to specify other colours on screen, particularly in the research areas of colour contrast and colour constancy, since the specified colours may not actually be displayed. Finally, an alternative calibration method is described that uses an iterative measurement procedure to obtain screen specifications that are accurate regardless of the display complexity, so that researchers can be confident that the required colours are actually displayed on the screen.

On the calibration of the Meteosat water vapor channel

The calibration of the Meteosat water vapor channel image data is of prime importance for a quantitative use. The vicarious calibration technique employs the use of data from radiosonde ascents. A screening technique, removing spurious radiosonde information, has been improved and used operationally since February 4, 1994. It involves new quality control checks on satellite zenith angle and the upper tropospheric relative humidity measured by the radiosonde, leading to a lower (about 8%) and more stable calibration. The operational calibration technique uses averages for the clear‐sky (above 700 hPa) satellite observations over large areas and relates them to expected radiances at the top of the atmosphere, determined from radiosonde data. The approach, valid owing to the small gradients in the water vapor field in such areas, restricts the number of usable radiosonde observations severely. An alternative calibration method is outlined, which uses a smaller clear‐sky area, thus accepting more radiosonde ascents. This method further decreases the variability of the calibration coefficient by about 20%.

Can GPS measurements be legally used for Cadastral Surveying?

This paper shows that, under existing Commonwealth and Victorian State legislation relating to measurements and cadastral surveying, there is a requirement for GPS derived measurements to be legally traceable to a standard of measurement. Without a proper calibration facility and methods, GPS measurements cannot be legally used for cadastral surveys. This paper contends that the current EDM baseline calibration method is not appropriate for the calibration of GPS measuring systems. Alternative calibration methods are described. Aspects of a GPS measuring system that must be considered when developing a calibration method are discussed.

Some theoretical results on second‐order calibration methods for data with and without rank overlap

AbstractGRAM, a method for second‐order calibration, has been introduced by Sanchez and Kowalski and later modified by Wilson, Sanchez and Kowalski. The methods are based on the claim that, in cases without measurement error they yield correct estimates for the concentration ratios and profiles of (rank‐one) analytes present in sample and mixture. This claim has not been proven rigorously. In the present paper, rigorous proofs are given for situations where the claims are valid indeed. In addition, it is shown that PARAFAC, an alternative method for second‐order calibration, can be used to obtain the same results. Next it is shown that the claims do not hold in cases with ‘rank overlap’ (partly overlapping profiles) and it is proven that a procedure by Wang et al. can still be used to assess some of the concentration ratios. A general framework is provided for a variety of second‐order calibration problems and the extent to which quantitative and qualitative information can be expected is given.

A Method of Self Calibration for Molecular Weight Distribution Determinations for Liquid Crystalline Polymers

Abstract A method of molecular weight calibration was devised for various substituted liquid crystalline polymers with substantial molecular weight repeat units. With the use of gel permeation chromatography, oligomer peak separation was achieved offering a method for self calibration for molecular weight distribution determinations. Employing an overlay of a low molecular weight polystyrene standard, a retention time marker was utilized as a source from which to mark an oligomer peak. The calibration plot produced using this technique showed much better correlation coefficients than that of the polystyrene calibration plot. In addition, molecular weight determinations made from the two techniques yielded two distinct molecular weight averages and distributions, indicating polystyrene to be a poor relative calibration method for the liquid crystalline polymers tested. The technique illustrates the utility of alternative calibration methods when samples show certain physical characteristics.