Determination of the full response function of personal neutron dosemeters

The response of neutron dosemeters may be determined directly from measurements, provided a sufficiently large number of measurements in monoenergetic neutron fields covering the entire energy range of interest is available. In practice this is not feasible due to the lack of monoenergetic neutron fields in the thermal and intermediate energy region (i.e. energies <24 keV). To deal with this difficulty, we have developed a method which can take into account additional information about the response of the dosemeter. Our analysis makes use of two types of data, measurements made using monoenergetic neutron beams and measurements made in neutron fields with broad energy distributions. The dosemeter responses are described using a parametrised model, based on a minimum of assumptions: that they should fit the data within experimental uncertainties, and that they should remain close to a simple interpolation of the monoenergetic and thermal neutron field data.     

Reflectometric measurements of polarization properties in optical-fiber links

Polarization sensitive reflectometric measurements are effective tools for the characterization of polarization properties of optical-fiber links. These techniques show two advantages compared with the standard ones: they can perform measurements using only one fiber end (both for transmission and for reception of the probe signal) and, most important, they can characterize the local evolution of the polarization properties of the fiber link. Reflectometric measurements of differential group delay and fiber birefringence have been already successfully performed. More recently, the possibility of measuring, also, polarization dependent loss has been theoretically explored. In this paper the theory and main applications of polarization sensitive reflectometric techniques are reviewed.     

The thermal conductivity of gases: Incorrect results due to desorbed air

Air desorbed from the measuring instrument can falsify the thermal conductivity of a gas measured by steady-state methods. For a guarded hot-plate apparatus the contamination effect was determined to depend on both the residence time in the system and the temperature. The investigation covered the gases H₂, He, Ne, CH₄, N₂, air, Ar, and Kr. For gases whose conductivity is better than that of air (H₂, He) the measured values are too small, and for gases of poorer conductivity they are too high. Corrections for the effect of impurity have been applied to the measurements presented. These impurity corrections are considerably larger than the precision of the measurements, but they are of the order of the estimated overall uncertainty of the measurements. The departures between the corrected thermal conductivities reported here and values taken from the correlations in the literature run up to 5 % at the highest temperatures.     

Magnetic measurements with Lorentz microscopy

The electron microscope may be operated in a mode which permits the exploration of the magnetization configurations in thin magnetic films. This mode of operation, known as Lorentz microscopy, is a powerful technique for investigating thin NiFe films because it offers high resolution, because it provides an unequivocal identification of the local magnetization direction, and because it permits correlations to be made between the magnetic structure and the underlying physical (crystallographic) structure of the film. In the past, Lorentz microscopy has found fruitful employment in the analysis of the magnetization configurations of domain walls, in studies of various magnetization reversal processes, and in specialized investigations of unusual magnetic structure. Besides these primarily qualitative investigations, however, some quantitative measurements may be made with this instrument. Such measurements are useful not only because they permit direct evaluation of basic magnetic parameters of films being studied by Lorentz microscopy, but because they afford insight into the fundamental processes which occur in the standard macroscopic magnetic measurements of NiFe films deposited on glass substrates. The following measurements are discussed: 1) determination of the Curie temperature; 2) measurement of the anisotropy field Hkby the standard hysteresigraph and the Feldtkeller techniques; 3) quantitative studies of wall motion by labyrinth propagation and by wall creep; 4) the investigation of anisotropy dispersion by the Crowther and Torok techniques. The accuracy of these measurements is, in general, lower than that of the analogous measurements made by macroscopic methods on films deposited on glass substrates. Nevertheless, macroscopic measurements performed on a film on a glass substrate showed good agreement with Lorentz measurements performed on a simultaneously-deposited film which was suitable for Lorentz microscopy.     

Filtering of Randomly Sampled Time-Stamped Measurements

This paper concerns the filtering of measurements that are taken by networked sensors at nonuniform intervals but that are accurately time stamped. Traditional digital filtering methods are difficult or impossible to use due to nonuniform sampling. Two filtering methods are described. Both are based on making an assumption about the signal behavior between measurements, such as the signal being constant between measurements. In the first method, a filter is formulated as an ordinary differential equation that is incrementally solved as measurements arrive. Such filtering is general; nonlinear and nontime invariant filters may be constructed. In the second method, signal convolution with a continuous-time finite impulse response filter is efficiently performed using a spline representation for the filter response. Such filters are ldquoFIR likerdquo in the sense that they have frequency-domain performance similar to FIR filters and have only slightly worse asymptotic computation time and memory requirements compared to FIR filters, yet have the advantage of being able to deal with nonuniformly sampled measurements. Examples of the operation of both sorts of filters are shown on actual measured data.     

Digital correction techniques for accuracy improvement in measurements of SnO/sub 2/ sensor impedance

In this paper, the performance improvement of a gas-sensing system by digital correction techniques is discussed. The considered system operates as a vectorial impedance meter and performs impedance measurements of eight sensors arranged in an array in the frequency range 10 Hz-15 MHz. The measurements of the chemical sensors' impedance is an innovative technique that allows highlighting different adsorption mechanisms taking place when the sensors are exposed to gases. Of course, impedance analyzers are commercially available, but they usually make measurements on only one device at time and they are very expensive. The proposed PC-based impedance analyzer is a versatile one and shows good performances for gas-sensing applications. A digital correction technique is used in this work to improve the impedance measurement accuracy of each channel of the gas-sensing system (eight sensors /spl rarr/ eight channels), in order to compensate for the conditioning electronics response. The latter is evaluated in a characterization procedure. A linear black box two-port model is used to take into account crosstalk, amplitude, and phase distortions. Two different techniques to evaluate the response of the measurement system are discussed in this paper, and experimental results are presented on both the measure of reference impedances and on the measure of chemical sensors.     

Measurement of air turbulence for on-machine interferometry

There is increasing demand for in situ shape measurements performed on ultraprecision processing machines. One major source of error during interferometric measurements performed on machines is fringe displacement due to external disturbances. We have developed an interferometer equipped with an electro-optic phase modulator that measures the phase of interference fringes before they are displaced by air turbulence. The frequency characteristics of air turbulence induced by a heat source are derived from successive measurements of a test surface. Experimental results show that the phase of the interference fringes can be accurately measured in the presence of air turbulence when the intensity of the fringes is sampled at a speed of several hundred hertz.     

Virtual enantiomers as the solution of optical activity's deterministic offset problem

Deterministic offsets have remained one of optical activity's most intractable problems. To the extent that the mechanisms by which they are produced do not depend on the chiroptical properties of the sample, they can be eliminated by the subtraction of measurements done on both enantiomers. We show that it is possible to create, by purely optical means, by the sole use of half-wave retarders, the optical antipode of a chiral molecule, to measure the chiroptical properties of the molecule and of its optically generated antipode, and to recover, by subtracting the measurements, the offset-free data of the enantiomer which is physically present. We moreover show that it is possible to do the measurements in a way that eliminates offsets that might occur through the influence of the differing chiroptical properties of the two antipodes. The procedure can be repeated, and by doing so, an almost arbitrarily high precision can be reached. The method is demonstrated by offset-free Raman optical activity back-scattering spectra measured in the so-called scattered circular polarization mode, one of optical activity's so far largely unsolved measurement problems. Such measurements can now be done with 2 mg of substance, in throw-away capillary cells, and on compounds sealed in cylindrical vials.     

Simulation of porosity by microballoon dispersion in epoxy and urethane: mechanical measurements and models

Effective mechanical properties of microballoon-dispersed epoxy and urethane are studied under quasi-static and dynamic loading conditions. Elastic modulus measurements of these mixtures over a volume fraction range of 0–0.45 are in good agreement with Hashin-Shtrikman lower-bound predictions for two-phase mixtures comprising of randomly distributed spherical pores in an elastic matrix. The measurements have also been predicted accurately by a LEFM based pore-flaw model for a selected flaw size to pore size ratio. These imply that the microballoons offer negligible reinforcement due to extremely small wall thickness to diameter ratio. Accordingly, feasibility of using these materials to simulate controlled porosity for tensile strength and fracture toughness modeling is explored. Measured tensile strength and fracture toughness values decrease monotonically similar to the Young's modulus variation with volume fraction of microballoons. Guided by the measurements linear elastic models for porous materials that predict tensile strength and fracture toughness of these mixtures are proposed and validated. The tensile strength predictions are in very good agreement with measurements for both epoxy and urethane compositions. The quasi-static crack initiation toughness prediction captures the measurement trends rather well in both cases. The agreement between the measurements and predictions are modest for epoxy matrix while they are good for urethane compositions. Based on fracture surface micrography, an empirical corrective procedure is advanced to improve the agreement between the measurements and the model. The dynamic crack initiation toughness measurements for epoxy, on the other hand, are in excellent agreement with the predictions.     

Repetitive genetic inversion of optical extinction data

We describe a genetic method of deriving aerosol size distributions from multiwavelength extinction measurements. The genetic inversion searches for log-normal size distribution parameters whose calculated extinctions best fit the data. By repetitively applying the genetic inversion using different random number seeds, we are able to generate multiple solutions that fit the data equally well. When these solutions are similar, they lend confidence to an interpretation, whereas when they vary widely, they demonstrate nonuniqueness. In this way we show that, even in the case of a single log-normal distribution, many different distributions can fit the same set of extinction data unless the misfit is reduced below typical measurement error levels. In the case of a bimodal distribution, we find many dissimilar size distributions that fit the data to within 1% at six wavelengths. To recover the original bimodal distribution satisfactorily, we found that extinctions at ten wavelengths must be fitted to within 0.5%. Our results imply that many size distributions recovered from existing extinction measurements can be highly nonunique and should be treated with caution.     

Application of the transient hot-wire method to gases at low pressures

The need to determine the thermal conductivity of non-ozone-depleting refrigerants implies measurements at pressures below 10 bar in the gaseous phase. In order to apply the transient hot-wire method with proven accuracy to this state, possible sources of systematic errors in the measurements have been carefully assessed theoretically and experimentally. The influence of the finite heat capacity of the hot wire and of the isothermal outer wall of the cell have been identified to affect the measurements substantially. An improved correction method to account for the wire heat capacity is presented, as well as criteria to choose the parameters in the experiments in order to avoid errors due to the outer boundary and due to the finite wire length. The results are presented in dimensionless quantities, and as an example, they are discussed for argon.     

Systematic errors in small deformations measured by use of shadow-moiré topography

Phase-shift shadow-moiré topography is a noncontact optical technique for measuring the shapes of surfaces. Artifactual bands resembling isoheight surface contours are observed during measurement of small changes in shape by use of this technique. The shape-reconstruction algorithm used in shadow-moiré topography is based on a mathematical model of the fringe patterns generated on the surface to be measured. We hypothesize that the observed bands reflect systematic errors caused by ignoring height-dependent terms in the mathematical model of the fringe patterns. We test the assumption by simulating the fringe patterns for a virtual test surface by using a model that contains height-dependent terms and one term that is idealized by ignoring these terms. Small systematic errors in shape are observed only when the surface is reconstructed from fringe patterns simulated with a model containing the height-dependent terms. Shape-error curves are computed as a function of the surface height by the subtraction of the reconstructed shape from the known shape. Simulated shape-error curves agree with experimental measurements in that they show an increase in error with surface height, and both the experimental and the simulated shape-error curves contain ripples. Although the errors are small in comparison with the dimensions of the surface and are negligible in shape measurements and in most deformation measurements, they may show up as noticeable bands in images of small deformations.     

Dose to persons assisting voluntarily during X-ray examinations of large animals

Pet owners often assist voluntarily while their pets are being X-rayed during a medical examination. Medical staff members occupationally exposed to radiation are monitored regularly, as they wear personal dosemeters, whereas no dose measurements are carried out on voluntarily assisting persons, as measurements are both cost- and time-intensive. However, the dose limits prescribed in the German radiation protection regulations have to be observed for these volunteers as well. To assist the legislator in deciding whether the German regulation should be changed so that in future the dose of voluntarily assisting persons should also be determined-either by wearing a dosemeter or in another way-investigations with regard to the radiation dose exposure suffered by volunteers were performed within the scope of a research project. The personal dose equivalent Hp(10) for persons assisting knowingly and willingly in X-ray examinations in veterinary medicine was measured for different examination scenarios. Typical exposure situations have been identified and measurements performed in the field of scattered X-rays. The measurements were carried out on animals in veterinary practices and, to verify these measurements, also under laboratory conditions. This paper deals with X-ray examinations of large animals, with the focus especially on horses. The measured personal dose equivalent values of voluntary helpers in equine radiology are in the order of a few microsieverts.     

Review of relationships between physical measurements and user evaluation of image quality

Some of the findings of a review of the relationship between physical measurements and clinical image quality have been summarised. Mixed results were found: some studies had no relationship at presently typical dose levels, whereas others had a clear correlation between them. It is concluded that the various image quality evaluation tasks in an X-ray department are best done by different methods. Presently, exact physical measurements cannot supersede subjective evaluation in judging the acceptability of clinical images, whereas they are indispensable in specification and testing of technical performance.     

Probe Characterization for Electromagnetic Near-Field Studies

Probes used for contactless electromagnetic field capture or injection are characterized. Depending on the probe structure, they interact preferentially with the electric or magnetic field. The optimal size of the probes for broad-frequency-band measurements is investigated. However, it is shown particularly for the magnetic field probe that considerations about the size and the structures presented in this paper are not sufficient for a good discrimination between electric and magnetic fields. Then, the space resolution of near-field measurements is discussed, with application to the field capture of a microstrip line under operation.      

Attenuation and velocity of first sound in a saturated 3He-4He mixture at very low temperatures and high magnetic field

We present experimental results on the attenuation and velocity of first sound in a saturated (X = 0.064) ³He-⁴He mixture. The measurements were performed at very low temperature (3.5 <T< 20 mK) with relatively low frequencies (around 1 MHz) at saturated vapor pressure, using a CW technique. Though the results are found to be in qualitative agreement with the theory for acoustic transmission in degenerate mixtures, they are not quantitatively consistent with theory. A phenomenological explanation is offered for this discrepancy. We compare our data with recent measurements at higher temperatures and frequency. We have also performed the measurements in a magnetic field of 9 T. Within our experimental accuracy we cannot detect any systematic difference from the measurements in zero field. This is expected from theory.     

Ground-based zenith sky abundances and in situ gas cross sections for ozone and nitrogen dioxide with the Earth Observing System Aura Ozone Monitoring Instrument

High-accuracy spectral-slit-function calibration measurements, in situ ambient absorption gas cell measurements for ozone and nitrogen dioxide, and ground-based zenith sky measurements with the Earth Observing System Aura Ozone Monitoring Instrument (OMI) flight instrument are reported and the results discussed. For use of high-spectral-resolution gas absorption cross sections from the literature in trace gas retrieval algorithms, accurate determination of the instrument's spectral slit function is essential. Ground-based measurements of the zenith sky provide a geophysical determination of atmospheric trace gas abundances. When compared with other measurements, they can be used to verify the performance of the OMI flight instrument. We show that the approach of using published high-resolution absolute absorption cross sections convolved with accurately calibrated spectral slit functions for OMI compares well with in situ gas absorption cell measurements made with the flight instrument and that use of these convolved cross sections works well for reduction of zenith sky data taken with the OMI flight instrument for ozone and nitrogen dioxide that are retrieved from measured spectra of the zenith sky with the differential optical absorption spectroscopy technique, the same method to be used for the generation of in-flight data products. Finally, it is demonstrated that the spectral stability and signal-to-noise ratio performance of the OMI flight instrument, as determined from preflight component and full instrument tests, are sufficient to meet OMI mission objectives.     

Implementation of a 3-D Hyperspectral Instrument for Skin Imaging Applications

The many bands acquired by typical multispectral, hyperspectral, and ultraspectral instruments are collected in either a scanning or staring fashion. Staring instruments, like that described in this paper, are popular because they are capable of producing spatially coherent images of a target scene; therefore, they are suitable for noncontact inspection applications. However, the wavebands need to be coregistered. A new application of hyperspectral instrumentation is proposed, where a sheet-of-light method, produced by a low-power laser light, is used to compute range measurements, and a hyperspectral instrument is used to acquire spectral information in the visible (VIS) range of the spectrum. The main advantage of this method is that a single hyperspectral tunable filter arrangement is used to sweep the image to get 3-D information and acquire hyperspectral spectral measurements of a scene. This paper describes the implementation of the image acquisition subsystem, which was done in LabView, and the method used to obtain coregistered radiometrically calibrated spectral imagery and range information. Test cases showed that the instrument may be used to retrieve height and spectral information of small areas and could be used for skin-imaging applications.      

Individual Characterization of an Oscillator by Means of Cross-Correlation or Cross-Variance Method

Two new methods using the concepts of cross correlation and cross variance are proposed for comparing three oscillators. They allow one to characterize individually each oscillator and they reduce the influence of the measurement system noise if the noise sources on each channel are independent. Therefore, better resolution can be obtained in the spectral purity and frequency stability measurements.     

Using Conditional Measurements to Combat Decoherence

With the help of some remarkable examples, it is shown that conditional measurements performed on two-level atoms just after they have interacted with a resonant cavity field mode are able to recover the coherence of number-state superpositions, which is lost due to dissipation.