Questions of processing the results of measurements in secondary standards

The existing model for processing results of measurements in secondary standards is analyzed, its disadvantages are demonstrated, and ways of avoiding them are suggested. __________ Translated from Izmeritel’naya Tekhnika, No. 6, pp. 6–8, June, 2006.     

Variable quadrature ac bridges for comparing capacitance and resistance standards

The structure of a precision quadrature ac bridge, and its calibration and balancing techniques including error correction are considered.Translated from Izmerital'naya Tekhnika, No. 10, pp. 50–53, October, 1995.     

Synthesis, characterization, and application of fluorescence sensing lipobeads for intracellular pH measurements

This paper describes the synthesis and characterization of micrometric phospholipid-coated polystyrene particles, named lipobeads, with pH-sensing capability and their application for intracellular pH measurements in murine macrophages. The phospholipids used to coat the particles are labeled with fluorescein (a pH-sensitive dye) and tetramethylrhodamine (a pH-insensitive dye), which serves as a referencing fluorophore for increased accuracy of the pH measurements. The synthesis of the pH-sensing lipobeads is realized by the covalent attachment of the fluorescent phospholipids to the surface of carboxylated polystyrene particles. The pH dynamic range of the sensing particles is between 5.5 and 7.0 with a sensitivity of 0.1 pH unit. The excitation light intensity is reduced to minimize photobleaching of the fluorescein-phospholipid conjugates. The fluorescent lipobeads are used to measure the pH in single macrophages. The lipobeads are ingested by the macrophages and directed to lysosomes, which are the cellular organelles involved in the phagocytosis process. Despite the high lysosomal levels of digestive enzymes and acidity, the absorbed particles remain stable for over 6 h in the cells when they are stored in a phosphate-buffered saline solution at pH 7.4.     

Calibration measurements and standards for radiation protection dosimetry

The safe use of ionising radiation for applications in medicine, electric power production and industrial processes requires accurate measurements that are traceable to national standards. Radiological calibration laboratories provide measurements that may be used to determine the calibration coefficients for personal dosemeters and survey meters. The wide range of ionising radiation applications results in the need for a wide range of reference radiation types and intensities to be available in the calibration laboratory. The methods used and the problems encountered while developing reference radiations are discussed.     

A system of secondary standards for photon dosimetry

Translated from Izmeritel'naya Tekhnika, No. 10, pp. 48–49, October, 1990.     

Procedures and standards for accurate spectrophotometric measurements of specular reflectance

Procedures and standards that have been developed at the National Research Council of Canada for the accurate measurement of specular reflectance are discussed for both absolute and relative methods over the spectral range 250 to 2500 nm. There has been an increasing demand for these types of measurements, particularly for coated samples approaching the extremes of 0% reflectance and 100% reflectance. In some applications of these coatings, such as energy conservation and control, conventional methods of measuring specular reflectance give insufficient accuracies for the prediction of optical performance. Details of alignment procedures for both absolute and relative reflectance methods, the preparation and application of several candidate reflectance standards, and the compensation, attenuation, and verification procedures that have been developed to improve the precision and accuracy of specular reflectance measurements are described. Using these various techniques, one can routinely achieve accuracies of 0.3% reflectance at reflectance values as high as 97% and as low as 4%.     

Synthesis and characterization of a disulfide reporter molecule for enhancing pH measurements based on surface-enhanced Raman scattering

In this paper, we describe the synthesis and characterization of 2,5-dimercaptobenzoic acid as a novel pH-sensitive disulfide reporter molecule for surface-enhanced Raman scattering (SERS) capable of inducing the controlled aggregation of gold (Au) colloids in solution without the addition of salts. While weak acids have been shown to yield some pH sensitivity as reporter molecules for SERS measurements, the reproducibility and signal strength of nanoparticle probes based on such molecules can vary greatly. This limited reproducibility depends greatly on the salt-induced aggregation of the colloidal nanoprobes, which is required in order to obtain SERS signals strong enough to probe individual clusters. This complicates their use in live cell sensing applications. We show that our approach results in primarily bridged nanoparticles comprising a pH-sensitive nanoprobe that can quantify accurately pH values well below 5.5. The robustness and sensitivity of this system makes it a powerful tool for measuring pH values on the nanoscale under in vitro conditions.     

Establishment of accuracy limits and standards for comparative thermal conductivity measurements

New techniques have been developed for reducing thermal conductivity data from thermal comparative measurements. The first of these techniques is based on making a Taylor-series expansion of the stack centerline temperature profile. The result is an expression giving the ratio of sample to reference conductivities at any temperature as a function of measured quantities, the stack thermocouple readings and stack element thicknesses. The conventional formula presently used to reduce comparative conductivity data is shown to be a special result of the general analysis. A second technique involves the use of linear least-squares (LS) techniques to derive both the sample and the reference conductivities from the measured data. The LS technique provides the coefficients for a polynomial temperature expansion of the reference and sample conductivities directly. Use of the new techniques is illustrated in a reduction of some comparative data on the conductivities of Pyrex 7740 and Pyroceram 9606. It is shown that a highly self-consistent pair of conductivity functions can be derived for these two commonly used reference materials if the conductivity vs temperature relation for Pyrex is modified slightly from its recommended value. The Pyroceram conductivity results from the comparative measurements are in good agreement with a conductivity derived from pulse diffusivity and differential scanning calorimetry measurements and also in good agreement with the recommended Pyroceram conductivity function.Paper presented at the Ninth Symposium on Thermophysical Properties, June 24–27, 1985, Boulder, Colorado, U.S.A.     

Determination of primary particle size distributions from time-resolved laser-induced incandescence measurements

For a polydisperse nanoparticle ensemble the evaluation of time-resolved laser-induced incandescence (LII) measurements yields a weighted average value for the primary nanoparticle size. Although this value is sufficient for narrow size distributions, a comprehensive characterization of a particle-evolution process requires the reconstruction of the size distribution. An easy-to-use online approach is presented to evaluate the LII signal regarding higher moments of the distribution. One advantage of this approach is that the size distribution results in a deceleration of the LII signal decay with time after the laser pulse. Therefore LII signal-decay curves are evaluated in two different time intervals after the laser pulse, providing information about the desired distribution parameters that has been tested successfully with experimental curves taken in different soot-formation processes.     

Investigations of noise in measurements of electronic voltage standards

We have investigated noise in measurements of the 10 V outputs of electronic voltage standards based on Zener diode references (Zeners). Zener outputs were compared to NIST Josephson standards using a digital voltmeter (DVM) to measure voltage differences. Because of the presence of serially correlated noise, the data were analyzed by calculating estimated Allan variances which were then used to determine the parameters of a power law model including white and 1/f noise. In many cases, the modeled Allan variances agree well with the estimated values over a wide range of sampling times. In all, we have estimated the 1/f noise floor for 25 Zeners of three types. We examined the impact on noise measurements of changes of the range of the DVM and of quantization of the recorded voltages by the DVM. We conclude that there is strong evidence of the presence of a high level of white noise in Zeners.     

Determination of appropriate price level in installed-capacity market

As one of the most important approaches for ensuring adequate generation capacity, and hence reliability of electricity supply, the capacity-obligation mechanism is employed in some operating electricity markets by imposing such an obligation on all load-serving entities (LSEs). To facilitate the enforcement of the obligation, an installed-capacity market is established for the LSEs and generation companies to trade installed capacity. In the paper, the optimal allocation strategies of generation capacity for generation companies between two electricity markets under different levels of installed-capacity prices, as well as the optimal purchasing strategies of LSEs, are first examined, and on this basis a new framework is developed to determine an appropriate level of generation-installed-capacity price for ensuring generation-capacity adequacy. Finally, the proposed method is illustrated by a numerical example.     

Temperature compensation for ultrasound measurements and characterization of materials

A major problem associated with quantitative ultrasound measurement, particularly in remote applications, is the variability of environmental temperature, affecting the characteristics of the signals received. In this paper, a practical approach to introduce temperature compensation against changes in amplitude of the received signals is presented. For this purpose, a theoretical investigation was first carried out, and based on the general conclusions of this investigation, a temperature correction function applicable to most materials has been developed. The compensated ultrasonic signals can then be used to obtain the characteristic acoustic properties of the material, irrespective of environmental changes in temperature, extending the scope of ultrasonic testing and characterization of materials in situ.     

Design of a low-cost optical instrument for pH fluorescence measurements

This paper describes the electronic design and the performance of a low-cost fiber-optic instrument for pH fluorescent measurements. The chemical sensing phase consists of an organic pH indicator (mercurochrome) immobilized in a sol-gel matrix placed at the end of a fiber optic by means of a steel grid. The active phase was excited by means of a high-intensity blue light-emitting diode. The light signal was modulated to avoid external interference. Fluorescence emission is detected by a low-cost photodiode. To avoid drifts in excitation light emission intensity, a ratiometric measurement was proposed. To perform such measurements, two fiber-optic measurement channels were used. One of them was employed to measure only the pH indicator fluorescent emission intensity. The second channel was employed to measure only the intensity of the excitation light reflected by the sensing phase. The ratio between both signals is only proportional to pH and proved to be independent of excitation light intensity. The sensor is useful over the pH range of 4-8, providing highly reliable results.