Improvement Of Measurement Precision Research Articles

Remote Sensing of Atmospheric Optical Depth Using a Smartphone Sun Photometer

In recent years, smart phones have been explored for making a variety of mobile measurements. Smart phones feature many advanced sensors such as cameras, GPS capability, and accelerometers within a handheld device that is portable, inexpensive, and consistently located with an end user. In this work, a smartphone was used as a sun photometer for the remote sensing of atmospheric optical depth. The top-of-the-atmosphere (TOA) irradiance was estimated through the construction of Langley plots on days when the sky was cloudless and clear. Changes in optical depth were monitored on a different day when clouds intermittently blocked the sun. The device demonstrated a measurement precision of 1.2% relative standard deviation for replicate photograph measurements (38 trials, 134 datum). However, when the accuracy of the method was assessed through using optical filters of known transmittance, a more substantial uncertainty was apparent in the data. Roughly 95% of replicate smart phone measured transmittances are expected to lie within ±11.6% of the true transmittance value. This uncertainty in transmission corresponds to an optical depth of approx. ±0.12–0.13 suggesting the smartphone sun photometer would be useful only in polluted areas that experience significant optical depths. The device can be used as a tool in the classroom to present how aerosols and gases effect atmospheric transmission. If improvements in measurement precision can be achieved, future work may allow monitoring networks to be developed in which citizen scientists submit acquired data from a variety of locations.

Probing topcolor-assisted technicolor from top charge asymmetry and triple-top production at the LHC

In a topcolor-assisted technicolor model (TC2) with large FCNC top quark couplings, we study its correlated contributions to the top quark forward–backward asymmetry (AFB) at the Tevatron, the top charge asymmetry (AC) and the triple-top production at the LHC. Under current constraints on the top quark from the LHC and Tevatron (such as the total and differential production rates), we scan the parameter space of such a TC2 model. We find that in the allowed parameter space the TC2 model can explain the Tevatron measured AFB at 2σ level, but meanwhile significantly enhance AC at the LHC. Such enhanced AC, albeit currently allowed by the LHC measurement at 2σ level, will serve as a test of TC2 with the improvement of measurement precision at the LHC. Then with all the constraints (including the requirement to explain AFB at 2σ level and satisfying the current LHC measurement of AC at 2σ level), we find that the TC2 model can induce sizable triple-top production at the 14 TeV LHC (the production rate can maximally reach 16 pb). Due to the low SM backgrounds, the triple-top production can also be a good probe for TC2 model, complementary to AC.

基于构建最优函数提高飞机姿态测量精度

A method based on optimization functions was proposed to improve the attitude measurement precision of a plane.First,the same feature that the plane was projected at two measuring stations was acquired by the template matching method.The coordinate value of the same feature for the plane was obtained by intersecting at a launching coordinate,and the initial value of the plane attitude was estimated in term of the characteristic triangle of the plane in space.Then,the object coordinate of the plane was established,the image coordinate according to the feature of plane was calculated by using a colinear equation and the least difference between the re-project result and an actual image was regarded as the optimizing goal function.Finally,the iterative method was used to improve the precision of the attitude parameter of a target.Experimental results show that the measuring error of the attitude angle is less than 0.1 ° when the axis of the plane imaging is more than 500 pixels.As compared with the middle axis method and the direction vector method of angle bisector lines,proposed method has a correct mathematical model,reasonable algorithm and can improve effectively the measurement precision of the plane.

Accurate frequency response characterization of photoreceivers

An accurate frequency response characterization method for photoreceivers with optical heterodyne technique is presented in this paper. The characterization is implemented with two single-mode tunable lasers operating near the wavelength of 1.55 μm. The errors introduced by extra fixtures as well as laser output fluctuations are considered and calibrated simultaneously. Compared with previous works, the proposed calibration procedures are more complete. Experimental results indicate that the significant improvement in measurement precision has been achieved with the proposed method in the frequency range from 0 to 30 GHz, which proves the proposed frequency response characterization method to be feasible and reliable.

Precision verification of a simplified three-dimensional DIC method

The traditional three-dimensional (3D) digital image measurement technique uses at least two images captured from different positions to determine the 3D coordinate of an object. One disadvantage of this method is that the mechanical and optical properties of the image capture devices are not fully identical, and the calibration procedure is quite complicated. This paper introduces a simplified 3D digital image correlation (DIC) method, in which only one image capture device is used. The theoretical measurement error equation is derived and experimentally verified. Experimental results show that distortion correction plays an important role in the improvement of measurement precision. After a radial distortion correction, the measurement precision of the object distance can reach 0.0043%. The optimal camera spacing should be set from 1/50 to 1/30 of the object distance, to obtain a satisfactory precision.

Compensation of Measurement Precision for Three-Dimensional Position Measurement Device Based on Disturbance Observer

Improvements in measurement precision will constitute a significant issue in designing control systems formeasurement devices. Specifically, positioning precision may be decreased if unpredicted disturbances from the environment are not taken into account. In this paper, we first estimate unknown disturbances based on the disturbance observer, then design control systems which can reduce the effects of such disturbances to propose a control system capable of compensating for any decreases in measurement precision due to such disturbances, and finally demonstrate the effectiveness of the proposed control system through a series of experiments.

Determination of Precise and Accurate 51V/50V Isotope Ratios by MC-ICP-MS, Part 1: Chemical Separation of Vanadium and Mass Spectrometric Protocols

We present the first technique to obtain precise and accurate vanadium (V) stable isotope compositions by chemical isolation and multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS). Separation of V from matrix elements was achieved via five separate ion exchange columns. The procedure quantitatively removed Ti and Cr, which contain direct isobaric interferences on the minor isotope 50V. Isotope compositions were determined using a conventional standard solution-sample bracketing technique. The V isotope composition for an in-house secondary standard solution from BDH Chemicals was δ51V = −1.19 ± 0.12‰ (2s, n = 600), measured as the per mil deviation relative to the composition of a widely available Specpure Alfa Aesar (AA) vanadium solution. This represents an improvement in measurement precision on previous techniques of almost two orders of magnitude. The effects of adding Cr, Ti and S to standard solutions were explored to determine the robustness of protocols. Only very low levels of these elements could be tolerated to obtain precise and accurate isotope compositions and was achieved with the chemical purification procedure. Standard solutions from AA and BDH processed as unknowns through the entire chemical separation and measurement protocols returned 100% yields and the same isotopic compositions as those of unprocessed standard solutions.

The Impact of Statistically Adjusting for Rater Effects on Conditional Standard Errors of Performance Ratings

Prior research indicates that the overall reliability of performance ratings can be improved by using ordinary least squares (OLS) regression to adjust for rater effects. The present investigation extends previous work by evaluating the impact of OLS adjustment on standard errors of measurement (SEM) at specific score levels. In addition, a cross-validation (i.e., resampling) design was used to determine the extent to which any improvements in measurement precision would be realized for new samples of examinees. Conditional SEMs were largest for scores toward the low end of the score distribution and smallest for scores at the high end. Conditional SEMs for adjusted scores were consistently less than conditional SEMs for observed scores, although the reduction in error was not uniform throughout the distribution. The improvements in measurement precision held up for new samples of examinees at all score levels.

Metrological performance verification of coordinate measuring systems with optical distance sensors

Optical coordinate measuring systems are gaining increasing interest in production quality control, due to their rapidity and other advantages with respect to traditional measuring techniques using contact probes. This paper presents an experimental investigation on procedures and standards for testing coordinate measuring systems equipped with optical distance sensors. Particular attention is given to methods for testing two of the most important specifications of optical coordinate measuring system: the probing error and the error of indication for size measurement. The investigation is aimed at improving the performance verification methods employed at the state of the art. This will help the industrial users in the selection process of those systems, with an improvement of measurement precision in manufacturing.

The impact of statistical adjustment on conditional standard errors of measurement in the assessment of physician communication skills

The use of standardized patients to assess communication skills is now an essential part of assessing a physician's readiness for practice. To improve the reliability of communication scores, it has become increasingly common in recent years to use statistical models to adjust ratings provided by standardized patients. This study employed ordinary least squares regression to adjust ratings, and then used generalizability theory to evaluate the impact of these adjustments on score reliability and the overall standard error of measurement. In addition, conditional standard errors of measurement were computed for both observed and adjusted scores to determine whether the improvements in measurement precision were uniform across the score distribution. Results indicated that measurement was generally less precise for communication ratings toward the lower end of the score distribution; and the improvement in measurement precision afforded by statistical modeling varied slightly across the score distribution such that the most improvement occurred in the upper-middle range of the score scale. Possible reasons for these patterns in measurement precision are discussed, as are the limitations of the statistical models used for adjusting performance ratings.

Calcium Isotopic Variations Produced by Biological, Kinetic, Radiogenic and Nucleosynthetic Processes

Study of the isotopic variations of calcium is of interest because Ca is important in geochemical and biochemical processes, and is one of few major cations in rocks and minerals with demonstrated isotopic variability. Calcium is critical to life and a major component of the global geochemical cycles that control climate. Studies to date show that biological processing of calcium produces significant isotopic fractionation (4 to 5‰ variation of the 44Ca/40Ca ratio has been observed). Calcium isotopic fractionation due to inorganic processing at high (e.g., magmatic) temperatures is small. There are few studies of calcium isotope fractionation behavior for low-temperature inorganic processes. The Ca isotopic variations observed in nature, both biological and inorganic, are mostly attributed to kinetic effects, but this inference cannot be confirmed until equilibrium Ca isotope fractionation is more thoroughly investigated. Evaporation of silicate liquids into vacuum at high temperature is expected to produce kinetic Ca isotopic fractionation, as is diffusion of calcium in silicate liquids and aqueous solutions. The evaporation effects have been observed in meteorite samples. Diffusion effects have been observed in the laboratory but not yet in natural samples. The potential value of Ca isotopic studies has barely been tapped. Improvements in measurement precision would increase the attractiveness of Ca isotopes as a geochemical tool, but such improvements have been slow in coming. Calcium is composed mainly of the isotope 40Ca, which is a highly stable, doubly magic nuclide (both the number of neutrons and the number of protons represent closed nuclear shells). There are a total of six stable isotopes covering a mass range from 40 to 48. Ca has been studied for isotopic variations in three ways. The major isotope, 40Ca is the primary radioactive decay product of radioactive 40K. About 89.5% of the 40K …

Improvement in measurement precision with SPME by use of isotope dilution mass spectrometry and its application to the determination of tributyltin in sediment using SPME GC-ICP-MS

A method is described for the accurate and precise determination of tributyltin (TBT) by species specific isotope dilution mass spectrometry (ID-MS) using solid phase microextraction (SPME) in combination with gas chromatographic (GC) separation and inductively coupled plasma mass spectrometric (ICP-MS) detection. Butyltin compounds were ethylated in aqueous solution with sodium tetraethylborate and the headspace sampled with a polydimethylsiloxane coated fused silica SPME fiber. The analyte was then directly transferred from the fiber to the head of the GC column for desorption following insertion of the fiber through the heated injection port. Reverse spike ID analysis was performed to determine the accurate concentration of a 117Sn-enriched TBT spike using two well characterized natural abundance TBT standards. A concentration of 0.923 ± 0.005 µg g−1 (one standard deviation, n = 5) as tin was obtained for TBT in National Research Council of Canada (NRCC) marine sediment PACS-2 using the present method, in good agreement with the certified value of 0.98 ± 0.13 µg g−1 (as 95% confidence interval). A TBT concentration of 0.93 ± 0.09 µg g−1 (one standard deviation, n = 5) as tin in PACS-2 was subsequently determined by standard additions calibration using tripropyltin (TPrT) as an internal standard. An eighteen-fold improvement in the precision of TBT concentration measured using ID was observed, clearly demonstrating its superiority in providing more accurate and precise results as compared to the method of standard additions. A detection limit (3s) of 0.09 ng g−1 was estimated for TBT in PACS-2 sediment.

Quantitative analysis of incomplete HPLC resolution of enantiomers. Fit of polarimetric detection for D- and L-phenylalanine to a gaussian function.

This report compares laser-based polarimetric and UV data for quantitating incompletely resolved enantiomers by HPLC. Using L- and D-phenylalanine as a working model, response data is shown across the entire detection region while emphasizing the regions at or near 100% L, 100% D and 50:50 L:D at resolutions between 0.4 and 1.4. In general, the poorer the resolution, the greater the improvement in detectability with the polarimeter when compared to UV detection. This is due to the inherent bipolar nature of the polarimetric signal, which creates a well-defined crossing point for integration of an enantiomeric pair. In our previous work, we described the improvement in measurement precision when applying a bipolar gaussian peak model to the raw chromatographic peak data. This study will measure the model's effect on improving accuracy. This study should be applicable to other chiroptical detection strategies that produce a bipolar signal for enantiomers, such as circular dichroism and circularly polarized luminescence.

Performance appraisals of digital spectroscopy systems for the measurement of bone lead

The performances of two new digital spectroscopy systems are compared to a conventional analogue amplifier ADC system for the 109Cd based K X-ray fluorescence in vivo measurement of bone lead. Canberra’s DSA-2000 and ORTEC’s DSPEC PLUS were found to show 27.3 and 10.8% improvements in measurement precision respectively, when compared to an optimized conventional system. The resulting improvements in minimum detection limit, compared with the conventional limit of 6–10 μg Pb/g bone mineral, were reductions of 1.5–2.5 μg Pb/g bone mineral for the DSA-2000, and 0.5–1.0 μg Pb/g bone mineral for the DSPEC PLUS.

Electron paramagnetic resonance dosimetry: Methodology and material characterization

Electron paramagnetic resonance(EPR) methodologies for radiationdosimetry are investigated using various dosimeter materials. Specifically, methodologies were developed and used which were intended to improve the accuracy and precision of EPR dosimetric techniques, including combining specimen rotation during measurement, use of an internal manganese standard, instrument stabilization techniques, and strict measurement protocols. Characterization and quantification of these improvements were performed on three specific EPR dosimeter materials. The dosimeter materials investigated were walrus teeth, human tooth enamel, and alanine dosimeters. Walrus teeth showed the least desirable properties for EPRdosimetry yielding large native signals and low radiation sensitivity. The methods for tooth enamel and alanine resulted in large improvements in precision and accuracy. The minimum detectable dose (MDD) found for alanine was approximately 30 mGy (three standard deviations from the measured zero dose value). This is a sensitivity improvement of 5 to 10 over other specialized techniques published in the literature that offer MDDs in the range of 150–300 mGy. The accuracy of the method on tooth-enamel was comparable to that typically reported in the literature although the measurement precision was increased by about 7. This improvement in measurement precision enabled a more nondestructive testing evaluation procedure to be developed (where the whole sample need not be additively irradiated in order to calibrate its radiation sensitivity). Using this virtually nondestructive evaluation procedure on numerous samples showed that the method could reconstruct the same doses to within 10 mGy of those evaluated destructively. Doses used for this assessment were in the range of 100–250 mGy.

A mass‐ and isotope‐balance model of DOC mixing in estuaries

Expanding knowledge of degradation kinetics coupled with significant improvements in measurement precision of dissolved organic carbon (DOC) necessitates a review of factors that influence its cycling in estuaries. A one dimensional, time‐dependent estuarine model was used to ascertain how sinks and sources of DOC produced conservative and nonconservative property‐salinity distributions. DOC from riverine and coastal mixing members was assumed to have labile (k = 0.1 d−1) and refractory (k = 0.001 d−1) components. The magnitude of other inputs (i.e., marshes and phytoplankton) varied with respect to riverine loading (20 mol C s−1). Also, marsh (δ13C = − 12) and phytoplankton (δ13C = −20) DOC had distinct isotopic ratios compared with riverine (δ13C = −28) and coastal (δ13C = −23) DOC. Diffusive mixing times were modified by adjusting the dispersion coefficient (velocity was constant). As expected, conservative profiles were obtained when time‐scales (half‐life, turnover time) associated with sources and sinks were significantly greater than estuarine mixing times. Degradation of coastal DOC, however, had little impact on property‐salinity relationships at all mixing times studied. Moreover, nonconservative profiles were detected when at least 10% of riverine DOC was labile. In turn, the magnitude of marsh or phytoplankton inputs compared to riverine loading had a greater impact on property‐salinity distributions than estuarine residence time. Reexamination of literature data (Parker River and Ipswich River estuaries, Massachusetts) indicated that DOC concentration and isotope data can, coupled with this modeling effort, be used to estimate the magnitude and origin of DOC in estuaries.

熱音響冷凍機 レイリー散乱を用いたパルス管内温度計測法の検討

Temperature measurement in a pulse tube is important to understand the gas behavior in particular. However, it has not been measured with few exceptions. In this paper, we propose temperature measurement in a pulse tube with Rayleigh scattering. Rayleigh scattering is elastic scattering of light quanta from molecules or small particles. The gas temperature can be calculated from Rayleigh-scattering light if the gas behaves according to the ideal gas law and the pressure of the gas is known. This method has the following advantages: (1) Temperature is measured without disturbing the flow in the pulse tube; (2) there is little time delay for measurement; and (3) a two-dimensional temperature image is presented. The disadvantages are: (1) Stray light interferences cause some errors in measurement; and (2) an excimer laser is needed. We installed an experimental system in a clean room and measured Rayleigh-scattering light using a CCD camera. A new energy-monitoring method contributed to improvement in measurement precision. We demonstrated that the temperature under static pressure conditions can be measured with a standard deviation of less than 1.7%. Furthermore temperature measurement under a steady flow with a thermocouple agrees approximately with that measured by Rayleigh scattering. Moreover, it was demonstrated that the temperature can be measured under oscillating pressure conditions.

Improvement of measurement precision in absorption spectra by apodization.

In in vivo MR spectroscopy studies, it is desirable to determine metabolite peak parameters with good precision and to estimate the uncertainties. How to achieve optimal precision for an apodized MR spectrum by using a weighted least squares estimator is discussed and demonstrated. Analytic methods for calculating the uncertainties of all parameters obtained from least squares estimators are described. The time domain apodization before Fourier transformation can substantially decrease the minimum variance bound in parameters obtained from the frequency domain absorption spectrum. A weighted least squares estimation is needed to reach the Cramer-Rao lower bound. When an unweighted least squares estimation is performed, the time domain apodization also leads to improvement in precision.

Determination of oxygen concentration in heavily doped silicon

A number of years ago secondary ion mass spectrometry was proposed as a viable technique to determine the oxygen content in low resistivity (<0.1 Ω cm) silicon substrates. Since then, significant advances have been made in analytical protocols and instrumentation specifically for the measurement of oxygen in silicon. This article focuses on recent improvements in measurement precision and sample throughput. Presently, precisions of <±2% can be obtained on a routine basis, and can be as good as ±1.4% in the most favorable circumstances. Sample throughput has been improved to 24 per 8 h per instrument during normal operations.

Effects of nonmineral tissues on measurement of bone mineral content by dual‐photon absorptiometry

Computer simulations were performed to investigate the effects of nonmineral tissue (overlying soft tissue and nonmineral components of bone) on the measurement of bone mineral content by dual-photon absorptiometry (DPA). Selected experimental studies were performed to test the predictions of the simulations. The results indicate that variations in the composition of nonmineral tissue can significantly affect measurement precision and accuracy at the levels achievable with modern x-ray based absorptiometry systems (0.5%). Thus biological variables may limit further improvements in measurement precision and accuracy. Biological variables also can affect intercalibration of systems that use different radiation sources and/or calibration techniques.