Home About us Contact
|
Home About us Contact | ||
|
|
||
Measurement Precision (measurement + precision)
Selected AbstractsRapid simulated hydrologic response within the variably saturated near surfaceHYDROLOGICAL PROCESSES, Issue 3 2008Brian A. Ebel Abstract Column and field experiments have shown that the hydrologic response to increases in rainfall rates can be more rapid than expected from simple estimates. Physics-based hydrologic response simulation, with the Integrated Hydrology Model (InHM), is used here to investigate rapid hydrologic response, within the variably saturated near surface, to temporal variations in applied flux at the surface boundary. The factors controlling the speed of wetting front propagation are discussed within the Darcy,Buckingham conceptual framework, including kinematic wave approximations. The Coos Bay boundary-value problem is employed to examine simulated discharge, pressure head, and saturation responses to a large increase in applied surface flux. The results presented here suggest that physics-based simulations are capable of representing rapid hydrologic response within the variably saturated near surface. The new InHM simulations indicate that the temporal discretization and measurement precision needed to capture the rapid subsurface response to a spike increase in surface flux, necessary for both data-based analyses and evaluation of physics-based models, are smaller than the capabilities of the instrumentation deployed at the Coos Bay experimental catchment. Copyright © 2007 John Wiley & Sons, Ltd. [source] Evaluation of antioxidant properties of dermocosmetic creams by direct electrochemical measurementsINTERNATIONAL JOURNAL OF COSMETIC SCIENCE, Issue 5 2005C. Guitton Cyclic voltammetry and linear sweep voltammetry were preliminarily used in order to evaluate the global antioxidant properties of dermocosmetic creams. Experiments were performed by introducing electrodes directly into the creams without any pretreatment of the samples. Current,potential curves showed significant anodic current depending on the antioxidant-containing cream studied. In comparison, little amperometric response was recorded with an antioxidant-free cream base. Aqueous solutions of the corresponding antioxidants showed analogous anodic waves and similar peak potentials. A correlation between the global anodic peak and the presence of the antioxidant species in the cream was made with eleven skin creams, attesting to the reliability of the method. Among the tested electrode materials, platinum gave the best results in terms of electrochemical kinetics and measurement precision (current peak standard deviation <5%). Exposure of a depilatory cream to oxidizing agents (e.g. hydrogen peroxide, air, or light) caused a decrease in peak current as expected. This methodology enabled us to evaluate the evolution of the total antioxidant capacity under oxidative stress and gives encouragement to further development of a voltammetric method to quantify cream antioxidant power. [source] Limiting Answer Review and Change on Computerized Adaptive Vocabulary Tests: Psychometric and Attitudinal ResultsJOURNAL OF EDUCATIONAL MEASUREMENT, Issue 1 2000Walter P. Vispoel Previous simulation studies of computerized adaptive tests (CATs) have revealed that the validity and precision of proficiency estimates can be maintained when review opportunities are limited to items within successive blocks. Our purpose in this study was to evaluate the effectiveness of CATs with such restricted review options in a live testing setting. Vocabulary CATs were compared under four conditions: (a) no item review allowed, (b) review allowed only within successive 5-item blocks, (c) review allowed only within successive lO-item blocks, and (d) review allowed only after answering all 40 items. Results revealed no trust-worthy differences among conditions in vocabulary proficiency estimates, measurement error, or testing time. Within each review condition, ability estimates and number correct scores increased slightly after review, more answers were changed from wrong to right than from right to wrong, most examinees who changed answers improved proficiency estimates by doing so, and nearly all examinees indicated that they had an adequate opportunity to review their previous answers. These results suggest that restricting review opportunities on CATs may provide a viable way to satisfy examinee desires, maintain validity and measurement precision, and keep testing time at acceptable levels. [source] IN-LINE CONSISTENCY MONITORING OF TOMATO BASED PRODUCTS USING VIBRATIONAL PROCESS VISCOMETRYJOURNAL OF FOOD PROCESSING AND PRESERVATION, Issue 5 2001P. J. CULLEN A vibrational process viscometer was evaluated as an in-line consistency monitoring technique for tomato based products. This sensor was installed in both pilot and industry scale production processes. Accuracy of the sensor and its ability to distinguish between varying concentrations of non-Newtonian fluids was evaluated with flowrate and temperature closely controlled. The sensor was shown to have the least inherent variability when compared to off-line techniques. However it was found to be flowrate dependent for the tomato based products. Good correlations between the sensor and off-line techniques were developed for the pilot scale trials. Plant trials revealed a number of problems in developing such correlations under industrial process conditions, however the instrument proved capable of tracking out of specification sauce as determined by the off-line Brookfield viscometer. It was concluded that use of the sensor would result in increased measurement precision over the off-line instruments coupled with the benefits of in-line monitoring. [source] Summary findings of the fourth international radiocarbon intercomparison (FIRI)(1998,2001)JOURNAL OF QUATERNARY SCIENCE, Issue 7 2002Elisabetta Boaretto Abstract Interlaboratory comparisons have been widely used in applied radiocarbon science. These are an important part of ongoing quality assurance (QA) programmes, which are vital to the appropriate interpretation of the evidence provided by the 14C record in Quaternary applications (including climate change and environmental reconstruction). International comparisons of laboratory performance are an essential component of the quality assurance process in radiocarbon dating. If the user community is to have confidence in radiocarbon results, it needs to be assured that laboratories world wide are producing measurements that are reliable and in accordance with ,good practice'. The findings from the most recent (completed in 2001) and extensive (more than 90 participating laboratories) radiocarbon intercomparison (FIRI) are reported here. This study was designed (i) to assess comparability, or otherwise, of the results from different laboratories and (ii) to quantify the extent and possible causes of any interlaboratory variation. The results demonstrate that there are no significant differences amongst the main measurement techniques (gas proportional counting, liquid scintillation counting and accelerator mass spectrometry (AMS)) but there is evidence of small laboratory offsets relative to known age samples for some laboratories. There is also evidence in some cases of underestimation of measurement precision. Approximately 10% of all results were classified as extreme (outliers) and these results were generated by 14% of the laboratories. Overall, the evidence supports the fact that radiocarbon laboratories are generally accurate and precise but that, notwithstanding internal QA procedures, some problems still occur, which can best be detected by participation in independent intercomparisons such as FIRI, where the results allow individual laboratories to assess their performance and to take remedial measures where necessary. The results from FIRI are significant in that they show a broad measure of agreement between measurements made in different laboratories on a wide range of materials and they also demonstrate no statistically significant difference between measurements made by radiometric or AMS techniques. Copyright © 2002 John Wiley & Sons, Ltd. [source] Effect of black blood MR image quality on vessel wall segmentationMAGNETIC RESONANCE IN MEDICINE, Issue 2 2001Jonathan B. Thomas Abstract Black blood MRI has become a popular technique for measuring arterial wall area as an indicator of plaque size. Computer-assisted techniques for segmenting vessel boundaries have been developed to increase measurement precision. In this study, the carotid arteries of four normal subjects were imaged at seven different fields of view (FOVs), keeping all other imaging parameters fixed, to determine whether spatial resolution could be increased at the expense of image quality without sacrificing precision. Wall areas were measured via computer-assisted segmentation of the vessel boundaries performed repeatedly by two operators. Analysis of variance (ANOVA) demonstrated that the variability of wall area measurements was below 1.5 mm2 for in-plane spatial resolutions between 0.22 mm and 0.37 mm. An inverse relationship between operator variability and the signal difference-to-noise ratio (SDNR) demonstrated that semi-automatic segmentation of the wall boundaries was robust for SDNR >3, defining a criterion above which subjective image quality can be degraded without an appreciable loss of information content. Our study also suggested that spatial resolutions higher than 0.3 mm may be required to quantify normal wall areas to within 10% accuracy, but that the reduced SNR associated with the higher resolution may be tolerated by semi-automated wall segmentation without an appreciable loss of precision. Magn Reson Med 46:299,304, 2001. © 2001 Wiley-Liss, Inc. [source] Theoretical and experimental study of polarization characteristics of polarization maintaining fiber based on wavelength-sweeping modulationMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 7 2010Zuo-Liang Duan Abstract We analyze theoretically the polarization characteristics of polarization maintaining fiber and study the basic measurement principles of beat length and polarization extinction ratio of this kind of optical fiber. According to the dependence of the phase difference between two orthogonally polarized modes (denoted as HE and HE) transmitted in the polarization maintaining fiber on the light wavelength, we propose the wavelength-sweeping modulation method to measure the beat length and the model birefringence. Based on this technique, the beat length and polarization extinction ratio of the PANDA polarization maintaining fibers (PMFs) (provided by Yangtze Optical Fiber and Cable Company, Wuhan, China) were investigated in detail. Experimental results show good consistent with the theoretical ones. We find that this method shows high measurement precision with the advantages of clear measurement principle and easy to operate. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 1466,1469, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25244 [source] Phytochemical Research Using Accelerator Mass SpectrometryNUTRITION REVIEWS, Issue 10 2004Le T. Vuong PhD Vegetables and fruits provide an array of microchemicals in the form of vitamins and secondary metabolites (phytochemicals) that may lower the risk of chronic disease. Tracing these phytochemicals at physiologic concentrations has been hindered by a lack of quantitative sensitivity for chemically equivalent tracers that could be used safely in healthy people. Accelerator mass spectrometry is a relatively new technique that provides the necessary sensitivity (in attomoles) and measurement precision (<3%) towards 14Clabeled phytochemicals for detailed kinetic studies in humans at dietary levels. [source] Comparing indirect methods of digit ratio (2D:4D) measurementAMERICAN JOURNAL OF HUMAN BIOLOGY, Issue 2 2009Christoph J. Kemper The ratio of the lengths of the second and fourth finger (2D:4D) has been proposed to index prenatal exposure to androgens. Different methods have been utilized to measure digit ratio, however, their measurement precision and economy have not been systematically compared yet. Using different indirect methods (plastic ruler, caliper, computer software), three independent raters measured finger lengths of 60 participants. Generally, measurement precision (intraclass correlation coefficient, technical error of measurement, and relative technical error of measurement) was acceptable for each method. However, precision estimates were highest for the computer software, indicating excellent measurement precision. Estimates for the caliper method were somewhat lower followed by ruler which had the lowest precision. On the contrary, the software-based measurements took somewhat longer to complete than the other methods. Nonetheless, we would favor the use of these tools in digit ratio research because of their relative superior reliability which could be crucial when associations with other variables are expected to be low to moderate or sample size is limited. Software offers several promising opportunities that may contribute to an accurate identification of the proximal finger crease (e.g., zooming, adjusting contrast, etc.). Am. J. Hum. Biol., 2009. © 2008 Wiley-Liss, Inc. [source] The determination of high-affinity protein/inhibitor binding constants by electrospray ionization hydrogen/deuterium exchange mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 16 2006Lee Frego Recently, a hydrogen/deuterium exchange method termed SUPREX (Stability of Unpurified Proteins from Rates of hydrogen/deuterium EXchange), capable of measuring protein/ligand binding constants, which utilizes matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS), has been reported. Unlike more conventional approaches, SUPREX is inherently capable of measuring Kd values of tight binding ligands. Here we present a SUPREX-based method, incorporating automation and electrospray ionization (ESI)-MS, to measure Kd values for very potent inhibitors of the kinase PKC,. The use of ESI offers an alternative to MALDI, with the advantages of improved mass measurement precision for larger proteins, and amenability to automation. Kd values generated by this method are in good agreement with those generated by a molecular protein kinase assay. Copyright © 2006 John Wiley & Sons, Ltd. [source] Methodology of retinal straylight assessmentACTA OPHTHALMOLOGICA, Issue 2007TJTP VAN DEN BERG Purpose: The psychophysical technique of "Compensation Comparison", embedded in the C-Quant instrument for clinical assessment of retinal straylight will be demonstrated. Retinal straylight is the cause of complaints such as glare hindrance and contrast loss. It results from disturbances in the optical media. Its assessment helps to decide on surgery of (early) cataract, or to evaluate corneal or vitreal problems. Methods: The subject's task is to compare in 20 short presentations two flickering half fields, and to indicate with push buttons which one flickers more strongly. Added value in comparison to visual acuity was assessed in 2422 active drivers of the European GLARE study. Repeatability of the obtained straylight value was tested for 17 naive subjects and several groups of patients. Absolute measurement precision of the C-Quant was tested using a scattering sample with known straylight value in front of the eyes of the 17 naive subjects. Results: Many individuals were found to suffer from increased straylight that is undetected in visual acuity: in 6% of cases with decimal visual acuity > 0.5 straylight was increased more than 4 times compared to normal. A psychometric function was derived and fitted to the patient responses, resulting in a straylight value including a reliability estimate. Repeated measures standard deviation for the method is about 0.07 log units, to be compared with differences of 1.0 log units or more units with (early) cataract or corneal disturbances. The check using known scatter samples showed virtually perfect (0.01 log units difference) correspondence. Conclusions: Absolute precision and repeated measures standard deviation is very good compared with differences in the population. Straylight measurement promises important extra diagnostic power. [source] UVA1 and UVB irradiated skin investigated by optical coherence tomography in vivo: a preliminary studyCLINICAL & EXPERIMENTAL DERMATOLOGY, Issue 1 2005T. Gambichler Summary In histological studies, it has frequently been demonstrated that ultraviolet (UV) exposure, in particular UVB, can induce significant thickening of the viable epidermis and/or stratum corneum. Since skin biopsy alters the original skin morphology and always requires an iatrogenic trauma, we aimed to introduce optical coherence tomography (OCT) in vivo for the investigation of changes of epidermal thickness (ET) following UVA1 and UVB irradiation. Twelve healthy subjects received daily 60 J/cm2 of UVA1 and 1.5 minimal erythema doses UVB on their upper back over 3 consecutive days. Twenty-four hours after the last irradiation, OCT assessments were performed on UV exposed and adjacent nonirradiated control sites. Data of ET as expressed by comparison of the averaged A-scans differed significantly between nonirradiated (94.2 ± 15.7 µm), UVA1 (105.4 ± 12.8 µm) and UVB (125.7 ± 22.1 µm) exposed sites. In comparison to the nonirradiated sites, UVA1 exposed skin showed significant (P = 0.022) increase of ET of 11% and UVB exposed sites a significant (P < 0.001) increase of 25%. ET of UVA1 and UVB exposed skin sites differed significantly (P =0.005). Our results obtained from OCT in vivo measurements confirm data of previous histological studies indicating that not only erythemogenic doses of UVB, but also suberythemogenic doses of UVA1 may have a significant impact on ET. OCT appears to be a promising bioengineering technique for photobiological studies. However, further studies are needed to establish its measurement precision and validity, and to investigate in vivo spectral dependence on UV induced skin changes such as skin thickening. [source] | ||||||||||||||||