Enhance Measurement Precision Research Articles

Research and Design of Nuclear Instrumentation Measurement Precision

There are many factors to influence measurement precision of nuclear instrumentation, which include radioactive statistical fluctuation, signal processing method, use environment and so on. Aiming at these factors, this article adopts some concrete methods to enhance measurement precision and makes the isotope level meter (instrumentation) achieve better effects through the designs of hardware and software.

SU‐FF‐T‐98: Characterization of Buildup Effects in OneDosePlus MOSFET‐Based Dosimeters

Purpose: Evaluate the buildup cap used on OneDosePlus™ MOSFET dosimeters and study the field size, angular, and SSD dependency. Method and Materials: OneDosePlus (ODP) dosimeters are single use, pre‐calibrated MOSFETs used to measure entrance patient dose. ODP has an integrated 1.2 mm thick tin cap. Custom dosimeters were created with buildup caps of varied thicknesses to determine the approximate tin dmax thickness for 6, 15, and 18 MV. Non‐calibrated ODP dosimeters were evaluated to assess the effect on response of the dosimeter as a function of field size, SSD, and anisotropy for different energies. Results: PDD curves for 6, 15 and 18MV show broad maximum responses centered near cap thicknesses of 1.2, 2.6 and 2.8 mm for 6, 15, and 18 MV, respectively. Evaluation of the field size response showed that higher energies have an over‐ and under‐response for larger/smaller field sizes as compared to 6 MV response, suggesting an increase in electron contamination dose contribution. Results of extended SSDs studies, typical of TBI treatments, show enhanced measurement precision, supporting these findings.For patient use, the dosimeter response is pre‐calibrated and adjusted such that the reading corresponds to Dmax in‐tissue for each specific energy. In addition, the dosimeters are corrected for the 6 MV field size and SSD dependency. Therefore, for higher energies, a slight over‐ or under‐response can be observed for larger/smaller field sizes but not in excess of the reported dosimeter accuracy (± 5%,2σ). Conclusion: The buildup cap for ODP provides a partial buildup effect with results within the expected accuracy for different dosimetric parameters. The dosimeter factory calibration corrects the response from the partial buildup effect seen from the buildup cap. Extended SSD data suggests that ODP could be used to measure dose for TBI treatments.This research was sponsored by Sicel Technologies, Inc.

Purification method development for chiral separation in supercritical fluid chromatography with the solubilities in supercritical fluid chromatographic mobile phases

A comprehensive approach was applied to develop a chiral purification method for an analyte that was found to be unusually difficult to scale-up in supercritical fluid chromatography (SFC). This was performed by studying major factors such as the solubility of an analyte in SFC mobile phases, impurity profiles, and cycle time. For this case study, the solubility in SFC mobile phase was measured by a packed column technique, coupled with a novel trapping mechanism to enhance measurement precision in SFC conditions. The solubility studies in SFC mobile phases suggested a couple of possible SFC mobile phases, in which the analyte would potentially be most soluble. The SFC methods were developed to purify a sample containing 15% of an impurity, after considering impurity profiles and cycle times of several potential methods in addition to SFC mobile phase solubility. An equal volume mixture of acetonitrile and ethanol was chosen for the final purification method, since this mixture demonstrated the relatively high SFC solubility among all solvent combinations with enhanced resolution between the analyte and the impurity as well as the shortest run time. The solubility of the compound was also determined in various organic solvents using a high throughput solubility screening system to better understand relative change of solubility from neat solution to SFC mobile phases.

Determinations of 15N Chemical Shift Anisotropy Magnitudes in a Uniformly 15N,13C-Labeled Microcrystalline Protein by Three-Dimensional Magic-Angle Spinning Nuclear Magnetic Resonance Spectroscopy

Amide 15N chemical shift anisotropy (CSA) tensors provide quantitative insight into protein structure and dynamics. Experimental determinations of 15N CSA tensors in biologically relevant molecules have typically been performed by NMR relaxation studies in solution, goniometric analysis of single-crystal spectra, or slow magic-angle spinning (MAS) NMR experiments of microcrystalline samples. Here we present measurements of 15N CSA tensor magnitudes in a protein of known structure by three-dimensional MAS solid-state NMR. Isotropic 15N, 13C alpha, and 13C' chemical shifts in two dimensions resolve site-specific backbone amide recoupled CSA line shapes in the third dimension. Application of the experiments to the 56-residue beta1 immunoglobulin binding domain of protein G (GB1) enabled 91 independent determinations of 15N tensors at 51 of the 55 backbone amide sites, for which 15N-13C alpha and/or 15N-13C' cross-peaks were resolved in the two-dimensional experiment. For 37 15N signals, both intra- and interresidue correlations were resolved, enabling direct comparison of two experimental data sets to enhance measurement precision. Systematic variations between beta-sheet and alpha-helix residues are observed; the average value for the anisotropy parameter, delta (delta = delta(zz) - delta(iso)), for alpha-helical residues is 6 ppm greater than that for the beta-sheet residues. The results show a variation in delta of 15N amide backbone sites between -77 and -115 ppm, with an average value of -103.5 ppm. Some sites (e.g., G41) display smaller anisotropy due to backbone dynamics. In contrast, we observe an unusually large 15N tensor for K50, a residue that has an atypical, positive value for the backbone phi torsion angle. To our knowledge, this is the most complete experimental analysis of 15N CSA magnitude to date in a solid protein. The availability of previous high-resolution crystal and solution NMR structures, as well as detailed solid-state NMR studies, will enhance the value of these measurements as a benchmark for the development of ab initio calculations of amide 15N shielding tensor magnitudes.

Development of a Computer-adaptive Test for Depression (D-CAT)

Depression is one of the most prevalent mental health problems and measuring depressive symptoms becomes increasingly important in science as well as medical practice. Computer Adaptive Tests (CAT) based on the Item Response Theory (IRT) promise to enhance measurement precision and reduce respondent's burden. Our aim was to develop a CAT application to measure depressive symptoms. Three thousand two hundred seventy psychosomatic patients answered an overall of 11 mental health questionnaires at the University Clinic in Berlin. Three independent reviewers rated 144 items out of these questionnaires as indicative of depressive symptoms. All items underwent six empirical steps to analyze unidimensionality, local independence and item discrimination. Finally 64 items could be used to calculate item parameters applying a Generalized Partial Credit Model (GPCM). CAT scores were estimated using an 'expected a posteriori' algorithm (EAP). Two simulation experiments showed that for theta values within the range of 2SD around the mean (98% of the cases), the latent trait can be estimated out of approximately six items with a predefined standard error of [Symbol: see text] 0.32 (reliability rho [Symbol: see text] 0.90). The CAT-scores correlated high with scores of all depression items (r = 0.95), with the Beck Depression Inventory (r = 0.79) and with a CES-D 8 item short form (r = 0.76). We conclude that the Depression-CAT measures depressive symptoms with high precision and low respondent burden.

Fourier multiport devices

A formalism for multiport devices is developed in which the creation and annihilation operators at the output are related with those at the input through a finite Fourier transform. By considering two specific inputs of number states and coherent states, we show how these devices can be used to produce multimode Schroedinger cat states and can be combined to create multipath interferometers. We introduce uncertainty relations for the distributions of particles in the input modes and the correlations between the output modes. These allow us to determine how the phase resolution of the output state scales with the number of ports and particles. This scaling is of fundamental interest for schemes that seek to use multipath interferometers for enhanced measurement precision.

Can an item response theory-based pain item bank enhance measurement precision?

were female. The majority (92%) had NSCLC and the remainder (8%) had SCLC. Among NSCLC patients, 51%, 12%, 24%, and 14% had stage I, II, III, or IV disease, respectively, and 69% of the SCLC patients had limited stage disease. Smoking status was unknown in 9 patients (<O.l%), 180 (18%) were never smokers, 591 (57%) were former smokers, and 248 (24%) were current smokers at diagnosis. None of the never smokers reported smoking at follow-up. Among former smokers, 562 (95%) remained abstinent; however, 29 patients (5%) relapsed to smoking (relapsed former smokers). Among current smokers, 173 (70%) had quit smoking at the time of the follow-up assessment (abstinent smokers); however, 75 (30%) continued to smoke at the time of their follow-up assessment (persistent smokers). The adjusted mean (SD) total LCSS score for the never and persistent smokers were 17.6 (4.02) and 28.7 (5.09), respectively (P < 0.001); the former smokers (abstinent and relapsed) had adjusted mean total LCSS scores similar to those of the never smokers, with 19.8 (4.12) and 18.1 (5.14), respectively The abstinent smokers had an adjusted mean total LCSS score of 22.1 (4.03). We will describe the adjusted scores for the individual LCSS items at the meeting. No dose responses were found between the number of cigarettes smoked per day or the total pack-years of use and the adjusted mean LCSS scores; strengths and limitations will also be discussed at the meeting. CONCLUSION: Current cigarette smoking does have an impact on QOL as measured with the LCSS among patients with lung cancer. ACKNOWLEDGMENTS: This research was supported by National Institutes of Health Grant CA-90628 and The Fraternal Order of the Eagles Cancer Grant Fund. Dr. Ping Yang is supported by National Institutes of Health Grant CA-84354.

Some Considerations for the Use of Visual Estimates of Plant Cover in Biomonitoring

SUMMARY (1) The magnitude of changes required to detect air pollution effects was determined by an error analysis of visual estimates of plant cover in a Pinus contorta var. latifolia stand in western Canada. (2) Species with the largest measurement errors had the smallest covers. Factors that appeared to contribute to the errors included plant morphology, distribution and the incorrect identification of species. (3) The observer's familiarity with the vegetation enhanced measurement precision but only for the short term. (4) Removal of species with measurement errors of 20% had little effect on the similarity of repetitive measurements. (5) The time of sampling influenced the results. Sampling between mid-June and mid-August, when there was minimal change in the vegetation, virtually eliminated this source of error. (6) Changes in the vegetation need to be >20% before they can be attributed to factors other than annual fluctuation and measurement error. This uncertainty may be a limiting factor in the utilization of plant cover estimates for bio-monitoring purposes.

Design and Operation of ETA, an Automated Ellipsometer

The design and operational features are described for a computer-assisted ellipsometer (called ETA for Ellipsometric Thickness Analyzer), developed to provide reliable. real-time measurement of field-effect transistor gate insulator thickness in a manufacturing environment. ETA illuminates the sample with light of fixed polarization and uses a rotating analyzer to measure the polarization of the reflected light. Sample alignment is done automatically by ETA, so that usually no operator adjustments are required. Fourier analysis of the light transmitted by the analyzer is used to reduce noise and enhance measurement precision. In its normal mode of operation (incident light linearly polarized at 45°), ETA can measure single and double-layer films of SiO2, and Si3N4, in the thickness range of 300 to 800 A with precision comparable to that of conventional ellipsometers. Other modes of operation, which make use of a fixed-position compensator in the incident light path, allow precise measurement of thin films (0 to 300A) and permit use of ETA as a general-purpose ellipsometer. The typical time interval required for wafer alignment, data acquisition, analysis and recorded output of film thickness is about five seconds, and the measurement reproducibility is typically about 1A.