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Raw Measurements (raw + measurement)

Distribution by Scientific Domains

Chemistry	50%

Selected Abstracts

A comparative study of linear regression methods in noisy environments

JOURNAL OF CHEMOMETRICS, Issue 12 2004
Marco S. Reis
Abstract With the development of measurement instrumentation methods and metrology, one is very often able to rigorously specify the uncertainty associated with each measured value (e.g. concentrations, spectra, process sensors). The use of this information, along with the corresponding raw measurements, should, in principle, lead to more sound ways of performing data analysis, since the quality of data can be explicitly taken into account. This should be true, in particular, when noise is heteroscedastic and of a large magnitude. In this paper we focus on alternative multivariate linear regression methods conceived to take into account data uncertainties. We critically investigate their prediction and parameter estimation capabilities and suggest some modifications of well-established approaches. All alternatives are tested under simulation scenarios that cover different noise and data structures. The results thus obtained provide guidelines on which methods to use and when. Interestingly enough, some of the methods that explicitly incorporate uncertainty information in their formulations tend to present not as good performances in the examples studied, whereas others that do not do so present an overall good performance. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Bladder diary patterns in detrusor overactivity and urodynamic stress incontinence,

NEUROUROLOGY AND URODYNAMICS, Issue 6 2007
Matthew Parsons
Abstract Aims Our aims were: (1) to describe and compare frequency-volume and incontinence episode patterns in patients with urodynamic stress incontinence (USI) and detrusor overactivity (DO) as measured by a hand-written and computer-analyzed bladder diary and (2) to compare degree of separation between these clinical groups produced by raw diary measurements and after age- and total-volume-adjustment against a reference population. Materials and Methods We studied 58 patients with USI, 29 with DO, and 22 with both USI and DO. From 3-day hand-written and computer-analyzed bladder diaries, we calculated average and maximum volume voided (Vol/Void), voiding frequency and volume voided over 24 hr, and number, size and type (whether accompanied by activity or urge) of incontinence episodes. Results Compared to the USI patients, the DO patients tended to have (1) higher voiding frequency, (2) lower Vol/Void, (3) more urge-related, than activity-related leaks, (4) smaller volume, and equally frequent leaks and (5) more severe incontinence symptoms. The age- and volume-adjusted percentiles better separated the USI and DO groups' frequency and volume measurements than did the raw measurements. Unexpectedly high percentages of our USI patients had low Vol/Void measurements, high voiding frequency, and predominantly urge-related leaks. A subgroup of 29 USI patients with "low" (average volume <30th reference population percentile) Vol/Void measurements had high incidences of urgency and urge-related leaks. Conclusions Reference population percentiles better separate the frequency/volume patterns of USI and DO than do the raw measurements. We found a subgroup of USI patients that had an OAB-like clinical picture. Neurourol. Urodynam. 26:800,806, 2007. © 2007 Wiley-Liss, Inc. [source]

Isotopic metrology of carbon dioxide.

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 8 2003

We report a pilot study of high-precision differential isotope ratio measurements made on replicate samples of pure carbon dioxide using three instruments of identical manufacture. Measurement protocols were designed to explore the effects of sample size, ion source conductance, and inlet changeover equilibration time on the raw measurements. Our goal was better understanding of factors that influence these measurements in order to establish procedures for highly reproducible and accurate determinations of Reference Material (RM) isotopic compositions. Evaluation and modeling of reported data illuminated effects consistent with two instrumental memory sources,one short-lived (t½,,,10 s) and the other long-lived (t½,,,6,10,min), uncompensated by normal background measurements,that can significantly influence measurements made by the dual inlet method. These biases, proportional to the difference in isotopic compositions between the measured sample and reference gases, decrease in magnitude with increasing sample size, source conductance, and equilibration time. We observed biases as high as 0.1, per 10, difference between sample and reference gases. These memory sources may be responsible for measured ,13C values of RMs generally being highly reproducible within any single laboratory but less reproducible among independent laboratories. The magnitude of the bias is consistent with the ranges of ,13C values reported in prior laboratory intercomparisons. Uncertainties are most likely due to high and variable long-lived memory among the instruments tested. Published in 2003 by John Wiley & Sons, Ltd. [source]

Application of SSM/I satellite data to a hurricane simulation

THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 598 2004
Shu-hua Chen
Abstract The impact of Special Sensor Microwave/Imager (SSM/I) data on simulations of hurricane Danny is assessed. The assimilation of SSM/I data is found to increase the atmospheric moisture content over the Gulf of Mexico, strengthen the low-level cyclonic circulation, shorten the model spin-up time, and significantly improve the simulation of the storm's intensity. Two different approaches for assimilating SSM/I data, namely assimilating retrieved products and assimilating raw measurements, are further compared. The data-assimilation analyses from these two approaches give different moisture distributions in both the horizontal and vertical directions in the storm's vicinity, which may potentially affect the simulated storm's development; however, the simulated storm intensities are considered comparable for the Danny case. From sensitivity tests performed in this study, it is also found that the choice of the observational error variances could be potentially important to the model simulations. Copyright © 2004 Royal Meteorological Society. [source]