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At least 1,153 records · Page 64Linked to original sources
PubMed1997

Body composition analysis by DEXA by using dynamically changing samarium filtration.

Dual-energy X-ray absorptiometry (DEXA) has a high accuracy for body composition analysis but is influenced by beam hardening and other error sources in the extremes of measurement. To compensate for beam hardening, the Norland XR-36 introduces a dynamically changing samarium filtration system, which depends on the current-absorber thickness. With this system we found a good agreement (r = 0.99) between reference and measured amounts of tissue or fat percentages in a plastic phantom and in smaller (approximately 0.5-4 kg) and larger (approximately 5-20 kg) piles of tissue (ox muscle and lard). Scans of six healthy volunteers covered with combinations of beef and lard (approximately 5-15 kg) showed a good agreement (r = 0.99) between reference and DEXA values of added soft tissue mass and fat percentage. We conclude that the DEXA method (and, in particular, the Norland XR-36 using dynamic filtration) has a high accuracy for body composition analysis. It has a potential for gaining status as a reference method in the future and may presently be used as a supplement to the traditional methods for body composition analysis.

Absorptiometry, Photon↗
PubMed2004

DNA-free RNA preparations from mycobacteria.

BACKGROUND: To understand mycobacterial pathogenesis analysis of gene expression by quantification of RNA levels becomes increasingly important. However, current preparation methods yield mycobacterial RNA that is contaminated with chromosomal DNA. RESULTS: After sonication of RNA samples from Mycobacterium smegmatis genomic DNA is efficiently removed by DNaseI in contrast to untreated samples. CONCLUSIONS: This procedure eliminates one of the most prevalent error sources in quantification of RNA levels in mycobacteria.

DNA, Bacterial↗
PubMed2002

Proposed algorithm for phase unwrapping.

A new, to our knowledge, two-dimensional phase-unwrapping algorithm is proposed. The algorithm, which is based on the global continuity of physical information (e.g. the three-dimensional surface profile of an object) being measured, uses the principle of least-phase difference to rectify errors caused by an erroneous 2pi-phase jump in the initial unwrapped phase map obtained by the conventional phase-unwrapping method. Experimental results show that the proposed algorithm works well on a phase map that contains error sources, such as noises, phase discontinuity of more than pi, and insufficient sampling. Moreover, the algorithm is most suitable for unwrapping a phase map generated during shape measurement with a step-change surface on the test object, which is usually a critical problem in shape measurement.

Journal Article↗
PubMed2003

Fourier-transform phase-shifting interferometry.

Phase-shifting interferometry is a preferred technique for high-precision surface form measurements, but the difficulty in handling the intensity distortions from multiple-surface interference has limited the general use of the technique to interferometer cavities producing strict two-beam interference. I show how the capabilities of phase-shifting interferometry can be extended to address this problem using wavelength tuning techniques. The basic theory behind the technique is reviewed and applied specifically to the measurement of parallel plates, where surfaces, optical and physical thickness, and homogeneity are simultaneously obtained. Basic system requirements are derived, common error sources are discussed, and the results of the measurements are compared with theory and alternative measurement methods.

Journal Article↗
PubMed2003

Atmospheric turbulence characterization with the Keck adaptive optics systems. I. Open-loop data.

We present a detailed investigation of different methods of the characterization of atmospheric turbulence with the adaptive optics systems of the W. M. Keck Observatory. The main problems of such a characterization are the separation of instrumental and atmospheric effects and the accurate calibration of the devices involved. Therefore we mostly describe the practical issues of the analysis. We show that two methods, the analysis of differential image motion structure functions and the Zernike decomposition of the wave-front phase, produce values of the atmospheric coherence length r0 that are in excellent agreement with results from long-exposure images. The main error source is the calibration of the wave-front sensor. Values determined for the outer scale L0 are consistent between the methods and with typical L0 values found at other sites, that is, of the order of tens of meters.

Journal Article↗
PubMed2004

Testing and applicability of the UPC-ZEBRA interferometer as a phasing system in segmented-mirror telescopes.

In segmented-mirror telescopes, wave-front discontinuities caused by segment misalignment are a major problem because they severely degrade optical performance. While angular misalignments are usually measured with deflectometric wave-front sensors (e.g., Shack-Hartmann sensors), a number of techniques have been proposed for the measurement of vertical discontinuities (pistons). In earlier papers we presented an instrument called UPC-ZEBRA that uses a novel interferometric technique to measure piston error during the daytime with an uncertainty of 5 nm within a 30-microm range. Here we present the most representative results obtained during the testing stage and a detailed analysis of error sources. The main modifications to be introduced for the instrument's use as a phasing calibration system are also outlined.

Journal Article↗
PubMed2005

Accurate polarization measurements with a dual photoelastic modulator.

Measurements of the polarization effects in multimirror experiments by using a dual photoelastic modulator are described. The effect of single and multiple mirrors in polarization measurements in two and three dimensions is discussed, and experimental results show how symmetrical placement of mirrors in three-dimensional geometry can eliminate changes in the polarization. Calibration procedures for a dual photoelastic modulator and potential error sources such as misalignment of analyzer, signal dc offset, and neglect of aperture size are presented. Mirror-surface evolution and how it can disturb the polarization measurement are also addressed.

Journal Article↗
PubMed2006

Effect of wavefront error on 10(-7) contrast measurements.

Received October 11, 2005; accepted November 10, 2005; posted December 2, 2005 (Doc. ID 65234) We have measured a contrast of 6.5 x 10(-8) from 10 to 25 lambda/D in visible light on the Extreme Adaptive Optics testbed, using a shaped pupil for diffraction suppression. The testbed was designed with a minimal number of high-quality optics to ensure low wavefront error and uses a phase-shifting diffraction interferometer for metrology. This level of contrast is within the regime needed for imaging young Jupiter-like planets, a primary application of high-contrast imaging. We have concluded that wavefront error, not pupil quality, is the limiting error source for improved contrast in our system.

Journal Article↗
PubMed2004

Hapten labeling of nucleic acids for immuno-polymerase chain reaction applications.

A method for the ultrasensitive protein detection in the range of 0.01 to 10,000 amol of the model antibody anti-mouse-IgG from rabbit is described, using a combination of Immuno-polymerase chain reaction (PCR) and PCR-enzyme-linked immunosorbent assay (PCR-ELISA). The antibody was first immobilized on antigen-coated microplates; in a second step, a commercially available DNA-labeled species-specific antibody was added; and finally the deoxyribonucleic marker was amplified in a PCR step, including twofold labeling with biotinylated primer and a hapten-coupled nucleotide during PCR. Subsequently, the labeled PCR product was immobilized on streptavidin-coated microplates and detected with an antibody-enzyme conjugate. The protocol could easily be adapted to the detection of other antibodies or antigens by exchanging the antigen-specific antibody. Several modifications of the method as well as optimization steps, potential error sources, and countermeasures are discussed.

Antibodies↗
PubMed2002

[Examining the accuracy of mechanical stiffness of the C-arm in navigation procedures].

During x-ray based navigation a number of errors causes distortions in the output image. These errors lead to a fail position of the surgical instrument relative to the patients anatomy. To minimize these influences and to develop dewarping techniques an exact error source identification is necessary. This paper examines the mechanical shift of the x-ray source relative to the image intensifier. Therefore three measurement methods will be used: an optical tracking system, a x-ray opaque probe and the integrated laser cross of the C-arm. The results of this examination show a notable shift of the C-arm geometry. However, no hysteresis effects could be found.

Algorithms↗
PubMedDate not supplied

Simulating nitrogen dynamics in agricultural soils fertilized with pig slurry and urea.

Within the framework of an interregional project in the Emilia Romagna region of northern Italy, the coupled MACRO-SOILN model was chosen to estimate soil protective capacity against pollutants. The aim of our study was to evaluate the model to better identify key parameters and processes that influence N losses in agricultural soils. Nitrate N content was monitored in soil under corn (Zea mays L.) fertilized with urea and/or pig slurry, in two field experiments performed on four different soils: a Fienili clay, a Barco-like silt, a Sant'Omobono silt loam, and a La Boaria silty clay soil. Measurements were compared with model predictions. For all soils, nitrate content was underestimated on average by 24 to 88% at lower N rates; it was overestimated by 1 to 104% at higher N rates. The root mean square error (RMSE) was equal to 81.1%. Simulation of crop N uptake and soil water flow, estimation of the ammonia losses at pig slurry spreading, and N transformation parameter setting were considered as possible error sources. The calibration of crop N uptake gave rise to good model efficiency index values. The RMSE for the simulation of soil water content varied between 9.8 and 20.2%. A more accurate setting of the ammonia losses and of the feces transformation parameter values could allow the RMSE for the simulation of soil nitrate content to be reduced by no more than 10 to 15%. It is possible for the model not to include the simulation of processes that could have relevant effects on the soil N dynamics.

Agriculture↗
PubMed1998

[On the "system repeatability" specified in the operating conditions for HPLC assay in JP monographs].

The system repeatability tests in the operating conditions for the HPLC assay by absolute calibration method are specified in 9 monographs in JP13 (Part 1). The reasonableness of the specified system repeatability, expressed in relative standard deviation(%), is discussed in consideration with the specified content and also the probability of Type 1 error(alpha). For simplification, it was assumed that the variance due to the analytical system(sigma s2) is equal to that due to other error sources(sigma e2). Based on the above considerations, it was concluded that the present specification of system repeatability(sigma s) in JP monographs is not always reasonable and some of them should be reexamined following to the described considerations in the text.

Chromatography, High Pressure Liquid↗
PubMed1999

[A reliability analysis of FACES III (the version in Spanish). Family Adaptability and Cohesion Evaluation Scales].

OBJECTIVE: To determine through five methods (Cronbach's alpha, split, Guttman method, parallel and strict parallel) the confidence coefficient of FACES III, instrument validated on spanish version, and to evaluate it's consistency with these five statistical methods. DESIGN: Descriptive, cross-sectional. SETTING: Tlalpan Area, south of Federal District, México, divided into geo-statistical zones. PATIENTS AND OTHER PARTICIPANTS: A randomised sample of 270 dwellings with proportional coverage, based on 17,895 ordinary dwellings of the area. INTERVENTION: Domicile survey using FACES III (Family Adaptability and Cohesion Evaluation Scales); April-May 1995. MEASUREMENTS AND MAIN RESULTS: The confidence coefficient of FACES III spanish version was calculated using no standardised Cronbach's Alpha = 0.69; split I = 0.73 and split II = 0.66; Guttman method = 0.75; parallel = 0.69 and strict parallel = 0.53. CONCLUSIONS: Cronbach's coefficient demonstrated more advantages than the other statistical methods in relation with the ordinal measurement scale of FACES III. We suggest to take into consideration three important aspects for the correct confidence analysis of this kind of instruments: Variance analysis depending on the scale of items (F test, Friedman or Cochran) Inter-items interactions analysis (nonadditivity) and the use of the balance value as purge element of error' source. Analysis of Tukey estimate, coefficient of concordance (W) and Hotelling's T squared. It's necessary the evaluation and analysis of this aspects before the report of confidence's coefficient values whose can have hidden skew.

Adaptation, Psychological↗
PubMed2000

Inertially compensated force plate: a means for quantifying subject's ground reaction forces in non-inertial conditions.

A system for the measurement of forces in noninertial reference systems, and a possible solution to compensate force plate readings by means of accelerometers were investigated. If the force plate can be considered a rigid body, six linear accelerometers can measure all linear and angular accelerations of the instrument in 3-D space. However, by using nine accelerometers in a proper layout, the force and moment generated by the movement of the plate can be quantified in a way that eliminates the errors due to the time integration of the accelerations. By doing so, no temporal limits are imposed to the compensation. A one degree of freedom numerical model was implemented to evaluate the importance of main error sources in the estimation of inertial forces using accelerometers with different technical characteristics. The inertial compensation of the force plate along one axis was tested, and the performances of a piezoelectric accelerometer and a capacitive accelerometer were compared. With the proposed inertially compensated force plate, accelerations up to 5 g's in amplitude and frequencies from 0 to 100 Hz can be compensated by means of capacitive accelerometers. Such a device can be used for force measurements in moving vehicles, or any situation where the surface on which the instrument is mounted is moving or vibrating.

Acceleration↗
PubMed2001

[Organizational fault in networked structures].

Medical malpractice may result from a violation of organizational rules, which are supposed to protect the patient. The high requirements of jurisdiction concerning the medical duty of care in organizational sequences lead to increased security and control levels of data transmission within medical networked structures. To achieve an optimized use of telemedical possibilities and to minimize technical error sources, it is necessary to merge the existing communication systems. The store of knowledge that is obtained through telemedicine must not reduce the specialist standard. The telemedical application requires a documented informing and consent of the patient about the extent, the risk and the alternatives of the data transfer.

Computer Communication Networks↗
PubMedDate not supplied

Reliable pKw values from potentiometric titrations: the striking effect of the titration final added volume.

Errors affecting the estimation of the ionic product of water from the potentiometric titration of weak acids have been analysed. A Fortran programme has been developed in order to simulate experimental titration data sets. This programme allows one to isolate experimental error sources and analyse their effect upon the final fitted equilibrium constant. pKw dependence with titration final added volume and the pK value of the weak acid, predicted with the simulation programme are coincident with experimental data, suggesting that obtaining reliable pKw values entails using experimental data of titrations up to a sufficiently large hydroxyl concentration which depends on the value of pK.

Environmental Monitoring↗
PubMed1994

Developments and prospects for population statistics in countries of the former Soviet Union.

"This paper examines recent developments and prospects for population statistics in the former Soviet Union, whose dissolution provides both opportunities and problems. It is important for scholars to be aware of past limitations of Soviet data, since the formation of independent states has neither removed bureaucratic impediments to the production of high-quality data, nor has it led to a population more ready to answer questions fully. Temporarily at least, there is a decrease in the amount and comparability of available information, and in some instances, in its quality. We begin with an overview of the system used to gather population statistics in the former Soviet Union and its inherent problems. We then discuss the challenges faced by the newly independent countries and the changes they need to make to achieve global comparability, including a shift toward the use of standard international definitions and away from political restrictions on data availability."

Data Collection↗
PubMed1989

Age at first marriage and age at first birth.

This paper presents findings on patterns of age of 1st marriage and age of 1st birth for 41 countries participating in the World Fertility Survey program. The age distribution of 1st marriage and 1st birth is summarized with 3 statistics: the mean, the standard deviation, and the proportion ever experiencing the event. The particular method of estimation is based on a model that ensures that estimates for all cohorts are comparable, even though some women have completed their reproductive experience while others have not. The analysis provides insights into sources of error in the reporting of age at 1st birth. In addition, trends and cross-country patterns are documented and conclusions are drawn about the adequacy of these statistics for the description of patterns of age at 1st birth and age at 1st marriage.

Age Factors↗