Standard Deviation Of Measurements Research Articles

Spatial variation of acoustic properties is related with mechanical properties of trabecular bone

In clinical applications, ultrasound parameters are measured as an average value over a region of interest (ROI) or as a value at a single measurement point. Due to natural adaptation to loading conditions, trabecular bone is structurally, compositionally and mechanically heterogeneous and anisotropic. Thus, spatial variation of ultrasound parameters within ROI may contain valuable information on the mechanical integrity of trabecular bone. However, this issue has not been thoroughly investigated. In the present study, we aimed at investigating the significance of the spatial variation of ultrasound parameters for the prediction of mechanical properties of human trabecular bone. For this aim, parametric maps of apparent integrated backscattering (AIB), integrated reflection coefficient (IRC), speed of sound (SOS), average attenuation (AA) and normalized broadband ultrasound attenuation (nBUA) were calculated for femoral and tibial bone cylinders (n = 19–20). Further, the effect of time window length on the AIB, variation of AIB within ROI and association between AIB and bone mechanical properties were characterized. Based on linear correlation analysis, spatial variation of AIB, assessed as standard deviation of measurements within ROI, was a strong predictor of bone ultimate strength (r = −0.82, n = 19, p < 0.01). Further, the time window length affected absolute values of AIB and strength of correlation between AIB and bone ultimate strength. Interestingly, linear combination of mean IRC and spatial variation of AIB within ROI was the strongest predictor of bone ultimate strength (r = 0.92, n = 19, p < 0.01). In conclusion, our findings suggest that the measurement of two-dimensional parametric maps of ultrasound parameters could yield information on bone status not extractable from single point measurements. This highlights the potential of parametric imaging in osteoporosis diagnostics.

Measuring thoracic excursion: reliability of the cloth tape measure technique.

To assess the reliability of using a cloth tape measure to determine thoracic respiratory excursion as a measurement of chest expansion or mobility. Physicians and residents experienced in osteopathic manipulative treatment measured thoracic excursion with a cloth tape measure held around the circumference of healthy male subjects' chests at two levels. Upper thoracic excursion measurements were taken at the level of the fifth thoracic spinous process and the third intercostal space at the midclavicular line. Lower thoracic excursion measurements were taken at the level of the 10th thoracic spinous process and the xiphoid process. At peak inhalation and exhalation, three examiners measured thoracic excursion at both levels. In the first session (n=5), examiners measured the same subject inhalation and exhalation. In the second session (n=4), examiners measured separate respiratory cycles. For each session, interexaminer intraclass correlation coefficients (ICCs) were calculated for thoracic excursion, inhalation, and exhalation in the upper and lower positions using a two-way random-effects analysis of variance model. Intraclass correlation coefficients for thoracic excursion ranged from 0.81 to 0.91 (95% confidence interval, 0.69-0.99) at both measurement levels in both sessions. When inhalation and exhalation were considered separately, interexaminer ICCs were 0.99 and greater. Standard deviations for measurements of each subject's thoracic excursion at both levels ranged from 0.5 cm to 0.8 cm with a mean of 0.6 cm. The method of using a tape measure to assess thoracic excursion was highly reliable in men, resulting in ICCs of substantial reliability. The SDs at each level of measurement indicate that this method may be most useful in measuring changes in thoracic excursion that are expected to be 0.6 cm or greater.

Measurement quality estimation of proton-precession magnetometers

Abstract A method for calculating quality estimation of the magnetic field value measured by proton-precession magnetometers from data of single measurement is presented. This method is appropriate for frequency measurement algorithms which process time-series of signal’s zero crossing. Expressions for measurement error estimation are obtained taking into account signal decay and correlated noise. Presented formulas allow a result reliability to be estimated immediately in single measurement and give an opportunity for complex control of a device performance. Correlation and relaxation corrections are given. It was experimentally tested that the standard deviation of measurements is in a good qualitative agreement with presented error estimation.

Fractionated stereotactic radiotherapy for pediatric patients with retinoblastoma

In this report, we discuss the application of a modified Gill‐Thomas‐Cosman (GTC) relocatable head frame to enable fractionated stereotactic radiotherapy (SRT) of infants under anesthesia. This system has been used to treat two infants, ages 12 and 18 months, for bilateral retinoblastoma on a Varian 6/100 linear accelerator. The GTC head frame was used to reproducibly position and treat the orbits of these children to between 2520 cGy and 3960 cGy in 180‐cGy fractions. A standard head and neck tray, with accompanying thermoplastic mask, was adapted to mount to the head frame to enable these treatments. We found the maximum average deviation in the repeat fixations, as compared with the initial fitting data, to be ±2mm. The overall average difference and standard deviation in measurement was 0.47±0.63mm for the first case and 0.19±0.94mm for the second case, with a combined average of 0.35±0.79mm overall from a total of 381 point measurements. The stereotactic treatment plan (Radionics®) incorporated a single isocenter for each orbit and 3 or 4 arcs per isocenter. An intercomparison has been made between this technique and a standard lateral field technique, designed using the stereotactic radiosurgery (SRS) planning system. Dose‐volume histograms and corresponding normal tissue complication probabilities (NTCP) based on pediatric bone growth inhibition have been calculated for each method for the orbital bone areas. We found that the NTCP is reduced from 95% or more in the standard treatment method to 16% or less with SRT. Use of the modified head frame provides excellent setup reproducibility, facilitates access to patients for anesthesia, and reduces the chances of a poor cosmetic result in these growing children.PACS number: 87.53.Ly

Determination of Chloramphenicol Residues in Milk, Eggs, and Tissues by Liquid Chromatography/Mass Spectrometry

A new liquid chromatography/mass spectrometry (LC/MS) method is presented for the determination of chloramphenicol (CAP) residues in milk, eggs, chicken muscle and liver, and beef muscle and kidney. CAP is extracted from the samples with acetonitrile and defatted with hexane. The acetonitrile extracts are then evaporated, and residues are reconstituted in 10mM ammonium acetate--acetonitrile mobile phase and injected into the LC system. CAP is determined by reversed-phase chromatography using an Inertsil ODS-2 column and MS detection with negative ion electrospray ionization. Calibration curves were linear between 0.5-5.0 ng/g for all matrixes studied. The relative standard deviations for measurements by this method were generally <12%, and average recoveries ranged from 80 to 120%, depending on the matrix involved. The method detection limits of CAP ranged from 0.2 to 0.6 ng/g, which are comparable to previously reported results. The proposed method is rapid, simple, and specific, allowing a single analyst to easily prepare over 40 samples in a regular working day.

Role of the Standard Deviation in the Estimation of Benchmark Doses with Continuous Data

For continuous data, risk is defined here as the proportion of animals with values above a large percentile, e.g., the 99th percentile or below the 1st percentile, for the distribution of values among control animals. It is known that reducing the standard deviation of measurements through improved experimental techniques will result in less stringent (higher) doses for the lower confidence limit on the benchmark dose that is estimated to produce a specified risk of animals with abnormal levels for a biological effect. Thus, a somewhat larger (less stringent) lower confidence limit is obtained that may be used as a point of departure for low-dose risk assessment. It is shown in this article that it is important for the benchmark dose to be based primarily on the standard deviation among animals, s(a), apart from the standard deviation of measurement errors, s(m), within animals. If the benchmark dose is incorrectly based on the overall standard deviation among average values for animals, which includes measurement error variation, the benchmark dose will be overestimated and the risk will be underestimated. The bias increases as s(m) increases relative to s(a). The bias is relatively small if s(m) is less than one-third of s(a), a condition achieved in most experimental designs.

Estimation of emissivities in a two-dimensional irregular geometry by inverse radiation analysis using hybrid genetic algorithm

An inverse radiation analysis is presented for estimating the wall emissivities for an absorbing, emitting, scattering media in a two-dimensional irregular geometry with diffusely emitting and reflecting opaque boundaries from the measured temperatures. The finite-volume method was employed to solve the radiative transfer equation for 2D irregular geometry. The hybrid genetic algorithm which contains local optimization algorithm was adopted to estimate wall emissivities by minimizing an objective function, while reducing computation time. It was found that an increase in the standard deviation in measurements significantly deteriorated the estimation of wall emissivities. Thus, a very accurate measurement was required in inverse radiation for better estimation of wall emissivities, especially, in a high temperature environment.

Repeatability and Reproducibility Standard Deviations in the Measurement of Trace Moisture Generated Using Permeation Tubes.

Permeation-tube moisture generators are used in industry as calibrated sources of water vapor and carrier gas mixtures. Measurements were made using three permeation-tube moisture generators of the type used in the semiconductor industry. This paper describes repeatability and reproducibility standard deviations in measurement of moisture concentration from such generators. Repeatability refers to measurements within a system and reproducibility refers to measurements between systems. Two independent methods were used to measure the realized concentration of water vapor. The first measurement, the calculated value, was determined using calibrated permeation rate of permeation-tube and flow rate of dry carrier gas. This is the industrial method of evaluating moisture concentration. The second measurement, the measured value, was determined using the low frost-point generator at the National Institute of Standards and Technology (NIST) and a quartz-crystal-micro-balance. Four pairs of independent measurements for each generator and for six nominal levels in the range from10 nL/L to 100 nL/L were made. The characteristic used to quantify repeatability and reproducibility standard deviations in industrial measurements is the calculated value minus the measured value. Repeatability standard deviation ranges from 1 nL/L to 2 nL/L, approximately. Reproducibility standard deviation ranges from 2 nL/L to 8 nL/L, approximately. The documentary ASTM standard E691-99 was used for both data validation and quantification of the repeatability and reproducibility standard deviations.

Development of adenosine sensor: effect of physiological buffers on activity and sensitivity in adenosine determinations by fast scan voltammetry.

A new fast scan voltammetry (FSV) method was tested in the determinations of adenosine in physiological buffers at pH 7.4. The buffers can be used in the determinations of adenosine in vivo and include 7 x 10(-2) M phosphate, Krebs-Henseleit (K-H) and Hanks' Balanced Salts (HBSS). A new method of fabrication of carbon fiber electrodes (CFEs) by polishing, followed by electrochemical pretreatment (ECP) was developed for the determination. After the ECP of CFE, CFE background current was stable in FSV determinations even though an increase in the background current was observed after the ECP in the buffers at pH 7.4. The sensitivity in FSV determinations of adenosine at the pretreated electrodes was tested in the physiological buffers at the potential scan rate of 500 V s(-1) at pH 7.4. Buffer composition and pH was the same during the ECP of CFE and in the FSV determinations. The sensitivity in the FSV determinations of adenosine at the new CFEs was high, compared to that previously reported at CFEs prepared by other methods, and showed a limited dependence on buffer composition. However, a small increase in buffer pH above 7.4 resulted in a decrease in sensitivity in the determinations of adenosine. The decrease in sensitivity was associated with an additional increase in CFE background current at pH > 7.4. At pH 7.4 best sensitivity and limit of detection was obtained in 7 x 10(-2) M phosphate buffer, where the background current was lowest. The sensitivity was half that in K-H and HBSS. Standard deviation of measurements was ca. 1%. The results demonstrate the feasibility of sensitive FSV determinations of adenosine in physiological buffers at pH 7.4 at CFEs.

Biofeedback-Assisted Relaxation as Part of Preincident Stress-Management Training within a Model of Comprehensive Crisis Intervention: A Pilot Study

The purpose of this study was to explore the potential applicability of biofeedback-assisted relaxation training using frontalis EMG as it might be applied as part of a preincident stress-management training program within a model of comprehensive crisis intervention. For 4 consecutive weeks, 37 treatment participants were taught a different relaxation technique followed by six weekly sessions of frontalis EMG biofeedback. The 25 control participants did not receive the relaxation training, but they did attend six weekly sessions of yoked biofeedback training. Compared to the control group, the treatment group evidenced significant reductions in frontalis EMG readings and individual standard-deviation measures from baseline pretest to baseline posttest. These preliminary data support the use of preincident stress-management training as it might be applied to a systematic, multicomponent approach to crisis management. [Brief Treatment and Crisis Intervention 3:437–443 (2003)]

TESTING THE PRECISION OF THE ELECTRO-OPTICAL DISTANCE METER MEKOMETER ME 5000 ON THE CALIBRATION BASELINE ZAGREB

The paper examines the precision (accuracy) obtained with the Leica-Kem Mekometer ME 5000 distance meter on the calibration baseline Zagreb. A new method for the processing and analysing the measurements on the baseline is presented It provides an estimate of the precision, and, with thefrequency in the distance meter measured, the approximate accuracy as wel.For distances up to 100 m the standard deviation of distance measurement in one direction S = 0.058 mm is obtained For distances in the range of 100 to 3000 m, applying the proposed method of data processing, the standard deviation of a measured distance (measured forward and backward, and on the basis of adjusting all measurements on the baseline) srDII = 0.12mm + 0.21mm. Dkm was obtained in 1988, and in 1996 s′rDII = 0.07 mm − 0.13 mm.Dkm + 0.37mm.D2km.

Gas chromatographic analysis of polyhydroxybutyrate in activated sludge: a round-robin test

Polyhydroxyalkanoates (PHA) and poly-beta-hydroxybutyrate (PHB) in particular have become compounds which is routinely investigated in wastewater research. The PHB analysis method has only recently been applied to activated sludge samples where PHA contents might be relatively low. This urges the need to investigate the reproducibility of the gas chromatographic method for PHB analysis. This was evaluated in a round-robin test in 5 European laboratories with samples from lab-scale and full-scale enhanced biological phosphorus removal systems. It was shown that the standard deviation of measurements in each lab and the reproducibility between the labs was very good. Experimental results obtained by different laboratories using this analysis method can be compared. Sludge samples with PHB contents varying between 0.3 and 22.5 mg PHB/mg sludge were analysed. The gas chromatographic method allows for PHV, PH2MB and PH2MV analysis as well.

Monte carlo sampling for microsegregation measurements in cast structures

The statistical random meshing method used for the measurement of microsegregation in a cast microstructure was simulated using the Monte Carlo method. The standard deviation of measurements, the effect of sample size, the electron beam diameter, and the scattering on obtained solute partition coefficients were analyzed and evaluated. It is found that a sample size between 100 to 200 points can give satisfactory measurement. A method to use the measured segregation profiles in solid is suggested. Partition coefficients obtained by the statistical random sampling method are found to represent real segregation characteristics in the alloys.

THE VALIDATION OF THE ROBUST INPUT ESTIMATION APPROACH TO TWO-DIMENSIONAL INVERSE HEAT CONDUCTION PROBLEMS

A novel adaptive and robust input estimation inverse methodology of estimating the time-varying unknown heat flux, named as the input, on the two active boundaries of a 2-D inverse heat conduction problem is presented. The algorithm includes using the Kalman filter to propose a regression model between the residual innovation and the two thermal unknown boundaries flux through given 2-D heat conduction state-space models and noisy measurement sequence. Based on this regression equation, a recursive least-square estimator (RLSE) weighted by the forgetting factor is proposed to on-line estimate these unknowns. The adaptive and robust weighting technique is essential since unknowns input are time-varied and have unpredictable changing status. In this article, we provide the bandwidth analysis together with bias and variance tests to construct an efficient and robust forgetting factor as the ratio between the standard deviation of measurement and observable bias innovation at each time step. Herein, the unknowns are robustly and adaptively estimated under the system involving measurement noise, process error, and unpredictable change status of time-varying unknowns. The capabilities of the proposed algorithm are demonstrated through the comparison with the conventional input estimation algorithm and validated by two benchmark performance tests in 2-D cases. Results show that the proposed algorithm not only exhibits superior robust capability but also enhances the estimation performance and highly facilitates practical implementation.

Comparison of Methods for Cutting Fluid Performance Testing

A comparison is made of those methods for cutting fluid performance evaluation that involve metal cutting operations under controlled laboratory conditions. An analysis in terms of repeatability, resolution and cost is carried out, based on results from comprehensive experimental investigations in turning, drilling, milling, reaming, and tapping. Different workpiece materials, such as carbon steels, stainless steels, and aluminium alloys, as well as different kinds of cutting fluids, including water based products, straight mineral oils, and vegetable oil based formulations, are considered. The analysis is carried out grouping the tests according to the main measurand: tool life, cutting forces, and workpiece surface finish. The ratio σ/ρ, where a is the standard deviation of measurements and ρ the range of variability of test results, was introduced to express the relative resolution of a test, and a cost model was developed. It was concluded from the analysis that tool life tests are connected with limited repeatibility (σ=10–50%) and resolution (σ/ρ ranging from 0.25–0.75), with costs ranging from 1000€ to 2000€. Tests based on cutting forces are connected with a much better repeatibility and resolution, featuring values for σ in the range 0.5–6% and a σ/ρ ratio of approximately 0.2, with test costs of about 500€. Surface finish tests feature repeatabilities of approximately 50% and resolutions of 0.3–0.4, with costs of approximately 1000€.

Direct Analysis of Coffee and Tea for Aluminium Determinationby Electrothermal Atomic Absorption Spectrometry

A method for direct analysis of tea and coffee samples by using electrothermal atomic absorption spectrometry is described. Coffee and tea from different sources were analyzed without digestion step. For slurry analyses the samples were ground, sieved at 105 μm and then suspended in 0.2% v/v HNO3 and 10% v/v Triton X-100 medium. For liquid phase aluminium determination the samples were prepared in the same way and only the liquid is introduced directly into the graphite furnace. Calibration was performed by aqueous standards for both cases and the determinations were carried out in the linear range between 50 and 250 μg L−1. The characteristic mass of aluminium and the detection limit were 45 pg and 2 μg L−1, respectively. Using a typical 0.1% m/v coffee slurry sample, the relative standard deviation of measurements (n=15) for repeatability was about 8.2%.

A technique for global assessment of respiratory muscle performance at different lung volumes

A system for noninvasive assessment of an all-inclusive function of respiratory muscles at different lung volumes is presented. The apparatus was based on the interrupter technique and facilitated simultaneous measurements of mouth pressure and airflow rate during dynamic or quasi-static manoeuvres. In this study, mouth pressure values were continuously acquired during and after interruption of a forced inspiratory or expiratory manoeuvre for as long as the subject could sustain an elevated mouth pressure against the obstructed opening. These measurements provided information on both muscle strength and power. A total of 420 forced maximal inspiratory and expiratory manoeuvres performed by six healthy subjects were monitored at different lung volumes. The pattern of maximal pressure-time curves was consistent for the same subject regardless of lung volume. Similar values of maximal mouth pressure can be generated by healthy subjects by using either a flange-style mouthpiece or facial mask. For both methods mouth pressure shows a significant ( p < 0.05) second order dependency on lung volume for both inspiration and expiration. The standard deviation of measurements from a single subject about a second order curve is of the order of 5-15%. The findings of interchangeability between methods of measurement may be useful in allegedly non-compliant patients. Keywords: mouth pressure, respiratory muscle strength, respiratory muscle endurance, interrupter technique

A NEW INSTRUMENTATION FOR MEASURING THE SMALL SCALE MALDISTRIBUTION OF LIQUID FLOW IN TRICKLE BEDS

A measurement system was developed to study the small scale liquid distribution in a trickle bed reactor. The system can measure the radial profile of liquid flow rate quasi-simultaneously with a rectilinear array of 29 measuring cells with 10×10 mm2 area, or the liquid flow rate with a single cell dynamically. The liquid flow rate in each cell was determined according to an electric conductivity method. A carefully devised system of calibration guarantees the standard deviation of measurement below 2%.

Investigation of conductometric humidity sensors

Sensors for determining humidity in air have been described and investigated. Sensing film of the devices was prepared from polyvinylalcohol and graphitized carbon black disperse phase. The composition, thermal treatment and design of sensing films were investigated and optimized. An optimized humidity sensor has better metrological parameters as compared with its prototype (response time ∼45 s, detection limit 0.17%, slope 6.25 ± 0.05 Θ/R.H., standard deviation of measurement 0.15%, standard deviation of analytical signal in the graduation equation 8.29Θ). Such construction of sensors have prospects in analytical practice.

Soil Suction Dispersion and Statistical Analysis with Depth at the Medford Airport

The use of soil suction measurements has steadily increased in geotechnical practice. A current standard test procedure that describes the use of laboratory filter papers as passive sensors to measure the soil matric and total suction is ASTM D5298-94. The principal objective of the research presented here was to evaluate dispersion of suction measurements with depth using the filter paper method described in the ASTM standard. In a single test boring to a depth of 5.33 m, 35 samples were taken at intervals of 152.4 mm. Each sample was separated into four replicate samples. The matric and total suction of each of the 35 sample intervals were then measured, resulting in a total of 278 suction measurements. To manage this volume of tests, the sample size was split approximately in half, and each portion was separately tested. This approach led to severall insights into the test procedure, such as the effect of delay in transferring the filter paper from the specimen container into the metal container. Sampling and testing are described. The dispersion of both the total and the matric suction measurements was characterized in three ways: the range of measurements in each sample interval, the standard deviation of measurements in each sample interval, and an error function defined as the difference between each measurement and the mean for the sample interval. Each of these statistics was plotted as a histogram. A chi-squared test was applied to measure the goodness-of-fit of a t-distribution fitted to the error as defined by the difference between each measurement and the mean for that sample interval. Results indicate precision for total and matric suction measurements of 0.0540 log kPa within one standard deviation. Analysis does not indicate a substantial difference between the error associated with total suction measurements and that associated with matric suction measurements. A brief description of the conventional geotechnical site characterization is presented for the Medford Airport.