Unreliable Measurement Research Articles

Impedance cardiography in cardiac surgery patients: abnormal body weight gives unreliable cardiac output measurements.

To study the accuracy of cardiac output measurement by means of Electrical Impedance Cardiography (EIC) in post-cardiac surgery patients. In a prospective study, we compared cardiac output measurements by means of thermodilution (COTD) with impedance cardiographic-derived values (COEIC) in 37 mechanically ventilated patients after cardiac surgery. Both methods were used simultaneously. COEIC values were weakly correlated with COTD in the total group when the equation of Sramek-Bernstein was employed to calculate COEIC (r = 0.60, P < 0.001, mean difference and standard deviation: -0.06 +/- 1.25 l.min-1). After exclusion of the 12 patients whose body weight differed > 15% from their ideal body weight, no significant difference was found between the mean values (5.40 +/- 1.80 l.min-1 (COEIC) vs 5.31 +/- 1.69 l.min-1, n = 25) while the correlation coefficient increased substantially (r = 0.85, P < 0.001, mean difference and standard deviation: 0.09 +/- 0.96 l.min-1). The results of this study indicate that weight is a very important factor in unreliable measurement of CO by impedance cardiography in cardiac surgery patients. The calculation equation as proposed by Sramek and Bernstein is not accurate enough in patients with more than 15% of weight deviation. Therefore, the use of impedance cardiography in these patients is of limited value until an accurate correction factor has been developed.

Reliability of Wear Volume Measurement Approaches in Relation to the Effect of Surface Finish on Friction and Wear of Al2O3

Wear measurements are notoriously variable. Even the experiments with the same type of material and test machine can give significantly different results. Such discrepancies are mostly due to a lack of adequate control of test conditions and unreliable measurement techniques. Specification and control of certain tribological quantities are a necessary prerequisite for obtaining reproducible and comparable results. To proceed forward in this direction, it is essential to review and analyze the existing test procedures and measuring techniques. In this study, the authors investigated the reliability of the most common wear volume measurement approaches and explored the influence of surface finish on the friction and wear performance of Al2O3 ceramics. The wear tests were performed with a pin-on-disc machine on polished and ground surfaces of Al2O3 disks. The wear volume was measured from height displacement, weight loss, and from worn surface profilometry. The results indicated that the wear volume measurements by surface profilometry and height displacement (by transducer) were highly reliable. The wear rates of ground and polished alumina were in the order of 10−7 mm3 /m·N. Finally, for the specific surface roughness range (Ra = 0.03 to 0.4 μm) explored in this study, the surface finish was only important during the initial run-in period.

Reliable substrate temperature measurements for high temperature AlGaAs molecular-beam epitaxy growth

We describe a reproducible and precise temperature control system for the molecular beam epitaxial growth of AlGaAs at substrate temperatures in the 700 °C range. Coating of the optical pyrometer window was observed to dramatically affect the pryometer readings making it an unreliable temperature measurement technique. By observing pyrometer interference oscillations during both GaAs and AlGaAs epitaxy, the Ga desorption rate during AlGaAs growth was estimated. The known temperature dependence of the Ga desorption rate allowed the substrate temperature to be calculated, and corrected, when necessary, during the growth. This method allowed the absolute AlGaAs substrate temperature to be controlled within ±3 °C over a six month production cycle.

Identifying Culture-Specifics in the Content and Structure of Values

Using data from 88 samples from 40 countries, the authors reevaluate the propositions of a recent values theory and provide criteria for identifying what is culture-specific in value meanings and structure. They confirm the widespread presence of 10 value types, arrayed on a motivational continuum, and organized on virtually universal, orthogonal dimensions: Openness to Change versus Conservation and Self-Transcendence versus Self-Enhancement. Forty-four values demonstrate high cross-cultural consistency of meaning. In the average sample, about 16% of single values diverge from their proto-typical value types, and one pair of motivationally close value types is intermixed. Test-retest and randomly split sample analyses reveal that some two thirds of deviations represent unreliable measurement and one third represent culture-specific characteristics. Ways to identify and interpret the latter are presented.

Estimation of blood pressure-related parameters by electrical impedance measurement.

In 13 healthy volunteers a computerized experimental set-up was used to measure the electrical impedance of the upper arm at changing cuff pressure, together with the finger arterial blood pressure in the contralateral arm. On the basis of a model for the admittance response, the arterial blood volume per centimeter length (1.4 +/- 0.3 ml/cm), the venous blood volume as a percentage of the total blood compartment (49.2 +/- 12.6%), and the total arterial compliance as a function of mean arterial transmural pressure were estimated. The effective physiological arterial compliance amounted to 2.0 +/- 1.3 microliters.mmHg-1.cm-1 and the maximum compliance to 33.4 +/- 12.0 microliters.mmHg-1.cm-1. Additionally, the extravascular fluid volume expelled by the occluding cuff (0.3 +/- 0.3 ml/cm) was estimated. These quantities are closely related to patient-dependent sources of an unreliable blood pressure measurement and vary with changes in cardiovascular function, such as those found in hypertension. Traditionally, a combination of several methods is needed to estimate them. Such methods, however, usually neglect the contribution of extravascular factors.

On fault-tolerant observers

The problem of designing asymptotic observers for multioutput systems with one unreliable output measurement is addressed. It is shown that observers designed on the basis of observability indexes are not fault tolerant, and an observer for linear systems which tolerates failures in one a priori known output is given. The results are extended to nonlinear systems with no inputs: it is pointed out that the proposed design procedure may enlarge the class of nonlinear systems for which a nonlinear observer can be obtained.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Unreliable measurement

Unreliable measurement

The reliability of duplex derived haemodynamic measurements in the assessment of femoro-distal grafts

The aim of this study was to assess the reliability of flow and velocity measurements obtained in the postoperative period by duplex scan monitoring of femoro-distal bypass grafts. Three points along each of 24 grafts were studied by 2 independent observers using a Diasonics 300 DRF duplex scanner. Results obtained for diameter, peak systolic velocity (PSV) and flow were compared. The mean PSV for all points studied was 70 cm/s (S.D. = 14.5): comparing observers the calculated experimental error (EE) for all points was 11 cm/s (coefficient of EE = 15%). In contrast, the experimental error for flow was 44.5 ml/min (coefficient of EE = 31). The mean flow for all grafts was 142 ml/min (S.D. = 66.5). Flow at the different points of individual grafts could also be compared since routine postoperative intravenous angiography showed all grafts to be devoid of branches. The coefficient of experimental error for flow was 58%. Four of the grafts studied were found to have asymptomatic stenoses. These 4 grafts had low flows (mean = 42 ml/min) but so did 7 other non-stenotic grafts. Although PSV measurements entailed a 15% error, the mean change in PSV in relation to the stenoses was 350%. These data suggest that flow is an unreliable measurement. PSV is more reliable, changes exponentially with luminal diameter and can detect, and perhaps grade, asymptomatic stenoses.

Changes in the redox potential and malate dehydrogenase activity of activated sludge

Abstract A 10l activated sludge plant, treating settled sewage, was operated in a fill‐and‐draw mode with aeration times of 4.5, 12 and 24 h followed by a settlement period of 30 min. In any aeration period, the output from a redox electrode showed a characteristic inflection in the potential/time trace. However, when two electrodes were used, the absolute values differed by as much as 70mV. This suggested that any single redox potential measurement was an unreliable measurement for control of an activated sludge system. Nevertheless, the activity of malate dehydrogenase could be correlated with the redox potential.

給水器具発生音の実験室測定法の検討

In accordance with the laboratory measurement methods of the noise generated by water supply appliances and equipment specified in the ISO Standards, the noise shall be evaluated according to the noise level (Ls) specified in the installation noise standards. In the previous measurements conducted by the authors using the ISO method the sounds levels measured exhibited rather poor uniformity and reproducibility for reasons not ascertainable at that time. In the attached papers it is shown that the main reason for unreliable measurement values was intrusion of air bubbles in the test water pipes. Now accurate measurement values of the noise emitted by the water supply appliances and equipment have been successfully obtained by preventing such intrusion of air bubbles into the test water pipes.

Flatband potential of a p-type phosphide electrode

Differential-capacitance measurements have been performed on p-type GaP in order to determine its flatband potential in buffered electrolytic solutions at various pH. The reproducibility of the flatband-potential determination is greatly improved by chemical etching of the semiconductor surface. The slope of the flatband-potential–vs–pH curve is that predicted by the Nernst equation. Deriving the acceptor concentration is hampered by the unreliable measurement of the effective area of the electrode which is in contact with the electrolyte.

Fecal enzyme assay as an aid to the diagnosis of pancreatic exocrine insufficiency

Trypsin and chymotrypsin activity in feces were measured in various gastrointestinal disorders. The level of chymotrypsin activity was found to be a somewhat unreliable measurement of exocrine pancreatic function; low values for trypsin activity were of no diagnostic significance.

Effect of Point Imperfections on the Electrical Properties of Copper. II. Thermoelectric Power

The changes in the thermoelectric power of copper due to the presence of interstitials and vacancies have been calculated in the free electron approximation. It is found that the changes for concentrations of defects encountered in experiments on radiation damage due to massive charged particles are, at liquid nitrogen temperature, of the same magnitude as the absolute thermoelectric power of pure copper. Both interstitials and vacancies tend to reduce the absolute thermoelectric power of copper, and this effect should be readily observable in a suitably designed experiment. It is suggested that the effect may also be used to throw additional light on the processes which occur in the annealing of an irradiated sample.The calculated changes in the thermoelectric property of copper due to Frenkel defects are also of such magnitude as to make adequate precautionary measures necessary whenever the thermocouple, which is used to measure the temperature of the specimen, is also in the beam of the massive charged particles. Unless the thermocouple is suitably screened from the beam, unreliable temperature measurement is likely to result. Curves showing the predicted temperature and concentration dependence of the thermoelectric power change due to Frenkel defects are presented.The effect of small concentrations of arsenic in solid solution in copper on the thermoelectric power of copper has also been calculated by the same procedure. The calculated results are in satisfactory agreement with experiment, indicating that the results for interstitials and vacancies are probably of the correct magnitude.