The widespread introduction of rapid pneumatic sample transfer systems has enabled instrumental neutron activation analysis to be based on an increasing number of very short-lived activities. Furthermore, these transfer systems have been interfaced to computer-based MCA's so that the experimenter has complete control over irradiation, decay and counting times, as well as being able to arrange the automatic transfer of numbers of samples between the various stations. Thus the analyst now has a series of options available to him to make the best use of time and facilities. Based on the requirements of detection limits and precisions, he will choose between various irradiation and counting régimes (a) single i.e. conventional (b) cyclic and (c) repeated; or he may choose to replicate the sample a number of times. This paper examines how detection limits and precisions are affected by the above options. By considering a specific isotope, being detected in backgrounds of different half-lives, it is possible to calculate signal-to-noise ratios in each of these cases, and hence compare these régimes from this aspect. Based on calculations for the isotope77mSe (17.5 s), which is now being widely accepted as the basis for selenium analysis, it is shown that, if a low detection limit is the prime consideration, then replicating samples is the procedure of choice; however, if commercial considerations of sample throughput are important then a pseudocyclic régime would provide the best compromise.
Authors:W. Görner, D. Alber, A. Berger, O. Haase, G. Monse, and Chr. Segebade
In activation analysis of traces in small samples, the non-equivalence of the activating radiation doses of sample and calibration material gives rise to sometimes tolerable systematic errors. Conversely, analysis of major components usually demands high trueness and precision. To meet this, beam geometry activation analysis (BEAMGAA) procedures have been developed for instrumental photon (IPAA) and neutron activation analysis (INAA) in which the activating neutron/photon beam exhibits broad, flat-topped characteristics. This results in a very low lateral activating flux gradient compared to known radiation facilities, however, at significantly lower flux density. The axial flux gradient can be accounted for by a monitor-sample-monitor assembly. As a first approach, major components were determined in high purity substances as well as selenium in a cattle fodder additive.
Lindsey recently examined the precision of the manuscript review process using a stochastic model. The study reported that the low reliability found by previous studies results in journals publishing a large number of papers that should otherwise be rejected and rejecting an equally large number of papers that should be accepted.Hargens andHerting have criticized this view. This paper addresses their criticisms. The paper includes an examination of sociology journals usingimpact scores. The differences between journals is noted. Part of the variation between sociology journals derives from their editorial operations. Central to their editorial operations is the reviewing of manuscripts for publication. Not all journals perform this task equally well. The consequences of poor editorial management are discussed. To improve the quality of published work journals need to reduce the low reliability of the current manuscript review process.
Authors:Mirko Prosek, Alenka Golc-Wondra, Irena Vovk, and Janko Zmitek
A wide spread of measurements is typical in quantitative TLC. Improved reproducibility and speed can be achieved by automatic and controlled sample application, chromatographic development, and data acquisition and processing. Secondary chromatography is the main reason for poor precision in TLC. With
up to 10% this is by far the largest source of uncertainty. During the drying process mobile phase evaporates from the upper surface of the plate, and molecules of separated components inside the layer move up or down. Our experimental results show the strong dependence of the intensity of reflected diffuse light on the position of the spots inside the layer. Experimental results gave us an idea how to construct a device for drying and derivatization of TLC plates and a device which reduces uncontrolled propagation and non-homogeneous vertical in-depth distribution of spots during drying and derivatization was constructed. In addition the device designed is safer to use than a hair dryer. A laminar flow of air or inert gas constantly removes solvent vapor from the upper layer of the adsorbent and accelerates drying. Temperature is controlled and varies in a predetermined manner at predetermined intervals. Temperature gradient, which cannot be avoided in flow systems is controlled and is oriented in the direction of chromatographic development. The construction of the device results in identical drying conditions for substances with the same
. Diffusion of the analyte is controlled and standardized and inhomogeneous in-depth distribution of compounds inside the adsorbent is minimized. Heating grade, heating intervals, pulses, switching, and other conditions are preset or programmable. The TLC dryer constructed reduces uncontrolled propagation and non-homogeneous vertical in-depth distribution of spots during drying and derivatization, which results in significantly improved reproducibility and precision. This is very important because in quantitative TLC most measurements are performed in reflectance mode.
We investigated the plutonium assay method that uses the plutonyl trinitrate tetrapropyl-ammonium ion-pair solvent extraction with spectrophotometry of the extract as a candidate method capable of providing robustness and precision. To identify and assess the effect of factors on the precision, we looked at sampling techniques, silver oxide oxidation conditions extraction time, extract stability, and temperature dependence of the extract analytical peak height and position. We obtained a precision of 0.12%.
This paper presents a new approach for precision estimation for algebraic ellipse fitting based on combined least squares method. Our approach is based on coordinate description of the ellipse geometry to determine the error distances of the fitting method. Since it is an effective fitting algorithm the well-known Direct Ellipse Fitting method was selected as an algebraic method for precision estimation. Once an ellipse fitted to the given data points, algebraic distance residuals for each data point and fitting accuracy can be computed. Generally, the adopted approach has revealed geometrical aspect of precision estimation for algebraic ellipse fitting. The experimental results revealed that our approach might be a good choice for precision estimation of the ellipse fitting method.
The credibility of the publication system in science is determined in large part by the precision of the manuscript review process. Studies on the precision of the review process in scientific journals have reported conflicting results. This paper reviews those studies and re-examines the data reported. The findings indicate that highly selective decision-making with imprecise reviewers results in outcomes that are only slightly better than chance.
There are different criteria for designing a geodetic network in an optimal way. An optimum network can be regarded as a network having high precision, reliability and low cost. Accordingly, corresponding to these criteria different single-objective models can be defined. Each one can be subjected to two other criteria as constraints. Sometimes the constraints can be contradictory so that some of the constraints are violated. In this contribution, these models are mathematically reviewed. It is numerically shown how to prepare these mathematical models for optimization process through a simulated network. We found that the reliability model yields small position changes between those obtained using precision respectively. Elimination of some observations may happen using precision and cost model while the reliability model tries to save number of observations. In our numerical studies, no contradictions can be seen in reliability model and this model seems to be more suitable for designing of the geodetic and deformation networks.
The -emitter32P was used to determine total phosphorus by INAA in Skim Milk Powder RM 63, a material now certified by the EEC Bureau of Reference (BCR). Samples and comparator were irradiated in the Danish reactor DR 3. One month later the samples were dissolved in water and aliquots counted with a GM end-window counter using absorber thicknesses of zero to 400 mg/cm2. The Synthesis of Precision was introduced to find the absorber best suited for discriminating against other -emitting isotopes and at the same time giving maximum precision.
The radiotracer method was applied to evaluate the precision of themeasurements of abrasivity data obtained for dentifrice samples and for abrasiveagents (silica and calcium carbonate). This method consists of measuring 32P transferred to a dentifrice or abrasive slurry when an irradiated dentinis submitted to a brushing simulation. Results obtained for abrasivity indiceshad good precision with relative standard deviations lower than 11.8%. Comparisonsmade between our abrasivity index data with those obtained at the Oral HealthResearch Institute of Indiana University also showed a good agreement.