Authors:A. Markowicz, N. Haselberger, H. El Hassan, and M. Sewando
Problems connected with quantitative EDXRF analysis of intermediate thickness samples are addressed. The first one is a systematic study of the various contributions to the total error of the E-T method. Special attention is also given to the enhancement effect for intermediate thickness samples; in this context both monochromatic and bichromatic approaches are adapted to a known theoretical model.
In radiotracer measurements of the flow rate of marine surface sands, the chief difficulty is to determine the average thickness of the radiotracer spot. The simultaneous use of two detectors may appreciably reduce the uncertainty in the final result.
Fejes Tóth  studied approximations of smooth surfaces in three-space by piecewise flat triangular meshes with a given number of vertices on the surface that are optimal with respect to Hausdorff distance. He proves that this Hausdorff distance decreases inversely proportional with the number of vertices of the approximating mesh if the surface is convex. He also claims that this Hausdorff distance is inversely proportional to the square of the number of vertices for a specific non-convex surface, namely a one-sheeted hyperboloid of revolution bounded by two congruent circles. We refute this claim, and show that the asymptotic behavior of the Hausdorff distance is linear, that is the same as for convex surfaces.
Authors:A. E. Veatch, J. D. Brockman, V. L. Spate, J. D. Robertson, and J. S. Morris
Selenium is a required trace-element that has been found to be protective against serious chronic diseases such as cancer and cardiovascular disease in some, but not all, epidemiological studies using both case-control and intervention designs. As a result, the fraction of the adult U.S. population now taking a daily selenium supplement is steadily increasing. In this study, we analyzed 10 or more replicate Se supplement tablets, from each of 15 different products representing 12 different brand names with most being sampled at two different times separated by approximately 30 months. Two chemical forms, seleno-yeast and selenate were tested in 50, 100 and 200 µg/tablet dosages (seleno-yeast) and 25 and 200 µg/tablet dosages (selenate). Variations in contemporary lots were evaluated at both sampling periods. The Se content provided on the product label is generally understated. One tablet contained 2.5 times more selenium than the stated dose. Selenate supplements are less accurately labeled and more highly variable compared to yeast supplements. One popular multivitamin, labeled at 200 µg/tablet, contained tablets in excess of 300 µg. Many subjects using this supplement will exceed the 400 µg/day tolerable upper limit of intake, recently established, for Se by the Institute of Medicine’s Food and Nutrition Board.
Preliminary attempts to georeference maps of early twentieth century made by the Military Geographic Institute (IGM, the Italian geodetic agency) for the city of Rome and its surroundings, reported residual errors larger than errors observed on similar maps. Previous studies carried out on one or two century older maps of the same area, showed similar or even smaller errors (Baiocchi and Lelo 2005).Six sheets of the “City of Rome and its surroundings” map in scale 1:5 000 dated 1908 have been studied. The identified errors can be referred to the different system of geodetic projection and geodetic datum or to the derivation of some details from maps at smaller scale, but in this case historic documents seem to suggest a different explanation.Parameters useful to perform the transformation of the geodetic systems used in historical maps to modern systems are not known; for this reason until now the various attempts of georeferencing maps of this type were based on collimation of points recognizable on modern cartographies such as corners of historical buildings. This method has often given unsatisfactory results; therefore it was decided to proceed by determining the parameters for the transformation of geodetic datum.The history of geodetic systems used in Italy at the beginning of the 20th century is complex and, in the past, this has led some researcher to misinterpretations. For this reason a full explanation of geodetic systems used in Italy in this period is reported below. Since the parameters of the projection used for the maps in our case study are not known for sure, the reprojection was considered the only way for a correct georeferencing.
The use of nuclide95Zr as radiotracer is often unfavourably influenced by the continuous accumulation of the radioactive daughter nuclide95Nb. The present paper gives a method showing how the daughter radioactivity can influence the value of the distribution coefficient
of zirconium calculated from radioactivity measurements. A simple method of continuous purification of95Zr, which yields a product of the required degree of purity, is also described.
Authors:S. Ismail, G. Wiesinger, R. Pavlovec, and F. Grass
Different reference materials of environmental and geological origin, such as NBS 1633a (Coal Fly Ash, CFA), NBS 1645 (River Sediment, RS), GXR-2, and IAEA Soil-5, were investigated by short time activation analysis. The samples were analyzed in 5 replicates each between 100 to 150 mg, at neutron flux of 1.3 E 12 cm–2 s–1, using a high rate — high resolution gamma spectroscopy with a Loss Free Counting (LFC) System to correct the dead time and pile up to 500,000 cps. The results of the measurements indicate that the precision in determination of28Al,46mSc, and52V is between 1 to 6%. Different evaluation programs (i.e. ALCHEM, AKTAN, and ND-PEAK) were used to calculate the peak areas. The results indicate that, at lower counts, the statistical error of peak area calculation becomes more significant. Finally, Mössbauer spectroscopy was used to investigate the main Fe compounds present in some reference materials.
Authors:Aziz Ahmed, Sayeed Ahmad, Mahfooz Ur-Rahman, Tamboli E. Tajuddin, Ranbir Verma, Mohd Afzal, and Prahlad Singh Mehra
Bacoside A, a triterpenoid saponin, is a major constituent isolated from Bacopa monnieri (L.) Wettst. (Scrophulariaceae), used as a memory enhancer. Bacoside A and B are active ingredients in Bacopa herb and have antioxidant and hepatoprotective activities
A new rapid, simple, and economical high-performance thin-layer chromatographic (HPTLC) method was developed and validated for densitometric quantitative analysis of bacoside A in powdered leaves from different geographical regions of India.
Materials and methods
An amount of 10 mg mL−1 methanol extract of powdered leaves from different geographic regions was used for sample application on precoated silica gel 60 F254 aluminum sheets. Standard bacoside A (1 mg mL−1) was used for calibration curve. HPTLC separation was performed on percolated silica gel aluminum plate 60 F254 (20 cm × 10 cm with 0.2 mm thickness) as a stationary phase using ethyl acetate–methanol–water (4:1:1) as the mobile phase. Quantification was achieved by densitometric analysis at 598 nm over the concentration range of 500–4000 ng band−1.
Compact and well-resolved bands for bacoside A from powdered leaves of different geographic regions were found at retardation factor (Rf) 0.53 ± 0.02. The linear regression analysis data for calibration curve showed good linear relationship with regression coefficient r2 = 0.9996 and r2 = 0.99810 with respect to peak area and peak height. The method was validated for precision, recovery, and robustness as per the International Conference on Harmonization (ICH) guidelines. Variation in quantitative analysis of bacoside A in powdered leaves sample from different geographic regions was found by HPTLC method.
Discussion and conclusion
The highest and lowest content of bacoside A in powdered leaves sample from Jammu and Kerala regions, respectively. The variety of B. monnieri in Jammu is superior to other regions of India. The proposed developed HPTLC method can be applied for the quantitative determination of bacoside A in powdered leaves of plant and its formulation.