The results from a proficiency test exercise for the determination of natural levels of radionuclides in mushroom reference
material carried out by laboratories in six different countries are discussed. These laboratories submitted data on seven
radionuclides, namely 134Cs, 137Cs, 40K, 90Sr, 241Am, 226Ra, and 210Po. However, only the data received for three of these radionuclides could be statistically evaluated to obtain consensus
mean values and confidence intervals (at a significance level of 0.05). The contents of 134Cs, 137Cs and 40K were quantified as 4.4, 2,899 and 1,136 Bq/kg, respectively. 相似文献
Organic beef coming principally from Germany was analysed for the hydrogen, carbon, oxygen, nitrogen and sulfur stable isotopic composition to test the possibility of tracing back the geographical origin. Since there is a well-known pattern of D/H and 18O/16O in meteoric water and in ground water, there is an existing link to tissue water in the beef. By including the stable isotope ratios of the other elements of life further information is available: soils show different isotope ratios of 15N/14N and 34S/32S depending on the geological composition, cultivation and atmospheric sulfur deposition. As organic farming is mainly obliged to use only their produced fodder, that ratio is reflected in the beef as well.Different organic beef samples from various German farms have been collected and analysed over nearly two years. To check the differentiation of foreign beef, samples from Argentina and Chile were also included in the study. The analyses of meat samples indicate that it is possible to trace back the region (e.g. Argentina and Germany) by using isotopes of oxygen and hydrogen. A local geographical differentiation can be done by using the stable isotopes of nitrogen and sulfur, as was demonstrated for three farms in Colonia Bay. An optimal differentiation also depends on the quality of further information (e.g. the season, kind of cattle breeding or the declaration of the local geographical origin). Certainly authenticity of beef is not only linked with the geographical origin but can also reflect the differentiation of organic and conventional farming. The fodder of organic cattle farming consists mainly of C3 plants and the use of C4 plants is more usual in conventional cattle farming. A 13C/12C ratio above –20 appears as a limit for organic farming. Increased values have to be controlled based on their authenticity. 相似文献
A measurement uncertainty estimated for aflatoxin M1 determination in milk sample has been calculated using data generated from analytical method validation studies. The protocol
adopted is described in detail in document LGC/VAM/1998/088. The uncertainty budget was based on precision, trueness and ruggedness
data. The individual contributions are described in detail. The expanded uncertainty for aflatoxin M1 at a concentration of 20 ng L−1 was estimated as 2.81 ng L−1. This was calculated using a coverage factor of two which gives a level of confidence of approximately 95%.
Presented at AOAC Europe / Eurachem Symposium March 2005, Brussels, Belgium 相似文献
The kinetics of sample evaporation was studied for four common injection liners at various temperatures. The rates of solvent and sample evaporation were measured. The sample distribution at the split point was probed by inserting two capillary columns in one injector. Greater homogeneity at the split point corresponded to higher precision (better correlation between the sample and internal standard peak areas). Evidence of aerosol formation using inverted cup inlet liners was seen. Packed column precision was better than capillary precision in each case, i.e., using straight split liners, inverted cup liners, and cold on-column injection. Capillary precision is best when the sample and internal standard elute close together, and may be improved by using solvents that vaporize slowly. 相似文献
Abstract Global warming is expected to affect the ecosystem in the Northeast Atlantic, and substantial changes will also affect the aquaculture industry. Farming of salmon and trout is the biggest aquaculture industry in Norway, with an export value of about 3 billion US dollars in 2007. The objective of the paper is to analyze the potential economic effect a general increase in sea temperature can have on the Norwegian salmon aquaculture industry. The assessment of the economic impact of global warming is made possible by estimating a growth function, which explicitly includes sea water temperature. The analysis compares the economic effect of a climate change on fish farming plants in the south and the north of Norway. The scenarios are based on a model with monthly seasonal variation in temperature. 相似文献
Data from proficiency testing can be used to increase our knowledge of the performance of populations of laboratories, individual
laboratories and different measurement methods. To support the evaluation and interpretation of results from proficiency testing
an error model containing different random and systematic components is presented. From a single round of a proficiency testing
scheme the total variation in a population of laboratories can be estimated. With results from several rounds the random variation
can be separated into a laboratory and time component and for individual laboratories it is then also possible to evaluate
stability and bias in relation to the population mean. By comparing results from laboratories using different methods systematic
differences between methods may be indicated. By using results from several rounds a systematic difference can be partitioned
into two components: a common systematic difference, possibly depending on the level, and a sample-specific component. It
is essential to distinguish between these two components as the former may be eliminated by a correction while the latter
must be treated as a random component in the evaluation of uncertainty.
Received: 20 November 2000 Accepted: 3 January 2001 相似文献
State of the art laser technology and modern spectroscopic methods allow to address issues of fundamental symmetries and fundamental
interactions in atoms with high precision experiments. In particular the discrete symmetries Parity (P), Charge Conjugation
(C), Time Reversal (T) as well as their combinations CP and CPT are in the center of interest at present. Actual projects
are concerned with Parity Violation in atoms, Time Reversal Violation in β-decays and searches for permanent Electric Dipole Moments (EDMs), and tests of CPT conservation in particle-antiparticle
properties, in particular antiprotonic atoms.
This work is supported in part by the Dutch Stichting voor Fundamenteel Onderzoek der Materie (FOM) under programme number
48 (TRIμP). 相似文献
Metal parts and residues from machining processes are usually polluted with cutting or grinding oil and have to be cleaned before further use. Supercritical carbon dioxide can be used for extraction processes and precision cleaning of metal parts, as developed at Forschungszentrum Karlsruhe. For optimizing and efficiently conducting the extraction process, in-line analysis of oil concentration is desirable. Therefore, a monitoring method using fiber-optic NIR spectroscopy in combination with PLS calibration has been developed. In an earlier paper we have described the instrumental set-up and a calibration model using the model compound squalane in the spectral range of the CH combination bands from 4900 to 4200 cm−1. With this model only poor prediction results were obtained if applied to technical oil samples in supercritical CO2. In this paper we describe a new calibration model, which was set up for the squalane/carbon dioxide system covering the 323–353 K temperature and the 16–35.6 MPa pressure range. Here, calibration data in the spectral range from 6100 to 5030 cm−1 have been used. This range includes the 5100 cm−1 CO2 band of the Fermi triad as well as the hydrocarbon 1st overtone CH stretching bands, where spectral features of oil compounds and squalane are more similar to each other.
The root mean-squared error of prediction obtained with this model is 4 mg cm−3 for carbon dioxide and 0.4 mg cm−3 for squalane, respectively. The utilizability of the newly developed PLS calibration model for predicting the oil concentration and CO2 density of solutions of technical oils in supercritical carbon dioxide has been tested. Three types of “real world” cutting and grinding oil formulations were used in these experiments. The calibration proved to be suitable for determining the technical oil concentration with an error of 1.1 mg cm−3 and the CO2 density with an error of 6 mg cm−3. Therefore, it seems possible to apply this in-line analytical approach on the basis of a cost-effective and time-saving model compound calibration for the surveillance of real world de-oiling and other extraction process based on supercritical carbon dioxide, and furthermore to establish an automated process termination criterion based on this technique. 相似文献
Abstract. The paper studies the economy and ecology of sheep farming at the farm level and includes 2 different categories of the animals, ewes (adult females) and lambs. The model is analyzed in a Nordic economic and biological setting. During the outdoor grazing season, animals face limited grazing resources so that the weight gain of lambs is determined by the per‐animal vegetation consumption. On the other hand, the number of grazing animals, lambs as well as ewes, determines the grazing pressure. This problem is studied under the assumption of a rational and well‐informed farmer who aims to maximize profit in ecological equilibrium with zero animal and vegetation growth. We find that lamb‐only slaughtering is optimal and that it is never beneficial for the farmer to keep livestock that overgraze pasture. It is also shown that higher meat prices and more profitable slaughtering make it economically rewarding for the farmer to keep more animals. A numerical illustration indicates that the optimal sheep farming decision may be more sensitive to changes in pasture quality and productivity than changes in economic conditions. 相似文献