The Taosi site in Xiangfen County, Shanxi Province, may be the capital of the King Yao. Archeologists recently discovered
a large semi-circular stamped-earth platform, II FJT1, which has a clear and definite pounded-earth central core together
with a curved wall perforated by twelve gaps. The platform is said to be an ancient observatory used to determine the seasons
by watching the sunrise. Each feature of II FJT1 was precisely measured and the data are reproduced in this paper. An astronomical
analysis of slots E2 and E12 was carried out using the azimuths of the slots’ centerlines and the vertical angle of the mountain
ridge opposite, above which the sun rises. The results show that at present the sun is close to the two slots but does not
exactly enter them at summer and winter solstice sunrise. Using 14C analysis archeologists dated the site to about 2100 BC.
Because of the secular change in the obliquity of the ecliptic, at that date on the summer solstice the half-risen sun would
have appeared inside slot E12 just to the right of the centerline, and on the winter solstice the sun would have been exactly
on the centerline of slot E2. This result provides compelling proof that II FJT1 is an ancient observatory. 相似文献
The ENEA fast neutron dosemeter is based on a planar poly allyl diglicol carbonate (PADC) placed in a polyethylene holder. The present paper reports the results of an experimental study of a CR-39® material with the addition of 0.1% of dioctylphthalate (DOP) produced by the Italian company Intercast Europe S.p.A.
The etching procedure is: pre-etching with 40% KOH water solution 6.25 N and 60% ethyl alcohol at 70°C followed by 12 h of etching in 6.25 N KOH water solution. For the energy dependence of response, dosemeters have been irradiated with neutron sources (241Am–Be, 252Cf, Pu–Li) and 14.9 MeV monoenergetic neutrons. The dosimetric performance of the material for fast neutrons is expressed in terms of sensitivity, background value, lowest detectable dose and energy dependence of response. Moreover, the results of a quality acceptance test of the material, performed on 11 sheets (980×980 mm2, 1.4 mm thick) of the same production batch, are given. Therefore, the homogeneity of the neutron sensitivity and of the background signal within a sheet and the whole batch is considered. The results are compared with the acceptance test outcome for a CR39 standard material batch. 相似文献
The reliability of reference materials (RMs) depends on properties such as fitness, robustness, commutability, stability and
homogeneity. The development of RMs for microbiological analysis is especially challenged through questions around the stabilisation
and recovery of viable cells, the dispersion of precise numbers of cells, matrix effects and, when using molecular techniques,
the presence of nucleic acids (e.g. DNA) of dead and live target organisms. However, RMs are indispensable tools for quality
control in microbiological analysis. The Institute for Reference Materials and Measurements (IRMM), as part of the European
Commission, concentrates its efforts on the development of RMs to support the development, implementation and monitoring of
EU legislation. A special focus is given to highly precise RMs for presence/absence and enumeration tests in microbiological
food and water analysis. Another group of new RMs certified by the IRMM comprise DNA-based materials to control the identity
of micro-organisms in qualitative assays. All of these activities serve to improve quality control in microbiological analysis.
Presented at ‘BERM-10’, April 2006, Charleston, SC, USA. 相似文献
The classical economic production quantity (EPQ) model assumes that items are produced by a perfectly reliable production process with a fixed set-up cost. While the reliability of the production process cannot be perfected cost-free, the set-up cost can be reduced by investment in flexibility improvement. In this paper, we propose an EPQ model with a flexible and imperfect production process. We formulate this inventory decision problem using geometric programming (GP), establish more general results using the arithmetic-geometric mean inequality, and solve the problem to obtain a closed-form optimal solution. Following the theoretical treatment, we provide a numerical example to demonstrate that GP has potential as a valuable analytical tool for studying a certain class of inventory control problems. Finally we discuss some aspects of sensitivity analysis of the optimal solution based on the GP approach. 相似文献
The implementation of a quality system based on the ISO/IEC 17025:1999 standard is a growing necessity for analytical laboratories to demonstrate their technical competence. In 2001, the Nuclear Analytical Techniques Group of the Argentine Atomic Energy Commission obtained the recognition of the International Atomic Energy Agency in the application of neutron activation analysis and the accreditation by the national accreditation body. The importance of the participation of the group in the Agency's Regional Programme for Latin America, ARCAL XXVI on Quality Assurance in Analytical laboratories is discussed, as well as the activities performed to attain these objectives. Some improvements worth mentioning resulted from the implementation of the quality system and, following the premise of continuous improvement, changes were introduced aiming at the laboratory re-accreditation. 相似文献
The accuracy of 210Pb determination via spontaneous deposition of 210Po on a silver disk and alpha spectrometric measurement was examined. The study focused on the storage conditions of the polonium-containing solutions, the tracer used in polonium analysis and the effect of storage time and acid concentration on 210Po deposition. The intermediate precision and repeatability associated with the improved 210Pb analysis of fresh groundwater samples was 5 and 14%, respectively. These improved values were achieved by using glass bottles as storage containers for the solution remaining from the first 210Po deposition, by rinsing the sample container with concentrated hydrochloric acid after storage and by using different isotopes of polonium as the yield determinant tracer in the first and the second deposition. Less polonium adsorption onto the storage container walls occurred with HCl than with HNO3. The overall uncertainty in 210Pb analysis was (11 ± 7)% at the 95% confidence level. The minimum detectable activity concentration was 0.1 mBq l−1 calculated from blank samples and 0.05 mBq l−1 using the background counts of the alpha spectrometer. 相似文献
This article investigates the behavior of cultural influence networks over time, using a computer simulation based on a formal model of cultural transmission in organizations. In the formal model, every organizational member exerts some cultural influence on, and is influenced by, every other member; these influence paths constitute a dense social network and the weights of paths (ties) vary throughout the network. Over time, each organizational member's enculturation level changes in response to influence from other members, and the influence weight of each path changes in relationship to the cultural similarity of the individuals connected by the path. Virtual experiments explore the configuration and evolution of the cultural influence network under varying demographic conditions and influence principles. Demographic effects are studied by varying organizational size, hiring selectivity and turnover rates. Two principles for determining initial influence path weights are examined, cohort-based influence and random influence. The simulations show that the cultural influence network evolves over time to a robust configuration, fluctuating around a stable dynamic equilibrium as individuals enter and leave the organization. As turnover rates rise, cohort-based influence strengthens the influence network and reduces network inequality. In this model, cohort-based influence processes promote cultural stability in organizations. 相似文献
The necessity for analytical quality assurance is primarily a feature of the analytical process itself. With the full establishment
of the EU domestic market, it is also becoming a legal necessity for an increasing number of analytical laboratories. The
requirements which laboratories will need to fulfil are stipulated in DIN EN 45 001. Accredited testing laboratories must
in fact provide evidence that they work solely in accordance with this standard. National and EU commissions, which are legislative
authorities, tend therefore to specify analytical methods, e.g. in the form of regulations or appendices thereto, intended
to ensure that results from different laboratories will be comparable and hence will stand up in a court of law. The analytical
quality assurance system (AQS), introduced by the Baden-Württemberg Ministry for the Environment in 1984, obliges laboratories
to regularly participate in collaborative studies and thereby demonstrate their ability to provide suitably accurate analyses.
This alone, however, does not sufficiently demonstrate the competence of a laboratory. Only personal appraisal of the laboratory
by an auditor, together with the successful analysis of a sample provided by the same and performed under his observation,
can provide proof of the competence of the laboratory. From an analytical point of view, the competence of a laboratory must
be regarded as the decisive factor. Competence can only be attained through analytical quality assurance, which thus must
be demanded of all laboratories.
Received: 4 October 1996 Accepted: 15 January 1997 相似文献