National Metrological Institutes (NMIs) from fifteen different countries participated in interlaboratory comparisons where concentrations of about 1gkg–1 in solutions of aluminium, copper, iron, magnesium, chloride and phosphate were measured. A very high comparability of the results irrespective of the analyte and the applied measurement technique was observed. The relative in-between laboratory standard deviations of the results as reported by the participating laboratories were between 0.13% for copper and chloride up to 0.33% for aluminium, and all of the 81 results were found in the range of ±1% with respect to the reference value. Due to the gravimetric preparation of the samples, a conventional true reference value was calculated, and no significant deviations of the reference values and the means of all results reported by the institutes were found. 相似文献
We sketch the foundations of classical electrodynamics, in particular the transition that took place when Einstein, in 1915, succeeded to formulate general relativity. In 1916 Einstein demonstrated that, with a choice of suitable variables for the electromagnetic field, it is possible to put Maxwells equation into a form that is covariant under general coordinate transformations. This unfolded, by basic contributions of Kottler, Cartan, van Dantzig, Schouten & Dorgelo, Toupin & Truesdell, and Post, to what one may call premetric classical electrodynamics. This framework will be described shortly. An analysis is given of the physical dimensions involved in electrodynamics and subsequently the question of units addressed. It will be pointed out that these results are untouched by the generalization of classical to quantum electrodynamics (QED). We compare critically our results with those of L.B. Okun which he had presented at a recent conference. 相似文献
In this paper we discuss a component-oriented architecture which we are employing to develop programmable exploratory software
for mathematics. We argue that the architecture can be used to provide synergy between end-user programming and efficient
behavior of components, i.e. Computational objects of a wide range of technical complexity and functionalities. We give examples
of components with mathematics in their behavior and components which in themselves embody mathematical relations. Through
both formal language and visual means, users can link them to form creative configurations with interesting functionalities
and use the resulting environments for exploratory activity. We conclude that this architecture enables a more efficient collaboration
between technical and educational expertise in developing exploratory software.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
The Contour Approach to Peak Picking was developed to aid in the analysis and interpretation and of multidimensional NMR spectra of large biomolecules. In essence, it comprises an interactive graphics software tool to computationally select resonance positions in heteronuclear, 3- and 4D spectra. 相似文献
The Discrete Element Method (DEM) is applied to predict draft forces of a simple implement in cohesionless granular material. Results are compared with small-scale laboratory tests in which the horizontal force is measured at a straight blade. This study is focused on the case of cohesionless material under quasi-static conditions.The DEM requires the calibration of the local contact parameters between particles to adjust the bulk material properties. The most important bulk property is the angle of internal friction ?. In the DEM, the shear resistance is limited in the case of spherical particles due to excessive particle rotations. This is cured by retaining rotations of the particles. Although this is known to prevent the material from developing shear bands, the model still turns out to be capable of predicting the reaction force on the blade.In contrast to empirical formulas for this kind of application, the DEM model can easily be extended to more complex tool geometries and trajectories. This study helps to find a simple and numerically efficient setup for the numerical model, capable of predicting draft forces correctly and so allowing for large-scale industrial simulations. 相似文献
Laser heating of a cemented carbide tool is considered and the temperature field as well as phase changes in the heated region is modeled. Temperature rise, liquid layer thickness, and mushy size are predicted numerically. A control volume approach is introduced to solve the governing equations of heat transfer and phase change. Consecutive pulses with the duty cycle of 60% are accommodated in the simulations in line with the experimental conditions. An experiment is carried out to treat the cemented carbide tool surfaces using the CO2 laser delivering consecutive pulses. The treated surfaces and their cross-sections are examined using the scanning electron microscope (SEM). It is found that the temperature gradient is high along the laser beam axis resulting in cracks at the irradiated surface. The rapid solidification of the surface causes compact structures with very fine grains in the surface region of the laser irradiated spot. 相似文献
The tribological characteristics of sliding surfaces have been remarkably improved by surface texturing. Surface texturing can be beneficial in many ways; for example, it can reduce friction and wear, increase load carrying capacity, and increase fluid film stiffness. The design process for surface texturing is highly correlated to the particular functions of any application for which texturing is required. Texture quality is greatly affected by manufacturing methods, therefore, it is important to have a detailed understanding of the related parameters of any technique.
The use of surface texturing to improve the cutting performance of tools is a relatively new application. These textures improve cutting performance by enhancing lubricant availability at the contact point, reducing the tool-chip contact area, and trapping wear debris. Reductions in crater and flank wear, friction force, cutting forces, and cutting temperature are the main benefits obtained by this technique. To date, surface texturing has been successfully used in drilling, milling, and turning operations.
This article provides an overview of the techniques that have been used in industry and research platforms to manufacture micro-/nano-textures for tribological applications, and it examines the effects of surface textures on cutting tool performance. 相似文献
8-Hydroxyflavone is not found in nature. While the (13)C chemical shifts of 8-hydroxyflavone have been reported previously, the observed (13)C chemical shifts were not assigned. A previously reported empirical predictive tool has been applied in reverse in order to deconvolute the (13)C chemical shifts for 8-hydroxyflavone from each of those of 7,8,4'-trihydroxyflavone and 7,8-dihydroxyflavone together with those of 7-hydroxyflavone, 4'-hydroxyflavone, and flavone. The two sets of calculated (13)C chemical shifts for 8-hydroxyflavone are in good agreement with each other in that the average absolute difference is 0.4 ppm. The previously reported but unassigned (13)C chemical shifts for 8-hydroxyflavone have been assigned by matching them with the averages of the two sets of calculated (13)C chemical shifts for 8-hydroxyflavone such that the minimum average absolute difference is 0.63 ppm. The assigned (13)C chemical shifts of 8-hydroxyflavone may be used, along with the (13)C chemical shifts of the remaining monohydroxyflavones, as part of a predictive tool to rapidly assess the (13)C NMR spectra of C8-hydroxylated flavonoids. 相似文献
The following paper addresses the experience of certain national metrology institutes (NMIs) with national accreditation bodies
(NABs), in particular in small countries with emerging economies in new EU or candidate member states. Specific cases have
been analysed primarily in some Central and South-East European countries. NABs under consideration are, in principle, members
of European Co-operation for Accreditation (EA). EA cross-frontier policy in these cases will be discussed and resulting dilemmas
outlined. Focus will be given to the problems of NMIs also performing calibrations, commercial calibration laboratories, and
their relations with NABs. Due to numerous problems of smaller NABs, cross-frontier policy should stimulate cooperation between
foreign and local accreditation bodies not only at the request of the calibration laboratory or some other conformity assessment
body, but at the request of the local accreditation body in order to provide the best service for their local economy. As
a solution to the accreditation problems, this paper proposes a process of gradual formation of a common European pool of
experts, real-life common practices and, finally, maybe even some form of joint European accreditation service.
The opinions expressed in the paper are personal statements of the author, and do not necessarily reflect the official opinions
of the institutions of the author.
Papers published in this section do not necessarily reflect the opinion of the Editors, the Editorial Board and the Publisher. 相似文献