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991.
It is now over two years since ISO/IEC 17025 General requirements for the competence of testing and calibration laboratories was published. The standard places increased emphasis on the demonstration of traceability of measurements made by laboratories. In the areas of chemical and biological metrology, the introduction of this standard has brought new challenges for laboratories to grapple with. This paper will examine the requirements regarding traceability for chemical and biological measurements, with specific reference to the use of reference materials by laboratories. This will be explored from the perspective of both accreditation bodies and a laboratory which is both a user and producer of certified reference materials. Moreover, the paper will describe mechanisms that are being used to improve the use of reference materials by accredited laboratories and hence the traceability of measurements. Finally the role of accreditation programs for reference material producers in assisting with this aspect will be examined.Electronic Supplementary Material Supplementary material is available for this article if you access the article at . A link in the frame on the left on that page takes you directly to the supplementary material.Presented at BERM-9—Ninth International Symposium on Biological and Environmental Reference Materials, June 15–19, 2003 Berlin, Germany. 相似文献
992.
Bosker WT Iakovlev PA Norde W Cohen Stuart MA 《Journal of colloid and interface science》2005,286(2):496-503
BSA adsorption onto bimodal PEO brushes at a solid surface was measured using optical reflectometry. Bimodal brushes consist of long (N=770) and short (N=48) PEO chains and were prepared on PS surfaces, applying mixtures of PS(29)-PEO(48) and PS(37)-PEO(770) block copolymers and using the Langmuir-Blodgett technique. Pi-A isotherms of (mixtures of) the block copolymers were measured to establish the brush regime. The isotherms of PS(29)-PEO(48) show hysteresis between compression and expansion cycles, indicating aggregation of the PS(29)-PEO(48) upon compression. Mixtures of PS(29)-PEO(48) and PS(37)-PEO(770) demonstrate a similar hysteresis effect, which eventually vanishes when the ratio of PS(37)-PEO(770) to PS(29)-PEO(48) is increased. The adsorption of BSA was determined at brushes for which the grafting density of the long PEO chains was varied, while the total grafting density was kept constant. BSA adsorption onto monomodal PEO(48) and PEO(770) brushes was determined for comparison. The BSA adsorption behavior of the bimodal brushes is similar to the adsorption of BSA at PEO(770) monomodal brushes. The maximum of BSA adsorption at low grafting density of PEO(770) can be explained by ternary adsorption, implying an attraction between BSA and PEO. The contribution of primary adsorption to the total adsorbed amount is negligible. 相似文献
993.
Lawrence SC Ward BD Dubberley SR Kozak CM Mountford P 《Chemical communications (Cambridge, England)》2003,(23):2880-2881
Reaction of [M(CH2SiMe3)3(THF)2] (M = Sc or Y) with the neutral fac-kappa3 N3 donor ligands (L) Me3[9]aneN3 or HC(Me2pz)3 gave the corresponding trialkyls [M(L)(CH2SiMe3)3]; activation of the scandium congeners with B(C6F5)3 in the presence of ethylene afforded highly active polymerisation catalysts (Me3[9]aneN3 = 1,4,7-trimethyltriazacyclononane). 相似文献
994.
Claro T. Llaguno Shiv K. Gupta Stuart M. Rothstein 《International journal of quantum chemistry》1973,7(4):819-834
H2+-type elliptical orbitals are defined in Section 1. These orbitals, which in elliptical coordinates involve a factor (1 + ξ)σ, are employed in variational calculations on the ground states of H2+ and H2 (Sections 2 and 3). Various choices of σ are explored for H2+, while two choices are used for H2 : the “boundary condition” (Equation 6) and the “cusp condition” (Equation 9) values. Variational energies are calculated and compared to the results of similar calculations. Section 3 concludes by employing the H2+-type orbitals in LCETO-MO-SCF calculations on the ground states of H2 and He2++. For both molecules a four-function basis set with two (nonlinear) variational parameters yields more than 99% of the Hartree-Fock limit. Section 4 deals with LCETO-MO-SCF calculations on triangular H3+. Three four-function basis sets are used, and the best energy is -1.2306 a.u., which is in reasonable agreement with the Hartree-Fock limit, -1.2999 a.u. Our best basis set is a four-term two-center expansion of the wave function with only one nonlinear variational parameter. Section 5 concludes the paper with a summary of the methods used to evaluate the integrals which arise in SCF calculations in the H2+-type elliptical orbital basis. 相似文献
995.
John G. Stuart Shinya Khora J. Dew McKenney Raymond N. Castle 《Journal of heterocyclic chemistry》1987,24(6):1589-1594
Three dimethoxy[1]benzothieno[2,3-c]quinolines 24–26 were prepared by photocyclization of the appropriate 3-chloro-N-phenylbenzo[b]thiophene-2-carboxamides 15–17 to [1]benzothieno[2,3-c]quinolin-6(5H)-ones 18–20 followed by chlorination to 6-chloro[1]benzothieno[2,3-c]quinolines 21–23 and then dechlorination resulting in the title compounds. Reaction of 24–26 with methyl iodide furnished the corresponding N-methyl quaternary salts 27–29 . Sodium methoxide readily converted 21–23 to trimethoxy[1]benzothieno[2,3-c]quinolines 30–32 . 相似文献
996.
Stuart R. Berryhill 《Journal of organometallic chemistry》1989,370(1-3):C1-C4
The silyl group migration observed upon treating (R)(+)-(η5-C5H5)Fe(CO)2-SiMePh(1-Np) with n-BuLi occurs with retention of configuration at silicon. The anion resulting from the migration, (η5-C5H4SiMePh(1-Np))Fe(CO)2Li, is alkylated with MeI to give (R)-(−)-(η5-C5H4SiMePh(1-Np))Fe(CO)2Me (II). Compound II is independently prepared from (η5-C5H5)Fe(CO)2Me. A concerted mechanism for the migration involving frontside nucleophilic attack at silicon is suggested. 相似文献
997.
R. G. Stuart 《Zeitschrift fur Physik C Particles and Fields》1987,34(4):445-449
The relationship between the \(\overline {MS} \) and on-shell renormalization schemes is discussed and the correction, for finite top quark mass, to the formula connecting sin2 θ W =1?M W 2 /M Z 2 and sin2 \(\widehat\theta _W (M_W )\) is given. A table is presented to allow easy conversion. The relative sensitivity, to the top quark and Higgs masses, of the two definitions, when extracted from semi-leptonic neutrino scattering experiments is considered. 相似文献
998.
A new six-dimensional variational code is presented for the determination of the vibrational energy levels of four-atom molecules which are either linearly connected or centrally connected. Internal (displacement) coordinates are used. It is demonstrated for the CCSD(T) surface of formaldehyde, due to Martin, Lee and Taylor, and it is shown that a small scaling of the force constants leads to a high-accuracy surface. 相似文献
999.
Scheuermann R Tucker IM Dilger H Staples EJ Ford G Fraser SB Beck B Roduner E 《Langmuir : the ACS journal of surfaces and colloids》2004,20(7):2652-2659
The temperature-dependent variation of local environment and reorientation dynamics of the small amphiphile 2-phenylethanol in lamellar phase dispersions of the dichain cationic surfactants, 2,3-diheptadecyl ester ethoxypropyl-1,1,1-trimethylammonium chloride (DHTAC) and dioctadecyldimethylammonium chloride (DODMAC), and the nonionic surfactant, tetra(ethylene glycol) n-dodecyl ether (C12E4), have been determined using avoided level crossing muon spin resonance spectroscopy (ALC-muSR). For cosurfactant radicals the hydrophobic or hydrophilic character of the surrounding media can be determined from their magnetic resonance signatures. Comparison of the three different bilayer-forming surfactant systems shows that the ALC-muSR technique is able to distinguish both major and subtle differences in the partitioning of the cosurfactant radicals between the different systems. 相似文献
1000.
Alan C. Bryan Christopher R. Haines Allan E. G. Stuart 《Letters in Mathematical Physics》1978,2(6):445-449
We discuss the implications of a recently established equivalence between the lynamics of interacting sine-Gordon solitons and the motions of poles of the corresponding Hamiltonian density. The connection is traced to the existence of a complex soliton whose limiting forms are the real soliton and a singular form. 相似文献