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排序方式: 共有10000条查询结果,搜索用时 218 毫秒
101.
Thomas P J Linsinger Alexander Bernreuther Philippe Corbisier Marta Dabrio Håkan Emteborg Andrea Held Andrée Lamberty Gaida Lapitajs Marina Ricci Gert Roebben Stefanie Trapmann Franz Ulberth Hendrik Emons 《Accreditation and quality assurance》2007,12(3-4):167-174
The potential approaches for third-party assessment of reference material producers are revisited and the activities of the
Reference Materials (RM) Unit of the Institute for Reference Materials and Measurements (IRMM) to obtain accreditation to
ISO Guide 34 and ISO 17025 are described. Accreditation was related to the Unit as all matrix RM activities of the institute
are concentrated there. A management system was established that allows sufficient flexibility to be applicable to a wide
range of RMs while being precise enough to ensure compliance with ISO Guides 30, 31 and especially 34 and 35. Accreditation
was achieved in 2004 with independent scopes for testing and RM production and was confirmed and extended in 2005. The key
aspects of the RM Unit's management system for RM production are presented.
Presented at BERM-10, April 2006, Charleston, SC, USA 相似文献
102.
J. C. Lpez V. A. L. Rivera Yu. F. Smirnov A. Frank 《International journal of quantum chemistry》2002,88(2):280-295
The calculation of Franck–Condon factors between different 1‐D Morse potential eigenstates using a formula derived from the Wigner function is discussed. Our numerical calculations using a simple program written in Mathematica are compared with other calculations. We show that our results have a similar accuracy as those calculations performed with more sophisticated methods. We discuss the extension of our method to include non‐Condon effects in the calculation. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem 88: 280–295, 2002 相似文献
103.
104.
The effects of the annealing on the properties of PET/PC block copolymers, obtained by reactive blending in the presence of different catalysts and for different mixing times, have been studied. The annealing, performed in conditions that promote the crystallization, has been used to better understand the role of block length in determining the phase behaviour. The copolymers characterized by blocks with molecular weight larger than 8000 are able to reorganize towards more ordered domains. This rearrangement maintains the phase separation, as two crystalline phases are present before and after annealing, due to the immiscibility of long blocks. In copolymers characterized by blocks with molecular weight equal to about 2500, that is the higher limit for the miscibility in the amorphous state in PET/PC block copolymers studied in this work, the rearrangement of the chains during annealing causes a phase separation leading to two crystalline phases. Only in the copolymers with molecular weight of blocks lower than 1500, the very short block length hinders the crystallization: therefore, only in this case a phase separation does not take place after annealing. 相似文献
105.
106.
Marina A Zhuravleva 《Journal of solid state chemistry》2003,173(2):280-292
The RE3Ga9Ge compounds (RE=Y, Ce, Sm, Gd and Yb) were synthesized at 850°C in quantitative yield from reactions containing excess liquid Ga. The orthorhombic crystal structure is characterized by a unique three-dimensional open Ga framework with parallel straight tunnels. In the tunnels, inserted are arrays of the RE atoms together with interpenetrated monoatomic RE-Ga-Ge planes. A complex disordered arrangement of the RE and Ga atoms is observed in the monoatomic plane. Depending on the extent of disorder, the crystal structure could be presented either in a sub-cell (no ordering) or in a super-cell (partial ordering). Single-crystal X-ray data for Ce3Ga9Ge sub-structure: space group Immm, Z=2, cell parameters a=4.3400(12) Å; b=10.836(3) Å; and c=11.545(3) Å; super-structure: space group Cmma, Z=8, cell parameters a=8.680(3) Å; b=23.090(7) Å; and c=10.836(3) Å. The refinement based on the full-matrix least squares on Fo2[I>2σ(I)] converged to final residuals R1/wR2=0.0226/0.0528 and 0.0729/0.1569 for the sub- and super-structures, respectively. The relationship between the disordered sub-structure and partially ordered super-structure is discussed. Magnetic susceptibility measurements show Curie-Weiss behavior at the temperatures above 30 K with the negative Weiss constants Θ=−49(1) and−7.7 K for Gd and Ce analogs, respectively. An antiferromagnetic transition is observed in the Gd analog at TN=26.1 K. The μeff obtained for both analogs is close to the RE3+ free-ion value. 相似文献
107.
108.
The stoichiometric pK
1
*
and pK
2
*
for the ionization of sulfurous acid has been determined from emf measurements in NaCl solutions with varying concentrations of added MgCl2 (m=0.1, 0.2 and 0.3) from I=0.5 to 6.0 molal at 25°C. These experimental results have been treated using both the ion pairing and Pitzer's specific ion-interaction models. The Pitzer parameters for the interaction of Mg2+ with SO2 and HSO
3
–
yielded =0.085±0.004, (0) = 0.35±0.02, (1) = 1.2±0.04, and C = –0.072±0.007. The Pitzer parameters (0) = –2.8±0.4, (1) = 12.9±2.9 and (2) = –2071±57 have been determined for the interactions of Mg2+ with SO
3
2–
. The calculated values of pK
1
*
and pK
2
*
using Pitzer's equations reproduce the measured values to within ±0.04 pK units. The ion pairing model with log KMgSO3=2.36±0.02 and logMgSO3 = 0.1021, reproduces the experimental values of pK
2
*
to ±0.01. These results demonstrate that treating the data by considering the formation of MgSO3 yields a better fit of the experimental measurements with fewer adjustable parameters. With these derived coefficients obtained from the Pitzer equations and the ion pairing model, it is possible to make reliable estimates of the activity coefficients of HSO
3
–
and SO
3
2–
in seawater, brines and marine aerosols containing Mg2+ ions. 相似文献
109.
110.
Arie L. Gutman Marina Etinger Gennady Nisnevich Felix Polyak 《Tetrahedron: Asymmetry》1998,9(24):1022
The enantiomerically pure chiral benzocyclic amines 6–8 were obtained by asymmetric transamination of the corresponding prochiral ketones 9a–c. The method involves: (a) formation of chiral imines 10a–c from the prochiral ketones 9a–c and the inexpensive chiral auxiliary (R)- or (S)-phenylethylamine (PEA); (b) asymmetrically induced reduction of these imines to the diastereomeric amines 11a–c and 12a–c; (c) catalytic hydrogenation to remove the benzylic fragment of the chiral PEA auxiliary. The stereoselectivity of the imine reduction, as well as the regioselectivity of the catalytic hydrogenation, are strongly dependent on the size of the saturated ring condensed with the benzene ring. This approach was used to develop a convenient, high yielding, and stereoselective route to several practically important optically active α-amino substituted benzocyclic compounds. 相似文献