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81.
L. Jorhem Joakim Engman Torbjörn Schröder 《Analytical and bioanalytical chemistry》2001,370(2-3):178-182
Certified reference materials (CRMs) have now been in regular use for several decades. Their production and certification are regulated by international standards. But, even today there are no agreements on procedures for evaluating results obtained by the users. As a consequence, the way CRM results are treated in the literature leaves a lot to be desired. A statistical evaluation is rarely, if ever, described in published reports. The most common approach is to compare the found mean and/or range with the certified range and then state if the mean falls within the certified range, or if the two ranges overlap. If this happens, the analyst is usually satisfied. In addition, usually no regard is paid to the fact that the certified interval is based on a 95% confidence interval (CI) and the found interval on standard deviation and that this evaluation has little, if any, statistical relevance. Long-term evaluation of a CRM often consists in nothing more than producing a control chart, which relates the found results to the certified mean and CI. This paper is an attempt to improve the situation by providing a set of easy-to-use guidelines for evaluating results from CRMs. During the process we have identified different areas in which there is a need for such guidelines: 1.?short-term evaluation of a single, or multiple, determination at one or several specific times; 2.?identification of systematic and random errors; 3.?evaluation of CRMs when used in a collaborative trial of a method; and 4.?long-term evaluation for monitoring an analytical process over extended periods of time. It is important that the guidelines do not require expert competence in statistics from the analyst. Such obstacles would probably render most guidelines unused. 相似文献
82.
83.
Sophie Manner Cecilia Hansson Johanna M. Larsson Viveca T. Oltner Torbjörn Frejd 《Tetrahedron: Asymmetry》2010,21(11-12):1374-1381
4-Substituted bicyclo[2.2.2]octane-2,6-diones have been synthesized and tested as substrates in the enantioselective reduction with baker’s yeast to give the corresponding hydroxy ketones. It was found that the derivative bearing a TIPSO group at the 4-position was not reduced at all while that with a TBDMSO group gave 87% yield and 46% ee. Other 4-oxy functionalized derivatives were reduced with varying yields (36–87%) and ees (10–82%). The best result was obtained for the 4-Oallyl derivative (80% yield, 82% ee). The hydroxy ketones carrying the benzyloxy and allyloxy groups at the 4-position were converted into the corresponding BODOLs, which were tested as catalysts in the diethylzinc addition to benzaldehyde. In this reaction the ees were 90% and 89%, respectively, which showed that BODOLs substituted at the 4-position are essentially as good catalysts in this reaction as those bearing a hydrogen. 相似文献
84.
Heavy objects like the W, Z and t are short-lived compared with typical hadronization times. When pairs of such particles are produced, the subsequent hadronic decay systems may therefore become interconnected. We study such potential effects at Linear Collider energies. 相似文献
85.
Torbj⊘rn Vrålstad Gisle Øye Johan Sjöblom Michael Stöcker 《Journal of Dispersion Science and Technology》2013,34(4):489-496
MCM‐41, MCM‐48, and SBA‐15 have been functionalized with cobalt by grafting of different organosilane molecules and then calcined to remove the organic moieties. The materials have been characterized by N2‐sorption, UV‐vis spectroscopy, TPR, ICP‐AES, XRD, and TGA. The nature of the formed cobalt species is dependent upon the number of amine groups in the organosilane molecules, due to the strength of the complexation. Only one amine group in the silane molecule leads to precipitation of Co3O4 particles during calcination, while two or more amine groups lead to the formation of cobalt silica at the surface. The obtained amount of precipitated cobalt in the samples is also dependent upon the number of amine groups and on the chain length of the silane molecules and the pore structure on the mesoporous material. 相似文献
86.
Therese Redin Anna Finne‐Wistrand Torbjörn Mathisen Ann‐Christine Albertsson 《Journal of polymer science. Part A, Polymer chemistry》2007,45(23):5552-5558
Poly(p‐dioxanone) with an inherent viscosity of over 1 dL/g has been synthesized using the cyclic tin alkoxide 1‐di‐n‐butyl‐1‐stanna‐2,5‐dioxacyclopentane as initiator. Poly(p‐dioxanone) was synthesized in bulk and the results have been compared with polymerizations using tin (II) 2‐ethylhexanoate (Sn(Oct)2) as catalyst. Sn(Oct)2 has often been reported to be an effective catalyst for the synthesis of poly(p‐dioxanone), but here it is compared with an initiator which is less prone to catalyze transesterification reactions. The results demonstrate that the cyclic tin initiator is a promising alternative for the synthesis of poly(p‐dioxanone) with a high inherent viscosity. Poly(p‐dioxanone) is a polymer with mechanical properties and a degradation rate suitable for tissue engineering applications. Both the cyclic tin initiator and Sn(Oct)2 gave, under some reaction conditions, inherent viscosities around 1 dL/g. The best polymer synthesized using the cyclic tin initiator had a strain‐at‐break of 515% and a stress‐at‐break of 43 MPa. The inherent viscosity of this polymer was 1.16 dL/g, while Sn(Oct)2 resulted in a polymer with an inherent viscosity less than 0.4 dL/g under the same reaction conditions. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5552–5558, 2007 相似文献
87.
The linear multicommodity network flow (MCNF) problem has many applications in the areas of transportation and telecommunications. It has therefore received much attention, and many algorithms that exploit the problem structure have been suggested and implemented. The practical difficulty of solving MCNF models increases fast with respect to the problem size, and especially with respect to the number of commodities. Applications in telecommunications typically lead to instances with huge numbers of commodities, and tackling such instances computationally is challenging.In this paper, we describe and evaluate a fast and convergent lower-bounding procedure which is based on an augmented Lagrangian reformulation of MCNF, that is, a combined Lagrangian relaxation and penalty approach. The algorithm is specially designed for solving very large scale MCNF instances. Compared to a standard Lagrangian relaxation approach, it has more favorable convergence characteristics. To solve the nonlinear augmented Lagrangian subproblem, we apply a disaggregate simplicial decomposition scheme, which fully exploits the structure of the subproblem and has good reoptimization capabilities. Finally, the augmented Lagrangian algorithm can also be used to provide heuristic upper bounds.The efficiency of the augmented Lagrangian method is demonstrated through computational experiments on large scale instances. In particular, it provides near-optimal solutions to instances with over 3,600 nodes, 14,000 arcs and 80,000 commodities within reasonable computing time. 相似文献
88.
Kärkäs MD Johnston EV Karlsson EA Lee BL Åkermark T Shariatgorji M Ilag L Hansson Ö Bäckvall JE Åkermark B 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(28):7953-7959
The new Ru complex 8 containing the bio-inspired ligand 7 was successfully synthesized and characterized. Complex 8 efficiently catalyzes water oxidation using Ce(IV) and Ru(III) as chemical oxidants. More importantly, this complex has a sufficiently low overpotential to utilize ruthenium polypyridyl-type complexes as photosensitizers. 相似文献
89.
Stefanie Tschierlei Martin Presselt Christian Kuhnt Arkady Yartsev Dr. Torbjörn Pascher Dr. Villy Sundström Prof. Dr. Michael Karnahl Matthias Schwalbe Dr. Bernhard Schäfer Dr. Sven Rau Prof. Dr. Michael Schmitt Dr. Benjamin Dietzek Dr. Jürgen Popp Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(31):7678-7688
Photoinduced electron‐transfer processes within a precatalyst for intramolecular hydrogen evolution [(tbbpy)2Ru(tpphz)PdCl2]2+ ( RuPd ; tbbpy=4,4′‐di‐tert‐butyl‐2,2′‐bipyridine, tpphz=tetrapyrido[3,2‐a:2′,3′c:3′′,2′′,‐h:2′′′,3′′′‐j]phenazine) have been studied by resonance Raman and ultrafast time‐resolved absorption spectroscopy. By comparing the photophysics of the [(tbbpy)2Ru(tpphz)]2+ subunit Ru with that of the supramolecular catalyst RuPd , the individual electron‐transfer steps are assigned to kinetic components, and their dependence on solvent is discussed. The resonance Raman data reveal that the initial excitation of the molecular ensemble is spread over the terminal tbbpy and the tpphz ligands. The subsequent excited‐state relaxation of both Ru and RuPd on the picosecond timescale involves formation of the phenazine‐centered intraligand charge‐transfer state, which in RuPd precedes formation of the Pd‐reduced state. The photoreaction in the heterodinuclear supramolecular complex is completed on a subnanosecond timescale. Taken together, the data indicate that mechanistic investigations must focus on potential rate‐determining steps other than electron transfer between the photoactive center and the Pd unit. Furthermore, structural variations should be directed towards increasing the directionality of electron transfer and the stability of the charge‐separated states. 相似文献
90.
We report on adaptive feedback control of photoinduced barrierless isomerization of 1,1'-diethyl-2,2'-cyanine in solution. We compare the effect of different fitness parameters and show that optimal control of the absolute yield of isomerization (photoisomer concentration versus excitation photons) can be achieved, while the relative isomerization yield (photoisomer concentration versus number of relaxed excited-state molecules) is unaffected by adaptive feedback control. The temporal structure of the optimized excitation pulses allows one to draw clear mechanistic conclusions showing the critical importance of coherent nuclear motion for the control of isomerization. 相似文献