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排序方式: 共有583条查询结果,搜索用时 31 毫秒
491.
Egmont Rohwer Christoph Richter Nadine Heming Kerstin Strauch Dr. Christian Litwinski Prof. Tebello Nyokong Prof. Derck Schlettwein Prof. Heinrich Schwoerer 《Chemphyschem》2013,14(1):132-139
We investigate the ultrafast dynamics of the photoinduced electron transfer between surface‐adsorbed indoline D149 dye and porous ZnO as used in the working electrodes of dye‐sensitized solar cells. Transient absorption spectroscopy was conducted on the dye in solution, on solid state samples and for the latter in contact to a I?/I3? redox electrolyte typical for dye‐sensitized solar cells to elucidate the effect of each component in the observed dynamics. D149 in a solution of 1:1 acetonitrile and tert‐butyl alcohol shows excited‐state lifetimes of 300±50 ps. This signature is severely quenched when D149 is adsorbed to ZnO, with the fastest component of the decay trace measured at 150±20 fs due to the charge‐transfer mechanism. Absorption bands of the oxidized dye molecule were investigated to determine regeneration times which are in excess of 1 ns. The addition of the redox electrolyte to the system results in faster regeneration times, of the order of 1 ns. 相似文献
492.
Markus Büttner Peter Weber Frank Schmidl Paul Seidel Michael Röder Matthias Schnabelrauch Kerstin Wagner Peter Görnert Gunnar Glöckl Werner Weitschies 《Journal of nanoparticle research》2011,13(1):165-173
In this work we address the question which relates between the size of the magnetically active core of magnetic nanoparticles
(MNPs) and the size of the overall particle in the solution (the so-called hydrodynamic diameter d
hyd) exists. For this purpose we use two methods of examination that can deliver conclusions about the properties of MNP which
are not accessible with normal microscopy. On the one hand, we use temperature dependent magnetorelaxation (TMRX) method,
which enables direct access to the energy barrier distribution and by using additional hysteresis loop measurements can provide
details about the size of the magnetically active cores. On the other hand, to determine the size of the overall particle
in the solution, we use the magnetooptical relaxation of ferrofluids (MORFF) method, where the stimulation is done magnetically
while the reading of the relaxation signal, however, is done optically. As a basis for the examinations in this work we use
a ferrofluid that was developed for medicinal purposes and which has been fractioned magnetically to obtain differently sized
fractions of MNPs. The two values obtained through these methods for each fraction shows the success in fractioning the original
solution. Therefore, one can conclude a direct correlation between the size of the magnetically active core and the size of
the complete particle in the solution from the experimental results. To calculate the size of the magnetically active core
we found a temperature dependent anisotropy constant which was taken into account for the calculations. Furthermore, we found
relaxation signals at 18 K for all fractions in these TMRX measurements, which have their origin in other magnetic effects
than the Néel relaxation. 相似文献
493.
494.
Thomas D. Schladt Mohammed Ibrahim Shukoor Dr. Kerstin Schneider Muhammad Nawaz Tahir Dr. Filipe Natalio Irene Ament Jan Becker Florian D. Jochum Stefan Weber Oskar Köhler Patrick Theato Dr. Laura Maria Schreiber Prof. Dr. Carsten Sönnichsen Prof. Dr. Heinz C. Schröder Prof. Dr. Dr. Werner E. G. Müller Prof. Dr. Wolfgang Tremel Prof. Dr. 《Angewandte Chemie (International ed. in English)》2010,49(23):3976-3980
495.
Through the oxidation of sulfides useful elements of stereocontrol in asymmetric synthesis and important targets of pharmaceutical interest can be obtained. A number of metal-free methods have been developed over recent years for sulfoxidation reactions. The results published after 1998 through the beginning of 2010 have been reviewed with a focus being placed on sulfoxidations with hypervalent iodine compounds; iminium- and oxaziridinium derivatives; organic hydroperoxides and organocatalysts. In addition, autocatalytic and catalyst-free variants are discussed. Although, the asymmetric organocatalytic sulfoxidation is still in its infancy, the reported results show the high potential and versatility of this metal-free methodology. 相似文献
496.
497.
498.
Vladimir Muravsky Tatjana Gurachevskaya Stephen Berezenko Kerstin Schnurr Andrey Gurachevsky 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2009,74(1):42-47
Bovine and human serum albumins and recombinant human albumin, all non-covalently complexed with 5- and 16-doxyl stearic acids, were investigated by ESR spectroscopy in solution over a range of pH values (5.5–8.0) and temperatures (25–50 °C), with respect to the allocation and mobility of fatty acid (FA) molecules bound to the proteins and conformation of the binding sites. In all proteins bound FA undergo a permanent intra-albumin migration between the binding sites and inter-domain residence. Nature identity of the recombinant human albumin to its serum-derived analog was observed. However, the binding sites of bovine albumin appeared shorter in length and wider in diameter than those of human albumin. Presumably, less tightly folded domains in bovine albumin allow better penetration of water molecules in the interior of the globule that resulted in higher activation energy of FA dissociation from the binding site. Thus, the sensitive technique based on ESR non-covalent spin labeling allowed quantitative analysis and reliable comparison of the fine features of binding proteins. 相似文献
499.
Kerstin Hesse 《Advances in Computational Mathematics》2009,30(1):37-59
This paper investigates the s-energy of (finite and infinite) well separated sequences of spherical designs on the unit sphere S
2. A spherical n-design is a point set on S
2 that gives rise to an equal weight cubature rule which is exact for all spherical polynomials of degree ≤n. The s-energy E
s
(X) of a point set of m distinct points is the sum of the potential for all pairs of distinct points . A sequence Ξ = {X
m
} of point sets X
m
⊂S
2, where X
m
has the cardinality card(X
m
)=m, is well separated if for each pair of distinct points , where the constant λ is independent of m and X
m
. For all s>0, we derive upper bounds in terms of orders of n and m(n) of the s-energy E
s
(X
m(n)) for well separated sequences Ξ = {X
m(n)} of spherical n-designs X
m(n) with card(X
m(n))=m(n).
相似文献
500.
We study interlacing properties of the zeros of two types of linear combinations of Laguerre polynomials with different parameters, namely and . Proofs and numerical counterexamples are given in situations where the zeros of Rn, and Sn, respectively, interlace (or do not in general) with the zeros of , , k=n or n−1. The results we prove hold for continuous, as well as integral, shifts of the parameter α. 相似文献