Laserspektroskopie

X-Ray spectra and chemical binding     

One‐ and two‐photon activity of cross‐conjugated photoinitiators with bathochromic shift

Intrigued by the good performance of 1,5‐diphenylpenta‐1,4‐diyn‐3‐one ( DPD ) as photoinitiator for radical polymerization we prepared and investigated several donor substituted derivatives. UV‐Vis spectroscopy revealed a gradual red‐shift of λ_max and higher extinction in the order of the donor capability. A methoxy‐substituted derivative ( O‐DPD ) exhibited significant photoinitiation activity in photo‐DSC experiments. Steady state photolysis experiments showed decreased decomposition rates with increasing donor capability. A dimethylamino derivative N‐DPD was even photostable under these conditions. Because of to the D‐π‐A‐π‐D system of these compounds two‐photon induced 3D photopolymerization experiments were performed and N‐DPD showed outstanding performance compared to often applied single photon initiators. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3280–3291, 2007     

叶轮机械设计自变数在内外环壁面上的限制条件及轴流式叶轮机械S1流面的翘曲

本文利用中心流面法的概念,指出叶轮机械的设计白变数在内、外环壁面上应有附加的限制条件,并导得其具体简明方程。同时,还定性地分析了S₁流面的翘曲情况。     

超导临界温度理论(Ⅰ)

本文求出了Eliashberg方程在T=T_c时的解,得到了下面的临界温度级数表示式: 其中α₀(μ^*),α₁(μ^*)等系数是μ^*的函数.此式表明,T_c不仅依赖于λ,〈ω²〉和μ^*,而且依赖于有效声子谱α²F(ω)的各级矩〈ω²n〉.这是区别于前人的T_c公式最重要的一点。这说明像McMillan以及Allen和Dynes的T_c公式不仅是近似的,而主要是他们没有能正确地概括出α²F(ω)对T_c的影响.     

Enzymatic hydroxylations with molecular oxygen

For thermodynamic reasons, biological hydroxylations cannot usually proceed according to the β-oxidation scheme, but are possible only with the aid of molecular oxygen by a route requiring a large amount of energy. The corresponding enzymes, known as “mixed function oxygenases” or more appropriately “monooxygenases”, require two reduction equivalents for the activation of oxygen. The cytochrome P-450-dependent monooxygenases are taken as examples for the discussion of the chemistry of the enzymatic catalysis. The central problem of the activation of oxygen has not yet been solved, but an “oxenoid” mechanism can be deduced from model investigations.     

Microprobe analysis of low alloyed sintered steels

Homogenization of Mo, W and Cr in alloyed P/M carbon steels during sintering with a transient liquid phase has been investigated by microscopic and microanalytical means. The reaction was found to start with carburization of the VIa metal, continues with the formation of different carbides, and generation of a liquid phase between the carbide and -Fe. The steady state equilibrium remains stable until all VIa metal has been consumed. Microprobe analysis was found to yield optimum results if selected model samples, in which homogenization should not proceed too fast, are investigated.Dedicated to Professor Günther Tölg on the occasion of his 60th birthday     

Diphenyloligothiophene-based dichromophoric macrocycles and their ability to form donor/acceptor complexes

A series of four dichromophoric rigid macrocycles 6a-6d, two with diphenyloligothiophene chromophores, the other two with more electron-rich diphenyl-EDOT or diphenyl-bis-EDOT chromophores, have been synthesized. The absorption spectrum of the diphenyl-bis-EDOT based macrocycle 6d displayed the most pronounced vibronic resolution with a well-resolved 0-0 transition, indicating a fully planarized geometry of the diphenyl-bis-EDOT chromophores. The (1)H NMR spectra of the macrocycles displayed weak to moderate chemical shifts of characteristic signals upon addition of pi-conjugated oligonitro-9-fluorenone acceptors. X-ray single-crystal analysis showed that columnar pi-stacked donor/acceptor complexes are formed with the stacks composed of alternating donor and acceptor molecules. The stoichiometry of the crystalline, dark-colored complexes was found to be 1:1 by elemental analysis and integration of the (1)H NMR peaks. The complex formation is accompanied by remarkably large Stern-Volmer constants of fluorescence quenching.     

Photocurrent theory based on coordinate dependent lifetime

Recent work by Pejova [Mater. Res. Bull. 43, 2887 (2008)] showed that the widely cited classical photocurrent theory of DeVore [Phys. Rev. 102, 86 (1956)] does not necessarily apply for photocurrent experiments carried out on thin-film semiconductors. In this Letter, we theoretically and experimentally justify the successful use of the photocurrent model published by Bouchenaki et al. [J. Opt. Soc. Am. B 8, 691 (1991)].     

The Haar System as a Schauder Basis in Spaces of Hardy–Sobolev Type

We show that, for suitable enumerations, the Haar system is a Schauder basis in the classical Sobolev spaces in \({\mathbb R}^d\) with integrability \(1<p<\infty \) and smoothness \(1/p-1<s<1/p\). This complements earlier work by the last two authors on the unconditionality of the Haar system and implies that it is a conditional Schauder basis for a nonempty open subset of the (1 / p, s)-diagram. The results extend to (quasi-)Banach spaces of Hardy–Sobolev and Triebel–Lizorkin type in the range of parameters \(\frac{d}{d+1}<p<\infty \) and \(\max \{d(1/p-1),1/p-1\}<s<\min \{1,1/p\}\), which is optimal except perhaps at the end-points.