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61.
It is well known that porphyrin derivatives play a key role in the primary process of photo-synthesis[1], in which porphyrins directly absorb the sunlight or indirectly acquire excitation en-ergy from light-harvesting antenna system to reach their excited state, and then donate electrons to quinone acceptors to yield a series of charge-separated species. In general, only first singlet ex-cited state of porphyrins is involved in energy transfer process[2]. However, highly excited state (S2 stat… 相似文献
62.
New spin-state-selective (S3) NMR pulse sequences exclusively applying cross-polarization schemes to achieve optimum homonuclear and heteronuclear 1H-X coherence transfer are reported for the simple and accurate measurement of the magnitude and sign of heteronuclear coupling constants for samples at natural abundance. The proposed spin-edited HCP-TOCSY experiments are based on clean heteronuclear S3 excitation, generated by simultaneous co-addition of two independent in-phase and anti-phase components created during the mixing heteronuclear J-cross-polarization (HCP) step, which is finally transferred to other protons by a conventional homonuclear TOCSY mechanism. Selective 1D and non-selective 2D approaches for the easy determination of long-range proton-carbon and proton-nitrogen coupling constants on any protonated and non-protonated heteronuclei are presented and discussed for several organic molecules. 相似文献
63.
64.
E.?V.?TsipisEmail author V.?V.?Kharton I.?A.?Bashmakov E.?N.?Naumovich J.?R.?Frade 《Journal of Solid State Electrochemistry》2004,8(9):674-680
Developments of intermediate-temperature solid oxide fuel cells (IT SOFCs) require novel anode materials with a high electrochemical activity at 800–1070 K. The polarization of cermet anodes, made of nickel, ceria and yttria-stabilized zirconia (YSZ) and applied onto a YSZ solid electrolyte, can be significantly reduced by catalytically active ceria additions, the relative role of which increases with decreasing temperature. Further improvement is observed when using Ce0.8Gd0.2O2–
(CGO) having a high oxygen ionic conductivity instead of undoped ceria, owing to enlargement of the electrochemical reaction zone. Nanocrystalline CGO powders with grain sizes of 8–35 nm were thus synthesized via the cellulose-precursor technique and introduced into Ni–CGO–YSZ cermets, and tested in contact with a (La0.9Sr0.1)0.98Ga0.8Mg0.2O3–
(LSGM) electrolyte at 873–1073 K. The results showed that the anode performance can be enhanced by additional surface activation, in particular by impregnation with a Ce-containing solution, and also by incorporation of YSZ, which probably acts as a cermet-stabilizing component. The overpotential of the surface-modified Ni–CGO (25 wt%–75 wt%) anode in a 10% H2/90% N2 atmosphere was approximately 110 mV at 1073 K with a current density of 200 mA/cm2.Presented at the OSSEP Workshop Ionic and Mixed Conductors: Methods and Processes, Aveiro, Portugal, 10–12 April 2003 相似文献
65.
Molecular mobility in thermotropic polyesters and side-chain polymers with different struc-ture of mesogens and spacers has been studied by dielectrical method in dilutesolutions. The results made it possible to establish the multiplicity of dielectric relaxationtransitions which reflects the small- and large-scale types of molecular motion. It was shownthat dielectric relaxation processes occurring in accordance with local mechanism (relaxationtimes 10~(-9)--10~(-7)s. and the activation energy 10--50kJ/mol) are due to the mobility of kineticchain elements of different length within a monomer units. It was found that the dielectricrelaxation process connected with a large-scale form of molecular motion (relaxation times10~(-5)--10~(-6)s. and the activation energy 100kJ/mol) did not depend on the molecular massbut was infiuenced by factors changing the conformational state of the macromolecule. It isestablished tha the cooperative reorientation mobility of associated mesogenic fragments isthe source of the large-scale process. 相似文献
66.
光谱实验室的建设和管理 总被引:1,自引:0,他引:1
阐述冶金、铸造等行业用于金属成分分析的直读发射光谱仪实验室的建设和管理。从仪器的调研、选型,实验室选址,基础设施设备的准备,仪器的安装、调试、验收、日常分析,实验室管理等几个方面,分别作了介绍。 相似文献
67.
68.
Here, we will show photo-induced supramolecular chirality in thin films of achiral amorphous polymers with azo groups in their side-chain. A matter of particular interest is the effect of various film thicknesses on azimuthal rotation and ellipticity of incident/transmitted polarized light. Furthermore, we investigated the temporal stability of inscribed chirality. By polarimetric measurements, we found out that the azimuthal rotation gets higher with layer thickness. In this scope, we were able to measure a very high azimuthal rotation of /μm. The inscribed chirality was stable for several days. Furthermore, we investigated the time-resolved behavior of incident and transmitted polarization ellipticities for various thicknesses. The time dependency may be explained by a two-step process: (1) fast trans-cis-isomerization resulting in photo-orientation and (2) slow photo-induced mass flow. 相似文献
69.
The mass resolution of a time-of-flight (TOF) mass spectrometer is directly proportional to its total flight pathlength. Multi-turn or multi-passage ion optical geometries are necessary to obtain fight distances of sufficient length within reasonable size limitations. We have investigated ion optics for a multi-turn TOF mass spectrometer with electrostatic sectors. The concept of 'perfect' focusing conditions is introduced. Furthermore, a new type of multi-turn TOF mass spectrometer, the MULTUM Linear plus, was developed. It consists of four cylindrical electric sectors and 28 electric quadrupole lenses. It has a vacuum chamber 60 x 70 x 20 cm in size. Mass resolution is demonstrated to increase according to the number of ion cycles. A mass resolution of 350 000 (m/z = 28, FWHM) was achieved after 501.5 cycles. The MULTUM Linear plus analyzer is not simple, however; 28 electric quadrupole lenses are used. In order to reduce the number of ion optical parts, an improved multi-turn TOF mass spectrometer, the MULTUM II, consisting of only four toroidal electric sectors, was also developed. The possibility of tandem mass spectrometric applications using multi-turn TOF mass spectrometers is also discussed. 相似文献
70.
Hiroshi Tatewaki Tomohiro Hashimoto Kimihiko Hirao 《Theoretical chemistry accounts》1997,98(2-3):71-74
Using optimal exponents for B through Ne given by Dunning and those for Al through Ar by Woon and Dunning, d-type contracted polarization functions (2d/1d), (3d/1d), and (3d/2d) are generated from natural orbitals of atomic single and double excitation configuration interaction (SDCI) calculations,
where the numbers before and after the slash are those of the primitive and contracted Gaussian type functions. The resulting
contracted functions are tested on N2 and P2 molecules by self-consistent field and SDCI calculations, which clarify characteristics of the present polarization functions.
Received: 5 June 1997 / Accepted: 20 August 1997 相似文献