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排序方式: 共有245条查询结果,搜索用时 31 毫秒
51.
N. Kalyvas I. Valais S. David Ch. Michail G. Fountos P. Liaparinos I. Kandarakis 《Optics and Spectroscopy》2014,116(5):743-747
Single crystal scintilators are used in various radiation detectors applications. The efficiency of the crystal can be determined by the Detector Optical Gain (DOG) defined as the ratio of the emitted optical photon flux over the incident radiation photons flux. A parameter affecting DOG is the intrinsic conversion efficiency (n C ) giving the percentage of the X-ray photon power converted to optical photon power. n C is considered a constant value for X-ray energies in the order of keV although a non-proportional behavior has been reported. In this work an analytical model, has been utilized to single crystals scintillators GSO:Ce, LSO:Ce and LYSO:Ce to examine whether the intrinsic conversion efficiency shows non proportional behavior under X-ray excitation. DOG was theoretically calculated as a function of the incident X-ray spectrum, the X-ray absorption efficiency, the energy of the produced optical photons and the light transmission efficiency. The theoretical DOG values were compared with experimental data obtained by irradiating the crystals with X-rays at tube voltages from 50 to 140 kV and by measuring the light energy flux emitted from the irradiated screen. An initial value for n C (calculated from literature data) was assumed for the X-ray tube voltage of 50 kV. For higher X-ray tube voltages the optical photon propagation phenomena was assumed constant and any deviations between experimental and theoretical data were associated with changes in the intrinsic conversion efficiency. The experimental errors were below 7% for each experimental setup. The behavior of n C values for LSO:Ce and LYSO:Ce were found very similar, i.e., ranging with values from 0.089 at 50 kV to 0.015 at 140 kV, while for GSO:Ce, n C demonstrated a peak at 80 kV. 相似文献
52.
A planar chiral non-metallocenic analogue of the most popular N,N-dimethylbenzylaminate palladacycle
Valery V. Dunina Eugeniya I. TurubanovaOlga N. Gorunova Michail V. LivantsovKonstantin A. Lyssenko Dmitrii Yu. AntonovYuri K. Grishin 《Polyhedron》2012,31(1):413-421
A racemic planar chiral tertiary amine pCp-CH2NMe2 (HL1, pCp = [2.2]paracyclophane-4-yl) was prepared by aminomethylation of the bromide pCp-Br with Eschenmoser’s salt. Direct cyclopalladation of this new ligand with palladium(II) acetate results in the formation of the racemic CN-dimer rac-3 in a moderate yield of 64%. The enantiomerically pure dimer (Spl, Spl)-3 was obtained by the standard procedure of racemic palladacycle resolution using (SC)-prolinate as a chiral derivatising agent. The ortho-palladated structure, absolute configuration of the chiral plane and stereochemical peculiarities of the new CN-palladacycle were established by means of NMR spectroscopy and an X-ray diffraction study of its (SC)-prolinate derivative. 相似文献
53.
Yuliya E. Ryzhkova Fedor V. Ryzhkov Michail N. Elinson Oleg I. Maslov Artem N. Fakhrutdinov 《Molecules (Basel, Switzerland)》2023,28(1)
Chromeno[2,3-b]pyridines are substances demanded in medicinal and material chemistry. PASE (pot, atom, and step economy) and in particular one-pot approaches are key green chemistry techniques that are applied for the synthesis of heterocyclic compounds. In this case, the PASE approach was extended with ‘component economy’, as solvent was used also as reactant (solvent-involved reaction). This approach was adopted for the one-pot synthesis of previously unknown O-substituted 5-alkoxy-5H-chromeno[2,3-b]pyridines via two-step transformation, namely the reaction of salicylaldehydes and malononitrile dimer, with the subsequent addition of alcohol. The mechanistic studies revealed the possibility of concurrent reaction. The studies aided in optimizing the reaction conditions for the best yields (77–93%). Thus, the one-pot reaction proceeds efficient and quickly, and the work-up procedure (only simple filtering) is very convenient. The structure of synthesized chromeno[2,3-b]pyridines was confirmed by 2D NMR spectroscopy. 相似文献
54.
Dr. Bruno Mattia Bizzarri Dr. Paola Manini Dr. Valeria Lino Prof. Marco d'Ischia Dr. Michail Kapralov Prof. Eugene Krasavin Klaudia Mráziková Prof. Jiří Šponer Dr. Judit E. Šponer Prof. Ernesto Di Mauro Prof. Raffaele Saladino 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(65):14919-14928
Formation and structural modification of oxygenated polycyclic aromatic hydrocarbons (oxyPAHs) by UV irradiation on minerals have recently been proposed as a possible channel of PAH transformation in astrochemical and prebiotic scenarios of possible relevance for the origin of life. Herein, it is demonstrated that high-energy proton-beam irradiation in the presence of various meteorites, including stony iron, achondrite, and chondrite types, promotes the conversion of two representative oxyPAH compounds, 1-naphthol and 1,8-dihydroxynaphthalene, to complex mixtures of oxygenated and oligomeric derivatives. The main identified products include polyhydroxy derivatives, isomeric dimers encompassing benzofuran and benzopyran scaffolds, and, notably, a range of quinones and perylene derivatives. Addition of urea, a prebiotically relevant chemical precursor, expanded the range of identified species to include, among others, quinone diimines. Proton-beam irradiation of oxyPAH modulated by nitrogen-containing compounds such as urea is proposed as a possible contributory mechanism for the formation and processing of insoluble organic matter in meteorites and in prebiotic processes. 相似文献
55.
Jens Hoppe Michail Olshanetsky Stefan Theisen 《Communications in Mathematical Physics》1993,155(3):429-448
We use quantum tori Lie algebras (QTLA), which are a one-parameter family of sub-algebras ofgl
, to describe local and non-local versions of the Toda systems. It turns out that the central charge of QTLA is responsible for the non-locality. There are two regimes in the local systems-conformal for irrational values of the parameter and non-conformal and integrable for its rational values. We also consider infinite-dimensional analogs of rigid tops. Some of these systems give rise to quantized (magneto-)hydrodynamic equations of an ideal fluid on a torus. We also consider infinite dimensional versions of the integrable Euler and Clebsch cases. 相似文献
56.
57.
58.
Dr. Dmitry S. Perekalin Dr. Valentin V. Novikov Alexander A. Pavlov Igor A. Ivanov Dr. Natalia Yu. Anisimova Alexey N. Kopylov Dr. Dmitry S. Volkov Dr. Irina F. Seregina Prof. Dr. Michail A. Bolshov Prof. Dr. Alexander R. Kudinov 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(13):4923-4925
Melittin is a membrane‐active peptide from bee venom with promising antimicrobial and anticancer activity. Herein we report on a simple and selective method for labeling of the tryptophan residue in melittin by the organometallic fragment [(C5H5)Ru]+ in aqueous solution and in air. Ruthenium coordination does not disturb the secondary structure of the peptide (as verified by 2D NMR spectroscopy), but changes the pattern of its intermolecular interactions resulting in an 11‐fold decrease of hemolytic activity. The high stability of the organometallic conjugate allowed the establishment of the biodistribution of the labeled melittin in mice by inductively coupled plasma MS analysis of ruthenium. 相似文献
59.
60.
Michail O. Danilov Gennady Ya. Kolbasov 《Journal of Solid State Electrochemistry》2010,14(12):2169-2172
An electrochemical method for the preparation of nanostructured composites based on multiwalled carbon nanotubes and chromium
oxide is proposed. The method involves electrodeposition of chromium oxides from a solution of hexavalent chromium oxide in
sulfuric acid on carbon nanotubes. By varying the electrolysis conditions one can obtain deposited—catalyst particles of different
size and vary the amount of catalyst. Oxygen electrodes have been made from the materials obtained for fuel cells with alkaline
electrolyte, which showed good electrocatalytic properties. 相似文献