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排序方式: 共有115条查询结果,搜索用时 31 毫秒
41.
42.
Following exposure to X-irradiation at low temperatures, the main reactions taking place in single crystals of cytosine monohydrate doped with minute amounts of 2-thiocytosine are hole transfer (HT) from the electron-loss centers to the dopant and recombination of oxidation and reduction products, assumedly by electron transfer. A huge deuterium kinetic isotope effect (KIE; >102-103) at 100 K, together with the kinetic curves obtained and density functional theory (DFT) calculations of equilibrium energy changes, indicates that these reactions proceed through a concerted proton-coupled electron/hole transfer where the proton transfer occurs between hydrogen-bonded cytosine molecules. The temperature dependence of these reaction rates between 10 and 150 K in normal and partially deuterated samples was investigated by monitoring the growth and decay of the various radical species over time using electron paramagnetic resonance (EPR) spectroscopy. By assuming a random distribution of the hole donors and acceptors in the crystals, the data are consistent with an exponential distance-dependent rate, giving a distance decay constant (beta) around 1 A-1 for the HT, which indicates that a long-range single-step superexchange mechanism mediates the charge transfer. The reactions undergo a transition from a slow, weakly temperature-dependent rate to an Arrhenius-type rate at 40-50 K, presumably being activated by excitation of low-frequency intermolecular vibrations that couple to the process. Below this transition temperature, the transfer probability might be dominated by temperature-independent nuclear tunneling. A similar beta value in both temperature regions suggests that hopping is not activated. 相似文献
43.
Kralj Slavko Rojnik Matija Kos Janko Makovec Darko 《Journal of nanoparticle research》2013,15(5):1-11
Electrode catalysts composed of carbon-supported PtRu nanoparticles (PtRu/C) for use as a direct methanol fuel cell anode were synthesized by the reduction of precursor ions in an aqueous solution via irradiation with a high-energy electron beam. The effect of pH control in the precursor solution on the PtRu mixing state and the methanol oxidation activity was studied in order to enhance the catalytic activity for methanol oxidation. The PtRu/C structures were characterized by transmission electron microscopy, inductively coupled plasma atomic emission spectrometry, X-ray fluorescence spectrometry, and X-ray diffraction and X-ray absorption fine structure techniques. The methanol oxidation activity was evaluated by linear sweep voltammetry. The initial pH of the precursor solution has little influence on the average grain size for the metal particles (approximately 3.5 nm) on the carbon particle supports, but the dispersibility of the metal particles, PtRu mixing state, and methanol oxidation activity differed. The maintenance of a low pH in the precursor solution gave the best dispersibility of the PtRu nanoparticles supported on the surface of the carbon particles, whereas, a high pH gave the best PtRu mixing state and the highest oxidation current although a low dispersibility of the PtRu nanoparticles supported on the surface of the carbon particles was obtained. The PtRu mixing state strongly correlated with the methanol oxidation current. In addition, a high pH was more effective for PtRu mixing when using an electron beam irradiation reduction method, because the complexation reaction of the chelating agents was improved, which resulted in an enhancement of the catalytic activity for methanol oxidation. 相似文献
44.
Let H be an infinite-dimensional complex Hilbert space and let B(H) be the algebra of all bounded linear operators on (H). In the paper the equivalent definition of the star partial order on B(H), using selfadjoint idempotent operators, is introduced. Also some properties of the generalized concept of order relations on B(H), defined with the help of idempotent operators, are investigated. 相似文献
45.
Janko?Lu?nik Janez?Pirnat Zvonko?Trontelj Toma??Apih Alan?Gregorovi? 《Applied magnetic resonance》2009,36(1):115-120
The field application of a 14N nuclear quadrupole resonance (NQR) detector needed for the detection of different explosives, including trinitrotoluene
(TNT), requires the examination of the distribution of 14N NQR lines stemming from the monoclinic and/or orthorhombic modifications of TNT, as well as from a mixture of both. In this
work, 30 different TNT samples up to 70 years old were measured. The main result of this study is that the measured 14N NQR spectrum is strongly influenced by the environmental conditions to which the explosive was subject during its history. 相似文献
46.
Janko Marovt 《Linear algebra and its applications》2010,432(6):1595-1607
Let D be an arbitrary division ring and Mn(D) the multiplicative semigroup of all n×n matrices over D. We study non-degenerate, injective homomorphisms from M2(D) to M4(D). In particular, we present a structural result for the case when D is the ring of quaternions. 相似文献
47.
48.
Zvonimir Janko 《Israel Journal of Mathematics》2013,197(1):1-22
We characterize the title p-groups for all primes p. 相似文献
49.
Janko Latschev 《manuscripta mathematica》2006,121(3):293-315
We describe a homological criterion for the existence of a closed form transverse to a foliation which is allowed to have certain tame singularities, generalizing results in the nonsingular case by Sullivan. As illustrations of the method, we derive results about the existence of singular symplectic forms and about the characterization of intrinsic harmonicity for forms. 相似文献
50.