排序方式: 共有18条查询结果,搜索用时 19 毫秒
1.
Miró P Pierrefixe S Gicquel M Gil A Bo C 《Journal of the American Chemical Society》2010,132(50):17787-17794
Uranyl-peroxide nanoclusters display different topologies based on square, pentagonal and hexagonal building blocks. Computed complexation energies of different cations (Li(+), Na(+), K(+), Rb(+), and Cs(+)) with [UO(2)(O(2))(H(2)O)](n) (n = 4, 5, and 6) macrocycles suggest a strong cation templating effect. The inherent bent structure of a U-O(2)-U model dimer is demonstrated and justified through the analysis of its electronic structure, as well as of the inherent curvature of the four-, five-, and six-uranyl macrocyles. The curvature is enhaced by cation coordination, which is suggested to be the driving force for the self-assembly of the nanocapsules. 相似文献
2.
Self-injection length in La0.7Ca0.3MnO3-YBa2Cu3O7-δ ferromagnet-superconductor multilayer thin films
We have carried out extensive studies on the self-injection problem in barrierless heterojunctions between La0.7Ca0.3MnO3 (LCMO) and YBa2Cu3O7-δ (YBCO) thin films. The heterojunctions were formed in situ by sequentially growing LCMO and YBCO films on 〈100〉 LaAlO3 (LAO) substrate using a pulsed laser deposition (PLD) system. YBCO micro-bridges with 64 μm width were patterned both on
the LAO (control) and LCMO side of the substrate. Critical current, I
c, was measured at 77 K on both the control side as well as the LCMO side for different YBCO film thickness. It was observed
that while the control side showed a J
c of ∼ 2 × 106 A/cm2, the LCMO side showed about half the value for the same thickness (1800 ?). The difference in J
c indicates that a certain thickness of YBCO has become ‘effectively’ normal due to self-injection. From the measurement of
J
c at two different thicknesses (1800 ? and 1500 ?) of YBCO films both on the LAO as well as the LCMO side, the value of self-injection
length (at 77 K) was estimated to be ∼ 900 ?. To the authors’ best knowledge, this is the first time that self-injection length
has been quantified. A control experiment carried out with LaNiO3 deposited by PLD on YBCO did not show any evidence of self-injection. 相似文献
3.
Pierrefixe SC Fonseca Guerra C Bickelhaupt FM 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(3):819-828
Why is silicon hypervalent and carbon not? Or why is [Cl? CH3? Cl]? labile with a tendency to localize one of its axial C? Cl bonds and to largely break the other one, while the isostructural and isoelectronic [Cl? SiH3? Cl]? forms a stable pentavalent species with a delocalized structure featuring two equivalent Si? Cl bonds? Various hypotheses have been developed over the years focusing on electronic and steric factors. Here, we present the so‐called ball‐in‐a‐box model, which tackles hypervalence from a new perspective. This model reveals the key role of steric factors and provides a simple way of understanding the above phenomena in terms of different atom sizes. Our bonding analyses are supported by computation experiments in which we probe, among other things, the shape of the SN2 potential‐energy surface of Cl? attacking a carbon atom in the series of substrates CH3Cl, .CH2Cl, ..CHCl, and ...CCl. Our findings for ClCH3Cl? and ClSiH3Cl? are generalized to other Group 14 central atoms (Ge, Sn, and Pb) and axial substituents (F). 相似文献
4.
5.
6.
CoFe2O4-BaTiO3 composites were prepared using conventional ceramic double sintering process with various compositions. Presence of two phases
in the composites was confirmed using X-ray diffraction. The dc resistivity and thermoemf as a function of temperature in
the temperature range 300 K to 600 K were measured. Variation of dielectric constant (ɛ′) with frequency in the range 100 Hz to 1 MHz and also with temperature at a fixed frequency of 1 kHz was studied. The ac
conductivity was derived from dielectric constant (ɛ′) and loss tangent (tan δ). The nature of conduction is discussed on the basis of small polaron hopping model. The static value of magnetoelectric
conversion factor has been studied as a function of magnetic field. 相似文献
7.
A Gurtu P K Malhotra I S Mittra P M Sood SC Gupta VK Gupta GL Kaul LK Mangotra Y Prakash NK Rao ML Sharma 《Pramana》1974,3(5):311-322
This is a continuation of our earlier investigation (Gurtuet al 1974Phys. Lett. 50 B 391) on multiparticle production in proton-nucleus collisions based on an exposure of emulsion stack to 200 GeV/c beam at the NAL. It is found that the ratioR em = 〈n s〉/〈n ch〉, where 〈n ch〉 is the charged particle multiplicity in pp-collisions, increases slowly from about 1 at 10 GeV/c to 1·6 at 68 GeV/c and attains a constant value of 1·71 ± 0·04 in the region 200 to 8000 GeV/c. Furthermore,R em = 1·71 implies an effectiveA-dependence ofR A =A 0.18,i.e., a very weak dependence. Predictions ofR em on various models are discussed and compared with the emulsion data. Data seem to favour models of hadron-nucleon collisions in which production of particles takes place through adouble step mechanism,e.g., diffractive excitation, hydrodynamical and energy flux cascade as opposed to models which envisage instantaneous production. 相似文献
8.
Pierrefixe SC Poater J Im C Bickelhaupt FM 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(23):6901-6911
Silicon in [Cl? SiH3? Cl]? is hypervalent, whereas carbon in [Cl? CH3? Cl]? is not. We have recently shown how this can be understood in terms of the ball‐in‐a‐box model, according to which silicon fits perfectly into the box that is constituted by the five substituents, whereas carbon is too small and, in a sense, “drops to the bottom” of the box. But how does carbon acquire hypervalency in the isostructural and isoelectronic noble gas (Ng)/methyl cation complexes [Ng? CH3? Ng]+ (Ng=He and Ne), which feature a delocalized D3h‐symmetric structure with two equivalent C? Ng bonds? From Ng=Ar onwards, the [Ng? CH3? Ng]+ complex again acquires a propensity to localize one of its axial C? Ng bonds and to largely break the other one, and this propensity increases in the order Ng=Ar3Ng+ and, for comparison, CH3Ng+, NgHNg+, and NgH+. It appears that, at variance with [Cl? CH3? Cl]?, the carbon atom in [Ng? CH3? Ng]+ can no longer be considered as a ball in a box of the five substituents. 相似文献
9.
Munshi G Mustafa Sudhir Raniwala T Awes B Rai RS Bhalerao JG Contreras RV Gavai SK Ghosh P Jaikumar GC Mishra AP Mishra H Mishra B Mohanty J Nayak J-Y Ollitrault SC Phatak L Ramello R Ray PK Sahu AM Srivastava DK Srivastava VK Tiwari 《Pramana》2006,67(5):961-981
This is the report of Heavy Ion Physics and Quark-Gluon Plasma at WHEPP-09 which was part of Working Group-4. Discussion and
work on some aspects of quark-gluon plasma believed to have created in heavy-ion collisions and in early Universe are reported. 相似文献
10.