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41.
基于全统一模型和密度泛函理论(DFT)计算,我们提出了具有高对称性和稳定性的巯基保护的中空金纳米球Au60(SR)20的原子结构。Au60(SR)20由一个二十面体Au50富勒烯中空笼子(由20个四面体Au4融合构成)和10个[―RS―Au―SR―]订书针结构组成,并遵循“分离和保护”规则。DFT计算表明,这种空心Au60(SR)20纳米球具有大的带隙(1.3 eV)以及在笼中心的核独立化学位移(NICS)为负值(−5),表明其高度的化学稳定性。此外,四面体Au4单元中心的NICS值远大于空心笼中心的NICS值,表明Au60(SR)20的总体稳定性可能来自每个四面体Au4单元的局部稳定性。正的谐波振动频率说明Au60(SR)20纳米球至少是势能表面的局部最小值。另外,我们还通过融合四面体Au4层设计了双层中空金纳米球,表明调整中空金纳米球壳层厚度是可行的。最后,我们还介绍了更大的中空金纳米球Au180(SR)60的设计。这项工作提供了可控设计中空金纳米球的新策略。 相似文献
42.
A. Wender A. Barreau C. Lefebvre A. Di Lella A. Boutin P. Ungerer A. H. Fuchs 《Adsorption》2007,13(5-6):439-451
We report an application of a previously developed force field for adsorption of hydrocarbons in silicalite (Pascual, P.,
et al. in Phys. Chem. Chem. Phys. 5:3684–3693, 2003), to the case of the linear alkane-sodium faujasite systems. In order to extend this force field from siliceous to cationic
zeolites, we propose to take into account the polarization part of the zeolite-molecule interaction energy. A first order
polarization term is explicitly considered for this purpose, using standard molecular polarizabilities. Polarization appears
to amount to 30–40% of the zeolite-alkane interaction energy, as a consequence of the strong electric field created by the
sodium cation distribution and negatively charged framework. This approach is compared with experimental adsorption isotherms
of ethane, propane, n-octane and n-decane in NaY from the literature and with original measurements of n-butane isotherms
in NaY obtained by thermal gravimetry. Henry constants and heats of adsorption at zero coverage of n-alkanes (n=6–10) are also compared with experimental measurements. Although no specific parameter has been calibrated for extending
the force field, the general agreement between simulation results and experiments is satisfactory. Cation redistribution upon
alkane adsorption is not observed in these simulations. 相似文献
43.
Naseem A. Ramsahye Guillaume Maurin Sandrine Bourrelly Philip L. Llewellyn Thomas Devic Christian Serre Thierry Loiseau Gerard Ferey 《Adsorption》2007,13(5-6):461-467
A Grand Canonical Monte Carlo study has been performed in order to compare the different CO2 adsorption mechanisms between two members of the MIL-n family of hybrid metal-organic framework materials. The MIL-53 (Al)
and MIL-47 (V) systems were considered. The results obtained confirm that there is a structural interchange between a large
pore and narrow pore forms of MIL-53 (Al), not seen with the MIL-47 (V) material, which is a consequence of the presence of
μ
2-OH groups. The interactions between the CO2 molecules and these μ
2 OH groups mainly govern the adsorption mechanism in this MIL-53 (Al) material. The subsequent breaking of these adsorption
geometries after the adsorbate loading increases past the point where no more preferred adsorption sites are available, are
proposed as key features of the breathing phenomenon. After this, any new adsorbates introduced into the MIL-53 (Al) large
pore structure experience a homogeneous adsorption environment with no preferential adsorption sites in a similar way to what
occurs in MIL-47 (V). 相似文献
44.
巨正则系综Monte Carlo模拟方法确定活性炭的微孔尺寸 总被引:3,自引:0,他引:3
根据299K下甲烷在活性炭中的吸附实验数据,通过调节狭缝微孔的孔宽参数,利用巨正则系综MonteCarlo(GCEMC)方法得到不同孔宽下流体的微观结构以及吸附等温线.比较并拟合模拟结果和实验数据,确定了活性炭微孔的平均孔宽,为下一步求解微孔尺寸分布以及为预测吸附剂在不同温度下吸附不同吸附质分子时的吸附性能提供了基础与指导.模拟中,甲烷分子采用单点Lennard-Jones球型分子模型,活性炭用狭缝孔来近似表征,流体分子与单个狭缝墙的相互作用采用著名的Steele的10-4-3势能模型.模拟表明,此方法为考察介孔材料的微孔分布以及微孔平均孔宽提供了新的思路. 相似文献
45.
在考察运河(杭州段)水道的历史变迁的基础上,明确了基含义和范围;并进而论述了其功能的演变及其对杭州城市发展所起的作用,认为:其主要功能有航运、水利、纳污和景观、生态、文化等几项;其中,航运功能在古代最为突出,对杭州城市的作用也最为显著,在早期,[决定了城市的兴起和繁荣,也控制了城市的基本空间形态;当代景观、生态和文化功能凸显,运河必将成为推动和促进城市发展、城市整体形象完善的重要因素。 相似文献
46.
We propose the complex group theoretical Clebsch-Gordan coefficients as a novel origin of CP violation. This is manifest in our model based on SU(5) combined with the double tetrahedral group, T′. Due to the presence of the doublet representations in T′, there exist complex CG coefficients, leading to explicit CP violation in the model, while the Yukawa couplings and the vacuum expectation of the scalar fields remain real. The tri-bimaximal neutrino mixing matrix arises from the CG coefficients of T′. In addition to the prediction for , the model gives rise to a sum rule, , which is a consequence of the Georgi-Jarlskog relations in the charged fermion sector. The leptonic Dirac CP violating phase, δ?, is predicted to be ∼227°, which turns out to be the value needed to account for the difference between the experimental best fit value for the solar mixing angle and the TBM prediction. The predicted CP violation measures in the quark sector are also consistent with the current experimental data. 相似文献
47.
We consider a class of rearrangement invariant Banach Function Spaces recently appeared in a paper by the same authors, containing at the same time some Lorentz spaces Γ(ν), classical Lebesgue spaces and small Lebesgue spaces. We discuss the main properties coming directly from the norm, and, for certain values of the involved parameters, we prove some estimates of the norm of the associate space. 相似文献
48.
Jogesh C. Pati 《Pramana》2003,60(2):291-336
It is noted that a set of facts points to the relevance in four dimensions of conventional supersymmetric unification based
on minimally a string-unifiedG(224) symmetry, or maximallySO(10). These include: (i) the observed family structure, (ii) quantization of electric charge, (iii) meeting of the three gauge
couplings, (iv) neutrino oscillations (in particular the value of δm
2(νμ−δ
τ), suggested by SuperK), (v) the intricate pattern of the masses and mixings of the fermions, including the smallness ofV
cb and the largeness ofθ
μνμτ
osc
, and (vi) the need for B-L as a generator to implement baryogenesis (via leptogenesis). A concrete proposal is presented
within a predictiveSO(10)/G(224) framework that successfully describes the masses and mixings of all fermions, including the neutrinos — with eight predictions,
all in agreement with observation. Within this framework, a systematic study of proton decay is carried out, which (a) pays
special attention to its dependence on the fermion masses, (b) limits the threshold corrections so as to preserve natural
coupling unification, and (c) uses recently improved values of the matrix element and renormalization effects. Allowing for
both minimal supersymmetric standard model (MSSM) and its proposed variant, the so-called extended supersymmetric standard
model (ESSM), as effective low-energy the ories, the study shows that a conservative upper limit on the proton lifetime is
about (l–2)× 1034 years, with ·−K+ being the dominant decay mode, and quite possibly μ+
K
0 ande
+π0 being prominent. This in turn strongly suggests that an improvement in the current sensitivity by a factor of five to ten
ought to reveal proton decay. For comparison, some alternatives to the conventional approach to unification pursued here are
mentioned at the end.
Invited paper presented at the International Summer School held at ICTP, Trieste (June, 2001) and at WHEPP-7 Conference, Allahabad,
India (January, 2002). This is an updated version of the paper presented at the Erice School (September, 2000), hep-ph/0106082. 相似文献
49.
采用巨正则蒙特卡罗方法(GCMC)研究了BC3复合纳米管的物理吸附储氢性能,获得了该纳米管在不同温度和压强下的吸附等温线,及其在不同条件下的物理储氢吸附量,并和相应的碳纳米管进行了对比研究。结果表明,BC3纳米管在所有条件下的储氢性能均优于相应的碳纳米管,因而它是一种比碳纳米管更强的氢存储介质,并从纳米管和H2分子以及H2分子和H2分子之间的平均总相互作用能的分布情况等因素出发解释了这两种纳米管有不同储氢行为的原因。 相似文献
50.
AbstractIn this paper, we study the continuum time dynamics of a stock in a market where agents behaviour is modelled by a Minority Game and a Grand Canonical Minority Game. The dynamics derived is a generalized geometric Brownian motion; from the Black&Scholes formula the calibration of both the Minority Game and the Grand Canonical Minority Game, by means of their characteristic parameters, is performed. We conclude that for both games the asymmetric phase with characteristic parameters close to critical ones is coherent with options implied volatility market. 相似文献