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1.
Ab initio SCF computations on the intrinsic preferences of the H+, CH
3
+
and C2H
5
+
cations towards the two principal sites of protonation or alkylation on cytosine, N3 or O2, show that this preference undergoes a continuous modification with the increase in size and complexity of the cation. N3 is the preferred site of fixation of H+, O2 the preferred site of C2H
5
+
, while CH
3
+
has no marked preference. The exchange repulsion term of the binding energy appears responsible for the preference of C2H
5
+
for O2.This work was supported by the Ligue Francaise contre le Cancer and the National Foundation for Cancer Research (USA) 相似文献
2.
《Composite Interfaces》2013,20(2-3):113-126
Polyamide66/polypropylene (PA66/PP) blend, graphite (Gr)-filled PA66/PP composite and nanoclay (NC)-filled PA66/PP nanocomposites were prepared by twin screw extrusion and injection molding. Three-body abrasive wear behaviour of the injection moulded composites was carried out using a rubber wheel abrasion wear tester. In this study, angular silica sand and quartz particles of size ranging from 200 to 250 μm were used as dry and loose abrasives. The tests were carried out for 150, 300, 450 and 600 m abrading distances at a constant load of 36 N. It was observed that inclusion of particulate fillers in PA66/PP have significant influence on wear under varied abrading distances for different abrasive particles. Further, it was found that NC-filled PA66/PP nanocomposite exhibited lower wear rate compared to Gr filled ones for different abrasive particles. In addition, the worn surfaces of the samples were examined by scanning electron microscopy (SEM) and the morphology was also discussed. 相似文献
3.
M. Laoues 《Letters in Mathematical Physics》1991,23(4):325-331
We consider the real vector space structure of the algebra of linear endomorphisms of a finite-dimensional real Clifford algebra (2, 4, 5, 6, 7, 8). A basis of that space is constructed in terms of the operators M
eI, eJ
defined by xe
I
· x · e
J
, where the e
I
are the generators of the Clifford algebra and I is a multi-index (3, 7).In particular, it is shown that the family (M
eI, eJ
) is exactly a basis in the even case. 相似文献
4.
A. Alvarez F. R. Romero J. F.R. Archilla J. Cuevas P. V. Larsen 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,51(1):119-130
We study the dynamics of moving discrete breathers in an interfaced piecewise DNA molecule.
This is a DNA chain in which all the base pairs are identical and
there exists an interface such that the base pairs dipole moments at each side are oriented in opposite
directions.
The Hamiltonian of the Peyrard-Bishop model is augmented with a
term that includes the dipole-dipole coupling between base pairs.
Numerical simulations show the existence of two dynamical regimes.
If the translational kinetic energy of a moving breather launched
towards the interface is below a critical value, it is trapped in
a region around the interface collecting vibrational energy. For
an energy larger than the critical value, the breather is
transmitted and continues travelling along the double strand with
lower velocity. Reflection phenomena never occur.
The same study has been carried out when a single dipole is oriented
in opposite direction to the other ones.
When moving breathers collide
with the single inverted dipole, the same effects appear. These
results emphasize the importance of this simple type of local
inhomogeneity as it creates a mechanism for the trapping of
energy.
Finally, the simulations show that, under favorable conditions,
several launched moving breathers can be trapped successively at the interface
region producing an accumulation of vibrational energy. Moreover,
an additional colliding moving breather can produce a saturation
of energy and a moving breather with all the accumulated energy
is transmitted to the chain. 相似文献
5.
V. I. Dimitrov J. D'Haan G. Knuyt C. Quasyhaegens L. M. Stals 《Applied Physics A: Materials Science & Processing》1996,63(5):475-480
A diffusion model of metal surface modification by plasma nitriding has been developed. This model takes into account the erosion effects at the plasma/solid interface occurring due to the ion bombardment of the surface. For constant sputtering rate, which is the usual situation during plasma nitriding, the growth of the sub-layers is well described by the analytical expressiong(t) =g
0,f
–1 (t/t
0), whereg(t) is the sub-layer thickness at timet,g
0 andt
0 are parameters which depend on the treated material and plasma characteristics,f
–1 is the inverse of the function — In(1 - x) + x), 0 x 1. Under negligible erosion effects, the expression forg(t) reduces to the parabolic law. The diffusion zone (substratum) growth does not follow the parabolic law as well. However, the deviation occurs after long plasma nitriding time. The model can be used for experimentally determining the effective diffusion coefficients and the erosion rate during plasma nitriding of metal surfaces. 相似文献
6.
作为一种广泛使用的工程塑料,尼龙的老化备受关注。当作为电力系统芯片的封装材料时,尼龙在自然环境下的老化有可能会导致封装失效,从而影响芯片使用的可靠性,严重时甚至导致芯片的失效,给电力行业带来巨大损失。常规的自然老化和人工加速老化评价周期非常漫长,不同因素对尼龙老化的影响机理十分复杂,且这种影响难以研究,使得评价尼龙的老化稳定性成为一大难题。采用自主开发的原位老化评价系统,对尼龙6(PA6)和尼龙66(PA66)的老化稳定性及湿度对老化的影响进行了研究。该系统可以实现光照/温度/湿度/氧气等环境因素的加载,通过高灵敏度地测定材料在综合环境因素作用下产生的气相降解产物来评价材料的老化稳定性,评价时间缩短到几小时。实验表明,PA6和PA66的气相降解产物以H2O和CO2为主,由于H2O在气相中的浓度不稳定,因此以CO2的产生量作为老化评价指标。通过对不同自然老化时间PA6和PA66的原位老化评价,并与其ATR-FTIR红外光谱图进行对照,证明了原位老化评价方法能够较好地反映尼龙的老化程度,自然老化时间越长,PA6和PA66的稳定性越低,CO2的产生量越大。进一步,采用该方法研究了湿度对PA6和PA66老化反应的影响,证明增大湿度对尼龙老化存在促进作用,而且升高温度会进一步促进湿度对老化的促进作用。研究表明,原位老化评价方法是一种快速评价尼龙老化稳定性及环境因素影响的有力手段。 相似文献
7.
In [L. Lebtahi, Lie algebra on the transverse bundle of a decreasing family of foliations, J. Geom. Phys. 60 (2010), 122–133], we defined the transverse bundle Vk to a decreasing family of k foliations Fi on a manifold M. We have shown that there exists a (1,1) tensor J of Vk such that Jk≠0, Jk+1=0 and we defined by LJ(Vk) the Lie Algebra of vector fields X on Vk such that, for each vector field Y on Vk, [X,JY]=J[X,Y]. 相似文献
8.
W. Fernengel H. Kronmüller M. Rapp Y. He 《Applied Physics A: Materials Science & Processing》1982,28(2):137-144
The isothermal crystallization of Fe40Ni40P14B6 (Metglas 2826) has been studied by transmission electron microscopy, using static observations of partially crystallized ribbons at room temperature and in situ dynamic registration of the crystallization process at elevated temperatures. At all temperatures crystallization takes place by the nucleation and growth of individual crystals. Analysis of the transformation kinetics allowed to determine the nucleation rates and the activation energy for crystal growth. The growth velocity of the crystal phase was found to be controlled by the diffusion coefficient of phosphorus in this alloy withD
0=2.5×1010±1cm{swu2}/s andQ=(3.4±0.15)eV. 相似文献
9.
10.
The infinitely many symmetries with arbitrary functions of timet for the potential modified Kadomtsev-Petviashvilli equation are obtained by using a simple direct method. These symmetries constitute a generalization of the well-knownW
algebra. 相似文献