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61.
62.
Swamy V Kuznetsov A Dubrovinsky LS McMillan PF Prakapenka VB Shen G Muddle BC 《Physical review letters》2006,96(13):135702
We investigated the size-dependent high-pressure phase transition behavior of nanocrystalline anatase TiO2 with synchrotron x-ray diffraction and Raman spectroscopy to 45 GPa at ambient temperature. Pressure-induced amorphization results in a high-density amorphous (HDA) form when the starting crystallite size is < 10 mm. The HDA-TiO2 transforms to a low-density amorphous form at lower pressures. Harnessing the nanometer length scale thus provides a new window for experimental investigation of amorphization in poor glass formers and a synthesis route for new amorphous materials. 相似文献
63.
The electronic and vibrational density of states of a semiconducting carbon nanotube in a crossed junction was investigated by elastic and inelastic scanning tunneling spectroscopy. The strong radial compression of the nanotube at the junction induces local metallization spatially confined to a few nanometers. The local electronic modifications are correlated with the observed changes in the radial breathing and G band phonon modes, which react very sensitively to local mechanical deformation. In addition, the experiments reveal the crucial contribution of the image charges to the contact potential at nanotube-metal interfaces. 相似文献
64.
65.
The amount of data collected during synchrotron X-ray diffraction (XRD) experiments is constantly increasing. Most of the time, the data are collected with image detectors, which necessitates the use of image reduction/integration routines to extract structural information from measured XRD patterns. This step turns out to be a bottleneck in the data processing procedure due to a lack of suitable software packages. In particular, fast-running synchrotron experiments require online data reduction and analysis in real time so that experimental parameters can be adjusted interactively. Dioptas is a Python-based program for on-the-fly data processing and exploration of two-dimensional X-ray diffraction area detector data, specifically designed for the large amount of data collected at XRD beamlines at synchrotrons. Its fast data reduction algorithm and graphical data exploration capabilities make it ideal for online data processing during XRD experiments and batch post-processing of large numbers of images. 相似文献
66.
Jacqueline Vitali 《Journal of chemical crystallography》1990,20(3):251-259
2,2-Anhydro-3-O-acetyl-2-thio-1--D-arabinofuranosylcytosine hydrochloride crystallizes in space group P212121 witha=10.373(1),b=14.517(2),c=9.496(1) Å. Reflections were measured on a diffractometer and the structure was solved by direct methods. Least-squares refinement converged atR=0.056 andR
w
=0.063. The study of this crystal structure showed that the alterations in the geometry of 2,2-anhydro-1--D-arabinofuranosylcytosine when the bridge oxygen is replaced by sulfur are localized in the region of the fused ring. The angle at the bridge atom decreases to nearly 90°, with concomitant enlargements of about 5°–7° in the angles opposite to the bridge atom. Angle C(1)-N(1)-C(6) decreases by 4°. Also, the amount of double bond character in the bond formed by C(2) and the bridge atom decreases. A survey of the conformational features of S,2-cyclonucleosides and comparison with O,2-cyclonucleosidcs showed that their preferred conformations are the same. However, S,2-cyclonucleosides exhibit a wider range of P and values. This correlates with a greater ease of the sulfur containing five-membered ring to pucker as compared to the oxygen-cyclo ring.This paper is part of the authors' dissertation (Vitali, 1986). 相似文献
67.
68.
Givenμ, κ, c>0, we consider the functional
defined on allR
n
-valued functionsu on the open subset Ω ofR
n
which are smooth outside a free discontinuity setS
u, on which the tracesu
+,u
− on both sides have equal normal component (i.e.,u has a tangential jump alongS
u).E
Du=Eu − 1/3 (divu)I, withEu denoting the linearized strain tensor.
The functionalF is obtained from the usual strain energy of linearized elasticity by addition of a term (the second integral) which penalizes
the jump discontin uities of the displacement.
The lower semicontinuous envelope
is studied, with respect to theL
1 (Ω;R
n
)-topology, on the spaceP(Ω) of the functions of bounded deformation with distributional divergence inL
2(Ω) (F is extended with value +∞ on the wholeP(Ω)). The following integral representation is proved:
whereϕ is a convex function with linear growth at infinity. NowEu is a measure,ɛ
Du represents the density of the absolutely continuous part of the absolutely continuous part ofE
Du, whileE
s
D
u denotes the singular part and ϕ∞ the recession function ofϕ.
Finally, we show that
coincides with the functional which intervenes in the minimum problem for the displacement in the theory of Hencky’s plasticity
with Tresca’s yield conditions. 相似文献
69.
Vitali Chkliar 《Integral Equations and Operator Theory》1997,29(3):364-367
Letu inH
2 be zero at one of the fixed points of a hyperbolic Möbius transform of the unit diskD. We will show, under some additional conditions onu, that the doubly cyclic subspaceS
u
=V
n=–
C
n
u contains nonconstant eigenfunctions of the composition operatorC
. This implies that the cyclic subspace generated byu is not minimal. If there is an infinite dimensional minimal invariant subspace ofC
(which is equivalent to the existance of an operator with only trivial invariant subspaces), then it is generated by a function with singularities at the fixed points of . 相似文献
70.