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971.
The possibility of Pt–Cr surface alloys formation on Pt(0 0 1) was investigated and their magnetism was calculated by the full-potential linearized augmented plane wave (FLAPW) method with eight different atomic configurations. The most stable structure was calculated to be the Pt-segregated L12 ferromagnetic surface alloy. A3B types (L12 or D022) were more stable compared to AB types (L10). It implies that the A3B type surface alloys may be formed when depositing a monolayer of Cr on Pt(0 0 1). It was found from the total energy calculations that there exists a strong tendency of the Pt segregation. The segregation further stabilizes the surface alloy significantly. The work function of the most stable surface alloy was calculated to be 6.02 eV and the magnetic moment of the surface Cr was much enhanced to 3.3 μB. It is a quite interesting finding that the coupling between Cr and Pt atoms on the surface plane is ferromagnetic in the Pt-segregated L12 ferromagnetic surface alloy, while the coupling is antiferromagnetic in the bulk. 相似文献
972.
Dan Archdeacon C. Paul Bonnington Joanna A. Ellis-Monaghan 《Discrete and Computational Geometry》2007,38(3):573-594
Steinitz's theorem states that a graph is the 1-skeleton of a convex polyhedron if and only if it is 3-connected and
planar. The polyhedron is called a geometric realization of the embedded graph. Its faces are bounded by convex polygons whose
points are coplanar. A map on the torus does not necessarily have such a geometric realization. In this paper we relax the
condition that faces are the convex hull of coplanar points. We require instead that the convex hull of
the points on a face can be projected onto a plane so that the boundary of the convex hull of the projected points is the
image of the boundary of the face. We also require that the interiors of the convex hulls of different faces do not intersect.
Call this an exhibition of the map. A map is polyhedral if the intersection of any two closed faces is simply connected. Our
main result is that every polyhedral toroidal map can be exhibited. As a corollary, every toroidal triangulation has a geometric
realization. 相似文献
973.
A. C. Orifici R. S. Thomson R. Degenhardt C. Bisagni J. Bayandor 《Mechanics of Composite Materials》2007,43(1):9-28
Analysing the collapse of skin-stiffened structures requires capturing the critical phenomenon of skin-stiffener separation,
which can be considered analogous to interlaminar cracking. This paper presents the development of a numerical approach for
simulating the propagation of interlaminar cracks in composite structures. A degradation methodology was introduced in MSC.Marc,
which involved the modelling of a structure with shell layers connected by user-defined multiple-point constraints (MPCs).
User subroutines were written that employ the virtual crack closure technique (VCCT) to determine the onset of crack growth
and modify the properties of the user-defined MPCs to simulate crack propagation. Methodologies for the release of failing
MPCs are presented and are discussed with reference to the VCCT assumption of self-similar crack growth. The numerical results
obtained by using the release methodologies are then compared with experimental data for a double-cantilever beam specimen.
Based on this comparison, recommendations for the future development of the degradation model are made, especially with reference
to developing an approach for the collapse analysis of fuselage-representative structures.
Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 43, No. 1, pp. 15–42, January–February, 2007. 相似文献
974.
The first twelve members of the n-alkyl 2,5-bis-(4'-cyanobiphenyloxybutyloxy)-benozates have been prepared. The compounds are nematogenic; in addition the first three members exhibit a smectic A phase. The nematic-isotropic transition temperatures decrease with little or no alternation on increasing the number of methylene groups in the lateral chain; this is analogous to the behaviour found in monomeric and polymeric mesogens possessing lateral alkyl chains. 相似文献
975.
976.
It is shown that the non-trivial cocycles on simple Lie algebras may be used to introduce antisymmetric multibrackets which
lead to higher-order Lie algebras, the definition of which is given. Their generalised Jacobi identities turn out to be satisfied
by the antisymmetric tensors (or higher-order “structure constants”) which characterise the Lie algebra cocycles. This analysis
allows us to present a classification of the higher-order simple Lie algebras as well as a constructive procedure for them.
Our results are synthesised by the introduction of a single, complete BRST operator associated with each simple algebra.
Received: 3 June 1996 / Accepted: 8 November 1996 相似文献
977.
Since 1945, Foldy’s method has been used to predict velocity and attenuation for various types of scatterers. In this paper, it is shown that Foldy’s method also yields predictions of reflection and transmission of scalar waves by a random distribution of point or line scatterers contained in a slab. Results are given in two and three dimensions, and for normal and oblique incidences. Formulae are also obtained for the reflection and transmission of longitudinal waves by point or line scatterers distributed in an elastic (non-viscous) fluid. Energy equations are derived, and expressions are obtained for the energy dissipated in the slab on average over one period. Curves for the reflection and transmission coefficients are presented in the case of solid cylindrical bars immersed in a fluid. The results obtained in this paper are expected to be valid for a low density of scatterers. Potential applications of this work occur in ultrasonic evaluation of materials, seismic exploration and medical ultrasonics, where reflected (or backscattered) data are used to construct maps or images of the materials (metals, composites, earth subsurface, tissue). The formulae of this work are expected to provide useful tools for better and more efficient mapping or imaging. 相似文献
978.
Dimitrios Tsikas Frank-Mathias Gutzki Jürgen C. Frölich 《Fresenius' Journal of Analytical Chemistry》1992,342(1-2):95-97
Summary A reversed-phase HPLC method for the determination of nitrite and nitrate in aqueous solutions, biological buffers and human urine is described. The method is based on the conversion of nitrite and nitrate into their 1-nitro-2,4,6-trimethoxybenzene (NTBM) derivatives by using 1,3,5-trimethoxybenzene and concentrated sulphuric acid. NTMB is extracted by benzene, the solvent evaporated, the residue reconstructed in methanol/water (3/4, v/v) and subsequently analyzed by reversed-phase HPLC and UV detection (360 nm). The specificity of the nitration reaction, good reproducibility (C.V. 6.2%) and high sensitivity (8.4 ng nitrite) show the applicability of this method to the quantitative analysis of nitrite and nitrate in several matrices including human urine. 相似文献
979.
Summary We review the phase behaviour of mixtures of colloids and non-adsorbing polymers. The exclusion of polymer molecules from
overlapping ?depletion zones? between two neighbouring colloidal particles results in an unbalanced osmotic pressure pushing
the particles together. This depletion potential is separately tunable in range and depth. Theory predicts that the resulting
phase behaviour is sensitive to ξ=r
g/R, the ratio of the radius of gyration of a polymer molecule, to the radius of the colloid. At large ξ, a stable colloidalliquid phase becomes possible. This has been confirmed by recent experiments. The formation of non-equilibrium ?transient gel? states
when the size ratio is small (≈0.08) is also introduced briefly.
Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994. 相似文献
980.