类椭球氧化锌纳米结构的制备与表征

"用普通氧化锌晶须作为原材料, 采用高压釜腐蚀法和高温(600 ℃)裂解结合的方法合成纳米棒构成的氧化锌类椭球结构．XRD、SEM和TEM结果表明这种类椭球结构是单晶的,纳米棒取向一致,自组装生长而成．"     

The Cayley–Dickson process for dialgebras

We adapt the algorithm of Kolesnikov and Pozhidaev, which converts a polynomial identity for algebras into the corresponding identities for dialgebras, to the Cayley–Dickson doubling process. We obtain a generalization of this process to the setting of dialgebras, establish some of its basic properties, and construct dialgebra analogues of the quaternions and octonions.     

标准算子代数上完全保对合性的可加映射

刻画了无限维实或复Banach空间上的标准算子代数间完全保对合性的可加映射,证明了这样的映射是同构的常数倍或(复情形下)共轭同构的常数倍.     

Mechanical Behavior of Bulk Poly(Ethylene Terephthalate) Subjected to Simple Shear

Abstract

Mechanical behavior of bulk semicrystalline poly(ethylene terephthalate) (PET) processed through simple shear is investigated. The equal channel angular extrusion (ECAE) process was used to achieve the simple shear condition. The PET samples were processed in one and two ECAE passes in the same direction, with the sample rotated 180° about the extrusion axis for the second pass. Microstructural features at the nanometer and micrometer scales were studied by small‐angle x‐ray scattering (SAXS) and scanning electron microscopy (SEM). SAXS results showed that at the nanometer scale, two types of lamellar orientations are induced in both samples, but with different extents of orientation. In the ECAE‐oriented PET structures on the micrometer scale, as revealed by SEM, are well‐defined macrofibrils. However, the fibrillar structures in the sample extruded once are more oriented than those in the sample extruded twice. Fractography investigations suggest that the ECAE‐induced fibrillar structure and stretched amorphous chains are responsible for the change in mechanical properties.     

Prime Rings with Involution Equipped with Some New Product

Let R be a ring with involution *. We consider R as a ring equipped with a new product r s = rs + sr^*. The relationship between (ordinary) ideals of R and right ideals of R with respect to the product is studied.AMS Subject Classification (2000): 16W10, 16D25     

Mod 2 cohomology of combinatorial Grassmannians

Matroid bundles, introduced by MacPherson, are combinatorial analogues of real vector bundles. This paper sets up the foundations of matroid bundles. It defines a natural transformation from isomorphism classes of real vector bundles to isomorphism classes of matroid bundles. It then gives a transformation from matroid bundles to spherical quasifibrations, by showing that the geometric realization of a matroid bundle is a spherical quasifibration. The poset of oriented matroids of a fixed rank classifies matroid bundles, and the above transformations give a splitting from topology to combinatorics back to topology. A consequence is that the mod 2 cohomology of the poset of rank k oriented matroids (this poset classifies matroid bundles) contains the free polynomial ring on the first k Stiefel-Whitney classes.     

A study of the headgroup motion of sphingomyelin using 31P NMR and an analytically soluble model

A 31P NMR investigation has been carried out of the headgroup dynamics of sphingomyelin molecules in bilayers for the L alpha and L beta' phases. The resulting line shapes have been analysed in terms of a reduced-parameter model, using van Faassen's method for obtaining an analytic solution to first-order stochastic differential equations to simulate the line shapes of oriented and non-oriented samples. Our treatment results in good fits to measured data but using fewer parameters than traditional methods. Angles and correlation times (tau parallel and tau perpendicular) describing the geometry and dynamics of the headgroup are obtained by optimising the agreement between simulated and experimental data. The results are contrasted with those obtained for the lecithins DMPC and DPPC using a similar analysis. Not only are tau parallel and tau perpendicular now equal in value for the L alpha phase, but this value is also found to be nearly four times larger than the longest correlation time for the lecithins. We interpret this as evidence of inter- and intramolecular hydrogen bonding in the L(alpha) phase of sphingomyelin. In the L beta' phase of sphingomyelin, however, although tau(parallel) and tau(perpendicular) remain equal their value is now 32% smaller than that of the lecithins in the same phase. This indicates less difference between the fluidities in the headgroup region of the two phases of sphingomyelin as compared to that of the lecithins. Another significant difference between the L beta' phases is that the tilt angle for sphingomyelin is found to be nearly twice as large as for the lecithins. We argue that these combined observations point to the existence of hydrogen bonding in this phase also. Again in contrast to our previous work on lecithins, our results provide evidence of a negative diamagnetic anisotropy in sphingomyelin molecules, even in the L beta' phase. This is provided for in our model by the assumption that our unoriented samples consist of prolate ellipsoidal liposomes whose major axes are oriented parallel to the static magnetic field. The apparently different diamagnetic behaviour of sphingomyelin in the present work is due to the higher static field used rather than any intrinsic difference in this respect between sphingomyelin and the lecithins DMPC and DPPC.     

Index Reduction Formulas for Twisted Flag Varieties, II

This is a continuation of the determination begun in K-Theory 10 (1996), 517–596, of explicit index reduction formulas for function fields of twisted flag varieties of adjoint semisimple algebraic groups. We give index reduction formulas for the varieties associated to the classical simple groups of outer type A _n-1 and D _n, and the exceptional simple groups of type E ₆ and E ₇. We also give formulas for the varieties associated to transfers and direct products of algebraic groups. This allows one to compute recursively the index reduction formulas for the twisted flag varieties of any semi-simple algebraic group.