Structure of 9,10-di(9,9-dioctylfluorenyl)anthracene in the solid and in solution

A new example of magnetic nonequivalence of chemically equivalent atoms is identified from the proton and carbon resonance spectra of 9,10-di(9,9-dioctylfluorenyl)anthracene with the aid of its conformation in the crystalline state. Molecular modeling suggests that it has a similar conformation in solution.     

Caminoside A,an antimicrobial glycolipid isolated from the marine sponge Caminus sphaeroconia

Extracts of the marine sponge Caminus sphaeroconia showed potent activity in a screen for bacterial type III secretion inhibitors. Bioassay guided fractionation of the extract led to the isolation of the novel antimicrobial glycolipid caminoside A (1). The structure of caminoside A was elucidated by analysis of spectroscopic data and chemical degradation.[structure: see text]     

重介质旋流器分选机理研究

物料分选过程 ,是整个体系能量降低的过程 ,从这一原理出发 ,不同性质的固体颗粒在重介质旋流器中将位于不同的位置 ,使不同性质的固体颗粒得以分离。固体颗粒在重介质旋流器中的运动轨迹大体呈圆锥螺旋线形状 ,实测出的密度线验证了该结论     

Shearing of oriented polyethylene and polypropylene

To learn more about the out-of-plane deformation of polymer lamellae during drawing, we have measured the resistance to shear along various planes in uniaxially oriented polyethylene and polypropylene. Fissures parallel to the orientation axis in oriented materials always cause too small an experimental value for the resistance of crystal glide parallel to the chain axes, but a rough estimate for the resistance to crystal glide is obtained using the elastic anisotropy. Also, the results suggest that kinking can be easier than glide when glide is inhibited by tie molecules.     

Approaches to selecting appropriate subjects for evaluating clinical tests

Appropriate selection of subjects is a critical element in assuring a valid evaluation of the clinical usefulness of a laboratory test. Careful definition of the clinical question to be answered by the test clearly points to the target population from which a representative sample must be obtained.     

Occurrence of rippling during the deformation of oriented polyethylene

Rippling is another mode, in addition to kink-band formation, by which oriented polyethylene can deform and results in a profuse and irregular waviness in the fibrils. For the medium-density and high-density polyethylenes investigated, rippling tended to occur only at strain rates below about 1 min^?1 at 25°C. Above this rate, kink bands tended to form. It is suggested that rippling results from easy slip between the fibrils of the oriented polymers and from the resistance of the fibrils to shortening under a compressive stress. The applied shear stress is reduced by the easy slip to a simple compression along the fibrils, and this distorts the fibril into the series of waves that constitutes rippling. Stress–strain measurements confirm that fibril slip is considerably easier under the rates at which rippling occurs than at the rates at which kink bands form.     

Forced axisymmetric motion of circular,viscoelastic plates

Williams' method for forced motion of elastic systems is applied to circular, viscoelastic plates where the effects of rotatory inertia, transverse shear and time-dependent boundary conditions are included. The viscoelastic material is assumed to have a constant Poisson's ratio. A particular problem is solved for a symmetrically loaded, completely free plate. The material used is vulcanized rubber where the viscoelastic behavior in shear is used in specifying the material parameters of a three-element solid.     

A model for the spherulite-to-fibril transformation

Based on an analogy with the growth of kink bands in oriented and annealed crystalline polymers, a mechanism is suggested for the deformation-induced spherulite-to-fibril transformation. Oriented and annealed material was employed as a model because it has roughly the same structure as the lamellar bundle of the spherulite. Under conditions that minimize the fibrillar quality and maximize the lamellar bundle quality, oriented and annealed crystalline polymers deform with the formation and growth of kink bands. The characteristics of kink bands are the sharpness of the kinks, occurring within zones ca. 100 Å wide, and mirror symmetry of the fibrils about the kink-zone planes. The spherulite-fibril transformation is suggested by analogy, then, to occur in the narrow zones that indeed are often found and to result in mirror symmetry of the chain axes about the transformation-zone planes, which may not exactly occur because of a tendency for the tie molecules to be pulled from the lamellae during drawing. The implications for the transformation are (a) that the microfibril backbones are derived from the tie molecules between lamellae and (b) though some unfolding occurs as blocks that were adjacent within the lamellae become separated, the crystals remain mostly intact during the transformation. The analog is supported by or at least is consistent with various other results, including those from morphological and small- and wide-angle x-ray studies.