We report the observation of nonlinear photorefraction in pure aligned nematic liquid crystals in the presence of an applied dc electric field. The effect is attributed to nematic axis reorientation created by the photoinduced space-charge field in combination with the applied dc field. Strong optical nonlinearity, self-diffraction, and beam-coupling effects are observed.

Polymer nanocomposites have formed an interesting field of materials research because considerable performance improvement can be achieved by the addition of trace amount of the nano-scale fillers. [1][2][3][4][5][6][7][8] Compared to the substantial experimental attempts, however, theoretical consideration of the mechanisms involved with adequate predictability is relatively less reported. Design and production of polymer nanocomposites have to be mostly conducted on a trial and error basis. Empirical extrapolation of the parameters related to components selection and processing technique is not very successful.Recently, Gersappe has made molecular dynamics simulations and suggested that the mobility of the nanofillers in a polymer controls their ability to dissipate energy, which would increase toughness of the polymer nanocomposites in the case of proper thermodynamic state of the matrix.[9] By examining elongation to break and area under stress-strain curve of treated nanoclay filled poly(vinylidene fluoride) (PVDF) composites, Giannelis and his co-workers evidenced the above hypothesis.[10] They showed that the incorporation of the nanoclay brought about significant toughening effect when the tensile test was carried out above the glass transition temperature (T g ) of the matrix polymer, whereas embrittlement was detected at a temperature below the matrix' T g . It was believed that mobility of the polymer matrix is a precondition for this mechanism, which dictates the mobility of the nanoparticles. However, verification with the literature data reveals that for the polymer composites consisting of nanoparticles without layered structure, toughness increase is not bound to be perceived even if the matrix possesses higher mobility. The room temperature ductility of natural rubber reinforced by nano-Fe, nano-Ni, nano-SiC particles and singlewalled carbon nanotubes (SWNT), for example, is lower than that of the matrix. [11,12] In this work we prepared nano-silica/ thermoplastics composites. The results demonstrate that the concept of nanoparticles mobility is still valid for toughening non-layered nanoparticles/polymer composites if both reduced interparticulates interaction and enhanced nano-filler/ matrix interaction are guaranteed besides sufficient mobility of the polymer matrix. These guidelines are applicable to formulation of technical route for manufacturing nanoparticles/ polymer composites with increased toughness, or for increasing the degree of improvement in toughness of the nanocomposites. Silica nanoparticles, either untreated or grafted by poly(dodecafluoroheptyl acrylate) (PDFHA, percent grafting = 13.3 %, number average molecular weight = 1.5 × 10 4 ), were melt compounded with crystalline isotactic polypropylene (PP) and amorphous polystyrene (PS) at a constant particle concentration of 1.36 vol %, respectively. Differential scanning calorimetry study and dynamic mechanical analysis indicate that crystallinity of PP nanocomposites and T g 's of both PP and PS nanocomposites remain nearly unc...

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Sheep (Ovis aries) are intermediate hosts for at least six named species of Sarcocystis: S. tenella, S. arieticanis, S. gigantea, S. medusiformis, S. mihoensis, and S. microps. Here, only two species, S. tenella and S. arieticanis, were found in 79 of 86 sheep (91.9%) in Kunming, China, based on their morphological characteristics. Four genetic markers, i.e., 18S rRNA gene, 28S rRNA gene, mitochondrial cox1 gene, and ITS-1 region, were sequenced and characterized for the two species of Sarcocystis. Sequences of the three former markers for S. tenella shared high identities with those of S. capracanis in goats, i.e., 99.0%, 98.3%, and 93.6%, respectively; the same three marker sequences of S. arieticanis shared high identities with those of S. hircicanis in goats, i.e., 98.5%, 96.5%, and 92.5%, respectively. No sequences in GenBank were found to significantly resemble the ITS-1 regions of S. tenella and S. arieticanis. Identities of the four genetic markers for S. tenella and S. arieticanis were 96.3%, 95.4%, 82.5%, and 66.2%, respectively.

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