Search

The synchrotron x-ray diffraction and transmission electron microscopy was used to investigate the ferroelectric domain structures and microstructure of epitaxial tetragonal Pb([Zr.sub.0.35], [Ti.sub.0.65])[O.sub.3] films which were grown on SrRu[O.sub.3](100)/SrTi[O.sub.3](100) substrates by metal organic chemical vapor deposition. The findings reveal that it is possible to obtain highly a-axis oriented films by reducing the compressive strain that was caused by reducing the growth temperature and increasing the film thickness.

The kinetics of the elimination reactions of (E)-2,4-dinitrobenzaldehyde O-aryloximes promoted by EtO-, PhC(CH3)=NO-/PhC(CH3)=NOH and CF3CH2O-/CF3CH2OH buffers in ethanol were investigated. The only products of the reactions were 2,4-dinitrobenzonitrile and aryloxides. The second-order kinetics were in agreement with the E2 mechanism. The Bronsted beta decreased as the leaving group was made more nucleofugic and the /beta(sub lg)/ increased with a weaker base.

The kinetics underlying the elimination reactions of aryl esters of arylacetic acids with R2NH-MeCN were determined to understand the relationship between the reactant structure and the E2 and E1cb transition states during the ketene-forming reactions. The reactions, which exhibited second-order kinetics, showed a reduction in Bronsted beta and beta(sub lg) in direct proportion to the electron-withdrawing ability of beta-withdrawing ability of the beta-aryl substituent. Likewise, concurrent E2 and E1cb mechanisms were found to be present during R2NH/R2NH+2-catalyzed eliminations from p-nitrophenyl p-nitrophenylacetate in aqueous MeCN.

Kinetic analysis of debromination reactions of erythro-dl-1-aryl-1,2-dibromo-2-nitropropanes with secondary amines in MeCN shows that these reactions progress through an E2 mechanism initiated by the attack of the base at the C-2-Br bond. The attack occurs by an E1cb-like transition with C(sub beta)-Br bond cleavage, negative charge development at beta-carbon and restricted C(sub alpha)-Br bond cleavage.

A 17 nm thick PbTiO3 (PTO) films were fabricated via PbO gas phase reaction with TiO2 starting layer in a sputtering chamber. The influence of deposition temperature of TiO2 on the piezoelectric properties of PTO thin films was investigated. The remnant piezoresponse of PTO films nonlinearly increased as a function of TiO2 deposition temperature, which is correlated with the increase in average grain diameter of PTO film. As grain size increases, the restriction on remnant piezoresponse imposed by the grain boundary via coupling between local strain and polarization becomes less pronounced, which results in the increase in remnant piezoresponse. Furthermore, we found that the vertical shift in piezoresponse hysteresis loops is closely related to the residual stress state. A strong correlation between the negative vertical shift and the residual tensile stress reveals that residual stress on the resulting PTO film contributed to the asymmetric piezoelectric property. [ABSTRACT FROM AUTHOR]

We have studied the effect of local surface potential distribution on its relaxation in the polycrystalline ferroelectric thin films. A lower surface potential region, i.e., potential pit, is generated near a grain boundary. The deep potential pit has a faster relaxation than the area far away from the potential pit due to the acceleration of the screen charge draining near the grain boundary and the domains formed by applying higher voltage have a faster relaxation due to the larger gradient of screen charge distribution. In addition, the surface potential and its relaxation depend on the sign of applying voltage. The result shows that the surface potential distribution may influence significantly to the reliability of bit signal on the memory devices. [ABSTRACT FROM AUTHOR]

Epitaxial (100)/(001)-oriented tetragonal Pb(Zr,Ti)O3 films above 1 μm thick were grown on (100)SrTO3 substrates by pulsed metal organic chemical vapor deposition, and the films with Zr/(Zr+Ti) ratios up to 0.43 were found to have a strain-relaxed domain structure. The domain structure determined by the volume fraction of (001) orientation (mainly decided by the thermal strain above the Curie temperature) and the lattice parameters dependent on the Zr/(Zr+Ti) ratio are explained by a geometrical model consistent with previous results for PbTiO3 films [J. Appl. Phys. 104, 064121 (2008)]. [ABSTRACT FROM AUTHOR]

Epitaxial (100)/(001)-oriented PbTiO3 films with thickness of 2.8 μm were grown on Nb-doped (100) SrTiO3 substrates by pulsed metal organic chemical vapor deposition. Complex domain structures consisting of c-domains (c1) and three types of a-domains (a1, a2, and a3) were observed by piezoresponse force microscopy in conjunction with high-resolution x-ray diffraction analysis. The obtained results suggest that (a2/a3) and (a1/c1) domain configurations represent mostly strain-relaxed structures. This conclusion is in good agreement with theoretical predictions made for thick films [Phys. State., Solidi 37, 329 (1976)]. [ABSTRACT FROM AUTHOR]

Epitaxial tetragonal Pb(Zr0.35,Ti0.65)O3 films were grown on SrRuO3(100)/SrTiO3(100) substrates by metal organic chemical vapor deposition. Their ferroelectric domain structures and microstructure were investigated using synchrotron x-ray diffraction and transmission electron microscopy. Highly a-axis oriented films were obtained by decreasing the compressive thermal strain resulting from the low growth temperature and thick film. The a and c domains were significantly tilted and had fourfold symmetry, and their tilt angles to the substrate normal were ∼0.5° and ∼0.9°, respectively. The film contained three domain structures: an a-c domain structure consisting of a periodic array of twin domains, an a1-a2 domain structure in which the a1 and a2 domains were rotated with respect to each other by 90° about the substrate normal direction, and a bilayer twinning structure coexisting with the a-c domain structure and a1-a2 domain structure. The bottom layer was the a1-a2 domain structure, and the top layer was the a-c domain structure. This bilayer structure may be due to a yet unknown domain evolution mechanism in which the strain of the films is inhomogeneous. [ABSTRACT FROM AUTHOR]

Lateral size effects of ferroelastic domain structures in epitaxial PbTiO3 thin films were investigated systematically with a viewpoint of misfit strain relaxation mechanism. The epitaxial PbTiO3 thin films were patterned into discrete islands and the effects of lateral dimension were analyzed by reciprocal space mapping using synchrotron x-ray diffraction as well as finite element simulation. As the lateral two-dimensional planar size decreases in the PbTiO3 patterns on MgO(001), some of the a domains turned into c domains due to the relaxed tensile strain. In the PbTiO3 patterns on Pt(001)/MgO(001), on the other hand, the formation of 90° domains is enhanced by the reduction in compressive misfit strain. As the pattern size decreases further to 100 nm, the untilted a domains arise due to the almost completely relaxed misfit strains. Equilibrium domain structures in the epitaxial thin films and discrete islands are also analyzed by the finite element simulation and found to be consistent with the experimental observation. These results manifest that the domain structure and evolution of the epitaxial thin films could be engineered by the control of misfit strain and its relaxation. [ABSTRACT FROM AUTHOR]

Canine parvovirus (CPV) was detected in three of 136 samples from dead raccoon dogs (Nyctereutes procyonoides) in the Republic of Korea (South Korea) during 2016–17. By sequence and phylogenetic analysis of the complete VP2 gene, the strain belonged to CPV-2 and would be distinct from the previous reported CPV-2a and CPV-2b strains from Korean domestic dogs (Canis lupus familiaris). The results indicated that the CPV strains from raccoon dogs and domestic dogs might be not circulated between wild and domestic carnivores in Korea. [ABSTRACT FROM AUTHOR]

Moving foreground objects detection in complex scenes is a tough job because it requires high recognition accuracy. Adaptive Gaussian mixture model (AGMM) can be used to extract the foreground objects and it shows good performance, however, the detection quality of the foreground objects under complex scenes is not excellent. In this paper, an AGMM and BP neural network hybrid method is proposed, which is used to extract the foreground objects in complex scenes such as, dynamic backgrounds, illumination changes and moving shadows. In this method, an improved BP neural network is used to post-process the images of the foreground objects that are extracted from the AGMM. The neural network has strong robustness by learning the statistical features of the images. Momentum term and adaptive learning rate are added in the BP neural network algorithm to improve the training speed and robustness of the network. The experimental results show that the proposed AGMM and BP neural network hybrid method can extract the complete foreground objects effectively when compared with some other moving objects detection algorithms. [ABSTRACT FROM AUTHOR]

By introducing the new concepts of characteristic rate curves and rate-curve decomposition, a generic source-modeling framework is developed for transform coding of videos. Based on this framework, the rate-quantization (R-Q) and distortion-quantization (D-Q) functions (collectively called R-D functions in this work) of the video encoder can be accurately estimated with very low computational complexity before quantization and coding. With the accurate estimation of the R-Q function, a frame-level rate control algorithm is proposed for DCT video coding. The proposed algorithm outperforms the TMN8 rate control algorithm by providing more accurate and robust rate regulation and better picture quality. Based on the estimated R-D functions, an encoder-based rate-shape-smoothing algorithm is proposed. With this smoothing algorithm, the output bit stream of the encoder has both a smoothed rate shape and a consistent picture quality, which are highly desirable in practical video coding and transmission. Index Terms--Rate control, rate-distortion estimation, rate smoothing, source modeling, video coding.