Application of Genetic Algorithms to Texture Analysis

Application of genetic algorithms to texture analysis is presented in this paper. The genetic algorithm technique was applied to the calculation of the orientation distribution function from a set of pole figures. The results are very satisfying. The same algorithm may be also applied to other problems of texture analysis, e.g., to find an optimal texture for a given application.     

Studies on the synthesis and properties of thermotropic liquid crystalline polycarbonates. VII. Liquid crystalline polycarbonates and poly(ester‐carbonate)s derived from various mesogenic groups

Three series of thermotropic liquid crystalline polycarbonates and poly(ester‐carbonate)s were prepared by solution polycondensation of 4,4′‐biphenyldiol (BP), 4′‐hydroxybiphenyl‐4‐hydroxybenzoate (HHB), or 4‐hydroxyphenyl‐4″‐hydroxybiphenyl‐4′‐carboxylate (HHBP), as mesogenic unit, with 1,10‐bis(p‐hydroxybiphenoxy)decane (N10), bisphenol A (BPA), 4,4′‐dihydroxy‐diphenyl ether (BPO), 4,4′‐[phenylbis(oxy)]bisphenol (BPOO), methylhydroquinone (MeHQ), or phenylhydroquinone (PhHQ). One series of cholesteric poly(ester‐carbonate)s were also prepared by using HHBP, the aromatic diols mentioned above and isosorbide as the chiral moiety. All polycondensations were implemented in pyridine by using triphosgene as the condensation agent. The synthesized polycarbonates were characterized by viscometer, FTIR, DSC, TGA measurements, polarizing microscopy equipped with a heating stage, and WAXD powder pattern. In this study, it was found that the liquid crystalline properties of polycarbonates strongly rely on the mesogenic unit applied. HHBP‐series exhibits a wide temperature region of liquid crystalline (LC) phase even with 50% of bisphenol A (BPA), which is a V‐shaped structure and usually destroys liquid crystalline properties. In addition, homopolycarbonate with HHBP structure possesses extraordinarily low phase‐transition temperature and wide liquid crystalline phase range, due to its asymmetric structure. This asymmetric structure results in head‐to‐tail, head‐to‐head, and tail‐to‐tail random conformation of polymer chain. The isosorbide containing poly(ester‐carbonate)s formed cholesteric phase, which showed homogeneous blue, green, or red Grandjean texture upon shearing in molten state and the Grandjean texture could be frozen easily while quenching the sample to the room temperature. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1852–1860, 2000     

Growth of Biaxial Textured MgO‐Layers by Ion‐Beam Assisted Pulsed Laser Deposition

MgO thin films were deposited on amorphous substrates using pulsed laser deposition. Without an assisting ion beam, strong fibre textures are observed changing with temperature. Using an ion beam at 55° with respect to the substrate normal and energies of more than 400 eV, biaxially textured films are grown with the <200> direction parallel to the ion beam. Decreasing the deposition rate the texture changes towards the desired cube texture and resputtering becomes more important. Investigations of the surface topography show an increase in roughness and grain size with increasing film thickness. Preliminary ideas of texture and microstructure development in this deposition process are presented.     

Synthesis and characterization of side-chain liquid crystal polyurethanes

A series of liquid crystal α-[bis(2-hydroxyethyl)amino]-ω-(4-nitroazobenzene-4′-oxy)alkanes (Cn-diol) with different alkyl chain length has been synthesized. All Cn-diols exhibit a smectic phase that has been identified by means of polarizing microscopy and differential scanning calorimetry. These compounds are suitable monomers for the synthesis of side-chain liquid crystalline polyurethanes and polyesters. They were polymerized with hexamethylene diisocyanate to corresponding SCLC polyurethanes in which the spacer length was varied from 2 to 12 methylene units. Polyurethanes (CnP) with spacer lengths n ≥ 4 exhibited liquid crystalline behavior. Fourier transform infrared temperature studies of the CnP were done focusing on H-bonds between the N H and CO groups of the urethane backbone. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2871–2888, 1997     

Orientation-dependent microstructure development during high-rate shear deformation of copper

ABSTRACT

The microstructure transformations in copper subjected to high-rate deformation via dynamic channel angular pressing (DCAP) have been examined after one and four DCAP passes using electron backscattering diffraction. The focus was on the interrelation between microstructure and texture evolution and on the role of deformation twinning in these processes. During the first pass, a mesoscopic banding is shown to be the main mechanism of grain fragmentation, while the texture is qualitatively similar to that of face-centered cubic metals subjected to equal channel angular pressing, including the presence of characteristic texture components C, A₁ and A₂. A correspondence between structural elements and texture components occurs. Specifically, the mesobands have orientations near either an A₁ or A₂ ideal orientation, whereas the matrix has an orientation near C. Inside the A₁-bands, microtwins with orientations near A₂ are observed. Detailed analysis of the A₂-bands suggests that they may be of twinning origin. Similar orientation dependence of microstructure, though on a much finer scale, is observed after four DCAP passes. Based on the microstructure examination, it was suggested that mesoscopic banding together with deformation twinning continue to be principal mechanisms of grain refinement until the fourth pass, resulting in the formation of ultrafine-grained structure.     

Rheo-Dielectric behavior of low molecular weight liquid crystals.

Dielectric relaxation behavior was examined for 4-4′-n-pentyl-cyanobiphenyl (5CB) and 4-4′-n-heptyl-cyanobiphenyl (7CB) under flow. In quiescent states at all temperatures examined, both 5CB and 7CB exhibited dispersions in their complex dielectric constant ε*(ω) at characteristic frequencies ω _c above 10⁶ rad s^–1. This dispersion reflected orientational fluctuation of individual 5CB and 7CB molecules having large dipoles parallel to their principal axis (in the direction of C≡N bond). In the isotropic state at high temperatures, these molecules exhibited no detectable changes of ε*(ω) under flow at shear rates . In contrast, in the nematic state at lower temperatures the terminal relaxation intensity of ε*(ω) as well as the static dielectric constant ε′(0) decreased under flow at . This rheo-dielectric change was discussed in relation to the flow effects on the nematic texture (director distribution) and anisotropy in motion of individual molecules with respect to the director. Received: 14 April 1998 Accepted: 29 July 1998     

基于方向多尺度变换和统计建模的纹理分类方法

纹理是图像分析和识别中经常使用的关键特征, 而小波变换则是图像纹理表示和分类中的常用工具. 然而, 基于小波变换的纹理分类方法常常忽略了小波低频子带信息, 并且无法提取图像纹理的块状奇异信息. 本文提出小波子带系数的局部能量直方图建模方法、轮廓波特征的Poisson 混合模型建模方法和基于轮廓波子带系数聚类的特征提取方法, 并将其应用于图像纹理分类上. 基于局部能量直方图的纹理分类方法解决了小波低频子带的建模难题, 基于Poisson 混合模型的纹理分类方法则首次将Poisson 混合模型用于轮廓子带特征的建模, 而基于轮廓波域聚类的纹理分类方法是一种快速的分类方法. 实验结果显示, 本文所提出的三类方法都超过了当前典型的纹理分类方法.     

Single Crystal EPR Studies of Radical Pairs in Dibenzoyl Peroxide

Four different phenyl-benzoyloxy (PB) radical pairs and two different benzoyloxy-benzoyloxy (BB) pairs, each existing in four symmetry-related orientations, have been observed by epr in single crystals of dibenzoyl peroxide after brief uv irradiation at low temperature. At 5 K two PB pairs are formed; PBT disappears in less than 2 minutes at 5 K. but PB5K persists to 15 K, where it converts to PB15K in a process that involves 39° in-plane rotation of the benzoyloxy radical. Further warming to 24 K generates PB24K from an unidentified precursor which gives no epr spectrum and is destroyed by visible light. PB15K and PB24K persist to 65 K. Irradiation at 10 K forms a BB pair which converts cleanly to a second BB at 25 K. Stability of the pairs and distinguishability of PB pairs are discussed in light of a crystal packing analysis.     

Synthesis and characterization of highly textured Pt–Bi thin films

Pt–Bi films were synthesized on glass and thermally oxidized silicon substrates by e-beam evaporation and annealing. The structures were characterized using X-ray diffraction (XRD) and transmission electron microscopy/selected area electron diffraction (TEM/SAED) techniques. Single-phase PtBi was obtained at an annealing temperature of 300°C, whereas a higher annealing temperature of 400°C was required to obtain the highly textured γ-PtBi₂ phase. TEM/SAED analysis showed that the films annealed at 400°C contain a dominant γ-PtBi₂ phase with a small amount of β-PtBi₂ and α-PtBi₂ phases. Both the PtBi and γ-PtBi₂ phases are highly textured in these two kinds of film: the c-axis of the hexagonal PtBi phase is mostly in the film plane, whereas the c-axis of the trigonal γ-PtBi₂ phase is perpendicular to the film plane. The electrical resistivity of the film with the γ-PtBi₂ phase was smaller by one order of magnitude than that of the film with the PtBi phase.