Synthesis and characterization of conducting copolymers of poly(vinyl alcohol) with thiophene side‐groups and pyrrole

Graft copolymers of poly(vinyl alcohol) with thiophene side‐groups and pyrrole were synthesized by electrochemical polymerization methods. Poly(vinyl alcohol) with thiophene side‐groups (PVATh) was obtained from the reaction between poly(vinyl alcohol) (PVA) and thiophene‐3‐acetic acid. The syntheses of copolymers of PVATh and pyrrole were achieved electrochemically by using three different supporting electrolytes, p‐toluene sulfonic acid (PTSA), sodium dodecyl sulfate (SDS) and tetrabutylammonium tetrafluoroborate (TBAFB). Characterization of PVATh and graft copolymers was performed by a combination of techniques including cyclic voltammetry, scanning electron microscopy, thermal gravimetry, differential scanning calorimetry, size‐exclusion chromatography, ¹H NMR and FT‐IR. The conductivities were measured by the four‐probe technique. Copyright © 2004 Society of Chemical Industry     

Dimensional analyses and surface quality of the laser cutting process for engineering plastics

In this study, the effect of the CO₂ laser cutting process parameters (gas pressure, cutting speed, and laser power) on the dimensional accuracy and measured surface roughness of engineering plastic (PTFE and POM) materials was investigated. Cutting surface profile of specimens was examined by using an optical microscope. The surface quality of specimens was examined by measuring surface roughness and form error. Analysis of variance (ANOVA) and regression analyses are employed to assess the effect of the process parameters on the dimensional accuracy.     

Ultra-Structural Imaging Provides 3D Organization of 46 Chromosomes of a Human Lymphocyte Prophase Nucleus

Three dimensional (3D) ultra-structural imaging is an important tool for unraveling the organizational structure of individual chromosomes at various stages of the cell cycle. Performing hitherto uninvestigated ultra-structural analysis of the human genome at prophase, we used serial block-face scanning electron microscopy (SBFSEM) to understand chromosomal architectural organization within 3D nuclear space. Acquired images allowed us to segment, reconstruct, and extract quantitative 3D structural information about the prophase nucleus and the preserved, intact individual chromosomes within it. Our data demonstrate that each chromosome can be identified with its homolog and classified into respective cytogenetic groups. Thereby, we present the first 3D karyotype built from the compact axial structure seen on the core of all prophase chromosomes. The chromosomes display parallel-aligned sister chromatids with familiar chromosome morphologies with no crossovers. Furthermore, the spatial positions of all 46 chromosomes revealed a pattern showing a gene density-based correlation and a neighborhood map of individual chromosomes based on their relative spatial positioning. A comprehensive picture of 3D chromosomal organization at the nanometer level in a single human lymphocyte cell is presented.     

Study of structure and magnetic properties of the perovskite Tb0.5Sr0.5CoO3

The perovskite compound Tb_0.5Sr_0.5CoO₃ has been prepared and studied for the first time. We report here the structural and magnetic properties of the compound using the DC magnetization and powder neutron diffraction techniques. The compound is found to be orthorhombic with Pbnm space group. The magnetic ground state of the system is ferromagnetic with T_c = 120 K. The ordered magnetic moment is found to be 1.57 (4) μ_B/Co ion at 12 K along the crystallographic b-axis. The observed effective paramagnetic moment μ_eff = 2.54 μ_B/f.u. The role of ionic size effect on the magnetic and transport properties of the compound through the variation of CoOCo bond angles is highlighted.     

Electrochemical polymerizatıon of hexachloroethane to form poly(hydridocarbyne): a pre-ceramic polymer for diamond production

Due to its structural similarity with diamond, poly(hydridocarbyne) (PHC), which is sp³-hybridized, is a unique polymer that can be easily converted to diamond and diamond-like-carbon ceramics upon heating. PHC can be easily synthesized via the electrochemical polymerization of chloroform as previously reported. Here, we report the electrosynthesis of PHC from hexachloroethane. Since hexachloroethane has six chlorine atoms in its structure, polymerization takes place through the carbons simultaneously. Thus, the polymer is bigger in chain length than PHC obtained from the polymerization of chloroform. UV-vis, FTIR, and NMR spectroscopy were utilized to determine the polymer structure. Conversion of the polymer to diamond was accomplished by heating at 1000 °C under a nitrogen atmosphere as confirmed by Optical Microscopy and Raman analysis. XRD studies showed that the product is an assortment of diamond forms.     

High speed CNC system design. Part III: high speed tracking and contouring control of feed drives

A servo control system capable of delivering rapid and accurate feed motion is a necessity for high speed machine tools. The control law must be designed to provide a high tracking bandwidth as well as adequate disturbance rejection and parameter variation robustness, in order minimize the following errors in each axis. This also contributes to the minimization of the contour errors in the machined part. This paper provides a systematic approach for designing such a control law. Position, velocity, and disturbance estimates are obtained using a Kalman filter. The feedback loop is closed using a pole placement controller with disturbance cancellation, in order to counteract the detrimental effects of friction, cutting forces, and drive parameter variations. The overall tracking bandwidth is widened by compensating for the closed loop dynamics in a feedforward manner. Also, the tracking errors due to friction transients at the corners and arc quadrants are reduced by precompensating for the expected friction forces. The contribution of each component in the control scheme to the contouring accuracy has been experimentally verified, and the overall contouring performance has been demonstrated in high speed machining tests. The experimental results were obtained using the smooth trajectory generation algorithm and identified axis and friction models which have been presented in Parts I and II respectively, of this paper.     

Study of threading dislocations in the plan-view sample of SiGe/Si(001) superlattices by transmission electron microscopy

Interfacial defects due to a mismatch of 1.378% between substrate and epilayer were examined in a Si_0.67Ge_0.33/Si(001) superlattice by transmission electron microscopy (TEM). Plan-view specimens from the superlattice were prepared to investigate the defects in the structure. It was observed that 60°C-type misfit dislocations associate with point contrast on and at their ends. This point contrast was found to represent threading dislocations by using tilt experiments in the microscope. Consequently, stereo electron microscopy was used to examine the threading dislocations. It was discovered that the threading dislocations are not on the {111} slip planes but can be almost parallel to the [001] zone axis.     

Hole effects on lateral buckling of laminated cantilever beams

In this study, the effects of hole diameter and hole location on the lateral buckling behaviour of woven fabric laminated composite cantilever beams have been investigated. In the experimental studies, two different groups of samples were used; samples with a single circular hole and samples with no hole. The critical buckling load for each sample was then determined experimentally. For the numerical analyses, ANSYS 10.0 finite element program was utilized. It has been noted that there is a good agreement between experimental results and those of finite element analyses. On the basis of this harmony, the numerical analyses of some models having different dimensions and fiber orientations have been done by changing length and width of the beam, diameter and location of the hole. It has been concluded that the effects of the hole diameter and hole location on the lateral buckling behaviours is very important, especially for the short beams.     

Conducting Copolymers of 3-Methylthienyl Methacrylate and p-Vinylbenzyloxy Poly(ethyleneoxide) and Their Electrochromic Properties

Summary A random copolymer (CP) containing 3-methylthienyl methacrylate (MTM) and p-vinylbenzyloxy poly(ethyleneoxide) (PEO-VB) units was synthesized. Further graft copolymerization of CP with pyrrole (Py) and thiophene (Th) were achieved in H₂O - sodium dodecyl sulfate (SDS), H₂O - p-toluenesulphonic acid (PTSA) and acetonitrile (AN) - tetrabutylammonium tetrafluoroborate (TBAFB) solvent electrolyte couples via constant potential electrolyses. Characterization was performed by cyclic voltammetry (CV), nuclear magnetic resonance spectroscopy (NMR), and fourier transform infrared spectroscopy (FTIR). The morphologies of the films were examined by scanning electron microscopy (SEM). Conductivities of the samples were measured by using four-probe technique. Moreover, spectroelectrochemical and electrochromic properties of the copolymer obtained from thiophene were investigated by UV-Vis spectrometry and colorimetry.