Synthesis and characterization of some polyamides incorporating modified isophthalic acid units

Some polyamides with side chains were prepared using a direct polycondensation reaction between carboxyl groups from O‐cinnamoyl‐5‐hydroxyisophthalic acid and N‐cinnamoyl‐5‐aminoisophthalic acid and various diisocyanates in the presence of 4‐dimethylaminopyridine, as catalyst, without use of condensing agents. The polymers were characterized by elemental analysis, viscosimetry, spectroscopic and thermal measurements. © 2002 Society of Chemical Industry     

Quarter-point elements for curved crack fronts

Ingraffea et al.[1] have presented a consistent method to compute stress-intensity factors from wedge quarter-point element nodal displacements for the straight crack front. The method was generalized to permit functional evaluation of stress-intensity factors along the crack front. Here the method is generalized for curved crack fronts.     

Transfer of a supernumerary chromosome between vegetatively incompatible biotypes of the fungus Colletotrichum gloeosporioides

Two biotypes (A and B) of Colletotrichum gloeosporioides infect the tropical legumes Stylosanthes spp. in Australia. These biotypes are asexual and vegetatively incompatible. However, field isolates of biotype B carrying a supernumerary 2-Mb chromosome, thought to originate from biotype A, have been reported previously. We tested the hypothesis that the 2-Mb chromosome could be transferred from biotype A to biotype B under laboratory conditions. Selectable marker genes conferring resistance to hygromycin and phleomycin were introduced into isolates of biotypes A and B, respectively. A transformant of biotype A, with the hygromycin resistance gene integrated on the 2-Mb chromosome, was cocultivated with phleomycin-resistant transformants of biotype B. Double antibiotic-resistant colonies were obtained from conidia of these mixed cultures at a frequency of approximately 10(-7). Molecular analysis using RFLPs, RAPDs, and electrophoretic karyotypes showed that these colonies contained the 2-Mb chromosome in a biotype B genetic background. In contrast, no double antibiotic colonies developed from conidia obtained from mixed cultures of phleomycin-resistant transformants of biotype B with biotype A transformants carrying the hygromycin resistance gene integrated in chromosomes >2 Mb in size. The results demonstrated that the 2-Mb chromosome was selectively transferred from biotype A to biotype B. The horizontal transfer of specific chromosomes across vegetative incompatibility barriers may explain the origin of supernumerary chromosomes in fungi.     

Optical modulators. The quantum well intersubband kind

Perfecting thin film growth techniques have made possible today's search for new, ultrafast optoelectronic devices. The techniques include: molecular beam epitaxy (MBE), organometallic chemical vapor deposition (OMCVD) and atomic layer epitaxy (ALE). By using these methods, scientists and engineers can grow multilayered semiconductor structures of different materials, with extremely high purity, sharp interfaces, and narrow doping profiles. The thickness of each layer has as its lower limit only one atomic layer. By superposing successive materials of different bandgaps, we can create quantum well structures in which electrons or holes are confined to potential wells in the conduction or valence bands. This quantization has allowed for the observation of quantum effects impossible to observe in the bulk materials. One effect is the electron or hole subband-to-subband transition within a conduction or a valence band in a quantum well. This is best known as the inter-subband transition. Before to this concept is examined, the author reviews the optical modulator, its pros and cons, and how quantum wells are used to realize a modulator     

Thyroid cancers

We have analysed factors that influenced on the patient survival in 195 cases of thyroid cancer. The survival is essentially influenced by the histology, the papillary forms (survival after 15 years: 83.1-93%) and follicular cancers (survival after 15 years: 84-94%) having an excellent evolution. The non-differentiated and mixed cancers have a very severe prognosis that is independent of the complex therapy that have been used (survival after 5 years: 17.1% in non-differentiated forms and 32.5% in mixed ones). The prognosis is better in subjects under the age of 45 and in female subjects. The cancers in the 1-st and 2-nd stage of tumor extension have a better evolution that those in the 3-rd stage. In differentiated cancers, the total or subtotal thyroidectomy followed by radioiodine administration determine the best survival.     

The value of scintigraphic imaging with 99mTc-MIBI for the diagnosis of gliomas

Imagery is the only possibility of early glioma diagnosis. Both the gravity of the evolution and the bad prognostic, through all CNS tumors, justify the necessity to asses new techniques in order to improve glioma imagery. From this point of view, cerebral tomoscintigraphy has developed, its usefulness depending highly on the radiotracer tumoral specificity. One of these tracers, 99mTc MIBI, has been found to be uptake in glioma malignant cells, in relation with their viability and even malignity. In our study, -14 cerebral tomoscintigraphies have been realized on patients with glioma (initial or recurrent tumor), after 20 mCi 99mTc MIBI i.v. doses. The results are in correlation with the histologic glioma grade: high grade astrocytoma has positive images, but low grade astrocytoma doesn't. In conclusion 99mTc MIBI glioma tomoscintigraphies can be useful in their initial or recurrent diagnosis; the uptake tracer intensity being correlated with the histologic tumoral pattern, 99mTc MIBI SPECT could make possible a better localization of highest malignity tumoral points, in further biopsies.     

Dynamics of field-driven domain-wall propagation in ferromagnetic nanowires

Ferromagnetic nanowires are likely to play an important role in future spintronic devices. Magnetic domain walls, which separate regions of opposing magnetization in a nanowire, can be manipulated and used to encode information for storage or to perform logic operations. Owing to their reduced size and dimensionality, the characterization of domain-wall motion is an important problem. To compete with other technologies, high-speed operation, and hence fast wall propagation, is essential. However, the domain-wall dynamics in nanowires has only been investigated in the last five years and some results indicate a drastic slowing down of wall motion in higher magnetic fields. Here we show that the velocity-field characteristic of a domain wall in a nanowire shows two linear regimes, with the wall mobility at high fields reduced tenfold from that at low fields. The transition is marked by a region of negative differential mobility and highly irregular wall motion. These results are in accord with theoretical predictions that, above a threshold field, uniform wall movement gives way to turbulent wall motion, leading to a substantial drop in wall mobility. Our results help resolve contradictory reports of wall propagation velocities in laterally confined geometries, and underscore the importance of understanding and enhancing the breakdown field for practical applications.     

Thermal and electrical properties of nitrile‐containing polyimide/BaTiO3 composite films

Polyimide composite films were prepared by mixing the BaTiO₃ particles into poly(amic acid) solution followed by film casting and thermal imidization under controlled temperature conditions. The poly(amic acid) was synthesized by solution polycondensation reaction of 4,4′‐oxydiphthalic anhydride with 2,6‐bis(4‐aminophenoxy)benzonitrile, using N‐methyl‐2‐pyrrolidone as solvent. The surface of BaTiO₃ particles was modified by treating with an aminosilane coupling agent, 3‐aminopropyltriethoxysilane. Fourier transform infrared spectroscopy, X‐ray diffraction and scanning electron microscopy were used to characterize the structure and properties of the composites. The influence of BaTiO₃ content on the composite film properties was evidenced. The films exhibited good thermal stability having the initial decomposition temperature above 520°C. They had stable dielectric properties over large intervals of temperature and frequency. The dielectric constant and the dielectric loss increased with the increase of BaTiO₃ content. The dynamic mechanical analysis and dielectric spectroscopy revealed subglass transitions γ and β. At higher temperature an α‐relaxation that corresponds to the glass transition and a conductivity process were evidenced. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers