Radiation-Induced graft copolymerization of methacrylic acid onto polypropylene fibers. V. Mechanical properties

Mechanical properties of polypropylene-g-poly(methacrylic acid) fibers, prepared by graft copolymerization of methacrylic acid onto polypropylene fiber using simultaneous gamma ray irradiation technique, were evaluated. In general, an improvement in the mechanical behavior of the polypropylene fiber by grafting was observed. Denier and initial modulus of the fiber showed a linear increase with the percent graft, and elongation showed an opposite trend. The results have been explained in terms of reinforcing effect of poly(methacrylic acid) grafts and reduction in the segmental mobility of the polymeric chains. Tenacity also increases up to certain graft level, beyond which a sharp decrease occurs, probably due to the influence on the compactness of the macromolecular chains with the further grafting.     

High modulus of isotactic polypropylene attained by coextrusion with atactic polystyrene

Orientation-induced crystallization of crystallizable polymer melts can occur, under certain conditions, during flow through converging channels. Attempts have been made to achieve this phenomenon in a two-phase system, i.e., during simultaneous extrusion of a continuous concentric core of polypropylene within a polystyrene matrix through a conical duct. On one occasion, using Carlona P SY6100 (MFI = 11.0) with Hostyren N2000-V-01 (MFI = 25.0), a highly oriented polypropylene thread with a modulus of 14.6 GPa and a melting point of 178°C was extruded at a die temperature of approximately 170°C and a pressure lower than 40 MPa. It is, in principle, possible to form highly oriented, fiber-like structures as reinforcing elements in a polymer matrix.     

Gigahertz signal processing using reflex optoelectronic switching matrices

The application of reflex optoelectronic switching matrices (ROSM) to signal processing in the gigahertz region is analyzed. Various signal processing functions such as delay generation, loop filtering, word generation/detection, integration, and digital to analog conversion are identified and their respective realizations in a ROSM are presented. It is found that for dedicated signal processing functions, simpler submatrices instead of full matrices can be employed with significant reduction in complexity and cost. The performance of ROSM's using currently commercially available components confirms the feasibility of gigahertz signal processing with ROSM's.     

Voting Technologies and Trust

The authors' propose manual voting systems that have significant security advantages over existing systems, yet retain the simplicity and familiarity that has led to widespread acceptance. The authors also discuss ways to improve efficiency without endangering this public trust     

University Networks and Data Security

In general, the problems of securing a university network are no different than those of securing any other large corporate network. But when it comes to data security, universities have their own unique problems. It's easy to point fingers at students--a large number of potentially adversarial transient insiders. Yet that's really no different from a corporation dealing with an assortment of employees and contractors--the difference is the culture.     

Mössbauer spectroscopic studies of Fe-substituted YIG

Compositional dependence of hyperfine parameters, determined through Mössbauer spectral analysis has been studied for Y_3−xFe_5+xO₁₂ (x = 0.0, 0.1, 0.3 and 0.5) garnet system at 300 K. The Mössbauer spectra have been fitted with three sextets in the ferrimagnetic state corresponding to Fe³⁺ ions at tetrahedral (d), octahedral (a) and dodecahedral (c) sites of the crystal structure. It is observed that isormershift, quadrupole shift and hyperfine field of d-site show no significant variation with Fe³⁺ concentration. The change in hyperfine fields of a- and c-sites with composition (x) has been explained on the basis of strength of exchange integrals, change in isomershift can be understood due to s-electron charge distribution and asymmetric displacement of oxygen ions surrounding the a- and c-sites seems to be responsible for observable quadrupole shift. The magneton number values obtained from magnetization and Mossbauer data are in agreement to those calculated using Neel's three sublattice model of ferrimagnetism.     

A system for real-time measurements of current-density distribution in low-energy electron beams with large cross sections

A system for real-time measurements of the current-density distribution in electron beams ejected from large-area electron accelerators has been developed. The system, which is based on Faraday cups, a microprocessor, and a PC, is designed for measuring the parameters of the electron beams ejected from large-area accelerators—devices for ionizing electroionization lasers and technological accelerators—and ensures real-time monitoring of the current-density distribution over the electron-beam cross section with a relative measurement accuracy of at least ±2%.