Photomodification of polymer films: azobenzene-containing polyurethanes Itoh, M; Harada, K; Matsuda, H; Ohnishi, S; Parfenov, A; Tamaoki, N; Yatagai, T
doi: 10.1088/0022-3727/31/5/001pmid: N/A
New results are presented on optical recording to the films of polymers substituted with azo dyes. Holographic gratings are formed in the polyurethane films by exposure to laser light without any post-treatment as in previous works using polyacrylates, epoxy-based polymers and polyesters substituted with azo dyes. It is shown for the first time that the principal mechanism of optical recording could be the mass transfer of polymers during the cis-trans isomerization of azo dye units on the polymers from illuminated areas to non-illuminated areas. Besides this transport, some irreversible photochemical reactions involving atmospheric oxygen are suggested as another possible origin for the holographic recording.
The piezoelectric effect and stored polarization in corona charged ABS films Hundal, Jasbir S; Nath, R
doi: 10.1088/0022-3727/31/5/003pmid: N/A
The piezoelectric coefficient of poly-(acrylonitrile-co-butadiene-co-styrene) (ABS) terpolymer films has been measured as a function of various poling and stretching conditions. has been measured in ABS films for a poling field of about , poling temperature C and stretching ratio 4. The stored polarization in piezo ABS films has been estimated using thermally stimulated depolarization current (TSC) experiments. The contributions of the dimensional effect and the polarization to the piezoelectricity in the ABS films have been determined. Cooperative dipolar behaviour is believed to be involved in the stored polarization.
Some new Nd-rich carbides formed by solid state reaction of and carbon Pan, F; Zhang, M; Zhao, R F; Liu, B X; Tokunaga, M
doi: 10.1088/0022-3727/31/5/004pmid: N/A
Thermal analysis, x-ray diffraction and TEM selected area electron diffraction (SAD) methods were used to investigate the phase evolution of the -C system upon solid state reaction. The experimental results revealed that there were some solid state reactions of carbon with the phase and two new Nd-enriched carbides were formed in the -C system, i.e. a bcc phase with a lattice parameter of and a tetragonal phase with lattice parameters , . It was also found that the formation of Nd-enriched carbides was related to the thermal reaction temperature and carbon concentration in the sample.
Dynamic coercive field of bistable amorphous FeSiB wires Aragoneses, P; Blanco, J M; Dominguez, L; Zhukov, A; Gonzalez, J; Kulakowski, K
doi: 10.1088/0022-3727/31/5/005pmid: N/A
The dynamic coercive field and area of the hysteresis loop A have been measured for bistable amorphous FeSiB wire as functions of frequency f and amplitude of an applied magnetic field. The results are presented in the form , . The values of the exponents m, p, x and z are given for an as-quenched wire with applied tension and without tension, and for an annealed wire with applied tension. The range of frequency f is from 0 to 700 Hz, and the range of amplitude is from 0 to 140 A . The exponents vary from 0.22 to 0.86. Differences are found for the first time between m and p, and between x and z. For higher frequencies (f >150-350 Hz) the bistable remagnetization process is not complete. Observed values of the exponents can be partially understood in terms of an equation of motion of reversible displacement of domain walls for the case of a small restoring force.
Measurements of range and energy loss of in Makrofol-G Kulshreshtha, A; Ghosh, S; Dwivedi, K K
doi: 10.1088/0022-3727/31/5/006pmid: N/A
Ranges and energy loss of 17.1 MeV ions in Makrofol-G polymer have been determined using a nuclear track technique. Calibrated polyallyldiglycol carbonate (PADC) detectors were used to determine the degraded energy of ions after they had passed through the various stacks of Makrofol-G. The energy-loss rates as a function of the depth of penetration and ion energy have been determined. The mean ranges of in Makrofol-G have also been measured at various energies up to 17.1 MeV . The experimental results are discussed and compared with the theoretical values obtained from four different computer codes.
Enhanced ion acceleration by focusing an intense electron beam inside a dielectric collimator Vijayan, T; Roychowdhury, P
doi: 10.1088/0022-3727/31/5/007pmid: N/A
Enhancements in the acceleration of positive ions were observed by converging an intense electron beam (250 keV, 6 kA, 80 ns, cm from the Kilo Ampere Linear Injector (KALI-200)), into a short dielectric collimator having a radius of about the beam radius and a length around the potential-well characteristic length . These were in comparison to the results of a beam injected from a planar diode into an collimator where the ion current, , recorded was only to 5 A of 150-250 ns pulse width which included - particles of , , of peak energy of , 10.8 and 14.4 MeV respectively. The ion energy increased with the electron beam propagation distance and resulted in the elongation of the ion pulse in total agreement with the theory. The magnitude of the ion current followed the trend of the propagated electron current which decreased with distance. When the electron beam was focused by a convex anode having , the ion current increased to 9-16 A and to MeV as a result of the field enhanced potential well. was further enhanced to 20-30 A and the energy to 1.5 MeV by increasing the collimator thickness to 4-8 mm. Peak energies of , and generated were of the order of 18, 24 and 28.5 MeV. In terms of the energy invested, these results are an improvement over other work.
Reflectivity experiments with 60 femtosecond laser pulses Riley, D; Langley, A J; Taday, P F; Shaikh, W; McCormack, I
doi: 10.1088/0022-3727/31/5/008pmid: N/A
The reflectivity of solid silicon and aluminium targets has been measured at a fixed angle of incidence as a function of focused intensity for 60 fs pulses of 750 nm laser light. It was found that, even for intensities in excess of W , there was no observable change in reflectivity from the low intensity value. This is taken to indicate that there is no formation of a high density gaseous plasma during the laser pulse. However, examination of the silicon target shows significant damage spots that indicate that melting and possibly gaseous plasma formation do occur after the pulse.
Instabilities in MPD thruster flows: 1. Space charge instabilities in unbounded and inhomogeneous plasmas Wagner, H P; Kaeppeler, H J; Auweter-Kurtz, M
doi: 10.1088/0022-3727/31/5/009pmid: N/A
For a few years, the study of magnetoplasmadynamic instabilities has received increased attention because they may explain the so-called `onset' phenomena which limit the efficiency and, thus, the use of coaxial plasma accelerators in space propulsion and other applications. A systematic investigation of instabilities in magnetoplasmadynamic flows was initiated at the Institut für Raumfahrtsysteme in 1987. Among other instabilities, a particular one with the characteristics of the space charge instability was found. This instability had until then been known to occur only in finite gas discharge geometries. It will be shown in this paper that, in the presence of gradients of the flow variables, space charge instabilities can also appear in unbounded plasmas. The conditions for their development and growth are determined and discussed.
Instabilities in MPD thruster flows: 2. Investigation of drift and gradient driven instabilities using multi-fluid plasma models Wagner, H P; Kaeppeler, H J; Auweter-Kurtz, M
doi: 10.1088/0022-3727/31/5/010pmid: N/A
The investigation of magnetoplasmadynamic (MPD) instabilities in connection with the performance of MPD thrusters has received increased attention for several years. A systematic investigation of macroscopic drift and gradient driven instabilities at the Institut für Raumfahrtsysteme (IRS), carried out since 1987, showed that the occurrence of acoustic wave and space charge instabilities was possible. The calculation of the linear development of instabilities using a three-fluid theory of the plasma flow will be presented. Furthermore, in order to identify the instabilities found in the three-fluid formalism, two-fluid and one-fluid models are investigated and links established. When possible, analytical approximations for the unstable roots of the linear dispersion relation are derived, giving the explicit dependence of the oscillation frequencies and growth rates on the wavevector and the various plasma parameters.