Growth structure investigation of MgF2 and NdF3 films grown by molecular beam deposition on CaF2(111) substrates

The growth structure of MgF₂ and NdF₃ films grown on polished CaF₂(111) substrates deposited by molecular beam deposition has been investigated using transmission electron microscopy (TEM) of microfractographical and surface replications as well as cross-sectional TEM, atomic force microscopy, packing density, and absorption measurements. It has been shown that by taking advantage of ultrahigh vacuum environments and a special stratification property of MgF₂ and NdF₃ films, the preparation of nanocrystalline films of high packing density and low optical absorption is possible at a substrate temperature of 425 K.     

Iron pyrite films prepared by sulfur vapor transport

Iron films deposited via thermal evaporation, with a thickness between 100 and 250 nm, were converted into FeS₂ by open sulfur transport using nitrogen as a gas vector. The films thus obtained constituted a single pyrite phase and were optically highly absorbing. The sulfurization process was optimized. As a result, sample temperature and conversion time were found to be the major determining parameters. The films were characterized using several methods. The crystallinity and phase identification were determined by X-ray diffractometry. Scanning electron microscopy showed a homogeneous surface of both iron and pyrite layers. Optical transmission measurements confirmed the highly absorbing character of FeS₂ and allowed the determination of direct (1.35 eV) and indirect (0.82 eV) transitions.     

Silicon carbide-toughened zirconia ceramics

Tetragonal zirconia polycrystalline (TZP) ceramics containing SiC reinforcement in the form of fine particles (nano-scale), particles (micro-scale), whiskers and platelets were synthesized by hot-pressing. The effects of morphology and grain size of SiC reinforcement on the strength and fracture toughness at room temperature were investigated. The addition of SiC (in whatever form) caused decreases in strength and toughness at room temperature with the exception of whisker-reinforced materials. Toughness fell off with increasing temperature, but nevertheless retained about one-half of the room-temperature value for that particular SiC reinforcement. However, the whisker- and particle-reinforced materials had higher K _lc values at high temperature than fine particle- or platelet-reinforced materials, with values in excess of 7 MPa m^1/2 at 1000 °C. The microstructure was examined for SiC whisker-reinforced/TZP materials by TEM and HREM, to examine the nature of the whisker/zirconia interface.     

The solubility of solidified bromoethane C2H5Br in liquid nitrogen at 77.4 K

The solubility of solidified bromoethane C₂H₅Br in liquid nitrogen at 77.4 K has been investigated. A combination of filtration and gas chromatography methods were used. The experimental value of the solubility of solidified bromoethane in liquid nitrogen at 77.4 K was compared with the solubility of halogenhydrocarbons previously investigated. The Preston-Prausnitz method was used for estimation of the solubility of bromoethane in liquid nitrogen and the value of the I₁₂ parameter was calculated.     

Measurement of the tunnel rate in SIS' tunnel junctions as function of bias voltage

Cryogenic detectors with superconducting tunnel junctions can provide an energy resolution improved by at least one order of magnitude compared with standard semiconductor detectors. While the detection principle was already demonstrated many years ago, the past years were dedicated to the transition from the laboratory sample to practical detectors. Our most favored detector design gives rise to tunnel junctions with electrodes of unequal energy gaps. In such hetero tunnel junctions bias conditions can be established which cause a negative signal current. We report the experimental verification of this effect, and we discuss the yield of charge signal of cryogenic detectors based upon superconducting tunnel junctions.     

Performance evaluation of the Golay code pulse compression technique

The Center for NDE, Iowa State University, has developed a laboratory prototype Golay code pulse compression system and tested it on a variety of materials. The performance of the system was evaluated in terms of signal-to-noise ratio enhancement (SNRE), resolution, and computation speed. The system's error sources also were discussed. The Golay code pulse compression was simulated on a computer and demonstrated the effective noise suppression. In addition, an equivalent pulse of the Golay code (delta-like pulse) was derived theoretically using a simple ultrasonic inspection model, which demonstrated its equivalence on the output correlated signal. Overall, the pulse compression technique extended the detection range for a given peak power and considerably reduced the system'swhite noise, hence providing enhanced signal-to-noise ratios (SNRs). An average of 30 dB improvement in SNR was obtained from highly energy-absorbent materials such as rubber, plastics, corks (insulation materials), and thick composites using the Golay codes of up to 512 bits. However, the technique did not effectively reduce coherent scattering noises from the coarse grain boundaries in cast stainless steels, Inconel weld metal, and material lay-ups in thin composites. Furthermore, it was found that, depending upon the system's hardware capabilities, the overall performance could be degraded considerably.     

A generalized model for the interaction between hydrogen and structural defects of the solid phase

A generalized mathematical model of the interaction between hydrogen and structural defects in metals is analyzed. The temporal dependence of hydrogen permeation flow is examined for three typical cases. The approximations to the general equation for hydrogen permeation flow obtained enable one to determine the interaction from experimental data. The extreme values of permeation flow are analyzed. A method for determining the kinetic parameters of interaction for a given permeation flow is suggested. The conclusion is made that, within the framework of the generalized model, it is possible to establish the mechanism of hydrogen trapping.Dnepropetrovsk Institute of Chemical Engineering, Dnepropetrovsk. Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 29, No. 5, pp. 25–29, September–October, 1993.     

Demonstration of a semiconductor external cavity laser using a UVwritten grating in a planar silica waveguide

The authors report the first demonstration of a semiconductor external cavity waveguide laser, modulated at 2.5 Gbit/s over 100 km of standard optical fibre using a UV written grating in a planar silica waveguide as the feedback element     

Selection of rainbow trout resistant to viral haemorrhagic septicaemia virus and transmission of resistance by gynogenesis

In 1984 a programme of selection for resistance to viral haemorrhagic septicaemia virus (VHSV) in rainbow trout was initiated. The progenies of 14 males were submitted to a VHSV waterborne challenge. The mortality ranged from 30 to 95% and the heritability of resistance was estimated to be 0.63 +/- 0.26. One male consistently provided the most resistant offspring, and the second generation was produced from sires and dams selected among these families. The mean resistance improved and several females giving birth to resistant offspring were identified (0-10% mortality while the mortality in the controls was from 70 to 90%). The meiotic gynogenetic progeny of these females also demonstrated high resistance (mortality less than 10%). The role of superficial tissues in the resistance was confirmed and there was a striking difference in the growth of VHSV in fins excised and infected in vitro. The fins from resistant fish replicated the virus poorly as compared with the fins of susceptible fish.