On a peculiarity of low-energy ion scattering from a well-ordered bcc W(2 1 1) surface

A peculiarity in the backscattering of keV He⁺ ions by a well-ordered high-purity W(2 1 1) surface is reported. Besides the normal elastic binary collision peak and the low-energy tail due to backscattering in deeper layers, an extra peak is observed for an inelastic loss of about 95 eV. This unusually large loss has a constant value over a wide range of primary energies (1.5-4.5 keV). An extra peculiarity is that the peak is only observed for the scattering in normal incidence towards the (2 1 1) plane. It is also not seen for polycrystalline W. The energy loss may be due to a quasi-double or -triple collisions of He particles with the row-trough structure of W(2 1 1) involving electronic excitation of both He and W atoms. Alternatively it may be due to a special channeling/dechanneling process for the incident ions.     

Age dependence of attitudes and knowledge in cyclists

A number of factors related to bicycle accidents were studied, namely, knowledge of priority rules, attitude and self-reported behavior regarding traffic rules, and general opinions about the safety of the traffic behavior of cyclists and drivers. In order to get an indication of the influence of these factors at different stages of the life span, subjects ranging from 9 to 83 years of age were represented in the study. The relationship between age and the various measures was found to be U-shaped in most cases. The older cyclists and the 9 to 11 year olds, the two groups that are most at risk, were deficient regarding knowledge while showing the most positive attitudes. Implications with respect to possible counter measures are discussed.     

A simple method for the evaluation of microwave mixer diodes

A simple method is described for the evaluation of the various microwave mixer diodes which can be used in 9-GHz electron paramagnetic resonance (EPR) spectrometers using magnetic field modulation below 1 kHz. The advantage of this method over other methods is that it is optimized for EPR applications and determines the optimum operating conditions for each microwave diode. This method utilizes a microwave bridge with a reference arm with an attenuator to control the microwave bias power level, and a signal arm where the signal is attenuated, phase shifted, and modulated at the typical magnetic field modulation frequencies. The microwave power from the two arms is recombined and demodulated by the microwave diode. The output of the microwave diode is then recorded with various video loads, microwave bias power, and modulation frequencies. Measurements are performed to determine the effect of the preamplifier that followed the microwave diode on the signal-to-noise ratio (SNR). The recorded spectra are used to determine the SNR, the noise floor, and the 1/f corner frequency. Comparison of these factors for the different types of microwave diodes shows that some Schottky-barrier diodes have noise figures at 1 kHz that are as low as those for tunnel diodes     

Thin film tape heads, analog and digital applications

Analog and digital applications of thin-film tape heads are discussed. Magnetoresistive tape heads are discussed. A thin-film tape head which is used in analog voice documentation recorders is described. A table that lists a number of relevant system and head parameters is given     

Thermal transport behavior of van der Waals solids and liquids in the neighborhood of the solid-liquid phase transition

The thermal conductivity, , is one of the few transport coefficients which shows a relatively small change at the solid-liquid phase transition, and hence it is a property that can be used in comparing dynamic properties of both ordered and disordered systems. Although the discontinuity in can be accounted for largely by the difference in density, , of solid and liquid at the phase transition, its volume dependence is examined more closely. The thermal diffusivity, which is known to dominate the dynamic structure factor of liquid argon, has been determined around the phase transition also; the sound velocity has been considered in addition. The results are discussed and a comparison is made with these properties in solid and liquid benzene and cyclohexane.Paper presented at the Ninth Symposium on Thermophysical Properties, June 24–27, 1985, Boulder, Colorado, U.S.A.     

Thermal conductivity of normal liquid3He at finite temperatures

Greywall's experimental data for the thermal conductivity of normal liquid³He are reanalyzed. The temperature dependence at various pressures seems consistent with a law of corresponding states in the sense that it can be described by a universal function of a reduced temperature. It is suggested that the appreciable dynamical screening of the scattering amplitude for the quasiparticles in³He is responsible for this behavior. For illustration the thermal conductivity is calculated at finite temperature for a class of screened interaction models to leading order in the screening parameter. Good agreement is found with experiment by fitting the single Landau parameterA _a ⁰ .     

Selffield losses and selffield stability of superconducting wires with low conductivity matrix material

The influence of the normal material in a superconducting wire on the selffield losses has been investigated. The results show that the contribution of the normal material is considerable in the case of a highly conductive material like Cu. Measurements on wires with CuNi-material show no significant contribution of the normal material to the losses. In the latter case, however, special attention should be paid to stability. Measurements show that the obtainable maximum current under a.c. conditions obeys the adiabatic stability criterion rather well. The dependence of the maximum current amplitude on the critical current density and the diameter of the wire has been obtained. Wires with Al cores inside the NbTi filaments for better stabilization have also been investigated regarding maximum current and selffield losses.     

Electrical properties of α-MnSe

Electrical resistivity, Hall effect and thermoelectric power of iodine-grown crystals of p-type α-MnSe are reported. The conductivity of α-MnSe is due to holes in a narrow 3d band (Mn³⁺) with effective mass $\text{m★}\text{m}{}_{\mathrm{o}}\text{?10}$. The (Hall) mobility of the holes at 280K is μ_H=0.14 cm₂V_?1s_?1, and is not thermally activated. At low temperature conduction occurs in a partly-filled impurity band, arising from the simultaneous presence of acceptors (Mn vacancies) and donors (substitutional iodine).     

Preface

The diffusion of platinum and gold in nickel at relatively low temperatures (250–725 °C) was measured by Rutherford backscattering spectrometry (RBS). The diffusion profile of the noble metal in nickel was calculated from RBS spectra. This method takes fully into account the dependence of the energy losses of the backscattered particle along the inward and outward paths on the changing energy of the particle and the changing composition of the target. Diffusion coefficients are calculated from the measured diffusion profile. The dependence of the diffusion coefficient on temperature obeys the Arrhenius law. The activation enthalpies are 78.2 kJ mol^-1 and 119.6 kJ mol^-1 for the diffusion of platinum and gold respectively into nickel. The frequency factors are respectively 2.6 × 10^?9cm²s^?1 and 1.4 × 10^?7cm²s^?1. Experimental data suggest that diffusion along the grain boundaries is 2–3 times as fast as bulk diffusion.     

A study of the stability of Record of Performance milk samples for infrared milk analysis

The effect of switching individual cow Record of Performance milk samples from on-farm Babcock analytical system to centralized infrared analysis was investigated. The effects of lipolytic activity on the signals of the fat (5.73/5.58 and 3.48/3.56 microns) and protein (6.46/6.68 microns) wavelengths of filter instruments showed that lipolysis decreased the infrared fat signal and concurrently increased the protein signal. The chain length (3.48/3.56 microns) signal was unaffected by lipolysis due to the concordant movement of the reference wavelength baseline with the changes in the sample wavelength signal. Storage trials (3 d) of preserved milk samples indicated no direct relation between fat signal depression and chemically determined free fatty acid levels. Microbial growth and agitation also contributed to changes observed in samples studied under controlled conditions. Based on concurrent infrared, Babcock, and Mojonnier analyses of approximately 900 samples on d 1 and 3, there was a consistent but marginal drop in the carbonyl (5.73/5.56 microns) fat signal and an increase in the amide (6.46/6.68 microns) protein signal, but these changes were of limited significance. A study of 3-d and older samples indicated that significant levels of acid were produced, indicative of microbial growth. A comparison of Babcock results carried out on-farm, Mojonnier analyses in the laboratory, and their corresponding infrared results did not show statistically significant differences. Other than the inherent variability present in the individual cow samples, there were minor quality changes occurring under the present sample handling system due to a combination of lipolysis, microbial growth, and acid production. Refrigeration of Record of Performance samples during transport and at the central laboratory is recommended to minimize these changes.