Critical behaviour of the linear birefringence in 3d-Heisenberg antiferromagnets : RbMnF3, KNiF3 and KCoF3

The linear birefringence of stress induced single antiferromagnetic T-domains of RbMnF₃, KNiF₃ and KCoF₃ has been measured in the vicinity of T_N. We deduce the critical behaviour in such 3d-Heisenberg systems, showing a symmetry breaking at the transition involving a unique wave vector of the order parameter in the Brillouin zone. The critical exponent $\text{β}$ of the linear birefringence has been found to be larger than 2β, in agreement with the theoretical predictions of G. Gehring.     

Resistivity measurements in silicon compressed by shock waves

Measurements of the relative resistance, $\text{R}\text{R}{}_0$, of p-type Silicon loaded by shock wave compression in the 〈 111 〉 direction, are reported. Stress amplitudes in the silicon were from 7 kb up to about 60kb.Electrical resistivity was found monotonically decreasing down to the ratio $\text{R}\text{R}{}_0$ ~ 0.14 at a stress amplitude of 34 kb. Then a sharp decrease to conducting state was detected at stresses over 56 kb.In the lower stress region the results are in agreement with theoretical calculations by Goroff and Kleinman [1]. The metallic transition observed in the neighbourhood of the Hugoniot Elastic Limit (55 kb) is suggested to be related to activation of plastic slip.     

Velocity dependence of azimuthal anisotropies in ion scattering from rhodium {111}

The scattering of He⁺, Ne⁺ and Ar⁺ ions from Rh {111} is measured as a function of the azimuthal angle of the primary ion for an incident polar angle of 70° from the surface normal and an inplane collection angle of 60°. In this case anisotropy is defined as the ratio of the yield of ions scattered having the azimuth of 〈110〉 to the yield of those having the azimuth of 〈211〉. The yield ratio for all particle types correlates with particle velocity. The ratio is ～ 1 at low velocities, decreases to ～ 0.2 at 8 × 10⁶$\text{cm}\text{s}$ and then increases to a value of 1.4 at 25 × 10⁶$\text{cm}\text{s}$. Molecular dynamics calculations have been performed for Ne⁺ ion scattering from Rh{111} in order to understand the changes in anisotropy with particle velocity. Qualitative agreement with the experimental results is obtained without having to account for neutralization. A neutralization probability that depends on the collision time improves the agreement between the calculated and experimental yield ratios. A velocity dependent probability will not affect the ratio of yields in two different azimuthal directions.     

Triple coincidence measurement of annihilation radiation — chemical application

Three photon yields and $\text{2γ}\text{3γ}$ ratios have been measured for several copper containing substances. The different extents of positronium formation have been substantiated through Doppler broadening, angular correlation and magnetic quenching in angular correlation and in peak-to-valley ratios of singles spectra at different fields. Application to chemical characterisation is indicated.     

A preliminary examination of rater-determined versus Hayre's voice-based psychological parameters

Rater-determined data on depression, anxiety and mania on some twenty subjects, receiving varying medication in each case, were compared with Hayre's voice-based psychological stress parameter, $\text{H}{}_{\mathrm{<mtext>1</mtext>}}$, determined solely from the voices of the subjects. Each subject was asked by raters to read a given paragraph, from which one word was taken for analysis. The analysis employed spectrum analysis and further processing in order to obtain the raw data for calculating Hayre's voice-based psychological stress parameter, $\text{H}{}_{\mathrm{<mtext>1</mtext>}}$. A comparison of the two results shows that manic measures were not significantly discernible by raters whereas a ratio of depression (D) and anxiety measure (A) seems to be very definitely correlated with Hayre's voice-based parameter, $\text{H}{}_{\mathrm{<mtext>1</mtext>}}$. Further work is continuing since it seems to show considerable promise in quantifying psychological measures obtained solely from the voice of the subject.     

Cross-correlation of voice and heart rate as stress measures

Heart rate and O₂ uptake, etc. have been widely used to assess the physical fitness of human subjects. Recently developed Hayre voice-based parameters for physical stress or fatigue are validated by the results of this work. These parameters are not only non-obtrusive means of real time observation of clinical, educational and physical training of subjects but also provide a unique comparative means of monitoring physical fatigue among various professionals such as athletes, truck drivers, pilots and doctors of medicine, etc. Subjects of various ages running on a treadmill were instrumented for recording heart rate, EKG, treadmill speed and slope. The treadmill was run at 3·3 mph (90 m/min) and the grade was increased by one per cent a minute up to a maximum of 25 per cent and then the speed was increased by 0·2 mph until exhaustion. Each subject was asked to count from one to ten and utter two other preselected words separated by silence gaps in between for ease of analysis. An analysis of these utterances indicates that a monotonic increase in heart rate is highly correlated with Hayre parameters $\text{G}{}_{\mathrm{<mtext>1</mtext>}}$ and $\text{F}{}_{\mathrm{<mtext>1</mtext>}}$ mentioned above, up to the time of maximum stress and the associated peak heart rate of 175. After stopping the treadmill run and letting the subject sit down, the heart rate starts dropping rapidly whereas the Hayre stress parameter $\text{G}{}_{\mathrm{<mtext>1</mtext>}}$ tends to increase to a saturation level, thus verifying that the continued physically stressed state of the subject has not significantly lessened as one would perceive from the above mentioned drop in heart rate.     

Pressure dependence of the metal-semiconductor transition in TaS3

TaS₃ exhibits the metal-semiconductor transition at 218 K due to the Peierls instability. The electrical resistance was measured under pressure. It was found that both the transition temperature, Tp, and the activation energy at T=0 K, △(0), decrease with pressure at the rates of $\text{dTp}\text{dP}\text{?-1.3}\text{K}\text{kbar}$ and $\text{d△(0)}\text{dP}\text{?-4}\text{K}\text{kbar}$, respectively, while the ratio, $\text{△ (0)}\text{Tp}$, is independent of pressure.     

Nuclear structure effect in internal conversion of the isomeric transition in 191Os

Measurements have been performed on relative conversion line intensities of the hindered 74.38 keV isomeric transition in ¹⁹¹Os with the $\text{1}\text{2}\text{π√13}$ iron-free β-ray spectrometer. Anomalies were observed for the L, M and N subshell intensity ratios and were explained with a nuclear structure parameter λ = 9.4 ± 0.5 and a mixing ratio $\text{¦δ(}\text{E4/M3}\text{)¦ = (3.0 ± 0.3) × 10}{}^{\mathrm{?3}}$.     

Scatter of fatigue data owing to material microscopic effects

A common phenomenon of fatigue test data reported in the open literature such as S-N curves exhibits the scatter of points for a group of same specimens under the same loading condition.The reason is well known that the microstructure is different from specimen to specimen even in the same group.Specifically,a fatigue failure process is a multi-scale problem so that a fatigue failure model should have the ability to take the microscopic effect into account.A physically-based trans-scale crack model is established and the analytical solution is obtained by coupling the micro-and macro-scale.Obtained is the trans-scale stress intensity factor as well as the trans-scale strain energy density(SED)factor.By taking this trans-scale SEDF as a key controlling parameter for the fatigue crack propagation from micro-to macro-scale,a trans-scale fatigue crack growth model is proposed in this work which can reflect the microscopic effect and scale transition in a fatigue process.The fatigue test data of aluminum alloy LY12 plate specimens is chosen to check the model.Two S-N experimental curves for cyclic stress ratio R=0.02 and R=0.6 are selected.The scattering test data points and two S-N curves for both R=0.02 and R=0.6 are exactly re-produced by application of the proposed model.It is demonstrated that the proposed model is able to reflect the multiscaling effect in a fatigue process.The result also shows that the microscopic effect has a pronounced influence on the fatigue life of specimens.     

Aeroelastic instability of rectangular cylinders in a torsional mode due to a transverse wind

This paper reports results of wind tunnel experiments on the aeroelastic instability in a torsional mode of two-dimensional rectangular cylinders in a uniform, transverse, two-dimensional flow. Both the free oscillation method and the forced oscillation method were employed for the experiments. Emphasis has been placed on finding the effect of the chord to thickness ratio $\text{c}\text{d}$, and also that of the structural damping, on the aeroelastic instability phenomena in the vicinity of the resonance speed.     

Analysis of crack propagation data for a strain ageing and a stabilized mild steel tested under R=0 and R=−1 loading conditions

Comparative studies of crack propagation in a strain ageing and a stabilized mild steel were carried out under axial loadings of the R = 0 and R = ?1 types. The results show the rate of fatigue crack propagation is dependent on both the tensile and the compressive stresses in the fatigue cycles, the compression stresses being less effective than the equivalent tensile stresses in causing crack growth. An equation is presented relating the rate of fatigue crack growth to a stress intensity range which is factored to allow for the variations in fatigue damage associated with the tensile and compressive parts of the stress cycle.     

Neutron diffraction study of magnetically ordered TbAsO4

TbAsO₄ undergoes a magnetic phase tranfition at T_N = 1.5 K into a helical antiferromagnetic moment configuration. The spiral is planar, with the propagation vector along [001] and the moments perpendicular to [001]. The propagation period is $\text{197 ± 12}\text{A}\text{?}$, equivalent to 31 ± 2 unit cell constants. The neutron diffraction results are discussed in connection with previously measured macroscopic data.     

Low-cycle fatigue small crack initiation and propagation behaviour of cast magnesium alloys based on in-situ SEM observations

In-situ observations on the initiation and propagation behaviour of low-cycle fatigue small cracks in cast magnesium–aluminium alloys (AM50 and AM60B) were carried out with scanning electron microscopy (SEM) to elucidate the resistance to fatigue cracking and to evaluate the fatigue small crack growth rate accurately and quantitatively. The results indicate that the fatigue small cracks formed preferentially on β-phase (Mg₁₇Al₁₂) boundaries at room temperature. In addition, the effects of the parameters of stress levels in low-cycle fatigue and temperatures as well as microstructure on fatigue small crack propagation behaviour are revealed. The variation of crack open displacement (COD) with stress levels and cycles at elevated temperature shows that it is unsuitable to estimate the fatigue small crack growth rate of cast magnesium alloys using conventional measurement methods such as the plastic-replica technique due to the obvious difference between microscopic cracks in the open and closed states. Stabilized crack propagation behaviour is limited to cases where the physical crack length is less than 1?mm in low-cycle fatigue.     

Temperature dependence of the elastic constants of aluminum

The single crystal elastic constants of aluminum have been measured using a piezoelectric composite oscillator from room temperature to just 20 K below the melting point. The elastic moduli differ markedly from previous high temperature results, but match in well with previous cryogenic results. Over the temperature range investigated the isothermal bulk modulus and the two shear moduli have a simple exponential dependence on isobaric volume, and the cryogenic data indicate this dependence may be preserved down to absolute zero. As has been found previously for a wide range of materials, the isothermal bulk modulus and the shear modulus $\text{(c}{}_{11}\text{– c}{}_{12}\text{)}\text{2}$ appear to be continuous functions of volume through the melting expansion, and melting seems to find its origin in the mechanical instability associated with this shear modulus vanishing at the volume of the melt at the freezing point. Grüneisen's parameter divided by the molar volume is very nearly independent of isobaric volume.     

Modal content of noise generated by a coaxial jet in a pipe

The problem investigated was that of noise generated by air flow through a coaxial obstruction in a long, straight pipe of inside diameter, D = 97 mm. Downstream modal pressure spectra in the 200–6000 Hz frequency range were measured by a new technique [1] for orifices and nozzles of diameter d where $\text{0·03 ? (}\text{d}\text{D}\text{) ? 0·52}$. The Mach numbers of the flow through the restrictions ranged from 0·15 to choked conditions. The shape of the modal frequency spectrum was found to be determined by the frequency ratio $\text{f}{}_{\mathrm{r}}\text{=}\text{He}\text{St}\text{=}\text{U}{}_{\mathrm{i}}\text{D}\text{a}{}_0\text{d}$, where U_i is the jet velocity and a₀ is the speed of sound in the gas downstream of the restriction. This parameter is the ratio of two non-dimensional frequencies: namely, He, which controls acoustic propagation inside circular ducts, and St, which scales the jet noise spectrum shape. At low f_r(<3) the higher modes dominate the noise spectrum above their cut-off frequencies, while for higher f_r all modes are approximately of equal amplitude. The nature of large scale turbulence structures in the region of the jet near the nozzle exit may be used to explain these phenomena. The measured modal pressure spectra were converted to modal power spectra and integrated over the frequency range 200–6000 Hz. The acoustic efficiency levels (acoustic power normalized by jet kinetic energy flow), when plotted vs. jet Mach number, depend strongly on the ratio of restriction diameter to pipe diameter ($\text{d}\text{D}$). Dividing the efficiency levels by the area ratio, $\text{(}\text{d}\text{D}\text{)}{}^2$, correlated the results over a moderate range of ($\text{d}\text{D}$).     

Refined theory for flexural motions of isotropic elastic plates

A technical theory for the flexural motions of isotropic elastic plates has been developed, taking into account the influence of transverse normal strain and transverse normal stress, together with rotatory inertia and transverse shear. The theory is tested by studying the classical wave propagation problem and results indicate the influence of the transverse normal strain on the wave speed at large values of $\text{h}\text{λ}$. In addition, a constant magnitude for the shear coefficient $\text{κ}{}^2\text{=}\text{5}\text{6}$ is obtained, which is in contrast to an undetermined coefficient form in previous flexural motion formulations but consistent with the value obtained in the Reissner static technical theory of plate bending.     

A note on the compression of cubic ZnS

Using X-ray diffraction the compression of cubic ZnS (sphalerite) has been measured to 9.4 GPa under hydrostatic pressure conditions. The results analysed using a two parameter Birch-Murnaghan equation may be presented by K₀ = 74.8 ± 3.2 GPa and K′₀ = 4.91 ± 1.2. These compare well with 3.76 ± 0.96 for K₀ = 76.5 GPa, the value calculated by Chang and Barsch from their wurzite data. $\text{Δa}\text{a}{}_{\mathrm{o}}$, the change in lattice parameter at 15 GPa in ZnS is $\text{0.255}\text{A}\text{?}\text{± 0.012}$ corresponding to a change of $\text{0.110}\text{A}\text{?}\text{± 0.005}$ in Zn-S distances at this transition to the metallic state.     

Repeated zones and Mahan cones in the angular dependence of photoemission

The intensity of photoemission from the Ta-derived d states in the layer compound 1T-TaS₂ has been measured as a function of both polar and azimuthal angle of emission at the photon energy $\text{h}\text{?}\text{ω=21.2}\text{eV}$. The light source was a high intensity He resonance lamp employing an aluminum window in place of the more conventional differentially pumped capillary system. The azimuthal dependence of the d emission displays three kinds of lobes which we refer to as “heads, chins and ears”. The heads and chins are oriented along directions close to the bifurcated lobes observed previously at $\text{h}\text{?}\text{ω=10.2}\text{eV}$. The ear lobes, however, are oriented quite differently and appear only at high polar angles, corresponding to larger relative values of the parallel wavevector. The results can be understood in terms of a repeated zone scheme in which the ears and chins (not necessarily at the same polar angle) correspond to different Mahan cones of the same optical transitions.     

X-ray intensity ratio ILαILℓ in the region 55 ⩽ Z ⩽ 94

The X-ray intensity ratio $\text{I}{}_{\mathrm{<mtext>L</mtext><mtext>\alpha </mtext>}}\text{I}{}_{\mathrm{<mtext>L</mtext><mtext>?</mtext>}}$ has been measured, using radioactive sources and high resolution Si(Li) X-ray detectors over a range of 55 ? Z ? 94. The theoretical ratios are found to be underestimated at low Z in the calculations of Scofield and of Rosner and Bhalla.