High-frequency dielectric properties of Mg-Al-Si,Ca-Al-Si and Y-Al-Si oxynitride glasses

Recently developed coaxial line techniques [1] have been used to determine, at room temperature, the values of the real () and imaginary (') parts of the dielectric constants for some Mg-Al-Si, Ca-Al-Si and Y-Al-Si oxynitride glasses over the frequency range 500 MHz to 5 GHz. The frequency dependencies of and ' are consistent with the universal law of dielectric response in that (-_t8)^(n–1) and '^(n–1) for all glass compositions; the high experimental value of the exponent (n=1.0±0.1) suggests the limiting form of lattice loss [2] situation. In this frequency range, as previously reported [3] at longer wavelengths, the addition of nitrogen increases the dielectric constant, (); in both the oxide and oxynitride glasses is also influenced by the cation, being increased with cation type in the order magnesium, yttrium, calcium as at lower frequencies.     

Types of superplasticm-δ curves of Ti-6Al-4V alloy and their intertransformation

The superplasticm- curves of Ti-6Al-4 alloy have been determined at different temperatures and strain rates; all were of them _L=m _max type, and were of either fundamental, descending or ascending types. The latter two types were transformed from the former through the processes ofm _Lm _O, _LO andm _Lm _F, _LF, respectively. The highest total elongation, _F, was 1150% obtained at 950C and 1.55×10^–3 s^–1. The Chin Liu equation has been applied to all types ofm- curves. The parameters characteristic of all types ofm- curves have been obtained and were found to vary with temperature and strain rate. The total elongation, _F, is determined by the resultant effects of all other parameters, not by a singlem value, theoretically considered to be constant and determined practically by a tensile strain of about 30%–50% (m _30%–50%) as usual.Nomenclature C (=k/k _o ) the normalized slope ofm- curve corresponding to - a material constant corresponding to - m strain-rate sensitivity index corresponding to - m _max maximum on them- curve corresponding to _L - m _min minimum on them- curve corresponding to _L - crosshead speed during the tensile test - the strain of the entire stretching process (has same significance as ordinarily adopted ) - _F total elongation at fracture chosen for the present work - _I intermediate strains including _I1, _I2, _I3, ..., _I(i–1), _Ii , _I(i+1), ..., chosen for the present work - _L limit strain separatingm- curves into sections - _O (=0) starting strain - strain rate - flow stress     

Some observations on the deformation characteristics of bulk polycrystalline zirconium hydrides

The deformation behaviour of bulk polycrystalline zirconium hydrides in the composition range ZrH_1.27 to ZrH_1.66 has been investigated by compressive loading at temperatures between room temperature and 500° C. Single-phase -zirconium hydride is brittle below 100° C. Analyses of slip traces on specimens deformed at temperatures between 100 and 250° C have shown that the glide planes are {111} types. The deformation characteristics of and ( + ) alloys at temperatures between 100 and 500° C are consistent with the hydrogen vacancies in the -phase providing significant lattice friction to the movement of dislocations in the zirconium lattice of the hydride structure. The room temperature fracture stress of ( + ) alloys increases with the volume fraction of the -phase and this can be related to the resistance offered by platelets to the propagation of cleavage cracks in the matrix. In a ( + + ) alloy the resistance to crack propagation at room temperature is further increased by the soft -zirconium phase.     

Localized spin fluctuations

Scaling arguments and renormalization group techniques are used in the Anderson model Hamiltonian for the nonmagnetic limit of a magnetic impurity. The range of validity of the theory is limited toU/ 1, where the electron-electron collisions can already compete strongly with the electron-hole collisions. A parquet approximation is developed; it gives for the static susceptibility in the symmetric case = ()^–1 exp (+U/). There are some hints that the exchange force might play a crucial role in the formation of localized magnetic moment. These considerations are consistent with the electron-hole symmetry in the symmetric Anderson model.     

Nonlinear Response of a Continuous Wave NMR Spectrometer for Samples with a Large Magnetization

We present a new insight in the response of a CW NMR spectrometer for highly magnetized samples above 100 MHz. The spectrometer is a bridge made of a magic T. The output of the bridge is proportional to the reflection coefficient, , of a resonant circuit, which is built with a coil containing the sample. The sensitivity of the reflection coefficient to the complex susceptibility of the sample, () = () – j(), depends on the quality factor, Q, of the circuit and filling factor, . When the condition Q 1 is not fulfilled, we show indeed that the use of a simple crystal detector, which is only sensitive to || gives rise to a strong nonlinear response of the spectrometer. Measurements of the complex value of by means of phase sensitive detection allow to recover a linear behavior. We discuss and illustrate those issues with a few circuits we designed for our measurements on liquid ³ He with spin polarizations up to 15 %. A method is described to build in a reproducible and predictable way resonant circuits matched to 50 in the frequency range 100 – 400 MHz with a quality factor as high as 1000 at 4 K.     

Phase transformations in permanent-mould-cast aluminium bronze

The phases obtained in aluminium bronze (Cu-10Al-4Fe) cast into a permanent mould were investigated. The parameters examined were the pre-heating temperature of the mould and the graphite coating thickness. The phases and ₂ were detected as well as the metastable phases and . The intermetallics of the system Fe-Al were obtained in various stoichiometric compositions. The different cooling rates of the casting resulted in two mechanisms of transformation to grains out of the unstable phase, one being nucleation and growth producing needle-shaped grains, the other exhibiting a massive transformation to spherical grains. These two mechanisms determine the changes in the size of the a grains as result of changes in the cooling rate in its various ranges.     

Loss of stress equivalence in solid-solution hardening

Available data on the temperature, T, and concentration, c, dependence of the critical resolved shear stress, , of numerous copper- and silver-based solid solutions have been examined with special reference to the stress equivalence of solid-solution hardening, i.e. a common single curve for all alloy concentrations and solute types in a correlation of =(78)–(298) with (78), as first demonstrated by Basinski et al. in 1972. For solid solutions based on a given solvent metal, the stress equivalence is lost if the value of exponent r in the relation (T) c^r varies with temperature. The critical concentration of the solute at which stress equivalence of solid-solution hardening is lost depends on the alloy system.     

A gradient method of defining smooth solutions to inverse boundary-value problems in thermal conduction

An iterative algorithm is described for solving boundary-value inverse problems in thermal conduction by steepest descent, which utilizes information on the smoothness of the solution.Notation A, B linear operators - u element of solution space U - f exact reference data - f reference data uncertainty - value of reference data uncertainty - A^–1 inverse operator - u^(k)() k-th derivative of function u - _m length of observation interval - _i(t) polynomials of degree i–1 - A^*, B^*, L^* operators conjugate to the operators A, B, L - Jg discrepancy functional gradient - _n descent step along the discrepancy antigradient for the n-th iteration - K( –) kernel of integral equation - q() heat flux - T() measured temperature inside body Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 39, No. 2, pp. 259–263, August, 1980.     

Transient heat conduction in hollow spheres with a moving inner boundary

The finite integral transform method is used to obtain the solution of unsteady heat conduction problems for a hollow sphere with a moving internal boundary and various boundary conditions at the outer surface. For the solution of the problems of interest integral transform formulas are presented with kernels (16), (20), and (24) and the corresponding inversion formulas (18), (22), (26), (29) and characteristic equations (17), (21), (25), (28), (31), (33).Nomenclature a, thermal diffusivity and conductivity - t temperature of phase transformation - density - heat transfer coefficient - Q total quantity of heat passing through inner boundary - F latent heat of phase transformation - Fo(1,)=a/R ₁ ² , Fo(i,)=/r _i ² , Fo(i, _i)=a _i/r _i ² Fourier numbers - Bi₂=R₂/ Biot number     

Anomalous normal state and high temperature superconductivity in the cuprates

It is generally believed that a high electronic density-of-states n(E_F), and therefore a low Fermi velocity v_F, are required to obtain a high transition temperature, since T_{c ph} exp(–1/) and = n(E_F)V. However, V = < I² >/M _ph ² , and Bardeen showed that I E_Fk_F = (1/2)k _F ² v_F. Thus one may expect that should increase with v_F. While it may not be feasable to increase the one-electron velocity v_F signifcantly, the velocity may increase greatly as a result of renormalization by electron-electron interactions. Such a renormalization exists in Hartree-Fock theory for an unscreened electron-gas. We found that for a medium-density electron-gas (r_s 10–20) imbedded in a background with a dielectric constant () such that / > 10, there is a significant increase of v_F by renormalization, even when screening is taken into consideration. The peak of v(k) at k = k_F is very narrow, the half width being somewhat less than the frequency ₀ at which () falls by a factor of 2. When () is due to ionic polarization, _o is a typical phonon frequency. The height of the peak v_F/v _F ⁰ is of order E_F/₀, and the width in units of momentum is: k/k_F (₀/E_F)². This velocity peak is associated with a minimum in the screening constant at E_p. Its sharpness causes the normal state properties to be highly anomalous; namely the conductivity is exceptionally high, with an anomalous temperature dependence; the conductivity anisotropy, thermoelectric power, and Hall constant are anomalous. Direct determination of v(k) in YBCO by several methods indeed suggests a large, sharp peak, the width being of order 10 me V. This peak manifests itself in the tunneling and point-contact spectroscopy I–V curves. We suggest that the reduced screening at the Fermi level, associated with this velocity peak, is responsible for the high T_c of the cuprates and several other exotic superconductors. Thus, the high T_c is a reflection of the anomalous normal-state properties.     

The age hardening effect in Ti-6 Al-4 V due to ω and α precipitation in the β grains

The structure at room temperature of a quenched TA6V titanium alloy has been investigated. This structure is + or + according to the treatment temperature; it is always metastable. During ageing the grains decomposed by the reaction + + +; this decomposition was accompanied by a large increase of the 0.2% yield stress. No structural modification was observed in. The and phase of TA6V were separately investigated in the form of single-phase alloys. The hardness of was insensitive to ageing, while was considerably hardened by and; we deduced that the strengthening of the minor phase during ageing is mainly responsible for the hardening of TA6V.     

Effect of elastic interaction energy on coarsening of γ′ precipitates in a mechanically alloyed ODS Ni-base superalloy

The coarsening behavior of precipitates with a uniform size distribution and with a bimodal size distribution in a mechanically alloyed ODS Ni-base superalloy were investigated to clarify the effect of elastic interaction energy on the coarsening behavior of precipitates. The coarsening rate decreased with increasing size of precipitates with a uniform size distribution, contrary to the classical LSW theory, and the coarsening behavior of precipitates with a bimodal size distribution exhibited Ostwald ripening in which the larger precipitates grow at the expense of smaller precipitates. The driving force for coarsening of precipitates was analyzed based on the two-particle model, considering the effect of elastic interaction energy in addition to the effect of interfacial energy. The contribution of elastic interaction energy on the total energy was found to increase with increasing size of precipitates, and the decelerated coarsening of precipitates was attributed to the decrease in the driving force for coarsening with increasing size of precipitates.     

New manifestations of the Josephson effect in helium

Using a method due to Bloch, it is shown that in thermodynamic equilibrium an annular container of mean radiusR, massM, containingN atoms of helium II of massm each will, when subjected to a torque , evince oscillations in its angular acceleration about the classical value. The frequency, , of these oscillations is given by /m=/(M+Nm). The difficulty of achieving equilibrium is pointed out.Supported in part by US Air Force Office of Scientific Research through Grant No. AFOSR 565-66.     

Measurements of the dynamic input impedance of a dc SQUID

The impedance of a circuit coupled magnetically via a mutual inductanceM _i to a dc SQUID of geometric inductanceL is modified by the dynamic input impedance of the SQUID, which can be characterized by the flux-to-current transfer functionJ J/;J is the current circulating in the SQUID loop and is the flux applied to the loop. At the same time, the SQUID is modified by the presence of the input circuit: in the lumped circuit approximation, one expects its inductance to be reduced toL ^r=(1– _e ² )L, where _e is an effective coupling coefficient. Calculations of J using an analog simulator are described and presented in the form of a dynamic inductance and a dynamic resistance versus bias currentI and . Experimental measurements of and were made on a planar, thin-film SQUID tightly coupled to a spiral input coil that was connected in series with a capacitorC _i to form a resonant circuit. Thus,J was determined from the change in the resonant freqency and quality factor of this circuit as a function ofI and . At low bias currents (low Josephson frequencies) the measured values of were in reasonable agreement with values simulated for the reduced SQUID, while at higher bias currents (higher Josephson frequencies) the measured values were in better agreement with values simulated for the unscreened SQUID. Similar conclusions were reached in the comparison of the experimental and simulated values of the flux-to-voltage transfer functionV . The reduction in the screening at the higher Josephson frequencies is believed to result from the parasitic capacitanceC _p between the SQUID and the input coil. In contrast to the behavior of the input inductance, the change in the input resistance R _i could not be explained in terms of the dynamic impedance of the SQUID reflected into the input circuit. Instead, R _i was dominated by capacitive feedback between the output of the SQUID and the input circuit viaC _p . The experimental values of R _i were satisfactorily explained by a simplified model that predicts R _i –M _iV ^r (C _p /C _i ).     

The Infrared Hall Effect in YBCO: Temperature and Frequency Dependence of Hall Scattering

We measure the Hall angle, _H , in YBCO films in the far- and mid-infrared to determine the temperature and frequency dependence of the Hall scattering. Using novel modulation techniques we measure both the Faraday rotation and ellipticity induced by these films in high magnetic fields to deduce the complex conductivity tensor. We observe a strong temperature dependence of the mid-infrared Hall conductivity in sharp contrast to the weak dependence of the longitudinal conductivity. By fitting the frequency dependent normal state Hall angle to a Lorentzian _H () = _H /( _H – i) we find the Hall frequency, _H , is nearly independent of temperature. The Hall scattering rate, _H , is consistent with _H T ² up to 200 K and is remarkably independent of IR frequency suggesting non-Fermi liquid behavior.     

Asymptotic behavior of the vector potential and the order parameter for an isolated vortex

Eilenberger's formulation of the theory of inhomogeneous superconductors is used to study an isolated vortex in a type-II superconductor. Exact integral expressions for the vector potential and the order parameter are obtained and used to determine the asymptotic behavior of these quantities. Far from the axis of the vortex, the vector potential approaches its BCS value in an approximately exponential fashion, the decay constant being equal to the quantity obtained by Eilenberger and Büttner in the local case, and equal to {2[(k _BT)²+ _BCS ² ]^1/2/v_F+(1/v _F)}^–1 in the case where nonlocal effects dominate. The order parameter also approaches its BCS value approximately exponentially, the decay constant being equal to the quantity of Eilenberger and Büttner when <2, and equal to 1/2 when >2.Supported in part by the National Research Council of Canada.Sole affiliation is now the University of Toronto.     

Intensity of critical opalescence of helium-4

We present measurements of the critical opalescence of helium-4. The results are analyzed by the Einstein and Ornstein-Zernike theory and the power laws. We obtain ==1.17±0.02, ==0.62±0.1,/=4.5±0.3,P _c =1706.008 mm Hg, andT _c =5,189.863 mK (T ₅₈ ). The critical behavior of helium-4 is almost the same as that of classical fluids and the influence of the quantum nature of helium-4 is not as evident as has been claimed.     

Spin hydrodynamic equations with external disturbances and suitable Green's functions for superfluid3He-B. New onsager relations

The spin hydrodynamic equations for superfluid³He-B have been obtained for the case of external, time-dependent fields. On the basis of a microscopic approach, expressions are found for additional terms in equations containing these fields. Considering the linear response of the system to the switching on of external fields, formulas are found for suitable Green's functions (magnetization-magnetization, rotation-rotation, magnetization-rotation, rotation-magnetization). The rotation-rotation Green's function has the 1/q ² singularity characteristic of superfluid systems. Connections between Green's functions lead to relations among kinetic coefficients v, ₁, and ₂. It is also shown that there is a conserved quantityQ ^(B) = div v _s ^(B) that describes sources or magnetic type charges (monopoles) of the superfluid velocity v _s ^(B) . Comparison with the phenomenological approach suggests thatQ ^(B) is proportional to a pseudoscalar giving the projection of the spin density onto the vector describing the axis of rotation.     

Precipitation phenomena in the Mg-31 at% Li-1 at% Al alloy

Precipitation phenomena produced in the -phase (b c c) of the Mg-31 at% Li-1 at%Al alloy subjected to different heat treatments have been studied by sensitive single-crystal X-ray diffraction techniques. The variation of the hardness values of specimens quenched and then aged was also examined. It was confirmed that AlLi is a stable phase at room temperature for the examined Al content; AlLi precipitation is only produced for very slow cooling rates from the -field. Phase reactions for specimens quenched and then aged can be summarized as follows: ++ after ageing at room temperature; + ++ AlLi after ageing at 473 K. A considerable increase of the hardness, which attains its maximum value after about 30 h ageing at room temperature, was observed. Neither the -phase nor the AlLi-phase precipitation can account for the observed hardening process. The presence of the -metastable phase when the hardness reaches its maximum value is verified.     

Recovery of a creep-deformed Type 316 stainless steel

The recovery of the dislocation structures produced in a Type 316 steel during creep has been examined by annealing over a range of temperatures and times, both in the presence and in the absence of stress. The influence of dislocation recovery on subsequent reloading behaviour has also been examined.Initial dislocation recovery occurs rapidly but the rate of recovery subsequently decreases as precipitate effects become more important. Dislocation recovery in the early, rapid stage appears to be controlled by vacancy diffusion between the dislocation links. The application of stress during recovery leads to an enhancement of the recovery rate in agreement with the network coarsening model whilst the incremental strains observed on reloading after recovery correlate well with the changes in dislocation structure produced during the recovery periods.List of symbols and appropriate values l dislocation link length - D _s self diffusion coefficient - b Burgers vector (2.5×10^–1 m) - C _j equilibrium jog concentration - dislocation link tension - k Boltzman's constant (1.38×10^–23 J atom^–1 K^–1) - T absolute temperature - t recovery time - M mobility term - Z frictional term associated with particles - _d dislocation density determined from micrographs - N _d number of dislocation intersections on test line - p length of test line - S foil thickness - ¯l mean dislocation link length - _c mean intragranular particle (carbide) spacing - r ₀ mean intragranular particle radius at timet=0 - r _t mean intragranular particle radius at timet - D solute diffusion coefficient - B solubility of M₂₃C₆ in austenite - particle-matrix interface energy - atomic volume (10^–29m³) - change in dislocation density during recovery period - incremental strain associated with reloading after recovery period - K constant - dislocation density - ₀ dislocation density at timet=0 - _t dislocation density at timet - ₀ friction stress associated with particles - constant (1) - shear modulus - angle between dislocation segments as dislocation breaks through a particle - A 1 cos (/2) - E constant - creep rate - F Taylor factor - L mean slip distance of dislocations - rate of dislocation recovery - stress - _y yield stress - J strength coefficient - _p plastic strain