Transport in the low-temperature limit of a Landau Fermi liquid

The Boltzmann equation for Landau quasiparticles is solved for T 0 by a specialization of a method discussed by Sykes and Brooker. The quasiparticle distribution function is expanded in Legendre polynomials, assuming a boundary condition which imposes axial symmetry, and even-order terms are assumed to relax together with relaxation time _e , odd-order terms with relaxation time _o . By letting wavelength , with finite, one obtains a first-sound solution, and by lettingT 0, and then , one obtains a zero-sound solution. When these solutions are used to calculate the pressure, it is found that the first-sound solution is consistent with hydrodynamics, exhibiting viscosity = _s , while the zero-sound velocityc ₁=[^–1(B₁+4/3_s)]^1/2, so that phenomenologically zero-sound propagates like a longitudinal elastic wave in a glass. A higher zero-sound mode is also predicted, but is heavily damped. The heat flux is calculated and found to obey Vernotte's equation, which contains an intertial term, added to Fourier's law, that becomes significant asT 0.     

The athermal α → ω transformation in Zr-2 at% Nb alloy

The athermal transformation in Zr-2 at.% Nb alloy has been investigated by transmission electron microscopy. Analysis of the selected-area diffraction pattern has shown that the orientation relationships between the omega and the parent-phase in quenched Zr-2 at.% Nb alloy are the same as have been previously observed for the reaction in pure zirconium. Thus it was deduced that the direct transition has taken place in the alloy during cooling. The-originated -particles were visualized using the dark-field technique. The formation of the athermal omega in the-region of-stabilized Zr-Nb alloy is discussed in terms of the relative positions of the free energy equilibrium curvesT ₀ ,T ₀ ,T ₀ and the correspondingM _s ,M _s andT _s start curves. It is concluded that the omega phase can occur over a much wider range of alloy compositions than is usually recognized on the basis of transformation data.     

The preparation of alumina fibre by sol-gel processing

Attempts have been made to prepare alumina fibre from the colloidal sol and polymerized alkoxides. The aluminium chloride or aluminium nitrate systems were found to be potential methods for producing continuous alumina fibre: the aluminium nitrate system had a better sintering behaviour than the aluminium chloride system. The aluminium isopropoxide system, however, was unsuitable for preparing alumina fibre but was suitable for the preparation of monoliths, membranes, powders, and multicomponent ceramics. The thermal changes of these precursors were studied by transmission electron microscopy, Fourier-transform infrared spectroscopy and X-ray diffraction. The results demonstrated the different routes of phase transformation as the temperature increases. The aluminium chloride system exhibits two routes for phase transformation: (a) boehmite -Al₂O₃, and (b) gibbsite -Al₂O₃.     

A new formulation of Gor'kov's theory of clean type II superconductors

From Gor'kov's theory a functional for the free energy of the flux line lattice is derived which depends explicitly on the potentials andA. It may be interpreted as an extension of the Ginzburg-Landau functional to arbitrary temperatures. For periodic || ² andH=rotA, the functional is a rapidly converging series, of which often the main term (corresponding to the Brandt-Pesch-Tewordt approximation) plus a correction term depending on the lattice structure suffices. From the cutoff series all previously known results for the special casesT T _c ,B H _c2 ,orB 0 are reproduced by minimization with respect to || ² andH.     

Microstructure and properties of supersaturated ZA27 alloy during natural ageing

The decomposition of the supersaturated solid solution of ZA27 alloy at room temperature has been investigated by X-ray diffraction, TEM and mechanical properties testing. Based on the results obtained, both continuous precipitation and cellular reaction occur during the decomposition process. The continuous precipitation follows the sequence: ₁ + spherical GP zones ₂ + elliptical GP zones ₃ + R + . The cellular reaction can be written: + + . The properties of the alloy depend on the microstructure. After 1 month of ageing, a series of changes of microstructure have taken place. The properties of the alloy are: _b=500 MPa, =13%,H _v=148.     

Amplifier based on a field-effect triode with negative current feedback

Conclusions A field-effect triode amplifier with series negative current feedback allows a voltage gain of the order of 200–300 to be obtained for a load resistance R_s1 M. The coefficient K_u begins to decrease noticeably only for a feedback resistance above 500 .The current gain reaches (8–10)·10³. Increasing the resistances R_s and R_L to hundreds of ohms has practically no effect on K_i. For a further increase of R_s and R_L the coefficient K_i decreases.The power gain reaches its maximum value (of the order of 10⁴ or more) for R_s100 and R_L=10–100 k. An increase in R_s leads to a reduction of K_pmax and to a shift of the extremum of the function K_p=f(R_L) into the range of higher values of R_L.A large input resistance of the amplifier (tens of megohms and higher) is obtained when R_s increases to 10–100 M. The maximum input resistance is obtained for R_L and R_s and may exceed values of from hundreds of megohms to several gigaohms. The minimum input resistance is hundreds of kilohms for R_L and R_s0.The minimum input resistance (5–10 k or less) is ensured for R_g and R_L0. An increase of the output resistance to hundreds of megohms or higher occurs for R_g and R_s.Translated from Izmeritel'naya Tekhnika, No. 9, pp. 67–70, September, 1971.     

Kinetics of phase transitions and dielectric relaxations in poly-bis(trifluorethoxy- phosphazene) (PBFP)

The kinetics of the high temperature (isotropic mesophase) and low temperature (mesophase crystalline) transition of PBFP at T_m and T(1), respectively, and its local dynamics were studied by differential scanning calorimetry (DSC) at variable heating and cooling rate and by dielectric relaxation spectroscopy (DRS). While on heating no substantial effect of the rate on both transition temperatures was found, T(1) and T_m showed a strong dependence on the cooling rate. The high temperature transition revealed thermally activated behaviour with an activation energy of E_a = 400 kJ/mol, whereas the transition at T(1) showed the typical signature of supercooling. This finding is consistent with the picture that the isotropic/mesophase transition at T_m is controlled by long-range, strongly hindered, chain diffusion that leads to the long-range orientational mesomorphic order. In contrast, the low temperature transition, the enthalpy of which is far larger and the temperature of which depending linearly on the cooling rate, indicates a kinetical control by nucleation as characteristic for a (2D 3D) crystallization process.Complementary information about the molecular dynamics in the various phases was obtained by DRS that revealed three relaxation processes, which were assigned to the dynamic glass transition (), local motions of CF₃—groups in the glassy state ( -process) and cooperative fluctuations of side-groups both in the mesophase and crystalline state ( -process). Interestingly, both the Arrhenius-type - and -relaxation are characterised by a non-zero activation entropy, which indicates the cooperative nature of the underlying molecular dynamics.     

Transport properties and determination of the basic parameters of superconductors with overlapping bands

The thermoconductivity and ultrasonic attenuation in non-single-band super-conductors are investigated. It is proved that the ratio ₂/₁ atT T _c is equal to that atT=0. It is also shown that ultrasonic measurements and data on the phonon thermoconductivity can be used very effectively for definition of the basic parameters of the superconductors with overlapping bands.     

The martensitic transformation in cold-worked Fe-Mn alloys studied by Mössbauer spectroscopy

The effect of cold-working on 16, 23 and 30 at% Mn iron-manganese alloys (C<0.05 at%) has been examined using Mössbauer spectroscopy and X-ray diffractometry. The induced martensitic transformation , depends on the composition and on the initial structure. It is found that the transformation in presence of the phase occurs only at high deformations.     

Development of Spectral Selective Multilayer Film for a Variable Emittance Device and Its Radiation Properties Measurements

A smart radiation device (SRD) that is a variable emittance radiator has been developed as a thermal control material for spacecraft. The SRD has the unique feature of large variation of the total hemispherical emittance _H near room temperature. The _H of the SRD changes depending on its temperature. However, there is a drawback of a large solar absorptance _S. It is too large to use as a thermal control material for spacecraft. In order to reduce the large _S, spectral selective multilayer film was developed. This multilayer film reflects solar radiation and transmits far-infrared radiation to maintain the variation in the _H of the SRD. This paper presents thermal radiative properties of the SRD with spectral selective multilayer film. The multilayer film was designed by using a genetic algorithm (GA). The designed multilayer film was evaporated on the surface of the SRD by the electron beam evaporation method. The experimental results of _S and _H of the SRD with the multilayer film agreed well with calculated results.     

Mutual friction and vortex motion near the superfluid transition

The mutual friction parametersB and B for a moving vortex are calculated near the superfluid transition. They are proportional to the kinetic coefficient associated with the order parameter and, asT , diverge as (T – T)^–1/3, in agreement with experiment. The nonlinear couplings between the order parameter and the entropym, both the reversible one and the one in the free energy, are found to be crucial in the mutual friction near the point. These couplings were neglected in a previous paper by the author. First, the reversible coupling in the dynamic equations makes the chemical potential deviation long-ranged and causes the dissipation to take place only near the vortex core. Second,B can diverge asT T only in the presence of the coupling of the formm||² in the free energy. Thus theE model of Halperin et al., where the latter coupling is absent, cannot explain the critical anomaly ofB. The helical mode of a single vertex line is also investigated and its dispersion relation is found to be quite different from that at low temperatures. This mode has the same time scale as that of the second-sound mode when the wave vectors are of the order of the inverse correlation length, thus obeying the usual dynamic scaling law. The time correlation functions of the displacement fluctuations of a vortex line are also obtained. The force acting on a moving vortex is calculated and is found to be equal to the classical Magnus force.     

On the flow of a stratified fluid over a barrier

Summary The flow of a stratified fluid over a barrier is considered. The initial-value problem is solved, and it is shown that there is no disturbance far upstream of the barrier whent . The stationary solution which is obtained by lettingt, is given in a simple closed form for a barrier of an arbitrary shape.     

Phase transformation ß→α in sintered SiC involving feathers formation

The phase transformation has been studied in SiC sintered with addition of boron and carbon by optical microscopy, and scanning and transmission electron microscopy. In the late stage of densification and during subsequent anneals, a feathers develop at the expense of the grains. They are constituted of two adjacent grains whose crystalline structures are related to one another by four symmetry operations. From the orientation relationship it is shown that the feathers can be describe as penetration twins.     

Density correlation function in superfluid helium nearT λ

The previously calculated hydrodynamic form of the density correlation function of liquid helium is written out explicitly forT nearT . This function, which is proportional to the intensity of light scattered from the fluid, has a finite value at =0, which grows asTT from below. In evaluating the precise form of this contribution in terms of transport coefficients, it is important to keep terms of order (C _p /C _v )–1.     

Low-temperature properties of the heavy-fermion compound CeRu2Si2 at the metamagnetic transition

Magnetization measurements performed below 1 K on a single-crystalline sample of the heavy fermion compound CeRu₂Si₂ are reported. The field variation of the linear term of the specific heat derived from these data (via a Maxwell relation) exhibits a large peak at the metamagnetic-like transition at B* (=7.7 atT 0). Thermal-expansion measurements, show a drastic drop of the temperature where a Fermi liquid behavior is reached whenB B*. Similar experiments performed on a single-crystalline Ce_0.95La_0.05Ru₂Si₂ sample show a broadening of all the anomalies atB* and a reduction of their intensities. These results strongly suggest that pure CeRu₂Si₂ approaches a magnetic instability atB* forT 0.     

The crystal growth and thermoelectric properties of chromium disilicide

Single crystals of chromium disilicide about 8 mm in diameter and 35 mm long were grown using the floating zone technique. Measurements of electrical resistivity , Hall coefficient R and thermoelectric power were carried out in the temperature range from 85 to 1100 K. The values of and showed the anisotropy over the temperature range studied. The ratios parallel and perpendicular to the c-axis were / =1.9 and /=1.7 respectively, at room temperature. It was found to be a degenerate semiconductor having the hole concentration of 6.3×10²⁰ cm^–3 below 600 K. The effective masses of holes parallel and perpendicular to the c-axis determined from the thermoelectric power and the hole concentration near room temperature were estimated to be five and three times as large as a free electron mass, respectively. The calculation on the values of and was made using those effective masses. These values showed good agreement with the observed values in the temperature range from 150 to 1100 K.     

Stress-induced phase transformations in a hot-deformed two-phase (α2+γ) TiAl alloy

Stress-induced 2, 2 and 9R phase transformations in a hot-deformed Ti–45 at% Al–10 at% Nb alloy have been investigated using high-resolution transmission electron microscopy. The 2 phase transformation is an interface-related process. The interfacial superdislocations emitted from the misoriented semicoherent 2– interface react with each other or with the moving dislocations in the phase, resulting in the formation of the 2 phase. The nucleation of the 2 phase transformation takes place either at the 2– interfaces or at the stacking faults on the basal plane of 2 phase, and the growth of plate is accomplished by the moving of a/61 0 1 0 Shockley partials on alternate basal plane (0 0 0 1)2. The 9R structure was usually found to form at incoherent twin or pseudotwin boundaries. During deformation the interfacial Shockley partial dislocations of these incoherent twin and pseudotwin boundaries may glide on (1 1 1) planes into the matrix, resulting in the formation of 9R structure. The interfaces (including 2– and – interfaces) as well as the crystallographic orientation relationship between the as-received or stress-induced 2, and 9R phase have been analysed. The mechanisms for the stress-induced 2, 2 and 9R phase transformations were also discussed. © 1998 Chapman & Hall     

Equation of state of3He near its liquid-vapor critical point

We report high-resolution measurements of the pressure coefficient (P/T) for³He in both the one-phase and two-phase regions close to the critical point. These include data on 40 isochores over the intervals–0.1t+0.1 and–0.2+0.2, wheret=(T–T _c )/T _c and =(– _c )/ _c . We have determined the discontinuity (P/T) of (P/T) between the one-phase and the two-phase regions along the coexistence curve as a function of . The asymptotic behavior of (1/) (P/T) versus near the critical point gives a power law with an exponent (+–1)^–1=1.39±0.02 for0.010.2 or–1×10 ^–2t–10 ^–6 , from which we deduce =1.14±0.01, using =0.361 determined from the shape of the coexistence curve. An analysis of the discontinuity (P/T) with a correction-to-scaling term gives =1.17±0.02. The quoted errors are fromstatistics alone. Furthermore, we combine our data with heat capacity results by Brown and Meyer to calculate (/T) _c as a function oft. In the two-phase region the slope (²/T ²)_c is different from that in the one-phase region. These findings are discussed in the light of the predictions from simple scaling and more refined theories and model calculations. For the isochores 0 we form a scaling plot to test whether the data follow simple scaling, which assumes antisymmetry of – ( _c ,t) as a function of on both sides of the critical isochore. We find that indeed this plot shows that the assumption of simple scaling holds reasonably well for our data over the ranget0.1. A fit of our data to the linear model approximation is obtained for0.10 andt0.02, giving a value of =1.16±0.02. Beyond this range, deviations between the fit and the data are greater than the experimental scatter. Finally we discuss the (P/T) data analysis for ⁴ He by Kierstead. A power law plot of (1/) P/T) versus belowT _c leads to =1.13±0.10. An analysis with a correction-to-scaling term gives =1.06±0.02. In contrast to ³ He, the slopes (²/T ²)_c above and belowT _c are only marginally different.Work supported by a grant from the National Science Foundation.     

Effect of thermal cycling on as-quenched and aged nickel-rich Ni-Ti alloy

The effect of Ni₄Ti₃ precipitates on the structure and transformation sequences in Ni-49%Ti alloy has been investigated using internal friction, electrical resistivity and electron microscopy studies. It has been confirmed that in the alloy without precipitates the transformation occurs following the sequence B2 R M on cooling and M B2 on heating with easily distinguished peaks on the internal friction curves and typical behaviour of the electrical resistivity, while the presence of the precipitates brings about complicated internal friction curves indicating either the appearance of two types of martensite or the transformation sequence: B2 ® B2 + R B2 + M M.     

Reaction mechanism for the formation of intermetallic compounds from layered Sm/Fe powder obtained by mechanical milling

Solid-state reactions in layered Sm/Fe powder particles with an overall composition of Sm₁₂Fe₈₈, obtained by ball milling, have been investigated by X-ray diffraction. During annealing at 500C, one reaction, Sm+2FeSmFe₂ was observed in the time-range studied. However, during annealing at 800C, five reactions were observed: Sm+2FeSmFe₂, Sm +3FeSmFe₃, 2Sm+17FeSm₂Fe₁₇, 2SmFe₂+13FeSm₂Fe₁₇, and 2SmFe₃ +11FeSm₂Fe₁₇. It is proposed that such reactions occur by a nucleation and growth process. Reactions of samarium with iron can be governed by nucleation; Sm/Fe interfaces possessing a higher free energy per unit area can play an important role in the nucleation. The observed results are discussed.