Magnetic properties of highly dilutedPdFex andPtFex-alloys. Part II. Susceptibility at micro- and milli-kelvin temperatures

We have measured the 16 Hz susceptibility of the giant magnetic moments induced by Fe impurities in highly dilutedPdFe_x andPtFe_x samples with 2.5 ppm x 75 ppm in a wide temperature range, 30 K T 300 mK, and at static magnetic fields 0,01 mT B 25 mT. We find spin glass freezing at Tf(X)/X0,19mK/ppm Fe forPdFe_x and the larger value 0.26 mK/ppm Fe forPtFe_x. This is the first observation of spin glass freezing inPtFe_x. In the low-temperature range T 0.5T_f(x), the susceptibilities follow — ₀ T with small zero-temperature ₀ values forPdFe_X and vanishing ₀ values forPtFe_x. In the paramagnetic high-temperature range, we find (T — )^it-1 at T 10 mK independent of x forPdFe_x, and at T 2Tf(x) dependent of x forPtFe_x with vanishing values for both systems. The data compare well to the predictions of the Thouless-Anderson-Palmer TAP approach of the Sherrington-Kirkpatrick SK model for spin glasses.     

The interdependence between the incidence angles associated with quasi-stable intersections during ion erosion

A general discussion, which is valid for any angular dependence of sputtering yieldS=S(), concerning the interdependence between the incidence angles _e and ₀, associated with quasi-stable intersections during ion erosion, is given. The object was firstly to establish the location of _e roots as a function of ₀ and secondly to identify the stationary points and general trend for the complex dependence _e= _e( ₀). The results obtained are applied to a quasi-stability analysis of some specific surface features during ion erosion. Various possible types of quasi-stable intersections (surface-surface, plane-surface, plane-plane) are reviewed from the point of view of their evolution caused by ion bombardment.     

Optimal design of a thick-walled pipeline cross-section against creep rupture

Summary Cylinder under combined loadings (pressure, bending, axial force) is subject to non-linear creep described by Norton-Odqvist creep law. In view of bending a circularly-symmetric cross-section is no longer optimal in this case. Hence we optimize the shape of the cross-section; minimal area being the design objective under the constraint of creep rupture. Kachanov-Sdobyrev hypothesis of brittle creep rupture is applied. The solution is based on the perturbation method (expansions into double series of small parameters), adjusted to optimization problems.Notation A cross-sectional area - C, , creep rupture constants - K, n, _C , _C creep constants - F dimensionless creep modulus - M bending moment - N axial force - a(),b() internal and external radii of the cross-section - j creep modulus - p internal pressure - r, ,z cylindrical coordinates - s _r ,s ,s _z ,t _r dimensionless stresses - t _R time to rupture - stress function - , () dimensionless internal and external radii - _e effective strain rate - _kl strain rates - rate of curvature - rate of elongation of the central axis - dimensionless radius - _e effective stress - _I maximal principal stress - _S Sdobyrev's reduced stress - _r , , _z , _r components of the stress tensor - measure of material continuity - measure of deterioration With 7 Figures     

Effect of crack shape,inclination angle,and friction coefficient in crack surface contact problems

In rolling/sliding contact fatigue, it is known that the crack propagates at a characteristic angle =15–30 deg to the surface. To analyze the mechanism, however, the body force method has been widely used assuming 3D crack models for =45–90. In this study, therefore, the unknown body force densities are newly approximated by using fundamental density functions and polynomials. Then, a semi-elliptical crack model is analyzed for =15–90 under compressive residual stresses and Hertzian contact loads. The stress intensity factors K _II, K _III are calculated with varying the crack shape b/a, inclination crack angle , and crack face friction coefficient . The calculations show that the present method is useful for the analysis for =15–30 deg with high accuracy. It is seen that the K _II-values when b/a0 are larger than the ones when b/a=1 by 0–24% for both under compressive residual stress and Hertzian contact load. Regarding the maximum K _II values under Hertzian contact load, the results of =15 deg are smaller than the ones of =45 deg by 23–34%. Regarding the amplitude of (K _{II max}–K _{II min}), the results of =15 deg are smaller than the ones of =45 deg by 4–24%. With increasing the value of friction coefficient for crack faces the value of K _II decreases significantly. When the crack is short and the inclination angle is small, the value of friction coefficient f for Hertzian contact load largely affect the K _II value.     

In-Plane Fourfold Symmetry of the Upper Critical Field Observed in La(Sr)214 Single Crystals

In order to establish the existence of in-plane anisotropy of the upper critical field H _c2 (), the out-of-plane resistivity _c measurements were performed on La(Sr)214 single crystals with rectangular and cylindrical shape under rotating magnetic field applied within the ab-plane. Although observed _c shows non-sinusoidal twofold symmetry, clear fourfold symmetry was obtained after subtracting twofold sinusoidal component in _c which is due to the unavoidable misalignment of the magnetic field with respect to ab-plane. H _c2 () is estimated from the extracted fourfold component of _c with the flux flow theory. Angular dependence of H _c2 () was well fitted by cos(4). Since the fourfold component of H _c2 () was largest at = n/2, which corresponds to the a-axis direction, the present results strongly suggest the type symmetry in La(Sr)214. In addition, the difference in fourfold component of H _c2 at = n/2 and n/2+/4 was found to increase with decreasing temperature.     

On the nucleation ofθ′ and T1 on Al3Zr precipitates in Al-Li-Cu-Zr alloys

Two quaternary Al-Li-Cu-Zr alloys have been investigated using electron microscopy. Ageing at 190° C resulted in the nucleation of precipitates on the Al₃Zr/matrix interface in addition to heterogeneous nucleation on matrix dislocations. In the majority of cases, the broad, coherent face of the plans ms in contact with the Al₃Zr precipitates. Similar evidence showed that nucleation of T₁ precipitates occurred on the Al₃Zr, but to a lesser extent than. Solid-solid nucleation theory has been used to account for the Al₃Zr acting as a nucleation substrate.     

Angular Dependence of the Activation Energy in YBCO/PBCO Multilayers

The activation energy in several (YBCO) _m /(PBCO) _n superconducting multilayers was deduced from resistivity measurements in magnetic fields up to 16 T, as a function of the angle between the magnetic field and the ab planes. The activation energy U ₀ (B,) scales with a reduced field B _red =B(sin ² +cos ² / ² ) ^1/2 , with an angle dependent anisotropy parameter . A crossover from U ₀ log B _red , at low B _red , to U ₀ (B _red ) at high B _red , is also observed. The implications of these results on vortex dynamics and on the coupling between the superconducting layers will be discussed.     

Debye-Waller parameters of lead sulphide powders

The Debye-Waller parameters, the effective valueB _eff, the dynamic componentB _d and the static componentB _s, of lead sulphide powders with different particle sizes were determined for the bulk and for each constituent atom, lead and sulphur. The effective values for each atom,B _eff (Pb) andB _eff (S), were linearly related to that for the bulk,B _eff (PbS). The effective value and the dynamic component for the bulk,B _eff (PbS) andB _d(PbS), were almost equal to those for lead,B _eff(Pb) andB _d (Pb), suggesting a small contribution of sulphur atoms to Debye-Waller parameters for the bulk. The mean square displacement of the bulk, u ²_Pbs, was expressed by the atomic mass averaged mean square displacements ;u ²;_Pb and u ²_s in PbS crystal. The Debye temperature _D calculated fromB _d (PbS) increased with the decrease inB _s(PbS), and was extrapolated to the _D-value of the single crystal atB _s(PbS) = 0. A similar relation between _D andB _s were found for lead atom, where _D (Pb) was a little bit smaller than _D (PbS).     

Grain growth in the two-phase Al-Cu alloys

Grain and phase growth in the two-phase Al-Cu alloys containing 6, 11, 1 7, 24 and 33 wt % Cu were investigated by annealing at 535 °C for 0.5–100 h. The grain and phase sizes of the phase are seen to be larger than that of the phase. The size of phase decreases whereas the size of phase increases with increasing copper content in the alloy. As such, the phase- and grain-size distributions are broader than the phase- and grain-size distributions, but the size range depends on annealing time and alloy composition. The grain sizes of the ,d , and ,d , phases can be related to the volume fraction of the phase,f , according to the equationd = 0.497d /f .     

A numerical solution of the blade-to-blade flow in turbomachines by the application of a transformation on the S1 stream surface

Summary The solution of the blade-to-blade (quasi-3-dimensional) steady, inviscid flow in turbomachines is considered as a quantitative prediction of the flow and as a good approximation of the real three-dimensional flow. The well known governing differential equation is of elliptic type and its numerical solution is a rather difficult problem (taking also into account the complex form of the S1 stream surface). By the procedure proposed, the S1 stream surface in the (m, ) coordinate system is transformed into a rectangular (x,, y, space, by the application of the following transformation:x=m/L, (–₁)/(₂–₁), where₁ and ₂ are the angular positions of the lines limiting the S1 surface, andL the length of the meridional projection of the blade.By the introduction of this transformation, extra terms are added to the differential equation, but now the definition of the grid is easier. From the transformed differential equation, a system of algebraic equations is obtained applying the finite volume method. The system of algebraic equations is solved by a relaxation method with periodic boundary conditions. The grid applied in the (x, y) coordinate system is not of uniform density in order to define better the geometry of the blades near the leading and trailing edges. Finally the results from the application of the procedure on a centrifugal, mixed flow pump are presented; i.e. relative velocity and static pressure distribution along the blade surfaces.With 11 Figures     

Development of solidification microstructures in a fibre reinforced alloy

The solidification behaviour of a fibre reinforced Al-6 wt% Cu alloy, containing 30 vol% of 3 m diameter, semi-continuous, aligned alumina fibres has been studied. Results are presented to show the influence of fibres on the microstructural development of and microsegregation in the matrix during freezing. The effect of total solidification time, _t, on solidification behaviour was examined for 1<_t<520 S. By using interrupted solidification experiments microstructural development was studied in detail. It was found that -Al begins to grow within interfibre regions, and grows towards the Al₂O₃ fibres, avoiding them where possible. Consequently fibres are located in the last regions to solidify. When _t>10 s the final microstructure is non-dendritic, and CuAl₂ is located predominantly at the fibre-matrix interface. When _t 1 s it was observed that the final microstructure is dendritic with a periodic segregation pattern, and the CuAl₂ is more dispersed. The matrix composition becomes more uniform, and the minimum matrix composition rises as _t increases. The growth and microsegregation are analysed and discussed using simple semi-analytical models. The implications are that fibres significantly influence solidification behaviour if _f/_s<1, where _f is the average interfibre spacing and _s the secondary dendrite arm spacing which would develop in the unreinforced alloy.     

Vibrations of axially compressed laminated orthotropic cylindrical shells,including transverse shear deformation

Summary The free vibrations, buckling and the effect of initial prestress upon the frequency spectrum of orthotropic composite cylindrical shells are examined in the context of a theory that includes transverse shear deformation. Results obtained are compared with the predictions of refined Love-type theory and simplified Donnell-type theory that do not consider shear deformation.The calculated examples indicate that transverse shear deformation can be significant not only for short composite shells but even for longer shells possessing low shear moduli.

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Schwingungen axial gedrückter, laminierter, orthotroper zylindrischer Schalen einschließlich Querschubverformung

Zusammenfassung Es werden die freien Schwingungen, das Beulen und der Einfluß einer Anfangsvorspannung auf das Frequenzspektrum orthotroper, kompositer, zylindrischer Schalen im Rahmen einer Theorie, die die Querschubverformung mitberücksichtigt, untersucht. Die erhaltenen Resultate werden mit den Vorhersagen der verbesserten Loveschen Theorie und der vereinfachten Donnellschen Theorie, welche keine Querschubverformung in Betrach ziehen, verglichen.Die durchgerechneten Beispiele zeigen, daß die Querschubverformung nicht nur für kurze, komposite Schalen sondern sogar für längere Schalen mit niederem Schubmodul Bedeutung gewinnen kann.

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Nomenclature a radius of reference surface of cylindrical shell - A _i amplitudes of displacements - A _ij elastic area - B _ij elastic statical moment - D _ij elastic moment of inertia - E _ij elastic stiffness modulus - h shell thickness - k ₄₄,k ₅₅ shear correction factors - l length of cylindrical shell - L _ij functional operator - m number of half-waves in axial direction - M ,M ,M axial, circumferential and twisting moments, respectively - n number of circumferential waves - N ⁰ axial compression force - N ,N ,N axial, circumferential and shear forces, respectively - Q ,Q transverse shear forces - R ₀,R ₁,R ₂ inertia terms - t time - T matrix defined in Eq. (25) - u, v, w displacements in axial, circumferential and radial directions, respectively - U _i time-independent displacement or rotation - nondimensional axial wave parameter - , , axial, circumferential and shear strains, respectively - radial coordinate, taken positive inward - polar angle - , , curvature changes - circular frequency - nondimensional axial coordinate - density - , , , , stress components - , rotations of normal to undeformed midsurface With 6 Figures     

Flux motion in anisotropic type-II superconductors nearH c 2 with arbitrary vortex orientation

Flux motion in anisotropic type-II superconductors near H_{c 2} is studied in the framework of the time-dependent Ginzburg-Landau (TDGL) theory for the case that the average flux densityB is oriented in an arbitrary direction relative to the principal axes of the sample. The linearized TDGL equation for a uniformly translating order parameter is solved and expressions for all elements of the flux-flow resistivity tensor _ij (including the off-diagonal Hall elements) are obtained. The diagonal elements _ii show the angular scaling property that _ii(B) = _ii(B/H_{c 2}(, ø)), whereas the Hall elements _ij (i j) have additional angular dependences that are not contained in H_c2. For the case that the normal state Hall elements _ij ⁽ⁿ⁾ B _k with i j k, the ratios _ij/ _ij ⁽ⁿ⁾ are functions of B/H_c2 (, ) only.     

Directional dependence of c-plane slip in single crystals of mercuric iodide

An experimental study of plastic deformation in thin single crystals of mercuric iodide (Hgl₂) subjected to (0 0 1) [1 0 0] and (0 0 1) [1 1 0] shear loadings has established a directional dependence to the phenomenon of (0 0 1) orc-plane slip in Hgl₂. The average stressess _c for the onset of yielding were 12.6 psi (86.9 kPa) for (0 0 1) [1 0 0] shear and 16.5 psi (113.8 kPa) for (0 0 1) [1 1 0] shear; the average values of the deformation parameters ₀, interpreted as a bulk yield stress, were 24.7 psi (170.3 kPa) for (0 0 1) [1 0 0] shear and 37.7 psi (259.9 kPa) for (0 0 1) [1 1 0] shear. These values are in agreement with the theoretical relationss _c()=s _c(0)/cos ands ₀()=s ₀(0)/cos, where is the smallest angle between 1 0 0 crystallographic axis and the direction of shear stress applied in the (0 0 1) plane.     

Hot electrons in metals at low temperatures

Hot electrons in metals at helium temperatures under steady conditions can be produced by passing an electric current of moderate density ( 10⁶ A/cm²) through thin, narrow (~1 m wide) metallic films in good thermal contact with bulk single-crystal dielectric substrates. This paper is concerned with the theory of hot electrons in normal metals at low temperatures (when _D, where is the average electron energy and _D is the Debye temperature). The theory is formulated in terms of realistic electron and phonon dispersion laws, taking into account the experimental possibility of heat removal from the sample. In the case in which the temperature approximation of Kagnov, Lifshitz, and Tanatarov is not satisfied when elastic scattering of electrons is dominant in a steady state electric field, the kinetic equation is derived for the energy-dependent, hot electron distribution function, which determines the associated nonlinear responses. The solution of this equation is discussed for a simple model. It is shown that the experimental information on the electron-phonon interaction in a metal can be obtained in terms of the well-known spectral functions S() ² F() and g() _tr ² F(). This is illustrated by experiments determining the nonlinear field dependence of the resistance, by tunnel experiments, and by critical current hysteresis measurements (for superconducting metals). Theoretical estimates which support the observability of the effects under discussion are presented.     

A boundary layer theory for the end problem of a circular cylinder

Summary This paper discusses the nature of an approximate solution for the hollow circular cylinder whose fixed ends are given a uniform relative axial displacement and whose cylindrical surfaces are free from traction. We shall take the solution of this problem to be given by a super-position of the following two problems: problem I considers a finite length cylinder whose ends are given a relative axial displacement, but are no longer fixed; problem II removes the radial displacement at the end of the cylinder obtained in problem I.Nomenclature a mid-surface radius of cylinder - c half-height of cylinder - E, in-plane elastic moduli - E_t, _t, G_t transverse elastic moduli - _z, , _r axial, circumferential, and normal strain - _rz transverse shear strain - h cylinder thickness - _z, , _r axial, circumferential, and normal stress - _rz transverse shear stress - z, r axial and radial coordinates - u_z, u_r axial and normal displacements     

Comparative study of solubilities of hydrogen,nitrogen and carbon in α-iron

Solubility data of hydrogen, nitrogen and carbon in -iron are analysed on the basis of statistical thermodynamics. Present analysis appears to yield realistic values for the enthalpy term of the solutions of these interstitial elements into -Fe, while the entropy terms remain ambiguous. During the course of this analysis a parameter _x, which refers to the solubility limit of the specific interstitial element X (X=hydrogen, nitrogen or carbon), is also estimated; _H< _N< _C. This order of _X values appears to be in accord with the observation that, under normal conditions, the solubility of carbon is the highest and that of hydrogen the lowest in -Fe, while the atomic size increases with the order hydrogen相似文献   

A calorimetric study of S′ and θ′ precipitation in Al2O3 particle-reinforced AA2618

Differential scanning calorimetry (DSC) was used to study the kinetics of S and precipitation in AA2618 and its composite containing 15 vol % Al₂O₃ particles . The unreinforced alloy and the composite were fabricated by a proprietary casting method, followed by extrusion. The DSC studies were carried out on as-quenched samples of the test materials. The precipitation of the S and phases in both materials was found to be kinetically controlled and obey the modified Avrami-Johnson-Mehl equation. The growth mechanisms for S and formation in AA2618 seemed unaffected by the addition of Al₂O₃ particles. The growth parameters obtained for the precipitation of these phases in the matrix alloy and the composite were not significantly different.     

Breakup of an anomolously viscous liquid film in a centrifugal force field

An equation is obtained for the breakup radius with consideration of tipping moments and Laplacian pressure forces acting on the liquid ridge at the critical point.Notation K, n rhenological constants - density - surface tension - r current cup radius - R maximum cup radius - r_c critical radius for film breakup - ¯r=¯r=r/R dimensionless current radius - ¯r_c=r_c/R dimensionless critical radius - ₀, _c actual and critical film thicknesses - current thickness - R_r ridge radius - h₀ ridge height - h current ridge height - ₀ limiting wetting angle - current angle of tangent to ridge surface - angle between axis of rotation and tangent to cup surface - angular velocity of rotation - q volume liquid flow rate - v₁ and v meridional and tangential velocities - =4vv _lm/r,=4v_m/r dimensionless velocities - M moments of surface and centrifugal forces - M_v moment from velocity head - p_r pressure within ridge - P_vm pressure from velocity head - p_m, p_pm pressures from centrifugal force components tangent and normal to cup surface - deviation range of breakup radius from calculated value - ¯r_max, ¯r_min limiting deviations of breakup radius - _c angle of tangent to curve _c/°₀=f(¯r) at critical point - t random oscillation of ratio _c/_c Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 39, No. 1, pp. 51–56, July, 1980.     

A scaled equation of state for real fluids in the critical region

A scaled equation of state is proposed for real fluids in the critical region which incorporates asymmetry with respect to the critical isochore. In the range of reduced densities 0.65(/ _c)1.4 and for reduced temperatures (T/T _c)1.2, the equation represents P-V-T data for steam within the experimental accuracy.