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1.
The singularity in the vapor-liquid interfacial tension, (T), of helium at the transition to superfluidity is analyzed theoretically. The universal amplitude ratio R + =K+( 0 + )d–1/k B T , where K+ and K are the amplitudes of the |T–T|µ singularity in , with =1.34 3 , is known from recent work to first order in =4–d for the general n-vector model in d dimensions. Extrapolation to d=3 for n=2 indicates R + =0.05–0.08, which is shown to be consistent with the experimental data. Further analysis of the experiments establishes that the universal ratio Q=K+/K exceeds 0.35, and is consistent with the recent prediction Q0.9; this demonstrates the inadequacies of earlier theoretical treatments. The existence in the observed surface tension of an anomalous, negative contribution of unknown origin at a few millikelvin beneath T is stressed.  相似文献   

2.
The superfluid density in 4 He was determined near T from the second-sound velocity as a function of TT and pressure. The critical exponent of the superfluid density was found to depend, even slightly, on the pressure. Furthermore, the fundamental length 0 in the coherence length = 0 [1–(T/T)]–' seemed to be proportional to the mean interatomic distance. The implications of the results are also discussed.This work was partly supported by The Ito Science Foundation and by The Nishina Memorial Foundation.  相似文献   

3.
The magnetoresistance of six untwinned YBa 2 Cu 3 O 7– crystals has been measured above T c for IBc. Fluctuation theories allowing for an in-plane coherence length anisotropy ( a b ) were used in the analyses. The results suggest that the anisotropy, = b / a , is considerably lower than that expected from the resistivity ratio, i.e., . Some magnetoresistive measurements with the field in the ab-plane are also presented.  相似文献   

4.
It is known that the Lucas sequenceV n(,c)=an + bn,a, b being the roots ofx 2 – x + c=0 equals the Dickson polynomial .n–2i Lidl, Müller and Oswald recently defined a number b to be a strong Dickson pseudoprime to the parameterc (shortlysDpp(c)) if [itgn(b, c)b modn for all b. These numbers seem to be very appropriate for a fast probabilistic prime number test. In generalizing results of the above mentioned authors a criterion is derived for an odd composite number to be ansDpp(c) for fixedc. Furthermore the optimal parameterc for the prime number test is determined.  相似文献   

5.
Scattered intensities of light were measured near the gas-liquid critical point of 4 He at scattering angles of 30, 60, and 90° as functions of the reduced temperature =|T–T c |/T c along the critical isochore (T>T c ) and the coexistence curve (T>T c ). The temperature range was 3×10 –5 <<1.5×10 –2 . Critical exponents and coefficients describing divergence of the generalized susceptibility and the correlation length are obtained as (T>T c )=1.31±0.02, v(T>T c )=0.66±0.02, 0 (T>T c )=4.2±0.6 Å, (T>T c )=1.32±0.02, v(T>T c )=0.68±0.02, ± (T>T c )=2.6±0.7 Å, =0.06±0.06(T>T c ), 0.05±0.05(T>T c ), and 0(T>T c )/x± (T>T c )=3.6±0.4. It is pointed out that the quantal nature of 4 He has remarkable influence on the critical behavior of 4 He in the above-mentioned temperature region.  相似文献   

6.
We measure the diamagnetic response of YBa 2 Cu 3 O y A x (A=Cl, F, H) ceramics. We obtain low-field effective penetration depths of a few 10 m, first flux-penetration field H1 distinguishable from the volume penetration field HC1 and two characteristic temperatures Ts and Tc, Tcs, defined by the onset of the real and imaginary parts of the susceptibility, respectively. H 1 (T) goes to zero as a power law H 1 (T, x)=H 1 (0, x) (T–T/Tc) 2.7 near TC. From the values of and H 1 we infer the correlation length at T=4.2 K. A large range of values for (4.2) suggests that chemical disorder plays an essential role in the phenomenology of cuprates. We find (4.2)H 1 (4.2) –1/3 . This, and the power law (4.2)H 1 (4.2) –2/3 result from the scaling properties of a phase transition governed by disorder.  相似文献   

7.
The consequences of a vortex unbinding picture of two-dimensional superconductivity are worked out. Although there is no true finite-temperature phase transition, dirty superconducting films should display anomalous behavior below the BCS transition temperature and above an effective Kosterlitz-Thouless vortex unbinding temperature. In particular, both the conductivity and fluctuation diamagnetism behave like + 2 in this regime, where + is the correlation length calculated by Kosterlitz, + c exp (B/T – T c)1/2. We estimate c, B, and the vortex unbinding temperature, and determine the nonlinear resistivity below T c. A recent theory of vortex dynamics, together with a time-dependent Ginzburg-Landau theory, lead to a determination of the frequency-dependent conductivity.This work was supported by the National Science Foundation under Grant No. DMR 77-10210.  相似文献   

8.
Summary Based on the von Kármán-type plate theory a solution is formulated for the large deflection of an unsymmetrically laminated angle-ply rectangular plate under transverse and inplane loads. Each pair of opposite edges is assumed to be elastically restrained against rotation to the same degree. The transverse deflection and force function in governing equations are expanded into generalize double Fourier series such that all required boundary conditions are exactly satisfied. Numerical results for maximum deflection, bending moment and inplane force in the plate are graphically presented for various aspect ratios, types of transverse load, high-modulus composite materials, numbers of layers, angles of orientation and boundary conditions. Present results for simple boundary conditions are in good agreement with previous data.Notations plate stiffnesses defined in [4], [9] - a, b, h length, width and thickness of plate - a i ,b i plate constants defined in [4] - E L ,E T ,G LT ,v itLT principal elastic constants of orthotropic material - F nondimensional force function defined in Eqs. (3) - F mn ,Q mn ,W mn Fourier constants defined in Eqs. (9), (10) and (21) - H i constant given by Eq. (19) - N ,M ,M nondimensional moments defined in Eqs. (6) - N ,N ,N nondimensional inplane forces defined in Eqs. (6) - nondimensional inplane load defined in Eqs. (8) - Q nondimensional transverse load defined in Eqs. (3) - q,q o intensities of general and uniform transverse loads - R m ,S n ,X m ,Y n orthogonal functions of or defined by Eqs. (11) and (12) - r inplane load ratio defined in Eqs. (8) - x, y, z rectangular cartesian coordinates - W, w nondimensional deflection,w/h, and deflection - m , m , m constant coefficients given by Eqs. (13)–(15) - , nondimensional coordinates defined in Eqs. (3) - aspect ratio (a/b) - 1, 2 rotational edge-restraint coefficients With 6 Figures  相似文献   

9.
Using superleak condenser transducers, the velocity of second soundU 2 has been measured near the superfluid transition temperature T in3He-4He mixtures with molar concentrationsX of3He of 0.0, 0.038, 0.122, 0.297, and 0.440. We have obtained the superfluid density s/ fromU 2 on the basis of linearized two-fluid hydrodynamics. The results for s/ are consistent with those obtained from the oscillating disk method, as expected from two-fluid hydrodynamics. The value of s/ at eachX could be expressed by a single power law, s/=k, where =1-T/R, with the experimental uncertainty. It is found that the exponent is independent of concentration forX0.44 within the experimental uncertainty. This concentration independence of is in agreement with the universality concept. From the conclusion that the values of are universal forX0.44, the concentration dependence of the superfluid component s is expressed by an empirical equation s(X, )=2s(0, ). It is found that corresponds to the volume fraction of4He in the superfluid3He-4He mixture. The value of is in agreement with that obtained from the measurement of the molar volume by others.This paper is based on a thesis submitted to Tokyo University of Education in partial fulfillment of the requirements for the Ph.D. degree.  相似文献   

10.
Hydraulic resistance of rotating tubes   总被引:3,自引:0,他引:3  
Parametric relations have been obtained, based on experimental data, for the hydraulic resistance coefficient of rotating tubes, allowing for the action of mass forces on the fluid flow.Notation d tube internal diameter - F mass force referred to unit volume - F* mass force applied to a fluid particle - F excess mass force (difference between the mass forces of two characteristic points of the system) - K similarity parameter - j difference between the inertia accelerations at two points of the system - l characteristic dimension - M moment of momentum of a fluid particle - n number of revolutions of the tube in unit time - r radial coordinate, tube radius - Re Reynolds number, based on the mean mass velocity of the fluid motion - Recirc Reynolds number based on the circular velocity of fluid motion - S similarity parameter - u circular velocity of the inner surface of the tube - v volume of a fluid particle - w mean mass velocity of the fluid - v kinematic viscosity - 0 - coefficient of hydraulic resistance of a rotating tube - 0 same for a fixed tube - fluid density - angular velocity of rotation of the tube  相似文献   

11.
We present the expressions of the generalized Ginzburg-Landau (GL) theory for the free energy and the supercurrent in terms of thed vector, the magnetic fieldH, and operators containing the spatial gradient and the rotation. These expressions are then specialized to the Anderson-Brinkman-Morel (ABM) state. We consider eight single-vortex lines of cylindrical symmetry and radiusR=[2m/]–1/2: the Mermin-Ho vortex, a second analytic vortex, and six singular vortices, i.e., the orbital and radial disgyrations, the orbital and radial phase vortices, and two axial phase vortices. These eight vortex states are determined by solving the Euler-Lagrange equations whose solutions minimize the GL free energy functional. For increasing field, the core radius of the texture of the Mermin-Ho vortex tends to a limiting value, while the core radius of the texture goes to zero. The gap of the singular vortices behaves liker forr 0, where ranges between and . The energy of the radial disgyration becomes lower than that of the Mermin-Ho vortex for fieldsH6.5H*=6.5×25 G (atT=0.99T c and forR=10L*=60 µm, or=2.9 rad/sec). ForR 2 T ( T is the GL coherence length) or c2 (upper critical rotation speed), the energies of the singular vortices become lower than the energies of the analytic vortices. This is in agreement with the exact result of Schopohl for a vortex lattice at c 2. Finally, we calculate the correction of order (1 -T/T c ) to the GL gap for the axial phase vortex.  相似文献   

12.
We carried out the extensive Cu-nuclear magnetic and quadrupole resonance (NMR/NQR) experiments on the Zn(Ni)-doped ladder compound SrCu 2 O 3 (Sr123), Sr(Cu 1–x M x ) 2 O 3 (M=Zn and Ni) with x 0.02 and the Ladoped Sr123, Sr 1–x La x Cu 2 O 3 with x 0.03. A spin-correlation length s /a (a: the lattice spacing between the Cu sites along the leg) of nonmagnetic impurity-induced staggered polarization (IISP) estimated from a quasi-one-dimensional (Q1D) IISP along the two legs in the 0.1–2 % Zn-doped Sr123 was found to be independent of temperature (T) and scaled to an mean impurity distance D AV with the relation of s /a = 2.5 + 0.1D AV The s /a's are much longer in x = 0.001 ( s /a 50) and 0.005 ( s /a 12) than an instantaneous spin-correlation length 0 /a 3 – 8 in Sr123. The formula of Néel T, T N (WC-Q1D)=J exp(–D AV /(s/a)) (J = 2000 K) based on the weakly interladder-coupled (WC) Q1D model explains the experimental T N values quantitatively.  相似文献   

13.
    
We have explored the effect of 2-MeVH+ irradiation on the superconducting transport properties of thin films of YBa2Cu3O7– [T c, Jc(B=0; 77 K, 4.2 K), andR s(36 GHz;T)]. The inductively measured critical temperatureT c changed slowly and uniformly (2 K per 1016/cm2) for fluences less than 3×1016/cm2. Beginning at 3–4×1016/cm2, the superconducting transition broadened and dropped more quickly with fluence. The critical current density measured at 77 and 4.2 K changed roughly linearly with fluence. The microwaveT c (as defined by the sharp transition inR s as a function of temperature) resembled the low-frequency inductiveT c measurement at low fluences but was depressed more strongly for large fluences. The residual surface resistance (6–10 m) was not affected for fluences up to 5×1016/cm2. We have interpreted the sudden and reproducible reduction in the microwaveT c transition as a sensitive indicator of disruption in the copper-oxygen chain sublattice and compared the proton-induced change to that observed in oxygen gettering studies of bulk materials.  相似文献   

14.
A mathematical model for the transient heat flow analysis in arc-welding processes is proposed, based on a unique set of boundary conditions. The model attempts to make use of the relative advantages of analytical as well as numerical techniques in order to reduce the problem size for providing a quicker solution without sacrificing the accuracy of prediction. The variation of thermo-physical properties with temperature has been incorporated into the model to improve the thermal analysis in the weld and heat-affected zones. The model has been evaluated using a five-point explicit finite difference method for analysing the welding heat flow in thin plates of two different geometric configurations. The temperature distribution closer to the heat source, primarily in the weld zone and the heat-affected zones, are predicted by the numerical technique. The thermal characteristics beyond the heat-affected zone are amenable to standard analytical techniques. The behaviour of the boundary condition in the model has been investigated in detail.Nomenclature q Rate of heat per unit thickness (Wm–1) - d Plate thickness (m) - v Velocity of source (m s–1) - t Time (s) - T Temperature value at the desired point (K) - T 0 Initial temperature (K) - K Thermal conductivity (W m–1 K–1) - Density (kg m–3) - c p Specific heat (J kg–1 K–1) - Thermal diffusivity (m2 s–1) - n - Distance of point considered from the source (=x–vt) (m) - K 0 Modified Bessel function of second kind and zero order - r Radial distance from the source (r=(x 2+y 2)1/2) (m) - Model width (m) - a Plate width (m) - Distance from the source =(2+4 ×10–4)1/2 (m) - n   相似文献   

15.
Major superconducting state parameter of high-T c electron-doped Nd-Ce-CuO and hole-doped La-Sr-CuO systems have been estimated. The analysis is based on the electronic energy band structure (EEBS) within the local density approximation. Anisotropy of the layered structure is well reflected in the shape of open Fermi surface. Determination of the effective mass of the charge carrier from the Fermi velocity using EEBS and estimates of the anisotropic superconducting state parameters, particularly the magnetic penetration depth ( L), lead to smaller values than those observed by muon spin relaxation (SR) measurements on polycrystalline samples. The coherence length ( and ) is evaluated and appears to be higher. The temperature dependence of the Ginzburg-Landau parameter (K) and along the plane magnetic penetration depth ( L ) shows the same nature as those revealed from experiments. Furthermore, results on lower and upper critical magnetic field are also presented. The results based on EEBS studies are consistent but do not agree well with experiments. On the other hand, if the Fermi Liquid approach (FLA) parameters are used for this analysis, the results are in better agreement with those reported earlier. The implications of the above investigations are discussed.  相似文献   

16.
We have performed NMR measurements on the flare-out texture of superfluid3He-B in a cylindrical container of 5 mm diameter in axial magnetic fields of 28.4 and 56.9 mT. The transverse cw NMR spectra have been analyzed both with respect to their overall shape and the spin-wave absorption peaks close to the Larmor frequency. Our analysis of the stationary state spectra, based on texture computations, yields the longitudinal resonance frequency v L (T), the magnetic healing length H (T), and the dipolar length D (T), which we report for pressures below 29 bar. A lattice of quantized vortex lines appears in the rotating state, and two additional textural free energy terms have to be included in the analysis. One of the terms is linear in the applied magnetic field and arises from the spontaneous magnetization of the vortex cores. The second term is quadratic in magnetic field; it is generated both by the superflow field v s (r) about the vortex core and the difference in the induced magnetizations of the vortex-core and the bulk superfluids. The rotational orienting effects have been studied for rotation speeds up to 2red/sec.  相似文献   

17.
The thermal expansion behavior of three epoxy-fiberglass composite specimens was measured from 20 to 120°C (70 to 250°F) using a fused quartz push-rod dilatometer. Billets produced by vacuum-impregnating layers of two types of fiberglass cloth with an epoxy were core-drilled to produce cylindrical specimens. These were used to study expansion perpendicular and parallel to the fiberglass layers. This type of composite is used to separate the copper conductors that form a helical field coil in the Advanced Toroidal Facility, a plasma physics experiment operated by the Fusion Energy Division at Oak Ridge National Laboratory. The coil is operated in a pulsed mode and expansion data were needed to assess cracking and joint stresses due to expansion of the copper-composite system. The dilatometer is held at a preselected temperature until steady state is indicated by stable length and temperature data. Before testing the composite specimens, a reliability check of the dilatometer was performed using a copper secondary standard. This indicated thermal expansion coefficient () values within ±2% of expected values from 20 to 200°C. The percentage expansion of the composite specimen perpendicular to the fiberglass layers exceeded 0.8% at 120°C, whereas that parallel to the fiberglass layers was about 0.16%. The expansion in the perpendicular direction was linear to about 70°C, with an value of over 55×10–6 °C–1. Anomalous expansion behavior was noted above 70°C. The expansion in the direction parallel to the fiberglass layers corresponds to an value of about 15×10–6 °C–1. The lower values in the parallel direction are consistent with the restraining action of the fiberglass layers. The values decreased with the specimen density and this is consistent with literature data on composite contraction from 20 to –195°C.Nomenclature Thermal expansion coefficient, °C–1 - L L(T 2)–L(T 1), cm - T T 2T 1, °C - L 0 Length at room temperature, cm - L(T i ) Length at temperature T i , cm - T i Temperature, °C - T 0 Room temperature, °C Paper presented at the Ninth International Thermal Expansion Symposium, December 8–10, 1986, Pittsburgh, Pennsylvania, U.S.A.  相似文献   

18.
Four thermophysical properties of both solid and liquid molybdenum, namely, the density, the thermal expansion coefficient, the constant-pressure heat capacity, and the hemispherical total emissivity, are reported. These thermophysical properties were measured over a wide temperature range, including the undercooled state, using an electrostatic levitation furnace developed by the National Space Development Agency of Japan. Over the 2500 to 3000 K temperature span, the density of the liquid can be expressed as L(T)=9.10×103–0.60(TT m) (kg·m–3), with T m=2896 K, yielding a volume expansion coefficient L(T)=6.6×10–5 (K–1). Similarly, over the 2170 to 2890 K temperature range, the density of the solid can be expressed as S(T)=9.49×103–0.50(TT m), giving a volume expansion coefficient S(T)=5.3×10–5. The constant pressure heat capacity of the liquid phase could be estimated as C PL(T)=34.2+1.13×10–3(TT m) (J·mol–1·K–1) if the hemispherical total emissivity of the liquid phase remained constant at 0.21 over the temperature interval. Over the 2050 to 2890 K temperature span, the hemispherical total emissivity of the solid phase could be expressed as TS(T)=0.29+9.86×10–5(TT m). The latent heat of fusion has also been measured as 33.6 kJ·mol–1.  相似文献   

19.
Several thermophysical properties of hafnium-3 mass % zirconium, namely the density, the thermal expansion coefficient, the constant pressure heat capacity, the hemispherical total emissivity, the surface tension and the viscosity are reported. These properties were measured over wide temperature ranges, including overheated and undercooled states, using an electrostatic levitation furnace developed by the National Space Development Agency of Japan. Over the 2220 to 2875 K temperature span, the density of the liquid can be expressed as L (T)=1.20×104–0.44(TT m ) (kgm–3) with T m =2504 K, yielding a volume expansion coefficient L (T)=3.7×10–5 (K–1). Similarly, over the 1950 to 2500 K span, the density of the high temperature and undercooled solid -phase can be fitted as S (T)=1.22×104–0.41(TT m ), giving a volume expansion coefficient S (T)=3.4×10–5. The constant pressure heat capacity of the liquid phase can be estimated as C PL (T)=33.47+7.92×10–4(TT m ) (Jmol–1K–1) if the hemispherical total emissivity of the liquid phase remains constant at 0.25 over the 2250 K to 2650 K temperature interval. Over the 1850 to 2500 K temperature span, the hemispherical total emissivity of the solid -phase can be represented as TS (T)=0.32+4.79×10–5(TT m ). The latent heat of fusion has also been measured as 15.1 kJmol–1. In addition, the surface tension can be expressed as (T)=1.614×103–0.100(TT m ) (mNm–1) and the viscosity as h(T)=0.495 exp [48.65×103/(RT)] (mPas) over the 2220 to 2675 K temperature range.  相似文献   

20.
This paper presents a new completely hierarchical three dimensional curved shell finite element formulation for linear static analysis of laminated composite plates and shells. The element displacement approximation can be of arbitrary polynomial orders p , p and p in the , , and directions thereby permitting strains of at least (p –1), (p –1) and (p –1) order. The element approximation functions as well as the nodal variables are hierarchical. The element formulation ensures C 0 continuity. The lamina properties are incorporated by numerically integrating the element stiffness matrix for each lamina. The formulation has no restriction on either the number of laminas or the layup pattern of the laminas. The geometry of the laminated shell element is described by the coordinates of the nodes lying on the middle surface of the element and the lamina thicknesses at each node. The element formulation is equally effective for very thin as well as very thick laminated plates and curved shells. The results obtained from the present formulation are compared with those available in the literature as well as available analytical solutions.  相似文献   

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