Simulation of the Process of Water Freezing in a Round Pipe

The problem of freezing of pure water in a round pipe is treated with due regard for convection under asymmetric thermal boundary conditions in the absence of motion along the pipe. The problem is solved numerically using the control volume approach, SIMPLER algorithm, and the enthalpy method. Results are obtained for three Grashof (Gr) and six Biot (Bi) numbers: Gr = 1.55 × 10⁶, Bi = 0.305 (0 < ), Bi = 0.044 ( < 2); Gr = 1.24 × 10⁷, Bi = 0.610 (0 < ), Bi = 0.087 ( < 2); Gr = 9.89 × 10⁷, Bi = 1.220 (0 < ), Bi = 0.174 ( < 2). The correctness of calculation of the problem disregarding free-convection flows is analyzed.     

Magnetic field dependence of zero-sound attenuation close to the pair-breaking edge in3He-B due toJ=1−,J z =±1 collective modes

Our previous theory yielded for the Zeeman splitting of the imaginaryJ=1 collective mode in³He-B the result =2+0.25J _z ( is the effective Larmor frequency). In this paper we take into account the downward shift of the pair-breaking edge from 2 to 2₂– (₂ and ₁ are the longitudinal and transverse gap parameters). This leads to a complex Landé factor: the frequencies of theJ _z =±1 components become =2+0.39J _z , and the linewidths of these resonances become finite: =0.18. The coupling amplitudes of theJ _z =±1 components to density are found to be proportional to gap distortion, (₁–₂/(/)². Our results for the ultrasonic attenuation due to theJ _z =±1,J=1 modes are capable of explaining the field dependence of the attenuation close to the pair-breaking edge as observed by Dobbs, Saunders, et al. The observed peak is caused by theJ _z =–1 component: its height increases due to gap distortion as the field is increased, and the peak shifts downward in temperature and its width increases with the field due to the complex Landé factor. TheJ _z =+1 component gives rise to a corresponding dip relative to the continuum attenuation.     

Nonlinear asymptotic theory of hypersonic flow past a circular cone

Summary The hypersonic small-disturbance theory is reexamined in this study. A systematic and rigorous approach is proposed to obtain the nonlinear asymptotic equation from the Taylor-Maccoll equation for hypersonic flow past a circular cone. Using this approach, consideration is made of a general asymptotic expansion of the unified supersonic-hypersonic similarity parameter together with the stretched coordinate. Moreover, the successive approximate solutions of the nonlinear hypersonic smalldisturbance equation are solved by iteration. Both of these approximations provide a closed-form solution, which is suitable for the analysis of various related flow problems. Besides the velocity components, the shock location and other thermodynamic properties are presented. Comparisons are also made of the zeroth-order with first-order approximations for shock location and pressure coefficient on the cone surface, respectively. The latter (including the nonlinear effects) demonstrates better correlation with exact solution than the zeroth-order approximation. This approach offers further insight into the fundamental features of hypersonic small-disturbance theory.Notation a speed of sound - H unified supersonic-hypersonic similarity parameter, - K hypersonic similarity parameter, M - M freestream Mach number - P pressure - T temperature - S entropy - u, v radial, polar velocities - V freestream velocity - shock angle - cone angle - density - density ratio, /() - ratio of specific heats - polar angle - stretched polar angle, / - (), (), () gage functions     

Investigations of the copper isotope effect in oxygen-deficient YBa2Cu3O7−δ

We present data on the copper isotope effect (⁶³Cu-⁶⁵Cu), C_u =-nT_c/nm_Cu, for two isotopic pairs of oxygen-deficient YBa₂Cu₃O_7–, where varies between 0.06 and 0.52. _Cu is below 0.01 at =0.06 (fully oxygenated), it takes values between –0.14 and –0.34 in the 60 K plateau. Larger negative values of _Cu are observed away from the plateau. The dependence of _Cu is similar to that of the pressure effect dnT_c/dP.     

γ ? α2 Phase transformation in fractured high temperature stress rupture Ti-48Al-2Nb(at.%)

The ₂ phase transformation in fractured high temperature stress rupture Ti-48Al-2Nb(at.%) alloy has been studied by analytical electron microscopy. ₂ and phases were found at grain boundaries. ₂ layers that suspended in layers and interfacial ledge higher than 2d ₍₁₁₁₎ at /₂ interfaces were observed in the lamellar grains. These facts indicated that ₂ phase transformation and dynamic recrystallization have occurred during high temperature stress rupture deformation. It can be concluded that deformation induced ₂ phase transformation and dynamic recrystallization resulted in the presence of particles at grain boundaries. A structural and compositional transition area between deformation-induced ₂(or ) and its adjacently original (or ₂) phases was found by HREM and EDS and is suggested as a way to transform between and ₂ phase during high temperature stress rupture deformation. The transition area was formed by slide of partial dislocations on close-packed planes and diffusion of atoms.     

Singularity parametersε andκ for interface cracks in transversely isotropic piezoelectric bimaterials

Two parameters, and (Suo et al., 1992), are of key importance in fracture mechanics of piezoelectric material interfaces. In this paper, it is shown, for any transversely isotropic piezoelectric (TIP) bimaterial, that one of the two parameters and always vanishes but the other one remains non-zero. Physically, it means that the non-oscillating crack-tip generalized stress field singularity exists for some TIP bimaterials (with vanishing ). Consequently, TIP bimaterials can be classified into two classes: one with vanishing performed crack tip generalized stress field oscillating singularity and the other one with vanishing is independent from the oscillating singularity. Some numerical results for and are given too.     

Mapping co-word structures: A comparison of multidimensional scaling and leximappe

The LEXIMAPPE method and Multidimensional Scaling (MDS) are discussed as methods to visualize (map) characteristics of structures of word-occurrence (co-word) relations. Utilization of MDS is proposed as an alternative mapping method able to circumvent problematic features of LEXIMAPPE maps of the total co-word structure. A comparison of both methods on the same real-life co-word matrix demonstrates topological advantages of an extended MDS-mapping.     

Chebyshev polynomial approximation of the roots of the transcendental equation Μ tan Μ=b

A polynomial approximation of the roots of the equation tan=b are tabulated, valid uniformly on the interval b [0, ].Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 20, No. 2, pp. 347–348, February, 1971.     

Experimental study and calculation of heat and mass transfer in moist bodies

Results of an experimental study of heat and mass transfer involved in convective drying of a model material (quartz sand-bentonite mixture) are reported. The main characteristics of the material are determined, namely, the curve of size distribution of capillaries, the curve of equilibrium states, etc. A method and experimental setups for determination of the thermophysical characteristics of the material and their dependences on moisture and temperature are discussed. A nonlinear system of differential equations of heat and mass transfer is solved by a numerical method. The numerical solution is compared to the experimentally obtained dependences u(x, ) and t(x, ).B. Kidri-Vina Institute of Heat and Power Engineering; Heat Engineering Equipment and Installing Enterprise Tser—aak; Belgrade University, Yugoslavia. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 67, Nos. 5–6, pp. 455–460, November–December, 1994.     

Microstructure-property studies in friction-stir welded, Thixomolded magnesium alloy AM60

Thixomolded magnesium alloy AM60 plates joined by friction-stir welding were observed to be as strong or stronger than the unwelded base material. The thixotropic microstructures of the as-molded plates consisted of either 3% or 18% primary solid fraction of -Mg globules (45 m average size) in a eutectic mixture consisting of -Mg grains (10 m) surrounded by Mg₁₇Al₁₂ intermetallic grains in the -Mg grain boundaries (having an average size of 1–2 m). This complex, composite microstructure became a homogeneous (Mg + 6% Al)), recrystallized, equiaxed grain (10–15 m) microstructure in the weld zone.     

Theory of RF SQUIDs Operating in the Presence of Large Thermal Fluctuations

A comprehensive analytical theory is presented for non-hysteretic RF SQUIDs operating in the adiabatic mode in the presence of large thermal fluctuations. When 1 ( = 2LI_c/₀ is the hysteresis parameter, L is the SQUID inductance, I_c is the critical current of the Josephson junction, and ₀ is the flux quantum) the theory is applicable also for RF SQUIDs operating in the non-adiabatic mode. In contrast to previous theories in which the noise is treated perturbatively and which therefore are applicable only if the product 1 ( = 2k_BT/ ₀ I_c is the noise parameter, k_B is the Boltzmann constant, and T is the absolute temperature)—the case of small thermal fluctuations—the present theory is valid for around unity or higher. In the limit 0 the theory reproduces the results of small thermal fluctuations theories. It has been found that in the presence of large thermal fluctuations the screening current in the SQUID inductance is suppressed by a factor that increases with increasing . Taking into account this new basic fact, all SQUID characteristics (output signal, transfer function, noise spectral density and energy sensitivity) have been recalculated and a good agreement with experimental data has been obtained. It has been also found that RF SQUIDs can be operated with substantially higher values of the inductance and of the noise parameter than DC SQUIDs. These two aspects, which are of particular importance at liquid nitrogen temperature, make high T_c RF SQUIDs very attractive.     

Antiplane strain problem of diamond inclusion

In this paper, the singular stress fields created by an antiplane deformation at an inclusion corner are studied. It is shown that these singular stress fields can be separated into two independent types: a symmetric type with the stress singularity of 1/ ^1–1 and a skew-symmetric type with the stress singularity of 1/ ^1–2. These two types of the singular stress field can not occur simultaneously at the corner. If G ₂<G ₁, there exists only the singularity of the skew-symmetric type, and if G ₂>G ₁, there exists only the singularity of the symmetric type. A general expression of stress fields in the vicinity of the corner is presented. In the expression the singular stress fields for the symmetric type and the skew-symmetric type are defined in terms of the constants K _III, ₁ and K _III, ₂, respectively. K _III, ₂ and K _III, ₂ have to be determined from the complete boundary conditions of the given problem. For the problem of an infinite plate containing a diamond inclusion and subjected to a uniform longitudinal shear stress at infinity, the values of K _III, ₁ and K _III, ₂ are obtained by body force method. In the body force method, the investigated stresses are simulated by the superposition of the fundamental stress fields due to point forces. In order to obtain accurate solutions, the basic density functions of the distributed point forces are used, so that the stress singularities at the corner tip can be simulated by the point forces.     

Retention of a metastable bcc ε-Pu solid solution: ε-Pu(Ti)

A metastable -Pu (bcc) solid solution has been retained to room temperature by rapid quenching of Pu-rich Pu-Ti alloys from the liquid state. Until now, -Pu solid solutions were limited to high temperatures and had not been successfully quenched to room temperature without transformation. The apparatus used to quench the specimens was a modified gun-type splat-cooling unit, capable of producing extremely high cooling rates of from 10⁶ to 10⁸ ° C sec^–1. -Pu(Ti) was retained in the composition region from 20 to more than 45 at.% Ti, and extrapolation of the lattice parameter/composition curve yielded a value of a ₀ = 3.53₀ Å for -Pu at 20° C. This modification differs from the -Pu modification derived by extrapolating from high temperature to 20° C by a small valence increase of 0.1. Metastable -Pu (Ti) (fcc) solid solutions were also quenched-in with alloys containing lesser amounts of Ti, and evidence was found to indicate that the was probably a product of -Pu(Ti) solid-state decomposition.     

Influence of the martensitic transformation on the deformation behaviour of an AISI 316 stainless steel at low temperatures

The deformation behaviour of an AISI 316 stainless steel under uniaxial tension was examined at 25, – 70 and – 196° C. The flow curves exhibited peculiar shapes and the work hardening rates were found to increase with strain beyond certain values of plastic strain. X-ray diffraction analyses showed that the transformation to-martensite commenced at these values of plastic strain and thereafter the volume fraction of increased steadily with strain. On the other hand, the amount of the-martensite was found to increase with plastic strain initially, reach a maximum and then decrease gradually. The contribution of the-phase to the flow stress of the alloy was found to be directly proportional to the volume fraction of. It is shown that the analysis of the flow curves provides a simple method of detecting the onset of the strain-induced martensitic transformation as well as estimating the amount of this martensite during further deformation.     

The Reissner-Sagoci problem for a non-homogeneous half-space with a penny-shaped crack

The present paper examines the elastostatic problem related to the axisymmetric rotation of a rigid circular disc bonded to a non-homogeneous half-space containing a penny-shaped crack. The shear modulus of the half-space is assumed to vary with depth according to the relation (z) = ₁(z + c), c > 0 and ₁, are constants. Using Hankel transforms, the solution of the problem is reduced to integral equations and finally to simultaneous Fredholm integral equations of the second kind. By solving numerically the simultaneous Fredholm integral equations, results are obtained which are used to estimate the stress intensity factor at the crack tip and the torque required to rotate the disc through an angle ₀.     

Formation of nanocrystalline phases in the Cu-Zn system during mechanical alloying

The evolution of various nanocrystalline phases in the Cu-Zn system during the course of mechanical alloying of elemental powder blends, manifests a similar sequence of phase formation in all the compositions. Zinc-rich phases were always first to form, which can be attributed to the diversities of diffusivities and diffusion distances in the constituents. The extent of zinc in -phase becomes significant only after turns nanocrystalline. The crystallite size of reached a minimum (18 nm) near the - phase boundary, while the and phases showed quite coarse crystallite size due to their low melting points. Alloying was sluggish during dry milling compared to wet milling, or at lower milling speed, which demonstrates the effects of oxidation during milling and lower milling energy.     

Varistor characteristics in PTCR-type (Ba,Sr)TiO3 ceramics prepared by single-step firing in air

This paper deals with donor, acceptor-codoped (Ba_0.4Sr_.6)TiO₃ ceramics with distinct varistor characteristics at room temperature, which were prepared by single-step firing in air. The materials, with the Curie point at around –90 °C, exhibited a large PTCR (positive temperature coefficient of resistivity) effect of more than seven orders of magnitude in the temperature range –90 °C (the resistivity 10³ · cm) to room temperature ( > 10¹⁰ · cm). An apparent dielectric constant of >20000 and tan < 0.05 (at 100 kHz) were observed for the present materials at room temperature, and moreover, the materials exhibited nonlinear current-voltage characteristics with the nonlinear coefficient, , in the range 7–12 and the varistor field, E_v, in the range 0.3–1.0 kV/cm. The value of in the present materials increased systematically with increasing in their PTCR temperature range. It has been found that there exists a close correlation between and the grain-boundary potential barrier height, e, obtained from the -T characteristic of the materials. An almost linear relationship was also found to exist between and log E_v for the present materials.     

Electronic Transport Properties of Speer Carbon Resistors—Experimental Results and Semi-empirical Fits

Speer carbon composition resistors, in particular the 470 and 220 1/2 W grade 1002 resistors, have been used as secondary thermometers at temperatures below 4 K for many years. Their zero field resistances have been measured between 300 K and 4 K using a dip probe. Above 10 K, the resistance behavior can be explained using a simple temperature power law, R(T) R₀/T^0.16. The resistance measurements have been extended to 0.02 K using dilution refrigerators. Between 4 K and 0.3 K, the resistances exhibited activated laws having hopping exponents y 0.5. Below 0.3 K, the 470 resistors exhibit a crossover to a weaker activated law. Crossover resistance expressions suggest that the resistances follow a Mott variable-range hopping (VRH) law below 0.05 K. The low temperature magnetoresistance (MR) data showed changes of less than ±12 % of the zero field resistance values in fields up to 10 T. Fits using the wave function shrinkage and the forward interference models gave only fair agreement with the MR data.     

Investigation of the excitonic insulator phase in bismuth-antimony alloys

Pressure-induced metal-semiconductor transitions in bismuth-antimony alloys in a strong magnetic field (up to 70 kOe) at helium temperatures have been investigated. It is found that for values of the overlap-gap |G|1 meV the alloy forms an excitonic insulator (EI) in magnetic fields above a certain threshold (30–40 kOe). It is inferred that the EI energy gap increases with the magnetic field. The maximum gap observed in fields of 70 kOe turns out to be ₀₀7.5 K. An analysis of the results shows that transitions to the EI phase are observed from both the semimetal and the semiconducting states. The critical transition temperatureT _c is related to the EI gap by the expressionT _c0.7. Arguments are advanced in support of the fact that the formation of the EI phase involves the pairing of electrons at theL point with holes at theT point.     

Solution of thermal conductivity problems with boundary condition of the third kind and arbitrary coordinate and time dependence of the biot number

An analytical solution of the thermal conductivity problem with boundary conditions of the third kind and arbitrary coordinate and time dependence of the Biot number is found in the form of a converging series of quadratures.Notation , z dimensionless coordinates - dimensionless temperature - Q dimensionless volume heat-liberation density per unit time - Fo=/² Fourier number - Bi₁(, Fo)=(, Fo) · / Biot number - thermal diffusivity coefficient - plate thickness - time - (, Fo) heat-liberation coefficient - thermal conductivity coefficient - i summation index - Jo zero order Bessel function of the first kind Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 41, No. 3, pp. 536–540, September, 1981.