Rheological properties of aqueous silicon nitride suspensions

The effect of surface modification of Si₃N₄ particle on the colloidal behavior and the rheological properties of aqueous Si₃N₄ suspensions under steady and oscillatory conditions are investigated in detail. Due to the decrease of the oxidizing level, the isoelectric point (IEP) of the modified particle shifts to basic region gently. Attempts have been made to apply rheological models to the suspensions with various solid volume fraction (). For the as-received suspensions, the Sisco model provides the best fit in the range of 0.30 while the Casson model in 0.35 0.45. The shear behavior of modified suspensions fits to Sisco model in the range of 0.40 and Casson model in 0.45 0.54. The rheological behavior of modified suspensions is improved efficiently. The critical strain decreases and the linear viscoelastic regime narrows continuously with increasing solid concentration. For the modified suspensions, the linear viscoelastic regime broadens and the corresponding elastic modulus decreases sharply. With increasing solid concentration, the characteristic frequency shifts toward lower frequencies and the suspension transforms from more viscous to more elastic.     

Computation of particle settling speed and orientation distribution in suspensions of prolate spheroids

A numerical technique for the dynamical simulation of three-dimensional rigid particles in a Newtonian fluid is presented. The key idea is to satisfy the no-slip boundary condition on the particle surface by a localized force-density distribution in an otherwise force-free suspending fluid. The technique is used to model the sedimentation of prolate spheroids of aspect ratio b/a=5 at Reynolds number 03. For a periodic lattice of single spheroids, the ideas of Hasimoto are extended to obtain an estimate for the finite-size correction to the sedimentation velocity. For a system of several spheroids in periodic arrangement, a maximum of the settling speed is found at the effective volume fraction (b/a)²04, where is the solid-volume fraction. The occurence of a maximum of the settling speed is partially explained by the competition of two effects: (i) a change in the orientation distribution of the prolate spheroids whose major axes shift from a mostly horizontal orientation (corresponding to small sedimentation speeds) at small to a more uniform orientation at larger , and (ii) a monotonic decrease of the the settling speed with increasing solid-volume fraction similar to that predicted by the Richardson–Zaki law (1–)⁵⁵ for suspensions of spheres.     

Environmental crazing in a glassy polymer: the role of solvent absorption

According to a recent theory of Andrews and Bevan, the work of solvent craze formation, ₀ is governed by the cavitation properties of a solvated zone of polymer at the craze tip. In particular, the shear yield stress of this zone and its temperature dependence dictate the variation of ₀ with temperature. In order to investigate this matter further, samples of poly-methylmethacrylate were swollen to equilibrium in a variety of alcohols at different temperatures, and the equilibrium polymer fraction ₂ determined as a function of temperature and solvent. The variation of yield stress with ₂, solvent and temperature was also investigated, and the glass transition temperatures determined as functions of ₂ and solvent.The temperature at which the equilibrium swelling was just sufficient to depress the polymerT _g to a co-incident value was found to correspond closely to the characteristic temperature, identified by Andrews and Bevan, at which the temperature dependence of ₀ changes abruptly. This is shown to be in complete accord with the cavitation theory referred to.     

Determination of the local angular radiation coefficients in certain two-body systems

A method is shown and formulas are derived by which local angular radiation coefficients can be determined in certain two-body systems where the configuration is arbitrary but one of the bodies is either a cylinder or a rectangular plate.Notation _int radiation vector of body 1 - _E ^int intrinsic radiation intensity of body 1 - _x, _y, _z components of the geometrical radiation vector along rectangular coordinates - r₀=x²+z² shortest distance from point M(x, y, z) to linear radiator - ₀ , ₀ ^' angles subtending the two segments of the linear radiator from point M(x, y, z) on area element 2 of irradiated surface - l length of the cylinders - x, y, z space coordinates of point M Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 22, No. 6, pp. 1080–1088, June, 1972.     

Second-order wave force on a large cylinder

Summary A new technique has been developed for estimating the wave loadings on large circular cylinders. The theory, mainly due to Lighthill, has been applied to the case of large cylinders. Comparison with the previously reported experimental results shows favourable agreement for the range of parameters indicated in the graphs.Notations The following symbols are used in this paper a Wave amplitude - b Radius of the cylinder - D Diameter of the cylinder - F _l Linear force - F _d Dynamic force - F _q Quadratic force - F _w Water line force - g Acceleration due to gravity - h Depth of water - H=2a Total wave height - k Wave number,k=2/L - L Wave length - n Outward normal to body surface - n _x Direction cosine between the normaln and the given force - S Body surface - t Time - T Wave period - x, y, z Cartesian coordinates - r, ,z Cylindrical coordinates - W Vertical velocity of fluid - Density of fluid - Wave frequency, =2/T - Total velocity potential - _r , _z Partial derivatives with respect tor andz, respectively - ⁽¹⁾, _l Linear theory velocity potential - ⁽²⁾, _q Second-order velocity potential - Water surface elevation or wave height - _i Linear theory wave height - _q Quadratic theory wave height With 3 Figures     

Short-range and long-range forces on a common basis in quantum crystals

A theory is developed which allows the determination of the ground-state energy and the phonons of quantum crystals on an equal footing in the collective picture. The central quantity required to dress the lines of the diagrams of the phonons as well as those of the kinetic and potential energy is the phonon self-energyM(). It is approximated in a systematic way, giving the force constants:M()M. This theory is in contrast to those using theT-matrix theory. We show that use of theT-matrix as an effective interaction in phonon calculations leads to an inconsistency.     

Disappearance of Bose-Glass Behavior in Transport Properties of YBa2Cu3O y Films with Columnar Defects

The glass transitions of the vortex system in Au-ion irradiated YBa₂Cu₃O _y films have been studied by the measurements of transport properties as a function of magnetic field B and angle of B to the direction of columnar defects. At =0°, we find an anomalous upturn behavior of the glass transition line B _g(T) at BB /3, where B is the matching field. In B>B /3, the dependence of glass transition temperature T _g reveals cusplike behavior with a peak at =0°, which is consistent with the Bose glass theory. In B<B /3, on the other hand, T _g is almost independent of , suggesting the system undergoes the vortex glass transition induced by the inherent point-like defects.     

Vanadium sesquioxide-polymer composites: the study of electrical conductivity

The electrical conductivity of V₂O₃-polymer composites were studied by examining the dependence of resistivity (conductivity) on the volume fraction of V₂O₃. The experimental data (_m versus ) were fitted (using a computer program) to the GEM equation with satisfactory accuracy. The critical volume fraction and other parameters evaluated by fitting (t, _h and _c) and calculated after fitting L and m , L _f and m _f were analysed by taking into account the geometry, orientation and arrangement of the two components. The physical meanings of L, m and t are further illustrated on the basis of their definitions.     

Collective oscillations at long wavelengths in liquid4He

The recent successful calculation of the lower collective branch of the excitation spectrum in liquid ⁴ He by Sunakawaet al. contains a phenomenological parameter (k) whose relation to microscopic theory is obscure. To clarify matters, an exact identity is presented for the absorptive part of the density-density correlation function and is employed to show that Pines' zero-sound concept of the phonon in liquid ⁴ He is accurate in the limit of infinitely long wavelengths. Since the zero-sound theory can be made to produce an explicit relation between (k) and the two-particle potential in the liquid, the foundation has been laid for a microscopic expression for the excitation spectrum in the range of very low wave numbers, where the classic Feynman theory of the phonon is known to be accurate. A numerical calculation of (k) using this expression results in a theoretical excitation spectrum which is in excellent agreement with neutron scattering measurements in the regionk0.4 Å ^–1 .     

Interfacial spring model for ultrasonic interactions with imperfect interfaces: Theory of oblique incidence and application to diffusion-bonded butt joints

The quasi-static distributed spring model is used to derive the ultrasonic reflectivity of an imperfectly-bonded interface as a function of frequency and angle of incidence. The results are then incorporated in a model for the corner reflection from a diffusion-bonded joint between two abutting plates, the corner being defined by the bond plane and the common lower surface plane of the plates. An immersion-inspection geometry is assumed, and seven categories of corner reflections are identified and examined in detail. These fall into two classes: those having parallel incident and exiting rays in water (=), and those having nonparallel water rays ( ). The = categories are suitable for single probe (pulse-echo) inspections of the joint. Based on the amplitude of the outgoing corner-reflected signal, two = geometries appear promising. These employ, respectively, a corner reflection involving only longitudinal waves with the interface illuminated at near-grazing incidence (LLL), and a corner reflection involving only transverse waves with the interface illuminated at near 45° incidence (TTT). In addition, two practical geometries are indicated; these both involve mode conversion upon reflection from the interface, with the incident or outgoing longitudinal wave traveling nearly parallel to the interface. Model predictions for LLL and TTT reflections are compared to measurements on diffusion-bonded Inconel specimens, and techniques for applying the model results to more complicated bond geometries are discussed.     

Comparison of energy and phase relaxation in metallic wires

We have determined the phase coherence time, , frommagnetoresistance measurements of long, narrow wires ofAu, Ag, and Cu, over the temperature range40 mK-6 K. In the Cu and Au wires, saturates at low temperature. In the Ag wire, continues to increase down to the lowesttemperatures measured; moreover, its temperature dependencebelow about 1 K is consistent with theoreticalpredictions of Altshuler, Aronov and Khmelnitskii published in1982. These results cast doubt on recent assertions thatsaturation of at low temperature is a universalphenomenon in metal wires. We compare these results with thoseof recent experiments on energy relaxation in similar metallicwires. The results of the two experiments are stronglycorrelated, suggesting that a single (unknown) mechanism isthe cause of the enhanced phase and energy relaxation observedin some samples.     

Effect of Normal-State Pseudogap on Physical Quantities in Hubbard Model for Underdoped High-T c Cuprates

We develop the strong-coupling theory of coexisting charge-density-wave (CDW) and superconductivityd-wave gaps within the framework of the FLEX (fluctuation exchange) approximation for the two-dimensional Hubbard model. For nested sections of the Fermi surface these equations reduce to the previous FLEX equations for superconductivity where the squared energy gap _s ² in the denominator of the Green's function is replaced by ( _s ² + _c ² ) (here _s is the superconductivity and _c the CDW gap). We solve these equations by taking for _c a phenomenologicald-wave gap. The resulting neutron scattering intensity, spin-lattice relaxation rate 1/T₁ , Knight shift, resistivity, and photoemission intensity are in qualitative agreement with the data on underdoped high-T_c cuprates. TheT_c for superconductivity decreases and the crossover temperature T_* for 1/T₁Tincreases with increasing gap amplitude of _c which is in qualitative agreement with the phase diagram for underdoped cuprates.     

Effect of wall conductances on hydromagnetic flow and heat transfer in a rotating channel

Summary Wall conductance effects on the hydromagnetic flow and heat transfer between two parallel plates in a rotating frame of reference has been studied when the liquid is permeated by a transverse magnetic field. An exact solution of the governing equations has been obtained. It is found that the velocity, current density and the temperature depend only on the sum of the wall conductances ₁ + ₂ = but magnetic field depends on the individual values of ₁ and ₂, where ₁ and ₂ are respectively the wall conductance ratios of the upper and lower walls.

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Einfluß der Wandleitfähigkeit auf die hydromagnetische Strömung und den Wärmeübergang in einem rotierenden Kanal

Zusammenfassung In der Arbeit wird der Einfluß der Leitfähigkeit der Wände auf die MHD-Strömung sowie auf den Wärmeübergang untersucht für den Fall, daß sich das zähe Medium zwischen zwei rotierenden Platten befindet und ein Magnetfeld parallel zur Rotationsachse angelegt wird. Es wird eine exakte Lösung des Problems gegeben. Es zeigt sich, daß die Geschwindigkeit, die Stromdichte und die Temperatur nur von der Summe der Leitfähigkeiten der Wände + ₂ = abhängen, dagegen hängt die magnetische Feldstärke von den individuellen Werten ₁ und ₂ ab, wobei ₁ und ₂ die Leitfähigkeiten der oberen bzw. unteren Wand bezeichnen.

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With 5 Figures     

Kondo Impurity in a Mesoscopic Ring: Charge Persistent Current

We study the influence of a magnetic impurity or ultrasmallquantum dot on the charge persistent current of a mesoscopicring. The system consists of electrons in a one-dimensionalring threaded by spin-dependent Aharonov–Bohm/Casher fluxes,coupled via an antiferromagnetic exchange interaction to alocalized electron. By passing to a basis of electron stateswith definite parities, the problem is mapped onto a Kondomodel for the even-parity channel plus free electrons in theodd-parity channel. The twisted boundary conditionsrepresenting the fluxes couple states of opposite parityunless the twist angles satisfy =f,where f are integers, with spin index=, . For these special values of, the model is solved exactly by a Bethe ansatz.Special cases are investigated in detail. In particular weshow that the charge stiffness in the case= is insensitive to the presenceof the magnetic impurity/quantum dot.     

Vibrational properties of wood along the grain

The dynamic Young's modulus (E_L) and loss tangent (tan _L ) along the grain, dynamic shear modulus (G_L) and loss tangent (tan _S) in the vertical section, and density () of a hundred spruce wood specimens used for the soundboards of musical instruments were determined. The relative acoustic conversion efficiency ( ) and a ratio reflecting the anisotropy of wood (, (E_L/G_L)(tan _S/tan _L)) were defined in order to evaluate the acoustic quality of wood along the grain. There was a positive correlation between and , and the variation in was larger than that in . It seemed logical to evaluate the acoustic quality of spruce wood by a measure of . By using a cell wall model, those acoustic factors were expressed with the physical properties of the cell wall constituents. This model predicted that the essential requirement for an excellent soundboard is smaller fibril angle of the cell wall, which yields higher and higher . On the other hand, the effects of chemical treatments on the and of wood were clarified experimentally and analyzed theoretically. It was suggested that the and of wood cannot be improved at the same time by chemical treatment.     

A new iterative technique of the finite element method for the analysis of the steady state incompressible viscous flow based on the transformation of variables

In this paper the convergence acceleration for solving steady-state incompressible flows, by using iterative solvers, is explored. The variable transformation: u = u – , p = –r, where u and are the rotational velocity and the velocity potential, respectively, is applied to the finite element discretized equations so as to get diagonal-dominant equations. The effectivity of the present techniques is demonstrated on the 2D lid-driven flow and the 3D flow in a disk-cylinder system.     

Rubber toughening of plastics

Creep measurements were made on a series of six ABS blends containing 0 to 20 vol% of 80m glass beads. At small strains, the beads raised the modulus of the ABS. However, debonding of the polymer from the glass resulted in a rapid drop in modulus with increasing strain and bead content, and at strains above 1.0% the order of stiffnesses was reversed. Debonding resulted in an increase in creep rate with, as measured by the time to reach 1% volume strain. Plots of In ^–1 against applied stress were linear, in accordance with the Eyring equation, and provided data for comparing stress concentration factors. The relationship between and fitted approximately to the Ishai Cohen effective area model. It is concluded that debonded glass beads accelerate multiple crazing by increasing average stresses in the ABS matrix, and in that respect resemble rubber particles. However, unlike rubber particles, debonded beads drastically reduce notched Charpy impact strength.     

Shear viscosity of liquid4He and3He-4He mixtures,especially near the superfluid transition

High-resolution measurements of are reported for liquid⁴He and³He-⁴He mixtures at saturated vapor pressures between 1.2 and 4.2 K with particular emphasis on the superfluid transition. Here is the mass density, the shear viscosity, and in the superfluid phase both and are the contributions from the normal component of the fluid ( _n and _n ). The experiments were performed with a torsional oscillator operating at 151 Hz. The mole fraction X of³He in the mixtures ranged from 0.03 to 0.65. New data for the total density and data for _n by various authors led to the calculation of . For⁴He, the results for are compared with published ones, both in the normal and superfluid phases, and also with predictions in the normal phase both over a broad range and close to T. The behavior of and of in mixtures if presented. The sloped/dT near T and its change at the superfluid transition are found to decrease with increasing³He concentration. Measurements at one temperature of versus pressure indicate a decreasing dependence of on molar volume asX(³He) increases. Comparison of at T, the minimum of _n in the superfluid phase and the temperature of this minimum is made with previous measurements. Thermal conductivity measurements in the mixtures, carried out simultaneously with those of , revealed no difference in the recorded superfluid transition, contrary to earlier work. In the appendices, we present data from new measurements of the total density for the same mixtures used in viscosity experiments. Furthermore, we discuss the data for _n determined for⁴He and for³He-⁴He mixtures, and which are used in the analysis of the data.     

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.     

Negative self-inductance in superconducting thin wires and weak links

One of the most promising implications of the phenomenological Ginzburg—Landau (GL) theory of superconductivity is the possible existence of current-carrying metastable states with a negative effective self-inductance. Microscopically this phenomenon can be explained as a result of the depairing mechanism which, when the center-of-mass velocityv _s of the Cooper pairs is sufficiently large, can be so strong that a further increase ofv _s will lead to a decrease of the total current. Using a one-dimensional formulation of the GL theory we investigate the thermodynamic stability of these states for different external constraints and obtain the result that a negative self-inductance can only be stable if the length of the system in the direction of the current is smaller than a critical value comparable to the GL coherence length /. It is an experimental fact that states of negative self-inductance are realized in Josephson junctions and other types of superconducting weak links because the dc supercurrent can be a decreasing function of the phase variable . The thermodynamic stability theory can therefore explain why weak links have to be short, and it also provides us with a unifying point of view by treating the phase and the current as a pair of thermodynamically conjugate variables for arbitrary one-dimensional systems. An important point is the operational phase definition as a thermodynamic parameter that can be controlled by the experimentalist. This requirement is essential for the general validity of the ac Josephson equation and it implies that must depend on the magnetic self-inductance of the system. By applying the GL theory to weak links we can delimit the validity of the usual dc Josephson equationI sin and see that deviations from this functional form are most likely to be found in thin-film bridges of the Anderson-Dayem (AD) type. When the currentI is the controlled variable the conjugate phase variable will fluctuate and the magnitude of these fluctuations depends strongly on the functional formI(). The phase fluctuations for constantI lead to a reduction of the critical current which will be absent when is the controlled variable. The observed microwave enhancement of the critical current in AD bridges, the so-called Dayem effect, can be explained as a result of a switch from current control to phase control, and the fluctuation formulae explain why the effect is negligible in structures exhibiting the classical Josephson sine law for the current-phase relation.