Isochoric Heat Capacity of Heavy Water at Subcritical and Supercritical Conditions

The heat capacity of heavy water was measured in the temperature range from 294 to 746 K and at densities between 52 and 1105 kg·m^–3 using a high-temperature, high-pressure adiabatic calorimeter. The measurements were performed at 14 liquid and 9 vapor densities between 52 and 1105 kg·m^–3. Uncertainties of the measurements are estimated to be within 3% for vapor isochores and 1.5% for the liquid isochores. In the region of the immediate vicinity of the critical point (0.97T/T _c1.03 and 0.75/_c1.25), the uncertainty is 4.5%. The original C _V data were corrected and converted to the new ITS-90 temperature scale. A parametric crossover equation of state was used to represent the isochoric heat capacity measurements of heavy water in the extended critical region, 0.8T/T _c1.5 and 0.35/_c1.65. The liquid and vapor one- and two-phase isochoric heat capacities, temperatures, and saturation densities were extracted from experimental data for each measured isochore. Most of the experimental data are compared with the Hill equation of state, and the overall statistics of deviations between experimental data and the equation of state are given.     

Fracture mechanics of blunt cracks in a ductile steel

The propagation of blunt notches in stainless steel has been studied experimentally and analysed using generalized fracture mechanics (GFM), which takes account of inelastic and non-linear deformation. According to this theory, the critical apparent energy release rate, which is equivalent toJ _c, is given byJ _c=k ₁ (₀)cW _0c for an edge crack of lengthc in a thin sheet (plane stress), wherek ₁ (₀) is a dimensionless function of strain, ₀, andW _0c is the input energy density remote from the crack at the time of crack propagation. The validity of this equation was demonstrated for blunt cracks and the functionk ₁ (₀) evaluated. The value ofJ _c was measured for blunt cracks of different lengths and tip diameters, and also for different crack extensions.J _c was found to be independent of crack length for the smallest tip radius, but became systematically length-dependent as the radius increased. However, the dependence ofJ _c on crack length, tip radius and crack extension can be expressed by a single empirical function, as is suggested by GFM. The propagation of cracks from blunt notches in ductile materials can, therefore, be handled by fracture mechanics methods.     

On the constancy of the specific enthalpy of fracture

The specific enthalpy of fracture due to ductile crack propagation in commercial polycarbonate sheet is calculated as ^* =A _1c/R _1c, whereA _1c is the critical energy release rate associated with the onset of unstable crack propagation andR _1c is the corresponding amount of damage (yielded material) formed per unit crack extension.A _1c andR _1c are determined from fatigue crack propagation experiments conducted at different maximum loads, load ratios and frequencies. The value of ^* obtained from all experiments is found to be 9.8±1.4 cal g^–1 (1cal = 4.184 J) which indicates that ^* is a material constant. This finding substantiates predictions of the crack layer theory.     

A method of determining the thermal conductivity of powdered and fibrous insulation as a function of filler gas pressure

An examination is made of the theoretical basis and implementation of a nonstationary method of rapid measurement of the thermal conductivity of powdered and fibrous insulation under conditions of monotonic change of filler gas pressure.Notation t temperature - ,a thermal conductivity and diffusivity of test material - k, k_a relative temperature coefficients of anda - thickness of test layer - x variable layer coordinate reckoned from shell - =(x), _c excess temperature of material at section x and of core over shell - b_c, b_v rate of cooling of core and of variation of volume-mean temperature of layer - c_c, c total heat capacity of core and material - f_s, F_c area of working surfaces of shell and core - d diameter of particles of bulk material - p material porosity - volume density of material     

Charge Complementarity and Interlayer Coupling Between Charge Ordered Layers of Cuprates

The interlayer Coulomb coupling between charge ordered superlattices with charge antisymmetry has been studied. The 2D pair-condensate can be characterized by a charge ordered state with a checkerboard like pattern seen recently by scanning tunneling microscopy. Interlayer charge complementarity is essential for getting interlayer energy gain which is found to be proportional to the condensation energy. The correlation between the condensation energy and the critical temperature is studied within our charge ordered superlattice bilayer model in which pairing is supported by interlayer Coulomb energy gain (potential energy-driven superconductivity). The static c-axis dielectric constant _c is calculated for various cuprates and compared with the available experimental data.     

Fracture toughness and hardness of zinc sulphide as a function of grain size

The erosion properties of brittle materials depend upon plastic deformation and crack generation at an impact or indented site. Vickers indentations have been used to investigate the plastic processes and crack systems in chemical vapour deposited zinc sulphide of different grain sizes. The hardness,H, and the local fracture toughnessK _c, are dependent upon the grain size of the material. For small grain size material (<50 m) the Vickers hardness was found to increase with decreasing grain size in accord with the Petch mechanism, i.e.H=H ₀ +kd ^–1/2 wherek andH ₀ are constants andd is the grain diameter. A maximum hardness of ca. 4 GPa has been observed for material with an average 0.5 m grain diameter. In large grain size material, hardness anisotropy within the grains causes significant experimental scatter in the hardness measurements because the plastic impression formed by the indenter (load 10 N and 100 N) is smaller than the grain diameter. The values ofK _c obtained using an indentation technique show that for grain sizes less than 8 mK _c decreases with decreasing grain size. For materials with a grain size in the range 500 m to 8 m, well developed median cracks were not observed, however, the radius of the fracture zone was measured in order to estimate an effectiveK _c. The effectiveK _c was found to increase approximately linearly with the reciprocal root of the grain size. Consideration of the models for elastic/plastic impact and micromechanics of crack nucleation in conjuction with the variation ofK _c andH, indicate that zinc sulphide with a mean grain size of 8 m will give the optimum solid particle and rain erosion resistance.     

Competition between brittle fracture and plastic collapse in the failure of thin rectangular panels

A centre-cracked panel of elastic-plastic material of unit thickness is loaded remotely by an uniaxial traction acting along its longitudinal axis. Making use of the Dugdale-Barenblatt model, the size of the plastic zones ahead of the crack tips can be obtained by equilibrium considerations. Connected to , a generalised elastic-plastic stress intensity factor K is defined which, as 0, approaches the ordinary elastic one. Once the critical values W _c or K _c at the onset of the unstable propagation of the crack have been specified, the residual-strength curves for plane stress state can be easily deduced. Moreover, conditions are sought for which ductile fracture, brittle fracture or plastic collapse takes place.     

Dependence of the contact heat conductivity of granular systems on the external load

An examination has been made of the dependence of the contact heat conductivity of granular systems on the external load. The calculation formulas proposed for contact heat conduction are applicable over a wide range of materials.Notation s_a area of actual contact of two particles in a granular material - _c conductivity of the contact between two particles - h_r height of a micro-roughness - _s thermal conductivity of the material of the particles - d=2r particle diameter - _c contact thermal conductivity of the granular material - p porosity of the system - S_a1, S_a2 area of contact of two particles in the freely poured state and under the action of a load - f thermal conductivity of the granular system in the freely poured state - () portion of the thermal conductivity of a granular material that depends on the external load - relative area of contact - s_n nominal area of contact of the two particles - external specific load - E modulus of elasticity of the particle material - E₀ effective modulus of elasticity of the granular material - k₁, k₂, k₃, k_m, k_b empirical coefficients     

Integral-equation representations of flow elastoplasticity derived from rate-equation models

Summary Two integral-equation representations are presented in this paper, based on the exact integrations of the conventional rate-equation model of associativeJ ₂ flow elastoplasticity with combined-isotropic-kinematic hardening-softening. Among them the strain-controlled integral-equation representation has two new naturally defined material functionsY(Z) andU(Z) of the normalized active workZ, which plays the role of intrinsic time. One of the immediate benefits derivable from the new representations is, owing to the explicit unfolding of the highly nonlinear path-dependence between stress and strain without a detour to the evolutions of internal state variables, their adaptability for direct calculations without any iteration. Indeed, it is itself a constructive algorithm. It is shown that at a realistic level of precision, the strain-controlled integral-equation representation saves 99% or more of the CPU time compared with the widely used elastic predictor-radial return algorithm of the rate-equation representation.List of symbols e _ij ,e _ij ^e ,e _ij ^p strain deviator, elastic strain deviator, plastic strain deviator - effective strain - ^p effective plastic strain - e ₁,e ₂,e ₃ principal strain deviator,e ₃=–e ₁–e ₂ - e _tan,e _rad tangential strain increment, radial strain increment - E Young's modulus, assumed to be constant - f yield function in stress space - F yield function in strain space - G shear modulus, assumed to be constant - G(Z ₁,Z ₂) shear relaxation function of elastoplasticity - h( ^p ),k( ^p ) material functions of plasticity for the stress-space rate-equation representation - material functions of plasticity for the strain-space rate-equation representation - I ₂ second invariant of the deviatoric strain tensor - J ₂ second invariant of the deviatoric stress tensor - J(z ₁,z ₂) shear creep function of elastoplasticity - K bulk modulus, assumed to be constant - p dummy variable of integration in place of the effective plastic strain - r _ij active stress - R _ij active strain - effective active-stress, i.e. times Euclidean length of active stress - effective active-strain, i.e. times Euclidean length of active strain - S _ij ,S _ij ^e ,S _ij ^r stress deviator, elastic stress deviator, stress relaxation - effective stress - effective stress relaxation - S ₁,S ₂,S ₃ principal stress deviator,S ₃=–S ₁–S ₂ - t, , , time - t ₀ zero-value time - t _u latest unloading time - y(z), u(z) material functions of plasticity for the stress-controlled integral-equation representation - Y(Z), U(Z) material functions of plasticity for the strain-controlled integral-equation representation - z normalized active complementary-work - material functions defined for use in convertingh( ^p ) andk( ^p ) toy(z) andu(z) - Z normalized active work - material functions defined for use in convertingh( ^p ) andk( ^p ) toY(Z) andU(Z) - _ij back stress - A _ij back strain - _ij , _ij ^e , _ij ^p strain, elastic strain, plastic strain - _y (initial) yield strain, _y =h(0)/2G - Poisson's ratio assumed to be constant - _ij , _ij ^e , _ij ^r stress, elastic stress, stress relaxation - _y (initial) yield stress, yield strength, _y =h(0)     

Research on research and some problems of research bureaucracy

The paper deals in its first part critically with the ideo-centric interpretation of the subject matter of the sociology of science. Especially American sociologists tend to regard sociology of science as apart of the sociology of knowledge, specialized in defining the nature of scientificideas and their relations to other kinds of ideas, institutional and personality factors, etc. However, in our days the center of gravity of sociological studies on science has shifted more and more outward of the domain of the sociology of knowledge.Research on research, particularly research on the objective socio-economic, organizational and operational aspects of institutionalized and professionalized research activity, have become very central to the sociology of science and have made probably some of the greatest contributions to its recent development. The material demands of society on science, and vice versa, the investiment of society in the scientific establishment, the bread-and-board questions of research activity, the hard realities of national and industrial research policies, etc., provide a vastterra incognita into which the contemporary sociology of science must foray. The second part of the present paper deals with the delineation of a stretch of the unknown land that has remained hitherto largely unexplored by the sociology of science, namely with the structure and the functions of contemporaryresearch bureaucracy. Some findings of a Hungarian empirical study are discussed which seem to indicate that big science tends to go hand in hand with big research bureaucracy, in particular with an increased share of administrative personnel in the total staff on research institutions.Presented at the Conference on Social Studies of Science (Cornell University, Ithaca, New York, November, 1976).     

Non-k-Diagonality in the Interlayer Pair-Tunneling Model of High-Temperature Superconductivity

We investigate the effect of k-space broadening of the interlayer pairing kernel on the critical temperature T_c and the k-dependence of the gap function in a one-dimensional version of the interlayer pair-tunneling model of high-T_c superconductivity. We consider constant as well as k-dependent intralayer pairing kernels. We find that the sensitivity to k-space broadening is larger the smaller the width of the peak of the Fermi-level gap calculated for zero broadening. This width increases with the overall magnitude of the interlayer tunneling matrix element, and decreases with the bandwidth of the single-electron intralayer excitation spectrum. The width also increases as the Fermi level is moved towards regions where the excitation spectrum flattens out. We argue that our qualitative conclusions are valid also for a two-dimensional model. This indicates that at or close to half-filling in two dimensions, when the Fermi-surface gap for zero broadening attains its peaks at (±/a, 0) and (0, ±/a) where the excitation spectrum is flat, these peaks should be fairly robust to moderate momentum broadening.     

Effects of rate,temperature and absorption of organic solvents on the fracture of plain and glass-filled polystyrene

The rate/temperature dependent fracture behaviour of plain and glass-filled polystyrene has been investigated over the crack speed (a) range of 10^–6 to 10^–2 m sec^–1 and in the temperature (T) range of 296 to 363 K. TheK _c (a, T) relationships obtained, whereK _c is the stress intensity factor at fracture, are shown to follow those given by the Williams/Marshall relaxation crack growth model and the toughness-biased rate theory. Crack propagation in both materials is shown to be controlled by a-relaxation molecular process associated with crazing. Crack instabilities observed in plain polystyrene are analysed successfully in terms of isothermal-adiabatic transitions at the crack tip. Fracture initiation experiments are also conducted in which the effects of organic liquids on the fracture resistances of both plain/glass-filled polystyrene have been determined. Good correlations betweenK _i ² (K _i being the crack initiation stress intensity factor) and _s, solvent solubility parameter, of various liquid environments have been obtained, which give a minimumK _i ² value at _{s p}, where _p is the solubility parameter of the polymer. For a given temperature, liquid environment and crack speed, the glass-filled polystyrene is shown to possess greater resistances to crack propagation than plain polystyrene.     

Convection in a shallow laterally heated cavity with conducting boundaries

Shallow cavity flows driven by horizontal temperature gradients are analysed over a range of Rayleigh numbersR and Prandtl numbers , whereR is comparable in size to the aspect ratioL(1). Eigenvalue calculations show the existence of a critical Prandtl number R > R _c (), below which the parallel core-flow structure is destroyed for Rayleigh numbersR>R _c(). For other Rayleigh numbers and Prandtl numbers the horizontal scale of influence of the end walls of the cavity is determined.     

Integral results for nonlinear diffusion equations

We show how to construct integral results for the multi-dimensional nonlinear diffusion equation c/t=·(D(c)c) and for some generalisations of this. For appropriate boundary conditions these become integral invariants. An application of these results to determining the large-time behaviour of some radially symmetric problems is indicated.     

Electrical properties of In/Yb/n-Hg1 − x Cd x Te contacts

The specific contact resistance, _c, and the modified sheet R _sk, of In/Hg_{1 – x} Cd _x Te contacts incorporating a Yb diffusion barrier were measured as a function of the layer thickness and composition (x = 0.32–0.65). Significant increases in _c, were evident only for x 0.56 and at Yb thicknesses between 2.5 and 6.0 nm, depending on the x-value. Analytical examination of the interfaces by Rutherford backscattering spectrometry (RBS) also showed a progressive reduction in the extent of inward diffusion of In with increasing thickness of the Yb interlayer.     

Linear response and instability of vortex lattice in type-II superconductors

The wave vector dependent linear response of the vortex lattice in type-II superconductors is studied by calculating the superfluid density and is shown to have a singular behavior with respect to the long wave length perturbation of vector potential. The calculations are carried out in terms of the nonlinear elastic theory of the vortex lattice, which is, in principle, a low temperature expansion, and the terms up to the first order in temperature are taken into account, which is beyond the usual Gaussian elastic theory. The superfluid density is found to behave as ~ k_BT ¦k¦² log ¦k¦,for the small wave vector,k,perpendicular to the external magnetic field, where Tand k_B are the temperature and the Boltzmann constant, respectively. This behavior causes the divergence of the magnetic susceptibility at a critical wave vector, k_c.We show that this behavior is associated with an instability of vortex lattice to the externally applied perturbation.     

Fracture initiation and crack propagation of acrylonitrile-butadiene-styrene (ABS) in organic solvents

The effects of organic liquid environments on the fracture behaviour of acrylonitrile-butadiene-styrene (ABS) have been investigated. Fracture initiation experiments showed thatK _i ² , (K _i being the stress intensity factor at crack/craze initiation), could be meaningfully correlated with the solvent solubility parameter ( _s) of the different liquid environments and had a minimum value at _s= _p, where _p was the solubility parameter of ABS. For the range of organic liquids used, hydrogen bonding did not have any significant effects on the correlations. It was demonstrated that theK _i ² – _s correlations could also be usefully extended to other materials such as plain and glass-filled polystyrenes. At a common crack speed (å), the fracture toughness (R) values in crazing liquids (i.e. alcohols) were greater than those in cracking solvents (i.e. acetone, benzene, toluene, etc.) which usually caused a dissolution effect on the plastic. From crack propagation experiments, and using fracture mechanics analyses, definiteR(å) andK _c(å) relationships for ABS immersed in toluene, carbon tetrachloride and methanol were determined. These experimental results showed that crack propagation was relaxation controlled and agreed well with a recent theoretical analysis due to Williams and Marshall for environmental crack and craze growth in polymers. Finally, SEM pictures were presented to show the remarkable differences in the fracture morphologies of ABS in both crazing and cracking liquid environments.     

On a bessel function integral

We consider the integral where, K, k andb are all positive real numbers. We reduce this integral to a linear combination of two integrals. The first of these is an exponential integral, which can be expressed as a difference of two Shkarofsky functions, or can easily be evaluated numerically. The second is the original integral, but withk andK both replaced by kK. We express this as a MeijerG function, and then reduce it to the sum of an associated Bessel function and a modified Bessel function.Previously at the Maple Symbolic Computation Group, University of Waterloo, Waterloo, Ontario, Canada, N2L-3G1     

Bifurcation of crack pattern in arrays of two-dimensional cracks

Theoretical calculations based on simple arrays of two-dimensional cracks demonstrate that bifurcation of crack growth patterns may exist. The approximation used involves the dipole asymptotic or pseudo-traction method to estimate the local stress intensity factor. This leads to a crack interaction parametrized by the crack length/spacing ratio =a/h. For parallel and edge crack arrays under far field tension, uniform crack growth patterns (all cracks having same size) yield to nonuniform crack growth patterns (bifurcation) if is larger than a critical value _cr. However, no such bifurcation is found for a collinear crack array under tension. For parallel and edge crack arrays, respectively, the value of _cr decreases monotonically from (2/9)^1/2 and (2/15.096)^1/2 for arrays of 2 cracks, to (2/3)^1/2/ and (2/5.032)^1/2/ for infinite arrays of cracks. The critical parameter _cr is calculated numerically for arrays of up to 100 cracks, whilst discrete Fourier transform is used to obtain _cr for infinite crack arrays. For infinite parallel crack arrays under uniaxial compression, a simple shear-induced tensile crack model is formulated and compared to the modified Griffith theory. Based upon the model, _cr can be evaluated numerically depending on (the frictional coefficient) and c ₀/a (c ₀ and a are the sizes of the shear crack and tensile crack, respectively). As an iterative method is used, no closed form solution is presented. However, the numerical calculations do indicate that _cr decreases with the increase of both and c ₀/a.