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.     

Relations Between Transport Coefficients in Lennard–Jones Fluids and in Liquid Metals

Several simple approximate hard-sphere relations for transport coefficients are compared with the results of molecular dynamics (MD) simulations performed on Lennard–Jones (LJ) fluids. Typically the individual transport coefficients: self-diffusion coefficients, D, shear viscosity, _s, bulk viscosity, _B, and thermal conductivity, , agree within a factor of two of the exact results over the fluid and liquid parts of the phase diagram, which seems reasonable in view of the approximations involved in the models. We have also considered the ratio, /_s, and the product, D_s, for which simple analytic expressions exist in the hardsphere models. These two quantities also agree within a factor of two of the simulation values and hard sphere analytic expressions. Using time correlation functions, Tankeshwar has recently related the ratio /D to thermodynamic quantities, in particular, to the differences in specific heats, C _p – C _V, and to the isothermal compressibility, T. Using D and thermodynamic values taken solely from LJ MD simulations, his relation was tested and found to give typically better than ~20% agreement at liquid densities, deteriorating somewhat as density decreases into the gas phase. Finally liquid metals are considered. In this case, is dominated by its electronic contribution, which is related approximately to the electrical conductivity by the Wiedemann–Franz Law. Some theoretical results for the electrical conductivity of Na are referenced, which allow a semiquantitative understanding of the measured thermal conductivity of the liquid metal. Shear viscosity is also discussed and, following the work of Tosi, is found to be dominated by ionic contributions; Nevertheless, at the melting temperature of Na, a relation emerges between thermal conductivity, electrical resistivity and shear viscosity.     

Experimental Study of Gas–Liquid Two-Phase Flow in Glass Micromodels

To estimate the most important flow variables in reservoir engineering, such as the relative permeability, it is required to know with high precision, other variables such as saturation, pressure drop of each phase, and porous media data such as porosity and absolute permeability. In this study, experimental tests were performed inside a glass micromodel using gas–liquid two-phase flow in steady-state conditions. The liquid-phase flow and the pressure drop of the porous media were determined. Additionally, the flow development inside the porous media was visualized using a high-speed video camera system. These pictures were recorded at 500 fps, and they were used to compute the phase saturation and the gas velocity in the glass micromodel. The visualization was performed in three regions of the glass micromodel demonstrating that saturation gradients were not present. The effect of the capillary number was studied over the gas–liquid relative permeability curves and on the flow mechanisms. It was concluded that high flow rates minimize edge effects, that the capillary number modifies the relative permeability values and the flow patterns inside the micromodel, and that the high-speed visualization is an efficient and accurate technique to determine saturation values and to study the flow patterns in transparent porous media such as glass micromodels.     

Self-Consistent Theory of Transport in Quasi–One-Dimensional Superconducting Wires

We study superconducting transport in quasi–one-dimensional homogeneous wires in the cases of both equilibrium and nonequilibrium quasiparticle populations, using the quasiclassical Green's function technique. We consider superconductors with arbitrary current densities and impurity concentrations ranging from the clean to the dirty limit. Local current conservation is guaranteed by ensuring that the order parameter satisfies the self-consistency equation at each point. For equilibrium transport, we compute the current, the order parameter amplitude, and the quasiparticle density of states as a function of the superfluid velocity, temperature, and disorder strength. Nonequilibrium is characterized by incoming quasiparticles with different chemical potentials at each -end of the superconductor. We calculate the profiles of the electrostratic potential, order parameter, and effective quasiparticle gap. We find that a transport regime of current-induced gapless superconductivity can be achieved in clean superconductors, the stability of this state being enhanced by nonequilibrium.     

Pyroceram 9606, A Certified Ceramic Reference Material for High-Temperature Thermal Transport Properties: Part 1—Material Selection and Characterization

A three-year program of work supported by the European Commission (EC) involving eleven partners from six countries has been carried out to select, procure, characterize, and certify the thermal transport properties (thermal conductivity, λ, and thermal diffusivity, a) of Pyroceram 9606, a polycrystalline glass ceramic identified as the most suitable reference material for use up to at least 1000 °C. For the initial calibration, six blocks were chosen from a batch of 30 blocks purchased for the project. Measurements of the following properties were undertaken: chemical analysis and microstructure, density and porosity, homogeneity, anisotropy, thermal cycling between 20 °C and 1000 °C, and long-term stability and reproducibility. In addition, specific heat capacity, linear thermal expansivity, and thermal transmissivity measurements were carried out so that the thermal conductivity could also be determined from thermal-diffusivity values obtained from the certification measurements. As a result of a successful characterization program, the partners had no hesitation in recommending to the European Commission that full certification of the thermal conductivity and thermal diffusivity of Pyroceram 9606 should be undertaken.     

E-Glass/Vinylester Composites in Aqueous Environments – I: Experimental Results

2- and 4-layered specimens of E-Glass/Vinylester fabricated from uniaxial, biaxial, and triaxial, non-woven fabrics processed using the resin infusion process are immersed in deionized water at 23°C (73°F) and 60°C (140°F), and a potassium based pH 10 buffer at 73°F, for a period of 57 weeks in order to investigate durability in aqueous environments. It is shown that the coefficients of apparent diffusion and levels of moisture gain are the highest for the deionized water immersed samples at 60°C (140°F), and this results in the highest levels of tensile strength and modulus degradation. Tensile tests show the presence of an aqueous medium based post-cure that competes with the conventionally recognized mechanisms of deterioration in the resin, at the level of the fiber-matrix interface, and in the fiber, resulting in a retardation of absolute level of effects. It is also shown that effects of the immersion are different in the warp and fill directions and can in fact be affected by intricacies of the fabric architecture and thickness. It is shown that damage takes place through interface debonding and degradation as well as fiber pitting, and cracking, each of which serve as the means for renewed absorption of water resulting in moisture uptake at levels above the initial plateau. Effects of immersion on short-beam-shear strength and glass transition temperature are also elucidated.     

Experimental Results on Tungsten-Wire Explosions in Air at Atmospheric Pressure—Comparison with a One-Dimensional Numerical Model

Experimental results on exploding tungsten wires in air at atmospheric pressure at current densities 10⁷ A·cm^–2 and a current rise 10¹⁰ A·s^–1 are presented. Besides the current through the probe and the voltage across it, the diameter of the wire material and its surface temperature have been measured. The final aim of this investigation is the determination of the thermophysical properties of a high-melting liquid metal up to its critical point. Here a first step should be made to demonstrate the reliability of the method and to justify the crucial assumptions. To determine the limits for the applicability of a homogeneous approach used so far, a one-dimensional numerical model in Z-pinch geometry has been used which gives the time evolution of the profiles of temperature, density, and pressure across the wire. The model describes well the main features observed in these experiments. A physical explanation for the maximum in the time dependences of the surface temperature is proposed. This behavior is related to special thermodynamic properties of a two-phase (liquid–gas) mixture forming in a peripheral layer around the liquid metal. The temperature limit is determined for which there are no remarkable gradients of temperature and density across the wire. The specific heat, the thermal expansion coefficient, and the electrical as well as thermal conductivity of liquid tungsten can now, in principle, be obtained. The parameters of the critical point of the liquid-vapor phase transition can also be estimated.     

Transport and Quantum Coherence in Graphene Rings: Aharonov–Bohm Oscillations,Klein Tunneling,and Particle Localization

Simulating quantum transport through mesoscopic, ring-shaped graphene structures, we address various quantum coherence and interference phenomena. First, a perpendicular magnetic field, penetrating the graphene ring, gives rise to Aharonov–Bohm oscillations in the conductance as a function of the magnetic flux, on top of the universal conductance fluctuations. At very high fluxes, the interference gets suppressed and quantum Hall edge channels develop. Second, applying an electrostatic potential to one of the ring arms, \(nn'n\)- or npn-junctions can be realized with particle transmission due to normal tunneling or Klein tunneling. In the latter case, the Aharonov–Bohm oscillations weaken for smooth barriers. Third, if potential disorder comes in to play, both Aharonov–Bohm and Klein tunneling effects rate down, up to the point where particle localization sets in.     

Pyroceram 9606, A Certified Ceramic Reference Material For High-Temperature Thermal Transport Properties: Part 2—Certification Measurements

Following the characterization of the batch of Pyroceram 9606 material, a number of the partners in the European Commission (EC) supported program carried out certification measurements of thermal conductivity and thermal diffusivity. Six laboratories undertook thermal-diffusivity measurements using either the flash or the modulated beam methods. Eight laboratories measured the thermal conductivity, using either the steady-state guarded-hot-plate method or one of the transient hot-wire methods. Results from each series of measurements were provided in a standard format as an aid to simplify the statistical analysis of the data. The results were corrected to the nominal measured temperature and for change in dimension, analyzed separately, and presented in a standard format. Outliers were identified and rejected where appropriate, based on both statistical and technical evidences. The individual data sets were combined, and the grand mean data for each property analyzed further to provide the certified values together with their uncertainty limits. Finally, using the specific heat capacity and density values obtained from the characterization tests, values of thermal conductivity were calculated from the measured thermal diffusivity. The difference between the calculated and certified values is less than 2.7 %, which is well within the uncertainty limit assigned for the certified thermal property values.     

Experimental Investigation of the Thermal Conductivity of Dibutyl‐ and Diisobutyl Sebacates at High Temperatures and Pressures

Results of experimental investigation of the thermal conductivity of dibutyl and diisobutyl sebacates in the interval of temperatures 308.1–641.3 K and pressures (0.1–40.0) MPa are given.     

Thermal decomposition of ZSM—5 and silicalite precursors

The combined technique of thermogravimetric analysis and mass spectrometry was used to observe the thermal decomposition of the following silicalite and zeolite precursors: tetraethylammonium-silicalite, tetrapropylammonium-silicalite, tetraethylammonium-ZSM—5, tetrapropylammonium-ZSM—5, methylamine-ZSM—5 and propylamine-ZSM—5. It was possible to distinguish the organic base molecules associated with acid sites from those not associated with acid sites by the composition of the evolved volatiles. Reaction sequences for the decomposition of the precursors have been proposed which involve a Hofmann elimination reaction followed by β-elimination reactions for tetraalkylammonium ions not associated with acid sites, and sequential Hofmann reactions for organic ions at acid sites. For the amine-ZSM—5 decompositions the physisorbed amines are evolved, unreacted, at ≈180°C while the amines at the acid sites undergo elimination reactions between 350° and 500°C.     

On Electronic and Transport “Anomalies” in Layered Oxides

We briefly discuss some electronic and transport anomalies observed in superconducting perovskites. In particular we consider: (i) the complex electronic (and crystallographic) phase diagram, (ii) the symmetry of the gap with a special emphasis on the evidence for s-wave component in various experiments, and (iii) non-Fermi-liquid transport in superconducting Sr₂RuO_4– perovskite (T _c<1 K) that, like LSCO cuprate, exhibits linear resistivity up to 1050 K.     

Thermal pressure coefficients of ethanenitrile,propanenitrile, and butanenitrile in the region 295–395 K

The thermal pressure coefficient (p/T) _v has been measured for ethanenitrile from 299 to 364 K, for propanenitrile from 295 to 377 K, and for butanenitrile from 297 to 398 K. The results are discussed in terms of the diminishing role of polarity in the alkanenitrile series and of a corresponding-states approach using gas-liquid critical properties as reduction factors. Although (p/T) _v varies unevenly with chain length, the reduced quantity shows a more regular behavior similar to that of the related quantity the cohesive energy density.     

Predictions of Multiband s?? Strong-Coupling Eliashberg Theory Compared to Experimental Data in Iron Pnictides

The experimental critical temperatures and the gap values of the superconducting materials LaFeAsO_1?x F _x , SmFeAsO_1?x F _x and Ba_1?x K _x Fe₂As₂, which are exponent of the most important families (1111 and 122) of iron pnictides, can be reproduced by an effective s-wave three-band Eliashberg model in which the dominant coupling is in the interband channel and the order parameter is nodeless but undergoes a sign reversal between hole and electron bands (s?? symmetry). In particular, high values of the electron-boson coupling constants and small typical boson energies (in agreement with neutron diffraction experiments) are necessary to reproduce the exact T _c, the experimental gap values and their temperature dependence. The same parameters allow fitting the experimental temperature dependence of the upper critical field and predicting the presence of characteristic structures related to the electron?Cboson coupling in the Andreev-reflection spectra.     

Kirchhoff Approximation Revisited—Some New Results for Scattering in Isotropic and Anisotropic Elastic Solids

Through a series of numerical studies that compare the Kirchhoff approximation to more exact scattering theories, it is demonstrated that the Kirchhoff approximation can accurately predict the pulse–echo peak-to-peak responses of spherical pores and circular cracks in isotropic media over a very wide range of cases that extend well beyond the limits normally associated with this approximation. The reason for this good agreement is shown to lie in the ability of the Kirchhoff approximation to model accurately the very early time response of the flaw. It is also shown that in the Kirchhoff approximation the pulse–echo response of an arbitrary traction-free scatterer in an isotropic elastic solid is identical to the same response obtained using a scalar (fluid) scattering model. This leads to simple analytical expressions for the pulse–echo far-field scattering amplitude of some canonical geometries (circular cracks, spherical voids, cylindrical holes) and to simplified numerical expressions for more general scatterers. For general anisotropic volumetric flaws in a anisotropic elastic solid, it is shown that a high-frequency asymptotic evaluation of the Kirchhoff approximation yields an explicit analytical expression for the pulse–echo leading-edge response of the flaw. Explicit expressions are also given for the pitch–catch response of an elliptical-shaped flat crack in a general anisotropic solid.     

Effects of Composition and Thermal Cycle on Transformation Behaviors, Thermal Stability and Mechanical Properties of CuAlAg Alloy

The phase transformation behavior, mechanical properties, and the thermal stability of CuAlAg alloy were studied and minor rare earth (0.1 wt pct La Ce) was added to improve the mechanical property of the studied alloy. It was found that Ag addition in the CuAl binary alloy can improve the stability of martensitic transformation and high Al content leads to the disappearing of martensitic transformation. The tensile strength and strain of the Cu-10.6Al-5.8Ag (wt pct) alloy were measured to be 383.5 MPa and 0.86%, respectively. With rare earth addition, the tensile strain increased from 0.86% to 1.47%. The CuAlAg alloy did not exhibit martensitic transformation on the second heating process. Its poor thermal stability still needs to be improved.     

Depletion and “Fines” Effects on Transport in Hard-Sphere Colloids

The effect of depletion forces induced by the presence of much smaller B spheres (diameter ratio 10/1) in dense hard A spheres has been investigated. Simulations for systems of 10⁴ spheres with mole fraction of larger spheres x _A = 0.05 and with total sphere volume fraction from 0.35 to 0.655 have been carried out. The depletion force steeply increases in the A–A pair distribution function at contact, and creates a lower first coordination and more open network A-structures. There is no evidence of demixing. It is found that in the amorphous solid region there is an enhanced diffusive mobility of the larger spheres, relative to that of pure spheres, at the same densification rates. This observation resembles the fines effect that occurs in colloidal suspensions and granular fluids.     

Taki Kōji,Provoke, and the Structuralist Turn in Japanese Image Theory, 1967–70

This article explores the intellectual underpinnings of the late-1960s Japanese photography collective Provoke. It argues that Provoke was more radical and theoretically inflected than is conventionally understood, its project being the forging of a ‘scientific’ photography capable of unveiling the ‘untruth’ of established relations of power and knowledge production in Japan. I present Provoke’s central figure to be Taki Kōji, who in 1967–68 published a series of articles that introduced structuralism into Japanese image discourse and established the basis for Provoke’s theoretically informed practice, or praxis. The article outlines how, in response to a variety of influences (Roland Barthes, Matsumoto Toshio, and Kevin Lynch, among others, but apparently not Antonio Gramsci or Louis Althusser), Taki formulated the notion of a unified and self-regulating ideological ‘environment’ (kankyō) that is made manifest in a variety of seemingly neutral and benign cultural forms. Additionally, he theorised a semiotically transgressive photographic image, derived from Barthes’s early studies of photography, which he believed could escape language and code – and thereby the ideological superstructure. I conclude by showing that Taki’s emancipatory project, while singular in relation to contemporaneous Marxist oppositional endeavours in Europe, was ultimately self-defeating: the efforts of Provoke’s photographers to strip their images of readable codes by deliberately ‘mishandling’ their cameras only worked to create new ones, and the shakiness and blurriness of the resulting photographs became a mere style.     

A Comparison of Experimental and Theoretical Relations Between Young’s Modulus and the Flexural and Longitudinal Resonance Frequencies of Uniform Bars

The relations from which Young’s modulus may be computed from mechanical flexural and longitudinal resonance frequencies have been established by an empirical method using two sets of steel bars. Both sets contained rectangular and cylindrical specimens. For longitudinal vibration of cylindrical specimens, the agreement between the empirical curves and Bancroft’s corresponding theoretical relation was within experimental error if Poisson’s ratio for both sets is taken to be 0.292. For flexural vibrations, the agreement between the empirical curve and the corresponding theoretical relation developed by Pickett is also within experimental error for about the same value of Poisson’s ratio for the rectangular specimens of both sets; but for cylindrical specimens, the empirical values are somewhat lower than those predicted by the theory.