Hydrogels with the ordered structures

A water-swollen hydrogel with a molecularly-ordered structure was prepared by copolymerizing acrylic acid and acrylic monomer containing hydrophobic long alkyl or mesogenic moiety. The gels with a long alkyl side chain formed the crystalline structure and undergo the reversible order–disorder transition with change in temperature or solvent composition which accompanied a dramatic change in Young’s modulus. These gels exhibited such chemomechanical behaviors as the shape memory and the rotational motility on the water surface. On the other hand, the gels with the mesogenic side chain formed the liquid crystalline structure with polymorphism in water, and mesophase diagram was established by changing copolymer composition and water content. Mechanism of these structural and chemomechanical behaviors has been explained in terms of order–disorder transition.     

Disorder-Induced Metal–Insulator Transition in Conducting Polymers

The metal–insulator (M-I) transition in conducting polymers is particularly interesting; critical behavior has been observed over a relatively wide temperature range in a number of systems, including polyacetylene, polypyrrole, poly (p-phenylene vinylene), and polyaniline. In each case, metallic, critical, and insulating regimes have been identified through Zabrodskii plots of the logarithmic derivative of the conductivity. The critical regime (in which the conductivity varies as T, where 1/3) is tunable by varying the extent of disorder and by applying external pressure and/or an external magnetic field. The transitions from metallic to critical behavior and from critical to insulating behavior have been induced with a magnetic field and from insulating to metallic behavior with applied pressure.     

Turbulent transition simulation using the k–ω model

This paper describes a novel approach in simulating laminar to turbulent transition by using two-equation models. The Total Stresses Limitation (TSL) concept is used to make the two-equation model capable of predicting high-Reynolds-number transitional flow. In order to handle the transition triggered by laminar separation at a low Reynolds number location, which commonly occurs in high speed flow, a sensor is introduced to detect separation and trigger transition in the separated zone. Test cases include the classical flat-plate turbulent boundary flow, and low-pressure turbine cascade flows at design and off-design conditions. © 1998 John Wiley & Sons, Ltd.     

The effect of silicon content on long crack fatigue behaviour of aluminium–silicon piston alloys at elevated temperature

The microstructure of aluminium piston alloys comprises primary and eutectic silicon together with numerous intermetallics. Previous research has shown that primary silicon strongly influences both fatigue crack initiation and subsequent propagation behaviour, however, the detailed effects of varying silicon volume fraction and morphology have not been fully addressed. Therefore, the fatigue properties of a number of candidate piston alloys with varying volume fractions of silicon have been studied. Long crack fatigue tests have been performed at room and elevated temperature typical of the gudgeon pin boss (200 °C) using a test frequency of 15 Hz (a typical engine frequency at engine idle condition).Microstructural characterisation using image analysis approaches combined with optical profilometry has been used to assess the fracture surfaces of test samples. The role of primary Si in enhancing crack growth rates at high ΔK levels, whilst affording improvements in crack growth rates at lower ΔK levels due to local crack deflections and shielding, has been confirmed. In the absence of primary Si (lower Si content alloys) the low ΔK level crack growth behaviour is dominated by matrix properties (intra-dendritic crack growth pre-dominates) whilst the high ΔK level crack growth behaviour is inter-dendritic and occurs along the weak path of the eutectic Si and/or intermetallic network.     

Probabilistic bounded non-linear control algorithm for linear structures

Non-linear control algorithms with limited control force has been widely explored and has shown promising results, but the probabilistic analysis of such control algorithms has been made restrictively due to their non-linear nature and corresponding difficulty in obtaining analytical solution of the joint probability density function (PDF). In this paper, the method for the probabilistic analysis on the bounded non-linear control algorithm is proposed based on the equivalent non-linear system method and additional regression analysis. Numerical examples show that the proposed approximate joint PDF of the closed-loop system subjected to a Gaussian white noise and a Kanai–Tajimi filtered Gaussian white noise matches closely with the joint PDF obtained statistically. The effectiveness of the bounded non-linear control is also investigated utilizing the calculated approximate joint PDF. Time history analysis results indicate that the same control performance level as the linear controller is achieved when 50% of the maximum control force of the linear controller is used for the non-linear controller.     

Superconductivity of the Induced Pairing Model in the Presence of Diagonal Disorder

We analyze the influence of randomness of local pair (LP) site energies on the superconducting properties of a mixture of coexisting local pairs and itinerant electrons coupled via charge exchange mechanism. It has been found that the diagonal disorder effects depend in a crucial way on the total particle concentration n and the LP level position ₀. Depending on the parameters, the system can exhibit various types of superconducting behaviors, including the LP-like, intermediate (MIXED), and the BCS-like.     

Nucleation and Boiling Near the Gas–Liquid Critical Point

Nucleation near the gas–liquid critical point depends sensitively on whether the pressure or the volume is fixed. We consider near-critical fluids close to the coexistence curve. (i) Upon decompression to a constant pressure with a fixed boundary temperature, bulk nucleation can well be induced from a gas state, whereas from a liquid state boiling is easily triggered in the thermal diffusion layer near the boundary. In this case, bulk nucleation in a metastable gas is described by the classical Lifshitz–Slyozov theory. (ii) Upon cooling of the boundary temperature under the fixed-volume condition, bulk nucleation can be realized in a liquid and a modified Lifshitz–Slyozov theory follows. However, if a gas is cooled from the boundary at a fixed volume, liquid droplets readily appear in the thermal diffusion layer, apparently suggesting no metastability in a gas in agreement with previous experiments. (iii) On the other hand, if a liquid is heated at the boundary wall, boiling readily occurs both at a fixed volume and at a fixed pressure.     

Giant Oxygen Isotope Effect on the Metal-Insulator Transition of RNiO3 Perovskites

The metal to insulator transition displayed by all the members of the perovskite family RNiO₃ (R=4f rare earth different from La) has attracted a lot of interest since it constitutes one of the few examples of this phenomenon in perfectly stoichiometric compounds. In spite of the great deal of work performed during the last 6 years, the mechanism responsible for the electronic localization is still a matter of controversy. The observation of unusually large O isotope shifts on the metal-insulator temperature T_MI reported in this study represents an important advance since it clearly proves the dominant role of the electron lattice interaction as driving force for the transition. Moreover, the good agreement between this observation and a simple model based on the existence of Jahn–Teller polarons in the metallic state gives further qualitative and quantitative support to the polaronic picture recently suggested to account for O isotope effects in other 3-D transition metal oxides containing Jahn–Teller ions.     

Thermo-optical effect of Nd0.3Sm0.7NiO3 ceramic in the infrared range

Nd_0.3Sm_0.7NiO₃ exhibits a reversible metal semiconductor phase transition which is, in the infrared range, responsible of a thermo-optical contrast. The variation of the thermal emittance for Nd_0.3Sm_0.7NiO₃ ceramic was measured, in the mid-infrared range, by using reflectance measurements and on a benchtest. The thermo-optical effect of the sample was measured in situ by thermal imaging camera. The emissivity contrast obtained is 18% between 293 and 373 K which induced a difference of 27 K between the real and the visible temperature at 373 K.     

An analytical model to study the effective stiffness of the composites with periodically distributed sphere particles

In order to analytically study the overall elastic stiffness of the composite containing periodically dispersed sphere particles, a new micro-mechanics model is developed in this paper. Three kinds of typical particle packing arrangements in the form of simple cubic lattice, body-centered cubic lattice and face-centered cubic lattice are considered and compared. The special characteristics of regular distribution are fully considered by incorporating the necessary geometrical symmetry conditions into strain Green’s function. It is found that particle arrangement obviously affects the macroscopic elastic response of such the kind of composite. Moreover, most of the predictions by the present model are in good agreement with the FEM computations. The effective Young’s modulus of BCC composite the effective shear modulus of SC composite are not in the range of the Hashin–Shtrikman bounds. The present model is also useful to verify some other numerical results mainly obtained by the unit-cell model, for instance, damage variables, matrix plasticity, etc.     

Synthesis of thorny BaCO3 dendritic structures via a simple PEG-assisted method

Thorny BaCO₃ dendritic structures were successfully synthesized by a simple PEG-assisted method. The results revealed that reaction conditions, such as aging time, and the concentration of the PEG, are important factors which determines the morphologies and growth process of the final products. The obtained barium carbonate was characterized by scanning electronic microscopy (SEM) and X-ray powder diffraction (XRD). As a result, it was found that the morphologies are different in different reaction system.     

A partitioning strategy for the coupled hygromechanical analysis with application to wood structures of cultural heritage

One of the main causes for damage of panel paintings of cultural heritage is due to the environmental micro‐climatic variations. Wood science and numerical modeling may help to analyze and calibrate restoration interventions, to predict the behavior of the artwork, taking into account the individual painted panels and the conservation environment. In this article, a partitioning numerical strategy is proposed to predict by simulation the behavior of such artworks. It is based on a multiphysics partition focusing on the interactions between the different physics that are described in a thermodynamical framework. It is applied to the case study of Mona Lisa, modeled as a strongly coupled hygromechanical structure. The strategy is designed to couple two different modelings: a plate model for the mechanical behavior of the panel and 1D transverse diffusion for the moisture evolution. Copyright © 2011 John Wiley & Sons, Ltd.     

BPSCCO Superconductor with Addition of Ag2O Synthesized Under Electrical Field

Ag₂O-doped (1.2% wt.) nitrate freeze-dried powders (Bi : Pb : Sr : Ca : Cu = 1.7 : 0.3 : 2 : 2.5 : 3.5) were processed under an external electrical field and 17.5 MPa pressure at 800°C, for 4 min in vacuum. Final heat treatments (HT) were applied at 835–850°C for 70 h. in air (Bi, Pb)₂Sr₂CaCu₂O _x (2212-phase) was formed by electrical field processing in just 4 min. Electrical field application enhanced (Bi, Pb)₂Sr₂Ca₂Cu₃O _y (2223-phase) formation during final HT. Ag₂O additions to field sintered BSCCO ceramics increased the amount of 2223-phase and the zero resistance critical temperature (T _e(R=0)) by 4 k.     

Synthesis of Superconducting 2212 Phase in the Bi–Pb–Sr–La–Cu–O System

There have been no report about synthesis of the Bi-2212 compound in the Bi–r–La–Cu–O system. We have succeeded in synthesizing the Bi-2212 compound by partial substitution of Pb for Sr and/or Bi in the Bi–Sr–La–Cu–O system. Two samples of nearly the single 2212 phase have been obtained at a nominal composition of Bi_1.5Pb_0.5Sr_2.5La_0.5Cu₂O _z . Both of the samples crystallize in a psedotetragonal lattice, and their lattice parameters are a = 0.5476 nm and c = 3.085 nm or a = 0.5479 nm and c = 3.055 nm. They are both superconductors. The sample with longer lattice parameter c shows an onset of the resistivity drop and zero resistivity at higher temperatures of about 40 K and about 13 K, respectively. This sample also shows a diamagnetic signal starting at about 35 K with lowering temperature.