New effects in highT c superconductors

We show that a proper interpretation of the critical field measurements can distinguish spin fluctuation mechanism from others in the context of the pairing hypothesis. We can predict the existence of a new mode in the mixed state of a superconductor.     

A microscopic theory of layered highT c superconductors

A generalized Gorkov formalism of superconductivity in a layered system with non-primitive lattice structure is given. This is used to justify theoretically a model of highT _c oxide superconductors proposed recently by one of us (SSJ). A numerical estimation of the critical temperature as a function of the number of superconducting layers is mentioned.     

Relative thermodynamic stabilities of constituent oxides of highT c superconductors

A thermodynamic scale of the relative stabilities of constituent oxides can help the choice of stoichiometric multi-component compositions and can provide guidance for judicious selection of heat-treatment conditions for high-T _c superconductors. A thermodynamic analysis was undertaken to study Y₂O₃-BaO-CuO, BaO-K₂O-Bi₂O₃ and La₂O₃-SrO-NiO systems. The relative stability of the oxides was expressed in terms of two ratios,S _v andS _p computed using free-energy of formation and vapour pressure data. CuO, Bi₂O₃ and NiO were taken as reference oxides for YBa₂Cu₃O_7\t-\gd, Ba_0·6K_0·4BiO₃ and La_1·9Sr_0·1NiO₄ respectively. Thermodynamically, the reference oxide was found to be the least stable amongst the constituent oxides in each of these systems.     

CESR in superconductors: Relevance of highT c copper oxide systems

CESR is a highly effective tool to study the interaction among conduction electrons in normal metals. In superconductors belowT _c it can reveal vital information concerning the pairing interactions. A comparative study of highT _c and conventional superconductors is presented and it is shown that the disappearance of CESR in the superconducting state is a feature common to both conventional and highT _c superconductors and establishes the importance of exchange interactions in pairing. This is supported by experimental observations.     

A phase diagram of new high-T c superconductors

A phase diagram of new high-T _c superconductors as highly pinning superconductors of the second type is presented. The diagram includes both vortex glass and vortex liquid phases.     

A new look at rubber-modified asphalt binders

The high-temperature rheological characteristics and the low-temperature fracture properties of asphalt binders containing crumb and devulcanized rubber waste have been investigated. Asphalt binders containing crumb rubber of different mesh sizes, with and without surface modification, and a commercially available binder containing devulcanized rubber, were tested and compared with an unmodified asphalt and three commercially available polymer-modified binders. Interfacial modification of asphalt systems containing crumb rubber was found to give binders that were far superior in their low-temperature performance to commercially available products. The data suggest that a crack-pinning or crack-blunting mechanism is responsible for the increase in toughness found in these systems. A commercially available binder containing devulcanized rubber showed reasonably good high-temperature properties; however, its low-temperature fracture performance was disappointing in that it was not significantly better than that of unmodified asphalt binders.     

A new look at radicals in cigarette smoke

Radicals in cigarette smoke have been proposed to contribute to the harm caused by cigarette smoking. For the first time, using HPLC and high-resolution mass spectrometry analysis of stable radical adducts, we have identified specific radical species in cigarette smoke: 7 acyl and 11 alkylaminocarbonyl radicals. Their combined abundance measured in fresh whole smoke from a single 2R4F cigarette is approximately 225 nmol (1.4 x 10(17) radicals). The fiberglass Cambridge filter pad conventionally employed to separate the gas phase from mainstream smoke was found to reduce the apparent yield of these radicals, introducing artifacts of measurement. The long-accepted steady-state mechanism for the formation of carbon-centered radicals in cigarette smoke involving NO2 chemistry cannot account for these newly identified radicals, and it does not in general appear to be a major source of carbon-centered radicals in fresh mainstream cigarette smoke. Consequently, we suggest that the precise nature of radicals in cigarette smoke warrants reexamination.     

T c and crystal structure distortions of high-temperature superconductors

The influence of orthorhombic distortions of CuO₂ layer onT _c is considered within the framework of kinematic mechanism. The dependence of the interaction constant on orthorhombicity is calculated. It is shown that orthorhombic distortions may result in the increase ofT _c by 10% in accordance with experiment.     

Primitive thermodynamics: A new look at the Clausius-Duhem inequality

New answers to an old question in a new context provide the basis for constructing a thermodynamics which is surprisingly simple and yet capable of modeling viscous fluids, viscoelastic bodies, elastic bodies, and heat conduction. The results obtain from a complete solution of the reduced dissipation inequality without considering functional dependences on histories. Constitutive relations are shown to take the form of a sum of two collections of terms; the first collection being the quasistatic part of classic thermodynamics, and the second is the dynamic part. This dynamic part consists of a gradient of a dissipation potential with respect to the dynamic variables and a collection of terms which gives an identically zero supply of entropy. Absolute minimia of the dissipation potential with respect to the dynamic variables are shown to be attained only in thermostatic states. The theory possesses a full system of symmetry relations and consistency with thermostatics is demonstrated.     

A.c. magnetic measurements on superconductors using two-channel dynamic analyser

A.c. magnetic measurements are powerful tools for characterizing superconducting materials. The a.c. susceptibility is the most used measurement and is commonly performed using a two-phase lock-in amplifier. This article describes a different method to carry out this measurement, employing a two-channel dynamic analyser. This instrument also allows us to measure further quantities, such as higher harmonics of the a.c. susceptibility, the so-called wide-band susceptibility and the magnetization loops. A remarkable feature of the dynamic analyser is its wide frequency range, from 244 μHz to 102 kHz, allowing simple, comprehensive and reliable characterization of superconductors.     

An X-ray spectral study of the influence on the electronic structure of highT c superconductors of the parameters determining the superconducting transition temperature

CuL _α and OK _α X-ray fluorescence spectra, corresponding to the Cd3d-Cu2p and O2p-O1s transitions, and XANES and EXAFS spectra (CuK, YK, BiL, PbL) have been obtained for the following series of samples: (i) YBa₂Cu₃O_7−δ (0<δ<0·8), (ii) La_2−x Sr _x CuO₄ (0<x<0·3) and (iii) Bi₂(Sr, Ca) _n+1 Cu _n O_2n+4 (n=1,2,3), Bi_1·8Pb_0·3Sr_1·9Ca₂Cu₃O _y . A correlation has been found between the decrease in the superconducting transition temperature (T _c ) with variation in the stoichiometric parametersδ andx in series (i) and (ii), and the shift of the maximum in their CuL _α spectra and the relative increase in the number of occupied states Cu3d in the upper part of the valence band. The changes in the distribution of the Cu3d and O2 _p densities and in the spectral parameters of the samples are discussed.     

A new look at energy release rate in fracture mechanics

The energy balance for fracture in elastic/perfectly plastic solids is examined using the finite element method. An extension-release procedure that gives numerically converged solutions is employed in the numerical simulation of crack extensions in elastic/plastic solids. Increments of work and energy during crack extension are calculated for various loading conditions. Several conclusions are obtained. First, the elastic separation work of creating new crack surfaces is shown to be negligible, indicating that the Griffith-type energy release does not exist. Second, as the yield stress increases, the plastic dissipation work rate associated with crack extension converges to the energy release rate in the limiting elastic solid. The latter result can be adopted to interpret the classical energy release rate in elastic solids as plastic dissipation work rate taken in the limit as the yield stress approaches infinity during crack extension. Lastly, it is shown that the energy release rate obtained according to Irwin's plastic zone adjustment approach is equal to the plastic dissipation work rate for the original crack, provided the plastic zone size is less than 10% of the original crack size.     

A new look at the effect of bandwidth and non-normality on fatigue damage

A new attempt is made in this paper to quantify the effect of bandwidth and non‐normality in fatigue damage analysis. For the lack of actual stress history, a series of non‐Gaussian and homogeneous random processes are generated with fast Fourier transform (FFT) acceleration. A factor is defined on the basis of rain‐flow counting and Palmgren–Miner rule to correct the narrow band and normality assumption. It is revealed that the fatigue damage evaluated through the traditional method may be either conservative or rather unconservative. The upper and lower bounds of the correction factor are studied with respect to kurtosis and skewness of the generated random process and the slope of S–N curve.     

Collective mode dynamics of the vortex lattice in a highT c superconductor

Dispersion relations have been obtained numerically for the collective modes of the flux line lattice of a highT _c superconductor in the London limit and the effect of pinning forces is included. It is found that the waves propagating along the magnetic field the dispersion consists of two branches and that the low frequency branch may interact with other low-frequency excitations in the lattice.     

A close look at proteins: submolecular resolution of two- and three-dimensionally folded cytochrome c at surfaces

Imaging of individual protein molecules at the single amino acid level has so far not been possible due to the incompatibility of proteins with the vacuum environment necessary for high-resolution scanning probe microscopy. Here we demonstrate electrospray ion beam deposition of selectively folded and unfolded cytochrome c protein ions on atomically defined solid surfaces in ultrahigh vacuum (10(-10) mbar) and achieve unprecedented resolution with scanning tunneling microscopy. On the surface folded proteins are found to retain their three-dimensional structure. Unfolded proteins are observed as extended polymer strands displaying submolecular features with resolution at the amino acid level. On weakly interacting surfaces, unfolded proteins refold into flat, irregular patches composed of individual molecules. This suggests the possibility of two-dimensionally confined folding of peptides of an appropriate sequence into regular two-dimensional structures as a new approach toward functional molecular surface coatings.     

Photoemission spectroscopy of high-T c superconductors: Proofs in favor of the impurity mechanism

A new interpretation of photoemission spectroscopy data is proposed. It is based on the impurity mechanism of high-temperature superconductivity proposed earlier. The band observed near the Fermi level in this interpretation is the impurity band, and the observed large “Fermi surface” is the surface of the mobility edge, different in different directions. Many other details are also explained naturally.     

新型包埋微生物材料-室温交联聚丙烯酰胺的合成

首先合成低分子量的聚丙烯酰胺，再用甲醛使其羟甲基化，最后羟甲基化聚丙烯酰胺和丙烯酰胺缩合得到可室温交联的聚丙烯酰胺。研究了反应物摩尔比、反应温度、反应时间和溶液pH值等因素对羟甲基化和缩舍反应的影响，确定了最佳反应条件。这种改性聚丙烯酰胺的水溶液和交联剂于室温可快速交联得到凝胶体。该工艺的优点是对微生物细胞无毒性，聚合（包埋）温度低，交联发生在侧链使抗水解性增强。