Polaronic Effect and Its Impact on <Emphasis Type=Italic>T</Emphasis><Subscript><Emphasis Type=Italic>c</Emphasis></Subscript> for Novel Layered Superconducting Systems

The crystal lattice of a complex compound may contain a subsystem of ions with each one possessing two close equilibrium positions (double-well structure). For example, the oxygen ions in the cuprates form such a subsystem. In such a situation it is impossible to separate electronic and local vibrational motions. This leads to a large increase in the effective strength of the electron–lattice interaction, which is beneficial for pairing.     

Repulsion and Attraction in High <Emphasis Type=Italic>T</Emphasis><Subscript>c</Subscript> Superconductors

The influence of repulsion and attraction in high-T _c superconductors to the gap functions is studied. A systematic method is proposed to compute the gap functions using the irreducible representations of the point group. It is found that a pure s-wave superconductivity exists only at very low temperatures, and attractive potentials on the near shells significantly expand the gap functions and increase significantly the critical temperature of superconductivity. A strong on-site repulsion drives the A _1g gap into a B _1g gap. It is expected that superconductivity with the A _1g symmetry reaches a high critical temperature due to the cooperation of the on-site and the next-nearest neighbor attractions.     

Progress in Critical Current Density (<Emphasis Type="Italic">J</Emphasis><Subscript><Emphasis Type="Italic">c</Emphasis></Subscript>) in Sintered MgB<Subscript>2</Subscript> Bulks

The present paper focuses on methods of further improving the flux pinning and critical current density of disk-shaped MgB₂ bulk superconductors by adding excess Mg metal in combination with an optimum silver content and optimized processing conditions. Bulk MgB₂ samples were produced by in situ solid-state reaction in Ar gas ambient using high purity commercial powders of Mg metal and 1.5 wt% carbon-coated amorphous B powders mixed in a fixed ratio of Mg/B = 1.1:2. Further, 4 wt% silver was added to improve flux pinning as well as mechanical performance of the bulk MgB₂ material. The magnetization measurements confirmed a sharp superconducting transition with T_c,onset at around 37 K, which is only by 1 K lower than in bulk MgB₂ material produced without carbon-coated amorphous boron. The critical current density (J_c) values significantly improved in the MgB₂ material with 4 wt% of silver and 1.5 wt% of carbon-coated amorphous boron, sintered at 775 ^°C for 3 h. At 20 K, this sample showed J_c at around 500 and 350 kA/cm² in the self-field and 1 T, respectively, which makes it suitable for several industrial applications.     

Kink State in a Stack of Intrinsic Josephson Junctions in Layered High-<Emphasis Type=Italic>T</Emphasis><Subscript><Emphasis Type=Italic>c</Emphasis></Subscript> Superconductors and Terahertz Radiation

A new family of dynamic states are found in a stack of inductively coupled intrinsic Josephson junctions in the absence of an external magnetic field. In this state, (2m _l +1)π phase kinks with integers m _l ’s stack along the c axis and lock neighboring junctions together. A significant part of the dc power is pumped into plasma oscillations via kinks at the cavity resonances. The plasma oscillation is uniform along the c axis with the frequency satisfying the ac Josephson relation. Thus this state supports strong terahertz radiation and seems to be compatible with the recent experimental observations.     

Half-Metallicity and High-<Emphasis Type=Italic>T</Emphasis><Subscript>c</Subscript> Ferromagnetism in Si-containing Half-Heusler Alloys

A possibility of half-metallic ferromagnetism for the homogeneous phase in the half-Heusler alloy-based DMS CoTi_1−x Fe _x Sb is predicted. A phase diagram of the spinodal and binodal decomposition is constructed through the evaluation of the mixing free energies. By applying the Monte Carlo simulation method to the Ising model with realistic chemical pair interactions between Fe magnetic impurities, we simulate the spinodal decomposition and nanoscale separation in this alloy.     

Symmetry of Superconductivity in YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7</Subscript>: <Emphasis Type=Italic>s</Emphasis> or <Emphasis Type=Italic>d</Emphasis>

The superconducting hole condensate of YBa₂Cu₃O₇ resides in its BaO layers, and involves s-wave paired holes. This picture differs from the currently widespread opinion that the superconductivity at the surface and in the bulk is d-like, and resides in the CuO₂ planes: it is the main reason why high-temperature superconductivity has been unsolved.     

Thermal decomposition of trimethylamine borane as a precursor to nanocrystalline CVD BC<Subscript><Emphasis Type=Italic>x</Emphasis></Subscript>N<Subscript><Emphasis Type=Italic>y</Emphasis></Subscript> films

We have studied the kinetics of BC _x N _y chemical vapor deposition through trimethylamine borane decomposition at atmospheric pressure. The rate constant of the heterogeneous interaction between trimethylamine borane and an adsorption center has been determined to be k _s ⁰ = 2.7 × 10⁷exp(−10560/T) cm/s. The obtained kinetic parameters of the reaction fully determine the growth rate of nanocrystalline carbonitride films under kinetic control. The film thickness has been determined as a function of time, temperature, reactant concentration, and reactor dimensions.     

The thermodynamic properties of liquid binary mixtures of <Emphasis Type=Italic>n</Emphasis>-alkanes: <Emphasis Type=Italic>n</Emphasis>-decane + <Emphasis Type=Italic>n</Emphasis>-hexadecane

Data on sound velocity are used for determining the density, the isobaric expansion coefficient, the isobaric and isochoric heat capacity, and the isothermal compressibility of liquid binary mixture of n-decane + n-hexadecane of three compositions in the temperature range of 298–433 K and pressure range of 0.1–100 MPa. The coefficients of Tait equation are calculated in the above-identified range of parameters. The calculation results are compared with experimental data on density. The divergence does not exceed 0.2% for the most reliable data.     

Dependence of Microstructure and <Emphasis Type="Italic">J</Emphasis><Subscript>c</Subscript> of YBCO Films on CeO<Subscript>2</Subscript> Cap Layers Deposited by Multi-plume PLD

In order to achieve high-performance YBa₂Cu₃O_7?x (YBCO)coated conductors (CCs) fabricated in industrial scale, it is necessary to enhance the transport properties and production speed of the CCs for use in various application forms. The transport performance of CCs depends upon the inner structure of the conductors, which make it important to analyze the microstructure and transport properties. The thickness of the buffer layer is a factor in improving speed. In this work, we deposited YBCO films on CeO₂ cap layers with different thicknesses ranging from 21 to 563 nm by multi-plume pulsed laser deposition (PLD) and investigated the dependence of the microstructure and superconducting properties of YBCO film on the thickness of CeO₂ films. The crystalline structure and surface morphology of YBCO films are systematically characterized by means of XRD, AFM, SEM and TEM. The critical current of YBCO film was measured by the conventional four-probe method at 77 K, in self-field. The results showed that the microstructure and superconducting performance of YBCO film were strongly dependent on the thickness of CeO₂ films. At the optimal CeO₂ layer thickness of 221 nm, the YBCO film exhibited a sharp in-plane and out-of-plane texture of full width at half maximum (FWHM) values of 1.5° and 2.4°, respectively, and smooth morphology of root mean square (RMS) value as low as 4.0 nm. The sharply biaxially textured YBCO films with the critical current density as high as 4.7 × 10⁶ A/cm² (77 K, in self-field) were obtained on CeO₂/MgO/Y₂O₃/Al₂O₃/C276 architecture.     

Pulsed cathodoluminescence of <Emphasis Type=Italic>F</Emphasis><Subscript>2</Subscript> centers in undoped and doped LiF crystals

This work examines the generation of F ₂ centers in LiF, LiF〈O,OH〉, and LiF:U〈O,OH〉 crystals by electron pulses at 300 K. We discuss nanosecond and microsecond mechanisms for the excitation of pulsed cathodoluminescence of F ₂ centers in the crystals.     

<Emphasis Type=Italic>hg</Emphasis>-index: a new index to characterize the scientific output of researchers based on the <Emphasis Type=Italic>h</Emphasis>- and <Emphasis Type=Italic>g</Emphasis>-indices

To be able to measure the scientific output of researchers is an increasingly important task to support research assessment decisions. To do so, we can find several different measures and indices in the literature. Recently, the h-index, introduced by Hirsch in 2005, has got a lot of attention from the scientific community for its good properties to measure the scientific production of researchers. Additionally, several different indicators, for example, the g-index, have been developed to try to improve the possible drawbacks of the h-index. In this paper we present a new index, called hg-index, to characterize the scientific output of researchers which is based on both h-index and g-index to try to keep the advantages of both measures as well as to minimize their disadvantages.     

Comparative Experimental and Density Functional Theory (<Emphasis Type="Italic">DFT</Emphasis>) Study of the Physical Properties of MgB<Subscript>2</Subscript> and AlB<Subscript>2</Subscript>

In the present study, we report an intercomparison of various physical and electronic properties of MgB₂ and AlB₂. In particular, the results of phase formation, resistivity ρ(T), thermoelectric power S(T), magnetization M(T), heat capacity (C _P ), and electronic band structure are reported. The original stretched hexagonal lattice with a=3.083 Å, and c=3.524 Å of MgB₂ shrinks in c-direction for AlB₂ with a=3.006 Å, and c=3.254 Å. The resistivity ρ(T), thermoelectric power S(T) and magnetization M(T) measurements exhibited superconductivity at 39 K for MgB₂. Superconductivity is not observed for AlB₂. Interestingly, the sign of S(T) is +ve for MgB₂ the same is ?ve for AlB₂. This is consistent with our band structure plots. We fitted the experimental specific heat of MgB₂ to Debye–Einstein model and estimated the value of Debye temperature (Θ _D) and Sommerfeld constant (γ) for electronic specific heat. Further, from γ, the electronic density of states (DOS) at Fermi level N(E _F) is calculated. From the ratio of experimental N(E _F) and the one being calculated from DFT, we obtained value of λ to be 1.84, thus placing MgB₂ in the strong coupling BCS category. The electronic specific heat of MgB₂ is also fitted below T _c using α-model and found that it is a two gap superconductor. The calculated values of two gaps are in good agreement with earlier reports. Our results clearly demonstrate that the superconductivity of MgB₂ is due to very large phonon contribution from its stretched lattice. The same two effects are obviously missing in AlB₂, and hence it is not superconducting. DFT calculations demonstrated that for MgB₂, the majority of states come from σ and π 2p states of boron on the other hand σ band at Fermi level for AlB₂ is absent. This leads to a weak electron phonon coupling and also to hole deficiency as π bands are known to be of electron type, and hence obviously the AlB₂ is not superconducting. The DFT calculations are consistent with the measured physical properties of the studied borides, i.e., MgB₂ and AlB₂.     

Superconducting State Parameters of MgB<Subscript>2</Subscript>: <Emphasis Type="Italic">Ab Initio</Emphasis> Study

Harrison’s first principle pseudopotential (HFPP) technique in conjunction with BCS theory and McMillan’s formalism has been used for the investigation of superconducting state parameters viz., Coulomb pseudopotential μ ^∗, electron–phonon coupling strength λ, SC transition temperature T _C , interaction strength N ₀ V, semi band gap Δ, energy or mass renormalization parameter Z ₀ and isotope effect exponent δ. The ground state properties of MgB₂ have also been calculated employing full-potential linearized augmented plane wave (FLAPW) method. This enables us to estimate the equilibrium values of bulk modulus and its pressure derivative through optimization of the crystal structure of the system. We have also described the total density of state (DOS) and the partial DOS (PDOS) around the Fermi energy.     

Preparation of nanocrystalline VO<Subscript><Emphasis Type=Italic>y</Emphasis></Subscript> by high-energy ball milling

We report high-energy milling of macrocrystalline nonstoichiometric cubic vanadium monoxide (VO _y ) powder in a planetary ball mill lined with stabilized zirconia. The results indicate that milling of macrocrystalline VO _y powder at 500 rpm for more than 2 h considerably broadens diffraction line profiles, with no changes in the crystal structure of the vanadium monoxide, VO_1.00. Microstructural examination of vanadium monoxide powder by high-resolution scanning electron microscopy and X-ray diffraction indicates that high-energy ball milling can be used to produce vanadium monoxide powder with an average crystallite size within 23 nm.     

Generalization of <Emphasis Type=Italic>T</Emphasis> and <Emphasis Type=Italic>A</Emphasis> integrals to time-dependent materials: analytical formulations

This paper deals with the generalization of T-integral to crack growth process in viscoelastic materials. In order to implement this expression in a finite element software, a modelling form of this integral, called Aθ, is developed. The analytical formulation is based on conservative law, independent path integral, and a combination of real, virtual displacement fields, and real, virtual thermal fields introducing, in the same time, a bilinear form of free energy density F. According to the generalization of Noether’s method, the application of Gauss Ostrogradski’s theorem combined with curvilinear cracked contour, T _v is obtained. By introducing a volume domain around crack tip, the modelling expression Aθ is also defined.. Finally, the viscoelastic generalization through a thermodynamic approach, called A _v , is introduced by using a discretisation of the creep tensor according to a generalized Kelvin Voigt representation.     

Catalytic property of TiO<Subscript>2</Subscript>/PS complex nanoparticles prepared <Emphasis Type=Italic>via</Emphasis> a novel TSM

With an average size of 7 nm and good catalytic property under the natural light, TiO₂/PS complex nanoparticles were successfully prepared through a novel two-step method (TSM) from TiCl₄, used as both the catalyst for polymerization of styrene and Ti source, and styrene monomer and characterized by TG-DTA, XRD, IR, TEM and UV-Vis techniques. Its catalytic property was evaluated by the decolourization and degradation of dye MB solution under the natural light. From its TEM, the particles with an average size of 7 nm were observed without the separation of TiO₂ and PS phases, i.e., TiO₂/PS was hybrid material in nanosize scale. IR spectrum of TiO₂/PS showed increase of unsaturated degree and growth of the group C=O on the chain of PS and Ti–O–C coordination bond between TiO₂ and PS. The nanosize of the TiO₂/PS complex particles and the conjugated structure and polar groups of PS were advantageous to good adsorptive property and strong interaction of PS and TiO₂. And they brought multi-functions of inorganic and organic materials in the single material. Catalytic experiments indicated that the complex nanoparticles could catalytically degrade dye MB solution in 10 min under the natural light while P25 basically showed adsorptive property for MB molecules under the same conditions.     

Gravireception in <Emphasis Type=Italic>Phycomyces Blakesleeanus</Emphasis> and <Emphasis Type=Italic>Arabidopsis Thaliana</Emphasis>: Hysteretic Behavior of Primary Reactions

The gravireception of the fungus Phycomyces blakesleeanus and seedlings of Arabidopsis thaliana is accompanied by gravity-induced absorption changes (GIACs) that occur very fast and most likely represent primary responses of gravireception. GIACs that were analyzed during parabolic flights in micro- and hypergravity invariably display hysteretic behavior. Even though the identity of the pigments generating the GIACs remain presently unknown, it is nevertheless clear that they are specific for gravireception. This is strongly suggested by the fact that hystereses loops of wild-type specimen are significant larger than of gravitropic mutants. Hystereses are largely kinetically determined, are specific for the different organisms and stimulus programs, and thus aid in characterizing the requisite transduction chains of gravireception. The fact that monocot as well as dicot plants display GIACs just in the area of highest gravitropic sensitivity at the tip supports the conclusion that gravireception is generally associated with primary reactions.