Relationship between T c and electronegativity differences in compound superconductors

The electronegativity differences, Delta" align="BASELINE" BORDER="0">N, between the anions and the cations in suggested resonating elements of some representative high-temperature superconductors with T _c - 10 K are evaluated adopting Pauling's scale. The relationship between Delta" align="BASELINE" BORDER="0">N and T _c was found to separate all the examined high-T _csuperconductors onto two curves: One for the cuprate superconductors having two-dimensional layered structures was a straight line, T _c=29.8+4.1Delta" align="BASELINE" BORDER="0">N; the other correlation curve representing the remaining compound superconductors including the doped 113 perovskite and the perovskite-related 214 structures was at lower T _c values but also suggested that increasing electronegativity differences was related to increasing T _c.This work was supported by the Director, Office of Energy Research, Office of Basic Energy Sciences, Materials Sciences Division of the U.S. Department of Energy under Contract No. DE-AC03-76SF00098     

A Photochemical Approach to a Potential Precursor of the Bicyclo [6.4.0] Dodecane Ring System of Taxane Diterpenes

The intermolecular [2+2] photocycloaddition of dimedone 6 and 1-acetoxy-2-methyl-5-dioxolan-1-hexene 7 followed by alkaline treatment, gave the 1,5,5,11-tetramethyl-7-dioxolan bicyclo [4,3,2]-4-decen-2,3-dione 12, and the 1,5,5-trimethyl-3-hydroxy-7-dioxolan bicyclo [5,4,1] dodecan-2,11-dione 13.     

Stability of polymer thin-film transistors based on poly(2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene)

Polymer thin-film transistors (PTFTs) based on poly(2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene) (MEH-PPV) semiconductor are fabricated by spin-coating process and characterized. In the experiments, solution preparation, deposition and device measurements are all performed in air for large-area applications. Hysteresis effect and gate-bias stress effect are observed for the devices at room temperature. The saturation current decreases and the threshold voltage shifts toward the negative direction upon gate-bias stress, but carrier mobility hardly changes. By using quasi-static C-V analysis for MOS capacitor structure, it can be deduced that the origin of threshold-voltage shift upon negative gate-bias stress is predominantly associated with hole trapping within the SiO₂ gate dielectric near the SiO₂/MEH-PPV interface due to hot-carrier emission.     

Legendre Transformation for Regularizable Lagrangians in Field Theory

Hamilton equations based not only upon the Poincaré–Cartan equivalent of a first-order Lagrangian, but also upon its Lepagean equivalent are investigated. Lagrangians which are singular within the Hamilton–De Donder theory, but regularizable in this generalized sense are studied. Legendre transformation for regularizable Lagrangians is proposed and Hamilton equations, equivalent with the Euler–Lagrange equations, are found. It is shown that all Lagrangians affine or quadratic in the first derivatives of the field variables are regularizable. The Dirac field and the electromagnetic field are discussed in detail.     

Properties of Strain Compensated Symmetrical Triangular Quantum Wells Composed of InGaAs/InAs Chirped Superlattice Grown Using Gas Source Molecular Beam Epitaxy

We investigate the properties of symmetrical triangular quantum wells composed of InGaAs/InAs chirped superlattice, which is grown by gas source molecular beam epitaxy via digital alloy method. In the quantum well structure tensile AlInGaAs are used as barriers to partially compensate for the significant compressive strain in the wells, the strain compensation effects are confirmed by x-ray measurement. The photoluminescence spectra of the sample are dominated by the excitonic recombination peak in the whole temperature range. The thermal quenching, peak energy shift and line-width broadening of the PL spectra are analysed in detail, the mechanisms are discussed.     

Metastable state and macroscopic quantum tunneling of binary mixtures

We provide a mixing model to explore the metastable state and the macroscopic quantum tunneling (MQT) of binary mixtures. For , we first observe the two condensates form the symmetry-breaking state (SBS) and then suddenly transfer to the symmetry-preserving state (SPS) through the MQT. The SBS is shown to be the metastable state in our system. We find the MQT does not spontaneously arise. The inducement mechanism is the damping but not the excitations. The damping mechanism can also control the lifetime and the tunneling decay rate of the SBS. Finally, we further present the origin of these phenomena by examining the energy of the system.     

AlGaInAs/InP eye-safe laser pumped by a Q-switched Nd:GdVO<Subscript>4</Subscript> laser

An AlGaInAs quantum-well structure grown on a Fe-doped InP transparent substrate is developed to be a gain medium in a high-peak-power nanosecond laser at 1570 nm. Using an actively Q-witched 1064 nm laser to pump the gain chip, an average output power of 135 mW is generated at a pulse repetition rate of 30 kHz and an average pump power of 1.25 W. At a pulse repetition rate of 20 kHz, the peak output power is up to 290 W at a peak pump power of 2.3 kW.     

Optimized temperature measurement with time-of-flight method

Driven by resonance probe light background Rubidium gas can emit fluorescence, which interacts with the falling atomic cloud in the temperature measurement with the time-of-flight (TOF) method and influence the experimental results. The dependencies of the acceleration and the temperature of the atomic cloud on the detuning of the probe beams were studied. We propose that the deviation of the acceleration from the gravity acceleration can be taken as a criterion of the accuracy of the temperature measurement using TOF method. Moreover, using the principle of the radiation force on the cold atomic cloud, one may measure the considerably weak intensity of the fluorescence.