Effect of Pr-Ca substitution on the transport and magnetic behavior of LaMnO3 perovskite

The effect of simultaneous substitution of a fluctuating cation and a divalent cation in LaMnO₃ perovskite modifies the properties of the material to exhibit large valence colossal magnetoresistance (CMR) effect. A good example of these properties is (La_1−2x Pr _x Ca _x )MnO₃ (LPCMO) type CMR material. In this communication it is reported that, with the increase in x (for x=0.1, 0.15, 0.2), the T _c varies between 100 and 120 K with improvisation in metal-insulator transition. Interestingly, resistance increases with x from few hundred ohms to few kilo ohms with corresponding decrease in the unit cell volume. The results of the studies using X-ray diffraction (XRD), electrical resistivity, magnetoresistance and ac susceptibility measurements on LPCMO samples for understanding the structural, transport and magnetic properties are discussed in detail.     

Cold and warm white light generation using Zn(PO3)2 glasses activated by Ce3+, Dy3+ and Mn2+

The photoluminescence of zinc metaphosphate glasses activated by Dy³⁺, Ce³⁺/Dy³⁺ and Ce³⁺/Dy³⁺/Mn²⁺ ions was investigated. Non-radiative energy transfers from Ce³⁺ to Dy³⁺ and Ce³⁺ to Mn²⁺ are observed upon 280 nm excitation. The non-radiative nature of these transfers is inferred from the increase in the decay rate of the Ce³⁺ emission when the glass is co-doped with Dy³⁺ or Dy³⁺/Mn²⁺. It is demonstrated that zinc metaphosphate glasses can generate cold or warm white light emission when they are doped with Ce³⁺/Dy³⁺ or Ce³⁺/Dy³⁺/Mn²⁺ and pumped at 280 nm (peak emission wavelength of AlGaN-based LEDs). The CIE1931 chromaticity coordinates and color temperature were (0.34, 0.35) and 5250 K for the cold light, and (0.47, 0.43) and 2700 K for the warm light.     

Cold white light generation through the simultaneous emission from Ce3+, Dy3+ and Mn2+ in 90Al2O3·2CeCl3·3DyCl3·5MnCl2 thin film

The photoluminescence of a CeCl₃, DyCl₃ and MnCl₂ doped aluminum oxide film deposited by ultrasonic spray pyrolysis was characterized by excitation, emission and decay time spectroscopy. A nonradiative energy transfer from Ce³⁺ to Dy³⁺ and Mn²⁺ is observed upon UV excitation at 278 nm (peak emission wavelength of AlGaN-based LEDs). Such energy transfer leads to a simultaneous emission of these ions in the blue, green, yellow and red regions, resulting in white light emission with CIE1931 chromaticity coordinates, x=0.34 and y=0.23, which correspond to cold white light with a color temperature of 4900 K.     

关于K个复相关矩阵相等的检验

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How well do Monte Carlo simulations distinguish between U(1) and SU(2)?: A study of the string tension in U(1) lattice gauge theory

To investigate how a system with a known deconfining phase transition behaves when studied on finite lattices via Monte Carlo simulations, we have made such studies of compact U(1) lattice gauge theory for 8⁴, 10⁴, and 12⁴ lattices. We have concentrated on the mean plaquette energy and the string tension. The string tension does not vanish on a finite lattice, but using finite size scaling arguments the indications are that it does vanish on an infinite lattice, where we predict the critical coupling β_c = 1.008 and the correlation length exponent $\text{ν =}\text{1}\text{3}$. We compare our results to those for SU(2) and find that although there are differences, they are not yet definitive.     

Structural studies and T c dependence in La2−x Dy x Ca y Ba2Cu4+y O z type mixed oxide superconductors

A new series of mixed oxide superconductors with the stoichiometric composition La_2−x Dy _x Ca _y Ba₂Cu_4+y O _z (x=0.0 − 0.5, y=2x) has been studied for structural and superconductiong properties. Our earlier studies on La_2−x (Y/Er) _x Ca _y Ba₂Cu_4+y O _z series, show a strong dependence of T _c on hole concentration (p _sh). In the present work, the results of the analysis of the neutron diffraction measurements at room temprerature on x=0.3 and 0.5 samples are reported. It is interesting to know that Ca substitutes for both La and Ba site with concomitant displacement of La onto Ba site. Superconductivity studies show that maximum T _c is obtained for x=0.5, y=1.0 sample (T _c ∼ 75 K), for La_1.5Dy_0.5Ca₁Ba₂Cu₅O _z (La-2125).     

The classical su(2) invariance of the su(2) q -invariant XXZ spin chain

The XXZ spin-chain Hamiltonian has been constructed to be su(2) _q -invariant, but naively does not appear to be su(2)-invariant. However, using recently discovered deforming maps between representations of su(2) _q and corresponding representations of su(2), we prove a theorem which states that if a Hamiltonian is su(2) _q -invariant, it is also su(2)-invariant. The theorem generalizes to any quantized Lie algebra.