Self-injection length in La0.7Ca0.3MnO3-YBa2Cu3O7-δ ferromagnet-superconductor multilayer thin films

We have carried out extensive studies on the self-injection problem in barrierless heterojunctions between La_0.7Ca_0.3MnO₃ (LCMO) and YBa₂Cu₃O_7-δ (YBCO) thin films. The heterojunctions were formed in situ by sequentially growing LCMO and YBCO films on 〈100〉 LaAlO₃ (LAO) substrate using a pulsed laser deposition (PLD) system. YBCO micro-bridges with 64 μm width were patterned both on the LAO (control) and LCMO side of the substrate. Critical current, I _c, was measured at 77 K on both the control side as well as the LCMO side for different YBCO film thickness. It was observed that while the control side showed a J _c of ∼ 2 × 10⁶ A/cm², the LCMO side showed about half the value for the same thickness (1800 ?). The difference in J _c indicates that a certain thickness of YBCO has become ‘effectively’ normal due to self-injection. From the measurement of J _c at two different thicknesses (1800 ? and 1500 ?) of YBCO films both on the LAO as well as the LCMO side, the value of self-injection length (at 77 K) was estimated to be ∼ 900 ?. To the authors’ best knowledge, this is the first time that self-injection length has been quantified. A control experiment carried out with LaNiO₃ deposited by PLD on YBCO did not show any evidence of self-injection.     

Solution of the dilaton problem in open bosonic string theories

All string theories naively contain a massless dilaton which couples with the strength of gravity in direct violation of experiment. We present a simple mechanism for giving the dilaton a mass In unoriented open bosonic string theories.This essay received an honourable mention from the Gravity Research Foundation, 1990. — Ed.     

Strong Direct Magnetic Coupling in a Dinuclear CoII Tetrazine Radical Single‐Molecule Magnet

The ligand‐centered radical complex [(CoTPMA)₂‐μ‐bmtz^.?](O₃SCF₃)₃ ? CH₃CN (bmtz=3,6‐bis(2′‐pyrimidyl)‐1,2,4,5‐tetrazine, TPMA=tris‐(2‐pyridylmethyl)amine) has been synthesized from the neutral bmtz precursor. Single‐crystal X‐ray diffraction studies have confirmed the presence of the ligand‐centered radical. The Co^II complex exhibits slow paramagnetic relaxation in an applied DC field with a barrier to spin reversal of 39 K. This behavior is a result of strong antiferromagnetic metal–radical coupling combined with positive axial and strong rhombic anisotropic contributions from the Co^II ions.     

六元gcd封闭集上Smith矩阵的整除性

我们给出了关于六元gcd封闭集S的充分必要条件,使得在整数矩阵环M_6(Z)中,定义在S上的e次幂GCD矩阵(S~e)整除e次幂LCM矩阵[S~e].这部分解决了Hong在2002年提出的一个公开问题.     

Acoustic absorption and dynamic compressibility studies of dilute and concentrated solutions of polystyrene in toluene and cyclohexane

Acoustic absorption and adiabatic compressibility measurements are reported on solutions of polystyrene (M_n = 89,000) in toluene and cyclohexane. The data in toluene cover a temperature range from 293 to 343°K and a concentration range of 10–400 Kg m^?3 (1–40 wt%). The dependence of acoustic absorption on concentration was found to be linear up to 100 kg m^?3, which corresponds to the concentration at which polymer–polymer interactions cause significant changes in the specific viscosity-concentration relationship. Up to 200 kg m^?3 the data could be fitted to computations based on an artificial separation of the dispersion into contributions from viscoelastic and segmental processes, using parameters obtained from a study of narrow molecular weight distribution samples at 25 kg m^?3. However, neither approach was capable of describing dispersions in the 300, 400 kg m^?3 solutions. The modification of the relaxation spectrum observed at the highest concentrations is ascribed to volume and entropy changes associated with alterations of the local environment around a segment of the polymer chain. These changes have their origin in interchain penetration and polymer–polymer contacts, and indicate that ‘entanglement’ is primarily entropic in effect. The adiabatic compressibility exhibited similar deviations from a simple concentration dependence, and allowed estimation of an incompressible volume increment associated with polymer–polymer interactions in the high-concentration entangled matrix. However, the adiabatic compressibilities of solutions of polystyrene, 10–15 kg m^?3, in cyclohexane showed no deviations from simple behavior in the region of the theta temperature. Measurements of the adiabatic compressibility of polystyrene in mixtures of cyclohexane-toluene have been used to obtain the relative magnitude of solvent and polymer contributions to the excess compressibility.     

Wavelength-resolved fluorescence lifetimes of gas-phase ions: CO2+ and CS2+

A method is described for measuring wavelength-resolved fluorescence lifetimes of ions formed by HeIα photoionization, using electric-field drift of the ions in competition with fluorescence. Fluorescence lifetimes of 216 and 232 ns for the 357 nm and 378 nm peaks of N₂O⁺, and 3.5 μs for the à → X? band of CS₂⁺, were measured. The wavelength-resolved à → X? band of CO₂⁺ showed no significant dependence of fluorescence lifetime on V′, but there is some indication of variation in the CS₂⁺ lifetimes in the à → X? band.     

Compactification on non-symmetric six dimensional coset spaces with torsion

The equations of motion of a ten dimensional model based on the Chapline-Manton lagrangian, modified by higher derivative terms, are solved using six dimensional coset spaces with torsion. Minkowski space, anti-de Sitter, de Sitter and Einstein static cosmology with negative curvature are possible four dimensional cosmologies. In all case symmetry breaking schemesE ₈×E ₈→E ₈×E ₆ with chiral 27's ofE ₆ can be obtained.