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).     

Poisson-type multiplicity distribution and the Giovannini-Van Hove model

Properties of a Poisson-type distribution satisfying the same recurrence relation as the negative binomial distribution are investigated using the charged multiplicity data of \(\bar p\) p,pp, π+ p,K ⁺ p ande ⁺ e ^? interactions. Its two parameters are found to deviate significantly from the predictions of the Giovannini-Van Hove model. Remarks are made on the property of quark content of the multiplicity due to fragmentation of colliding particles such asp,π/K ande under investigation.     

Cross-sections of high energy nuclear reactions

Cross-sections of high-energy hadron-nucleus reactions σ _h (A) are investigated using ther optical model. A closed formula is drived for σ _h (A); itsA-dependence agrees with the rms radius of the Fermi distribution of nuclear matter. The properties of the radius parameter and the absorption mean free pathλ _h are investigated using Serpukhov data forp, π^α,K ^± , and \(\bar p\) . It is foundλ _p =1.44 ± 0.23 fm ～-1/m _π andλ _π =2.14 ± 0.21 fm forp and π-reactions, respectively; withλ _π /λ _p ?3/2 as expected from quark-counting. The approach extended to heavyion (HI) reactions leads to a formula of Bradt-Peters type, with an overlapping parameter decreasing withA. Analyses of HI data of LBL and ISR with this formula are presented.     

A facile synthesis of perfluoroalkyl vinyl iodides and their palladium-mediated cross-coupling reactions

Catalytic amounts of zinc, as low as 10 mol %, in the presence of trifluoroacetic acid (TFA) initiate the radical addition of perfluoroalkyl iodides to terminal alkynes with high regio- and stereoselectivities. Palladium-mediated cross-coupling of these (E)-perfluoroalkyl vinyl iodides allows for a facile synthesis of potentially useful fluoroorganic intermediates.     

Solvent effects on oxygen-17 chemical shifts in methyl formate: linear solvation shift relationships

A multiple linear regression analysis has been carried out using the Kamlet-Abboud-Taft solvatochromic parameters in order to quantify the solvent effects on the (17)O chemical shifts of methyl formate (MF). The influence of the solvents upon the carbonyl oxygen chemical shifts is smaller for MF than for N-methylformamide (NMF). The influence (in parts per million) of the solvent polarity-polarizability reduces from -21.9pi* in amides to -9.6pi* in MF. The influence of the solvent hydrogen-bond-donor acidities reduces from -42.0alpha in formamides to -16.9alpha in MF. The solvent effects upon the dicoordinated oxygen chemical shifts of MF are smaller in magnitude and opposite in direction, i.e., 4.8pi* and 2.6alpha, than those for the carbonyl oxygen. (17)O hydration shifts have been calculated for the NMF + (H(2)O)(6) and MF + (H(2)O)(5) complexes by the ab initio GIAO method at the 6-311 + G** level. The hydration shifts calculated for the carbonyl oxygens of NMF and MF and for the dicoordinated oxygen of MF, -102.4, -64.7, and 17.6 ppm, respectively, show the same trend as the corresponding empirical hydration shifts, -101.7, -42.0, and 14.2 ppm.