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31.
Non-resonant microwave absorption (NRMA) studies of superconducting MgB2 and a sample containing ∼10% by weight of MgO in MgB2 are reported. The NRMA results indicate near absence of intergranular weak links in the pure MgB2 sample. A linear temperature dependence of the lower critical field H
c1 is observed indicating a non-s wave superconductivity. However, the phase reversal of the NRMA signal which could suggest d wave symmetry is also not observed. In the MgB2 + MgO sample, much larger low field dependent absorption is observed indicating the presence of intergranular weak links.
The hysteretic behavior of NRMA is compared and contrasted in the two samples. In the pure MgB2 sample, a large hysteresis is observed between the forward and the reverse scans of the magnetic field indicating strong
pinning of flux lines. This hysteresis saturates a few degrees below T
c while in the MgB2 + MgO sample, a much slower increase of hysteresis with decreasing temperature is observed, a signature of weaker pinning. 相似文献
32.
33.
Ala'a K. Abdul-Sada Anthony M. Greenway Kenneth R. Seddon Thomas Welton 《Journal of mass spectrometry : JMS》1993,28(7):759-765
Previous studies of 1-ethyl-3-methylimidazolium chloride–aluminium(III) chloride ([emim]Cl–AlCl3) ionic liquids have been hampered by significant contamination of these liquids by oxide impurities. Treatment of these liquids with phosgene removes the oxide impurities, and the use of a specially constructed sample inlet system for air-sensitive materials permitted them to be studied by fast atom bombardment mass spectrometry. The ions Cl?, [Cl2]?, [AlCl4]?, [Al2Cl7]?, [emim]+ and [(emim)2X]+ (X = Cl or AlCl4) were observed for the basic ionic liquid. In addition, the anion [Al3Cl10]? was observed for the acidic composition. Within the mass spectrometer, the hydrolyses of [Al3Cl10]? to produce [Al3Cl8O]? and of [Al2Cl7]? to produce [Al2Cl5O]? were observed. Comparison of these results with published 17O NMR data suggests that the primary hydrolysis products in acidic ionic liquids are [Al3Cl8O]? and [Al2Cl5O]? and that the principal secondary hydrolysis product is [Al2Cl6(OH)]?. 相似文献
34.
This paper is concerned with an experimental investigation of a comparison of the rheological performance of an ER fluid, consisting of a carrier with a range of solid phase sizes, in oscillatory squeeze-flow under DC conditions. The fluid is sandwiched between two parallel plane electrodes, the upper one stationary and the lower one oscillating normal to its plane. It is seen that the dynamic performance of the fluid, in terms of the capacity for the transmission of imposed forces across the fluid, is highly dependent on the size of the dispersed solid phase and has an optimum value which is dependent on the mean value of the interelectrode gap. In addition the paper includes some measurements of the current through the fluid which may help to shed some further light on the mechanism of the ER effect. Finally the implications of the results to vibration control are discussed. Copyright 1999 Academic Press. 相似文献
35.
Densities ρ and ultrasonic speeds u of the binary mixtures of tetrahydrofuran (THF) with 1-butanol and tert-butanol, at 30°C, over the entire composition range
were measured. From these data isentropic compressibility, K
s, intermolecular free length L
f, relative association R
A, acoustic impedance Z, molar sound speed R
m, deviations in isentropic compressibility ΔK
s, and excess volume V
E were calculated. The variation of these parameters with composition of the mixture helps us in understanding the nature and
extent of interaction between unlike molecules in the mixtures. Further, theoretical values of ultrasonic speed were evaluated
using theories and empirical relations. The relative merits of these theories and relations were discussed. 相似文献
36.
We study the rheology of semi-dilute solutions of the sodium salt of calf-thymus DNA in the linear and nonlinear regimes.
The frequency response data can be fitted very well to the hybrid model with two dominant relaxation times τ0 and τ1. The ratio (τ0/τ1) ∼5 is seen to be fairly constant on changing the temperature from 20 to 30°C. The shear rate dependence of viscosity can
be fitted to the Carreau model. 相似文献
37.
Ala'a K. Abdul-Sada Anthony M. Greenway Kenneth R. Seddon Thomas Welton 《Journal of mass spectrometry : JMS》1989,24(10):917-918
A negative-ion fast-atom-bombardment mass spectrometric study of the room temperature chloroaluminate ionic liquids AlCl3-[MeEtim]Cl ([MeEtim]+ = 1-methyl-3-ethylimidazolium cation) has produced the first unambiguous experimental evidence for the existence of [Al3C110]?. 相似文献
38.
Vandana Tripathi Lagy T Baby PV Madhusudhana Rao SK Hui R Singh JJ Das P Sugathan N Madhavan AK Sinha 《Pramana》1999,53(3):535-539
The ground state and excited state transfer yields for the 2-neutron pickup channel in the 28Si+68Zn system have been measured explicitly. The recoil mass separator at the nuclear Science Centre, New Delhi was used for the
measurement. A NaI(T1) detector was used for detecting the deexcitation γ’s from the transfer products. The kinematic coincidence technique was employed for the transfer measurement. Simplified coupled
channels calculations show that out of all transfer channels the major contribution to the sub-barrier enhancement comes from
the ground state 2 neutron pickup channel with a ground state Q-value of+1.83 MeV. 相似文献
39.
A comparative study of the thermomagnetic memory effects of J
c in two weakly pinned low T
c superconductors, Ca3Rh4Sn13 (CaRhSn) and Yb3Rh4Sn13 (YbRhSn), is presented. In both the systems, the peak effect (PE) phenomenon appears as an order-disorder transformation
through stepwise amorphization of the flux line lattice (FLL). However, in CaRhSn. we can witness another disorder-driven
transition (Bragg glass (BG) to a vortex glass (VG) in a distinct manner as in a single crystal of high T
c YBa2Cu3O7-δ for H‖c. 相似文献