Heavy fermion state and pressure-induced resistive behaviour in CeRu2Si2

Pressure-induced variation in the resistive behaviour of CeRu₂Si₂, a Kondo-lattice system, has been studied in the temperature interval 1.5K – 300K. At low temperatures, resistivity exhibits (i) a linear temperature dependence at low applied pressures (P ?2.26 kbar) and (ii) a quadratic temperature dependence

(T) ～ AT² at higher pressures (6.5 kbar ? P ? 16.8 kbar). The coefficient A decrease, which in turn implies that the spin fluctuation temperature T_sf increases, with increasing applied pressure. The temperature coefficient γ of specific heat C = γ T at low temperature (0.3K ? T ? 1.6K) is quite large (385 mJ/mole-K²) confirming the heavy fermi liquid nature of the material.     

CVT法生长GaP多晶

阐述了CVT(化学气相输运)法生长GaP的基本反应和输运速度,采用CVT法生长出了GaP多晶.设计了石英管的结构以制造出一个局部的低温区域,防止了GaP在管壁的生长.生长出的GaP多晶相对密度为98;,红外透过率达到30;,努普硬度为611kg/mm2.散射颗粒测试表明主要的光散射颗粒为多晶中存在的孔隙.     

An adeno-associated viral vector transduces the rat hypothalamus and amygdala more efficient than a lentiviral vector

Background  

This study compared the transduction efficiencies of an adeno-associated viral (AAV) vector, which was pseudotyped with an AAV1 capsid and encoded the green fluorescent protein (GFP), with a lentiviral (LV) vector, which was pseudotyped with a VSV-G envelop and encoded the discosoma red fluorescent protein (dsRed), to investigate which viral vector transduced the lateral hypothalamus or the amygdala more efficiently. The LV-dsRed and AAV1-GFP vector were mixed and injected into the lateral hypothalamus or into the amygdala of adult rats. The titers that were injected were 1 × 10⁸ or 1 × 10⁹ genomic copies of AAV1-GFP and 1 × 10⁵ transducing units of LV-dsRed.     

Effect of fiber geometry on stress in fiber-reinforced composite materials

Eleven two-dimensional photoelastic models of fiber-reinforced composite-material configurations were designed for the purpose of investigating the effects of various fiber-end shapes, various fiber arrangements and broken fibers on the shear-stress distribution in an elastic matrix. Maximum shear stresses in the matrix in the vicinity of fiber discontinuities are presented. The peak stress resulting from a gradually tapered fiber was found to be slightly higher than that from a square-ended fiber, and a round-ended fiber produced a peak stress which was slightly lower than that from the square-ended fiber. Peak stresses resulting from two square-ended fibers butted closely together were considerably higher and decreased with increasing gap length between fiber ends. It made little difference whether the gap between the butted fiber ends was open, simulating a void resulting from a broken fiber, or filled with matrix material.Paper was presented at 1966 SESA Spring Meeting held in Detroit, Mich., on May 4–6.     

Glassy spin dynamics in non-fermi-liquid UCu5-xPdx, x = 1.0 and 1.5

Local f-electron spin dynamics in the non-Fermi-liquid heavy-fermion alloys UCu5-xPdx, x = 1.0 and 1.5, have been studied using muon spin-lattice relaxation. The sample-averaged asymmetry function G(t) indicates strongly inhomogeneous spin fluctuations and exhibits the scaling G(t,H) = G(t/H(gamma)) expected from glassy dynamics. At 0.05 K gamma(x = 1.0) = 0.35+/-0.1, but gamma(x = 1.5) = 0.7+/-0.1. This is in contrast to inelastic neutron scattering results, which yield gamma = 0.33 for both concentrations. There is no sign of static magnetism approximately greater than 10(-3)(B)/U ion in either material above 0.05 K. Our results strongly suggest that both alloys are quantum spin glasses.     

Magnetic field dependence of impurity-induced muon depolarization in noble metals

We have measured the magnetic field dependence of the muon depolarization rate up to 5 kOe in AuGd (350 ppm), AgGd (340 ppm) and AgEr (300 ppm). A simple model which includes both dipolar and nearest-neighbor contact interactions between the muon and the magnetic impurity does not fit the data. An axial crystal-field interaction, arising from the electric field gradient induced by the muon at the site of the impurity, is found to dominate the Hamiltonian, and may have a large effect on the field dependence.Supported in part by the U.S. Department of Energy and the National Science Foundation.Work performed at Sandia National Laboratories supported by the U.S. Department of Energy under contract DE-AC04-76DP000789.     

Nuclear spin-lattice relaxation in the mixed state of superconducting niobium

Pulsed NMR measurements of the spin-lattice relaxation timeT ₁ have been carried out in niobium metal, in order to investigate the elementary excitation spectrum in the superconducting mixed state. The dependences ofT ₁ on temperature, external field, and mean free path were determined. The results below ～5°K were in agreement with the theory of field-induced gapless superconductivity. The best fit was obtained with a scale factor 0.35±0.2, in agreement with recent ultrasonic attenuation results. Anomalously fast relaxation was observed above ～5°K, which could not be interpreted in terms of the present theory of thermal vortex fluctuations.     

Observation of two time scales in the ferromagnetic manganite La1-xCaxMnO3, x approximately 0.3

We report new zero-field muon spin relaxation and neutron spin echo measurements in ferromagnetic (FM) (La,Ca)MnO3 which suggest at least two spatially separated regions possessing very different Mn-ion spin dynamics. One region displays diffusive relaxation, "critical slowing down" near T(C) and an increasing volume fraction below T(C), suggesting overdamped FM spin waves below T(C). The second region possesses more slowly fluctuating spins, a linewidth independent of q, and a decreasing volume fraction below T(C). The estimated length scale for the inhomogeneity is 相似文献   

Effect of modulus ratio on stress near a discontinuous fiber

The effect of the fiber to matrix modulus of elasticity ratio varying from 1.0 to 200 was investigated for a two-dimensional plane-stress composite configuration having a simulated fiber volume fraction of 0.45 and containing a discontinuous fiber. Uniaxial loading parallel to the fibers was considered. Two independent techniques were used: moiré strain analysis and finite-element analysis. Displacements were measured from four experimental models by utilizing optical fringe-multiplication techniques. The finite-element method yielded stresses which agreed closely with those obtained from the experimental analysis. Matrix stress-concentration factor near the discontinuous fiber was found to increase rapidly with increasing modulus ratio, reaching a value of 20 for a modulus ratio of 200. The finite-element method was shown to be a valuable tool for micromechanical stress analysis of composite materials, and the accuracy of strain analysis by moiré-fringemultiplication techniques was demonstrated for problems containing sever strain gradients.