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51.
52.
Parasuraman Karthikeyan Sythana Suresh Kumar Aswar Sachin Arunrao Muskawar Prashant Narayan Pundlik Rambhau Bhagat 《Research on Chemical Intermediates》2013,39(3):1335-1342
An environmentally benign, cheap and reusable L-amino acid functionalized ionic liquid [L-AAIL]/AlCl3 was found to be an effective catalyst for the synthesis of 3,4-dihydropyrimidine-2-(1H)-thione derivatives in good to excellent yield under solvent-free condition. Compared with the classical Biginelli reactions, this method consistently enjoys the advantages of mild reaction conditions, easy work-up, and short reaction time. These one-pot three-component Biginelli products could be separated easily from the catalyst–water system, and the catalyst could be reused at least five times without noticeably reducing catalytic activity. 相似文献
53.
Wright AC Lemdiasov R Connick TJ Bhagat YA Magland JF Song HK Toddes SP Ludwig R Wehrli FW 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2011,210(1):113-122
A Helmholtz-pair local transmit RF coil with an integrated four-element receive array RF coil and foot immobilization platform was designed and constructed for imaging the distal tibia in a whole-body 7T MRI scanner. Simulations and measurements of the B(1) field distribution of the transmit coil are described, along with SAR considerations for operation at 7T. Results of imaging the trabecular bone of three volunteers at 1.5T, 3T and 7T are presented, using identical 1.5T and 3T versions of the 7T four-element receive array. The spatially registered images reveal improved visibility for individual trabeculae and show average gains in SNR of 2.8× and 4.9× for imaging at 7T compared to 3T and 1.5T, respectively. The results thus display an approximately linear dependence of SNR with field strength and enable the practical utility of 7T scanners for micro-MRI of trabecular bone. 相似文献
54.
We report EPR measurements on amorphous FexNi80-xP14B6 alloys for concentrations less than that required for ferromagnetism. Measurements were made at microwave frequencies between 10 and 35 GHz and at temperatures between 2 and 150 K. We find i) at high temperatures the alloys are simple paramagnets with ? ≈ 2.14 and a relaxation rate (linewidth) increasing linearly with temperature, ii) the linewidth increases at low T and follows an empirical form proposed earlier, iii) as the temperature is decreased, the susceptibility (measured by reference to the line intensities) increases, iv) in order to account for the frequency dependence of the resonance field we must introduce an anisotropy energy with uniaxial symmetry; the “hard axis” being normal to the sample plane. The associated anisotropy constant K' appears at several times the spin glass transition temperature TSG, v) at still lower temperatures ( < 2TSG) another type of anisotropy field appears. The corresponding anisotropy energy is similar to that introduced to explain data on the reentrant alloys of this system and the archetypal spin glasses CuMn and AgMn and the anisotropy constant K has the same type of temperature dependence. However, the frequency dependence of K is different. 相似文献
55.
Spin resonance measurements have been used to obtain the temperature dependence of the magnetization in (FexNi1?x)75P16B6A?3 alloys for 4 ? T ? 300K. With x = 0.5, spin wave theory is adequate to account for the observations. For x = 0.4 and 0.3 marked deviations from behavior are noted below ~ 70K and we propose a simple model to account for these deviations. 相似文献
56.
粉粒体两相流的电容层析成象测量 总被引:4,自引:0,他引:4
粉粒体系统中的固相浓度分布的在线测量是十分困难的问题.电容层析成象技术是一种近年来发展起来的非侵入式快速浓度场测量技术.它不干扰流场,不受流动中颗粒浓度、加速度、不透明等因素的制约.本文讨论其测量原理、应用、近期进展、存在的主要问题及其解决的对策. 相似文献
57.
ac Conductivity measurements are carried out across the metal to insulator transition in NiAl0.7Cr0.7Fe0.6O4. The low frequency data is analyzed using Summerfield scaling theory for hopping conductivity. The exponent of the scaling
behavior has significantly different values in the conducting and insulating regimes. The hopping frequency and the zero frequency
conductivity are found to increase with temperature, slowly in the metallic regime and rapidly in the insulating regime. 相似文献
58.
Hysteresis loop and ac susceptibility measurements were performed on three series of amorphous alloys: (AwB1-w)75P16B6Al3, where (A, B) are (Fe, Ni), (Co, Ni) and (Fe, Mn). Upon cooling, low w alloys undergo paramagne t to spin glass transitions. Alloys with higher w first experience a Curie transition to a ferromagnetic state, and then a spin freezing transition to a spin glass state. the T dependence of the width of the ac hysteresis loop is used to determine the spin freezing transition temperature. A magnetic phase diagram is presented for each alloy series and the value of w required for ferromagnetism, wC, is determined. When measured in the presence of small constant fields, the ac susceptibility of alloys with w just above wC has maxima near both transition temperatures. The field and temperature dependences of the peaks are explained by scaling arguments, used to determine the critical exponent δ for the Curie transition, and suggest that a similar scaling law holds for the ferromagnet to spin glass transition. 相似文献
59.
It is found that the electrical resistance for several metal-metalloid amorphous alloys decreases with increasing temperature as ?√T from about 20 mK to several K. The form and magnitude of this temperature dependence is in agreement with recent predictions from interaction theories. 相似文献
60.
We have measured the d.c. conductivity at 300 K, the spin density and the optical absorption in amorphous silicon films deposited at rates between 0.4 and 10 Å/sec. It is found that all these quantities reduce sharply as the deposition rate is decreased. The data are compared to the heat treatment behavior reported recently. The possibility of oxygen contamination is discussed. 相似文献