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991.
We have investigated the nonlinear low-frequency microwave absorption of an ensemble of small metallic grains. Earlier Zhou et al. [Phys. Rev. Lett. 77, 1958 (1996)] have proved that linear absorption by such a system is due to a mesoscopic relaxation mechanism for which important contribution is from the grains with small level spacings between the ground state and the first excited state. Here we have shown further that such grains are anomalously sensitive to the field amplitude and the distribution of level spacings. Since such a behavior depends on external magnetic field, we expect the appearance of a giant nonlinear magnetoresistance, as well as a very strong temperature dependence of the nonlinear microwave conductivity. 相似文献
992.
Ren‐Shen Lee Yi‐Ting Huang 《Journal of polymer science. Part A, Polymer chemistry》2008,46(13):4320-4331
A straightforward strategy is proposed for the synthesis of novel, amphiphilic block–graft MPEG‐b‐(PαN3CL‐g‐alkyne) degradable copolymers. First, the ring‐opening polymerization of α‐chloro‐ε‐caprolactone (αClCL) was initiated by hydroxy‐terminated macroinitiator monomethoxy poly(ethylene glycol) (MPEG) with SnOct2 as the catalyst. In a second step, pendent chlorides were converted into azides by the reaction with sodium azide. Finally, various kinds of terminal alkynes were reacted with pendent azides by copper‐catalyzed Huisgen's 1,3‐dipolar cycloaddition, and thus a “click” reaction. These copolymers were characterized by differential scanning calorimetry (DSC), 1H NMR, IR, and gel permeation chromatography. By fixing the length of the MPEG block and increasing the length of PαClCL (or PαN3CL) block, an increase tendency in Tgs was observed. However, the copolymers of MPEG‐b‐PαClCL and MPEG‐b‐PαN3CL were semicrystalline when the Mn of MPEG was above 2000 g mol?1. The block–graft copolymers formed micelles in the aqueous phase with critical micelle concentrations (CMCs) in the range of 1.4–12.0 mg L?1 depending on the composition of polymers. The lengths of hydrophilic segment influence the shape of the micelle. The mean hydrodynamic diameters of the micelles from dynamic light scattering were in the range of 90–160 nm. In vitro hydrolytic degradation of block–graft copolymers is faster than the corresponding block copolymers. The drug entrapment efficiency and the drug loading content of micelles depending on the composition of block–graft polymers were described. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4320–4331, 2008 相似文献
993.
Isolation of Phosphate-Solubilizing Fungi from Phosphate Mines and Their Effect on Wheat Seedling Growth 总被引:1,自引:0,他引:1
Chunqiao Xiao Ruan Chi Huan He Guanzhou Qiu Dianzuo Wang Wenxue Zhang 《Applied biochemistry and biotechnology》2009,159(2):330-342
Three phosphate-solubilizing fungi, identified as Penicillium expansum, Mucor ramosissimus, and Candida krissii, were isolated from phosphate mines (Hubei, People’s Republic of China) and characterized. All the isolates demonstrated
diverse levels of phosphate-solubilizing capability in National Botanical Research Institute’s phosphate growth medium containing
rock phosphate as sole phosphate source. Acidification of culture medium seemed to be the main mechanism for rock phosphate
solubilization. Indeed, citric acid, oxalic acid, and gluconic acid were shown to be present in the culture medium inoculated
with these isolates. Moreover, the isolates produced acid and alkaline phosphatases in culture medium, which may also be helpful
for RP solubilization. A strong negative correlation between content of soluble phosphorus and pH (r = – 0.89; p < 0.01) in culture medium was observed in this study. All the isolates promoted growth, soil available phosphorus, phosphorus,
and nitrogen uptake of wheat seedling in field soil containing rock phosphate under pot culture conditions, thus demonstrating
the capability of these isolates to convert insoluble form of phosphorus into plant available form from rock phosphate, and
therefore hold great potential for development as biofertilizers to enhance soil fertility and promote plant growth. 相似文献
994.
L. de Arcangelis H. J. Herrmann M. Kolb René Thomas C. Amitrano L. Peliti M. Saber G. Weisbuch Sara A. Solla F. Bagnoli A. Francescato R. Livi S. Ruffo Pablo Tamayo Michel Droz Peter Jörg Plath S. Romano Yves Pomeau Stéphane Zaleski D. Stauffer Luciano R. da Silva Alex Hansen Stéphane Roux Antonio Coniglio B. Derrida Henrik Flyvbjerg Naeem Jan Dietrich Stauffer Peter Grassberger A. Zippelius K. E. Kurten Werner Krauth Jean -Pierre Nadal Marc Mézard Per Bak Chao Tang Itzhak Webman M. L. Martins H. F. V. Resende C. Tsallis A. C. N. Magalhaes 《Journal of statistical physics》1989,55(5-6):1333-1359
995.
Roger Yue Chi Ming 《Monatshefte für Mathematik》1986,101(3):173-182
A generalization of semi-prime rings, calledSRN rings, is introduced. Reduced ideals, annihilators and various properties of semi-prime and self-injective rings are considered. 相似文献
996.
Ping‐Chung Kuo Chao‐Chen Chm Li‐Shian Shi Chia‐Ying Li Shwu‐Jen Wu A. G. Damu Pei‐Lin Wu Chang‐Sheng Kuoh Tian‐Shung Wu 《中国化学会会志》2002,49(1):113-116
Seven triterpenes, two lignans, and twelve other known compounds were isolated from the non‐alkaloidal fractions of the stem of Ficus septica Among these triterpenoids, a rare triterpene skeleton derivative, 13,27‐cycloursan‐3β‐ylacetate was isolated from natural sources for the first time. All the structures of these compounds were elucidated by spectroscopic methods. 相似文献
997.
Ting Cheng 《Journal of Differential Equations》2008,244(4):766-802
The blow-up rate estimate for the solution to a semilinear parabolic equation ut=Δu+V(x)|u|p−1u in Ω×(0,T) with 0-Dirichlet boundary condition is obtained. As an application, it is shown that the asymptotic behavior of blow-up time and blow-up set of the problem with nonnegative initial data u(x,0)=Mφ(x) as M goes to infinity, which have been found in [C. Cortazar, M. Elgueta, J.D. Rossi, The blow-up problem for a semilinear parabolic equation with a potential, preprint, arXiv: math.AP/0607055, July 2006], is improved under some reasonable and weaker conditions compared with [C. Cortazar, M. Elgueta, J.D. Rossi, The blow-up problem for a semilinear parabolic equation with a potential, preprint, arXiv: math.AP/0607055, July 2006]. 相似文献
998.
999.
1000.
Improvements in the Multiplex Sample NMR method are investigated to explore its capabilities of analyzing multiple samples simultaneously. Issues of quantitation and resolution in the multiple-coil probe are examined in one- and two-dimensional experiments. Improvements in quantitation are shown to result from the use of reference deconvolution for one-dimensional experiments, while the use of two-dimensional methods has much improved resolution and shows the potential for significantly increased parallelism. A multiplicative scheme is shown to be an easily implemented, effective method for generating individual sub-spectra from individual samples. 相似文献