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971.
T. Saikawa A. Ferraz 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,20(1):65-74
A precursor effect on the Fermi surface in the two-dimensional Hubbard model at finite temperatures near the antiferromagnetic
instability is studied using three different itinerant approaches: the second order perturbation theory, the paramagnon theory
(PT), and the two-particle self-consistent (TPSC) approach. In general, at finite temperature, the Fermi surface of the interacting
electron systems is not sharply defined due to the broadening effects of the self-energy. In order to take account of those
effects we consider the single-particle spectral function A(, 0) at the Fermi level, to describe the counterpart of the Fermi surface at T = 0. We find that the Fermi surface is destroyed close to the pseudogap regime due to the spin-fluctuation effects in both
PT and TPSC approaches. Moreover, the top of the effective valence band is located around = (π/2,π/2) in agreement with earlier investigations on the single-hole motion in the antiferromagnetic background. A crossover
behavior from the Fermi-liquid regime to the pseudogap regime is observed in the electron concentration dependence of the
spectral function and the self-energy.
Received 8 September 2000 and Received in final form 20 December 2000 相似文献
973.
Ya‐Xian Yuan Li Ling Xi‐Yu Wang Mei Wang Ren‐Ao Gu Jian‐Lin Yao 《Journal of Raman spectroscopy : JRS》2007,38(10):1280-1287
A new method is reported for detecting heavy metal ions by using the self assembled monolayer (SAM) technique and surface enhanced Raman spectroscopy (SERS). The p‐mercaptobenzoic acid (MBA) served as the SERS readout molecule and the modified tag to attach on the smooth gold substrate as well as the tag of nanoparticles by the SAM method. Two carboxyl groups from MBA molecules which were attached respectively to gold substrate and gold nanoparticles were linked through the heavy metal ions (Cu2+, Pb2+ and Zn2+) as bridge, and thus sandwich structure of ‘MBA modified gold substrate/heavy metal ions/MBA modified gold nanoparticles’ was built for detection. The observation of the oxidation peak of metal nanoparticles from cyclic voltammetry (CV) curve, gold nanoparticles from scanning electron microscopy (SEM) images and SERS signal of MBA from the sandwich structure indicated the existence of heavy metal ions. The difference in the wavenumbers of vibrational modes from MBA in the sandwich structure constructed by different could be used to identify different heavy metal ions. The assembled structure was rinsed by strong chelator of EDTA solution to remove the heavy metal ions from the sandwich structure and thus to obtain a fresh gold substrate modified with MBA for the cyclic detection. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
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利用污水厂污泥、河道淤泥、粉煤灰和加拿大一枝黄花等废弃物为主要原料, 制备出一种污泥基陶土(SBPC), 研究了其对Pb2+、Cd2+、Ni2+、Cr3+ 4种重金属混合溶液的吸附效果, 并以Cr3+为例研究其吸附机理. 结果表明, 在低浓度重金属混合溶液中, SBPC对Cr、Pb的去除率可达90%以上, 而对Cd、Ni的去除率低于15%; 在单一重金属铬溶液中, SBPC对Cr3+的最大吸附量为4.32mg?g-1, 其吸附等温线符合Freundlich模型; 吸附机理主要包括表面沉降、阳离子置换、取代反应、Cr3+水解以及静电吸附. 相似文献
978.
2005年10月,采集了乐安江及其支流漫滩区表层土中的优势植物--稗草,并测定了其中6种重金属(Cd、Cr、N i、Cu、Pb、Zn)的含量。流经亚洲最大露天铜矿(德兴铜矿)的乐安江,其三条支流由于被德兴铜矿的酸性矿山废水(AMD)和一个活性炭厂排出的废液所污染,以至其漫滩区表层土中的稗草含有高浓度的Cd、Cu、Pb、Zn。稗草中6种金属的生物体内累积性按下列次序退减:Cd>Zn>Cu>Pb>N i>Cr,这与它们在环境中的迁移性相一致。 相似文献
979.
Heavy quarks play an important role in probing the properties of strongly interacting quark-gluon plasma(QGP)created in ultra-relativistic heavy-ion collisions.We study the interactions of single heavy(charm)quarks and correlated charm and anticharm(ccˉ)quark pairs with the medium constituents of QGP by performing fireball+Langevin simulations of the pertinent Brownian motion with elastic collisions.Besides studying the traditional observables,the nuclear modification factor and the elliptic flow of single heavy quarks in QGP for different thermal relaxation rates,we also study the broadening of the azimuthal correlations of charm and anticharm quark pairs in the QGP medium for different relaxation rates and transverse momenta classes.We quantified the smearing of ccˉpair azimuthal correlations with an increasing thermal relaxation rate:while the(nearly)back-to-back correlations among ccˉpairs are almost completely washed out at low transverse momentum(pT),these correlations at high pT largely survive the pair diffusion.This provides a novel observable for diagnosing the properties of QGP. 相似文献
980.
Non-linear heavy ion-acoustic waves (HIAWs) are studied in a homogeneous magnetized four-component multi-ion plasma composed of inertial heavy negative ions, light positive ions, and inertia-less non-extensive electrons and positrons. The non-linear Schrödinger equation is derived in this model using the perturbation method. The criteria for modulational instability of HIAWs and the basic features of finite-amplitude heavy ion acoustic rogue waves (HIARWs) are investigated. The presence of the magnetic field was found to reduce the amplitude of HIARWs and enhances the stability. It is interesting to note that increasing positive ion mass causes decreases in the amplitude and width of rogue waves, which is opposite behaviour to that demonstrated in the previous study of these waves in an unmagnetized plasma. Furthermore, it is also shown that striking parameters, such as the non-extensive parameter, the positron number density, the electron number density, the electron temperature, and the magnetic field parameter, play an undeniable role on the stability of waves packets. The findings of the present investigation may be of wide relevance to some plasma environments, such as active galactic nuclei, pulsar magnetospheres, and other magnetic confinement systems. 相似文献