共查询到20条相似文献，搜索用时 62 毫秒
1.
The spin response of a nested Fermi surface represented by a tight binding energy band is found to exhibit scaling in frequency divided by temperature within a restricted regime close to half-filling of the band. Computations of the spin susceptibility reveal a surprising momentum variation at various temperatures and frequencies. Neutron scattering data on the high-temperature superconductor YBa(2)Cu(3)O(6+x) are analyzed for scaling near a momentum vector that spans nested regions of the orbit. Changes in the Fermi energy remove the scaling properties and reduce the susceptibility to the conventional Fermi liquid behavior of ordinary metals. These results imply that pairing mechanisms of superconductivity need to cope with competing spin density wave and charge density wave instabilities. 相似文献
2.
[目的]湖泊水生态系统(表层水、上覆水和孔隙水)重金属元素的研究对于评价重金属元素对水体的影响具有重要意义。[方法]用ICP-MS仪,测定了大明湖水系统中Fe、Mn、Ni和Cr浓度。[结果]同一采样点重金属元素的浓度由高到低的顺序为Fe>Mn>Ni>Cr,且孔隙水中重金属元素浓度高于表层水和上覆水。Fe和Mn元素在孔隙水中的浓度峰值出现在界面较深处,Cr和Ni元素的迁移较为复杂,在孔隙水中的浓度随深度的变化趋势基本一致,在6~8 cm深度处达到最大值。[结论]大明湖水系统中活泼重金属元素的含量高于稳定态重金属,且人为活动对水系统重金属元素的分布产生重要影响。大明湖沉积物中Fe是重要的有机质分解氧化剂,湖水溶氧较强使得铁锰氧化边界下移。 相似文献
3.
We demonstrate a quantum coherent electron spin filter by directly measuring the spin polarization of emitted current. The spin filter consists of an open quantum dot in an in-plane magnetic field; the in-plane field gives the two spin directions different Fermi wavelengths resulting in spin-dependent quantum interference of transport through the device. The gate voltage is used to select the preferentially transmitted spin, thus setting the polarity of the filter. This provides a fully electrical method for the creation and detection of spin-polarized currents. Polarizations of emitted current as high as 70% for both spin directions (either aligned or anti-aligned with the external field) are observed. 相似文献
4.
基于GIS在土壤污染研究中的应用,结合地累积指数法,研究了某典型石油开采区土壤重金属的空间分布规律和污染等级。利用地累积指数进行插值绘制出的重金属污染分布图。结果表明,研究区内重金属的水平分布差异较大,而Cr、Fe、Ni的地累积指数分布相似度较高,可能属同一来源;除Pb、Zn、Ni在不同深度水平变化较大外,其余重金属均保持稳定;从地累积指数等级上来看,Pb在各井处均达到2级及以上污染;Cu、Co在少数井处达到1级或1级以上污染。地累积指数与GIS相结合能更加直观地反映重金属的污染分布状况。 相似文献
5.
贵阳阿哈湖表层沉积物中重金属化学形态组成及污染研究 总被引：2，自引：0，他引：2
采用Tessier连续提取法,对贵阳阿哈湖枯水季节表层沉积物中Pb、Fe、Cu、Zn、Mn、Ni6种重金属元素的5种化学形态进行了连续提取测定,分析了水体单元表层沉积物重金属元素的形态组合特征和人为污染状况。结果表明：采用Tessier方法对阿哈湖沉积物重金属元素形态进行提取。提取结果具有较高的精密度和稳定性;沉积物中重金属元素Ph、Zn、Fe、Mn、Ni除残渣态外主要以Fe—Mn氧化物结合态为主,而Cu是以有机物结合态和残渣态为主。烂泥沟处重金属的人为污染最为严重。 相似文献
6.
重金属作为一类主要的污染物近年受到人们的广泛关注，为了解安阳地区土壤和小麦籽粒重金属状况，采集了周边农田土壤和小麦籽粒样品各60个。运用相关分析法及主成分分析法，探讨了土壤和小麦籽粒中重金属含量的分布特征。结果表明：土壤和小麦籽粒中各元素的变异幅度和均值差异较大，各元素在小麦籽粒中含量低于土壤中含量。土壤中重金属Cr、Mn、Fe、Ni、Cu之间有明显的相关性。小麦籽粒重金属Fe、Pb与土壤重金属Cr、Mn、Fe、Ni、Cu有明显的相关性，小麦籽粒重金属Cd含量与土壤中Cd、Pb含量有明显的相关性。重金属Cr、Mn、Fe、Ni、Cu、Cd、Pb在第一主成分上有很高荷载，且在第一主成分上的荷载远大于在第二主成分上的荷载。安阳地区小麦籽粒中重金属Cr、Mn、Fe、Ni、Cu、Cd、Pb来源具有一定的相似性。 相似文献
7.
A quantum critical point transforms the behavior of electrons so strongly that new phases of matter can emerge. The interactions at play are known to fall outside the scope of the standard model of metals, but a fundamental question remains: Is the basic concept of a quasiparticle-a fermion with renormalized mass-still valid in such systems? The Wiedemann-Franz law, which states that the ratio of heat and charge conductivities in a metal is a universal constant in the limit of zero temperature, is a robust consequence of Fermi-Dirac statistics. We report a violation of this law in the heavy-fermion metal CeCoIn5 when tuned to its quantum critical point, depending on the direction of electron motion relative to the crystal lattice, which points to an anisotropic destruction of the Fermi surface. 相似文献
8.
Crooker SA Furis M Lou X Adelmann C Smith DL Palmstrøm CJ Crowell PA 《Science (New York, N.Y.)》2005,309(5744):2191-2195
We directly imaged electrical spin injection and accumulation in the gallium arsenide channel of lateral spin-transport devices, which have ferromagnetic source and drain tunnel-barrier contacts. The emission of spins from the source was observed, and a region of spin accumulation was imaged near the ferromagnetic drain contact. Both injected and accumulated spins have the same orientation (antiparallel to the contact magnetization), and we show that the accumulated spin polarization flows away from the drain (against the net electron current), indicating that electron spins are polarized by reflection from the ferromagnetic drain contact. The electrical conductance can be modulated by controlling the spin orientation of optically injected electrons flowing through the drain. 相似文献
9.
The mutual control of the electric and magnetic properties of a solid is currently of great interest because of the possible application for novel electronic devices. We report on the low-magnetic-field (for example, B values of +/-30 milliteslas) control of the polarization (P) vector in a hexaferrite, Ba2Mg2Fe12O22, which shows the helimagnetic spin structure with the propagation vector k0 parallel to [001]. The B-induced transverse conical spin structure carries the P vector directing perpendicular to both B and k0, in accord with the recently proposed spin-current model. Then, the oscillating or multidirectionally rotating B produces the cyclic displacement current via the flexible handling of the magnetic cone axis. 相似文献
10.
Yu. N. Vodyanitskii 《Russian Agricultural Sciences》2009,35(3):185-188
It is suggested to characterize concretions in contaminated soils by geochemical modules based on the affinity of heavy metals and metalloids with carrier phases, which is indicated by significant positive correlation coefficients between them. The modules include molar ratios Cu: Fe, Ni: Fe, As: Fe, P: Fe, and Pb: Mn, with increase of which the strength of fixation of the trace element by the corresponding carrier phase decreases. 相似文献
11.
微量金属元素添加频率对牛粪厌氧发酵特性的影响 总被引：1，自引：0，他引：1
为研究微量金属元素对牛粪厌氧发酵特性的影响,每隔1,3,5,7d向牛粪厌氧发酵液中添加Fe、Co、Ni元素。结果表明,7d添加1次微量金属元素的发酵组效果最佳,产气率和总产气量最高,COD去除率最高;每1d添加1次的挥发性有机酸(VFA)和产气量都最低,分析认为微量金属元素添加频率过高会破坏反应器内的营养平衡。 相似文献
12.
Shimojima T Sakaguchi F Ishizaka K Ishida Y Kiss T Okawa M Togashi T Chen CT Watanabe S Arita M Shimada K Namatame H Taniguchi M Ohgushi K Kasahara S Terashima T Shibauchi T Matsuda Y Chainani A Shin S 《Science (New York, N.Y.)》2011,332(6029):564-567
The origin of superconductivity in the iron pnictides has been attributed to antiferromagnetic spin ordering that occurs in close combination with a structural transition, but there are also proposals that link superconductivity to orbital ordering. We used bulk-sensitive laser angle-resolved photoemission spectroscopy on BaFe(2)(As(0.65)P(0.35))(2) and Ba(0.6)K(0.4)Fe(2)As(2) to elucidate the role of orbital degrees of freedom on the electron-pairing mechanism. In strong contrast to previous studies, an orbital-independent superconducting gap magnitude was found for the hole Fermi surfaces. Our result is not expected from the superconductivity associated with spin fluctuations and nesting, but it could be better explained invoking magnetism-induced interorbital pairing, orbital fluctuations, or a combination of orbital and spin fluctuations. Regardless of the interpretation, our results impose severe constraints on theories of iron pnictides. 相似文献
13.
汉江上游铁矿尾矿库区土壤重金属污染分析 总被引：4，自引：4，他引：0
应用地累积指数法和生态危害指数法对汉江上游某铁矿尾矿库区周边土壤重金属污染特征和潜在生态环境污染风险进行了研究。结果表明尾矿库区土壤中重金属除Ti外均超出当地土壤背景值,以Cd超标最严重(超标12倍);形态分析表明Fe、Ti、As、Hg的主要存在形态是残渣态,Mn的可交换态和碳酸盐结合态所占比例最高(均值24.07%),Zn的易还原态所占比例最高(均值22.07%),Ni和Co的易氧化态所占比例最高(均值分别为28.99%、25.46%);地累积指数法评价表明尾矿库区土壤Hg和Cd达到中-强污染等级,As和Co属中度污染等级,Fe、Zn、Mn、Ni以无污染-中污染为主,其余金属无污染;生态危害指数法结果显示Cd和Hg的生态风险等级为极强,As生态风险等级为中等,其余元素生态风险等级为轻微,尾矿库采样区域整体处于很强的生态风险等级,尤其需要加强对Cd、Hg、As的污染防治。 相似文献
14.
Schunck CH Shin Y Schirotzek A Zwierlein MW Ketterle W 《Science (New York, N.Y.)》2007,316(5826):867-870
We used radio-frequency spectroscopy to study pairing in the normal and superfluid phases of a strongly interacting Fermi gas with imbalanced spin populations. At high spin imbalances, the system does not become superfluid even at zero temperature. In this normal phase, full pairing of the minority atoms was observed. Hence, mismatched Fermi surfaces do not prevent pairing but can quench the superfluid state, thus realizing a system of fermion pairs that do not condense even at the lowest temperature. 相似文献
15.
16.
Matsumoto Y Nakatsuji S Kuga K Karaki Y Horie N Shimura Y Sakakibara T Nevidomskyy AH Coleman P 《Science (New York, N.Y.)》2011,331(6015):316-319
Fermi liquid theory, the standard theory of metals, has been challenged by a number of observations of anomalous metallic behavior found in the vicinity of a quantum phase transition. The breakdown of the Fermi liquid is accomplished by fine-tuning the material to a quantum critical point by using a control parameter such as the magnetic field, pressure, or chemical composition. Our high-precision magnetization measurements of the ultrapure f-electron-based superconductor β-YbAlB(4) demonstrate a scaling of its free energy that is indicative of zero-field quantum criticality without tuning in a metal. The breakdown of Fermi liquid behavior takes place in a mixed-valence state, which is in sharp contrast with other known examples of quantum critical f-electron systems that are magnetic Kondo lattice systems with integral valence. 相似文献
17.
研究了金属Fe、Ni纳米颗粒对蛋白核小球藻Chlorella pyrenoidosa生长活性的影响,探讨了金属纳米材料的生物安全性问题。结果表明：Fe、Ni金属纳米颗粒不仅能吸附在藻细胞表面,造成其团聚沉淀,而且还能进入细胞内部,引起细胞的形变和结构损伤,从而抑制了小球藻的正常生长,降低小球藻的生物量,对小球藻具有一定的毒性效应。 相似文献
18.
对巢湖湖区不同位点的表层沉积物中的Fe、Cr、Pb、Cu、Co、Zn、Ni7种重金属含量进行的分析表明,湖泊沉积物中重金属含量分布呈现一定的区域特征,由于巢湖西半湖靠近合肥市区,大量的工业废水和生活污水通过河道排入巢湖,引起西半湖区中重金属含量高于东半湖区。采用富集因子法和地积累指数法对巢湖沉积物重金属污染现状进行了评价,结果表明,巢湖沉积物中存在Pb、Cu污染,个别地区已相当严重,并呈现沿湖心区至东半湖区逐渐降低趋势。研究表明,两种方法均能对人为污染行为做出较为科学的评价,且两种方法得到的评价结果基本一致。由于重金属元素有很强的毒性,并且能够在食物链中传递,有关部门应及早从流域环境综合规划入手,对重金属污染问题采取有力的控制对策,保护沿湖地区居民免受危害。此外,对巢湖表层沉积物中重金属污染物来源进行了初步分析,据分析结果判断,巢湖沉积物中重金属总量Co、Fe、Cr的来源相似,Zn和Cu的来源相似。 相似文献
19.
用非限制性密度泛函方法UBP86泛函结合def2-TZVP基组获得了Ni2～6团簇的几何结构并用ELF(ElectronLocalized Function)和LOL(Localized Orbital Locator)函数对小镍团簇的电子结构进行拓扑分析.研究结果表明,除Ni2团簇外,团簇中Ni—Ni键的成键临界点不在键轴上,为弯曲键.镍团簇中Ni—Ni间的金属键为部分共价键,其价层Basin的布局数均小于1e,并且团簇中存在多个多中心价层Basin.团簇中各个化学键均强烈离域化.团簇中的单电子主要位于内层轨道,并没有参与成键. 相似文献
20.
大冶龙角山矿区农田土壤重金属形态分布及其来源 总被引：5，自引：3，他引：2
为研究大冶龙角山矿区某溪流段沿岸农田土壤基本理化性质和重金属分布情况,采用Tessier五步连续提取法提取并测定土壤中Mn、Cu、Zn、Pb、Cr、Ni和Cd 7种重金属的形态与含量,并分析了重金属含量与土壤Fe和S含量之间的相关性。结果表明:所有重金属在大部分取样点总含量均超出湖北省土壤背景值;Cu和Cd总含量超过土壤环境质量三级标准(GB 15618—1995)限值,Zn、Pb、Cr和Ni符合土壤环境质量二级标准;Mn、Cu、Zn、Pb、Ni和Cd均以残渣态和铁锰氧化物结合态为主,Pb、Cr和Cd存在一定比例的可交换态。矿山矿石组分主要为黄铁矿和黄铜矿,且Mn、Cu、Zn、Pb和Cd的铁锰氧化物结合态、残渣态以及总含量的分布均与土壤Fe和S含量分布表现出较好的正相关关系,表明硫化物矿物开采引发了重金属Mn、Cu、Pb、Zn和Cd在该矿区农田土壤中的累积与污染。 相似文献