石墨烯反铁磁关联的数值研究

从定义在Honeycomb晶格上的Hubbard模型出发,使用量子蒙特卡罗方法研究了石墨烯在低掺杂时的磁学关联.通过计算系统的自旋结构因子、自旋关联函数和自旋磁化率发现:系统在低掺杂时表现为反铁磁自旋关联,反铁磁自旋关联在低温时更为显著,并随着电子相互作用强度的增大而增强,但随着电子浓度的减小而减弱;次近邻跃迁元对反铁磁波矢点的自旋磁化率有较为显著的加强作用.

邻苯二甲酸单甲酯双核铜配合物的强反铁磁性和磁构关联研究

以邻苯二甲酸单甲酯(mMP)为配体合成了一个新的双核铜配位化合物[Cu_2(mMP)_2(H_2O)_2]_2·2H_2O(1),并通过元素分析、红外光谱和X射线单晶衍射等方法对化合物晶体结构进行了表征.化合物1通过四羧酸桥联的方式形成了桨轮状双金属笼结构.每个Cu(Ⅱ)离子采用四方单锥的五配位构型,其中四个氧原子来自于四个不同的邻苯二甲酸单甲酯配体,轴向位置上的氧原子则来自于水分子.配化水分子和溶剂水分子与配体中未配位的氧原子形成了分子间氢键,并进一步形成三维网络结构.磁性数据显求双核铜内为强的反铁磁交换作用,磁耦合作用常数2J=-324 cm^(-1).通过与相关双核铜化合物的对比,详细分析了化合物的磁构关联并讨论了羧酸类双核铜中强反铁磁性作用的结构因素.研究表明,影响羧酸类双核铜强反铁磁性作用的主要结构因素是配体中桥联双核铜的O-C-O部分的电子结构.

以N—N基团为单桥的双核Cu(Ⅱ)体系磁-结构关联的理论研究

在密度泛函理论的框架下 ,应用对称性破损方法 ,研究了以N—N基团为单桥的二嗪类双核Cu(Ⅱ )体系的磁耦合强度及磁 -结构关联 .计算结果表明 ,随着旋转角θ的减小 ,反铁磁性耦合作用逐渐减小 ,直至出现铁磁性耦合 ,与实验得到的趋势一致 .破损态能量随着θ的增大发生逆转 ,先降低后增大 .磁耦合常数J与 (ε1 -ε2 ) 2 的关系受到破损态能量逆转的影响 .当θ由 6 5°逐渐增大到 14 0°时 ,破损态能量依次降低 ,J与 (ε1 -ε2 ) 2 呈线性关系 ;当θ=15 0°时 ,破损态能量发生逆转 ,由降低变为升高 ,二者不再保持原有线性关系 .另外 ,(ε1 -ε2 ) 2 与θ的关系也受到破损态能量逆转的影响 .在θ=6 5°～ 14 0°范围内 ,J与θ以及 (ε1 -ε2 ) 2 与θ的图形相似 ,因此可用 (ε1 -ε2 ) 2 代替J讨论磁性与结构的关系 ;θ=15 0°时 ,二者图形不同 .破损态能量的逆转对磁耦合常数J的影响不大 ,而旋转角θ是影响磁耦合常数的关键因素 .

邻苯二甲酸单乙酯铜配合物的晶体结构与强反铁磁性(英文)

Copper(Ⅱ)carboxylates have been extensivelystudied from different points of view because thecarboxylato anions exhibit different bonding

氢键桥联双核铜配合物磁耦合的密度泛函研究

在密度泛函理论的基础上 ,应用对称性破损方法研究了氢键桥联双核铜模型配合物的磁耦合行为以及磁耦合常数随 O_ O距离的变化趋势 .计算结果表明 ,反铁磁耦合作用来源于 Cu原子的 dx2 - y2 和氧原子的 px 或 py 磁轨道的部分重叠 ,而 H原子不参与磁耦合作用 .磁耦合常数 J与 O_ O距离 r之间存在指数关系 ,而不是线性关系 .

3D inversion modeling of joint gravity and magnetic data based on a sinusoidal correlation constraint

Joint inversion based on a correlation constraint utilizes a linear correlation function as a structural constraint.The linear correlation function contains a denominator,which may result in a singularity as the objective function is optimized,leading to an unstable inversion calculation.To improve the robustness of this calculation,this paper proposes a new method in which a sinusoidal correlation function is employed as the structural constraint for joint inversion instead of the conventional linear correlation function.This structural constraint does not contain a denominator,thereby preventing a singularity.Compared with the joint inversion method based on a cross-gradient constraint,the joint inversion method based on a sinusoidal correlation constraint exhibits good performance.An application to actual data demonstrates that this method can process real data.

深溪沟水电站发电机保护装置改造与应用实践

发电机保护装置是保障发电厂机组安全平稳运行的重要设备,通过采集发电机各个节点的电压、电流、阻抗、无功功率、有功功率等电气参量,以及断路器位置、导水叶位置等机械参量,结合保护装置内部逻辑和根据用户自身需求对发电机进行保护。发电机保护的应用极大提升了一次设备的安全性,防止因设备故障或人的不安全行为造成一次设备损坏,在保障人员安全和资产安全上发挥着不可替代的作用。随着生产现场的复杂性和电网安全的重要性不断提升,发电机保护装置需要进行升级改造,本文主要结合深溪沟水电站发电机保护装置升级改造进行探讨分析,向并网水电站保护装置升级改造提供参考。

New Correlation Ratio in Chemistry and Biology with Respect to Time and Magnetic Field

The authors reviewed the influence of various factors--inductive, mesomeric and steric effects, and magnetic fields and time correlation ratio. The authors offered the new correlation ratio in Chemistry and Biology with respect to time and magnetic field. The proposed formula takes into account the influence of the magnetic field on the correlation ratio.

Trispectrum and correlation dimension analysis of magnetorheological damper in vibration screen

In order to improve the screening efficiency of vibrating screen and make vibration process smooth,a new type of magnetorheological (MR) damper was proposed. The signals of displacement in the vibration process during the test were collected. The trispectrum model of autoregressive (AR) time series was built and the correlation dimension was used to quantify the fractal characteristics during the vibration process. The result shows that,in different working conditions,trispectrum slices are applied to obtaining the information of non-Gaussian,nonlinear amplitude?frequency characteristics of the signal. Besides,there is correlation between the correlation dimension of vibration signal and trispectrum slices,which is very important to select the optimum working parameters of the MR damper and vibrating screen. And in the experimental conditions,it is found that when the working current of MR damper is 2 A and the rotation speed of vibration motor is 800 r/min,the vibration screen reaches its maximum screening efficiency.

Slave-Fermion Mean-Field Theory of Heisenberg Model

A nearly half-filled two-dimensional Heisenberg model is investigated. A slave-fermion method with fermions as the charge carriers and bosons as the spin carriers is proposed. The ground state shows antiferromagnetic long range order at T = 0. The spin-spin correlation and static susceptibility are also obtained.

Effects of heavy ions on kinetic Alfven waves

Kinetic Alfven Wave (KAW) is one of the low-frequency electromagnetic fluctuations that are identified extensively in space plasmas by in situ observations of satellites and has been an interesting topic for discussion widely in the fields of laboratory, space, and astrophysical plasmas because of its potential importance in plasma particle energization. Some satellite observations show that the number density ratio of the oxygen ions to the ambient plasma is 30% similar to 50%, sometimes, even as high as 80%. In this paper, effects of heavy ion species on KAWs are studied in a low-beta plasma. The results show that heavy ions not only considerably reduce the propagation speed of KAWs, but also remarkably influence the parallel component of perturbed electric field of KAWs (to the ambient magnetic field). The ratio of parallel to perpendicular components of perturbed field decreases (or increases) with the heavy ion abundance for KAWs dominated by the electron inertial length (or by ion acoustic gyroradius). In particular, the resonant condition of KAWs with thermal electrons is modified by the heavy ion species.

Symmetry Breaking in the Strong Interaction – The Chiral Magnetic Effect

The chiral magnetic effect (CME) refers to a charge separation along a strong magnetic field due to an imbalanced chirality of quarks from interactions with the vacuum topological gluon field. This chiral anomaly is a fundamental property of quantum chromodynamics (QCD) and, therefore, an observation of the CME would have far-reaching impact on our understanding of QCD and Nature. The measurements of the CME-sensitive azimuthal correlator Δγ observable in heavy-ion collisions are contaminated by a major background induced by elliptic flow anisotropy. Several novel approaches have been carried out, including a dedicated isobar collision program, to address this flow-induced background. Further background effects, arising from nonflow correlations, have been studied. While the isobar data are consistent with zero CME signal with an upper limit of 10% of the measured Δγ, the Au+Au midcentral data suggest a positive CME signal on the order of 10% of the measured Δγ with a significance of ~2 standard deviations. Future increased statistics and improved detector capability should yield a firm conclusion on the existence (or the lack) of the CME in relativistic heavy-ion collisions.

Titanium doped kagome superconductor CsV_(3-x)Ti_(x)Sb_(5)and two distinct phases

The vanadium-based kagome superconductor CsV_(3)Sb_(5) has attracted tremendous attention due to its unexcepted anomalous Hall effect(AHE),charge density waves(CDWs),nematicity,and a pseudogap pair density wave(PDW)coexisting with unconventional strong-coupling superconductivity.The origins of CDWs,unconventional superconductivity,and their correlation with different electronic states in this kagome system are of great significance,but so far,are still under debate.Chemical doping in the kagome layer provides one of the most direct ways to reveal the intrinsic physics,but remains unexplored.Here,we report,for the first time,the synthesis of Ti-substituted CsV_(3)Sb_(5) single crystals and its rich phase diagram mapping the evolution of intertwining electronic states.The Ti atoms directly substitute for V in the kagome layers.CsV_(3-x)Ti_(x)Sb_(5) shows two distinct superconductivity phases upon substitution.The Ti slightly-substituted phase displays an unconventional V-shaped superconductivity gap,coexisting with weakening CDW,PDW,AHE,and nematicity.The Ti highly-substituted phase has a U-shaped superconductivity gap concomitant with a short-range rotation symmetry breaking CDW,while long-range CDW,twofold symmetry of in-plane resistivity,AHE,and PDW are absent.Furthermore,we also demonstrate the chemical substitution of V atoms with other elements such as Cr and Nb,showing a different modulation on the superconductivity phases and CDWs.These findings open up a way to synthesise a new family of doped CsV_(3)Sb_(5) materials,and further represent a new platform for tuning the different correlated electronic states and superconducting pairing in kagome superconductors.

Recent advances on stimuli-responsive macromolecular magnetic resonance imaging (MRI) contrast agents

Magnetic resonance imaging(MRI) has been extensively used in clinical diagnosis and currently over 30% MRI runs are performed in the presence of contrast agents. However, commercially available contrast agents originated from small molecules typically exhibit relatively low relaxivities and insufficient circulation time. Therefore, there is a long pursuit to develop new contrast agents with high relaxivities to discriminate pathological tissues from normal ones. Compared with small molecule MRI contrast agents, the incorporation of small molecule contrast agents into macromolecular scaffolds allows for constructing macromolecular MRI contrast agents, remarkably elevating the relaxivities due in part to increased rotational correlation time(τR). Moreover, if the macromolecular scaffolds are responsive to external stimuli, the MRI signals could be selectively switched on at the desired sites(e.g., pathological tissues), further intensifying the imaging contrast. In this feature article, we outline the recent achievements in the fabrication of stimuli-responsive macromolecular MRI contrast agents. Specifically, macromolecular contrast agents being responsive to acidic p H, redox potentials, and other stimuli including photoirradiation, pathogens, and salt concentration are discussed. These smart contrast agents could affect either longitudinal(T1) or transverse(T2) relaxation times of water protons or other nuclei(e.g.,19 F), exhibiting enhanced signals in pathological tissues yet suppressed signals in normal ones and displaying promising potentials in in vitro and in vivo MRI applications.

Effect of Transverse Correlation Function on the Thermodynamic Quantities of Ferromagnetic Systems

The effect of transverse correlation between spins on the thermodynamic properties of ferromagnetic systems is investigated in details. Qualitatively, at finite temperature the transverse correlation reflects the short-range interaction between spins, so that lowers the internal energy and consequently raises the free energy. It also means the introduction o[ some ordering, and hence lowers the entropy. It is depressed by the field which forces the spins to turn to the field direction, so that it decreases with the field when temperature is fixed. The low-temperature expansion of the energy shows that the inclusion of the transverse correlation at least partly considers the interaction between spin waves.

Experimental simulation of the Unruh effect on an NMR quantum simulator

The Unruh effect is one of the most fundamental manifestations of the fact that the particle content of a field theory is observer dependent. However, there has been so far no experimental verification of this effect, as the associated temperatures lie far below any observable threshold. Recently, physical phenomena, which are of great experimental challenge, have been investigated by quantum simulations in various fields. Here we perform a proof-of-principle simulation of the evolution of ferrnionic modes under the Unruh effect with a nuclear magnetic resonance （NMR） quantum simulator. By the quantum simulator, we experimentally demonstrate the behavior of Unruh temperature with acceleration, and we fiarther investigate the quantum correlations quantified by quantum discord between two fermionic modes as seen by two relatively accelerated observers. It is shown that the quantum correlations can be created by the Unrtfia effect from the classically correlated states. Our work may provide a promising way to explore the quantum physics of accelerated systems.