Secondary plasmon resonance in graphene nanostructures

The plasmon characteristics of two graphene nanostructures are studied using time-dependent density functional theory (TDDFT). The absorption spectrum has two main bands, which result from π and σ + π plasmon resonances. At low energies, the Fourier transform of the induced charge density maps exhibits anomalous behavior, with a π phase change in the charge density maps in the plane of the graphene and those in the plane 0.3 ? from the graphene. The charge density fluctuations close to the plane of the graphene are much smaller than those above and beneath the graphene plane. However, this phenomenon disappears at higher energies. By analyzing the electronic properties, we may conclude that the restoring force for the plasmon in the plane of the graphene does not result from fixed positive ions, but rather the Coulomb interactions with the plasmonic oscillations away from the plane of the graphene, which extend in the surface-normal direction. The collective oscillation in the graphene plane results in a forced vibration. Accordingly, the low-energy plasmon in the graphene can be split into two components: a normal component, which corresponds to direct feedback of the external perturbation, and a secondary component, which corresponds to feedback of the Coulombic interaction with the normal component.     

Photoionization microscopy of Rydberg hydrogen atom near a dielectric surface

Based on the semiclassical analysis of photoionization microscopy, we study the ionization of the Rydberg hydrogen atom near a dielectric surface. The radial electron probability density distributions on a given detector plane are calculated at different scaled energies and near different dielectric surfaces. We find due to the interference effect of different types of electron trajectories arriving at a given point on the detector plane, oscillatory structures appear in the electron probability density distributions. With the increase in the scaled energy, more types of electron ionization trajectories appear and the oscillatory structure in the electron probability density distributions becomes complex. Besides, the dielectric constant of the dielectric surface can also affect the electron probability density distributions. Since the photoionization microscopy interference pattern recorded on the detector plane reflects the distribution of the square modulus of the transverse component of the electronic wave function, with the recorded interference pattern, we can investigate the ionization dynamics of the Rydberg atom near surfaces clearly. This study provides some reference values for the future experiment research on the photoionization microscopy of the Rydberg atom near dielectric surfaces.     

Dynamics of charged plane symmetric gravitational collapse

In this paper, we study dynamics of the charged plane symmetric gravitational collapse. For this purpose, we discuss non-adiabatic flow of a viscous fluid and deduce the results for adiabatic case. The Einstein and Maxwell field equations are formulated for general plane symmetric spacetime in the interior. Junction conditions between the interior and exterior regions are derived. For the non-adiabatic case, the exterior is taken as plane symmetric charged Vaidya spacetime while for the adiabatic case, it is described charged plane symmetric spacetime. Using Misner and Sharp formalism, we obtain dynamical equations to investigate the effects of different forces over the rate of collapse. In non-adiabatic case, a dynamical equation is joined with transport equation of heat flux. Finally, a relation between the Weyl tensor and energy density is found.     

Photoionization microscopy of Rydberg hydrogen atom in a non-uniform electrical field

In this paper,we investigate the photoionization microscopy of the Rydberg hydrogen atom in a gradient electric field for the first time.The observed oscillatory patterns in the photoionization microscopy are explained within the framework of the semiclassical theory,which can be considered as a manifestation of interference between various electron trajectories arriving at a given point on the detector plane.In contrast with the photoionization microscopy in the uniform electric field,the trajectories of the ionized electron in the gradient electric field will become chaotic.An infinite set of different electron trajectories can arrive at a given point on the detector plane,which makes the interference pattern of the electron probability density distribution extremely complicated.Our calculation results suggest that the oscillatory pattern in the electron probability density distribution depends sensitively on the electric field gradient,the scaled energy and the position of the detector plane.Through our research,we predict that the interference pattern in the electron probability density distribution can be observed in an actual photoionization microscopy experiment once the external electric field strength and the position of the electron detector plane are reasonable.This study provides some references for the future experimental research on the photoionization microscopy of the Rydberg atom in the non-uniform external fields.     

Theoretical Investigation of the Lead-Free K2InBiX6 (X = Cl,Br) Double Perovskite Compounds Using Ab Initio Calculation

JETP Letters - In this study, we employ the full potential linearized augmented plane wave technique based on density functional theory applied in the WIEN2k code to examine the structural,...     

Dynamics of Shock Waves in Media with Longitudinal Stratification

Doklady Physics - In this paper, we consider the problems of the dynamics of plane shock waves in media with one-dimensional longitudinal density stratification. The rationale, features, and limits...     

Dynamics of density waves in a two dimensional funnel on an inclined plane

We report here experiments on two-dimensional funnel flow of diameter glass beads on an inclined plane. We have investigated the properties of the flow according to the outlet size D of the funnel and the gravity. We have identified three different regimes. For small funnel outlet sizes, there is no significant change in flow density: the flow is rather steady and homogeneous. For intermediate outlet sizes (), the flow is intermittent, consisting of spatially ordered density waves propagating upwards. At bigger outlet sizes, density waves do not exhibit any ordering and the flow dynamics becomes chaotic. In addition, we find that the flow dynamics is independent of the funnel opening angle except close to the channel flow configuration. Finally, it is stressed that the interactions between the beads and the inclined plane play a crucial role in the mechanism of formation of density waves. Received: 9 July 1998 / Received in final form and Accepted: 18 September 1998     

Density fluctuations of two-dimensional active-passive mixtures

Dimension-dependent giant density fluctuations are a typical feature of active matter systems. In this work, we study the density fluctuation in two-dimensional mixtures of active and passive particles by Brownian dynamics simulations. The boundary of motility-induced phase separation is determined by the transition from unimodal to bimodal density distribution. A rapid increase of the fluctuation exponent near the boundary of phase separation in the plane of density and Péclet number was observed. When phase separation occurs, the fluctuation exponent is an approximate constant of $0.85.$     

Wavefront and ray-density plots using seventh-order matrices

The optimization of an optical system benefits greatly from a study of its aberrations and an identification of each of its elements’ contribution to the overall aberration figures. The matrix formalism developed by the author was the object of a previous paper and allows the expression of image-space coordinates as high-order polynomials of object-space coordinates. In this paper we approach the question of aberrations, both through the evaluation of the wavefront evolution along the system and its departure from the ideal spherical shape and the use of ray density plots. Using seventh-order matrix modelling, we can calculate the optical path between any two points of a ray as it travels along the optical system and we define the wavefront as the locus of the points with common optical path length; the results are presented on the form of traces of the wavefront on the tangential plane, although the formalism would also permit sagittal plane plots. Ray density plots are obtained by actual derivation of the seventh-order polynomials.     

单晶固体中正电子波函数的计算

介绍了正电子波函数计算的两种基本方法——有限差分方法(FDM)与平面波方法(PW).并以单晶Si为例,计算出正电子的波函数,从而计算出正电子在Si中的密度分布,由该正电子密度,进一步计算出了正电子在Si中的体寿命.计算结果与我们最近的实验结果(220 ps)符合得很好.最后,探讨了这两种方法各自的优缺点.     

Asymptotic nodal planes in the electron density and the potential in the effective equation for the square root of the density

It is known that the asymptotic decay (|r|→∞) of the electron density n(r) outside a molecule is informative about its first ionization potential I₀. It has recently become clear that the special circumstance that the Kohn–Sham (KS) highest-occupied molecular orbital (HOMO) has a nodal plane that extends to infinity may give rise to different cases for the asymptotic behavior of the exact density and of the exact KS potential [P. Gori-Giorgi et al., Mol. Phys. 114, 1086 (2016)]. Here we investigate the consequences of such a HOMO nodal plane for the effective potential in the Schrödinger-like equation for the square root of the density, showing that for atoms and molecules it will usually diverge asymptotically on the plane, either exponentially or polynomially, depending on the coupling between Dyson orbitals. We also analyze the issue in the external harmonic potential, reporting an example of an exact analytic density for a fully interacting system that exhibits a different asymptotic behavior on the nodal plane.     

A single current density component imaging by MRCDI without subject rotations

Magnetic resonance current density imaging (MRCDI) is a useful method for measuring electrical current density distribution inside a subject. Due to the requirement of subject rotations in MRCDI, MRCDI has not been widely applied to in vivo studies. In this paper, we propose a new current density image (CDI) reconstruction method by which a single component of the current density can be imaged by MRCDI without subject rotations. After measuring one of the two magnetic field components, produced by the current density component passing through the measurement plane, we have reconstructed the current density component images in the spatial frequency domain. Even though the proposed method has a limitation that the area of magnetic field measurement should be much larger than that of the current density, the proposed method is expected to expedite MRCDI applications to in vivo studies.     

Ordering at Solid-Liquid Interfaces Between Dissimilar Materials

In an earlier report we explored structural correlations at a liquid-solid interface with molecular dynamics simulations of a model aluminium system using the Ercolessi-Adams potential and up to 4320 atoms. Substrate atoms were pinned to their equilibrium fcc crystalline positions while liquid atoms were free to move. A direct correlation between the amount of ordering in the liquid phase and the underlying substrate orientation was found. In the present paper we extend this study to the case of a fixed bcc substrate in contact with liquid aluminium. We find surprisingly similar results for the density profiles of both (100) and (110) substrates. However, there is a far greater in-plane ordering in the (100) than for the (110) system. For the (100) substrates we observe adsorption of liquid atoms into the terminating plane of the bcc (100) substrate, effectively transforming the bcc (100) plane into an fcc (100) plane.     

切伦科夫辐射“双成像法”测量电子束发射度

利用切伦科夫辐射,OTR或荧光靶等光学诊断方法进行发射度测量,国内外绝大部分实验是用CCD相机观测电子束打靶产生的光斑,变化四极透镜的磁场梯度,应用“三梯度法”计算出发射度.文中提出了一种新的“双成像法”测量方法,使切伦科夫辐射光通过一长焦距的消色差薄透镜,分别在焦平面和像平面获取图像.通过图像处理,前者可分析出电子束散角分布,后者可分析出电子束径向分布,从而直接得到均方根发射度.该方法对束流相空间和电荷密度分布无需假设,无需借助“三梯度法”,较其他常规测量方法具有实验装置更简便、测量精度更高和适用性更广等优点.文中给出了该测量方法对北京大学DC?SC光阴极注入器的发射度测量进行计算机模拟实验的结果和分析.     

高速运动分层介质界面上的时间平均能流密度

利用坐标变换和高速运动介质界面上平面电磁波入射、反射和透射电场、磁场之间的关系,详细讨论了当介质界面运动时入射、反射和透射时间平均能流密度的变化规律.     

A New Measurement of Electron Beam Emittance with Cerenkov Radiation “Double Imaging” Method

A new way in electron beam emittance measurement with Cerenkov radiation "double imaging" method is proposed in this paper. In the standard emittance measurements with optical diagnostics such as Cerenkov radiation, OTR (Optical Transition Radiation), fluorescence screen or BMP (beam profile monitor) etc., the emittance is indirectly calculated through quadrupole-scanning technique, with the prior ssumption that the beam phase space density distribution is ellipse, which will certainly induce systematic error when the beam profile is quite irregular or the space-charge effects can not be omitted. In proposed method, the Cerenkov radiation pass through a 1-meter focal-length thin convex lens, and a CCD camera is used to capture two images of Cerenkov radiation at the focal plane and at the image plane of the lens respectively. Then, with image processing technique, we acquire the angular divergence information of the electron beam from the image of the focal plane and the radial distribution information from the image of the image plane, which we call Cerenkov radiation "double imaging" method. Therefore, the emittance can be directly attained according to the definition of the RMS emittance. By this method, we can measure the actual phase space distributions without making any prior assumptions about the density distributions. Compared with other general measurements, this "double imaging" method has advantages of simpler equipment, higher precision and wider application. This paper also presents the computer simulation results of emittance measurement on the DC-SC (DC-Superconducting) photocathode injector of PKU-SCAF (Peking University Superconducting Accelerator Facility) being built at Peking University.     

Effect of planar defects on the stability of the Bragg glass phase of type-II superconductors

It is shown that the Bragg glass phase can become unstable with respect to planar crystal defects as twin or grain boundaries. A single defect plane that is oriented parallel to the magnetic field as well as to one of the main axis of the Abrikosov flux line lattice is always relevant, whereas we argue that a plane with higher Miller index is irrelevant, even at large defect potentials. A finite density of parallel defects with random separations can be relevant even for larger Miller indices. Defects that are aligned with the applied field restore locally the flux density oscillations which decay algebraically with distance from the defect. The current-voltage relation is changed to lnV(J) approximately -J(-1). The theory exhibits striking similarities to the physics of Luttinger liquids with impurities.     

Symplectic Tomography of De Broglie Wave

We consider tomograms and quasidistribution functions like the Wigner functions that violate the standard normalization condition and obtain the conditions under which a reconstruction of the density matrix using these tomograms and quasidistribution functions is possible. Then we study an example of the de Broglie plane wave.     

Non-relativistic approximate numerical ideal-magneto-hydrodynamics of (1+1D) transverse flow in Bjorken scenario

In this study, we investigate the impact of the magnetic field on the evolution of the transverse flow of QGP matter in the magneto-hydrodynamic (MHD) framework. We assume that the magnetic field is perpendicular to the reaction plane and then we solve the coupled Maxwell and conservation equations in (1+1D) transverse flow, within the Bjorken scenario. We consider a QGP with infinite electrical conductivity. First, the magnetic effects on the QGP medium at mid-rapidity are investigated at leading order; then the time and space dependence of the energy density, velocity and magnetic field in the transverse plane of the ideal magnetized hot plasma are obtained.