Non-nearest-neighbor interactions in nonlinear dynamical lattices

We revisit the theme of non-nearest-neighbor interactions in nonlinear dynamical lattices, in the prototypical setting of the discrete nonlinear Schrödinger equation. Our approach offers a systematic way of analyzing the existence and stability of solutions of the system near the so-called anti-continuum limit of zero coupling. This affords us a number of analytical insights such as the fact that, for instance, next-nearest-neighbor interactions allow for solutions with nontrivial phase structure in infinite one-dimensional lattices; in the case of purely nearest-neighbor interactions, such phase structure is disallowed. On the other hand, such non-nearest-neighbor interactions can critically affect the stability of unstable structures, such as topological charge S=2 discrete vortices. These analytical predictions are corroborated by numerical bifurcation and stability computations.     

Eliminating interactions between non-neighboring qubits in the preparation of cluster states in quantum molecules

We propose a scheme to eliminate the effect of non-nearest-neighbor qubits in preparing cluster state with double-dot molecules. As the interaction Hamiltonians between qubits are Ising-model and mutually commute, we can get positive and negative effective interactions between qubits to cancel the effect of non-nearest-neighbor qubits by properly changing the electron charge states of each quantum dot molecule. The total time for the present multi-step cluster state preparation scheme is only doubled for one-dimensional qubit chain and tripled for two-dimensional qubit array comparing with the time of previous protocol leaving out the non-nearest-neighbor interactions.     

非近邻跳跃对扶手椅型石墨烯纳米带电子结构的影响

根据π电子的紧束缚模型,将电子的次近邻和第三近邻跳跃能考虑在内,得到扶手椅型石墨烯纳米带（AGRNs）能带结构的解析解.讨论了由次近邻和第三近邻电子跳跃引起的能带和能隙变化,发现次近邻和第三近邻跳跃分别对带隙产生增大和减小的影响. 比较了边界弛豫与非近邻跳跃之间的互相竞争关系. 当纳米带的宽度n为奇数时,二维石墨面的紧束缚模型中所固有的van Hove奇异性表现为AGRNs中的无色散带. 当AGRNs宽度增加时,能谱趋向于二维石墨烯时的能谱结构. 关键词： 扶手椅型石墨烯纳米带 非近邻跳跃 边界弛豫 电子结构     

Robust thermal quantum correlation and quantum phase transition of spin system on fractal lattices

We investigate the quantum correlation measured by quantum discord (QD) for thermalized ferromagnetic Heisenberg spin systems in one-dimensional chains and on fractal lattices using the decimation renormalization group approach. It is found that the QD between two non-nearest-neighbor end spins exhibits some interesting behaviors which depend on the anisotropic parameter Δ, the temperature T, and the size of system L. With increasing Δ continuously, the QD possesses a cuspate change at Δ = 0 which is a critical point of quantum phase transition (QPT). There presents the “regrowth” tendency of QD with increasing T at Δ < 0, in contrast to the “growth” of QD at Δ > 0. As the size of the system L becomes large, there still exists considerable thermal QD between long-distance end sites in spin chains and on the fractal lattices even at unentangled states, and the long-distance QD can spotlight the presence of QPT. The robustness of QD on the diamond-type hierarchical lattices is stronger than that in spin chains and Koch curves, which indicates that the fractal can affect the behaviors of quantum correlation.     

RF-thermal-structural-RF coupled analysis on atravelling wave disk-loaded a ccelerating structure

The travelling wave (TW) disk-loaded accelerating structure is one of the key components in normal conducting (NC) linear accelerators, and has been studied for many years. In the design process, usually after the dimensions of each cell and the two couplers are finalized, the structure is fabricated and tuned, and then the whole structure RF characteristics are measured by using a vector network analyzer. Before fabrication, the whole structure characteristics (including RF, thermal and structural ones) are less simulated due to the limited capability of currently available computers. In this paper, we described a method for performing RF-thermal-structural-RF coupled analysis on a TW disk-loaded structure using only one PC. In order to validate our method, we first analyzed and compared our RF simulation results on the 3 m long BEPCⅡ structure with the corresponding experimental results, which shows very good consistency. Finally, the RF-thermal-structure-RF coupled analysis results on the 1.35 m long NSC KIPT linac accelerating structure are presented.     

Numerical investigation of measurement error of the integrating sphere based on the Monte-Carlo method

To accurately measure the directional-hemispherical reflectance of a material surface using an integrating sphere, we investigated the effects of the integrating sphere’s interior structure and coating properties on the measured data by numerical simulation. The results showed that the integrating sphere’s structure and the reflectance of the coating codetermine the accuracy of the measured results. When the integrating sphere’s structure is fixed, choosing an appropriate internal coating using the method proposed in this paper ensures the accuracy of the results. If a proper coating is not available, we propose a method to effectively correct the measured results.     

RF-thermal-structural-RF coupled analysis on a travelling wave disk-loaded accelerating structure

The travelling wave (TW) disk-loaded accelerating structure is one of the key components in normal conducting (NC) linear accelerators, and has been studied for many years. In the design process, usually after the dimensions of each cell and the two couplers are finalized, the structure is fabricated and tuned, and then the whole structure RF characteristics are measured by using a vector network analyzer. Before fabrication, the whole structure characteristics (including RF, thermal and structural ones) are less simulated due to the limited capability of currently available computers. In this paper, we described a method for performing RF-thermal-structural-RF coupled analysis on a TW disk-loaded structure using only one PC. In order to validate our method, we first analyzed and compared our RF simulation results on the 3 m long BEPCⅡ structure with the corresponding experimental results, which shows very good consistency. Finally, the RF-thermal-structure-RF coupled analysis results on the 1.35 m long NSC KIPT linac accelerating structure are presented.     

同轴交错圆盘加载波导慢波结构高频特性的研究

采用多导体传输线分析方法, 对同轴交错圆盘加载波导慢波结构进行了理论分析, 得到了这种慢波结构的色散方程; 利用该色散方程, 得到的色散特性与HFSS仿真软件模拟结果符合良好. 分析了结构参数的变化对同轴交错圆盘加载波导慢波结构的色散特性影响. 结果表明: 增加内径和减小慢波结构的单位周期长度可以拓展慢波结构的带宽. 对同轴圆盘加载波导和同轴交错圆盘加载波导两种慢波结构的色散特性进行了比较, 结果表明: 采用圆盘交错加载方式可以减弱色散, 拓展带宽. 研究结果对同轴交错圆盘加载波导在毫米波行波管中的应用具有指导意义. 关键词： 行波管 同轴交错圆盘加载波导 慢波结构 色散特性     

一种扩展方形环异向介质结构的设计

为拓宽异向介质结构的带宽和维数,在方形环结构的基础上,提出了一种异向介质的交叉网状结构的设计,并对其介电常数和磁导率的频率特性进行了计算机仿真。研究结果表明,该结构在特定的频段内表现出了明显的负折射特性,与传统的裂环谐振器相比,新结构的结构对称、具有更宽的响应带宽和三维各向异性等特点。     

Epidemic spreading on networks with overlapping community structure

Many real networks are characterized by overlapping community structures in which vertices may belong to more than one community. In this paper, we propose a network model with overlapping community structure. The analytical and numerical results show that the connectivity distribution of this network follows a power law. We employ this network to investigate the impact of overlapping community structure on susceptible-infected-susceptible (SIS) epidemic spreading process. The simulation results indicate that significant overlapping community structure results in a major infection prevalence and leads to a peak of the spread velocity in the early stages of the emerging infection.     

A comparative study on radiation reliability of composite channel InP high electron mobility transistors

This paper proposes a reasonable radiation-resistant composite channel structure for In P HEMTs. The simulation results show that the composite channel structure has excellent electrical properties due to increased modulation doping efficiency and carrier confinement. Moreover, the direct current(DC) and radio frequency(RF) characteristics and their reliability between the single channel structure and the composite channel structure after 75-ke V proton irradiation are compared in detail. The results show that the composite channel structure has excellent radiation tolerance. Mechanism analysis demonstrates that the composite channel structure weakens the carrier removal effect. This phenomenon can account for the increase of native carrier and the decrease of defect capture rate.     

混合准周期异质结构的带隙补偿与展宽

基于一维光子晶体异质结构的多帯隙交叠补偿思想,提出了一种新颖的混合准周期级联结构,用于扩大全方位光子带隙.该全方位反射器结构由Fibonacci准周期结构和Thue-Morse准周期结构级联构成,研究表明,相比单种准周期结构,其全方位光子带隙宽度有显著提高.系统研究了结构参数(如周期数、阶数、介质折射率和厚度)对该结构光子带隙的影响,通过与周期结构带隙特性的比较,分析了准周期结构易于实现多带隙交叠的原因,为更复杂带隙结构的补偿和展宽奠定了设计基础.     

Asymptotic Structure of Constrained Exponential Random Graph Models

In this paper, we study exponential random graph models subject to certain constraints. We obtain some general results about the asymptotic structure of the model. We show that there exists non-trivial regions in the phase plane where the asymptotic structure is uniform and there also exists non-trivial regions in the phase plane where the asymptotic structure is non-uniform. We will get more refined results for the star model and in particular the two-star model for which a sharp transition from uniform to non-uniform structure, a stationary point and phase transitions will be obtained.     

Slow-Wave Characteristics of Elliptical Corrugated Waveguides with a Concentric Circular Hole

We present the formulation of elliptical corrugated waveguides with a concentric circular hole using the fieldmatching method and the addition theorem for Mathieu functions. The dispersion equation and the mean interaction impedance of this structure are derived separately. The numerical results, which are generally based on the current approach, agree well with the results obtained by the commercial software package CST. As a slow-wave structure, this structure has potential applications in high power microwave amplifiers and possibly filtering structures.     

Coupled fluid–structure solver: The case of shock wave impact on monolithic and composite material plates

An unstructured adaptive mesh flow solver, a finite element structure solver and a moving mesh algorithm were implemented in the numerical simulation of the interaction between a shock wave and a structure. In the past, this interaction is mostly considered as one-way in the sense that the shock causes a transient load on the structure while it is reflected uneffected by the impact. A fully coupled approach was implemented in the present work which can account for the effects associated with a mutual interaction. This approach included a compressible flow Eulerian solver of second order accuracy in finite volume formulation for the fluid and a Langargian solver in finite element formulation for the solid structure. A novel implementation of advancing front moving mesh algorithm was made possible with the introduction of a flexible and efficient quad-edge data structure. Adaptive mesh refinement was introduced into the flow solver for improved accuracy as well. Numerical results are further validated by theoretical analysis, experimental data and results from other numerical simulations. Grid dependency study was performed and results showed that the physical phenomena and quantities were independent of the numerical grid chosen in the simulations. The results illuminated complicated flow phenomena and structure vibration patterns, which in order to be detected experimentally require capabilities beyond those of the current experimental techniques. The numerical simulations also successfully modelled the aero-acoustic damping effects on the structure, which do not exist in previous numerical models. Further analysis of the results showed that the mutual interaction is not linear and that the non-linearity arises because the wave propagation in the fluid is not linear and it cascades a non-linear and non-uniform loading on the plate. Non-linearity intensifies when the plate is vibrating at high frequency while the wave propagation speed is low.     

小型Offner凸光栅光谱成像系统的结构设计及分析

根据小型Offner凸光栅光谱成像仪光学系统的特点,对其反射镜支撑结构和桁架结构进行了研究,完成了小型Offner光谱成像系统的结构设计,建立了系统的3D实体模型。为了验证结构设计的合理性,对设计的3D模型进行有限元分析。在模态分析中得到该结构的第一阶固有频率为362 Hz,高于系统设计要求的120 Hz;在加速度及温度载荷分析中,得到主要光学元件的面形值以及它们之间的相对位置变化,其离轴及偏角均在允许公差范围内,说明结构刚度满足使用要求,证明了结构设计的合理性。     

The potential energy curves for the two structures of H_4

Two potential energy curves for the tetrahedron structure and the centered equilateral triangle structure of the H 4 system are calculated by a simple method. The results of the calculation show that the tetrahedron structure is more stable than the centered equilateral triangle structure.     

Effect of structural conduction and heat loss on combustion in micro-channels

This paper presents a simple analytical model for the effects of heat exchange within the structure of a micro-channel combustor, and heat loss from the structure to the environment. This is accomplished by extending reasoning similar to that employed by Mallard and Le Chatelier in their thermal theory for flame propagation. The model is used to identify some of the basic parameters that must be considered when designing an efficient micro-combustor and its predictions are compared with the results of a numerical simulation of stoichiometric premixed combustion of a hydrogen–air mixture stabilized between two parallel plates. The simulation incorporates a one-dimensional continuity/energy equation solver with full chemistry coupled with a model for thermal exchange in the structure. The results show that heat exchange through the structure of the micro-combustor can lead to a broadening of the reaction zone. Heat loss to the environment decreases the broadening effect and eventually results in flame quenching. This behaviour, which arises from the thermal coupling between the gas and the structure, influences the maximum achievable power density of microscale combustors.     

GaN-based LEDs surrounded with a two-dimensional nanohole photonic crystal structure for effective laterally guided mode coupling

Traditional implementation of photonic crystals (PhCs) on LED light emission surfaces results in weak coupling of light with the PhCs. Here we introduce a GaN-based LED surrounded with a nanohole PhC structure along the mesa edges. The laterally guided modes in the epi-structure can be effectively coupled with the two-dimensional periodic structure. The proposed structure results in the improvement of LED light extraction and provides flexibility of radiation directionality control.     

Broad Stopband Characteristic of Dielectric Chiral Photonic Crystals

In this paper, a novel chiral photonic crystal structure is presented. The formula of reflection coefficient of multi-layer chiral media is applied to dielectric-chiral photonic crystal structure, which is composed of thin chiral layers sandwiched by conventional media. To compare with previous literature, we consider the dielectric structure with alternate glass and GaAs layers. The power reflectance as a function of wavelength for this photonic crystal structure has been calculated. The results are in good agreement with that of Reference. However, our method is simpler. From these graphs, it is found that 100% reflectance is only in finite wavelength ranges, and reflection bandwidth is also small for conventional photonic crystal structure. For chiral photonic crystal, the results show that the chiral photonic band gap (PBG) structure gives nearly 100% reflections in the near-infrared region in addition to some parts of the visible region of the wavelengths. Therefore, it can be used as a broadband reflector and filter.