Calorimetric study and thermodynamic description of Ga-Ge-Li liquid alloys

This publication contains the thermodynamic results received by the drop calorimetry method. The experiments were conducted for four different cross sections, at the temperature of 1080 K. The investigated alloys were as follows: (Ga_0.75Li_0.25)_1-xGe_x, (Ge_0.50Li_0.50)_1-xGa_x, (Ga_0.50Li_0.50)_1-xGe_x, (Ga_0.25Li_0.75)_1-xGe_x. The mixing enthalpy changes measured for all four cross sections of the Ga-Ge-Li system are characterized by negative deviations from the ideal solutions. The Muggianu model with the ternary interaction parameters was applied to elaborate the experimental data of the mixing enthalpy change with the use of the optimized thermodynamic parameters of the binary systems available in the literature.     

First-principles calculations of binary Al compounds: Enthalpies of formation and elastic properties

Systematic first-principles calculations of energy vs. volume (E-V) and single crystal elastic stiffness constants (c_ij’s) have been performed for 50 Al binary compounds in the Al-X (X = Co, Cu, Hf, Mg, Mn, Ni, Sr, V, Ti, Y, and Zr) systems. The E-V equations of state are fitted by a four-parameter Birch-Murnaghan equation, and the c_ij’s are determined by an efficient strain-stress method. The calculated lattice parameters, enthalpies of formation, and c_ij’s of these binary compounds are compared with the available experimental data in the literature. In addition, elastic properties of polycrystalline aggregates including bulk modulus (B), shear modulus (G), Young’s modulus (E), B/G (bulk/shear) ratio, and anisotropy ratio are calculated and compared with the experimental and theoretical results available in the literature. The systematic predictions of elastic properties and enthalpies of formation for Al-X compounds provide an insight into the understanding and design of Al-based alloys.     

Numerical solutions of the one-phase classical Stefan problem using an enthalpy green element formulation

The enthalpy method is exploited in tackling a heat transfer problem involving a change of state. The resulting governing equation is then solved with a hybrid finite element - boundary element technique known as the Green element method (GEM). Two methods of approximation are employed to handle the time derivative contained in the discrete element equation. The first involves a finite difference method, while the second utilizes a Galerkin finite element approach. The performance of both methods are assessed with a known closed form solution. The finite element based time discretization, despite its greater challenge, yields less reliable numerical results. In addition a numerical stability test of both methods based on a Fourier series analysis explain the dispersive characters of both techniques, and confirms that replication of correct results is largely attributed to their ability to handle the harmonics of small wavelengths which are usually dominant in the vicinity of a front.     

A new hierarchical notation system and its application to the estimation of the standard enthalpy of formation

A new computer-readable hierarchical notation system is proposed and used as input to computers for estimating the standard enthalpy of formation.     

Structural stability of intermetallic phases in the Ga-Ti system

The total energies of intermetallic compounds in the Ga-Ti system are calculated employing electronic density functional theory (DFT) using pseudopotentials constructed by the projector augmented waves (PAW) method in the generalized gradient (GGA) approximation for the exchange and correlation energy. The calculations are performed for the experimentally observed compounds at their ideal stoichiometry as well as for structures which are stable in systems of early transition metals or rare earth elements with p elements of columns IIIB, IVB, and VB. The calculated formation enthalpy of the hexagonal B8₂-GaTi₂ compound is in excellent agreement with the value obtained by direct reaction calorimetry. The composition dependence of the enthalpies of formation is slightly asymmetric, the values of the enthalpies of formation being slightly more negative in the Ga-rich side. For the stable intermetallic compounds, the calculated zero-temperature lattice parameters agree well with those obtained experimentally at ambient temperature. Furthermore, for stable phases with unit-cell-internal degree(s) of freedom, the results of ab initio calculations show good agreement when compared with data obtained by structural analysis of X-ray diffraction.     

Thermodynamic assessment of the Molybdenum–Rhenium system

A thermodynamic optimization of the Mo–Re system by the Calphad method is proposed, taking into account new experimental data obtained in this work. According to recent crystal chemistry work, the χ and σ Frank–Kasper phases were modeled using two independent sublattices of variable occupation. This was made possible by including experimental site fractions in the different sublattices as input data for the parameter optimization. A consistent set of parameters is proposed. Good agreement is found between calculated and selected experimental values for different kinds of data: phase diagram, thermodynamic and crystallographic data.     

Structural stability of intermetallic phases in the Sn–Ti system

The total energies of intermetallic compounds in the Sn–Ti system are calculated employing electronic density-functional theory (DFT) using pseudopotentials constructed by the projector augmented waves (PAW) method in the generalized gradient (GGA) approximation for the exchange and correlation energy. The calculations are performed for the experimentally observed compounds at their ideal stoichiometry as well as for structures which are stable in systems of early transition metals or rare earth elements with p-elements of columns IIIB, IVB, and VB. The calculated formation enthalpy of the hexagonal Sn₅Ti₆ compound is slightly less exothermic than the value obtained by direct reaction calorimetry. For the stable intermetallic compounds, the calculated zero-temperature lattice parameters agree well with those obtained experimentally at ambient temperature. More, for stable phases with unit cell-internal degree(s) of freedom, the results of ab initio calculations show good agreement when compared with data obtained by structural analysis of X-ray diffraction. The composition dependence of the enthalpies of formation is slightly asymmetric. The electronic densities of state of the D8₈- Sn₃Ti₅ compound have been computed; the curve shows the hybridization of Sn 5p states with Ti 3d states. The stability of the intermetallic compounds in the Ti–Sn system is due to this hybridization.     

基于双处理器架构的地层压力测控系统设计

针对地层压力随钻测量困难、耗时等问题,以及工具下入困难、工具遇卡等潜在风险,提出了一种基于双处理器的随钻地层压力测量控制系统。在随钻过程中通过压力传感器测量井下压力,由主处理器TMS320F2812对地层压力值进行采集与处理;从处理器ATMEGA8对电磁阀进行智能控制,实现分流器、换向器与执行机构的协调配合,从而获得实时地层压力数据。实验结果表明：该系统实现了在井下高温、高压和强干扰的恶劣环境下对压力信号进行采集、分析、传输和存储,系统设计合理并具有较好的抗干扰性与实用性。     

编队卫星相对位置测量信息自主确定月球引力场的方法

针对月球远月面引力场的数据不能直接测量而导致其测量精度不高的问题,提出了一种基于双星编队的月球引力场自主确定方法。该方法考虑到月球引力场对编队卫星相对运动的影响,通过扩展卡尔曼滤波算法对星间距离测量数据的处理,利用观测量的测量值与一步预测测量值之间的偏差来修正一步预测状态值,从而得到状态估计量,即实现了卫星自主定轨以及月球引力场的自主确定。仿真结果表明,根据对编队卫星在7 430s内的相对位置测量数据的处理,卫星轨道位置和速度确定精度分别能达到5.04m和6.07×10~(-3) m/s;月球J2项摄动常数的精度能达到9.14×10~(-8) ;月球引力场常数的精度能达到3.47×10~7 m~3/s~2。此结果能在一定程度上改善现有的月球引力场模型,为我国"嫦娥工程"提供更多的技术资料。     

Entanglement of formation and concurrence for mixed states

We review some results on analytical computations of the measures for quantum entanglement: entanglement of formation and concurrence. We introduce some estimations of the lower bounds for the entanglement of formation in bipartite mixed states, and of lower bounds for the concurrence in bipartite and tripartite systems. The results on lower bounds for the concurrence are also generalized to arbitrary multipartite systems.     

Investigation and development of the atlas of chromaticity for formation of raster elements and basic link fragments in synthesizing color halftone images

A direction of improvement of a method for formation of color images on offset plates is proposed. The method and tools developed for synthesizing color images are experimentally tested. Translated from Kibernetika i Sistemnyi Analiz, No. 3, pp. 99–109, May–June, 2000.     

Thermodynamic modelling of the general NiAs-type structure: A study of first principle energies of formation for binary Ni-containing B8 compounds

Energies of formation of binary Ni-containing compounds with NiAs (B8)-type structure were calculated using ab-initio density functional theory. Structural relaxations and calculation of the total energies of the binary structures NiX₂ as CdI₂-type structure, NiX as NiAs-type structure and Ni₂X as Ni₂In-type structure (with X= Al, Ga, In, Si, Ge, Sn, As, Sb, Bi, Se, Te) were done using the projector augmented wave (PAW) method with a generalised gradient approximation (GGA).Overall, the calculated values are in good agreement with comparable experimental literature data. General trends of the lattice parameters and the energies of formation are discussed in detail. Nearly all of the calculated compounds are thermodynamically stable compared to the elements at zero Kelvin, although not all of them are present in the equilibrium phase diagrams.According to a recent investigation of the system Ni–Sn–Te, continuous solid solutions from CdI₂-type, over NiAs-type, up to Ni₂In-type regions are possible. Hence, a modified sublattice model according to the compound energy formalism within Calphad is proposed to give this possibility consideration. The use of the calculated energies of formation at 0 K as endmember energies within this model is discussed.     

分数阶多机器人的领航–跟随型环形编队控制

针对多机器人系统的环形编队控制复杂问题,提出一种基于分数阶多机器人的环形编队控制方法,应用领航–跟随编队方法来控制多机器人系统的环形编队和目标包围,通过设计状态估测器,实现对多机器人的状态估计.由领航者获取系统中目标状态的信息,跟随者监测到领航者的状态信息并完成包围环绕编队控制,使多机器人系统形成对动态目标的目标跟踪....     

Decentralized nonlinear robust control of UAVs in close formation

This paper treats the design of a decentralized nonlinear robust control system for formation flying of multiple unmanned aerial vehicles (UAVs). In close formation, it is assumed that vortex of any UAV affects the motion of all the UAVs behind it. The forces produced by these vortices are complex functions of relative position co‐ordinates of the UAVs. In this paper, these forces are treated as unknown functions, which cannot be parameterized. Since the system is not invertible in the wind axes system, a simplified co‐ordinate system obtained from the wind axes system for which the velocity roll (bank angle) is zero, is considered for the design of the control system. A nonlinear robust control system for the separation trajectory control of the wing aircraft in the simplified wind coordinate system is derived. Uncertain functions and unmeasured variables are estimated using a high‐gain observer for the synthesis of the control system. Each wing UAV synthesizes its control law using its own state variables and the relative position of the preceding UAV with respect to the wing UAV. Thus the control system is decentralized since each UAV has to communicate (depending on sensors for position measurement) with at most one (preceding) UAV, and no data transmission from the remaining vehicles is required. Simulation results for two UAVs are presented which show precise separation trajectory control of each wing UAV in spite of the presence of unknown and unstructured vortex forces, while the lead aircraft maneuvers. Furthermore, these results confirm that when the wing aircraft is positioned properly in the vortex of the lead aircraft, it experiences reduction in its required flight power. Copyright © 2003 John Wiley & Sons, Ltd.     

Modeling the width of exciton formation zone in organic light emitting diode

The width of exciton formation zone has been simulated in a single-layer organic light emitting diode (OLED) based on the model of carrier device lifetimes. The width of exciton formation zone decreases with device current density increasing. Increasing the thickness of emissive layer (EML) is able to widen exciton formation zone. There is an optimal value of EML’s charge carrier mobility to maximize the width of exciton formation zone. In addition, the width of exciton formation zone increases markedly with the trap density of EML increasing, and shows certain correlation with the dielectric constant of EML. The current modeling provides novel insights on optimizing EMLs towards wide exciton formation zone, helpful for extending operational stability of OLED.     

Robust formation control without velocity measurement of the leader robot

In this paper a control problem of leader–follower motion coordination of multiple nonholonomic mobile robots is addressed and subsequently in the proposed scheme, a reference trajectory generated based on the information from the leader is tracked by the follower robots. To alleviate demanded information on the leader, specifically to eliminate the measurement requirement or estimation of the leader's velocity and dynamics, a virtual vehicle is constructed whereby its trajectory converges to the reference trajectory of the follower. Trajectory tracking controller is then designed to allow the follower robot to track the virtual vehicle using neural network approximation, in combination with the backstepping and Lyapunov direct design technique and finally the performance and effectiveness of the controller is verified throughout the experiments.     

Fault detection and isolation of the attitude control subsystem of spacecraft formation flying using extended Kalman filters

In this paper, the problem of fault detection and isolation (FDI) of the attitude control subsystem (ACS) of spacecraft formation flying systems is considered. For developing the FDI schemes, an extended Kalman filter (EKF) is utilised which belongs to a class of nonlinear state estimation methods. Three architectures, namely centralised, decentralised, and semi-decentralised, are considered and the corresponding FDI strategies are designed and constructed. Appropriate residual generation techniques and threshold selection criteria are proposed for these architectures. The capabilities of the proposed architectures for accomplishing the FDI tasks are studied through extensive numerical simulations for a team of four satellites in formation flight. Using a confusion matrix evaluation criterion, it is shown that the centralised architecture can achieve the most reliable results relative to the semi-decentralised and decentralised architectures at the expense of availability of a centralised processing module that requires the entire team information set. On the other hand, the semi-decentralised performance is close to the centralised scheme without relying on the availability of the entire team information set. Furthermore, the results confirm that the FDI results in formations with angular velocity measurement sensors achieve higher level of accuracy, true faulty, and precision, along with lower level of false healthy misclassification as compared to the formations that utilise attitude measurement sensors.     

柴油馏分深度加氢脱硫过程中有色体形成机理的研究

为了生产含低硫、色度好的柴油产品，采用计算机分子模拟技术研究了柴油馏分深度加氢脱硫(HDS)过程中多环芳烃有色体的形成机理。研究结果显示，柴油馏分中难脱除硫化物4-MDBT、4，6-DMDBT的HDS中间产物生成多环芳烃的反应历程中每步反应的活化能较低，其中的缩合环化反应为吸热反应。模拟产物符合实验事实，表明模拟计算的多环芳烃有色体形成路径是可能的、合理的。     

编队舰船对各自拖线阵声纳DOA估计性能的影响

拖船辐射噪声是影响拖曳线列阵声纳探测性能的重要因素。就编队舰船辐射噪声对各自拖曳线列阵声纳采用常规波束形成方法、最小方差无失真响应（Minimum Variance Distortionless Response,MVDR）波束形成方法和盲源分离与MVDR波束形成融合方法时方位估计性能的影响,进行了全面的仿真比较。结果表明,编队舰船噪声对常规波束形成方法、MVDR波束形成方法的影响非常严重,必须采取措施对其进行抑制;而盲源分离与MVDR融合方法则表现出了优越的性能,一定程度上抑制了编队舰船噪声对拖曳线列阵声纳方位估计的影响。     

Effectiveness of spatial representation in the formation of network communities: experimental study on community organizer

In this paper, we present and discuss Community Organizer, a system designed to support network communities. The main characteristic of Community Organizer is the use of spatial representations for the relationships among community members including the communications exchanged among these members. These spatial representations reflect the degree of closeness of interests and concerns among the members, and are intended to provide users with clues on how to form network communities. In order to investigate the effectiveness of the proposed spatial representations, we conducted experiments with two different versions of the software. One version offered meaningful spatial representations while the other version did not. The subjects who used the former software version felt a greater sense of ‘community’, enjoyed using the software more, and actively used it longer than the subjects using the latter software version (control condition). These results indicated that the proposed spatial representations are effective in supporting network community formation.