Coupled Cluster Method Calculations of Quantum Magnets with Spins of General Spin Quantum Number

We present a new high-order coupled cluster method (CCM) formalism for the ground states of lattice quantum spin systems for general spin quantum number, s. This new general-s formalism is found to be highly suitable for a computational implementation, and the technical details of this implementation are given. To illustrate our new formalism we perform high-order CCM calculations for the one-dimensional spin-half and spin-one antiferromagnetic XXZ models and for the one-dimensional spin-half/spin-one ferrimagnetic XXZ model. The results for the ground-state properties of the isotropic points of these systems are seen to be in excellent quantitative agreement with exact results for the special case of the spin-half antiferromagnet and results of density matrix renormalization group (DMRG) calculations for the other systems. Extrapolated CCM results for the sublattice magnetization of the spin-half antiferromagnet closely follow the exact Bethe Ansatz solution, which contains an infinite-order phase transition at =1. By contrast, extrapolated CCM results for the sublattice magnetization of the spin-one antiferromagnet using this same scheme are seen to go to zero at 1.2, which is in excellent agreement with the value for the onset of the Haldane phase for this model. Results for sublattice magnetizations of the ferrimagnet for both the spin-half and spin-one spins are non-zero and finite across a wide range of , up to and including the Heisenberg point at =1.     

High-Order Coupled Cluster Method (CCM) Calculations for Quantum Magnets with Valence-Bond Ground States

In this article, we prove that exact representations of dimer and plaquette valence-bond ket ground states for quantum Heisenberg antiferromagnets may be formed via the usual coupled cluster method (CCM) from independent-spin product (e.g. Néel) model states. We show that we are able to provide good results for both the ground-state energy and the sublattice magnetization for dimer and plaquette valence-bond phases within the CCM. As a first example, we investigate the spin-half J ₁–J ₂ model for the linear chain, and we show that we are able to reproduce exactly the dimerized ground (ket) state at J ₂/J ₁=0.5. The dimerized phase is stable over a range of values for J ₂/J ₁ around 0.5, and results for the ground-state energies are in good agreement with the results of exact diagonalizations of finite-length chains in this regime. We present evidence of symmetry breaking by considering the ket- and bra-state correlation coefficients as a function of J ₂/J ₁. A radical change is also observed in the behavior of the CCM sublattice magnetization as we enter the dimerized phase. We then consider the Shastry-Sutherland model and demonstrate that the CCM can span the correct ground states in both the Néel and the dimerized phases. Once again, very good results for the ground-state energies are obtained. We find CCM critical points of the bra-state equations that are in agreement with the known phase transition point for this model. The results for the sublattice magnetization remain near to the “true” value of zero over much of the dimerized regime, although they diverge exactly at the critical point. Finally, we consider a spin-half system with nearest-neighbor bonds for an underlying lattice corresponding to the magnetic material CaV₄O₉ (CAVO). We show that we are able to provide excellent results for the ground-state energy in each of the plaquette-ordered, Néel-ordered, and dimerized regimes of this model. The exact plaquette and dimer ground states are reproduced by the CCM ket state in their relevant limits. Furthermore, we estimate the range over which the Néel order is stable, and we find the CCM result is in reasonable agreement with the results obtained by other methods. Our new approach has the dual advantages that it is simple to implement and that existing CCM codes for independent-spin product model states may be used from the outset. Furthermore, it also greatly extends the range of applicability to which the CCM may be applied. We believe that the CCM now provides an excellent choice of method for the study of systems with valence-bond quantum ground states.     

Determination the ability of military vehicles to override vegetation

Military operations usually include movement over existing roads and also through natural terrain. Wooded terrain is one of the most challenging environments which affect vehicle mobility. The ability of a vehicle to cross a forest area depends on the possibility of determining if the vehicle is able to manoeuvre between tree stems or can override individual trees. Overriding tree obstacles can be more effective if a vehicle needs a shorter time to cross some tree stems rather than manoeuvring around them. Vehicle movement to cross a forest stand depends on vegetation factors as the stem diameter, stem spacing, and also on tree root parameters, which determine the mechanical tree stability, and a vehicle’s ability to override the trees. Also, the technical parameters (width, length, turning radius, weight, traction force) of the selected military vehicle are important to classify the cross-country movement options. This study describes both the theoretical predictions of the movement of vehicles in forest stands and summarizes the results of one of the most extensive testing of vehicles’ ability to cross individual trees.     

Contemporary Commercial Music (CCM) Survey: Who''s Teaching What in Nonclassical Music

Currently, there is an increasing interest in and demand for training in a wide variety of nonclassical music--contemporary commercial music (CCM)--and most particularly for music theater. A survey of singing teachers was completed to elucidate their training, education, and experience with and methods of teaching CCM. Teachers were at colleges, universities, and conservatories as well as in private studios, both nationally and in several foreign countries. A substantial percentage of those teaching CCM had neither formal education in teaching it nor professional experience. Many of the respondents indicated conflict between classical and CCM styles. Respondents were generally familiar with voice science and voice medicine as well as certain CCM terminology. Teachers expressed an interest in obtaining more information, with an emphasis on healthy vocal production. These results are discussed, as well as implications for the singing teacher who desires specific training to teach CCM.     

有机溶剂对PEM燃料电池CCM结构和性能的影响

采用直接喷涂法将催化剂涂覆在质子交换膜上形成CCM(catalyst coated membrane),CCM与碳纸扩散层组成膜电极用于质子交换膜燃料电池.制备CCM的混合液由质量分数20%的Pt/C催化剂、质量分数5%的Nafion溶液、有机溶剂和水组成.不同的有机溶剂(乙醇、异丙醇和叔丁醇)、有机溶剂的含量、溶剂的...     

基于构件的企业信息系统架构模式的研究与应用

本文针对企业信息化进程中传统软件模式存在的问题,在探究具体构件技术,比如：基于构件开发方式过程阶段的划分、构件模型的选择、构件的分类和层次结构的基础上,结合具体工程实践,提出了一种基于构件的企业信息系统架构模式,并就其具体应用效果进行了说明．