Performance of a skilled motor task in virtual and real environments

Three experiments compared the performances of adult participants (three groups of 10) on a perceptuo-motor task in both real world (RW) and virtual environments (VEs). The task involved passing a hoop over a bent wire course, and three versions of the task were used: a 3-D wire course with no background, a flattened version of the 3-D course (2½-D course) with no background, and the 2½-D course with added background to provide spatial context. In all three experiments the participants had to prevent the hoop from touching the wire as they moved it. In the first experiment, the VE condition produced about 18 times more errors than the RW task. The VE 2½-D task was found to be as difficult as the 3-D, and the 2½-D with the added background produced more errors than the other two experiments. Taken together, the experiments demonstrate the difficulty of performing fine motor tasks in VEs, a phenomenon that has not been given due attention in many previous studies of motor control in VEs.     

Quantum disorder due to singlet formation: The Plaquette lattice

I study the order/disorder transition due to singlet formation in a quantum spin system by means of exact diagonalization. The systems is build by spin 1/2 on a two-dimensional square lattice with two different kinds of antiferromagnetic Heisenberg interactions. The interaction J_p connects 4 nearest neighbor spins on a plaquette. The interaction J_n connects the plaquettes with each other. If J_p=J_n the systems reduces to the simple square lattice case. If one of the interactions becomes sufficiently larger then the other the purely quantum effect of singlet formation drives the system into a disordered phase with only short range correlations in the plaquettes and a spin gap. I study the transition point by evaluating the spin gap and spin-spin correlations. I compare the results with previously calculated data from a non-linear σ model approach, spin wave theory and series expansion calculations. I confirm a critical value of J_n≈0.6 for the quantum phase transition point.     

On the stability of a single-species population model with time lag

The stability of equilibrium positions of a single-species population model suggested by Ayala et al. (1973) is studied in the presence of time lag and constant forcing term p. This model is a generalization of the well known logistic model and depends on an additional parameter θS. It is shown that for θ ≥1 the maximum delay for which stability holds decreases as p increases while for 0< θ ≤ ½ it increases. The maximum delay for ½ < θ < 1 is not monotone and has a unique minimum. The conditions that equilibrium position be stable for all time lags are also obtained.     

基于MEMS传感器的风洞尾旋姿态测量研究

尾旋是飞机在失去控制后的一种极危险的飞行状态,陷入尾旋极易造成飞机的坠毁,在飞机研制过程中为了提高其机动性及抗尾旋能力,必须对这种极限飞行状态进行研究。在立式风洞中开展尾旋试验是目前效率最高,安全性最有保障的技术手段。试验测试的主要参数是飞机在尾旋及改出过程中的姿态角（包括俯仰角、偏航角和滚转角）。在此简要介绍了通过陀螺仪、加速度计和地磁计进行姿态数据融合的算法,以及采用了一种MEMS传感器进行尾旋姿态测量的试验技术,并且其姿态数据可由Zigbee无线数据模块实时传送到测量计算机。通过试验验证,该技术简单有效,不受现场环境限制,系统动态性能稳定可靠,角度测试精度为优于1°,满足了试验需求,提高了试验效率及数据质量。     

Simulating spin systems on IANUS, an FPGA-based computer

We describe the hardwired implementation of algorithms for Monte Carlo simulations of a large class of spin models. We have implemented these algorithms as VHDL codes and we have mapped them onto a dedicated processor based on a large FPGA device. The measured performance on one such processor is comparable to O(100) carefully programmed high-end PCs: it turns out to be even better for some selected spin models. We describe here codes that we are currently executing on the IANUS massively parallel FPGA-based system.     

Construction of four-qubit quantum entanglement for SI (S = 3/2, I = 3/2) spin system

In quantum information processing, spin-3/2 electron or nuclear spin states are known as two-qubit states. For SI (S = 3/2, I = 3/2) spin system, there are 16 four-qubit states. In this study, first, four-qubit entangled states are obtained by using the matrix representation of Hadamard and CNOT logic gates. By considering ⁷⁵As@C₆₀ molecule as SI (S = 3/2, I = 3/2) spin system, four-qubit entangled states are also obtained by using the magnetic resonance pulse sequences of Hadamard and CNOT logic gates. Then, it is shown that obtained entangled states can be transformed into each other by the transformation operators.     

Spin-box algorithm for low temperature dynamics of short range disordered Ising spin systems

An approximate parallel approach was developed to describe efficiently the low temperature dynamics in short range Ising spin systems, based on the dynamically relevant sequence technique. It relates the low temperature dynamics to the structural properties of the state space of spin glasses and disordered ferromagnets, which has been proved to give accurate results for low temperatures. Large samples can be handled, which allows the analysis of domain formation and the discussion of the growth laws. The results are consistent with existing numerical and experimental data.     

‘Actions not as planned’ in military air-traffic control

Observations were made of the errors made by eight air-traffic controllers over two periods each of 2½ hours. Errors were classified using a recently devised classification of motor-program errors (Reason 1979) and all the controllers were observed under three conditions of workload, and performing two ostensibly similar air-traffic tasks.

More errors were found with increasing workload, but only in one of the tasks This was interpreted in terms of the pacing and time stress inherently imposed in that task. The assessment of error incidence seems a good candidate as a non-intrusive measure of workload. Analysis of errors in terms of Reason's typology showed no interaction with any of the other variables.

The association of errors with the use of particular pieces of equipment demonstrated ergonomic deficiencies which may have otherwise remained unnoticed It seems that error auditing may also be a useful investigative technique in ergonomic assessment.     

Canopy bidirectional reflectance dependence on leaf orientation

Abstract

The bidirectional reflectance patterns of a complete (dense) canopy are examined as functions of canopy architecture, as specified by azimuth angle δ_e and zenith angle ψ for a leaf normal. The leaves are assumed to be opaque Lambertian reflectors, all with identical orientation and reflectance properties throughout the canopy, and randomly distributed with respect to the irradiation field and the viewing direction. Multiple reflections are not considered and irradiation is by direct beam only. Simple analytical expressions for the bidirectional reflectance factor are presented and analysed. The nadir reflectance (expressed as a fraction of the leaf reflectance) for canopies whose leaves face the sun, δ_e = 0, is bounded by cos ψ and 1/2; cos ψ. The nadir reflectance initially increases with increasing ψ, but then decreases when ψ reaches moderate to large values. For a δ_e = π canopy, on the other hand, the much lower nadir reflectance is bounded by ½ cos ψ and 0, and decreases with increasing ψ throughout the entire range of ψ (0 to ½π). The maximum bidirectional reflectance occurs at large viewing zenith angles (i.e. close to the horizon). The maximum reflectance is always higher for a δ_e = 0 canopy than for a δ_e = π canopy, but the differences become small when ψ approaches ½π. The bidirectional reflectance thus depends on the leaf azimuth as well as the zenith angle. Leaf-area azimuthal distributions should be considered when conducting model inversions to infer canopy characteristics and architecture.     

Symplectic integrators for classical spin systems

We suggest a numerical integration procedure for solving the equations of motion of certain classical spin systems which preserves the underlying symplectic structure of the phase space. Such symplectic integrators have been successfully utilized for other Hamiltonian systems, e.g., for molecular dynamics or non-linear wave equations. Our procedure rests on a decomposition of the spin Hamiltonian into a sum of two completely integrable Hamiltonians and on the corresponding Lie-Trotter decomposition of the time evolution operator. In order to make this method widely applicable we provide a large class of integrable spin systems whose time evolution consists of a sequence of rotations about fixed axes. We test the proposed symplectic integrator for small spin systems, including the model of a recently synthesized magnetic molecule, and compare the results for variants of different order.     

主动水雷攻击成功率试验考核方法研究

主动水雷作为水雷武器的一个重要分支,具有适用面广、打击范围大、单雷封锁效率高等优点。攻击成功率是衡量主动水雷作战效能的重要战技指标。为解决该项指标考核鉴定这一工程实际问题,在简要介绍主动水雷工作原理与攻击机制的基础上,对水雷的攻击成功率试验考核问题进行了系统剖析。创新性地提出分项试验考核方法,并根据作战态势与想定进行绘图分析,运用概率论与数理统计相关理论进行公式推导,建立了一套主动水雷攻击成功率的试验考核与评定方案。解决了水雷攻击成功率这一试验鉴定难题,为后续水雷战作战效能评估奠定了基础,也为后续改进型号试验鉴定工作提供了参考。本方案最终通过相关单位的一致认可,进行了工程实施,取得了理想的效果。     

四烷氧基酞菁铜(Ⅱ)旋涂膜的气敏特性

设计合成了可溶性的四 a (2.2.4 三甲基 3 戊氧基)酞菁铜(C64H80N8O4Cu),利用旋涂技术制备了四 a (2.2.4 三甲基 3 戊氧基)酞菁铜旋涂膜,研究了配合物旋涂膜的红外光谱、电子吸收光谱、对NO2和乙醇蒸汽的敏感特性以及气敏机理。结果表明:可溶性的四 a (2.2.4 三甲基 3 戊氧基)酞菁铜可制得较理想的旋涂膜,与溶液相比较旋涂膜的电子吸收光谱明显变宽,且Q带的2个吸收峰分别红移了16nm和12nm。室温下配合物旋涂膜对较低体积分数NO2呈现出良好的气敏性,在NO2为1.0～5.0×10-6体积分数范围内表现出较好的线性关系,而薄膜对乙醇蒸汽响应的体积分数为3.0×10-5。动力学研究表明:四 a (2.2.4 三甲基 3 戊氧基)酞菁铜旋涂膜对气体的吸附和脱附分2个过程完成。     

Reweighting histogram technique for the quantum Heisenberg ferromagnet

In this work, we extend the reweighting histogram technique (RHT) to make it suitable for the study of quantum spin systems. Combining the Handscomb quantum Monte Carlo method with RHT, we compute some equilibrium critical parameters for the quantum S=1/2 Heisenberg ferromagnet on simple cubic lattices of sizes up to L=48. We found k_BT_c/J=1.67764(2), U∗=0.4504(1), γ=1.397(20), β=0.360(6) and ν=0.705(10). These are in perfect agreement with the best field theory and high temperature series results. Also, we found that the auto-correlation time near criticality scales roughly with the system's volume. Potential applications of the method to the study of general quantum spin systems are discussed.     

Extracting contour lines from a hierarchical surface model

The Hierarchical Triangulated Irregular Network (HTIN) is a structure for representing 2½-dimensional surfaces at different levels of detail through piecewise-linear approximations based on triangulations of the surface domain. In this paper, we present two algorithms that allow extracting a representation of the surface and contour lines at a given level of detail, directly from the HTIN.     

Mean interface magnon dispersion curves obtained by means of the matching procedure

A theoretical approach based on the matching procedure in the random-phase approximation has been developed to investigate the spin fluctuations dynamics on an interface of the Heisenberg biferromagnetic layers. The two ferromagnetic layers are considered directly coupled by magnetic exchange interactions. No electronic effects are considered. The analytical approach solves for the three-dimensional crystal spin field in the bulk and the interface domain, that arises owing to the reduced of magnetic translation symmetry for the system. The calculations presented here are an application of a theoretical method based on Green functions formalism discussed in previous work. Analytic expressions are obtained for the dispersion relations and spectral intensities of the localized spin-waves and the quantized bulk spin waves near an interface. The effects of varying the bulk-interface coupling exchange near the interface are studied. Also, the condition for the appearance of the acoustic and optical interface modes is discussed. Numerical examples of the modes are given and provide some indication of how the magnon spectrum is affected by interface parameters. These factors influence the energies of localized modes, as well as their frequency, intensity and attenuation.     

Stability and error analysis of mixed finite-volume methods for advection dominated problems

We consider a convection-diffusion-reaction problem, and we analyze a stabilized mixed finite-volume scheme introduced in [1]. The scheme is presented in the format of discontinuous Galerkin methods, and error bounds are given, proving O(h^½) convergence in the L²-norm for the scalar variable, which is approximated with piecewise constant elements.     

滨海土壤I-69杨根际无机磷形态分布及有效性研究

对滨海脱盐土壤或轻度盐渍土壤上不同林龄I -69杨根际、非根际无机磷存在形态、数量和有效性进行了研究 ,结果表明 :I -69杨根系活动能明显提高根际土壤供磷能力 ,3、5、11年生I -69杨根际有效磷明显富集 ,富集量分别为3 .87、4.3 2、4.3 5mg/kg ;Ca2 -P在不同林龄I -69杨根际含量明显高于非根际土 ,差异都达到极显著水平 ,R/S随林龄增大分别是 2 .15、2 .5 9、5 .5 4;Ca8-P在 5、11年生I -69杨根际明显富集 ,而Ca10 -P明显亏缺 ;不同林龄I -69杨根际、非根际土Al-P、Fe -P和O -P含量无明显差异 ,盐渍土壤中它们的生物有效性较低。     

The structure of enumerated spin glass state spaces

We enumerate the low energy part of the state space of an Ising spin glass using an efficient branch-and-bound algorithm. A coarse graining algorithm (NB-clustering) is employed to condense the inherent information to a system size which is treatable in computer simulations. The reduced state space still incorporates all ingredients necessary to simulate aging effects. We investigate its structure in detail and find that certain assumptions made in heuristical state space models which have been presented in the past to reproduce aging phenomena in spin glass experiments are indeed compatible with the data from the observed state spaces.     

Erratum: An Approximation Algorithm for Minimum-Cost Vertex-Connectivity Problems

Abstract. There is an error in our paper ``An Approximation Algorithm for Minimum-Cost Vertex- Connectivity Problems' (Algorithmica (1997), 18:21—43). In that paper we considered the following problem: given an undirected graph and values r _ij for each pair of vertices i and j , find a minimum-cost set of edges such that there are r _ij vertex-disjoint paths between vertices i and j . We gave approximation algorithms for two special cases of this problem. Our algorithms rely on a primal—dual approach which has led to approximation algorithms for many edge-connectivity problems. The algorithms work in a series of stages; in each stage an augmentation subroutine augments the connectivity of the current solution. The error is in a lemma for the proof of the performance guarantee of the augmentation subroutine. In the case r _ij = k for all i,j , we described a polynomial-time algorithm that claimed to output a solution of cost no more than 2 H (k) times optimal, where H = 1 + 1/2 + · · · + 1/n . This result is erroneous. We describe an example where our primal—dual augmentation subroutine, when augmenting a k -vertex connected graph to a (k+1) -vertex connected graph, gives solutions that are a factor Ω(k) away from the minimum. In the case r _ij ∈ {0,1,2} for all i,j , we gave a polynomial-time algorithm which outputs a solution of cost no more than three times the optimal. In this case we prove that the statement in the lemma that was erroneous for the k -vertex connected case does hold, and that the algorithm performs as claimed.     

Cube cluster approximation for the spin glass in the simple cubic lattice

The spin glass in the random-bond Ising model on a simple cubic lattice is considered. A simple method to calculate the partial trace of the density matrices of a fairly large cluster by use of the REDUCE system is presented. The phase diagram showing the paramagnetic, ferromagnetic, antiferromagnetic and spin glass states is obtained for the ±J model on the simple cubic lattice by the cube cluster approximation. The spin glass transition temperature is obtained with the inclusion of enough frustration of the cube clusters, and kTg/J=0.9850 for p (the concentration of the +J bond) = 1/2.