Irreducible function bases of isotropic invariants of a third order three-dimensional symmetric and traceless tensor

Third order three-dimensional symmetric and traceless tensors play an important role in physics and tensor representation theory. A minimal integrity basis of a third order three-dimensional symmetric and traceless tensor has four invariants with degrees two, four, six, and ten, respectively. In this paper, we show that any minimal integrity basis of a third order three-dimensional symmetric and traceless tensor is also an irreducible function basis of that tensor, and there is no syzygy relation among the four invariants of that basis, i.e., these four invariants are algebraically independent.     

Phase separation and crystallization in a melt-spun Ti45Zr35Ni17Cu3 alloy

Structure and crystallization behavior of amorphous and quasicrystalline Ti₄₅Zr₃₅Ni₁₇Cu₃ alloy have been studied. DSC trace of the amorphous alloy obtained during continuous heating to 1300 K shows distinctly an exothermic peak and two endothermic peaks. The amorphous alloy has different structures depending on annealing temperature. The first exothermic reaction at low temperature region from 400 K to 900 K is due to the precipitation of an icosahedral quasicrystalline phase, and the second endothermic reaction at higher temperature region from 950 K to 990 K results from the transformation of the I-phase to C14 Laves and α-(Ti, Zr) phases.     

Tomography analysis of the sawtooth crash with post-cursor in LHCD plasma on HT-7 tokamak

Sawtooth oscillations with post-cursor were observed in LHCD plasma on HT-7 tokamak. The mode exists and decays gradually after the crash, which implies that the magnetic reconnection is incomplete and the central safety factor remains below unity after the crash. From results of the singular value decomposition (SVD) and tomographic reconstructions describing the magnetic surface structures in the crash, it was found that the m/n=1/1 mode survives in the crash. It is shown that, the appearance of the preservation of this mode is inconsistent with the secondary reconnection theory, and we conjecture that the evolving of this mode may be understood with the stochastic field model.     

超高效液相色谱-串联质谱法快速测定地表水中联苯胺、苦味酸、甲萘威、阿特拉津和溴氰菊酯

建立了一种经简单过滤即可直接进样的超高效液相色谱-串联质谱（UPLC-MS/MS）分析方法,可快速测定地表水中联苯胺、苦味酸、甲萘威、阿特拉津和溴氰菊酯5种有机物的残留。样品经0.2 μ m针式滤头过滤除去颗粒性杂质后,进行UPLC-MS/MS分析,采用UPLC HSS T₃色谱柱,2 mmol/L乙酸铵甲醇溶液和2 mmol/L乙酸铵水溶液作为流动相进行梯度洗脱,电喷雾离子源电离,正、负离子切换多反应监测模式进行定性和定量分析。5种目标化合物分别在0.10~10.0 μ g/L或1.00~100 μ g/L范围内线性关系良好,相关系数为0.996~0.999,方法的检出限为0.01~0.22 μ g/L;高、中、低3个添加水平的回收率为81.4%~113%,相对标准偏差为0.84%~14.0%。利用该方法对杭州市部分河流和水库的地表水样品进行分析,其中阿特拉津和溴氰菊酯在部分水样中有阳性检出。结果表明,该方法简便快捷、灵敏准确,适用于地表水样品中联苯胺、苦味酸、甲萘威、阿特拉津和溴氰菊酯的快速测定。     

EAST托卡马克杂质输运蒙特卡洛模拟

介绍DIVIMP程序的基本思想和采用的物理模型,研究EAST托卡马克欧姆放电条件下碳杂质的产生与输运.模拟结果与实验测量具有较好的一致性,说明将该程序应用于EAST装置中杂质输运模拟的合理性.并利用DIVIMP程序预测EAST在8MW加热功率条件下钨杂质的输运特性.     

弹性反冲探测分析技术在材料氦行为研究中的应用

弹性反冲探测分析技术（ERDA）对轻元素的测定具有灵敏度高、包含深度信息的优势,因此在材料氦行为研究中发挥着重要作用。镍基哈氏N合金被认为是未来熔盐堆的结构材料,氦脆是其服役性能下降的主要因素之一。利用掠入射模式的ERDA,解析了哈氏N合金样品中的氦原子浓度及其分布,但仅局限于0~175 nm深度范围内。结果表明:在800℃的退火条件下,距离样品辐照表面~33 nm深度区域内,出现了氦原子逃逸现象。更高温度的退火（1 050℃）可加剧氦原子的逃逸,但样品中仍有氦原子滞留。另外,采用透射式的ERDA,极大地扩大了对氦原子分析的深度范围,得到了纯镍薄膜在0~950 nm深度区域内的氦原子浓度分布。这表明将块体材料制备成薄膜样品,利用透射模式的ERDA,将可以得到氦原子在更大范围内的扩散、逃逸行为。Since the elastic recoil detection analysis (ERDA) technique has the advantages of high sensitivity and deep information in analyzing the light elements, it plays an important role in the study of helium behavior in materials. Helium embrittlement is one of the main reasons for the degradation of the Hastelloy N alloy, which has been considered as the promising candidate structural material for the further molten salt reactor. In this work, the profile of helium concentrationin sample of Hastelloy N alloy was analyzed by ERDA experiments applying grazing-incidence geometry. However, the result was limited within the depth range of 0~175 nm, and it shown that helium atoms escaped in the range from the irradiated surface of the sample to the depth of ~33 nm when annealing the sample at 800℃ The annealing at higher temperature (1 050℃) increased the escape of helium atoms, but a small fraction of helium atoms still trapped in the sample. In addition, the profile of helium concentration was obtained in the helium-irradiated pure nickel film in the depth range of 0~950 nm, using the ERDA experiments in transmission geometry. This indicates that the diffusion behavior of helium atoms in bulk samples can be completely obtained using the ERDA experiments in tranmission geometry if the bulk material can be prepared into a thin film sample.     

Optimal reorientation of underactuated spacecraft using genetic algorithm with wavelet approximation

The optimal attitude control of an underactuated spacecraft is investigated in this paper. The flywheels of the spacecraft can somehow only provide control inputs in two independent directions. The dynamic equations are formulated for the spacecraft under a nonholonomic constraint resulting from the constant time-rate of the total angular momentum of the system. The reorientation of such underactuated spacecraft is transformed into an optimal control problem. A genetic algorithm is proposed to derive the control laws of the two flywheels angle velocity inputs. The control laws are approximated by the discrete orthogonal wavelets. The numerical simulations indicate that the genetic algorithm with the wavelet approximation is an effective approach to deal with the optimal reorientation of underactuated spacecraft.     

ON GALERKIN DISCRETIZATION OF AXIALLY MOVING NONLINEAR STRINGS

A computational technique is proposed for the Galerkin discretization of axially moving strings with geometric nonlinearity. The Galerkin discretization is based on the eigenfunctions of stationary strings. The discretized equations are simplified by regrouping nonlinear terms to reduce the computation work. The scheme can be easily implemented in the practical programming. Numerical results show the effectiveness of the technique. The results also highlight the feature of Galerkin＇s discretization of gyroscopic continua that the term number in Galerkin＇s discretization should be even. The technique is generalized from elastic strings to viscoelastic strings.     

How entangled can a multi-party system possibly be?

The geometric measure of entanglement of a pure quantum state is defined to be its distance to the space of pure product (separable) states. Given an n-partite system composed of subsystems of dimensions $d_1,\dots ,d_n$, an upper bound for maximally allowable entanglement is derived in terms of geometric measure of entanglement. This upper bound is characterized exclusively by the dimensions $d_1,\dots ,d_n$ of composite subsystems. Numerous examples demonstrate that the upper bound appears to be reasonably tight.     

Efficient algorithms for computing the largest eigenvalue of a nonnegative tensor

Consider the problem of computing the largest eigenvalue for nonnegative tensors. In this paper, we establish the Q-linear convergence of a power type algorithm for this problem under a weak irreducibility condition. Moreover, we present a convergent algorithm for calculating the largest eigenvalue for any nonnegative tensors.