A generalized formulation for the refractive index at the geometric-optics limit

Starting from the concept of rapidity considered as generalization of the group velocity, we establish a generalized mathematical expression for the refractive group index of a material medium with little refraction at sufficiently small wavelengths, this index becoming approximately the refractive index at the geometric-optics limit and the phase velocity being approximately equal to the group velocity at the above limit. As main result, we derive an approximate relationship for the refractive index of a medium of small refraction at the geometric-optics limit. This medium is found to be left-handed at sufficiently small wavelengths.     

The specific heat of potassium holmium double tungstate

The results of measurements of thermal properties (specific heat) of potassium holmium double tungstate KHo(WO₄)₂ as a function of temperature (from 0.5 to 300?K) and magnetic field (up to 2?T) are presented. The total specific heat without the phonon and Schottky contributions is found to have the anomaly with maximum at T _SPT?～?5?K. This anomaly is likely related with the structural phase transition (SPT) caused by the cooperative Jahn–Teller effect. The increase of specific heat at very low temperatures and its shift towards high temperatures with increasing magnetic field are observed. The origin of this behaviour can be connected with possible magnetic phase transition induced by magnetic field.     

Calculations of electron collision and ionisation of rare gas dimers

Thresholds to 2000 eV electron impact total inelastic cross-sections for rare gas dimers were calculated employing a spherical complex optical potential formalism. From these inelastic cross-sections, total ionisation cross-sections are derived by applying a complex scattering potential-ionisation contribution method. This is a maiden attempt to study the total ionisation cross-section for most of these targets. To the best of our knowledge, no measurements or calculations are available for all the targets in the literature with which we can compare our results. The results show a linear relationship between maximum ionisation cross-section and target radius, depending on its size. Such dependence can confirm the consistency of the data presented here.     

核桃品质的综合评价

用主成分分析法分析了不同产地的11种核桃的蛋白质、不溶性膳食纤维、脂肪、水分、灰分、多种微量金属元素、单宁等12项品质指标,欲就核桃品质对其进行排序.结果表明,最终运用SPSS得到的2个主成分的累计贡献率达到86.057%,从而极大地简化了果实品质的评价因素,为制订评价核桃品质体系提供了理论依据.     

基于相对熵的多粒度语言判断矩阵的群决策方法

针对多粒度语言判断矩阵的群决策问题提出基于相对熵的最优化模型的排序方法.在多粒度语言偏好信息的导出函数基础上定义了语言判断矩阵对应的导出模糊互补判断矩阵,并给出其排序向量的计算式;同时采用语言判断矩阵的一致性指标来确定专家重要性程度的权向量;在相对熵的意义下构建了群决策排序向量的最优化模型,探讨了模型的求解方法.实例分析表明该模型是可行和有效的.     

Machine-part cell formation using biclustering

Cellular manufacturing is the cornerstone of many modern flexible manufacturing techniques, taking advantage of the similarities between parts in order to decrease the complexity of the design and manufacturing life cycle. Part-Machine Grouping (PMG) problem is the key step in cellular manufacturing aiming at grouping parts with similar processing requirements or similar design features into part families and by grouping machines into cells associated to these families. The PMG problem is NP-complete and the different proposed techniques for solving it are based on heuristics. In this paper, a new approach for solving the PMG problem is proposed which is based on biclustering. Biclustering is a methodology where rows and columns of an input data matrix are clustered simultaneously. A bicluster is defined as a submatrix spanned by both a subset of rows and a subset of columns. Although biclustering has been almost exclusively applied to DNA microarray analysis, we present that biclustering can be successfully applied to the PMG problem. We also present empirical results to demonstrate the efficiency and accuracy of the proposed technique with respect to related ones for various formations of the problem.     

Group edge choosability of planar graphs without adjacent short cycles

In this paper,we prove that 2-degenerate graphs and some planar graphs without adjacent short cycles are group(Δ(G)+1)-edge-choosable,and some planar graphs with large girth and maximum degree are groupΔ(G)-edge-choosable.     

Lamb wave mode decomposition for structural health monitoring

Lamb waves propagate over large distances in plate-like thin structures and they have received great attention in the structural health monitoring (SHM) field as an efficient means to inspect a large area of a structure by using only a small number of sensors. The times-of-flight of the Lamb wave modes are useful for detecting damage generated in a structure. However, due to the dispersive and multi-mode nature of Lamb waves, it is very challenging to decompose Lamb wave modes into symmetric and anti-symmetric modes for potential applications to structural health monitoring. Thus, we propose an efficient Lamb wave mode decomposition method based on two fundamental rules: the group velocity ratio rule and the mode amplitude ratio rule. The group velocity ratio rule means that the ratio of the group velocities of _A0$A_0$ and _S0$S_0$ modes must be constant. The mode amplitude ratio rule means that the ratio of the magnitudes of _A0$A_0$ and _S0$S_0$ modes in a measured response signal must be always greater than one once the center frequency of the input signal is determined, such that the magnitude of the _A0$A_0$ mode in the excited signal is larger than that of the _S0$S_0$ mode, and vice versa. The proposed method is verified through experiments conducted for a plate specimen.     

On coherently driven group index of probe pulse at double-frequency regimes: An analytical formulation

The group index and its lineshape of a relatively weak double-resonance probe pulse (signal) propagates through an open doubly driven N-type five-level atomic system are analytically formulated. It is shown that the signal can be controlled by manipulating the driving contribution of the two coupling fields, so that both superluminal and subluminal propagation can take place simultaneously at two different (probe field induced transition) frequency regimes with reduced absorption/gain. Hence the proposed double-control scheme may be exploited to observe the double-switching effect (i.e. from superluminal to subluminal and vice versa) with negligible distortion. In our realization this double-controlling mechanism may be regarded as simultaneous tuning of two knobs, to regulate the group index of the signal at double-frequency regimes.     

A novel method of optimal apodization selection for chirped fiber Bragg gratings

Apodization is a crucial technology for improving the dispersion performance of fiber Bragg gratings (FBGs). In this paper, we focus on how to select an optimal apodization for chirped fiber Bragg gratings and demonstrate a novel apodization selection method capable of choosing the optimal apodization based on the relationship between the bandwidth change and variation in average group delay ripple (GDR). Compared with current approaches, the novel method can select an optimal apodization profile and parameter for FBGs easily and accurately. Two numerical experiments are used to demonstrate the advantages of this method, one exhibits the different performances of five different apodization profiles, the other evaluates the influence of FBG parameters such as grating length, period, chirp, and index change on the apodization performance.