Mode shift and stability control of a current mode controlled buck-boost converter operating in discontinuous conduction mode with ramp compensation

By establishing the discrete iterative mapping model of a current mode controlled buck-boost converter, this paper studies the mechanism of mode shift and stability control of the buck-boost converter operating in discontinuous conduction mode with a ramp compensation current. With the bifurcation diagram, Lyapunov exponent spectrum, time-domain waveform and parameter space map, the performance of the buck-boost converter circuit utilizing a compensating ramp current has been analysed. The obtained results indicate that the system trajectory is weakly chaotic and strongly intermittent under discontinuous conduction mode. By using ramp compensation, the buck-boost converter can shift from discontinuous conduction mode to continuous conduction mode, and effectively operates in the stable period-one region.     

Acoustic band pinning in the phononic crystal plates of anti-symmetric structure

Acoustic bands are studied numerically for a Lamb wave propagating in an anti-symmetric structure of a one-dimensional periodic plate by using the method of supercell plane-wave expansion. The results show that all the bands are pinned in pairs at the Brillouin zone boundary as long as the anti-symmetry remains and acoustic band gaps (ABGs) only appear between certain bands. In order to reveal the relationship between the band pinning and the anti-symmetry, the method of eigenmode analysis is introduced to calculate the displacement fields of different plate structures. Further, the method of harmony response analysis is employed to calculate the reference spectra to verify the accuracy of numerical calculations of acoustic band map, and both the locations and widths of ABGs in the acoustic band map are in good agreement with those of the reference spectra. The investigations show that the pinning effect is very sensitive to the anti-symmetry of periodic plates, and by introducing different types of breakages, more ABGs or narrow pass bands will appear, which is meaningful in band gap engineering.     

The periodic solution to the model for the El Nio-Southern oscillation

A class of oscillator of the El Ni?o-Southern oscillation model is considered. Using Mawhin's continuation theorem, a result on the existence of periodic solutions for ENSO model is obtained.     

New integrable hierarchies from vertex operator representations of polynomial Lie algebras

We give a representation–theoretic interpretation of recent discovered coupled soliton equations using vertex operators construction of affinization of not simple but quadratic Lie algebras. In this setup we are able to obtain new integrable hierarchies coupled to each Drinfeld–Sokolov of A, B, C, D hierarchies and to construct their soliton solutions.     

Structural and electronic properties of Bin (n = 2-14) clusters from density-functional calculations

The structural and electronic properties of Bi_n (n = 2-14) clusters have been systematically studied using gradient-corrected density-functional theory. For each cluster size, a number of structural isomers were constructed and optimized to search for the lowest-energy structure. The competition of several structural patterns such as cages, superclusters, and layered structures leads to the alternating appearance of these configurations as global minima. Although the tendency of Bi to form puckered-layer structures is already well-known, the electronic states of Bi_n clusters are still far from that of the bulk. As well, a remarkable even-odd atom number oscillation is observed in the structural and electronic properties of the clusters, implying that the stability of Bi_n clusters is mainly dominated by the electron shell effect rather than by geometrical packing. The theoretically calculated values for electron affinities agree well with available experimental data.     

海森堡模型中量子隐形传递的研究

通过对海森堡模型中量子热纠缠的研究,进而研究以海森堡热纠缠混合态为信道的量子隐形传递,计算出纠缠度和保真度,分析外界环境(温度、磁场等)对热纠缠及隐形传递的影响.     

Gaps in the base set of primitive nonpowerful sign patterns

For a primitive nonpowerful square sign pattern A, the base of A, denoted by l(A), is the least positive integer l such that every entry of A ^l is #. In this article, we consider the base set of the primitive nonpowerful sign pattern matrices. Some useful results about the bases for the sign pattern matrices are presented there. Some special sign pattern matrices with given bases are characterized and more ‘gaps’ in the base set are shown.     

A simple hydrothermal route to synthesis of rod-like MnOOH and spindle-shaped MnCO3

A simple hydrothermal route was developed to synthesis of rod-like manganese oxyhydroxide (MnOOH) and spindle-shaped manganese carbonate (MnCO₃) based on the redox reactions between potassium permanganate (KMnO₄) and ??-cyclodextrin (??-CD) without extra surfactant or template. At the mass ratio between ??-CD and KMnO₄ of 0.25, MnOOH nanorods with the diameter about 40?C400?nm and the length in the range of 2?C10???m could be facilely prepared in high yield. However, spindle-shaped MnCO₃ microparticles were prepared when the mass ratio between ??-CD and KMnO₄ was increased to 1.5. The as-prepared products were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and high-resolution transmission electron microscopy. The formation mechanisms of rod-like MnOOH and spindle-shaped MnCO₃ were preliminarily discussed.     

中立型对数种群模型正周期解的存在性新结果

运用k-集压缩算子的拓扑度抽象连续定理,研究了如下一类高阶微分方程的周期解存在性问题x(m)(t)= r(t)-a(t)x(t-σ)-b(t)x(m)(t-τ).并将其应用于研究一类中立型对数种群模型dN/dt= N(t) [r(t)-a(t) In N(t-σ-b(t)d/(dt)In N(t-τ)]的正周期解存在性...