碱金属钾对Ni基催化剂纤维素水蒸气气化活性的影响

采用两段式催化气化方式研究了生物质热解气化过程中碱金属的挥发对Ni基催化剂活性的影响。实验结果表明,负载K盐的纤维素水蒸气催化气化过程中,K挥发后会在催化剂表面沉积,而少量K的存在和表面沉积不但能够提高镍基催化剂的抗积炭能力,而且有助于提高其催化活性,产生更多的氢气。然而纤维素中K的浓度过大,将会抑制Ni基催化剂的效果;K在催化剂上的沉积随催化剂循环次数的增加而增加,K的含量愈高,对催化剂的抑制效果愈明显,从而缩短了催化剂的使用寿命。     

The complexity of a basic impact mapping for rigid bodies with impacts and friction

We consider two impact mappings, the Brach impact mapping and an energetic impact mapping, for rigid-body mechanisms with impacts and friction. The two impact mappings represent the opposite end of the spectrum from basic to advanced impact mappings. Both impact mappings are briefly derived and described. For the Brach impact mapping we will introduce the concept of impulse ratio and discuss how the kinetic energy changes during an impact as the impulse ratio is varied. This analysis is used to further extend the Brach impact mapping to cover situations that were previously omitted. Finally, we make comparisons between the two impact mappings and show how the Painlevé paradox appears in the two impact mappings. The conclusion of the comparisons is that while the basic impact mapping seems easy to implement in a computer simulator it may in the end be more complex and also introduce unnecessary complications that are completely artificial.     

用于 EAST 上低杂波平行波数测量的磁探针设计与测试

针对EAST上2.45GHz低杂波，完成了低杂波平行波数测量磁探针的设计、仿真与测试。利用有限元仿真软件COMSOL Multiphysics 5.2对磁探针尺寸进行仿真优化，确定了单匝环、矩形缝以及陶瓷片厚度等影响磁探针耦合性能的关键尺寸。测试结果表明，该磁探针对2.45GHz低杂波有良好的耦合性能和鉴别波极化的能力，与仿真结果一致。研究结果为EAST装置上低杂波平行波数测量诊断系统的建立提供重要的参考依据，从而为进一步开展高密度低杂波电流驱动实验研究提供必要的实验数据。     

Corner bifurcations in non-smoothly forced impact oscillators

We consider an impacting mechanical system in which a particle at position u(t) impacts with a periodically moving obstacle at position z(t), the motion of which is non-smooth. In particular we look at corner events when u impacts with z very close to a point where z loses smoothness. We show that this leads, through a corner bifurcation, to complex dynamics in u which can include periodic orbits of arbitrary period and period-adding cascades. By analysing associated maps close to the corner event, we show that this dynamics can be understood in terms of the iterations of a two-dimensional, piecewise linear, discontinuous map. We also show some links between this analysis and the difficult problem of understanding the motion of three objects which may have simultaneous impacts.     

Stable periodic motion of a controlled segmented leg model of pedal locomotion with inelastic ground-foot collision

Nonlinear Dynamics - Human and robotic legged locomotion can be described with complex multi-degree-of-freedom dynamic models, whose bifurcation or parameter analysis may explain some features of...     

Interactions between global and grazing bifurcations in an impacting system

It is well known that the locus of boundary crises in smooth systems contains gaps that give rise to periodic windows. We show that this phenomenon can also be observed in an impacting system, and that the mechanism by which these gaps are created is different. Namely, here gaps are created and disappear at points along the branches of boundary crises where they are intersected by branches of grazing bifurcations. We locate a novel type of double-crisis vertex which we call a grazing-crisis vertex. Additionally, we illustrate several types of basin-boundary metamorphosis that are intricately related with grazing bifurcations.     

Phase-alternated compositeπ/2 pulses for solid state quadrupole echo NMR spectroscopy

Phase-alternated compositeπ/2 pulses have been constructed for spinI=1 to overcome quadrupole interaction effects in solid state nuclear magnetic resonance (NMR) spectroscopy. Magnus expansion approach is used to design these sequences in a manner similar to the NMR coherent averaging theory. It is inferred that the symmetric phase-alternated compositeπ/2 pulses reported here are quite successful in producing quadrupole echo free from phase distortions. This effectiveness of the present composite pulses is due to the fact that most of them are of shorter durations as compared to the ones reported in literature. In this theoretical procedure, irreducible spherical tensor operator formalism is employed to simplify the complexity involved in the evaluation of Magnus expansion terms. It has been argued in this paper that compositeπ/2 pulse sequences for this purpose can also be derived from the broadband inversionπ pulses which are designed to compensate electric field gradient (efg) inhomogeneity in spinI=1 nuclear quadrupole resonance (NQR) spectroscopy.     

Two-parameter sliding bifurcations of periodic solutions in a dry-friction oscillator

This paper is concerned with numerical continuation and analytical investigations of sliding bifurcations in Filippov systems. In particular, a methodology developed for the continuation of grazing bifurcations in impacting systems is used to continue sliding bifurcations in Filippov systems. A dry-friction oscillator is investigated from a sliding bifurcations point of view and a complex two-parameter bifurcation diagram of sliding bifurcations is presented. A number of codimension-two sliding bifurcation points that act as organising centres for codimension-one sliding bifurcations are revealed. Two representative codimension-two points are analysed and unfolded, and the analysis is used to explain the dynamics of the dry-friction oscillator in the neighbourhood of these points.     

Saddle-point solutions and grazing bifurcations in an impacting system

This paper focuses on the intricate relationship between smooth and nonsmooth phenomena in an impacting system. In particular a boundary saddle-point solution, that is born in a nonsmooth fold, is analysed. Accessible boundary saddle-point solutions play a key role in determining the global dynamics of a system and here we will show how grazing bifurcations can affect their existence.     

Normal-form analysis of the cusp-transcritical interaction: applications in population dynamics

Nonlinear Dynamics - Bistability, the presence of alternative stable states, is an important feature of population models as it indicates that long-term predictions are dependent on the current...