时频域独立元分析方法实现超声兰姆波的多模式分离

为方便兰姆波信号分析与模式定征,提出一种将短时傅里叶变换(Short-Time Fourier Transform,STFT)与独立元分析(Independent Component Analysis,ICA)相结合的多模式超声兰姆波识别方法.首先通过STFT将兰姆波时域信号投影至时频域,基于各模式信号在时频域相对独立...     

2-羟基-1-萘甲醛缩氨基胍铜配合物的合成及表征

铜是生物体内必需的微量元素,是一些重要酶的活性中心,其配合物不仅在生命体系有着特殊的生物活性[1],而且由于具有特殊的磁学、电学、光学等性质而在材料、催化等许多领域中表现出潜在应用价值,因而成为人们关注的热点课题之一[2],为此我们合成了2-羟基-1-萘甲醛缩氨基胍铜配合物,并对此配合物进行了一系列表征.     

ChemInform Abstract: Relationships Among Ionic Lattice Energies,Molecular (Formula Unit) Volumes,and Thermochemical Radii

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

New simple procedures for the prediction of monomer reactivity ratios and transfer constants in radical polymerisation

The Q-e and Patterns of Reactivity schemes for the quantitative treatment of the reactions of polymer radicals both suffer from drawbacks which seriously limit their usefulness. Two revised versions of the Patterns of Reactivity scheme, in which all the necessary parameters are derived from experimental data, are summarised here. Both new schemes provide significantly more accurate assessments of monomer reactivity ratios and transfer constants than do their predecessors.     

Reactivity in radical polymerisation: An improved method for the prediction of monomer reactivity ratios and transfer constants

Half a century after the Q-e scheme was promulgated, a substantially improved method for predicting monomer reactivity ratios and transfer constants has been developed from the Patterns of Reactivity scheme. It is based on the same premise as its predecessors, that reactivity is controlled partly by thermodynamic and partly by polar factors, but the new treatment yields values much closer, on average, to the reported experimental data.     

Enthalpic relaxation and the glass transition in polymer blends

The kinetics of enthalpic relaxation are reviewed and applied to the ageing of a range of blends made from polyether imide and polyether ether ketone. DSC has been used to follow the development of enthalpic relaxation and a Williams-Watt stretched exponential equation relating the extent of relaxation, ϕ(t), to the ageing time t and an average relaxation time, t́_a', has been used to quantify the ageing process. where β' is inversely related to the breadth of the relaxation spectrum such that 0<β>1.0. The relationship was modified to incorporate non-linearity in the relaxation behaviour. ϕ(t) was measured directly from the enthalpy change observed in the endotherms on heating aged specimens through the glass transition in the DSC. The PEI/PEEK blends were compatible over the full composition range in that they exhibited a single glass transition with a temperature that varied almost linearly with composition between those of the homopolymers. Enthalpic relaxation was found to be a useful technique for probing the molecular relaxations of polymer blends and confirming the degree of compatibility of the system. The β' values changed systematically with the blend composition between those of the homopolymers suggesting that the breadth of the relaxation spectra were similar in the blends to that in the homopolymers. Physical ageing was observed to embrittle the blends, and there was a close correlation between the extent of enthalpic ageing and the change in mechanical and impact behaviour. The yield stress increased and the elongation to break decreased progressively with ϕ(t) in addition to a reduction in impact strength. The model of enthalpic relaxation and the kinetic relationships, outlined above, have been used to determine the onset of the glass transition temperature and subsequent progress of enthalpic relaxation at fixed ageing temperatures, for direct comparison with the change in specific heat observed in DSC experiments. Good agreement was observed between experiment and calculated glass transitions and the effect of variables, such as activation enthalpies, pre-exponential factors, non-linear factors such as X and β' and fictive temperature on the observed glass transition temperatures and the temperature range over which the glass transition occurred determined. Modifications to the model for the enthalpic relaxation have been suggested.