4-甲基-邻苯二胺荧光光度法测定痕量硒

明胶为稳定剂,EDTA-2Na为掩蔽剂,硒与4-甲基-邻苯二胺生成络合物,其激发波长和发射波长分别为442nm和493nm.硒浓度在0.125-0.75μg/mL范围内具有良好的线性关系,检出限为0.46μg/L,此法用于测定银杏叶中的痕量硒,获得满意的结果.     

具有脉冲效应和综合害虫控制的捕食系统

本文通过生物控制和化学控制提出了具有周期脉冲效应与害虫控制的捕食系统. 系统保护天敌避免灭绝,在一些条件下可以使害虫灭绝.就是说当脉冲周期小于某一临界值时,存在全局稳定害虫灭绝周期解.脉冲周期增大大于临界值时,平凡害虫灭绝周期解失去稳定性并产生正周期解,利用分支理论来研究正周期解的存在性.进而,利用李雅普诺夫函数和比较定理确定了持续生存的条件.     

Cascade of Random Rotation and Scaling in a Shell Model Intermittent Turbulence

The time behaviors of intermittent turbulence in Gledzer-Ohkitani-Yamada model are investigated. Two kinds of orbits of each shell which is in the inertial range are discussed by portrait analysis in phase space. We find intermittent orbit parts wandering randomly and the directions of unstable quasi-periodic orbit parts of different shells form rotational, reversal and locked cascade of period three with shell number. We calculate the critical scaling of intermittent turbulence and the extended self-similarity of the two parts of orbit and point out that nonlinear scaling in inertial-range is decided by intermittent orbit parts.     

包结物晶析法选择分离辛夷挥发油中1,8-桉叶素

主客体化学的分子识别在同分异构体选择分离、外消旋异构体光学拆分中已有广泛研究[1～3].我们利用中草药挥发油中化学组分的分子形状、几何拓扑性质、官能团数量和键力性质的不同,选定主体分子对挥发油中某一组分进行分子识别,并以结晶的形式从挥发油体系中离析出来,达到选择分离单一挥发油化学组分的目的[4～7].本文利用主体分子1,1,6,6-四苯基-2,4-己二炔-1,6-二醇(A)作为主体分子[8],以辛夷挥发油为研究对象,其主要成分1,8-桉叶素(B)为分子识别的客体分子,与化合物A形成稳定的包结物晶体(A+B),并从辛夷挥发油中析出,得到纯度为100%的…     

Unravelling the Structure of Electrocatalytically Active Fe–N Complexes in Carbon for the Oxygen Reduction Reaction

Non‐precious Fe/N co‐modified carbon electrocatalysts have attracted great attention due to their high activity and stability in oxygen reduction reaction (ORR). Compared to iron‐free N‐doped carbon electrocatalysts, Fe/N‐modified electrocatalysts show four‐electron selectivity with better activity in acid electrolytes. This is believed relevant to the unique Fe–N complexes, however, the Fe–N structure remains unknown. We used o,m,p‐phenylenediamine as nitrogen precursors to tailor the Fe–N structures in heterogeneous electrocatalysts which contain FeS and Fe₃C phases. The electrocatalysts have been operated for 5000 cycles with a small 39 mV shift in half‐wave potential. By combining advanced electron microscopy and Mössbauer spectroscopy, we have identified the electrocatalytically active Fe–N₆ complexes (FeN₆, [Fe^III(porphyrin)(pyridine)₂]). We expect the understanding of the FeN₆ structure will pave the way towards new advanced Fe–N based electrocatalysts.     

Exploring diamagnetic susceptibility of impurity doped quantum dots in presence of Gaussian white noise

We explore diamagnetic susceptibility (DMS) of impurity doped quantum dot (QD) in presence of Gaussian white noise. Noise has been introduced to the system additively and multiplicatively. In view of these profiles of DMS have been pursued with variations of several important quantities e.g. magnetic field strength, confinement frequency, dopant location, dopant potential, and aluminium concentration, both in presence and absence of noise. We have invariably envisaged noise-induced suppression of DMS. Moreover, the extent of suppression noticeably depends on mode of application (additive/multiplicative) of noise. The said mode of application also plays a governing role in the onset of saturation of DMS values. The present study provides a deep insight into the promising role played by noise in controlling effective confinement imposed on the system which bears significant relevance.     

Allowable propagation of short pulse laser beam in a plasma channel and electromagnetic solitary waves

Nonparaxial and nonlinear propagation of a short intense laser beam in a parabolic plasma channel is analyzed by means of the variational method and nonlinear dynamics. The beam propagation properties are classified by five kinds of behaviors. In particularly, the electromagnetic solitary wave for finite pulse laser is found beside the other four propagation cases including beam periodically oscillating with defocussing and focusing amplitude, constant spot size, beam catastrophic focusing. It is also found that the laser pulse can be allowed to propagate in the plasma channel only when a certain relation for laser parameters and plasma channel parameters is satisfied. For the solitary wave, it may provide an effective way to obtain ultra-short laser pulse.     

NiCrBSi涂层在酸性介质中耐腐蚀性能

研究了NiCrBSi涂层在沸腾的H2SO4和HCl溶液中的耐腐蚀性能,分析了其腐蚀过程.实验结果表明,NiCrBSi涂层具有良好的耐腐蚀性能,腐蚀过程主要为腐蚀剂通过涂层中的通孔进入涂层,引起腐蚀,腐蚀一定时间后,在涂层与基体之间产生腐蚀产物,涂层鼓泡.     

Numerical simulation and experimental validation of a direct current air corona discharge under atmospheric pressure

Air corona discharge is one of the critical problems associated with high-voltage equipment. Investigating the corona mechanism plays a key role in enhancing the electrical insulation performance. An improved self-consistent multi-component two-dimensional plasma hybrid model is presented for the simulation of a direct current atmospheric pressure corona discharge in air. The model is based on plasma hydrodynamic and chemical models, and includes 12 species and 26 reactions. In addition, the photoionization effect is introduced into the model. The simulation on a bar-plate electrode configuration with an inter-electrode gap of 5.0 mm is carried out. The discharge voltage-current characteristics and the current density distribution predicted by the hybrid model agree with the experimental measurements. In addition, the dynamics of volume charged species generation, discharge current waveform, current density distribution at an electrode, charge density, electron temperature, and electric field variations are investigated in detail based on the model. The results indicate that the model can contribute valuable insights into the physics of an air plasma discharge.     

Electron-Positron Pair Production in an Arbitrary Polarized Ultrastrong Laser Field

Electron-positron pair production in an arbitrary polarized ultrastrong laser field is investigated in the first order perturbation approximation in which the Volkov states are used for convenient calculation of scattering amplitude and cross section. It is found surprisingly that the optimal pair production depends strongly on the polarization. For some cases of field parameters, the optimal field is elliptically polarized or evenly circularly polarized one, rather than the usual linear polarization as indicated by previous works. Some insights into pair generation are given and some interesting unexpected features are also discussed briefly.