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排序方式: 共有349条查询结果,搜索用时 15 毫秒
341.
微波消解ICP-MS法同时测定蔬菜中14种元素 总被引:4,自引:0,他引:4
研究了蔬菜中Ag、Al、As、Cd、Co、Cr、Cu、Mn、Ni、Pb、Sb、Se、Zn、Hg 14种元素同时准确测定的方法。用具孔电子控温加热板蒸干蔬菜样品,高压密闭微波化学工作站消解蔬菜干样,采用电感耦合等离子体质谱(ICP-MS)测定蔬菜中的14种元素。优化了微波消解条件和仪器测定条件。所有标准曲线的线性范围在0~200.0μg/L之间,回归方程的相关系数皆大于0.999,方法的检出限均小于0.22μg/L,加标回收率在81%~118%之间,精密度RSD小于4.44%;西红柿叶国家标准样品(GSBZ 51001-94)的验证分析,测定值均在保证值范围内。本方法具有快速、准确、可靠、灵敏度高及多元素同时分析等特点,可进行批量蔬菜样品测定,赋予"无公害蔬菜市场准入制度"的实施。 相似文献
342.
M. Zandieh S. Molla-Alizadeh-Zavardehi 《Journal of Computational and Applied Mathematics》2009,230(2):546-558
Traditional scheduling problems assume that there are always infinitely many resources for delivering finished jobs to their destinations, and no time is needed for their transportation, so that finished products can be transported to customers without delay. So, for coordination of these two different activities in the implementation of a supply chain solution, we studied the problem of synchronizing production and air transportation scheduling using mathematical programming models. The overall problem is decomposed into two sub-problems, which consists of air transportation allocation problem and a single machine scheduling problem which they are considered together. We have taken into consideration different constraints and assumptions in our modeling such as special flights, delivery tardiness and no delivery tardiness. For these purposes, a variety of models have been proposed to minimize supply chain total cost which encompass transportation, makespan, delivery earliness tardiness and departure time earliness tardiness costs. 相似文献
343.
For Chebyshev spectral solutions of the forced Burgers equation with low values of the viscosity coefficient, several bifurcations and stable attractors can be observed. Periodic orbits, quasiperiodic and strange ones may arise. Bistability can also be observed. Necessary conditions for these attractors to appear are discussed and justification for the non emerging of bistability for an example of a system symmetry break is presented. As an application for the dynamical behavior of spectral solutions of Burgers equation, the dynamics and synchronization of unidirectionally coupling of Chebyshev spectral solutions of Burgers equations by means of a linear coupling are described and discussed. Also, a nonlinear coupling is proposed and discussed. 相似文献
344.
345.
综合考虑了无线传感器网络中节点间时间偏移的来源,为了提高无线传感器网络中时间同步精度,降低能量开销,提出了一种在簇结构中基于偏差补偿的同步方法.该方法在完成簇内节点一次信息交换之后,通过簇头对各节点时间偏差进行有效估计并进行补偿来维持同步时间精度,很好地降低了能量消耗.通过仿真实验,该方法在信息开销和同步精度上体现出良... 相似文献
346.
《Physics letters. A》2014,378(22-23):1579-1583
We study the synchronization (sync) properties of a ring of N units with excitable FitzHugh–Nagumo dynamics, when the inhibitor fields of nearest-neighbor units are coupled diffusively (electric coupling). The system is submitted to a common subthreshold adiabatic signal , and independent Gaussian white noises with common variance η. By running numerical integrations with increasing η, we observe the excitation activity to become spatiotemporally self-organized, until η is so strong that spoils sync. By means of a two-cell model and projecting the dynamics along the slow manifolds, we obtain a (signal-dependent) potential landscape which explains qualitatively the sync regime, and whose barrier heights give a good estimate of the optimal noise intensity. 相似文献
347.
Y. Zhang H.A. Cerdeira G. Hu 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,23(1):97-102
A ring of diffusively coupled R?ssler oscillators, which can develop the conventional rotating wave from high-dimensional
chaos by increasing the coupling ɛ continuously is studied. The chaotic generator for the rotating wave emerges around ɛ =
ɛ, where the topological transition induced by the coupling not only changes the topological structure of all the oscillators,
which share a common strange attractor, but also changes them into being different from each other. Starting from this transition,
infinitely long range temporal correlation and spatial order in the style of antiphase state are established gradually, which
gives rise to the chaotic generator of the rotating wave.
Received 15 March 2001 相似文献
348.
It is possible that self-excited vibrations in turbomachine blades synchronize due to elastic coupling through the shaft.
The synchronization of four coupled van der Pol oscillators is presented here as a simplified model. For quasilinear oscillations,
a stability condition is derived from an analysis based on linearizing the original equation around an unperturbed limit cycle
and transforming it into Hill’s equation. For the nonlinear case, numerical simulations show the existence of two well-defined
regions of phase relationships in parameter space in which a multiplicity of periodic attractors is embedded. The size of
these regions strongly depends on the values of the oscillator and coupling constants. For the coupling constant below a critical
value, there exists a region in which a diversity of phase-shift attractors is present, whereas for values above the critical
value an in-phase attractor is predominant. It is observed that the presence of an anti-phase attractor in the subcritical
region is associated with sudden changes in the period of the coupled oscillators. The convergence of the coupled system to
a particular periodic attractor is explored using several initial conditions. The study is extended to non-identical oscillators,
and it is found that there is synchronization even over a wide range of difference among the oscillator constants. 相似文献
349.
Dynamics of firing patterns, synchronization and resonances in neuronal electrical activities: experiments and analysis 总被引:11,自引:3,他引:8
Qishao Lu Huaguang Gu Zhuoqin Yang Xia Shi Lixia Duan Yanhong Zheng 《Acta Mechanica Sinica》2008,24(6):593-628
Recent advances in the experimental and theoretical study of dynamics of neuronal electrical firing activities are reviewed. Firstly, some experimental phenomena of neuronal irregular firing patterns, especially chaotic and stochastic firing patterns, are presented, and practical nonlinear time analysis methods are introduced to distinguish deterministic and stochastic mechanism in time series. Secondly, the dynamics of electrical firing activities in a single neuron is concerned, namely, fast-slow dynamics analysis for classification and mechanism of various bursting patterns, one- or two-parameter bifurcation analysis for transitions of firing patterns, and stochastic dynamics of firing activities (stochastic and coherence resonances, integer multiple and other firing patterns induced by noise, etc.). Thirdly, different types of synchronization of coupled neurons with electrical and chemical synapses are discussed. As noise and time delay are inevitable in nervous systems, it is found that noise and time delay may induce or enhance synchronization and change firing patterns of coupled neurons. Noise-induced resonance and spatiotemporal patterns in coupled neuronal networks are also demonstrated. Finally, some prospects are presented for future research. In consequence, the idea and methods of nonlinear dynamics are of great significance in exploration of dynamic processes and physiological functions of nervous systems. 相似文献