人口动力学中非线性发展方程解的爆破现象

讨论描述人口发展规律的一类非线性发展方程具有第三类非线性边界条件的混合问题．在已知函数满足某些假设条件下,证明了其解在有限时间内爆破．     

Influence of detergent concentration on aggregation and spectroscopic properties of light-harvesting complex II

Aggregation of photosynthetic light-harvesting complexes strongly influences their spectroscopic properties. Fluorescence yield and excited state lifetimes of the main light-harvesting complex (LHC II) of higher plants strongly depend on its aggregation state. Detergents are commonly used to solubilize membrane proteins and/or to circumvent their aggregation in aqueous environments. Nonlinear polarization spectroscopy in the frequency domain (NLPF) was performed with LHC II over a wide concentration range of the mild detergent n-dodecyl β-d-maltoside (β-DM). Additionally, conventional absorption-, fluorescence- and circular dichroism-spectra were measured. The results indicate that: (i) conventional spectroscopic techniques are not well suited to investigate aggregation effects. NLPF provides a novel approach to overcome this problem: NLPF spectra display dramatic alterations upon even minor β-DM concentration changes. (ii) Commonly used detergent concentrations (around or slightly above the critical micellar concentration) apparently do not lead to complete trimerization of LHC II. A long-wavelength species in the NLPF spectra (peaking at about 685 nm), indicative of residual aggregation, persists up to DM-concentrations of 0.06%. (iii) High-resolution NLPF spectra indicate the existence of a species with a considerably shortened excited state lifetime. (iv) No indication of denaturation was found even at the highest β-DM concentrations used. (v) A specific change in interaction between certain chlorophyll(s) b and a xanthophyll molecule, probably neoxanthin, was detected upon aggregation as well as at higher β-DM concentrations. The results are discussed with respect to the still elusive mechanism of nonradiative dissipation of excess excitation energy in the antenna system.     

A Multi-Type HPV Transmission Model

A prophylactic quadrivalent (types 6/11/16/18) vaccine against oncogenic and warts-causing genital Human papillomavirus (HPV) types was approved by the US Food and Drug Administration in 2006. This paper presents a nonlinear, deterministic, age-structured, mathematical model of the transmission dynamics of HPV and disease occurrence in a US population stratified by gender and sexual activity group. The model can assess both the epidemiologic consequences and cost effectiveness of alternative vaccination strategies in a setting of organized cervical cancer screening in the United States. Inputs for the model were obtained from public data sources, published literature, and analyses of clinical trial data. The results suggest that a prophylactic quadrivalent HPV vaccine can: (i) substantially reduce the incidence of disease, (ii) increase survival among females, (iii) improve quality of life for both males and females, (iv) be cost-effective when administered to females age 12–24 years, and (v) be cost-effective when implemented as a strategy that combines vaccination of both females and males before age 12 vaccination with a 12 to 24 years of age catch-up vaccination program.     

Otoacoustic emissions from insect ears: evidence of active hearing?

Sensitive hearing organs often employ nonlinear mechanical sound processing which generates distortion-product otoacoustic emissions (DPOAE). Such emissions are also recordable from tympanal organs of insects. In vertebrates (including humans), otoacoustic emissions are considered by-products of active sound amplification through specialized sensory receptor cells in the inner ear. Force generated by these cells primarily augments the displacement amplitude of the basilar membrane and thus increases auditory sensitivity. As in vertebrates, the emissions from insect ears are based on nonlinear mechanical properties of the sense organ. Apparently, to achieve maximum sensitivity, convergent evolutionary principles have been realized in the micromechanics of these hearing organs-although vertebrates and insects possess quite different types of receptor cells in their ears. Just as in vertebrates, otoacoustic emissions from insects ears are vulnerable and depend on an intact metabolism, but so far in tympanal organs, it is not clear if auditory nonlinearity is achieved by active motility of the sensory neurons or if passive cellular characteristics cause the nonlinear behavior. In the antennal ears of flies and mosquitoes, however, active vibrations of the flagellum have been demonstrated. Our review concentrates on experiments studying the tympanal organs of grasshoppers and moths; we show that their otoacoustic emissions are produced in a frequency-specific way and can be modified by electrical stimulation of the sensory cells. Even the simple ears of notodontid moths produce distinct emissions, although they have just one auditory neuron. At present it is still uncertain, both in vertebrates and in insects, if the nonlinear amplification so essential for sensitive sound processing is primarily due to motility of the somata of specialized sensory cells or to active movement of their (stereo-)cilia. We anticipate that further experiments with the relatively simple ears of insects will help answer these questions.     

Synthesis, crystal structures, and molecular hyperpolarizabilities of a new Schiff base ligand, and its copper(II), nickel(II), and cobalt(II) metal complexes

A new ligand (HL) obtained from the Schiff base condensation of 4-(diethylamino)salicylaldehyde with 4-nitroaniline is reported, with its nickel(II), copper(II), and cobalt(II) complexes. The crystal structures are reported for the four derivatives. While, Ni^IIL₂ and Cu^IIL₂ are centrosymmetric molecules, Co^IIL₂ exhibits a pseudo-tetrahedral molecular structure. The quadratic hyperpolarizabilities (β) of HL and Co^IIL₂, measured by electric field induced second harmonic (EFISH) technique, are equal to 66 and 110 × 10⁻³⁰ cm⁵ esu⁻¹, respectively. Beside a geometric effect (pseudo-T_d symmetry), the coordination of the metal center provides an intrinsic enhancement of the NLO response. In addition, an enhancement of the thermal stability of about 60° is found upon metal complexation.     

A Study of Stand Growth Model for Pinus yunnanensis (Pinaceae) Based on Plots Data——A Case Study in Yangliu Township,Baoshan, Yunnan Province

Pinus yunnanensis is one of most important timber species in Yunnan Province, and widely distributed in southwest China. Studies on growth model have been reported, however, most of which focused on a specific part of growth model. To build detailed, easily used and accurate empirical stand growth model from the same dataset, a case study was conducted in Yangliu Township, Baoshan, Yunnan Province. A total of 86 sample plots data were collected using two stages sampling design. Several popular non-linear growth functions were fitted and compared, including Chapman-Richards, Mitscherlich, Schumacher, Gompertz, Logistic, Korf and Allometric function. Models of site index, density index, average diameter at breast height (DBH) and stock volume growth model were fitted respectively. The different models performed more or less similarly in terms of coefficients of determination and root mean square error (RMSE). However, empirical growth function “Schumacher” had lower coefficient of variation for all parameters than other models. Schumacher function was the most suitable one for site index, average DBH and stock volume growth model in all alternative functions.     

我国洪涝灾害受灾及成灾面积的预测分析

运用ＳＡＳ软件的非线性回归,并结合马尔可夫链方法建立了因洪涝灾害造成的我国农田受灾及成灾面积的２个预测模型,结果表明本文所作的预测效果较好,为我国的灾害预测提供了一种方便实用的方法。     

Stability and motor adaptation in human arm movements

In control, stability captures the reproducibility of motions and the robustness to environmental and internal perturbations. This paper examines how stability can be evaluated in human movements, and possible mechanisms by which humans ensure stability. First, a measure of stability is introduced, which is simple to apply to human movements and corresponds to Lyapunov exponents. Its application to real data shows that it is able to distinguish effectively between stable and unstable dynamics. A computational model is then used to investigate stability in human arm movements, which takes into account motor output variability and computes the force to perform a task according to an inverse dynamics model. Simulation results suggest that even a large time delay does not affect movement stability as long as the reflex feedback is small relative to muscle elasticity. Simulations are also used to demonstrate that existing learning schemes, using a monotonic antisymmetric update law, cannot compensate for unstable dynamics. An impedance compensation algorithm is introduced to learn unstable dynamics, which produces similar adaptation responses to those found in experiments.     

Fractal rigidity by enhanced sympatho-vagal antagonism in heartbeat interval dynamics elicited by central application of corticotropin-releasing factor in mice

The dynamics of heartbeat interval fluctuations were studied in awake unrestrained mice following intracerebroventricular application of the neuropeptide corticotropin-releasing factor (CRF). The cardiac time series derived from telemetric ECG monitoring were analyzed by non-parametric techniques of nonlinear signal processing: delay-vector variance (DVV) analysis, higher-order variability (HOV) analysis, empirical mode decomposition (EMD), multiscale embedding-space decomposition (MESD), multiexponent multifractal (MEMF) analysis. The analyses support the conjecture that cardiac dynamics of normal control mice has both deterministic and stochastic elements, is nonstationary, nonlinear, and exerts multifractal properties. Central application of CRF results in bradycardia and increased variability of the beat-to-beat fluctuations. The altered dynamical properties elicited by CRF reflect a significant loss of intrinsic structural complexity of cardiac control which is due to central neuroautonomic hyperexcitation, i.e., enhanced sympatho-vagal antagonism. The change in dynamical complexity is characterized by an effect referred to as fractal rigidity, leading to a significant impairment of adaptability to extrinsic challenges in a fluctuating environment. The impact of dynamical neurocardiopathy as a major precipiting factor for the propensity of cardiac arrhythmias or sudden cardiac death by unchecked central CRF release in significant acute life events in man is critically discussed.     

一类非线性环链系统的混沌反控制

针对一类系统—非线性环链系统,利用非线性反馈控制的方法,研究了该系统的混沌反控制问题.该方法不需计算Lyapunov函数,从而降低了混沌反控制的计算量.仿真结果表明了该系统可快速有效地跟踪给定的混沌系统,充分的显示了该系统的优势.