共查询到20条相似文献，搜索用时 359 毫秒
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以北京疫情的有关数据进行研究,给出SARS病毒传播的SIR模型.定义σ=(λ)/(δ)为接触数.并指出(1)/(σ)是模型SIR的一个阈值.给出了λ及σ的估计值.认为σ对疫情的发展及判断上起到非常重要的作用.利用一元线性回归及MATLAB数学软件拟合出模型中的几个初始值(S0,I0,R0)及参数值(λ,σ).并绘出S(t)、I(t)的相轨线,并对相轨线进行了分析,得到了满意的结果,为预防类SARS传染病及控制疫情发展提供较为可靠的依据. 相似文献
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目的 研究贮藏期内不同温度下菠菜上的微生物生长趋势.方法 将用保鲜膜封装好的菠菜分别置于3℃、15℃、25℃、35℃四个温度下贮藏,定期对菌落总数进行测定.首先,使用修正的Compertz方程建立不同温度下微生物生长的初级模型,其次,结合Belehradek方程讨论微生物的μmax（最大比生长速率）和λ（延滞时间）与温度的关系,并建立微生物生长的二级模型和货架期模型.结果 研究认为,修正的Compertz方程能够较好地拟合不同温度下菠菜微生物生长的一级模型,R2均大于0.90;微生物的Nmax随着温度的变化波动不大,平均值为（9.4704±1.1472）lg（CFU/g）;μmax随着温度的上升而变大,λ随温度的增加而减小,二级模型为√μmax=0.0215×[T-（-26.5286）]、√1/λ=0.0226 × [T-（-34.0620）],R2分别为0.9967、0.9461.结论 建立了具有较高的拟合度的微生物生长的初级模型、二级模型,也确立了菠菜的微生物货架期模型. 相似文献
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李小丽 《商丘师范学院学报》2009,25(6):17-23
研究了一类两个物种同时带有饱和项的互惠模型平衡态正解的存在性,首先利用单调解的方法得到了此解的先验估计,然后利用分歧理论和度理论研究了在λ1-c＜a＜λ1和a＞λ1两种情况下非常数平衡解的存在性以及全局分歧解的结构. 相似文献
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本文对分割数λ>2时,子波基函数的选取问题进行了一般性的研究,并具体找到了λ=3时的一种子波基函数。将所得结果应用于随机级联α模型,讨论了λ=3时的几率密度分布的子波展开;并对子波关联进行了研究,得到了子波关联解除耦合的结果。 相似文献
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《绵阳师范学院学报》2016,(8):32-38
本文利用线性全连续场谱理论,中心流形约化与非线性耗散系统吸引子分歧与跃迁理论研究了一类带有扩散项的病毒模型的动态分歧,该模型的分歧与区域Ω的选取有关,当∫_Ωψ_13dx≠0时,控制参数λ大于临界点时,方程从平衡态处发生分歧,原有的平衡态失稳,分歧出一个稳定的奇点吸引子,在λ小于临界点一侧分歧出唯一的鞍点;当∫_Ωψ_13dx≠0时,控制参数λ大于临界点时,方程从平衡态处发生分歧,原有的平衡态失稳,分歧出一个稳定的奇点吸引子,在λ小于临界点一侧分歧出唯一的鞍点;当∫_Ωψ_13dx=0时,本文给出了上述模型发生分歧的条件及临界点,当λ大于临界点,原有平衡态失稳,方程从平衡态处发生分歧,分歧出两个稳定奇点,当λ小于临界点时,方程从平衡态处分歧出两个鞍点.本文给出了在Dirichlet边界条件下,方程分歧出的稳定奇点吸引子和两个鞍点的表达式. 相似文献
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在非自然联系情形下讨论了广义线性模型拟似然方程的解βn在λ—n→∞和其他一些正则性条件下证明了解的弱相合性,并得到其收敛于真值β0的速度为Op(λ—n-1/2),其中λ—n(λ—n)为方阵Sn=iΣ=n1XiX'1的最小(最大)特征值. 相似文献
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考虑食物有限模型N′(t) =r(t)N(t) 1-N(t-τ)1-λN(t-τ) ,t≥ 0 ,其中λ∈ [0 ,1)、r(t)∈C([0 ,+∞ ) ,(0 ,+∞ ) ) ,τ>0 ,给出了保证方程每一解N(t)满足limt→∞ N(t) =1的一族充分条件 ,推广和改进了已有文献 [1- 4]的相应定理 相似文献
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文章基于SCP模型,运用结构方程方法从市场结构、企业行为和企业绩效三大模块构建了我国旅行社业SCP分析模型,并对我国旅行社业的市场结构、企业行为和企业绩效的状况及它们之间的关系进行了定量测度。研究得出:目前我国旅行社企业行为是旅行社企业绩效的主要影响因素(β=-1.590),而旅行社企业行为受旅行社业市场结构的影响也很大(Y11=0.988)。从三大模块的具体影响因素来看,产品差异性和市场集中度是对市场结构影响最关键的因素(λ16=-0.937;λ13=0.690),价格恶性竞争的程度是对旅行社业行为影响最大的因素(λ21=0.521)。 相似文献
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对无密度制约的Lotka-Volterra模型捕食-食饵系统的平衡点进行了定性分析,从生态学意义上解释了中心奇点外周围周期解的存在性。此外分λ为已知正常数和λ未知两种情况给出了此系统的两种群同时捕获时的最大持续受益的条件。 相似文献
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A distortion identification technique is presented based on Hilbert-Huang transform to identify distortion model and distortion frequency of distorted real-world image sequences. The distortion model is identified simply based on Hilbert marginal spectral analysis after empirical mode decomposing. And distortion frequency is identified by analyzing the occurrence frequency of instantaneous frequency components of every intrinsic mode functions. Rational digital frequency filter with suitable cutoff frequency is designed to remove undesired fluctuations based on identification results. Experimental results show that this technique can identify distortion model and distortion frequency of displacement sequence accurately and efficiently. Based on identification results, distorted image sequence can be stabilized effectively. 相似文献
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Fibroblast proliferation alters cardiac excitation conduction and contraction: a computational study
He-qing Zhan Ling Xia Guo-fa Shou Yun-liang Zang Feng Liu Stuart Crozier 《Journal of Zhejiang University. Science. B》2014,15(3):225-242
In this study, the effects of cardiac fibroblast proliferation on cardiac electric excitation conduction and mechanical contraction were investigated using a proposed integrated myocardial-fibroblastic electromechanical model. At the cellular level, models of the human ventricular myocyte and fibroblast were modified to incorporate a model of cardiac mechanical contraction and cooperativity mechanisms. Cellular electromechanical coupling was realized with a calcium buffer. At the tissue level, electrical excitation conduction was coupled to an elastic mechanics model in which the finite difference method (FDM) was used to solve electrical excitation equations, and the finite element method (FEM) was used to solve mechanics equations. The electromechanical properties of the proposed integrated model were investigated in one or two dimensions under normal and ischemic pathological conditions. Fibroblast proliferation slowed wave propagation, induced a conduction block, decreased strains in the fibroblast proliferous tissue, and increased dispersions in depolarization, repolarization, and action potential duration (APD). It also distorted the wave-front, leading to the initiation and maintenance of re-entry, and resulted in a sustained contraction in the proliferous areas. This study demonstrated the important role that fibroblast proliferation plays in modulating cardiac electromechanical behaviour and which should be considered in planning future heart-modeling studies. 相似文献
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汤海梅 《天津职业院校联合学报》2012,14(5):76-79
随着电力电子器件的广泛应用,非线性负荷日益增加,使电网电压产生畸变,造成电网质量下降,采用有源滤波和功率补偿装置可以改善电网质量,提高经济效益。APF投入将会使国家电力建设发展电网质量的提高,起到关键的作用。 相似文献
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The performance of speaker verification systems is often compromised under real-world environments. For example, variations in handset characteristics could cause severe performance degradation. This paper presents a novel method to overcome this problem by using a non-linear handset mapper. Under this method, a mapper is constructed by training an elliptical basis function network using distorted speech features as inputs and the corresponding clean features as the desired outputs. During feature recuperation, clean features are recovered by feeding the distorted features to the feature mapper. The recovered features are then presented to a speaker model as if they were derived from clean speech. Experimental evaluations based on 258 speakers of the TIMIT and NTIMIT corpuses suggest that the feature mappers improve the verification performance remarkably. 相似文献
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The performance of speaker verification systems is often compromised under real-world environments.For example,variations in handset characteristics could cause severe performance degradation.This paper presents a novel method to overcome this problem by using a non-linear handset mapper.Under this method,a mapper is constructed by training an elliptical basis function network using distorted speech features as inputs and the corresponding clean features as the desired outputs.During feature recuperation,clean features are recovered by feeding the distorted features to the feature mapper.The recovered features are then presented to a speaker model as if they were derived from clean speech.Experimental evaluation based on 258 speakers of the TIMIT and NTIMIT corpuses suggest that the feature mappers improve the verification performance remarkably. 相似文献
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A novel method was used to investigate developmental changes in face processing: attractiveness aftereffects. Consistent with the norm-based coding model, viewing consistently distorted faces shifts adults' attractiveness preferences toward the adapting stimuli. Thus, adults' attractiveness judgments are influenced by a continuously updated face prototype. To investigate the development of this process, a novel method was developed for 8-year-olds. After reading a storybook composed of faces with either compressed or expanded features, 8-year-olds' ratings of faces distorted in the direction of the adapting stimuli increased. Nonetheless, they required larger distortions than adults to rate undistorted faces as most attractive preadaptation. Thus, although 8-year-olds' attractiveness preferences are influenced by a continuously updated prototype, their face space is less refined than that of adults. 相似文献
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从近年来的房地产市场状况入题,用房地产市场相关项目的历年数据,通过计量经济学软件Eviews5.0对我国的房地产市场供给与需求曲线进行了研究,结果表明,我国的房地产市场供给曲线基本合理,而房地产市场需求曲线存在失真现象。前几年我国的房价上涨过快,目前的房价下跌正是其回归合理区间的表现。 相似文献
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针对扭曲的影像加强器(X-ray image intensifier,XRII)图像对后继工作产生不利影响的问题,提出使用Delaunay三角网插值对扭曲的XRII图像进行校正.首先分析了XRII图像扭曲的原因、经典的校正方法和Delaunay三角网插值;然后,使用程序流程图对算法过程进行了解释.最后,通过实验来证明所提算法的有效性和可行性.实验结果表明:在中心对齐时,使用Delaunay三角插值方法校正后的XRII图像网格线交叉点坐标值与理想校正靶网格线交叉点坐标值的残留误差和标准误差分别为5.760 4×10-14和5.354 2×10-14,使用经典的全局四次多项式、模型L1和模型L2校正之后残留误差和标准误差分别为1.790 3,2.388 8,2.338 8和1.262 0,1.268 1,1.202 6;在中心不对齐时,使用Delaunay三角插值方法校正后的XRII图像网格线交叉点坐标值与理想校正靶网格线交叉点坐标值的残留误差和标准误差分别为2.489×10-13和2.449 8×10-13,使用经典的全局四次多项式、模型L1和模型L2校正后残留误差和标准误差分别为1.770 3,2.388 8,2.338 8和1.269 9,1.268 1,1.202 6. 相似文献
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实证结果显示：长春市农村金融发展与农村经济发展具有负相关关系;农村投资对农村经济发展的作用不明显;实际利率与农村经济发展负相关。实证结果分析表明,长春市农村金融未能有效支持农村经济发展,并存在严重的金融抑制,这导致了农村金融资源配置扭曲,大量农村金融资源外流,农村投资效率低下。农村金融对农村经济发展支持乏力,已经成为长春市农村经济发展的“瓶颈”。因此,必须大力推进农村金融体系改革,破除农村金融抑制,使农村金融更好地服务于农村经济发展。 相似文献