四种传染病疫情病死率估计模型的比较

探讨四种病死率估计模型在疫情初期,对不同疫情类型、疫情规模下估计效能的差异。根据病死率恒定与逐渐下降两种模拟设计,以样本量为1 500及200分别完成四种估计模型、两个真实估计值在四个时间点的1 000次独立估计。病死率恒定时,Modified Kaplan-Meier法和基于gamma分布的参数混合模型的方法具有明显优势;病死率逐渐降低时,早期Modified Kaplan-Meier法、基于gamma分布的参数混合模型的方法以及治愈—死亡危险率比半参数模型的方法均能较理想估计病死率,后期效果欠佳,且敏感性低;但Modified Kaplan-Meier法和SIR模型与竞争风险模型相结合的估计模型的方法在后期无论在精度还是敏感性都较好。样本量的差异对模型估计效能影响不大。说明Modified Kaplan-Meier法和基于gamma分布的参数混合模型的方法在病死率恒定时以及逐渐递减的早期能较准确估计病死率,在逐渐递减后期Kaplan-Meier法和SIR模型与竞争风险模型相结合的估计模型的方法效果有优势;疫情规模对其影响不大。     

小麦品种（系）叶绿素含量变化及其与光合叶面积关系研究

对3种类型11个小麦品种（系）的叶绿素含量变化及其与光合叶面积关系进行了研究。结果表明,中粒型品种（系）的叶绿素（a b）高峰出现早,且生育后期下降快;小粒型和大粒型品种（系）叶绿素（a b）高峰出现较迟。为同类型品种（系）叶绿素（a/b）值在整修生育期呈下降趋势,中粒型品种（系）的chl(a/b）均低于另外两种类型品种（系）。高产品种生育后期叶绿素含量高值期持续时间长,叶绿素（a/b0低。多元相关分析表明,在籽粒灌浆期,叶绿素（a b）值呈显著负相关;叶绿素（a b）值与旗叶面积呈显著负相关。小麦育种上应选择生育后期叶绿素（a b）较高,叶绿素(a/b）值低,且旗叶面积相对较大的品种。     

含二呋喃环系西佛碱型大环的合成研究

在Ba(ClO4)2存在下，用2，2-(5-甲酰基-2-呋喃基)烷(1a，1b)与三乙烯四胺模板缩合，接着用饱和硫酸钠溶液脱钡离子，合成了含二个呋喃环系的19-元西佛碱大环化合物(4a，4b),新型含四个呋喃环系的26-元西佛碱大环(2a，2b，3a，3b)，通过2，2-(5-甲酰基-2-呋喃基)烷(1a，1b)与乙二胺或邻苯二胺由非模板法直接合成，产率高。     

离散GM(1,1)参数估计的3种方法比较

针对离散灰色模型GM(1,1)中参数估计方法及模型稳定性问题,选取3种估计参数的方法进行讨论——最小二乘法、最小一乘法和累积法;为了更好地比较不同估计方法的差异,统一赋以相同的初值,并以拟合误差、关联度和条件数作为评价指标,借助MATLAB软件对两类实例数据进行分析——递增序列和递减序列;实验结果表明:在误差方面,累积法优于最小一乘和最小二乘,在模型稳定性方面,累积法优于最小二乘法,总之,对于递增和递减序列数据,累积法估计GM(1,1)中参数最优。     

离散GM(1,1)参数估计的三种方法比较

针对离散灰色模型GM(1,1)中参数估计方法及模型稳定性问题,选取3种估计参数的方法进行讨论——最小二乘法、最小一乘法和累积法;为了更好地比较不同估计方法的差异,统一赋以相同的初值,并以拟合误差、关联度和条件数作为评价指标,借助MATLAB软件对两类实例数据进行分析——递增序列和递减序列;实验结果表明:在误差方面,累积法优于最小一乘和最小二乘,在模型稳定性方面,累积法优于最小二乘法,总之,对于递增和递减序列数据,累积法估计GM(1,1)中参数最优。     

冲击时间间隔服从[a,b]均匀分布的截断δ冲击模型参数的Bayes估计

截断δ冲击模型是一类特殊的冲击模型,在可靠性数学理论中具有一定的研究价值.在对冲击时间间隔服从[a,b]均匀分布的截断δ冲击模型做参数估计时,运用极大似然法,在最小均方误差下得出其参数的Bayes估计.     

北方天然次生林主要阔叶树种树冠建模及应用

选择黑龙江省帽儿山林场天然次生林内176株10个阔叶树种的解析木,共收集了3 401个枝条的详细数据,建立了一种树冠轮廓模型。分析发现,树冠的形状随着枝深度变化,在树冠上部、中部逐渐扩展,在下部收缩,每个树种呈现不同的曲线形式,天然次生林主要阔叶树种树冠模型可分为上中层和下层两部分建模,上中层模型为hRPCA=a0+a1/ln(RB)+a2/ln(RB)2+a3/ln(RB)3,下层轮廓模型因种不同而有不同,即hRPCB,白桦=b0+b1·(exp(b2)·ln(RB)-1)/b3;hRPCB,黄菠萝=b0+b1·ln(RB)+b2·ln(RB)2;hRPCB,其他=b0+b1·ln(RB)+b2·ln(RB)2+b3·ln(RB)3。经过验证,所建立的树冠轮廓模型拟合和检验效果较好,相关系数都在0.97以上。     

纳米Fe_3O_4微晶电磁波吸收性能的神经网络研究

应用基于人工神经网络的计算机模拟的方法 ,研究了粒度在 10 nm和 10 0 nm之间的多种 Fe3O4纳米材料分别在 ( a) 1～ 10 0 0 MHz和 ( b) 10 0 0～ 10 0 0 0 MHz频率范围内的电磁波吸收效能 .结果表明 ,在频率范围 ( a)内 ,平均粒度小的 Fe3O4磁导率虚部 μ"(即磁损耗 )大于平均粒度大的 Fe3O4的 μ",且 Fe3O4对电磁波的吸收能力逐渐增强 ,这与实验结果吻合良好 ;根据频率范围 ( a)的所得结果 ,利用人工神经网络 ,预测了在频率范围 ( b)内可能出现的情况 .文中就其物理本质也作了简单的分析和探讨     

关于n长路的(a,b;n)-优美标号

证明了a=4时,Gvozdjak猜想成立.即路Pn存在一个(a,b;n)-优美标号,当且仅当整数a,b,n满足:(1)b-a与n(n+1)/2有相同的奇偶性;(2)0<|b-a|≤(n+1)/2;(3)n/2≤a+b≤3n/2.在a=4时,成立.     

广西北海凡纳滨对虾养殖池塘叶绿素a和微藻的变化研究

于不同养殖时间,采集广西北海市3口凡纳滨对虾（Litopenaeus vannamei）养殖池塘水样,调查养殖水中叶绿素a浓度和微藻组成。叶绿素a浓度用分光光度三波长法测定,微藻分类计数用镜检法进行,微藻多样性分析用Shannon-Wiener多样性指数、Pielou种类均匀度指数和种类优势度指数进行。结果表明,3口池塘叶绿素a的浓度养殖前期低,在10.0μg/L以内,养殖中期增长迅速,养殖后期达到150.0μg/L;微藻细胞密度在养殖前期低于20×106cells/L,养殖后期高于100×106cells/L;微藻多样性指数和均匀度指数皆为养殖前期高,养殖中后期逐渐降低,多样性指数0.98～3.15,均匀度指数0.28～0.82;在养殖前期,微藻的种类较多,优势种是硅藻和绿藻,养殖中后期种类减少,优势种是绿藻、蓝藻和甲藻。     

Markedness and its Interpretation in Language Use

Language markedness is a common phenomenon in languages, and is reflected from hearing, vision and sense, i.e. the variation in the three aspects such as phonology, morphology and semantics. This paper focuses on the interpretation of markedness in language use following the three perspectives, i.e. pragmatic interpretation, psychological interpretation and cognitive interpretation, with an aim to define the function of markedness.     

Characterization of Ordovician carbonate reservoirs, southeastern Saskatchewan, Canada

The discovery of the prolific Ordovician Red River reservoirs in 1995 in southeastern Saskatchewan was the catalyst for extensive exploration activity which resulted in the discovery of more than 15 new Red River pools. The best yields of Red River production to date have been from dolomite reservoirs. Understanding the processes of dolomitization is, therefore, crucial for the prediction of the connectivity, spatial distribution and heterogeneity of dolomite reservoirs.The Red River reservoirs in the Midale area consist of 3～4 thin dolomitized zones, with a total thickness of about 20 m, which occur at the top of the Yeoman Formation. Two types of replacement dolomite were recognized in the Red River reservoir: dolomitized burrow infills and dolomitized host matrix. The spatial distribution of dolomite suggests that burrowing organisms played an important role in facilitating the fluid flow in the backfilled sediments. This resulted in penecontemporaneous dolomitization of burrow infills by normal seawater. The dolomite in the host matrix is interpreted as having occurred at shallow burial by evaporitic seawater during precipitation of Lake Almar anhydrite that immediately overlies the Yeoman Formation. However, the low δ18O values of dolomited burrow infills (-5.9‰～ -7.8‰, PDB) and matrix dolomites (-6.6‰～ -8.1‰, avg. -7.4‰ PDB) compared to the estimated values for the late Ordovician marine dolomite could be attributed to modification and alteration of dolomite at higher temperatures during deeper burial, which could also be responsible for its 87Sr/86Sr ratios (0.7084～0.7088) that are higher than suggested for the late Ordovician seawaters (0.7078～0.7080). The trace amounts of saddle dolomite cement in the Red River carbonates are probably related to "cannibalization" of earlier replacement dolomite during the chemical compaction.     

低渗透非均质砂岩油藏启动压力梯度研究

理论推导与室内实验相结合,建立了低渗透非均质砂岩油藏启动压力梯度确定方法。首先借助油藏流场与电场相似的原理,推导了非均质砂岩油藏启动压力梯度计算公式。其次基于稳定流实验方法,建立了非均质砂岩油藏启动压力梯度测试方法。结果表明:低渗透非均质砂岩油藏的启动压力梯度确定遵循两个等效原则。平面非均质油藏的启动压力梯度等于各级渗透率段的启动压力梯度关于长度的加权平均;纵向非均质油藏的启动压力梯度等于各渗透率层的启动压力梯度关于渗透率与渗流面积乘积的加权平均。研究成果可用于有效指导低渗透非均质砂岩油藏的合理井距确定,促进该类油藏的高效开发。     

On Tragic Consciousness In The Works By Ernest Hemingway

As an American modern novelist who were famous in the literary world, Hemingway was not a person who always followed the trend but a sharp observer. At the same time, he was a tragedy maestro, he paid great attention on existence, fate and end-result. The dramatis personae's tragedy of his works was an extreme limit by all means tragedy on the meaning of fearless challenge that failed. The beauty of tragedy was not produced on the destruction of life, but now this kind of value was in the impact activity. They performed for the reader about the tragedy on challenging for the limit and the death.     

A computer generator for randomly layered structures

AcomputergeneratorforrandomlylayeredstructuresYUJia shun1,2,HEZhen hua2(1.TheInstituteofGeologicalandNuclearSciences,NewZealand;2.StateKeyLaboratoryofOilandGasReservoirGeologyandExploitation,ChengduUniversityofTechnology,China)Abstract:Analgorithmisintrod…     

An Index mechanism for multi-scale view in spatial databases

There are numerous geometric objects stored in the spatial databases. An importance function in a spatial database is that users can browse the geometric objects as a map efficiently. Thus the spatial database should display the geometric objects users concern about swiftly onto the display window. This process includes two operations:retrieve data from database and then draw them onto screen. Accordingly, to improve the efficiency, we should try to reduce time of both retrieving object and displaying them. The former can be achieved with the aid of spatial index such as R-tree, the latter require to simplify the objects. Simplification means that objects are shown with sufficient but not with unnecessary detail which depend on the scale of browse. So the major problem is how to retrieve data at different detail level efficiently. This paper introduces the implementation of a multi-scale index in the spatial database SISP (Spatial Information Shared Platform) which is generalized from R-tree. The difference between the generalization and the R-tree lies on two facets: One is that every node and geometric object in the generalization is assigned with a importance value which denote the importance of them, and every vertex in the objects are assigned with a importance value,too. The importance value can be use to decide which data should be retrieve from disk in a query. The other difference is that geometric objects in the generalization are divided into one or more sub-blocks, and vertexes are total ordered by their importance value. With the help of the generalized R-tree, one can easily retrieve data at different detail levels.Some experiments are performed on real-life data to evaluate the performance of solutions that separately use normal spatial index and multi-scale spatial index. The results show that the solution using multi-scale index in SISP is satisfying.     

Achieving Unusual States of Matter Under High Pressure

正The periodicity of the elements and the non-reactivity of the inner-shell electrons are two related principles of chemistry,rooted in the atomic shell structure.Within compounds,Group I elements,for example,invariably assume the+1 oxidation state,and their chemical properties differ completely from those of the p-block elements.These general rules govern our understanding of chemical structures and reactions.Using first principles calcula-     

Exchange-Correlation and Electronic Excitation Energies from Pairing Matrix Fluctuations

We have developed an adiabatic connection to formulate the ground-state exchange-correlation energy in terms of pairing matrix linear fluctuations.This formulation of the exchange-correlation energy opens a new channel for density functional approximations based on the many-body perturbation theory.We illustrate the potential of such approaches with an approximation based on the particle-particle Random Phase Approximation(pp-RPA).This re-     

Density Functional Theory for the Response of Periodic Systems to Electric Fields Based on the Vector Potential Approach

正The electronic and nuclear(structural/vibrational)response of 1D-3D nanoscale systems to electric fields gives rise to a host of optical,mechanical,spectral,etc.properties that are of high theoretical and applied interest.Due to the computational difficulty of treating such large systems it is convenient to model them as infinite and periodic(at least,in first approximation).The fundamental theoretical/computational problem in doing so is that     

On the Thermodynamic Limit for Responses to Static Electromagnetic Fields

For molecular systems,the quantum-mechanical treatment of their responses to static electromagnetic fields usually employs a scalar-potential treatment of the electric field and a vector-potential treatment of the magnetic field.Although the potential for each field separately is associated with the choice of an(unphysical)origin,the precise choice of the origin for the electrostatic field has little consequences for the results.This is different for the