On norms of composition operators acting on Bergman spaces

For arbitrary composition operators acting on a general Bergman space we improve the known lower bound for the norm and also generalize a related recent theorem of D.G. Pokorny and J.E. Shapiro. Next, we obtain a geometric formula for the norms of composition operators with linear fractional symbols, thus extending a result of C. Cowen and P. Hurst and revealing the meaning of their computation. Finally, we obtain a lower bound for essential norm of an arbitrary composition operator related to the well-known criterion of B. MacCluer and J.H. Shapiro. As a corollary, norms and essential norms are obtained for certain univalently induced noncompact composition operators in terms of the minimum of the angular derivative of the symbol.     

ON AN OPEN PROBLEM PRESENTED BY LADAS

ConsiderneutraldifferentialdiffereflceequatinwhereTE(0,co),ae[0,co),Q(t)EC[[t.,co),R ].In1988,G.Ladaspresentedanopenprobleminprivatecommuni(:ationandthenin[1].Theproblemisasfollowing:Assumethatfi:Q(s)ds=co,showthateverynonoscillatorysollltioTIot'equation(…     

中立双曲型时滞偏微分方程解振动的充要条件

本文讨论一类线性中立双曲型时滞微分方程解的振动性质，获得了其一切解振动的充要条件．     

“黄水病”对拟穴青蟹免疫指标的影响

以血细胞分析和酶学分析方法,比较研究了患“黄水病”拟穴青蟹和正常拟穴青蟹的细胞免疫及血清免疫酶指标．结果表明：患病拟穴青蟹与正常拟穴青蟹不同性别之间血细胞密度、3种血细胞比例和LZM、ACP、AKP、SOD、PO酶活性差异皆不显著（P〉0．05）,而同性别之间变化明显,差异极显著（P〈0．01）;雄性患病拟穴青蟹与正常拟穴青蟹的血细胞吞噬百分比（PP）和血清LZM活力没有明显差别（P〉0．05）,而雌性患病拟穴青蟹PP和LZM均显著低于正常拟穴青蟹（P〈0．05）;同性别的患病青蟹PI极显著低于正常青蟹（P〈0．01）;患病拟穴青蟹与正常拟穴青蟹不同性别之间POD活性差异不显著（P〉0．05）,同性别之间POD活性显著高于正常拟穴青蟹（P〈0．05）．     

Stability of neutral stochastic functional differential equations with Markovian switching driven by G-Brownian motion

Little seems to be known about stability results on the neutral stochastic function differential equations with Markovian switching driven by G-Brownian (G-NSFDEwMSs). This paper aims at investigating the pth moment exponential stability for G-NSFDEwMSs to fill this gap. Some sufficient conditions on the pth moment exponential stability of the trivial solution are derived by employing the Razumikhin-type method, stochastic analysis, and algebraic inequality technique. Moreover, an example is provided to illustrate the effectiveness of the obtained results.     

Mass distribution and skewness for passive scalar transport in pipes with polygonal and smooth cross sections

We extend our previous results characterizing the loading properties of a diffusing passive scalar advected by a laminar shear flow in ducts and channels to more general cross‐sectional shapes, including regular polygons and smoothed corner ducts originating from deformations of ellipses. For the case of the triangle and localized, cross‐wise uniform initial distributions, short‐time skewness is calculated exactly to be positive, while long‐time asymptotics shows it to be negative. Monte Carlo simulations confirm these predictions, and document the timescale for sign change. The equilateral triangle appears to be the only regular polygon with this property—all others possess positive skewness at all times. Alternatively, closed‐form flow solutions can be constructed for smooth deformations of ellipses, and illustrate how both nonzero short‐time skewness and the possibility of multiple sign switching in time is unrelated to domain corners. Exact conditions relating the median and the skewness to the mean are developed which guarantee when the sign for the skewness implies front (more mass to the right of the mean) or back (more mass to the left of the mean) “loading” properties of the evolving tracer distribution along the pipe. Short‐ and long‐time asymptotics confirm this condition, and Monte Carlo simulations verify this at all times. The simulations are also used to examine the role of corners and boundaries on the distribution for short‐time evolution of point source , as opposed to cross‐wise uniform, initial data.     

聚酰亚胺复合材料的摩擦性能及其机理研究

研究了含有固体润滑剂的炭纤维增强 PI复合材料在干摩擦和水润滑 2种状态下的摩擦磨损性能及其磨损机理 .结果表明 ,在水润滑条件下 ,摩擦系数和磨损率都有不同程度的降低 ,其中含 PTFE的炭纤维增强 PI复合材料的耐磨性最佳 ,最低磨损率为 9.9× 10 - 7mm3/ N· m.其主要原因可能与材料存在极性酰胺基团有关 ,酰胺基易通过氢键与水分子结合 ,在摩擦表面形成水吸附膜 ,使摩擦表面直接接触减少 ,从而改善材料的摩擦磨损性能     

在封闭结构中水对爆炸冲击波的削波、减压作用

采用数值方法计算了封闭矩形空间中布置在炸药周围的水对爆炸冲击波的削波作用以及对于气室压力的削减作用。计算结果显示 ,在各种不同的载荷密度和水 /药质量比参数条件下 ,冲击波峰值压力和气室压力均得到明显的削减。还计算了一个具有开口的模型隧道中水的削波作用 ,并将计算结果与实验测量数据进行了比较。     

Theoretical analysis of using airflow to purge residual water in an inclined pipe

ＩｎｔｒｏｄｕｃｔｉｏｎＰｕｒｇｉｎｇｒｅｓｉｄｕａｌｌｉｑｕｉｄｉｎａＵ＿ｓｈａｐｅｄｐｉｐｅｌｉｎｅｉｓｃｈａｌｌｅｎｇｅｆｏｒｃｈｅｍｉｃａｌａｎｄｔｒａｎｓｐｏｒｔａｔｉｏｎｉｎｄｕｓｔｒｙ[1].Ｍａｎｙｔｅｃｈｎｉｑｕｅｓｈａｖｅｂｅｅｎｅｍｐｌｏｙｅｄｔｏｐｕｒｇｅｏｕｔｒｅｓｉｄｕａｌｗａｔｅｒ[2 ],ｂｕｔｎｏｎｅｈａｖｅｂｅｅｎｃｏｍｐｌｅｔｅｌｙｓａｔｉｓｆａｃｔｏｒｙ .Ｏｎｅｐｏｓｓｉｂｌｅｍｅｔｈｏｄｆｏｒｄｏｉｎｇｔｈｉｓｈａｓｂｅｅｎｔｏｂｌｏｗａｇｒｅａｔｑｕａｎｔｉｔ…     

Problem of periodic solutions for neutral functional differential equation

ＩｎｔｒｏｄｕｃｔｉｏｎＬｅｔＣ(ｋ- 1)2π =ｈ(ｔ) ｜ｈ :Ｒ →Ｒｉｓ (ｋ -1 )＿ｔｈｏｒｄｅｒｃｏｎｔｉｎｕｏｕｓｄｉｆｆｅｒｅｎｔｉａｂｌｅａｎｄｈ(ｔ+ 2π) ≡ｈ(ｔ) ,　　Ｃ2π =ｈ(ｔ) ｜ｈ :Ｒ →Ｒｉｓｃｏｎｔｉｎｕｏｕｓａｎｄｈ(ｔ+ 2π) ≡ｈ(ｔ) ,　　‖ｈ(ｔ)‖ =ｓｕｐｔ∈ [0 ,2π] ｜ｈ(ｔ) ｜ ,　　‖ｈ(ｔ)‖Ｐｋ- 1 =ｍａｘ‖ｈ(ｔ)‖ ,‖ｈ′(ｔ)‖ ,… ,‖ｈ(ｋ- 1) (ｔ)‖ ,　　ｘ(ｍ) (ｔ+ ·) (θ) =ｘ(ｍ) (ｔ+θ)　　θ∈Ｒ (ｍ =0 ,1 ,2 ,… ,ｋ-1 ) .Ｃｌｅａｒｌｙ ,ｘ(ｍ) (ｔ + ·) ∈Ｃ2π, …