Coexistence in a discrete competition model with dispersal

We propose a discrete-time competition model between two populations to study the effects of dispersal upon population interactions. It is assumed that dispersal occurs after reproduction and in synchrony. We first analyse a two-patch single species population model with no interspecific competition. Based on these results, we derive sufficient conditions for population coexistence. It is proved that the system is uniformly persistent and possesses a unique coexisting equilibrium.     

Global dynamics of a special class of nonlinear semelparous Leslie matrix models

ABSTRACT

This paper considers the dynamics of nonlinear semelparous Leslie matrix models. First, a class of semelparous Leslie matrix models is shown to be dynamically consistent with a certain system of Kolmogorov difference equations with cyclic symmetry. Then, the global dynamics of a special class of the latter is fully determined. Combining together, we obtain a special class of semelparous Leslie matrix models which possesses generically either a globally asymptotically stable positive equilibrium or a globally asymptotically stable cycle. The result shows that the periodic behaviour observed in periodical insects can occur as a globally stable phenomenon.     

Some results on a heat conduction problem by Myshkis

An infinite homogeneous d-dimensional medium initially is at zero temperature. A heat impulse is applied at the origin, raising the temperature there to a value greater than a constant value u₀>0. The temperature at the origin then decays, and when it reaches u₀, another equal-sized heat impulse is applied at a normalized time τ₁=1. Subsequent equal-sized heat impulses are applied at the origin at the normalized times τ_n, n=2,3,…, when the temperature there has decayed to u₀. This sequence of normalized waiting times τ_n can be defined recursively by a difference equation and its asymptotic behavior was known recently. This heat conduction problem was first studied in [J. Difference Equations Appl. 3 (1997) 89–91].

A natural subsequent question is what happens if the problem is set in a finite region, like in a laboratory, with the temperature at the boundary being kept zero forever. In this paper we obtain the asymptotic behavior of the heating times for the one-dimensional case.     

两种型式水中用的压电水晶机电转换器

我们设计了并制造了两种不同型式的水中用水晶机电转换器:(i)镶嵌型,(ii)叠片型;尤其注意于水晶片的胶合、振动体的支持等问题,其目的在于减少转换器在无负荷时的等值电阻r。测得一个面积为609平方毫米其支持点完全自由的镶嵌型转换器的r为60kΩ;又测得另一个面积为256平方毫米四块水晶叠片型转换器的r焉15kΩ。再后讨论了两种型式转换器的优缺点,显见得叠片型的优于镶嵌型的很多,并进一步考虑了可能改进之点。     

VOID FORMATION IN UNIDIRECTIONAL SOLIDIFICATION

Abstract

Visual and photographic observations of unidirectional solidification of liquids that shrink by about 10%% is reported. The liquid is contained in a constant-volume (sealed) cylindrical cell. To estimate the effect of gravity, cooling is provided from above or below. For degassed liquids, when solidified from below, it is observed that the shrinkage is accommodated at the top (like a cavity). However, when solidified from above, the shrinkage is accommodated by formation of voids and worms filled with vapor. The effect of dissolved gases is also investigated. It is observed that dissolved gases tend to distribute the voids for both solidification from below and above. Hence, dissolved gases may be used to control the location of shrinkage voids. Some discussions and predictions are made regarding the location of voids formed under zero gravity.     

复合聚合物CTNI/PMMA薄膜的制备及传输特性的研究

合成了一种新型有机金属配合物:[C16H33(CH3)3N]Ni(dmit)2(简称为CTNI),通过旋涂法制备了不同质量比的复合聚合物CTNI/PMMA薄膜,用视频摄像技术测量了其光传输损耗。结果表明,对8%质量分数掺杂浓度的CTNI/PMMA聚合物复合薄膜的光传输损耗为3.001dB/cm,随着CTNI在复合聚合物薄膜中浓度的增加,薄膜的光传输损耗线性增长。     

萘甲腈和2,3-二甲基丁烯-2-光环加成反应:三氟醋酸的效应

在低转光解情况下,1-萘甲腈(1-NpCN)和2,3-二甲基丁烯-2(DMB)在环已烷或苯中的光环加成反应主要得到环丁烷3,但2-NpCN主要得到氨杂环丁烯6和少量的环丁烷5,三氟醋酸(TFA)量增加抑制1-NpCN和DMB的光环加成反应,表明TFA与基态及单激发态1-NpCN生成非光反应的复合物,它也淬灭^*(1-NpCN-DMB)激基复合物.在低浓度范围(0.1M以下)TFA加速2-NpCN和DMB光环加成反应,但在高浓度范围(大于0.1M)时又抑制反应.这些结果被解析如下:^*(2-NpCN-DMB)激基复合物和TFA反应增加5和6的得率,反之,是由于生成非光反应的基态复合物及淬灭单激发态2-NpCN.在非极性溶剂中二种单激发态萘甲腈生成TFA激基复合物的萤光与母体^*NpCN萤光区域几乎相同.     

ClONO2及其异构体光解反应的从头算研究(Ⅱ)——ClONO2→ClO+NO2反应机理研究

用从头算方法讨论了大气臭氧层主要破坏物ClONO2在光照下分解反应途径:ClONO2→ClO+NO2的反应机理.该反应的2个过渡态ClO…NOO(TS2a)和OCI…NOO(TS2b)中TS2a能垒较高,始态难于越过如此高的势垒;TS2b势垒较低,而产物到过渡态TS2b的能垒也仅有1.20 eV,故预测该反应为一个可逆反应.     

Fluorescence Quenching Effects of Donor-Acceptor Pairs Through A Rigid Spacer

Heptacyclo [6.6.0.02,6.03,13.04,11.05,9,010,14] tetradecane is a cage-shaped molecule of both high symmetry (D2d) and high rigidity. In our previous reports, it has been used as an unique spacer group for electron transfer processes between a donor (D) and an acceptor (A) substituent. The D and A chromophores can be aligned along a straight line, either coplanar (0° dihedral angle) or perpendicular (90° dihedral angle) with respect to each other. Knowledge collected in this work may be useful for the design of photo-electronic devices, such as electrochemical sensors, photovoltaic cells, molecular rectifiers and switches, etc.     

聚氨酯弹性体的热分解动力学研究

聚氨酯弹性体的热分解动力学研究;聚醚型聚氨酯;聚酯型聚氨酯;热分解;动力学;模型拟合法