人口发展系统解的渐近性质及对生育模式的依赖关系

在一个安定社会中,人口发展过程可以用下列偏微分方程描写其中,p(r,t)表示在时刻t、人口年龄密度分布函数,r表示年龄,r_m表示社会人口中所能活到的最高年龄,[r_1,r_2](0相似文献   

人口发展算子的谱性质及人口系统的能控性

本文应用泛函分析方法解决了人口算子空间的完备性问题,由此给出了人口系统能控性的结论。     

妙趣横生的歧中易数列——数学建模一例

中国古环已有两千余年的历史,《战国策》齐策六记述:秦王遣使入齐,出玉连环,对齐君王后曰:“齐多知,能解此环不?”王后以示群臣,莫能解者,王后随引椎椎破之,谢秦使曰:“谨以解矣”.南宋临安(今杭州)市上,有专售“解玉板之类”的玩具,民间俗语云“解不开,歧中易,卸不下,九连环”     

Preparation of some new coumarin dyes

Series of coumarins containing heterocyclic substituent in 3-position were prepared. Sulfonyl chloride, a reactive group, was drawn into the heterocycle, and further condensed with amines to give series of new compounds that contain N-alkyl sulfamide. The spectral properties and dyeing character of these new dyes are discussed. A bathochromic shift (10 nm), enhanced fastness in light and sublimation (1-2 grade) and larger molar extinction coefficient (increase 104 L ·mol-1 ·cm-1) are apparent with these new compounds. In the meantime, larger solubility appears with these new compounds.     

δ效应下的非纬向基本气流的斜压不稳定

在推广的β平面近似下(δ效应)对大气的两层模式研究了一般非纬向基本气流情况下的斜压不稳定.给出了基本气流斜压不稳定的影响,结果表明,在非纬向基本气流情况下,δ效应(球面效应)会使斜压不稳定更明显,β随纬度的变化可能是中高纬度产生斜压不稳定的原因之一.     

正压大气模式下大地形和β变化的Rossby波

在正压大气模式下从准地转位涡方程出发,考虑地形和β随纬度变化下引进参数δ对Rossby波的共同作用,应用正交模方法得到在中高纬度具有大地形、Froude数以及参数δ的Rossby波相速度公式; 分析β变化下大地形和Froude数对Rossby波稳定度的影响,表明大地形、Froude数和参数δ对Rossby波的稳定性作用.     

Charge transfer modification of inverted planar perovskite solar cells by NiOx/Sr:NiOx bilayer hole transport layer

Perovskite solar cells (PSCs) are the most promising commercial photoelectric conversion technology in the future. The planar p-i-n structure cells have advantages in negligible hysteresis, low temperature preparation and excellent stability. However, for inverted planar PSCs, the non-radiative recombination at the interface is an important reason that impedes the charge transfer and improvement of power conversion efficiency. Having a homogeneous, compact, and energy-level-matched charge transport layer is the key to reducing non-radiative recombination. In our study, NiO$_{x}$/Sr:NiO$_{x}$ bilayer hole transport layer (HTL) improves the holes transmission of NiO$_{x}$ based HTL, reduces the recombination in the interface between perovskite and HTL layer and improves the device performance. The bilayer HTL enhances the hole transfer by forming a driving force of an electric field and further improves $J_{\rm sc}$. As a result, the device has a power conversion efficiency of 18.44%, a short circuit current density of 22.81 mA$\cdot$cm$^{-2}$ and a fill factor of 0.80. Compared to the pristine PSCs, there are certain improvements of optical parameters. This method provides a new idea for the future design of novel hole transport layers and the development of high-performance solar cells.     

九连环序列赏析--中国古环拆装的数学模型

“九连环”是中国古典拓扑益智玩具中流传最广、研究最多的一种 ,其结构如图 1所示 .玩法是把钗 H从九重连环扣中解脱出来 ,或图 1相反 (把钗装入九重环扣 ) .九连环起源于两千余年前的战国时代 ,如《战国策 .齐策六》曾记述秦使出玉连环 ,难住齐国群臣的故事 .南宋临安 (今杭州 )市面上有专售“解玉版”之类的玩具 ,且民间俗语云 :“解不开 ,歧中易 ,卸不下 ,九连环”.待到明代 ,此玩具已相当普及 .明人杨慎在《丹铅总录》中说 :“九连环之制 ,玉人之功者为之 .两环互贯为一 ,得其关捩解之为二 ,又合而为一 .今有此器 ,谓之九连环 .以铜或…