一类捕食—食饵模型的动力学性质研究

本文研究一个含一般功能反应第四型的捕食—食饵模型的动力学性质,得到该模型存在1个边界平衡点,正平衡点最多3个。进一步分析平衡点的定性性质,并利用Matlab进行数值模拟验证了所得结论。     

湖泊富营养物标准方法学及案例研究

《湖泊营养物基准和富营养化控制标准丛书：湖泊富营养物标准方法学及案例研究》在近几年的研究成果基础上,整理了大量国内外相关文献资料,结合该领域的最新研究成果．从水体营养物标准的概念出发,介绍了我国湖泊环境管理的现状,在分析研究美国、欧盟、日本等国家和地区的水质标准发展历程的基础上,建立了湖泊营养物标准的制定框架,     

东江支流夏季小型浮游动物群落特征研究

于2010年7月对东江流域主要支流进行调查,共布设79个有效样点,定量鉴定出原生动物和轮虫共计36属,据此研究小型浮游动物群落种类组成特征及其与环境因子的关系,探讨运用小型浮游动物辅助评估河流水环境状况可能性.结果表明:①研究区多数样点内小型浮游动物群落呈现种类少、密度小的特征,在样点内相对密度占绝对优势的种类多,但在样点内相对密度和区域频度均占优势的种类少;②顺流而下,小型浮游动物的种类数、密度、多样性均趋向增大,第一优势种类相对密度趋向降低,优势种类频繁变化,种类组成结构不稳定;③小型浮游动物密度与环境因子关系较为密切,具备成为评估河流水环境状况辅助或备选指标的可能性.     

虾池塘养殖中的浮游动物及应对措施分析

在虾养殖的过程中,采取合理的措施来控制水体中的浮游动物,是一项非常重要的工作。河里的浮游动物数量能够便于虾类保持充分的营养摄入,但过多的浮游动物会导致虾摄食量减少,生病甚至出现死亡的现象,因此控制浮游动物在虾池塘养殖的过程中非常重要。本文主要针对于在虾池塘养殖过程中,浮游动物对生态的影响和当下对此类现象的生态调控措施进行分析,希望能够通过本文的分析来让我国虾池塘养殖过程中浮游动物数量的控制措施得到进一步的提升。     

市场竞争的博弈分析

利用文献[1]中的Nash-Cournot平衡点求解算法,通过编制C语言程序后来求出一个现实中有关市场竞争问题的Nash平衡点并分析其结果.     

武汉东湖浮游生物间相互关系的多元分析

本文应用典型相关分析，辅以简单相关、多元回归分析以及逐步回归分析等方法，研究浮游植物指标中影响浮游动物的主要因子。１９７９─１９８５年逐月观测数据表明，武汉东湖浮游动物和浮游植物之间的关系，主要由浮游动物的密度与叶绿素ａ含量决定，其中，在浮游动物四大类（原生动物，轮虫，枝角类，桡足类）中，与叶绿素ａ密切相关的依次（由大到小）是轮虫，桡足类和原生动物的密度，而枝角类与叶绿素ａ无关。     

坝式水电站蓄水前后浮游动物的变化研究

通过对金鸡水利枢纽进行水生生物现场踏勘及调查采样,探讨坝式水电站蓄水前后对浮游动物的影响。金鸡电站在建坝前和建坝后浮游动物的各类组成变化不大。浮游动物密度减少了,生物量增加了。金鸡水利枢纽工程的建设,在施工及营运阶段都会对所涉水域生态环境及水生生物自然资源产生一定的负面影响,这些影响有的是可以逐步消除和恢复的。     

具有时滞类Lorenz系统的Hopf分岔

本文研究的是关于时滞类Lorenz混沌系统在平衡点的稳定性问题以及产生相应的Hopf分岔的条件。首先对系统引入时滞参量得到平衡点并且判断系统的稳定性,然后通过对系统在平衡点的线性化系统的特征方程根进行分析,得出此系统在平衡点产生Hopf分岔的条件,最后再通过Matlab软件对系统进行数值模拟,所得到的结果与理论分析的结果相同。     

差分方程x(n+1)=(δx(n-k)+x(n-k-1))/(A+x(n-k-1))全局性质

研究差分方程xn+1=δxn-k+xn-k-1/A+xn-k-1,(n=0,1…)的全局性质.得到的结论是:若δ≤(A-1),方程的零平衡点全局渐进稳定;若A-1＜δ≤A+1,方程的每个正解全局收敛于正平衡点.     

一类具功能反应的食饵——捕食者模型的定性分析

研究了具功能反应的食饵-捕食者两种群模型：x=xg（x）-yφ（x） y=y（-d＋eφ（x）），在g（x）和φ（x）均为非线性的情形下，讨论了系统的平衡点的性态，系统无环的充分条件和在正平衡点外围存在极限环的条件。     

可分生成域扩张的生成元

设K为域, L= K(a1;…… ; an) 为K的可分生成的扩域, tr:deg:(L/K) = r。证明了存在有限多个非零n(r + 1) 元 多项式 , 使得对任意 ,只要某一个 ,令 就有 ,结论中多 项式的系数范围控制得足够好。     

MINRES法和有限元法解奇摄动反应扩散方程

讨论奇摄动反应扩散方程 的数值逼近求解问题, 及 均为正实数. 利用有限元方法并结合最小残量法, 给出求解该问题的一个新方 法, 该方法修正了单纯采用有限元方法求解时在边界附近呈现出的非正常扰动的 现象, 避免了因为 过小所引起的解的变异, 从而得到更加精确的数值结果.     

Microfluidic sterilization

Nowadays, microfluidics is attracting more and more attentions in the biological society and has provided powerful solutions for various applications. This paper reported a microfluidic strategy for aqueous sample sterilization. A well-designed small microchannel with a high hydrodynamic resistance was used to function as an in-chip pressure regulator. The pressure in the upstream microchannel was thereby elevated which made it possible to maintain a boiling-free high temperature environment for aqueous sample sterilization. A 120 °C temperature along with a pressure of 400 kPa was successfully achieved inside the chip to sterilize aqueous samples with E. coli and Staphylococcus aureus inside. This technique will find wide applications in portable cell culturing, microsurgery in wild fields, and other related micro total analysis systems.Microfluidics, which confines fluid flow at microscale, attracts more and more attentions in the biological society.^1–4 By scaling the flow domain down to microliter level, microfluidics shows attractive merits of low sample consumption, precise biological objective manipulation, and fast momentum/energy transportation. For example, various cell operations, such as culturing^5–7 and sorting,^8–10 have already been demonstrated with microfluidic approaches. In most biological applications, sterilization is a key sample pre-treatment step to avoid contamination. However, as far as the author knew, this important pre-treatment operation is generally achieved in an off-chip way, by using high temperature and high pressure autoclave. Actually, microfluidics has already been utilized to develop new solution for high pressure/temperature reactions. The required high pressure/temperature condition was generated either by combining off-chip back pressure regulator and hot-oil bath,^11,12 or by integrating pressure regulator, heater, and temperature sensor into a single chip.¹³ This work presented a microfluidic sterilization strategy by implementing the previously developed continuous flowing high pressure/temperature microfluidic reactor.Figure ​Figure11 shows the working principle of the present microfluidic sterilization chip. The chip consists of three zones: sample loading (a microchannel with length of 270 mm and width of 40 μm), sterilization (length of 216 mm and width of 100 μm), and pressure regulating (length of 42 mm and width of 5 μm). Three functional zones were separated by two thermal isolation trenches. The sample was injected into the chip by a syringe pump and experienced two-step filtrations (feature sizes of 20 μm and 5 μm, not shown in Figure ​Figure1)1) at the entrance to avoid the channel clog. All channels had the same depth of 40 μm. According to the Hagen–Poiseuille relationship,¹⁵ the pressure regulating channel had a large flow resistance (around 1.09 × 10¹⁷ Pa·s/m³, see supplementary S1 for details¹⁶) because of its small width, thereby generated a high working pressure in the upstream sterilization channel under a given flow rate. The boiling point of the solution will then be raised up by the elevated pressure in the sterilization zone followed by the Antoine equation.¹⁶ By integrating heater/temperature sensors in the pressurized zone, a high temperature environment with temperature higher than 100 °C can thereby be realized for aqueous sample sterilization. The sample was collected from the outlet and cultured at 37 °C for 12 h. Bacterial colony was counted to evaluate the sterilization performance.Open in a separate windowFIG. 1.Working principle of the present microfluidic sterilization. Only microfluidic channel, heater, and temperature sensor were schematically shown. The varied colour of the microchannel represents the pressure and that of the halation stands for the temperature.Fabrication of this chip has been introduced elsewhere.¹⁴ The fabricated chip and the experimental system are shown in Figure ​Figure2.2. There were two inlets of the chip. While, in the experiment, only one inlet used and connected to the syringe pump. The backup one was blocked manually. The sample load zone was arranged in between of the sterilization zone and the pressure regulating zone based on thermal management consideration. A temperature control system (heater/temperature sensor, power source, and multi-meter) was setup to provide the required high temperature. The heater and the temperature sensor were microfabricated Pt resistors. The temperature coefficient of resistance (TCR) was measured as 0.00152 K⁻¹.Open in a separate windowFIG. 2.The fabricated chip and the experimental system. (a) Two chips with a penny for comparison. The left chip was viewed from the heater/temperature sensor side, while the right one was observed from the microchannel side (through a glass substrate). (b) The experimental system.Thermal isolation performance of the present chip before packaging with inlet/outlet was shown in Figure ​Figure3,3, to show the thermal interference issue. The results indicated that when the sterilization zone was heated up to 140 °C, the pressure regulating zone was about 40 °C. At this temperature, the viscosity of water decreases to 0.653 mPa·s from 1.00 mPa·s (at 20 °C), which will make the pressure in the sterilization zone reduced from 539 kPa (calculated at 20 °C and flow rate of 4 nl/s) to 387 kPa. The boiling point will then decrease to 142.8 °C, which will guarantee a boiling-free sterilization. In the cases without the thermal isolation trenches, the temperature of the pressure regulating zone reached as high as 75 °C because of the thermal interference from the sterilization zone, as shown in Figure ​Figure3.3. The pressure in the sterilization zone was then reduced to 268 kPa (calculated at flow rate of 4 nl/s) and the boiling temperature was around 130 °C, which was lower than the set sterilization temperature. Detail calculation can be found in supplementary S2.¹⁶Open in a separate windowFIG. 3.The temperature distribution of the chips (before packaged) with and without thermal isolation trenches (powered at 1 W). The data were extracted from the central lines of infrared images, as shown as inserts.Bacterial sterilization performance of the present chip was tested and the experimental results were shown in Figure ​Figure4.4. E. coli with initial concentration of 10⁶/ml was pumped into and flew through the chip with the sterilization temperatures varied from 25 °C to 120 °C at flow rates of 2 nl/s and 4 nl/s. The outflow was collected and inoculated onto the SS agar plate evenly with inoculation loops. The population of bacteria in the outflow was counted based on the bacterial colonies after incubation at 37 °C for 12 h. Typical bacterial colonies were shown in Figure ​Figure4.4. The low flow rate case showed a better sterilization performance because of the longer staying period in the sterilization channel. The population of E. coli was around 1.25 × 10⁴/ml after a 432 s-long, 70 °C sterilization (at flow rate of 2 nl/s). While at the flow rate of 4 nl/s, the cultivation result indicated the population was around 3.8 × 10⁴/ml because the sterilization time was shorten to 216 s. A control case, where the solution flew through an un-heated chip at 2 nl/s, was conducted to investigate the effect of the shear stress on the sterilization performance (see the supplementary S3 for details¹⁶). As listed in Table ​TableI,I, the results indicated that the shear stress did not show any noticeable effect on the bacterial sterilization. When the chip was not heated, i.e., the case with the largest shear stress because of the highest viscosity of fluid, the bacterial cultivation was nearly the same as the off-chip results (no stress). The temperature has the most significant effect on the sterilization performance. No noticeable bacteria proliferation was observed in the cases with the sterilization temperature higher than 100 °C, as shown in Figure ​Figure44.

Table I.

The E. coli cultivation results under different flow rates and sterilization temperatures. ^a