Harvesting of a phytoplankton–zooplankton model

Considering that some phytoplankton and zooplankton are harvested for food, a phytoplankton–zooplankton model with harvesting is proposed and investigated. First, stability conditions of equilibria and existence conditions of a Hopf-bifurcation are established. Our results indicate that over exploitation would result in the extinction of the population and an appropriate harvesting strategy should ensure the sustainability of the population which is in line with reality. Furthermore, the existence of bionomic equilibria and the optimal harvesting policy are discussed. The present value of revenues is maximized by using Pontryagin’s maximum principle subject to the state equations and the control constraints. We discussed the case of optimal equilibrium solution. It is found that the shadow prices remain constant over time in optimal equilibrium when they satisfy the transversality condition. It is established that the zero discounting leads to the maximization of economic revenue and that an infinite discount rate leads to complete dissipation of economic rent. Finally, some numerical simulations are given to illustrate our results.     

抛光区域几何特征与流场创成关键参数关系

磁流变抛光在其实际工作过程中,抛光区域几何特征的不同将会对流场创成的关键参数产生很大的影响。针对此问题建立三维模型与实验仿真展开研究。在研究抛光区域几何特征与流场创成关键参数的关系时,先改变抛光区域形状,观察其对流场创成中剪切应力、压力产生的影响;再控制抛光区域的形状相同时,通过改变抛光区域尺寸大小,观察对流场创成中剪切应力、压力产生的影响。结果表明：当抛光区域形状不同时,抛光区域为凹面时剪切应力最大,抛光区域为凸面时剪切应力最小。当抛光区域形状为凸面时,抛光区域两边的剪切应力随着抛光区域曲率大小增大而增大;当抛光区域形状为凹面,抛光区域两边的剪切应力随着抛光区域曲率大小增大而减小。当抛光区域形状不同时,抛光区域为凹面时压力最大,抛光区域为凸面时压力最小。当抛光区域形状为凸面时,抛光区域处的压力随着抛光区域曲率增大而增大;当抛光区域形状为凹面时,抛光区域处的压力随着抛光区域曲率增大而减小。     

Preparation, structure, magnetic properties and special magnetoresistance effect of Lao.67Sr0.33Mn03+δ/Pr0.7Cao.3 Mn03+δ/Lao.67Sro.33Mn03+δ trilayered thin films

The La_0,67Sr_0.33Mn0_{3 +δ}/Pr_0.7Ca_o.3Mn0_3+δ/La_0.67Sr_0.33Mn0_3+δ(LPL) trilayered films on (100)LaA-1O₃ substrates are prepared by using direct current (DC) magnetron sputtering method. The results obtained by means of X-ray powder diffractometer show that all films are the high quality epitaxial films. The results gained by SQUID magnetometer indicate that there is a magnetic coupling in the LPL trilayered films. The resistivities of LSMO, PC-MO and LPL films are measured using standard four-probe method and analyzed log_p-1/T curve. From the results it is concluded that the middle-layered PCMO which is ferromagnetic may play a role of intra-magnetic field, which weakens the paramagnetism of LSMO film, lowersp _max and enlargesT _p which is the transition temperature from metal to insulator, just as the applied magnetic field does. And the middle-layered PCMO may induce the change of the density of states in the LSMO’s gap. The two reasons above make the resistivity andT _p of the samples in zero field change with the thickness of PCMO layers. Project supported by the Chinese Academy of Sciences and the Foundation of State Science and Technology Commission of China.     

Performance characteristics of single photon pulse ranging system using Monte Carlo simulation

Single photon pulse ranging system with extremely high sensitivity has been widely used in distance measurement and 3D imaging. To analyze the factors that affect the measurement precision and accuracy will help to improve system performance. According to system structure and principle, we mainly discussed the following factors: laser intensity, pulse width, detection efficiency and time jitter. A simulation model based on Monte Carlo stochastic method was constructed in this paper, and we get the specific influence of factors on measurement precision and accuracy by simulation. Finally, we set up laboratory experiment system and took effective experiments on ranging precision and accuracy.     

Vibrational spectroscopic study of the mineral penkvilksite Na 2TiSi 4O 11·2H 2O – a mineral used for the uptake of radionuclides

We have used vibrational spectroscopy to study the formula and molecular structure of the mineral penkvilksite Na ₂TiSi ₄O ₁₁·2H ₂O. Penkvilksite is a mineral which may be used in the uptake of radioactive elements. Both Raman and infrared spectroscopies identify a band at ～3638 cm^?1 attributed to an OH-stretching vibration of hydroxyl units. The inference is that OH units are involved in the structure of penkvilksite. The formula may be well written as Na ₂TiSi ₄O ₁₀(OH)₂·H ₂O. The mineral is characterised by a very intense Raman band at 1085 cm^?1 and a broad infrared band at 1080 cm^?1 assigned to SiO-stretching vibrations. Raman bands at 620, 667 and 711 cm^?1 are attributed to SiO and TiO chain bonds. Water-stretching vibrations are observed as Raman bands at 3197, 3265, 3425 and 3565 cm^?1. Vibrational spectroscopy enables aspects of the molecular structure of the mineral penkvilksite to be ascertained. Penkvilksite is a mineral which can incorporate actinides and lanthanides from radioactive waste.     

基于梯度聚类离散思想的磁流变抛光自适应轨迹

针对磁流变抛光过程中抛光轨迹会引入迭代误差的问题,设计了步长和行距随光学表面梯度自适应变化的光栅线抛光轨迹。首先根据光学元件的表面误差分布,利用标准五点法获得面形各点的梯度值,再基于聚类离散思想将所有面形点根据梯度值大小进行了归类,从而得到轨迹步长和行距随面形误差变化的自适应轨迹。在自研的磁流变加工机床上进行了实验研究,将一块直径50 mm的微晶玻璃,从峰谷值为65 nm、均方根值为12 nm收敛到峰谷值为21 nm、均方根值为2.5 nm,并且在加工后的表面功率谱密度曲线上没有出现明显的尖峰误差。实验结果表明,这种自适应轨迹能有效抑制中高频误差。     

Adsorbed para-nitrophenol on HDTMAB organoclay--a TEM and infrared spectroscopic study

para-Nitrophenol adsorbed on hexadecyltrimethylammonium bromide modified montmorillonite has been studied using a combination of X-ray diffraction TEM and infrared spectroscopy. Upon formation of the organoclay, the properties change from hydrophilic to hydrophobic. It is proposed that para-nitrophenol is adsorbed onto the water in the cation hydration sphere of the organoclay. As the cation is replaced by the surfactant molecules the para-nitrophenol replaces the surfactant molecules in the clay interlayer. Significant changes in the water vibrations occur in this process. Bands attributed to CH stretching and bending vibrations in general decrease as the concentration of the surfactant (CEC) increases up to 1.0 CEC. After this concentration the bands increase approaching a value the same as that of the surfactant. Strong changes occur in the HCH deformation modes of the methyl groups of the surfactant. These changes are attributed to the methyl groups locking into the siloxane surface of the montmorillonite. Such a concept is supported by changes in the SiO stretching bands of the montmorillonite siloxane surface. This study demonstrates that para-nitrophenol will penetrate into the untreated clay interlayer and replace the intercalated surfactant in surfactant modified clay, resulting in the change of the arrangement of the intercalated surfactant.     

Modification of the surfaces of Wyoming montmorillonite by the cationic surfactants alkyl trimethyl, dialkyl dimethyl, and trialkyl methyl ammonium bromides

Surfaces of a Wyoming SWy-2 sodium montmorillonite were modified using microwave radiation through intercalation with the cationic surfactants octadecyl-trimethyl ammonium bromide, dimethyldioctadecylammonium bromide, and methyl-tri-octadecyl ammonium bromide by an ion exchange mechanism. Changes in the surfaces and structure were characterized using X-ray diffraction (XRD), thermal analysis (TG) and infrared (IR) spectroscopy. Different configurations of surfactants within montmorillonite interlayer are proposed based on d(001) basal spacings. A range of surfactant molecular environments within the surface-modified montmorillonite are proposed based upon their thermal decomposition. IR spectroscopy using a smart endurance single bounce diamond attenuated total reflection (ATR) cell has been used to study the changes in the spectra of CH asymmetric and symmetric stretching modes of the surfactants to provide more information of the surfactant molecular configurations.