The dynamics of cavitation bubbles in a sealed vessel

A model of cavitation bubbles is derived in liquid confined in an elastic sealed vessel driven by ultrasound. In this model, an assumption that the pressure acting on the sealed vessel due to bubble pulsations is proportional to total volume change of bubbles is made. Numerical simulations are carried out for a single bubble and for bubbles. The results show that the pulsation of a single bubble can be suppressed to a large extent in sealed vessel, and that of two matched bubbles with same ambient radius can be further suppressed. However, when two mismatched bubbles have the same ambient radii, an interesting breathing phenomenon takes place, where one bubble pulsates inversely with the other one. Due to this breathing phenomenon the suppression effect becomes weak, so the maximum radii of two mismatched bubbles can be larger than that of a single bubble or that of two matched bubbles in sealed vessel. Besides that, for two mismatched bubbles with different ambient radii, the small one in sealed vessel under some certain parameters can pulsate as strong as or even stronger than that of a single bubble in an open vessel.     

Preparation and characterization of a novel green tea essential oil nanoemulsion and its antifungal mechanism of action against Magnaporthae oryzae

Blast is one of the most devastating fungal diseases of rice caused by Magnaporthe oryzae. Plant essential oil (EO) can function as antifungal agents and are regarded as a safe and acceptable method for plant disease control. However, EOs are unstable and hydrophobic, which limits its use. In the present study, we aimed for the preparation and characterization of a nanoemulsion (NE) from green tea essential oil (GTO) by ultrasonication method and determined the antifungal activity of NE on M. oryzae. The particle size and zeta potential of the NE were 86.98 nm and −15.1 mV, respectively. The chemical composition and functional groups of GTO and NE were studied by using GC–MS analysis, portable Raman spectroscopy, and FTIR coupled with chemometric analysis. GC–MS analysis showed the major components in GTO and NE were n-Hexyl cinnamaldehyde and L-α-Terpineol. Both GTO and NE showed good antioxidant activity and total phenol content. Moreover, the NE showed good antifungal activity against M. oryzae which was further confirmed by scanning electron microscopy (SEM) examination. Also, confocal Raman micro-spectroscopy (CRM) revealed the antifungal mechanism of GTO and NE on M. oryzae which proves the cell damage. To the best of our knowledge, this is the first study on the antifungal activity of GTO and NE against M. oryzae and also the use of CRM for the evaluation of the chemical changes in single fungal hyphae in a holistic approach. This study suggests that the prepared NE could be a potential candidate for use as a substitute for synthetic fungicides.     

15N-Traceruntersuchungen zum Mechanismus der N2O-Bildung in Böden

Nitrous oxide is a potential environmental hazard responsible for the green house effect and the destruction of the ozone layer in the lower stratosphere. Biological denitrification under anaerobic conditions in soils results in the formation of both N₂O and N₂, whereby highly nitrogen-fertilized agricultural soils contribute to a considerable extent of the N₂O emission. Latest results in the literature indicate that nitrous oxide can also be formed as a byproduct of the microbial nitrification. This is of importance for soils in central Germany because of the non-existence of typical denitrification conditions in a semiaride climate.

This study was conducted to measure the path of N₂O formation in Haplic Phaeozen: using [¹⁵N] ammonium and [¹⁵N] nitrat and a GC-MS aided incubation system. The kinetic isotope method was used to evaluate the experimental data. The results are:

- Under anaerobic conditions (～ 90% of the water holding capacity = WHC) N₂O originates mainly from the nitrate pool by denitrification.

- As expected, the N₂O formation is low under aerobic conditions (～ 80% WHC) but the gas originates directly from the ammonium and not from the nitrate pool, probably as a byproduct of the nitrification process.     

基于PdSe2/GaAs异质结的高灵敏近红外光伏型探测器的制备和图像传感的应用

本文制备了一种基于PdSe₂/GaAs异质结的高灵敏近红外光电探测器,该探测器是通过将多层PdSe₂薄膜转移到平面GaAs上制成的. 所制备的PdSe₂/GaAs异质结器件在808 nm光照下表现出明显的光伏特性,这表明近红外光电探测器可以用作自驱动器件. 进一步的器件分析表明,这种杂化异质结在零偏电压和808 nm光照下具有1.16×10⁵的高开关比. 光电探测器的响应度和比探测度分别约为171.34 mA/W和2.36×10¹¹ Jones. 而且,该器件显示出优异的稳定性和可靠的重复性. 在空气中2个月后,近红外光电探测器的光电特性几乎没有下降,这归因于PdSe₂的良好稳定性. 最后,基于PdSe₂/GaAs的异质结器件还可以用作近红外光传感器.     

Singular perturbation of first boundary value problem for higher order elliptic equations (II)

In this paper we discuss singular perturbations of first boundary value problem for higher order elliptic equations of two parameter and obtain the asymptotic expression for the formal solution containing two-parameter as well as the estimation of its remainder term. These results are the extensions of (2) and (3).     

A new Monte Carlo simulation for two models of self-avoiding lattice trees in two dimensions

By means of a new Monte Carlo sampling of a grand canonical ensemble, we verify universality for the critical exponents and of two models of lattice trees constrained to be self-avoiding on sites or on bonds. The attrition constants are also obtained. This algorithm, a generalization of that recently proposed by Berretti and Sokal for random walks, appears to optimize the critical slowing down in the scaling region. Systematic and statistical errors are carefully estimated.     

自聚焦透镜高效批量加工的双面研磨抛光法研究

依据双面研磨抛光原理,提出了加工自聚焦透镜平面和斜面辅助工装设计.从工艺技术特点和生产实际过程等方面对设计的工装使用情况进行分析验证.多次大批量加工实践证明,该辅助工装的设计完全满足了自聚焦透镜高效批量加工技术要求,简化整个生产线工艺,减少工艺流程时间,降低材辅料的消耗成本,从而验证了双面研磨抛光法是一种实用的加工自聚焦透镜的新方法.     

多级轴流压气机全工况特性计算

本文使用三维粘性流动计算软件Fine／Numeca,对某十五级轴流压气机进行了内流流场和全工况特性的数值计算尝试。分析了该压气机在设计工况和非设计工况的性能,同时把整机计算结果和前七级叶片的计算结果进行了比较。计算结果表明,当计算的级数较少时,目前的软件和硬件平台可以比较合理地预测压气机的全工况特性;而当计算的级数较多时,准确的数值模拟仍需要更为准确的多级模型和数值方法。