质粒浓度对氯化钙转化法转化效率的影响

在保证其他条件一致的情况下,设置质粒浓度梯度并建立阴性对照进行研究来确定大肠杆菌DH5α氯化钙转化法时的最佳质粒浓度,结果表明质粒浓度为102 ng/μL时的转化效率最高。与其他质粒浓度相比,质粒浓度为102 ng/μL时的转化效率最高,实验重复性好,成本低廉,操作简便,而且对目的基因的克隆也具有重要意义,因此值得推广使用。

德氏乳杆菌保加利亚亚种电转化平台的构建和优化

德氏乳杆菌保加利亚亚种(Lactobacillus delbrueckiisub sp.bulgaricus)是最具经济价值的乳酸菌之一,在世界上广泛应用于酸奶和其它发酵乳生产。当前对该菌的代谢机制研究甚少。外源基因的转化效率是制约其分子代谢机制研究的重要因素。本研究以pMG36c为材料,对L.delbrueckiisub sp.bulgaricus CH3进行电转化条件研究。结果表明,在电转化过程中,电场强度、质粒的浓度、细胞生长状态均对转化效率有明显影响,得到了该菌株的最适电转化条件为:对数初期的细胞,质粒浓度为100 ng/50μl菌液,在10 kV/cm电场强度下电转化,转化后细胞在复壮培养液中培养3 h后涂布选择性培养基,转化率可达2.6×103CFU/μg DNA。以甘氨酸、醋酸锂、二硫苏糖醇处理细胞壁,发现醋酸锂和二硫苏糖醇共同处理对转化效率有明显改善,可提高转化效率。

花粉管通道法转化小麦影响因素的研究

以西农1376和中13小麦品种(系)为受体,携带叶片衰老抑制基因PSAG12-IPT的pCM-LA35-1质粒为转化载体,对花粉管通道转化法中的基因型、转化时间、质粒DNA浓度进行了研究.结果表明:不同基因型、转化时间对结实率影响不显著,质粒DNA浓度对结实率影响显著.在0～700 ng/μl范围内,小麦结实率随着质粒DNA浓度的增加而降低,其中质粒DNA浓度300 ng/μl和500ng/μl与对照相比结实率差异达到显著水平,而700 ng/μl则达到极显著差异.不同基因型的转化率因转化时间和质粒DNA浓度的不同而有所差异,其中西农1376的适宜转化时间为40～80min,适宜质粒DNA浓度为300～500ng/μl,以500ng/μl×40min处理的转化率最高,而中13小麦的适宜转化时间为80～120min,适宜质粒DNA浓度为300ng/μl.

A New Method for Measurement of Local Solid Flux in Gas-Solid Two-phase Flow

Previous works have shown that the suction probe cannot be used to accurately measure the upward and downward particle fluxes independently. A new method using a single optical probe to measure the local solid flux is presented. The measurement of upward, downward and net solid fluxes was carried out in a cold model circulating fluidized bed (CFB) unit. The result shows that the profile of the net solid flux is in good agreement with the previous experimental data measured with a suction probe. The comparison between the average solid flux determined with the optical measuring system and the external solid flux was made, and the maximum deviationturned out to be 22%, with the average error being about 6.9%. These confirm that the optical fiber system can be successfully used to measure the upward, downward and net solid fluxes simultaneously by correctly processing the sampling signals obtained from the optical measuring system.

Variations in retention efficiency of bivalves to different concentrations and organic content of suspended particles

Retention efficiencies (RE) of scallop (Chlamys farreri),oyster (Crassostrea gigas) and mussel (Mytilus edulis) in a flow-through system were measured to understand the short-term response to various particle and organic matter concentrations.By comparing the RE of C.farreri with that of C.gigas and M.edulis,we gained further knowledge on the feeding physiological characteristics of C.farreri and ascertained the possible cause of high summer mortalities of this species.The experimental feeding conditions included natural differences in the abundance and composition of suspended seston,as well as conditions in which seston abundance and composition were manipulated by adding natural silt or cultured microalgae.The results show that in natural sea water,the minimum particle size for maximal retention in M.edulis,C.gigas and C.farreri was approximately 4,6,and 8 μm,respectively;the RE of 2-μm (equivalent spherical diameter) particles was 17%,19%,and 8%,respectively;and the relative standardized RE was 58%,49%,and 18%,respectively.In C.gigas and M.edulis,the minimal particle size for maximal retention did not change with food quality (organic content).C.farreri was more sensitive to fluctuations in particle concentration and organic content.With particle concentration increase,the minimal particle size for maximal retention in scallop shifted to large particles and the RE for 2-μm particle decreased from 8% in natural seawater to 1.6%-6% in silt-enriched groups.With organic content increase,the minimal particle size for maximal retention shifted from 8 to 5 μm in natural seawater.Variation in RE of C.farreri with food conditions and the relationship between lower RE and smaller particle size may hamper C.farreri from food taking due to the decrease in the size distribution of phytoplankton in Sungo Bay.

Investigation of condition-induced bubble size and distribution in electroflotation using a high-speed camera

In the flotation process, bubble is a key factor in studying bubble-particle interaction and fine particle flo- tation. Knowledge on size distribution of bubbles in a flotation system is highly important. In this study, bubble distributions in different reagent concentrations, electrolyte concentrations, cathode apertures, and current densities in electroflotation are determined using a high-speed camera. Average bubble sizes under different conditions are calculated using Image-Pro@ Plus （Media Cybernetics@, MD, USA） and SigmaScan@ Pro （Systat Software, CA, USA） software. Results indicate that the average sizes of bubbles, which were generated through 38, 50, 74, 150, 250, 420, and 1000 μm cathode apertures, are 20.2, 29.5, 44.6, 59.2, 68.7, 78.5, and 88.8 μm, respectively. The optimal current density in electroflotation is 20 A/m2. Reagent and electrolyte concentrations, current density, and cathode aperture are important factors in controlling bubble size and nucleation. These factors also contribute to the control of fine- Particle flotation.

The Relationship between Major Components of PM2.5 and Meteorological Factors in Urban Tokyo, Japan

In this research, the main purpose is to estimate the variation of PM2.5 mass concentration and study the influence of meteorological characteristics on major components of PM2.5 concentrations in urban Tokyo, Japan. The results shown that the annual mean mass concentration of PM2.5 in urban Tokyo was higher than JEQS （Japanese Environmental Quality Standard） of the MOEJ （Ministry of the Environment Japan） （15 μg/m^3）, and 41.1% of the daily PM2.5 mass concentration exceeded the annual JEQS concentration during observation period. The major components of PM2.5 including SO4^2-, NO3^-, NH4^＋, OC and EC were tightly related to the meteorological conditions, the correlations results shown that the wind speed and relative humidity had significant correlations with major components of PM2.5 than the other meteorological factors. Higher relative humidity, windless and less rainfall conditions were favorable for elimination of PM2.5 concentration. Higher temperature was beneficial to the formation of SO42＂, but higher temperature and stronger sunshine duration were not conducive to the formation of NO3^-.

Particle Size and Concentrations of the Harmattan Dust Near the Gulf of Guinea

The seasonal transport of the Saharan dust to the West African region, near the Gulf of Guinea, during northem winter has been studied over 12 years. Using an optical particle counter, the dust aerosols in the diameter range 0.5-25 μm have been sampled at Kumasi （6040＇ N, l°34＇ W） in Ghana during the winter months of January-February from 1997 to 2009. The settling atmospheric dust particles observed during the peak Harmattan and the background Harmattan periods are analysed for the mean particle size, number and mass concentrations as well as the particle size-frequency. It is shown that the average daily particle diameter, number and mass concentrations obtained in the peak Harmattan periods are 1.57 ± 0.54 μm, 50 ± 25 particles/cm3 and 1,130 ± 994 μg/m3, respectively, while for the background Harmattan these values are correspondingly, 1.31 ±0.31 μm, 32 ±12 particles/cm3 and 576 ±429 μg/m3, respectively. These experimental results will be useful for the design of ambient air-filters and for understanding the West African climate change.

Nanoparticle distribution in a rotating curved pipe considering coagulation and dispersion

We study the evolution of the particle number concentration, mass concentration, particle polydispersity, particle diameter and geometric standard deviation considering particle coagulation and dispersion in a rotating curved pipe at different Reynolds number, Schmidt number and F number. It is found that, when the Coriolis force and the centrifugal force point to the same direction, particles concentrate near the outside edge of the pipe, which becomes more obvious as time goes by. The particle number and mass concentration increase faster at the early stage than that at the later stage, and approach a stable value finally. As the coagulation proceeds, the particle diameter, polydispersity and geometric standard deviation increase and have high values in the region close to the outside edge of the pipe. When the Coriolis force and the centrifugal force point to the oppo- site direction and the Coriolis force is more dominant than the centrifugal force, particles concentrate near the inside edge of the pipe. The particles in the region with a high number concentration have high mass concentration, large diameter and high polydispersity as well as large geometric standard deviation. The particle distribution is dependent on the balance of the pipe curvature and rotating speed. The Reynolds number and the Schmidt number have effects on the particle distribution when other parameters remain unchanged. An increase in the Reynolds number leads to an increase in particle number concentration and mass concentration, and a decrease in particle polydispersity, particle diameter and geometric standard deviation. With the increase of Schmidt number the particle number concentration and mass concentration increase, and the particle polydispersity, particle diameter and geometric standard deviation decrease.

Filtration of fine particles in atmospheric aerosol with electrospinning nanofibers and its size distribution

In this study, the size distribution of atmospheric aerosol in Beijing was monitored by the scanning mobility particle sizer spectrometer and the optical particle sizer. The size of particles in atmospheric aerosol was primarily distributed in the range of less than 1 pm. It showed different changes with the mass concentrations of particulate matters with an aerodynamic diameter of 〈2.5 pm （PM2.5） for different sizes of fine particles. The amount of ultrafine particles （less than about 60 nm） decreased while the larger ones （〉60 nm） increased along with the mass concentration of PM2.5 in atmospheric aerosol. This was be- cause of the formation of the secondary atmospheric aerosol. The polylactic acid （PLA） nanofibers were prepared for filtering the aerosol by electrospinning. PLA nanofiber mats were used as the middle layer to design the composite filter membranes. Atmospheric aerosol was used as dust source in the filtration test. The results showed that the filtration efficiency of the com- posite filter media increased along with the thickness of nanofiber mats, which was controlled by the collection time during electrospinning. Filtration efficiency can be improved obviously by compositing with a thin layer of nanofibers.

Effects of sediment physical properties on the phosphorus release in aquatic environment

Particle size, porosity, and the initial phosphorus concentration in sediments are the main factors affecting phosphorus release flux through the sediment-water interface. Sediments can be physically divided to muddy and sandy matters, and the adsorption-desorption capacity of sediment with phosphorus depends on particle size. According to phosphorus adsorption-desorption experiments, phosphorus sorption capacity of the sediment decreases with the increase of particle dimension. But among the size-similar particles, sediment with a bigger particle size has the larger initial phosphorus release rate. In terms of muddy and sandy sediments, there are inversely proportional relationships between the release rate and the flux. Due to the contact of surface sediment and the overlying water, the release flux from the sediment is either from direct desorption of surface sediment layer or from the diffusion of pore water in the sediment layer, which is mainly determined by sediment particle size and porosity. Generally, static phosphorus release process may include two stages: the first is the initial release. As for coarse particles, phosphorus is desorbed from surface sediment. And for fine particles, phosphorus concentration in water often decreases, mainly from pore water by the molecular diffusion. During the second stage, pore water flows faster in coarse sediment, and phosphorus is easy to desorb from the surface of the particles as diffusion dominates. For the smaller liquid-solid ratio of fine particles and the larger amount of phosphorus adsorption, the release flux from pore water due to diffusion is very small with longer sorption duration.