基于TDR原理探究不同土壤质地下溶质弥散与水流通量的关系

溶质弥散是评价和预测土壤和地下水迁移的关键物理参数,然而,在较高的实时和原位测量中,没有全面、严格地评价水通量(J_(w))和土壤质地对溶质分散的影响。该研究以Cl^(-)为示踪剂,定量分析饱和充填砂土、粉壤土和砂质粘壤土的溶质分散特征。采用反演模型,通过将溶质输运模型拟合到时域反射技术测量的溶质穿透曲线中,导出溶质弥散系数(D)。结果表明:Jw为3.2×10^(-6)~6.0×10^(-5)m/s,D与土壤质地和Jw密切相关。随着Jw的增加和土壤质地的变细,D呈非线性增加。这可以用D和Jw之间的幂函数来描述。弥散度几乎保持不变,砂质粘壤土的弥散度约为砂土的5.3倍,粉质壤土的2.5倍。研究结果进一步证明,弥散度主要由土壤质地决定,这将有助于评估和预测污染物和养分在土壤和地下水中的迁移。

Combined MR Imaging for Pulmonary Embolism and Deep Venous Thrombosis by Contrast-enhanced MR Volume Interpolated Body Examination

MR pulmonary angiography(MRPA)combined with indirect MR venography(MRV)was attempted by using 3D contrast-enhanced MR volume interpolated body examination(VIBE)sequence.Agreement rate for deep venous thrombosis(DVT)detection between MRV and duplex sonography(DUS)was evaluated;the potential of this method for venous thromoembolism(VTE)was also investigated.Thirty-four patients with DUS-identified DVT were enrolled in this study.MRI was performed after a single administration of Gadopentetate dimeglumine.Fatsuppressed 3D VIBE was applied for visualizing pulmonary arteries,abdominal veins,pelvic and leg veins,ranging from lung apex to ankle level.Two radiologists observed the MR images in consensus,recorded the location and number of emboli.MRV images were assessed based on per-vein segment.The agreement rate between MRV and DUS for venous segment-to-segment comparison was analyzed by Wilcoxon rank sum test.All the patients were diagnosed as having DV 1 by MRV.MRV detected 55 more venous segments with thrombi than DUS based on per-vein segment analysis.Twenty-three patients with pulmonary embolism(PE)were detected by MRPA.Twenty-one patients underwent both pulmonary CT angiography and MRPA,and consistency for PE detection was 100%.Total examination time of the combined MR protocol was 7 min for each patient.The contrast-enhanced VIBE sequence proves to be a feasible and reliable method for VTE diagnosis in one-stop MR scanning procedure,and contrast-enhanced VIBE performs better to depict DVT than DUS on per-vein segment basis.

Research Progress and Prospect on the Effects of Abiotic Stress on Plant Photosynthesis

Photosynthesis is the basis of plant growth and development as well as the existence of the biological world. Photosynthesis is of great theoretical and practical significance. In this paper, the effects of temperature, drought, salt, light and other abiotic stress factors on plant photosynthesis were reviewed.

Degradation behaviors of Nabumetone and its metabolite during UV/monochloramine process:Experimental and theoretical study

This study investigated degradation behaviors of a nonsteroidal anti-inflammatory drug Nabumetone(NMT)and its major metabolite 6-methoxy-2-naphthylacetic acid(MNA)in the coupling process of ultraviolet and monochloramine(UV/NH2Cl).The second-order rate constants of the contaminants reacting with reactive radicals(HO·,Cl·,Cl_(2)·-,and CO_(3)·^(-))were determined by laser flash photolysis experiments.HO·and Cl·contributed predominantly with 52.3%and 21.7%for NMT degradation and 60.8%and 22.3%for MNA degradation.The presence of chlorides retarded the degradation of NMT,while promoted the destruction of MNA,which was ascribed to the photosensitization effects of MNA under UV irradiation.Density functional theory(DFT)calculations revealed that radical adduct formation(RAF)was dominant pathway for both HO·and Cl·reacting with the contaminants,and hydrogen atom transfer(HAT)preferred to occur on side chains of NMT and MNA.NMT reacted with NO_(2)·through single electron transfer(SET)with the second-order rate constant calculated to be 5.35×10^(7)(mol/L)^(-1)sec^(-1),and the contribution of NO_(2)·was predicted to be 13.0%of the total rate constant of NMT in pure water,which indicated that NO_(2)·played a nonnegligible role in the degradation of NMT.The acute toxicity and developmental toxicity of NMT were enhanced after UV/NH_(2)Cl treatment,while those of MNA were alleviated.The transformation products of both NMT and MNA exhibited higher mutagenicity than their parent compounds.This study provides a deep understanding of the mechanism of radical degradation of NMT and MNA in the treatment of UV/NH2Cl.

Composite Converter Combined APFC with Switched-capacitor Converter

To reduce switch numbers and voltage stress in semiconductor devices,this paper proposes a novel single-phase converter combined Active Power Factor Correction(APFC)with switched-capacitor converter.In addition,dynamic voltage regulation and voltage gain are improved by integrating the boost converter and switching capacitor cells.The interstage bulk capacitor is no longer needed.An average current control with redistribution of voltage in cells is proposed to obtain voltage lift ability of the switching capacitor cells and maintain a high-power factor.To study and verify the proposed converter preliminarily,theoretical analysis and simulation are presented in the paper.Furthermore,a 50o W prototype with two different configurations is built for experimental verification.The proposed converter can reach 95.62%of maximum efficiency,0.99 of power factor,and 3.55%of THD with 600 V output voltage,simultaneously.

Ammonia pollution characteristics of centralized drinking water sources in China

The characteristics of ammonia in drinking water sources in China were evaluated during 2005-2009. The spatial distribution and seasonal changes of ammonia in different types of drinking water sources of 22 provinces, 5 autonomous regions and 4 municipalities were investigated. The levels of ammonia in drinking water sources follow the order of fiver 〉 lake/reservoir 〉 groundwater. The levels of ammonia concentration in river sources gradually decreased from 2005 to 2008, while no obvious change was observed in the lakes/reservoirs and groundwater drinking water sources. The proportion of the type of drinking water sources is different in different regions. In river drinking water sources, the ammonia level was varied in different regions and changed seasonally. The highest value and wide range of annual ammonia was found in South East region, while the lowest value was found in Southwest region. In lake/reservoir drinking water sources, the ammonia levels were not varied obviously in different regions. In underground drinking water sources, the ammonia levels were varied obviously in different regions due to the geological permeability and the natural features of regions. In the drinking water sources with higher ammonia levels, there are enterprises and wastewater drainages in the protected areas of the drinking water sources.

Phlebotomine sand flies(Diptera:Psychodidae)transmitting visceral leishmaniasis and their geographical distribution in China:a review

After the existence of phlebotomine sand flies was first reported in China in 1910,the distribution of different species and their role in the transmission of visceral leishmaniasis(VL)have been extensively studied.Up until 2008,four species have been verified as vectors of VL,namely,Phlebotomus chinensis(Ph.sichuanensis),Ph.longiductus(Ph.chinensis longiductus),Ph.wui(Ph.major wui),and Ph.alexandri.The sand fly species vary greatly depending on the natural environments in the different geographic areas where they are endemic.Ph.chinensis is euryecious and adaptable to different ecologies,and is thus distributed widely in the plain,mountainous,and Loess Plateau regions north of the Yangtze River.Ph.longiductus is mainly distributed in ancient oasis areas south of Mt.Tianshan in the Xinjiang Uygur autonomous region.Ph.wui is the predominant species in deserts with Populus diversifolia and Tamarix vegetation in Xinjiang and the western part of the Inner Mongolia autonomous region.Finally,Ph.alexandri is steroecious and found only in stony desert areas,such as at the foot of the mountains in Xinjiang and the western Hexi Corridor,in Gansu province.This review summarized the relationship between the geographic distribution pattern of the four sand fly species and their geographical landscape in order to foster research on disease distribution and sand fly control planning.Furthermore,some problems that remained to be solved about vectors of VL in China were discussed.

Distribution characteristics of poly-and perfluoroalkyl substances in the Yangtze River Delta

In this work, a method was developed and optimized for the analysis of polyfluoroalkyl and/or perfluoroalkyl substances（PFASs） content in surface water and sediment samples with high instrumental response and good separation. Surface water and sediment samples were collected from the Yangtze River Delta（YRD） to analyze the distribution characteristics of perfluoroalkyl carboxylic acids（PFCAs）, perfluoroalkane sulfonic acids（PFSAs）, perfluoroalkyl phosphonic acids（PFPAs）, perfluoroalkyl phosphinic acids（PFPiAs）, and polyfluoroalkyl phosphoric acid diesters（di PAPs）. The results showed that the total concentrations of PFCAs and PFSAs in YRD varied from 31 to 902 ng/L. PFCAs（≥ 11 carbons） and PFSAs（≥ 10 carbons atoms） were not detected in any surface water samples. The mean concentrations of all PFCAs and PFSAs in surface water from the sampling areas decreased in the following order：Yangtze river（191 ng/L） ≈ Taihu lake（189 ng/L） 〉 Huangpu river（122 ng/L） ≈ Qiantang river（120 ng/L） 〉 Jiaxing urban river（100 ng/L）. Strong significant（p 〈 0.05） correlations between the concentrations of many of the compounds were found in the sampling areas, suggesting a common source for these compounds. Only perfluorooctanoic acid（PFOA） was observed in all sediment samples, at concentrations varying from 0.02 to 1.35 ng/g. Finally, detection rates of two di PAPs were only 8% and 10%, respectively and the concentration of di PAPs was two to three times lower compared to PFCAs and PFSAs.