基于多时相Landsat8影像赣南地区水体污染识别研究

赣南地区水资源丰富,受人类活动、农业、资源开采等的影响,存在一定水质污染问题.传统多采用单点化验分析水污染,此方法只代表局部和典型情况,而基于多光谱遥感反演水质参数能区域高精度定量反演.以赣南区域部分河段为研究区,利用Landsat8 OLI卫星影像,采用支持向量机方法对水体识别.结合赣南地区实际情况,选取水质参数氨氮、总磷、叶绿素a为研究对象,采用统计回归方法建立遥感波普信息与实测数据间的响应关系模型,反演结果氨氮总体浓度在0.2~0.4 mg/L、总磷0.06~0.18 mg/L、叶绿素a 5.01~6.81μg/L.同时采用决定系数(R2)和平均绝对误差(MAE)进行模型可行性及反演精度验证,反演结果R2分别为0.840、0.745、0.745,MAE分别为0.054、0.049、0.069,反演模型方法可靠,能够准确识别排污口,为保护水资源及防治水体污染提供可靠的技术支撑.

硫酸锌和碳酸钠抑制滑石浮选机理

通过浮选试验、溶液化学计算和多种表征技术,深入研究硫酸锌和碳酸钠在黄铜矿和辉钼矿浮选中对滑石的抑制机理。浮选试验表明,在pH值为7~9的范围内滑石浮选得到有效抑制。在该pH范围内,对硫酸锌和碳酸钠混合溶液的溶液化学计算表明,碱式碳酸锌是主要的含锌物种;X射线衍射和红外光谱分析进一步证明了这一点。Zeta电位测试表明:在滑石抑制发生的pH范围内,碱式碳酸锌表面带正电荷,而滑石表面带负电荷。X射线光电子能谱和场发射扫描电子显微镜证实:经硫酸锌和碳酸钠混合溶液处理的滑石颗粒表面存在含锌沉淀物。结果表明,由于静电吸引,形成的碱式碳酸锌与滑石发生异相聚沉,从而抑制滑石浮选。

界面耦合的PbSO_(4)溶解和PbS沉淀及其对铅矾硫化浮选的影响

通过浮选试验、X射线光电子能谱(XPS)、场发射扫描电子显微镜(FESEM)、拉曼光谱和紫外-可见漫反射光谱(UV-VisDRS)系统研究铅矾浮选中的硫化机理。浮选试验证明硫化钠对铅矾浮选具有活化作用;但必须控制硫化钠浓度,以避免过量硫离子对浮选的抑制。XPS、拉曼光谱和UV-VisDRS结果表明,用硫化钠水溶液处理铅矾时,PbSO_(4)被PbS取代。FESEM观察结果显示硫化过程中PbSO_(4)的溶解和PbS纳米粒子的沉淀。因此,可认为铅矾与硫化钠水溶液的反应是通过界面耦合溶解–沉淀机制进行的:在与硫化钠水溶液接触时,铅矾溶解将Pb^(2+)和SO_(4)^(2-)释放到流体边界层中,该流体边界层相对于PbS相变得过饱和;然后,PbS纳米粒子在铅矾表面成核并生长。生长在铅矾表面的PbS纳米颗粒可以提高铅矾的可浮性。

Review:Ferromagnetism in Undoped ZrO2 Thin Films

Diluted magnetic oxides have evolved into a popular branch of materials science during the last decade. In the first few years,people attributed the ferromagnetism to the magnetic dopants. However,the observation of ferromagnetism in undoped HfO_2 thin films made it more controversial and promoted extensive research on the ferromagnetism in various undoped oxides. Both of the experimental works and theoretical studies have shown that intrinsic defects in oxide nanomaterials play a crucial role in the origin of such an unexpected ferromagnetism,in spite of some contradicting views which kind of defects is predominant. In the past several years,we have conducted systematic and thorough research on the room temperature ferromagnetism in undoped ZrO_2 thin films,and clarify some physics behind it. We firstly prepared undoped ZrO_2 thin films by different ways,such as Pulsed electron beam deposition,magnetron sputtering,and electron beam evaporation,and successfully obtained ZrO_2 thin films with different crystalline structure,in particular a pure high-temperature stabilized one,by adjusting some preparation parameters during the deposition process or post-annealing treatment. A phase-dependent ferromagnetism was then confirmed to exist in such ZrO_2 thin films. Further,we conducted exhaustive defect analysis and characterization by X-ray photoelectron spectroscopy,photoluminescence spectra,and electron paramagnetic resonance,respectively,and found the oxygen vacancy,specifically the single ionized oxygen vacancy( V_O^+),has a remarkable influence on the enhancement of ferromagnetism. Herein,we will review the work in detail on the phase-dependent and oxygen vacancy-enhanced room temperature ferromagnetism in undoped ZrO_2 thin films.

Thickness dependence of the crystallization and phase transition in ZrO_(2)thin films

Fluorite-structure binary oxides(e.g.,HfO_(2)and ZrO_(2))have attracted increasing interest for a broad range of applications including thermal barrier coatings,high-k dielectrics,and novel ferroelectrics.A crystalline structure plays a crucial role in determining physical and chemical properties.Structure evolution of ZrO_(2)thin films,particularly down to the nanometer scale,has not been thoroughly studied.In this work,we carried out systematic annealing analysis on the ZrO_(2)thin films.Through in-situ high-temperature X-ray diffraction(XRD)characterizations,a thickness dependence of crystallization and phase transition is observed.Irrespective of the thickness(10-300 nm),the as-prepared amorphous ZrO_(2)thin films are preferentially crystallized into a tetragonal(t)structure(high-temperature phase),which can be preserved down to room temperature(RT)upon anncaling at the corresponding crystallization temperaturc(T).When anncaling at temperaturcs higher than Tc,the transition from t to monoclinic(m;RT phase)will occur,and the quantity of the transition strongly depends on the film thickness.Our work expands the basic understanding of the phase transition in the ZrO_(2)thin films,and offers a path to the selective control over the phase structure for novel functionalities.

Ferroelectric domains and phase transition of sol-gel processed epitaxial Sm-doped BiFeO_(3)(001)thin films

BiFeO_(3),a room-temperature multiferroic material,has recently been increasingly applied as a potential lead-free piezoelectric material due to its large piezoelectricity achieved by doping.In this work,12%Smdoped BiFeO_(3)epitaxial thin films were fabricated on Nb-doped SrTiO_(3)(001)single crystal substrates via sol-gel method.The epitaxy was verified by reciprocal space mapping(RSM)and transmission electron microscope(TEM).The TEM results indicated the coexistence of R3c and Pbam phases in the film.The domains and piezoelectric properties from room temperature to 200℃were characterized by piezoresponse force microscopy(PFM).Domains became active from 110℃to 170℃,and domain configurations changed obviously.A partially fading piezoresponse indicated the emergence of antiferroelectric Pbam.The in-situ domain analysis suggested that the phase transition was accompanied by domain wall motion.Switching spectroscopy PFM(SS-PFM)was further conducted to investigate the piezoresponse during the phase transition.Anomalous responses were found in both ON and OFF states at 170℃,and the film exhibits typical antiferroelectric behavior at 200℃,implying that the completion of phase transition and structure turned to the Pbam phase.This work revealed the origin of the high piezoresponse of Sm-doped BiFeO_(3)thin films at the morphotropic phase boundary(MPB).

Challenges and opportunities for spintronics based on spin orbit torque

Spintronic devices based on spin orbit torque(SoT)have become the most promising pathway to the nextgeneration of ultralow-power nonvolatile logic and memory applications.Typical SOT-based spintronic devices consist of two functional materials:a spin source and a magnetic material.Spin source materials possess a strong spin orbit coupling,enabling efficient interconversion between charge and spin current,Magnetic materials are used to process and archive the information via the interaction between the local magnetic moment and the spin current generated from spin source.Considerable efforts have been put into the design of materials and devices in the past decades to realize the electrical control of magnetic switching.However,a number of key challenges stll remain to be addressed for the practical application.In this paper,we reviewed the development of a range of novel materials for both the spin source and the magnetic functionalities,particularly the complex oxides and organic spintronic materials.We also discussed and highlighted several key issues,such as the mechanism and manipulation of SOT and the large-scale integration of sOT-based devices,which merit more attention in the future.

Defects-Driven Ferromagnetism in Undoped Dilute Magnetic Oxides:A Review

In the past several decades, dilute magnetic semiconductors, particularly the dilute magnetic oxides have evolved into an important branch of materials science due to their potential application in spintronic devices combining of properties of semiconductors and ferromagnets. In spite of a major effort devoted to the mechanism of ferromagnetism with a high Curie temperature in these materials, it still remains the most controversial research topic, especially given the unexpected do ferromagnetism in a series of undoped wide-band-gap oxides films or nanostructures. Recently, an abundance of research has shown the critical role of various defects in the origin and control of spontaneous magnetic ordering, but contradicting views from intertwined theoretical calculations and experiments require more in-depth systematic research. In our previous work, considerable efforts have been focused on two major oxides, i.e. ZnO and Zr02. This review will present a summary of current experimental status of this defect-driven ferromag- netism in dilute magnetic oxides （DMOs）.