Currently, the rare earth luminescent materials are very popular and have been widelyused in the fields of lighting, display and detection. In1998, Danielson et al synthesized anew blue white emitting phosphor, which can be effectively excited by ultraviolet,cathode ray and x-ray, together with high physical and chemistry stability. These indicate thatthe phosphor possesses potential application value.In our present work, a series of phosphors were successfully prepared byhydrothermal method. The precursors and the samples were analyzed and characterized byTG-DTA、FTIR、XRD、SEM and fluorescence spectrophotometer. The effect of different s, s, dosage of PEG-1000, the doping metal ions and rare earth ions onthe phase structure, morphology and luminescent properties of the samples have beenstudied systematically The following results are obtained.(1) The effects of different s including aqueous ammonia and ammoniumbicarbonate on the phase structure, morphology and luminescent properties of Sr2CeO4phosphors synthesized by hydrothermal method were investigated. The results show that theprecursors obtained by using ((NH4)2CO3and Na2CO3as precipitant respectively have samecrystal phases compositions, which consists of Ce2(CO3)2O·H2O, CeCO3OH and SrCO3,Sr2CeO4crystallites with orthorhombic phase can be obtained after the precursors werecalcined at1000℃for2h. Sr2CeO4particles obtained using (NH4)2CO3as the precipitantshow spherical-like shape and better dispersion, while those obtained using Na2CO3as theprecipitant show irregular shape and serious aggregation. The excitation spectrum ofas-synthesized Sr2CeO4crystallite is a wide band with double peaks in the range of200-400nm. The emission spectrum is a broad band too, which is located in the range of400-600nmwith the main peak at466nm, and it is ascribed to the f→t1gtransition of Ce4+ions, resultingin a blue-white emission. The luminescent intensity of the sample using (NH4)2CO3as theprecipitant is relatively strong under the main excitation wavelength.(2) The effects of s including PEG-1000, DSASS, CTAB and GL on the phasestructure, morphology and luminescent properties of Sr2CeO4phosphors synthesized by hydrothermal method were investigated. The results show that Sr2CeO4crystallites withorthorhombic phase can be synthesized after the precursors obtained under the four different s were calcined at1000℃. The particles obtained using DSASS as the surfactantshow large block structure. While using PEG-1000、CTAB、GL as the surfactants, theparticles show rod-like shape with different slenderness ratio. Different surfactants have greateffects on the intensity of emission peak and excitation peak of the samples, the order fromstrong to weak is PEG-1000> GL>CTAB>DSASS.(3) The effects of hydrothermal reaction time and the dosage of PEG-1000on theproperties of the samples were investigated. The results show that hydrothermal reaction timeand the amount of PEG-1000has little effect on the phase structure, orthorhombic phaseSr2CeO4crystallites can be obtained after the precursors were calcined at1000℃for2h.When the hydrothermal reaction time is6h, the dosage of surfactant PEG-1000is0.2g, theas-synthesized Sr2CeO4phosphors have better crystallization, uniform particles distribution,better dispersity and excellent luminescent performance.(4) In this paper, a series of Sr2CeO4:M doped with non rare earth and rare earth ions,have been synthesized in order to investigate the effect of the doping metal ions on theluminescent properties and find the high-efficient material. The results showthat doping with metal ions has little effect on shape and position of peaks in emissionspectrum of Sr2CeO4, which is located in the range of400-600nm with main peak at466nm.Among these metal ions, doping with Zn2+or Mg2+can effectively enhance thephoto of Sr2CeO4phosphor, the appropriate doping concentration of Mg2+andZn2+is4%and5%respectively. Moreover, a red-shift is found in the excitation spectrum ofSr2CeO4phosphor after doping with Zn2+or Mg2+. For rare earth ion Dy3+doped Sr2CeO4phosphors, it is found that the sample shows large hexagon-like granular shape and differencein size, the particle is assembled by countless net structure. The excitation spectrum is a wideband with double peaks, which is similar to that of Sr2CeO4, and the main peak located at305nm. The emission spectrum mainly consists of two parts, the blue emitting band in the rangeof400nm~550nm and the yellow-green emitting peaks in the range of550nm~600nm. The former is mainly due to the emission of Sr2CeO4, while the latter is ascribed to the transitionof4F9/2-6H13/2of Dy3+. The doped-Dy3+concentration has great effect on the fluorescenceintensity and emitting colour of Sr2CeO+4:Dy3. With the increase of Dy3+concentration, theratio of yellow emission to blue emission (RY/B) increases, and the luminescent colourchanges from blue-white to yellow. Meanwhile, the luminescent intensity decrease with theincrease of Dy3+doping concentration, which maybe due to the increase in the degree of latticdistortion caused by Dy3+doping and partly destruction of the one-dimensional chainstructure of Sr2CeO4.
Synthesis of Series of Sr2CeO4Luminescent Materials by Hydrothermal Method and Their Luminescent Properties
is a class of conjugated polymer which is composed of Si-Si main chain and organic side groups. Due to the lower electronegativity of Si atom and its unoccupied3d orbital, the σ electron of polysilane can delocalize along the main chain widely, thus providing electronically analogous properties to the π-conjugated polymers. The delocalization of polysilane can make the σ transition happen easily as a result of lower excitation energy and induce a fluorescent emission in UV region or visible light region, which make it has the potential application in light emitting diodes (LED) and non-linear optical materials.This article summarized lasted research advances of polysilane at home and abroad and combined it with the recent attracted researches on the modified optoelectronic materials. Then, two kinds of functionalized linear and branched (starlike) polysilanes were designed and prepared, and the effects of the introduction of on the optoelectronic properties of polysilane, especially the fluorescence quantum efficiency and stability, were also discussed.The mono-vinyl-POSS was synthesized by cohydrolytic and cocondensation reaction and the mono-methyl-β-ethyl-dichlorasilane-POSS was synthesized by hydrosilylation reaction. Then, a serious of linear polysilanes with POSS as side groups were prepared by Wurtz coupling reaction through varying the feed ratio of chloral-containing POSS monomer and MePhSiCl2.The octa-methyl-β-ethyl-dichlorasilane-POSS was synthesized by hydrosilylation reaction and two kinds of Si-OH end-capping linear polysilanes were prepared via Wurtz coupling reaction. Then, two kinds of branched (starlike) polysilanes were obtained by the condensation reaction of Si-Cl and Si-OH of two products by the removal of HCl.The structures of synthesized products were investigated using FT-IR and1H-NMR, and the molecular weight and molecular weight distribution of polysilanes were observed by GPC. The aggregation structures of polysilanes were studied using XRD and the results showed that the introduction of POSS reduce the crytallinity of polysilane molecules, therefore endowing them a better solubility. The properties of polysilanes were investigated by spectra. The results indicated that the incorporation of POSS into the polysilane will not change molecular orbital energy levels or change it slightly. Furthermore, for linear polysilanes, when the number of POSS side groups attached on main chain increased, the UV resistant stability of polysilanes was increased accordingly. However, for branched (starlike) polysilanes, it possessed a superior UV resistant stability–without any degradation with an increase of radiation time.The fluorescent emission properties were studied using fluorescent emission spectra, and combined with the UV absorption spectra, the relative fluorescence quantum efficiency of them were also calculated. The results showed that for linear polysilane, with a decrease of POSS content,ΦLa:ΦLb:ΦLc:Φ0=1.92:1.33:1.19:1.03:1; for branched (starlike) polysilanes, ΦB1:ΦL1=5:1.The thermal stabilities of polysilanes were tested by TGA. The results demonstrated that they possessed an excellent and had a degradation above320℃. For linear polysilanes, by tuning the number of POSS side groups, the starting decomposition temperature can pass370℃; for branched(starlike) polysilanes, they also have a high mass remains, always over60%, thus making them become a promising candidate in the SiC ceramic industry.In summary, this class of POSS-containing linear or branched(starlike) polysilanes can obviously improve the fluorescence quantum efficiency and stabilities of polysilanes, therefore providing an excellent optoelectronic properties.
The properties, applications and preparation of ultrafine powder materials are reviewed on the basis of studying lots of literature at home and abroad. Ultrafine SnO2 powder, which has the surface structure and physical function, has been widely used in the fields of function ceramics, information materials and photosensitive materials as a new type of function materials and are comprehensively discussed in this paper. The distinctive functions of ultrasonic wave on the preparation of ultrafine powder materials are introduced and the ultrasonic wave-sol-gel method is determined in this paper to prepare ultrafine SnO2 powder.Based on the experimental results, the mechanism of ultrasonic wave inthis work has been proved and the problems existing in this work and the corresponding improvements have been pointed out. Then the influence of ultrasonic wave, reaction time and temperature on the quality of products has also been studied. Experimental results manifest that ultrasonic wave has the advantage of restraining the formation of greater grains and keep higher surface activation of the ultrafme powder in the preparation of the SnO2 powder.Thetechnological process of preparation of ultrafine SnO2 powder is put forward according to ultrasonic wave combined with sol-gel method. In this process, SnCl4 solution is added and react with NH3 H2O under the use of ultrasonic wave, controlling the acidity pH, reaction time and temperature and the sol can be got. Then sol changes into gel. After washing, dehydration, drying and roasting the gel, ultrafine SnO2 powder can be obtained. Kinetics features and reunion problems in chemical method of producing single dispersing particles in liquid are discussed and some improvements are given. After extensive conditional experiments such as reactant concentration, acidity pH, temperature and time of reaction have been done, and the factors influencing the sol stability such as washing method, drying temperature and roasting temperature and time have been discussed, the best conditions in this work are given.Some properties of the product have been determined by TEM, XRD, IR and TG-DSC techniques. The conclusion is that ultrasonic waye-sol-gel method is a promising and recommendable technique for its simple procedure, lower cost and better properties of the products.
Effects of Developmental Lead Exposure on nitric oxide synthase Activity in different brain Regions of rat
Lead is a heavy metal element primarily for neurotoxicity, which has obvious and sure damage to nervous system. Children’s nervous system is under rapid and perfecting period, sensitive to lead poisoning . And it is known that subclinical lead poisoning might do harm to children’s intelligence as well as memories ability. Nitric oxide (NO) is regarded as typical retrograde messenger, important in learning and memory. Its biosynthesis is modulated by nitric oxide synthase (NOS). At present, the level of NO is reflected mainly by. Lead can inhibit and therefore reduce NO. By means of establishing a series of rat models exposed to different low level lead during developing period, we observed effects of developmental on nitric oxide synthase activity in different brain regions ( , , , )of rat, researched the relationship between and lead level , time of exposure, and provided experiment evidence on how lead harms learning and memory function. Methods:Twenty-nine Female SD rats were randomly assigned to distilled water containing 0, 0.025%, 0.05%, 0/075% lead acetate (PbAc-3H2O). Treatment was started two weeks prior to mating. Pups were weaned at 21 day of age andfed the same diet as the dams. At each developmental time point (7,14,21 and 28 days age), pups were euthanized by decapitation and , , , were dissected on an ice-chilled plate, stored at -70C until used for NOS activity studies. Blood samples of pups for lead analysis were obtained by heart puncture, and the samples of dams were obtained by thigh venous puncture. Analysis of Pb concentrations in blood was performed by graphite furnace atomic absorption spectrometry. Statistical analysis:All values were expressed as mean ?SD. All statistical comparisons among groups were conducted using one way analysis of variance (ANOVA). All statistical comparisons in different brain regions were also conducted using analysis of covariance. Results:(1) No differences in body weight of dams were measured between any two groups (P>0.05). The level of Pb-exposed dams were higher than those of control group (PO.05)(2) There were no differences in body weight of pups between any two groups at nay age (P>0.05). The level of Pb-exposed pups were higher, having significant difference with control, and the exposed groups have significant difference with one another (P<0.05). As lead increased in dam’s drinking water, the in pups increased correspondingly and changed regularly: at age of 14th day, it was lower than that of 7th day, and increased to a highest level at 21st day, then returned to lower level at 28th day.(3) NOS activity in hippocampus showed: NOS activity of 0.05% and 0.075% groups were higher than that of 0.025% group, but on the 7th day and 14th day of the birth, the three groups showed no difference, and no significant difference compared with control (P>0.05). While on the 21st and 28th day, NOS activity of each experiment group were obviously higher than that ofcontrol group (P<0.01). On the 21st day 0.075%group had higher NOS activity than 0.025% group. While on the 28th day, NOS activity of both 0.05% and 0.075% groups were higher than that of 0.025% group, having significant difference by testing.(4) On the 7th day and 14th day after birth, NOS activity in cerebellums from each group had no difference by comparison (P>0.05). While on the 21st day and 28th day, each group had obvious difference in NOS activity (P<0.01). On the 28th day, NOS activity of 0.075% and 0.05% groups were higher than that of 0.025% group, having significant difference by testing (P<0.05).(5) NOS activity in showed: on different time points, NOS activity of 0.075% group was obviously lower than that of control, 0.025% group and 0.05%group (P<0.05). While the last three groups had no significant difference compared with each other on the same time p
Kennedy Wolts the founder of theadvanced a new highly simple realism theory in his “international Political Theories” , and abandoned the hypothesis of classical realism humanity etc which is difficult to use as a scientific concept for incorporating anarchic order, self-aid system, power distribution, national interests arguments and existence needs etc into a core concept of international relations theory. Here, the departure point of study is anarchic state of international community. It is insisted that a country should be regarded as materialistic and rational behavioral object on the basis of scientific positivism. The study of international relations will at last be furnished with system structure. Therefore, Wolts’ s “new realism” is also called “ ” .The theory provides a complete explanation of Sino-US relations. Its angle of view of the Sino-US relations is not optimistic. But, at the same time when we consider a grim possibility for the Sino-US relations, we should not gloomily believe that such Sino-US relations are unavoidable. The decision and confidence pursuing full rejuvenation of Chinese nation or taking of irrational steps to blindly starting struggle against the USA pursuing final victory. These two courses of action are not the best way to enhance and maintain national interests. The result will be just the opposite. After all, we should know that international politics is not a 3D picture at all. We have a changeable, complex structure with variable stereo points resulting frominteraction of multitude of variables. As a normal mode, the structural realism of course has its own rationality and advantages but also limitations and shortcomings when applied to international politics (including Sino-US relations).First, the premise hypotheses of structural realism have their own rationality and one-sidedness. So, it can reflect part of the actual situation of international community and but cannot reflect entirely. The structural realism ignores or neglects the importance of joint interests of the international community. In an age of globalization and integration, structural realism can only see competition and conflict, but fails to see cooperation and “joint victory” . Thus, its view of Sino-US relations looks reasonable but it cannot account for several facts. The structural realism founded during the “cold war” certainly failed to pay sufficient attention to the rich content and the many factors influencing Sino-US relations after the cold war and as a result, it cannot correctly describe some facts of the cold war.Second, the structural realism provides a new view of international community and helps to understand the mutual relations of countries and their systems. But, it again makes a mistake with “structural determinism” and fails to grasp the whole changing picture international politics. As a result, it specially brings out the essence of hegemonism. As a result, it can only see the negative factors influencing on the relations between China and USA, and is unable to see the positive factors. Outwardly, the structural realism wants to establish a kind of purely scientific theory of international politics. But actually, it enbodies a clear vestige of cold war and only assists the American hegemonism and privileges.Third, according to behaviorism, the structural realism has indeedscored an achievement in respect of macro changes which have occurred during a period, but it lacks historical sense as well as microanalysis when analyzing international political relations. Therefore, structural realism appears to be analyzing the relations between China and USA properly and scientifically, but actually it is full of shortcomings.Finally, structural realism has made a contribution to forecasting of international systems. But it cannot properly and deeply explain and forecast their properties. In a word, it is both effective but at the same time limited when explaining the relations between the two powers
Since reform and opening up, with the intensifying ofsystem reform, state-owned reform, the release of rural surplus labor force, coupled with incoming labor force each year, make the problem of labor supply and demand in China become increasingly acute. By the end of 2007,there has been more than 1.3 billion people in China,0.78 billion of whom were labor force,and the number will continue to grow in the future. Employment is a subject of primary concern for each government. Growing working population and mass un cased by restructuring,make our country experience unprecedented challenge. In order to make economic operation increase efficiently and improve the state comprehensive competitiveness,our country is speeding up the realization of economic restructuring,especially the realization of economic growth pattern. Labor productivity now in China is low, so the potential market is enormous. According to China’s national conditions, how to properly handle the relationship between the and , and how to formulate industrial policies from a strategic point of view, become a topic that people generally care about. Economic development and improvement of have a positive or negative effect on employment. People have different views. Therefore,in-depth studying the relationship of labor productivity and employment,and putting forward a number of suggestions and countermeasures to achieve the coordinated development of labor productivity and employment,both are of great practical significance to unswervingly push forward reform and opening up and the cause of building a well-off society.In this paper,there are six parts to analyze labor productivity and employment status during the society transformation. The first part is the introductory part,in which introduces the background,the significance of the study of labor productivity and the employment,labor productivity and employment theories in foreign countries and in mainland,as well as research thoughts and methods in this article,and research innovation point. The second part analyzes the transition period of Chinese labor productivity trends,mainly involving the concept and formula of labor productivity,the changes of Chinese labor productivity and their reasons. The third part studies the employment structure,employment levels and the trends of their change trends,primarily by studying the changing of the employment structure and employment in our country. The fourth part deeply analyzes relationship of labor productivity and employment during the transformation period by the way of empirical analysis and one-dimensional linear Recursive Analysis. The fifth part sets forth proposals towards the coordinate development of labor productivity and employment,according to China’s national conditions. The sixth part is the concluding part.
The U.S. subprime mortgage crisis, which broke out in 2007, is a warning for the necessity and urgency of the riskof Residential Mortgage-backed Product Innovation, of which (Residential Mortgage Backed Securitization) is one important form. However, the underlying assets of China’s residential mortgage-backed securities, whose interest rate is based on the annual benchmark given by the People’s Bank of China, differ from the counterparts in U.S.A. The interest rate of the residential loans in China is similar to the floating rate, while the rate of U.S. residential mortgage loans is fixed. Therefore, China’s showed different characteristics. However, according to the papers which the author masters, there was little systematic theory research and empirical research on the risks of China’s . Based on the background, this paper using three mainly risks of China’s RMBS as the research object, trying to view from the macroscopic aspect, recognized the main factors influencing the prepayments risk, and real estate market reversal risk. The paper then made regression analysis to prepayments risk and , trying to provide banks of effectively risk of RMBS on theoretical and technical basis.This article summarizes the domestic and overseas scholars’ research results, which provided this variable selection and quantitative methods theoretical guidance of the empirical study. On the basis of normative analysis, the authors use the factor analysis, Logistic model, the multivariate linear regression analysis in SPSS 16.0 and Credit Portfolio View model to do empirical studies on the prepayments risk and of Jianyuan 2005-1.The paper obtained the following conclusions and innovative points:First, the paper focuses on three major risks of China’s RMBS, namely , default risk as well as the of real estate market. Interest rate, macro situation, the stock market and gold market, real estate market are factors contributing to the three major risks from a macro perspective. Second, according to results, the currency factor, macroeconomic factor and the market value factor of stock are taken into the model as variables, which showed great impacts on . Currency factor and the market value factor of stock have negative impacts on the prepayment risk, while the macroeconomic factor has a positive influence on the borrowers’ prepayment behavior.Third, interest rate factor, market expectation factor and the overall factor entered the default risk model as variables, which showed great impacts on default risk of RMBS in China. The greater the interest rate factor and the market expectation factor is, the greater the default risk is; meanwhile, the greater the overall factor is, the smaller the default risk is; and vice versa.
Urban Water is the critical infrastructure to theand development. The urban water industry has a significant welfare. project has significant internal benefits and externality, and the externality brings far greater than the internal gains. Therefore, properly handled the urban water industry will generate enormous and social benefits. Accompanied western countries in the wave of public administration reform by the late1970s and early1980s, urban water and the model of public utilities supplied by government must be broken, people began to realize that it is necessary to distinguish between public goods “supply” and “production”. And widespread introduction of competition mechanism in the urban water industry, cancellation of the government monopoly, allow more enterprises to participate in the supply of services, implementation of privatization and market-oriented, improving the quality and efficiency of public services. Therefore, how to use economic theory researching on urban water market reform and selecting the model of market-oriented from the perspective of economy, undoubtedly has important theoretical and practical significance.This article is divided into seven chapters, focuses on the following questions:1、 Through the study of China’s water market reform process and status, analyzing the lack of public interest、funds for construction of water supply and the absence of government through China’s water market reform process.2、Analysis the problems in China’s urban water reform model selection, and by comparison of the governance model of the water market in developed countries to find international experience.3、 On the basis of description of the product concept of the water supply、classification and properties characterized, using cost-benefit analysis of the theory of market-oriented water projects to study the reasonable water market reform model path selection.4、As Lanzhou water company market reform model for example, empirical test of the path of the proposed urban water market reform model.
Emission spectra of Tm3+-doped fiber laser which contains two atmospheric windows and a strong water absorption peak covers from1.5μm to2.2μm. Because the wavelength is safe to man’s eyes,it is being applied in many areas such as laser medicine,long-distance detective systems,laser radar,and military.Laser power is increasing from hundreds of watts to thousands of watts and now Tm3+-doped fiber laser is becoming the research focus of fiber lasers.Recently,much work about Tm3+-doped double clad fiber laser focuses on experiment research.It is urgent to make a deep research on mathematical model which is very important to carry out a further study about Tm3+-doped double clad fiber laser.This paper gets a series of useful conclusions by numerical simulation.On the other hand this paper includes the work related to coherent beam combination.is a method for achieving a high-power,high-brightness source.This paper makes a research about multi-core double-clad fiber laser and .The results of this paper can gave some suggestions in design of high power and brightness Tm3+-doped fiber laser.The main contents in this paper are as follows:1.The characteristic of the energy level structure of thulium and the absorption spectrum are investigated.Three kinds of pump scheme of the Tm-doped fiber laser are discussed in detail.Research on the common pump scheme 3H6→3H4 are carried out.We obtain the equation about the number of Thulium ions in ground state and excited states in fiber laser.2.About forward pump scheme 3H6→3H4 using 790nm laser resource,we design simulation program which draw some conclusions about the relationship between laser properties and pump power,fiber length,doped concentration of Thulium ions and loss.3.We derive the coherent beam intensity of the far-field about multi-core double-clad fiber laser by applying diffraction theory.Simulation program is designed and we obtain some conclusions about the relationship between the intensity of the tar-field and multi-core number,distance of adjacent core axes,diameter of core and wave length.4.Through the study of the coherent beam combination principle by applying all-fiber ,we discuss the spectral response fun.By designing simulation program,we analyze the effects of different branch-arms number, adjacent length difference,and reflectivity of public resonator,and get some useful conclusions.