980 resultados para 612


Relevância:

10.00% 10.00%

Publicador:

Resumo:

为探求便捷有效的小面积城市森林三维绿量的测算方法,根据林木生长的分形原理,采用逐步回归方法获取了沈阳城市森林三维绿量的13个模拟方程,并对其影响因素进行分析.结果表明:13个模拟方程的决定系数(R2)在0.612~0.842,残差分析没有呈现明显图样,模型精度均在87%(α=0.05)和83%(α=0.01)以上,其中最便捷的模拟方程是ln■=7.468+0.926 lnx1[■为模拟三维绿量,x1为每公顷胸高断面积(SDB)].模拟方程的标准回归系数与16个树木特征间的相关关系显示,影响沈阳城市森林三维绿量的最主要因素是每公顷胸高断面积(SDB).

Relevância:

10.00% 10.00%

Publicador:

Resumo:

根据1957-2005年中国各省区煤炭调出和调入数据,运用SPSS和GIS方法,首先对"一五"~"十五"各省区的煤炭流动地域类型进行了判别,然后在省域尺度研究了煤炭资源区域流动的时空过程,最后探讨了煤炭资源流动时空演变的驱动力。"一五"~"十五"中国省际间煤炭流动演变特征有:中国省际间煤炭资源流动规模逐年增大,省际间煤炭调出总量年均增长5.9%,煤炭调入总量年均增长5.6%。流动范围逐年扩展,无流地由1957年的10个省区缩小至近年的1个左右。流场呈集中输流、分散汇流的特征,调出省区个数<调入省区个数,调

Relevância:

10.00% 10.00%

Publicador:

Resumo:

Sphere NH4Y1.9Eu0.1F7 nanoparticles were successfully synthesized by a hydrothermal method at 180 degrees C for 10 h. SEM and TEM images show the particles are spheres and have lots of hollows in them. The mean particle size is about 60 nm. The shape and size of the particles can be controlled by changing temperature and time of reactants. The luminescent property of the sample indicates that strong emission peaks of the Eu3+ ions are located at about 589 and 612 mm.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

Starting from metal nitrate aqueous solutions and H3BO3, Y0.9-xGdxEu0.1Al3(BO3)(4) (0 <= x <= 0.9) phosphors were synthesized by spray pyrolysis followed by annealing at high temperature. The obtained phosphor particles have spherical morphology with size in the range 0.5-2 mu m. Independent of the x values in Y0.9-xGdxEu0.1Al3(BO3)(4) (0 <= x <= 0.9) phosphors, the Eu3+ ion shows its characteristic D-5(0), (1)-F-7(J) (J = 0, 1, 2, 3, 4) transitions with D-5(0)-F-7(2) red emission (612 nm) as the most prominent group. The photoluminescence intensity of phosphors increases with the increase of x value in Y0.9-xGdxEu0.1Al3(BO3)(4) (0 <= x <= 0.9) due to an energy migration process like Gd3+-(Gd3+)(n)-Eu3+ that occurred in the host materials.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

In this study, KMgF3:Eu2+ luminescent nanocrystals (NCs) were prepared in water/cetyltrimethylammonium bromide (CTAB)/2-octanol microemulsions. The KMgF3:Eu2+ NCs were characterized by transmission electron microscopy (TEM), X-ray diffractometer (XRD), fluorescence spectrum, infrared spectroscopy (IR) and elementary analysis. The results showed that the size of the KMgF3:Eu2+ NCs was hardly affected by water content and surfactant (CTAB) concentration. The emission spectrum showed that the position of the 362 nm peak is due to the K+ sites substituted Eu2+. Two emission peaks located at 589 and 612 nm can be attributed to Eu3+, which exist at two different types of Eu3+ centers: one is Eu3+ at a K+ site, the other is clustering of Eu3+ ions in the interstices of KMgF3 host lattice.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

We demonstrated high-efficiency red organic light-emitting diodes (OLEDs) employing a europium complex, Eu (III) tris( thenoyltrifluoroacetone) 3,4,7,8-tetramethyl-1,10-phenanthroline (Eu(TTA)(3)(Tmphen)), as an emitter and a blue electrophosphorescent complex, Iridium ( III) bis[4,6-di-fluorophenyl-pyridinato-N,C-2] picolinate (FIrpic), as an assistant dopant codoped into 4,4-N, N-dicarbazole-biphenyl (CBP) host as an emissive layer. A pure red electroluminescence (EL) only from Eu3+ ions at 612 nm with a full width at half maximum of 3 nm was observed and the EL efficiency was significantly enhanced. The maximum EL efficiency reached 7.9 cd A(-1) at 0.01 mA cm(-2) current density, which is enhanced by 2.8 times compared with electrophosphorescence-undoped devices. The large improvements are attributed to energy transfer assistance effects of FIrpic, indicating a promising method for obtaining efficient red OLEDs based on rare-earth complexes.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

Pure red organic light-emitting diodes based on a dinuclear europium complex with a structure of (TTA)(3)Eu(PYO)(2)Eu(TTA)3 (TTA = thenoyltrifluoroacetonate, PYO = pyridine N-oxide) were presented. The devices showed pure red emission at a peak wavelength of 612 nm with a full width at half maximum of 3 nm, which is a characteristic emission from Eu3+ ion based on D-5(0) -> F-7(2) transition. The maximum brightness and electroluminescent (EL) efficiency reached 340 cd/m(2) at a driving voltage of 19 V and 2.4 cd/A (0.78 lm/W) at a current density of 0.14 mA/cm(2), respectively.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

采用高温固相反应法制备了一种新的用于白光LED的红色荧光粉SrCaSiO4:Eu3+.XRD表明其属于正交晶系,空间群Pmnb;在SrCaSiO4:Eu3+的体系中掺入<12%(原子分数)的Eu3+不会引起相的转变.光谱测试表明,荧光粉的激发峰位于397nm,能与近紫外LED相匹配,其发射峰位于612、592和586nm;在SrCaSiO4:Eu3+的体系中Eu3+的猝灭浓度约为10%(原子分数),其临界传递距离(Re)约为1.2nm.测得样品的衰减曲线,并得到其荧光寿命约为3ms.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

在液相中合成了邻苯二甲酸(H2L)铕发光配合物.通过元素分析、滴定分析和红外光谱确定其化学组成为Eu2L3·6H2O.热分析结果表明,配合物在472℃以下稳定性较好.X射线衍射和扫描电镜分析结果表明,配合物为块状晶体物质,晶粒大小为10~20μm.荧光光谱分析结果表明,配合物在紫外光的激发下发出铕的特征荧光.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

By doping a fluorescent dye in the emissive layer, we realized high efficient red organic light-emitting diodes (OLEDs) based on a europium complex. The OLEDs realized by this method showed pure red emission at 612 nm with a full width at half maximum Of 3 nm. The Commission International de L'Eclairage Coordination keeps approximately the same as the emission of pure Eu3+. The maximum brightness and EL efficiency reached 2450 cd/m(2) at 20 V and 9.0 cd/A (6.0 lm/w) at a current density of 0.012 mA/cm(2), respectively. At the brightness of 100 cd/m(2), the current efficiency reached 4.4 cd/A.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

Nanocrystalline CaTiO3:Pr3+ phosphor layers were coated on nonaggregated, monodisperse, and spherical SiO2 particles by the sol-gel method, resulting in the formation of core-shell structured SiO2-CaTiO3:Pr3+ particles. X-ray diffraction, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, photoluminescence, cathodoluminescence spectra, as well as lifetimes were utilized to characterize the core-shell structured SiO2-CaTiO3:Pr3+ phosphor particles. The obtained core-shell structured phosphors consist of well dispersed submicron spherical particles with a narrow size distribution. The thickness of the CaTiO3:Pr3+ shell could be easily controlled by changing the number of deposition cycles (about 70 nm for four deposition cycles). The core-shell SiO2-CaTiO3:Pr3+ particles show a strong red emission corresponding to D-1(2)-H-3(4) (612 nm) of Pr3+ under the excitation of ultraviolet (326 nm) and low voltage electron beams (1-5 kV). These particles may be used in field emission displays.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

A new type of organically modified sol-gel/chitosan composite material was developed and used for the construction of glucose biosensor. This material provided good biocompatibility and the stabilizing microenvironment around the enzyme. Ferrocene was immobilized on the surface of glassy carbon electrode as a mediator. The characteristics of the biosensor were studied by cyclic voltammetry and chronoamperometry. The effects of enzyme-loading, buffer pH, applied potential and several interferences on the response of the enzyme electrode were investigated. The simple and low-cost glucose biosensor exhibited high sensitivity and good stability.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

An efficient organic light-emitting device using a trivalent europium (Eu) complex Eu(Tmphen)(TTA)(3) (TTA=thenoyltrifluoroacetone, Tmphen=3,4,7,8-tetramethyl-1,10-phenanthroline) as the dopant emitter was fabricated. The devices were a multilayer structure of indium tin oxide/N,N-diphenyl-N,N-bis(3-methylphenyl)-1,1-biphenyl-4,4-diamine (40 nm)/ Eu complex:4,4-N,N-dicarbazole-biphenyl (1%, 30 nm)/2,9-dimethyl,4,7-diphenyl-1,10phenanthroline (20 nm)/AlQ (30 nm)/LiF (1 nm)/Al (100 nm). A pure red light with a peak of 612 nm and a half bandwidth of 3 nm, which is the characteristic emission of trivalent europium ion, was observed. The devices show the maximum luminance up to 800 cd/m(2), an external quantum efficiency of 4.3%, current efficiency of 4.7 cd/A, and power efficiency of 1.6 lm/W. At the brightness of 100 cd/m(2), the quantum efficiency reaches 2.2% (2.3 cd/A).

Relevância:

10.00% 10.00%

Publicador:

Resumo:

Analysis of the isothermal and nonisothermal transitions of hexagonal crystal formation from the melt (transition 1) and of monoclinic crystal formation from hexagonal crystals (transition 2) for trans-1,4-polybutadiene (TPBD) was carefully carried out by differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). Isothermal transitions I and 2 are described by Avrami exponents (n) of approximate to1, whereas nonisothermal transitions I and 2 are described by n approximate to 4. These different eta values indicate that different crystallization mechanisms took place for different crystallization driving forces under isothermal and nonisothermal crystallization. The Ozawa equation was also used to analyze the nonisothermal crystallization data. For transition I at lower temperature, the Ozawa equation fits the data well; however, at higher temperature, there is an inflection that shifts to lower crystallinity with increasing temperature. Inflections are also observed with the Ozawa analysis for transition 2. Furthermore, the crystallinities at the turning points are almost in the same range as those determined by Avrami analysis for nonisothermal transitions I and 2, which suggests that the Ozawa analysis inflections are due to secondary crystallization. However, TEM revealed no morphology discrepancy between the TPBD hexagonal crystals formed from melt by isothermal and nonisothermal crystallization.