A numerical study of two-and three-dimensional detonation dynamics of pulse detonation engine by the CE/SE method

In this paper, the CE/SE method is developed to simulate the two- and three-dimensional flow-field of Pulse Detonation Engine (PDE). The conservation equations with stiff source terms for chemical reaction are solved in two steps. The detailed analysis of computational results of a PDE with a single detonation tube and a PDE with five detonation tubes are given in this paper. Complex wave systems are observed inside and outside a PDE. For a PDE with 5 detonation tubes, there is a big bow shock produced from a number of little shocks near the open ends of tubes. A lot of vortexes interact with shocks and a large expansion wave propagates forward and backward with respect to the PDE in a semi-oval shape.

NaYSiO_(4)∶Ce^(3+)蓝色荧光粉的发光性质及其在白光发光二极管上的应用

采用高温固相法合成了NaYSiO_(4)∶xCe^(3+)(0.01≤x≤0.05)系列蓝色荧光粉。NaYSiO_(4)∶xCe^(3+)荧光粉在250~360 nm之间的宽带吸收能与紫外LED芯片很好地匹配。NaYSiO_(4)∶xCe^(3+)荧光粉中存在多个Ce^(3+)离子荧光中心,且在紫外光激发下表现出峰值波长位于414 nm附近的宽带蓝光发射。NaYSiO_(4)∶0.02Ce^(3+)荧光粉在300~350 nm紫外光激发下量子效率在25%以上。NaYSiO_(4)∶0.02Ce^(3+)荧光粉表现出优良的化学稳定性,在水中浸泡14 d后荧光强度和量子效率几乎不变。将NaYSiO_(4)∶0.02Ce^(3+)蓝色荧光粉、商用(Sr,Ba)_2SiO_(4)∶Eu^(2+)绿色荧光粉和商用(Ca,Sr)AlSiN_(3)∶Eu^(2+)红色荧光粉涂覆于310 nm紫外LED芯片上制备得到了显色指数高达95的LED器件。当驱动电流从50 mA逐渐增大到300 mA时,制备的LED器件表现出稳定的暖白光发射,其色坐标几乎不变。上述结果说明,本研究报道的NaYSiO_(4)∶0.02Ce^(3+)蓝色荧光粉在紫外LED芯片驱动的白光发光二极管照明上有着潜在应用价值。

Application of Two-dimensional Viscous CE/SE Method in Calculation of Two-phase Detonation

The method of two-dimensional viscous space-time conservation element and solution element (CE/SE) can be used to calculate the gas-liquid two-phase interior flow field in pulse detonation engine (PDE). In this paper, the evolution of the detonation wave and the distribution of its physical parameters were analyzed. The numerical results show that the change of axial velocity of gas is the same as that of detonation pressure. The larger the liquid droplet radius is, the longer the time to get stable detonation wave is. The calculated results coincide with the experimented results better.

Abnormal variation of magnetic properties with Ce content in(PrNdCe)_2Fe_(14)B sintered magnets prepared by dual alloy method

Resource-saving（PrNdCe）_2Fe_（14）B sintered magnets with nominal composition（PrNd）_（15-x）Ce_xFe_（77）B_8（x=0–10）were prepared using a dual alloy method by mixing（PrNd）_5Ce_（10）Fe_（77）B_8 with（PrNd）_（15）Fe_（77）B_8 powders. For Ce atomic percent of 1% and 2%, coercivity decreases dramatically. With further increase of Ce atomic percent, the coercivity increases, peaks at 6.38 kOe in（PrNd）_（11）Ce_4Fe_（77）B_8, and then declines gradually. The abnormal dependence of coercivity is likely related to the inhomogeneity of rare earth chemical composition in the intergranular phase, where Pr Nd concentration is strongly dependent on the additive amount of（PrNd）_5Ce_（10）Fe_（77）B_8 powders. In addition, for Ce atomic percent of 8%,7%, and 6% the coercivity is higher than that of magnets prepared by the conventional method, which shows the advantage of the dual alloy method in preparing high abundant rare earth magnets.

Sulfur-resistant methanation over MoO_3/CeO_2–ZrO_2 catalyst: Influence of Ce-addition methods

In this paper, Ce_(0.2)Zr_(0.8)O_2 composite supports were prepared by different Ce-addition methods including impregnation of cerium(CeZr-imp), impregnation of citric acid and cerium(CeZr-CA) simultaneously and deposition precipitation method(CeZr-DP), respectively. The as-prepared supports were applied to prepare 10 wt% MoO_3/Ce_(0.2)Zr_(0.8)O_2 catalysts for sulfur-resistant methanation. The N_2 adsorption/desorption,X-ray diffraction(XRD), Raman spectroscopy(RS), X-ray photoelectron(XPS), temperature-programmed reduction by hydrogen(H_2-TPR) were undertaken to get textural properties, morphological information and structures of the catalysts. The results showed that Mo O_3 was highly dispersed on the surface of these three supports and Ce was mostly of coexisted in Ce^(4+)/Ce^(3+) redox pairs. Compared with Mo/CeZrimp, the CO conversion increased by 10% and 15% for Mo/CeZr-CA and Mo/CeZr-DP, respectively. This was mainly attributed to the larger specific surface area, Ce^(3+) concentration and content of active MoS_2 on the surface of catalysts.

Synthesis and luminescent properties of Ce^(3+) doped LuAG nano-sized powders by mixed solvo-thermal method

Polycrystalline LuAG:Ce3+(cerium3+-doped lutetium aluminum garnet) powders were prepared by mixed solvo-thermal method.Fourier-transform IR spectroscopy(FTIR) and X-ray diffraction(XRD) measurements showed that the precursors were ethanol derivatives AlO(OH) crystal with hydroxyl and carbonate group.XRD results showed that phase of Lu2O3 disappeared with the precursors were annealed at 400 °C,cubic phase LuAG:Ce3+ appeared but only one diffraction peaks of LuAP(LuAlO3) at calcination temperature to 700 °C,a...

Synthesis of LaPO_4:Ce,Terbium by Co-Precipitation Method

The synthesis of precursor of green phosphors, LaPO4: Ce, Tb, by means of co-precipitation with cocurrent flow feed was studied. The effects of the reaction temperature, the kind and concentration of the acid in the bottom water, and the charging rate on the physical properties, such as particle size, were investigated. It is found that the particle size of the powder is controllable by adjusting acidity in bottom water and charging rate. The powder with diameter size of 3 to 5μm was obtained. Its XRD and SEM were analyzed. XRD patterns of the as-prepared green phosphor powders display the typical peaks of CePO4. SEM shows that the morphology of powders is ball-shaped.

Simulation of shock-induced instability using an essentially conservative adaptive CE/SE method

An essentially conservative adaptive space time conservation element and solution element （CE/SE） method is pro- posed for the effective simulation of shock-induced instability with low computational cost. Its implementation is based on redefined conservation elements （CEs） and solution elements （SEs）, optimized interpolations and a Courant number insensitive CE/SE scheme. This approach is used in two applications, the Woodward double Mach reflection and a two- component Richtmyer-Meshkov instability experiment. This scheme reveals the essential features of the investigated cases, captures small unstable structures, and yields a solution that is consistent with the results from experiments or other high order methods.

Surface and Texture Properties of Tb-Doped Ceria-Zirconia Solid Solution Prepared by Sol-Gel Method

The three-way catalysts （TWCs） promoters Ce0.6Zr0.4- x TbxO2-y were prepared by sol-gel method. BET surface areas analysis indicated that an increase of the dopant Tb content from x = 0.05 to x = 0.15 favors an increase of surface area from 66.8 to 80.4 m^2· g^-1 compared with the undoped sample Ce0 .6oZr0.40O2 65.1 m^2·g^- 1 after calcination at 650℃. Transmission electron microscopy （TEM） observation indicated that the doped samples have a higher thermal stability. The XRD and Raman spectra confirmed that the Ce0.6Zr0.4-xTbxO2-y cubic solid solution is formed. XPS analysis revealed that Ce and Tb mainly existed in the form of Ce^4＋ and Tb^3 ＋ , and Zr existed in the form of Zr^4＋ on the surface of the samples. The doped samples were homogenous in composition ; the introduction of Tb into the CeO2-ZrO2 promoters resuited in the formation of a solid solution, and the concentration of surface lattice oxygen was increased.

Synthesis of visible light responsive ultrafine K_4Ce_2Nb_(10)O_(30) by a stearic acid method

K4Ce2Nb10O30 ultrafine powders were prepared by stearic acid method (SAM). The obtained products were analyzed by X-ray diffraction, transmission electron microscopy, energy dispersive X-ray spectrometry, scanning electron microscopy and UV-visible absorption spectra. XRD patterns revealed that K4Ce2Nb10O30 powders treated at 900 oC for 2 h presented tetragonal structure without the presence of deleterious phases. Furthermore, the K4Ce2Nb10O30 prepared by SAM had considerable activity under visible light irradiation.

Backbone formulation algorithm in wireless sensor network based on cross-entropy method

In wireless sensor network,virtual backbone is a cost effective broadcasting method.Connected dominating set formation is proposed to construct a virtual backbone.However,it is NP-Hard to find a minimum connected dominating set in an arbitrary graph.In this paper,based on cross-entropy method,we present a novel backbone formulation algorithm(BFA-CE)in wireless sensor network.In BFA-CE,a maximal independent set is got at first and nodes in the independent set are required to get their action sets.Based on those action sets,a backbone is generated with the cross-entropy method.Simulation results show that our algorithm can effectively reduce the size of backbone network within a reasonable message overhead,and it has lower average node degree.This approach can be potentially used in designing efficient broadcasting strategy or working as a backup routing of wireless sensor network.

Effect of pretreatment methods on the performance of Cu-Zr-Ce-O catalyst for CO selective oxidation

The Cu-Zr-Ce-O catalysts prepared using the coprecipitation method exhibited better catalytic performance for CO selective oxidation. The Cu-Zr-Ce-O catalysts pretreated with different methods were studied by CO-TPR and XPS techniques. The results showed that the Cu-Zr-Ce-O catalyst pretreated with oxygen exhibited the best catalytic performance and had the widest operating temperature window, with CO conversion above 99% from 160 to 200 ℃. The O2 pretreatment caused an enrichment of the oxygen storaged on the Cu active species and promoted the conversion of adsorbed oxygen into surface lattice oxygen. It also improved the amount of Cu＋/Cu^2＋ ionic pair, and then facilitated the formation of CuO active species on the catalyst for selective CO oxidation.

Application of Space-time Conservation Element and Solution Element Method in Intake and Exhaust Flows of High Power Density Diesel Engine

A one-dimensional pipe flow model of single-cylinder diesel engine is established to investigate the intake and exhaust flow characteristics of diesel engine in the condition of high power density(HPD).A space-lime conservation element and solution element(CE/SE)method is used to derive the discrete equations of the partial differential equation for the intake and exhaust systems.The performance parameters of diesel engine with speed of 2100 r/min are simulated.The simulated results are in accordance with the experimental data.The effect of increased power density on charging coefficient is analyzed using a validated model.The results show that the charging coefficient is slowly improved with the increase in intake pressure,and is obviously reduced with the increase in engine speed.

Structural and Optical Properties of Cu2+ + Ce3+ Co-Doped ZnO by Solution Combustion Method

In this work, ZnO, Ce3+ doped ZnO (ZnO/Ce3+) and Cu2+ + Ce3+ co-doped ZnO (ZnO/Cu2+ + Ce3+ ) solid solutions powders were synthesized by a solution combustion method maintaining the Ce3+ ion concentration constant in 3%Wt while the Cu2+ ion concentration was varied in 1, 2, 3, 10 and 20%Wt. After its synthesis, all the samples were annealed at 900?C by 24 h. The ZnO, ZnO/Ce3+ and ZnO/Cu2+ + Ce3+ powders were structurally characterized using X-ray diffraction (XRD) technique, and the XRD patterns showed that for pure ZnO, Cu2+ undoped ZnO/Ce3+ and ZnO/Ce3+ doped with the Cu2+ ion, the three samples exhibited the hexagonal wurtzite ZnO crystalline structure. However, the morphology and particle size of both samples were observed by means of a scanning electron microscopy (SEM);from SEM image, it is observed that the crystallites of both samples are agglomerated forming bigger amorphous particles with an approximate average size of 1 μm. In addition, the photoluminescence of the ZnO, Ce3+ doped ZnO and Cu2+ + Ce3+ doped ZnO samples was measurement under an illumination of 209 nm wavelength (UV region): for the ZnO/Ce3+ sample, your emission spectrum is in the visible region from blue color until red color;the UV band of the ZnO is suppressed. The multicolor emission visible is attributed to the Ce3+ ion photoluminescence, while for the ZnO/Cu2+ + Ce3+, its emission PL spectrum is quenching by the Cu2+ ion, present in the ZnO crystalline.

Structural and Electrochemical Properties of Ceria-Doped SnO_2 Prepared by Sol-Gel Method

Tin dioxide (SnO2) and Ce-doped SnO2 were successfully synthesized by sol-gel method and electrochemical properties were studied in cell with Li as counter electrode. The samples were characterized by X-ray diffraction (XRD) and Transmission electron microscopy (TEM). XRD patterns presented that a second phase (CeO) was observed when the Ce content reached 5%. TEM micrograph indicated that Ce-doped SnO2 had a small particle with mean size of 30 nm. The electrochemical properties were also characterized at room temperature, and the results demonstrated that the Ce-doped SnO2 samples exhibited promising electrochemical properties and Ce doped in as-prepared samples plays an important role.

湿法制备Cu基Mn-Ce改性甲醇重整制氢催化剂及其催化性能研究

为了提升Cu基催化剂的高温稳定性和使用寿命,并研究过渡金属Mn及轻稀土金属Ce对Cu基甲醇重整催化剂的影响,本文采用新型湿法制备了Cu基Mn-Ce改性催化剂,并在气-固相固定床催化反应装置上评价了其甲醇重整制氢的性能。甲醇转化实验结果显示,Cu基Mn-Ce改性催化剂的甲醇转化率达到98.77%,产出的(H2+CO)含量达到92.5%。高温碳化性能对比实验结果表明,相比未改性的催化剂,Mn-Ce改性催化剂的高温稳定性更强,使用寿命更长。高温碳化后,205℃下的甲醇转化率均在40%以上,未改性催化剂的转化率仅为20%左右。催化剂性能评价实验结果表明,催化反应温度与其制氢性能呈正相关,高温下催化剂有更优异的制氢表现。Mn、Ce的加入可以有效提高Cu基催化剂甲醇重整制氢的性能。

CeO_2纳米水溶胶的制备

采用胶溶法合成了纳米CeO2 水溶胶 ,探讨了合成CeO2 水溶胶的最佳实验条件 ,研究了pH值、反应物浓度、水浴温度对胶溶过程的影响。TEM分析表明 :所制备的水溶胶中的CeO2 纳米粒子呈球形 ,约 3nm ,粒径分布均匀 ,无明显团聚现象 ;ED分析表明 ,CeO2 纳米粒子为多晶结构 ,并有少量单晶结构。

运动学统计定轨法应用于CE-1落月轨迹确定

运动学统计定轨方法不同于常规动力学统计定轨方法和几何法,既不需要建立飞行器的动力学模型,又可以利用整个弧段的测量信息进行统计计算,所以采用运动学统计定轨的方法描述飞行轨迹特别适用于嫦娥二期的动力落月过程。对嫦娥一号(CE-1)落月过程,采用运动学统计定轨方法,联合USB和VLBI数据进行轨道计算并确定CE-1的落月轨迹以及撞月点的位置,将所得结果与动力学统计定轨结果进行比较。计算表明,运动学统计定轨方法精度可以满足工程要求,可以为探月工程二期软着陆阶段的导航提供一种较为可行的定轨方法。

Ce掺杂TiO2纳米粉体的制备及其光催化性能研究

以钛酸丁酯为前驱体,冰醋酸为螯合剂,以硝酸铈为掺杂剂,采用溶胶-凝胶法制备了铈掺杂TiO2纳米粉体。研究了铈掺杂对TiO2相组成和晶粒尺寸的影响及不同掺杂量对TiO2光催化活性的影响,确定了Ce的最佳掺杂量。结果表明:Ce掺杂缩小了TiO2的锐钛矿相→金红石相(A→R)的相变温区范围,抑制了TiO2的晶粒增长。热处理温度升高,二氧化钛的比表面积下降。掺杂适量的铈提高了TiO2的光催化活性,Ce掺杂为0.05%摩尔分数时Ce-TiO2的光催化活性达到最佳,甲基橙降解率可达90%左右。

Ce^(3+)掺杂YAG透明陶瓷的制备与光性能研究

采用高纯微米级商业原料(≥99.99%)α-Al2O3、Y2O3和CeO2,用固相反应法制备了0.3at%Ce3+∶YAG透明陶瓷.粉体经行星式球磨,陶瓷素坯在1750℃真空烧结10h,真空度10-3Pa,双面抛光后,厚度为1.2mm的透明陶瓷试样在可见光区500~900nm的直线透过率可达80%左右,光学均匀性良好.荧光光谱分析表明,发射峰位于500~700nm之间,这是Ce3+的特征发射.结果表明,Ce∶YAG透明陶瓷的发光性能与相应的单晶相当,有望作为闪烁材料应用于中低能量射线(α、β粒子等)的探测.