Obtainment of hierarchical ZSM-5 zeolites by alkaline treatment for the polyethylene catalytic cracking

Great efforts have been applied in order to achieve the synthesis of hierarchical zeolites through post-synthesis alkaline treatment. In this case, the use of hierarchical ZSM-5 zeolites as acid catalysts in the catalytic cracking of polyolefins overcomes some diffusional limitations and expands the selectivity of products. Thus, the purpose of work was to promote a secondary porosity in ZSM-5 zeolite by NaOH treatment (using conventional electric and microwave heating methods), applying cetyltrimethylammonium bromide as pore-directing agent. Both heating methods generated additional secondary porosity, with microwave heating promoting a narrow pore size distribution, when compared to conventional. All hierarchical ZSM-5 have been showed low-density polyethylene conversions superior to the purely microporous ZSM-5, however the hierarchical zeolite processed by conventional electric heating reached the higher temperature reduction (42.6 K). It was evidenced through measurements of morphological and textural properties, ion exchange capacity and catalytic activity in the LDPE cracking that the CTAB cations exerts a protective effect at alkaline treatment avoiding the desilication process. The additional secondary porosity promoting the generation of compounds of lower molecular mass in LDPE catalytic cracking, by thermogravimetric analysis, proving that the alkaline treatment increases the accessibility to the active acidic sites of zeolitic catalysts for bulky molecules.     

Rapid synthesis of hierarchical ZSM-5 zeolites for the reactions involving larger reactant molecules

In this study, the ZSM-5 zeolites with a high hierarchy factor were synthesized rapidly and tested for the furfural hydroxymethylation (FH) to 5-hydroxymethylfurfural (HMF). The effect of seeding techniques (STs) and templates (both soft (Cetrimonium bromide, CTAB) and hard (bio-sourced secondary template, BSST)) on the final zeolite properties were studied. A significant variation in crystallinity and morphology with the ST and type of seed was observed. The CTAB addition increased the hierarchy factor (H factor) by 3 times, and the implicit seeds decreased the hydrothermal time by 2 times. The zeolite yield, crystallinity, and pore geometry were a strong function of [CTA⁺]/[Na⁺] ratio. Slit and ink bottle-shaped pore morphologies were observed with only seed or seed + BSST and with seed + CTAB, respectively, and both exhibited the bimodal pore size distribution. The zeolites with ink bottle-shaped pores outperformed those with slit pores in the FH and showed the highest selectivity to HMF of 65%, at 34% furfural conversion. The zeolites with high H factor showed catalytic and structural stability up to 5 successive recycle runs.     

Upper critical field of Bi1·5-Pb0·5-Ca2-Sr2-Cu3-O x superconductor

The highT _c superconductor of nominal composition Bi_1·5-Pb_0·5-Ca₂-Sr₂-Cu₃-O _x was prepared by solid-state reaction method. The upper critical fieldH _c2 of the material with a zero-resistance transition at 110K was investigated by observing variations in resistance with temperature down to 90 K and with a magnetic field up to7T. The slope ofH _c2 with temperature was about −0·41T/K for zero resistance transition and −6·86T/K for onset of superconductivity.H _c2 values at 0K were estimated to be 31·3T and 563T for zero-resistance transition and onset of superconductivity respectively.     

Theoretical studies on the defect structure for Mn in KTaO3

The defect structure for Mn²⁺ in KTaO₃ is theoretically studied by using perturbation formulas of the spin Hamiltonian (SH) parameters for 3d⁵ ions in tetragonal symmetry based on the strong-field scheme. By analyzing the electron paramagnetic resonance (EPR) data of the studied system, we suggest that the impurity Mn²⁺ ion occupy the dodecahedral K⁺ site, rather than the octahedral Ta⁵⁺ site. Based on the studies, it is found that the Mn²⁺ impurity undergoes an off-center displacement away from the ideal K⁺ site by about 0.60 Å along the C₄ axis. The above displacement is qualitatively consistent with the recent result based on the generalized gradient approximation (GGA) and that obtained from EPR and dielectric spectroscopy studies.     

Voltage contrast studies on 0·5 μm integrated circuits by scanning force microscopy

A scanning force microscope (SFM) test system is used for voltage contrast studies on 0·5 μm integrated circuits. Waveform measurements are performed on passivated 0·5 μm conducting lines up to 4 GHz. Additionally two-dimensional measurements at 10 MHz demonstrate the potential for device internal function and failure analysis in the sub-μm regime by direct correlation between voltage contrast and quantitative topography images.     

基于虚拟力场的海洋涡旋空间显著形状提取算法及应用

基于海洋涡旋表面形态特征和"虚拟力场的形状提取方法",提出了一种海洋遥感图像涡旋空间显著形状提取自动检测方法.首先采用常规检测算子对海洋遥感影像进行涡旋边缘的提取,并对其进行矢量化,继之在涡旋边缘进行参数化的基础上分析计算作用于边缘曲线之间的吸引力和融化力,最后采用一定的优化策略经过逐次迭代自动提取海洋涡旋的显著形状,并以多景不同来源的遥感影像为例,进行了各种海洋涡旋空间形状定量提取的实例研究,验证了该方法对于形态非常复杂的涡旋识别与提取的有效性.     

Analysis of magnetic field and levitation force characteristics for 3-DOF deflection type PM motors

The mechanism and characteristics of the electromagnetic radial force are important for motors with complicated structures. The three-dimensional analytical model of the air gap between the rotor and stator is established under rotor eccentricity conditions. Then, aiming at solving the unbalanced radial force problem with rotor static eccentricity, the air-gap flux density, radial electromagnetic force, and the comparisons of harmonic contents are calculated and presented based on FEA (Finite Element Analysis) and MATLAB simulation. Finally, the magnetic field model has been validated by experiments utilizing a prototype system. The results provide a theoretical guide for configuration design, optimization, and levitation control research on three degree of freedom deflection type motors.     

Experimental study on a Nb3Al insert coil under high magnetic field

Nb₃Al is one of the most promising superconductors to replace Nb₃Sn in large scale, high field superconducting magnet. Since the complicated conductor manufacturing process, long and stable Nb₃Al conductor is difficult to acquire in a commercial scale. Based on a 70 m length of Nb–Al precursor conductor, we designed and fabricated a Nb₃Al coil. The coil winding, low temperature diffusion heat treatment and epoxy impregnation are described in detail. The finished Nb₃Al coil is tested as an insert in a background magnet. The test is performed at the background field from 7 T to 15 T. The test results are analyzed and presented in this paper.     

轴向磁场对铌酸锂半波电压的影响

提出了平行与铌酸锂波导方向的轴向磁场对其半波电压产生影响的机理:加在电极上的电场对其中传播的偏振光产生线双折射,而磁场产生圆双折射,两者作用的结果是使得半波电压随磁场而变化。由此导出了半波电压随外界磁场变化的数学模型。仿真和实验结果表明,对于平均波长为1.30μm,20T的磁场,铌酸锂的半波电压可以减小了2.13%。     

温度和电场对纳米晶钛酸钡陶瓷铁电性的影响

100nm是介于微米晶和纳米晶之间的重要临界尺寸,研究了平均晶粒尺寸为100nm的钛酸钡(BTO)陶瓷的微结构和铁电性能,分析了测试温度和外加电场对纳米晶钛酸钡陶瓷铁电性的影响。与超细纳米晶BTO陶瓷不同的是,100nm BTO陶瓷主要以四方相形式存在的;介电温谱显示,正交到四方相的相变具有典型的弥散特征,低温时介电损耗<0.02。此外,铁电性能测试表明,100nm BTO陶瓷具有良好的铁电滞后特征,随着电场的增加,能量损耗密度、剩余极化强度和矫顽场均增加;随着温度的升高,陶瓷的铁电性在逐渐减弱,高于居里温度时由铁电相转为顺电相,铁电性消失。实验结果表明,100nm BTO陶瓷的铁电性与测试温度和外加电场有着密切的关系。     

Study on using cellulose derivatives as pore directing agent for preparation of hierarchical ZSM-5 zeolite catalyst

Cellulose derivatives such as hydroxyethylmethylcellulose (HEMC), and hydroxypropylmethylcellulose (HPMC), which are originated from biomass, were used as mesoporous directing agent for the synthesis of hierarchical ZSM-5 zeolite. Hierarchical ZSM-5 zeolites with outstanding mesoporosity and high hierarchy factors were achieved by hydrothermal method in the presence of bio-mesoporogen. The as-synthesized hierarchical ZSM-5 zeolites were characterized by X-ray diffraction (XRD), nitrogen adsorption–desorption (BET), scanning electron microscope (SEM) to determine the structure of samples. The influences of different mesoporogens with different dosage in the synthetic process on the physicochemical and catalytic properties of hierarchical ZSM-5 zeolite were investigated. Possession of the high mesopores, high surface areas and abundant accessible acid sites, the hierarchical zeolites exhibited excellent catalytic performance in the alkylation reaction of benzene and benzyl alcohol.     

膜法／深冷法联合空分的理论研究

利用硅橡胶膜分离器将空气的氧气，氩气，氪气和氙气等浓度提高，使氮气，氦气和氖气的浓度降低，再借助于深冷法提高空分过程中的氧气，氩气，氪气和氙气等的产量和浓度。此外，还获得了不抽氩馏份工作的空分设备上的塔塔板上的蒸汽和液体的计算浓度及温度分布等，并和法斯托夫斯基的数据进行了对比。     

近场条件下视觉距离感知对响度的影响

文章研究了近场条件下,当声源距离改变时,视觉距离感知对响度的影响。在消声室中,使用球形声源在试听者的正前方发声。8位试听者分别在睁眼和闭眼的条件下,对3种中心频率(500 Hz、1 kHz和2 kHz)、8个距离(0.3～1.0 m,1.0 m为参考距离)的声信号进行了响度匹配。结果显示,随着声源距离的减小,睁眼时响度增加得要比闭眼时少一些。而闭眼时的响度匹配结果与封闭耳道口声压级的变化情况相一致。这说明闭眼时试听者根据耳道口的声压级来判断响度,而睁眼时视觉距离信息会对响度产生影响。结果还显示,对于频率越低的声信号,视觉距离感知造成的影响越大。     

Electrochemical synthesis of Sn doped ZnO nanowires on zinc foil and their field emission studies

Sn doped ZnO films were obtained by cathodic electrodeposition on Zn foil. The X-ray diffraction analysis revealed formation of the wurtzite phase of ZnO only. The scanning electron microscopic images showed formation of randomly oriented ZnO nanowires having diameter less than 150 nm and lengths of several micrometers. The relative atomic percentage of Sn, estimated from the energy-dispersive spectra, was found to be 0.5 and 2.0 in the post-annealed ZnO films deposited for 10 and 40 min durations, respectively. The field emission characteristics of the Sn doped ZnO nanowires are found to be appreciable in terms of the threshold field and emission current stability.     

网格对超声清洗槽内声场的影响

用网篮盛放待清洗工件是最常用的一种清洗方法,影响清洗效果的一个关键因素是清洗槽内的声场分布,而网篮的存在会影响超声清洗槽内声场的分布。从实用的角度研究了清洗网篮对超声清洗槽内声场的影响。在用驻波场理论对清洗槽内声场分布情况进行分析之后．实验上用水听器法和染色法分别测量了放人网格前后超声清洗槽内声场的分布特点。结果表明,当丝径远小于1／4波长时,网格的存在对声场分布的影响很小,只是引起声波传播能量不同程度的衰减。这项研究对使用清洗网篮的超声清洗具有一定的参考价值。     

10T平行强磁场下Ni-纳米Al2O3复合共沉积的研究

将Ni-纳米Al2O3复合电镀过程移置于10T平行强磁场（B∥J）中，探讨了有无平行强磁场条件下电流密度对镀层形貌及镀层中纳米颗粒含量的影响规律。结果表明，在10T平行强磁场下，氧化铝颗粒在复合镀层中呈网格状分布，并且网格的尺寸随着电流密度的增加而增加；电流密度显著影响镀层中纳米氧化铝的含量，不论是否施加磁场，当电流密度为2A·dm^-2时镀层中颗粒含量最高。施加强磁场时，可使镀层在低电流密度下获得较高的纳米颗粒含量。     

Effect of twist on the longitudinal field loss for an in situ superconductor

The effect of twist on the full penetration loss of an in situ superconductor is calculated for the case of a longitudinal applied magnetic field. An increase in hysteresis with increasing twist is predicted due to a large anisotropy in the critical current density. The anisotropy results from the fact that the critical current density along the length of a filament in the in situ material is determined by the filament, while along the thickness it is determined by the proximity effect in the matrix surrounding the filament. From the measurements of Braginski and Wagner the ratio of these critical current densities is calculated to be about 70, which is in order of magnitude agreement with the value previously found from transverse field measurement.     

The effect of external cusp magnetic field on Ar ICP characteristics

In this paper, three permanent magnet rings, which were placed alternatively between the three antenna coils of a cylindrical inductively coupled radio frequency (rf) argon plasma for rf enhanced ionized magnetron sputtering system, were used to produce a closed magnetic field distribution with the magnetic field of the unbalanced magnetron sputtering to confine discharge plasma. Langmuir probe measurement was used to study the effect of the magnetic field on the plasma characteristics and their spatial distribution. The results show that the presence of the closed magnetic field leads to the increase of the ion density and the decrease of electron temperature and plasma potential. With the closed magnetic field, the plasma density distribution in radial direction will become more uniform.     

Magnetic field effects on force convection flow of a nanofluid in a channel partially filled with porous media using Lattice Boltzmann Method

In this paper the Lattice Boltzmann Method (LBM) is utilized to investigate the effects of uniform vertical magnetic field on the flow pattern and fluid–solid coupling heat transfer in a channel which is partially filled with porous medium. Al₂O₃–water nanofluid as a work fluid with temperature sensitive properties is forced to flow into the channel while the top and bottom walls of the channel is heated and kept at a constant temperature. In the present study, with respect to previous works and experimental data, a new correlation is presented for density of Al₂O₃–water nanofluid as a function of temperature. The result also shows that the step approximation which is used for the complex boundaries of porous medium is reliable. Finally, the effect of various volume fractions of nanoparticles (ϕ = 0%, 3%, 5% and 7%) and different magnitude of magnetic field (Ha = 0, 5, 10 and 15) on the rate of heat transfer are thoroughly explored. In accordance with the results, by raising the nanoparticle volume fraction, average temperature and velocity at the outlet of the channel increase and the average Nusselt number rises dramatically. In addition, the increase the Hartmann number leads to the slow growth in the average Nusselt number, although the outlet average temperature and velocity shows a little drop.