Pd Nanoparticles Supported on Triangle-Shaped La2O2CO3 Nanosheets: A New Highly Efficient and Durable Catalyst for Selective Hydrogenation of Cinnamaldehyde to Hydrocinnamaldehyde

A catalyst in which Pd nanoparticles are supported on triangle-shaped La₂O₂CO₃ nanosheets exposing predominantly the (001) planes (Pd/La₂O₂CO₃-TNS; where TNS denotes triangular nanosheets) was prepared by a facile solvothermal method. The Pd/La₂O₂CO₃-TNS catalysts exhibited excellent catalytic activity and recycling stability for hydrogenation of cinnamaldehyde to hydrocinnamaldehyde with turnover frequency of up to 41 238 h⁻¹. This enhanced activity of Pd/La₂O₂CO₃-TNS results from strong metal–support interactions. Structure analysis and characterization demonstrated that surface-oxygen-enriched La₂O₂CO₃-TNS supports exposing (001) planes are beneficial to charge transfer between the Pd nanoparticles and triangle-shaped La₂O₂CO₃ nanosheets and increase the electron density of Pd. Moreover, the modulated electronic states of the Pd/La₂O₂CO₃-TNS catalysts can enhance the adsorption and activation of hydrogen to enhance the hydrogenation activity.     

Fluorimetric Method Based on Diazotization-Coupling Reaction for Determination of Clenbuterol

A novel fluorimetric method based on diazotization-coupling reaction (DCR) for the determination of clenbuterol is described. In acidic solution, clenbuterol was first diazotized with sodium nitrite, followed by coupling with bisphenol A to produce an azo-compound in NH₃- NH₄Cl buffer. It has found the diazotized clenbuterol- bisphenol A- NH₃- NH₄Cl (DCBN) system has strong fluorescence efficiency compare with the bisphenol A solution. There is a linear relationship between the increased intensity of the fluorescence emission spectra (λ_ex/λ_em?=?276 nm/306 nm) and the concentration of clenbuterol. The effects of the amount of sodium nitrite, diazo reaction time, the amount of bisphenol A, coupling reaction time and coupling reaction temperature have been examined. Under the optional conditions, clenbuterol can be determined over the concentration range of 0.02 to 2.0 μg mL^?1 with a correlation coefficient of 0.9953. The detection limit is 0.01 μg mL^?1 at a signal-to-noise ratio of 3. The relative standard deviation (RSD) for 11 repetitive determinations of 0.9 μg mL^?1 clenbuterol is 0.22 %. The utility of this method was demonstrated by determining clenbuterol in meat samples.     

Synthesis and photovoltaic performances of donor-π-acceptor dyes utilizing 1,3,5-triazine as π spacers

A series of new-type of donor-π-acceptor dyes (TCT-1-6) utilizing 1,3,5-triazine as π spacers were synthesized. These dyes were characterized by ¹H NMR, ESI-MS, EA, and X-ray crystallography. Their photovoltaic performances were also investigated. An overall photon-to-electron conversion efficiency of 1.8% was achieved with the DSSC based on the dye TCT-1(J_sc = 3.33 mA/cm², V_oc = 757 mV, FF = 71.8%) under AM 1.5G illumination (100 mW/cm²).     

电感耦合等离子体-质谱法快速测定尿铅含量

尿样用1% HNO3稀释50倍,并以209Bi为内标元素校准基体效应及信号漂移,用电感耦合等离子体-质谱法直接测定,外标法绘制校准曲线进行定量.分别用ICP-MS和双硫腙分光光度法测定同一批尿样中铅的含量,统计并比较两种方法的测定结果,结果经t检验差异无统计学意义.该方法测定尿样中铅的检出限为0.010mg/L,线性良...     

On the cumulative microslip phenomenon

The cumulative microslip phenomenon is the accumulation of relative slips in a tangential direction on the contact interface of two solids under cyclic loadings. This leads to significant global relative displacement between components and can account for the failure of some assembly parts in mechanical structures. Practical examples from the automotive industry are presented in this paper to describe cumulative microslip effects in real situations. The phenomenon is then characterized from a theoretical point of view as an asymptotic behaviour for the contact interface under cyclic loads, by analogy with Ratcheting effects in elasto-plasticity. Accommodation and slip-shakedown are introduced in the same light. These various behaviours are illustrated with a reference discrete example that includes an original friction dissymmetry. Then we investigate the phenomenon's occurrence in various models. The existence of a dissymmetry in the assembly turns out to be a necessary condition for the phenomenon to occur. However, this condition proves not sufficient and the additional characteristics required to reproduce it are analysed. As dissymmetries are bound to exist in some assemblies because of the prescribed environment at work, a theoretical analysis of the phenomenon is performed and a slip-shakedown theorem is proposed. It leads to the introduction of a safety coefficient with respect to slips when a standard friction law is assumed. The safety coefficient can be computed from two static and kinematic approaches in min–max duality, which are illustrated on the reference discrete example.     

NONLINEAR NUMERICAL ANALYSIS OF A FLEXIBLE ROTOR EQUIPPED WITH SQUEEZE COUPLE STRESS FLUID FILM JOURNAL BEARINGS

This study performs a dynamic analysis of a rotor supported by two squeeze couple stress fluid film journal bearings with nonlinear suspension.The numerical results show that the stability of the system varies with the non-dimensional speed ratios and the dimensionless parameter l*.It is found that the system is more stable with higher dimensionless parameter l*. Thus it can conclude that the rotor-bearing system lubricated with the couple stress fluid is more stable than that with the conventional Newtonian fluid.The modeling results thus obtained by using the method proposed in this paper can be used to predict the stability of the rotor-bearing system and the undesirable behavior of the rotor and bearing center can be avoided.     

Fractal microstructure of Ag film via plasma discharge as SERS substrates

According to the atmospheric pressure plasma (APP) technology, we propose a rapid synthetic approach of the substrates for enhanced Raman spectroscopy. The plasma is used to modify and etch the surface of silver film, which generates large scale hotspots' aggregation. By switching the discharge polarity and adjusting the film thickness, different surface morphologies are formed due to the oxidation, reactive etch and accumulation of the plasma product in a certain space. Especially under positive corona discharge condition, dense snake-like microstructures are formed by the gradual connection of individual nanoparticles, which are driven by the influence of the electric field on surface diffusion. In addition, the experiments verify that the corresponding enhancement factor (EF) raises at least five orders of magnitude and the treatment time is about 10 min.     

金属粒子阵列共振的偏振特性

当金属纳米粒子形成规则分布且阵列周期与单粒子的共振波长近似匹配时, 会形成一种特殊的阵列共振, 这种共振比单粒子的局域表面等离子体共振具有更窄的共振线宽和更高的共振强度. 基于修正的长波近似方法, 讨论了矩形阵列的消光截面与阵列因子和单粒子的极化率之间的关系; 并详细研究了在不同偏振的入射光照射下, 阵列因子随着电偶极子方向的改变而产生的变化, 以及这一效应对阵列共振和消光截面所产生的影响. 结果表明, 大型的方阵是偏振无关的; 在矩形阵列中, 沿着阵列两个轴向的相邻粒子之间的耦合形成了阵列因子的两个极值, 并且分别对应了散射截面的最小值.     

Interface property of silicon nitride films grown by inductively coupled plasma chemical vapor deposition and plasma enhanced chemical vapor deposition on In0.82Al0.18As

Au/silicon nitride/In_0.82Al_0.18As metal insulating semiconductor (MIS) capacitors were fabricated and then investigated by capacitance voltage (C–V) test at variable frequencies and temperatures. Two different technologies silicon nitride (SiN_x) films deposited by inductively coupled plasma chemical vapor deposition (“ICPCVD”) and plasma enhanced chemical vapor deposition (“PECVD”) were applied to the MIS capacitors. Fixed charges (N_f), fast (D_it) and slow (N_si) interface states were calculated and analyzed for the different films deposition MIS capacitors. The D_it was calculated to be 4.16 × 10¹³ cm⁻² eV⁻¹ for “ICPCVD” SiN_x MIS capacitors, which was almost the same to that of “PECVD” SiN_x MIS capacitors. The D_it value is obviously higher for the extended wavelength In_xGa_1−xAs (x > 0.53) epitaxial material as a result of lattice mismatch with substrate. Compared to the results of “PECVD” SiN_x MIS capacitors, the N_si was significantly lower and the N_f was slightly lower for “ICPCVD” SiN_x MIS capacitors. X-ray photoelectron spectroscopy (XPS) analysis shows good quality of the “ICPCVD” grown SiN_x. The low temperature deposited SiN_x films grown by “ICPCVD” show better effect on decreasing the dark current of In_xGa_1−xAs photodiodes.     

Modeling of the multi-cable supported arch and a novel technique to investigate the natural vibratory characteristics

A fully analytical model of the multi-cable supported arch (MSA) is presented and a parametric study of the structural parameters on the planar natural vibratory characteristics is performed. Unlike the existing models, the structure is modeled with the idea “dividing the whole into parts, assembling the parts to whole” to simulate the stayed cable erection construction of the arch bridge. The global MSA under both the cantilever state and the closed state is divided into a series of chained cable-arch substructures along the span direction, The Hamilton principle is used to build the model of each substructure, in which the cable and arch segment are defined in local and global Cartesians, respectively. By assembling the equations of all substructures through the match conditions and boundary conditions, the global equation is established. Also, the global characteristic equation is determined by the transferring of coefficients vectors of substructures and some coordinate transformations. In each substructure, the interaction between the cable and the arch segment are isolated and the mutual effects are considered in the connected matrix of the coefficients vectors. The unification of the substructures converts to the transferring of the arch segments. This substructure transferring technique (STT), which is compared and verified by the finite element method (FEM), is able to effectively acquire the frequencies and the modes. The results show the sag-to-span ratios and inclined angles of the cables play significant role on the veering phenomenon in some specific intervals. Local and global modes exist simultaneously in the frequency spectrum, the involved resonant zone and veering area is needed to avoid in the parametrical design for structural safety.