SMA纤维复合材料梁振动半主动控制

分析了一类形状记忆合金(SMA)纤维混杂层合粱用于振动控制的动力学模型和作用机理．采用多胞模型、形状记忆合金一维本构关系分析方法，同时考虑横向剪切的影响，建立了层合梁的数学模型．半主动控制是通过改变受控结构的参数来减小结构振动的响应．根据开关控制原理确定可变刚度系统的控制律，进行SMA纤维混杂层合粱的半主动控制的数值仿真．结果表明，将半主动控制应用于梁的振动控制是一种有效的方法．     

Pressurised hot water extraction followed by simultaneous derivatization and headspace solid-phase microextraction and gas chromatography-tandem mass spectrometry for the determination of aliphatic primary amines in sewage sludge

In this paper we describe an environmentally friendly and sensitive method for the determination of ten primary amines in sewage sludge. The method is based on pressurised hot water extraction (PHWE) followed by simultaneous derivatization with pentafluorobenzaldehyde (PFBAY) and headspace solid-phase microextraction (HS-SPME) and subsequent gas-chromatography ion-trap tandem mass spectrometry (GC-IT-MS-MS) analysis. The influence of the main factors on the PHWE of sludge was optimized by a central composite design. For all species the optimal conditions were water at pH 4 as the extracting solvent, an extraction temperature of 100 °C and an extraction time of 15 min. The separation and detection of the ten amines by GC-IT-MS-MS took just 10 min and the entire process took approximately 1 h. Repeatability and reproducibility between days, expressed as RSD (%) (n = 5), were less than 19 and 24%, respectively. The average limit of detection (LOD) was of 65 μg kg⁻¹ s (range found 9-135) and the average limit of quantification (LOQ) was of 230 μg kg⁻¹ (range found 50-450) of dry weight (d.w.). Under optimized conditions we used this method to determine the compounds in industrial and municipal sewage sludge samples and in sludge from a potable water treatment plant. Methylamine and isobutylamine showed the highest levels in one of the industrial sewage sludge samples (404 and 543 mg kg⁻¹ (d.w.), respectively). To our knowledge, this paper presents for the first time the determination of ten primary amines in sewage sludge samples using PHWE.     

Effect of carbon nanotubes and their dispersion on thermal curing of polyimide precursors

The process of thermal imidization reaction is significant for temperature and time control in the polyimide industry. Here, we report the effect of carbon nanotubes and their states of dispersion on the thermal imidization of the precursor films of polyimide (poly(amic acid)) for the first time. The curing process was followed by measuring Fourier transform-infrared (FT-IR) spectra, fluorescence spectra, thermogravimetric-differential scanning calorimeter (TG-DSC) properties and the refractive indices of films. It was found that by evenly dispersing 1 wt% of carbon nanotubes assisted by a dispersant in the poly(amic acid),the full imidization temperature of the polyimide can be reduced from 300 °C to 250 °C. Different states of distribution of CNTs were observed by light microscopy and scanning electron microscopy, and proved that a better dispersion of carbon nanotubes dramatically enhanced the speed of imidization. Moreover, the DSC results showed that lower decomposition temperature of poly(amic acid) could be obtained with more uniform distribution of carbon nanotubes, which means the process of cyclodehydration of the poly(amic acid) was accelerated.     

高体分SiC_p/Al复合材料螺纹性能的测试

从SiCp/Al复合材料性能分析着手,讨论了预置件法、焊接法和粘接法等在空间遥感器研制中常用的联接方法的优缺点,提出了在高体积分数（体分）SiCp/Al复合材料上直接加工螺纹,并加装钢丝螺套的方法来改善螺纹联接性能。对在某高体分SiCp/Al复合材料上加工的M4、M5螺纹进行了拉伸测试,结果表明：加装钢丝螺套前,复合材料螺纹有被拉脱现象;加装钢丝螺套后,M4螺纹、螺杆在3 000～4 000 N被拉断;M5螺纹、螺杆在8 000～9 000 N被拉断,测试后两种规格的螺纹状态良好,可以满足实际应用对该材料拉伸强度的要求,其已应用于工程项目中。     

Nonlinear magnetoelectric response of a bulk magnetostrictive-piezoelectric composite

Magnetoelectric effect in a bulk composite of nickel ferrite and lead zirconate titanate has been investigated by applying an ac magnetic field with no bias field. The measurements were carried out in the low-frequency region for harmonic magnetic field modulation with amplitude up to 3 kOe. The electric field induced by out-of-plane magnetic field exceeds that induced by in-plane magnetic field by approximately 4 times. Nonlinearity of ferrite magnetostriction of the sample results in a doubling in the frequency and a strong distortion of the ME signals. The magnetically induced voltage can be found by integrating the ordinary ME voltage coefficient over magnetic field.     

Electrochemical synthesis of ammonia based on doped-ceria-carbonate composite electrolyte and perovskite cathode

Electrochemical synthesis of ammonia was investigated using a cobalt-free La_0.6Sr_0.4Fe_0.8Cu_0.2O_3-δ-Ce_0.8Sm_0.2O_2-δ (LSFCu-SDC) composite cathode and SDC-ternary carbonate composite electrolyte. La_0.6Sr_0.4Fe_0.8Cu_0.2O_3-δ and Ce_0.8Sm_0.2O_2-δ were prepared via combined EDTA-citrate complexing sol-gel and glycine nitrate processes, respectively, and characterised by X-ray diffraction (XRD). Ammonia was successfully synthesised from wet hydrogen and dry nitrogen under atmospheric pressure using Ni-SDC, SDC-carbonate and LSFCu-SDC composites as anode, electrolyte and cathode respectively. Ammonia formation was observed at 400, 425, 450 and 475 °C and the maximum rate of ammonia production was found to be 5.39 × 10⁻⁹ mol s⁻¹ cm⁻² at 450 °C and 0.8 V. The AC impedance measurements were recorded before and after the ammonia synthesis in the range of temperature 400-475 °C. The formation of ammonia at the N₂ side together with stable current at 450 °C under constant voltage demonstrates that SDC-(Li/Na/K)₂CO₃ composite electrolyte exhibits significant proton conduction at a temperature around 450 °C.     

Frequency dispersive complex permittivity and permeability of ferromagnetic metallic granular composite at microwave frequencies

We experimentally studied the frequency dependent complex permittivity ε and permeability μ of composite composed of carbonyl iron powder (CIP) and epoxy resin in the frequency range 1-18 GHz. We found that the intrinsic ε and μ of CIP extracted from the measured ε and μ of composites follow the classical Maxwell equations and the Landau-Lifshitz-Gilbert (LLG) equation, respectively. The dependences of ε and μ of composites on the volume fraction of CIP (vf_CIP) were investigated using the two-exponent phenomenological percolation equation (TEPPE). We found that the TEPPE can fit the experimental results very well. Comparing the results of percolation parameters derived by experimental data at different frequencies, we show that the TEPPE is frequency independent for the composites at microwave frequencies. The results also show that the ε and μ spectrums of composites with definite vf_CIP can be correctly calculated by combining the TEPPE with the theoretical models of intrinsic ε and μ.     

Electro-osmotic flow of a viscoelastic fluid in a channel : Applications to physiological fluid mechanics

The paper presents a comprehensive theoretical study on the electro-osmotic flow of a viscoelastic fluid past a channel having stretching walls. An attempt has been made to investigate the effect of rheological and electro-osmotic parameters on the kinematics of the fluid. Results presented here pertain to the case where the channel height is much greater than the thickness of electrical double layer comprising the Stern and diffuse layers. The study reveals that an increase in electro-osmotic parameter leads to an increase in the axial velocity throughout the channel for a fluid having viscoelastic coefficient equal to that of blood. This aspect provides a source of novel insight into the process of designing bio-sensing and micro-fluidic devices.     

Curved domain walls dynamics driven by magnetic field and electric current in hard ferromagnets

The propagation of curved domain walls in hard ferromagnetic materials is studied by applying a reductive perturbation method to the generalized Landau–Lifshitz–Gilbert equation. The extended model herein considered explicitly takes into account the effects of a spin-polarized current as well as those arising from a nonlinear dissipation.     

Metric Inequality, Subdifferential Calculus and Applications

In this paper we establish characterizations of Asplund spaces in terms of conditions ensuring the metric inequality and intersection formulae. Then we establish chain rules for the limiting Fréchet subdifferentials. Necessary conditions for constrained optimization problems with non-Lipschitz data are derived.