Model order determination and noise removal for modal parameter estimation

Given a noisy impulsive response function (IRF) that has been contributed by an unknown number of modes, this article proposes a different approach from the traditional methods for estimating modal parameters from this noisy IRF. The major difference lies in the way of handling noise and choosing the computational model order. Whereas the traditional approach accommodates noise by purposely increasing the computational model order, the proposed approach uses the actual system order as the computational model order and rejects noise prior to performing the modal parameter estimation. The proposed approach includes three steps: (1) model order (or number of modes) determination from the measured IRF—by finding the rank of a Hankel matrix constructed from the measured IRF, (2) noise removal from the measured IRF to obtain a filtered IRF—by implementing Cadzow's algorithm for the structured low rank approximation (SLRA) on the Hankel matrix, and (3) modal parameters estimation from the filtered IRF—by using the complex exponential method (Prony's method). Numerical studies include both synthesized and experimental data. While measured IRFs with mild and strong noise levels are simulated for a 5 degree-of-freedom mass-spring-dashpot system, the modal parameter estimations based on the filtered IRFs are very good for both noise levels. While experimental data are measured from two accelerometers mounted at a cantilever beam, the modal parameters estimated from the filtered IRFs of the two accelerometers are in excellent agreement.     

In situ crosslinking of hyperbranched polyglycerol in casting solutions and its effect on the structure and properties of porous PVDF membranes

Porous membranes were prepared via phase inversion process from casting solutions composed of poly(vinylidene fluoride), hyperbranched polyglycerol (HPG), and N,N‐dimethylacetamide. To seek a stable presence of HPG in the resulting membranes, it was crosslinked in the casting solutions using 4,4′‐oxydiphthalic anhydride as the crosslinking agent. The membranes were characterized in terms of morphology, surface and bulk chemical compositions, water contact angle, porosity, water flux, and bovine serum albumin (BSA) adsorption experiments. The effects of HPG content and crosslinking degree on the membrane structure and properties were investigated. The increasing of crosslinking degree resulted in a significant improvement in HPG stability in the membrane matrix, and a remarkable enrichment of the crosslinked HPG at the separation surface was observed when the membrane was shaken in water at a relatively high temperature (60°C). This enrichment led to a decrease in the value of water contact angle and an improvement in fouling‐resistance. To optimize the membrane performance, a small amount of poly(vinylpyrrolidone) (PVP) was used as an additive, and it was found that the addition of PVP led to a considerable increase in water flux. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

亚洲帘线钢线材生产现状及发展趋势

介绍亚洲帘线钢线材生产现状:日本新日铁开发了DLP控冷工艺保证帘线钢产品的高质量；日本神户制钢开发的超洁净钢冶炼工艺,很好地控制了钢中P,S,O的含量,以及夹杂物的含量、性质,使得神户的帘线钢线材成为世界最优；韩国浦项通过优化斯太尔摩冷却工艺来生产高品质帘线钢线材；宝钢帘线钢经历了转炉模铸、电炉小方坯、电炉大方坯连铸工...     

Hydrogenation and dehydrogenation processes of palladium thin films measured in situ by spectroscopic ellipsometry

The hydrogenation and dehydrogenation switching processes of Pd thin films were analyzed by measuring in situ in real time the variation in ellipsometric Ψ and Δ during hydrogenation and dehydrogenation using spectroscopic ellipsometry. The hydrogenation proceeded from the film surface and a mixture layer of metal and hydride was formed at the surface. With time elapse, the thickness of the mixture layer increased rapidly. After the whole Pd metal layer transformed to the mixture layer, the concentration of hydride in the mixture layer increased. Finally, the concentration reached 1; the whole Pd in the mixture layer was hydrogenated, and the hydrogenation of Pd was complete. On the other hand, the dehydrogenation proceeded in a way completely opposite to the hydrogenation process; the concentration of hydride in the mixture layer decreased, Pd metal layer was formed at the interface between the film and the substrate, and the whole layer returned to Pd metal. The dehydrogenation proceeds much faster than hydrogenation.     

A new and direct preparation method of iron-based bimodal catalyst and its application in Fischer–Tropsch synthesis

A bimodal iron-based catalyst was prepared by a new one-step impregnation method. The active components were used as the “brick” to directly build the small pores inside the large pores of support, which was quite different from the previous bimodal catalysts that were prepared once more on a bimodal support. Comparing with the unimodal catalysts and conventional co-precipitated catalyst, the prepared bimodal catalyst exhibited excellent activity in Fischer–Tropsch synthesis due to the improved active metal dispersion and fastened diffusion efficiency. This preparation method is much simpler than the previous methods and can be extended to prepare various bimodal catalysts with different chemical compositions.     

影剧院舞台夏季不同送风方式的模拟及优化

通过运用FLUENT软件模拟夏季影剧院舞台上送上回形式下,三种不同送风方式下的舞台气流组织,通过对温度场、速度场的分布的比较,得出了最优送风方式。     

由小动物引发的电压力锅漏电故障分析

现有电压力锅产品的电气控制底仓散热通气孔因孔隙设计太大,而不能有效阻止部分小动物通过散热通气孔进入电气控制底仓,从而可能引发漏电故障.这是我国电压力锅普遍存在的安全隐患.本文通过配电开关箱电气用电线路系统,分析了几种典型案例,并提出了改进方法.     

Effect of repetitive processing on the mechanical properties and fracture toughness of dynamically vulcanized iPP/EPDM blends

The effect of repetitive processing on the mechanical properties and fracture toughness of dynamically vulcanized isotactic polypropylene/ethylene‐propylene‐diene rubber blends (TPVs) with and without addition of β‐nucleating agent (β‐NA) was studied. The results showed that the repetitive processing did not cause much loss in the mechanical properties of TPVs, especially for TPVs with β‐NA, and TPVs with β‐NA showed better performance stability than TPVs without β‐NA. Essential work of fracture (EWF) approach was used to study the fracture behavior, and the results showed that the value of w_e (the specific essential work of fracture) of TPVs without β‐NA showed a significant decrease while that of TPVs with β‐NA almost kept constant after repetitive processing. Differential scanning calorimetry and wide‐angle X‐ray diffraction were used to study the variation of crystalline structures, and the results indicated that the repetitive processing showed no significant influence on the crystalline structures of TPVs, and the β‐NA maintained high‐nucleating efficiency after repetitive processing. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Experimental research of unsupervised Cameron/maximum-likelihood classification method for fully polarimetric synthetic aperture radar data

In this study, experimental research on classification is applied to fully polarimetric data in X-band from China. Considering the amplitude and phase error between H and V channels in the system, the authors firstly correct the error in original data. The authors also deduce the formula of Cameron?s classification method for the real data in our study. Then Cameron?s method is used to initially classify the site image. Finally, the initial classification map defines training sets for the maximum-likelihood (ML) classifier. The advantages of this method are the automated classification and interpretation of each class based on the scattering mechanism. The experiment demonstrates the feasibility of the proposed approach, which dramatically improves the X-band data classification result compared with the Cameron method and H/α/ML method.