(Fe, Ni)/C nanocapsules for electromagnetic-wave-absorber in the whole Ku-band

The natural resonance appears at 16 GHz for (Fe, Ni)/C nanocapsules with (Fe, Ni) alloys as cores and graphite as shells. Reflection loss (RL) exceeding −10 dB was obtained in the whole Ku-band (12.4-18 GHz) for an absorber thickness of 2.0 mm, while it exceeds −20 dB over the 13.6-16.6 GHz range. In addition, the bandwidth does not change dramatically for the thicknesses of 1.87-2.1 mm for the RL values exceeding −10 dB. The (Fe, Ni)/C nanocapsules with wide bandwidth absorption can be used as excellent electromagnetic-wave-absorption materials in the whole Ku-band.     

Preparation of novel bilayer hydrogels by combination of irradiation and freeze–thawing and their physical and biological properties

BACKGROUND: Hydrogels made by irradiation or freeze–thawing often exhibit poor mechanical strength; therefore we investigated a novel synthetic method to circumvent this detrimental effect. We report a series of novel bilayer poly(vinyl alcohol) (PVA)/water‐soluble chitosan (ws‐chitosan)/glycerol hydrogels prepared by a combination of irradiation and freeze–thawing. Scanning electron microscopy morphology, swelling behavior, mechanical strength, elongation at break, PVA dissolution behavior and bovine serum albumin (BSA) release profile of the bilayer hydrogels were compared with those of hydrogels made by irradiation and freeze–thawing followed by irradiation. The cytotoxicity of the bilayer hydrogels was studied using a tetrazolium salt (MTT) assay. RESULTS: The novel bilayer hydrogels contain one layer made by freeze–thawing followed by irradiation and the other layer made by irradiation. The preparation method provides the two layers with good combination force in the wet state. However, the two layers are not combined very well in the freeze‐dried state due to the difference in microstructure. The bilayer hydrogels have large swelling capacity and good mechanical strength, and these properties can be varied by changing freeze–thawing cycles, irradiation doses and the relative thickness of the two layers. The PVA and BSA release behaviors show that the bilayer hydrogels have a small amount of dissolved PVA and can prolong the BSA release time. The MTT assay shows that extracts of the bilayer hydrogels are non‐toxic towards L929 mouse fibroblasts. CONCLUSION: The novel bilayer hydrogels prepared in this study show good physical properties with no cytotoxicity, indicating that they are suitable for biomedical applications, such as in wound dressings and drug delivery devices. Copyright © 2009 Society of Chemical Industry     

接枝聚合物聚酯多元醇增强聚氨酯弹性体的性能

用接枝聚合物聚酯多元醇(GPOPs)增强聚氨酯弹性体(PUE),并对GPOPs的组成和形态进行了表征,考察了GPOPs的用量对PUE性能的影响.结果表明,GPOPs是乙烯基单体在聚酯多元醇介质中聚合得到的改性聚酯多元醇,它能显著提高PUE的邵尔A硬度、拉伸强度、撕裂强度,并改善其尺寸稳定性和热稳定性;能够在保持PUE硬度、拉伸强度基本不变的条件下,减少二异氰酸酯的用量,降低成本.     

Shrinkage cracking of styrene butadiene polymeric emulsion‐modified concrete using rapid‐hardening cement

This study was performed to resolve the problem of cracks caused by the rapid hydration heat produced during the early setting stages of rapid‐hardening cement. To address the hydration heat of rapid‐hardening cement, we prepared a modified rapid‐hardening cement using calcium sulfoaluminate clinker combined with a styrene butadiene (SB) polymer. The performance of SB polymeric emulsion‐modified concrete made from modified rapid‐hardening cement was assessed by determining shrinkage (change in length, and plastic and autogenous shrinkage). The modified rapid‐hardening cement in combination with SB polymeric emulsion effectively reduced cracking. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

The physical and mechanical properties of polyurethanes from oleic acid polyols

Three different polyester polyols, with various oleic acid content, were used in the preparation of polyurethane (PUR) coatings. The polyols were designated as Alk28, Alk40, and Alk65, in which 28, 40, and 65 represent the percentage of oleic acid of the polyol formulations. These polyester polyols were reacted with aromatic diisocyanate [toluene diisocyanate (TDI)] to form PUR coatings. The acid value, hydroxyl value, molecular weight, and viscosity of the polyols have been determined. The reaction between the polyols and TDI was studied by Fourier Transform Infrared spectroscopy and X‐ray diffraction (XRD). The effects of varying NCO/OH ratio and oleic acid content of polyols on physical and mechanical properties of PUR films were studied. XRD results indicate that the samples are amorphous. PURs, made with Alk28, have the best mechanical properties followed by Alk40 and Alk65. The mechanical properties of the samples have increased as the NCO/OH ratio was increased from 1.2 to 1.6. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Parameter change test for random coefficient integer-valued autoregressive processes with application to polio data analysis

Abstract.  In this paper, we consider the problem of testing for a parameter change in a first-order random coefficient integer-valued autoregressive [RCINAR(1)] model. We employ the cumulative sum (CUSUM) test based on the conditional least-squares and modified quasi-likelihood estimators. It is shown that under regularity conditions, the CUSUM test has the same limiting distribution as the supremum of the squares of independent Brownian bridges. The CUSUM test is then applied to the analysis of the monthly polio counts data set.     

Mesophase structure discovered through in-situ X-ray measurement in drawing process of poly(ethylene 2,6-naphthalene dicarboxylate) fiber

The structure development in the continuous laser-heated drawing process of poly(ethylene 2,6-naphthalene dicarboxylate) (PEN) fiber was analyzed by in-situ X-ray diffraction measurement. Because of the rapid and uniform laser heating, and the resultant steady-state nature of the necking-drawing, the structure development after the on-set of necking could be measured in the time resolution of several hundred microseconds. We found for the first time the temporal appearance of meridional (001′) diffraction at several milliseconds after the on-set of necking indicating that the mesophase structure similar to the one reported for poly(ethylene terephthalate) was also formed in the initial stage of fiber structure development of PEN. The d-spacing of the (001′) diffraction 1.230 ± 0.003 nm was shorter than the c-axis lengths of both α and β crystals.     

空气压力对油雾发生器雾化特性的影响

采用计算流体力学软件FLUENT对油雾发生器内部流动现象及雾化现象进行数值模拟,研究在一定温度条件下空气压力及油雾出口压力对油雾平均粒径、油耗量、气耗量的影响.计算结果表明:空气压力越大,油滴平均直径越小,油耗量先增大,后减小,气耗量增大;油雾出口压力越大,达到最大油耗量的空气压力越大,并且达到的最大油耗量越大,油雾出口压力对气耗量影响较小.     

The influence of current load on fretting of electrical contacts

The fretting corrosion behavior of tin coated brass contacts is studied at various current loads (1, 2 and 3 A). The typical characteristics of the change in contact resistance with fretting cycles are explained. The fretted surface is examined using scanning electron microscope, laser scanning electron microscope and energy dispersive analysis of X-rays to assess the surface morphology, extent of fretting damage, extent of oxidation, surface profile and elemental distribution across the contact zone. The degradation of contacts at high and low values of current is explained with reference to the thermal and electrical phenomena occurring at the contact interface. The results showed that irrespective of the current loads under study, the contact resistance is maintained at 1.0±0.02 Ω where the oxide debris formation and the electrical breakdown of oxide particles competed with each other maintaining the equilibrium. The number of cycles to failure of the contacts is delayed at lower current. The fretting corrosion degradation of tin coated contacts occurs much faster at higher currents as it generates more accumulation of oxide wear debris at the contact zone. The observed surface morphology and the tin profile of the fretted surface are in agreement with the experimental results.     

铝镁合金分馏塔冬季焊接施工要点

2009年10月,我公司承揽的内蒙古大唐国际克什克腾煤制气项目48000Nm3/h空分装置两台冷箱铝镁合金分馏塔组焊时,冬季温度-10℃左右,施工环境温差较大,铝镁合金因环境温差大易造成焊缝开裂,影响工程正常施工.我们采用电加热器加热保证塔壁温差,焊接时采用局部加热、加固点固焊、分段倒退焊等一些列焊接措施,克服了铝镁合金焊缝开裂、气孔、变形等缺陷,顺利完成了任务,为我公司冬季铝镁合金焊接施工积累了经验.