双层微通道换热特性优化分析

为强化微通道换热器换热效果,建立了三维双层微通道换热器模型,通过优化分析计算得出微通道最佳设计尺寸。在底部热流密度qw=100W·cm-2时,最优占空比K=74%,下层通道高度Hc1=0.5mm,上层通道高度Hc2=0.9mm,其最高温度分布于受热面中部,最大温差比未经优化时降低20.37%。并对比了凹槽微通道与普通微通道的换热特性,结果表明,在入口速度大于3m/s时,凹槽微通道换热效果比普通微通道换热效果好。     

Synthesis of Fe3O4 nanoparticles by wet milling iron powder in a planetary ball mill

Fe3O4 nanoparticles with sizes ranging from 30 to 80 nm were synthesized by wet milling iron powders in a planetary ball mill. The phase composition and the morphologies of the as-synthesized products were measured by X-ray diffraction （XRD）, scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. Nanosized Fe3O4 particles were prepared by wet milling metallic iron powder （-200 mesh, 99%） in a planetary ball mill equipped with stainless steel vials using iron balls under distilled water with a ball-to-powder mass ratio of 50：1 and at a rotation speed of 300 rpm. The use of the iron balls in this method played a key role in Fe3O4 formation. The present technique is simple and the process is easy to carry out.     

Shape‐Controlled Synthesis of NiCo2O4 Microstructures and Their Application in Supercapacitors

The shape‐controlled synthesis of NiCo₂O₄ microstructures through a facile hydrothermal method and subsequent calcinations was explored. By employing CoSO₄, NiSO₄, and urea as the starting reactants, flower‐like NiCo₂O₄ microstructures were obtained at 100 °C after 5 h without the assistance of any additive and subsequent calcination at 300 °C for 2 h; dumbbell‐like NiCo₂O₄ microstructures were prepared at 150 °C after 5 h in the presence of trisodium citrate and subsequent calcination at 300 °C for 2 h. The as‐prepared NiCo₂O₄ microstructures were characterized by X‐ray powder diffraction, field‐emission scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, and (high‐resolution) transmission electron microscopy. Both the flower‐like and dumbbell‐like NiCo₂O₄ microstructures could be used as electrode materials for supercapacitors, and they exhibited excellent electrochemical performance, including high specific capacitance, good rate capability, and excellent long‐term cycle stability. Simultaneously, the shape‐dependent electrochemical properties of the product were investigated.     

结构振动的滑模变结构半主动控制

研究应用磁流变阻尼器(MRD)对结构振动半主动控制的算法和原理。研制并对磁流变阻尼器进行了阻尼特性实验，采用非线性滞回双粘性模型描述磁流变阻尼器的阻尼特性，模型结果与实验结果非常一致。采用滑模控制算法和趋近律方法设计了半主动控制器。利用滑模控制方法所建立的控制器，本文给出了地震激励下结构振动半主动控制算例。计算分析表明，半主动滑模控制具有控制效果明显、鲁棒性好等优点，是一种非常有发展前途的控制方法。     

混合边界下开弧外区域声波散射问题的数值解法

关于时间调和声波在一个无限长圆柱形导体上的散射,可以转化为R2中一段光滑开弧上的散射问题.利用单双层位势来逼近散射波,通过单双层位势在开弧两侧的跳跃关系建立了混合边界的积分方程组,然后对此方程组进行参数化和离散化,最终得到离散化后的积分方程组.此边界积分方程组的解是存在唯一的.     

The influence of concentration and supersaturation ratio of CuI·HI on CuI crystal growth by decomplexation method

The fundamental role of solubility and supersaturation of solute for crystal growth from solution has been widely realized. In order to optimize the process of CuI crystal growth by CuI·HI decomplexation in HI acid, the solubility and supersaturation curves of CuI in HI‐H₂O mixed solvent were measured, and then a modified concentration programming scheme was designed, which could grow high quality CuI single crystals of 2.5 mm on edge successfully. In this scheme, the concentration distribution of CuI·HI complex and HI acid in silica gel along their diffused direction were measured with spectrophotometer, and the evolution of CuI·HI complex supersaturation ratio was analysed. It was found that the excess CuI·HI complex concentration would lead to the high supersaturation ratio and the formation CuI dendrites. The condition for regular CuI single crystal growth in silica gel was measured as follow: when the crystal nuclei appears, the CuI·HI complex concentration in HI‐H₂O solvent should be kept in the range of 0.033–0.050 mol/L and its corresponding supersaturation ratio is 1.24–1.45, and then they should be respectively declined to a range of 0.025–0.033 mol/L and 1.14–1.26 at the stage of crystal growth. The results may provide a useful clue for further improvement of the experimental scheme. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Energy transfer of highly vibrationally excited biphenyl

The energy transfer between Kr atoms and highly vibrationally excited, rotationally cold biphenyl in the triplet state was investigated using crossed-beam/time-of-flight mass spectrometer/time-sliced velocity map ion imaging techniques. Compared to the energy transfer of naphthalene, energy transfer of biphenyl shows more forward scattering, less complex formation, larger cross section for vibrational to translational (V→T) energy transfer, smaller cross section for translational to vibrational and rotational (T→VR) energy transfer, larger total collisional cross section, and more energy transferred from vibration to translation. Significant increase in the large V→T energy transfer probabilities, termed supercollisions, was observed. The difference in the energy transfer of highly vibrationally excited molecules between rotationally cold naphthalene and rotationally cold biphenyl is very similar to the difference in the energy transfer of highly vibrationally excited molecules between rotationally cold naphthalene and rotationally hot naphthalene. The low-frequency vibrational modes with out-of-plane motion and rotationlike wide-angle motion are attributed to make the energy transfer of biphenyl different from that of naphthalene.     

Studies on core–shell structural nano-micelles based on star block copolymer of poly(lactide) and poly(2-(dimethylamino)ethyl methacrylate)

Inorganic/polymer hybrid star-shaped block copolymer nano-micelles were synthesized. In the synthetic route, multi-hydroxyl polyhedral oligomeric silsequioxane(POSS-(OH)₃₂) was employed as the starting molecule to initiate ring-opening polymerization of d,l-lactide. 2-(Dimethylamino)ethyl methacrylate was found to polymerize at the end of polylactic acid chains, following mechanism of atom transfer radical polymerization. The well-defined star block copolymer core–shell nano-micelles were finally obtained. The structures of the copolymer and the micelles were characterized extensively. The micelles exhibited a regular spherical shape with an average diameter of 170 nm which was confirmed by transmission electron microscopy and dynamic laser scattering. The sizes of both the core and the shell were controlled by adjusting the feed ratios during the syntheses. The micelles demonstrated pH- and temperature-sensitive behaviors.     

Comparative analysis of automotive paints by laser induced breakdown spectroscopy and nonparametric permutation tests

Laser-induced breakdown spectroscopy (LIBS) has been investigated for the discrimination of automobile paint samples. Paint samples from automobiles of different makes, models, and years were collected and separated into sets based on the color, presence or absence of effect pigments and the number of paint layers. Twelve LIBS spectra were obtained for each paint sample, each an average of a five single shot “drill down” spectra from consecutive laser ablations in the same spot on the sample. Analyses by a nonparametric permutation test and a parametric Wald test were performed to determine the extent of discrimination within each set of paint samples. The discrimination power and Type I error were assessed for each data analysis method. Conversion of the spectral intensity to a log-scale (base 10) resulted in a higher overall discrimination power while observing the same significance level. Working on the log-scale, the nonparametric permutation tests gave an overall 89.83% discrimination power with a size of Type I error being 4.44% at the nominal significance level of 5%. White paint samples, as a group, were the most difficult to differentiate with the power being only 86.56% followed by 95.83% for black paint samples. Parametric analysis of the data set produced lower discrimination (85.17%) with 3.33% Type I errors, which is not recommended for both theoretical and practical considerations. The nonparametric testing method is applicable across many analytical comparisons, with the specific application described here being the pairwise comparison of automotive paint samples.