在高压CO_2中聚乙二醇-聚己内酯嵌段共聚物的结晶行为

通过广角X射线衍射(WAXD)和小角X射线散射(SAXS)方法研究了PEO-b-PCL在CO2中的结晶形貌和片晶厚度的变化,利用高压示差扫描量热仪(HP DSC)考察了压力对熔融和等温结晶过程的影响.结果表明,PEO-b-PCL的结晶度、片晶厚度、熔融温度均随压力的升高而减小,结晶结构变得不完善.在等温结晶过程中,结晶速率随压力的升高而下降,结晶过程处于成核控制区,Avrami指数n在3.7~4.7,表明晶体的生长方式为三维生长.     

Onset of Buoyancy-driven Instability in Porous Media Melted from Below

When a nonhomogeneous solid is melting from below, convection may be induced in a thermally–unstable melt layer. In this study, the onset of buoyancy-driven convection during time-dependent melting is investigated by using similarly transformed disturbance equations. The critical Darcy–Rayleigh numbers based on the melt-layer thickness, Ra _H,c, are found numerically for various conditions. For small superheats, the present predictions show that Ra _H,c is located between 27.1 and 4π ² and it approaches the well-known results of the original Horton–Rogers–Lapwood problem. However, for high superheats, it is dependent on the phase change rate λ and the relation of Ra _H,c λ = 25.89 is shown.     

Fast computation of bounds for two-terminal network reliability

In this paper, an algorithm for the fast computation of network reliability bounds is proposed. The evaluation of the network reliability is an intractable problem for very large networks, and hence approximate solutions based on reliability bounds have assumed importance. The proposed bounds computation algorithm is based on an efficient BDD representation of the reliability graph model and a novel search technique to find important minpaths/mincuts to quickly reduce the gap between the reliability upper and lower bounds. Furthermore, our algorithm allows the control of the gap between the two bounds by controlling the overall execution time. Therefore, a trade-off between prediction accuracy and computational resources can be easily made in our approach. The numerical results are presented for large real example reliability graphs to show the efficacy of our approach.     

《论数值修约》的补充——数值修约的误差

本文用补数定义论述了四舍五入的误差问题.并用图示法显示各修约规则的误差.     

Surface temperature evolution in pulsed laser action of millisecond range

An originally developed multi-wavelength pyrometer (12 wavelengths in the range 1.001-1.573 μm, 50 μs acquisition time for each photodiode, 800 μm spatial resolution, 900-3500 °C brightness temperature range) is used to measure brightness temperature under the pulsed action of Nd:YAG laser (HAAS-HL62P) on stainless steel (INOX 304L) substrates. Specially developed “notch” filters (10⁻⁶ transparency at 1.06 μm wavelength) are applied to avoid the influence of laser radiation on temperature measurements. The true temperature is restored on the basis of method of multi-colour pyrometry. The accuracy of brightness temperature measurements is examined by comparing the temperature evolution for pulses with different durations but with the same value of energy density flux.The influence of the following parameters is studied keeping the remaining ones constant: pulse duration (6-20 ms, rectangular pulse shape), energy per pulse (10-33 J, rectangular pulse shape), pulse shape (three types of triangulars and one rectangular). Finally the evolution of surface temperature for pulses with more complex shapes but with the same pulse duration and energy per pulse is compared.     

Raman spectra and thermal analysis of a new lead–tellurium–germanate glass system

Differential scanning calorimetry (DSC) and Raman scattering studies of a new glass system, lead–tellurium–germanate glasses in the form of (90−x)GeO₂·xTeO₂·27PbO·10CaO with x=0, 10, 20, 30, and 40, are reported. The glass samples were fabricated using a conventional melt-quenching method. The Raman spectra and possible glass structures are discussed for different TeO₂ contents. The results indicate that increasing TeO₂ content up to 40 mol% in the glass system decreases the glass transition temperature and melting temperature, and suppresses the crystallization tendency in the fiber pulling temperature range. The lead–tellurium–germanate glass, GTPC, possesses a larger refractive index and a smaller maximum phonon energy than that of a lead–germanate glass, 63GeO₂·27PbO·10CaO, and shows a better thermal stability compared to a tellurite glass, 75TeO₂·20ZnO·5Na₂O (TZN). These improved properties could be beneficial for fabricating rare-earth doped fiber devices.     

Effects of montmorillonite interlayer micro-circumstance on the PP melting intercalation

1-Octadecyl-3-methylimidazolium chloride ([C₁₈ mim]Cl) is a kind of imidazolium ionic liquid with high thermal stability. [C₁₈ mim]Cl was used to modify pristine Na-montmorillonite and a series of organo-montmorillonite (OMMT) with different loading levels of 1-octadecyl-3-methylimidazolium cation ([C₁₈ mim]⁺) were obtained. X-ray diffraction (XRD) and thermogravimetric analysis (TGA) results show that there are different loading levels and aggregative state of [C₁₈ mim]⁺ in the interlayer of OMMT. The effects of OMMT interlayer micro-circumstances on the PP melting intercalation were studied by XRD and transmission electron microscopy (TEM). Results indicate that the melting intercalation of PP into the interlayer of OMMT is not only related with d-spaces but also has something to do with the interlayer micro-circumstance of OMMT. Based on these facts, three types of interlayer absorption models of [C₁₈ mim]⁺ in the interlayer of OMMT were conceived. In addition, the aggregative state of [C₁₈ min]⁺ in the interlayer of OMMT, interlayer polarity and d-spaces of OMMT were discussed. According to these models, we try to illustrate the effect of interlayer micro-circumstance of OMMT on the PP melting intercalation.     

共沉淀法制备PEOUIC的形貌与结构分析

包合复合物(ICs)是超分子化学的重要组成部分。以尿素作为主体分子,PEO作为客体分子,通过共沉淀法制备了不同PEO与Urea比例的PEOUIC,而后分别利用DSC、XRD、SEM、POM分析了PEOUIC晶体的形貌与结构。结果表明:利用共沉淀法可制备六方以及四方晶系的PEOUIC晶体;当PEO与Urea质量比小于为1时,形成四方晶系PEOUIC晶体;而当质量比大于1时,形成六方晶系PEOUIC晶体;随着Urea含量的增大,PEOUIC的T_m先增大在趋于稳定不变;四方晶系PEOUIC晶体呈现球晶形貌,六方晶系呈现中心突起的六边形柱状体形貌。     

Effect of lead on microstructure and some physical properties of Sn–Zn–Cd alloy

The effect of lead on the structure, electrical resistivity, internal friction, elastic modulus and thermal properties of Sn₈₁Zn₉Cd₁₀ ternary alloys have been investigated using different experimental techniques with their analysis. In addition, properties of this alloy were compared with other Sn–Zn or Sn–Zn–Cd alloys and commercial solder alloys. It has a higher electrical resistivity, internal friction and lower elastic modulus when compared with Sn–Zn or Sn–Zn alloys with other additions such as Cd, Bi or In. The Sn₆₁Zn₉Cd₁₀Pb₂₀ alloy has a lower melting point, electrical resistivity and internal friction when compared with the commercial Pb–Sn solder alloy, but it has a similar elastic modulus.     

New lead-free solder alloy

As the electronics industry is moving towards lead-free manufacturing processes, a new lead-free solder alloy based on Sn–9Zn–1Bi–2Cu–In is described. The quaternary alloy with indium additions exhibits melting, wetting, and mechanical properties superior to those in binary, ternary, and quaternary alloys. Indium as a penternary addition decreases the melting point of this alloy to 181 ^°C which it is a lower value when compared with the eutectic Sn–Pb solder (183 ^°C), it decreases the contact angle to 23^° which is very close to that for Sn–Pb solder alloy, it increases the Young’s modulus to higher values, and it increases its hardness to 19 kgf/mm² when compared with 12.9 kgf/mm² for the Sn–Pb solder alloy.