High‐order accurate numerical solutions of incompressible flows with the artificial compressibility method

A high‐order accurate, finite‐difference method for the numerical solution of incompressible flows is presented. This method is based on the artificial compressibility formulation of the incompressible Navier–Stokes equations. Fourth‐ or sixth‐order accurate discretizations of the metric terms and the convective fluxes are obtained using compact, centred schemes. The viscous terms are also discretized using fourth‐order accurate, centred finite differences. Implicit time marching is performed for both steady‐state and time‐accurate numerical solutions. High‐order, spectral‐type, low‐pass, compact filters are used to regularize the numerical solution and remove spurious modes arising from unresolved scales, non‐linearities, and inaccuracies in the application of boundary conditions. The accuracy and efficiency of the proposed method is demonstrated for test problems. Copyright © 2004 John Wiley & Sons, Ltd.     

Synthesis and structural characterization of novel,fluorinated poly(phthalazinone ether)s containing perfluorophenylene moieties

The synthesis and structural characterization of a series of novel, fluorinated poly(phthalazinone ether)s containing perfluorophenylene moieties are described. The monomers, 4‐(4′‐hydroxyaryl)phthalazin‐1(2H)‐ones ( 2a – 2d ), were conveniently and efficiently synthesized from phenols and phthalic anhydride in two steps via 2‐(4′‐hydroxybenzoyl)benzoic acids, which were first obtained by the Friedel–Crafts reaction in good yields and with high stereoselectivity and were then converted into 2a – 2d by fusion with hydrazine. All the polymers were prepared by nucleophilic aromatic substitution (S_NAr) polycondensation between the compounds perfluorobiphenyl and 4‐(4′‐hydroxyaryl)phthalazin‐1(2H)‐ones ( 2a ‐ 2d ). The resulting fluorinated polymers were readily soluble in common organic solvents (e.g., CHCl₃, tetrahydrofuran, dimethylformamide, dimethyl sulfoxide, N‐methylpyrrolidone, etc.) at room temperature. Their weight‐average molecular weights and the polydispersities ranged from (7.96–18.25) × 10³ to 1.31–2.71, respectively. Their glass‐transition temperatures varied from 213 to 263 °C. They were all stable up to 390 °C both in air and in argon. The 5% weight‐loss temperatures of these polymers in air and argon ranged from 393–487 to 437–509 °C, respectively. Wide‐angle X‐ray diffraction studies indicated they were all amorphous and could be attributed to the presence of kink nonplanar moiety, phenyl phthalazinone along the polymer backbone. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 925–932, 2004     

Novel,organosoluble, light‐colored fluorinated polyimides based on 2,2′‐bis(4‐amino‐2‐trifluoromethylphenoxy)biphenyl or 2,2′‐bis(4‐amino‐2‐trifluoromethylphenoxy)‐1,1′‐binaphthyl

Two series of fluorinated polyimides were prepared from 2,2′‐bis(4‐amino‐2‐trifluoromethylphenoxy)biphenyl ( 2 ) and 2,2′‐bis(4‐amino‐2‐trifluoromethylphenoxy)‐1,1′‐binaphthyl ( 4 ) with various aromatic dianhydrides via a conventional, two‐step procedure that included a ring‐opening polyaddition to give poly(amic acid)s, followed by chemical or thermal cyclodehydration. The inherent viscosities of the polyimides ranged from 0.54 to 0.73 and 0.19 to 0.36 dL/g, respectively. All the fluorinated polyimides were soluble in many polar organic solvents, such as N,N‐dimethylacetamide and N‐methylpyrrolidone, and afforded transparent and light‐colored films via solution‐casting. These polyimides showed glass‐transition temperatures in the ranges of 222–280 and 257–351 °C by DSC, softening temperatures in the range of 264–301 °C by thermomechanical analysis, and a decomposition temperature for 10% weight loss above 520 °C both in nitrogen and air atmospheres. The polyimides had low moisture absorptions of 0.23–0.58%, low dielectric constants of 2.84–3.61 at 10 kHz, and an ultraviolet–visible absorption cutoff wavelength at 351–434 nm. Copolyimides derived from the same dianhydrides with an equimolar mixture of 4,4′‐oxydianiline and diamine 2 or 4 were also prepared and characterized. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2416–2431, 2004     

Reversible nonlinear conduction in high‐density polyethylene/acetylene carbon black composites at various ambient temperatures

The reversible nonlinear conduction (RNC) in of high‐density polyethylene/acetylene carbon black composites with different degrees of crosslinking was studied above room temperature and below the melting point of high‐density polyethylene (HDPE). The experimental current density‐electric field strength curves can be overlapped onto a master curve, suggesting that the microscopic mechanisms for the appearance of RNC exist regardless of the ambient temperature and the crosslinking degree of the HDPE matrix. The relationship between the crossover current density and the linear conductivity can be explained in the framework of the dynamic random‐resistor‐network model. According to these results, two electron‐tunneling models are suggested to interpret the microscopic conduction behavior. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1212–1217, 2004     

电子束蒸发制备HfO_2高k薄膜的结构特性

使用高真空电子束蒸发在p型Si(1 0 0 )衬底上制备了高kHfO2 薄膜 .俄歇电子能谱证实薄膜组分符合化学配比 ;x射线衍射测量表明刚沉积的薄膜是近非晶的 ,高温退火后发生部分晶化 ;原子力显微镜和扫描电子显微镜检测显示在高温退火前后薄膜均具有相当平整的表面 ,表明薄膜具有优良的热稳定性 ;椭偏测得在 6 0 0nm处薄膜折射率为 2 0 9;电容 电压测试得到的薄膜介电常数为 1 9.这些特性表明高真空电子束蒸发是一种很有希望的制备作为栅介质的HfO2 薄膜的方法     

高压增氧T′相R_2CuO_(4+δ)(R=Nd～Tm)低温磁性研究

T′相R2CuO4稀土铜氧化合物由于尺度效应而产生弱铁磁性行为已经被人们关注,报导了通过高温高氧压(6GPa,1000℃)合成稀土T′相R2CuO4(R=Nd,Sm,Eu,Gd,Tb,Dy,Ho,Er和Tm)化合物的结构和磁学性能。磁化率曲线显示,在低温下所有的高压增氧R2CuO4样品都出现新的低温弱铁磁性反常行为,转变温度在28K附近。新的低温弱铁磁性行为是由于CuO2面上微量氧空穴的掺入,使处于反铁磁有序CuO2面形成局域化的铁磁性团簇造成。实验证明新发现的低温弱铁磁性行为与尺度效应产生弱铁磁性行为属于完全不同的物理机制。结果还预示T′相R2CuO4稀土铜氧化合物很难通过空穴掺杂而实现超导。     

强流离子束离子径向密度分布的模拟研究

对初始分布为K-V分布的离子束进行模拟研究.除观察到存在束晕现象外，还发现离子束在通 道内运行过程中，离子沿径向密度分布发生了变化. 通过延迟反馈控制，不仅可以消除束晕 ，而且只要控制参数适当，也可以使束中心部分呈均匀分布状态. 关键词： 强流离子束 束晕 填充因子 离子密度分布     

Investigation and optimization of the covering power and coloristic properties of paint coatings of complex composition

A method for finding the optimum sizes of pigment particles, their volume concentration, and the paint coating thickness that provide the covering power and the required coloristic characteristics of reflected light for the minimum flow rate of pigments is based on using a four-flow approximation of the solution to the equation of radiation transfer in dispersion media and is extended to coatings of complex composition. The capabilities of the method are demonstrated by examples of coatings of mixtures of hematite and rutile particles in a binder with n=1.5 for variations of the modal size and the half-width of the size distribution of the pigment particles. B. I. Stepanov Institute of Physics, Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 90–96, January–February, 1997.     

一种漂移室定位子性能反常现象的研究

研究了一种漂移室定位子性能的反常现象,它关系到定位子的使用寿命．着重测量了暗电流和随机噪声与时间、高压及温度的关系.     

高压下聚苯胺的结构和电性能研究

 以金刚石压腔高压装置为工具，用Ⅱ型金刚石作压砧兼红外窗口，对本征态聚苯胺进行了高压（0~8.4 GPa）就位红外光谱测试。结果表明：在4.8~5.2 GPa压力区间，代表醌环振动的吸收峰相对代表苯环振动的吸收峰变小，表明聚苯胺在此压力区间结构上发生了显著变化，且这种变化是不可逆的。聚苯胺的高压（0~14.5 GPa）电阻测量结果表明：当压力小于7.5 GPa时，电阻随压力升高而显著降低，据此认为聚苯胺为电子性导电物质；在7.5 GPa处电阻出现极小值，然后又缓慢升高，至10 GPa后基本不变。推测聚苯胺电阻极小值是由结构变化引起的。至于红外光谱与电阻测量结果反映聚苯胺结构变化的压力值不一致，可能是由于测试条件不同所致。