摄影艺术在数字媒体动态展示中的运用

区别于传统静态展示如今动态展示已经发展成主流呈现方式之一,文章主要通过景别、视角、构图来分析摄影在数字媒体动态展示中的应用,从中反映摄影技术对数字媒体动态展示的推动作用。     

Methacrylate-endcapped poly(d,l-lactide-co-trimethylene carbonate) oligomers. Network formation by thermal free-radical curing

A series of 3-arm, methacrylate-endcapped poly(

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-lactide-co-trimethylene carbonate) prepolymers was synthesized using

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-lactide:trimethylene carbonate (DLL:TMC) molar feed ratios of 100:0, 80:20, 60:40, 40:60, 20:80, and 0:100. Number average molecular weights were in the range (2.3–2.6) × 10³ g mol⁻¹. The prepolymers were free-radically crosslinked in the absence of reactive diluents to give amorphous, bioabsorbable networks with a broad range of thermal, mechanical, and degradative properties. Extraction studies indicated that sol-contents ranged from 2.89%–6.17%. Tensile modulus, ultimate strength, and T_g increased with increasing

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-lactide content. Networks containing higher contents of

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-lactide, 100:0, 80:20, and 60:40 (DLL:TMC), were strong and fairly rigid, but failed catastrophically at the yield point; networks containing lower contents of

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-lactide, 20:80 and 0:100, showed a higher elongation to break, failing catastrophically at the yield point. A 40:60 DLL:TMC network fit perfectly within the series of compositions with regard to modulus and tensile strengh; however, it showed a yield point, followed by a regime of plastic flow prior to break. Hydrolytic degradation experiments revealed that the network based on poly(

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-lactide) homopolymer degraded fastest owing to its hydrophilicity. Hydrolytic degradation in the copolymer networks was controlled by two opposing effects which occurred as the trimethylene carbonate was increased: T_g depression, which increased water uptake, and increased hydrophobicity, which decreased water uptake. Increasing trimethylene carbonate in the 80:20 and 60:40 DLL:TMC copolymer networks caused a decrease in the water uptake and the degradation rate since these network are both glassy at the degradation temperature of 37°C. The observed increase in degradation rate in the 40:60 copolymer network was due to increased water uptake caused by depression of the T_g to a value below the test temperature of 37°C. The 20:80 and 0:100 DLL:TMC networks were the slowest to degrade owing to their hydrophobicity. © 1997 Elsevier Science Ltd.     

EMPIRICAL TWO-PARAMETER MIXING RULES FOR A CUBIC EQUATION-OF-STATE

Four two-parameter mixing rules are presented along with expressions for the fugacity coefficient and compressibility factor obtained when they are used in conjunction with the Peng-Robinson equation of state. A comparison of the forms of these expressions and results obtained in the prediction of VLE for nine systems with these temperature-, pressure-, density-, and composition-dependent rules provides a guideline for the applicability, advantages and disadvantages of each. Excellent results were obtained, especially in the near critical region, when these simple pressure- and density-dependent rules were used to describe P-x data. The density-dependent mixing rule consistently yielded better predictions of VLE over a range of temperatures (using parameters obtained at a single temperature) than the results obtained by optimizing the interaction parameter of conventional mixing rule at each temperature. The composition-dependent rule was slightly less effective for most systems, but for highly polar, asymmetric systems, this rule was superior     

Effects of chemical composition and structure of unsaturated polyester resins on the miscibility, cured sample morphology and mechanical properties of styrene/unsaturated polyester/low-profile additive ternary systems: 2. Mechanical properties

The effects of three series of unsaturated polyester (UP) resins with different chemical composition or structure on the mechanical properties of three low-shrink UP resins containing thermoplastic polyurethane, poly(vinyl acetate) and poly(methyl methacrylate) respectively have been investigated by an integrated approach of static phase characteristics–cured sample morphology–reaction conversion–property measurements. The three series of UP resins synthesized include: maleic anhydride (MA)–neopentyl glycol (NPG)–diethylene glycol (DEG) types, with various molar ratios of NPG and DEG; MA–1,2-propylene glycol (PG) types with and without modification by a saturated dibasic aromatic anhydride or acid, such as phthalic anhydride (PA) or isophthalic acid; and MA–PA–PG types modified by a second glycol, such as DEG, 2-methyl-1,3-propanediol or NPG, to partially replace PG. Based on the Takayanagi mechanical models, the effects of glycol ratios, saturated dibasic aromatic acid modification, second glycol modification, C=C unsaturation of UP and molecular weight of UP on the mechanical properties will be discussed.     

Thermodynamic optimization of ejector actuated refrigerating cycles

A cold generation system featuring a Rankine cycle powered refrigeration cycle actuated by a supersonic ejector was theoretically investigated in view of the thermo-fluid-dynamic optimization of the working fluid characteristics.

The ejector model was validated against well established performance charts relating to water. A reference system was considered in which a Rankine cycle at moderate top temperature delivers its expansion power by means of an ideal turbine to an ideal compressor of a refrigeration cycle. Two main optimizing variables were ascertained: the fluid critical temperature and the complexity of the fluid molecule. The best performance of such reference cycle is around 80% of that of an ideal fully reversible, Carnot cycle based, system (COP of 2.0 for t_E,PC = 150 °C, t_E,RC = 5 °C, and t_C = 35 °C). As easily predictable the ejector compression introduces severe losses mainly due to the normal shock and the mixing of the motive and of the driven fluid. Overall COP for the above quoted temperatures decreases from 2.0 (reference cycle) to 0.4–0.7. The optimization of the working fluid showed that comparatively low critical temperatures are favoured and that a fluid complexity similar to that of CH₅N or CH₂Cl₂ gives the best performance. A detailed losses analysis explains this behaviour. In particular at low reduced temperatures the theoretical gain related to the better shape in the T–S plane of both the power and the refrigeration cycle is more than offset by the higher ejector losses due to the stronger normal shock needed to cope with an increased pressure ratio.

Notwithstanding an extensive fluid screening we did not succeed in finding a fluid that could be considered optimum from all points of view including ambient and safety issues. However, a number of traditional (non-zero ODP) chloro-fluoro-carbons and of new (zero ODP) refrigerants were found that yield, on the whole, a satisfactory performance.

Provided calculated COP will be confirmed by experimental testing, ejector powered refrigerators could compete with absorption systems in many applications.     

温度对B炸药力学性能与感度的影响

利用分子动力学软件Material Studio,研究了B炸药在不同温度下的力学性能与感度。根据B炸药的组成成分,建立了B炸药的晶胞模型。通过数值仿真,得到了B炸药在不同温度下的力学参数、最大键长分布、键连双原子作用能与内聚能密度。通过比较分析仿真结果,得到不同温度下B炸药力学参数与感度变化情况。结果表明:随着温度的升高,B炸药的力学参数逐渐减小,表明其力学性能逐渐减弱,最大键长分布逐渐增大,键连双原子作用能与内聚能密度逐渐减小,表明炸药的感度逐渐增大。     

Characteristics of Oil from Seeds of 4 Mungbean [<Emphasis Type="Italic">Vigna radiata</Emphasis> (L.) Wilczek] Cultivars Grown in Pakistan

Mungbean is a widely consumed legume globally. This study was carried out for detailed characterization of oils from mungbean seeds from four indigenously cultivated varieties, as very little information is available on the oil composition of mungbean seeds and inter-varietal variation in oil composition. The oil content was relatively low (2.1–2.7%). The investigated physiochemical parameters included refractive indices (RI) at 40 °C (1.4673–1.4698), relative density (0.9580–0.9618), iodine value (IV) (111.4 –117.1), saponification value (SV) (173.1–181.7 mg KOH/g) and unsaponifiable matter (UM) (13.8–15.01%). Phospholipids and triglycerides were the dominant lipid fractions followed by monoglycerides. Linoleic acid and oleic acid were the dominant fatty acids (FA). Characterization was also made by TLC. Tocopherol analysis demonstrated highest content of γ-tocopherol among its isomers, while α-tocotrienol was present in highest amount in all studied cultivars, among its isomers. Results from most of the parameters revealed significant (P ≤ 0.05) differences among the cultivars. The findings of the study reveal mungbean [Vigna radiata (L.) wilczek], to be a potentially valuable legume crop with comparable nutritional quality oil among all the cultivars.     

铝厂变电站新型自动控制系统的配置与功能剖析

丹江铝业股份公司开发了用于铝厂变电站的自动控制系统，文章在介绍系统组成的基础上，分别对相关部分的配置和功能进行了详细的阐述，最后指出这一系统其可用率大于99．9％，平均无故障时间大于30000h，具有一定的推广价值。     

电流变液的发展现状

电流变液自1947年被Winslow发现以来,因其能快速、可逆地实现液一固相转变,并具有响应快（毫秒级）、连续可调、能耗低等优良特性,越来越为有关工程技术人员所关注。研究表明,电流变液在工程机械、液压系统、航空航天、机器人等众多领域具有广泛的应用前景。本文回顾了电流变液的发展和国内外的研究现状,阐述了电流变液的特点、组成、相关参数、理论模型及应用和优缺点,详细论述了产生电流变的机理、设计制造高性能电流变液的方法,并在此基础上提出了一些笔者对介电模型和电导模型的观点。     

电解液成分对电解金属锰生产过程的影响

电解金属锰生产中的电解液成分很复杂,其组成对金属锰的电解过程具有很大的影响,主要表现在对电流效率、电解过程的稳定性、添加剂二氧化硒的分解等方面。就电解液中的各种杂质对电解过程的影响进行了重点分析,提出了一些技术措施,对有害成分进行相应地处理,可减少对电解过程的影响。