Snapping of an elastica under various loading mechanisms

This paper studies the snap-through buckling of a hinged elastica subject to a midpoint force. The focus is placed on how different load models affect the deformation and snapping load. Three different load models are considered. In the first model, the point force is fixed onto a midpoint of the elastica. In the second model, the point force is fixed on a central line in space. In the third model, the external force is applied through a rigid bar, which is allowed to slide along the central line in space. When the loaded elastica deforms symmetrically, as in the case when the magnitude of the point force is small, there is no difference between these three load models. However, when the elastica deforms unsymmetrically, the three load models produce different results. Vibration method is used to determine the stability of the equilibrium configurations. It is found that the elastica may snap via either a sub-critical pitchfork bifurcation or a limit-point bifurcation. If the elastica snaps via a sub-critical pitchfork bifurcation, the pre-snapping deformation is symmetric. If the elastica snaps via a limit-point bifurcation, on the other hand, the pre-snapping deformation is unsymmetric. For a specified initial shape of the elastica, different load models predict different snapping loads and pre-snapping deformations. The theoretical predictions are confirmed by experimental observations.     

二维随机粗糙面上导体目标复合瞬态散射的混合算法

提出用时域积分方程法(TDIE)与时域基尔霍夫近似法(TDKA)的混合算法来求解二维导体随机粗糙面及其上方二维导体目标的复合瞬态散射,推导出了在TM波入射情形下显式及隐式格式的时间步进方程.将粗糙面与目标分别进行TDKA和TDIE计算,并考虑目标与粗糙面之间的耦合,对TDKA和TDIE进行混合迭代,既大大降低了粗糙面求解的复杂度,又保证了计算精度.数值算例中,考虑了角反射器(开放体)和圆柱(封闭体)两种目标,分别计算了目标表面电流响应和电场远场响应.计算结果表明,和单纯TDIE法相比,本文混合方法计算效率 关键词： 随机粗糙面 复合瞬态散射 时域积分方程法和时域基尔霍夫近似法 混合算法     

碳纳米管在肿瘤诊断与治疗研究中的新进展

碳纳米管具有独特的结构及性质,被广泛应用于生物医学领域.本文对碳纳米管在生物医学特别是肿瘤早期诊断以及治疗方面的研究现状进行了综述,分析了现有的研究特点,并展望了该领域的发展趋势.     

时域小波Galerkin法在有耗地面与任意目标复合散射中的应用

采用时域小波Galerkin(WGTD)方法计算了有耗地面与三维目标的复合散射,其中连接边界采用三波法.得到近场数据后,为避免复杂的Sommerfeld积分用互易原理简化了外推过程.计算了地面目标的雷达散射截面,验证了WGTD方法的精度和有效性.与时域有限差分方法相比,WGTD方法具有色散线性好、节省内存、计算速度快等优点. 关键词： 时域小波Galerkin法 复合散射 有耗半空间     

铟硼磷酸盐结构中的交叠生长规律研究(英)

Ｓｅｖｅｒａｌ ｉｎｄｉｕｍ ｂｏｒｏｐｈｏｓｐｈａｔｅｓ ｈａｖｅ ｂｅｅｎ ｒｅｐｏｒｔｅｄ ｒｅｃｅｎｔｌｙ, ｉｎｃｌｕｄｉｎｇ ＫＩｎ[ＢＰ_２Ｏ_８(ＯＨ)](Ⅰ) ａｎｄ ＮａＩｎ[ＢＰ_２Ｏ_８(ＯＨ)](Ⅱ)． Ｔｈｅ ｌａｔｔｅｒ ｔｗｏ ｃｏｍｐｏｕｎｄｓ ｗｅｒｅ ｓｙｎｔｈｅｓｉｚｅｄ ｕｎｄｅｒ ｍｉｌｄ ｈｙｄｒｏｔｈｅｒｍａｌ ｃｏｎｄｉｔｉｏｎｓ, ａｎｄ ｈａｖｅ ｔｈｅ ｓａｍｅ ｍｏｌａｒ ｒａｔｉｏ (Ｍ^Ⅰ∶Ｉｎ∶Ｂ∶Ｐ∶Ｏ∶Ｈ) ｉｎ ｍｏｌｅｃｕｌａｒ ｆｏｒｍｕｌａ ｂｕｔ ｗｉｔｈ ｄｉｆｆｅｒｅｎｔ ｓｔｒｕｃｔｕｒｅ ｔｙｐｅｓ． Ｃｏｍｐｏｕｎｄ Ⅰ ｃｒｙｓｔａｌｌｉｚｅｓ ｉｎ ｔｈｅ ｔｒｉｃｌｉｎｉｃ ｓｙｓｔｅｍ ｗｉｔｈ ｓｐａｃｅ ｇｒｏｕｐ P1 (Ｎｏ．２), ａ＝０．５２６３８(４) ｎｍ, ｂ＝０．８４７９１(５) ｎｍ, ｃ＝０．８１４６９(９) ｎｍ, α＝９１．１７４１(７) °, β＝９３．０６１(７) °, γ＝７９．８２３(５) °, Ｖ＝０．３５７３ ｎｍ^３, Ｚ＝２; ｗｈｉｌｅ ｃｏｍｐｏｕｎｄ Ⅱ ｐｏｓｓｅｓｓｅｓ ａ ｍｏｎｏｃｌｉｎｉｃ ｓｔｒｕｃｔｕｒｅ ｗｉｔｈ ｓｐａｃｅ ｇｒｏｕｐ Ｐ２_１／ｎ (Ｎｏ．１４) ｗｉｔｈ ａ＝０．５１７７(１) ｎｍ, ｂ＝１．６８１５(３) ｎｍ, ｃ＝０．７６８４(２) ｎｍ, β＝９４．１０(３) °, Ｖ＝０．６６７２(２) ｎｍ^３, Ｚ＝４． Ｅｉｇｈｔ-ｍｅｍｂｅｒｅｄ-ｒｉｎｇ ａｎｄ ｓｉｘ-ｍｅｍｂｅｒｅｄ-ｒｉｎｇ ａｒｅ ｆｏｒｍｅｄ ｂｙ ａｌｔｅｒｎａｔｉｎｇ ｂｏｒａｔｅ, ｐｈｏｓｐｈａｔｅ ｔｅｔｒａｈｅｄｒａ ａｎｄ Ｉｎ-ｃｏｏｒｄｉｎａｔｉｏｎ ｏｃｔａｈｅｄｒｏｎ ｓｈａｒｉｎｇ ｃｏｒｎｅｒｓ ｖｉａ ｃｏｍｍｏｎ ｏｘｙｇｅｎ ａｔｏｍｓ ｉｎ ｃｏｍｐｏｕｎｄ Ⅰ ａｎｄ Ⅱ ｒｅｓｐｅｃｔｉｖｅｌｙ． Ｔｈｅ ｐｏｌｙｈｅｄｒａ ｉｎ ｔｈｅ ｓｔｒｕｃｔｕｒｅ ａｒｅ ｏｒｉｅｎｔｅｄ ａｌｏｎｇ ｃｅｒｔａｉｎ ｄｉｒｅｃｔｉｏｎ ｔｏ ｆｏｒｍ ａｌｔｅｒｎａｔｉｎｇ ｌａｙｅｒｅｄ ｆｒａｇｍｅｎｔｓ． Ｔｈｅｓｅ ｔｗｏ ｓｔｒｕｃｔｕｒｅ ｔｙｐｅｓ ｃａｎ ｂｅ ｃｏｎｓｉｄｅｒｅｄ ａｓ ｉｎｔｅｒｇｒｏｗｔｈ ｓｔｒｕｃｔｕｒｅｓ, ｗｈｉｃｈ ｃｏｎｓｉｓｔ ｏｆ ｔｈｅ ｓａｍｅ ｌａｙｅｒｅｄ ｆｒａｇｍｅｎｔｓ ｇｒｏｗｉｎｇ ｉｎ ｄｉｆｆｅｒｅｎｔ ｏｒｉｅｎｔａｔｉｏｎｓ． Ｏｔｈｅｒ ｓｔｒｕｃｔｕｒｅ ｉｎｔｅｒｇｒｏｗｔｈ ｐｏｓｓｉｂｉｌｉｔｉｅｓ ａｒｅ ａｌｓｏ ｅｘｐｅｃｔｅｄ ｉｎ ｓｉｍｉｌａｒ ｓｙｓｔｅｍｓ． ＣＳＤ: Ⅰ, ４０９５８３; Ⅱ, ４１３３４３．     

元素分析-同位素比质谱法测定葡萄酒中乙醇δ 13C值

比较了旋转蒸发仪、全玻璃蒸馏装置和全自动蒸馏控制系统3种蒸馏方法,对葡萄酒乙醇δ13C值的影响,确定了元素分析-同位素比质谱仪(Elementary analysis-isotope ratio mass spectrometer)最佳测定条件,建立了元素分析-同位素比质谱法测定乙醇δ13C值方法。在重复性和再现性条件下,对乙醇标准及葡萄酒乙醇δ13C值进行测定,标准偏差低于0.25‰。检测食品同位素分析技术-能力测试计划(FIT-PTS)两个葡萄酒样品乙醇δ13C值,与给定值相差0.2‰。采用液相色谱-同位素比质谱法(Liquid chromatography-isotope ratio mass spectrometry)与本方法分别对16个国家和地区40个葡萄酒样品的乙醇δ13C值测定,其结果为!23.90‰~28.29‰,且两种检测方法的检测结果差值︳Δδ(EA-LC)max︳<0.3‰,具有较强的相关性(R2=0.9749)。本方法无同位素分馏,适用于葡萄酒中乙醇δ13C值测定。     

DFT study of self-coupling reaction of CF2(ads) coadsorbed on Cu(111) surface for forming CF2=CF2(g)

Total energy calculations based on the density functional theory (DFT) with ultrasoft pseudopotential, generalized gradient spin-polarized approximation and the partial structural constraint path minimization (PSCPM) method were carried out to establish the energetically more favorable reaction pathways for the self-coupling reaction of coadsorbed CF_2(ads) leading to the formation of CF₂=CF_2(ads) on the Cu(111) surface. In addition, the calculated electronic properties, namely partial density of states (PDOS), suggest that the initial breaking of the Cu(111)–CF_2(ads) bond associating with the electron delocalization on the Cu(111) surface and the electron transfer from Cu(111) to both units of CF_2(ads) are factors controlling the energy barrier for self-coupling reaction. Finally, the calculated energy barrier (0.310 eV) for the self-coupling reaction of CF_2(ads) coadsorbed on the Cu(111) surface in comparison with that (0.204 eV) for the single α-fluoride elimination of adsorbed CF_3(ads) on the Cu(111) surface qualitatively manifests that the formation of CF₂ = CF_2(g) at 250 K is limited by the self-coupling reaction of coadsorbed CF_2(ads) instead of the single α-fluoride elimination of adsorbed CF_3(ads).     

Vanadium-based Mixed Oxides Prepared from Thermal Decomposition of Citratorvanadium(IV) Precursor

Citrate method is broadly used for the preparation of mixed oxides and their highly dispersive pure phases^[1]. Up to now, most of the mixed oxides are prepared from putting the related chemical compounds together and sintering the mixture at high temperature, while the complexes formed during this process are uncertain. This will limit the design of high dispersibility and the purities of the resulted mixed oxides. Vanadium-based oxides are catalysts used in the partial oxidation of propane and butane. It has been demonstrated previously that the vanadium citrate complex with well-defined composition and structure is the better precursors for the preparation of V-based mixed oxide^[2], Using the precursor of barium dimeric(citrato) oxovanadium(IV) tetrahydrates Ba₂[VO(cit)]₂·4H₂O, barium pyrovanadate may be prepared with pre-determinated compositions and higher purities from thermal decomposition of the well-defined complexes at lower temperature.     

乙二醇辅助水热法制备不同形貌的CaTiO_3/CaTiO_3:Pr微晶

对乙二醇存在下水热法制备CaTiO3微晶的形貌进行了研究。对所得样品用X射线衍射、扫描电子显微镜(SEM)、热重分析及红外光谱(FTIR)进行了表征。结果表明,制备的CaTiO3微晶随着乙二醇和水配比的不同,可以形成立方体、三维十字架形及正十二面体等规整的外形。乙二醇在晶粒表面的配位吸附对这些不同形貌的形成有决定的作用。所得样品粒度分布均匀,基本不团聚。掺杂少量Pr3+离子后对样品的微观形貌基本不影响,在200℃低温水热获得的CaTiO3∶Pr样品就有明显的荧光和长余辉发光性能。样品在900℃煅烧后其外形并不发生变化,也不会团聚,但发光性质得到大幅度提高。     

中药透皮剂的研究

透皮给药比口服和注射给药具有避免肝脏首过效应、避免胃肠道降解、避免皮肤损伤、释药速率稳定、血药浓度可控,毒副作用小,停、用药方便和给药频率低等优点,利于长期治疗。本实验中草药组成复方以水提醇沉法、回流法、浸制法制得浸膏,采用改良的Franz扩散装置,以离体鸡皮为屏障生理盐水为接受介质,用紫外分光光度法测定中药复方在不同条件下的吸光度,来判断其透皮效果。结果表明,回流法制得透皮剂浸膏的吸光度最大。回流法所制透皮剂渗透效果最佳,随着时间的延长,渗透效果不断加强,其透皮效果明显优于水提醇沉法和浸渍法;水提醇沉法和浸渍法所制透皮剂效果不显著。