单面完整约束力学系统的形式不变性

研究单面完整约束力学系统的形式不变性.根据运动微分方程的形式在无限小变换下的不变性，给出了单面完整约束力学系统形式不变性的定义和判据，建立了系统的形式不变性与Noether对称性、Lie对称性之间的关系，并举例说明结果的应用. 关键词： 分析力学 单面约束 形式不变性 Lie对称性 Noether对称性 守恒量     

奇异变质量单面非完整系统Nielsen方程的Noether-Lie对称性与守恒量

在群的无限小变化下, 研究奇异变质量单面非完整系统Nielsen方程的Noether-Lie对称性. 建立系统运动微分方程的Nielsen形式, 给出系统Nielsen方程的Noether-Lie对称性的定义、判据和命题, 得到系统Nielsen 方程的Noether-Lie对称性所导致的Noether守恒量和广义Hojman守恒量. 最后给出说明性算例说明结果的应用. 关键词： 奇异变质量系统 单面非完整约束 Nielsen方程 Noether-Lie对称性     

含时滞的非保守系统动力学的Noether对称性

提出并研究含时滞的非保守系统动力学的Noether对称性与守恒量. 首先,建立含时滞的非保守系统的Hamilton原理,得到含时滞的Lagrange方程;其次,基于含时滞的Hamilton作用量在依赖于广义速度的无限小群变换下的不变性,定义系统的Noether对称变换和准对称变换,建立Noether对称性的判据;最后,研究对称性与守恒量之间的关系,建立含时滞的非保守系统的Noether理论. 文末举例说明结果的应用. 关键词： 时滞系统 非保守力学 Noether对称性 守恒量     

约束系统的对称变换

对于用非独立态函数描述的受约束系统,在对称变换下将导致推广的Noether定理,一般说,此时不产生Noether定理的守恒量,在有限约束下内部对称变换的推广Noether定理,就化为通常Noether定理的结果。 关键词：     

单面Chetaev型非完整系统的共形不变性、Noether对称性和Lie对称性

研究单面Chetaev型非完整系统在无限小变换下的共形不变性及其与Noether对称性和Lie对称性的关系. 首先,给出了单面Chetaev型非完整系统的共形不变性的定义; 其次,研究了系统的共形不变性与Noether对称性之间的关系;最后, 研究了系统的共形不变性与Lie对称性之间的关系,得到了共形不变性同时是Lie 对称性导致的Hojman守恒量.最后分别举例说明了结果的应用.     

离散差分变分Hamilton系统的Lie对称性与Noether守恒量

研究离散差分Hamilton系统的Lie对称性与Noether守恒量. 根据扩展的时间离散力学变分原理构建Hamilton系统的差分动力学方程.定义离散系统运动差分方程在无限小变换群下的不变性为Lie对称性, 导出由Lie对称性得到系统离散Noether守恒量的判据. 举例说明结果的应用. 关键词： 离散力学 差分Hamilton系统 Lie对称性 Noether守恒量     

非保守力与非完整约束对Lagrange系统Noether对称性的影响

研究非保守力和非完整约束对Lagrange系统的Noether对称性的影响. Lagrange系统受到非保守力或非完整约束作用时，系统的Noether对称性和守恒量都会发生变化. 原有的一些Noether对称性消失了，一些新的Noether对称性产生了，在一定条件下，一些Noether对称性仍保持不变. 分别给出系统的Noether对称性以及守恒量保持不变的条件，并举例说明结果的应用. 关键词： Lagrange系统 非保守力 非完整约束 Noether对称性     

相空间中单面完整约束力学系统的对称性与守恒量

在增广相空间中研究单面完整约束力学系统的对称性与守恒量.建立了系统的运动微分方程；给出了系统的Norther对称性，Lie对称性和Mei对称性的判据；研究了三种对称性之间的关系；得到了相空间中单面完整约束力学系统的Noether守恒量以及两类新守恒量——Hojman守恒量和Mei守恒量，研究了三种对称性和三类守恒量之间的内在关系.文中举例说明研究结果的应用. 关键词： 分析力学 单面约束 对称性 守恒量 相空间     

约束对Birkhoff系统Noether对称性和守恒量的影响

研究约束对Birkhoff系统的Noether对称性和守恒量的影响．首先，建立了Birkhoff系统的运动微分方程．其次，给出了系统Noether对称性的判据．然后，讨论了受约束作用后，Birkhoff系统的Noether对称性发生的变化，并给出了系统的Noether对称性以及守恒量保持不变的条件．最后，举例说明结果的应用． 关键词： 分析力学 Birkhoff系统 约束 Noether对称性 守恒量     

单面非Chetaev型非完整约束系统的非Noether守恒量

研究单面非Chetaev型非完整约束力学系统的对称性与非Noether守恒量.建立了系统的运动微分方程；给出了系统的Lie对称性和Mei对称性的定义和判据；对于单面非Chetaev型非完整系统，证明了在一定条件下，由系统的Lie对称性可直接导致一类新守恒量——Hojman守恒量，由系统的Mei对称性可直接导致一类新守恒量——Mei守恒量；研究了对称性和新守恒量之间的相互关系.文末，举例说明结果的应用. 关键词： 分析力学 单面约束 非完整系统 对称性 Hojman守恒量 Mei守恒量     

Crystallization of Ge2Sb2Te5 phase—change optical disk media

In this paper, the crystallization behaviour of amorphous Ge₂Sb₂Te₅ thin films is investigated using differential scanning calorimetry), x-ray diffraction and optical transmissivity measurements. It is indicated that only the amorphous phase to face-centred-cubic phase transformation occurs during laser annealing of the normal phase-change structure, which is a benefit for raising the phase-change optical disk's carrier-to-noise ratio (CNR). For amorphous Ge₂Sb₂Te₅ thin films, the crystallization temperature is about 200℃ and the melting temperature is 546.87℃. The activation energy for the crystallization, E_a, is 2.25eV. The crystallization dynamics for Ge₂Sb₂Te₅ thin films obeys the law of nucleation and growth reaction. The sputtered Ge₂Sb₂Te₅ films were initialized by an initializer unit. The initialization conditions have a great effect on the reflectivity contrast of the Ge₂Sb₂Te₅ phase-change optical disk.     

Invariance of the Massless Field Equations under Changes of the Metric

It is shown that the Maxwell equations with sources, expressed in terms of the covariant tensor field F_ijand the current density four-vector Jⁱ, are invariant under the change of the metric g_ijby g_ij = g_ij+ l_il_jif l_iis a principal null direction of F_ijand that an analogous result holds in the case of the massless Klein-Gordon equation if l_iis null and orthogonal to the gradient of the field and in the case of the null dust equations if l_iis parallel to the dust four-velocity. An elementary proof of the following generalization of the Xanthopoulos theorem is also given: Let (g_ij, F_ij) be an exact solution of the Einstein-Maxwell equations and let l_ibe a principal null direction of F_ij, then (g_ij+ l_il_j, F_ij) is also an exact solution of the Einstein-Maxwell equations if and only if (l_il_j, 0) satisfies the Einstein-Maxwell equations linearized about the background solution (g_ij, F_ij). Furthermore, analogous theorems, where the source of the gravitational field is a massless Klein-Gordon field or null dust, are presented.     

Simultaneous formation of contacts and diffusion barriers for VLSI by rapid thermal silicidation of TiW

The formation of (Ti_xW_1–x)Si₂/(Ti_xW_1–x)N, by rapid thermal processing of Ti_xW_1–x on Si in an N₂ ambient is investigated. An activation energy of 1.7 eV is obtained for silicide formation. A distinct snow-ploughing of As atoms is observed during silicide formation whereas the interfacial B concentration decreases with increasing silicide formation temperature. The diffusion barrier properties of the (Ti_xW_1–x)Si₂/(Ti_xWi_1–x)N stack in contact with Al is investigated upon post-metal annealing. No interaction between the layers is found for temperatures as high as 475°C after 60 min. The improved thermal stability of the (Ti_xW_1–x)N layer in contact with Al is attributed to nitrogen blocking of the grain boundaries.     

氧化石墨烯负载的Pt单原子催化硼胺烷水解机理的理论研究

本文研究了氧化石墨烯负载Pt单原子(Pt₁/Gr-O)催化硼胺烷(NH₃BH₃)全水解反应机理,即一分子的NH₃BH₃生成三分子的氢气(H₂)的过程. 在水解路径中,首先吸附的硼胺烷连续断裂两个B-H键生成第一分子的H₂. 接着,一个H₂O分子与^*BHNH₃基团(^*表示吸附态)反应生成^*BH(H₂O)NH₃,其中伸长的O-H键断裂后形成^*BH(OH)NH₃. 然后,第二个H₂O与^*BH(OH)NH₃反应生成^*BH(OH)(H₂O)NH₃,在指向Pt₁/Gr-O表面的O-H断裂后,生成BH(OH)₂NH₃并脱附到水溶液中. 两个水分子脱氢产生的两个H原子脱附生成第二个H₂分子,且Pt₁/Gr-O催化剂恢复. 脱附后的BH(OH)₂NH₃在水溶液中水解生成第三个H₂分子. 纵观整个水解反应,H₂O分子和^*BHNH₃基团的结合是反应速控步,其反应能垒是16.1 kcal/mol. 因此,Pt₁/Gr-O有希望成为室温催化NH₃BH₃全水解催化剂.     

非晶态Cu56Zr44合金的结构及其等温退火晶化过程的研究

利用X射线衍射技术、差示扫描量热分析技术和透射电子显微镜研究了非晶态Cu₅₆Zr₄₄合金的结构及其等温退火条件下的晶化过程.实验结果表明,非晶态Cu₅₆Zr₄₄合金在室温下的短程结构类似于硬球无规密堆积分布.在703K过冷液相区内等温退火时发现,当退火时间为3min时,晶化产物主要为Cu₈Zr₃相;当退火时间为6min时,Cu₈Zr₃关键词： 非晶态 56Zr₄₄合金')" href="#">Cu₅₆Zr₄₄合金 结构 等温退火     

Effects of oblique-incidence evaporation on magnetic properties of Fe20Ni80/Fe70Co30 bilayer film

Evaporative deposition at oblique incidence is shown to enhance the magnetic anisotropy of an Fe₂₀Ni₈₀ magnetic film and induce magnetic anisotropy in an overlying, strongly isotropic Fe₇₀Co₃₀ film. This deposition method for the formation of an underlayer of several lattice parameters in thickness and semi-hard overlayer of a few thousands Angstroms in thickness achieves a significant change in the magnetization process and strong suppression of the coercive forces of Fe₇₀Co₃₀ in the hard magnetization direction. Soft magnetization of the Fe₇₀Co₃₀ overlayer is not achieved when one of the layers is deposited at oblique incidence. It is anticipated that shape magnetic anisotropy is responsible in part for the magnetic anisotropy induced in both in Fe₂₀Ni₈₀ under- and Fe₇₀Co₃₀ overlayer by oblique incidence evaporation.     

Response improvement for In2O3-TiO2 thick film gas sensors

In₂O₃ is introduced into TiO₂ by sol-gel method to improve the response/recovery rate and expand the operating temperature, when the In₂O₃-TiO₂ mixed system is exposed to H₂/O₂. The sensor is fabricated by thick film technology. Influence of In₂O₃ on the film phase composition, microstructure and sensing characteristics is discussed. Dynamic response properties show that the operating temperature of the mixed system is at 500-800 °C, which is about 600-800 °C for pure TiO₂. Response time of the sensor is about 200-260 ms (millisecond) while recovery time is in a narrow range of 60-280 ms at 600-800 °C. The promoting mechanism is suggested to arise from the introduction of In₂O₃ and grain size effect of the sensing film. Then In₂O₃-TiO₂ thick films are surface-modified by Pt using chloroplatinic acid. The promoting effect of Pt dispersed on the mixed system is also investigated.     

包钴型γ-Fe2O3磁粉矫顽力的研究

包钴型γ-Fe₂O₃磁粉分为包钴γ-Fe₂O₃(简记为Co-γ-Fe₂O₃)和包钴包亚铁γ-Fe₂O₃(简记为CoFe-γ-Fe₂O₃)两种,它们的矫顽力可比γ-Fe₂O₃磁粉的提高100至400Oe左右,本工作对这两种磁粉矫顽力增大的原因作了探讨,认为它们矫顽力增大的机制不同:CO-γ-Fe₂O₃矫顽力增大是由于表面包覆一层Co(OH)₂使表面各向异性增大,而CoFe-γ-Fe₂O₃则是由于表面包覆的是钴铁氧体,γ-Fe₂O₃与钴铁氧体之间发生耦合作用,使矫顽力增大。     

在氧-水蒸气存在下单相Sr2(Gd,Ce)2Cu2RuO10的合成及其电学性质

传统固相反应所合成的锶系钌铜氧化物，通常总伴有少量铁磁性SrRuO₃杂相.采 用氧(或空 气)_水蒸气混合气氛下的新型固相反应，既能成功合成锶系钌铜氧化物的前驱物纯相Sr₂G dRuO₆(211相), 也能进一步在相对低的温度下成功合成锶系钌铜氧1222纯相化 合物RuSr₂(Gd,Ce)₂Cu₂O₁₀ (Ru_1222）， 使其中SrRuO _{关键词： 水蒸气参与的新型固相反应 2}(Gd')" href="#">RuSr₂(Gd 2Cu_{2< /sub>O10纯相')" href="#">Ce)2Cu2< /sub>O10纯相 3杂相')" href="#">SrRuO3杂相 电学性质}     

Comprehensive evolution mechanism of SOx formation during pyrite oxidation

Pyrite (FeS₂) oxidation during coal combustion is one of the main sources of harmful SO₂ emission from coal-fired power plants. Density functional theory (DFT) study was performed to uncover the evolution mechanism of SO_x formation during pyrite oxidation. The results show that chemisorption mechanism is responsible for O₂, SO₂ and SO₃ adsorption on FeS₂ surface. The presence of formed oxidation layer (Fe₂O₃) weakens the interaction between O₂ molecule and FeS₂ surface. The adsorbed O₂ molecule easily dissociates into active surface O atom for SO_x formation. The dissociation reaction of O₂ is activated by 77.38?kJ/mol, and exothermic by 138.46?kJ/mol. Compared to the further oxidation of SO₂ into SO₃, SO₂ prefers to desorb from FeS₂ surface. The dominant reaction pathway of SO₂ formation from the oxidation of the outermost FeS₂ surface layer is a three-step process: surface lattice S oxidation, SO₂ desorption and replenishment of S vacancy by activated surface O atom. The elementary reaction of surface lattice S oxidation has an activation energy barrier of 197.96?kJ/mol, and is identified as the rate-limiting step. SO₂ formation from the further oxidation of bulk FeS₂ layer is controlled by a four-step process: bulk lattice S migration, lattice S oxidation, SO₂ desorption and surface O atom deposition. Migration of lattice S from bulk position to the outermost surface shows a high activation energy barrier of 175.83?kJ/mol. The deposition process of surface O atom is a relatively easy step, and is activated by 21.05?kJ/mol.