沉积在液相基底表面磁性薄膜的形成机理和特性研究

采用气相沉积方法在硅油基底表面成功制备了一种具有近似自由支撑的新型铁薄膜系统，并研究了其生长机制、内应力分布以及低温磁特性．实验发现，此类铁薄膜的生长机制与沉积在液相基底表面非磁性薄膜的情况类似，即服从二阶段生长模型．在固定基底温度的条件下，当沉积速率较小时，可制得近似透明的连续铁薄膜，薄膜中呈现明显的特征尺寸达10^2μm数量级的带状准周期有序结构，它是由铁薄膜样品中内应力释放时所引起的薄膜板块间相互挤压而逐渐形成的．当沉积速率较大时，制得的连续铁薄膜呈金属色．实验发现，在临界温度Tc=10—15K附近，具有金属色的铁薄膜样品的矫顽力Hc有一明显的极大值峰．研究表明，这一奇异的矫顽力特性与液相基底表面铁薄膜中的原子团簇尺寸分布、无序的薄膜表面磁各向异性以及团簇间的磁性相互作用等因素有关．     

受火作用铝合金梁的临界温度及其参数分析

基于ANSYS数值模拟结果,首次对铝合金梁在火荷载作用下的响应行为进行模拟。系统比较了简支、铰支、固支、一端固支另一端简支等几种典型边界约束条件下铝合金梁的抗火特性,着重讨论了各自的临界温度并与已有规范进行了对比,在此基础上考察了端部约束条件、载荷比、载荷类型等因素对铝合金梁弯曲屈曲失效行为的影响。结果表明:设计规范公式计算出的临界温度偏于保守,比有限元结果低2.5%~16.7%,而有限元更能反映真实情况;对于不同的约束情形,铰支梁的抗火能力最强,其次是固支梁,简支梁的抗火能力最差;载荷比越大,铝合金梁的临界温度越低,抗火能力越弱,载荷比由0.3增加到0.7时,简支梁和一端固支另一端简支梁的临界温度减小约43℃,固支和铰支梁的临界温度分别减小37℃和30℃;载荷类型对铝合金梁的影响较小。本文研究为铝合金结构抗火设计提供了理论依据。     

百年超导,魅力不减

超导电性发现已有百年了,它已经成为物理学中的一个重要分支,与超导有关的诺贝尔奖已经授予了5次.超导电性的应用也已在许多方面发挥着不可替代的作用.100年虽然已经过去,但人们对超导研究的兴趣依然未减.例如,虽然很多一流的物理学家都在努力,但铜氧化合物超导体以及新发现的     

神奇的超导

 电阻起源于载流子(电子或空穴)在材料中运动过程中受到的各种各样的阻尼.按照材料的常温电阻率从大到小可以分为绝缘体、半导体和导体.绝大部分金属都是良导体,他们在室温下的电阻率非常小但不为零,在10^-12 mΩ·cm量级附近.自然界是否存在电阻为零的材料呢？答案是肯定的,这就是超导体.当把超导材料降到某个特定温度以下的时候,将进入超导态,这时电阻将突降为零(图1),同时所有外磁场磁力线将被排出超导体外,导致体内磁感应强度为零,即同时出现零电阻态和完全抗磁性.超导态开始出现的温度一般称为超导临界温度,表示为T_c.微观上来说,当超导材料处于超导临界温度之下时,材料中费米面附近的电子将通过相互作用媒介而两两配对,这些电子对将同时处于稳定的低能组态,叫“凝聚体”.在外加电场驱动下,所有电子对整体能够步调一致地运动,因此超导又属于宏观量子凝聚现象.对于零电阻态,实验上已经证实超导材料的电阻率小于10^-23 mΩ·cm,在实验精度允许范围内已经可以认为是零.如果将超导体做成环状并感应产生电流,电流将在环中流动不止且几乎不衰减.超导体的完全抗磁性并不依赖于超导体降温和加场的次序,也称为迈斯纳(Meissner)效应.一个材料是否为超导体,零电阻态和完全抗磁性是必须同时具有的两个独立特征.     

1,3,3-三硝基氮杂环丁烷的热安全性

借助不同加热速率(β)的非等温DSC曲线离开基线的初始温度(T₀)、onset温度(T_e)和峰顶温度(T_p), Kissinger法和Ozawa法求得的热分解反应的表观活化能(E_k和E_O)和指前因子(A_k), Hu-Zhao-Gao方程ln β_i＝ln[A₀/(b_{e0 or p0}G(α))]＋   b_{e0 or p0}T_{ei or pi}求得的b_{e0 or p0}, Zhao-Hu-Gao方程ln β_i＝ln[A₀/((a_{e0 or p0}＋1)G(α))]＋(a_{e0 or p0}＋1) ln T_{ei or pi}求得的a_{e0 or p0}, 微热量法确定的比热容(C_p), 以及密度(ρ)、热导率(λ)和分解热(Q_d, 取爆热之半)数据, Zhang-Hu-Xie-Li公式、Hu-Yang-Liang-Xie公式、Hu-Zhao-Gao公式、Zhao-Hu-Gao公式、Smith方程、Friedman公式和Bruckman-Guillet公式, 计算了TNAZ在β→0时的T₀, T_e和T_p值(T₀₀, T_eo和T_p0)、热爆炸临界温度(T_be和T_bp)、绝热至爆时间(t_Tlad)、撞击感度50%落高(H₅₀)和热点起爆临界温度(T_cr), 得到了评价TNAZ热安全性的结果: T_SADT＝T_e0＝485.81 K, T_p0＝497.38 K, T_beo＝499.50 K, T_bp0＝513.45 K, t_Tlad＝8.90 s (n＝0), t_Tlad＝8.96 s (n＝1), t_Tlad＝9.01 s (n＝2), H₅₀＝28.88 cm, T_cr＝641.46 K (T_room＝293.15 K), T_cr＝658.89 K (T_room＝300 K), 表明: (1) TNAZ对热是稳定的; (2)撞击感度好于环三亚甲基三硝胺(RDX); (3)热点起爆临界温度高于RDX, 而界于1,3,5-三氨基-2,4,6-三硝基苯(TATB)和六硝基茋(HNS)之间.     

Entanglement in a two-qubit Heisenberg XXZ chain with different Dzyaloshinskii-Moriya couplings and an inhomogeneous magnetic field

Ground state entanglement and thermal entanglement of a two-qubit Heisenberg XXZ chain in the presence of the different Dzyaloshinski-Moriya interaction and inhomogeneous magnetic field are investigated.By the concept of concurrence,we find that the inhomogeneity of the magnetic field may make entanglement last for a long time and the critical temperature is dependent on Jz and b.The entanglement can be increased by increasing the temperature in some cases.We also find that the x-component parameter Dx has a higher critical temperature and more entanglement for a certain condition than the z-component parameter Dz.     

随机边界对相对论气体玻色-爱因斯坦凝聚临界温度的影响

研究了随机边界对立方箱中相对论气体玻色-爱因斯坦凝聚临界温度的影响.在均匀分布、双模分布和高斯分布情况下,分别计算了临界温度与固定箱中的气体临界温度的比值,发现随机边界降低了系统的临界温度.相对于极端相对论情况,非相对论极限下的临界温度更低.     

Critical Temperature Characteristics of Layered High-Temperature Superconductor Under Pressure

We consider a Ginzburg-Landau modified model of layered high-temperature superconductor under pressure. We have theoretically studied the relation between the pressure and the temperature of layered high-temperature superconductor. If the pressure is not a constant, we have a relation of quadratic equation between the pressure and the temperature of layered high-temperature superconductor. In a special case, we find the critical temperature decreases with further increasing pressure. In another special case, the critical temperature increases with furtherincreasing pressure.     

液体的表面张力与内压

在利用Onsager模型推导液体表面张力与内压间的关系时, 文献[4]忽视了曲率对表面张力的影响, 致使计算值与实验值的偏差较大。本文对此作了修正, 建立了一个新的关系式, 用实验数据检验表明, 它能满意地适用于广阔温度范围内的各种液体。     

气体临界温度以上吸附平衡的预测研究

Experimental adsorption isotherms of CH4 and N2 higher than critical temperatures on K02 activated carbon were measured with the volumetric method The pressure and temperature ranges were 0～12 MPa and 273～333 K respectively. A model, which took into account the adsorbate properties above critical temperatures and the adsorbent surface heterogeneity by pore size distribution, was proposed in this paper to predict the equilibrium data only using one adsorption isotherm. The gamma distribution was adopted to express the pore size distribution of the activated carbon, and the adsorption potential was calculated bythe 10-4-3 equation for slit shape micro pores. The relationships between the adsorbate density, the saturated adsorption amount and the equilibrium temperature have been discussed in detail. Through this method, the experimental adsorption data of CH4 and N2 were compared with the prediction equilibria. The study illustrates that the predicting method could present the adsorption equilibria accurately in the whole research range. And the mean relative deviations of the prediction of CH4 and N2 are only about 1.9% and 2.9%. This proves that the analyses of the adsorbate properties are reasonable. Inaddition, the model was applied to calculating the equilibrium data of various supercritical adsorption systems published in literatures. Despite different adsorbents and equilibriaconditions, the investigation results demonstrate that the suggested model performs well in predicting the gases adsorption equilibrium data with all mean relatived eviations less than 6.8%. Therefore, the model could be utilized to calculate the gases adsorption equilibrium data above critical temperatures in a wide range.