块体非晶合金的黏度与玻璃形成能力的关系

基于经典结晶理论讨论了非晶合金的晶化动力学因素和晶化热力学因素对玻璃形成能力（GFA）的影响.分析表明,合金的等温转变（TTT）曲线“鼻尖”温度T_n对应的黏度与晶化阻力因子成正比;重新加热时晶化开始温度T_x对应的黏度与晶化驱动力因子成反比.由此得到了新的GFA参数ω₀=（T_g-T₀）/（T_x-T₀）-（T_g-T₀）/（T_n-T₀）,其中T_g为玻璃转变温度,T₀为理想玻璃转变温度.统计结果显示,ω₀与临界冷却速率具有较高的相关性,R²高达09626.进一步分析表明：新提出的ω₀参数可以合理地解释过冷熔体的黏度、脆性、液相稳定性、热稳定性以及T_rg、ΔT_x、γ、γ_m、ΔT_rg、α、β、δ和φ等参数与GFA的关系. 关键词： 块体非晶合金 黏度 脆性 玻璃形成能力     

基于拓扑结构的碱金属化合物摩尔磁化率的支持向量回归研究

基于经典电动力学导出的表征简单离子磁化率的磁性点价g_i所构建的分子磁性连接性指数?^mF及45种碱金属化合物的摩尔磁化率χ_m的实测数据集,利用粒子群寻优的支持向量回归（SVR）方法,建立了基于⁰F和¹F的碱金属化合物χ_m的预测模型,并与基于多元线性回归（MLR）模型的计算结果进行了比较.结果显示,基于9次交叉验证的SVR模型预测的平均绝对误差、平均相对误差绝对值以及均方根误差均比MLR模型小,表明SVR模型的回归预测能力优于MLR.研究表明,磁性连接性指数^mF是一种合适的分子描述符,SVR是一种预测碱金属化合物χ_m的有效方法. 关键词： 碱金属化合物 摩尔磁化率 支持向量回归 预测     

Cu1-xHxZr2(PO4)3中Cu2+的EPR谱和局域结构研究

本文采用Cu²⁺斜方对称电子顺磁共振（EPR）参量的高阶微扰公式计算了晶体Cu_1-xH_xZr₂（PO₄）₃中Cu²⁺的EPR参量（g因子和超精细结构常数A因子）．计算结果表明，晶体Cu_1-xH_xZr₂（PO₄）₃中[CuO₆]^10-基团的Cu-O键长分别为R_||≈0.241 nm，R_⊥≈0.215 nm，平面键角τ≈80.1°；由于对称性降低，中心金属离子基态²A_1g（θ）和²A_1g（ε）有一定程度混合，混合系数α≈0.995．所得EPR谱图的理论计算值与实验数据符合得很好．     

用耦合簇方法及相关一致基研究PH$lt;sub$gt;2$lt;/sub$gt;($lt;i$gt;X$lt;/i$gt;$lt;sup$gt;2$lt;/sup$gt;$lt;i$gt;B$lt;/i$gt;$lt;sub$gt;1$lt;/sub$gt;)自由基的解析势能函数

利用耦合簇方法和Dunning等提出的系列相关一致基对PH₂自由基的基态结构进行优化, 并使用优选出的cc-pV5Z基组对其进行频率计算. 结果表明,平衡核间距R_P—H=0.14185 nm, 键角α_HPH=91.8624°, 离解能D_e（HP—H）=3.483 eV, 对称伸缩振动频率ν₁（a₁）=2399.9781 cm^-1, 弯曲振动频率ν₂（a₁）=1128.4213 cm^-1,反对称伸缩振动频率ν₃（b₂）=2407.8374 cm^-1. 在此基础上采用多体项展式理论导出了PH₂自由基的解析势能函数, 其等值势能图准确再现了PH₂自由基分子的平衡结构特征和动力学特征. 关键词： 2自由基')" href="#">PH₂自由基 多体项展式理论 解析势能函数     

Nd3+螯合物的含氢有机溶液光谱性能研究

研究了Nd(TTA)₃螯合物溶于二甲基甲酰胺溶剂的光谱性质，溶液中所有氢未置换为氘.测量了这种溶液体系的吸收谱、荧光谱和荧光寿命.在898和1058 nm波长处观察到明显的Nd³⁺荧光特征峰.用Judd-Ofelt理论对吸收谱进行分析计算，得到了三个强度参数Ω_t(t=2,4,6)分别为Ω₂=4.9×10^-20 cm², Ω₄=5.1×10^-20 cm²和Ω₆=2.5×10^-20 cm².利用强度参数计算了⁴F_3/2能级与⁴I_9/2和⁴I_11/2之间的跃迁强度S_ed、自发辐射系数A_ed以及荧光分支比β等，估算了⁴F_3/2能级的辐射跃迁寿命τ_r＝682 μs.实测1058和898 nm波长处荧光寿命τ大约为460和505 μs，因此荧光量子效率分别高达0.67和0.74.荧光量子效率高表明Nd³⁺在这种溶液中无辐射跃迁比较弱；强度参数Ω₂比较大，表明Nd³⁺在溶液中具有不对称配位场环境，不对称的配位场环境可大大促进Nd³⁺吸收激发能量.光谱质量因子Ω₄/Ω₆>1，使得898 nm的辐射强于1058 nm的辐射. 关键词： Nd 有机溶液 光谱性能 Judd-Ofelt理论     

用耦合簇理论及相关一致五重基研究SiH$lt;sub$gt;2$lt;/sub$gt;($lt;i$gt;X$lt;/i$gt;$lt;sup$gt;1$lt;/sup$gt;$lt;i$gt;A$lt;/i$gt;$lt;sub$gt;1$lt;/sub$gt;)自由基的解析势能函数

运用单双迭代三重激发耦合簇理论和相关一致五重基对SiH₂的基态结构进行了优化, 并在优化结构的基础上进行了离解能和振动频率的计算. 结果表明: SiH₂的基态为C_2v结构, 平衡核间距R_Si—H= 0.15163 nm, H—Si—H键的键角α=92.363°, 离解能D_e（HSi—H）=3.2735 eV, 频率ν₁（a₁）=1020.0095 cm^-1, ν₂（a₁）=2074.8742 cm^-1, ν₃（a₁）=2076.4762 cm^-1. 这些结果与实验值均较为相符. 对H₂的基态使用优选出的cc-pV6Z基组、对SiH的基态使用优选出的aug-cc-pV5Z基组进行几何构型与谐振频率的计算并进行单点能扫描, 且将扫描结果拟合成了解析的Murrell-Sorbie函数. 与实验结果及其他理论计算结果的比较表明, 本文关于SiH自由基光谱常数（D_e,R_e, ω_e, B_e, α_e和ω_eχ_e）的计算结果达到了很高的精度. 采用多体项展式理论导出了SiH₂（C_2v, X¹A₁）自由基的解析势能函数, 其等值势能图准确再现了它的离解能和平衡结构特征. 同时还给出了SiH₂（C_2v, X¹A₁）自由基对称伸缩振动等值势能图中存在的两个对称鞍点, 对应于SiH+H→SiH₂反应, 势垒高度为0.5084 eV. 关键词： 2')" href="#">SiH₂ Murrell-Sorbie函数 多体项展式理论 解析势能函数     

基态MgB2分子的结构与分析势能函数

应用群论及原子分子反应静力学方法推导MgB₂分子的电子状态及其离解极限,采用密度泛函B3LYP和从头计算QCISD方法在6-311++G**基组水平上,对MgB₂分子可能的状态进行优化计算,得出MgB₂的三重态能量最低,其稳定构型为C_2v,平衡核间距R_e=2.2977,键角α_BMgB=41.5521°,能量为-248.9645a.u.同时还计算了基态的简正振动频率:对称伸缩振动频率ν（B₂）=315.4430 cm^-1,反对称伸缩振动频率ν（A₁）=418.1883 cm^-1和弯曲振动频率ν（A₁）=968.9672 cm^-1.在此基础上,使用多体项展式理论方法,导出了基态MgB₂分子的解析势能函数,其等势面准确再现了基态MgB₂平衡结构和离解能,并由此讨论了B+MgB和Mg+BB分子反应的势能面静态特征. 关键词： 2')" href="#">MgB₂ 多体项展式理论 解析势能函数     

反应物NO的振动激发对反应C(3P)+NO(X2Π)→CO(X1Σ+)+N(2D)立体动力学性质的影响

采用准经典轨线方法研究碰撞能为0.23 eV时,反应物分子NO在不同初始振动态（v=0~3）下发生在两个电子态（²A″和²A'）势能面上反应C（³P）+NO（X²Π）→CO（X¹Σ⁺）+N（²D）的立体动力学性质。计算反应产物的转动角动量矢量分布（P（θ_r）和P（φ_r））以及微分散射截面（P₀₀（ω_t）,P₂₀（ω_t））。结果表明：反应物的振动激发对发生在²A'势能面上的反应立体动力学性质影响显著,而对发生在²A″势能面上的反应立体动力学性质影响较小,这可能与两个势能面的构型有关。在两个电子态势能面上发生的反应均受内平面反应机理支配。     

镁基合金自由枝晶生长的相场模拟研究

利用定量相场模型, 以Mg-0.5 wt.%Al合金为例模拟了基面((0001)面)内镁基合金的等温自由枝晶生长过程. 通过研究该合金体系数值模拟的收敛性, 获得了最优化值耦合参数λ = 5.5及网格宽度Δx/W₀ = 0.4, 并在该参数下系统研究了各向异性强度和过饱和度对枝晶尖端生长速度、尖端曲率半径、Péclet数及稳定性常数σ^* 的影响. 结果表明, 由微观可解性理论得到的稳定性系数σ^* 与ε₆ 拟合值σ^*≅ ε₆ ^1.81905, 更接近理想值σ ^* (ε₆) ≅ε₆ ^1.75. 此外, 当过饱和度Ω < 0.6时, 稳定性系数σ ^* 不随ε₆ 的变化而变化, 而当Ω > 0.6时, 稳定性系数σ ^* 随着ε₆ 的增加而减小. 这反映了枝晶的生长由扩散控制向动力学控制的转变. 随着过饱和度的增加, 枝晶形貌由雪花状枝晶向圆状枝晶转变.     

非对称量子点中磁极化子性质的磁场和温度依赖性

采用Tokuda线性组合算符法和Lee-Low-Pines变换法,研究了温度和磁场对非对称抛物量子点中强耦合磁极化子性质的影响,简捷地得到了作为量子点的横向受限强度ω₁、纵向受限强度ω₂、电子-声子耦合强度α、外磁场的回旋频率ω_c和温度参数γ的函数的磁极化子的振动频率λ、基态能量E₀和有效质量m 关键词： 非对称量子点 强耦合磁极化子 磁场和温度依赖性     

C2H221分子转动角动量定向分布(Orientation)及其碰撞弛豫和转移

利用圆偏振激光受激Raman抽运,以 C₂H₂分子为样品选择性地制备了它的电子基态单一转动态(X¹Σ⁺_g,ν″₂＝1,J″的角动量定向布居(orientation)．并从圆偏振紫外激光诱导的A¹A_u(ν′₃＝1)←X¹Σ⁺_g(ν″₂＝1)的荧光（谱）,直接测定了 C₂H₂(X¹Σ^＋_g,ν″₂＝1,J″＝4,7,8,…,13）的角动量定向布居值．从时间分辨的荧光信号谱测定了角动量定向布居的碰撞弛豫速率常数,同时还研究了由各初始激励的转动态向其他邻近转动态碰撞诱导的角动量定向布居转移． 关键词：     

高Jc Tl系2223相银包套带材的磁通钉扎和耗散

测量了Ｔｌ系２２２３相银包套超导带（Ｊ_c＝１．５×１０^４Ａ·ｃｍ^-2，７７Ｋ，０Ｔ）在０－０．８Ｔ磁场下电阻转变展宽，实验结果引用热激活磁通蠕动模型加以解释。磁场平行于带面（Ｈ∥ａｂ面）和磁场垂直于带面（Ｈ⊥ａｂ面）两种情况下，激活能与磁场之间满足幂指数关系：Ｕ_0∥＝０．２１ H^-0.3(eV),Ｕ_0⊥＝０．１5 H^-0.4(eV)，其中Ｈ的单位为ｋＧ。 关键词：     

三角对称下3d3离子2E态g因子性质研究

采用完全对角化方法,以尖晶石结构的ZnAl₂Ｏ₄:Cr^3＋,ZnGa₂Ｏ₄:Cr^3＋和MgAl₂Ｏ₄:Cr^3＋系列晶体为例,联系晶格局域结构,对三角对称下3d³离子²E态g因子性质进行了研究.研究中考虑了包括自旋与自旋相互作用、自旋与另一轨 关键词： 2E态g因子')" href="#">²E态g因子 3离子')" href="#">3d³离子 尖晶石结构 磁相互作用     

Quenching of SO2 phosphorescence by a magnetic field

Phosphorescence excitation spectra of the ã³B₁← [Xtilde]¹A₁ transition of SO₂ were measured in the absence and presence of a magnetic field (B = 0?44 T², P(SO₂) = 0?7 Torr). The absorption and phosphorescence excitation spectra of the ã³B₁← [Xtilde]¹A₁ transition of SO₂ measured in the absence of a magnetic field show that the relative intensity of the bands of the phosphorescence excitation spectrum is smaller than the relative intensity of the corresponding bands of the absorption spectrum beginning with the (0, 2, 0) band. In the presence of a magnetic field, the intensity of the phosphorescence excitation band falls, for ν_exc> 26400 cm^-1. Under the direct excitation of the ã³B₁← [Xtilde]¹A₁ transition, the dependence of the magnetic quenching of the SO₂ phosphorescence on the excitation frequency (ν_exc) was studied at P(SO₂) = 0?7 Torr and B = 0?44 T. The dependence of the magnetic field effect on ν_excshows that only the vibrationally excited levels of the ã³B₁ state are sensitive to an external magnetic field. The magnetic field strength and the pressure dependence of the magnetic field effects were studied under indirect excitation of the ã³B₁← [Xtilde]¹A₁ transition at λ_exc = 308 nm. The magnetic field and the pressure dependence were investigated for pure SO₂ and for SO₂ + RH (RH n-C₅H₁₂) mixtures. It was found that the magnetic field effect was saturated at B ? 0?25 T. The saturation value (Gr = l(0?3 T)/l(0)) increases with increasing gas pressure. The magnetic field, the pressure and the excess vibrational energy (ν_excess) dependence of the magnetic quenching of SO2 phosphorescence show that the data observed can be explained by an indirect mechanism within the framework of a low level density approximation.     

Graviton mass,quintessence, and oscillatory character of Universe evolution

On the basis of the field relativistic theory of gravity, an upper limit on the graviton mass, m_g≤1.6×10^?66 g, is obtained at a 95% C.L. by using data on the density parameter Ω_tot. Within one standard deviation, the probable value of the graviton mass is m_g=1.3×10^?66 g. It is indicated that, according to the relativistic theory of gravity, the existence of quintessence is needed for explaining the accelerated expansion of the Universe. Experimental data on the age of the Universe and on the density of cold matter make it possible to determine the allowed interval of the parameter ν that enters into the equation of state for the quintessence and to indicate the instants of time that correspond to the beginning and cessation of the era of accelerated expansion, as well as the maximum-expansion time, which corresponds to the half-period of the oscillatory evolution of the Universe.     

Magnetic field effects on the hydrogen abstraction reaction of triplet 4-methoxybenzophenone with thiophenol as studied by a picosecond laser flash photolysis technique

The hydrogen abstraction reaction of triplet 4-methoxybenzophenone with thiophenol at 265 K has been studied with a newly developed picosecond laser flash photolysis apparatus under magnetic fields of 0–1.7 T. The decay rate constant of the radical pair generated was found to increase from 3.42 × 10⁹ s^?1 to 4.15 × 10⁹ s^?1 with increasing the magnetic field from 0 to 1.7 T. The observed magnetic field effects can be explained by the Δg mechanism. Using the simple kinetics model with the Δg mechanism, the rate constant of the escape process from the pair (k _esc) and two rate constants for the T-S spin conversion process (k _T-S) at 0 and 1.7 T were found to be 1.97 × 10⁹ s^?1, 1.45 × 10⁹ s^?1, and 2.12 × 10⁹ s^?1, respectively. From the magnetic field dependence on k _T-S, the difference in the g values of the 4-methoxybenzophenone ketyl and phenylthiyl radicals was estimated to be 0.0087.     

Determination of the g-factor of electrons in N-type silicon surface inversion layers

The g-factor of conduction electrons in the surface inversion layer on a silicon (100) surface has been determined using the tilted magnetic field method developed by Fang and Stiles.The value of (m¹/m₀)·g at the fixed magnetic field was independent of surface carrier density n_s, whereas it had a sharp peak at about 97 koe. At strong magnetic field limit the value was constant and 0.4. If we take the effective mass of conduction electrons in the inversion layer on the (100) surface as 0.2m₀, the g-factor is about two which is the same as that for conduction electrons in bulk silicon.     

Classical in-plane negative magnetoresistance and quantum positive magnetoresistance in undoped InSb thin films on GaAs (1 0 0) substrates

Magnetoresistance (MR) effects have been investigated in perpendicular and parallel magnetic fields at 300, 80 K and liquid He temperatures for undoped InSb thin films 0.1–2.3 μm thick grown on GaAs(1 0 0) substrates by MBE. At high temperatures, the intrinsic carriers show the parabolic negative MR observable only in magnetic fields parallel to the film. The skipping-orbit effect due to surface boundary scattering in the classical orbits in the plane vertical to the film has been argued to be responsible for the negative MR. At low temperatures (T=80 K), the transport is dominated by the two-dimensional (2D) electrons in the accumulation layers at the InSb/GaAs(1 0 0) hetero interface; MR is positive and shows a logarithmic increase with anisotropy between parallel and perpendicular field orientation, arising from the 2D weak anti-localization (WAL) that reflects the interplay between the spin-Zeeman effect and strong spin–orbit interaction caused by the asymmetric potential at the interface (Rashba term). The zero-field spin splitting energy of Δ₀13 meV, the electron effective mass of m^*0.10m₀ seven times of the band edge mass in bulk InSb and the effective g-factor of |g^*|15 in the accumulation layer have been inferred from fits of MR for the 0.1 μm thick film to the 2D WL theory.     

A Variable-Temperature X-Band EPR Study of the Gd<Superscript>3+</Superscript> Ion in a La<Subscript>2</Subscript>Si<Subscript>2</Subscript>O<Subscript>7</Subscript> Crystal Characterized by Monoclinic Site Symmetry

Electron paramagnetic resonance (EPR) studies on a single crystal of diamagnetic compound La₂Si₂O₇, potentially a phosphorescent/luminescent/laser material, with the Gd³⁺ ion substituting for the La³⁺ ion, were carried out at X-band (9.61 GHz) over the 4–295 K temperature range. The asymmetry exhibited by the Gd³⁺ EPR line positions for the orientations of the external magnetic field about the magnetic Z- and Y-axes in the ZY-plane was ascribed to the existence of monoclinic site symmetry at the site of the Gd³⁺ ion, as confirmed by the significant values of the spin Hamiltonian parameters g _YZ , b ₂ ⁻¹, b ₄ ^−m (m = 1, 3), b ₆ ^−m (m = 1, 3, 5), estimated by fitting all EPR line positions observed at room temperature for the orientation of the magnetic field in the magnetic ZX- and ZY-planes using a rigorous least-squares fitting procedure. At 8 K measurements were only carried out for orientation of B in the magnetic ZX-plane, due to difficulty in orientation of the crystal inside the cryostat, enabling estimation of all spin Hamiltonian parameters b _n ^m except those characterized by negative m values and g _YZ . The absolute sign of the zero-field splitting parameter b ₂ ⁰ was determined to be negative from the relative intensities of the lines at 8 K. Authors' address: Sushil K. Misra, Physics Department, Concordia University, 1455 de Maisonneuve Boulevard West, Montreal, Quebec H3G 1M8, Canada