Ergodic theorems for queuing systems with dependent inter-arrival times

We study a G/GI/1 single-server queuing model with i.i.d. service times that are independent of a stationary process of inter-arrival times. We show that the distribution of the waiting time converges to a stationary law as time tends to infinity provided that inter-arrival times satisfy a Gärtner-Ellis type condition. A convergence rate is given and a law of large numbers established. These results provide tools for the statistical analysis of such systems, transcending the standard case with independent inter-arrival times.     

Density functional theory study of the NO2-sensing mechanism on a WO3 (0 0 1) surface: the role of surface oxygen vacancies in the formation of NO and NO3

The trapping and detection of nitrogen oxide with tungsten trioxide has become a popular research topic in recent years. Knowledge of the complete reaction mechanism for nitrogen oxide adsorption is necessary to improve detector performance. In this work, we used density functional theory (DFT) calculations to study the adsorption characteristics and electron transfer of nitrogen dioxide on an oxygen-deficient monoclinic WO₃ (0 0 1) surface. We observed different reactions of NO₂ on slabs with different O- and WO-terminated WO₃ (0 0 1) surfaces with oxygen vacancies. Our calculations show that the bridging oxygen atom on an oxygen defect on an O-terminated WO₃ (0 0 1) surface is the active site where an NO₂ molecule is oxidised into nitrate and is adsorbed onto the surface. On a WO-terminated (0 0 1) surface, one of the oxygen atoms from the NO₂ molecule fills the oxygen vacancy, and the resulting NO fragment is adsorbed onto a W atom. Both of these adsorption models can cause an increase in the electrical resistance of WO₃. We also calculated the adsorption energies of NO₂ on slabs with different oxygen-deficient WO₃ surfaces.     

溴化苄及其阳离子红外光谱的理论研究

利用密度泛函理论（DFT）在B3LYP/6-311G++（d,p）水平上对溴化苄分子进行了结构优化和频率计算,得到了该分子的稳定构型和全部振动模式。计算得到的几何参数通过与苯分子的实验值相比,发现理论值与其相吻合;理论计算和实验测得的红外光谱数据的比较分析表明,理论计算与实验测量结果符合得较好,并对其振动模式进行了归属。最后,在B3LYP/6-311G++（d,p）水平上计算得到了溴化苄阳离子的红外光谱,并与溴化苄进行了比较,计算表明电离对振动偶极距产生了较大影响。     

气相中Fe+催化CO与N2O循环反应的理论计算研究

采用密度泛函UB3LYP/6–311+G(2d)方法计算研究了Fe+在基态和激发态与CO与N2O反应的反应机理。全参数优化了反应势能面上各驻点的几何构型,用频率分析方法和内禀反应坐标（IRC）方法对过渡态进行了验证,并用UB3LYP/6–311++G(3df,3pd)、单点垂直激发等方法分别进行各驻点单点能校正,四重态和六重态反应势能面交叉点CP确定,计算结果表明,该反应为两步反应,且反应机理都为插入—消去反应,势能面上的两个交叉点能够有效的降低反应的活化能,这在动力学和热力学上都是有利的。     

二氧化铬阴离子光电子能谱的理论研究

凭借密度泛函理论,采用不同基组对中性分子CrO2的基态（ 3B1）以及阴离子CrO2‾的基态（ 4B 1）进行几何优化和振动频率分析;应用量化计算得到的力常数及结构和光谱参数,基于推得的两维四模Franck-Condon重叠积分的代数表示,对CrO2 ( 3B1)－CrO2‾ ( 4B1) 的光脱附过程进行Franck-Condon分析和光谱模拟,理论上得到光电子能谱的谱线相对强度及振动结构分布,理论谱与实验测得的二氧化铬阴离子光电子能谱达到一致,并对光电子能谱的振动结构进行归属及热带分析;另外,在光谱模拟过程中通过迭代Franck-Condon分析过程,推得CrO2‾（ 4B1）与CrO2（ 3B1）平衡几何结构之差：ΔR(Cr-O)= 0.05Å,Δ(O-Cr-O)=12o.     

Nin(n=1-9)小团簇的密度泛函理论研究

采用密度泛函理论(DFT)方法对Nin(n=1-9)团簇的结构, 稳定性和磁性进行了详细的研究. 得到了一些以前文献中没有提到的稳定结构, 并与其它方法得到的结构进行了比较, 得到的最稳定结构与实验结果相一致. 团簇能量的二阶差分、分裂能、HOMO-LUMO能隙随团簇尺寸的演化都没有表现出明显的奇偶振荡行为, 但在n=5、7时均有较大的值, 说明相对应的团簇具有较高的稳定性、较低的化学活性. 团簇磁性的研究表明团簇的平均每原子磁矩随团簇尺寸的增加有一定振荡, 但有逐渐减小的趋势, n≥5时团簇的构型对团簇磁性的影响较小.     

金红石结构TiO2结构和热力学性质的第一性原理研究

利用基于密度泛函理论的第一性原理计算方法以及准谐德拜模型研究了金红石TiO2的结构和热力学性质。常温常压下所计算的晶格常数、体弹模量及其对压强的一阶导数与实验值和其他理论计算结果相符的较好。另外,我们还计算了体弹模量、热膨胀系数、热容与温度和压强的关系。     

Hyperthermal cluster-surface scattering

Using molecular-dynamics simulation, we study the processes occurring after impact of clusters on a rigid wall. Comparing the impact of model clusters consisting of 13 atoms, or of 13 diatomic molecules with varied bond strength, the systematics in the results of the collision process are investigated. Four regimes of impact-induced cluster fragmentation are identified: intact reflection, shattering into large fragments, complete fragmentation, and molecule dissociation. The effect of the number of degrees of freedom activated in the collision on the translational and internal energies of the reflected fragments is discussed in detail. As a rule, with increasing number of degrees of freedom which can be activated in the collision, the translational energy sinks. On the other hand, for weak intramolecular bonding, intramolecular vibrations are easily excited at small impact energies, reducing the resulting translational energy. The presence of even a very weak attractive well epsilon_w at the surface has a major influence on the sticking behavior of the clusters — and hence also on the absolute reflected energies — even at impact energies E₀ ≫ epsilon_w.     

Study of correlation effects on stability of many-body complexes in III–V nitride quantum dots

The aim of this work is to analyze theoretically the correlation energies, for neutral, positive and negative excitons and bi-excitons in the III–V nitride In_xGa_1−xN/GaN quantum dot; where x=17.5% denotes the indium concentration. So, we propose a model consistent with experimental observations that is small In_xGa_1−xN truncated pyramids with circular base lying on wetting layer, both buried into GaN matrix. The correlation energies of many-body complexes X, X⁻, X⁺ and XX are investigated as a function of the quantum dot radius r_c and the intrinsic electric field.     

Methyl hydrogen peroxide dimer: A structural study

Methyl hydrogen peroxide (MHP) exhibits a tendency to form a stable dimer by hydrogen-bonding. Ab initio theoretical investigations on methyl hydrogen peroxide dimer (MHPD) carried out herein lead to several energetically stable structures that have a direct bearing on the reactivity of the monomer in terms of its molecular electrostatic potential (MESP). To gauge the role played by the electron-correlation in lending stability to MHP and its dimer, we employ the density functional theory (DFT) (as implemented by B3LYP-functional), and subsequently second order Møller-Plesset (MP2) perturbation theory, using the basis sets 6-31G(d, p) and 6-311++G(2d, 2p). Simulated infra-red vibrational spectra lead to spectral intensity redistribution upon dimerization. Energetically the lowest MHPD is endowed with inversion symmetry and has two hydrogen bonds, while three other structures emerge: one energetically very close with two H-bonds, and the two others, with three H-bonds each, yet higher by about 2 kcal mol⁻¹.