工作休假的Geo/Geo/1排队

本文研究多重工作休假的Geo/Geo/1离散时间排队。工作休假排队在光通信网络的网关路由器性能分析中有重要应用。我们使用矩阵几何解的方法得到了稳态队长和逗留时间的分布及随机分解性质,并使用交替更新过程理论,得到了忙期和忙循环的均值。     

基于GI/M/1型Markov过程的Geo/Geo/1多重工作休假排队系统分析

本文研究Geo/Geo/1多重工作休假排队系统。首先,应用GI/M/1型Markov链给出了该排队问题的一个新数学模型。其次,应用矩阵解析方法对模型求解,不但得到了排队模型平稳队长分布的具体形式,还给出了平稳状态时服务台具体处于第几次工作休假的概率。这些关于服务台状态更为精确的描述是该模型的新结果。最后用数值例子说明了分析方法的有效性。     

服务时间累积量控制的GeoX/G/1排队的稳态队长

考虑服务台的启动由服务台闲期所有到达的服务时间累积之和(即顾客即将被服务的时间累积量)控制的离散时间批到达Geo^X/G/1排队服务系统。顾客成批到达系统,当顾客的被服务时间累积量超过某个非负整数D时,服务台立刻为顾客提供服务直到忙期结束(此策略被称为D策略)。该模型可为无线传感网络的从业者提供一些理论基础。首先,在准备工作中,讨论了忙期开始时刻的顾客数、服务时间累积量以及服务台的忙期和闲期分布;然后,通过闲、忙期到达顾客的分类和概率分析方法,研究了系统的离去时刻稳态队长和任意时刻n⁺的稳态队长分布的概率母函数。作为特例,分析得到了离散时间Geo^X/G/1排队和D策略离散时间Geo/G/1排队的队长分布结果。最后,模拟分析了一类无线传感节点,并在数值上获得了节点的最低能耗。     

阈值调控的GI/Geo/1多重工作休假排队

在随机服务系统中,减少系统能源消耗,提高服务效率,是人们关注的焦点．基于此目的,本文加入阈值和休假中止策略,具体分析了离散时间GI/Geo/1工作休假排队系统．首先,建立了顾客到达前夕二维嵌入马尔可夫链,给出了GI/M/1型结构矩阵．其次,应用矩阵分析方法得到系统稳态队长分布,并进一步求得系统稳态下的平均队长和平均逗留时间等指标．最后,通过Matlab仿真软件,对模型中的性能指标给予刻画和展示,结果表明平均队长和平均逗留时间随阈值的增大而增大,随休假服务率的增加而减少．本文的结果将为交换虚通道以及无线网络等方面的研究提供一定的参考．     

多服务速率多重休假M/G(M/G)/1可修排队

本文通过对系统中顾客数设置门限N,考虑研究了服务台的服务速度依门限发生变化且当服务台未服务顾客(休假或故障)时到达顾客仅以概牢p进入系统的多重休假可修M／G(M／G)／1排队系统。通过L-变换、母函数以及补充变量方法得到了队长分布的瞬态解、稳态解及一些可靠性结果,并指出当两个服务速度相等时该模型与前人研究的M／G／1(E,MV）排队一致。     

假期中顾客以概率θ进入的Geo/G/1(E,MV)排队系统分析

本文考虑多重休假的Geo/G/1离散时间排队系统,其中在服务员休假期间到达的顾客以概率θ(0<θ1)进入系统.通过引入服务员忙期和使用全概率分解技术,讨论了队长的瞬时性质,得到了队长瞬时分布的z-变换的递推式,以及队长平稳分布的递推式,并且证明了稳态队长的随机分解性质.最后,给出了在特殊情形下相应的一些结果和数值计算实例.     

具有阀值策略的M/M/2/K多重休假排队系统

本文研究了带有阀值策略的服务器不同的M/M/2/K异步多重休假排队系统.第一个服务器在服务完一个顾客后,若发现系统中无等待的顾客,则立刻开始休假.当系统中等待的顾客数小于阀值时,第二个服务器开始休假.论文通过深入研究该系统的性能,为决策者提供一些参考.利用矩阵分析的方法,求出了系统的平稳概率向量和排队指标的解析表达式.最后,我们构造了一个费用模型,并分析了各参数对系统最小费用和最优阀值的影响.     

考虑顾客体验的排队系统研究

随着经济社会的发展,服务系统排队的顾客不再被看作被动进入的群体,而是当作具有自我决策行为的个体来研究。部分学者给出了较为简单的顾客排队决策模型,但是其结果与现实系统仍然有一定的差距。探索其核心原因,从考虑沉没成本及时间价值非线性两个角度对现有决策模型进行了修正,提出了新的更加灵活的模型,数值分析证明该模型更有效地阐述了现实中的顾客排队决策。进一步阐述了在该模型条件下的M/M/1排队模型服务率优化问题。此外,提出一种基于队长变换服务速率的策略来减少顾客不耐烦行为对系统的影响,并提出了服务率转换点优化决策的算法,数值实验证明这种可变服务率的策略比固定服务率的策略能够使服务商提高0.1%(参数取值均较小的情况下)。     

Min(N,D)-策略下M/G/1排队系统的离去过程

考虑Min(N,D)-策略下M/G/1排队系统的离去过程.运用全概率分解技术和更新过程理论,从任意初始状态出发,讨论系统在有限时间区间内离去顾客的平均数,得到了离去顾客平均数的瞬态表达式和稳态表达式,并给出了离去过程、服务员状态过程和服务员忙期中的服务更新过程之间的重要关系,该关系揭示了离去过程的随机分解特性:离去顾客的平均数被分解为两部分,一部分是服务员忙的概率,另一部分是服务员忙期中的离去顾客平均数,从而简化了对离去过程的研究.最后,得到了便于有效计算离去顾客平均数的渐近展开式,以及一些特殊情形下的相应结果.在排队网络中,由于一个排队系统的输出即为下游排队系统的输入,希望本文所得结果为排队网络的研究提供有用的信息.     

带有启动时间和单重工作休假的GI/M/1排队系统分析

在过去的二十年里,休假排队系统已经得到了广泛的研究.在各种休假排队模型中,在休假期内服务台是完全停止为顾客服务的.为了更客观地反映现实情况,本文在单重休假GI/M/1排队系统的基础上引入了在休假时服务台仍可低速服务而不是完全停止服务的工作休假策略和启动时间策略.对此模型的分析,我们重点关注顾客到达前夕时刻系统的状态,运用矩阵几何解方法得到了该系统的状态转移概率矩阵,并以概率矩阵为基础求出了系统的稳态平均队长和顾客的平均等待时间.     

Structural and optical properties of AlxOy/Pt/AlxOy multilayer absorber

We report on the microstructure and optical properties of Al_xO_y–Pt–Al_xO_y interference-type multilayer films, deposited by electron beam (e-beam) deposition onto corning 1737 glass, silicon (1 1 1) and copper substrates. The structural properties were investigated by Rutherford backscattering spectrometry, X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy and atomic force microscopy. The optical properties were extracted from specular reflection/transmission, diffuse reflectance and emissometer measurements. The stratification of the coatings consists of a semi-transparent middle Pt layer sandwiched between two layers of Al_xO_y. The top and bottom Al_xO_y layers were non-stoichiometric with no crystalline phases present. The Pt layer is in the fcc crystalline phase with a broad size distribution and spheroidal shape in and between the rims of Al_xO_y. The surface roughness of the stack was found to be comparable to the inter-particle distance. The optical calculations confirm a high solar absorptance of ∼0.94 and a low thermal emittance of ∼0.06 for the multilayer stack, which is attributed not only to the optimized nature of the multilayer interference stacks, but also to the specific surface morphology and texture of the coatings. These optical characteristics validate the spectral selectivity of the Al_xO_y–Pt–Al_xO_y interference-type multilayer stack for use in high temperature solar-thermal applications.     

Bulk crystalline BaPb34Bi14O3: A ceramic superconductor

The preparation conditions of the high T_C ceramic superconductor Ba(Pb,Bi)O₃ is correlated with the superconducting transition. Transition onsets of all materials are similar, but transition widths and transition completeness is strongly dependent on firing temperature. Only materials prepared over a narrow temperature range, resulting in a nearly ideal weight loss, have a complete and narrow transition.     

Electrostriction in Pb (Zn13Nb23)O3

The electrostriction in $\text{Pb (Zn}{}_{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}\text{Nb}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{)}\text{O}{}_3$ crystals has been investigated using a strain gauge method. In the ferroelectric phase below 140 C, the strain vs the electric field shows a hysteresis, which is ascribed to the effect of ferroelectric domains. A quadratic relation holds between the strain x and the electric polarization P as x = QP² above about 170 C in the paraelectric phase. Values of the electrostrictive Q coefficients are determined from the measurements near 190 C, as Q₁₁ = 1.6·10^?2m⁴/C², Q₁₂ = ?0.86·10^?2m⁴/C², and Q₄₄ = 0.85·10^?2m⁴/C².     

Synthesis of a new perovskite Pb(Li14Nb34)O3

A high-pressure technique was adopted to obtain perovskite-type $\text{Pb(Li}{}_{\mathrm{<mtext>1</mtext><mtext>4</mtext>}}\text{Nb}{}_{\mathrm{<mtext>3</mtext><mtext>4</mtext>}}\text{)}\text{O}{}_3$. A new perovskite $\text{Pb(Li}{}_{\mathrm{<mtext>1</mtext><mtext>4</mtext>}}\text{Nb}{}_{\mathrm{<mtext>3</mtext><mtext>4</mtext>}}\text{)}\text{O}{}_3$ was characterized to have a cubic symmetry with $\text{a}{}_{\mathrm{<mtext>o</mtext>}}\text{= 4.069}\text{A}\text{?}$; Li and Nb ions in the B-site of perovskite lattice may be in a random arrangement.     

Magnetic,electrical and thermal studies on the V1−xMox02

The monoclinic-to-tetragonal structure transition of oxides V_1?xMo_x0₂ with $\text{0≤}\text{x}\text{≤0.20}$ has been studied by means of DTA, X-ray diffraction, magnetic susceptibility (powder samples) and electrical conductivity (single crystals) measurements within the temperature region 80 K to 400 K. A linear decrease of the transition temperature of 11 K per atom % Mo was observed. The magnetic susceptibility of the low temperature phase was found to be temperature independent paramagnetic for all preparations. Electrical conductivity measurements on the same phase showed crystals with $\text{x}\text{? 0.04}$ to be semiconducting, while a metallic behavior was observed in the region $\text{0.10 ?}\text{x}\text{? 0.14}$.     

n-PbTep+−Pb1−xSnxTe heterojunctions prepared by a modified hot wall technique

$\text{n-PbTe}\text{p}{}^{\mathrm{+}}\text{?}\text{Pb}{}_{\mathrm{1?x}}\text{Sn}{}_{\mathrm{x}}\text{Te}$ heterojunctions with a long wavelength spectral cutoff (λ_c ≈ 6 μm) were prepared using the double-channel hot wall technique. The electrical and photoelectrical properties of the heterojunctions at 77, 197 and 300 K were investigated. Detectors with R_oA equal to 170 Ω cm² and a quantum efficiency of 25–40% were obtained. Reasons for the shift of the long wavelength spectral cutoff of the heterojunctions towards shorter wavelengths are given.     

Optimization of AlxOy/Pt/AlxOy multilayer spectrally selective coatings for solar-thermal applications

Spectrally selective Al_xO_y/Pt/Al_xO_y multilayer absorber coatings were deposited onto corning 1737 glass, Si (111) and copper substrates using electron beam (e-beam) vacuum evaporator at room temperature. The employment of ellipsometric measurements and optical simulation was proposed as an effective method to optimize and deposit multilayer solar absorber coatings. The optical constants (n and k) measured using spectroscopic ellipsometry, showed that both Al_xO_y layers, which used in the coatings, were dielectric in nature and the Pt layer was semi-transparent. The optimized multilayer coatings exhibited high solar absorptance α ∼ 0.94 ± 0.01 and low thermal emittance ? ∼ 0.06 ± 0.01 at 82 °C. The Rutherford backscattering spectroscopy (RBS) data of Al_xO_y/Pt/Al_xO_y multilayer absorber indicated the Al_xO_y layers present in the coating were nearly stoichiometry. The scanning electron microscope analysis (SEM) result indicated that the average diameter and inter-particles distance of Pt grains were statistically about 146 ± 0.17 nm and 6-10 ± 0.2 nm respectively.     

Reactive plasma deposited SixCyHz films

Si_xC_yH_z films have been prepared at 200°C by reactive plasma deposition from SiH₄ and CH₄ diluted in helium in a tubular reactor. These films have a ratio s (equal to $\text{Si}\text{(}\text{Si+C}\text{))}$ ranging from 0.2 to 0.8, a refractive index ranging from 1.96 to 2.6 and an optical energy band gap in the range 2.7-2.2 eV. The total quantity of hydrogen in the film is 40% when s=0.5. Infrared analysis shows that these films have large fractions of homonuclear bonds and that this material is best described as a polymer. Mass spectrometric measurements of the gaseous products formed in the SiH₄-CH₄-He plasma have been performed and the results are related to the composition of the deposited layers.