A Bitcoin-inspired infinite-server model with a random fluid limit

The synchronization process inherent to the Bitcoin network gives rise to an infinite-server model with the unusual feature that customers interact. Among the closed-form characteristics that we derive for this model is the busy period distribution which, counterintuitively, does not depend on the arrival rate. We explain this by exploiting the equivalence between two specific service disciplines, which is also used to derive the model’s stationary distribution. Next to these closed-form results, the second major contribution concerns an asymptotic result: a fluid limit in the presence of service delays. Since fluid limits arise under scalings of the law-of-large-numbers type, they are usually deterministic, but in the setting of the model discussed in this paper the fluid limit is random (more specifically, of growth-collapse type).     

达里厄垂直轴风力机叶片螺旋变异优化研究

针对传统达里厄( Darrieus)直叶片垂直轴风力机在运行过程中出现叶片动转矩周期波动性大,动转矩系数曲线 震荡剧烈,造成对风轮旋转主轴的强烈冲击及风力机功率输出不稳定等问题,文章提出对Darrieus垂直轴风力机传统直 叶片进行螺旋扭曲变异设计,以改善风力机叶片的动转矩输出性能。结合SolidWorks和MATLAB完成风力机模型的三 维参数化建模,在流体仿真软件FLUENT中完成模型的数值模拟仿真计算。通过螺旋扭曲角的单因素试验验证了变异 设计叶片输出的动转矩性能周期波动性降低,平均动转矩得到提高,并确定螺旋扭曲角的优化区间。文章构建了风力机 系统模型建立与仿真体系,采取螺旋扭曲变异设计,改善了风力机叶片输出的动转矩性能,初步确定合理的螺旋扭曲角 分布范围为：70°~ ll0°。     

A generalized negative binomial and applications

A generalized negative binomial distribution is derived from the Markov Bernoulli sequence of successes and failures. We study the properties and applications of this distribution. The properties are illustrated by two examples of discrete time queueing systems. The distribution is then fitted to two data sets, the eruption record of Mt. Sangay, and a record of computer disk failure accesses. In the first case there is a strong serial dependence in the data and the generalized negative binomial provides a good fit, while in the second case, although there is a significant serial dependence, it is insufficient to justify the additional parameter of the distribution. We conclude by demonstrating the usefulness of the distribution in the field of statistical quality control.     

流体力学新型通用函数Y的变分有限元分析

本文应用通用函数Y及其变分原理,为求解具有自由面流动问题提出了一种新方法。将物理平面变换成映象平面。在映象平面上,引出通用函数Y,并且写出关于Y的变分原理。用这个变分原理及有限元法求解自由面流动可克服边界未知的困难。文中以水坝闸门出流问题为例进行了计算,结果表明,该方法是非常有效的。     

夹具浮动介质的选择原则

根据外现形态对浮动介质进行分类,对各自的性能特点进行了分析比较,较系统地总结了浮动介质的选择原则.     

洗扫车专用风机数值模拟与内流特性分析

针对洗扫车专用风机内流场强旋转和强曲率特点,提出了适宜于分析强旋转和强曲率效应的湍流新模型,并继 而建立了针对洗扫车专用风机的CFD数值模拟策略。研究结果表明：专用风机内流呈现复杂的强旋转效应,该效应下 叶轮间隙流易造成严重的能量损失,叶轮间隙尺寸是专用风机气动设计的关键要素;专用风机叶轮在强曲率、强旋转效 应的作用下,小流量工况时更易出现大面积流动分离甚至回流;不同流量下,回转面静压和总压均呈现出非对称性。随 着流量的增加,静压、总压分布的非对称性会逐渐减弱。分析结果对于提高专用风机的性能,改进其气动特性提供了理 论支持,更好地为生产实践提供指导。     

Structural properties and estimation in m|EK| 1 queue

In this paper we study the distribution of the number of customers served in a busy period in the framework of modified power series distribution introduced by Gupta (197U) and obtain the moments and probability generating function of this distribution. We also study the maximum likelihood estimation of the parameter θand the variance and the asymptotic bias of the MLE are also obtained. The minimum variance unbiased estimate of θ^ris investigated and an estimate of the probabilities is given.     

A note on Bayesian estimation of traffic intensity in single-server Markovian queues

ABSTRACT

In queuing theory, a major interest of researchers is studying the behavior and formation process and analyzing the performance characteristics of queues, particularly the traffic intensity, which is defined as the ratio between the arrival rate and the service rate. How these parameters can be estimated using some statistical inferential method is the mathematical problem treated here. This article aims to obtain better Bayesian estimates for the traffic intensity of M/M/1 queues, which, in Kendall notation, stand for Markovian single-server infinity queues. The Jeffreys prior is proposed to obtain the posterior and predictive distributions of some parameters of interest. Samples are obtained through simulation and some performance characteristics are analyzed. It is observed from the Bayes factor that Jeffreys prior is competitive, among informative and non-informative prior distributions, and presents the best performance in many of the cases tested.     

Level-Phase Independence for Fluid Queues

ABSTRACT

A Markov-modulated fluid queue is a two-dimensional Markov process; the first dimension is continuous and is usually called the level, and the second is the state of a Markov process that determines the evolution of the level, it is usually called the phase. We show that it is always possible to modify the transition rules at the boundary level of the fluid queue in order to obtain independence between the level and the phase under the stationary distribution. We obtain this result by exploiting the similarity between fluid queues and Quasi-Birth-and-Death (QBD) processes.