Sojourner与火星探测

Ｓｏｊｏｕｒｎｅｒ与火星探测丁悌平（地质矿产部矿床地质研究所，北京，１０００３７）自阿波罗登月飞行开始，人类进入了太阳系行星及卫星进行实地访问的新纪元。７０年代的海盗着陆器对火星的探测，８０年代旅行者１号与２号对土星、木星及其卫星的近距离观测，９０年...

Ethnocentrism and Language Barrier for Learning Sojourners

As two of the main challenges for students studying abroad,ethnocentrism and language barrier are the most common issues they will probably encounter.The essay will illustrate these two aspects separately.

Culture Shock for Learning Sojourners

When attempting to adapt to unfamiliar learning environments within new cultures,learning sojourners,represented by in-ternational students will face a challenging and dynamic process.Based on the understanding of literature and previous research,the essay will concentrate on the most common issue that sojourners probably encounter,i.e.culture shock,which accounts for themost due to its universality.

Can hypobaric hypoxia affect human thermal comfort?An experimental study in Tibet,China

Hypobaric hypoxia is the main environmental feature of the Tibetan plateau which would influence the efficiency of human metabolic heat production and the ability of thermal regulation.In order to understand the influence of the hypoxic environment on the plateau on the thermal comfort of short-term sojourners in Tibet,China,oxygen generators were used to create oxygen-enriched environments,and physiological and psychological reactions of subjects were compared under different oxygen partial pressures(p_(O_(2)))and air temperatures(t_(a)).The results showed that subjects’thermal sensation,thermal comfort and mean skin temperature decreased with a decrease in the oxygen partial pressure.When t_(a)=17℃,the influence of oxygen partial pressure was more pronounced,compared to p_(O_(2))=16.4 kPa,the thermal sensation of subjects under p_(O_(2))=13.7 kPa decreased by 33%.The rate of subjects feeling comfortable decreased by 25%,and the mean skin temperature decreased by 0.7℃.The hypoxic environment of the plateau exacerbates human discomfort.Therefore,it is necessary to fully understand the actual thermal requirements of sojourners in Tibet,China.The results of this study would have implications for a better understanding of thermal comfort characteristics in the hypoxia environment in plateau.

A Simulation Engine for Stochastic Timed Petri Nets and Application to Emergency Healthcare Systems

In many service delivery systems,the quantity of available resources is often a decisive factor of service quality.Resources can be personnel,offices,devices,supplies,and so on,depending on the nature of the services a system provides.Although service computing has been an active research topic for decades,general approaches that assess the impact of resource provisioning on service quality matrices in a rigorous way remain to be seen.Petri nets have been a popular formalism for modeling systems exhibiting behaviors of competition and concurrency for almost a half century.Stochastic timed Petri nets(STPN),an extension to regular Petri nets,are a powerful tool for system performance evaluation.However,we did not find any single existing STPN software tool that supports all timed transition firing policies and server types,not to mention resource provisioning and requirement analysis.This paper presents a generic and resource oriented STPN simulation engine that provides all critical features necessary for the analysis of service delivery system quality vs.resource provisioning.The power of the simulation system is illustrated by an application to emergency health care systems.

A Network Selection Scheme Based on TOPSIS in Heterogeneous Network Environment

This paper deals with network selection problem for users in heterogeneous network environment. The main context is to improve the TOPSIS( Technique for Order Preference by Similarity to Ideal Solution) network scheme by combining the network properties and the users' requirement accurately and decrease ping-pong effect. The method of entropy and FAHP( Fuzzy Analytic Hierarchy Process) are used to calculate weight value and the sojourn time calculation is used to avoid ping-pang effect. The simulation results show that the improved scheme enhances the more accuracy of network selection than the existing methods and reduces the number of ping-pang effect.

Modeling the Sojourn Time of Items for In-Networ Cache Based on LRU Policy

To reduce network redundancy,innetwork caching is considered in many future Internet architectures,such as Information Centric Networking.In in-network caching system,the item sojourn time of LRU(Least Recently Used) replacement policy is an important issue for two reasons:firstly,LRU is one of the most common used cache policy;secondly,item sojourn time is positively correlated to the hit probability,so this metric parameter could be useful to design the caching system.However,to the best of our knowledge,the sojourn time hasn't been studied theoretically so far.In this paper,we first model the LRU cache policy by Markov chain.Then an approximate closedform expression of the item expectation sojourn time is provided through the theory of stochastic service system,which is a function of the item request rates and cache size.Finally,extensive simulation results are illustrated to show that the expression is a good approximation of the item sojourn time.

EXTREMA OF A GAUSSIAN RANDOM FIELD:BERMAN'S SOJOURN TIME METHOD

In this paper we devote ourselves to extending Berman’s sojourn time method,which is thoroughly described in[1-3],to investigate the tail asymptotics of the extrema of a Gaussian random field over[0,T]^(d) with T∈(0,∞).

SOJOURN TIME ANALYSIS OF DQDB MAN FOR LANs INTERCONNECTION

The Distributed Queue Dual Bus(DQDB) Metropolitan Area Network(MAN) is a promising solution for the evolution from current networks to B-ISDN. The performance of the DQDB MAN for Local Area Networks(LANs) interconnection is analyzed. The effects of message length, traffic load of upstream and downstream nodes and the parameters of bandwidth balancing mechanism and network counters on the sojourn time of message in the buffer are investigated, which present a valuable reference for the implementation of the DQDB MAN.

PERFORMANCE ANALYSIS OF PRIORITIZED DQDB MAN FOR LANs INTERCONNECTION

The sojourn time of the prioritized OQDB MAN with bursty traffic input is studied in this paper. The expressions for the mean sojourn time of the message with two transmission priority are obtained. The conclusions drawn from the paper are that, the mean sojourn time of the message, at either higher or lower priority, is a linear function of the mean message length approximately, and the performance improvement by adopting the higher priority level for the user is remarkable, especially when the lower-priority traffic load from the downstream users is heavy.

Stationary Analysis of Geo/Geo/1 Queue with Two-Speed Service and the Optimal Switching Threshold for the Service Rate

This paper considers a Geo/Geo/1 queueing system with infinite capacity, in which the service rate changes depending on the workload. Initially, when the number of customers in the system is less than a certain threshold L, low service rate is provided for cost saving. On the other hand, the high service rate is activated as soon as L customers accumulate in the system and such service rate is preserved until the system becomes completely empty even if the number of customers falls below L. The steady-state probability distribution and the expected number of customers in the system are derived. Through the first-step argument, a recursive algorithm for computing the first moment of the conditional sojourn time is obtained. Furthermore, employing the results of regeneration cycle analysis, the direct search method is also implemented to determine the optimal value of L for minimizing the long-run average cost rate function.

Data Flow Fuzzy Control of Communication Network with Finite Terminal

We consider the problem of data flow fuzzy control of discrete queuing systems with three different service-rate servers. The objective is to dynamically assign customers to idle severs based on the state of the system so as to minimize the mean sojourn time of customers. Simulation shows the validity of the fuzzy controller.

English for International Purposes: Guidance for Chinese Students on an Oversea Sojourn

English has been widely used for various purposes and the number of students studying abroad has mushroomed in recent years.This article focuses on the preparation an oversea sojourn for Chinese students to practice English as an international language for intercultural communication.The article also reviews some literature to explain the process of intercultural acculturation and explore how to maximize the culture learning.Finally,the implications suggest that students should prepare for the sojourn in advanced to identify the culture difference,simulation games could also help students to improve their intercultural awareness and facilitate them to be adapted in the new cultural environment.

Exponential H_∞ filtering analysis for discrete-time switched neural networks with random delays using sojourn probabilities

This paper is concerned with the exponential H_∞ filtering problem for a class of discrete-time switched neural networks with random time-varying delays based on the sojourn-probability-dependent method. Using the average dwell time approach together with the piecewise Lyapunov function technique, sufficient conditions are proposed to guarantee the exponential stability for the switched neural networks with random time-varying delays which are characterized by introducing a Bernoulli stochastic variable.Based on the derived H_∞ performance analysis results, the H_∞ filter design is formulated in terms of Linear Matrix Inequalities(LMIs). Finally, two numerical examples are presented to demonstrate the effectiveness of the proposed design procedure.

Some problems on balls and spheres for Brownian motion

<正> The distributions of the sojourn time of a ball and hitting time for a sphere for Brownian motion starting at any point in space, as well as the joint distributions of the maximum excursion before last exit sphere and first instance of attaining such a maximum for Brownian motion starting at the inside of a ball are given.

Analysis of Stationary Queue Length Distribution for Geo/T-IPH/1 Queue

In this paper we study a Geo/T-IPH/1 queue model,where T-IPH denotes the discrete time phase type distribution defined on a birth-and-death process with countably many states.The queue model can be described by a quasi-birth-anddeath(QBD)process with countably phases.Using the operator-geometric solution method,we first give the expression of the operator and the joint stationary distribution.Then we obtain the probability generating function(PGF)for stationary queue length distribution and sojourn time distribution,respectively.

On the M/G/1 queueing system with multiclass customers and fixed feedback

The M/G/1 queueing system with multiclass customer arrivals, fixed feedback, and first come first served policy is considered, where different classes of customers have different arrival rates, service-time distributions, and feedback numbers. The joint probabifity generation function of queue size of each class and the Laplace-Stieltjes transform of the total sojourn time of a customer in each class are presented, which extended the results obtained by Choi B D. The mean queue size of each class and mean total sojourn time of a customer in each class are obtained with this result. The results can be used in computer and communication networks for their performance analysis.

System Model and Equilibrium Strategy of Mobile Users in a Hybrid Access Network

Mobile users usually access the Internet via a hybrid access network, in which cellular and Wi-Fi networks are available alternatively. In the hybrid access network, a mobile user decides to send or not to send a packet according to the number of packets already in the system and the phase of the server. In order to evaluate the system performance of the hybrid access network, in this paper we first establish a fully observable continuous time Markovian queueing system. Then, we present an exact analysis to investigate the behavior of the mobile users in the network. Through iterations and diagonalization, we obtain the expected sojourn time of a newly arriving packet in a closed form. Moreover, with the monotonicity for the expected sojourn time of a newly arriving packet, we prove the existence of the Nash equilibrium strategy. Finally, we analyze the socially optimal strategy and motivate the mobile users to accept the socially optimal strategy by changing the sojourn cost.

STRONG APPROXIMATIONS FOR THE OPEN QUEUEING NETWORK IN HEAVY TRAFFIC

In this paper, we prove strong approximations for the open queueing network in heavytraffic. Strong approximations are given for the queueing length, the virtual waiting timeand the sojourn time processes, and for the embedded sequences associated with the queueinglength processes.

The One-Dimensional Distribution and Construction of Semi-Markov Processes

In this paper, we obtain the transition probability of jump chain of semi-Markov pro- cess, the distribution of sojourn time and one-dimensional distribution of semi-Markov process. Furthermore, the semi-Markov process X（t, ω） is constructed from the semi-Markov matrix and it is proved that two definitions of semi-Markov process are equivalent.