scholarly journals On the retrial queue with imperfect coverage and delay reboot

2020 ◽  
Author(s):  
Tzu-Hsin Liu ◽  
Jau-Chuan Ke ◽  
Ching-Chang Kuo ◽  
Fu-Min Chang
Keyword(s):  
Call Center ◽  
Fault Tolerant ◽  
Retrial Queue ◽  
Optimization Procedure ◽  
Minimum Cost ◽  
Optimal Number ◽  
Death Process ◽  
Service Rate ◽  
Performance Indices ◽  
Imperfect Coverage

This paper presents a design for a fault-tolerant call center consisting of a multi-server retrial queue, and including detection, location and coverage variables. Basically, incoming calls are immediately detected and located. However, it is not always possible to detect and locate because of some fault issues. If incoming calls are not detected and located, the system is cleared by a reboot. Once incoming calls are detected and located, they are attended to when a consultant is available; otherwise, they join a retrial orbit and generate repeated attempts till a free consultant is found. We analyze the presented model as a quasi-birth-and-death process and develop various performance indices. The optimal number of consultants and optimal service rate are searched by constructing an average cost function. A heuristic search technique is employed to obtain the optimization approximate solution at a minimum cost. Numerical illustrations are given to demonstrate the optimization procedure and the effects of varying parameters on performance indices.

scholarly journals Optimal Band Selection for the Calculation of Planck Mean Absorption Coefficients

2017 ◽  
Vol 4 (1) ◽  
pp. 70-73
Author(s):  
M. Gnybida ◽  
Ch. Rümpler ◽  
V. R. T. Narayanan
Keyword(s):  
Temperature Profile ◽  
Low Voltage ◽  
Optimization Procedure ◽  
Optimal Number ◽  
Discrete Ordinates ◽  
Radiation Balance ◽  
Absorption Coefficients ◽  
Loss Mechanism ◽  
Spectral Solution ◽  
Dependent Absorption

Radiative heat transfer is a major heat loss mechanism in thermal plasmas generated during arc flashes/faults in switchgear applications or during high current interruption in low voltage circuit breakers. A common way to calculate the radiation balance is by means of approximate non-gray radiation models like P1 or discrete ordinates (DOM), where the frequency dependent absorption and emission are described in a number of frequency intervals (bands) using a constant absorption coefficient in each band. Current work is focused on finding the optimal number of bands as well as band interval boundaries that provide a reasonable level of accuracy in comparison to a full spectral solution. An optimization procedure has been applied to different SF<sub>6</sub> and copper vapor gas mixtures for an assumed temperature profile. Radiation model results using optimized band averaged absorption coefficients as well as spectral values are provided and discussed for the exemplary temperature profile.

A Cross-Layer Fault Tolerant Protocol with Recovery Mechanism for Clustered Sensor Networks

2020 ◽  
pp. 197-220 ◽  
Author(s):  
Yasmine Djebaili ◽  
Azeddine Bilami
Keyword(s):  
Fault Tolerance ◽  
Fault Tolerant ◽  
Minimum Cost ◽  
Estimation Algorithm ◽  
Link Quality ◽  
Sensor Nodes ◽  
Detection Mechanism ◽  
Network Applications ◽  
Congestion Detection ◽  
Congested Area

This article describes how fault tolerance is an essential issue for many WSN (Wireless Sensor Network) applications such as wildlife monitoring, battlefield surveillance and health monitoring. It represents a great challenge for researchers regarding to the characteristics of sensor nodes which are prone to failures due essentially to their limited resources. Faults may occur, not only when sensor nodes exhaust their energy, but also when the congestion phenomenon emerges, because of a high traffic in the network and limited storage capacity of the sensor nodes. In order to support fault tolerance in WSNs, the authors propose a new scheme which incorporates a link quality estimation algorithm and a congestion detection mechanism to enable nodes that present high quality links to be chosen for routing in a non-congested area in case of faults. Evaluations through simulations under NS2 show that our proposed protocol tolerates faults with a minimum cost relatively to HEEP protocol and improves network's performances comparatively to other fault tolerant protocols such as EF-LEACH.

Optimal Thresholds of an Infinite Buffer Discrete-Time Two-Server System with Triadic Policy

2011 ◽  
Vol 2 (4) ◽  
pp. 75-88
Author(s):  
Veena Goswami ◽  
G. B. Mund
Keyword(s):  
Discrete Time ◽  
Queueing System ◽  
Minimum Cost ◽  
Service Rate ◽  
Closed Form Solutions ◽  
Optimal Thresholds ◽  
Optimal Service ◽  
Number Of Customers ◽  
System Operating ◽  
Server System

This paper analyzes a discrete-time infinite-buffer Geo/Geo/2 queue, in which the number of servers can be adjusted depending on the number of customers in the system one at a time at arrival or at service completion epoch. Analytical closed-form solutions of the infinite-buffer Geo/Geo/2 queueing system operating under the triadic (0, Q N, M) policy are derived. The total expected cost function is developed to obtain the optimal operating (0, Q N, M) policy and the optimal service rate at minimum cost using direct search method. Some performance measures and sensitivity analysis have been presented.

scholarly journals Radiative Properties and Numerical Modeling of C4F7N-CO2-O2 Thermal Plasma

2019 ◽  
Vol 6 (2) ◽  
pp. 144-147
Author(s):  
M. Gnybida ◽  
Ch. Ruempler ◽  
V. R. T. Narayanan
Keyword(s):  
Thermal Plasma ◽  
Spectral Band ◽  
Optimization Procedure ◽  
Optimal Number ◽  
Radiative Properties ◽  
Absorption Coefficients ◽  
Medium Voltage ◽  
Spectral Bands ◽  
Computational Fluid Dynamics Cfd ◽  
Low Global Warming Potential

C<sub>4</sub>F<sub>7</sub>N and C<sub>4</sub>F<sub>7</sub>N-CO<sub>2</sub> mixtures are considered as alternatives to SF<sub>6</sub> for use in medium voltage gas insulated switchgear applications (GIS), due to the low global warming potential and good dielectric properties of C<sub>4</sub>F<sub>7</sub>N. Current work is focused on the calculation of radiative properties (absorption coefficients) of C<sub>4</sub>F<sub>7</sub>N-CO<sub>2</sub> thermal plasma and computational fluid dynamics (CFD) simulations of free burning C<sub>4</sub>F<sub>7</sub>N-CO<sub>2</sub> arcs that are stabilized by natural convection. Absorption coefficients of C<sub>4</sub>F<sub>7</sub>N-CO<sub>2</sub> plasma used in the CFD model are derived from spectral absorption coefficients by Planck averaging. An optimization procedure has been applied to find the optimal number of spectral bands as well as spectral band interval boundaries. Radiation and flow model results for C<sub>4</sub>F<sub>7</sub>N-CO<sub>2</sub> in comparison to SF<sub>6</sub> and air are provided and discussed.

scholarly journals OPTIMAL LATENT PERIOD IN A BACTERIOPHAGE POPULATION MODEL STRUCTURED BY INFECTION-AGE

2011 ◽  
Vol 21 (04) ◽  
pp. 693-718 ◽  
Author(s):  
ÀNGEL CALSINA ◽  
JOSEP M. PALMADA ◽  
JORDI RIPOLL
Keyword(s):  
Latent Period ◽  
Evolutionarily Stable Strategy ◽  
Optimization Procedure ◽  
Infection Process ◽  
Death Process ◽  
Single Infection ◽  
Arbitrary Distribution ◽  
Infection Age ◽  
Population Dynamics Model ◽  
Age Structured

We study the lysis timing of a bacteriophage population by means of a continuously infection-age-structured population dynamics model. The features of the model are the infection process of bacteria, the death process, and the lysis process which means the replication of bacteriophage viruses inside bacteria and the destruction of them. The time till lysis (or latent period) is assumed to have an arbitrary distribution. We have carried out an optimization procedure, and we have found that the latent period corresponding to maximal fitness (i.e. maximal growth rate of the bacteriophage population) is of fixed length. We also study the dependence of the optimal latent period on the amount of susceptible bacteria and the number of virions released by a single infection. Finally, the evolutionarily stable strategy of the latent period is also determined as a fixed period taking into account that super-infections are not considered.

scholarly journals Fault-tolerant communication topology management based on minimum cost arborescence for leader–follower UAV formation under communication faults

2017 ◽  
Vol 14 (2) ◽  
pp. 172988141769396 ◽  
Author(s):  
Guoqiang Wang ◽  
He Luo ◽  
Xiaoxuan Hu ◽  
Huawei Ma ◽  
Shanlin Yang
Keyword(s):  
Graph Theory ◽  
Fault Tolerant ◽  
Minimum Cost ◽  
Formation Flight ◽  
Communication Cost ◽  
Topology Management ◽  
Simulation Experiments ◽  
Communication Topology ◽  
Aerial Vehicle ◽  
Management Method

A novel fault-tolerant communication topology management method for the leader–follower unmanned aerial vehicle (UAV) formation is proposed to minimize the formation communication cost while keeping the formation shape, even in the case of communication faults during the formation flight. This method is based on Edmonds’ algorithm for the minimum cost arborescence problem in graph theory. When a formation shape is given before the formation flight, this method can get the optimal initial communication topology with the minimum formation communication cost for keeping the formation shape. When some communication faults occur during the formation flight, which will cause the formation shape cannot be kept, this method can reconfigure the communication topology in time to guarantee the safety of all UAVs and recover the formation shape, and then it can reoptimize the communication topology by UAV position reconfiguration in the formation shape to minimize the formation communication cost for continuously keeping the formation shape. The effectiveness of this method is demonstrated through several simulation experiments.

scholarly journals M/M/1 Retrial Queue with Working Vacation Interruption and Feedback under N-Policy

2014 ◽  
Vol 2014 ◽  
pp. 1-9 ◽  
Author(s):  
Li Tao ◽  
Liyuan Zhang ◽  
Shan Gao
Keyword(s):  
Retrial Queue ◽  
Stochastic Decomposition ◽  
Service Rate ◽  
Working Vacation ◽  
Stationary Probability Distribution ◽  
The Matrix ◽  
Vacation Interruption ◽  
Necessary And Sufficient ◽  
Vacation Period ◽  
Conditional Stochastic Decomposition

We consider an M/M/1 retrial queue with working vacations, vacation interruption, Bernoulli feedback, and N-policy simultaneously. During the working vacation period, customers can be served at a lower rate. Using the matrix-analytic method, we get the necessary and sufficient condition for the system to be stable. Furthermore, the stationary probability distribution and some performance measures are also derived. Moreover, we prove the conditional stochastic decomposition for the queue length in the orbit. Finally, we present some numerical examples and use the parabolic method to search the optimum value of service rate in working vacation period.

scholarly journals A location optimization method for aircraft weakly-rigid structures

2014 ◽  
Vol 5 ◽  
pp. A18
Author(s):  
Zhong-Qi Wang ◽  
Yuan Yang ◽  
Yong-Gang Kang ◽  
Zheng-Ping Chang
Keyword(s):  
Optimization Procedure ◽  
Optimization Method ◽  
Optimal Number ◽  
Deformation Analysis ◽  
Element Analysis ◽  
Application Study ◽  
Location Optimization ◽  
Large Size ◽  
Analysis Theory ◽  
Nonlinear Programming Methods

Since aircraft weakly-rigid structure has large size and weak stiffness, there has serious deformation during assembly process. The current deformation analysis theory of rigid assembly is not applicable. Based on the N-2-1 (N > 3) locating principle, this paper presents a methodology for weakly-rigid parts. An optimization algorithm combines finite element analysis and nonlinear programming methods to find the optimal number and position of the locating points in order to minimize the assembly deformation. An example application study is presented to demonstrate the optimization procedure and its effectiveness by using the software of ABAQUS.

scholarly journals Two-way communication retrial queue with unreliable server and multiple types of outgoing calls

2020 ◽  
Vol 28 (1) ◽  
pp. 49-61
Author(s):  
Anatoly A. Nazarov ◽  
Svetlana V. Paul ◽  
Olga D. Lizyura
Keyword(s):  
Probability Distribution ◽  
Call Center ◽  
Poisson Point Process ◽  
Retrial Queue ◽  
Idle Time ◽  
High Rate ◽  
Exponential Distributions ◽  
Limit Condition ◽  
Different Types ◽  
Incoming Call

Retrial queue under consideration is the model of call center operator switching between input and outgoing calls. Incoming calls form a Poisson point process. Upon arrival, an incoming call occupies the server for an exponentially distributed service time if the server is idle. If the server if busy, an incoming call joins the orbit to make a delay before the next attempt to take the server. The probability distribution of the length of delay is an exponential distribution. Otherwise, the server makes outgoing calls in its idle time. There are multiple types of outgoing calls in the system. Outgoing call rates are different for each type of outgoing call. Durations of different types of outgoing calls follow distinct exponential distributions. Unsteadiness is that the server crashes after an exponentially distributed time and needs recovery. The rates of breakdowns and restorations are different and depend on server state. Our contribution is to obtain the probability distribution of the number of calls in the orbit under high rate of making outgoing calls limit condition. Based on the obtained asymptotics, we have built the approximations of the probability distribution of the number of calls in the orbit.

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