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Highlight s • Summarize the works of the related fields including the reliability analysis of the retrial machine repair system with a controllable server in the literature. • Adopt the Laplace transform technique to derive the system reliability and the mean time to system failure of the model. • Address the sensitivity analyses of the system reliability and the mean time to system failure. • Design and execute the numerical experiments. The important results are presented and discussed. Abstract This study analyzes the system reliability of the retrial machine repair system with M operating units, S warm standby units and a single repair server with N -policy. Failure times of operating units and standby units are assumed to have exponential distributions with rates λ and η , respectively. When the repair server normally operates in serving failed units, it is subject to breakdown. The time to failure and the repair time for the single server are assumed to follow exponential distributions. When the server is broken down, it can also provide partial repair service with lower service rate. The repair times of failed units also have exponential distributions. Extensive numerical experiments are designed and executed to realize how performance measures are affected by the change of each system parameter. [ABSTRACT FROM AUTHOR]

• Four retrial systems with preventive maintenance and spares are investigated. • An application for air compressor systems with preventive maintenance is provided. • The state-transition diagram and laplace transform equations are established. • The availability function and mean time to system failure are derived explicitly. • The best system configuration with the highest performance is obtained. In various industrial problems, repairable models have been widely employed to derive performance measures. The current investigation compares four unreliable retrial systems with preventive maintenance. The objective is to offer a proper analysis procedure helpful for managers to determine the best configuration resulting in a better performance. A potential application in which the proposed model can be applied is provided. For each system, the state-transition diagram and associated differential-difference equations are presented. Using the Laplace-Stieltjes transform, we derive the explicit formulas for the mean time-to-failure and the steady-state availability, commonly considered critical criteria. Numerical results are tabulated and displayed graphically, and then a comparative cost-benefit analysis is performed. Finally, observed insights into decision-making are provided. [ABSTRACT FROM AUTHOR]

This paper examines an M/G/1 machine repair problem with multiple imperfect coverage. When an operating machine fails, it is immediately detected and located with coverage probability c. We first use a recursive method and supplementary variable technique to develop steady-state analytic solutions. Various system performance measures are developed based on the steady-state probability distributions. We then construct the expected cost function per machine per unit time and formulate an optimization problem to determine the minimum cost. Direct search and Quasi-Newton methods are implemented to search for the optimal number of operating machines, the optimal repair rate, and the optimal coverage factor. Sensitivity analysis and numerical illustrations are also provided. [ABSTRACT FROM AUTHOR]

This paper investigates a multiple-vacation M/M/1 warm-standby machine repair problem with an unreliable repairman. We first apply a matrix-analytic method to obtain the steady-state probabilities. Next, we construct the total expected profit per unit time and formulate an optimisation problem to find the maximum profit. The particle swarm optimisation (PSO) algorithm is implemented to determine the optimal number of warm standbysS* and the service rate μ* as well as vacation rate ν* simultaneously at the optimal maximum profit. We compare the searching results of the PSO algorithm with those of exhaustive search method to ensure the searching quality of the PSO algorithm. Sensitivity analysis with numerical illustrations is also provided. [ABSTRACT FROM AUTHOR]

Abstract: This paper considers the controllable M/M/2 machine repair problem with L operating machines operating under the triadic policy. Expressions for the steady-state probabilities of the number of failed machines in the system are derived and taken in neat closed-form. We establish the total expected cost function per machine per unit time and formulate an optimization problem to find the minimum cost. The genetic algorithm (GA) is implemented to determine the optimal operating policy and the service rate simultaneously at the global minimum cost. Sensitivity analysis with numerical illustrations is also provided. [Copyright &y& Elsevier]

Abstract: In this paper we analyze the warm-standby M/M/R machine repair problem with multiple imperfect coverage which involving the service pressure condition. When an operating machine (or warm standby) fails, it may be immediately detected, located, and replaced with a coverage probability c by a standby if one is available. We use a recursive method to develop the steady-state analytic solutions which are used to calculate various system performance measures. The total expected profit function per unit time is derived to determine the joint optimal values at the maximum profit. We first utilize the direct search method to measure the various characteristics of the profit function followed by Quasi-Newton method to search the optimal solutions. Furthermore, the particle swarm optimization (PSO) algorithm is implemented to find the optimal combinations of parameters in the pursuit of maximum profit. Finally, a comparative analysis of the Quasi-Newton method with the PSO algorithm has demonstrated that the PSO algorithm provides a powerful tool to perform the optimization problem. [Copyright &y& Elsevier]

This paper considers two randomized control policies. One is (p, F)-policy queue which deals with the issue of randomized controlling arrivals to a queueing system and the server requires a start-up time before allowing customers to enter the system. Another is (q, N)-policy queue which considers the common issue of controlling service in a queueing system randomly, and the server requires a start-up time before providing service. The steady-state probability distribution of the system size and system performances measures are developed for both queues. In addition, we uncover an interrelationship between the (p, F)- and (q, N)-policy M/M/1/K queues by a series of propositions. The advantage created through interrelationship is that the solution of one queue has been derived, which assists us in obtaining that of the other queue easily. Finally, numerical results are presented for illustration purposes. [ABSTRACT FROM AUTHOR]

This article analyzes an M/G/1 queueing system with second optional service, server breakdowns, and general start-up times under (N, p)-policy. Customers arrive into the system according to a Poisson process. Service times, repair times, and start-up times are assumed to be generally distributed. The first service is essential for all arrived customers, and the second service is optional, which is demanded by some customers after their essential service is completed. For this queuing system, the expected cost function per unit time is constructed to search the joint optimum threshold values of the (N, p) at the minimum cost. We also obtain the explicit closed-form expression of the optimal solutions. A sensitivity analysis is performed to evaluate the impacts on the optimum threshold value. Finally, numerical results are presented for several cases. [ABSTRACT FROM AUTHOR]

Abstract: We analyze a single removable and unreliable server in an M/G/1 queueing system operating under the 〈p, N〉-policy. As soon as the system size is greater than N, turn the server on with probability p and leave the server off with probability (1− p). All arriving customers demand the first essential service, where only some of them demand the second optional service. He needs a startup time before providing first essential service until there are no customers in the system. The server is subject to break down according to a Poisson process and his repair time obeys a general distribution. In this queueing system, the steady-state probabilities cannot be derived explicitly. Thus, we employ an improved maximum entropy method with several well-known constraints to estimate the probability distributions of system size and the expected waiting time in the system. By a comparative analysis between the exact and approximate results, we may demonstrate that the improved maximum entropy method is accurate enough for practical purpose, and it is a useful method for solving complex queueing systems. [Copyright &y& Elsevier]

Abstract: We consider a finite capacity M/M/R queue with second optional channel. The interarrival times of arriving customers follow an exponential distribution. The service times of the first essential channel and the second optional channel are assumed to follow an exponential distribution. As soon as the first essential service of a customer is completed, a customer may leave the system with probability (1− θ) or may opt for the second optional service with probability θ (0⩽ θ ⩽1). Using the matrix-geometric method, we obtain the steady-state probability distributions and various system performance measures. A cost model is established to determine the optimal solutions at the minimum cost. Finally, numerical results are provided to illustrate how the direct search method and the tabu search can be applied to obtain the optimal solutions. Sensitivity analysis is also investigated. [Copyright &y& Elsevier]

Abstract: The problem addressed in this paper is to compare the minimum cost of the two randomized control policies in the M/G/1 queueing system with an unreliable server, a second optional service, and general startup times. All arrived customers demand the first required service, and only some of the arrived customers demand a second optional service. The server needs a startup time before providing the first required service until the system becomes empty. After all customers are served in the queue, the server immediately takes a vacation and the system operates the (, )-policy or (, )-policy. For those two policies, the expected cost functions are established to determine the joint optimal threshold values of (, ) and (, ), respectively. In addition, we obtain the explicit closed form of the joint optimal solutions for those two policies. Based on the minimal cost, we show that the optimal (, )-policy indeed outperforms the optimal (, )-policy. Numerical examples are also presented for illustrative purposes. [Copyright &y& Elsevier]

Abstract: This paper analyzes the -policy M/M/1/K queueing system with working vacation and an exponential startup time. The -policy deals with the issue of controlling arrivals to a queueing system, and the server requires a startup time before allowing customers to enter the system. For the queueing systems with working vacation, the server can still provide service to customers rather than completely stop the service during a vacation period. The matrix-analytic method is applied to develop the steady-state probabilities, and then obtain several system characteristics. We construct the expected cost function and formulate an optimization problem to find the minimum cost. The direct search method and Quasi-Newton method are implemented to determine the optimal system capacity , the optimal threshold and the optimal service rates at the minimum cost. A sensitivity analysis is conducted to investigate the effect of changes in the system parameters on the expected cost function. Finally, numerical examples are provided for illustration purpose. [Copyright &y& Elsevier]

Abstract: This paper studies the M/M/1 machine repair problem with working vacation in which the server works with different repair rates rather than completely terminating the repair during a vacation period. We assume that the server begins the working vacation when the system is empty. The failure times, repair times, and vacation times are all assumed to be exponentially distributed. We use the MAPLE software to compute steady-state probabilities and several system performance measures. A cost model is derived to determine the optimal values of the number of operating machines and two different repair rates simultaneously, and maintain the system availability at a certain level. We use the direct search method and Newton’s method for unconstrained optimization to repeatedly find the global minimum value until the system availability constraint is satisfied. Some numerical examples are provided to illustrate Newton’s method. [Copyright &y& Elsevier]

Abstract: This paper compares the availability characteristics between three different systems with reboot delay and standby switching failures. Three systems are studied under the assumption that the time-to-failure and the time-to-repair of the primary and standby units are exponentially and generally distributed, respectively. The reboot times are assumed to be exponentially distributed with parameter . It is assumed that there is a significant probability q of a switching failure. Using the supplementary variable technique, we develop the explicit expressions for the steady-state availability, Av, for three configurations and perform comparative analysis for three various repair time distributions, such as exponential, gamma, and uniform. Under the cost/benefit criterion, comparisons are made based on assumed numerical values given to the distribution parameters, and to the cost of the primary and standby units. [Copyright &y& Elsevier]

Abstract: This paper deals with the control policy of a removable and unreliable server for an M/M/1/K queueing system, where the removable server operates an F-policy. The so-called F-policy means that when the number of customers in the system reaches its capacity K (i.e. the system becomes full), the system will not accept any incoming customers until the queue length decreases to a certain threshold value F. At that time, the server initiates an exponential startup time with parameter γ and starts allowing customers entering the system. It is assumed that the server breaks down according to a Poisson process and the repair time has an exponential distribution. A matrix analytical method is applied to derive the steady-state probabilities through which various system performance measures can be obtained. A cost model is constructed to determine the optimal values, say (F ∗, μ ∗, γ ∗), that yield the minimum cost. Finally, we use the two methods, namely, the direct search method and the Newton-Quasi method to find the global minimum (F ∗, μ ∗, γ ∗). Numerical results are also provided under optimal operating conditions. [Copyright &y& Elsevier]

Abstract: This paper investigates the policy M/G/1 queue with server breakdowns, and startup times. Customers arrive at the system according to a Poisson process. Service times, repair times, and startup times are assumed to be generally distributed. The server is turned on after a fixed length of time repeatedly until at least one customer is present in the waiting line. The server needs a startup time before starting the service. We analyze various system performance measures and develop the total expected cost function per unit time in which is a decision variable. We determine the optimum threshold and derive analytical results for sensitivity investigations. The sensitivity analysis is particularly valuable to the system analyst when evaluating future conditions. We also present extensive numerical computation for illustration purpose. [Copyright &y& Elsevier]

Abstract: This paper analyzes a single removable and unreliable server in the -policy M/G/1 queue in which the server breaks down according to a Poisson process and the repair time obeys an arbitrary distribution. We assume that when the number of customers in the system becomes N, turn the server on with probability p and leave the server off with probability . The use of maximum entropy approach is to develop the approximate formulae for the probability distributions of the number of customers and the expected waiting time in the system. We perform a comparative analysis between the derived approximate results with exact analytic results for three different service time and repair time distributions such as exponential, uniform, and gamma. It is shown from numerical results that the maximum entropy approach is sufficiently accurate for practical use. [Copyright &y& Elsevier]

Abstract: This paper deals with the optimal control of a finite capacity G/M/1 queueing system combined the F-policy and an exponential startup time before start allowing customers in the system. The F-policy queueing problem investigates the most common issue of controlling arrival to a queueing system. We provide a recursive method, using the supplementary variable technique and treating the supplementary variable as the remaining interarrival time, to develop the steady-state probability distribution of the number of customers in the system. We illustrate a recursive method by presenting three simple examples for exponential, 3-stage Erlang, and deterministic interarrival time distributions, respectively. A cost model is developed to determine the optimal management F-policy at minimum cost. We use an efficient Maple computer program to determine the optimal operating F-policy and some system performance measures. Sensitivity analysis is also studied. [Copyright &y& Elsevier]

Abstract: This paper deals with an N policy M/G/1 queueing system with a single removable and unreliable server whose arrivals form a Poisson process. Service times, repair times, and startup times are assumed to be generally distributed. When the queue length reaches N(N ⩾1), the server is immediately turned on but is temporarily unavailable to serve the waiting customers. The server needs a startup time before providing service until there are no customers in the system. We analyze various system performance measures and investigate some designated known expected cost function per unit time to determine the optimal threshold N at a minimum cost. Sensitivity analysis is also studied. [Copyright &y& Elsevier]

We consider an M/M/R queueing system with finite capacity N, where customers have two arrival modes under steady-state conditions. It is assumed that each arrival mode is serviced by one or more servers, and that the two arrival modes have equal probabilities of receiving service. Arrival times of the customers and service times of the severs follow an exponential distribution. A cost model is developed to determine the optimal number of servers and the optimal system capacity. The minimum expected cost, the optimal number of servers, the optimal system capacity, and various system characteristics are obtained for some designated system parameters’ values. Sensitivity for the minimal cost is also investigated. [ABSTRACT FROM AUTHOR]

Abstract: This paper studies the machine repair problem consisting of M operating machines with two types of spare machines (S = S 1 + S 2), and R servers (repairmen) who leave for a vacation of random length when there are no failed machines queuing up for repair in the repair facility. At the end of the vacation the servers return and operate two vacation policies. First, the servers take vacations repeatedly until they find the repair facility has at least one waiting failed machine in the queue. Second, the servers do not take a vacation again and remain idle until the first arriving failed machine arrives, which starts a busy period in the repair facility. For both policies, the servers have two service rates for repair-slow and fast. The matrix geometric theory is used to find the steady-state probabilities of the number of failed machines in the system as well as the performance measures. Some special cases are given. A direct search algorithm is used to simultaneously determine the optimal values of the number of two types of spares and the number of servers while maintaining a minimum specified level of system availability. [Copyright &y& Elsevier]

This paper deals with the reliability and sensitivity analysis of a repairable system with M operating units, S warm standby units, and R unreliable service stations. Failure times and service times of operating or standby units are assumed to be exponentially distributed. While the service station is working, it is subject to breakdowns according to a Poisson process. When the station breaks down, it requires repair at a repair facility, where repair times follow the negative exponential distribution. This paper provides the expressions for system reliability, R Y ( t), and the mean time to system failure, MTTF. We perform a sensitivity analysis for changes in the reliability characteristics, along with changes in specific values of the system parameters. Sensitivity analysis for the MTTF is also investigated. [ABSTRACT FROM AUTHOR]

Abstract: Four different system configurations with warm standby components and standby switching failures are compared based on their reliability and availability. The time-to-repair and the time-to-failure for each of the primary and warm standby components are assumed to follow the negative exponential distribution. We develop the explicit expressions for the mean time-to-failure, MTTF, and the steady-state availability, A T (∞), for four configurations. For all four configurations, comparisons are made for specific values of distribution parameters and of the cost of the components. The configurations are ranked based on MTTF, A T (∞), and cost/benefit where benefit is either MTTF or A T (∞). [Copyright &y& Elsevier]

Abstract: We study the cost benefit analysis of availability systems with warm standby units and imperfect coverage. The time-to-failure and the time-to-repair of the active and standby units are assumed to be exponentially and generally distributed, respectively. We assume that the coverage factor is the same for an active-unit failure as that for a standby-unit failure. We present a recursive method, using the supplementary variable technique and treating the supplementary variable as the remaining repair time, to develop the steady-state availability, (or Av), for three availability models. For each availability model, the explicit expressions for the Av for three various repair time distributions, such as exponential, k-stage Erlang, and deterministic are provided. Under the cost/benefit criterion, comparisons are performed based on assumed numerical values given to the distribution parameters, and to the cost of the active and standby units. [Copyright &y& Elsevier]

Abstract: We study a single removable and unreliable server in the N policy M/G/1 queueing system with general startup times where arrivals form a Poisson process and service times are generally distributed. When N customers are accumulated in the system, the server is immediately turned on but is temporarily unavailable to the waiting customers. He needs a startup time before providing service until the system becomes empty. The server is subject to breakdowns according to a Poisson process and his repair time obeys an arbitrary distribution. We use maximum entropy principle to derive the approximate formulas for the steady-state probability distributions of the queue length. We perform a comparative analysis between the approximate results with established exact results for various distributions, such as exponential (M), fc-stage Erlang (E k ), and deterministic (D). We demonstrate that the maximum entropy approach is accurate enough for practical purposes and is a useful method for solving complex queueing systems. [Copyright &y& Elsevier]

In this paper, the steady-state availability and the mean time to system failure of a repairable system with m operating units, w warm standby units and R repairmen in which units balking and reneging are considered. It is assumed that failed units balk (refuse to join) with a constant probability (1−b) and renege (leave the queue after joining) according to a negative exponential distribution with parameter r. The failure times of the operating and warm standby units are assumed to be exponentially distributed with parameters λ and α, respectively. The repair time distribution of each server is also exponentially distributed with parameter μ. This paper presents derivations for the steady-state availability, AT(∞), the mean time to system failure, MTTF and numerical examples. Several cases are analyzed to study the effects of various system parameters on the AT(∞) and the MTTF. [Copyright &y& Elsevier]

We study a single removable server in an M/G/1 queueing system operating under the N policy in steady-state. The server may be turned on at arrival epochs or off at departure epochs. Using the maximum entropy principle with several well-known constraints, we develop the approximate formulae for the probability distributions of the number of customers and the expected waiting time in the queue. We perform a comparative analysis between the approximate results with exact analytic results for three different service time distributions, exponential, 2-stage Erlang, and 2-stage hyper-exponential. The maximum entropy approximation approach is accurate enough for practical purposes. We demonstrate, through the maximum entropy principle results, that the N policy M/G/1 queueing system is sufficiently robust to the variations of service time distribution functions. [Copyright &y& Elsevier]

• This paper investigates the cost benefit analysis of four different retrial systems with warm standby units and imperfect coverage. Each retrial system contains various amount of primary and warm standby units. We derive the explicit expressions of the mean time-to-failure and the steady-state availability among four retrial system and perform comparisons. The cost/benefit is also compared among four retrial systems with given to the distribution parameters, and to the cost of the primary and warm standby units. Retrial systems have been extensively used to model many practical problems in communication network, data center, cloud service computing center, computer network, etc. This paper deals with the cost benefit analysis of four different retrial systems with warm standby units and imperfect coverage. Each retrial system contains various amount of primary and warm standby units. Failure times and repair times of the primary and warm standby units are exponentially distributed. We assume that the coverage factor is the same for a primary-unit failure as that for a standby-unit failure and is denoted by c. We derive the explicit expressions of the mean time-to-failure and the steady-state availability for each retrial system and perform comparisons. The cost/benefit is also compared among four retrial systems with given to the distribution parameters, and to the cost of the primary and warm standby units. [ABSTRACT FROM AUTHOR]

This paper deals with the N policy M/G/1 queue with working breakdowns. The supplementary variable and probability generating function techniques are implemented to develop the steady-state results. The stability condition of a stable queue, as well as several system performance measures, are also derived. A two-stage optimization method is employed to determine the optimal threshold N and the optimal joint values of two mean service rates until the stability constraint is satisfied. To demonstrate the effectiveness of two-stage optimization method, some numerical results are presented. Finally, we carry out sensitivity analysis for the expected cost function with numerical illustrations. [ABSTRACT FROM AUTHOR]

Abstract: We study the statistical inferences of an availability system with imperfect coverage. The system consists of two active components and one warm standby. The time-to-failure and time-to-repair of the components are assumed to follow an exponential and a general distribution respectively. The coverage factors for an active-component failure and for a standby-component failure are assumed to be the same. We construct a consistent and asymptotically normal estimator of availability for such repairable system. Based on this estimator, interval estimation and testing hypothesis are performed. To implement the simulation inference for the system availability, we adopt two repair-time distributions, namely, lognormal and Weibull and three types of Weibull distributions characterized by their shape parameters are considered. Finally, all simulation results are displayed in appropriate tables and curves for highlighting the performance of the statistical inference procedures. [Copyright &y& Elsevier]

This article we study the statistical inferences of an availability system with imperfect coverage. The time-to-failure and time-to-repair of the active and standby components are assumed to be exponential and general distribution, respectively. Assume that the coverage factor is the same for an active-component failure as that for a standby-component failure. Firstly, we propose a consistent and asymptotically normal (CAN) estimator of availability for such repairable system. Based on the CAN estimator of the system availability, interval estimation and testing (hypothesis) are performed. To implement the simulation inference for the system availability, we adopt two repair-time distributions, such as lognormal and Weibull distribution, in which three types of Weibull distribution are considered according to the shape parameter β. The component holds the decreasing repair rate (DRR), constant repair rate (CRR), and increasing repair rate (IRR) if β < 1, β = 1, and β > 1, respectively. Finally, all simulation results are displayed by appropriate tables and curves for understanding performance of the statistical inference procedures presented in this article. [ABSTRACT FROM AUTHOR]

• We investigate the availability of four retrial systems with general repair times. • The steady-state probability and the associated availability are derived explicitly. • A comparison cost-benefit analysis among four retrial systems are presented. • The availabilities and the cost-benefit ratios for four retrial systems are compared. • Based on the numerical results, the optimal system configuration is provided. In various industries, system availability assessment has been extensively investigated. Particularly, a stable power supply system is essential and critical in many service systems such as communication networks, mass transit systems, data storage centers and product manufacturing processes, etc. When an unreliable power supply unit fails, the repair services may be unavailable and a random period of (retrial) time for contact and confirmation is needed. Thus, this paper compares four retrial power supply systems with general repair time, warm standby units, and imperfect coverage possibility. That is, the power generation equipment is assumed unreliable and may fail anytime. The steady-state probabilities and the associated availabilities of four retrial systems are derived explicitly. A comparative analysis of the availability and the cost-benefit ratio among four retrial systems is presented. The efficiencies of four considered retrial systems are sorted and the optimal retrial system is provided. Based on the calculated numerical results, the management insights for practical applications are also proposed for decision making. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents the reliability and sensitivity analysis of a system with M primary units, W warm standby units, and R unreliable service stations where warm standby units switching to the primary state might fail. Failure times of primary and warm standby units are assumed to have exponential distributions, and service times of the failed units are exponentially distributed. In addition, breakdown times and repair times of the service stations also follow exponential distributions. Expressions for system reliability,, and mean time to system failure, MTTF are derived. Sensitivity analysis, relative sensitivity analysis of the system reliability and the mean time to failure, with respect to system parameters are also investigated. [Copyright &y& Elsevier]

This study analyzes three availability systems with warm standby units, fault detection delay, and general repair times. The failure times and repair times of failed components were assumed to follow exponential and general distributions, respectively. The detection delay times were assumed to be exponentially distributed. This study exploited the supplementary variable technique to develop a recursive method for deriving the steady-state availability for three systems. By using extensive numerical computations, we compared three systems in terms of system availability based on specific values given to the system parameters. The state transition rate diagrams of the three systems revealed the symmetry property approximately. The three systems were ranked based on the system availability and the cost/benefit for the three various repair time distributions: exponential, three-stage Erlang, and deterministic, where the benefit was system availability. [ABSTRACT FROM AUTHOR]

Asian rice, Oryza sativa, consists of two major subspecies, indica and japonica, which are physiologically differentiated and adapted to different latitudes. Genes for photoperiod sensitivity are likely targets of selection along latitude. We examined the footprints of natural and artificial selections for four major genes of the photoperiod pathway, namely PHYTOCHROME B ( PhyB), HEADING DATE 1 ( Hd1), HEADING DATE 3a ( Hd3a), and EARLY HEADING DATE 1 ( Ehd1), by investigation of the patterns of nucleotide polymorphisms in cultivated and wild rice. Geographical subdivision between tropical and subtropical O. rufipogon was found for all of the photoperiod genes in plants divided by the Tropic of Cancer (TOC). All of these genes, except for PhyB, were characterized by the existence of clades that split a long time ago and that corresponded to latitudinal subdivisions, and revealed a likely diversifying selection. Ssp. indica showed close affinity to tropical O. rufipogon for all genes, while ssp. japonica, which has a much wider range of distribution, displayed complex patterns of differentiation from O. rufipogon, which reflected various agricultural needs in relation to crop yield. In japonica, all genes, except Hd3a, were genetically differentiated at the TOC, while geographical subdivision occurred at 31°N in Hd3a, probably the result of varying photoperiods. Many other features of the photoperiod genes revealed domestication signatures, which included high linkage disequilibrium (LD) within genes, the occurrence of frequent and recurrent non-functional Hd1 mutants in cultivated rice, crossovers between subtropical and tropical alleles of Hd1, and significant LD between Hd1 and Hd3a in japonica and indica. [ABSTRACT FROM AUTHOR]

SUMMARY Energy saving is an important issue in wireless sensor networks for majority of sensor nodes equipped with non-rechargeable batteries. To prolong the lifetime of sensor nodes, most research works have focused on how to tune the duty cycling schemes among nodes to save the communication cost using multifarious wake-up strategies. To this aim, we propose a novel design strategy for mitigating the average power consumption of sensor node using the Min( N, T) policy M/G/1 queuing theory. The basic point of our approach is that Min( N, T) dyadic policy would mitigate the total average times of medium contention by having both a counter ( N) and a timer ( T) for the control of triggering on a radio server to transmit queued packets, and then the power consumption of communication can be alleviated. A comprehensive mathematical analysis on the optimal control parameters had been made. Much data analysis and simulations had been conducted to validate the proposed model. In this article, we show how the improvement level on power consumption can be achieved through analytical and simulation results. With little or no extra management cost, the proposed add-on power-saving technique can provide a design strategy to optimize relevant system parameters including power consumption and latency delay. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Outcrossing Arabidopsis species that diverged from their inbreeding relative Arabidopsis thaliana 5 million yr ago and display a biogeographical pattern of interspecific sympatry vs intraspecific allopatry provides an ideal model for studying impacts of gene introgression and polyploidization on species diversification., Flow cytometry analyses detected ploidy polymorphisms of 2× and 4× in Arabidopsis lyrata ssp. kamchatica of Taiwan. Genomic divergence between species/subspecies was estimated based on 98 randomly chosen nuclear genes. Multilocus analyses revealed a mosaic genome in diploid A. l. kamchatica composed of Arabidopsis halleri-like and A. lyrata-like alleles., Coalescent analyses suggest that the segregation of ancestral polymorphisms alone cannot explain the high inconsistency between gene trees across loci, and that gene introgression via diploid A. l. kamchatica likely distorts the molecular phylogenies of Arabidopsis species. However, not all genes migrated across species freely. Gene ontology analyses suggested that some nonmigrating genes were constrained by natural selection., High levels of estimated ancestral polymorphisms between A. halleri and A. lyrata suggest that gene flow between these species has not completely ceased since their initial isolation. Polymorphism data of extant populations also imply recent gene flow between the species. Our study reveals that interspecific gene flow affects the genome evolution in Arabidopsis. [ABSTRACT FROM AUTHOR]