Application of Lagrangian relaxation to computer network control

AbstractThe problem of routing and flow control in a computer communication network is formulated as a mixed integer nonlinear programming problem. The Lagrangian relaxation method is used to decompose the problem into subproblems that are relatively easier to solve than the original problem. An algorithm is then developed which can obtain an optimal solution to the problem

Analysis and Optimization of M/G/l Vacation Queueing Systems with Server Timeout

We consider a single-server vacation queueing system that operates in the following manner. When the server returns from a vacation it observes the following rule. If there is at least one customer in the system, the server commences service and serves exhaustively before taking another vacation. If the server finds the system empty, it waits a fixed time c. At the expiration of this time the server commences another vacation if no customer has arrived; otherwise, it serves exhaustively before commencing another vacation. Analytical results are derived for the mean waiting time in the system. The timeout scheme is shown to be a generalized scheme of which both the single vacation and multiple vacations schemes are special cases, with c = ∞ and c = 0 respectively. The model is extended to the N-policy vacation queueing system. In both schemes we use a linear cost model to obtain an optimal operating value of c.Рассмотрена односерверная система массового обслуживания (СМО) с перерывами, работающая в таком режиме: при включении сервера после перерыва, если, по крайней мере, один клиент находится в системе, сервер начинает обслуживание и продолжает его до наступления очередного перерыва. Если обнаруживается, что система пуста, сервер находится в режиме ожидания фиксированное время с. По истечении этого времени наступает следующий перерыв в работе сервера, если новый клиент не появился. В противном случае, клиент обслуживается до наступления очередного перерыва. Получены аналитические оценки для среднего времени ожидания в системе. Показано, что схема прерываний является обобщенной схемой, в которой единичная и множественная схемы прерываний — частные случаи соответственно при c c = ∞ и c = 0. Модель распространяется на СМО с N-стратегиями перерывов. В обеих схемах использована линейная модель затрат для получения оптимального параметра срабатывания с.Розглянуто односерверну систему масового обслуговування (СМО) з перервами, що працює у такому режимі: при включенні сервера після перерви, якщо хоча б один клієнт перебуває у системі, сервер починає обслуговування і продовжує його до наступної перервиикщо виявляється, що система є пустою, сервер перебуває у режимі очікування фіксований час с. По закінченні цього часу починається наступна перерва у роботі сервера, якщо новий клієнт не з’явився. У протилежному випадку клієнт обслуговується до початку чергової перерви. Отримано аналітичні оцінки для середнього часу очікування в системі. Показано, що схема переривань є узагальненою схемою, в якій одинична та множинна схеми переривань — окремий випадок відповідно при c = ∞ і c = 0. Модель розповсюджується на СМО з N-стратегіями переривань. У обох схемах використано лінійну модель витрат для отримання оптимального параметра спрацьовування с

The Impact of Working Capital Management on Profitability of Nigerian Firms: A Preliminary Investigation

This study investigated the impact of working capital policies of Nigerian firms on profitability for the period, 2004-2008. Adopting the aggressive investment working capital policies and aggressive financing policies as independent variables and return on assets as dependent variable and controlling for size and leverage, the study revealed that aggressive investment working capital policies of Nigerian firms have a positive significant impact on profitability while aggressive financing policies have a positive non-significant impact on profitability. The findings from this study indicate that firms pursuing aggressive investment working capital policy will become risky in the long-run because as profitability increases; the firm grows and the amount of outsiders’ contributions also increases. The result also indicates that as the firm grows and outsiders’ contribution increases; the use of aggressive financing working capital policy decreases the profitability of the firm. Appropriate management of working capital is therefore essential if the firms are to achieve their objective of improved profitability and value creation for shareholders. Keywords: Working Capital Management, Profitability, Nigerian Firms

The Impact of Labour Turnover on Survival of Small and Medium Scale Enterprises: Evidence from Nigeria

Small and medium scale enterprises all over the world are now looked upon as the engine room of the economy. Governments especially in developing countries are becoming aware of the importance of this sector in the growth of their economies, hence attention are been given to this sector especially in the provision of funds, reduction of legal and bureaucratic bottlenecks involved in incorporation of small scale businesses, provision of manpower training to small scale business owner and other ancillary services that not only will enhance survival but assist in alleviating the level of poverty prevalent to the lower class and  the poor in their economies. It is against this background that this study empirically investigated the impact of labour turnover on survival of small and medium scale enterprises in Nigeria. Samples of fifty SMEs were used for the study and survival proxies such as profit after tax, age and size as dependent variables. The study adopted the two-variable regression models to test the study propositions. The results obtained indicate that labour turnover has positive and significant impact on age and size but was positive and non-significant on profitability of SMEs in Nigeria. The study therefore recommends that, business owners should ensure that workers are not turned over but should be retained. This will ensure their survival in business. Keywords: Labour Turnover, SMEs, Surviva

Probabilistic Reachability for Parametric Markov Models

Abstract. Given a parametric Markov model, we consider the problem of computing the formula expressing the probability of reaching a given set of states. To attack this principal problem, Daws has suggested to first convert the Markov chain into a finite automaton, from which a regular expression is computed. Afterwards, this expression is evaluated to a closed form expression representing the reachability probability. This paper investigates how this idea can be turned into an effective procedure. It turns out that the bottleneck lies in an exponential growth of the regular expression relative to the number of states. We therefore proceed differently, by tightly intertwining the regular expression computation with its evaluation. This allows us to arrive at an effective method that avoids the exponential blow up in most practical cases. We give a detailed account of the approach, also extending to parametric models with rewards and with non-determinism. Experimental evidence is provided, illustrating that our implementation provides meaningful insights on non-trivial models.