Energy–delay tradeoff in a two-way relay with network coding

A queueing model for a relay in a communication network that is employing network coding is introduced. It is shown that communication networks with coding are closely related to queueing networks with positive and negative customers. The tradeoff between minimizing energy consumption and minimizing delay for a two-way relay is investigated. Analytical upper and lower bounds on the energy consumption and the delay are obtained using a Markov reward approach. Exact expressions are given for the minimum energy consumption and the minimum delay that are attainable

Stability of two exponential time-limited polling models

In this article, we consider the stability of two single-server polling models. More specifically, we will state and prove the stability conditions of single-server polling systems operating under the pure and exhaustive exponential time-limited service discipline. These conditions will be proven for the polling system operating under the periodic polling strategy and preemptive service. The stability proof of the pure time-limited discipline is straightforward as stability may be considered for each queue in isolation. The proof for the exhaustive time-limited discipline is more laborious. We follow the line of proof as introduced by Fricker and Ja\"{i}bi for a large class of service disciplines. Unfortunately, the preemptive nature of the exhaustive time-limited discipline excludes it from this class and as a result substantial efforts are required to modify the proof as to allow for preemptive disciplines. Finally, the extension of the proofs to the Markovian polling strategy is discussed

Green Wave Analysis in a Tandem of Traffic-Light Intersections

Green waves in urban settings are seen to be beneficial both for the drivers and the environment because they lower delays and reduce pollution. To obtain these benefits, it is important to determine the optimal network parameters, e.g., green splits and offsets, that yield the desired traffic behaviour. We consider two possibilities for network optimization. The first one is minimising the average lost time per vehicle; the second one is maximizing the green wave efficiency. We compare the results with the MAXBAND algorithm, which is used at the design stage of arterial traffic light settings to facilitate green waves. Using our optimisation method, the average delay per vehicle can be reduced by up to 10% and more vehicles can encounter a green wave compared to the MAXBAND approach. The reduction of the average delay for the main stream reaches 20%

Designing cyclic appointment schedules for outpatient clinics with scheduled and unscheduled patient arrivals

We present a methodology to design appointment systems for outpatient clinics and diagnostic facilities that offer both walk-in and scheduled service. The developed blueprint for the appointment schedule prescribes the number of appointments to plan per day and the moment on the day to schedule the appointments. The method consists of two models that are linked by an algorithm; one for the day process that governs scheduled and unscheduled arrivals on the day and one for the access process of scheduled arrivals. Appointment schedules that balance the waiting time at the facility for unscheduled patients and the access time for scheduled patients, are calculated iteratively using the outcomes of the two models. The method is of general nature and can therefore also be applied to scheduling problems in other sectors than health care

Average case analysis of the MST-heuristic for the power assignment problem:Special cases

We present an average case analysis of the minimum spanning tree heuristic for the power assignment problem. The worst-case approximation ratio of this heuristic is 2. We have the following results: (a) In the one-dimensional case, with uniform [0,1]-distributed distances, the expected approximation ratio is bounded above by 2-2=(p+2), where p denotes the distance power gradient. (b) For the complete graph, with uniform [0,1] distributed edge weights, the expected approximation ratio is bounded above by 2-1/2ζ(3), where ζ denotes the Riemann zeta function

Performance analysis of wireless LANs: an integrated packet/flow level approach

In this paper we present an integrated packet/flow level modelling approach for analysing flow throughputs and transfer times in IEEE 802.11 WLANs. The packet level model captures the statistical characteristics of the transmission of individual packets at the MAC layer, while the flow level model takes into account the system dynamics due to the initiation and completion of data flow transfers. The latter model is a processor sharing type of queueing model reflecting the IEEE 802.11 MAC design principle of distributing the transmission capacity fairly among the active flows. The resulting integrated packet/flow level model is analytically tractable and yields a simple approximation for the throughput and flow transfer time. Extensive simulations show that the approximation is very accurate for a wide range of parameter settings. In addition, the simulation study confirms the attractive property following from our approximation that the expected flow transfer delay is insensitive to the flow size distribution (apart from its mean)

Breve análisis de los factores que intervienen en el aprendizaje ortográfico

Si revisamos el rendimiento escolar de nuestros alumnos referido a la lengua escrita comprobaremos cómo uno de los problemas que frecuentemente se nos plantea, además de la alarmante pobreza de vocabulario y la precariedad de la expresión, son las faltas de ortografía. Ello se debe a la complejidad de los factores que intervienen en el proceso escritor donde está implicada esta disciplina lingüística. En este artículo estudiamos cada uno de estos elementos que, a nuestro juicio, deben considerarse al analizar el fracaso ortográfico de nuestros estudiantes.If we reexamine our students school efficiency relating written language, we will verify that one of the problems that we usually find, besides the alarming vocabulary poverty and the precarious expression, are orthographic mistakes. This fact is due to the complexity of the writing process factors where this linguistic discipline is implicated. In the present paper we specify every one of these elements that we must be considered on analysing the wrong spelling of our students.Facultad de Educación y Humanidades - Campus de Melilla (Universidad de Granada

An exact approach for relating recovering surgical patient workload to the master surgical schedule

No other department influences the workload of a hospital more than the Department of Surgery and in particular, the activities in the operating room. These activities are governed by the master surgical schedule (MSS), which states which patient types receive surgery on which day. In this paper we describe an analytical approach to project the workload for downstream departments based on this MSS. Specifically the ward occupancy distributions, patient admission/discharge distributions, and the distributions for ongoing interventions/treatments is computed. Recovering after surgery requires the support of multiple departments, such as nursing, physiotherapy, rehabilitation and long term care. With our model, managers from these departments can determine their workload by aggregating tasks associated with recovering surgical patients. The model, which supported the development of a new MSS at the Netherlands Cancer Institute-Antoni van Leeuwenhoek Hospital, provides the foundation for a decision support tool to relate downstream hospital departments to the operating room