Sharif Digital Repository

A two-machine flowshop scheduling problem is addressed to minimize setups and makespan where each job is characterized by a pair of attributes that entail setups on each machine. The setup times are sequence-dependent on both machines. It is shown that these objectives conflict, so the Pareto optimization approach is considered. The scheduling problems considering either of these objectives are N p - hard, so exact optimization techniques are impractical for large-sized problems. We propose two multi-objective metaheurisctics based on genetic algorithms (MOGA) and simulated annealing (MOSA) to find approximations of Pareto-optimal sets. The performances of these approaches are compared with... 

A bicriteria two-machine flowshop scheduling problem is addressed to minimize the number of setups and makespan. The jobs have sequence dependent setup times. Scheduling problems considering either of these objectives are NP-hard. Two multi-objective metaheurisctics based on genetic algorithms (MOGA) and simulated annealing (MOSA) are proposed to find approximations of Pareto-optimal frontiers. The performances of these approaches are compared with lower bounds for small problems. In larger problems, their performance is compared with each other. Experimentations revealed that both algorithms perform very similar on small problems and that MOGA outperforms MOSA in terms of the quality of... 

We consider the effect of caching in wireless networks where fading is the dominant channel effect. First, we propose a one-hop transmission strategy for cache-enabled wireless networks, which is based on exploiting multi-user diversity gain. Then, we derive a closed-form result for throughput scaling of the proposed scheme in large networks, which reveals the inherent trade-off between cache memory size and network throughput. Our results show that substantial throughput improvements are achievable in networks with sources equipped with large cache size. We also verify our analytical result through simulations  

Many applications in wireless networks impose locally distributed traffic on the network. We consider the effect of traffic localization on throughput of large wireless networks in the scaling sense. We show that by careful exploitation of traffic localization, one can enhance the throughput of various schemes in wireless networks. Also, the important case of Small World traffic distribution in wireless networks is addressed. In this type of traffic, in addition to the local traffic, a non-negligible amount of global traffic should be handled by the network. It is shown that a non-negligible amount of network-wide traffic can be tolerated by network without any performance degradation in the... 

In this study, the authors propose a novel power allocation scheme in time division multiple access (TDMA)-based distributed multiple-input multiple-output (MIMO) channels. By modelling the problem with a TDMA MIMO interference channel, the authors have derived closed-form expressions for power and time slot assigned to each MIMO transmission. Although our scheme is sub-optimal, with the aid of Jensen's inequality, it is shown to be superior to solutions based on channel inversion. In addition, the proposed scheme is compared with the optimal solution, and also with the scheme proposed by Dohler. By applying our proposed power allocation to the hierarchical cooperation strategy, the authors... 

We consider one-hop communication in wireless networks with random connections. In the random connection model, the channel powers between different nodes are drawn from a common distribution in an i.i.d. manner. In a wireless network with n nodes, a simple one-hop scheme achieving the throughput scaling of order n 1/3-δ, for any arbitrarily small δ > 0, is proposed. This scheme is based on maximizing the number of successful concurrent transmissions. Such achievable throughput, along with the order n 1/3 upper bound derived by Cui et al., characterizes the throughput of one-hop schemes for the class of connection models with distribution having finite mean and variance  

We consider the problem of determining throughput of one-hop unicast transmissions in ad hoc wireless networks. We consider an interference-limited scenario in which wireless links between different nodes are modeled by independently and identically distributed random variables. The main decoding challenge for receive nodes is due to interference of nonintended concurrent transmissions. In this scenario, we consider a heuristic one-hop transmission strategy based on activating source-destination pairs with strongest direct links and forcing other pairs to be silent. We present a closed-form expression for throughput scaling of such strategy, for a completely general channel power... 

In this paper, we derive the rate of route discovery process for finding a randomly chosen destination in large wireless networks. The well-known protocol for route discovery is flooding in which each node simply rebroadcasts the route request packet once. Rate of route discovery process is defined as the inverse of time between transmitting two successive route request packets which shows how fast a node can request a route to its destination. Discovery time is another parameter of interest. For a single node discovering routes to its destination, at most the rate of Eθ (1/3√n) is feasible when n identical nodes are optimally placed in network area and the discovery time is of order... 

Concepts like peculiar velocity, gravitational force, and power spectrum and their inter-relationships are of utmost importance in the theories of structure formation. The observational implementation of these concepts is usually based on the Newtonian hydro-dynamic equations, but used up to scales where general relativistic effects come in. Using a perturbation of FRW metric in harmonic gauge, we show that the relativistic effects reduce to light cone effects including the expansion of the universe. Within the Newtonian gravitation, the linear perturbation theory of large scale structure formation predicts the peculiar velocity field to be directly proportional to gravitational force due to... 

Mobile-edge computing (MEC) is envisioned to address the computation demands of Internet of Things (IoT) devices. However, it is crucial for the MEC to operate in coordination with the cloud tier to achieve a highly scalable IoT system. In addition, IoT devices require regular maintenance to either recharge or replace their batteries which may not always be feasible. Wireless energy transfer (WET) can provide IoT devices with a stable source of energy. Nonetheless, proper scheduling of energy harvesting and efficient allocation of computing resources are the key to the sustainable operation of these devices. In this article, we introduce a three-tier wireless-powered MEC (WPMEC) consisting... 

User churn is an important issue in online services that threatens the health and profitability of services. Most of the previous works on churn prediction convert the problem into a binary classification task where the users are labeled as churned and non-churned. More recently, some works have tried to convert the user churn prediction problem into the prediction of user return time. In this approach which is more realistic in real world online services, at each time-step the model predicts the user return time instead of predicting a churn label. However, the previous works in this category suffer from lack of generality and require high computational complexity. In this paper, we... 

In this study, decolorization of the diazo dye, Reactive Black 5 (RB5) in a Coprinus cinereus peroxidase-catalyzed reaction has been investigated. A bisubstate kinetic model for the reaction rate based on the Ping-Pong mechanism was assumed for the enzymatic decolorization. Experiments were conducted at different RB5 and hydrogen peroxide concentrations in a batch manner to estimate the intrinsic kinetic parameters. These parameters were used for the modeling of decolorization in a continuous reactor that was compared with experimental results. An acceptable agreement was observed between the model and experimental data  

Some Applications need to propagate important and critical data to all nodes in a wireless ad-hoc network. Flooding and its variants are good and simple protocols to achieve this target, but they are not efficient. Network coding can improve the performance of these algorithms. In designing such algorithms there are some important parameters which should be taken into account. Energy consumption, coverage and total delay are the most important parameters in a wireless ad-hoc network. Also in the network coding based algorithms, complexity of coding and packet overhead that network coding inserts to the system are important design parameters. In this article, XRBCast, a reliable and energy... 

Using a proposed evolutionary algorithm, we have solved the inverse problem of finding the incident field on a high-aperture lens for generating a desired focused field, for the first time (to our knowledge). Further, we have achieved the global solution to the problem using this novel algorithm  

We consider a planar gravitating thick domain wall of the λφ4 theory as a space-time with finite thickness glued to two vacuum space-times on each side of it. Darmois junction conditions written on the boundaries of the thick wall with the embedding space-times reproduce the Israel junction condition across the wall in the limit of infinitesimal thickness. The thick planar domain wall located at a fixed position is then transformed to a new coordinate system in which its dynamics can be formulated. It is shown that the wall's core expands as if it were a thin wall. The thickness in the new coordinates is not constant anymore and its time dependence is given. © World Scientific Publishing... 

We extend our previous formalism in order to analyse the dynamics of a general shell of matter with an arbitrary finite thickness immersed in a curved spacetime. Within this new formulation, we obtain the equations of motion of a spherically symmetric dust thick shell immersed in vacuum as well as Friedmann-Robertson-Walker spacetimes. © 2006 IOP Publishing Ltd  

Mobile devices are equipped with a multi-core heterogeneous processing architecture to balance the trade-off between performance and power efficiency. To take advantage of this architecture, in this paper, we propose a task scheduling algorithm that allocates the cores to computation tasks and adjusts the cores' operating frequency by using the dynamic voltage and frequency scaling (DVFS) technique. Our objective is to minimize the battery energy consumption of devices. We also consider offloading the tasks to a cloud server to address their ever increasingly computation demand. In order to design the task scheduling algorithm, we first formulate a combinatorial optimization problem. To... 

Mass transfer rates to the drops in liquid-liquid extraction equipment are often likely to be reduced by the presence of surface active contaminants. This reduction in mass transfer is said to be due to a reduction in terminal velocity, and to changes in pattern of internal circulation. A single-drop extraction apparatus was used to investigate the dependency of mass transfer coefficient on the amount of surfactant added in a system of n-butanol/succinic acid/water. Three types of surfactants, SDS, DTMAC and Triton X-100, were used to study their effects on the inhibition of mass transfer in liquid-liquid extraction. The effect of surfactants concentration on extraction percentage, overall... 

Concepts developed in the gravitational lensing techniques such as shear, convergence, tangential, and radial arcs maybe used to see how tenable inhomogeneous models proposed to explain the acceleration of the universe models are. We study the widely discussed Lemaitre-Tolman-Bondi (LTB) cosmological models. It turns out that for the observer sitting at origin of a global LTB solution the shear vanishes as in the Friedmann-Robertson-Walker models, while the value of convergence is different, which may lead to observable cosmological effects. We also consider Swiss-cheese models proposed recently based on LTB with an observer sitting in the Friedmann-Robertson-Walker part. It turns out that... 

The present study was an attempt to explore international English-medium publication in humanities and social sciences in Iran. In so doing, 50 PhD students from 8 humanities and social sciences disciplines, who had already published or attempted to publish in English-medium journals, were requested to write reflection guide accounts and to take part in follow-up semi-structured interviews. The reflection guide and interview data were analyzed based on the principles of grounded theory research yielding the four major themes of motivations, hurdles, strategies, and call for support. The results indicated that the Iranian PhD students in the fields of humanities and social sciences are...