Sharif Digital Repository

Quality of Service (QoS) of Web services plays an essential role in selecting Web services by consumers. The dynamic QoS attributes of Web services have different values for different users. Therefore, the value of many Web services' QoS features for many users are undetermined, and these values should be predicted. The collaborative filtering (CF) method is one of the most successful approaches to predict these values. CF-based methods use the QoS values contributed by the other users for prediction and, consequently, the values contributed by unreliable users can decrease the accuracy of prediction. To utilize the reputation of users can be regarded as one of the conventional approaches to... 

Virtual organization (VO) is aimed to provide inter-organizational collaborations. Constructing a VO necessitates provision of security and access control requirements which cannot be satisfied using the traditional access control models. This is basically due to special features of VOs; such as temporality, unknown users, and diverse resources. In this paper, after expressing our assumption on a framework for VOs; the concept of organizational trust and reputation is used to establish an access control model for VOs. Each member of an organization inherits its organizational reputation. Resource providers announce the behavior of their interacting users to their organization manager.... 

The connectivity between two points in porous media is important for evaluating hydrocarbon recovery in underground reservoirs or toxic migration in waste disposal. For example, the connectivity between a producer and an injector in a hydrocarbon reservoir impact the fluid dispersion throughout the system. The conventional approach, flow simulation, is computationally very expensive and time consuming. Alternative method employs percolation theory. Classical percolation approach investigates the connectivity between two lines (representing the wells) in 2D cross sectional models whereas we look for the connectivity between two points (representing the wells) in 2D aerial models. In this... 

The endurance time (ET) method is a dynamic analysis in which structures are subjected to intensifying excitations, also known as ET excitation functions (ETEF). The ET method is a tool for structural response prediction. The main advantage of the ET method over conventional approaches is its much lower demand for computational efforts. The concept of acceleration spectra is used in generating existing ETEFs. It is expected that ETEF acceleration spectra increase consistently with time and remain proportional to a target spectrum. Nonlinear unconstrained optimization is commonly used to generate ETEFs. Generating new ETEFs is a complicated time-consuming mathematical problem. If the target... 

New technologies such as smart homes and appliances and renewable energy production have been attracting much attention in recent years. In practice, the management of these technologies to get the minimum household payment has become a challenge due to the time-varying electricity price. In this paper, we propose a real time energy management system to manage the appliances and storages. The solar energy is charged in the storages and used together with the grid electricity to supply the appliances. The proposed management system uses an ILP-based Home Energy Management (ILPHEM) optimization engine. ILPHEM schedules appliances requests and storage usage based on updated real time input data... 

Models capable of accurate simulation of the microcantilever dynamics coupled with complex tip-sample interactions are essential for interpretation of the imaging results in non-contact atomic force microscopy (AFM). In the present research, a combination of finite element and molecular dynamics methods are used for modelling the AFM system to overcome the drawbacks of conventional approaches that use a lumped system with van der Waals interaction. To illustrate the ability of the proposed scheme in providing images with atomic resolution, some simulations have been performed. In the conducted simulations, a diamond tip is interacting with nickel samples having different surface plane... 

In this brief, a transformer-type power combiner for a fully integrated high-power CMOS power amplifier (PA) is presented. The proposed power combiner is composed of a number of transformers that, unlike the ones in conventional approaches, have different sizes. This leads to higher efficiency and smaller chip area. After considering several power stage topologies, analysis and optimization of the transformer network (the power combiner) are presented. To demonstrate the advantages of the proposed architecture, a 900-MHz CMOS PA with the proposed power combiner was implemented with a 0.18-μm radio-frequency CMOS process. The amplifier achieved an efficiency value of 24% at the maximum output... 

Magnetic flux leakage is the most widely used method for oil and gas pipeline non destructive testing. The saturation level of the sample under test has a significant effect on its efficiency; therefore, the magnetizing yoke requires an elaborate design. The finite element method is the conventional approach used for this purpose, but it is very time consuming. In this article, a neuro-fuzzy method is presented to model the behavior of the magnetizing yoke. Modeling a few different designs with the finite element method and using the results for training the neuro-fuzzy model eradicates the necessity of modeling a huge number of designs with the finite element method. The acquired... 

The conventional solar cell architectures include a p-n junction of c-Si sandwiched by rear and front contacts. The conventional approach features a complex as well as expensive procedure. Here, we propose a new architecture for p-n heterojunction solar cells prepared by a simple and cost-effective procedure. In this regard, (1) a silicon wafer underwent surface treatment through electrochemical anodization. To prepare a stick junction, (2) photoactive TiO2 nanoparticles were deposited over the porous layer by electrophoretic technique. Finally, (3) indium tin oxide (ITO) was sputtered. During the fabrication steps, we examined various anodization times ranging from 6 to 12 min to study the... 

In this paper, we study the problem of delay minimization in NFV-based networks. In such systems, the ultimate goal of any request is to compute a sequence of functions in the network, where each function can be computed at only a specific subset of network nodes. In conventional approaches, for each function, we choose one node from the corresponding subset of the nodes to compute that function. In contrast, in this work, we allow each function to be computed in more than one node, redundantly in parallel, to respond to a given request. We argue that such redundancy in computation not only improves the reliability of the network, but would also, perhaps surprisingly, reduce the overall... 

The inception of transformation optics has opened avenues for designing of a plethora of applications related to the propagation of electromagnetic waves in anisotropic media. In this paper, an algorithm is proposed using a coordinate transformation for the purpose of designing a cloak for a body having an arbitrary convex geometry. For the purpose of verification of the algorithm, a ray tracing process is carried out for an ellipsoid as well as an irregularly shaped body, both having axial symmetry. The ray tracing is carried out in a two dimensional plane since the transmitted ray vector would lie in the plane of incidence containing the incident ray vector and the normal vector to the... 

Photovoltaic (PV) panels provide a suitable way for the direct conversion of solar energy into electricity. The electrical output and efficiency of PV modules are dependent on working temperature. The present study contributes to investigate the efficiency of utilizing a flat plate closed-loop pulsating heat pipe (CLPHP) to cool down a PV panel in both thermal and economic aspects. Accordingly, a numerical investigation is employed to obtain the surface temperature and electrical gain of the PV panel through four scenarios, including natural cooling without additional equipment, CLPHP-based passive cooling, CLPHP-based active cooling, and a conventional flat plate cooling methods. The... 

Energy Return on Investment (EROI) is an indicator of how efficient is an energy supply system. In the present study, the conventional approach of EROI assessment is extended to include the equivalent energy investment needed for offsetting the life cycle environmental impacts. Moreover, the issue of allocation of the invested energy among different by-products is addressed. The EROI of multiple products has been specified using different benchmarks of price, energy content, exergy content, and exergy costs. The application of the concept is demonstrated through a case study of an Iranian oil production unit. The overall conventional and environmentally-extended EROI values of the produced... 

Decision on the location of new wells through infill drilling projects is a complex problem that depends on the reservoir rock and fluid properties, well and surface facilities specifications, and economic measures. Conventional approach to address this is a direct optimization that uses the numerical flow simulation. However, this is computationally very extensive. In this study the authors use a hybrid genetic algorithm (HGA) optimization technique based on the genetic algorithm (GA) with helper functions based on the polytope algorithm and the neural network. This hybridization introduces hill-climbing into the stochastic search and makes use of proxies created and calibrated iteratively... 

Decision on the location of new wells through infill drilling projects is a complex problem that depends on the reservoir rock and fluid properties, well and surface facilities specifications, and economic measures. Conventional approach to address this is a direct optimization that uses the numerical flow simulation. However, this is computationally very extensive. In this study the authors use a hybrid genetic algorithm (HGA) optimization technique based on the genetic algorithm (GA) with helper functions based on the polytope algorithm and the neural network. This hybridization introduces hill-climbing into the stochastic search and makes use of proxies created and calibrated iteratively... 

Flow assurance is a major challenge in offshore and deepwater operations. Conventional approaches for preventing gas-hydrate formation involve using thermodynamic inhibitors (e.g., methanol, glycol) or kinetic hydrate inhibitors or operating outside the hydratestability zone by insulating the pipeline and/or active heating. These techniques are not always economical and in some cases are not practical for deepwater operations, long tiebacks, or aging reservoirs with high water cuts. The industry needs new and novel flow-assurance techniques to address these challenging conditions. The approach presented in this paper is a wet cold-flow-based method in which gas-hydrate management rather than...