Sharif Digital Repository

Spectrum sensing is the basic step in cognitive radio networks. Its accuracy directly affects spectrum utilization. In this paper we propose a new method for blind cooperative spectrum sensing using spatial information. We model our sensing matrix as a graph, taking advantage of signal and spatial correlation of antennas. We prove that the general settings of the problem are hard to approximate. Taking spatial information into account, we propose a new scheme to find white space subregions. Cognitive radio users residing in the region may be able to transmit, but must keep their transmission power to the extent that no interference is caused to primary receivers out of the region  

On-demand resource provisioning and elasticity are two of the main characteristics of the cloud computing paradigm. As a result, the load on a cloud service provider (CSP) is not fixed and almost always a number of its physical resources are not used, called spare resources. As the CSPs typically don't want to be overprovisioned at any time, they procure physical resources in accordance to a pessimistic forecast of their loads and this leads to a large amount of spare resources most of the time. Some CSPs rent their spare resources with a lower price called the spot price, which varies over time with respect to the market or the internal state of the CSP. In this paper, we assume the spot... 

Interesting properties of ionic liquids lead to their application as sub-component of membrane structures. Supported ionic liquid membranes (SILMs) are porous membranes whose pores are saturated with ionic liquids. Two ionic liquids, pr[mim]2[Tf2N]2 [1,3-di(3-methyl-imidazolium) propane bis(trifluoromethylsulfonyl) imide] and, h[mim]2 [Tf2N]2 [(1,6-di(3-methylimidazolium)hexane bis(trifluoromethylsulfonyl)imide)], were synthesized in our laboratory and stabilized on an alumina porous support. Permeability and permselectivity of carbon dioxide and methane using membranes containing these ionic liquids were then measured. The experiments were performed in the pressure range of 10-50kPa and... 

Controlling networked dynamical systems is a complex endeavor, specifically keeping in mind the fact that in many scenarios the actors that are engaged in the dynamism behave selfishly and therefore only take into account their own individual utility, a setting that has been widely studied in the field of game theory. One way that we can control the system dynamics is through the use of control parameters that are at our disposal, but finding optimal values for these parameters is a complex and time consuming task. In this paper we use the relation between network structural properties and control parameters to create a mathematical model that uses learning methods to find optimal values... 

This paper is an attempt to develop a design methodology for a special deployable structure for potential use in micro-satellites. The basic form of this structure is a hexagonal prismatic tensegrity structure, which, after being rigidified, is used as the supporting structure of a mesh-like antenna. Here, the objectives of presenting the design methodology are to prevent structural elements from failure, while maintaining the structural natural frequency and mesh tension above an intended value and in addition, to minimize the overall mass. Here, the suggested design strategy combines the need for a behavioral study (i.e. fast and wide range evaluation) at the beginning of the design, with... 

Given a random variable O ∈ R and a set of experts E, we describe a method for finding a subset of experts S ⊆ E whose aggregated opinion best predicts the outcome of O. Therefore, the problem can be regarded as a team formation for performing a prediction task. We show that in case of aggregating experts’ opinions by simple averaging, finding the best team (the team with the lowest total error during past k rounds) can be modeled with an integer quadratic programming and we prove its NP-hardness whereas its relaxation is solvable in polynomial time. At the end, we do an experimental comparison between different rounding and greedy heuristics on artificial datasets which are generated based... 

A set of recursive equations are introduced for optimum design of a wide range of hierarchical truss beams to satisfy a minimum required natural frequency. The design equations are based on a general analytical solution, which are derived based on a critical dimensional analysis. A practical example is examined in both 2D and 3D spaces, which promises substantial mass reduction, as much as 99%, when using high order hierarchical truss beams. The results are verified by numerical evaluation of three case studies. The approach looks also very promising to design nanostructures when it comes to the problems associated with vibration  

In this paper, a new model reference adaptive controller (MRAC) for uncertain switched linear systems is developed. A class of uncertain switched linear systems with parametric mismatched and input matched uncertainties, control input effectiveness and unmodeled dynamics is studied in this paper. The difference in input matrix for different switching modes which means the input channel degradation is investigated through this paper. By using common Lyapunov function method and developing new linear matrix inequality based sufficient conditions, uniform ultimate boundedness of the reference tracking error is guaranteed by switched MRAC and by using a novel nonlinear controller term, the size... 

In this paper we study envy free pricing problem in general graphs where there is not a seller in every graph's nodes. We assume unique establishment cost for initiating a store in each node and we wish to find an optimal set of nodes in which we would make the maximum profit by initiating stores in them. Our model is motivated from the observation that a same product has different prices in different locations and there is also an establishing cost for initiating any store. We consider both of these issues in our model: first where should we establish the stores, and second at what price should we sell our items in them to gain maximum possible profit. We prove that in a case of constant... 

With thousands of new questions posted every day on popular Q&A websites, there is a need for automated and accurate software solutions to replace manual moderation. In this paper, we address the critical drawbacks of crowdsourcing moderation actions in Q&A communities and demonstrate the ability to automate moderation using the latest machine learning models. From a technical point, we propose a multi-view approach that generates three distinct feature groups that examine a question from three different perspectives: 1) question-related features extracted using a BERT-based regression model; 2) context-related features extracted using a named-entity-recognition model; and 3) general lexical... 

We introduce a network creation game in which each player (vertex) has a fixed budget to establish links to other players. In this model, each link has a unit price, and each agent tries to minimize its cost, which is either its eccentricity or its total distance to other players in the underlying (undirected) graph of the created network. Two versions of the game are studied: In the MAX version, the cost incurred to a vertex is the maximum distance between the vertex and other vertices, and, in the SUM version, the cost incurred to a vertex is the sum of distances between the vertex and other vertices. We prove that in both versions pure Nash equilibria exist, but the problem of finding the... 

Given a random variable (Formula presented.) and a set of experts (Formula presented.), we describe a method for finding a subset of experts (Formula presented.) whose aggregated opinion best predicts the outcome of (Formula presented.). Therefore, the problem can be regarded as a team formation for performing a prediction task. We show that in case of aggregating experts' opinions by simple averaging, finding the best team (the team with the lowest total error during past (Formula presented.) rounds) can be modeled with an integer quadratic programming and we prove its NP-hardness whereas its relaxation is solvable in polynomial time. At the end, we do an experimental comparison between... 

In this research, an efficient biosorption system was developed for methylene blue adsorption over in situ hydrothermally synthesized magnetite 4-hydroxybenzoic acid cellulose nanohybrid. The material was characterized with EDX, VSM, FT-IR, FESEM, and TEM techniques. Results showed that the nanohybrid is a micro-cluster composed of stacked nanoscale particles. Multivariate optimization with Box–Behnken design was used to evaluate effective parameters on adsorption and their interaction. Results showed that pH, shacking time, and adsorbent dosage are effective parameters on MB adsorption. Adsorption rate is fast with equilibrium time of 5.5 min. Isotherm study revealed that the adsorption... 

In this research, an efficient biosorption system was developed for methylene blue adsorption over in situ hydrothermally synthesized magnetite 4-hydroxybenzoic acid cellulose nanohybrid. The material was characterized with EDX, VSM, FT-IR, FESEM, and TEM techniques. Results showed that the nanohybrid is a micro-cluster composed of stacked nanoscale particles. Multivariate optimization with Box–Behnken design was used to evaluate effective parameters on adsorption and their interaction. Results showed that pH, shacking time, and adsorbent dosage are effective parameters on MB adsorption. Adsorption rate is fast with equilibrium time of 5.5 min. Isotherm study revealed that the adsorption... 

An efficient dye decolorization platform was developed through one-step hydrothermally route based on magnetic polymeric resin and employed in aqueous crystal violet (CV) adsorption. The polymer nanohybrid composed of ZnFe2O4 and hydroxybenzoic acid–resorcinol resin as metal and organic fragment, respectively. Several techniques such as X-ray diffraction, N2 – adsorption desorption, vibration sample magnetometer, field emission scanning electron microscopy and Fourier transform infrared spectroscopy were employed for characterization of as-prepared nanohybrid. CV adsorption showed low equilibrium time within 10 min with the adsorption capacity of 83.3 mg g–1. Regeneration of the sorbent... 

Modeling is one of the major research areas in social network analysis whose goal is to study networks structure and its evolution. Motivated by the intuition that members in social networks behave selfishly, network creation games have been introduced for modeling social networks. In this paper, our aim is to measure how much the output graphs of a given network creation game are compatible with a social network. We first show that the precise measurement is not possible in polynomial time. Then we propose a method for its approximation; finally, we show the usability of our method by conducting experiments on real network data  

The spread of influence in social networks is studied in two main categories: progressive models and non-progressive models (see, e.g., the seminal work of Kempe et al. [8]). While the progressive models are suitable for modeling the spread of influence in monopolistic settings, non-progressive models are more appropriate for non-monopolistic settings, e.g., modeling diffusion of two competing technologies over a social network. Despite the extensive work on progressive models, non-progressive models have not been considered as much. In this paper, we study the spread of influence in the non-progressive model under the strict majority threshold: given a graph G with a set of initially...