Nikola S. Nikolov

Nikola S. Nikolov
University of Limerick | UL · Department of Computer Science and Information Systems (CSIS)

PhD in Computer Science

About

87
Publications
30,455
Reads
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633
Citations
Introduction
Dr. Nikola S. Nikolov is an academic faculty member of the Department of Computer Science and Information Systems (CSIS) at the University of Limerick, Ireland. He is a co-head of the Big Data and Analytics Research Group (BDARG) at CSIS. His most important research contributions are in hierarchical network visualisation. See http://bdarg.org for further information.
Additional affiliations
December 2007 - present
University of Limerick
Position
  • Lecturer
June 2004 - May 2005
National ICT Australia Ltd
Position
  • Researcher Level B
Description
  • Postdoctoral researcher in the IMAGEN group. Involved in the VALACON (Visualization of Large and COmplex Networks) project.
July 2001 - December 2007
University of Limerick
Position
  • Junior Lecturer
Education
November 1998 - June 2002
University of Limerick
Field of study
  • Theoretical Computer Science
September 1990 - July 1995

Publications

Publications (87)
Article
Full-text available
With the development of ubiquitous computing, recommendation systems have become essential tools in assisting users in discovering services they would find interesting. This process is highly dynamic with an increasing number of services, distributed over networks, bringing the problems of cold start and sparsity for service recommendation to a new...
Chapter
Full-text available
Conference Paper
Full-text available
We introduce a new graph drawing convention for 3D hierarchical drawings of directed graphs. The vertex set is partitioned into layers of vertices drawn in parallel planes. The vertex set is further partitioned into k>=2 subsets, called walls. The layout consists of a set of parallel walls which are perpendicular to the set of parallel planes of th...
Conference Paper
Full-text available
We introduce a new force-directed graph drawing algorithm for large undirected graphs with at least a few hundreds of vertices. Our algorithm falls into the class of multilevel force-directed graph drawing algorithms. Unlike other multilevel algorithms it has no pre-processing step and it also ignores repulsion forces between pairs of non-adjacent...
Article
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This paper presents a comprehensive evaluation of data pre-processing and word embedding techniques in the context of Arabic document classification in the domain of health-related communication on social media. We evaluate 26 text pre-processings applied to Arabic tweets within the process of training a classifier to identify health-related tweets...
Conference Paper
Full-text available
Collaborative filtering (CF) has achieved great success in the field of recommender systems. In recent years, many novel CF models, particularly those based on deep learning or graph techniques, have been proposed for a variety of recommendation tasks, such as rating prediction and item ranking. These newly published models usually demonstrate thei...
Article
Full-text available
Deep learning models are now considered state-of-the-art in many areas of pattern recognition. In speaker recognition, several architectures have been studied, such as deep neural networks (DNNs), deep belief networks (DBNs), restricted Boltzmann machines (RBMs), and so on, while convolutional neural networks (CNNs) are the most widely used models...
Article
Full-text available
Matrix Factorization (MF) is one of the most successful Collaborative Filtering (CF) techniques used in recommender systems due to its effectiveness and ability to deal with very large user-item rating matrix. However, when the rating matrix sparseness increases its performance deteriorates. Expanding MF to include side-information of users and ite...
Preprint
This era is witnessing a great and rapid development in the field of communications and informatics, that including the use of the Internet and social media platforms, these platforms are witnessing unprecedented use in the last two decades. This use is the way people interact with each other. There is no doubt that this interaction has a positive...
Preprint
This paper presents the results of several ML experiments, conducted with a dataset of YouTube comments in Arabic. The experiments aim at studying the impact of various text pre-processing, feature-extraction and feature-selection techniques on the accuracy of a document classifier for detection of offensive language in online communication in Arab...
Article
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In the era of global-scale services, organisations produce huge volumes of data, often distributed across multiple data centres, separated by vast geographical distances. While cluster computing applications, such as MapReduce and Spark, have been widely deployed in data centres to support commercial applications and scientific research, they are n...
Preprint
Full-text available
Collaborative filtering (CF) has achieved great success in the field of recommender systems. In recent years, many novel CF models, particularly those based on deep learning or graph techniques, have been proposed for a variety of recommendation tasks, such as rating prediction and item ranking. These newly published models usually demonstrate thei...
Article
Full-text available
The Dimensionality Curse is one of the most critical issues that are hindering faster evolution in several fields broadly, and in bioinformatics distinctively. To counter this curse, a conglomerate solution is needed. Among the renowned techniques that proved efficacy, the scaling-based dimensionality reduction techniques are the most prevalent. To...
Article
Full-text available
We propose a novel usage of convolutional neural networks (CNNs) for the problem of speaker recognition. While being particularly designed for computer vision problems, CNNs have recently been applied for speaker recognition by using spectrograms as input images. We believe that this approach is not optimal as it may result in two cumulative errors...
Conference Paper
This paper presents a novel matrix factorization (MF) recommendation model, FeatureMF, which extends item latent vectors with item representation learned from metadata. By taking into account item features, the model addresses the coldstart item problem and data-sparsity problem of collaborative filtering (CF). Extensive experiments conducted on a...
Conference Paper
This paper presents a novel matrix factorization (MF) model, called FeatureMF, which takes into account item features and thus addresses the cold-start item and data sparsity problems of collaborative filtering (CF). More specifically, the model extends item latent vectors with item representation learned from metadata. Experiments conducted on a p...
Article
Full-text available
Background: Social media platforms play a vital role in the dissemination of health information. However, evidence suggests that a high proportion of Twitter posts (ie, tweets) are not necessarily accurate, and many studies suggest that tweets do not need to be accurate, or at least evidence based, to receive traction. This is a dangerous combinati...
Conference Paper
Full-text available
Offensive content on social media such as verbal attacks, demeaning comments or hate speech has many negative effects on its users. The automatic detection of offensive language on Arabic social media is an important step towards the regulation of such content for Arabic speaking users of social media. This paper presents the results of evaluating...
Article
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Abstract In the era of accelerating growth of genomic data, feature-selection techniques are believed to become a game changer that can help substantially reduce the complexity of the data, thus making it easier to analyze and translate it into useful information. It is expected that within the next decade, researchers will head towards analyzing t...
Article
Full-text available
We present the results of predictive modelling for the detection of anti-social behaviour in online communication in Arabic, such as comments which contain obscene or offensive words and phrases. We collected and labelled a large dataset of YouTube comments in Arabic which contains a broad range of both offensive and inoffensive comments. We used t...
Article
Full-text available
Warning: this paper contains a range of words which may cause offence. In recent years, many studies target anti-social behaviour such as offensive language and cyberbullying in online communication. Typically, these studies collect data from various reachable sources, the majority of the datasets being in English. However, to the best of our knowl...
Chapter
We consider the question of whether a given graph drawing \(\varGamma \) of a triconnected planar graph G is a weighted barycenter drawing. We answer the question with an elegant arithmetic characterisation using the faces of \(\varGamma \). This leads to positive answers when the graph is a Halin graph, and to a polynomial time recognition algorit...
Conference Paper
Full-text available
The publication presents the results of empirical research on web technologies used in the home pages of the Finland commercial banks authorized under Finland Legislation to carry on commercial banking business and supervised by the Finland Financial Supervisory Authority (FIN-FSA). The home pages of 9 commercial banks were studied. Our survey reve...
Preprint
Full-text available
We consider the question of whether a given graph drawing $\Gamma$ of a triconnected planar graph $G$ is a weighted barycenter drawing. We answer the question with an elegant arithmetic characterisation using the faces of $\Gamma$. This leads to positive answers when the graph is a Halin graph, and to a polynomial time recognition algorithm when th...
Poster
Full-text available
The goal of our study is to develop techniques based on Natural Language Processing (NLP) for detection of offensive language on a social media platform. This work aims at identifying the characterristics of the language generated on social media by Arabs from multiple countries in the Arab region, and finding proper solutions based on machine lear...
Poster
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NetvizGL is a C++ OpenGL application for the visualisation of network graphs. It is a lightweight application designed to be minimal, extensible and scalable. NetvizGL can draw networks per a set of graph drawing algorithms. These algorithms are either be pre-packaged or a user may choose to write their own. With an an adaptation mechanism in place...
Poster
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Semantic Recommendation Prototype Adapted for the Ubiquitous Consumer Wireless World
Conference Paper
Full-text available
With the rapid growth of the Web, recommender systems have become essential tools to assist users to find high-quality personalized recommendations from massive information resources. Content-based filtering (CB) and collaborative filtering (CF) are the two most popular and widely used recommendation approaches. In this paper, we focus on ways of t...
Conference Paper
Recommendation systems employed on the Internet aim to serve users by recommending items which will likely be of interest to them. The recommendation problem could be cast as either a rating estimation problem which aims to predict as accurately as possible for a user the rating values of items which are yet unrated by that user, or as a ranking pr...
Conference Paper
Full-text available
This study focuses on the performance improving of social assisted search by using the Redis system as a cache layer between an application and a MySQL system which stores data extracted from the behavior of many users. Since searches made by one particular user can be viewed as a Markov chain, there is need for a lot of data to be read and display...
Conference Paper
Full-text available
This paper proposes an improvement to item recommendation systems based on collaborative filtering (CF) with implicit feedback data. Combined with the Bayesian Personalized Ranking (BPR) optimization approach, recommended for implicit-only feedback contexts, CF has been shown to be effective in generating accurate recommendations. The method, based...
Conference Paper
Full-text available
In recent years, there has been significant growth in the uptake of personal communication technologies across the world. This has been largely afforded by the wide availability of social media (SM) and facilitated by the increase in smartphone ownership. However, this growth does not come without disadvantages. For example, there is growing eviden...
Conference Paper
Exploiting additional item meta-data is proposed in this paper for solving data sparsity and cold start problems found in item-based collaborative filtering (CF) techniques, which are employed in recommendation systems. Additional item meta-data provides the foundation for generating a heterogeneous information network (HIN). The proposed approach...
Conference Paper
Full-text available
This paper describes the general service recommendation process matched to the telecommunication service delivery characteristics of the Ubiquitous Consumer Wireless World (UCWW). The goal is to provide consumers with the `best' service instances that match their dynamic, contextualized and personalized requirements and expectations, thereby aligni...
Conference Paper
Full-text available
The item-based collaborative filtering (CF) is one of the most successful approaches utilized by the recommendation systems. The basic concept behind it is to recommend those items to users which are similar to other items that these users have been interested in recently. This paper proposes a hybrid method that integrates user trust relations wit...
Article
Full-text available
We report on our findings using a genetic algorithm (GA) as a preprocessing step for force-directed graph drawings to find a smart initial vertex layout (instead of a random initial layout) to decrease the number of edge crossings in the graph. We demonstrate that the initial layouts found by our GA improve the chances of finding better results in...
Conference Paper
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We report on our findings using Simulated Annealing (SA) as a preprocessing step for force-directed graph drawing. Our proposed SA algorithm finds a smart initial vertex placement (instead of a random initial vertex placement) in order to decrease the chance of having edge crossings (local minima) and also to decrease the number of required iterati...
Conference Paper
Full-text available
Context-aware recommendation systems make recommendations by adapting to user's specific situation, and thus by exploring both the user preferences and the environment. In this paper, we propose a context-aware service recommendation framework utilising semantic knowledge in the Ubiquitous Consumer Wireless World (UCWW). The main objective of the f...
Article
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We introduce a force-directed algorithm, called Sync-and-Burst, which falls into the category of classical force-directed graph drawing algorithms. A distinct feature in Sync-and-Burst is the use of simplified forces of attraction and repulsion whose magnitude does not depend on the distance between vertices. Instead, magnitudes are uniform through...
Conference Paper
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We propose a genetic algorithm (GA) for solving the maximization version of the Optimal Linear Arrangement problem and we also demonstrate how solutions found by it can be used for constructing smart initial layouts for force-directed graph drawing. Effectively, we show that our GA can be used as a first step in force-directed graph drawing for ach...
Conference Paper
Full-text available
Context-aware recommendation systems make recommendations by adapting to user's specific situation, and thus by exploring both the user preferences and the environment. In this paper, the design of a context-aware service recommendation framework utilising semantic knowledge in the Ubiquitous Consumer Wireless World (UCWW) is outlined. The main obj...
Conference Paper
Full-text available
The exponential growth of various social media platforms in recent years has created the opportunity for people to interact and communicate with each other to a degree unprecedented before the invention of the Web. This development is without doubt beneficial for society; however, it has also been associated with an escalation of cyberbullying acti...
Technical Report
Full-text available
With software development becoming a very popular hobby and career for many, the range of technologies and programming languages that are available today is very wide and diverse; each language being crafted for certain problem areas. The goal of this project is to utilise the public data available in a large online source control system for creati...
Article
Full-text available
We present an algorithm which produces circular-shape layouts of trees by simulating synchronisation dynamics on the tree. Our approach consists of evolving scalar dynamical values assigned to the nodes. Then the dissimilarities between the values of each pair of nodes are utilised to calculate the coordinates of the nodes by using a lower bound on...
Conference Paper
Full-text available
This paper describes research into a new cloud-based service recommendation system for the Ubiquitous Consumer Wireless World (UCWW). The main objective of the system is to provide users with the 'best' service instances that match their dynamic, contextualised and personalised requirements and expectations, thereby achieving the goal of the always...
Technical Report
Full-text available
The aim of this report is to review existing technologies in the area of big data and information visualisation with a view to narrowing the focus of the author's research project. The preliminary concept of this project is to investigate whether it is possible to define an effective way for people to search for patterns in a large dataset as well...
Article
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We present a visualization technique for radial drawing of trees consisting of two slightly different algorithms. Both of them make use of node-link diagrams for visual encoding. This visualization creates clear drawings without edge crossing. One of the algorithms is suitable for real-time visualization of large trees, as it requires minimal recal...
Article
Full-text available
This paper describes the design and development of a novel cloud-based system for increased service contextualization in future wireless networks. The principal objective is the support of mobile users (consumers) in a Ubiquitous Consumer Wireless World (UCWW) seeking to choose and select the ‘best’ service instance in a UCWW environment matched to...
Conference Paper
Full-text available
Abstract: Recent years have seen the relatively staid and conservative environment of the museum access the potential that is the new wave of new technologies incorporating Web 2.0, the Social Web, Netknowing and Net Collaborative Practices for collaboration and ubiquitous learning. Some – only a few, as of yet - have embraced the use of 3D game te...
Article
A wireless solution for context- and service-awareness in mobile communications is the theme of this paper. Respecting mobile users’ desire for minimal intrusion of unsolicited advertisements, here we show how the novel push-advertisement technology and medium of ‘wireless billboard channels’ (WBCs) could be employed by service providers to broadca...
Conference Paper
Full-text available
This paper presents various methods for visualization and analysis of email networks; visualization on the surface of a sphere to reveal communication patterns between different groups, a hierarchical drawing displaying the centrality analysis of nodes to emphasize important nodes, a 2.5D visualization for temporal email networks to analyze the evo...
Article
Full-text available
We introduce a new graph drawing convention for 2.5D hierarchical drawings of directed graphs. The vertex set is partitioned both into layers of vertices drawn in parallel planes and into k � 2 subsets, called walls, and also drawn in parallel planes. The planes of the walls are perpen- dicular to the planes of the layers. We present a method for c...
Conference Paper
Full-text available
This paper presents the design and implementation of an ant colony optimization based algorithm for solving the DAG layering problem. This algorithm produces compact layerings by minimising their width and height. Importantly it takes into account the contribution of dummy vertices to the width of the resulting layering.
Conference Paper
Full-text available
This poster presents various methods for visualization and analysis of small-world email networks with various perspectives: vi-sualization on the surface of a sphere to reveal the relationships between different groups, a 2.5D hierarchical visualization method combined with the centrality value of nodes to analyze important people, a 2.5D visualiz...
Article
Full-text available
This work contributes to the wide research area of visualization of hierarchical graphs. We present a new polynomial-time heuristic which can be integrated into the Sugiyama method for drawing hierarchical graphs. Our heuristic, which we call Promote Layering (PL), is applied to the output of the layering phase of the Sugiyama method. PL is a simpl...
Conference Paper
Full-text available
This paper describes the GEOMI system, a visual analysis tool for the visualisation and analysis of large and complex networks. GEOMI provides a collection of network analysis methods, graph lay- out algorithms and several graph navigation and interaction methods. GEOMI is part of a new generation of visual analysis tools combining graph visualisat...
Technical Report
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This report presents the design and implementation of Ant Colony Optimisation (ACO) based heuristic for solving the Layer Assignment Problem (LAP) for a directed acyclic graph (DAG). This heuristic produces compact layerings by trying to minimise their width and height. It takes into account the contribution of dummy vertices to the width of the re...
Article
Full-text available
We propose two fast heuristics for solving the NP-hard problem of graph layering with the minimum width and consideration of dummy nodes. Our heuristics can be used at the layer-assignment phase of the Sugiyama method for drawing of directed graphs. We evaluate our heuristics by comparing them to the widely used fast-layering algorithms in an exten...