VLDB 2026 Research / reviewers in the wild / expert
Vassilis Vassiliades
dblp:08/7361
· DBLP profile ↗
19ranked-venue papers
7as first author
7since 2021 · last 2025
0000-0002-1336-5629ORCID · verified
Domains — the database's venue-derived domains; a paper can count in several
Artificial intelligence and machine learning · 12 · 7 first-author · 3 since 2021Applied, interdisciplinary, general and emerging computing · 4 · 2 since 2021Computer networks · 2 · 1 since 2021Security and privacy · 2 · 2 since 2021Systems, architecture and hardware · 1Software engineering, systems software and programming languages · 1 · 1 since 2021Graphics, computer vision, multimedia, augmented reality and games · 1 · 1 since 2021
| Year | Publication | Venue | Position |
|---|---|---|---|
| 2025 | Optimizing Camera Placement for Chicken Farm Monitoring
Kyriacos Mosphilis, Vassilis Vassiliades |
EvoApplications (2) | 2 |
| 2024 | Towards understanding animal welfare by observing collective flock behaviors via AI-powered AnalyticsabstractAnimal farming has undergone significant transformation and evolved from small-scale businesses to largescale commercial ventures.While maximizing productivity and profitability has always been a major concern in animal farming, during recent years there has been an increasing rise of concern regarding the welfare of the animals.In this context, the integration of artificial intelligence (AI) technologies offers immense potential for monitoring the well-being of chickens on farms and optimizing revenue streams simultaneously.Several works have integrated AI methodologies into everyday animal farming activities.Still, very few (if any) have proposed efficient and practical solutions that may facilitate farm owners in making impactful decisions regarding their business profitability and the welfare of the animals.In this direction, we propose a noninvasive chicken farm monitoring system that relies on onfield sound and video recordings integrated with sensory data acquired from the farm.The system consists of hardware that handles data acquisition and storage, a sensory data collection system and audio/video processing AI models.The last component of the system will be an inference engine that analyzes the collected data and infers useful facts about the flock's welfare and even psychological state. Savvas Karatsiolis, Pieris Panagi, Vassilis Vassiliades, Andreas Kamilaris, Nicolas C. Nicolaou, Efstathios Stavrakis |
FedCSIS | 3 |
| 2023 | Exploring Model Inversion Attacks in the Black-box SettingabstractModel Inversion (MI) attacks, that aim to recover semantically meaningful reconstructions for each target class, have been extensively studied and demonstrated to be successful in the white-box setting. On the other hand, black-box MI attacks demonstrate low performance in terms of both effectiveness, i.e., reconstructing samples which are identifiable as their ground-truth, and efficiency, i.e., time or queries required for completing the attack process. Whether or not effective and efficient black-box MI attacks can be conducted on complex targets, such as Convolutional Neural Networks (CNNs), currently remains unclear. In this paper, we present a feasibility study in regards to the effectiveness and efficiency of MI attacks in the black-box setting. In this context, we introduce Deep-BMI (Deep Black-box Model Inversion), a framework that supports various black-box optimizers for conducting MI attacks on deep CNNs used for image recognition. Deep-BMI’s most efficient optimizer is based on an adaptive hill climbing algorithm, whereas its most effective optimizer is based on an evolutionary algorithm capable of performing an all-class attack and returning a diversity of images in a single run. For assessing the severity of this threat, we utilize all three evaluation approaches found in the literature. In particular, we (a) conduct a user study with human participants, (b) demonstrate our actual reconstructions along with their ground-truth, and (c) use relevant quantitative metrics. Surprisingly, our results suggest that black-box MI attacks, and for complex models, are comparable, in some cases, to those reported so far in the white-box setting. Antreas Dionysiou, Vassilis Vassiliades, Elias Athanasopoulos |
Proc. Priv. Enhancing Technol. | 2 |
| 2023 | GREIL-Crowds: Crowd Simulation with Deep Reinforcement Learning and ExamplesabstractSimulating crowds with realistic behaviors is a difficult but very important task for a variety of applications. Quantifying how a person balances between different conflicting criteria such as goal seeking, collision avoidance and moving within a group is not intuitive, especially if we consider that behaviors differ largely between people. Inspired by recent advances in Deep Reinforcement Learning, we propose Guided REinforcement Learning (GREIL) Crowds, a method that learns a model for pedestrian behaviors which is guided by reference crowd data. The model successfully captures behaviors such as goal seeking, being part of consistent groups without the need to define explicit relationships and wandering around seemingly without a specific purpose. Two fundamental concepts are important in achieving these results: (a) the per agent state representation and (b) the reward function. The agent state is a temporal representation of the situation around each agent. The reward function is based on the idea that people try to move in situations/states in which they feel comfortable in. Therefore, in order for agents to stay in a comfortable state space, we first obtain a distribution of states extracted from real crowd data; then we evaluate states based on how much of an outlier they are compared to such a distribution. We demonstrate that our system can capture and simulate many complex and subtle crowd interactions in varied scenarios. Additionally, the proposed method generalizes to unseen situations, generates consistent behaviors and does not suffer from the limitations of other data-driven and reinforcement learning approaches. Panayiotis Charalambous, Julien Pettré, Vassilis Vassiliades, Yiorgos Chrysanthou, Nuria Pelechano |
ACM Trans. Graph. | 3 |
| 2022 | Deep reinforcement learning for improving competitive cycling performance
Giorgos Demosthenous, Marios Kyriakou, Vassilis Vassiliades |
Expert Syst. Appl. | 3 |
| 2021 | HoneyGen: Generating Honeywords Using Representation LearningabstractHoneywords are false passwords injected in a database for detecting password leakage. Generating honeywords is a challenging problem due to the various assumptions about the adversary's knowledge as well as users' password-selection behaviour. The success of a Honeywords Generation Technique (HGT) lies on the resulting honeywords; the method fails if an adversary can easily distinguish the real password. In this paper, we propose HoneyGen, a practical and highly robust HGT that produces realistic looking honeywords. We do this by leveraging representation learning techniques to learn useful and explanatory representations from a massive collection of unstructured data, i.e., each operator's password database. We perform both a quantitative and qualitative evaluation of our framework using the state-of-the-art metrics. Our results suggest that HoneyGen generates high-quality honeywords that cause sophisticated attackers to achieve low distinguishing success rates. Antreas Dionysiou, Vassilis Vassiliades, Elias Athanasopoulos |
AsiaCCS | 2 |
| 2021 | DNS Tunneling Detection by Cache-Property-Aware FeaturesabstractMany enterprises are under threat of targeted attacks aiming at data exfiltration. To launch such attacks, in recent years, attackers with their malware have exploited a covert channel that abuses the domain name system (DNS) named DNS tunneling. Although several research efforts have been made to detect DNS tunneling, the existing methods rely on features that advanced tunneling techniques can easily obfuscate by mimicking legitimate DNS clients. Such obfuscation would result in data leakage. To tackle this problem, we focused on a “trace” left by DNS tunneling that cannot be easily hidden. In the context of data exfiltration by DNS tunneling, the malware connects directly to the DNS cache server and the generated DNS tunneling queries produce cache misses with absolute certainty. In this study, we propose a DNS tunneling detection method based on the cache-property-aware features. Our experiments show that one of the proposed features can efficiently characterize the DNS tunneling traffic. Furthermore, we introduce a rule-based filter and a long short-term memory (LSTM)-based filter using this proposed feature. The rule-based filter achieves a higher rate of DNS tunneling attack detection than the LSTM one, which instead detects the attack more quickly, while both maintain a low misdetection rate. Naotake Ishikura, Daishi Kondo, Vassilis Vassiliades, Iordan Iordanov, Hideki Tode |
IEEE Trans. Netw. Serv. Manag. | 3 |
| 2020 | The named data networking flow filter: Towards improved security over information leakage attacks
Daishi Kondo, Vassilis Vassiliades, Thomas Silverston, Hideki Tode, Tohru Asami |
Comput. Networks | 2 |
| 2020 | A Survey on Policy Search Algorithms for Learning Robot Controllers in a Handful of TrialsabstractMost policy search (PS) algorithms require thousands of training episodes to find an effective policy, which is often infeasible with a physical robot. This survey article focuses on the extreme other end of the spectrum: how can a robot adapt with only a handful of trials (a dozen) and a few minutes? By analogy with the word “big-data,” we refer to this challenge as “micro-data reinforcement learning.” In this article, we show that a first strategy is to leverage prior knowledge on the policy structure (e.g., dynamic movement primitives), on the policy parameters (e.g., demonstrations), or on the dynamics (e.g., simulators). A second strategy is to create data-driven surrogate models of the expected reward (e.g., Bayesian optimization) or the dynamical model (e.g., model-based PS), so that the policy optimizer queries the model instead of the real system. Overall, all successful micro-data algorithms combine these two strategies by varying the kind of model and prior knowledge. The current scientific challenges essentially revolve around scaling up to complex robots, designing generic priors, and optimizing the computing time. Konstantinos Chatzilygeroudis, Vassilis Vassiliades, Freek Stulp, Sylvain Calinon, Jean-Baptiste Mouret |
IEEE Trans. Robotics | 2 |
| 2018 | Discovering the elite hypervolume by leveraging interspecies correlationabstractEvolution has produced an astonishing diversity of species, each filling a different niche. Algorithms like MAP-Elites mimic this divergent evolutionary process to find a set of behaviorally diverse but high-performing solutions, called the elites. Our key insight is that species in nature often share a surprisingly large part of their genome, in spite of occupying very different niches; similarly the elites are likely to be concentrated in a specific "elite hypervolume" whose shape is defined by their common features. In this paper, we first introduce the elite hypervolume concept and propose two metrics to characterize it: the genotypic spread and the genotypic similarity. We then introduce a new variation operator, called "directional variation", that exploits interspecies (or inter-elites) correlations to accelerate the MAP-Elites algorithm. We demonstrate the effectiveness of this operator in three problems (a toy function, a redundant robotic arm, and a hexapod robot). Vassilis Vassiliades, Jean-Baptiste Mouret |
GECCO | 1 |
| 2018 | Using Centroidal Voronoi Tessellations to Scale Up the Multidimensional Archive of Phenotypic Elites AlgorithmabstractThe recently introduced multidimensional archive of phenotypic elites (MAP-Elites) is an evolutionary algorithm capable of producing a large archive of diverse, high-performing solutions in a single run. It works by discretizing a continuous feature space into unique regions according to the desired discretization per dimension. While simple, this algorithm has a main drawback: it cannot scale to high-dimensional feature spaces since the number of regions increase exponentially with the number of dimensions. In this paper, we address this limitation by introducing a simple extension of MAP-Elites that has a constant, predefined number of regions irrespective of the dimensionality of the feature space. Our main insight is that methods from computational geometry could partition a high-dimensional space into well-spread geometric regions. In particular, our algorithm uses a centroidal Voronoi tessellation (CVT) to divide the feature space into a desired number of regions; it then places every generated individual in its closest region, replacing a less fit one if the region is already occupied. We demonstrate the effectiveness of the new “CVT-MAP-Elites” algorithm in high-dimensional feature spaces through comparisons against MAP-Elites in maze navigation and hexapod locomotion tasks. Vassilis Vassiliades, Konstantinos Chatzilygeroudis, Jean-Baptiste Mouret |
IEEE Trans. Evol. Comput. | 1 |
| 2017 | Black-box data-efficient policy search for roboticsabstractThe most data-efficient algorithms for reinforcement learning (RL) in robotics are based on uncertain dynamical models: after each episode, they first learn a dynamical model of the robot, then they use an optimization algorithm to find a policy that maximizes the expected return given the model and its uncertainties. It is often believed that this optimization can be tractable only if analytical, gradient-based algorithms are used; however, these algorithms require using specific families of reward functions and policies, which greatly limits the flexibility of the overall approach. In this paper, we introduce a novel model-based RL algorithm, called Black-DROPS (Black-box Data-efficient RObot Policy Search) that: (1) does not impose any constraint on the reward function or the policy (they are treated as black-boxes), (2) is as data-efficient as the state-of-the-art algorithm for data-efficient RL in robotics, and (3) is as fast (or faster) than analytical approaches when several cores are available. The key idea is to replace the gradient-based optimization algorithm with a parallel, black-box algorithm that takes into account the model uncertainties. We demonstrate the performance of our new algorithm on two standard control benchmark problems (in simulation) and a low-cost robotic manipulator (with a real robot). Konstantinos Chatzilygeroudis, Roberto Rama, Rituraj Kaushik, Dorian Goepp, Vassilis Vassiliades, Jean-Baptiste Mouret |
IROS | 5 |
| 2016 | Training Bidirectional Recurrent Neural Network Architectures with the Scaled Conjugate Gradient Algorithm
Michalis Agathocleous, Chris Christodoulou, Vasilis J. Promponas, Petros Kountouris, Vassilis Vassiliades |
ICANN (1) | 5 |
| 2016 | Behavioral plasticity through the modulation of switch neurons
Vassilis Vassiliades, Chris Christodoulou |
Neural Networks | 1 |
| 2013 | Toward Nonlinear Local Reinforcement Learning Rules Through NeuroevolutionabstractWe consider the problem of designing local reinforcement learning rules for artificial neural network (ANN) controllers. Motivated by the universal approximation properties of ANNs, we adopt an ANN representation for the learning rules, which are optimized using evolutionary algorithms. We evaluate the ANN rules in partially observable versions of four tasks: the mountain car, the acrobot, the cart pole balancing, and the nonstationary mountain car. For testing whether such evolved ANN-based learning rules perform satisfactorily, we compare their performance with the performance of SARSA(λ) with tile coding, when the latter is provided with either full or partial state information. The comparison shows that the evolved rules perform much better than SARSA(λ) with partial state information and are comparable to the one with full state information, while in the case of the nonstationary environment, the evolved rule is much more adaptive. It is therefore clear that the proposed approach can be particularly effective in both partially observable and nonstationary environments. Moreover, it could potentially be utilized toward creating more general rules that can be applied in multiple domains and transfer learning scenarios. Vassilis Vassiliades, Chris Christodoulou |
Neural Comput. | 1 |
| 2012 | A Comparative Study on Filtering Protein Secondary Structure PredictionabstractFiltering of Protein Secondary Structure Prediction (PSSP) aims to provide physicochemically realistic results, while it usually improves the predictive performance. We performed a comparative study on this challenging problem, utilizing both machine learning techniques and empirical rules and we found that combinations of the two lead to the highest improvement. Petros Kountouris, Michalis Agathocleous, Vasilis J. Promponas, Georgia Christodoulou, Simos Hadjicostas, Vassilis Vassiliades, Chris Christodoulou |
IEEE ACM Trans. Comput. Biol. Bioinform. | 6 |
| 2011 | Multiagent Reinforcement Learning: Spiking and Nonspiking Agents in the Iterated Prisoner's DilemmaabstractThis paper investigates multiagent reinforcement learning (MARL) in a general-sum game where the payoffs' structure is such that the agents are required to exploit each other in a way that benefits all agents. The contradictory nature of these games makes their study in multiagent systems quite challenging. In particular, we investigate MARL with spiking and nonspiking agents in the Iterated Prisoner's Dilemma by exploring the conditions required to enhance its cooperative outcome. The spiking agents are neural networks with leaky integrate-and-fire neurons trained with two different learning algorithms: 1) reinforcement of stochastic synaptic transmission, or 2) reward-modulated spike-timing-dependent plasticity with eligibility trace. The nonspiking agents use a tabular representation and are trained with Q- and SARSA learning algorithms, with a novel reward transformation process also being applied to the Q-learning agents. According to the results, the cooperative outcome is enhanced by: 1) transformed internal reinforcement signals and a combination of a high learning rate and a low discount factor with an appropriate exploration schedule in the case of non-spiking agents, and 2) having longer eligibility trace time constant in the case of spiking agents. Moreover, it is shown that spiking and nonspiking agents have similar behavior and therefore they can equally well be used in a multiagent interaction setting. For training the spiking agents in the case where more than one output neuron competes for reinforcement, a novel and necessary modification that enhances competition is applied to the two learning algorithms utilized, in order to avoid a possible synaptic saturation. This is done by administering to the networks additional global reinforcement signals for every spike of the output neurons that were not "responsible" for the preceding decision. Vassilis Vassiliades, Aristodemos Cleanthous, Chris Christodoulou |
IEEE Trans. Neural Networks | 1 |
| 2010 | Multiagent Reinforcement Learning in the Iterated Prisoner's Dilemma: Fast cooperation through evolved payoffsabstractIn this paper, we investigate the importance of rewards in Multiagent Reinforcement Learning in the context of the Iterated Prisoner's Dilemma. We use an evolutionary algorithm to evolve valid payoff structures with the aim of encouraging mutual cooperation. An exhaustive analysis is performed by investigating the effect of: i) the lower and upper bounds of the search space of the payoff values, ii) the reward sign, iii) the population size, and iv) the mutation operators used. Our results indicate that valid structures that encourage cooperation can quickly be obtained, while their analysis shows that: i) they should contain a mixture of positive and negative values and ii) the magnitude of the positive values should be much smaller than the magnitude of the negative values. Vassilis Vassiliades, Chris Christodoulou |
IJCNN | 1 |
| 2009 | Multiagent Reinforcement Learning with Spiking and Non-Spiking Agents in the Iterated Prisoner's Dilemma
Vassilis Vassiliades, Aristodemos Cleanthous, Chris Christodoulou |
ICANN (1) | 1 |