Nikolaos Dimitriou

Dr. Nikolaos Dimitriou

Information Technologies Institute, Centre for Research and Technology Hellas, Thessaloniki, Greece
orcid

Research Focus & Metrics

Academic Career Length

15Years (2012-Present)

(Calculated once Scilit publication data is synced: current year − year of first publication + 1)

Representative Publications

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5 August 2019 in IEEE Transactions on Industrial Electronics
Verified
Journal Article
Closed access
NDNikolaos Dimitriou
Nikolaos Dimitriou
LLLampros Leontaris
Lampros Leontaris
TVThanasis Vafeiadis
Thanasis Vafeiadis
DIDimosthenis Ioannidis
Dimosthenis Ioannidis
TWTracy Wotherspoon
Tracy Wotherspoon
DTDimitrios Tzovaras
Dimitrios Tzovaras
A common source of defects in manufacturing miniature Printed Circuits Boards (PCB) is the attachment of silicon die or other wire bondable components on a Liq- uid Crystal Polymer (LCP) substrate. Typically, a conductive glue is dispensed prior to attachment with defects caused either by insufficient or excessive glue. The current prac- tice in electronics industry is to examine the deposited glue by a human operator a process that is both time consuming and inefficient especially in preproduction runs where the error rate is high. In this paper we propose a system that automates fault diagnosis by accurately estimating the vol- ume of glue deposits before and even after die attachment. To this end a modular scanning system is deployed that produces high resolution point clouds whereas the actual estimation of glue volume is performed by (R)egression- Net (RNet), a 3D Convolutional Neural Network (3DCNN). RNet outperforms other deep architectures and is able to estimate the volume either directly from the point cloud of a glue deposit or more interestingly after die attachment when only a small part of glue is visible around each die. The entire methodology is evaluated under operational conditions where the proposed system achieves accurate results without delaying the manufacturing process.

29 January 2018 in Journal of Management Analytics
Verified
Journal Article
Closed access
TVThanasis Vafeiadis
Thanasis Vafeiadis
NDNikolaos Dimitriou
Nikolaos Dimitriou
DIDimosthenis Ioannidis
Dimosthenis Ioannidis
TWTracy Wotherspoon
Tracy Wotherspoon
GTGregory Tinker
Gregory Tinker
DTDimitrios Tzovaras
Dimitrios Tzovaras
Decision Support Systems are considered as a robust technology able to provide an advantage to several manufacturing companies. As part of the Z-Fact0r EU project Early Stage-Decision Support System, a framework for the inspection of a printed circuit boards (PCB) and the inference of faults, regarding the excess or insufficient glue, is proposed. For the inspection of the PCB, a pixel-based vector of the regions of interest is utilized and several very popular in research community machine learning algorithms are tested on their performance on fault recognition. In order to determine the most efficient and effective classifier, a schema of Monte Carlo simulations for each classification algorithm and set of hyper-parameters was performed. Simulation results show a superiority of the support vector machine (SVM) classifier with polynomial and radial basis function kernels, compared to the rest. The best overall classifier was the SVM polynomial (accuracy: 81.39%, f-measure: 78.72%).

1 April 2020 in Simulation Modelling Practice and Theory
Verified
Journal Article
Closed access
NDNikolaos Dimitriou
Nikolaos Dimitriou
LLLampros Leontaris
Lampros Leontaris
TVThanasis Vafeiadis
Thanasis Vafeiadis
DIDimosthenis Ioannidis
Dimosthenis Ioannidis
TWTracy Wotherspoon
Tracy Wotherspoon
DTDimitrios Tzovaras
Dimitrios Tzovaras

1 September 2020 in Sensors
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Journal Article
Open access
PDF file
Dimitris TsiktsirisDimitris Tsiktsiris
Dimitris Tsiktsiris
NDNikolaos Dimitriou
Nikolaos Dimitriou
ALAntonios Lalas
Antonios Lalas
Minas DasygenisMinas Dasygenis
Minas Dasygenis
KVKonstantinos Votis
Konstantinos Votis
DTDimitrios Tzovaras
Dimitrios Tzovaras
Autonomous vehicles (AVs) are already operating on the streets of many countries around the globe. Contemporary concerns about AVs do not relate to the implementation of fundamental technologies, as they are already in use, but are rather increasingly centered on the way that such technologies will affect emerging transportation systems, our social environment, and the people living inside it. Many concerns also focus on whether such systems should be fully automated or still be partially controlled by humans. This work aims to address the new reality that is formed in autonomous shuttles mobility infrastructures as a result of the absence of the bus driver and the increased threat from terrorism in European cities. Typically, drivers are trained to handle incidents of passengers’ abnormal behavior, incidents of petty crimes, and other abnormal events, according to standard procedures adopted by the transport operator. Surveillance using camera sensors as well as smart software in the bus will maximize the feeling and the actual level of security. In this paper, an online, end-to-end solution is introduced based on deep learning techniques for the timely, accurate, robust, and automatic detection of various petty crime types. The proposed system can identify abnormal passenger behavior such as vandalism and accidents but can also enhance passenger security via petty crimes detection such as aggression, bag-snatching, and vandalism. The solution achieves excellent results across different use cases and environmental conditions.

21 January 2022 in Open Research Europe
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Journal Article
Open access
KAKonstantinos Apostolakis
Konstantinos Apostolakis
NDNikolaos Dimitriou
Nikolaos Dimitriou
George MargetisGeorge Margetis
George Margetis
SNStavroula Ntoa
Stavroula Ntoa
DTDimitrios Tzovaras
Dimitrios Tzovaras
CSConstantine Stephanidis
Constantine Stephanidis
Background: Augmented reality (AR) and artificial intelligence (AI) are highly disruptive technologies that have revolutionised practices in a wide range of domains, including the security sector. Several law enforcement agencies (LEAs) employ AI in their daily operations for forensics and surveillance. AR is also gaining traction in security, particularly with the advent of affordable wearable devices. Equipping police officers with the tools to facilitate an elevated situational awareness (SA) in patrolling and tactical scenarios is expected to improve LEAs’ safety and capacity to deliver crucial blows against terrorist and/or criminal threats. Methods: In this paper we present DARLENE, an ecosystem incorporating novel AI techniques for activity recognition and pose estimation tasks, combined with a wearable AR framework for visualization of the inferenced results via dynamic content adaptation according to the wearer’s stress level and operational context. The concept has been validated with end-users through co-creation workshops, while the decision-making mechanism for enhancing LEAs’ SA has been assessed with experts. Regarding computer vision components, preliminary tests of the instance segmentation method for humans’ and objects’ detection have been conducted on a subset of videos from the RWF-2000 dataset for violence detection, which have also been used to test a human pose estimation method that has so far exhibited impressive results, constituting the basis of further developments in DARLENE. Results: Evaluation results highlight that target users are positive towards the adoption of the proposed solution in field operations, and that the SA decision-making mechanism produces highly acceptable outcomes. Evaluation of the computer vision components yielded promising results and identified opportunities for improvement. Conclusions: This work provides the context of the DARLENE ecosystem and presents the DARLENE architecture, analyses its individual technologies, and demonstrates preliminary results, which are positive both in terms of technological achievements and user acceptance of the proposed solution.

19 February 2024 in Virtual Reality
Verified
Journal Article
Open access
PDF file
IKIason Karakostas
Iason Karakostas
KVKaterina Valakou
Katerina Valakou
DGDespoina Gavgiotaki
Despoina Gavgiotaki
ZSZinovia Stefanidi
Zinovia Stefanidi
IPIoannis Pastaltzidis
Ioannis Pastaltzidis
DTDimitrios Tzovaras
Dimitrios Tzovaras
Real-time performance is critical for Augmented Reality (AR) systems as it directly affects responsiveness and enables the timely rendering of virtual content superimposed on real scenes. In this context, we present the DARLENE wearable AR system, analysing its specifications, overall architecture and core algorithmic components. DARLENE comprises AR glasses and a wearable computing node responsible for several time-critical computation tasks. These include computer vision modules developed for the real-time analysis of dynamic scenes supporting functionalities for instance segmentation, tracking and pose estimation. To meet real-time requirements in limited resources, concrete algorithmic adaptations and design choices are introduced. The proposed system further supports real-time video streaming and interconnection with external IoT nodes. To improve user experience, a novel approach is proposed for the adaptive rendering of AR content by considering the user’s stress level, the context of use and the environmental conditions for adjusting the level of presented information towards enhancing their situational awareness. Through extensive experiments, we evaluate the performance of individual components and end-to-end pipelines. As the proposed system targets time-critical security applications where it can be used to enhance police officers’ situational awareness, further experimental results involving end users are reported with respect to overall user experience, workload and evaluation of situational awareness.