| 1. |
- Ivanenko, Yevhen, et al.
(författare)
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Quasi-Herglotz functions and convex optimization
- 2020
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Ingår i: Royal Society Open Science. - : The Royal Society Publishing. - 2054-5703. ; 7:1, s. 1-15
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Tidskriftsartikel (refereegranskat)abstract
- We introduce the set of quasi-Herglotz functions and demonstrate that it has properties useful in the modelling of non-passive systems. The linear space of quasi-Herglotz functions constitutes a natural extension of the convex cone of Herglotz functions. It consists of differences of Herglotz functions and we show that several of the important properties and modelling perspectives are inherited by the new set of quasi-Herglotz functions. In particular, this applies to their integral representations, the associated integral identities or sum rules (with adequate additional assumptions), their boundary values on the real axis and the associated approximation theory. Numerical examples are included to demonstrate the modelling of a non-passive gain medium formulated as a convex optimization problem, where the generating measure is modelled by using a finite expansion of B-splines and point masses.
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| 2. |
- Mochaourab, Rami, et al.
(författare)
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Post-hoc Explainability for Time Series Classification: Towards a Signal Processing Perspective
- 2022
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Ingår i: IEEE signal processing magazine (Print). - : Institute of Electrical and Electronics Engineers (IEEE). - 1053-5888 .- 1558-0792. ; 39:4, s. 119-129
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Tidskriftsartikel (refereegranskat)abstract
- Time series data correspond to observations of phenomena that are recorded over time [1]. Such data are encountered regularly in a wide range of applications, such as speech and music recognition, monitoring health and medical diagnosis, financial analysis, motion tracking, and shape identification, to name a few. With such a diversity of applications and the large variations in their characteristics, time series classification is a complex and challenging task. One of the fundamental steps in the design of time series classifiers is that of defining or constructing the discriminant features that help differentiate between classes. This is typically achieved by designing novel representation techniques [2] that transform the raw time series data to a new data domain, where subsequently a classifier is trained on the transformed data, such as one-nearest neighbors [3] or random forests [4]. In recent time series classification approaches, deep neural network models have been employed that are able to jointly learn a representation of time series and perform classification [5]. In many of these sophisticated approaches, the discriminant features tend to be complicated to analyze and interpret, given the high degree of nonlinearity.
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| 3. |
- Homem, Irvin, 1985-
(författare)
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Advancing Automation in Digital Forensic Investigations
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Digital Forensics is used to aid traditional preventive security mechanisms when they fail to curtail sophisticated and stealthy cybercrime events. The Digital Forensic Investigation process is largely manual in nature, or at best quasi-automated, requiring a highly skilled labour force and involving a sizeable time investment. Industry standard tools are evidence-centric, automate only a few precursory tasks (E.g. Parsing and Indexing) and have limited capabilities of integration from multiple evidence sources. Furthermore, these tools are always human-driven.These challenges are exacerbated in the increasingly computerized and highly networked environment of today. Volumes of digital evidence to be collected and analyzed have increased, and so has the diversity of digital evidence sources involved in a typical case. This further handicaps digital forensics practitioners, labs and law enforcement agencies, causing delays in investigations and legal systems due to backlogs of cases. Improved efficiency of the digital investigation process is needed, in terms of increasing the speed and reducing the human effort expended. This study aims at achieving this time and effort reduction, by advancing automation within the digital forensic investigation process.Using a Design Science research approach, artifacts are designed and developed to address these practical problems. Summarily, the requirements, and architecture of a system for automating digital investigations in highly networked environments are designed. The architecture initially focuses on automation of the identification and acquisition of digital evidence, while later versions focus on full automation and self-organization of devices for all phases of the digital investigation process. Part of the remote evidence acquisition capability of this system architecture is implemented as a proof of concept. The speed and reliability of capturing digital evidence from remote mobile devices over a client-server paradigm is evaluated. A method for the uniform representation and integration of multiple diverse evidence sources for enabling automated correlation, simple reasoning and querying is developed and tested. This method is aimed at automating the analysis phase of digital investigations. Machine Learning (ML)-based triage methods are developed and tested to evaluate the feasibility and performance of using such techniques to automate the identification of priority digital evidence fragments. Models from these ML methods are evaluated in identifying network protocols within DNS tunneled network traffic. A large dataset is also created for future research in ML-based triage for identifying suspicious processes for memory forensics.From an ex ante evaluation, the designed system architecture enables individual devices to participate in the entire digital investigation process, contributing their processing power towards alleviating the burden on the human analyst. Experiments show that remote evidence acquisition of mobile devices over networks is feasible, however a single-TCP-connection paradigm scales poorly. A proof of concept experiment demonstrates the viability of the automated integration, correlation and reasoning over multiple diverse evidence sources using semantic web technologies. Experimentation also shows that ML-based triage methods can enable prioritization of certain digital evidence sources, for acquisition or analysis, with up to 95% accuracy.The artifacts developed in this study provide concrete ways to enhance automation in the digital forensic investigation process to increase the investigation speed and reduce the amount of costly human intervention needed.
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| 4. |
- Hidvegi, Attila, et al.
(författare)
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A high-speed data acquisition system for segmented Ge-detectors
- 2007
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Ingår i: 2007 IEEE Nuclear Science Symposium Conference Record. - : IEEE. - 1424409233 - 9781424409235 - 9781424409228 ; , s. 536-537
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Konferensbidrag (refereegranskat)abstract
- When using segmented Ge-detectors for gamma ray tracking it is necessary to determine the segment pulse shapes with high accuracy. A high-speed data acquisition system with many channels, high precision and with high sampling rate is required. There are also many other applications for such a system. Our system uses high performance FPGAs (Xilinx Virtex-V [2]) to cope with the data rates delivered by the high speed ADC chosen (Atmel 2Gsps, 10 bits) and to make all the data processing onboard in real time. Each board contains four such ADCs, which can either handle four channels up to full speed, or achieve higher sampling rates with interleaving. The boards can communicate with each other over different types of high-speed communication links. Control and monitoring is implemented with embedded processors. The processed result will be transmitted over Ethernet to final storage. The project introduces many challenging issues: signal integrity, ADC performance, interfacing ADCs to the FPGA, synchronisation of ADCs across the entire system, implementing flexible processing algorithms, high speed interconnection between boards and managing the significant heat generation. This is an ongoing project with interesting potentials for the future.
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| 5. |
- Hidvegi, Attila, et al.
(författare)
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A high-speed data acquisition system for segmented Ge-detectors
- 2007
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Ingår i: 2006 IEEE Nuclear Science Symposium Conference Record, Vol 1-6. - : IEEE. - 1424405610 - 9781424405619 - 1424405602 ; , s. 999-1001
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Konferensbidrag (refereegranskat)abstract
- When using segmented Ge-detectors for gamma ray tracking it is necessary to determine the segment pulse shapes with high accuracy. A high-speed data acquisition system with many channels, high precision and with high sampling rate is required. To find the optimum performance, we are investigating what can be achieved by a system with extremely high sampling rates, 10 bits @2GS/s. There are many other applications for such a system. Higher sampling rates usually mean lower bit resolution of the ADC, but with oversampling we expect to achieve a very good energy and time resolution. The system uses high performance FPGAs (Xilinx Virtex-IV) to cope with the data rates delivered by the high speed ADCs and to make all the data processing onboard in real time. Control and monitoring is implemented in an embedded soft processor. This processor is also in charge of the offboard gigabit Ethernet communication. The final system will consist of several separate boards, each with a number of input channels that will have to communicate with each other in real time over a high-speed communication link. The processed result will be transmitted over Ethernet to final storage. The project introduces many challenging issues, which are being addressed in turn with different prototype designs. These issues are: the ADC performance, interfacing the ADCs to the FPGA, implementing the flexible processing algorithms and high speed interconnection between the boards.
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| 6. |
- Hidvegi, Attila, et al.
(författare)
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A Small Portable Test System for the TileCal Digitizer System
- 2008
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Konferensbidrag (refereegranskat)abstract
- The hadronic Tile Calorimeter (TileCal) of the ATLAS detector at LHC has a digitization, pipeline and readout system composed of nearly 2000 boards [1][2], developed and maintained by Stockholm University. Prior to now a rather complex test system been used to verify the functionality of the boards. However this system was developed nearly 10 years ago and now difficult to maintain due to several already obsolete components. A new, simpler, more reliable, and portable test system was therefore initiated. Its components have been chosen to reduce problems with obsolescence, and to allow easy migration to new platforms over the lifetime of the digitizer system.
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| 7. |
- Hidvegi, Attila, et al.
(författare)
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A system for distributing high-speed synchronous high-precision clock and trigger data over large distances
- 2008
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Ingår i: Nuclear Science Symposium Conference Record, 2008. NSS '08. IEEE. - 9781424427147 ; , s. 2581-2584
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Konferensbidrag (refereegranskat)abstract
- The distribution of precise timing throughout the European X-ray Free Electron Laser project [1] (XFEL) and its triggering system is a very challenging part of the system design. ADCs in data acquisition systems and DACs in control systems will require very high precision clocks. The clocks need to be synchronous to each other, both in frequency and phase, with a jitter performance better than 5 ps (RMS). At some high-speed ADCs it might even need a precision down to 0.1 ps. The frequencies that must be available are the main 1.3 GHz and some frequencies below, which are all derived from the main frequency. The phase needs to be adjustable to allow synchronization between separate devices. Triggering information needs to be distributed over the system, so that controlling instructions can be carried out at a very precise time. This is very important since the beam will travel with the speed of light, and there is no possibility for information to be sent back and forth. This requires an absolute timing to be distributed over the system. Both the main clock and triggering information will be transmitted over the same fiber cable, one to each device. An advanced synchronization method needs to be developed to synchronize the phases of the clocks throughout the whole system. The delay through the cable can change with temperature, and due to long cables the total change through a single cable can be significant. It is essential that the clocks are stable and not drifting away from each other. Therefore a continuous calibration method is needed, ensuring that the clocks are synchronous throughout the whole system. A prototype of such a system is being developed and a first version is expected to be completed in 2009 Ql.
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| 8. |
- Hidvegi, Attila, et al.
(författare)
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An Advanced FPGA Based Phase-Lock-Loop System as an Alternative Solution for the XFEL Timing System
- 2009
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Ingår i: Nuclear Science Symposium Conference Record (NSS/MIC), 2009 IEEE. - 9781424439614 ; , s. 1871-1872
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Konferensbidrag (refereegranskat)abstract
- The European XFEL project requires a high-speed, very precise clock and timing distribution over large distances. A prototype system which fulfils current requirements that uses high-end components has just been completed and is being tested. However, the system is quite complicated and the boards are very complex, being designed using the small micro-TCA form factor. A way to simplify the system, and perhaps reduce cost, would be to implement an Advanced PLL in the programmable logic of an FPGA, which then would control an external VCO. By doing so several major issues could be resolved at the same time, while making more use of the advanced features of modern FPGAs. Such a system could be an alternative solution to the complex part of the Timing and Triggering System for XFEL.
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| 9. |
- Hidvegi, Attila, et al.
(författare)
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Timing and Triggering System Prototype for the XFEL Project
- 2010
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Ingår i: IEEE Transactions on Nuclear Science. - 0018-9499 .- 1558-1578. ; 58:4, s. 1852-1856
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Tidskriftsartikel (refereegranskat)abstract
- The European X-ray Free Electron Laser (XFEL) [1] at DESY in Hamburg will begin operating in the next few years, enabling new, ground-breaking research opportunities. The entire system requires very precise clock and trigger distribution, synchronous with the 1.3 GHz system RF-frequency, over distances of more than 3.4 km. The new experiment demanded features that other commercial solutions could not yet provide. Researchers at Stockholm University and DESY have developed a prototype for the timing system of XFEL. It has been decided that XFEL will use modern ATCA and Micro-TCA systems because of their advanced features and reliability. The timing system has been adapted to the Micro-TCA bus standard and also follows the new upcoming xTCA for physics standard. The prototype is fully functional and complete. It will serve as a platform for future development of the whole timing system. This paper describes the hardware design and some test results using the prototype board.
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| 10. |
- Hussein, Ahmed, et al.
(författare)
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Towards a Multi-Level Model of Enterprise Architecture Modeling Notations
- 2023
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Ingår i: Proceedings of the 25th International Conference on Enterprise Information Systems - Volume 2, ICEIS 2023. - : INSTICC. - 9789897586484 ; , s. 466-473
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Konferensbidrag (refereegranskat)abstract
- Over the past few decades, the field of enterprise architecture (EA) has grown, and many EA modeling notations have been proposed. In order to support the different needs, the different notations vary in the element types that they provide in their metamodel. This abundance of elements makes it difficult for the end-user to differentiate between the various elements and complicates the model transformation between different EA model notations. Therefore, this research analyzes existing EA frameworks and their modeling notations and extracts common properties. First, we performed a literature review to identify common EA frameworks and their modeling notations. Second, based on the found notations’ concepts, we create a taxonomy based on their similarities that leads to a multi-level model of EA notations. Our results showed that The Open Group Architecture Framework, ArchiMate, Department of Defense Architecture Framework, and Integrated Architecture Framework are the most used EA frameworks. Those frameworks served as input for a multi-level model comprising the common concepts of the different modeling notations.
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