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Evacuation trials from a double-deck electric train unit: Experimental data and sensitivity analysis

Authors
Najmanová, H.; Kuklík, L.; Pešková, V.; Bukáček, M.; Vašata, D.; Hrabák, P.
Year
2022
Published
Safety Science. 2022, 146 ISSN 0925-7535.
Type
Article
Annotation
Passenger trains represent a challenging environment in emergencies, with specific evacuation conditions resulting from the typical layout and interior design inherent to public transportation vehicles. This paper describes a dataset obtained in a full-scale controlled experiment emulating the emergency evacuation of a double-deck electric unit railcar carried out in Prague in 2018. 15 evacuation trials involving 91 participants were conducted under various evacuation scenarios considering different compositions of passenger crowd, exit widths, and exit types (egress to a high platform, to an open rail line using stairs, and a 750 mm jump without any supporting equipment). The study’s main goals were to collect experimental data on the movement conditions in the railcar and to study the impact of various boundary conditions on evacuation process and total evacuation time. Movement characteristics (exit flows, speeds) and human behaviour (pre-movement activities, exiting behaviours) were also analysed. The data obtained was used to validate and adjust a Pathfinder model to capture important aspects of evacuation from the railcar. Furthermore, a series of simulations using this model was performed to provide sensitivity analysis of the influence of crowd composition, exit width, and exit type on total evacuation time. As a key finding, we can conclude that for the case of a standard exit path (platform or stairs) the width of the main exit had the greatest impact on total evacuation time, however, crowd composition played the prevailing role in evacuation scenarios involving a jump.

Three counter value based ROPUFs on FPGA and their properties

Year
2022
Published
Microprocessors and Microsystems. 2022, 88 ISSN 0141-9331.
Type
Article
Annotation
This paper investigates the behavior of the Physical Unclonable Function (PUF) design proposed in our previous work that is based ring oscillators (ROs). Our approach is able to extract multiple output bits from each RO pair in contrary to the classical approach, where frequencies of ROs are compared. We study the behavior of our PUF design together with other two similar proposals that are also based on extracting PUF bits from counter values. In this work we compare the behavior of three PUF designs that are based on extracting PUF bits from counter values with one of them being proposed in our previous work. We evaluate these proposals at both stable and varying temperature and voltage in order to determine their robustness. The results show that our proposed technique, the frequency ratio, is the most reliable one. Furthermore, we compare the behavior of all of the three designs when mutually asymmetric and symmetric ROs are used. All of the measurements were performed on Cmod S7 FPGA boards (Xilinx XC7S25-1CSGA225C).

Topological groups with invariant linear spans

Year
2022
Published
Revista Matematica Complutnes. 2022, 35(1), 219-226. ISSN 1139-1138.
Type
Article
Annotation
Given a topological group G that can be embedded as a topological subgroup into some topological vector space (over the field of reals) we say that G has invariant linear span if all linear spans of G under arbitrary embeddings into topological vector spaces are isomorphic as topological vector spaces. For an arbitrary set A let Z(A) be the direct sum of |A|-many copies of the discrete group of integers endowed with the Tychonoff product topology. We show that the topological group Z(A) has invariant linear span. This answers a question from a paper of Dikranjan et al. (J Math Anal Appl 437:1257–1282, 2016) in positive. We prove that given a non-discrete sequential space X, the free abelian topological group A(X) over X is an example of a topological group that embeds into a topological vector space but does not have invariant linear span.

Waypoint routing on bounded treewidth graphs

Year
2022
Published
Information Processing Letters. 2022, 173 106165:1-106165:9. ISSN 0020-0190.
Type
Article
Annotation
In the Waypoint Routing Problem one is given an undirected capacitated and weighted graph G, a source-destination pair s, t∈V(G) and a set W⊆V(G), of waypoints. The task is to find a walk which starts at the source vertex s, visits, in any order, all waypoints, ends at the destination vertex t, respects edge capacities, that is, traverses each edge at most as many times as is its capacity, and minimizes the cost computed as the sum of costs of traversed edges with multiplicities. We study the problem for graphs of bounded treewidth and present a new algorithm for the problem working in 2^{O(tw)}·n time, significantly improving upon the previously known algorithms. We also show that this running time is optimal for the problem under Exponential Time Hypothesis

A Design and Stand Tests of Real-time Vehicle Active Suspension

Authors
Year
2021
Published
international scientific journal tran&MOTAUTO WORLD. 2021, 2021(4), 116-119. ISSN 2367-8399.
Type
Article
Annotation
The paper deals with innovations in vehicle suspension technology developed in Josef Bozek´s Research Center of Combustion Engines and Automobiles at CTU in Prague, Czech Republic. A unique innovative suspension system that uses a linear electric motor as a controlled actuator has been designed. Many experiments on energy management in the system have been accomplished. In order to verify various control strategies and to test different ways of energy consumption optimization we designed and constructed a unique one-quarter-car test stand. To realize simulation and practical experiments at the test stand it is necessary to find a proper experimental road disturbance signal to excite the active suspension system. The disturbance signal is applied on one more linear motor that is placed under a wheel of the one-quarter-car test stand to excite the active suspension system. The paper deals with the way and results of experimental verification of vehicle active suspension behavior when robust control is applied and also with the energy management strategy that is used in the system. A modified H-infinity controller that enables to set energy management strategy is mentioned in the paper. At the close of the paper, some experiments taken on the one quarter-car model and their evaluation are discussed.

A Design and Stand Tests of Real-timeVehicle Active Suspension

Authors
Year
2021
Published
Proceedings of the VII International Scientific Congress "Innovations 21". Sofia: Scientific-technical union of mechanical engineering, 2021. p. 32-36. vol. 1. ISSN 2603-3763.
Type
Proceedings paper
Annotation
In the paper, energy recuperation and management in automotive suspension systems with linear electric motors controlled using a proposed H∞ controller to obtain a variable mechanical force for a car damper is presented. Vehicle suspensions in which forces are generated in response to feedback signals by active elements obviously offer increased design flexibility compared to the conventional suspensions using passive elements such as springs and dampers. The main advantage of the proposed solution using a linear AC motor is the possibility to generate desired forces acting between the unsprung and sprung masses of the car, providing good insulation of the car sprung mass from the road surface disturbances. In addition, under certain circumstances using linear motors as actuators enables to transform mechanical energy of the vertical car vibrations to electrical energy, accumulate it, and use it when needed. Energy flow control (management) enables to reduce or even eliminate the demands concerning the external power source.

A characterization of Sturmian sequences by indistinguishable asymptotic pairs

Authors
Barbieri, S.; Labbé, S.; Starosta, Š.
Year
2021
Published
European Journal of Combinatorics. 2021, 95 ISSN 0195-6698.
Type
Article
Annotation
We give a new characterization of biinfinite Sturmian sequences in terms of indistinguishable asymptotic pairs. Two asymptotic sequences on a full -shift are indistinguishable if the sets of occurrences of every pattern in each sequence coincide up to a finitely supported permutation. This characterization can be seen as an extension to biinfinite sequences of Pirillo’s theorem which characterizes Christoffel words. Furthermore, we provide a full characterization of indistinguishable asymptotic pairs on arbitrary alphabets using substitutions and biinfinite characteristic Sturmian sequences. The proof is based on the well-known notion of derived sequences.

A Parameterized Complexity View on Collapsing k-Cores

Authors
Luo, J.; Molter, H.; Suchý, O.
Year
2021
Published
Theory of Computing Systems. 2021, 65(8), 1243-1282. ISSN 1432-4350.
Type
Article
Annotation
We study the NP-hard graph problem Collapsed k-Core where, given an undirected graph G and integers b, x, and k, we are asked to remove b vertices such that the k-core of remaining graph, that is, the (uniquely determined) largest induced subgraph with minimum degree k, has size at most x. Collapsed k-Core was introduced by Zhang et al. (2017) and it is motivated by the study of engagement behavior of users in a social network and measuring the resilience of a network against user drop outs. Collapsed k-Core is a generalization of r-Degenerate Vertex Deletion (which is known to be NP-hard for all r >= 0) where, given an undirected graph G and integers b and r, we are asked to remove b vertices such that the remaining graph is r-degenerate, that is, every its subgraph has minimum degree at most r. We investigate the parameterized complexity of Collapsed k-Core with respect to the parameters b, x, and k, and several structural parameters of the input graph. We reveal a dichotomy in the computational complexity of Collapsed k-Core for k <= 2 and k >= 3. For the latter case it is known that for all x >= 0 Collapsed k-Core is W[P]-hard when parameterized by b. For k <= 2 we show that Collapsed k-Core is W[1]-hard when parameterized by b and in FPT when parameterized by (b + x). Furthermore, we outline that Collapsed k-Core is in FPT when parameterized by the treewidth of the input graph and presumably does not admit a polynomial kernel when parameterized by the vertex cover number of the input graph.

Active Directory Kerberoasting Attack: Detection using Machine Learning Techniques

Authors
Kotlaba, L.; Fornůsek, S.; Lórencz, R.
Year
2021
Published
Proceedings of the 7th International Conference on Information Systems Security and Privacy. Madeira: SciTePress, 2021. p. 376-383. ISSN 2184-4356. ISBN 978-989-758-491-6.
Type
Proceedings paper
Annotation
Active Directory is a prevalent technology used for managing identities in modern enterprises. As a variety of attacks exist against Active Directory environment, its security monitoring is crucial. This paper focuses on detection of one particular attack - Kerberoasting. The purpose of this attack is to gain access to service accounts’ credentials without the need for elevated access rights. The attack is nowadays typically detected using traditional ”signature-based” detection approaches. Those, however, often result in a high number of false alerts. In this paper, we adopt machine learning techniques, particularly several anomaly detection al- gorithms, for detection of Kerberoasting. The algorithms are evaluated on data from a real Active Directory environment and compared to the traditional detection approach, with a focus on reducing the number of false alerts.

Aggregate Function Generalization to Temporal Data

Year
2021
Published
2021 IEEE 33rd International Conference on Tools with Artificial Intelligence (ICTAI). Los Alamitos: IEEE Computer Society, 2021.
Type
Proceedings paper
Annotation
In this article, we define an approximate generalization of aggregate functions for relational data with temporal attributes. This generalization is parametrized to allow simulation of a range of common aggregate functions and optionally take into account time. The parameters are not optimized, but we rather rely on repeated stochastic sampling of the parameters. We then apply a common regularized linear model to train a model on this high-dimensional space. Experimental results on 11 datasets suggest that there are datasets where incorporating time dimension into the model leads to an improvement in the predictive accuracy of the trained models.

Application of Distance Metric Learning to Automated Malware Detection

Year
2021
Published
IEEE Access. 2021, 2021(9), 96151-96165. ISSN 2169-3536.
Type
Article
Annotation
Distance metric learning aims to find the most appropriate distance metric parameters to improve similarity-based models such as k -Nearest Neighbors or k -Means. In this paper, we apply distance metric learning to the problem of malware detection. We focus on two tasks: (1) to classify malware and benign files with a minimal error rate, (2) to detect as much malware as possible while maintaining a low false positive rate. We propose a malware detection system using Particle Swarm Optimization that finds the feature weights to optimize the similarity measure. We compare the performance of the approach with three state-of-the-art distance metric learning techniques. We find that metrics trained in this way lead to significant improvements in the k -Nearest Neighbors classification. We conducted and evaluated experiments with more than 150,000 Windows-based malware and benign samples. Features consisted of metadata contained in the headers of executable files in the portable executable file format. Our experimental results show that our malware detection system based on distance metric learning achieves a 1.09 % error rate at 0.74 % false positive rate (FPR) and outperforms all machine learning algorithms considered in the experiment. Considering the second task related to keeping minimal FPR, we achieved a 1.15 % error rate at only 0.13 % FPR.

Automata Approach to Inexact Tree Pattern Matching Using 1-degree Edit Distance

Year
2021
Published
Proceedings of the Prague Stringology Conference 2021. Praha: CESKE VYSOKE UCENI TECHNICKE V PRAZE, 2021. p. 1-15. ISBN 978-80-01-06869-4.
Type
Proceedings paper
Annotation
We compare labeled ordered trees based on unit cost 1-degree edit distance that uses operations vertex relabeling, leaf insertion, and leaf deletion. Given an input tree T and a tree pattern P, we find all subtrees in T that match P with up to k errors. We show that this problem can be solved by finite automaton when T and P are represented in linear, prefix bar, notation. First, we solve this problem by a pushdown automaton. Then, we show that it can be transformed into a nondeterministic finite automaton due to its restricted use of the pushdown store. We also show a simulation of the nondeterministic finite automaton by dynamic programming.

Automatic Detection and Decryption of AES by Monitoring S-box Access

Authors
Kokeš, J.; Matějka, J.; Lórencz, R.
Year
2021
Published
Proceedings of the 7th International Conference on Information Systems Security and Privacy. Madeira: SciTePress, 2021. p. 172-180. ISSN 2184-4356. ISBN 978-989-758-491-6.
Type
Proceedings paper
Annotation
In this paper we propose an algorithm that can automatically detect the use of AES and automatically recover both the encryption key and the plaintext. It makes use of the fact that we can monitor accesses to the AES S-Box and deduce the desired data from these accesses; the approach is suitable to software-based AES implementations, both naíve and optimized. To demonstrate the feasibility of this approach we designed a tool which implements the algorithm for Microsoft Windows running on the Intel x86 architecture. The tool has been successfully tested against a set of applications using different cryptographic libraries and common user applications.

Automorphisms of the cube n^d

Authors
Dvořák, P.; Valla, T.
Year
2021
Published
Discrete Mathematics. 2021, 2021(344(3)), ISSN 0012-365X.
Type
Article
Annotation
Consider a hypergraph n^d where the vertices are points of the d-dimensional cube [n]^d and the edges are all sets of n points such that they are in one line. We study the structure of the group of automorphisms of n^d, i.e., permutations of points of [n]^d preserving the edges. In this paper we provide a complete characterization. Moreover, we consider the Colored Cube Isomorphism problem of deciding whether for two colorings of the vertices of n^d there exists an automorphism of n^d preserving the colors. We show that this problem is GI-complete.

Backward Pattern Matching on Elastic Degenerate Strings

Authors
Procházka, P.; Cvacho, O.; Krčál, L.; Holub, J.
Year
2021
Published
Proceedings of 14th International Joint Conference on Biomedical Engineering Systems and Technologies (BIOSTEC 2021). Lisboa: SCITEPRESS – Science and Technology Publications, Lda, 2021. p. 50-59. vol. 3. ISSN 2184-4305. ISBN 978-989-758-490-9.
Type
Proceedings paper
Annotation
Recently, the concept of Elastic Degenerate Strings (EDS) was introduced as a way of representing a sequenced population of the same species. Several on-line Elastic Degenerate String Matching (EDSM) algorithms were presented so far. Some of them provide practical implementation. We propose a new on-line EDSM algorithm BNDM-EDS. Our algorithm combines two traditional algorithms BNDM and the Shift-And that were adapted to the specifics needed by Elastic Degenerate Strings. BNDM-EDS is running in O (Nmd m w e) worst-case time. This implies O (Nm) time for small patterns, where m is the length of the searched pattern, N is the size of EDS, and w is the size of the computer word. The algorithm uses O (N + n) space, where n is the length of EDS. BNDM-EDS requires a simple preprocessing step with time and space O (m). Experimental results on real genomic data show superiority of BNDM-EDS over state-of-the-art algorithms.

Binary intersection formalized

Authors
Holub, Š.; Starosta, Š.
Year
2021
Published
Theoretical Computer Science. 2021, 866 14-24. ISSN 0304-3975.
Type
Article
Annotation
We provide a reformulation and a formalization of the classical result by Juhani Karhumäki characterizing intersections of two languages of the form $\{x,y\}^* \cap \{u,v\}^*$. We use the terminology of morphisms which allows to formulate the result in a shorter and more transparent way, and we formalize the result in the proof assistant Isabelle/HOL.

Building Normalized Systems from Domain Models in Ecore

Authors
Suchánek, M.; Mannaert, H.; Uhnák, P.; Pergl, R.
Year
2021
Published
New Trends in Intelligent Software Methodologies, Tools and Techniques. Amsterdam: IOS Press, 2021. p. 169-182. Frontiers in Artificial Intelligence and Applications. vol. 337. ISBN 978-1-64368-194-8.
Type
Proceedings paper
Annotation
Normalized Systems (NS) theory describes how to design and develop evolvable systems. It is applied in practice to generate enterprise information systems using NS Expanders from models of NS Elements. As there are various wellestablished modelling languages, the possibility to (re-)use them to create NS applications is desired. This paper presents a mapping between the NS metamodel and the Ecore metamodel as a representant of essential structural modelling. The mapping is the basis of the transformation execution tool based on Eclipse Modeling Framework and NS Java libraries. Both the mapping and the tool are demonstrated in a concise case study but cover all essential Ecore constructs. During the work, several interesting similarities of the two metamodels were found and are described, e.g., its meta-circularity or ability to specify data types using references to Java classes. Still, there are significant differences between the metamodels that prevent some constructs from being mapped. The issues with information loss upon the transformation are mitigated by incorporating additional options that serve as key-value annotations. The results are ready to be used for any Ecore models to create an NS model that can be expanded into an NS application.

Can investment incentives potentially cause unemployment? An empirical analysis of the relationship between FDI and employment based on the OLI framework

Authors
Evan, T.; Bolotov, I.
Year
2021
Published
Central European Business Review. 2021, 11(03), 1-17. ISSN 1805-4862.
Type
Article
Annotation
Unemployment, particularly in depressed regions, is more often than not used by politicians as the main argument for investment incentives provided to MNCs. This paper applies Dunning’s OLI Framework to the relationship between FDI and employment with the assumption that political negotiation between MNCs and the host government might actually have zero effect or a negative effect on employment. Since the last letter of OLI, internalization, suggests that MNCs optimize all production factors available to them and “subsidies” provided to MNCs by governments decrease the relative price of capital, MNCs may try to use more labour-saving techniques. Two hypotheses are tested using the dynamic panel model (DPD) and Granger causality tests for 193 countries for the years 1985–2019 where the first is supported with no strong relationship discovered between the variables. The results of the paper should support debate on the efficiency of investment incentives.

Combinatorics of Bricard's octahedra

Authors
Gallet, M.; Grasegger, G.; Legerský, J.; Schicho, J.
Year
2021
Published
Comptes Rendus Mathématique. 2021, 359(1), 7-38. ISSN 1778-3569.
Type
Article
Annotation
We re-prove the classification of motions of an octahedron - obtained by Bricard at the beginning of the XX century - by means of combinatorial objects satisfying some elementary rules. The explanations of these rules rely on the use of a well-known creation of modern algebraic geometry, the moduli space of stable rational curves with marked points, for die description of configurations of graphs on the sphere. Once one accepts the objects and the rules, the classification becomes elementary (though not trivial) and can be enjoyed without the need of a very deep background on the topic.

Comparison of OpTeX with other formats: LaTeX and ConTeXt

Authors
Year
2021
Published
TUGboat, The Communication of the TeX Users Group. 2021, 2021(42:1), ISSN 0896-3207.
Type
Article
Annotation
OpTEX [1] was introduced in an article [2] in the previous issue of TUGboat. It is a macro package that creates a format for LuaTEX. Its features are comparable with other formats like LaTEX or ConTEXt. One may ask why to use a new format, particularly when it requires a different markup syntax. I try to answer this question here. I present a comparison among the LaTEX, ConTEXt, and OpTEX formats, from various points of view.
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The person responsible for the content of this page: doc. Ing. Štěpán Starosta, Ph.D.