Search

Continuous-time quantum walks provide a natural framework to tackle the fundamental problem of finding a node among a set of marked nodes in a graph, known as spatial search. Whether spatial search by continuous-time quantum walk provides a quadratic advantage over classical random walks has been an outstanding problem. Thus far, this advantage is obtained only for specific graphs or when a single node of the underlying graph is marked. In this Letter, we provide a new continuous-time quantum walk search algorithm that completely resolves this: our algorithm can find a marked node in any graph with any number of marked nodes, in a time that is quadratically faster than classical random walks. The overall algorithm is quite simple, requiring time evolution of the quantum walk Hamiltonian followed by a projective measurement. A key component of our algorithm is a purely analogue procedure to perform operations on a state of the form e-tH2, SCOPUS: ar.j, info:eu-repo/semantics/published

Isogeny-based cryptography is a promising approach for post-quantum cryptography. The best-known protocol following that approach is the supersingular isogeny Diffie–Hellman protocol (SIDH); this protocol was turned into the CCA-secure key encapsulation mechanism SIKE, which was submitted to and remains in the third round of NIST's post-quantum standardisation process as an ‘alternate’ candidate. Isogeny-based cryptography generally relies on the conjectured hardness of computing an isogeny between two isogenous elliptic curves, and most cryptanalytic work referenced on SIKE's webpage exclusively focusses on that problem. Interestingly, the hardness of this problem is sufficient for neither SIDH nor SIKE. In particular, these protocols reveal additional information on the secret isogeny, in the form of images of specific torsion points through the isogeny. This paper surveys existing cryptanalysis approaches exploiting this often called ‘torsion point information’, summarises their current impact on SIKE and related algorithms, and suggests some research directions that might lead to further impact., SCOPUS: re.j, info:eu-repo/semantics/published

Priced timed games are two-player zero-sum games played on priced timed automata (whose locations and transitions are labeled by weights modelling the cost of spending time in a state and executing an action, respectively). The goals of the players are to minimise and maximise the cost to reach a target location, respectively. We consider priced timed games with one clock and arbitrary integer weights and show that, for an important subclass of them (the so-called simple priced timed games), one can compute, in pseudo-polynomial time, the optimal values that the players can achieve, with their associated optimal strategies. As side results, we also show that one-clock priced timed games are determined and that we can use our result on simple priced timed games to solve the more general class of so-called negative-reset-acyclic priced timed games (with arbitrary integer weights and one clock). The decidability status of the full class of priced timed games with one-clock and arbitrary integer weights still remains open., SCOPUS: ar.j, info:eu-repo/semantics/published

Controller synthesis for general linear temporal logic (LTL) objectives is a challenging task. The standard approach involves translating the LTL objective into a deterministic parity automaton (DPA) by means of the Safra-Piterman construction. One of the challenges is the size of the DPA, which often grows very fast in practice, and can reach double exponential size in the length of the LTL formula. In this paper, we describe a single exponential translation from limit-deterministic Büchi automata (LDBA) to DPA and show that it can be concatenated with a recent efficient translations from LTL to LDBA to yield a double exponential, ‘Safraless’ LTL-to-DPA construction. We also report on an implementation and a comparison with other LTL-to-DPA translations on several sets of formulas from the literature., SCOPUS: ar.j, info:eu-repo/semantics/published

In the framework of embedded and time-critical systems we consider the scheduling of preemptive real-time periodic tasks upon uniprocessor. We consider the notion of simulation interval, a finite time interval such that the schedule starts to repeat in a cycle. The interest is to design a time interval which includes all possible (reachable) schedule states. Our study focuses on a model where preemption costs are explicitly considered, i.e. the time required by the real-time operating system (RTOS) or the hardware to load the context of execution of preempted jobs. We present and prove correct a simulation interval for asynchronous arbitrary deadline tasks with preemption delays and that holds for any deterministic and memoryless scheduler upon uniprocessor. This first contribution is valid for all schedulers one can imagine (but deterministic and memoryless), including non-preemptive schedulers, not work-conserving, not necessarily popular “real-time” ones. We then consider a particular case, regarding the preemption delays, for EDF scheduling for which we extend the work of Leung & Merrill showing that [0, O^{max} + 2 cdot H) is a simulation interval (significantly shorter than the general result). We also show that [0, S_n+H) from our previous work remains a simulation interval for fixed task priority (FTP) schedulers. Before concluding we open a discussion on the scope of the results, paths for reducing pessimism as well as other potential results opened by this work., info:eu-repo/semantics/published

We study the relation between the linear programming relaxation of two classes of models for the Steiner tree problem with hop constraints. One class is characterized by having hop-indexed arc variables. Although such models have proved to have a very strong linear programming bound, they are not easy to use because of the huge number of variables. This has motivated some studies with models involving fewer variables that use, instead of the hop-indexed arc variables, hop-indexed node variables. In this article, we contextualize the linear programming relaxation of these node-based models in terms of the linear programming relaxation of known arc-based models. We show that the linear programming relaxation of a general node-based model is implied by the linear programming relaxation of a straightforward arc-based model., SCOPUS: ar.j, info:eu-repo/semantics/published

Geophysical data from open sources are widely used as support of integrated analysis in regional geologic studies in seismically active areas, such as Mexico. High seismicity with repetitive earthquakes occurs in areas of the subduction zones formed during the tectonic evolution and correlates with geophysical anomalous fields. This paper investigates the correspondence between the geophysical, topographic and seismic setting of Mexico using Generic Mapping Tools (GMT) scripting toolset for data processing. The approach for automated mapping using GMT console and shell scripts is presented as an advanced cartographic method aimed to get insights into in the geology and geophysics of Mexico. The data were obtained from open source high-resolution datasets: GEBCO, EGM-2008, satellite-derived gravity, EMAG2 magnetic anomaly and IRIS seismic database. The correspondence between the geological and geophysical data of Mexico has been verified through the comparison between the thematic maps, regional distribution of gravity anomalies and locations of earthquakes. Seven new maps are performed on geologic, geophysical, topographic and seismic data. Seismic mapping is presented for the period of 2007-2021 demonstrating events with magnitude from 1.5 to 7.2. The impact of tectonic processes that formed Middle American Trench and active Trans-Mexican Volcanic Belt on high regional seismicity with intensive earthquakes is explored. The study finds that GMT is an effective tool for high-quality mapping and cartographic analysis. The IRIS data can be used for geologic analysis of Mexico., Dados geofísicos de fontes abertas são amplamente usados como suporte de análise integrada em estudos geológicos regionais em áreas sismicamente ativas, como o México. Alta sismicidade com terremotos repetitivos ocorre em áreas das zonas de subducção formadas durante a evolução tectônica e se correlaciona com campos anômalos geofísicos. Este artigo investiga a correspondência entre o cenário geofísico, topográfico e sísmico do México usando o conjunto de ferramentas de script Generic Mapping Tools (GMT) para processamento de dados. A abordagem para mapeamento automatizado usando o GMT e scripts de shell é apresentada como um método cartográfico avançado com o objetivo de obter insights sobre a geologia e a geofísica do México. Os dados foram obtidos de conjuntos de dados de alta resolução de código aberto: GEBCO, EGM-2008, gravidade derivada de satélite, anomalia magnética EMAG2 e banco de dados sísmico IRIS. A correspondência entre os dados geológicos e geofísicos do México foi verificada através da comparação entre os mapas temáticos, distribuição regional de anomalias gravitacionais e localizações de terremotos. Sete novos mapas são realizados em dados geológicos, geofísicos, topográficos e sísmicos. O mapeamento sísmico é apresentado para o período de 2007-2021 demonstrando eventos com magnitude de 1,5 a 7,2. O impacto dos processos tectônicos que formaram a trincheira da América Central e o cinturão vulcânico transmexicano ativo na alta sismicidade regional com terremotos intensos é explorado. O estudo concluiu que o GMT é uma ferramenta eficaz para mapeamento e análise cartográfica de alta qualidade. Os dados IRIS podem ser usados para análises geológicas do México., info:eu-repo/semantics/published

The growing expectations for ubiquitous sensing have led to the integration of countless embedded sensors, actuators, and RFIDs in our surroundings. Combined with rapid developments in high-speed wireless networks, these resource-constrained devices are paving the road for the Internet-of-Things paradigm, a computing model aiming to bring together millions of heterogeneous and pervasive elements. However, it is commonly accepted that the Privacy consideration remains one of its main challenges, a notion that does not only encompasses malicious individuals but can also be extended to honest-but-curious third-parties. In this paper, we study the design of a privacy-enhanced communication protocol for lightweight IoT devices. Applying the proposed approach to MQTT, a highly popular lightweight publish/subscribe communication protocol prevents no valuable information from being extracted from the messages flowing through the broker. In addition, it also prevents partners re-identification. Starting from a privacy-ideal, but unpractical, exact transposition of the Oblivious Transfer (OT) technology to MQTT, this paper follows an iterative process where each previous model’s drawbacks are appropriately mitigated all the while trying to preserve acceptable privacy levels. Our work provides resistance to statistical analysis attacks and dynamically supports new client participation. Additionally the whole proposal is based on the existence of a non-communicating 3rd party during pre-development. This particular contribution reaches a proof-of-concept stage through implementation, and achieves its goals thanks to OT’s indistinguishability property as well as hash-based topic obfuscations., SCOPUS: ar.j, info:eu-repo/semantics/published

The Totten Glacier in East Antarctica is of major climate interest because of the large fluctuation of its grounding line and of its potential vulnerability to climate change. The ocean above the continental shelf in front of the Totten ice shelf exhibits large extents of landfast sea ice with low interannual variability. Landfast sea ice is either crudely or not at all represented in current climate models. These models are potentially omitting or misrepresenting important effects related to this type of sea ice, such as its influence on coastal polynya locations. Yet, the impact of the landfast sea ice on the ocean–ice shelf interactions is poorly understood. Using a series of high-resolution, regional NEMO-LIM-based experiments, including an explicit treatment of ocean–ice shelf interactions, over the years 2001–2010, we simulate a realistic landfast sea ice extent in the area of Totten Glacier through a combination of a sea ice tensile strength parameterisation and a grounded iceberg representation. We show that the presence of landfast sea ice impacts seriously both the location of coastal polynyas and the ocean mixed layer depth along the coast, in addition to favouring the intrusion of mixed Circumpolar Deep Water into the ice shelf cavities. Depending on the local bathymetry and the landfast sea ice distribution, landfast sea ice affects ice shelf cavities differently. The Totten ice shelf melt rate is increased by 16% on average and its variance decreased by 38%, while the Moscow University ice shelf melt rate is increased by +54% in winter. This highlights the importance of including an accurate landfast sea ice representation in regional and eventually global climate models., SCOPUS: ar.j, info:eu-repo/semantics/published

Time series forecasting deals with the prediction of future values of time-dependent quantities (e.g. stock price, energy load, city traffic) on the basis of their historical observations. In its simplest form, forecasting concerns a single variable (ie univariate problem) and deals with the prediction of a single future value (ie one-step-ahead).Existing studies in the literature focused on extending the univariate time series framework to address multiple future predictions (also called multiple-step-ahead) and multiple variables (multivariate approaches) accounting for their interdependencies. However, most of the approaches deal either with the multiple-step-ahead aspect or the multivariate one, rarely with both. Moreover state-of-the-art multivariate forecasting methods are restricted to low dimensional problems, linear dependencies among the values and short forecasting horizons. The recent technological advances (notably the Big Data revolution) are instead shifting the focus to problems characterized by a large number of variables, non-linear dependencies and long forecasting horizons.Those forecasting tasks are recently more and more addressed with a representation learning approach, by feeding the data into large scale deep neural networks and letting the model learn the most suitable data representation for the task at hand. This approach, despite its success and effectiveness, often requires considerable computational power, intensive model calibration and lacks interpretability of the learned model.The motivation of this thesis is that the potential of more interpretable approaches to multi-variate and multi-step-ahead tasks has not been sufficiently explored and that the use of complex neural methods is often neither necessary nor advantageous. In this perspective we explore two multivariate and multiple-step-ahead forecasting strategies based on dimensionality reduction :The first strategy, called Dynamic Factor Machine Learning,is a machine learning, Doctorat en Sciences, info:eu-repo/semantics/nonPublished

We consider two covering variants of the network design problem. We are given a set of origin/destination pairs, called O/D pairs, and each such O/D pair is covered if there exists a path in the network from the origin to the destination whose length is not larger than a given threshold. In the first problem, called the Maximal Covering Network Design problem, one must determine a network that maximizes the total fulfilled demand of the covered O/D pairs subject to a budget constraint on the design costs of the network. In the second problem, called the Partial Covering Network Design problem, the design cost is minimized while a lower bound is set on the total demand covered. After presenting formulations, we develop a Benders decomposition approach to solve the problems. Further, we consider several stabilization methods to determine Benders cuts as well as the addition of cut-set inequalities to the master problem. We also consider the impact of adding an initial solution to our methods. Computational experiments show the efficiency of these different aspects., SCOPUS: ar.j, info:eu-repo/semantics/published

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Active learning is a setting in which a student queries a teacher, through membership and equivalence queries, in order to learn a language. Performance on these algorithms is often measured in the number of queries required to learn a target, with an emphasis on costly equivalence queries. In graybox learning, the learning process is accelerated by foreknowledge of some information on the target. Here, we consider graybox active learning of subsequential string transducers, where a regular overapproximation of the domain is known by the student. We show that there exists an algorithm to learn subsequential string transducers with a better guarantee on the required number of equivalence queries than classical active learning., SCOPUS: cp.k, info:eu-repo/semantics/published

The fragile complexity of a comparison-based algorithm is f(n) if each input element participates in O(f(n)) comparisons. In this paper, we explore the fragile complexity of algorithms adaptive to various restrictions on the input, i.e. algorithms with a fragile complexity parameterized by a quantity other than the input size n. We show that searching for the predecessor in a sorted array has fragile complexity Θ(log k), where k is the rank of the query element, both in a randomized and a deterministic setting. For predecessor searches, we also show how to optimally reduce the amortized fragile complexity of the elements in the array. We also prove the following results: Selecting the kth smallest element has expected fragile complexity O(log log k) for the element selected. Deterministically finding the minimum element has fragile complexity Θ(log (Inv ) ) and Θ(log (Runs ) ), where Inv is the number of inversions in a sequence and Runs is the number of increasing runs in a sequence. Deterministically finding the median has fragile complexity O(log (Runs ) + log log n) and Θ(log (Inv ) ). Deterministic sorting has fragile complexity Θ(log (Inv ) ) but it has fragile complexity Θ(log n) regardless of the number of runs., SCOPUS: cp.k, info:eu-repo/semantics/published

Ant colony optimization (ACO) algorithms have originally been designed for static optimization problems, where the input data is known in advance and is not subject to changes over time. Later, the long term memory of ACO proved effective for reoptimization over environment changes when extended to deal with dynamic combinatorial optimization problems (DCOPs). Among the major proposals of this kind, several adaptations of ACO procedures to improve information reuse can be identified, as well as a population-based ACO algorithm (P-ACO) specifically designed for DCOPs. Indeed, P-ACO drew the attention of the research community due to its ability to faster process pheromone information, but the few works assessing the effectiveness of the adapted ACO procedures and also P-ACO are not enough to reach more general conclusions on the current state-of-the-art in ACO for dynamic optimization. In this work, we conduct an extensive experimental campaign to evaluate the most common ACO procedure adaptations identified in the literature, using as underlying algorithms the state-of-the-art in ACO for static optimization (MAX-MIN Ant System, MMAS) and the most relevant ACO algorithm proposed for dynamic optimization (P-ACO). A variant of the traveling salesman problem with dynamic demands (DTSP) is used as test benchmark, similarly to most investigations on ACO for combinatorial optimization. Besides the carefully designed experimental setup we adopt, our work represents a significant contribution for, at least, three reasons. First, our work is the first to acknowledge that DCOPs require custom-configured parameter settings, and also the first to use automatic configuration tools for this task. Concretely, we show how the hypervolume indicator can be used to evaluate and configure the anytime behavior of algorithms for DCOPs. Second, we directly compare MMAS and P-ACO, isolating local search as an experimental factor. While P-ACO proves indeed effective in the absence of local s, SCOPUS: ar.j, info:eu-repo/semantics/published

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Database systems play a central role in modern data-centered applications. Their performance is thus a key factor in the efficiency of data processing pipelines. Modern database systems expose several parameters that users and database administrators can configure to tailor the database settings to the specific application considered. While this task has traditionally been performed manually, in the last years several methods have been proposed to automatically find the best parameter configuration for a database. Many of these methods, however, use statistical models that require high amounts of data and fail to represent all the factors that impact the performance of a database, or implement complex algorithmic solutions. In this work we study the potential of a simple model-free general-purpose configuration tool to automatically find the best parameter configuration of a database. We use the irace configurator to automatically find the best parameter configuration for the Cassandra NoSQL database using the YCBS benchmark under different scenarios. We establish a reliable experimental setup and obtain speedups of up to 30% over the default configuration in terms of throughput, and we provide an analysis of the configurations obtained., SCOPUS: ar.j, info:eu-repo/semantics/published

MobilityDB is an open source moving object database. It extends PostgreSQL and PostGIS with types and operations for managing continuous geospatial trajectories. This hand-on tutorial will introduce the attendees to: (1) trajectory data management in MobilityDB, (2) visualization of moving object data in QGIS, and (3) distributed spatiotemporal query processing using MobilityDB. All the tutorial queries will be in SQL., info:eu-repo/semantics/published

In a recent work, we reported on an Extreme Learning Machine (ELM) implemented in a photonic system based on frequency multiplexing, where each wavelength of the light encodes a different neuron state. In the present work, we experimentally demonstrate the parallelization potentialities of this approach. We show that multiple frequency combs centered on different frequencies can copropagate in the same system, resulting in either multiple independent ELMs executed in parallel on the same substrate or a single ELM with an increased number of neurons. We experimentally tested the performances of both these operation modes on several classification tasks, employing up to three different light sources, each of which generates an independent frequency comb. We also numerically evaluated the performances of the system in configurations containing up to 15 different light sources., info:eu-repo/semantics/published

We show that the functional analogue of QMA∩COQMA, denoted F(QMA∩COQMA), equals the complexity class Total Functional QMA (TFQMA). To prove this, we need to introduce an alternative definition of QMA∩COQMA in terms of a single quantum verification procedure. We show that if TFQMA equals the functional analogue of BQP (FBQP), then QMA∩COQMA=BQP. We show that if there is a QMA complete problem that (robustly) reduces to a problem in TFQMA ,then QMA∩COQMA=QMA. Our results thus imply that if some of the inclusions between functional classes FBQP ⊆ TFQMA ⊆ FQMA are in fact equalities, then the corresponding inclusions in BQP⊆QMA∩COQMA⊆QMA are also equalities., SCOPUS: ar.j, info:eu-repo/semantics/published

Tremendous increase in the use of the mobile devices equipped with the GPS and other location sensors has resulted in the generation of a huge amount of movement data. In recent years, mining this data to understand the collective mobility behavior of humans, animals and other objects has become popular. Numerous mobility patterns, or their mining algorithms have been proposed, each representing a specific movement behavior. Convoy pattern is one such pattern which can be used to find groups of people moving together in public transport or to prevent traffic jams. A convoy is a set of at least m objects moving together for at least k consecutive time stamps where m and k are user-defined parameters. Existing algorithms for detecting convoy patterns do not scale to real-life dataset sizes. Therefore in this paper, we propose a generic distributed convoy pattern mining algorithm called DCM and show how such an algorithm can be implemented using the MapReduce framework. We present a cost model for DCM and a detailed theoretical analysis backed by experimental results. We show the effect of partition size on the performance of DCM. The results from our experiments on different data-sets and hardware setups, show that our distributed algorithm is scalable in terms of data size and number of nodes, and more efficient than any existing sequential as well as distributed convoy pattern mining algorithm, showing speed-ups of up to 16 times over SPARE, the state of the art distributed co-movement pattern mining framework. DCM is thus able to process large datasets which SPARE is unable to., SCOPUS: ar.j, DecretOANoAutActif, info:eu-repo/semantics/published

We present Séta (To be pronounced [ʃe:tɒ] meaning “walk” in Hungarian.), a new family of public-key encryption schemes with post-quantum security based on isogenies of supersingular elliptic curves. It is constructed from a new family of trapdoor one-way functions, where the inversion algorithm uses Petit’s so called torsion attacks on SIDH to compute an isogeny between supersingular elliptic curves given an endomorphism of the starting curve and images of torsion points. We prove the OW-CPA security of Séta and present an IND-CCA variant using the post-quantum OAEP transformation. Several variants for key generation are explored together with their impact on the selection of parameters, such as the base prime of the scheme. We furthermore formalise an “uber” isogeny assumption framework which aims to generalize computational isogeny problems encountered in schemes including SIDH, CSDIH, OSIDH and ours. Finally, we carefully select parameters to achieve a balance between security and run-times and present experimental results from our implementation., SCOPUS: cp.k, info:eu-repo/semantics/published

We introduce a notion of split extension of (non-associative) bialgebras which generalizes the notion of split extension of magmas introduced by M. Gran, G. Janelidze and M. Sobral. We show that this definition is equivalent to the notion of action of (non-associative) bialgebras. We particularize this equivalence to (non-associative) Hopf algebras by defining split extensions of (non-associative) Hopf algebras and proving that they are equivalent to actions of (non-associative) Hopf algebras. Moreover, we prove the validity of the Split Short Five Lemma for these kinds of split extensions, and we examine some examples., SCOPUS: ar.j, info:eu-repo/semantics/published

The paper presents the application of ArcGIS for environmental modelling of the landscapes in northern Iceland (17.00°W-23.00°W, 64.30°N-67.00°N). The aim was to explore the vegetation distribution by NDVI and ISOCLUST classification of the land cover types. Data include the Landsat TM image. Freely available satellite remote sensing data from the Landsat mission have been processed by GIS to deliver information on land cover types from image classification and NDVI vegetation index. Landsat products provide geospatial data on regional scale with moderate temporal (weekly) and spatial (30-10 m) resolution, making them useful for environmental monitoring and landscape studies. The tools include the ArcGIS software used for raster processing. Data processing was performed in the three steps: 1) comparative analysis of the visualized sixteen band combinations to assess the distinguishability of vegetation and other land cover types in colour composites; 2) computed NDVI standardized vegetation index; 3) unsupervised classification of the Landsat TM by the ISOCLUST algorithm. Large glaciers Hofsjökull and Langjökull were detected on various colour composites, and the visibility of the water/land borders is assessed (Blöndulón lake), agricultural areas near the Varmahlíð, vegetated areas around the Akrahreppur municipality. Computing the NDVI and using ISOCLUST by ArcGIS software enabled to distinguish various land cover types and map landscapes in the study area. The computed NDVI shown the presence and condition of vegetation, that is, a relative biomass in the area of northern Iceland. The NDVI was used based on the contrast of the two channels from a multispectral Landsat TM raster data., info:eu-repo/semantics/published

Ghana is a country exceptionally rich in geologic mineral resources with contrasting topographic relief and varied geophysical setting. This paper evaluated the geological and geophysical setting of Ghana with a special focus on the impact of the geologic setting and topography on gravity. Specifically, it assessed how variations in geology, topography, landscapes and the environment control the geophysical parameters and how these vary among the major regions of the country – the Volta Basin, Northern Plains, Ashanti-Kwahu (Kumasi) and Coastal Plains in the Accra surroundings. Previous studies utilizing traditional Geographic Information System (GIS) approaches have documented the geologic evolution of Ghana evolved as a part of the West African Craton. As a contribution to the existing research, this paper presents a regional analysis of Ghana by integrated mapping of geology, geophysics and topography of the country. The technical approach of this research focuses on utilizing the console-based scripting cartographic toolset Generic Mapping Tools (GMT) integrated with QGIS for processing and mapping the datasets: General Bathymetric Chart of the Oceans (GEBCO), Earth Gravitational Model 2008 (EGM-2008), gravity grids. The theoretical background is based on the geologic research of West Africa supported by high-resolution data. The paper defines a conceptual cartographic framework for integrated geologic and geophysical visualization in a regionalscale mapping project on Ghana., Gana je zemlja iznimno bogata geološkim mineralnim resursima s kontrastnim topografskim reljefom i raznolikim geofizičkim okruženjem. U ovom se članku procjenjuje geologija i geofizika Gane s posebnim naglaskom na utjecaj geološkog okruženja i topografije na gravitaciju. Konkretno, procjenjuje se kako varijacije u geologiji, topografiji, krajolicima i okolišu kontroliraju geofizičke parametre i kako se oni razlikuju među glavnim regijama zemlje – bazen Volte, Sjeverne ravnice, Ashanti-Kwahu (Kumasi) i obalne ravnice u okruženju Akre. Prethodne studije, koje su koristile tradicionalne pristupe s pomoću geoinformacijskih sustava (GIS), dokumentirale su geološku evoluciju Gane koja je evoluirala kao dio zapadnoafričkog kratona. Kao doprinos postojećem istraživanju, ovaj članak daje regionalnu analizu Gane integriranim kartiranjem geologije, geofizike i topografije te zemlje. Tehnički se pristup ovog istraživanja fokusira na upotrebu kartografskog skupa alata za skriptiranje na konzoli (Generic Mapping Tools – GMT) integriranog s QGIS-om za obradu i kartiranje skupova podataka: Opća batimetrijska karta oceana (General Bathymetric Chart of the Oceans – GEBCO) i Gravitacijski model Zemlje 2008 (Earth Gravitational Model 2008 – EGM-2008). Teorijska se pozadina temelji na geološkim istraživanjima zapadne Afrike potkrijepljenima podatcima visoke razlučivosti. Rad definira konceptualni kartografski okvir za integriranu geološku i geofizičku vizualizaciju u projektu kartiranja na regionalnoj razini u Gani., SCOPUS: ar.j, info:eu-repo/semantics/published

In order to speed up the synthesis of Petri nets from labelled transition systems, a divide and conquer strategy consists in defining decompositions of labelled transition systems, such that each component is synthesisable iff so is the original system. Then corresponding Petri Net composition operators are searched to combine the solutions of the various components into a solution of the original system. The paper presents two such techniques, which may be combined: products and articulations. They may also be used to structure transition systems, and to analyse the performance of synthesis techniques when applied to such structures., SCOPUS: ar.j, info:eu-repo/semantics/published

In 2016, Galbraith et al. presented an adaptive attack on the SIDH key exchange protocol. In SIKE, one applies a variant of the Fujisaki-Okamoto transform to force Bob to reveal his encryption key to Alice, which Alice then uses to re-encrypt Bob’s ciphertext and verify its validity. Therefore, Bob can not reuse his encryption keys. There have been two other proposed countermeasures enabling static-static private keys: k-SIDH and its variant by Jao and Urbanik. These countermeasures are relatively expensive since they consist in running multiple parallel instances of SIDH. In this paper, firstly, we propose a new countermeasure to the GPST adaptive attack on SIDH. Our countermeasure does not require key disclosure as in SIKE, nor multiple parallel instances as in k-SIDH. We translate our countermeasure into a key validation method for SIDH-type schmes. Secondly, we use our key validation to design HealSIDH, an efficient SIDH-type static-static key interactive exchange protocol. Thirdly, we derive a PKE scheme SHealS using HealSIDH. SHealS uses larger primes compared to SIKE, has larger keys and ciphertexts, but only 4 isogenies are computed in a full execution of the scheme, as opposed to 5 isogenies in SIKE. We prove that SHealS is IND-CPA secure relying on a new assumption we introduce and we conjecture its IND-CCA security. We suggest HealS, a variant of SHealS using a smaller prime, providing smaller keys and ciphertexts. As a result, HealSIDH is a practically efficient SIDH based (interactive) key exchange incorporating a “direct” countermeasure to the GPST adaptive attack., SCOPUS: cp.k, info:eu-repo/semantics/published

Swarm intelligence studies self-organized collective behavior resulting from interactions between individuals, typically in animals and artificial agents. Some studies from cognitive science have also demonstrated self-organization mechanisms in humans, often in pairs. Further research into the topic of human swarm intelligence could provide a better understanding of new behaviors and larger human collectives. This requires studies with multiple human participants in controlled experiments in a wide variety of scenarios, where a rich scope of possible interactions can be isolated and captured. In this paper, we present HuGoS—‘Humans Go Swarming’—a multi-user virtual environment implemented using the Unity game development platform, as a comprehensive tool for experimentation in human swarm intelligence. We demonstrate the functionality of HuGoS with naïve participants in a browser-based implementation, in a coordination task involving collective decision-making, messaging and signaling, and stigmergy. By making HuGoS available as open-source software, we hope to facilitate further research in the field of human swarm intelligence., SCOPUS: ar.j, info:eu-repo/semantics/published

We cryptanalyse the SIDH-based oblivious pseudorandom function from supersingular isogenies proposed at Asiacrypt’20 by Boneh, Kogan and Woo. To this end, we give an attack on an assumption, the auxiliary one-more assumption, that was introduced by Boneh et al. and we show that this leads to an attack on the oblivious PRF itself. The attack breaks the pseudorandomness as it allows adversaries to evaluate the OPRF without further interactions with the server after some initial OPRF evaluations and some offline computations. More specifically, we first propose a polynomial-time attack. Then, we argue it is easy to change the OPRF protocol to include some countermeasures, and present a second subexponential attack that succeeds in the presence of said countermeasures. Both attacks break the security parameters suggested by Boneh et al. Furthermore, we provide a proof of concept implementation as well as some timings of our attack. Finally, we examine the generation of one of the OPRF parameters and argue that a trusted third party is needed to guarantee provable security., SCOPUS: cp.k, info:eu-repo/semantics/published

This paper presents a novel and unconventional NAS method called DensEMANN, which can automatically build DenseNet and DenseNet-BC architectures layer by layer and kernel by kernel while they are being trained. DensEMANN is a complex method, divided into a macro-algorithm (which adds dense layers one by one to the network) and a micro-algorithm (which builds new layers by adding and/or pruning convolution kernels from them). Using the micro-algorithm alone, it is possible to build one-layer DenseNet trained on CIFAR-10 and SVHN with similar or greater accuracy levels than those obtained with equivalent prebuilt architectures. As for the macro-algorithm, its results are still unpredictable, and further research is needed before its automatically-generated DenseNet can compete with neural networks designed by humans., info:eu-repo/semantics/published

info:eu-repo/semantics/published

In this paper, we provide an effective characterization of all the subgame-perfect equilibria in infinite duration games played on finite graphs with mean-payoff objectives. To this end, we introduce the notion of requirement, and the notion of negotiation function. We establish that the plays that are supported by SPEs are exactly those that are consistent with the least fixed point of the negotiation function. Finally, we show that the negotiation function is piecewise linear, and can be analyzed using the linear algebraic tool box. As a corollary, we prove the decidability of the SPE constrained existence problem, whose status was left open in the literature., SCOPUS: cp.p, info:eu-repo/semantics/published

Customer churn is a major concern for large companies (notably telcos), even in a big data world. Customer retention campaigns are routinely used to prevent churn, but targeting the right customers on the basis of their historical profile is a difficult task. Companies usually have recourse to two data-driven approaches: churn prediction and uplift modeling. In churn prediction, customers are selected on the basis of their propensity to churn in a near future. In uplift modeling, only customers reacting positively to the campaign are considered. Though uplift is better suited to maximize the efficiency of the retention campaign because of its causal aspect, it suffers from several estimation issues. To improve the uplift accuracy, this paper proposes to leverage historical data about the reachability of customers during a campaign. We suggest several strategies to incorporate reach information in uplift models, and we show that most of them outperform the classical churn and uplift models. This is a promising perspective for churn prevention in the telecommunication sector, where uplift modeling has failed so far to provide a significant advantage over non-causal approaches., SCOPUS: cp.k, info:eu-repo/semantics/published

info:eu-repo/semantics/published

This paper demonstrates a swarm robotics construction system where the intelligence that coordinates construction has been moved from the robots to an advanced building material. This building material, that we call Stigmergic Blocks, is capable of computation and local communication. Using comprehensive simulation models based on real hardware, we investigate approaches to improving the efficiency and flexibility of a swarm robotics construction system., SCOPUS: cp.k, info:eu-repo/semantics/published

Researchers in the multicriteria analysis community have recently started to study the application of clustering techniques. Different methods have been proposed leading to complete or partial multicriteria partitions. Recently, a method based on the exploitation of the ordinal properties of a valued preference relation has been developed in order to obtain a totally ordered clustering. The underlying idea is to find a partition that minimizes the inconsistencies between the obtained ordered clusters and the input preference matrix. The exact algorithm gives the guarantee to achieve this goal based on a lexicographic order. In this contribution, we propose to further extend their approach to the case where minimum and maximum capacities are imposed on the cluster sizes. This leads to add a constraint satisfaction test (that is based on the levels and the ranks of the graph built during the procedure). The algorithm is evaluated regarding its execution time and illustrated on the academic ranking of world universities., SCOPUS: cp.k, info:eu-repo/semantics/published

In a competitive market, online auction systems enable optimal trading of digital products and services. Bidders can participate in existing blockchain-based auctions while protecting the confidentiality of their bids in a decentralized, transparent, secure, and auditable manner. However, in a competitive market, parties would prefer not to disclose their interests to competitors, and to remain anonymous during auctions. In this paper, we firstly analyze the specific requirements for blockchain-based anonymous fair auctions. We present a formal model tailored to study auction systems that facilitate anonymity, as well as a generic protocol for achieving bid confidentiality and bidder anonymity using existing cryptographic primitives such as designated verifier ring signature. We demonstrate that it is secure using the security model we presented. Towards the end, we demonstrate through extensive simulation results on Ethereum blockchain that the proposed protocol is practical and has minimal associated overhead. Furthermore, we discuss the complexity and vulnerabilities that a blockchain environment might introduce during implementation., SCOPUS: ar.j, info:eu-repo/semantics/published

We remark that the quantum key agreement protocol (Yang et al. in Quantum Inf Process 18(10):322, 2019) is flawed. It is unnecessary for Bob to prepare his secret key KB, because it is finally announced and accessible to adversaries. We find, KB has no relation to the confidentiality of the final agreed key KAB= KA⊕ KB. It is just a key transfer scheme, not a general key agreement scheme. We also find there is short of a code for Bob to extract bits from the measured results., SCOPUS: no.j, info:eu-repo/semantics/published

Neuro-evolution is an appealing approach to generating collective behaviors for robot swarms. In its typical application, known as off-line automatic design, the neural networks controlling the robots are optimized in simulation. It is understood that the so-called reality gap, the unavoidable differences between simulation and reality, typically causes neural network to be less effective on real robots than what is predicted by simulation. In this paper, we present an empirical study on the extent to which the reality gap impacts the most popular and advanced neuro-evolutionary methods for the off-line design of robot swarms. The results show that the neural networks produced by the methods under analysis performed well in simulation, but not in real-robot experiments. Further, the ranking that could be observed in simulation between the methods eventually disappeared. We find compelling evidence that real-robot experiments are needed to reliably assess the performance of neuro-evolutionary methods and that the robustness to the reality gap is the main issue to be addressed to advance the application of neuro-evolution to robot swarms., SCOPUS: ar.j, info:eu-repo/semantics/published

Instead of synthesising a labelled transition system into a weighted Petri net, we shall here consider the larger class of nets with reset arcs, allowing to instanciate a larger class of transition systems. We shall also target an extension of choice-free nets with reset arcs, since choice-free nets appeared to be especially interesting in terms of properties, synthesis and implementation. In addition to a general algorithm, we shall analyse how to speed it up by reducing the number and complexity of the linear systems of constraints to be solved and how to set up a pre-synthesis phase. We shall also envisage how to implement the result of such a synthesis as a concurrent program., SCOPUS: cp.k, info:eu-repo/semantics/published

The complexity class QMA is the quantum analog of the classical complexity class NP. The functional analogs of NP and QMA ,called functional NP (FNP) and functional QMA (FQMA), consist in either outputting a (classical or quantum) witness or outputting NO if there does not exist a witness. The classical complexity class total functional NP (TFNP) is the subset of FNP for which it can be shown that the NO outcome never occurs. TFNP includes many natural and important problems. Here we introduce the complexity class total functional QMA (TFQMA), the quantum analog of TFNP. We show that FQMA and TFQMA can be defined in such a way that they do not depend on the values of the completeness and soundness probabilities. We provide examples of problems that lie in TFQMA ,coming from areas such as the complexity of k-local Hamiltonians and public key quantum money. In the context of black-box groups, we note that group non-membership, which was known to belong to QMA ,in fact belongs to TFQMA. We also provide a simple oracle with respect to which we have a separation between FBQP and TFQMA., SCOPUS: ar.j, info:eu-repo/semantics/published