Electrocatalytic Properties of BDD Anodes: Its Loosely Adsorbed Hydroxyl Radicals

The high oxidative action of boron doped diamond (BDD) anodes on the biorefractory organic compounds has been attributed to the low adsorption of the generated hydroxyl radicals on the BDD surface in respect to other anodic materials. In a previous paper, the effect of low adsorption of BBD has been studied by proposing a continuum approach to represent the adsorption layer. The oxidative action of the hydroxyl radicals is attributed to the values of their diffusivity into the adsorption and adjacent reactive layer as well as to the value of kinetic constant in both layers. In this paper, more details on both layers are reported in order to justify the proposed continuum approach as well as the assumptions concerning diffusivity and kinetic constant in both adsorption and reactive layers, where the oxidative action of hydroxyl radicals occurs

Mixing Within Patterned Vortex Core

The video shows the flow dynamics within inner and outer regions of a vortex core. The observed phenomena mimic a transport process occurring within the Antarctic vortex. The video shows two distinct regions: a strongly mixed core and broad ring of weakly mixed region extending out the vortex core boundaries. The two regions are separated by a thin layer that isolates the weakly and strongly mixed regions; this thin layer behaves as barrier to the mixing of the two regions. The video shows that the barriers deplete when a swirl of the vortex core increases and the vortex core espouses a triangular pattern.Comment: 62nd Annual Meeting of the APS Division of Fluid Dynamics, Fluid Dynamics Vide

Διερεύνηση της επίδρασης του εδαφικού καλύμματος βραχωδών πρανών στις καταπτώσεις βράχων

131 σ.Το φαινόμενο των καταπτώσεων βράχων είναι ιδιαίτερα καταστροφικό για τα έργα υποδομής και εξαιρετικά επικίνδυνο για τις ανθρώπινες ζωές. Καθώς είναι ένα σχετικά τυχαίο στην εκδήλωσή του φαινόμενο, με πολλές παραμέτρους που το επηρεάζουν, δεν υπάρχει πλήρης κατανόηση των μηχανισμών που το ελέγχουν, παρά την εκτεταμένη έρευνα που έχει γίνει και συνεχίζεται. Για τους απαιτούμενους υπολογισμούς, με σκοπό τον σχεδιασμό των καταλλήλων μέτρων προστασίας, χρησιμοποιούνται ένας ή και περισσότεροι συντελεστές αναπήδησης των βραχωδών τεμαχών που καταπίπτουν, οι οποίοι λαμβάνουν υπ’ όψιν το γεωυλικό του πρανούς πάνω στο οποίο πραγματοποιείται η κατάπτωση. Αρκετές έρευνες έχουν πραγματοποιηθεί για διάφορα βραχώδη υλικά και την επιρροή τους στους συντελεστές αναπήδησης, αλλά ελάχιστες από αυτές λαμβάνουν υπ’ όψιν την περίπτωση πρανών που είναι καλυμμένα με κάποια στρώση εδαφικού υλικού, κατάσταση η οποία είναι και αρκετά συνήθης στη φύση. Για τον λόγο αυτό στην παρούσα διπλωματική εργασία διεξήχθησαν περίπου 500 δοκιμές, με σκοπό την διερεύνηση του βαθμού επιρροής της επικάλυψης με αργιλικό ή αμμώδες υλικό στον συντελεστή αναπήδησης και έγινε προσπάθεια να δοθεί μια ποιοτική και ποσοτική ερμηνεία για την περιγραφή των πειραματικών αποτελεσμάτων. Οι επιφάνειες πρόσπτωσης διαμορφώθηκαν από δύο τύπου αργιλικά υλικά, ένα χαμηλής και ένα μέσης πλαστικότητας είτε καθαρά, δηλαδή χωρίς προσμίξεις, είτε με την προσθήκη σε συγκεκριμένα ποσοστά δυο τύπων άμμου, της Μ31 και της M34 (Longstone). Η καταγραφή των δοκιμών έγινε από ειδική κάμερα υψηλής ταχύτητας, στο εργαστήριο Τεχνικής Γεωλογίας και Βραχομηχανικής του Ε.Μ.Π. και η επεξεργασία των καταγραφών έγινε με την χρήση ειδικού κώδικα που έχει αναπτυχθεί στο πλαίσιο της σχετικής έρευνας που βρίσκεται υπό εξέλιξη στο Εργαστήριο. Κατά την επεξεργασία των δεδομένων προέκυψε ότι, η αύξηση της ενέργειας πρόσκρουσης, δηλαδή η αύξηση της ταχύτητας πρόσκρουσης και της μάζας, κατ’ επέκταση και της ορμής πρόσκρουσης, προκαλεί μείωση του συντελεστή αναπήδησης. Επίσης, η αύξηση του πάχους στρώσης του εδαφικού υλικού και της περιεχόμενης υγρασίας είτε σε καθαρό είτε σε μείγμα αργιλικού υλικού προκαλεί μείωση του συντελεστή αναπήδησης. Επίσης, η αύξηση του ποσοστού της αργίλου σε εδαφικό μείγμα άμμου - αργίλου προκαλεί αύξηση του αντίστοιχου συντελεστή αναπήδησης εάν πρόκειται για ξηρό υλικό, ενώ αντίθετα προκαλεί μείωση του συντελεστή με προσθήκη νερού και αύξηση της περιεχόμενης υγρασίας. Τέλος, δεν κατορθώθηκε να δοθεί μια στατιστικά σημαντική σχέση που να συνδέει την επιρροή του συντελεστή αναπήδησης για στρώση αργιλικού υλικού συναρτήσει της πλαστικότητας της αργίλου, του πάχους της στρώσης, της ενέργειας πρόσκρουσης και της περιεχόμενης υγρασίας, αλλά προέκυψαν αρκετά χρήσιμα ποιοτικά συμπεράσματα.Rockfalls poses a significant threat on infrastructure and human lives. Since it is a very random phenomenon which depends on various parameters, there is no advanced understanding through the academic circles; therefore its thorough study is required in order for the engineer to design the mitigation measures. For the necessary calculations the coefficients of restitution are used, whose values are qualitatively expressed based on the slope material composition. Many researches have been performed in order to study the coefficient of restitution values for impacts into various rock materials, however very few have been held for slopes covered with soil materials such as clay or sand, which are very common in nature. Therefore, in the context of the present thesis, approximately 500 tests were carried out in order to study the effect of the soil cover layer on the coefficients of restitution. The impact surfaces were covered with two different clay types, one of low and one of medium plasticity mixed with two types of quartizic sand, M31 and M34 (Longstone) on various combinations. The study was carried out at the Engineering Geology and Rock Mechanics laboratory in the National Technical University of Athens. The tests were recorded by a high speed camera and the data acquisition was made using a machine vision code created in the context of the relative ongoing studies performed in the lab. The obtained data resulted in some satisfactory observations. To begin with, the increase of the block’s impact energy, which is originated from either the increase of the block’s mass or its impact velocity; leads to a decrease in the values of the coefficient of restitution. Furthermore, the increase of the soil’s layer thickness and moisture causes a significant reduction to the corresponding coefficients’ of restitution values. In addition, in a dry soil mix composed of clay and sand, while the clay proportion increases the respective coefficient of restitution increases as well. However, if the soil containes water then an increase of the clay proportion to the mix yields the exact opposite effect. Last but not least, although there was an effort to establish a formula that would link the coefficient of restitution with the plasticity, the water contamination and the thickness of the clay layer as well as with the impact energy, the outcome was not statistically significant but some useful qualitative interpretations were made.Παναγιώτης Χ. Βατίστα

Enabling hardware randomization across the cache hierarchy in Linux-Class processors

The most promising secure-cache design approaches use cache-set randomization to index cache contents thus thwarting cache side-channel attacks. Unfortunately, existing randomization proposals cannot be sucessfully applied to processors’ cache hierarchies due to the overhead added when dealing with coherency and virtual memory. In this paper, we solve existing limitations of hardware randomization approaches and propose a cost-effective randomization implementation to the whole cache hierarchy of a Linux-capable RISC-V processor.This work has been supported by the European HiPEAC Network of Excellence, by the Spanish Ministry of Economy and Competitiveness (contract TIN2015-65316-P), and by Generalitat de Catalunya (contracts 2017-SGR-1414 and 2017- SGR-1328). The DRAC project is co-financed by the European Union Regional Development Fund within the framework of the ERDF Operational Program of Catalonia 2014-2020 with a grant of 50% of total cost eligible. We also thank Red-RISCV for the efforts to promote activities around open hardware. This work has received funding from the EU Horizon2020 programme under grant agreement no. 871467 (SELENE). M. Doblas has been partially supported by the Agency for Management of University and Research Grants (AGAUR) of the Government of Catalonia under Beques de Col·laboració d’estudiants en departaments universitaris per al curs 2019- 2020. V. Kostalabros has been partially supported by the Agency for Management of University and Research Grants (AGAUR) of the Government of Catalonia under Ajuts per a la contractació de personal investigador novell fellowship number 2019FI_ B01274. M. Moreto has been partially supported by the Spanish Ministry of Economy, Industry and Competitiveness under Ramón y Cajal fellowship number RYC- 2016-21104.Peer ReviewedPostprint (published version

HLS-based HW/SW co-design of the post-quantum classic McEliece cryptosystem

While quantum computers are rapidly becoming more powerful, the current cryptographic infrastructure is imminently threatened. In a preventive manner, the U.S. National Institute of Standards and Technology (NIST) has initiated a process to evaluate quantum-resistant cryptosystems, to form the first post-quantum (PQ) cryptographic standard. Classic McEliece (CM) is one of the most prominent cryptosystems considered for standardization in NIST’s PQ cryptography contest. However, its computational cost poses notable challenges to a big fraction of existing computing devices. This work presents an HLS-based, HW/SW co-design acceleration of the CM Key Encapsulation Mechanism (CM KEM). We demonstrate significant maximum speedups of up to 55.2 ×, 3.3 ×, and 8.7 × in the CM KEM algorithms of key generation, encapsulation, and decapsulation respectively, comparing to a SW-only scalar implementation.This research was supported by the European Union Regional Development Fund within the framework of the ERDF Operational Program of Catalonia 2014-2020 with a grant of 50% of the total cost eligible, under the DRAC project [001- P-001723]. It was also supported by the Spanish goverment (grant RTI2018-095094-B-C21 “CONSENT”), by the Spanish Ministry of Science and Innovation (contracts PID2019- 107255GB-C21, PID2019-107255GB-C21) and by the Catalan Government (contracts 2017-SGR-1414, 2017-SGR-705). This work has also received funding from the European Union Horizon 2020 research and innovation programme under grant agreement No. 871467. V. Kostalabros has been partially supported by the Agency for Management of University and Research Grants (AGAUR) of the Government of Catalonia under "Ajuts per a la contractació de personal investigador novell" fellowship No. 2019FI B01274. M. Moreto was also partially supported by the Spanish Ministry of Economy, Industry and Competitiveness under "Ramón y Cajal" fellowship No. RYC-2016-21104.Peer ReviewedPostprint (author's final draft

A security model for randomization-based protected caches

Cache side-channel attacks allow adversaries to learn sensitive information about co-running processes by using only access latency measures and cache contention. This vulnerability has been shown to lead to several microarchitectural attacks. As a promising solution, recent work proposes Randomization-based Protected Caches (RPCs). RPCs randomize cache addresses, changing keys periodically so as to avoid long-term leakage. Unfortunately, recent attacks have called the security of state-of-the-art RPCs into question. In this work, we tackle the problem of formally defining and analyzing the security properties of RPCs. We first give security definitions against access-based cache sidechannel attacks that capture security against known attacks such as Prime+Probe and Evict+Probe. Then, using these definitions, we obtain results that allow to guarantee security by adequately choosing the rekeying period, the key generation algorithm and the cache randomizer, thus providing security proofs for RPCs under certain assumptions.This research was supported by the European Union Regional Development Fund withinthe framework of the ERDF Operational Program of Catalonia 2014-2020 with a grant of50% of the total cost eligible, under the DRAC project [001-P-001723], and by the SpanishGovernment, under the CONSENT project [RTI2018-095094-B-C21]. Carles Hernándezis partially supported by Spanish Ministry of Science, Innovation and Universities under“Ramón y Cajal”, fellowship No. RYC2020-030685-I. Vatistas Kostalabros is partiallysupported by the Agency for Management of University and Research Grants (AGAUR) ofthe Government of Catalonia, under “Ajuts per a la contractació de personal investigadornovell”, fellowship No. 2019FI B01274. Miquel Moretó is partially supported by theSpanish Ministry of Economy, Industry and Competitiveness under “Ramón y Cajal”,fellowship No. RYC-2016-21104.Peer ReviewedPostprint (published version