366 research outputs found
Biometric cryptosystems: Overview, state-of-the-art and perspective directions
No full textModern cryptographic systems are constantly evolving and improving. This is due to the development of new computing systems and advanced cryptographic analysis methods, as well as increasing requirements for speed, security and reliability of used tools. In particular, it was announced an advent of universal quantum computers, which will be able to provide cryptanalysis with advanced calculation methods based on fundamentally new physical principles. The possible use of such devices encourages the development, research and standardization of algorithms for post-quantum cryptographic information protection. Another factor for the development of advanced cryptographic systems is the biometric technologies popularization. In this work, a critical review and analysis of the current application of biometric technologies in cryptographic systems, is conducted. In particular, biometric cryptographic systems, which are designed to generate secure pseudorandom sequences that can be used as cryptographic keys, passwords etc., are investigated. A comparative analysis of various biometric cryptosystems with the determination of their advantages and disadvantages is carried out. The perspective directions for further research are substantiated. Also this work presents a new key generation scheme which uses fuzzy extractors from the biometric data of iris. The proposed method is based on the code-based public key cryptosystems which are considered to be resistant to quantum cryptanalysis. A software implementation of this method with experimental studies of the key generation algorithm and recommendations on the practical application are proposed
Code-based key encapsulation mechanisms for post-quantum standardization
No full textThe code-based key encapsulation mechanisms for post-quantum standardization, which were presented on the NIST PQC competition, are investigated. The results of the primary comparative analysis of the cryptographic properties and the performance of the key encapsulation schemes are presented
The research of modern stream ciphers
No full textSynchronous stream ciphers produce long keystreams to be XORed with plaintext. The output keystreams should be indistinguishable from truly random sequences and should not leak any information about the secret key and the internal state of the cipher. In this study, we analyze of modern stream ciphers according to various criteria using methodology eSTREAM
A high-performance custom photodetection system to probe the light yield enhancement in oriented crystals
No full textScintillating homogeneous detectors represent the state of the art in
electromagnetic calorimetry. Moreover, the currently neglected crystalline
nature of the most common inorganic scintillators can be exploited to achieve
an outstanding performance boost in terms of compactness and energy resolution.
In fact, it was recently demonstrated by the AXIAL/ELIOT experiments that a
strong reduction in the radiation length inside PWO, and a subsequent
enhancement in the scintillation light emitted per unit thickness, are attained
when the incident particle trajectory is aligned with a crystal axis within
. A SiPM-based system has been developed to directly probe this
remarkable effect by measuring the scintillation light emitted by a PWO sample.
The same concept could be applied to full-scale detectors that would feature a
design significantly more compact than currently achievable and unparalleled
resolution in the range of interest for present and future experiments
A high-performance custom photodetection system to probe the light yield enhancement in oriented crystals
No full textOverview of T and D-T results in JET with ITER-like wall
No full textIn 2021 JET exploited its unique capabilities to operate with T and D–T fuel with an ITER-like Be/W wall (JET-ILW). This second major JET D–T campaign (DTE2), after DTE1 in 1997, represented the culmination of a series of JET enhancements—new fusion diagnostics, new T injection capabilities, refurbishment of the T plant, increased auxiliary heating, in-vessel calibration of 14 MeV neutron yield monitors—as well as significant advances in plasma theory and modelling in the fusion community. DTE2 was complemented by a sequence of isotope physics campaigns encompassing operation in pure tritium at high T-NBI power. Carefully conducted for safe operation with tritium, the new T and D–T experiments used 1 kg of T (vs 100 g in DTE1), yielding the most fusion reactor relevant D–T plasmas to date and expanding our understanding of isotopes and D–T mixture physics. Furthermore, since the JET T and DTE2 campaigns occurred almost 25 years after the last major D–T tokamak experiment, it was also a strategic goal of the European fusion programme to refresh operational experience of a nuclear tokamak to prepare staff for ITER operation. The key physics results of the JET T and DTE2 experiments, carried out within the EUROfusion JET1 work package, are reported in this paper. Progress in the technological exploitation of JET D–T operations, development and validation of nuclear codes, neutronic tools and techniques for ITER operations carried out by EUROfusion (started within the Horizon 2020 Framework Programme and continuing under the Horizon Europe FP) are reported in (Litaudon et al Nucl. Fusion accepted), while JET experience on T and D–T operations is presented in (King et al Nucl. Fusion submitted)
Overview of T and D–T results in JET with ITER-like wall
No full textIn 2021 JET exploited its unique capabilities to operate with T and D–T fuel with an ITER-like
Be/W wall (JET-ILW). This second major JET D–T campaign (DTE2), after DTE1 in 1997,
represented the culmination of a series of JET enhancements—new fusion diagnostics, new T
injection capabilities, refurbishment of the T plant, increased auxiliary heating, in-vessel
calibration of 14 MeV neutron yield monitors—as well as significant advances in plasma theory
and modelling in the fusion community. DTE2 was complemented by a sequence of isotope
physics campaigns encompassing operation in pure tritium at high T-NBI power. Carefully
conducted for safe operation with tritium, the new T and D–T experiments used 1 kg of T (vs
100 g in DTE1), yielding the most fusion reactor relevant D–T plasmas to date and expanding
our understanding of isotopes and D–T mixture physics. Furthermore, since the JET T and
DTE2 campaigns occurred almost 25 years after the last major D–T tokamak experiment, it was
also a strategic goal of the European fusion programme to refresh operational experience of a
nuclear tokamak to prepare staff for ITER operation. The key physics results of the JET T and
DTE2 experiments, carried out within the EUROfusion JET1 work package, are reported in this
paper. Progress in the technological exploitation of JET D–T operations, development and
validation of nuclear codes, neutronic tools and techniques for ITER operations carried out by
EUROfusion (started within the Horizon 2020 Framework Programme and continuing under the
Horizon Europe FP) are reported in (Litaudon et al Nucl. Fusion accepted), while JET
experience on T and D–T operations is presented in (King et al Nucl. Fusion submitted)
Investigations of primary active transporters expressed in Xenopus laevis oocytes : Wilson Disease Protein, a p-type ATPase and Proteorhodopsin, a light driven proton pump
No full textThe present work wishes to contribute with information on two members of the primary active transporter group, which differ both in structure and function: Wilson Disease Protein which uses the energy released by ATP hydrolysis to transport copper across cell membranes, and Proteorhodopsin, which uses the energy of light to build up a proton gradient across the bacterial cell membrane, both heterologously expressed in Xenopus laevis oocytes. The surface detection experiments using HA-tagged WNDP confirm the proposed topology of WNDP. The HA-tag per se does not interfere with the function of WNDP, as shown for WNDP HA56 by ATP-dependent phosphorylation after expression in Sf9 cells. Sequence modifications within the WNDP HA56 template-construct reveal some interesting features: i) the N-terminal domain, which contains the 6 metal binding sites, is not necessary for plasma membrane targeting; ii) elevated surface expression of WNDP was observed when the carboxy terminus containing the tri-Leu motif is missing, which suggests that this motif might be involved in the retrieval of the protein from the plasma membrane; iii) the mutations TGE>AAA (proposed to lock the protein in the E1 conformation and lead to constitutive plasma membrane localisation) and D1027A (phosphorylation deficient) did not interfere with the surface localisation of the protein; iv) the mutations CPC>SPS (copper transport deficient) and H1069Q (phosphorylation deficient, most common mutation in Wilson Disease) reduced plasma membrane expression to less then 50%. Western blot analysis shows that the overall expression level of all constructs is similar to that of the reference construct WNDP HA56. These findings suggest that motifs involved in copper binding and catalytic activity do not interfere with plasma membrane targeting of WNDP in Xenopus oocytes. However, the H1069Q mutation could interfere with the distribution of WNDP protein within the cells. In the case of Proteorhodopsin, data presented in this work support earlier observations according to which proteorhodopsin can operate as an outwardly and inwardly directed light-driven ion pump. The residues proposed to play the roles of proton donor (E108) and acceptor (D97) are important for proton translocation. In the absence of an anionic residue at position 97 no outward pumping takes place, but inward charge translocation may occurs under appropriate conditions. An M-like state similar to that known from BR detectably accumulates under neutral pH conditions or under conditions where reprotonation of the Schiff base from the cytoplasmic side is slowed down, as in case of the mutants at position 108. Under acidic conditions PR pumps inwardly under the concerted action of pH and transmembrane potential. The experiments performed in parallel with PR and BR wild-types brought not only interesting information about similarities and differences between the two retinylidene ion pumps, but also led to the observation that the life-time of the M state in BR wild-type can be extended in addition to hyperpolarising transmembrane potentials also by extracellular acidic pH, when the proton gradient through the cell membrane is directed opposite to the ion transport (i.e. when the electrochemical gradient opposing the direction of proton transport increases). Direct photocurrent measurements of HA-tagged PR and BR have shown that the inserted tag may interfere with the functionality of the protein. Next to E108 and D97 in PR other residues in the vicinity of the retinal binding pocket contribute to the translocation of protons, as exemplified by the mutant L105Q: additionally to changing the absorption maximum of the protein, this mutant is a less effective proton pump than the wild type. The example of PR suggests that transduction of light energy by – and reaction mechanisms of retinylidene ion pumps have not been entirely deciphered by the extensive studies of bacteriorhodopsin.Die vorliegende Arbeit beinhaltet Experimente zum Studium zweier primär aktiver, in Membran lokalisierter Transportproteinen. Sie wurden heterolog in Oozyten von Xenopus laevis exprimiert. Hierbei handelt es sich um eine Schwermetall-ATPase, das „Wilson Disease Protein“, und eine lichtgetriebene Protonenpumpe, „Proteorhodopsin“. Das „Wilson Disease Protein“ (WNDP) ist eine, aus 1465 Aminosäuren bestehende P1-Typ Cu+-ATPase, die wichtig ist, um während der Proteinsynthese im Trans-Golgi-Netzwerk (TGN) Kupfer Ionen (Cu+) bereitzustellen, und im Falle einer Erhöhung des intrazellulärem Kupfer- Konzentrazion trägt, durch nicht ausreichend geklärten Mechanismen, zur Wiederherstellung des physiologischen Cu-Spiegels bei. Durch Mutationen bedingte Fehlfunktionen von WNDP führen zu der Erbkrankheit Morbus Wilson. Die vorliegende Arbeit versucht, die Xenopus-Oozyten – ein bekanntes System zum Studium von Transportproteinen der Plasmamembran – als ein alternatives Expressionssystem zu evaluiren. Die Experimente zeigen, dass das Wilson Disease Protein in Xenopus-Oozyten exprimiert werden kann. Es befindet sich in der Plasmamembran der Oozyten und kann durch Chemilumineszenz und Elektronenmikroskopie detektiert werden. Die Experimente zu Oberflächenexpression, bei denen mit HA-Epitopen markiertes WNDP verwendet wurde, bestätigen die für WNDP vorgeschlagene Topologie. Sequenzänderungen, die in das Konstrukt WNDP HA56 eingefügt wurden, offenbaren einige interessante Eigenschaften des Proteins: i) Die N-terminale Domäne, die 6 Metall-Bindestellen enthält, ist offensichtlich für die Zielsteurung in die Plasmamembran targeting nicht notwendig. ii) Bei fehlendem Carboxy-terminus – wodurch das triple-Leucin-Motiv deletiert wird – kommt es zu einer verstärkten Oberflächenexpression von WNDP, woraus sich Hinweise auf eine Beteiligung dieses Motives bei der Relokalisation des Proteins aus der Plasmamembran zum TGN ergeben. Ausserderm, die Resultate weisen darauf hin, dass die Motive, die für die Kupferbindung und die katalytische Aktivität wichtig sind in Xenopus-Oozyten, keinen Einfluss auf Zielsteuerung zur Plasmamembran von WNDP haben. Allerdings könnte die Mutation H1069Q mit der Verteilung von WNDP innerhalb der Zellen interferieren. Proteorhodopsin (PR), das erste “Bakterio-Rhodopsin“ im eigentlichen Sinne, ist eine lichtgetriebene, auswärtsgerichtete Protonenpumpe, die in Meeresbakterien identifiziert werden konnte. Das Protein besteht aus 249 Aminosäuren und zeigt eine erhebliche Sequenzähnlichkeit mit Bakteriorhodopsin (BR). Die entscheidenden Elemente für die Translokation der Protonen sind konserviert. Die Expression in Xenopus-laevis-Oozyten erlaubt nicht nur die Untersuchung des pHEinflusses auf perfekt orientierte PR Moleküle, sondern auch die des Membranpotentials (beide zusammen bilden das elektrochemische Potential für Protonen, ΔμH+). Wildtyp und PR-Mutanten wurden in diesem System heterolog exprimiert und untersucht, um mehr über die Faktoren, die die Eigenschaften des Protontransfers kontrollieren, zu erfahren. Mittels des Two-Electrode Voltage-Clamp Methode (Zwei-Elektroden Spannungsklemme), wurde das Aktionsspektrum vom PR Wildtyp aufgenommen und mit früheren Messungen an künstlichen Lipid Membranen (BLM) verglichen. Außerdem wurden die Spannungsabhängigkeit der stationären Photoströme von PR Wild-Typ (I-V Kennlinien) bei verschiedene intra- und extrazellulären pHWerten bestimmt. Mutationen der Proton-Akzeptor und –Donor-Gruppen D97 und E108 wurden ebenfalls auf ihre Auswirkungen untersucht. Stationäre Belichtung bei neutralem pH löst bei den Mutanten D97N und D97T nur transiente und stationäre Einwärtsströme, eine Tatsache, die die wichtige Rolle des Protonenakzeptors D97 für das Auswärtspumpen bestätigt. Die Mutante E108G zeigt im Vergleich zum Wild-Typ viel kleinere auswärts gerichtete transiente und stationäre Ströme. Die stationäre Pumpfunktion wird in Anwesenheit von Azid deutlich stimuliert, in Analogie zur BR Mutanten D96G. Die Lebenszeit des M-ähnlichen Intermediates von PR Wildtyp und E108G wurde mittels eines speziellen Belichtungsprotokolls studiert, und dabei BR Photoströme unter gleiche Bedingungen als Kontrolle verwendet. Die Ergebnisse zeigen, dass während der stationären Belichtung bei pH 7.4 blaue Laserblitze deutliche auswärtsgerichtete transiente Ströme bei PR hervorrufen, im Gegensatz zu BR, was darauf hinweist, dass unter gleichen experimentellen Bedingungen immer noch weitere PRMoleküle angeregt werden können. Die Richtung der transienten Ladungstranslokation ist bei negativen Membranpotentialen invertiert (einwärtsgerichtet). Bei extrazellulär saurem pH konnten einwärtsgerichtete transiente Ströme sowohl bei blauen als auch bei grünen Laserblitzen beobachtet werden. Ein M-ähnlicher Zustand wie im Falle von BR kann spektroskopischen Messungen zufolge bei PR nur bei neutralem pH-Wert akkumulieren, oder unter Bedingungen unter denen die Reprotonierung der Schiff’schen Base von der zytoplasmatischen Seite her verlangsamt ist, wie im Fall der Mutationen des Protonendonors E108 (unterstüzt von den Experimenten mit PR E108G in der An- oder Abwesenheit von Azid, und unterschiedliche pH Werte). Diese Ergebnisse bestätigen die früheren Aussagen von Friedrich et al. (2002), dass die Richtung des Protonentransports durch den Protonenkonzentrationsgradienten und das Membranpotential bestimmt wird. Die Experimente, die parallel an PR- und BR-Wildtypen ausgeführt wurden, haben nicht nur interessante Informationen über Ähnlichkeiten und Unterschiede zwischen den beiden Retinyliden- Ionenpumpen gebracht. Außerdem führten sie zu der Beobachtung, dass die Lebenszeit des M-Zustand in BR – außer durch hyperpolarisierende Membranpotentiale (Geibel et al, 2001) – auch durch einen der Richtung der Ionenpumpe entgegengesetzten Protonengradienten verlängert werden kann. Direkte Photostrom-Messungen von HA-Epitop markiertem PR und BR haben gezeigt, dass das HA-Epitop abhängig von der Insertionsstelle die Funktion des Proteins beeinträchtigen kann
Correlated Interball/ground-based observations of isolated substorm: The pseudobreakup phase
No full textInternational audienceWe study the isolated substorm that occurred after a long quiet period, which showed all of the substorm signatures except for the first half hour of the expansion phase, which could be characterized as a pseudobreakup sequence, rather than a full-scale substorm onset. During the considered event, the substorm's instability leads to a current disruption, which starts at the near-Earth plasma sheet and then propagates tailward. Based on auroral observations, the analysis of geosynchronous plasma injections, and the plasma sheet observations at ~15 RE at the meridian of auroral substorm development we show that (1) before and probably during "pseudobreakup phase", the plasma sheet stayed cold and dense, (2) during the pseudobreakup phase, particle injections at 6.6 RE were only seen in unusually low energy components, and (3) the electron precipitation into the ionosphere was very soft. We conclude that the basic difference between pseudobreakups and "real" substorm activations was found in the low energy of all manifestations. We suggest that high density and low electron temperature in the plasma sheet are the reasons for low energization in the magnetic reconnection operated on closed field lines in the plasma sheet, as well as the weak field-aligned acceleration, as predicted by the Knight's relationship. The low Hall conductivity could then be the reason for the weak ground magnetic effects observed. This explanation suggests that the role of the ionospheric conductivity is "passive" as the plasma sheet, rather than the ionosphere, controls the development of the magnetospheric instability
Enhanced electromagnetic radiation in oriented scintillating crystals at the 100-MeV and sub-GeV scales
No full textNowadays, it is well known that the electromagnetic interaction between high-energy particles and matter experiences substantial modifications when the latter consists of a crystalline medium and its lattice axes are almost parallel to the input beam direction. In particular, a strong boost to the cross section of bremsstrahlung by electrons and positrons in high-density oriented crystals has been observed in the 10-to-100 GeV regime. This effect proves particularly appealing when it comes to inorganic scintillators, given the possibility to exploit it for the development of high-performance, ultra-compact electromagnetic calorimeters. This work provides a detailed discussion of the results obtained by probing a PWO (lead tungstate) oriented sample with 120 GeV/c electrons and positrons at the CERN North Area: in particular, a comparison between the outcomes obtained with electrons and positrons is made. Moreover, output radiation measurements on a thinner oriented PWO sample have been recently performed in the sub-GeV regime at the MAMI-B facility: an overview on the resulting characterisation is given
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