263,386 research outputs found
Recent Advances in the Synthesis and Functions of Reconfigurable Interlocked DNA Nanostructures
No full textInterlocked circular DNA nanostructures, e.g., catenanes or rotaxanes, provide functional materials within the area of DNA nanotechnology. Specifically, the triggered reversible reconfiguration of the catenane or rotaxane structures provides a means to yield new DNA switches and to use them as dynamic scaffolds for controlling chemical functions and positioning functional cargoes. The synthesis of two-ring catenanes and their switchable reconfiguration by pH, metal ions, or fuel/anti-fuel stimuli are presented, and the functions of these systems, as pendulum or rotor devices or as switchable catalysts, are described. Also, the synthesis of three-, five-, and seven-ring catenanes is presented, and their switchable reconfiguration using fuel/anti-fuel strands is addressed. Implementation of the dynamically reconfigured catenane structures for the programmed organization of Au nanoparticle (NP) assemblies, which allows the plasmonic control of the fluorescence properties of Au NP/fluorophore loads associated with the scaffold, and for the operation of logic gates is discussed. Interlocked DNA rotaxanes and their different synthetic approaches are presented, and their switchable reconfiguration by means of fuel/anti-fuel strands or photonic stimuli is described. Specifically, the use of the rotaxane as a scaffold to organize Au NP assemblies, and the control of the fluorescence properties with Au NP/fluorophore hybrids loaded on the rotaxane scaffold, are introduced. The future prospectives and challenges in the field of interlocked DNA nanostructures and the possible applications are discussed
Dual switchable CRET-induced luminescence of CdSe/ZnS quantum dots (QDs) by the hemin/G-quadruplex-bridged aggregation and deaggregation of two-sized QDs
No full textThe hemin/G-quadruplex-catalyzed generation of chemiluminescence through the oxidation of luminol by H2O2 stimulates the chemiluminescence resonance energy transfer (CRET) to CdSe/ZnS quantum dots (QDs), resulting in the luminescence of the QDs. By the cyclic K+-ion-induced formation of the hemin/G-quadruplex linked to the QDs, and the separation of the G-quadruplex in the presence of 18-crown-6-ether, the ON-OFF switchable CRET-induced luminescence of the QDs is demonstrated. QDs were modified with nucleic acids consisting of the G-quadruplex subunits sequences and of programmed domains that can be cross-linked through hybridization, using an auxiliary scaffold. In the presence of K+-ions, the QDs aggregate through the cooperative stabilization of K+-ion-stabilized G-quadruplex bridges and duplex domains between the auxiliary scaffold and the nucleic acids associated with the QDs. In the presence of 18-crown-6-ether, the K+-ions are eliminated from the G-quadruplex units, leading to the separation of the aggregated QDs. By the cyclic treatment of the QDs with K+-ions/18-crown-6-ether, the reversible aggregation/deaggregation of the QDs is demonstrated. The incorporation of hemin into the K+-ion-stabilized G-quadruplex leads to the ON-OFF switchable CRET-stimulated luminescence of the QDs. By the mixing of appropriately modified two-sized QDs, emitting at 540 and 610 nm, the dual ON-OFF activation of the luminescence of the QDs is demonstrated
Metodi di autenticazione: Nuovi attacchi e difese
No full textAl giorno d'oggi, i sistemi di autenticazione sono molto diffusi nei nostri dispositivi. Proteggono la sicurezza dei nostri sistemi, garantendo che solo le persone autorizzate abbiano accesso a servizi e dati riservati. Grazie a questo ruolo, i sistemi di autenticazione hanno fatto la loro prima apparizione negli anni '60, con la diffusione dei primi computer nelle università. Nel corso degli anni, questi sistemi si sono evoluti. Se i primi sistemi di autenticazione erano basati solo su password, oggi sono notevolmente avanzati. In particolare, con l'ampia diffusione degli smartphone, i sistemi di autenticazione sono diventati di uso comune, focalizzandosi su sistemi user-friendly come quelli biometrici. Questa evoluzione ha generato un mercato in forte crescita, e si prevede che nei prossimi anni aumenterà ancora del 15%, con un fatturato di centinaia di miliardi di dollari.
L'usabilità non è l'unico fattore che influenza l'evoluzione dei sistemi di autenticazione. Anche la loro sicurezza determina la loro evoluzione nel tempo. Se un metodo di autenticazione garantisce la sicurezza di un sistema, è anche vero che è il primo a soffrire di attacchi informatici.
Dopo la comparsa di nuove tecnologie di autenticazione sul mercato, è frequente notare la diffusione di nuovi metodi per aggirare la sicurezza della nuova tecnologia.
La ricerca in queste aree diventa fondamentale: da un lato, per scoprire nuovi sistemi di autenticazione che possano migliorare l'usabilità dei nostri dispositivi, e dall'altro, per anticipare le possibili vulnerabilità e rendere questi sistemi più sicuri.
Questa tesi studia la sicurezza dei metodi di autenticazione, ed è composta da due parti logiche che si concentrano su: (i) lo sviluppo di nuovi attacchi contro i metodi di autenticazione esistenti, (ii) lo sviluppo di nuovi metodi di autenticazione.
Nella prima parte di questa tesi, ci concentriamo sugli attacchi contro i metodi di autenticazione. In particolare, mostriamo l'efficacia di tre attacchi contro la sicurezza dei metodi di autenticazione con password e PIN.
Il primo lavoro mostra come un attaccante possa utilizzare l'audio registrato durante una chiamata VoIP per dedurre i tasti premuti da una vittima. Abbiamo mostrato come questo attacco possa essere usato per dedurre le password con successo. Gli altri due lavori della prima parte consistono in due metodi distinti per rubare i codici segreti dai PIN pad dei bancomat. Per tutti questi attacchi, proponiamo contromisure efficaci mostrando quanto sia importante partecipare attivamente alla ricerca in questo campo per migliorare la sicurezza dei sistemi di autenticazione.
Nella seconda parte di questa tesi, abbiamo esplorato i sistemi di autenticazione sia dal punto di vista dell'autenticazione di utenti che di dispositivi. In particolare, abbiamo studiato un nuovo metodo biometrico basato sul riconoscimento del movimento masticatorio di un utente e un nuovo metodo di autenticazione per garantire la sicurezza dei cyber-physical systems datati. Nel primo lavoro, presentiamo i nostri risultati sperimentali, mostrando come il nostro metodo può garantire la sicurezza dell'utente mantenendo un ambiente user-friendly. Per il secondo lavoro, presentiamo il nostro metodo di autenticazione mostrando come può migliorare la sicurezza delle infrastrutture legacy, mantenendo bassi i costi.Nowadays, authentication systems are widespread in our devices. They protect the security of our systems, guaranteeing that only authorized people have access to reserved services and data. Thanks to this role, authentication systems made their first appearance in the `60s, with the diffusion of the first computers in universities. Over the years, these systems have evolved. If the first authentication systems were based only on passwords, they are considerably advanced today. In particular, with the widespread diffusion of smartphones, authentication systems became commonly used, focusing on user-friendly systems such as biometrics. This evolution generated a market that is growing strongly, and it is expected to increase by 15% again in the next few years, with revenues of hundreds of billions of dollars.
Usability is not the only factor influencing the evolution of authentication systems. Their safety also determines their evolution over time. If an authentication method guarantees the security of a system, it is also true that it is the first to suffer from cyber-attacks.
After the appearance of new authentication technologies on the market, it is frequent to notice the spread of new methods to bypass the security of the novel technology.
Research in these areas becomes fundamental: on one side, to discover new authentication systems that can improve the usability of our devices, and on the other, to anticipate possible vulnerabilities and make these systems more secure.
This thesis investigates the security of authentication methods, and it is composed of two logical parts that focus on: (i) the development of novel attacks against existing authentication methods, (ii) the development of novel authentication methods.
In the first part of this thesis, we focus on attacks against authentication methods. In particular, we show the effectiveness of three attacks against the security of password and PIN authentication methods.
The first work shows how an attacker can use the audio recorded during a VoIP call to infer the keys pressed by a victim. We showed how this attack could be used to infer passwords successfully. The other two works of the first part consist of two distinct methods to steal secret codes from ATM PIN pads. For all these attacks, we propose effective countermeasures showing how important it is to actively participate in research in this field to improve the security of authentication systems.
In the second part of this thesis, we explored authentication systems from the perspective of both users and devices authentication. In particular, we investigated a novel biometrics method based on recognizing the user's chewing movement and a new authentication method to ensure the security of legacy cyber-physical systems. We present our experimental results for the former, showing how our method can guarantee user security by keeping a user-friendly environment. For the latter, we present our authentication method showing how it can improve the security of legacy infrastructures, keeping costs down
Au nanoparticle/DNA rotaxane hybrid nanostructures exhibiting switchable fluorescence properties
No full textThe preparation of a DNA rotaxane consisting of a circular nucleic acid interlocked, through hybridization, on a nucleic acid axle and stoppered by two 10-nm-sized Au nanoparticles (NPs) is described. By the tethering of 5-nm- or 15-nm-sized Au NPs on the ring, the supramolecular structure of the rotaxane is confirmed. Using nucleic acids as "fuels" and "anti-fuels", the cyclic and reversible transition of the rotaxane ring across two states is demonstrated. By the functionalization of the ring with fluorophore-modified nucleic acids in different orientations, the transitions of the rings between the sites are followed by fluorescence quenching or surface-enhanced fluorescence. The experimental results are supported by theoretical modeling. © 2013 American Chemical Society
Orthogonal Dual-Triggered Shape-Memory DNA-Based Hydrogels
No full textDNA-based shape-memory hydrogels revealing switchable shape recovery in the presence of two orthogonal triggers are described. In one system, a shaped DNA/acrylamide hydrogel is stabilized by duplex nucleic acids and pH-responsive cytosine-rich, i-motif, bridges. Separation of the i-motif bridges at pH 7.4 transforms the hydrogel into a quasi-liquid, shapeless state, that includes the duplex bridges as permanent shape-memory elements. Subjecting the quasi-liquid state to pH 5.0 or Ag+ions recovers the hydrogel shape, due to the stabilization of the hydrogel by i-motif or C-Ag+-C bridged i-motif. The cysteamine-induced transformation of the duplex/C-Ag+-C bridged i-motif hydrogel into a quasi-liquid shapeless state results in the recovery of the shaped hydrogel in the presence of H+or Ag+ions as triggers. In a second system, a shaped DNA/acrylamide hydrogel is generated by DNA duplexes and bridging Pb2+or Sr2+ions-stabilized G-quadruplex subunits. Subjecting the shaped hydrogel to the DOTA or KP ligands eliminates the Pb2+or Sr2+ions from the respective hydrogels, leading to shapeless, memory-containing, quasi-liquid states that restore the original shapes with Pb2+or Sr2+ions
Chiroplasmonic DNA-based nanostructures
No full textChiroplasmonic properties of nanoparticles, organized using DNA-based nanostructures, have attracted both theoretical and experimental interest. Theory suggests that the circular dichroism spectra accompanying chiroplasmonic nanoparticle assemblies are controlled by the sizes, shapes, geometries and interparticle distances of the nanoparticles. In this Review, we present different methods to assemble chiroplasmonic nanoparticle or nanorod systems using DNA scaffolds, and we discuss the operations of dynamically reconfigurable chiroplasmonic nanostructures. The chiroplasmonic properties of the different systems are characterized by circular dichroism and further supported by high-resolution transmission electron microscopy or cryo-transmission electron microscopy imaging and theoretical modelling. We also outline the applications of chiroplasmonic assemblies, including their use as DNA-sensing platforms and as functional systems for information processing and storage. Finally, future perspectives in applying chiroplasmonic nanoparticles as waveguides for selective information transfer and their use as ensembles for chiroselective synthesis are discussed. Specifically, we highlight the upscaling of the systems to device-like configurations
Metal nanoparticle-functionalized DNA tweezers: From mechanically programmed nanostructures to switchable fluorescence properties
No full textDNA tweezers are modified with two 10-nm sized Au NPs and one 5-nm sized Au NP. Upon treatment of the tweezers with fuel and antifuel nucleic acid strands, the switchable closure and opening of the tweezers proceed, leading to the control of programmed nanostructures of the tethered NPs. The tweezers are further modified with a single 10-nm sized nanoparticle, and a fluorophore unit (Cy3), positioned at different distinct sites of the tweezers. The reversible and cyclic fluorescence quenching or fluorescence enhancement phenomena, upon the dynamic opening/closure of the different tweezers, are demonstrated. © 2013 American Chemical Society
Rehabilitation needs after bariatric surgery
No full textBackground. Bariatric surgery has grown from an obscure experimental procedure to one of the most popular operations in the world. Such accelerated progress left many gaps, notably concerning subsequent rehabilitation needs of this population. Aim. In the present study, a brief description of both the patients and the interventions is provided, along with potentially disabling features especially concerning the locomotor system, which has received comparatively little attention. Design. Based on reported protocols and actual experience, major issues are addressed. Setting. Bariatric patients are initially managed in the hospital, however long-term and even lifetime needs may be recognized, requiring major lifestyle and physical activity changes. These have to be focused in all settings, inside and outside the healthcare institutions. Population. Initially only adults were considered bariatric candidates, however currently also adolescents and the elderly are admitted in many centers. Results. Bariatric weight loss is certainly successful for remission or prevention of metabolic, cardiovascular and cancer comorbidities. Yet benefits for bones, joints and muscles, along with general physical performance are still incompletely established. This should be no reason for denying continued care to such individuals, within the context of well-designed protocols, as available evidence points toward favorable rehabilitation in the realms of physical, social and workplace activities. Conclusion. The importance of a physiatric curriculum in medical schools has been emphasized. Even more crucial is the presence of such a specialists in obesity and bariatric teams, a requirement recognized in a few countries but not in others. Clinical Rehabilitation Impact. The relevance of obesity as a disabling condition is reviewed, along with the positive changes induced by surgical weight loss. Although obesity alleviation is a legitimate end-point it is not a sufficient one. The shortcomings of such result from the point of view of physical normalization are outlined, and recommendations are suggested
A three-station DNA catenane rotary motor with controlled directionality
No full textThe assembly of DNA machines represents a central effort in DNA nanotechnology. We report on the first DNA rotor system composed of a two-ring catenane. The DNA rotor ring rotates in dictated directions along a wheel, and it occupies three distinct sites. Hg(2+)/cysteine or pH (H(+)/OH(-)) act as fuels or antifuels in positioning the rotor ring. Analysis of the kinetics reveals directional clockwise or anticlockwise population of the target-sites (>85%), and the rotor's direction is controlled by the shortest path on the wheel
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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