MILo-DB: a personal,secure and portable database machine

Mass-storage secure portable tokens are emerging and provide a real breakthrough in the management of sensitive data. They can embed personal data and/or metadata referencing documents stored encrypted in the Cloud and can manage them under holder’s control. Mass on-board storage requires efficient embedded database techniques. These techniques are however very challenging to design due to a combination of conflicting NAND Flash constraints and scarce RAM constraint, disqualifying known state of the art solutions. To tackle this challenge, we proposes a log-only based storage organization and an appropriate indexing scheme, which (1) produce only sequential writes compatible with the Flash constraints and (2) consume a tiny amount of RAM, independent of the database size. We show the effectiveness of this approach through a comprehensive performance study.     

Data confidentiality: to which extent cryptography and secured hardware can help

Data confidentiality has become a major concern for individuals as well as for companies and administrations. In a classical client-server setting, the access control management is performed on the server, relying on the assumption that the server is a trusted party. However, this assumption no longer holds given the increasing vulnerability of database servers facing a growing number of external and even internal attacks. This paper studies different alternatives exploiting cryptographic techniques and/or tamper-resistant hardware to fight against these attacks. The pros and cons of each alternative are analyzed in terms of security, access control granularity and preserved database features (performance, query processing, volume of data). Finally, this paper sketches a hybrid approach mixing data encryption, integrity control and secured hardware that could pave the way for future highly securedDbmsS.     

Langues de présentation des consignes et performances motrices chez des bilingues fran?ais/créole aux Antilles fran?aises.

In this study, I examine whether the language used for instructions influences motor performance among bilingual children in a learning situation. Eighty bilingual French/Creole children (age means 10.4) were distributed into two experimental groups to learn how to perform a motor task. One group received instructions in French and the other one in Creole. The data suggest that the language of presentation affects the execution of a motor task. Both groups had the same performance level at the beginning of the experiment. However, the group taught in Creole obtained better performances than the group taught in French at the end of the learning situation. The results are discussed in terms of their implications to physical education and motor rehabilitation of bilinguals. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Stress relaxation of austenitic stainless steels at 290 °c

Stress relaxation tests were performed on three austenitic stainless steels at 290 °C. The tests were conducted in a strain controlled servo-hydraulic test machine near yield point strain levels. This kind of stress relaxation test simulates the strain history of a bolted joint. Long-term relaxation behavior is conservatively estimated by using high temperature relaxation data to extrapolate the 290 °C test data. This extrapolation allows the designer to conservatively estimate the pretension remaining in a bolt throughout its life.     

The Contact of Elastic Regular Wavy Surfaces Revisited

We revisit the classic problem of an elastic solid with a two-dimensional wavy surface squeezed against an elastic flat half-space from infinitesimal to full contact. Through extensive numerical calculations and analytic derivations, we discover previously overlooked transition regimes. These are seen in particular in the evolution with applied load of the contact area and perimeter, the mean pressure and the probability density of contact pressure. These transitions are correlated with the contact area shape, which is affected by long range elastic interactions. Our analysis has implications for general random rough surfaces, as similar local transitions occur continuously at detached areas or coalescing contact zones. We show that the probability density of null contact pressures is nonzero at full contact. This might suggest revisiting the conditions necessary for applying Persson’s model at partial contacts and guide the comparisons with numerical simulations. We also address the evaluation of the contact perimeter for discrete geometries and the applicability of Westergaard’s solution for three-dimensional geometries.     

Contact mechanics at the nanoscale,a 3D multiscale approach

We present a multiscale coupling method to address contact problems. The components of the model are a molecular dynamics engine, a finite element program and a coupling scheme. We validate the approach, first on Hertzian contact and then with a rough surface contacting a rigid body plane. Various measures are provided to highlight limitations and new opportunities in conducting large‐scale simulations of contact brought by the proposed multiscale approach. Copyright © 2009 John Wiley & Sons, Ltd.     

DiSC: Benchmarking Secure Chip DBMS

Secure chips, e.g. present in smart cards, USB dongles, i-buttons, are now ubiquitous in applications with strong security requirements. And they require embedded data management techniques. However, secure chips have severe hardware constraints which make traditional database techniques irrelevant. The main problem faced by secure chip DBMS designers is to be able to assess various design choices and trade-offs for different applications. Our solution is to use a benchmark for secure chip DBMS in order to (1) compare different database techniques, (2) predict the limits of on-chip applications, and (3) provide co-design hints. In this paper, we propose DiSC (Data management in Secure Chip), a benchmark which matches these three objectives. This work benefits from our long experience in developing and tuning data management techniques for the smart card. To validate DiSC, we compare the behavior of candidate data management techniques thanks to a cycle-accurate smart card simulator. Finally, we show the applicability of DiSC to future designs involving new hardware platforms and new database techniques.     

Dry Sliding Contact Between Rough Surfaces at the Atomistic Scale

Although, a lot is known about the factors contributing to friction, a complete physical understanding of the origins of friction is still lacking. At the macroscale several laws have long since described the relation between load (Amontons, Coulomb), apparent and real area of contact (Bowden and Tabor), and frictional forces. But it is not yet completely understood if these laws of friction extend all the way down to the atomistic level. Some current research suggests that a linear dependence of friction on the real contact area is observed at the atomistic level, but only for specific cases (indentors and rigid substrates). Because continuum models are not applicable at the atomic scale, other modeling techniques (such as molecular dynamics simulations) are necessary to elucidate the physics of friction at the small scale. We use molecular dynamics simulations to model the friction of two rough deformable surfaces, while changing the surface roughness, the sliding speed, and the applied normal load. We find that friction increases with roughness. Also all sliding cases show considerable surface flattening, reducing the friction close to zero after repetitive sliding. This questions the current view of (static) roughness at the atomistic scale, and possibly indicates that the macroscopic laws of friction break down several orders of magnitude before reaching the atomic scale.     

The effect of loading on surface roughness at the atomistic level

One of the key points to better understand the origins of friction is to know how two surfaces in contact adhere to one another. In this paper we present molecular dynamics (MD) simulations of two aluminium bodies in contact, exposed to a range of normal loads. The contact surfaces of both aluminium bodies have a self-affine fractal roughness, but the exact roughness varies from simulation to simulation. Both bodies are allowed to have an adhesive interaction and are fully deformable. Tracking important contact parameters (such as contact area, number of contact clusters, and contact pressure) during a simulation is challenging. We propose an algorithm (embedded within a parallel MD code) which is capable of accessing these contact statistics. As expected, our results show that contact area is increasing in proportion with applied load, and that a higher roughness reduces contact area. Contact pressure distributions are compared to theoretical models, and we show that they are shifted into the tensile regime due to the inclusion of adhesion in our model.     

A concurrent atomistic and continuum coupling method with applications to thermo‐mechanical problems

We present a novel method to couple molecular dynamics with finite elements at finite temperatures using spatial filters. The mismatch in the dispersion relations between continuum and atomistic models leads, at finite temperature, to unwanted mesh vibrations, which are illustrated using a standard least square coupling formulation. We propose the use of spatial filters with the least square minimization to selectively damp the unwanted mesh vibrations. Then, we extend the idea of selective damping of wavelength modes to couple atomistic and continuum models at finite temperatures. The restitution force from the generalized Langevin equation is modified to perform a two‐way thermal coupling between the two models. Three different numerical examples are shown to validate the proposed coupling formulation in two‐dimensional space. Finally, the method is applied to a high‐speed impact simulation. Copyright © 2013 John Wiley & Sons, Ltd.