Microarchitected Stretching‐Dominated Mechanical Metamaterials with Minimal Surface Topologies

Historically, the creation of lightweight, yet mechanically robust, materials have been the most sought‐after engineering pursuit. For that purpose, research efforts are dedicated to finding pathways to emulate and mimic the resilience offered by natural biological systems (i.e., bone and wood). These natural systems evolved over time to provide the most attainable structural efficiency through their architectural characteristics that can span over multiple length scales. Nature‐inspired man‐made cellular metamaterials have effective properties that depend largely on their topology rather than composition and are hence remarkable candidates for a wide range of application. Despite their geometrical complexity, the fabrication of such metamaterials is made possible by the emergence of advanced fabrication techniques that permit the fabrication of complex architectures down to the nanometer scale. In this work, we report the fabrication and mechanical testing of nature‐inspired, mathematically created, micro‐architected, cellular metamaterials with topologies based on triply periodic minimal surfaces (TPMS) with cubic symmetries fabricated through direct laser writing two‐photon lithography. These TPMS‐based microlattices are sheet/shell‐ and strut‐based metamaterials with high geometrical complexity. Interestingly, results show that TPMS sheet‐based microlattices follow a stretching‐dominated mode of deformation, and further illustrate their mechanical superiority over the traditional and well‐known strut‐based microlattices and microlattice composites. The TPMS sheet‐based polymeric microlattices exhibited mechanical properties superior to other micrloattices comprising metal‐ and ceramic‐coated polymeric substrates and, interestingly, are less affected by the change in density, which opens the door for fabricating ultralightweight materials without much sacrificing mechanical properties.

     

Flood monitoring using microwave passive remote sensing (AMSR-E) in part of the Brahmaputra basin,India

In this work, Advanced Microwave Scanning Radiometer Earth Observing System (AMSR-E) signatures were analysed over some critical sites in Lakhimpur District in Brahmaputra basin, India, characterized by a high frequency of flooding events. The site is mostly covered by paddy fields. Results obtained were compared with water level measurements in three stations close to the main channel of the river. Information about surface temperature, which allowed us to estimate the emissivity, was also available. Investigations were carried out at the C, X, and K_a bands of the AMSR-E channel. A multi-frequency analysis indicated that the X band would represent a good compromise between resolution and sensitivity requirements, while at the C band the resolution was too coarse and at the K_a band the signatures were affected by raindrops. Samples collected during rain were eliminated using techniques based on the 89.0 GHz channel. However, even after this correction, the K_a band showed poor sensitivity due to higher attenuation by vegetation. The correlations between different pairs of variables, viz. polarization index (PI), water level (WL), and fractional water surface area (F _WS), were also investigated. At the X band, the water level was better correlated with the PI than with emissivity and other parameters defined in the literature. The correlation was good in cases of slow variation in WL. In cases of sudden variation in the river, the PI followed the variations with some time delay related to the propagation of water within the covered AMSR-E pixel.     

p53-dependent ceramide response to genotoxic stress

Both p53 and ceramide have been implicated in the regulation of growth suppression. p53 has been proposed as the "guardian of the genome" and ceramide has been suggested as a "tumor suppressor lipid. " Both molecules appear to regulate cell cycle arrest, senescence, and apoptosis. In this study, we investigated the relationship between p53 and ceramide. We found that treatment of Molt-4 cells with low concentrations of actinomycin D or gamma-irradiation, which activate p53-dependent apoptosis, induces apoptosis only in cells expressing normal levels of p53. In these cells, p53 activation was followed by a dose- and time-dependent increase in endogenous ceramide levels which was not seen in cells lacking functional p53 and treated similarly. Similar results were seen in irradiated L929 cells whereby the p53-deficient clone was significantly more resistant to irradiation and exhibited no ceramide response. However, in p53-independent systems, such as growth suppression induced by TNF-alpha or serum deprivation, ceramide accumulated irrespective of the upregulation of p53, indicating that p53 regulates ceramide accumulation in only a subset of growth-suppressive pathways. Finally, ceramide did not increase p53 levels when used at growth-suppressive concentrations. Also, when cells lacking functional p53, either due to mutation or the expression of the E6 protein of human papilloma virus, were treated with exogenous ceramide, there was equal growth suppression, cell cycle arrest, and apoptosis as compared with cells expressing normal p53. These results indicate that p53 is unlikely to function "downstream" of ceramide. Instead, they suggest that, in situations where p53 performs a critical regulatory role, such as the response to genotoxic stress, it functions "upstream" of ceramide. These studies begin to define a relationship between these two pathways of growth inhibition.     

A hybrid electronic-density-functional/molecular-dynamics simulation scheme for multiscale simulation of materials on parallel computers: applications to silicon and alumina

In hybrid electronic-density-functional/molecular-dynamics schemes, a total system is partitioned in real space into the quantum-mechanical (QM) region treated by the electronic-density-functional theory and the molecular dynamics (MD) region in which atoms are interacting through the empirical inter-atomic potential. In the former hybrid scheme [Ogata et al. Comput. Phys. Commun. 149 (2002) 30], appropriate selection of QM atoms for seamless coupling between the QM and MD regions is limited in Si systems, and applications of the scheme to other materials are difficult. Novel hybrid scheme that is free from the limitation and applicable to both Si and alumina systems, is presented.     

Speed control of automotive diesel engines

This paper deals with Diesel engine control. More precisely, a model-based approach is considered to stabilise engine speed around a defined value. The model taken into account is nonlinear and contains explicitly the expression of fuel conversion efficiency. In general in the literature, this experimentally obtained quantity is modelled with either a polynomial or an exponential form (see for instance Younes, R. (1993). Elaboration d’un modèle de connaissance du moteur diesel avec turbocompresseur à géométrie variable en vue de l’optimisation de ses émissions. Ecole Centrale de Lyon; Omran, R., Younes, R., Champoussin, J., & Outbib, R. (2011). New indicated mean effective pressure (IMEP) model for predicting crankshaft movement. Energy Conversion and Management, 52, 3376–3382). This paper focuses on engine speed feedback stabilisation when fuel conversion efficiency is modelled with an exponential form, which is more suitable for automative applications. Simulation results are proposed to highlight the closed-loop control performances.     

The pseudo-self-similar traffic model: application and validation

Since the early 1990s, a variety of studies have shown that network traffic, both for local- and wide-area networks, has self-similar properties. This led to new approaches in network traffic modelling because most traditional traffic approaches result in the underestimation of performance measures of interest. Instead of developing completely new traffic models, a number of researchers have proposed to adapt traditional traffic modelling approaches to incorporate aspects of self-similarity. The motivation for doing so is the hope to be able to reuse techniques and tools that have been developed in the past and with which experience has been gained. One such approach is the so-called pseudo-self-similar traffic (PSST) model. This model is appealing, as it is easy to understand and easily embedded in Markovian performance evaluation studies.

In applying this model in a number of cases, we have perceived various problems which we initially thought were particular to these specific cases. However, we recently have been able to show that these problems are fundamental to the PSST model.

In this paper we review the PSST model, validate it experimentally and discuss its shortcomings. As far as we know, this is the first paper that discusses these shortcomings formally. We also report on ongoing work to overcome some of these problems.     

Modelling and solving the intrusion detection problem in computer networks

We introduce a novel anomaly intrusion detection method based on a Within-Class Dissimilarity, WCD. This approach functions by using an appropriate metric WCD to measure the distance between an unknown user and a known user defined respectively by their profile vectors. First of all, each user performs a set of commands (events) on a given system (Unix for example). The events vector of a given user profile is a binary vector, such that an element of this vector is equal to “1” if an event happens, and to “0” otherwise. In addition to this, each user's class k has a typical profile defined by the vector P_k, in order to test if a new user i defined by its profile vector P_i belongs to the same class k or not. The P_k vector is a weighted events vector E_k, such that each weight represents the number of occurrences of an event e_k. If the “distance” d_ki (measured by a dissimilarity parameter) between an unknown profile P_i and a known profile P_k is reasonable according to a given threshold and to some constraints, then there is no intrusion. Else, the user i is suspicious. A simple example illustrates the WCD procedure. A survey of intrusion detection methods is presented.Our proposed method based on clustering users and using simple statistical formulas is very easy for implementation.     

Multiscale-Engineered Muscle Constructs: PEG Hydrogel Micro-Patterning on an Electrospun PCL Mat Functionalized with Gold Nanoparticles

The development of new, viable, and functional engineered tissue is a complex and challenging task. Skeletal muscle constructs have specific requirements as cells are sensitive to the stiffness, geometry of the materials, and biological micro-environment. The aim of this study was thus to design and characterize a multi-scale scaffold and to evaluate it regarding the differentiation process of C2C12 skeletal myoblasts. The significance of the work lies in the microfabrication of lines of polyethylene glycol, on poly(ε-caprolactone) nanofiber sheets obtained using the electrospinning process, coated or not with gold nanoparticles to act as a potential substrate for electrical stimulation. The differentiation of C2C12 cells was studied over a period of seven days and quantified through both expression of specific genes, and analysis of the myotubes’ alignment and length using confocal microscopy. We demonstrated that our multiscale bio-construct presented tunable mechanical properties and supported the different stages skeletal muscle, as well as improving the parallel orientation of the myotubes with a variation of less than 15°. These scaffolds showed the ability of sustained myogenic differentiation by enhancing the organization of reconstructed skeletal muscle. Moreover, they may be suitable for applications in mechanical and electrical stimulation to mimic the muscle’s physiological functions.     

Thin Layer Chromatography for the Detection of Unexpected Reactions in Organometallic Combinatorial Catalysis

Thin layer chromatography (TLC) represents a fast and inexpensive alternative to NMR spectroscopy or analytical methods based on chromatography for the detection of unexpected products in organometallic combinatorial catalysis. This screening test led to the detection of the catalytic system [Ir(COD)Cl]₂/PPh₃ for isomerisation of diolefinic substrates instead the expected ring closing metathesis (RCM) reaction.     

Heterogeneous nanofluids: natural convection heat transfer enhancement

Convective heat transfer using different nanofluid types is investigated. The domain is differentially heated and nanofluids are treated as heterogeneous mixtures with weak solutal diffusivity and possible Soret separation. Owing to the pronounced Soret effect of these materials in combination with a considerable solutal expansion, the resulting solutal buoyancy forces could be significant and interact with the initial thermal convection. A modified formulation taking into account the thermal conductivity, viscosity versus nanofluids type and concentration and the spatial heterogeneous concentration induced by the Soret effect is presented. The obtained results, by solving numerically the full governing equations, are found to be in good agreement with the developed solution based on the scale analysis approach. The resulting convective flows are found to be dependent on the local particle concentration φ and the corresponding solutal to thermal buoyancy ratio N. The induced nanofluid heterogeneity showed a significant heat transfer modification. The heat transfer in natural convection increases with nanoparticle concentration but remains less than the enhancement previously underlined in forced convection case.