Debonding of cellular structures with fibre-reinforced cell walls under shear deformation

Many natural structures are cellular solids at millimetre scale and fibre-reinforced composites at micrometre scale. For these structures, mechanical properties are associated with cell strength, and phenomena such as cell separation through debonding of the middle lamella in cell walls are key in explaining some important characteristics or behaviour. To explore such phenomena, we model cellular structures with non-linear hyperelastic cell walls under large shear deformations, and incorporate cell wall material anisotropy and unilateral contact between neighbouring cells in our models. Analytically, we show that, for two cuboid walls in unilateral contact and subject to generalised shear, gaps can appear at the interface between the deforming walls. Numerically, when finite element models of periodic structures with hexagonal cells are sheared, significant cell separation is captured diagonally across the structure. Our analysis further reveals that separation is less likely between cells with high internal cell pressure (e.g. in fresh and growing fruit and vegetables) than between cells where the internal pressure is low (e.g. in cooked or ageing plants).     

Nanostructured quaternary Ni1-xCuxFe2-yCeyO4 complex system: Cerium content and copper substitution dependence of cation distribution and magnetic-electric properties in spinel ferrites

Quaternary Ni_1-xCu_xFe_2-yCe_yO₄ complex nano-ferrites system with different cerium content ratio and copper substitution degree were synthesized via co-precipitation wet chemical technique. The newly obtained nanoparticles, with general formula Ni_1-xCu_xFe_2-yCe_yO₄ (where x = 0.0, 0.3, 0.6 and y = 0.00, 0.03, 0.05, 0.08 and 0.10) were heated up to 600 °C to stabilize the specific crystalline spinel structure. The limit of cerium content was quantitively determined to be around 0.08 and up to 0.10. Furthermore, the powders were pelletized in a 13 mm wide pellets and thermally treated at 950 °C. The thermal treatment affected even more the phases segregation process, as CeO₂ was identified in the sample with lowest degree of cerium insertion – 0.03. Also, a difference in color and size of pelletized samples was noticed after the 950 °C thermal treatment. The Rietveld refinement, crystal structure confirmation, morphology magnetic and electrical properties of samples have been deeply studied. The cation distribution carried out from Rietveld refinement confirms the occupancy of (Fe³⁺) on tetrahedral sites and [Ni²⁺], [Cu²⁺], [Fe³⁺] and [Ce²⁺] on octahedral sites in the crystal lattice. Preliminary information regarding the cation distribution in spinel structures were suggested by FTIR spectral results, precisely in the 650-520 cm^?1 region, as a consequence of peak shape and lack of shiftiness of M^Td – O bond. Spherical-shaped quaternary nano-ferrites of 17–28 nm were determined from FE-SEM analysis and the samples composition was confirmed by EDX analysis. Hysteresis loops shows modifications in coercivity, magnetization and magnetic remanence with Ni²⁺ and Cu²⁺ ions doping in Ni_1-xCu_xFe_2-yCe_yO₄ complex systems with typical ferrimagnetic behavior. Dielectric measurements were employed in order to determine the electrical permittivity, dielectric losses and conductivity values in a 10 Hz – 1 MHz frequency range.     

Preparation and characterisation of Fe/Fe3O4 fibres based soft magnetic composites

Soft magnetic composites (FSMCs) have been prepared by using Fe fibres coated with a layer of Fe₃O₄, this layer playing the role of insulating material. The coating was made via blackening method by simply immersing the fibres in the blackening bath for 5, 10 and 15 min. The formation of the Fe₃O₄ coating on the surface of the fibres was confirmed by X-ray diffraction. The SEM investigation, used to evaluate the thickness of the coatings, has proved that increasing the coating duration leads to the increase of the coating thickness and complete coverage of the surface of the fibres. Differential scanning calorimetry and thermomagnetic measurements were used to investigate the thermal stability of the composite fibres. The fibres coated with Fe₃O₄ were compacted at a compaction pressure of 700 MPa to obtain toroidal magnetic cores. The obtained cores were characterised in DC and AC magnetisation regime. The analysis of the quasi-static hysteresis loops evidenced that increasing the thickness of the Fe₃O₄ leads to a slight deterioration of the compact's magnetic properties. However, as the thickness of the Fe₃O₄ layer increases, the development of eddy currents at a larger scale is hindered as proved by the AC magnetic investigations. A model for analytic separation of the core losses is proposed. By applying this model to the prepared samples, we are now able to discriminate between the occurring losses and adjust the preparation process of new samples to the targeted characteristics.     

Calcium carbonate and wood reinforced hybrid PVC composites

In this article, poly(vinyl chloride) (PVC) sandwich‐structured hybrid composites with amorphous calcium carbonate and wood‐filled cores were obtained by compression molding. It has been determined that wood addition up to a weight ratio of 33% reported to the total filler amount is beneficial in improving both the inter‐filler and filler‐matrix interfacial adhesion, which alongside with the promoting of the amorphous PVC matrix crystallization is responsible for an increase up to 34% in the flexural strength of the composites, compared to unfilled PVC. The hybrid filled composites present up to 35% lower friction coefficients and up to 20% higher Brinell hardness values than the composites filled with calcium carbonate alone. Subsequently, wood addition determines an increase in the oxidation onset temperature for PVC and an increase with up to 20% in the sound and thermal‐insulative properties of the composites, compared to unfilled PVC. The dominating dispersive part of the composites surface energy aids in improving the mass and dimensional stability of the assembly to both water and dilute hydrochloric acid aqueous solutions. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46317.     

Synthesis of polysulfone block copolymers containing polydimethylsiloxane

The synthesis of polysulfone-polydimethylsiloxane (PSU-PDMS)linear block copolymers has been carried out in solution by condensation of chloro-terminated bisphenol A, diphenylsulfone and , -di (hydrogensilyl)-polydimethylsiloxane with Si–C bond. ¹H-NMR spectra of the block copolymers allow the estimation of siloxane and polysulfone ratio. The molecular weight of the polysulfone and polysiloxane oligomers and the block copolymers was determined by GPC. Thermogravimetric analysis indicates a thermal stability of block copolymers up to 400°C and allows estimation of the process activation energy. Microphase separation of the block copolymers was observed by differential scanning calorimetry (DSC).     

Quantum particles on graphenic systems. Part 1. roadmap for semiconductor based graphenes

Advances in green nano-technologies is the main field under which the present paper series is firstly envisaged; therefore, advanced, research-progressive nano-science is aimed to shorten the distance from fundamental concepts to applications, devices and their implementations. It however would gather both physics and chemistry fundamental and applicative fields in dealing with solar/black body radiation as well as with new materials based on inorganic-organic hybrids, composites and electron quantum features (excitons, bondons, diffusion, electrical circuits, semiconductors, quantum dots, etc.). Such research is therefore equally highly necessary for both communities (physical engineering and chemical engineering) enlightening the dedicated international forums on quantum-dots based solar cells, as well as for giving further impetus to this new field of photovoltaics by gathering active international scientists in solar energy. The present paper offers a review on the progresses regarding the application of defective graphene and other defect-doped carbon nanostructures in the construction of solar cells devices towards introducing the semiconductor based graphenes. Competitiveness and eco-ecological aspects of such projects are also considered in a resumed scientific and innovative research.     

Optimizing at the end-points the Akima's interpolation method of smooth curve fitting

In this paper we propose an optimized version, at the end-points, of the Akima's interpolation method for experimental data fitting. Comparing with the Akima's procedure, the error estimate, in terms of the modulus of continuity, is improved. Similarly, we optimize at the end points the Catmull–Rom's cubic spline. The properties of the obtained splines are illustrated on a numerical experiment.     

Cholesteric and photoreactive polyesters

Several classes of cholesteric and photoreactive homo- and copolyesters were synthesized and characterized. Most of these polyesters were prepared in such a way that a chiral spacer (e.g. isosorbide) was polycondensed with a photoreactive dicarboxylic acid, such as 4-carboxycinnamic acid, benzene- 1,4-bisacrylic acid, 4-(4′-carboxyphthalimido)cinnamic acid. In several cases other dicarboxylic acids, such as naphthalene-2,6-dicarboxylic acid or 4-aminobenzoic acid trimellitimide were cocondensed to favor the formation of a Grandjean texture. When ‘sugar diols’ such as isosorbide or isomannide were used as chiral building blocks, suitable diphenols were required as comonomers to stabilize the LC phase. Most polyesters were capable of forming a selectively reflecting Grandjean texture, which can be fixed by crosslinking using UV light. An alternative synthetic strategy based on chiral, substituted terephthalic acids is discussed.     

Anomaly detection in large-scale data stream networks

This paper addresses the anomaly detection problem in large-scale data mining applications using residual subspace analysis. We are specifically concerned with situations where the full data cannot be practically obtained due to physical limitations such as low bandwidth, limited memory, storage, or computing power. Motivated by the recent compressed sensing (CS) theory, we suggest a framework wherein random projection can be used to obtained compressed data, addressing the scalability challenge. Our theoretical contribution shows that the spectral property of the CS data is approximately preserved under a such a projection and thus the performance of spectral-based methods for anomaly detection is almost equivalent to the case in which the raw data is completely available. Our second contribution is the construction of the framework to use this result and detect anomalies in the compressed data directly, thus circumventing the problems of data acquisition in large sensor networks. We have conducted extensive experiments to detect anomalies in network and surveillance applications on large datasets, including the benchmark PETS 2007 and 83 GB of real footage from three public train stations. Our results show that our proposed method is scalable, and importantly, its performance is comparable to conventional methods for anomaly detection when the complete data is available.