Elasticity Solution for Bending Response of Functionally Graded Sandwich Plates Under Thermomechanical Loading

The thermomechanical bending response of functionally graded sandwich plates has been investigated by the use of the new four variable refined plate theories. The plate properties are assumed to be varied through the thickness following a simple power law distribution in terms of volume fraction of material constituents. The theory presented is variationally consistent, does not require shear correction factor, and gives rise to transverse shear stress variation such that the transverse shear stresses vary parabolically across the thickness satisfying shear stress free surface conditions. The no symmetric sandwich plate faces are made of isotropic, two-constituent (ceramic–metal) material distribution through the thickness. The core layer is still homogeneous and made of an isotropic metal material. Several kinds of no symmetric sandwich plates are presented. The validity of the present theory is investigated by comparing some of the present results with those of the classical, the first-order, and the other higher-order theories. Field equations for functionally graded sandwich plates whose deformations are governed by either the shear deformation theories or the classical theory are derived. Displacement and stress functions of the plate for different values of the power-law exponent and thickness to-side ratios are presented. Numerical results for deflections and stresses of functionally graded metal–ceramic plates are investigated.     

Vision-based navigation of unmanned aerial vehicles

This paper presents a vision-based navigation strategy for a vertical take-off and landing (VTOL) unmanned aerial vehicle (UAV) using a single embedded camera observing natural landmarks. In the proposed approach, images of the environment are first sampled, stored and organized as a set of ordered key images (visual path) which provides a visual memory of the environment. The robot navigation task is then defined as a concatenation of visual path subsets (called visual route) linking the current observed image and a target image belonging to the visual memory. The UAV is controlled to reach each image of the visual route using a vision-based control law adapted to its dynamic model and without explicitly planning any trajectory. This framework is largely substantiated by experiments with an X4-flyer equipped with a fisheye camera.     

Recursive versus sequential multiple error measures reduction: a curve simplification approach to ECG data compression

Previous time domain compression methods have been tackled by sequential one point at a time sub-optimal selection strategies running in approximately O(N) or all points at a time optimal strategies running in approximately O(N3) temporal complexities. Yet basically, the selected dominant points (DPs) are locally only significant in these methods, which may lead to inaccurate reconstruction or even loss of clinical data. Alternatively, the recursive one point at a time selection strategy, through different variants of the Douglas-Peucker line simplification algorithm, computes globally significant DPs for an approximately O(N.log2(N)) temporal complexity. We illustrate that the recursive strategy performs numerically almost two times better than the sequential one. The piecewise linear approximation of the input ECG is formally expressed as a curve simplification problem, through reduction of the Hausdorff error measure. We also illustrate that reduction of two error measures performs better than reduction of one error measure. An additional compression option is proposed in the case of the recursive strategy through simplification of the sorted distances associated to the selected set of points. The outcome is a compression algorithm that yields compression ratios ranging from 8:1 to 22:1 for a perceptually good reconstruction quality and near linear execution time. The tests have been conducted on the MIT-BIH public ECG database. Results show that the proposed recursive algorithm is an excellent compromise on compression ratio - computational time - reconstruction quality.     

Recycling process of defective aged uranium dioxide pellets

The work was devoted to study the recycling process of the unirradiated defective uranium dioxide pellets stored during 10 years. The effect of the temperature on the kinetics of the oxidation and reduction of dioxide uranium was investigated, respectively, in the range 250 °C–600°C and 300 °C–800 °C. For the oxidation process, the kinetics is low below 350 °C, and is fast at higher temperatures. The same phenomenon is observed for the reduction process, where the rate accelerates at above 500 °C and the reduction completed in shorter time. Using a laser particle size analyzer and a Brunauer, Emmett, Teller (BET) analyzer, it was determined that the oxidation at 400 °C gives a triuranium octoxide powder with an adequate particle size (33 μm) and a specific surface area of 0.9 m²/g in reasonable time (210 min). Reducing the triuranium octoxide to uranium dioxide powder at 600 °C in pure hydrogen was completely achieved after only 16 minutes, without affecting its characteristics. To ameliorate the specific surface area, several oxidation–reduction cycles were performed on the obtained uranium dioxide powder. It is found that after five cycles, the specific surface area of uranium dioxide was improved to more than 2.5 m²/g, minimum value required to the powder sinterability.     

Multifunctional “Hydrogel Skins” on Diverse Polymers with Arbitrary Shapes

Slippery and hydrophilic surfaces find critical applications in areas as diverse as biomedical devices, microfluidics, antifouling, and underwater robots. Existing methods to achieve such surfaces rely mostly on grafting hydrophilic polymer brushes or coating hydrogel layers, but these methods suffer from several limitations. Grafted polymer brushes are prone to damage and do not provide sufficient mechanical compliance due to their nanometer‐scale thickness. Hydrogel coatings are applicable only for relatively simple geometries, precluding their use for the surfaces with complex geometries and features. Here, a new method is proposed to interpenetrate hydrophilic polymers into the surface of diverse polymers with arbitrary shapes to form naturally integrated “hydrogel skins.” The hydrogel skins exhibit tissue‐like softness (Young's modulus ≈ 30 kPa), have uniform and tunable thickness in the range of 5–25 µm, and can withstand prolonged shearing forces with no measurable damage. The hydrogel skins also provide superior low‐friction, antifouling, and ionically conductive surfaces to the polymer substrates without compromising their original mechanical properties and geometry. Applications of the hydrogel skins on inner and outer surfaces of various practical polymer devices including medical tubing, Foley catheters, cardiac pacemaker leads, and soft robots on massive scales are further demonstrated.     

Design and deformation behavior of high strength Fe–Mn–Al–Cr–C duplex steel

The influence of cold rolling reduction on microstructures and mechanical properties at room temperature of the duplex Fe–28Mn–7Al–5Cr–0.3C steel was investigated. In the Fe–28Mn–7Al alloy system, the duplex microstructure was obtained by lowering the carbon content to about 0.3 wt.%. The steel was austenito-ferritic with a low to moderate stacking fault energy. Two thermomechanical cycles were performed, which included cold rolling/annealing at 1100 °C, and cold rolling/annealing at 1100 °C/cold rolling/annealing at 1000 °C.The effects produced by cold rolling on the duplex steel were grain refinement and different strain-induced marks within the ferrite and austenite phases. They were easily observed within the austenite phase at a relatively smaller reduction than within the ferrite phase. Mechanical twinning plays a dominant role within the austenite phase during deformation at room temperature, resulting in extreme mechanical properties. No edge or longitudinal cracks were observed during cold rolling of the duplex steel.     

Mechanical and Metallurgical Characterization of HSLA X70Welded Pipeline Steel Subjected to Successive Repairs

The aim of this work is to study the influence of successive weld repairs on the microstructure and the mechanical behavior of the heat-affected zone(HAZ) of an HSLA X70 steel. Detailed microstructural examination combined to grain size measurement showed that beyond the second weld repair, the microstructure of the HAZ undergoes significant change in the grain morphology and grain growth. The results of the X-ray diffraction analyzed using MAUD software indicated an increase in the crystallite size and a decrease in the dislocation density according to the number of weld repair operations. Consequently, a loss of mechanical properties, namely the yield strength and the toughness with the number of weld repairs, was recorded. Beyond the second weld repair operation, the properties of the welded joint do not fulfill the standards applied in piping industry.     

Nonlinear supersonic flutter of truncated conical shells

A numerical model was developed to investigate the flutter instability of truncated conical shells subjected to supersonic flows. The exact solution of Sanders’ best firstorder approximation was used to develop the finite elements model of the shell. Nonlinear kinematics of Donnell’s, Sanders’ and Nemeth’s theories, in conjunction with the generalized coordinates method, were used to formulate the nonlinear strain energy of the shell. A pressure field was formulated using the piston theory with the correction term for the curvature. Lagrangian equations of motion based on Hamilton’s principle were obtained. A variation of the harmonic balance method was used for developing the amplitude equations of the shell, and a numerical method was used for solving these equations. Results of linear and nonlinear flutter of truncated conical shells were validated against the existing data in the literature. It was observed that geometrical nonlinearities have a softening effect on the stability of the shell in supersonic flows.     

Potential Role of Selenium in the Treatment of Cancer and Viral Infections

Selenium has been extensively evaluated clinically as a chemopreventive agent with variable results depending on the type and dose of selenium used. Selenium species are now being therapeutically evaluated as modulators of drug responses rather than as directly cytotoxic agents. In addition, recent data suggest an association between selenium base-line levels in blood and survival of patients with COVID-19. The major focus of this mini review was to summarize: the pathways of selenium metabolism; the results of selenium-based chemopreventive clinical trials; the potential for using selenium metabolites as therapeutic modulators of drug responses in cancer (clear-cell renal-cell carcinoma (ccRCC) in particular); and selenium usage alone or in combination with vaccines in the treatment of patients with COVID-19. Critical therapeutic targets and the potential role of different selenium species, doses, and schedules are discussed.     

Generation of Stable Isopentenyl Monophosphate Aryloxy Triester Phosphoramidates as Activators of Vγ9Vδ2 T Cells

Aryloxy triester phosphoramidate prodrugs of the monophosphate derivatives of isopentenyl pyrophosphate (IPP) and dimethylallyl pyrophosphate (DMAPP) were synthesized as lipophilic derivatives that can improve cell uptake. Despite the structural similarity of IPP and DMAPP, it was noted that their phosphoramidate prodrugs exhibited distinct stability profiles in aqueous environments, which we show is due to the position of the allyl bond in the backbones of the IPP and DMAPP monophosphates. As the IPP monophosphate aryloxy triester phosphoramidates showed favorable stability, they were subsequently investigated for their ability to activate Vγ9/Vδ2 T cells and they showed promising activation of this subset of T cells. Together, these findings represent the first report of IPP and DMAPP monophosphate prodrugs and the ability of IPP aryloxy triester phosphoramidate prodrugs to activate Vγ9/Vδ2 T cells highlighting their potential as possible immunotherapeutics.