Abstract: The thermal and mechanical stability of a functionally graded composite truncated conical shell reinforced by carbon nanotube fibers and surrounded by the elastic foundations are studied in this paper. Distribution of reinforcements across the shell thickness is assumed to be uniform or functionally graded. The equilibrium and linearized stability equations for the shells are derived based on the classical shell theory. Using Galerkin method, the closed – form expression for determining the linear thermal and mechanical buckling load is obtained. The paper also analyzed and discussed the effects of semi-vertex angle, shell length, volume fraction of fibers, distribution pattern of fibers, temperature, elastic foundations on the linear thermal and mechanical buckling loads of the functionally graded carbon nanotube fibers-reinforced composite (FG CNTRC) truncated conical shell in thermal environment.

Abstract: Le jeu de données est issu d'observation collectées par l'équipe des Marine Mammals Observers dans le cadre des prospections sismiques pétrolières en 2012 en Guyane française. Les directives et protocoles d'observation ont été fournis par CGGVeritas afin de minimiser l'impact sur la vie sous-marine pendant les études sismiques. Les Marine Mammals Observers employés ont été formés par CGGVeritas. Des experts locaux ont analysé et confirmé les données. Ce jeu a contribué à l'atlas des Mammifères marins publié en 2016.

Abstract: Photonic microcapsules with onion-like topology are microfluidically designed to have cholesteric liquid crystals with opposite handedness in their core and shell. The microcapsules exhibit structural colors caused by dual photonic bandgaps, resulting in a rich variety of color on the optical palette. Moreover, the microcapsules can switch the colors from either core or shell depending on the selection of light-handedness.

Abstract: In recent years, aluminum alloy single-layer latticed shell has been extensively used in civil and industrial infrastructure. The elasticity modulus of aluminum alloy is low, the rigidity of aluminum joints are weak and the roof load transmission path is different. Therefore, the stability performance of this dome is unique. To clarify the stability performance of aluminum alloy single-layer latticed shell, over 500 aluminum alloy single-layer spherical latticed shells were analyzed with nonlinear finite method. The suggested values of rise/span ratio and initial imperfection were presented. The influencing coefficients of initial imperfection, material nonlinearity and stressed skin effect on stability bearing capacity were obtained. And the structural stability safety coefficient and the approximate calculation formula for stability bearing capacity of aluminum alloy single-layer spherical latticed shell were derived. The influences of joint semi-rigidity were investigated. All the aforementioned results provide a scientific basis for future stability design of aluminum alloy single-layer spherical latticed shell structure.

Abstract: Due to some technical issues that can appear during the manufacturing process of Functionally Graded Materials (FGMs), it can be extremely difficult to produce perfect materials. Indeed, one of the biggest problems is the presence of porosities. For this purpose, the vibrational behavior of doubly-curved shells made of FGM including porosities is investigated in this paper. With respect to previous research, the porosity has been added to the mechanical model that characterizes the through-the-thickness distribution of the graded constituents and applied to doubly-curved shell structures. Few papers have been published on this topic. In fact, it is easier to find works related to one-dimensional structures and beam models that take account the effect of porosities. The First-order Shear Deformation Theory (FSDT) is considered as the theoretical framework. In addition, the mechanical properties of the constituents vary along the thickness direction. For this purpose, two power-law distributions are employed to characterize their volume fraction. Strain components are established in an orthogonal curvilinear coordinate system and the governing equations are derived according to the Hamilton’s principle. Finally, Navier’s solution method is used and the numerical results concerning three different types of shell structures are presented.

Abstract: Core/shell nanostructure is versatile for improving or integrating diverse functions, yet it is still limited to homeomorphism with isomorphic core and shell structure. Here, we delineate a selective cation exchange strategy to construct lanthanide core/shell nanoparticles with dissimilar structure. Hexagonal NaLnF4, a typical photon conversion material, was selected to grow cubic CaF2 shell to protect surface exposed Ln3+. Preferential cation exchange between Ca2+ and Na+ triggered the surface hexagonal-to-cubic structure evolution, which remediated the large barrier for heteroepitaxy of monocrystalline CaF2 shell. The heterostructured CaF2 shell leads to greatly enhanced upconversion emission with increased absolute quantum yield from 0.2% to 3.7%. Moreover, it is advantageous in suppressing the interfacial diffusion of Ln3+, as well as the leakage of Ln3+ from nanoparticle to aqueous system. These findings open up a new avenue for fabricating heterostructured core/shell nanoparticles, and are instructi...

Abstract: In this article, the nonlinear vibration frequencies of functionally graded carbon nanotube-reinforced composite doubly curved shell panels under elevated thermal environment are numerically investigated using finite element method. The doubly curved carbon nanotube-reinforced shell panel has been modeled mathematically using higher-order kinematics theory and Green–Lagrange geometrical nonlinear strains. The properties of the individual constituents of the graded composite are assumed to be temperature dependent. In addition, the properties of the media are obtained based on the modified rule of mixture. The carbon nanotubes are dispersed nonuniformly through the thickness direction. The large deformation kinematic effects on the structural responses are counted by including all the nonlinear higher-order terms in the formulation. The desired nonlinear responses are computed numerically using our in-house computer code in conjunction with the direct iterative scheme. The convergence and the accur...

Abstract: Forced vibration response of a conical panel subjected to the action of a moving load is investigated in the current research Panel is made from a carbon nanotube (CNT) reinforced composite where the CNTs as reinforcements are distributed either uniformly or functionally graded across the panel thickness Panel is formulated using the first order shear deformation shell theory and the Donnell kinematic assumptions It is subjected to a moving load whose path and velocity are both arbitrary The properties of the composite media are estimated according to a refined rule of mixtures approach The governing equations of motion of the shell are obtained according to the Ritz method where the shape functions are obtained according to the Gram-Schmidt process The developed equations with the aid of Ritz method are transformed into time-dependent ordinary differential equations whose solution is traced in time by means of the Newmark time marching scheme Numerical results are provided to explore the influences of semi-vertex and opening angles of the cone, geometrical parameters and also CNT characteristics of the shell It is shown that, dynamic deflection of the shell decreases significantly with the introduction of FG-X pattern of CNTs Furthermore, enrichment of the matrix with more CNTs alleviates the dynamic deflection of the conical shell

Abstract: Metal oxide semiconductor (MOS) based gas sensors for triethylamine (TEA) are anticipated with low operating temperature, high response, and robust manufacturing process. TEA sensors with the α-Fe2O3@NiO or α-Fe2O3@CuO core-shell nanorods (NRs) heterostructure are successfully fabricated and their sensing performance is optimized by controlling the shell thickness based on Debye length. Porous α-Fe2O3 NRs are directly prepared on flat Al2O3 substrates by convenient hydrothermal process. The p-type shell layer is deposited by pulsed laser deposition (PLD) method, which width is controlled by changing the applied laser pulses. Due to the formation of PN heterojunction, the core-shell NR heterostructures show enhanced performances than pristine α-Fe2O3 NRs at near room-temperature, e.g. 40 °C. Moreover, such heterostructural sensor performances also exhibit a strong dependence on the shell thickness. When the p-type shell thickness is close to its Debye length (λd), the core-shell sensor of the highest response is realized. The enhanced sensing properties of this core-shell NR heterostructure toward TEA can be explained by the increase of initial resistance (Ra) due to the modulation of depletion layer through optimizing the p-type shell thickness.

Abstract: We present a pedagogical introduction to the In-Medium Similarity Renormalization Group (IM-SRG) framework for ab initio calculations of nuclei. The IM-SRG performs continuous unitary transformations of the nuclear many-body Hamiltonian in second-quantized form, which can be implemented with polynomial computational effort. Through suitably chosen generators, it is possible to extract eigenvalues of the Hamiltonian in a given nucleus, or drive the Hamiltonian matrix in configuration space to specific structures, e.g., band- or block-diagonal form. Exploiting this flexibility, we describe two complementary approaches for the description of closed- and open-shell nuclei: The first is the Multireference IM-SRG (MR-IM-SRG), which is designed for the efficient calculation of nuclear ground-state properties. The second is the derivation of nonempirical valence-space interactions that can be used as input for nuclear Shell model (i.e., configuration interaction (CI)) calculations. This IM-SRG+Shell model approach provides immediate access to excitation spectra, transitions, etc., but is limited in applicability by the factorial cost of the CI calculations. We review applications of the MR-IM-SRG and IM-SRG+Shell model approaches to the calculation of ground-state properties for the oxygen, calcium, and nickel isotopic chains or the spectroscopy of nuclei in the lower $sd$ shell, respectively, and present selected new results, e.g., for the ground- and excited state properties of neon isotopes.

Abstract: Precise morphology and composition control is vital for designing multifunctional lanthanide-doped core/shell nanocrystals. Herein, we report controlled isotropic and anisotropic shell growth techniques in hexagonal sodium rare-earth tetrafluoride (β-NaLnF4) nanocrystals by exploiting the kinetics of the shell growth. A drastic change of the shell morphology was observed by changing the injection rate of the shell precursors while keeping all other reaction conditions constant. We obtained isotropic shell growth for fast sequential injection and a preferred growth of the shell layers along the crystal’s c-axis [001] for slow dropwise injection. Using this slow shell growth technique, we have grown rod-like shells around different almost spherical core nanocrystals. Bright and efficient upconversion was measured for both isotropic and rod-like shells around β-NaYF4 nanocrystals doped with Yb3+/Er3+ and Yb3+/Tm3+. Photoluminescence upconversion quantum yield and lifetime measurements reveal the high quality...

Abstract: We report an in situ, temperature and H2 pressure-dependent, characterization of (2.6 ± 0.4) nm palladium nanoparticles supported on active carbon during the process of hydride phase formation. For the first time the core–shell structure is highlighted in the single-component particles on the basis of a different atomic structure and electronic configurations in the inner “core” and surface “shell” regions. The atomic structure of these particles is examined by combined X-ray powder diffraction (XRPD), which is sensitive to the crystalline core region of the nanoparticles, and by first shell analysis of extended X-ray absorption fine structure (EXAFS) spectra, which reflects the averaged structure of both the core and the more disordered shell. In the whole temperature range (0–85 °C), XRPD analysis confirms the existence of two well-separated α- and β-hydride phases with the characteristic flat plateau in the phase transition region of the pressure-lattice parameter isotherms. In contrast, first shell in...

Abstract: MoO2@C core shell nanofibers are synthesized via a simple electrospinning method with a single nozzle. The formation mechanism of MoO2@C core shell nanofibers is investigated in detail and it is discovered that the phase-segregation phenomenon may be the main driving force of thermodynamics to form MoO2@C core shell nanofibers, and the high temperature as the dynamic factor can accelerate the formation of these core shell nanofibers. The carbon shell of the MoO2@C core shell nanofibers acts as both conductive bond to increase electrical conductivity and structural skeleton to maintain the integrity of MoO2 during Li+ insertion/extraction to achieve both high specific capacity and good cyclic stability. So as an anode for lithium-ion batteries, the MoO2@C core shell nanofiber electrode exhibits high specific capacity and extraordinary lifetime even at a large current density. Their reversible capacities are 665 mA h g−1 in the 600th cycle at 0.5 A g−1. Even at a high current density of 1 A g−1, a capacity of 537 mA h g−1 is obtained after 600 cycles. The present work may provide a facile and broadly applicable way for the fabrication and utilization of metal oxide/carbon core shell composites in fields of batteries, catalysts, and fuel cells.

Abstract: We present a systematic study of core-shell Au/Fe3O4 nanoparticles produced by thermal decomposition under mild conditions. The morphology and crystal structure of the nanoparticles revealed the presence of Au core of d = (6.9 ± 1.0) nm surrounded by Fe3O4 shell with a thickness of ~3.5 nm, epitaxially grown onto the Au core surface. The Au/Fe3O4 core-shell structure was demonstrated by high angle annular dark field scanning transmission electron microscopy analysis. The magnetite shell grown on top of the Au nanoparticle displayed a thermal blocking state at temperatures below TB = 59 K and a relaxed state well above TB. Remarkably, an exchange bias effect was observed when cooling down the samples below room temperature under an external magnetic field. Moreover, the exchange bias field (HEX) started to appear at T~40 K and its value increased by decreasing the temperature. This effect has been assigned to the interaction of spins located in the magnetically disordered regions (in the inner and outer surface of the Fe3O4 shell) and spins located in the ordered region of the Fe3O4 shell.

Abstract: Micromachined hemispherical shell resonators (HSRs) can be used in high accuracy vibratory gyroscopes. These resonators need to have very low energy loss to achieve very high quality factor. Energy might be lost through the anchor, fluid-structure interaction, thermoelastic dissipation, phonon-phonon and phonon-electron interactions, and the resonator surface. This paper investigates energy loss through the anchor of HSRs using a numerical approach. To numerically determine wave radiation from the anchor to the infinite substrate, a perfectly matched layer is used around a finite substrate. Anchor loss investigations in HSRs are classified into four categories. First, the effects of shell properties-material, geometry, and imperfections-are investigated. Second, the relationships between anchor loss and properties of the stem, such as material, geometry, and stemshell misalignments, are studied. Third, the effects of substrate characteristics-substrate material, attachment material between the stem and substrate, and attachment configuration of the substrate and stem-are investigated. Finally, the effects of external motions, such as shock and rotation, are analyzed. It is found that anchor loss in HSRs strongly depends on the shell, stem, and substrate properties. This study also shows that any imperfection in the shell or any misalignment between the shell and stem increases anchor loss by orders of magnitude.

Abstract: A unified solution for coupled cylindrical shell and annular plate systems with general boundary and coupling conditions is presented in the study by using a modified Fourier-Ritz method. Under the framework, regardless of the boundary and continuity conditions, each displacement for the cylindrical shell and the annular plate is invariantly expressed as the modified Fourier series composed of the standard Fourier series and auxiliary functions. The introduction of the auxiliary functions can not only remove the potential discontinuities at the junction and the extremes of the combination but also accelerate the convergence of the series expansion. All the expansion coefficients are determined by the Rayleigh-Ritz method as the generalized coordinates. The arbitrary axial position of the annular plate coupling with the cylindrical shell considered in the theoretical formulation makes the present method more general. The theoretical model established by present method can be conveniently applied to cylindr...