Using a pseudo-functionally graded interlayer in order to improve the static and dynamic behavior of wind turbine blade T-bolt root joints

The large wind turbines blades with multi-ton composite structures are mostly connected to the peach-bearings flanges using T-bolt joints which induce shear and bearing stress fields around the cross bolts. The significant differences between the modulus of elasticity of metallic bolts and composite surrounding materials cause stress concentration around interfaced zones and, also, limit the load capacity of the joints. In the present research, a pseudo functionally graded material (PFGM) as an interlayer is used around the cross bolts to examine the reduction of the stress concentration. Some radial variation of the mechanical properties would be considered for this interlayer. The finite element method is used to analyze the structures. Loadings are applied to the center of the cross bolts analogous to the real cases. Both the static and dynamic loadings are studied. For the finite element of the functionally graded material interlayer, a multilayer alternative material with constant properties in each layer is used. The results show that using an isotropic single layer with an average modulus of elasticity and specific thickness decreases the stress concentration of the composite part up to 47%. The various property models for the interlayer also show that an appropriated model can decrease the stress concentration up to 55%. Dynamic transient analyses would be implemented over the joint structure and improved considering to the practical cases. Using the PFGM interlayer decreases the constant and variable parts of the stresses up to 55% and also causes significant increasing of the joint fatigue life.     

On three-dimensional stress analysis of periodic notched plates under tension

By using the finite element method, three-dimensional models of a number of periodic blunt and sharp notches subjected to tension loading are investigated. The aim of this research is to investigate the thickness effect on the location of maximum stress and notch stress intensity factor (NSIF) of corresponding blunt and sharp periodic notches respectively. With this aim, different number of periodic notches as well as different notch opening angles are examined. While for two-dimensional plates weakened by periodic notches some results are available in the literature, this paper first faces the problem of three-dimensional cases. A total of about 100 geometrical configurations are investigated. It is found that, the effect of plate thickness of periodic notched components can be characterized by the relative value with respect to the depth of the notch (H/t). For the blunt periodic notches with relatively higher values of H/t ratio, the value of the maximum tensile stress is located near the free surface. On the contrary for lower values of H/t, it is placed at the middle plane. The same behaviour is observed for sharp periodic notches in terms of notch stress intensity factors.     

LCAO studies of hydrogen chemisorption on nickel: II. Cluster models for adsorption sites

The adsorption of single hydrogen atoms, investigated by means of cluster calculations, has been compared with the adsorption of hydrogen monolayers on periodic crystals (paper I). From the similarity of the adsorption energy curves we conclude that the (direct and indirect) interactions between adsorbed hydrogen atoms are relatively small up to monolayer coverage. For adsorption on different sites of ideal low index surfaces the stability decreases in the order Atop > Bridge > Centred. For Atop adsorption it increases with a decreasing number of nearest neighbours to the nickel atom in the NiH “surface molecule”, thus leading to especially strong adsorption sites at the edges of a stepped surface and to low stability in the notches. In general, we find that the Ni_nH “surface molecule” with n = 1, 2, 3 or 4 determines the equilibrium positions for H adsorption; the inclusion of one shell of neighbours to the nickel atoms is sufficient to explain the differences in adsorption energy. The Extended Hückel method is not well suited to study dissociative chemisorption of H₂, although some qualitative trends are correct.     

Control of sound and vibration for cylindrical shells by utilizing a periodic structure of functionally graded material

A periodic shell made of functionally graded material (FGM) is proposed in this Letter. Wave propagation and vibration transmission in the FGM periodic shell for different circumferential modes are investigated. By illustrating the dynamical behavior of the periodic FGM shell within the pass/stop band frequency ranges, the mechanism of wave propagation and vibration transmission in the shell are illuminated. Moreover, the suppression characteristics of structure-borne sound in the internal field of the shell, either within the stop or pass band frequency ranges, are studied.     

Buckling and free vibration analysis of functionally graded cylindrical shells subjected to a temperature-specified boundary condition

Linear thermal buckling and free vibration analysis are presented for functionally graded cylindrical shells with clamped-clamped boundary condition based on temperature-dependent material properties. The material properties of functionally graded materials (FGM) shell are assumed to vary smoothly and continuously across the thickness. With high-temperature specified on the inner surface of the FGM shell and outer surface at ambient temperature, 1D heat conduction equation along the thickness of the shell is applied to determine the temperature distribution; thereby, the material properties based on temperature distribution are made available for thermal buckling and free vibration analysis. First-order shear deformation theory along with Fourier series expansion of the displacement variables in the circumferential direction are used to model the FGM shell. Numerical studies involved the understanding of the influence of the power-law index, r/h and l/r ratios on the critical buckling temperature. Free vibration studies of FGM shells under elevated temperature show that the fall in natural frequency is very drastic for the mode corresponding to the lowest natural frequency when compared to the lowest buckling temperature mode.     

TEM preparation methods and influence of radiation damage on the beam sensitive CaCO3 shell of Emiliania huxleyi

The ultrastructure of biologically formed calcium carbonate crystals like the shell of Emiliania huxleyi depends on the environmental conditions such as pH value, temperature and salinity. Therefore, they can be used as indicator for climate changes. However, for this a detailed understanding of their crystal structure and chemical composition is required. High resolution methods like transmission electron microscopy can provide those information on the nanoscale, given that sufficiently thin samples can be prepared. In our study, we developed sample preparation techniques for cross-section and plan-view investigations and studied the sample stability under electron bombardment. In addition to the biological material (Emiliania huxleyi) we also prepared mineralogical samples (Iceland spar) for comparison. High resolution transmission electron microscopy imaging, electron diffraction and electron energy-loss spectroscopy studies revealed that all prepared samples are relatively stable under electron bombardment at an acceleration voltage of 300 kV when using a parallel illumination. Above an accumulated dose of ∼10⁵ e/nm² the material – independent whether its origin is biological or geological – transformed to poly-crystalline calcium oxide.     

Synthesis and magnetic properties of Cu-coated Fe composite nanoparticles

The Fe/Cu nanocomposites with iron as core and copper as shell have been successfully synthesized by a two-step reduction method. A spherical nanoparticle of γ-Fe was first fabricated by the reduction of ferrous chloride, and then the Fe particle was coated by nanocrystalline Cu through the reduction of copper sulfate. The thickness of copper shell has been tuned by varying the initial concentration of copper sulfate. The morphology, crystalline structure, chemical composition and magnetic properties of the products were investigated by using transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS) and vibrating sample magnetometer (VSM). It was found that the saturation magnetization (M_s) values of the Fe/Cu core–shell particles are varied owing to the different thickness of copper layer. Though the M_s value of the Fe/Cu nanocomposite is lower than that of pure iron nanoparticles, the higher M_s value (22.411 emu/g) of the Fe/Cu composites is also investigated. The result of the thermogravimetric analysis (TGA) showed the enhanced antioxidation capacity of the Fe/Cu nanocomposites. This kind of nanocomposites combined the excellent magnetism of iron and the electronic, thermal conductivity of copper, suggesting potential application as a novel electromagnetic material.     

Shell structure of a circular quantum dot in weak magnetic fields

The conductance of a circular quantum dot in a two-dimensional electron gas of a GaAlAs/GaAs heterostructure has been measured. Conductance oscillations as functions both of the magnetic field B and of the size of a dot confining about 1000 electrons are related to the formation of electronic shell structure. Modeling the dot by a circular billiard, we interpret the results semiclassically in terms of periodic orbit theory, providing a simple explanation of the B-periodic oscillations. A comparison to a harmonic confinement suitable for smaller quantum dots is given.     

Three-dimensional vibration analysis of joined thick conical — Cylindrical shells of revolution with variable thickness

A three-dimensional (3-D) method of analysis is presented for determining the free vibration frequencies of joined thick conical-cylindrical shells of revolution with variable thickness. Unlike conventional shell theories, which are mathematically two-dimensional (2-D), the present method is based upon the 3-D dynamic equations of elasticity. Displacement components u_r, u_θ, and u_z in the radial, circumferential, and axial directions, respectively, are taken to be periodic in θ and in time, and algebraic polynomials in the r and z directions. Potential (strain) and kinetic energies of the joined shells are formulated, and the Ritz method is used to solve the eigenvalue problem, thus yielding upper bound values of the frequencies by minimizing the frequencies. As the degree of the polynomials is increased, frequencies converge to the exact values. Convergence to four-digit exactitude is demonstrated for the first five frequencies. Natural frequencies are presented for different boundary conditions. Comparisons are made between the frequencies from the present 3-D Ritz method and 2-D thin shell theories by previous researchers.     

Evolution of a finite Olver beam propagating in a right handed and double negative index slab system

In this work, we investigate the evolution of a first order finite Olver beam and a zeroth order one (finite Airy beam) propagating in a right handed and double negative index cascaded slab system based on the transfer matrix and generalized Huygens-Fresnel integral equation. It is discovered that the incident finite Olver beam could reappear on the output cross section by using a periodic slab system with a negative index material as long as n_l=??n_r, L?=?R; for n_l≠?n_r, the bigger abs(n_l) is, the longer the needed unit length L to achieve an original beam intensity reproduction, and vice versa; the relations between the negative refractive index and the double negative material unit length are also quantitative explored by using the Origin Lab. It is expected that the derived analytical formulae and conclusions can provide a convenient and effective way for studying the evolution of a finite Olver beam propagating in multilayered structures, especially for periodic and quasi-periodic slab systems.     

Structuring of material parameters in lithium niobate crystals with low-mass, high-energy ion radiation

Ferroelectric lithium niobate crystals offer a great potential for applications in modern optics. To provide powerful optical components, tailoring of key material parameters, especially of the refractive index n and the ferroelectric domain landscape, is required. Irradiation of lithium niobate crystals with accelerated ions causes strong structured modifications in the material. The effects induced by low-mass, high-energy ions (such as ³He with 41?MeV, which are not implanted, but transmit through the entire crystal volume) are reviewed. Irradiation yields large changes of the refractive index ??n, improved domain engineering capability within the material along the ion track, and waveguiding structures. The periodic modification of ??n as well as the formation of periodically poled lithium niobate (PPLN) (supported by radiation damage) is described. Two-step knock-on displacement processes, ³He??Nb and ³He??O causing thermal spikes, are identified as origin for the material modifications.     

Preparation and in vitro evaluation of poly(D,L-lactide-co-glycolide) air-filled nanocapsules as a contrast agent for ultrasound imaging

The aim of this study was to prepare air-filled nanocapsules intended ultrasound contrast agents (UCAs) with a biodegradable polymeric shell composed of poly(d,l-lactide-co-glycolide) (PLGA). Because of their size, current commercial UCAs are not capable of penetrating the irregular vasculature that feeds growing tumors. The new generation of UCAs should be designed on the nanoscale to enhance tumor detection, in addition, the polymeric shell in contrast with monomolecular stabilized UCAs improves the mechanical properties against ultrasound pressure and lack of stability. The preparation method of air-filled nanocapsules was based on a modification of the double-emulsion solvent evaporation technique. Air-filled nanocapsules with a mean diameter of 370 ± 96 nm were obtained. Electronic microscopies revealed spherical-shaped particles with smooth surfaces and a capsular morphology, with a shell thickness of ∼50 nm. Air-filled nanocapsules showed echogenic power in vitro, providing an enhancement of up to 15 dB at a concentration of 0.045 mg/mL at a frequency of 10 MHz. Loss of signal for air-filled nanocapsules was 2 dB after 30 min, suggesting high stability. The prepared contrast agent in this work has the potential to be used in ultrasound imaging.     

Building quasimodes in integrable billiards

It is shown, by means of a simple specific example, that for integrable billiards it is possible to build up approximate eigenfunctions, called asymptotic eigenfunctions, which, in the semiclassical limit, are concentrated arbitrarily close to a classical periodic orbit and have an arbitrarily long lifetime. These states are directly related to the presence of shell structures in the quantal spectrum of the system. The results appear to verify a conjecture by Arnold about quasimodes and provide a method to construct them.     

Preparation of Highly Stable and Photoluminescent Cadmium-Free InP/GaP/ZnS Core/Shell Quantum Dots and Application to Quantitative Immunoassay

Indium phosphide (InP) quantum dots (QDs) are ideal substitutes for widely used cadmium-based QDs and have great application prospects in biological fields due to their environmentally benign properties and human safety. However, the synthesis of InP core/shell QDs with biocompatibility, high quantum yield (QY), uniform particle size, and high stability is still a challenging subject. Herein, high quality (QY up to 72%) thick shell InP/GaP/ZnS core/shell QDs (12.8 ± 1.4 nm) are synthesized using multiple injections of shell precursor and extension of shell growth time, with GaP serving as the intermediate layer and 1-octanethiol acting as the new S source. The thick shell InP/GaP/ZnS core/shell QDs still keep high QY and photostability after transfer into water. InP/GaP/ZnS core/shell QDs as fluorescence labels to establish QD-based fluorescence-linked immunosorbent assay (QD-FLISA) for quantitative detection of C-reactive protein (CRP), and a calibration curve is established between fluorescence intensity and CRP concentrations (range: 1–800 ng mL⁻¹, correlation coefficient: R² = 0.9992). The limit of detection is 2.9 ng mL⁻¹, which increases twofold compared to previously reported cadmium-free QD-based immunoassays. Thus, InP/GaP/ZnS core/shell QDs as a great promise fluorescence labeling material, provide a new route for cadmium-free sensitive and specific immunoassays in biomedical fields.     

Influence of microporosity on the strength properties of SiC ceramic materials

A series of silicon carbide ceramic samples with variable characteristics of the microporosity and strength, such as the ballistic strength σ _B and the static strength σ _S , are investigated. The dependences of the strength on the integral porosity for ceramic materials are determined. It is established that the strength (both σ _B and σ _S ) is directly proportional to the average length of the bridges between micropores. The mechanism of the influence of microporosity on the strength of the ceramic materials is elucidated. According to this mechanism, interpore bridges are concentrators of stresses and, hence, are broken when a load is applied to the ceramic material. Numerous breakings of bridges bring about the failure of the ceramic body. The average stress concentration coefficient is estimated as a function of the integral porosity of the ceramic material. It is demonstrated that the static strength of the ceramic material is determined by the presence of large micropores (50–100 μm).     

Alternative evaluation of statistical indicators in atoms: The non-relativistic and relativistic cases

In this work, the calculation of a statistical measure of complexity and the Fisher-Shannon information is performed for all the atoms in the periodic table. Non-relativistic and relativistic cases are considered. We follow the method suggested in [C.P. Panos, N.S. Nikolaidis, K.Ch. Chatzisavvas, C.C. Tsouros, arXiv:0812.3963v1] that uses the fractional occupation probabilities of electrons in atomic orbitals, instead of the continuous electronic wave functions. For the order of shell filling in the relativistic case, we take into account the effect due to electronic spin-orbit interaction. The increasing of both magnitudes, the statistical complexity and the Fisher-Shannon information, with the atomic number Z is observed. The shell structure and the irregular shell filling is well displayed by the Fisher-Shannon information in the relativistic case.     

Nucleation of misfit dislocations and plastic deformation in core/shell nanowires

During fabrication of metal nanowires, an oxide layer (shell) that surrounds the metal (core) may form. Such an oxide-covered nanowire can be viewed as a cylindrical core/shell nanostructure, possessing a crystal lattice mismatch between the core and shell. Experimental evidence has shown that, in response to this mismatch, mechanical stresses induce plastic deformation in the shell and misfit dislocations nucleate at the core/shell interface. As a result, the mechanical, electrical and optoelectronic properties of the nanowire are affected. It is therefore essential to be able to predict the critical conditions at which misfit dislocation nucleation at the nanowire interface takes place and the critical applied load at which the interface begins deforming plastically. Two approaches are explored in order to analyze the stress relaxation processes in these oxide-covered nanowires: (i) energy considerations are carried out within a classical elasticity framework to predict the critical radii (of the core and shell) at which dislocation nucleation takes place at the nanowire interface; (ii) a strain gradient plasticity approach is applied to estimate the flow stress at which the interface will begin deforming plastically (this stress is termed “interfacial-yield” stress). The interfacial-yield stress, predicted by gradient plasticity, depends, among other material parameters, on the radii of the core and shell. Both approaches demonstrate how the geometric parameters of nanowires can be calibrated so as to avoid undesirable plastic deformation; in particular, method (i) can give the radii values that prevent misfit dislocation formation, whereas method (ii) can provide, for particular radii values, the critical stress at which interface deformation initiates.     

Interaction of a spherical acoustic wave with an elastic spherical shell

The interaction of a spherical acoustic wave with an elastic spherical shell is treated analytically. The solution includes the coupling between the acoustic sound field and vibration of the shell with any degree of fluid loading. The formulation for the far-field acoustic pressure is derived in terms of natural spherical wave functions, the properties of the acoustic medium, and the material constants of the shell. The far acoustic field is computed for a thin aluminum shell and several sound source locations over a large range of ka, where k is the wavenumber, and a is the shell radius. It is shown that the acoustic pressure depends significantly on whether the shell is in air or is submerged in water, particularly when the sound source is very near the surface. In air, the sound field of the shell is nearly identical to that of a rigid sphere but, in water, the shell is more compliant, which results in a damped radiation field that is characterized by vibrational resonances throughout the range of frequencies considered. As the sound sources is moved further away from the surface, however, this resonance response decreases very rapidly, and the sound field corresponds more closely to that of the shell in air.     

Towards nonlinear stability of sources via a modified Burgers equation

Coherent structures are solutions to reaction-diffusion systems that are time-periodic in an appropriate moving frame and spatially asymptotic at x=±∞ to spatially periodic travelling waves. This paper is concerned with sources which are coherent structures for which the group velocities in the far field point away from the core. Sources actively select wave numbers and therefore often organize the overall dynamics in a spatially extended system. Determining their nonlinear stability properties is challenging as localized perturbations may lead to a non-localized response even on the linear level due to the outward transport. Using a Burgers-type equation as a model problem that captures some of the essential features of sources, we show how this phenomenon can be analysed and asymptotic nonlinear stability be established in this simpler context.