Closed-form nonlinear sectional analysis of pretwisted anisotropic beam with multiple delaminations

Fiber reinforced laminated composite open-section beams are widely used as bearingless rotor flex beams because of their high specific strength and stiffness as well as fatigue life. These laminated composite structures exhibit a number of different failure modes, including fiber-matrix debonding within individual layers, delamination or separation of the layers, transverse cracks through one or more layers and fiber fracture. Delamination is a predominant failure mode in continuous fiber reinforced laminated composites and often initiate near the free edges of the structure. The appearance of delaminations in the composite rotorcraft flexbeams can lead to deterioration of the mechanical properties and, in turn, the helicopter performance as well as safety. Understanding and predicting the influence of free-edge delamination on the overall behavior of the laminates will provide quantitative measures of the extent of the damage and help ensure their damage tolerance.

Small-Angle Neutron Scattering Studies of Hemoglobin Confined Inside Silica Tubes of Varying Sizes

In addition to the chemical nature of the surface, the dimensions of the confining host exert a significant influence on confined protein structures; this results in immense biological implications, especially those concerning the enzymatic activities of the protein. This study probes the structure of hemoglobin (Hb), a model protein, confined inside silica tubes with pore diameters that vary by one order of magnitude (approximate to 20-200 nm). The effect of confinement on the protein structure is probed by comparison with the structure of the protein in solution. Small-angle neutron scattering (SANS), which provides information on protein tertiary and quaternary structures, is employed to study the influence of the tube pore diameter on the structure and configuration of the confined protein in detail. Confinement significantly influences the structural stability of Hb and the structure depends on the Si-tube pore diameter. The high radius of gyration (R-g) and polydispersity of Hb in the 20 nm diameter Si-tube indicates that Hb undergoes a significant amount of aggregation. However, for Si-tube diameters greater or equal to 100 nm, the R-g of Hb is found to be in very close proximity to that obtained from the protein data bank (PDB) reported structure (R-g of native Hb=23.8 angstrom). This strongly indicates that the protein has a preference for the more native-like non-aggregated state if confined inside tubes of diameter greater or equal to 100 nm. Further insight into the Hb structure is obtained from the distance distribution function, p(r), and ab initio models calculated from the SANS patterns. These also suggest that the Si-tube size is a key parameter for protein stability and structure.

Quantum-Confined ZnO Nanoshell Photoanodes for Mesoscopic Solar Cells

We present a photoanode for dye-sensitized solar cell (DSC) based on ZnO nanoshell deposited by atomic layer deposition at 150 degrees C on a mesoporous insulating template. An ultrathin layer of ZnO between. 3 and 6 nm, which exhibits quantum confinement effect, is found to be sufficient to transport the photogenerated electrons to the external contacts and exhibits near-unity collection efficiency. A 6 nm ZnO nanoshell on a 2.5 mu m mesoporous nanoparticle Al2O3 template yields photovoltaic power conversion efficiency (PCE) of 4.2% in liquid DSC. Perovskite absorber (CH3NH3PbI3) based solid state solar cells made with similar ZnO nanostructures lead to a high PCE of 7%.

Spectral finite element based on an efficient layerwise theory for wave propagation analysis of composite and sandwich beams

In this paper, we present a spectral finite element model (SFEM) using an efficient and accurate layerwise (zigzag) theory, which is applicable for wave propagation analysis of highly inhomogeneous laminated composite and sandwich beams. The theory assumes a layerwise linear variation superimposed with a global third-order variation across the thickness for the axial displacement. The conditions of zero transverse shear stress at the top and bottom and its continuity at the layer interfaces are subsequently enforced to make the number of primary unknowns independent of the number of layers, thereby making the theory as efficient as the first-order shear deformation theory (FSDT). The spectral element developed is validated by comparing the present results with those available in the literature. A comparison of the natural frequencies of simply supported composite and sandwich beams obtained by the present spectral element with the exact two-dimensional elasticity and FSDT solutions reveals that the FSDT yields highly inaccurate results for the inhomogeneous sandwich beams and thick composite beams, whereas the present element based on the zigzag theory agrees very well with the exact elasticity solution for both thick and thin, composite and sandwich beams. A significant deviation in the dispersion relations obtained using the accurate zigzag theory and the FSDT is also observed for composite beams at high frequencies. It is shown that the pure shear rotation mode remains always evanescent, contrary to what has been reported earlier. The SFEM is subsequently used to study wavenumber dispersion, free vibration and wave propagation time history in soft-core sandwich beams with composite faces for the first time in the literature. (C) 2014 Elsevier Ltd. All rights reserved.

Topological blocking in quantum quench dynamics

We study the nonequilibrium dynamics of quenching through a quantum critical point in topological systems, focusing on one of their defining features: ground-state degeneracies and associated topological sectors. We present the notion of ``topological blocking,'' experienced by the dynamics due to a mismatch in degeneracies between two phases, and we argue that the dynamic evolution of the quench depends strongly on the topological sector being probed. We demonstrate this interplay between quench and topology in models stemming from two extensively studied systems, the transverse Ising chain and the Kitaev honeycomb model. Through nonlocal maps of each of these systems, we effectively study spinless fermionic p-wave paired topological superconductors. Confining the systems to ring and toroidal geometries, respectively, enables us to cleanly address degeneracies, subtle issues of fermion occupation and parity, and mismatches between topological sectors. We show that various features of the quench, which are related to Kibble-Zurek physics, are sensitive to the topological sector being probed, in particular, the overlap between the time-evolved initial ground state and an appropriate low-energy state of the final Hamiltonian. While most of our study is confined to translationally invariant systems, where momentum is a convenient quantum number, we briefly consider the effect of disorder and illustrate how this can influence the quench in a qualitatively different way depending on the topological sector considered.

Shape Memory Alloy based Active Chiral Composite Cells

Wing morphing is one of the emerging methodology towards improving aerodynamic efficiency of flight vehicle structures. In this paper a morphing structural element is designed and studied which has its origin in the well known chiral structures. The new aspect of design and functionality explored in this paper is that the chiral cell is actuated using thermal Shape Memory Alloy (SMA) actuator wires to provide directional motion. Such structure utilizes the potential of different actuations concepts based on actuator embedded in the chiral structure skin. This paper describes a new class of chiral cell structure with integrated SMA wire for actuation. Chiral topological constructs are obtained by considering passive and active load path decoupling and sub-optimal shape changes. Single cell of chiral honeycomb with actuators are analyzed using finite element simulation results and experiments. To this end, a multi-cell plan-form is characterized showing interesting possibilities in structural morphing applications. The applicability of the developed chiral cell to flexible wing skin, variable stiffness based design and controlling longitudinal-to-transverse stiffness ratio are discussed.

Semiconductor-like Sensitivity in Metallic Ultrathin Gold Nanowire-Based Sensors

Due to the ease of modification of electronic structure upon analyte adsorption, semiconductors have been the preferred materials as chemical sensors. At reduced dimension, however, the sensitivity of semiconductor-based sensors deteriorates significantly due to passivation, and often by increased band gap caused by quantum confinement. Using first-principles density functional theory combined with Boltzmann transport calculations, we demonstrate semiconductor-like sensitivity toward chemical species in ultrathin gold nanowires (AuNWs). The sensing mechanism is governed by the modification of the electronic structure of the AuNW as well as scattering of the charge carriers by analyte adsorption. Most importantly, the sensitivity exhibits a linear relationship with the electron affinities of the respective analytes. Based on this relationship, we propose an empirical parameter, which can predict an analyte-specific sensitivity of a AuNW, rendering them as effective sensors for a wide range of chemical an alytes.

Heteronuclear proton double quantum-carbon single quantum scalar correlation in solids

A new NMR experiment that exploits the advantages of proton double quantum (DQ) NMR through a proton DQ-carbon single quantum (SQ) correlation experiment in the solid state is proposed. Analogous to the previously proposed 2D H-1 (DQ)-C-13 refocused INEPT experiment (Webber et al., 2010), the correlation between H-1 and C-13 is achieved through scalar coupling evolution, while the double quantum coherence among protons is generated through dipolar couplings. However, the new experiment relies on C-13 transverse coherence for scalar transfer. The new experiment dubbed MAS-J-H-1 (DQ)-C-13-HMQC, is particularly suited for unlabeled molecules and can provide higher sensitivity than its INEPT counterpart. The experiment is applied to four different samples. (C) 2014 Elsevier Inc. All rights reserved.

Polymer-grafted multiwall carbon nanotubes functionalized by nitrene chemistry: effect on cooperativity and phase miscibility

The demixing of polystyrene (PS) and poly(vinyl methylether) (PVME) was systematically investigated in the presence of surface functionalized multiwall carbon nanotubes (MWNTs) by melt rheology. As PS-PVME blends are weakly interacting blends, the contribution of conformational entropy increases, resulting in thermo-rheological complexity wherein the concentration fluctuation persists even beyond the critical demixing temperature. These phenomenal changes were followed here in the presence of MWNTs with different surface functional groups. Polystyrene was synthesised by atom transfer radical polymerization and was immobilized onto carboxyl acid functionalized multiwall carbon nanotubes (COOH-MWNTs) via nitrene chemistry in order to improve the phase miscibility in PS-PVME blends. Interestingly, blends with 0.25 wt% polystyrene grafted multiwall carbon nanotubes (PS-g-MWNTs) delayed the spinodal decomposition temperature in the blends by similar to 33 degrees C with respect to both control blends and those with COOH-MWNTs. While the localization of COOH-MWNTs in PVME was explained from a thermodynamic point of view, the localization of PS-g-MWNTs was understood to result from favorable PS-PVME contact and the degree of surface coverage of PS on the surface of MWNTs. The length of the cooperative rearranging region (xi) decreased in presence of PS-g-MWNTs, suggesting confinement effects on large scale motions and enhanced interchain concentration fluctuation.

Generation of multiple sheets of light using spatial-filtering technique

We develop an optical system for generating multiple light sheets. This is enabled by employing a special class of spatial filters in a cylindrical lens geometry. The proposed binary filter placed at the back aperture of the cylindrical lens results in the generation of a periodic transverse pattern extending along the z axis (i.e., multiple light sheets). Experimental results confirm the generation of multiple light sheets of thickness 6.6 mu m with an intersheet spacing of 13.4 mu m. The proposed imaging technique may facilitate three-dimensional imaging in nano-optics, fluorescence microscopy, and nanobiology. (C) 2014 Optical Society of America

Comparative study of different nonconserving time integrators for wave propagation in hyperelastic waveguides

This paper addresses the formulation and numerical efficiency of various numerical models of different nonconserving time integrators for studying wave propagation in nonlinear hyperelastic waveguides. The study includes different nonlinear finite element formulations based on standard Galerkin finite element model, time domain spectral finite element model, Taylor-Galerkin finite element model, generalized Galerkin finite element model and frequency domain spectral finite element model. A comparative study on the computational efficiency of these different models is made using a hyperelastic rod model, and the optimal computational scheme is identified. The identified scheme is then used to study the propagation of transverse and longitudinal waves in a Timoshenko beam with Murnaghan material nonlinearity.

Combustion synthesized tetragonal ZrO2: Eu3+ nanophosphors: Structural and photoluminescence studies

Novel crystalline tetragonal ZrO2: Eu3+ phosphors were prepared by a facile and efficient low temperature solution combustion method at 400 +/- 10 degrees C using oxalyl dihydrazide (ODH) as fuel. The powder X-ray diffraction patterns and Rietveld confinement of as formed ZrO2: Eu3+ (1-11 mol%) confirmed the presence of body centered tetragonal phase. The crystallite size estimated from Scherrer's and W-H plots was found to be in the range of 7-17 nm. These results were in good agreement with transmission electron microscopy studies. The calculated microstrain in most of the planes indicated the presence of tensile stress along various planes of the particles. The observed space group (P4(2)/nmc) revealed the presence of cations in the 2b positions (0.75, 0.25, 0.25) and the anions in the 4d positions (0.25, 0.25, 0.45). The optical band gap energies estimated from Wood and Tauc's relation was found to be in the range 4.3-4.7 eV. Photoluminescence (PL) emission was recorded under 394 and 464 nm excitation shows an intense emission peak at 605 nm along with other emission peaks at 537, 592, 605 and 713 nm. These emission peaks were attributed to the transition of D-5(0) -> F-7(J) (J = 0, 1, 2, 3) of Eu3+ ions. The high ratio of Intensity of (D-5(0) -> F-7(2)) and (D-5(0) -> F-7(1)) infers that Eu3+ occupies sites with a low symmetry and without an inversion center. CIE color coordinates indicated the red regions which could meet the needs of illumination devices. (C) 2014 Elsevier B.V. All rights reserved.

Influence of source concentration on structural and optical properties of SnO2 nanoparticles prepared by chemical precipitation method

In present work, a systematic study has been carried out to understand the influence of source concentration on structural and optical properties of the SnO2 nanoparticles. SnO2 nanoparticles have been prepared by using chemical precipitation method at room temperature with aqueous ammonia as a stabilizing agent. X-ray diffraction analysis reveals that SnO2 nanoparticles exhibit tetragonal structure and the particle size is in range of 4.9-7.6 nm. High resolution transmission electron microscopic image shows that all the particles are nearly spherical in nature and particle size lies in range of 4.6-7 nm. Compositional analysis indicates the presence of Sn and O in samples. Blue shift has been observed in optical absorption spectra due to quantum confinement and the bandgap is in range of 4-4.16 eV. The origin of photoluminescence in SnO2 is found to be due to recombination of electrons in singly occupied oxygen vacancies with photo-excited holes in valance band.

Structural and magnetic properties of ultra-small scale eutectic CoFeZr alloys

Aiming to develop high mechanical strength and toughness by tuning ultrafine lamellar spacing of magnetic eutectic alloys, we report the mechanical and magnetic properties of the binary eutectic alloys Co90.5Zr9.5 and Fe90.2Zr9.8, as well as the pseudo-binary eutectic alloys Co82.4Fe8Zr9.6, Co78Fe12.4Zr9.6 and Co49.2Fe49.2Zr9.6 developed by suction-casting. The lower lamellar spacing around 100 nm of the eutectics Co49.2Fe49.2Zr9.6 yields a high hardness of 713(+/- 20) VHN. Magnetic measurements reveal high magnetic moment of 1.92 mu B (at 5 K) and 1.82 mu B (at 300 K) per formula unit for this composition. The magnetization vs. applied field data at 5 K show a directional preference to some extent and therefore smaller non-collinear magnetization behavior compared to Co11Zr2 reported in the literature due to exchange frustration and transverse spin freezing owing to the presence of smaller Zr content. The decay of magnetization as a function of temperature along the easy axis of magnetization of all the eutectic compositions can be described fairly well by the spin wave excitation equation Delta M/M(0) = BT3/2 + CT5/2. (C) 2014 Elsevier B.V. All rights reserved.

Instabilities in a fluid overlying an inclined anisotropic and inhomogeneous porous layer

In this paper, linear stability analysis on a Newtonian fluid film flowing under the effect of gravity over an inclined porous medium saturated with the same fluid in isothermal condition is carried out. The focus is placed on the effect of the anisotropic and inhomogeneous variations in the permeability of the porous medium on the shear mode and surface mode instabilities. The fluid-porous system is modelled by a coupled two-dimensional Navier-Stokes/Darcy problem. The perturbation equations are solved numerically using the Chebyshev collocation method. Detailed stability characteristics as a function of the depth ratio (the ratio of the depth of the fluid layer to that of the porous layer), the anisotropic parameter (the ratio of the permeability in the direction of the basic flow to that in the direction transverse to the basic flow) and the inhomogeneity functions are presented.