Evaluation of 2D image reconstruction using fan-beam FBP algorithm with no backprojection weight from WLP completed truncated projection data

This paper presents the image reconstruction using the fan-beam filtered backprojection (FBP) algorithm with no backprojection weight from windowed linear prediction (WLP) completed truncated projection data. The image reconstruction from truncated projections aims to reconstruct the object accurately from the available limited projection data. Due to the incomplete projection data, the reconstructed image contains truncation artifacts which extends into the region of interest (ROI) making the reconstructed image unsuitable for further use. Data completion techniques have been shown to be effective in such situations. We use windowed linear prediction technique for projection completion and then use the fan-beam FBP algorithm with no backprojection weight for the 2-D image reconstruction. We evaluate the quality of the reconstructed image using fan-beam FBP algorithm with no backprojection weight after WLP completion.

Size dependent bandgap of molecular beam epitaxy grown InN quantum dots measured by scanning tunneling spectroscopy

InN quantum dots (QDs) were grown on Si (111) by epitaxial Stranski-Krastanow growth mode using plasma-assisted molecular beam epitaxy. Single-crystalline wurtzite structure of InN QDs was verified by the x-ray diffraction and transmission electron microscopy. Scanning tunneling microscopy has been used to probe the structural aspects of QDs. A surface bandgap of InN QDs was estimated from scanning tunneling spectroscopy (STS) I-V curves and found that it is strongly dependent on the size of QDs. The observed size-dependent STS bandgap energy shifts with diameter and height were theoretical explained based on an effective mass approximation with finite-depth square-well potential model.

Growth of silicon nanowires by electron beam evaporation using indium catalyst

For the first time silicon nanowires have been grown on indium (In) coated Si (100) substrates using e-beam evaporation at a low substrate temperature of 300 degrees C. Standard spectroscopic and microscopic techniques have been employed for the structural, morphological and compositional properties of as grown Si nanowires. The as grown Si nanowires have randomly oriented with an average length of 600 nm for a deposition time of 15 min. As grown Si nanowires have shown indium nanoparticle (capped) on top of it confirming the Vapor Liquid Solid (VLS) growth mechanism. Transmission Electron Microscope (TEM) measurements have revealed pure and single crystalline nature of Si nanowires. The obtained results have indicated good progress towards finding alternative catalyst to gold for the synthesis of Si nanowires. (C) 2011 Elsevier B.V. All rights reserved.

Colloidal calcium nanoparticles: digestive ripening in the presence of a capping agent and coalescence of particles under an electron beam

The nanochemistry of calcium remains unexplored, which is largely due to the inaccessibility of calcium nanoparticles in an easy to handle form by conventional methods of synthesis as well as its highly reactive and pyrophoric nature. The synthesis of colloidal Ca nanoparticles by the solvated metal atom dispersion (SMAD) method is described. The as-prepared Ca-THF nanoparticles, which are polydisperse, undergo digestive ripening in the presence of a capping agent, hexadecyl amine (HDA) to afford highly monodisperse colloids consisting of 2-3 nm sized Ca-HDA nanoparticles. These are quite stable towards precipitation for long periods of time, thereby providing access to the study of the nanochemistry of Ca. Particles synthesized in this manner were characterized by UV-visible spectroscopy, high resolution electron microscopy, and powder X-ray diffraction methods. Under an electron beam, two adjacent Ca nanoparticles undergo coalescence to form a larger particle.

Isolating CP-violating gamma ZZ coupling in e(+)e(-) -> gamma Z with transverse beam polarizations

We revisit the process e(+)e(-) -> gamma Z at the ILC with transverse beam polarization in the presence of anomalous CP- violating gamma ZZ coupling lambda(1) and gamma gamma Z coupling lambda(2). We point out that if the final- state spins are resolved, then it becomes possible to fingerprint the anomalous coupling Re lambda(1). 90% confidence level limit on Re lambda(1) achievable at ILC with center- of- mass energy of 500 GeVor 800 GeV with realistic initial beam polarization and integrated luminosity is of the order of few times of 10(-2) when the helicity of Z is used and 10(-3) when the helicity of gamma is used. The resulting corrections at quadratic order to the cross section and its influence on these limits are also evaluated and are shown to be small. The benefits of such polarization programmes at the ILC are compared and contrasted for the process at hand. We also discuss possible methods by which one can isolate events with a definite helicity for one of the final- state particles.

Growth of rutile TiO2 nanorods on TiO2 seed layer deposited by electron beam evaporation

Dense rutile TiO2 nanorods were grown on anatase TiO2 seed layer coated glass substrate by solution technique. The crystalline nature of nanorods has confirmed by transmission electron microscopy. The band gap of the TiO2 seed layer and nanorods were calculated using the UV-vis absorption spectrum and the band gap value of the anatase seed layer and rutile nanorods were 3.39 eV and 3.09 eV respectively. Water contact angle measurements were also made and showed that the contact angle of rutile nanorods was (134 degrees) larger than the seed layer contact angle (93 degrees). The RMS surface roughness of the TiO2 seed layer (0.384 nm) and nanorods film (18.5 nm) were measured by an atomic force microscope and correlated with their contact angle values. (C) 2011 Elsevier B.V. All rights reserved.

Spectral Element Approach to Wave Propagation in Uncertain Composite Beam Structures

This paper presents a study of the wave propagation responses in composite structures in an uncertain environment. Here, the main aim of the work is to quantify the effect of uncertainty in the wave propagation responses at high frequencies. The material properties are considered uncertain and the analysis is performed using Neumann expansion blended with Monte Carlo simulation under the environment of spectral finite element method. The material randomness is included in the conventional wave propagation analysis by different distributions (namely, the normal and the Weibul distribution) and their effect on wave propagation in a composite beam is analyzed. The numerical results presented investigates the effect of material uncertainties on different parameters, namely, wavenumber and group speed, which are relevant in the wave propagation analysis. The effect of the parameters, such as fiber orientation, lay-up sequence, number of layers, and the layer thickness on the uncertain responses due to dynamic impulse load, is thoroughly analyzed. Significant changes are observed in the high frequency responses with the variation in the above parameters, even for a small coefficient of variation. High frequency impact loads are applied and a number of interesting results are presented, which brings out the true effects of uncertainty in the high frequency responses. [DOI: 10.1115/1.4003945]

Generalization of the collision cone approach for motion safety in 3-D environments

Avoidance of collision between moving objects in a 3-D environment is fundamental to the problem of planning safe trajectories in dynamic environments. This problem appears in several diverse fields including robotics, air vehicles, underwater vehicles and computer animation. Most of the existing literature on collision prediction assumes objects to be modelled as spheres. While the conservative spherical bounding box is valid in many cases, in many other cases, where objects operate in close proximity, a less conservative approach, that allows objects to be modelled using analytic surfaces that closely mimic the shape of the object, is more desirable. In this paper, a collision cone approach (previously developed only for objects moving on a plane) is used to determine collision between objects, moving in 3-D space, whose shapes can be modelled by general quadric surfaces. Exact collision conditions for such quadric surfaces are obtained and used to derive dynamic inversion based avoidance strategies.

Reactive biased target ion beam deposited W-DLC nanocomposite thin films - Microstructure and its mechanical properties

Tungsten incorporated diamond like carbon (W-DLC) nanocomposite thin films with variable fractions of tungsten were deposited by using reactive biased target ion beam deposition technique. The influence of tungsten incorporation on the microstructure, surface topography, mechanical and tribological properties of the DLC were studied using X-ray photoelectron spectroscopy (XPS), Raman spectroscopy. Atomic force microscope (AFM), transmission electron microscopy (TEM), nano-indentation and nano-scratch tests. The amount of W in films gets increases with increasing target bias voltage and most of the incorporated W reacts with carbon to form WC nanoclusters. Using TEM and FFT pattern, it was found that spherical shaped WC nanoclusters were uniformly dispersed in the DLC matrix and attains hexagonal (W2C) crystalline structure at higher W concentration. On the other hand, the incorporation of tungsten led to increase the formation of C-sp(2) hybridized bonding in DLC network and which is reflected in the hardness and elastic modulus of W-DLC films. Moreover, W-DLC films show very low friction coefficient and increased adhesion to the substrate than the DLC film, which could be closely related to its unique nanostructure of the W incorporated thin films. (C) 2011 Elsevier B.V. All rights reserved.

Bending of metal-filled carbon nanotube under electron beam irradiation

Electron beam irradiation induced, bending of Iron filled, multiwalled carbon nanotubes is reported. Bending of both the carbon nanotube and the Iron contained within the core was achieved using two approaches with the aid of a high resolution electron microscope (HRTEM). In the first approach, bending of the nanotube structure results in response to the irradiation of a pristine kink defect site, while in the second approach, disordered sites induce bending by focusing the electron beam on the graphite walls. The HRTEM based in situ observations demonstrate the potential for using electron beam irradiation to investigate and manipulate the physical properties of confined nanoscale structures. Copyright 2012 Author(s). This article is distributed under a Creative Commons Attribution 3.0 Unported License. doi:10.1063/1.3688083]

Valence band offset at GaN/beta-Si3N4 and beta-Si3N4/Si(111) heterojunctions formed by plasma-assisted molecular beam epitaxy

Ultra thin films of pure beta-Si3N4 (0001) were grown on Si (111) surface by exposing the surface to radio- frequency nitrogen plasma with a high content of nitrogen atoms. Using beta-Si3N4 layer as a buffer layer, GaN epilayers were grown on Si (111) substrate by plasma-assisted molecular beam epitaxy. The valence band offset (VBO) of GaN/beta-Si3N4/ Si heterojunctions is determined by X-ray photoemission spectroscopy. The VBO at the beta-Si3N4 /Si interface was determined by valence-band photoelectron spectra to be 1.84 eV. The valence band of GaN is found to be 0.41 +/- 0.05 eV below that of beta-Si3N4 and a type-II heterojunction. The conduction band offset was deduced to be similar to 2.36 eV, and a change of the interface dipole of 1.29 eV was observed for GaN/ beta-Si3N4 interface formation. (c) 2011 Elsevier B.V. All rights reserved.

Wave propagation in single-walled carbon nanotube under longitudinal magnetic field using nonlocal Euler-Bernoulli beam theory

In the present work, the effect of longitudinal magnetic field on wave dispersion characteristics of equivalent continuum structure (ECS) of single-walled carbon nanotubes (SWCNT) embedded in elastic medium is studied. The ECS is modelled as an Euler-Bernoulli beam. The chemical bonds between a SWCNT and the elastic medium are assumed to be formed. The elastic matrix is described by Pasternak foundation model, which accounts for both normal pressure and the transverse shear deformation. The governing equations of motion for the ECS of SWCNT under a longitudinal magnetic field are derived by considering the Lorentz magnetic force obtained from Maxwell's relations within the frame work of nonlocal elasticity theory. The wave propagation analysis is performed using spectral analysis. The results obtained show that the velocity of flexural waves in SWCNTs increases with the increase of longitudinal magnetic field exerted on it in the frequency range: 0-20 THz. The present analysis also shows that the flexural wave dispersion in the ECS of SWCNT obtained by local and nonlocal elasticity theories differ. It is found that the nonlocality reduces the wave velocity irrespective of the presence of the magnetic field and does not influences it in the higher frequency region. Further it is found that the presence of elastic matrix introduces the frequency band gap in flexural wave mode. The band gap in the flexural wave is found to independent of strength of the longitudinal magnetic field. (C) 2011 Elsevier Inc. All rights reserved.

Structural Characterization and Ultraviolet Photoresponse of GaN Nanodots Grown by Molecular Beam Epitaxy

The present work explores the electrical transport and UV photoresponse properties of GaN nanodots (NDs) grown by molecular beam epitaxy (MBE). Single-crystalline wurtzite structure of GaN NDs is verified by X-ray diffraction and transmission electron microscopy (TEM). The interdigitated electrode pattern was created and current-voltage (I-V) characteristics of GaN NDs were studied in a metal-semiconductor-metal configuration. Dark I-V characteristics of lateral grown GaN NDs obeyed the Frenkel-Poole emission model, and the UV response of the device was stable and reproducible with on/off. The responsivity of the detectors is found to be 330 A/W with an external quantum efficiency of 1100%. (C) 2012 The Japan Society of Applied Physics

Pressure-sensitive paint on a truncated cone in hypersonic flow at incidences

The flow over a truncated cone is a classical and fundamental problem for aerodynamic research due to its three-dimensional and complicated characteristics. The flow is made more complex when examining high angles of incidence. Recently these types of flows have drawn more attention for the purposes of drag reduction in supersonic/hypersonic flows. In the present study the flow over a truncated cone at various incidences was experimentally investigated in a Mach 5 flow with a unit Reynolds number of 13.5�10 6m -1. The cone semi-apex angle is 15° and the truncation ratio (truncated length/cone length) is 0.5. The incidence of the model varied from -12° to 12° with 3° intervals relative to the freestream direction. The external flow around the truncated cone was visualised by colour Schlieren photography, while the surface flow pattern was revealed using the oil flow method. The surface pressure distribution was measured using the anodized aluminium pressure-sensitive paint (AA-PSP) technique. Both top and sideviews of the pressure distribution on the model surface were acquired at various incidences. AA-PSP showed high pressure sensitivity and captured the complicated flow structures which correlated well with the colour Schlieren and oil flow visualisation results. © 2012 Elsevier Inc.