Now showing 1 - 10 of 10
  • Publication
    Experimental Detection of Sudden Stiffness Change in a Structural System Employing Laser Doppler Vibrometry
    (Erredi Grafiche Editoriali, 2012-06-20) ; ; ;
    Sudden changes in the stiffness of a structure are often indicators of structural damage. Detection of such sudden stiffness change from the vibrations of structures is important for Structural Health Monitoring (SHM) and damage detection. Non-contact measurement of these vibrations is a quick and efficient way for successful detection of sudden stiffness change of a structure. In this paper, we demonstrate the capability of Laser Doppler Vibrometry to detect sudden stiffness change in a Single Degree Of Freedom (SDOF) oscillator within a laboratory environment. The dynamic response of the SDOF system was measured using a Polytec RSV-150 Remote Sensing Vibrometer. This instrument employs Laser Doppler Vibrometry for measuring dynamic response. Additionally, the vibration response of the SDOF system was measured through a MicroStrain G-Link Wireless Accelerometer mounted on the SDOF system. The stiffness of the SDOF system was experimentally determined through calibrated linear springs. The sudden change of stiffness was simulated by introducing the failure of a spring at a certain instant in time during a given period of forced vibration. The forced vibration on the SDOF system was in the form of a white noise input. The sudden change in stiffness was successfully detected through the measurements using Laser Doppler Vibrometry. This detection from optically obtained data was compared with a detection using data obtained from the wireless accelerometer. The potential of this technique is deemed important for a wide range of applications. The method is observed to be particularly suitable for rapid damage detection and health monitoring of structures under a model-free condition or where information related to the structure is not sufficient.
  • Publication
    Block copolymer mediated stabilization of sub-5 nm superparamagnetic nickel nanoparticles in an aqueous medium
    The paper presents a facile method for decreasing the size of water dispersible Ni nanoparticles from 30 nm to 3 nm by the incorporation of a passivating surfactant combination of pluronic triblock copolymer and oleic acid into a wet chemical reduction synthesis. A detailed study revealed that the size of the Ni nanoparticles is critically governed not only by the concentration of the tri block copolymers but also dependent on the hydrophobic nature of the micelle-core formed. The synthesized Ni nanoparticles were thoroughly characterized by TEM, XRD, XPS and temperature and field dependent magnetic measurements along with a comprehensive FTIR analysis to predict a possible mechanism of formation.
      817Scopus© Citations 35
  • Publication
    Centimetre scale assembly of vertically aligned and close packed semiconductor nanorods from solution
    (RSC publications, 2009-09-08) ;
    Assembly of CdS nanorods (8 × 100 nm) into vertically aligned arrays over very large areas on a substrate either as a monolayer or several multilayers is shown by electrophoresis.
      449Scopus© Citations 53
  • Publication
    Metal surface nucleated supercritical fluid–solid–solid growth of Si and Ge/SiOx core–shell nanowires
    High yields of single-crystalline silicon nanowires and germanium/silicon oxide core-shell nanostructures were synthesized using a supercritical fluid-solid-solid growth mechanism. The formation of the one-dimensional nanostructures was investigated on stainless steel and titanium reactor cell walls. The nanowire growth is diffusion controlled with no catalyst particles being observed at the tip of the nanowires, which is contrary to the characteristic feature of a one-dimensional growth based on the vapor-liquid-solid mechanism. The diameter and length of the nanowires were in the ranges of 30-60 nm and 1-10 µm, respectively, as found by high-resolution electron microscopy. The nanowires were characterized by transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX) and scanning electron microscopy (SEM).
      630Scopus© Citations 21
  • Publication
    Directing semiconductor nanorod assembly into 1D or 2D supercrystals by altering the surface charge
    Coulomb repulsion due to the surface charge on semi-conductor nanorods works against the dipole–dipole attraction that tends to direct the nanorods to self-assemble; the nature of this self-assembly for CdSe nanorods can be thus altered by pyridine washing, which charges the rods surface—thereby allowing the Coulomb repulsion to tailor the alignment.
      719Scopus© Citations 49
  • Publication
    Size controlled gold tip growth onto II–VI nanorods
    Gold tip size and multiplicity is controlled in hybrid gold-semiconductor nanorods (CdS-Au, CdSe-Au and CdTe-Au) in fast reaction times of less than 2 minutes by optimising precursor type, concentration, and temperature. Controllable gold tips up to as large as 40 nm on a rod diameter of 7 nm are reported with the tip size shown to be directly related to the redox potentials of the dangling atoms on the nanorod and the gold chloride precursors (mono or trivalent). The preference for symmetric (both ends) over asymmetric (single end) is achieved by simply elevating the reaction temperature to 80ºC without changing the reaction time. TEM and XRD analysis were preformed to verify both the gold nanoparticle size and crystallinity of the hybrid nanostructures. Increased quenching of nanorod emission is observed as the size of the gold tip increases suggesting optimisation of charge transfer between the semiconductor and the metal.
      752Scopus© Citations 36
  • Publication
    Spontaneous room temperature elongation of CdS and Ag2S nanorods via oriented attachment
    Spontaneous elongation from nanorod to nanowire in the presence of an amine is reported for nanocrystals of cadmium sulfide and silver sulfide (cation exchanged from CdS). Elongation occurs instantaneously where the final aspect ratio is a controllable multiple of the original nanorod length. Transmission electron microscopy (TEM) analysis reveals the influential factors on the attachment processare the concentration of amine, duration and temperature of the reaction. The elongated nanorods are further characterized by X-ray diffraction (XRD), photoluminescence (PL), ultraviolet-visible spectroscopy(UV-vis) and X-ray photoelectron spectroscopy (XPS). A mechanism of oriented attachment is evidenced by the doubling in length of asymmetrically gold tipped CdS nanorods with the corresponding absence of elongation in symmetrically tipped nanorods.
      855Scopus© Citations 86
  • Publication
    A comprehensive study of the delay vector variance method for quantification of nonlinearity in dynamical systems
    Although vibration monitoring is a popular method to monitor and assess dynamic structures, quantification of linearity or nonlinearity of the dynamic responses remains a challenging problem. We investigate the delay vector variance (DVV) method in this regard in a comprehensive manner to establish the degree to which a change in signal nonlinearity can be related to system nonlinearity and how a change in system parameters affects the nonlinearity in the dynamic response of the system. A wide range of theoretical situations are considered in this regard using a single degree of freedom (SDOF) system to obtain numerical benchmarks. A number of experiments are then carried out using a physical SDOF model in the laboratory. Finally, a composite wind turbine blade is tested for different excitations and the dynamic responses are measured at a number of points to extend the investigation to continuum structures. The dynamic responses were measured using accelerometers, strain gauges and a Laser Doppler vibrometer. This comprehensive study creates a numerical and experimental benchmark for structurally dynamical systems where output-only information is typically available, especially in the context of DVV. The study also allows for comparative analysis between different systems driven by the similar input.
      582Scopus© Citations 16
  • Publication
    Electrophoretic deposition of poly(3-decylthiophene) onto gold-mounted cadmium selenide nanorods
    Molecular mechanisms of electrophoretic deposition (EPD) of poly(3-decylthiophene) (P3DT) molecules onto vertically aligned cadmium selenide arrays have been studied using large-scale, nonequilibrium molecular dynamics (MD), in the absence and presence of static external electric fields. The field application and larger polymer charges accelerated EPD. Placement of multiple polymers at the same lateral displacement from the surface reduced average deposition times due to “crowding”, giving monolayer coverage. These findings were used to develop and validate Brownian dynamics simulations of multilayer polymer EPD in scaled-up systems with larger inter-rod spacings, presenting a generalized picture in qualitative agreement with random sequential adsorption.
      700Scopus© Citations 6
  • Publication
    A facile spin-cast route for cation exchange of multilayer perpendicularly-aligned nanorod assemblies
    A facile spin cast route was developed to convert perpendicularly aligned nanorod assemblies of cadmium chalcogenides into their silver and copper analogues. The assemblies are rapidly cation exchanged without affecting either the individual rod dimensions or collective superlattice order extending over several multilayers.
      770Scopus© Citations 36