Application of adaptive time-frequency decomposition in ultrasonic NDE of highly-scattering materials

In the paper, adaptive time-frequency decomposition by basis pursuit (BP) is utilized to improve ultrasonic flaw detection in highly-scattering materials as an alternative to the Wavelet Transform technique. The detection of ultrasonic pulses using the BP is described. Computer simulation was performed to verify the signal detection improvements for an ultrasonic wave embodied in white noise, and numerical results show good detection even for signal-noise ratio (SNR) of -18 dB. The improvement in detection is experimentally verified using cast steel samples with artificial flaws.     

Critical behavior of metal-insulator transition in La1-(x)Sr(x)VO3

Critical behavior of the metal-insulator transition (MIT) coupled with spin/orbital correlations has been investigated for single crystals of La1-(x)Sr(x)VO3. In the paramagnetic (PM) metal phase (x > 0.260), the precursor to the MIT manifests itself as an enhancement of carrier effective mass. In the antiferromagnetic (AF) metal phase (0.178 < or = x < or = 0.260), the carrier density decreases and the correlation of the orbital seems to evolve towards the MIT (x = 0.178). In the AF insulating phase (x < 0.178), the distinct first-order structural phase transition occurs with the decrease of temperature, perhaps concomitantly with the orbital ordering.     

Phase-resolved optical coherence tomography and optical Doppler tomography for imaging blood flow in human skin with fast scanning speed and high velocity sensitivity

We have developed a novel phase-resolved optical coherence tomography (OCT) and optical Doppler tomography (ODT) system that uses phase information derived from a Hilbert transformation to image blood flow in human skin with fast scanning speed and high velocity sensitivity. Using the phase change between sequential scans to construct flow-velocity imaging, this technique decouples spatial resolution and velocity sensitivity in flow images and increases imaging speed by more than 2 orders of magnitude without compromising spatial resolution or velocity sensitivity. The minimum flow velocity that can be detected with an axial-line scanning speed of 400 Hz and an average phase change over eight sequential scans is as low as 10 microm/s, while a spatial resolution of 10 microm is maintained. Using this technique, we present what are to our knowledge the first phase-resolved OCT/ODT images of blood flow in human skin.     

Fragmentation of the two-phonon γ-vibration in166Er

Two-phonon γ-vibrational states in¹⁶⁶Er have been populated using Coulomb excitation. The K^π=4⁺ component of the vibration appears to be fragmented over several states, whereas only one K^π=0⁺ state is observed.     

Aspects of oscillating flames

Photography and chemieluminescence from CH radicals have been used to identify the reaction zones and quantify the areas and shapes of kerosene-fuelled flames with swirl numbers of 0.7 and 0.8 and an overall equivalence ratio of 0.25. The air flow was oscillated at a frequency of 350 Hz and the results suggest that the oscillations caused a sequence of vortex rings at the burner exit and that these distorted the reaction zone and increased its area in the near burner region leading to an overall shorter flame. For the swirl number of 0.7, the flame was lifted and the oscillations led to an increase in the average lift off length whereas the higher swirl number caused an attached flame with and without oscillations. The stretch rate, evaluated from the variation of the flame area in time, was higher for the lifted flame suggesting that lift off was caused by local extinction.     

Design and modeling of microwave photonic devices

Different types of finite element methods (FEMs) for microwave and optical waveguides are reviewed and are utilized for modeling of a traveling-wave (TW) optical modulator, as one of the typical microwave photonic devices. Using the quasi-TEM and the full-wave vector FEM solvers for microwave waveguides and the scalar FEM solver for optical waveguides, the behaviour of a TW Z-cut Ti:LiNbO3 Mach–Zehnder optical modulator with a ridge structure is investigated.     

A high-gain porous silicon metal–semiconductor–metal photodetector through rapid thermal oxidation and rapid thermal annealing

2 tungsten lamp at 1.83 mA excited by a 0.85-mW 675-nm laser diode. We also demonstrate that the dark current could be greatly reduced through rapid thermal oxidation and rapid thermal annealing. Received: 4 August 1997/Accepted: 28 May 1998     

ESR study of calix[4]arene by spin-trapping method

Electron spin resonance (ESR) measurements are introduced to investigate the interaction between 5,11,17,23-tetrabromo-25,26,27,28-tetramethoxycalix[4]arene (II ₄) and 2-methyl-2-nitrosopropane (MNP) or nitrosodurene (ND) which are used as spin-trapping reagents under ultraviolet irradiation. In most cases, the complicated ESR spectra were observed because of the overlap of ESR signals attributed to several spin adducts in different conformations or in an inclusion state. However, after the optimum amount of ND was added into theII ₄ solution, the ESR spectrum showed that each nitrogen hyperfine line was further split to 1:2:1 triplet lines, and this is a typical spectrum ascribed to the spin adduct of ND at one para position ofII ₄.     

Three-Body Phase Shift in One-Dimensional 2 + 1 Scattering

For a model of three particles on a line, subject to attractive delta-function interactions, we consider the phase shift. We do this from the point of view of the calculation of the S-matrix in a hyperspherical adiabatic basis (an adiabatic S-matrix), and for energies ranging from the (negative) energy of the two-body bound state to a total energy of zero. We derive analytical expansions and present numerical work, for different approximations, and compare with the exact results that we obtain from the work of McGuire, whose model we have borrowed. We show that the simplest adiabatic approximation gives results that are qualitatively wrong, but that better approximations yield, for most of our range, excellent agreement with the exact result. Understanding the threshold behaviour, however, requires a zero-energy three-body bound state, or resonance, previously unsuspected for this model. The methods developed for the case of the simplest adiabatic approximation also yield threshold and low-energy results applicable to the two-body problem in two dimensions. Received December 23, 1996; revised May 13, 1997; accepted for publication June 19, 1997     

Formation of small single-layer and nested BN cages under electron irradiation of nanotubes and bulk material

12 N₁₂, B₁₆N₁₆ and B₂₈N₂₈ octahedra which were predicted to be magic clusters for the BN system from electronic structure calculations. Received: 2 March 1998