Experiments on through-wall imaging using ultra wideband radar

Through-wall imaging (TWI) may provide vital information on interior environment in cases when physically entering such environment would pose danger to the person involved. The concept of ultra wideband radar (UWB radar) is an emerging technology, which offers high spatial resolution, as opposed to narrow band radars. Thus, TWI applications using UWB radar have become a growing field of research with several applications in the civil and defense areas such as rescue and surveillance. For this study, a prototype system of UWB radar to TWI has been built. Analyses and result to several kinds of experiments have been presented, that is, detection and visualization of metallic targets behind wooden board wall and concrete blocks wall. The results are encouraging and show the advantages of using UWB radar for TWI. (C) 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett, 54:339-344, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26543

Structural refinement, growth process, photoluminescence and photocatalytic properties of (Ba1-xPr2x/3)WO4 crystals synthesized by the coprecipitation method

Barium praseodymium tungstate (Ba1-xPr2x/3)WO4 crystals with (x = 0, 0.01, and 0.02) were prepared by the coprecipitation method. These crystals were structurally characterized by X-ray diffraction (XRD), Rietveld refinements, Fourier-transform Raman (FT-Raman) and Fourier-transform infrared (FT-IR) spectroscopies. The shape and size of these crystals were observed by field emission scanning electron microcopy (FE-SEM). Their optical properties were investigated by ultraviolet visible (UV-vis) absorption and photoluminescence (PL) measurements. Moreover, we have studied the photocatalytic (PC) activity of crystals for degradation of rhodamine B (RhB) dye. XRD patterns, Rietveld refinements data, FT-Raman and FT-IR spectroscopies indicate that all crystals exhibit a tetragonal structure without deleterious phases. FT-Raman spectra exhibited 13 Raman-active modes in a range from 50 to 1000 cm(-1), while FT-IR spectra have 8 infrared active modes in a range from 200 to 1050 cm(-1). FE-SEM images showed different shapes (bonbon-, spindle-, rice-and flake-like) as well as a reduction in the crystal size with an increase in Pr3+ ions. A possible growth process was proposed for these crystals. UV-vis absorption measurements revealed a decrease in optical band gap values with an increase of Pr3+ into the matrix. An intense green PL emission was noted for (Ba1-xPr2x/3)WO4 crystals (x = 0), while crystals with (x = 0.01 and 0.02) produced a reduction in the wide band PL emission and the narrow band PL emission which is related to f-f transitions from Pr3+ ions. High photocatalytic efficiency was verified for the bonbon-like BaWO4 crystals as a catalyst in the degradation of the RhB dye after 25 min under UV-light. Finally, we discuss possible mechanisms for PL and PC properties of these crystals.

Assessing biophysical variable parameters of bean crop with hyperspectral measurements

Recently high spectral resolution sensors have been developed, which allow new and more advanced applications in agriculture. Motivated by the increasing importance of hyperspectral remote sensing data, the need for research is important to define optimal wavebands to estimate biophysical parameters of crop. The use of narrow band vegetation indices (VI) derived from hyperspectral measurements acquired by a field spectrometer was evaluated to estimate bean (Phaseolus vulgaris L.) grain yield, plant height and leaf area index (LAI). Field canopy reflectance measurements were acquired at six bean growth stages over 48 plots with four water levels (179.5; 256.5; 357.5 and 406.2 mm) and tree nitrogen rates (0; 80 and 160 kg ha-1) and four replicates. The following VI was analyzed: OSNBR (optimum simple narrow-band reflectivity); NB_NDVI (narrow-band normalized difference vegetation index) and NDVI (normalized difference index). The vegetation indices investigated (OSNBR, NB_NDVI and NDVI) were efficient to estimate LAI, plant height and grain yield. During all crop development, the best correlations between biophysical variables and spectral variables were observed on V4 (the third trifoliolate leaves were unfolded in 50 % of plants) and R6 (plants developed first flowers in 50 % of plants) stages, according to the variable analyzed.

New Improved Version of J 1 ...J 4 Interferometry Method and its Application to Nanometric Vibration Measurements

Piezoelectric ceramics, such as PZT, can generate subnanometric displacements, bu t in order to generate multi- micrometric displacements, they should be either driven by high electric voltages (hundreds of volts ), or operate at a mechanical resonant frequency (in narrow band), or have large dimensions (tens of centimeters). A piezoelectric flextensional actuator (PFA) is a device with small dimensions that can be driven by reduced voltages and can operate in the nano- and micro scales. Interferometric techniques are very adequate for the characterization of these devices, because there is no mechanical contact in the measurement process, and it has high sensitivity, bandwidth and dynamic range. A low cost open-loop homodyne Michelson interferometer is utilized in this work to experimentally detect the nanovi brations of PFAs, based on the spectral analysis of the interfero metric signal. By employing the well known J 1 ...J 4 phase demodulation method, a new and improved version is proposed, which presents the following characteristics: is direct, self-consistent, is immune to fading, and does not present phase ambiguity problems. The proposed method has resolution that is similar to the modified J 1 ...J 4 method (0.18 rad); however, differently from the former, its dynamic range is 20% larger, does not demand Bessel functions algebraic sign correction algorithms and there are no singularities when the static phase shift between the interferometer arms is equal to an integer multiple of  /2 rad. Electronic noise and random phase drifts due to ambient perturbations are taken into account in the analysis of the method. The PFA nanopositioner characterization was based on the analysis of linearity betw een the applied voltage and the resulting displacement, on the displacement frequency response and determination of main resonance frequencies.

First principles calculations for vacancies and antisites in PbSe and PbTe: bulk and nanowire.

The energetic stability and the electronic properties of vacancies (VX) and antisites (XY) in PbSe and PbTe are investigated. PbSe and PbTe are narrow band gap semiconductors and have the potential to be used in infrared detectors, laser, and diodes. They are also of special interest for thermoelectric devices (TE). The calculations are based in the Density Functional Theory (DFT) and the General Gradient Approximation (GGA) for the exchange-correlation term, as implemented in the VASP code. The core and valence electrons are described by the Projected Augmented Wave (PAW) and the Plane Wave (PW) methods, respectively. The defects are studied in the bulk and nanowire (NW) system. Our results show that intrinsec defects (vacancies and antisites) in PbTe have lower formation energies in the NW as compared to the bulk and present a trend in migrate to the surface of the NW. For the PbSe we obtain similar results when compare the formation energy for the bulk and NW. However, the Pb vacancy and the antisites are more stable in the core of the NW. The intrinsec defects are shallow defects for the bulk system. For both PbSe and PbTe VPb is a shallow acceptor defect and VSe and VT e are shallow donor defects for the PbSe and PbTe, respectively. Similar electronic properties are observed for the antisites. For the Pb in the anion site we obtain an n-type semiconductor for both PbSe and PbTe, SeP b is a p-type for the PbSe, and T eP b is a n-type for PbTe. Due the quantum con¯nement effects present in the NW (the band gap open), these defects have different electronic properties for the NW as compared to the bulk. Now these defects give rise to electronic levels in the band gap of the PbTe NW and the VT e present a metallic character. For the PbSe NW a p-type and a n-type semiconductor is obtained for the VP b and P bSe, respectively. On the other hand, deep electronic levels are present in the band gap for the VSe and SePb. These results show that due an enhanced in the electronic density of states (DOS) near the Fermi energy, the defective PbSe and PbTe are candidates for efficient TE devices.

EDGE-PRESERVING SPECKLE TEXTURE REMOVAL BY INTERFERENCE-BASED SPECKLE FILTERING FOLLOWED BY ANISOTROPIC DIFFUSION

Ultrasonography has an inherent noise pattern, called speckle, which is known to hamper object recognition for both humans and computers. Speckle noise is produced by the mutual interference of a set of scattered wavefronts. Depending on the phase of the wavefronts, the interference may be constructive or destructive, which results in brighter or darker pixels, respectively. We propose a filter that minimizes noise fluctuation while simultaneously preserving local gray level information. It is based on steps to attenuate the destructive and constructive interference present in ultrasound images. This filter, called interference-based speckle filter followed by anisotropic diffusion (ISFAD), was developed to remove speckle texture from B-mode ultrasound images, while preserving the edges and the gray level of the region. The ISFAD performance was compared with 10 other filters. The evaluation was based on their application to images simulated by Field II (developed by Jensen et al.) and the proposed filter presented the greatest structural similarity, 0.95. Functional improvement of the segmentation task was also measured, comparing rates of true positive, false positive and accuracy. Using three different segmentation techniques, ISFAD also presented the best accuracy rate (greater than 90% for structures with well-defined borders). (E-mail: fernando.okara@gmail.com) (C) 2012 World Federation for Ultrasound in Medicine & Biology.