Solvent Free Microwave Assisted Isomerization of N‐Nitropyrazoles

This paper describes solvent‐free isomerization of N‐nitropyrazoles under microwave irradiation to achieve a new green chemistry procedure for the synthesis of C‐ nitropyrazoles in good to excellent yields. The presented procedure requires less time, offers simplified workup procedure, needs no obnoxious solvents, and may be used for the preparation of several C‐nitropyrazoles.     

Study of light-induced annealing effects in a-Si:H thin films

Light-induced metastability was examined in hydrogenated amorphous silicon thin films using a 500 W xenon lamp and a 10 mW HeCd laser. Positron beam annihilation spectroscopy (PAS) and fourier transform infrared spectroscopy (FTIR) were examined to investigate the effects of light on the structural properties of the films. The experimental results exhibited significant decrease in the S-parameter of the PAS, indicating marked reduction in the defect density of the films. The FTIR spectroscopy showed significant reduction in the transmission coefficient of IR radiation at frequencies corresponding to Si–H and Si–H₃ phonon modes, indicating that the observed annealing effects were due to light-induced formation of Si–H and Si–H₃ bonds. A second thermal annealing process conducted after the light exposure experiment resulted in a further substantial decrease in defect density for the sample exposed to HeCd laser. The experimental results are explained by a competing, light induced, dangling bond creation/annealing process, in which the incoming photons caused the annealing of dangling bonds, particularly those at around the voids. However, in the bulk region, the photons caused both the breaking of weak Si–Si bonds as well as the annealing of dangling bonds.     

Direct Imaging of Atomic Ordering in Undoped and La-Doped Pb(Mg1/3Nb2/3)O3

In this paper, we report the first direct observations of local ordering in undoped and La-doped Pb(Mg_1/3Nb_2/3)O₃ (PMN) on an atomic scale by high-resolution (∼1.26 Å) Z -contrast imaging. The 1:1 ordering occurs by a variation in the occupancy of Mg and Nb cations between B^I and B^II sublattices. In ordered regions, the B^II sublattice is dominantly occupied by Nb cations, but a small Mg occupancy cannot be excluded. The Mg cations were found to dominantly occupy the B^I sublattice. Within the B^I sublattice, the local Mg/Nb ratio was found to vary among the various B^I sublattices. The results show that the random-site model, rather than the space-charge model, is a better structural model for the 1:1 ordering observed in PMN. A random distribution of Mg and Nb cations on the B^I sublattice within 1:1 ordered regions is believed to be responsible for the relaxor behavior of mixed B-site cation relaxors, such as PMN.     

Studies of high DC current induced degradation in III-V nitridebased heterojunctions

We report experiments on high dc current stressing in commercial III-V nitride based heterojunction light-emitting diodes. Stressing currents ranging from 100 mA to 200 mA were used. Degradations in the device properties were investigated through detailed studies of the current-voltage (I-V) characteristics, electroluminescence, deep-level transient Fourier spectroscopy and flicker noise. Our experimental data demonstrated significant distortions in the I-V characteristics subsequent to electrical stressing. The room temperature electroluminescence of the devices exhibited a 25% decrement in the peak emission intensity. Concentration of the deep-levels was examined by deep-level transient Fourier spectroscopy, which indicated an increase in the density of deep-traps from 2.7×10¹³ cm^-3 to 4.2×10¹³ cm^-3 at E₁=E _C-1.1 eV. The result is consistent with our study of 1/f noise, which exhibited up to three orders of magnitude increase in the voltage noise power spectra. These traps are typically located at energy levels beyond the range that can be characterized by conventional techniques including DLTS. The two experiments, therefore, provide a more complete picture of trap generation due to high dc current stressing     

Intelligent distributed simulation and control of power plants

This paper presents summaries of five research and development activities in intelligent distributed simulation and control of power plants which were presented in a panel session of the same name at the IEEE Power Engineering Society Winter Meeting on February 6, 1997 in New York City. Each of the panelists discussed methods of how they have incorporated intelligent systems techniques into their research and development efforts in power plant control. The panel was organized by the Working group on intelligent methods in station control, station control subcommittee, and the energy development and power generation committee of the IEEE power engineering society     

Electrochemical corrosion behaviour of Pb-free Sn-8.5Zn-0.05Al-XGa and Sn-3Ag-0.5Cu alloys in chloride containing aqueous solution

The electrochemical corrosion behaviour of Pb-free Sn-8.5Zn-0.05Al-XGa and Sn-3Ag-0.5Cu alloys was investigated in 3.5% NaCl solution by using potentiodynamic polarization techniques. The results obtained from polarization studies revealed that there was a negative shift in the corrosion potential with increase in Ga content from 0.02 to 0.2 wt% in the Sn-8.5Zn-0.05Al-XGa alloy. These changes were also reflected in the corrosion current density (I_corr) value, corrosion rate and linear polarization resistance (LPR) of the four element alloy. However, for Sn-3Ag-0.5Cu alloy a significant increase in the corrosion rate and corrosion current density was observed as compared to the four element alloys. SIMS depth profile results established that ZnO present on the outer surface of Sn-8.5Zn-0.05Al-0.05Ga alloy played a major role in the formation of the oxide film. Oxides of Sn, Al and Ga contributed a little towards the formation of film on the outer surface of the alloy. On the other hand, Ag₂O was primarily responsible for the formation of the oxide film on the outer surface of Sn-3Ag-0.5Cu alloy.     

Applications of the Phase-Coded Generalized Hough Transform to Feature Detection,Analysis, and Segmentation of Digital Microstructures

The generalized Hough transform is a common technique for feature detection in image processing. In this paper, we develop a size invariant Hough framework for the detection of arbitrary shapes in three dimensional digital microstructure datasets. The Hough transform is efficiently implemented via kernel convolution with complex Hough filters, where shape is captured in the magnitude of the filter and scale in the complex phase. In this paper, we further generalize the concept of a Hough filter by encoding other parameters of interest (e.g. orientation of plate or fiber constituents) in the complex phase, broadening the applicability of Hough transform techniques. We demonstrate the application of these techniques to feature detection in micrographs (2-D) and three-dimensional (3-D) microstructure datasets, and explore their utility to the closely related applications of feature based image segmentation and calculation of 3-D microstructure metrics.     

SEEING DOUBLE: THE SUBJECT OF VISION IN LEE FRIEDLANDER’S SELF-PORTRAITURE

American photographer Lee Friedlander’s photographs are often deemed to be unreadable. This critical assessment of his work is principally based on his manipulation of reflection, framing, and superimposition. This essay takes these manipulations as its subject. I suggest one method of reading the unreadable, focusing particularly on two self-portraits: Tallahassee, Florida 1969 and Madison, Wisconsin 1966. My approach weaves together the ideas of Jacques Lacan and Homi Bhabha. In the first section, I place Lacan’s concept of the stain into dialogue with the recurring appearance of Friedlander’s own shadow in his self-portraiture. In the second, I bring Bhabha into conversation with Lacan, showing crossovers in how they conceptualise reflections. I argue that Tallahassee and Madison visually articulate these crossovers. In the third, I use Bhabha’s concept of doubling to approach the two photographs’ delineation of the Lacanian gaze. In forging links between Friedlander, Lacan, and Bhabha, I propose two complementary ideas. The first is that Friedlander’s photographs help to illustrate commonality between Lacan’s and Bhabha’s work. The second is that Lacan and Bhabha help us read Friedlander’s often perplexing self-portraits. By expressing an absence of the self, these photographs comment on the impossibility of self-portraiture.