Ultrasonic guided wave parameters for detection of axial cracks in feeder pipes of PHWR nuclear power plants

The dispersion curves for the feeder pipes in PHWR nuclear power plants were determined. The wave modes used for the detection of notches in the feeder pipe were confirmed as F(m,2) and/or L(0,1) by an analysis of short time Fourier transformation (STFT). The axial notches in the straight pipe were not detectable, but an axial notch in a bent pipe was detected with the mode at the frequency of 500 kHz. Initial F(m,2) and/or L(0,1) modes contains a circumferential displacement and might be converted to certain complicated modes in the bent region, which is sensitive to the axial notch. The circumferential guided wave technique was also applied for quantitative evaluation of the axial notches. The waves generated by a rocking motion of the transducer along the circumferential direction were estimated as the circumferential guided waves after a review of the acquired data and the dispersion curves.     

Fabrication of concave refractive microlens arrays in solgel glass by a simple proximity-effect-assisted reflow technique

We report a simple method for fabricating a concave refractive microlens array (MLA) in solgel glass by using a proximity-effect-assisted reflow technique. The solgel concave refractive MLA that we fabricated had excellent surface smoothness; good dimensional conformity, with an 8.23% nonuniformity of the microlens elements; and structural perfection, with a biggest deviation of 1% from a perfect concave spherical crown. The relative error between the measured and the designed values of the concave MLA's focal length was only 1.83%. Compared with the conventional fabrication techniques for concave MLAs, the proposed method has significant advantages including simplicity, low cost, good element conformity, and smooth device surface.     

Origins of selectivities in proline-catalyzed alpha-aminoxylations

The mechanisms, transition structures, regioselectivity, and stereoselectivity of proline-catalyzed alpha-aminoxylation reactions were studied with density functional theory (B3LYP/6-31G(d)). The most favorable transition structure involves the nucleophilic attack of the (E)-proline enamine to the oxygen of the nitrosobenzene with proton transfer from the carboxylic acid to the nitrogen. Enamine attack to the oxygen is favored over the attack on the nitrogen due to the greater basicity of the nitrogen. Previously proposed zwitterionic enaminium pathways are highly disfavored due to the energetic penalty associated with charge separations.     

Pressure-induced structural and electronic transition in KTb(MoO4)2 through Raman and optical studies

Raman and optical absorption studies under pressure have been conducted on KTb(MoO₄)₂ up to 35.5 GPa. A phase transformation occurs at 2.7 GPa when the crystal is pressurized at ambient temperature in a hydrostatic pressure medium. The sample changes to a deep yellow color at the transition and visibly contracts in theα-axis direction. The color shifts to red on further pressure increase. The Raman spectral features and the X-ray powder pattern change abruptly at the transition indicating a structural change. The pressure-induced transition appears to be a property of the layer-type alkali rare earth dimolybdates. However, the color change at the transition in KTb(MoO₄)₂ is rather unusual and is attributed to a valence change in Tb initiated by the structural transition and consequent intervalence charge transfer between Tb and Mo.In situ high pressure X-ray diffraction data suggest that phase II could be orthorhombic with a unit cell having 3 to 4% smaller volume than that of phase I.     

Stationary Headband for Clinical Time-of-Flight Optical Imaging at the Bedside

Conventional brain-imaging modalities may be limited by high cost, difficulty of bedside use, noncontinuous operation, invasiveness or an inability to obtain measurements of tissue function, such as oxygenation during stroke. Our goal was to develop a bedside clinical device able to generate continuous, noninvasive, tomographic images of the brain using low-power nonionizing optical radiation. We modified an existing stage-based time-of-flight optical tomography system to allow imaging of patients under clinical conditions. First, a stationary headband consisting of thin, flexible optical fibers was constructed. The headband was then calibrated and tested, including an assessment of fiber lengths, the existing system software was modified to collect headband data and to perform simultaneous collection of data and image reconstruction, and the existing hardware was modified to scan optically using this headband. The headband was tested on resin models and allowed for the generation of tomographic images in vitro; the headband was tested on critically ill infants and allowed for optical tomographic images of the neonatal brain to be obtained in vivo.     

Cations of aldehydes and ketones: an ESR study

Exposure of dilute solutions of acetaldehyde, acetone and cyclohexanone in fluorotrichloromethane to ⁶⁰Co γ-rays at 77 K gave the corresponding radical cations, characterised by ESR spectroscopy.     

Radical cations of aldehydes and ketones

We confirm the observation made by Snow and Williams in the previous letter that the quartet substructure observed in the ESR spectrum of acetaldehyde is due to hyperfine coupling to a single chlorine nucleus of the solvent, fluorotrichloromethane. Reasons for this reversible interaction, and its absence for other similar cations are discussed.     

Simulation of flexoelectricity effect on imprint behavior of ferroelectric thin films

The impact of flexoelectricity on the imprint behavior in ferroelectric thin films has been investigated within the framework of Landau-Khalatnikov theory, by incorporating the coupling effect between the stress gradient and polarization. It is found that the imprint phenomenon can be in part induced by flexoelectricity. In the presence of flexoelectric coupling, the compressive stress shifts the hysteresis loop to the negative electric field axis, but the tensile stress shifts it to the opposite direction, which is in good agreement with experimental result. Besides, the characteristic length of stress distribution has a significant influence on the upper part of hysteresis loop. It highlights the pressing need to avoid the stress gradient in order to prevent degradation of device performance in ferroelectric thin films.