Atlantic bottlenose dolphin (Tursiops truncatus) hearing threshold for brief broadband signals.

The hearing sensitivity of an Atlantic bottlenose dolphin (Tursiops truncatus) to both pure tones and broadband signals simulating echoes from a 7.62-cm water-filled sphere was measured. Pure tones with frequencies between 40 and 140 kHz in increments of 20 kHz were measured along with broadband thresholds using a stimulus with a center frequency of 97.3 kHz and 88.2 kHz. The pure-tone thresholds were compared with the broadband thresholds by converting the pure-tone threshold intensity to energy flux density. The results indicated that dolphins can detect broadband signals slightly better than a pure-tone signal. The broadband results suggest that an echolocating bottlenose dolphin should be able to detect a 7.62-cm diameter water-filled sphere out to a range of 178 m in a quiet environment. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effect of sexual hormone abnormalities on proximal femur bone mineral density in hemodialysis patients and the possible role of RANKL

Sexual hormone concentrations are commonly affected in chronic renal failure. The contribution of sex steroids to bone turnover regulation implies that sex steroid's dysfunction may be implicated in the emergence of renal osteodystrophy. This study was conducted to evaluate sex steroids and gonadotrophins in hemodialysis (HD) patients and to investigate their role in bone homeostasis in concert with other hormones and cytokines. Bone mineral density (BMD) at the proximal femur and intact parathyroid hormone (iPTH), osteoprotegerin, soluble receptor activator of NF-kappaB ligand (sRANKL), prolactin, total testosterone, estradiol, follicle-stimulating hormone (FSH), and luteinizing hormone (LH) were measured in serum samples in 42 patients, 21 men and 21 women, on maintenance HD therapy. Possible associations between clinical characteristics, biochemical parameters, and BMD values were investigated. In male HD patients, the testosterone concentration declined significantly with aging, whereas the estradiol level increased with longer duration of HD. Concurrently, testosterone correlated negatively with sRANKL concentrations (r=-0.520, p=0.016). Luteinizing hormone levels in male patients demonstrated statistically significant negative correlations with BMD values of the proximal femur. In the entire cohort of patients, FSH and LH were negatively associated with absolute values of proximal femur BMD. Gonadotrophin and sexual hormone concentrations in HD patients are associated with bone mineral status and consequently their derangements appear to contribute to the development of bone composition abnormalities in different types of renal osteodystrophy. Furthermore, testosterone's association with sRANKL levels in male HD patients suggests that RANKL may mediate the effect of testosterone on bone metabolism in these patients.     

Experimental studies on syngas catalytic combustion on Pt/Al2O3 in a microreactor

Synthesis gas (a mixture of CO and H₂) oxidation is studied over a supported Pt/Al₂O₃ catalyst in a novel microreactor fabricated for studying the intrinsic chemical kinetics of highly exothermic reactions. CO was found to significantly inhibit H₂ oxidation. In contrast, H₂ addition promotes CO oxidation at low mole fractions but has a small promoting effect at high hydrogen mole fractions. As a result, the apparent reaction order of H₂ changes from positive to zero. The change in hydrogen reaction order is associated with hysteresis. Possible mechanisms for the observed behavior are discussed.     

Polarization-entangled photon generation in a semiconductor quantum dot coupled to a cavity interacting with external fields

We theoretically investigate polarization-entangled photon generation using a semiconductor quantum dot embedded in a microcavity. The entangled states can be produced by the application of two cross-circularly polarized laser fields. The quantum dot nanostructure is considered as a four-level system (ground, two excitons and bi-exciton states), and the theoretical study relies on the dressed states scheme. The quantum correlations, reported in terms of the entanglement of formation, are extensively studied for several values of the important parameters of the quantum dot system as the bi-exciton binding energy, the decoherence times of the characteristic transitions, the quality factor of the cavity and the intensities of the applied fields.     

Multispectral processing for color particle image velocimetry

Since the adoption of digital video cameras and cross-correlation methods for particle image velocimetry (PIV), the use of color images has largely been abandoned. Recently, however, with the re-emergence of color-based stereo and volumetric techniques, and the extensive use of color microscopy, color imaging for PIV has again become relevant. In this work, we explore the potential advantages of color PIV processing by developing and proposing new methods for handling multi-color images. The first method uses cross-correlation of every color channel independently to build a color vector cross-correlation plane. The vector cross-correlation can then be searched for one or more peaks corresponding to either the average displacement of several flow components using a color ensemble operation, or for the individual motion of colored particles, each with a different behavior. In the latter case, linear unmixing is used on the correlation plane to separate each known particle type as captured by the different color channels. The second method introduces the use of quaternions to encode the color data, and the cross-correlation is carried out simultaneously on all colors. The resulting correlation plane can be searched either for a single peak, corresponding to the mean flow or for multiple peaks, with velocity phase separation to determine which velocity corresponds to which particle type. Each of these methods was tested using synthetic images simulating the color recording of noisy particle fields both with and without the use of a Bayer filter and demosaicing operation. It was determined that for single-phase flow, both color methods decreased random errors by approximately a factor of two due to the noise signal being uncorrelated between color channels, while maintaining similar bias errors as compared to traditional monochrome PIV processing. In multi-component flows, the color vector correlation technique was able to successfully resolve displacements of two distinct yet coupled flow components with errors similar to traditional grayscale PIV processing of a single phase. It should be noted that traditional PIV processing is bound to fail entirely under such processing conditions. In contrast, the quaternion methods frequently failed to properly identify the correct velocity and phase and showed significant cross talk in the measurements between particle types. Finally, the color vector method was applied to experimental color images of a microchannel designed for contactless dielectrophoresis particle separation, and good results were obtained for both instantaneous and ensemble PIV processing. However, in both the synthetic color images that were generated using a Bayer filter and the experimental data, a significant peak-locking effect with a period of two pixels was observed. This effect is attributed to the inherent architecture of the Bayer filter. In order to mitigate this detrimental artifact, it is suggested that improved image interpolation or demosaicing algorithms tuned for use in PIV be developed and applied on the color images before processing, or that cameras that do not use a Bayer filter and therefore do not require a demosaicing algorithm be used for color PIV.     

Effect of magnetic field on near-wall coherent structures and heat transfer in magnetohydrodynamic turbulent channel flow of low Prandtl number fluids

A numerical study is carried out of the magnetic field effects on the coherent structures and the associated heat transfer in a turbulent channel flow with constant temperature at the bottom (cold) and top (hot) walls. Results from direct numerical simulations are conditionally sampled in order to extract the dominant coherent structures in the near-wall region for flows with and without a uniform external magnetic field in the wall-normal direction. The Reynolds number based on the bulk velocity and the wall distance is 5600, while only a representative small Stuart number of 0.01 is explored. Two fluids with Prandtl numbers of 0.01 and 0.71 are studied. It is shown that the conditionally averaged quasi-streamwise vortices are modified by the magnetic field with their size being increased and their strength decreased. The underlying organized fluid motions are damped by the Lorentz force and the turbulent heat transfer related to the action of quasi-streamwise vortices is decreased by the magnetic field. For the higher Prandtl number fluid, a similarity between the coherent temperature and the coherent streamwise velocity fluctuations is observed for both types of flow. This is diminished for the lower Prandtl number fluid, especially in the magnetohydrodynamic flow, inhibiting the intrusion of cold (hot) fluid from the cold (hot) wall towards the central region.     

Multiple-Input-Buffer and Shared-Buffer Architectures for Optical Packet- and Burst-Switching Networks

We present an architecture for implementing optical buffers, based on the feed-forward-buffer concept, that can truly emulate input queuing and accommodate asynchronous packet and burst operation. The architecture uses wavelength converters and fixed-length delay lines that are combined to form either a multiple-input buffer or a shared buffer. Both architectures are modular, allowing the expansion of the buffer at a cost that grows logarithmically with the buffer depth, where the cost is measured in terms of the number of switching elements, and wavelength converters are employed. The architectural design also provides a tradeoff between the number of wavelength converters and their tunability. The buffer architectures proposed are complemented with scheduling algorithms that can guarantee lossless communication and are evaluated using physical-layer simulations to obtain their performance in terms of bit-error rate and achievable buffer size.