Testing the odontocete acoustic prey debilitation hypothesis: no stunning results

The hypothesis that sounds produced by odontocetes can debilitate fish was examined. The effects of simulated odontocete pulsed signals on three species of fish commonly preyed on by odontocetes were examined, exposing three individuals of each species as well as groups of four fish to a high-frequency click of a bottlenose dolphin [peak frequency (PF) 120 kHz, 213-dB peak-to-peak exposure level (EL)], a midfrequency click modeled after a killer whale's signal (PF 55 kHz, 208-dB EL), and a low-frequency click (PF 18 kHz, 193-dB EL). Fish were held in a 50-cm diameter net enclosure immediately in front of a transducer where their swimming behavior, orientation, and balance were observed with two video cameras. Clicks were presented at constant rates and in graded sweeps simulating a foraging dolphin's "terminal buzz." No measurable change in behavior was observed in any of the fish for any signal type or pulse modulation rate, despite the fact that clicks were at or near the maximum source levels recorded for odontocetes. Based on the results, the hypothesis that acoustic signals of odontocetes alone can disorient or "stun" prey cannot be supported.     

The use of trehalose in the preparation of specimens for molecular electron microscopy

Biological specimens have to be prepared for imaging in the electron microscope in a way that preserves their native structure. Two-dimensional (2D) protein crystals to be analyzed by electron crystallography are best preserved by sugar embedding. One of the sugars often used to embed 2D crystals is trehalose, a disaccharide used by many organisms for protection against stress conditions. Sugars such as trehalose can also be added to negative staining solutions used to prepare proteins and macromolecular complexes for structural studies by single-particle electron microscopy (EM). In this review, we describe trehalose and its characteristics that make it so well suited for preparation of EM specimens and we review specimen preparation methods with a focus on the use of trehalose.     

Effects of low-frequency biasing on spontaneous otoacoustic emissions: amplitude modulation

The dynamic effects of low-frequency biasing on spontaneous otoacoustic emissions (SOAEs) were studied in human subjects under various signal conditions. Results showed a combined suppression and modulation of the SOAE amplitudes at high bias tone levels. Ear-canal acoustic spectra demonstrated a reduction in SOAE amplitude and growths of sidebands while increasing the bias tone level. These effects varied depending on the relative strength of the bias tone to a particular SOAE. The SOAE magnitudes were suppressed when the cochlear partition was biased in both directions. This quasi-static modulation pattern showed a shape consistent with the first derivative of a sigmoid-shaped nonlinear function. In the time domain, the SOAE amplitudes were modulated with the instantaneous phase of the bias tone. For each biasing cycle, the SOAE envelope showed two peaks each corresponded to a zero crossing of the bias tone. The temporal modulation patterns varied systematically with the level and frequency of the bias tone. These dynamic behaviors of the SOAEs are consistent with the shifting of the operating point along the nonlinear transducer function of the cochlea. The results suggest that the nonlinearity in cochlear hair cell transduction may be involved in the generation of SOAEs.     

Quark-hadron duality in neutron (3He) spin structure

We present experimental results of the first high-precision test of quark-hadron duality in the spin-structure function g_{1} of the neutron and 3He using a polarized 3He target in the four-momentum-transfer-squared range from 0.7 to 4.0 (GeV/c);{2}. Global duality is observed for the spin-structure function g_{1} down to at least Q;{2}=1.8 (GeV/c);{2} in both targets. We have also formed the photon-nucleon asymmetry A1 in the resonance region for 3He and found no strong Q2 dependence above 2.2 (GeV/c);{2}.     

Felkin–Anh is not enough

The understanding of the electronic effects of the diastereoselective addition of a nucleophile to a polar substituted aldehyde or ketone is not complete, with several theories competing to explain the data. For numerous hydride reductions of 3‐X‐2‐butanones (X = F, Cl, Br), the selectivity for the major syn isomer is significantly and consistently higher for X = Br than for X = F. This result is rationalized as a shift in mechanism from Cornforth (X = F) to Felkin–Anh (X = Br). The experimental data is well modeled by ab initio calculations for the addition to these ketones by BH₃, but not by other nucleophiles such as LiH or LiAlH₄. The energetic ordering of the BH₃ transition states largely follows the trends for the ground state ketones. Here, consistent with electrostatic arguments, the anti orientation of the C―X and C?O bonds is always lower in energy than the syn arrangement. The gauche conformer is intermediate between these two, becoming gradually lower in energy as X increases in size. The hyperconjugative interaction invoked by the Felkin–Anh model provides only a modest stabilization of the relevant transition states as judged by NBO analysis. Copyright © 2014 John Wiley & Sons, Ltd.     

Onset of quark-hadron duality in pion electroproduction

A large data set of charged-pion (pi+/-) electroproduction from both hydrogen and deuterium targets has been obtained spanning the low-energy residual-mass region. These data conclusively show the onset of the quark-hadron duality phenomenon, as predicted for high-energy hadron electroproduction. We construct several ratios from these data to exhibit the relation of this phenomenon to the high-energy factorization ansatz of electron-quark scattering and subsequent quark-->pion production mechanisms.     

Controlling speckle using lenses and free space

The correlation properties of speckle fields are studied for general paraxial systems. The previous studies on lateral and longitudinal speckle size for the case of free-space propagation (Fresnel transform) are generalized to the case of the linear canonical transform. These results have implications for the control of speckle size, through appropriate design of optical systems, with particular relevance for speckle interferometry.