Cyano-Carbonates (I) Efficient Latent Acyl Carbanions

Cyano-carbonates, conveniently prepared in excellent yields by in-situ trapping of cyanohydrin anions with chloroform[acaron]tes under PTC conditions, have been found to be efficient ketone precursors.     

Similarities in echolocation strategy and click characteristics between a Pseudorca crassidens and a Tursiops truncatus

A previous comparative analysis of normalized click amplitude spectra from a Tursiops truncatus has shown that those frequencies with the lowest click-to-click variability in spectral content were the frequencies the animal paid attention to during target discrimination tasks. In that case, the dolphin only paid attention to the frequency range between 29-42 kHz which had a significantly higher degree of consistency in spectral content than frequencies above 42 kHz. Here it is shown that despite their morphological and behavioral differences, this same pattern of consistency was used by a Pseudorca crassidens performing a similar discrimination task. This comparison between species provides a foundation for using spectral level variability to determine the frequencies most important for echolocation in rare species and non-captive animals. Such results provide key information for successful management.     

A re-evaluation of auditory filter shape in delphinid odontocetes: evidence of constant-bandwidth filters

The auditory filter shape of delphinid odontocetes was previously considered to be typically mammalian constant-quality in which filter bandwidths increase proportionally with frequency. Recent studies with porpoises demonstrate constant-bandwidth portions of the auditory filter. The critical ratios for a bottlenose dolphin were measured between 40 and 120 kHz by behaviorally determining the subject's ability to detect pure tones in the presence of white noise. Critical ratios as a function of frequency were constant, indicating the auditory filter acts as a constant-bandwidth system in this frequency range. Re-analysis of past studies supports these findings, and suggests the delphinid auditory system is best characterized as a constant-Q system below 40 kHz and a constant-bandwidth-like system between 40 kHz and 120 kHz before returning to a constant Q pattern at the highest frequencies.     

Near-field spatial correlations from partially coherent homogeneous planar sources: effects on surface wave excitation

We show that an increase of the coherence length of a statistically homogeneous planar source diminishes the contribution of surface waves to the spatial coherence of the near field, as well as producing changes in the enhancement of the near-field spectrum.     

Mixed Silane-based Self-assembled Monolayers Deposited on Fluorine Doped Tin Oxide as Model System for Development of Biosensors for Toxin Detection

In this work mixed hybrid phospholipid bilayers (mhBLM) were deposited on fluorine doped tin oxide (FTO) films. Two component silane-based self-assembled monolayers (SAMs) formed on FTO surface trigger vesicle fusion and formation of mhBLMs which are stable, can be easily regenerated, and therefore, used for multiple experiments. We found that certain chemical and physical conditions under which mixed SAMs are fabricated translate into functional properties of mhBLMs. In all cases we observed interaction of melittin with mhBLMs demonstrating biological relevance of these biomimetic surface constructs and their possible application in biosensors for toxin detection.     

Electromagnetic cross sections of double giant dipole resonances in 136Xe and 208Pb within the phonon damping model

The electromagnetic cross sections of the double giant dipole resonances (DGDR) in 136Xe and 208Pb are calculated using the strength functions obtained within the phonon damping model. The parameters of the model have been selected to describe reasonably well the single giant dipole resonance in these nuclei. The results are found in an overall agreement with the recent experimental data for the DGDR cross sections in exclusive measurements at near-relativistic energies.     

Target detection by the beluga using a surface-reflected path

During an echolocation-in-noise experiment we suspected that a beluga (Delphinapterus leucas) was using a surface-reflected path to maximize detection performance. We tested and confirmed this suspicion by acoustically and mechanically denying access to surface path information. The whale's performance varied as the surface-reflected path was denied.     

Unit responses in ventral cochlear nucleus reflect cochlear coding of rapid frequency sweeps

This study examines the encoding of rapid frequency sweeps in single units of the ventral cochlear nucleus (VCN). Sweeps were designed to explore the role of cochlear mechanics in shaping the temporal responses across cells in the VCN. The time course of frequency change for rapidly rising frequency sweeps theoretically produced simultaneous displacement maxima by cancelling travel time along the cochlear partition. Rising sweeps with longer time courses only partially canceled travel time, while falling sweeps had time courses of frequency change equal to or greater than travel time. Falling sweeps thus augmented normal travel time. Latency of unit firing to sweeps across unit characteristic frequency (CF) reflected cochlear delay-line mechanics. The latency-CF functions agreed with predictions from travel-time estimates for rising-frequency sweeps, but responses to falling sweeps were less predictable.     

Triangular Bézier sub-surfaces on a triangular Bézier surface

This paper considers the problem of computing the Bézier representation for a triangular sub-patch on a triangular Bézier surface. The triangular sub-patch is defined as a composition of the triangular surface and a domain surface that is also a triangular Bézier patch. Based on de Casteljau recursions and shifting operators, previous methods express the control points of the triangular sub-patch as linear combinations of the construction points that are constructed from the control points of the triangular Bézier surface. The construction points contain too many redundancies. This paper derives a simple explicit formula that computes the composite triangular sub-patch in terms of the blossoming points that correspond to distinct construction points and then an efficient algorithm is presented to calculate the control points of the sub-patch.     

Formation and dynamics of van der Waals molecules in buffer-gas traps

We show that weakly bound He-containing van der Waals molecules can be produced and magnetically trapped in buffer-gas cooling experiments, and provide a general model for the formation and dynamics of these molecules. Our analysis shows that, at typical experimental parameters, thermodynamics favors the formation of van der Waals complexes composed of a helium atom bound to most open-shell atoms and molecules, and that complex formation occurs quickly enough to ensure chemical equilibrium. For molecular pairs composed of a He atom and an S-state atom, the molecular spin is stable during formation, dissociation, and collisions, and thus these molecules can be magnetically trapped. Collisional spin relaxation is too slow to affect trap lifetimes. However, (3)He-containing complexes can change spin due to adiabatic crossings between trapped and untrapped Zeeman states, mediated by the anisotropic hyperfine interaction, causing trap loss. We provide a detailed model for Ag(3)He molecules, using ab initio calculation of Ag-He interaction potentials and spin interactions, quantum scattering theory, and direct Monte Carlo simulations to describe formation and spin relaxation in this system. The calculated rate of spin-change agrees quantitatively with experimental observations, providing indirect evidence for molecular formation in buffer-gas-cooled magnetic traps. Finally, we discuss the possibilities for spectroscopic detection of these complexes, including a calculation of expected spectra for Ag(3)He, and report on our spectroscopic search for Ag(3)He, which produced a null result.