The bat head-related transfer function reveals binaural cues for sound localization in azimuth and elevation

Directional properties of the sound transformation at the ear of four intact echolocating bats, Eptesicus fuscus, were investigated via measurements of the head-related transfer function (HRTF). Contributions of external ear structures to directional features of the transfer functions were examined by remeasuring the HRTF in the absence of the pinna and tragus. The investigation mainly focused on the interactions between the spatial and the spectral features in the bat HRTF. The pinna provides gain and shapes these features over a large frequency band (20-90 kHz), and the tragus contributes gain and directionality at the high frequencies (60 to 90 kHz). Analysis of the spatial and spectral characteristics of the bat HRTF reveals that both interaural level differences (ILD) and monaural spectral features are subject to changes in sound source azimuth and elevation. Consequently, localization cues for horizontal and vertical components of the sound source location interact. Availability of multiple cues about sound source azimuth and elevation should enhance information to support reliable sound localization. These findings stress the importance of the acoustic information received at the two ears for sound localization of sonar target position in both azimuth and elevation.     

Domain growth in ternary fluids: A level set approach

We analyze phase separation in ternary systems in the asymptotic hydrodynamic regime when the volume fractions and concentrations are constant. The multiphase Navier-Stokes equations are solved using a level set method. A new projection method was developed to treat multiple junctions for systems with more than two phases. It is found that surface tension ratios can alter the growth mechanism of a minority phase in the presence of two majority phases. When the minority phase wets the interface of the majority phases the domain growth rate of all three phases is initially similar to that of a symmetric binary fluid but slows down at later times.     

Bis{2,6‐bis[3‐(2,4,6‐trimethylphenyl)pyrazol‐1‐yl‐κN2]pyridine‐κN}zinc(II) diperchlorate bis(nitromethane) solvate

The title compound, [Zn(C₂₉H₂₉N₅)₂](ClO₄)₂·2CH₃NO₂, contains a Zn^II ion showing only small deviations from local D_2d symmetry. The lower rhombicity exhibited by this complex compared with that of its Cu^II congener suggests that the highly rhombic stereochemistry exhibited by the latter is largely imposed by the stereoelectronic preferences of the Cu^II ion.     

Simultaneous quantification of terpenelactones and flavonol aglycones in hydrolyzed ginkgo biloba extract by liquid chromatography with inline ultraviolet and evaporative light scattering detection

We report here a liquid chromatography (LC) method with inline ultraviolet/evaporative light scattering (UV/ELS) detection for the simultaneous quantification of the terpenelactones and flavonol aglycones in a single sample of hydrolyzed Ginkgo biloba extract (GBE). The sample is hydrolyzed by a rapid and convenient oven heating method for 1 h at 90 degrees C with 10% hydrochloric acid. The 1 h hydrolysis was found to be equivalent to the 2.25 h reflux treatment for dry powder extract, where total flavonol glycosides were 28.4 and 28.1%, respectively. Acceptable precision was achieved for total terpenelactones [relative standard deviation (RSD) = 4.8%] by ELS detection, and total flavonol aglycones (RSD = 2.3%) by UV detection. The analytical range was 1.5 to 7.3% (w/w) for the individual terpenelactones (ELS) and 2.5 to 15.0% (w/w) for the individual glycosides (UV) calculated from the aglycones quercetin, kaempferol, and isorhamnetin. This improved method allows for the first time high throughput sample preparation coupled with the quantification of the predominant compounds generally used for quality control of GBE in a single assay.     

Thermal degradation in a trimodal poly(dimethylsiloxane) network studied by (1)H multiple quantum NMR

Thermal degradation of a filled, cross-linked siloxane material synthesized from poly(dimethylsiloxane) chains of three different average molecular weights and with two different cross-linking species has been studied by (1)H multiple quantum (MQ) NMR methods. Multiple domains of polymer chains were detected by MQ NMR exhibiting residual dipolar coupling () values of 200 and 600 Hz, corresponding to chains with high average molecular weight between cross-links and chains with low average molecular weight between cross-links or near the multifunctional cross-linking sites. Characterization of the values and changes in distributions present in the material were studied as a function of time at 250 degrees C and indicate significant time-dependent degradation. For the domains with low , a broadening in the distribution was observed with aging time. For the domain with high , increases in both the mean and the width in were observed with increasing aging time. Isothermal thermal gravimetric analysis reveals a 3% decrease in weight over 20 h of aging at 250 degrees C. Degraded samples also were analyzed by traditional solid-state (1)H NMR techniques, and off-gassing products were identified by solid-phase microextraction followed by gas chromatography-mass spectrometry. The results, which will be discussed here, suggest that thermal degradation proceeds by complex competition between oxidative chain scissioning and postcuring cross-linking that both contribute to embrittlement.     

Fluoropropenoates as dienophiles in the Diels-Alder reaction

Several fluorinated alkenes were prepared from known ethyl (R)-2-fluoro-4,5-dihydroxyisopropylidine-2-pentenoate (1). The fluoroalkenoates were tested as dienophiles with several dienes and showed cycloaddition only with the very reactive diene, 1,3-diphenylisobenzofuran (5). Fluorobutenolide 2 reacted with 5 to produce the endo-syn adduct 9 in a highly stereoselective manner.     

Solid-state structures of cis- and trans-1-cyclohexyl-2-phenyl-3-(p-toluyl)aziridines

Solid-state structures have been determined for cis- and trans-1-cyclohexyl-2-phenyl-3-(p-toluyl)aziridines using single-crystal X-ray diffraction techniques. The cis isomer crystallizes in the centrosymmetric monoclinic space group P2₁/c (No. 14), with a = 18.669(3)Å, b = 5.709(1)Å, c = 17.412(2)Å, β = 96.29(1)° and Z = 4; the trans isomer crystallizes in the noncentrosymmetric orthorhombic space group Pna2₁ (No. 33), with a = 17.089(2)Å, b = 18.729(3)Å, c = 5.749(1)Å and Z = 4. Full-matrix least-squares refinement of the structural parameters led to the following final agreement factors: R₁ (unweighted, based on F) = 0.040 and R₂ (weighted, based on F) = 0.054 for the 2592 independent reflections of the cis isomer having 2θ_MoK¯α <55° and I>3σ₁, and R₁ = 0.033 and R₂ = 0.031 for the 1504 independent reflections of the trans isomer having 2θ_MoK¯α <55° and I>3σ₁. The statistically significant differences that exist between the two isomers for two bond lengths and ten bond angles (p < 0.05) appear to be the direct result of the p-toluyl group orientation with respect to the cyclohexyl and phenyl substituents. In the cis isomer it is anti with respect to the N-cyclohexyl group and cis with respect to the phenyl group, whereas in the trans isomer it is syn with respect to the N-cyclohexyl and trans with respect to the phenyl group. Three-ring to carbonyl hyperconjugation is correlated with stereoelectronic interactions in the trans isomer. Bonding, determined by X-ray and nmr studies, is discussed for the three-membered aziridine ring proper; while bonding, determined by X-ray studies, is discussed for substituents of the aziridine ring. These aziridinyl ketone compounds are of importance as potential mammalian DNA alkylating anti-tumor agents in solid-state solid-state systems. To date only a trans isomer has demonstrated this biological activity in tumor-bearing rats.     

2,6‐Bis‐(3‐trifluoromethylpyrazol‐1‐yl)pyridine

The title compound, C₁₃H₇F₆N₅, is one of a series of hindered tris‐imine ligands for meridonial co­ordination to transition metals. The mol­ecule has crystallographic C₂ symmetry, the pyrazole and pyridine rings adopting a near‐coplanar transoid conformation.     

A Double Isotopic Labelling Study of the Infrared Spectra of the Linkage Isomers [Pd(bipy)(SCN)2], [Pd(bipy)(NCS)2] and Related Complexes

Abstract

The IR spectra of the linkage isomers [Pd(bipy)(SCN)₂] and [Pd(bipy)(NCS)₂] have been determined in the C≡N stretching region (2200–2000 cm^?1) and below 500 cm^?1. The band shifts resulting from deuteration of the 2,2′-bipyridine (bipy) ring and ¹⁵NCS-labelling are shown to provide a ready means for distinguishing between the internal ligand modes, the μPd-N(bipy) and μPd-SCN/μPd-NCS vibrations. The assignment technique has been further extended to the complexes [Pt(bipy)(SCN)₂] and [Pd(phen)(SCN)₂] (phen = 1,10-phenanthroline). Finally, a comparison between the IR spectra of [Pd(bipy)(NCO)₂], [Pd(bipy)(NCS)₂] and [Pd(bipy)(SCN)₂] reveals that the frequencies μM-NCO, μM-NCS and μM-SCN decrease in the sequence NCO > NCS > SCN.