Crystal and molecular structure of bis(8-phenylmenthyl) 2-(2-methyl-5-oxo-3-cyclohexen-1-yl)propandioate, C42H54O5· CH3CN

The X-ray crystal structure of the title compound, as crystallized from acetonitrile-water was determined. The relative stereochemistry of the cyclohexenone ring with respect to the 8-phenylmenthyl esters was determined. The title compound crystallizes in the noncentrosymmetric space group P2₁, with a=8.9850(10) ?, b=15.575(3) ?, c=14.478(2) ?, β=94.61(2)°, and D _calc=1.118 g cm⁻³ for Z=2.     

Degenerate periodic orbits and homoclinic torus bifurcation

A one-parameter family of periodic orbits with frequency omega and energy E of an autonomous Hamiltonian system is degenerate when E'(omega) = 0. In this paper, new features of the nonlinear bifurcation near this degeneracy are identified. A new normal form is found where the coefficient of the nonlinear term is determined by the curvature of the energy-frequency map. An important property of the bifurcating "homoclinic torus" is the homoclinic angle and a new asymptotic formula for it is derived. The theory is constructive, and so is useful for physical applications and in numerics.     

Synthesis of cyclopropanes via organoiron methodology: preparation and rearrangement of divinylcyclopropanes

Addition of alkenyl Grignard reagents to (1-methoxycarbonylpentadienyl)iron(1+) cation generates the corresponding (2-alkenylpent-3-en-1,5-diyl)iron complexes. Oxidatively induced-reductive elimination of these complexes gives divinylcyclopropanes which can undergo subsequent Cope rearrangement to give 1,4-cycloheptadienes.     

Place-pitch sensitivity and its relation to consonant recognition by cochlear implant listeners using the MPEAK and SPEAK speech processing strategies

Two related studies investigated the relationship between place-pitch sensitivity and consonant recognition in cochlear implant listeners using the Nucleus MPEAK and SPEAK speech processing strategies. Average place-pitch sensitivity across the electrode array was evaluated as a function of electrode separation, using a psychophysical electrode pitch-ranking task. Consonant recognition was assessed by analyzing error matrices obtained with a standard consonant confusion procedure to obtain relative transmitted information (RTI) measures for three features: stimulus (RTI stim), envelope (RTI env[plc]), and place-of-articulation (RTI plc[env]). The first experiment evaluated consonant recognition performance with MPEAK and SPEAK in the same subjects. Subjects were experienced users of the MPEAK strategy who used the SPEAK strategy on a daily basis for one month and were tested with both processors. It was hypothesized that subjects with good place-pitch sensitivity would demonstrate better consonant place-cue perception with SPEAK than with MPEAK, by virtue of their ability to make use of SPEAK's enhanced representation of spectral speech cues. Surprisingly, all but one subject demonstrated poor consonant place-cue performance with both MPEAK and SPEAK even though most subjects demonstrated good or excellent place-pitch sensitivity. Consistent with this, no systematic relationship between place-pitch sensitivity and consonant place-cue performance was observed. Subjects' poor place-cue perception with SPEAK was subsequently attributed to the relatively short period of experience that they were given with the SPEAK strategy. The second study reexamined the relationship between place-pitch sensitivity and consonant recognition in a group of experienced SPEAK users. For these subjects, a positive relationship was observed between place-pitch sensitivity and consonant place-cue performance, supporting the hypothesis that good place-pitch sensitivity facilitates subjects' use of spectral cues to consonant identity. A strong, linear relationship was also observed between measures of envelope- and place-cue extraction, with place-cue performance increasing as a constant proportion (approximately 0.8) of envelope-cue performance. To the extent that the envelope-cue measure reflects subjects' abilities to resolve amplitude fluctuations in the speech envelope, this finding suggests that both envelope- and place-cue perception depend strongly on subjects' envelope-processing abilities. Related to this, the data suggest that good place-cue perception depends both on envelope-processing abilities and place-pitch sensitivity, and that either factor may limit place-cue perception in a given cochlear implant listener. Data from both experiments indicate that subjects with small electric dynamic ranges (< 8 dB for 125-Hz, 205-microsecond/ph pulse trains) are more likely to demonstrate poor electrode pitch-ranking skills and poor consonant recognition performance than subjects with larger electric dynamic ranges.     

Intensity discrimination and detection of amplitude modulation in electric hearing

Wojtczak and Viemeister [J. Acoust. Soc. Am. 106, 1917-1924 (1999)] demonstrated a close relationship between intensity difference limens (DLs) and 4-Hz amplitude modulation (AM) detection thresholds in normal-hearing acoustic listeners. The present study demonstrates a similar relationship between intensity DLs and AM detection thresholds in cochlear-implant listeners, for gated stimuli. This suggests that acoustic and cochlear-implant listeners make use of a similar decision variable to perform intensity discrimination and modulation detection tasks. It can be shown that the absence of compression in electric hearing does not preclude this possibility.     

An AES study of surface segregation of AgAu alloys with ion bombardment and annealing

Equilibrium segregation and selective sputtering in the surface of AgAu alloys have been investigated systematically with argon ion bombardment and with annealing by means of AES measurements. Slight enrichment of Ag was observed on the alloy surfaces after the annealing of the alloys at 550°C, while relatively large enrichment of Au was observed on the ion-bombarded surfaces with the use of Au (240 eV) and Ag (300 eV) Auger electrons. With the aid of other Auger electrons with different escape lengths, it was found that the concentration varies with distance from the surface within the sampling depth of the Auger electrons. On the basis of the above facts, the depth profiles were proposed for the annealed and the ion-bombarded surfaces. The uppermost surface layer is enriched more with Ag than the apparent AES observations on both the ion-bombarded and the annealed surfaces. The proposed depth profiles on both the surface layers were compared with previous results by different authors.     

Energy loss to resonantly accelerated ions in laser-plasma

A group of non-thermal ions has been observed when 1.06 μm laser radiation is resonantly absorbed by its own self-generated plasma. The ratio between the kinetic energy carried by this ion group and the total kinetic energy of the plasma ions has been measured. From X-ray measurements indirect evidence has been found for modification of the electron energy distribution due to the acceleration of electrons in the resonant longitudinal field. The experimental results are interpreted by a simple theoretical model.     

Convergence of osculatory quadrature formulae

The regions of analyticity of functions to be integrated using equally spaced osculatory quadrature formulae are obtained. As a by-product it is noted that the asymptotic forms used are applicable to estimating or placing bounds on errors.