The two-dimensional anharmonic oscillator: The CCC bending mode of C3O2

Newly observed data on the rotational constants of carbon su?ide in excited vibrational states of the low-wavenumber bending vibration ν₇ have been successfully interpreted in terms of the two-dimensional anharmonic oscillator wavefunctions associated with this vibration. By combining these results with published infrared and Raman spectra the vibrational assignment has been extended and a refined bending potential for ν₇ has been derived: this has a minimum at a bending angle of about 24° at the central C atom, with an energy maximum at the linear configuration some 23 cm^?1 above the minimum. From similar data on the combination and hot bands of ν₇ with ν₄ (1587 cm^?1) and ν₂ (786 cm^?1) the effective ν₇ bending potential has also been determined in the one-quantum excited states of ν₄ and ν₂. The effective ν₇ potential shows significant changes from the ground vibrational state; the central hump in the ν₇ potential surface is increased to about 50 cm^?1 in the v₄ = 1 state, and decreased to about 1 cm^?1 in the v₂ = 1 state. In the light of these results vibrational assignments are suggested for most of the observed bands in the infrared and Raman spectra of C₃O₂.     

Intensity perturbations due to ν3/ν4 Coriolis interaction in methane

Formulas are obtained for the intensity asymmetry (Herman-Wallis) factors in the ν₃ and ν₄ fundamentals of methane due to the ζ₃₄ Coriolis interaction. The results are also applicable to the ν₃ and ν₄ bands of SF₆.     

Electron and positron work functions of Cr(100)

We report measurements of the electron and positron work functions of submonolayer contaminated single crystal surfaces of Cr(100) in ultra high vacuum. The positron work function ø₊ is obtained by measuring the spectrum of slow positrons reemitted by the Cr(100) surface when it is bombarded with keV energy positrons. The electron work function ø_- is measured relative to Al(100) by comparing the target biases at which the slowest emitted positrons are recollected by the target. We obtain ø₊ = ?1.76(10) eV and ø_- = 4.46(6) eV for our Cr(100) surface using the value ø_- = 4.41(3) eV for Al(100) reported by Grepstad, Gartland and Slagsvold. The ø₊ value is in agreement with the ?2.2 eV calculated by Nieminen and Hodges. The positronium work function for Cr implied by these results is ?4.10(10) eV; the positronium negative ion (Ps^-) work function for this surface is calculated to be + 0.37(7) eV. A search for Ps^- showed that at a 90% confidence level less than one in 10³ thermalized positrons reaching the Cr surface are emitted as Ps^-. The slow positron emission spectrum was observed not to change over the 70–300 K range in contrast to recent theoretical predictions.     

Laser excitation of positronium in the Paschen-Back regime

Zeeman mixing of singlet and triplet 2P states of positronium (Ps) atoms, followed by decay back to the ground state, can effectively turn a long-lived triplet atom into a short-lived singlet state, which would seem to preclude laser cooling of Ps in a magnetic field. Here we report experiments which show that, in fact, because of the large splitting of the n=2 states in a high magnetic field (the Paschen-Back regime), the amount of such mixing diminishes approximately exponentially with an increasing magnetic field >0.01 T and is essentially eliminated above ～2 T. Thus, laser cooling of Ps should be feasible at high fields, which will facilitate the production of a Ps Bose-Einstein condensate.     

The infra-red spectra of silyl fluoride and silyl fluoride-d 3

Infra-red spectra have been recorded for silyl fluoride and silyl fluoride-d ₃ at a resolution of circa 0·3 cm^-1. Rotational structure has been observed for parallel fundamentals in both molecules, and for all perpendicular fundamentals. In both SiH₃F and SiD₃F the A ₁ and E species deformation modes interact strongly via a Coriolis perturbation; this has been analysed, and the band origin of v ₅ for SiH₃F is reassigned. A hybrid-orbital force field based on the experimental data is also reported.     

Sensitive and automated detection of iron-oxide-labeled cells using phase image cross-correlation analysis

Superparamagnetic iron oxide (SPIO) nanoparticles are increasingly being used to noninvasively track cells, target specific molecules and monitor gene expression in vivo. Contrast changes that are subtle relative to intrinsic sources of contrast present a significant detection challenge. Here, we describe a postprocessing algorithm, called Phase map cross-correlation Detection and Quantification (PDQ), with the purpose of automating identification and quantification of localized accumulations of SPIO agents. The method is designed to sacrifice little flexibility - it works on previously acquired data and allows the use of conventional high-SNR pulse sequences with no extra scan time. We first investigated the theoretical detection limits of PDQ using a simulated dipole field. This method was then applied to three-dimensional (3D) MRI data sets of agarose gel containing isolated dipoles and ex vivo transplanted allogenic rat hearts infiltrated by numerous iron-oxide-labeled macrophages as a result of organ rejection. A simulated dipole field showed this method to be robust in very low signal-to-noise ratio images. Analysis of agarose gel and allogenic rat heart shows that this method can automatically identify and count dipoles while visualizing their biodistribution in 3D renderings. In the heart, this information was used to calculate a quantitative index that may indicate its degree of cellular infiltration.     

Upward spread of masking, hearing loss, and speech recognition in young and elderly listeners

Upward spreading of masking, measured in terms of absolute masked threshold, is greater in hearing-impaired listeners than in listeners with normal hearing. The purpose of this study was to make further observations on upward-masked thresholds and speech recognition in noise in elderly listeners. Two age groups were used: One group consisted of listeners who were more than 60 years old, and the second group consisted of listeners who were less than 36 years old. Both groups had listeners with normal hearing as well as listeners with mild to moderate sensorineural loss. The masking paradigm consisted of a continuous low-pass-filtered (1000-Hz) noise, which was mixed with the output of a self-tracking, sweep-frequency Bekesy audiometer. Thresholds were measured in quiet and with maskers at 70 and 90 dB SPL. The upward-masked thresholds were similar for young and elderly hearing-impaired listeners. A few elderly listeners had lower upward-masked thresholds compared with the young control group; however, their on-frequency masked thresholds were nearly identical to the control group. A significant correlation was found between upward-masked thresholds and the Speech Perception in Noise (SPIN) test in elderly listeners.