Mechanisms effecting analysis of volatile flavour components by solid-phase microextraction and gas chromatography.

Quantitative properties of solid-phase microextraction (SPME) have been studied in order to investigate a simple and reliable method for analysing volatile flavour components in strawberries. Monitoring the chemical composition profile of berries will be of interest for the producers in order to optimise growth and storage conditions. By the use of SPME and capillary gas chromatography selected standard components were quantified with accuracy within +/-7% and a linear response were found in all concentration ranges studied, covering three orders of magnitude. Equilibrium constants that describe how various components are distributed between the three phases present, sample, headspace and fibre coating were determined. In the system studied, the majority of analytes remained in the sample. This means that repeated analysis can be performed from a single sample without significantly changing the results. The mass transfers of the flavour components, from the sample and into the fibre, were fitted to a transport model assuming that the rate-controlling step is diffusion within the fibre. The experimental results agreed well with the model for most of the components studied. The response for three of the components (geraniol, linalool and trans-2-hexenyl butanoate) did not agree with the model. These components were present in the gas phase in only minute amounts explaining the deviation from the model. Such components will require a long absorption time (longer than 30 min). For quantitative analysis, it is important to use a very precise pre-determined absorption period and well defined sampling conditions. Internal standards can be omitted.     

Localization of aerial pure tones by pinnipeds

In this study, minimum audible angles (MAAs) of aerial pure tones were measured in and compared between a northern elephant seal (Mirounga angustirostris), a harbor seal (Phoca vitulina), and a California sea lion (Zalophus californianus). Testing was conducted between 0.8 and 16 kHz in the elephant seal and 0.8 and 20 kHz in the harbor seal and sea lion in a hemi-anechoic chamber using a left/right psychophysical procedure. Performance for the same frequencies was also quantified for discrete speaker separation of 5 degrees from the mid-line. For all subjects, MAAs ranged from approximately 3 degrees to 15 degrees and were generally equal to or larger than those previously measured in the same subjects with a broadband signal. Performance at 5 degrees ranged from chance to 97% correct, depending on frequency and subject. Poorest performance in the sea lion and harbor seal occurred at intermediate frequencies, which is consistent with the duplex theory of sound localization. In contrast, the elephant seal's poorest performance occurred at higher frequencies. The elephant seal's result suggests an inferior ability to utilize interaural level differences and is perhaps related to best hearing sensitivity shifted toward lower frequencies in this species relative to other pinnipeds.     

Exact Solution of Locomotive Scheduling Problems

Given a daily repeating timetable and locomotives of various types, each timetabled train must be assigned a locomotive. This paper presents an exact algorithm for the solution of this problem, based on an approach used to solve multiple-depot bus scheduling problems. The algorithm is used to solve moderately large scheduling problems drawn from real world data.     

Anisotropy in the Compton profiles of Nb and NbH0.76

The Compton profiles of Nb and NbH_0.76 single crystals have been measured along [100] and [110] using 412 keV gamma-radiation from a¹⁹⁸Au source. The changes in the band electron profile of the metal following the introduction of hydrogen are interpreted in terms of the protonic model of the hydride. Qualitative changes in the directional profiles can be understood within the rigid band approximation.     

Measurements of the double polarisation parameters G and H in neutral pion photoproduction

Measurements have been made of the double polarisation parameters G and H in the photoproduction of neutral pions from protons, for incident photon energies between 1300 MeV and 2300 MeV and for pion c.m. angles between 50δ and 80δ. The results are compared with predictions from a recent comprehensive analysis of earlier photoproduction data.     

Simultaneous and sequential adsorption of deuterium and nitrous oxide by rhenium

The addition of nitrous oxide to a stream of deuterium passing over a rhenium filament reduced the initial sticking probability of the latter gas from 0.24 to 0.09 when the proportion of N₂O exceeded 40%. For the addition of deuterium to nitrous oxide the equivalent figures were 0.45 and 0.30 when deuterium exceeded 30% of the gas phase. These results are attributed to a competition between the two gases for places in the precursor state on the surface. The replacement of adsorbed deuterium from a saturated layer by the oxygen atom of nitrous oxide proceeded initially with a high probability, 0.27, at room temperature and with each oxygen atom replacing one deuterium atom. However, the reaction was incomplete, about 2 × 10¹⁴ atoms cm^?2 of deuterium remaining on the surface. It is suggested that kinetic rather than thermodynamic factors are responsible for the incomplete reaction, possibly as the result of a high activation energy for the migration of deuterium atoms over an oxygenated rhenium surface.     

Bubble dynamics and size distributions during focused ultrasound insonation

The deposition of ultrasonic energy in tissue can cause tissue damage due to local heating. For pressures above a critical threshold, cavitation will occur, inducing a much larger thermal energy deposition in a local region. The present work develops a nonlinear bubble dynamics model to numerically investigate bubble oscillations and bubble-enhanced heating during focused ultrasound (HIFU) insonation. The model is applied to calculate two threshold-dependent phenomena occurring for nonlinearly oscillating bubbles: Shape instability and growth by rectified diffusion. These instabilities in turn are shown to place physical boundaries on the time-dependent bubble size distribution, and thus the thermal energy deposition.