Head Stability in Walking in Children With Cerebral Palsy and in Children and Adults Without Neurological Impairment

Background and Purpose. The location of several sensory systems in the head implies that maintenance of head stability may be a potentially important part of locomotor activity. A limited amount of research, however, has been conducted to measure stability or to compare head stability among different groups. The purpose of this study was to determine whether a method for measuring head stability during walking could differentiate among 3 groups: (1) children with cerebral palsy, (2) children without neurological impairment, and (3) adults without neurological impairment. Subjects. Eight adults without known neurological impairment, 6 children without known neurological impairment, and 6 children with cerebral palsy and mild spastic hemiplegia were compared. Methods. Subjects walked on a treadmill at their preferred speed at a number of frequencies. Head stability was characterized by fluctuations in period and amplitude of head motion in the sagittal plane across walking cycles. Results. Mean period fluctuation was lower for the adults than for the children, and it was lower for the children without neurological impairments than for the children with cerebral palsy. Conclusion and Discussion. The method can be used to differentiate head stability among different groups during functional activities.

Fine structure in Raman spectroscopy and X-ray reflectometry and its uses for characterization of superlattices

Fine structure in the folded longitudinal acoustic (FLA) phonon peaks from high-resolution Raman spectra of Si/Si1−xGex superlattices has been observed. The observed FLA fine structure is attributed to fluctuations in the superlattice periodicity. A 0.2 cm−1 splitting in the FLA peaks is observed in the Raman spectrum of a 15-period superlattice. According to the Rytov theory for the FLA phonons, the peak splitting corresponds to a change in period of about four monolayers (~0.5 nm) during growth. X-ray reflectometry on these samples also shows a similar doublet formation on the main reflection peaks, consistent with a 2–3 monolayer period fluctuation. A test sample with a built-in period variation was also well characterized by both techniques. The good agreement between the two techniques, as well as between the theories and the experiments, demonstrates that both techniques are capable of high precision and allow detailed and quantitative characterization of the superlattice perfection. In addition to determining the phonon velocity, dispersion relation, layer thickness, period, and composition of the superlattices, these results demonstrate the possibility of measuring the fluctuation in the period and the interface quality, as well as the numbers of given periods in some special cases.