Dynamics of water confined in single- and double-wall carbon nanotubes.

Using high-resolution quasielastic neutron scattering, we investigated the temperature dependence of single-particle dynamics of water confined in single- and double-wall carbon nanotubes with the inner diameters of 14+/-1 and 16+/-3 A, respectively. The temperature dependence of the alpha relaxation time for water in the 14 A nanotubes measured on cooling down from 260 to 190 K exhibits a crossover at 218 K from a Vogel-Fulcher-Tammann law behavior to an Arrhenius law behavior, indicating a fragile-to-strong dynamic transition in the confined water. This transition may be associated with a structural transition from a high-temperature, low-density (<1.02 gcm(3)) liquid to a low-temperature, high-density (>1.14 gcm(3)) liquid found in molecular dynamics simulation at about 200 K. However, no such dynamic transition in the investigated temperature range of 240-195 K was detected for water in the 16 A nanotubes. In the latter case, the dynamics of water simply follows a Vogel-Fulcher-Tammann law. This suggests that the fragile-to-strong crossover for water in the 16 A nanotubes may be shifted to a lower temperature.

Anomalous behavior of proton zero point motion in water confined in carbon nanotubes.

The momentum distribution of the protons in ice Ih, ice VI, high density amorphous ice, and water in carbon nanotubes has been measured using deep inelastic neutron scattering. We find that at 5 K the kinetic energy of the protons is 35 meV less than that in ice Ih at the same temperature, and the high momentum tail of the distribution, characteristic of the molecular covalent bond, is not present. We observe a phase transition between 230 and 268 K to a phase that does resemble ice Ih. Although there is yet no model for water that explains the low temperature momentum distribution, our data reveal that the protons in the hydrogen bonds are coherently delocalized and that the low temperature phase is a qualitatively new phase of ice.

Glass formation at the limit of insufficient network formers.

Inorganic glasses normally exhibit a network of interconnected, covalent-bonded, structural elements that has no long-range order. In silicate glasses, the network formers are based on SiO4 tetrahedra interconnected through oxygen atoms at the corners. Conventional wisdom implies that alkaline and alkaline-earth orthosilicate materials cannot be vitrified, because they do not contain sufficient network-forming SiO2 to establish the needed interconnectivity. We studied a bulk magnesium orthosilicate glass obtained by containerless melting and cooling. We found that the role of network former was largely taken on by corner and edge sharing of highly distorted, ionic Mg-O species that adopt 4-, 5-, and 6-coordination with oxygen. The results suggest that similar glassy phases may be found in the containerless environment of interstellar space.

Evidence of hydroxyl-ion deficiency in bone apatites: an inelastic neutron-scattering study.

The novelty of very large neutron-scattering intensity from the nuclear-spin incoherence in hydrogen has permitted the determination of atomic motion of hydrogen in synthetic hydroxyapatite and in deproteinated isolated apatite crystals of bovine and rat bone without the interference of vibrational modes from other structural units. From an inelastic neutron-scattering experiment, we found no sharp excitations characteristic of the vibrational mode and stretch vibrations of OH ions around 80 and 450 meV (645 and 3630 cm(-1)), respectively, in the isolated, deproteinated crystals of bone apatites; such salient features were clearly seen in micron- and nanometer-size crystals of pure hydroxyapatite powders. Thus, the data provide additional definitive evidence for the lack of OH(-) ions in the crystals of bone apatite. Weak features at 160-180 and 376 meV, which are clearly observed in the apatite crystals of rat bone and possibly in adult mature bovine bone, but to a much lesser degree, but not in the synthetic hydroxyapatite, are assigned to the deformation and stretch modes of OH ions belonging to HPO(4)-like species.

Post-stroke depression: outcome following rehabilitation.

OBJECTIVE: This prospective study looks at the outcome of rehabilitation on mood and physical recovery in patients with post-stroke depression. METHODS: Fifty-two patients in a rehabilitation centre were assessed for depression, modified Barthel's score and Hamilton Rating Scale for depression on admission to and discharge from the rehabilitation centre. Aphasic, demented and delirious patients were excluded. RESULTS: Fifty-five percent of the patients were assessed to have depression on admission and 98% had physical impairment. At the time of discharge, only 28.6% were depressed and two-thirds had improved in physical function. Patients with all degrees of functional impairment showed equal improvement and there was no difference between Barthel's scores for patients whose mood improved and those who remained depressed. There were very strong associations between functional assessment and depression, functional assessment on discharge with depression on admission, and patients' mood on admission and discharge. Depressed patients did not stay longer in the rehabilitation centre than non-depressed patients. Low doses of anti-depressants did not have an impact on mood or functional improvement. CONCLUSION: We have found that depression might not have a clear negative impact on rehabilitation, that mood improved at the end of rehabilitation and that the degree of depression on admission was a good predictor of the outcome of final physical impairment.