RESUMEN
This work reports on frequency dependent ambient-pressure dielectric measurements of hyperquenched glassy water, ice IV, ice VI, as well as a CO2-filled clathrate hydrate, the latter featuring a chiral water network. The dipolar time scales and the spectral shapes of the loss spectra of these specimens are mapped out and compared with literature data on low-density and high-density amorphous ices as well as on amorphous solid water. There is a trend that the responses of the more highly dense amorphous ices are slightly more dynamically heterogeneous than those of the lower-density amorphous ices. Furthermore, practically all of the amorphous ices, for which broadband dielectric spectra are available, display a curved high-frequency wing. Conversely, the high-frequency flanks of the nominally pure ice crystals including ice V and ice XII can be characterized by an approximate power-law behavior. While the spectral shapes of the nominally pure ices thus yield some hints regarding their amorphicity or crystallinity, a comparison of their time scale appears less distinctive in this respect. In the accessible temperature range, the relaxation times of the crystalline ices are between those of low-density and high-density amorphous ice. Hence, with reference also to previous work, the application of suitable doping currently seems to be the best dielectric spectroscopy approach to distinguish amorphous from crystalline ices.
RESUMEN
This corrects the article DOI: 10.1038/ncomms8349.
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The pressure-temperature phase diagram of ice displays a perplexing variety of structurally distinct phases. In the century-long history of scientific research on ice, the proton-ordered ice phases numbered XIII through XV were discovered only recently. Despite considerable effort, none of the transitions leading from the low-temperature ordered ices VIII, IX, XI, XIII, XIV and XV to their high-temperature disordered counterparts were experimentally found to display the full Pauling entropy. Here we report calorimetric measurements on suitably high-pressure-treated, hydrogen chloride-doped ice XIV that demonstrate just this at the transition to ice XII. Dielectric spectroscopy on undoped and on variously doped ice XII crystals reveals that addition of hydrogen chloride, the agent triggering complete proton order in ice XIV, enhances the precursor dynamics strongest. These discoveries provide new insights into the puzzling observation that different dopants trigger the formation of different proton-ordered ice phases.
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OBJECTIVE: To investigate the influence of several magnetic resonance imaging (MRI) sequences on amniotic fluid temperature and intrauterine sound pressure. MATERIAL AND METHODS: Temperature and sound pressure measurements during MRI (1.5 T) in pregnant ewes were done. Linear levels and third octave band spectra were compared. RESULTS: No significant changes in the temperature of amniotic fluid were observed. Intrauterine summation levels reached peak levels up to 103.0 dB(A) before starting the MRI sequence and levels up to 116.0 dB(A) during a real-time sequence. Evaluating the octave band spectra, peak levels did not exceed 100.0 dB(L). CONCLUSIONS: Our delimited data revealed no harm for the fetus by an increase in amniotic fluid temperature or hazards for the fetal auditory system by different MRI sequences.
