Biomedical subjects

Joseph M Zaug

Publications and source records attributed to Joseph M Zaug.

4 recordsLinked to original sources

PubMed2005

Dynamic ionization of water under extreme conditions.

Raman spectroscopy in a laser heated diamond anvil cell and first principles molecular dynamics simulations have been used to study water in the temperature range 300 to 1500 K and at pressures to 56 GPa. We find a substantial decrease in the intensity of the O-H stretch mode in the liquid phase with pressure, and a change in slope of the melting line at 47 GPa and 1000 K. Consistent with these observations, theoretical calculations show that water beyond 50 GPa is "dynamically ionized" in that it consists of very short-lived (<10 fs) H2O, H3O+, and OH- species, and also that the mobility of the oxygen ions decreases abruptly with pressure, while hydrogen ions remain very mobile. We suggest that this regime corresponds to a superionic state.

Journal Article↗

PubMed2005

Polymerization of formic acid under high pressure.

We report Raman, infrared, and x-ray diffraction (XRD) measurements, along with ab initio calculations on formic acid (FA) under pressure up to 50 GPa. We find an infinite chain Pna2(1) structure to be a high-pressure phase at room temperature. Our data indicate the symmetrization and a partially covalent character of the intrachain hydrogen bonds above approximately 20 GPa. Raman spectra and XRD patterns indicate a loss of long-range order at pressures above 40 GPa, with a large hysteresis upon decompression. We attribute this behavior to a three-dimensional polymerization of FA.

Journal Article↗

PubMed2004

Elastic and vibrational properties of cobalt to 120 GPa.

Impulsive stimulated light scattering and Raman spectroscopy measurements have been made on hcp cobalt to a static pressure of 120 GPa. We find that at pressures above 60 GPa the shear elastic modulus and the Raman frequency of the E(2g) transverse optical phonon exhibit a departure from a linear dependence on density. We relate this behavior to a collapse of the magnetic moment under pressure that has been predicted theoretically, but until now not observed experimentally.

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PubMed2002

Monitoring high-temperature solid-solid phase transitions of HMX with atomic force microscopy.

Using high-temperature atomic force microscopy we have observed the solid-solid phase transition of octahydro-1,3,5,7,-tetrazocine (HMX) in real time. Massive surface reconstruction occurs during the first-order transition. The temperature induced increase in void space and surface roughness observed in the delta polymorph of HMX serve to increase the growth rate and volume of shock initiated hot spots and hence reaction sensitivity.

Journal Article↗