Search Results - (Author, Cooperation:M. D. Knudson)

2018-11-27

American Physical Society (APS)

1098-0121

1095-3795

Physics

Structure, structural phase transitions, mechanical properties, defects

2015-06-27

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

1089-7550

AIP Digital Archive

Physics

In previous studies, ruby R-line shifts under shock compression and tension have been measured using the spontaneous luminescence from optically pumped samples. The signal intensities obtained are limited by the short time duration of the experiments in comparison to the long lifetime of the luminescence. We have investigated the use of stimulated emission for measuring R-line shifts in shocked ruby crystals. Experiments were performed both at ambient conditions and under shock compression to 6 GPa using an experimental configuration similar to that used for time resolved ruby luminescence measurements in previous shock wave studies. Signal gain due to stimulated emission was observed, with gains ranging from 1.1 to 3.4, in agreement with calculations performed for the particular experimental configuration used. The present results make a good case for incorporating this technique into the measurement of shock induced R-line shifts in ruby. © 1999 American Institute of Physics.

Electronic Resource

1089-7623

AIP Digital Archive

Physics

Electrical Engineering, Measurement and Control Technology

An experimental method was developed to perform picosecond time-resolved electronic spectroscopy in single-event, plate impact, shock wave experiments. Several experimental difficulties had to be addressed due to the fast time resolution (100 ps) and short time duration (12.7 ns) of such experiments. Procedures are described to address the following experimental issues: (i) synchronization of the light source, detection equipment, and the shock event within the experimental duration, (ii) incorporation of a Nd:YAG laser (operative in a repetitive mode) into the experimental configuration, and (iii) sources of temporal dispersion. Representative results are shown from experiments performed on single crystal CdS. The developments described here are also expected to be useful for shock wave experiments involving Raman, fluorescence, or other types of spectroscopy which require the use of a laser. © 1999 American Institute of Physics.

Electronic Resource

1089-7690

AIP Digital Archive

Physics

Chemistry and Pharmacology

A thermodynamically consistent equation of state (EOS) was developed for unreacted liquid nitromethane (NM). The specific heat cv, the coefficient of thermal pressure (∂P/∂T)v, and the isothermal bulk modulus BT, were modeled as functions of temperature and volume using existing experimental data. To test our EOS predictions, temperature measurements using time-resolved Raman spectroscopy were obtained from NM subjected to stepwise loading. In contrast to previous EOS developments, calculations using our EOS show good agreement with the measured temperatures. Comparison with previous EOS models shows that simplifying assumptions, such as holding (∂P/∂T)v or Γ/v constant, lead to significant inaccuracies in temperature predictions for shocked NM. The assumption that the Gruneisen parameter Γ is a function of volume only is not consistent with our EOS. © 2000 American Institute of Physics.

Electronic Resource

1089-7623

AIP Digital Archive

Physics

Electrical Engineering, Measurement and Control Technology

A capability to produce quasi-isentropic compression of solids using pulsed magnetic loading on the Z accelerator has recently been developed and demonstrated [C. A. Hall, Phys. Plasmas 7, 2069 (2000)]. This technique allows planar, continuous compression of materials to stresses approaching 1.5 Mbar. In initial stages of development, the experimental configuration used a magnetically loaded material cup or disk as the sample of interest pressed into a conductor. This installation caused distortions that limited the ability to attach interferometer windows or other materials to the rear of the sample. In addition, magnetic pressure was not completely uniform over sample dimensions of interest. A new modular configuration is described that improves the uniformity of loading over the sample surface, allows materials to be easily attached to the magnetically loaded sample, and improves the quality of data obtained. Electromagnetic simulations of the magnetic field uniformity for this new configuration will also be presented. Comparisons between data on copper to ∼300 kbar using the old and new experimental configurations will also be made. Results indicate that to within experimental error, the configurations produce similar results in the pressure-volume plane. © 2001 American Institute of Physics.

Electronic Resource