Numerical and Experimental Study on Progressive Failure of Marble

This study presents a framework for numerical simulations based upon micromechanical parameters in modeling progressive failures of heterogeneous rock specimens under compression. In our numerical simulations, a Weibull distribution of the strength and elastic properties of the finite elements is assumed, and the associated Weibull parameters are estimated in terms of microstructural properties, such as crack size distribution and grain size, through microscopic observations of microcracks. The main uncertainty in this procedure lies on the fact that various ways can be used to formulate a ``microcrack size distribution' in relating to the Weibull parameters. As one possible choice, the present study uses the number of counted cracks per unit scanned volume per grain size to formulate the crack distributions. Finally, as a tool, the Rock Failure Process Analysis code (RFPA^2D) is adopted for simulating the progressive failure and microseismicity of heterogeneous rocks by using an elastic-damage finite-element approach. To verify our framework, compression tests on marble specimens are conducted, and the measured acoustic emissions (AE) are compared with those predicted by the numerical simulations. The mode of failure, compressive strength and AE pattern of our simulations basically agree with experimental observations.     

Detection of new sources of methanol emission at 107 and 108 GHz with the Mopra telescope

A southern hemisphere survey of methanol emission sources in two millimetre-wave transitions has been carried out using the ATNF Mopra millimetre telescope. 16 emission sources have been detected in the 3₁–4₀ A⁺ transition of methanol at 107 GHz, including six new sources exhibiting class II methanol maser emission features. Combining these results with the similar northern hemisphere survey, a total of eleven 107-GHz methanol masers have been detected. A survey of the methanol emission in the 0₀–1₋₁ E transition at 108 GHz has resulted in the detection of 16 sources; one of them showing maser characteristics. This is the first methanol maser detected at 108 GHz, presumably of class II. The results of large velocity gradient statistical equilibrium calculations confirm the classification of these new sources as class II methanol masers.     

Detection of new sources of methanol emission at 95 GHz with the Mopra telescope

A southern hemisphere survey of methanol emission sources has been carried out using the Australia Telescope National Facility Mopra millimetre telescope. 85 sources, the majority of them masers, have been detected in the 8₀−7₁ A⁺ transition of methanol at 95 GHz. Together with a similar northern hemisphere survey, this completes the search for 95-GHz methanol emission from the Galactic plane. The previously found correlation between intensities of methanol emission at 44 and 95 GHz is confirmed here with the larger sample of sources. The results of large velocity gradient statistical equilibrium calculations confirm the classification of these sources as class I methanol masers pumped through collisional excitation.     

Kinematics of the Gum nebula region

To investigate the kinematics of the neutral material around the Gum nebula, emission from hydroxyl at 1667 MHz was observed at many positions over the region. Fitting models of expanding shells to these data together with previously published molecular line data shows that the diffuse molecular clouds and cometary globules form a single expanding shell centred on G261−2.5. The mean angular radius is 10.5° and its maximum radius is 14°. The models show that the distance range to the expansion centre is from 200 pc to 500 pc.
The path of the runaway O-star ζ Puppis passed within <0.5° of the expansion centre of the neutral shell ∼1.5 Myr ago. The supernova of the erstwhile binary companion of ζ Puppis is the probable origin of the Gum nebula and the swept up expanding neutral shell. The 500-pc distance to the supernova is adopted as the distance to the expansion centre of the neutral shell. At this distance the energy required to produce the observed expansion could have been met with a single supernova. The radii of the front and back faces of the shell are 130 and 70 pc respectively. The front face is expanding faster than the back face, at 14 and 8.5 km s⁻¹ respectively.
The extent of the neutral shell matches the radio continuum and H α emission of the Gum nebula well. The photoionized gas in the nebula is probably primarily ionized by ζ Puppis, which is still within the neutral shell. No evidence was found for the IRAS -Vela shell as a separate expanding shell.     

Hydroxyl lines towards Puppis A

The 1667-MHz ground-state hydroxyl (OH) line has been observed towards positions on Puppis A as well as in the immediate vicinity of this supernova remnant (SNR). The spectra at two positions on Puppis A show absorption lines at velocities less than +7.6 km s¹, and emission lines above this velocity. Analysis of all four 18 cm OH lines indicates that Puppis A must lie between the OH clouds seen in absorption and emission, giving it a v _lsr of +7.6 km s¹. This implies that the kinematic distance to Puppis A is The OH clouds in front of Puppis A are slightly anomalously excited, as shown by analysis of the four 18 cm OH lines at the two observed positions on Puppis A. There is no evidence of any interaction of the SNR with the clouds in front of and behind it.     

Hydrogen recombination lines from the Gum nebula

Hydrogen recombination lines in the H156 α and H139 α transitions have been detected at four widely separated positions in the Gum nebula. This confirms that the radio continuum emission seen in parts of the nebula is predominantly bremsstrahlung rather than synchrotron emission.
The derived electron temperatures and emission measures are in the range 4200 to 8500 K and 220 to 470 pc cm⁻⁶ respectively. This is consistent with the presence of a low-density, photoionized plasma. The linewidth observed at the position away from the edge of the nebula is significantly larger than those near the edge of the nebula. Together with the negative line velocity observed at this position, this suggests there is systematic expansion of the near side of the nebula.