The consequence analysis for the unconfined vapor cloud explosion(UVCE) accident by the continuous release of butane vapor was performed and effects of process parameters on consequences were analyzed in standard conditions. For the case of continuous release(87.8 kg/s) of butane vapor at 8 m elevated height in the debutanizing process of tile naphtha cracking plant operating at 877 kPa ＆ 346.75 K, we found that combustion ranges of dispersed vapor estimated by HMP model were 11.2~120.2 m and overpressures estimated by TNT equivalency model at 200 m were about 37.35~55.1 kPa. Also, overpressures estimated by Model UVCE I based on advective travel time to XLFL were smaller than those estimated by Model UVCE IIbased on real travel time between XUFL and XLFL. At the same time, damage intensities at 200 m and effect ranges by overpressure could be predicted. Furthermore, simulation results showed that effects of operating pressures on consequences were larger than those of operating temperatures and results of accidents were increased with increasing operating pressures. At this time, sensitivities of overpressures for UVCE accident by the continuous release were about 5 kPa/atm.

We have investigated the properties of the high-latitude cloud MBM 7 using the 3 mm transitions of CO, CS, HCN, HCO+,C3H2,N2H+, and SiO. The molecular component of MBM 7 shows a very clumpy structure with a size of ≤0.5 pc, elongated along the northwest-southeast direction, perpendicularly to an extended HI component, which could be resulted from shock formation. We have derived physical properties for two molecular cores in the central region. Their sizes are 0.1-0.3 pc and masses 1-2 M⊙ having an average volume density ~2×10 3 cm-3 at the peak of molecular emission. We have tested the stability of the cores using the full version of the virial theorem and found that the cores are stabilized with ambient medium, and they are expected not to be dissipated easily without external perturbations. Therefore MBM 7 does not seem to be a site for new star formation. The molecular abundances in the densest core appear to be much less (by about one order of magnitude) than the 'general' dark cloud values. If the depletions of heavy elements are not significant in the HLCs compared with those in typical dark clouds, our results may suggest different chemical evolutionary stages or different chemical environments of the HLCs compared with dense dark clouds in the Galactic plane.

We have made an extensive mapping of the 13CO 13CO J=1-0 transition line in the dark cloud L1535. We also constructed the 100μm 100μm IRAS map in the region. We found a semi-detached cloud component of 13CO 13CO in the northeast direction of the 13CO 13CO main cloud which forms a dumbbell-like structure. This additional component with an angular size of 20′×16′ 20′×16′ has not been observed before in any molecular surveys of the cloud. The IRAS map shows a similar structure with two intensity peaks whose positions coincide with those of the 13CO 13CO clouds.

We present the results of one-dimensional numerical simulations of SNR evolution in the in­homogeneous medium considering the effects of the evaporation of the cloud and the thermal conduction. We have included the effects of changing evaporation rate as a function of cloud size and the ambient temperature so that the clouds could be evaporated completely before they reach the center of the SNR. The heat conduction markedly changes the density distribution in the remnant interior. To explain the observed morphologies of the centrally peaked X-ray SNRs(for example W44), the maximal thermal conduction is required. However, this is unlikely due to the magnetic field and the turbulent motion. The effects of the evaporation of the cloud and the thermal conduction described here may explain the class of remnants observed to have centrally peaked X-ray emmision.

We have mapped about 1.5 square degree regions of Lynds 1299, a well isolated dark cloud in the Outer Galaxy (l = 122°, b = -7°), in the J = 1- 0 transition of 12CO and 13CO with the 13.7 m radio telescope at Taeduk Radio Astronomy Observatory (TRAO). We found that there are two velocity components in the molecular emission, at VLSR = -52 km S-1 (Cloud A) and -8.8 km s-1 (Cloud B), respectively. We have derived physical parameters of two molecular clouds and discussed three different mass estimate techniques. We found that there are large discrepancies between the virial and LTE mass estimates for both clouds. The large virial mass estimate reflects the fact that both are not gravitationally bound. We adopt the mass of 5.6 ×10 3 M⊙ for Cloud A and 1.2 × 10 3 M⊙ for Cloud B using conversion factor. Cloud A is found to be associated with a localized star forming site, and its morphology is well matching with that of far-infrared (FIR) dust emission. It shows a clear ring structure with an obvious velocity gradient. We suggest that it may be a remnant cloud from a past episode of massive star formation. Cloud B is found to be unrelated to Cloud A (d = 800 pc) and has no specific velocity structure. The average dust color temperature of the uncontaminated portion of Cloud A is estimated to be 24~27.4 K. The low dust temperature may imply that there is no additional internal heating source within the cloud. The heating of the cloud is probably dominated by the interstellar radiation field except the region directly associated with the new-born B5 star. Overall, the dust properties of Cloud A are similar to those of normal dark cloud even though it does have star forming activity.

We have observed the 10-9 transitions of HC3N and its 13C substitutes (H13CCCN,HC13CCN, and HCC13CN), and the vibration ally excited 12-11 (vr=1) HC3N transition toward the Sgr B2 molecular cloud. The observed HC3N emission shows an elongated shape around the Principal Cloud (~4.5 pc in R.A. × 7.4 pc in Decl.). The optically thin H13CCCN line peaks around the (N) core and we derive the total column density N(H13CCCN) = 4 ×10 13 cm-2 at this position. Toward the 2' N cloud which shows the peculiar chemistry, the HC3N lines show enhancements compared to the extended envelope. The shocks of the 2' N may have resulted in the enhancement of HC3N. The hot component of HC3N is strongly concentrated around the (N) core and its HPW is ~0.9 pc in diameter. We derive the lower limit of the abundance ratio N(HC3N)/N(H13CCCN) to be larger than 40 in most regions except the (M) and (N) cores. The fractionation processes of 13C at this region may not be as effective as previously reported.

We have made observations of the dark cloud, B5 in the transitions of H2CO, J = 1 10 ― 1 11, and 2 12 ― 1 11. We compared the H2CO result with the observational results of CO and with the visual extinction. There exists an overall correspondence of molecules and extinction. However, a detailed agreement is lacking. We discussed the kinematics and the spatial relationship of molecules and extinction in this cloud.

We present the recent results of an HI aperture synthesis mosaic of the Large Magellanic Cloud(LMC), made by combining data from 1344 separate pointing centers using the Australia Telescope Compact Array(ATCA). The resolution of the mosaiced images is 1'.0 (15 pc, using a distance to the LMC of 50 kpc). In contrast with its appearance at other wavelengths, the LMC is remarkably symmetric in HI on the largest scales, with the bulk of the HI residing in a disk of diameter 7.3 kpc. Outer spiral structure is clearly seen, though the features appear due to differential rotation, therefore transient in nature. A good correlation is seen between the supershells previously identified in Halpha (e.g. Meaburn 1980) and HI structures.

We have studied the star forming activities and dust properties of Lynds 1251, a dark cloud located at relatively high galactic latitude. Eleven IRAS point sources identified toward Lynds 1251 are discussed. Estimate of stellar masses, and far-infrared lumnosities of the young stars associated with two prominent IRAS point sources imply that these are T-Tauri stars with masses smaller than 0.3M⊙. The low dust temperature of 27 K and low ratio of FIR emission to hydrogen column density are probably due to the lack of internal heating sources. Presumably two low mass young stars do not have enough energy to heat up the dust and gas associated. The dust heating is dominated by the interstellar heating source, and the weaker interstellar radiation field can explain the exceptionally low dust temperatures found in Lynds 1251. The estimated dust mass of Lynds 1251 is just ~1 M⊙, or about 1/1000 of gas mass, which implies that there must be a substantial amount of colder dust. The infrared flux at 100μm is matching well with 13CO peak temperature, while the 12CO integrated intensity is matching with the boundary of dust emission. Overall, the dust properties of Lynds 1251 is similar to those of normal dark clouds even though it does have star forming activities.

We observed the molecular transitions of 12CO(1−0) 12CO(1−0) , 13CO(1−0) 13CO(1−0) , C18O(1−0) C18O(1−0) , CS(2-1), HCO+(1−0) HCO+(1−0) , and HCN(1-0) toward the high-latitude mole cular cloud MBM12. We derived total H2 H2 column densities for the two velocity components using the optically thin C18O C18O transition. Molecular abundances have been derived for the observed species at the core of this cloud, which appear to be less than an order of magnitude in fractional abundances relative to H2 H2 , compared to typical cold dark clouds.

We have mapped the whole extent of a dark cloud Lynds 1251 in the emission of the J=1-0 transitions of 12CO and 13CO using FCRAO's fifteen-beam array receiver in high angular resolution of 50'. We have derived physical parameters of L1251, discussed three different mass estimate techniques, and obtained a large range of mass, 600 to 6,000 M⊙, depending on the techniques. The factor of 10 discrepancy between the virial and LTE masses is much larger than expected based on the uncertainties residing in two methods. The large virial mass may reflect the fact that L1251 is not gravitationally bound system as in the case of dark clouds in solar neighborhood. Two outflows are affecting the dynamics of cloud significantly but not enough to reshape the whole extent of the cloud. The small cloud, 'Stripe', which is apparently connected with main cloud, is not likely to be associated with L1251. The velocity gradient composed on this small cloud may be driven by other unknown sources. It is found that L1251 cloud itself is very quiescent except the two bipolar outflow regions.

We have obtained high angular resolution maps toward a molecular cloud associated with an HII region S287 and studied mainly kinematics of the cloud. The mapped region is 1.5 square degrees of the cloud in the transitions of 12CO and 13CO J=1-0. We have obtained a large range of mass, 1.3×104⊙, to $7.2×104⊙ using three different techniques. The S287 molecular cloud shows a very disturbed feature: velocity field of the cloud is very complicated, and shows several arcs. It is likely that the southern part of cloud is being disrupted by the residing HII region S287 as well as external perturbing sources. In addition to an HII region, five bipolar outflows are also disturbing the molecular gas significantly. The large virial mass and the very disturbed morphology may reflect the fact that the cloud is not gravitationally bound system, as in the case of nearby giant molecular cloud (GMC) G216-2.5. The several arc structure and the filamentary features are possibly driven by external strong stellar winds, and these external perturbing sources may be driving the second generation of star-forming activities on the edges of the S287 molecular cloud.