We have started a systematic survey of molecular clumps with infall motions to study the very early phase of star formation.Our first step is to utilize the data products by MWISP to make an unbiased survey for blue a...We have started a systematic survey of molecular clumps with infall motions to study the very early phase of star formation.Our first step is to utilize the data products by MWISP to make an unbiased survey for blue asymmetric line profiles of CO isotopical molecules.Within a total area of~2400 square degrees nearby the Galactic plane,we have found 3533 candidates showing blue-profiles,in which 3329 are selected from the^(12)CO&^(13)CO pair and 204 are from the^(13)CO&C^(18)O pair.Exploration of the parametric spaces suggests our samples are in the cold phase with relatively high column densities ready for star formation.Analysis of the spatial distribution of our samples suggests that they exist virtually in all major components of the galaxy.The vertical distribution suggest that the sources are located mainly in the thick disk of~85 pc,but still a small part are located far beyond Galactic midplane.Our follow-up observation indicates that these candidates are a good sample to start a search for infall motions,and to study the condition of very early phase of star formation.展开更多
We have conducted a large-field simultaneous survey of 12 CO,13 CO and C18O J=1-0 emission toward the Orion A giant molecular cloud(GMC)with a sky coverage of4.4 deg2 using the Purple Mountain Observatory(PMO)-13.7 m ...We have conducted a large-field simultaneous survey of 12 CO,13 CO and C18O J=1-0 emission toward the Orion A giant molecular cloud(GMC)with a sky coverage of4.4 deg2 using the Purple Mountain Observatory(PMO)-13.7 m millimeter-wavelength telescope.We use the probability distribution function of the column density(N-PDF)to investigate the distribution of molecular hydrogen in the Orion A GMC.The H2 column density,derived from the 13CO emission,of the GMC is dominated by a log-normal distribution in the range from4×1021 to1.5×1023 cm-2 with excesses both at the low-density and high-density ends.The excess of the low-density end is possibly caused by an extended and low-temperature(10 K)component with velocities in the range of 5-8 km s-1.Compared with the northern sub-regions,the southern sub-regions of the Orion A GMC contain less gas with column density in NH2>1.25×1022 cm-2.The dispersions of the N-PDFs of the sub-regions are found to correlate with the evolutionary stages of the clouds across the Orion A GMC.The structure hierarchy of Orion A GMC is explored with the DENDROGRAM algorithm,and it is found that the GMC is composed of two branches.All structures except one in the tree have virial parameters less than 2,indicating self-gravity is important on the spatial scales from0.3 to4 pc.Although power-laws and departures from lognormal distributions are found at the high-density end of N-PDFs for active star-forming regions,the N-PDFs of structures in the Orion A GMC are predominantly lognormal on scales from R0.4 to 4 pc.展开更多
Cloud-based video communication and networking has emerged as a promising new research paradigm to significantly improve the quality of experience for video consumers.An architectural overview of this promising resear...Cloud-based video communication and networking has emerged as a promising new research paradigm to significantly improve the quality of experience for video consumers.An architectural overview of this promising research area was presented.This overview with an end-to-end partition of the cloud-based video system into major blocks with respect to their locations from the center of the cloud to the edge of the cloud was started.Following this partition,existing research efforts on how the principles of cloud computing can provide unprecedented support to 1)video servers,2)content delivery networks,and 3)edge networks within the global cloud video ecosystems were examined.Moreover,a case study was exemplfied on an edge cloud assisted HTTP adaptive video streaming to demonstrate the effectiveness of cloud computing support.Finally,by envisioning a list of future research topics in cloud-based video communication and networking a coclusion is made.展开更多
基金supported by the National Key R&D Program of China(Grant No.2017YFA0402702)the National Natural Science Foundation of China(NSFC,Grant Nos.,11873093,U2031202,and 11903083)+1 种基金sponsored by the National Key R&D Program of China with Grant 2017YFA0402701CAS Key Research Program of Frontier Sciences with grant QYZDJ-SSW-SLH047。
文摘We have started a systematic survey of molecular clumps with infall motions to study the very early phase of star formation.Our first step is to utilize the data products by MWISP to make an unbiased survey for blue asymmetric line profiles of CO isotopical molecules.Within a total area of~2400 square degrees nearby the Galactic plane,we have found 3533 candidates showing blue-profiles,in which 3329 are selected from the^(12)CO&^(13)CO pair and 204 are from the^(13)CO&C^(18)O pair.Exploration of the parametric spaces suggests our samples are in the cold phase with relatively high column densities ready for star formation.Analysis of the spatial distribution of our samples suggests that they exist virtually in all major components of the galaxy.The vertical distribution suggest that the sources are located mainly in the thick disk of~85 pc,but still a small part are located far beyond Galactic midplane.Our follow-up observation indicates that these candidates are a good sample to start a search for infall motions,and to study the condition of very early phase of star formation.
基金supported by National Key R&D Program of China(2017YFA0402701)Key Research Program of Frontier Sciences of CAS(QYZDJSSW-SLH047)supports by the National Natural Science Foundation of China(Grant Nos.11503086 and 11503087)。
文摘We have conducted a large-field simultaneous survey of 12 CO,13 CO and C18O J=1-0 emission toward the Orion A giant molecular cloud(GMC)with a sky coverage of4.4 deg2 using the Purple Mountain Observatory(PMO)-13.7 m millimeter-wavelength telescope.We use the probability distribution function of the column density(N-PDF)to investigate the distribution of molecular hydrogen in the Orion A GMC.The H2 column density,derived from the 13CO emission,of the GMC is dominated by a log-normal distribution in the range from4×1021 to1.5×1023 cm-2 with excesses both at the low-density and high-density ends.The excess of the low-density end is possibly caused by an extended and low-temperature(10 K)component with velocities in the range of 5-8 km s-1.Compared with the northern sub-regions,the southern sub-regions of the Orion A GMC contain less gas with column density in NH2>1.25×1022 cm-2.The dispersions of the N-PDFs of the sub-regions are found to correlate with the evolutionary stages of the clouds across the Orion A GMC.The structure hierarchy of Orion A GMC is explored with the DENDROGRAM algorithm,and it is found that the GMC is composed of two branches.All structures except one in the tree have virial parameters less than 2,indicating self-gravity is important on the spatial scales from0.3 to4 pc.Although power-laws and departures from lognormal distributions are found at the high-density end of N-PDFs for active star-forming regions,the N-PDFs of structures in the Orion A GMC are predominantly lognormal on scales from R0.4 to 4 pc.
基金supported by National Science Foundation Grants(ECCS-1405594).
文摘Cloud-based video communication and networking has emerged as a promising new research paradigm to significantly improve the quality of experience for video consumers.An architectural overview of this promising research area was presented.This overview with an end-to-end partition of the cloud-based video system into major blocks with respect to their locations from the center of the cloud to the edge of the cloud was started.Following this partition,existing research efforts on how the principles of cloud computing can provide unprecedented support to 1)video servers,2)content delivery networks,and 3)edge networks within the global cloud video ecosystems were examined.Moreover,a case study was exemplfied on an edge cloud assisted HTTP adaptive video streaming to demonstrate the effectiveness of cloud computing support.Finally,by envisioning a list of future research topics in cloud-based video communication and networking a coclusion is made.
