Competitive accretion in the protocluster G10.6-0.4?

We present the results of high spatial resolution observations at 1.1 mm waveband, with the Submillimetre Array (SMA), towards the protocluster G10.6-0.4. The 1.1 mm continuum emission reveals seven dense cores, towards which infall motions are all detected with the red-shifted absorption dips in HCN (3--2) line. This is the first time that infall is seen towards multiple sources in a protocluster. We also identified four infrared point sources in this region, which are most likely Class 0/I protostars. Two jet-like structures are also identified from Spitzer/IRAC image. The dense core located in the centre has much larger mass than the off-centre cores. The clump is in overall collapse and the infall motion is supersonic. The standard deviation of core velocities and the velocity differences between the cores and the cloud/clump are all larger than the thermal velocity dispersion. The picture of G10.6-0.4 seems to favor the "competitive accretion" model but needs to be tested by further observations.Comment: 9 pages, 9 figures, 2 tables, Submitted to MNRA

Continuum Observations at 350 Microns of High-Redshift Molecular Emission Line Galaxies

We report observations of 15 high redshift (z = 1-5) galaxies at 350 microns using the Caltech Submillimeter Observatory and SHARC-II array detector. Emission was detected from eight galaxies, for which far-infrared luminosities, star formation rates, total dust masses, and minimum source size estimates are derived. These galaxies have star formation rates and star formation efficiencies comparable to other high redshift molecular emission line galaxies. The results are used to test the idea that star formation in these galaxies occurs in a large number of basic units, the units being similar to star-forming clumps in the Milky Way. The luminosity of these extreme galaxies can be reproduced in a simple model with (0.9-30) *10^6 dense clumps, each with a luminosity of 5 *10^5 Lsun, the mean value for such clumps in the Milky Way. Radiative transfer models of such clumps can provide reasonable matches to the overall SEDs of the galaxies. They indicate that the individual clumps are quite opaque in the far-infrared. Luminosity to mass ratios vary over two orders of magnitude, correlating strongly with the dust temperature derived from simple fits to the SED. The gas masses derived from the dust modeling are in remarkable agreement with those from CO luminosities, suggesting that the assumptions going into both calculations are reasonable.Comment: 17 pages, 8 figures. Accepted by Ap

SMA Observations of W3(OH) Complex: Physical and Chemical Differentiation between W3(H2_2O) and W3(OH)

We report on the Submillimeter Array (SMA) observations of molecular lines at 270 GHz toward W3(OH) and W3(H$_2$O) complex. Although previous observations already resolved the W3(H$_2$O) into two or three sub-components, the physical and chemical properties of the two sources are not well constrained. Our SMA observations clearly resolved W3(OH) and W3(H$_2$O) continuum cores. Taking the advantage of the line fitting tool XCLASS, we identified and modeled a rich molecular spectrum in this complex, including multiple CH$_3$CN and CH$_3$OH transitions in both cores. HDO, C$_2$H$_5$CN, O$^{13}$CS, and vibrationally excited lines of HCN, CH$_3$CN, and CH$_3$OCHO were only detected in W3(H$_2$O). We calculate gas temperatures and column densities for both cores. The results show that W3(H$_{2}$O) has higher gas temperatures, and larger column densities than W3(OH) as previously observed, suggesting physical and chemical differences between the two cores. We compare the molecular abundances in W3(H$_2$O) to those in the Sgr B2(N) hot core, the Orion KL hot core and the Orion Compact Ridge, and discuss the chemical origin of specific species. An east-west velocity gradient is seen in W3(H$_2$O), and the extension is consistent with the bipolar outflow orientation traced by water masers and radio jets. A north-south velocity gradient across W3(OH) is also observed. However, with current observations we can not assure if the velocity gradients are caused by rotation, outflow or radial velocity differences of the sub-components in W3(OH).Comment: Accepted by Ap

Indications of Inflow Motions in Regions Forming Massive Stars

Observational evidence for inflowing motions in massive star forming regions has been extremely rare. We have made a spectroscopic survey of a sample of 28 massive star forming cores associated with water masers. An optically thick line of HCN (3-2) was used in combination with optically thin lines [H^{13}CN (3-2) or C^{34}S (5-4), (3-2), and (2-1)], to identify ``blue'' line profiles that can indicate inflow. Comparing intensities for 18 double-peaked line profiles yields 11 blue and 3 red profiles that are statistically significant. In the full sample of 28 sources, 12 show blue profiles and 6 show red profiles that are statistically significant based on the velocity offsets of lines that are optically thick from those that are optically thin. These results indicate that HCN (3-2) emission may trace inflow in regions forming high-mass stars.Comment: 6 pages, 2 figures. In press for Aug.1 ApJ Letter

Probing Endothelial Cell Mechanics Under Disturbed Fluid Flow

Endothelial cells, which form the inner layer of the vasculature, interact with the extracellular matrix (ECM) by exerting mechanical contractile cell-substrate stress called tractions and cell-cell stresses called intercellular stresses. This cellular mechanical behavior involves many fundamental biological processes, including cell migration, differentiation, angiogenesis, and wound healing. Also, the inner surface of the vasculature, where endothelial cells reside, is constantly exposed to various fluid flows. The most variable fluid flow regimes occur primarily within branching regions of the vasculature. Endothelial cells residing within these regions experience disturbed flow, which consists of irregular flow patterns and extreme wall shear stress gradients. This phenomenon could upregulate endothelial cell signaling and gene expression into the proliferative and pro-inflammatory phase to promote endothelial dysfunction and contributes to the development of vascular diseases such as atherosclerosis, aneurysms, and coronary artery disease. However, the influence of disturbed flow on cellular mechanics has remained unclear. To get a better idea of how disturbed flow may affect traction, intercellular stresses, and various cell morphological parameters, a variety of studies were performed. The first study was conducted with a 3D flow chamber, and endothelial mechanical properties under disturbed flow were measured. The second study was performed with microchannels to visualize tractions differences among different vessel geometries and conditions in the abovementioned pathologies. The results yielded from this work will further our understanding of cellular mechanics under disturbed flow and potentially lead to novel therapeutics for endothelial dysfunction

Determinants of Capital Structure of IT Listed Firms: Comparative Evidence from China and India

ABSTRACT Purpose – This thesis explores the firm-specific factors that impact the capital structures of IT listed companies in China and India during the ten- year period from 2006 to 2015 and make a comparison between China and India, and to examine whether the capital structure theories derived from western countries can provide much better explanations for the capital structure decisions of IT listed companies in China and India. Methodology/approach – To achieve this goal, different classical theories about capital structures are reviewed, such as the Trade-Off model, the Pecking-Order theory, the Principal-Agency theory and the Free Cash Flow theory, for the sake of formulating testable propositions concerning the determinants of debt levels of IT service sectors in China and India. The work of the capital structure has emphasized on the Trade-Off model which indicates that companies finance their investment projects for tax benefits, while the Pecking-Order hypothesis suggests that firms should have a sequence of priority on gaining funds. I use the Pooled Ordinary Least Squares (Pooled OLS) and panel econometric techniques like Fixed Effects model and Random Effects model to investigate a sample of 52 and 176 IT companies listed on the Shenzhen Stock Exchange and Shanghai Stock Exchange and National Stock Exchange of India Ltd. (NSE) or Bombay Stock Exchange (BSE), respectively during the period between 2006 and 2015. Findings – The results gained confirm that firm size, profitability and liquidity are negatively linked with leverage ratio both in China and India, whereas there is contradiction relationship between China and India. To illustrate, tangibility is positively linked to the total leverage ratio in Chinese IT listed companies, whereas a negative correlation exists in Indian IT listed companies. Growth opportunity is positively related to leverage ratio in Indian IT sectors as opposed to Chinese IT sectors in which growth opportunity does not show to be significantly linked to the total leverage ratio. And the consequences show that the Pecking-Order theory has received reasonable support about the financing decisions of Chinese and Indian IT listed firms, while there is weak explaining power for the Trade- Off model. That is to say, the classical capital structure theories derived from western countries have an explanatory power for understanding the financing decisions of IT companies in China and India. Practice implications – This research to investigate the specific determinants of capital structure of Chinese and Indian IT companies upon which a more detailed description can be based. Additionally, these findings can help policymakers and managers in protecting the rights of investors and making optimal capital structure decisions. Originality/value – This is a pilot project comparing determinants of capital structure in Chinese IT industry and Indian IT industry, which contributes to the recent debate, i.e., although China and India are the developing countries, there is still a subtle difference in their determinants of capital structures. This is an extension literature of the determinants of capital structures, however, it is the first comparative study examined for IT sectors between China and India. Keywords Capital structure, China, India, IT listed companies Paper type Research pape