6,120 research outputs found

    A molecular line study towards massive extended green object clumps in the southern sky: chemical properties

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    We present a molecular line study towards 31 extended green object (EGO) clumps in the southern sky using data from MALT90 (Millimetre Astronomy Legacy Team 90 GHz). According to previous multiwavelength observations, we divide our sample into two groups: massive young stellar objects (MYSOs) and HII regions. Our results seem to support that N2H+ and C2H emissions mainly come from the gas inside quiescent clumps. In addition, we also find that the [N2H+]/[H13CO+] and [C2H]/[H13CO+] relative abundance ratios decrease from MYSOs to HII regions. These results suggest depletion of N2H+ and C2H in the late stages of massive-star formation, probably caused by the formation of HII regions inside. N2H+ and C2H might be used as chemical clocks for massive-star formation by comparing with other molecules such as H13CO+ and HC3N

    A multiwavelength study of the star forming H II region Sh2-82

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    Based on a multiwavelength study, the interstellar medium and young stellar objects (YSOs) around the HII region Sh2-82 have been analyzed. Two molecular clumps were found from the archival data of the Galactic Ring Survey, and using the Two Micron All-Sky Survey catalog, we found two corresponding young clusters embedded in the molecular clumps. The very good relations between CO emission, infrared shells and YSOs suggest that it is probably a triggered star formation region from the expansion of Sh2-82. We further used the data from the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire from Spitzer to study the YSOs within the two clumps, confirming star formation in this region. By spectral energy distribution fits to each YSO candidate with infrared excess, we derived the slope of the initial mass function. Finally, comparing the HII region's dynamical age and the fragmentation time of the molecular shell, we discard the "collect and collapse" process as being the triggering mechanism for YSO formation. Sh2-82 can be a mixture of other processes such as radiative-driven implosion and/or collisions with pre-existing clumps.Comment: in raa, 2012, 12, 65

    A multi-transition molecular line study of infrared dark cloud G331.71+00.59

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    Using archive data from the Millimeter Astronomy Legacy Team Survey at 90 GHz (MALT90), carried out using the Mopra 22-m telescope, we made the first multi-transition molecular line study of infrared dark cloud (IRDC) MSXDC G331.71+00.59. Two molecular cores were found embedded in this IRDC. Each of these cores is associated with a known extended green object (EGO), indicating places of massive star formation. The HCO+ (1-0) and HNC (1-0) transitions show prominent blue or red asymmetric structures, suggesting outflow and inflow activities of young stellar objects (YSOs). Other detected molecular lines include H13CO+ (1-0), C2H (1-0), HC3N (10-9), HNCO(404-303) and SiO (2-1), which are typical of hot cores and outflows. We regard the two EGOs as evolving from the IRDC to hot cores. Using public GLIMPS data, we investigate the spectral energy distribution of EGO G331.71+0.60. Our results support this EGO being a massive YSO driving the outflow. G331.71+0.58 may be at an earlier evolutionary stage

    Kinematics and chemistry of the hot core in G20.08-0.14N

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    We present Submillimeter Array observations of the massive star-forming region G20.08-0.14N at 335 and 345 GHz. With the SMA data, 41 molecular transitions were detected related to 11 molecular species and their isotopologues, including SO2, SO, C34S, NS, C17O, SiO, CH3OH, HC3N, H13CO+, HCOOCH3 and NH2CHO. In G20.08-0.14N, 10 transition lines of the detected 41 transition lines belong to SO2, which dominates the appearance of the submillimeter-wave spectrum. To obtain the spatial kinematic distribution of molecules in G20.08-0.14N, we chose the strongest and unblended lines for the channel maps. The channel maps of C34S an SiO, together with their position-velocity diagrams, present that there are two accretion flows in G20.08-0.14N. Additionally, SiO emission shows a collimated outflow at the NE-SW direction. The direction of the outflow is for the first time revealed. The rotational temperature and the column density of CH3OH are 105 K and 3.1*10^{17} cm^{-2}, respectively. Our results confirm that a hot core is associated with G20.08-0.14N. The hot core is heated by a protostar radiation at it center, not by the external excitation from shocks. The images of the spatial distribution of different species have shown that the different molecules are located at the different positions of the hot core. Through comparing the spatial distributions and abundances of the molecules, we discuss possible chemical processes for producing the complex sulfur-bearing, nitrogen-bearing and oxygen-bearing molecules in G20.08-0.14N.Comment: 13 pages, 7 figures. Accepted by MNRA

    CO J=2-1 and CO J=3-2 observations toward the high-mass protostellar candidate IRAS 20188+3928

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    We have carried out 12CO J=2-1 and 12CO J=3-2 observations toward the high-mass protostellar candidate IRAS 20188+3928. Compared with previous observations, the 12CO J=2-1 and 12CO J=3-2 lines both have asymmetric profiles with an absorption dip. The velocity of the absorption dip is 1.0 km/s. The spectral shape may be caused by rotation. The velocity-integrated intensity map and position-velocity diagram of the 12CO J=2-1 line present an obvious bipolar component, further verifying that this region has an outflow motion. This region is also associated with an HII region, an IRAS source, and an H2O maser. The H2O maser has the velocity of 1.1 km/s. Compared with the components of the outflow, we find that the H2O maser is not associated with the outflow. Using the large velocity gradient model, we concluded that possible averaged gas densities of the blueshifted lobe and redshifted lobe are 1.0*10^{5}cm3and2.010 cm^{-3} and 2.0*10^{4} cm^{-3}, while kinetic temperatures are 26.9 K and 52.9 K, respectively. Additionally, the outflow has {a} higher integrated intensity ratio (I_{CO J=3-2}/I_{CO J=2-1}).Comment: 8 pages, 5 figures, Accepted by Research in Astronomy and Astrophysic

    Predict Forex Trend via Convolutional Neural Networks

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    Deep learning is an effective approach to solving image recognition problems. People draw intuitive conclusions from trading charts; this study uses the characteristics of deep learning to train computers in imitating this kind of intuition in the context of trading charts. The three steps involved are as follows: 1. Before training, we pre-process the input data from quantitative data to images. 2. We use a convolutional neural network (CNN), a type of deep learning, to train our trading model. 3. We evaluate the model's performance in terms of the accuracy of classification. A trading model is obtained with this approach to help devise trading strategies. The main application is designed to help clients automatically obtain personalized trading strategies.Comment: 30 pages, 41 figure

    Numerical Study of Drop Motion on a Surface with Wettability Gradient and Contact Angle Hysteresis

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    In this work, the motion of a 2-D drop on a surface with given wettability gradient is studied numerically by a hybrid lattice-Boltzmann finite-difference method using the multiple-relaxation-time collision model. We incorporate the geometric wetting boundary condition that allows accurate implementation of a contact angle hysteresis model. The method is first validated through three benchmark tests, including the layered Poiseuille flow with a viscosity contrast, the motion of a liquid column in a channel with specified wettability gradient and the force balance for a static drop attached to a surface with hysteresis subject to a body force. Then, simulations of a drop on a wall with given wettability gradient are performed under different conditions. The effects of the Reynolds number, the viscosity ratio, the wettability gradient, as well as the contact angle hysteresis on the drop motion are investigated in detail. It is found that the capillary number of the drop in steady state is significantly affected by the viscosity ratio, the magnitudes of the wettability gradient and the contact angle hysteresis, whereas it only shows very weak dependence on the Reynolds number

    Wetting Boundary Conditions in Phase-Field-Based Simulation of Binary Fluids: Some Comparative Studies and New Development

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    We studied several wetting boundary conditions (WBCs) in the simulation of binary fluids based on phase-field theory. Five WBCs, three belonging to the surface energy (SE) formulation using the linear, cubic and sine functions (denoted as LinSE, CubSE and SinSE), the fourth using a geometric formulation (Geom), and the fifth using a characteristic interpolation (CI), were compared with each other through the study of several problems: (1) the static contact angle of a drop; (2) a Poiseuille flow-driven liquid column; (3) a wettability gradient (WG)-driven liquid column; (4) drop dewetting. It was found that while all WBCs can predict the static contact angle fairly accurately, they may affect the simulation outcomes of dynamic problems differently, depending on the driving mechanism. For the flow-driven problem, to use different WBCs had almost no effect on the flow characteristics over a large scale. But for other capillarity-driven problems, the WBC had some noticeable effects. For the WG-driven liquid column, Geom gave the most consistent prediction between the drop velocity and dynamic contact angles, and LinSE delivered the poorest prediction in this aspect. Except for Geom, the dynamic contact angle differed from the prescribed (static) one when other WBCs were used. For drop dewetting, Geom led to the most violent drop motion whereas CubSE caused the weakest motion; the initial contact line velocity was also found to be dependent on the WBC. For several problems, CubSE and SinSE gave almost the same results, and those by Geom and CI were close as well, possibly due to similar consideration in their design. Besides various comparisons, a new implementation that may be used for all WBCs was proposed to mimic the wall energy relaxation and control the degree of slip. This new procedure made it possible to allow the simulations to match experimental measurements well

    Tests of the Einstein Equivalence Principle using TeV Blazars

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    The observed time delays between different energy bands from TeV blazars provide a new interesting way of testing the Einstein Equivalence Principle (EEP). If the whole time delay is assumed to be dominated by the gravitational field of the Milky Way, the conservative upper limit on the EEP can be estimated. Here we show that the strict limits on the differences of the parameterized post-Newtonian parameter γ\gamma values are γTeVγkeV<3.86×103\gamma_{\rm TeV}-\gamma_{\rm keV}<3.86\times10^{-3} for Mrk 421 and γTeVγkeV<4.43×103\gamma_{\rm TeV}-\gamma_{\rm keV}<4.43\times10^{-3} for Mrk 501, while expanding the scope of the tested EEP energy range out to the TeV--keV range for the first time. With the small time lag from the 0.2--0.8 TeV and >0.8>0.8 TeV light curves of PKS 2155-304, a much more severe constraint on γ\gamma differences of 106\sim10^{-6} can be achieved, although the energy difference is of order of \sim TeV. Furthermore, we can combine these limits on the energy dependence of γ\gamma with the bound on the absolute γ\gamma value γ10.3%\gamma-1\sim0.3\% from light deflection measurements at the optical (eV) bands, and conclude that this absolute bound on γ\gamma can be extended from optical to TeV energies.Comment: 4 pages, accepted for publication in the Astrophysical Journal Letter

    HNCO: A Molecule Traces Low-velocity Shock

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    Using data from MALT90 (Millimetre Astronomy Legacy Team Survey at 90 GHz), we present molecular line study of a sample of ATLASGAL (APEX Telescope Large Area Survey of the Galaxy) clumps. Twelve emission lines have been detected in all. We found that in most sources, emissions of HC3_3N, HN13^{13}C, CH3_3CN, HNCO and SiO show more compact distributions than those of HCO+^+, HNC, HCN and N2_2H+^+. By comparing with other molecular lines, we found that the abundance of HNCO (χ\chi(HNCO)) correlates well with other species such as HC3N, HNC, C2H, H13CO+ and N2H+. Previous studies indicate the HNCO abundance could be enhanced by shocks. However, in this study, we found the abundance of HNCO does not correlate well with that of SiO, which is also a good tracer of shocks. We suggest this may be because HNCO and SiO trace different parts of shocks. Our analysis indicates that the velocity of shock traced by HNCO tends to be lower than that traced by SiO. In the low-velocity shocks traced by HNCO, the HNCO abundance increases faster than that of SiO. While in the relatively high-velocity shocks traced by SiO, the SiO abundance increases faster than that of HNCO. We suggest that in the infrared dark cloud (IRDC) of MSXDC G331.71+00.59, high-velocity shocks are destroying the molecule of HNCO
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