The HNCO ring in the Sgr B2 region     

Y.C. Minh  W.M. Irvine   《New Astronomy》2006,11(8):594-599

The large-scale structure associated with the 2′N HNCO peak in Sgr B2 [Minh, Y.C., Haikala, L., Hjalmarson, Å., Irvine, W.M., 1998. ApJ 498, 261 (Paper I)] has been investigated. A ring-like morphology of the HNCO emission has been found; this structure may be colliding with the Principal Cloud of Sgr B2. This “HNCO Ring” appears to be centered at (l,b) = (0.7°,−0.07°), with a radius of 5 pc and a total mass of 1.0 × 10⁵ to 1.6 × 10⁶ M. The expansion velocity of the Ring is estimated to be 30–40 km s⁻¹, which gives an expansion time scale of 1.5 × 10⁵ year. The morphology suggests that collision between the Ring and the Principal Cloud may be triggering the massive star formation in the Sgr B2 cloud sequentially, with the latest star formation taking place at the 2′N position. The chemistry related to HNCO is not certain yet, but if it forms mainly via reaction with the evaporated OCN⁻ from icy grain mantles, the observed enhancement of the HNCO abundance can be understood as resulting from shocks associated with the collision between the Principal Cloud and the expanding HNCO Ring.  相似文献   

Annual variation of atmospheric carbonyl sulfide in the marine atmosphere in the Southern Indian Ocean     

N. Mihalopoulos  J. P. Putaud  B. C. Nguyen  S. Belviso 《Journal of Atmospheric Chemistry》1991,13(1):73-82

Measurements of the concentrations of carbonyl sulfide (COS) in the marine atmosphere were made over a period of two years in the southern Indian Ocean (Amsterdam Island, 37°50 S–77°31 E; March 1987–February 1988 and April 1989–February 1990). The mean atmospheric COS concentration for the whole period was 475±48 pptv (n=544). Atmospheric COS concentrations show no significant seasonal variation with a summer to winter ratio of 1.05. Taking into account the observed variability of the atmospheric COS concentration (10%), a value of 1.4 yr is estimated as a lower limit for the atmospheric COS lifetime. A comparison of the COS data at Amsterdam Island with those obtained in the Southern Hemisphere in the past 12 yr does not reveal any significant trend in the tropospheric background COS mixing ratio.  相似文献   

Observations of interstellar HOCO+: abundance enhancements toward the galactic center     

Minh YC  Irvine WM  Ziurys LM 《The Astrophysical journal》1988,334(1):175-181

A survey of the 4(04)-3(03) and 1(01)-0(00) transitions of HOCO+ has been made toward several molecular clouds. The HOCO+ molecule was not observed in any sources except Sgr B2 and Sgr A. The 5(05)-4(04) and 4(14)-3(13) transitions were also detected toward Sgr B2. The results indicate that gas phase CO2 is not a major carbon reservoir in typical molecular clouds. In Sgr B2, the HOCO+ antenna temperature exhibits a peak approximately 2' north of the Sgr B2 central position (Sgr B2[M]) and the 4(04)-3(03) line emission is extended over a approximately 10' x 10' region. The column density of HOCO+ at the northern peak in Sgr B2 is approximately 3 x 10(14) cm-2, and the fractional abundance relative to H2 > or = 3 x 10(-10), which is about 2 orders of magnitude greater than recent predictions of quiescent cloud ion-molecule chemistry.  相似文献   

Controlling geological and hydrogeological processes in an arsenic contaminated aquifer on the Red River flood plain,Vietnam   总被引：1，自引：0，他引：1  

Flemming Larsen  Nhan Quy Pham  Nhan Duc Dang  Dieke Postma  Søren Jessen  Viet Hung Pham  Thao Bach Nguyen  Huy Duc Trieu  Luu Thi Tran  Hoan Nguyen  Julie Chambon  Hoan Van Nguyen  Dang Hoang Ha  Nguyen Thi Hue  Mai Thanh Duc  Jens Christian Refsgaard 《Applied Geochemistry》2008

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Biodiversity of meiofauna in the intertidal khe nhan mudflat,can gio mangrove forest,vietnam with special emphasis on free living nematodes     

Quang Ngo Xuan  Ann Vanreusel  Nguyen Vu Thanh  Nic Smol 《Ocean Science Journal》2007,42(3):135-152

The ecological aspect of meiofaunal communities in Can Gio mangrove forest, Ho Chi Minh city, Vietnam has not been investigated before. The composition, distribution, density and biodiversity of meiofaunal communities were studied along an intertidal transect at the Khe Nhan mudflat. Each time, three replicate samples were collected in four stations along a transect following the water line from low tide level up to the mangrove forest edge. In total, 18 meiofaunal taxa were found with the dominant taxa belonging to Nematoda, Copepoda, Sarcomastigophora and Polychaeta. The densities of meiofauna ranged from 1156 inds/10 cm² to 2082 inds/10 cm². The increase in densities from the mangrove forest edge towards the low water line was significant. Along the mudflat transect, the biodiversity (expressed by different indices) was relatively high at different taxonomic levels but did not vary significantly along the mudflat except for taxa richness. Eighty nematode genera belonging to 24 families with Comesomatidae having the highest abundance 33.8 % were found.Theristus andNeochromadora decreased in densities from the lower water line towards the mangrove forest edge, whileParacomesoma andHopperia are typical and more abundant at the middle of the mudflat.Halalaimus increased from high on the mudflat to the low water line.  相似文献   

Adaptive fisheries management in Vietnam: The use of indicators and the introduction of a multi-disciplinary Marine Fisheries Specialist Team to support implementation     

Jesper Raakjær  Dao Manh Son  Karl-Johan Stæhr  Holger Hovgård  Nguyen Thi Dieu Thuy  Kristine Ellegaard  Frank Riget  Dang Van Thi  Phung Giang Hai 《Marine Policy》2007

Vietnam is in the process of introducing adaptive management based on indicators and time-series to manage its marine fisheries. The development of indicator-based frameworks for fisheries management has accelerated in recent years. This article describes the suite of indicators being suggested or used in Vietnam including the data-collection system. The Vietnamese approach is supported by an institutional structure consisting of a multi-disciplinary advisory system to facilitate the process of using indicators and to introduce knowledge-based management. The article concludes by identifying current problems and weaknesses and by providing suggestions for future improvement of the system.  相似文献   

Seasonal variations of atmospheric sulfur dioxide and dimethylsulfide concentrations at Amsterdam Island in the southern Indian Ocean     

J. P. Putaud  N. Mihalopoulos  B. C. Nguyen  J. M. Campin  S. Belviso 《Journal of Atmospheric Chemistry》1992,15(2):117-131

Daily measurements of atmospheric sulfur dioxide (SO₂) concentrations were performed from March 1989 to January 1991 at Amsterdam Island (37°50 S–77°30 E), a remote site located in the southern Indian Ocean. Long-range transport of continental air masses was studied using Radon (²²²Rn) as continental tracer. Average monthly SO₂ concentrations range from less than 0.2 to 3.9 nmol m^-3 (annual average = 0.7 nmol m^-3) and present a seasonal cycle with a minimum in winter and a maximum in summer, similar to that described for atmospheric DMS concentrations measured during the same period. Clear diel correlation between atmospheric DMS and SO₂ concentrations is also observed during summer. A photochemical box model using measured atmospheric DMS concentrations as input data reproduces the seasonal variations in the measured atmospheric SO₂ concentrations within ±30%. Comparing between computed and measured SO₂ concentrations allowed us to estimate a yield of SO₂ from DMS oxidation of about 70%.  相似文献   

Seasonal variation of atmospheric dimethylsulfide at Amsterdam Island in the southern Indian Ocean     

B. C. Nguyen  N. Mihalopoulos  S. Belviso 《Journal of Atmospheric Chemistry》1990,11(1-2):123-141

Daily measurements of atmospheric concentrations of dimethylsulfide (DMS) were carried out for two years in a marine site at remote area: the Amsterdam Island (37°50S–77°31E) located in the southern Indian Ocean. DMS concentrations were also measured in seawater. A seasonal variation is observed for both DMS in the atmosphere and in the sea-surface. The monthly averages of DMS concentrations in the surface coastal seawater and in the atmosphere ranged, respectively, from 0.3 to 2.0 nmol l^-1 and from 1.4 to 11.3 nmol m^-3 (34 to 274 pptv), with the highest values in summer. The monthly variation of sea-to-air flux of DMS from the southern Indian Ocean ranges from 0.7 to 4.4 mol m^-2 d^-1. A factor of 2.3 is observed between summer and winter with mean DMS fluxes of 3.0 and 1.3 mol m^-2 d^-1, respectively.  相似文献   

Groundwater resources management under environmental constraints in Shiroishi of Saga plain,Japan     

Nguyen Cao Don  Nguyen Thi Minh Hang  Hiroyuki Araki  Hiroyuki Yamanishi  Kenichi Koga 《Environmental Geology》2006,49(8):1223-1223

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Study of a semi‐active stiffness damper under various earthquake inputs     

S. L. Djajakesukma  B. Samali  H. Nguyen 《地震工程与结构动力学》2002,31(10):1757-1776

Semi‐active stiffness damper (SASD) is one of many semi‐active control systems with the capability to mitigate the dynamic response using only a small amount of external power. The system consists of a hydraulic damper connected to the bracing frame in a selected story unit. In this paper, study of a SASD in two building models of five‐stories under four benchmark earthquake records is reported. The purpose of this study is to evaluate the effectiveness of the control system against structure type and varying earthquake inputs. Various control laws are chosen to work with SASD, such as: resetting control, switching control, linear quadratic regulator (LQR) and modified LQR, and the results are compared with no control and passive control cases. Numerical results show that the use of a SASD is effective in reducing seismic responses. Control effectiveness is dependent on the type of structure and earthquake excitation. Passive control is less effective than other control cases as expected. Resetting control, switching control and LQR generally perform similarly in response reduction. While modified LQR is more efficient and robust compared with other control algorithms. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献