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   

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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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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Parameter identification for lined tunnels in a viscoplastic medium   总被引：2，自引：0，他引：2  

B. Lecampion  A. Constantinescu  D. Nguyen Minh 《国际地质力学数值与分析法杂志》2002,26(12):1191-1211

This paper is dedicated to the identification of constitutive parameters of elasto‐viscoplastic constitutive law from measurements performed on deep underground cavities (typically tunnels). This inverse problem is solved by the minimization of a cost functional of least‐squares type. The exact gradient is computed by the direct differentiation method and the descent is done using the Levenberg–Marquardt algorithm. The method is presented for lined or unlined structures and is applied for an elastoviscoplastic constitutive law of the Perzyna class. Several identification problems are presented in one and two dimensions for different tunnel geometries. The used measurements have been obtained by a preliminary numerical simulation and perturbed with a white noise. The identified responses match the measurements. We also discuss the usage of the sensitivity analysis of the system, provided by the direct differentiation method, for the optimization of in situ monitoring. The sensitivity distribution in space and time assess the location of the measurements points as well as the time of observation needed for reliable identification. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

On the Thermo-Hydro-Mechanical Behaviour of a Sheared Callovo-Oxfordian Claystone Sample with Respect to the EDZ Behaviour     

Hamza Menaceur  Pierre Delage  Anh Minh Tang  Nathalie Conil 《Rock Mechanics and Rock Engineering》2016,49(5):1875-1888

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Mobilization of arsenic and iron from Red River floodplain sediments, Vietnam   总被引：3，自引：0，他引：3  

Dieke Postma  Søren Jessen  Mai Thanh Duc  Pham Hung Viet  Flemming Larsen 《Geochimica et cosmochimica acta》2010,74(12):3367-508

Sediments from the Red River and from an adjacent floodplain aquifer were investigated with respect to the speciation of Fe and As in the solid phase, to trace the diagenetic changes in the river sediment upon burial into young aquifers, and the related mechanisms of arsenic release to the groundwater. Goethite with subordinate amounts of hematite were, using Mössbauer spectroscopy, identified as the iron oxide minerals present in both types of sediment. The release kinetics of Fe, As, Mn and PO₄ from the sediment were investigated in leaching experiments with HCl and 10 mM ascorbic acid, both at pH 3. From the river sediments, most of the Fe and As was mobilized by reductive dissolution with ascorbic acid while HCl released very little Fe and As. This suggests As to be associated with an Fe-oxide phase. For oxidized aquifer sediment most Fe was mobilized by ascorbic acid but here not much As was released. However, the reduced aquifer sediments contained a large pool of Fe(II) and As that is readily leached by HCl, probably derived from an unidentified authigenic Fe(II)-containing mineral which incorporates As as well. Extraction with ascorbic acid indicates that the river sediments contain both As(V) and As(III), while the reduced aquifer sediment almost exclusively releases As(III). The difference in the amount of Fe(II) leached from river and oxidized aquifer sediments by ascorbic acid and HCl, was attributed to reductive dissolution of Fe(III). The reactivity of this pool of Fe(III) was quantified by a rate law and compared to that of synthetic iron oxides. In the river mud, Fe(III) had a reactivity close to that of ferrihydrite, while the river sand and oxidized aquifer sediment exhibited a reactivity ranging from lepidocrocite or poorly crystalline goethite to hematite. Mineralogy by itself appears to be a poor predictor of the iron oxide reactivity in natural samples using the reactivity of synthetic Fe-oxides as a reference. Sediments were incubated, both unamended and with acetate added, and monitored for up to 2 months. The river mud showed the fastest release of both Fe and As, while the effect of acetate addition was minor. This suggests that the presence of reactive organic carbon is not rate limiting. In the case of the river and aquifer sediments, the release of Fe and As was always stimulated by acetate addition and here reactive organic carbon was clearly the rate limiting factor. The reduced aquifer sediment apparently can sustain slower but prolonged microbially-driven release of As. The highly reactive pools of Fe(III) and As in the river mud could be due to reoxidation of As and Fe contained in the reducing groundwater from the floodplain aquifers that are discharging into the river. Deposition of the suspended mud on the floodplain during high river stages is proposed to be a major flux of As onto the floodplain and into the underlying aquifers.  相似文献   

Experimental study on the mechanical behaviour of a heat exchanger pile using physical modelling     

Neda Yavari  Anh Minh Tang  Jean-Michel Pereira  Ghazi Hassen 《Acta Geotechnica》2014,9(3):385-398

This study aims to provide knowledge on the thermo-mechanical behaviour of heat exchanger piles, through a laboratory scale model. The model pile (20 mm in external diameter) was embedded in dry sand. The behaviour of the axially loaded pile under thermal cycles was investigated. After applying the axial load on the pile head, the pile temperature was varied between 5 and 30 °C. Seven tests, corresponding to various axial loads ranging from 0 to 70 % of the pile estimated bearing capacity, were performed. The results on pile head displacement show that heating under low axial load induced heave and cooling induced settlement; the pile temperature-displacement curve was found to be reversible and compatible with the thermal expansion curve of the pile. However, at higher axial loads, irreversible settlement of the pile head was observed after a few thermal cycles. The axial load profile measured by the strain gauges evidenced that the pile head load was mainly transferred to the pile toe. Nevertheless, thermal cycles modified significantly the mobilised skin friction along the pile. The total pressure measured at various locations in the soil mass was also slightly influenced by the thermal cycles.  相似文献   

XMM-LSS discovery of a  z= 1.22  galaxy cluster     

M. N. Bremer  I. Valtchanov  J. Willis  B. Altieri  S. Andreon  P. A. Duc  F. Fang  C. Jean  C. Lonsdale  F. Pacaud  M. Pierre  D. L. Shupe  J. A. Surace  I. Waddington 《Monthly notices of the Royal Astronomical Society》2006,371(3):1427-1434

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Zero is the only acceptable leakage rate for geologically stored CO 2 : an editorial comment     

Minh Ha-Duong  Rodica Loisel 《Climatic change》2009,93(3-4):311-317

Leakage is one of the main concerns of all parties involved with the development of Carbon Capture and Storage. From an economic point of view, van der Zwaan and Gerlagh (2009) suggest that CCS remains a valuable option even with CO₂ leakage rate as high as of a few % per year. But what is valuable is, ultimately, determined by social preferences and parameters that are beyond economic modeling. Examining the point of view of four stakeholder groups: industry, policy-makers, environmental NGOs and the general public, we conclude that there is a social agreement today: zero is the only acceptable carbon leakage rate.  相似文献