Multitransition study and new detections of class II methanol masers     

Dinah M. Cragg  rej M. Sobolev  Simon P. Ellingsen  J. L. Caswell  Peter D. Godfrey  Svetlana V. Salii  Richard G. Dodson 《Monthly notices of the Royal Astronomical Society》2001,323(4):939-951

We have used the ATNF Mopra antenna and the SEST antenna to search in the directions of several class II methanol maser sources for emission from six methanol transitions in the frequency range 85–115 GHz. The transitions were selected from excitation studies as potential maser candidates. Methanol emission at one or more frequencies was detected from five of the maser sources, as well as from Orion KL. Although the lines are weak, we find evidence of maser origin for three new lines in G345.01+1.79, and possibly one new line in G9.62+0.20.
The observations, together with published maser observations at other frequencies, are compared with methanol maser modelling for G345.01+1.79 and NGC 6334F. We find that the majority of observations in both sources are consistent with a warm dust (175 K) pumping model at hydrogen density ∼10⁶ cm⁻³ and methanol column density ∼ 5×10¹⁷ cm⁻². The substantial differences between the maser spectra in the two sources can be attributed to the geometry of the maser region.  相似文献   

A new late Pleistocene subfossil site (Tsaramody,Sambaina basin,central Madagascar) with implications for the chronology of habitat and megafaunal community change on Madagascar's Central Highlands     

Karen E. Samonds  Brooke E. Crowley  Tojoarilala Rinasoa Nadia Rasolofomanana  Miora Christelle Andriambelomanana  Harimalala Tsiory Andrianavalona  Tolotra Niaina Ramihangihajason  Ravoniaina Rakotozandry  Zafindratsaravelo Bototsemily Nomenjanahary  Mitchell T. Irwin  Neil A. Wells  Laurie R. Godfrey 《第四纪科学杂志》2019,34(6):379-392

Madagascar is a complex ‘biodiversity hotspot’ with a rapidly dwindling biota. The Late Quaternary subfossil record includes many extinct species whose loss is attributed to natural climate change and human impacts. Investigation of the chronology of these events is challenging because few localities document pre‐Holocene communities not impacted by humans. Caves with extinct lemurs of large body size comprise some of Madagascar's richest subfossil sites, but provide only a limited window into the island's past. Open highland sites may have fewer primates, but may better document other megafauna, and allow the analysis of the role of the Central Highlands as refugia and as corridors for the dispersal of vertebrates before and after human arrival. Here we present a new subfossil site, Tsaramody (Sambaina basin, Central Madagascar), a high‐altitude wetland area that preserves a diverse late glacial and postglacial vertebrate community. Tsaramody bears testimony to fluctuations in the highland flora during the transition from glacial to postglacial conditions, and the composition of a highland vertebrate community before humans arrived. We compare its biota to those of other sites to begin to document the decline and disappearance of megafauna from some of Madagascar's open ecosystems – wetlands dominated by hippopotamuses and crocodylians. © 2019 John Wiley & Sons, Ltd.  相似文献   

Development of techniques for monitoring gas-phase sodium species formed during coal combustion and gasification     

B. L. Chadwick  R. A. Ashman  A. Campisi  G. J. Crofts  P. D. Godfrey  P. G. Griffin  A. L. Ottrey  R. J. S. Morrison 《International Journal of Coal Geology》1996,32(1-4)

The development of techniques suitable for on-line analysis of gas-phase molecular sodium species, resulting from the combustion and gasification of low-rank coals is described. In particular two techniques have been demonstrated, these are: (a) laser-induced photofragment fluorescence and (b) microwave spectroscopy. The photofragment technique can be applied in situ and yields excellent detection limits (<0.1 ppb of NaCl and 1 ppb NaOH) with good discrimination between the two major gas-phase species — NaCl and NaOH. Limitations of this technique include absorption of the ultraviolet (UV) photolysis excitation by other chemical species and particulates. Microwave spectroscopy shows promise in determining the sodium species distribution in the gas-phase. A purpose built analytical instrument (known as MILLIJET HT) is being developed for application in high-temperature environments. Early results indicate detection limits of <100 ppb NaCl. Lack of sensitivity for NaOH is being attributed to the formation of NaOH dimers and larger clusters. Detailed calculations of the dimer structure and the dimer-monomer reaction have been undertaken in order to maximise the performance of the instrument.  相似文献   

The Shallow Meridional Overturning Circulation in the Northern Indian Ocean and Its Interannual Variability   总被引：3，自引：0，他引：3  

HU Ruijin  LIU Qinyu  WANG Qi  J. Stuart GODFREY  MENG Xiangfeng 《大气科学进展》2005,22(2):220-229

The shallow meridional overturning circulation (upper 1000 m) in the northern Indian Ocean and its interannual variability are studied, based on a global ocean circulation model (MOM2) with an integration of 10 years (1987-1996). It is shown that the shallow meridional overturning circulation has a prominent seasonal reversal characteristic. In winter, the flow is northward in the upper layer and returns southward at great depth. In summer, the deep northward inflow upwells north of the equator and returns southward in the Ekman layer. In the annual mean, the northward inflow returns through two branches: one is a southward flow in the Ekman layer, the other is a flow that sinks near 10°N and returns southward between 500 m and 1000 m. There is significant interannual variability in the shallow meridional overturning circulation, with a stronger (weaker) one in 1989 (1991) and with a period of about four years. The interannual variability of the shallow meridional overturning circulation is intimately r  相似文献   

Mass Movement of Mancos Shale Crust Near Caineville, Utah: A 30-year Record     

Andrew E. Godfrey 《Geografiska Annaler: Series A, Physical Geography》1997,79(3):185-194

Rates of soil creep were studied periodically over a 30-year period in southeastern Utah on Mancos Shale badland slopes averaging 35 degrees. More intensive studies were carried out over a 10-year period on slopes averaging 40 degrees. On the 35 degree slope the average rate of movement was 2.71 cm yr⁻¹.On the 40 degree slopes, rates varied from 3.14 to 5.94 cm yr⁻¹.
Individual rates of movement varied widely, but average movement of a given line was consistent. No statistical differences in rates of movement were found between north- and south-facing slopes.
About two-thirds of the total movement occurred during the winter/spring period; episodes of rapid movement coincided with years in which storms deposited at least 0.6 cm of precipitation per day for at least two consecutive days. Downslope rotation of nails indicates that creep involves only the top few centimeters of soil.  相似文献   

The clouds of Venus: Sulfuric acid by the lead chamber process     

Godfrey T. Sill 《Icarus》1983,53(1):10-17

The Pioneer Venus atmospheric probe provided new data on the louds of Venus. A model consistent with this data involves SO₂ being oxidized to H₂SO₄ by NO_x in the presence of H₂O. NO_x also forms nitrosylsulfuric acid (NOHSO₄) dissolved in the H₂SO₄ droplets. This acid solution, along with SO₂ and perhaps NO₂, can explain the uv and visible reflection spectrum of Venus. In the middle and lower clouds NOHSO₄ forms solid particles.  相似文献   

Monitoring coastal morphology: the potential of low-cost fixed array action cameras for 3D reconstruction     

Samantha Godfrey  James Cooper  Frederic Bezombes  Andrew Plater 《地球表面变化过程与地形》2020,45(11):2478-2494

The combination of structure-from-motion with multi-view stereo (SfM-MVS) photogrammetry has become an increasingly popular method for the monitoring and three-dimensional (3D) reconstruction of coastal environments. Climate change is driving the potential for increased coastal landward retreat meaning geomorphological monitoring using methods such as SfM-MVS has become essential for detecting and tracking impacts. SfM-MVS has been well-researched with a variety of platforms and spatial and temporal resolutions using mainly rectilinear digital cameras in coastal settings. However, there has been no assessment of the potential of fixed multi-camera arrays to monitor landward retreat or on the significance of camera placement in relation to the scene. This study presents an innovative method of image acquisition using a purpose-built camera grid and GoPro© action camera to evaluate the combined effects of camera height, obliqueness and overlap at a site of known landward retreat. This approach examines the effect of camera placement on scene reconstruction to aid the design of a multi-camera array. SfM-MVS dense point clouds display millimetre accuracy when compared to equivalent terrestrial laser scans and strong image network geometry with internal precision estimates of < 3 mm. Comparable point cloud reconstruction can be achieved with a small number of images stationed in appropriate positions. Initial results show as few as five images positioned at a cliff to camera ratio of 3:4.18 and camera obliqueness of 40° can provide reconstruction in the range of millimetres (mean error of 4.79 mm). These findings illustrate the importance of camera placement when using multiple cameras and aid the design of a low-cost, fixed multi-camera array for use at sites of small-scale landward retreat. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd  相似文献   

Pharmaceuticals in on-site sewage effluent and ground water, Western Montana   总被引：2，自引：0，他引：2  

Godfrey E  Woessner WW  Benotti MJ 《Ground water》2007,45(3):263-271

  相似文献   

On the mechanism of the seasonal variability of SST in the tropical Indian Ocean   总被引：5，自引：1，他引：4  

HU Ruijin  LIU Qinyu  MENG Xiangfeng  J. Stuart GODFREY 《大气科学进展》2005,22(3):451-462

A general form of an equation that "explicitly" diagnoses SST change is derived. All other equations in wide use are its special case. Combining with the data from an ocean general circulation model (MOM2) with an integration of 10 years (1987-1996), the relative importances of various processes that determine seasonal variations of SST in the tropical Indian Ocean are compared mainly for January, April, July and October. The main results are as follows. (1) The net surface heat flux is the most important factor affecting SST over the Arabian Sea, the Bay of Bengal and the region south of the equator in January; in April, its influence covers almost the whole region studied; whereas in July and October, this term shows significance only in the regions south of 10°S and north of the equator, respectively. (2) The horizontal advection dominates in the East African-Arabian coast and the region around the equator in January and July; in October, the region is located south of 10°S. (3) The entrainment is s  相似文献   

Modelling hydrological connectivity of tropical floodplain wetlands via a combined natural and artificial stream network          下载免费PDF全文

Fazlul Karim  Anne Kinsey‐Henderson  Jim Wallace  Paul Godfrey  Angela H. Arthington  Richard G. Pearson 《水文研究》2014,28(23):5696-5710

The ecological condition and biodiversity values of floodplain wetlands are highly dependent on the hydrological connectivity of wetlands to adjacent rivers. This paper describes a method for quantifying connectivity between floodplain wetlands and the main rivers in a wet tropical catchment of northern Australia. We used a one‐dimensional hydrodynamic model to simulate time‐varying water depths across the stream network (i.e. rivers, streams and man‐made drains). The timing and duration of connectivity of seven wetlands (four natural and three artificial) with the two main rivers in the catchment were then calculated for different hydrological conditions. Location and areal extent of the wetlands and the stream network were identified using high‐resolution laser altimetry, and these data formed key inputs to the hydrodynamic model. The model was calibrated using measured water depths and discharges across the floodplain. An algorithm was developed to identify contiguous water bodies at daily time steps, and this gave the temporal history of connection and disconnection between wetlands and the rivers. Simulation results show that connectivity of individual wetlands to both rivers varies from 26 to 365 days during an average hydrological condition. Location, especially proximity to a main river, and wetland type (natural stream or artificial drain) were identified as key factors influencing these levels of connectivity. Some natural wetlands maintain connection with the river for most or all of the year, whereas the connectivity of some artificial wetlands varies from 26 to 36 days according to their patterns of network connection to adjacent rivers – a result that has important implications for the accessibility of these types of wetland to aquatic biota. Using readily available river gauge data, we also show how connectivity modelling can be used to identify periods when connectivity has fallen below critical thresholds for fish movement. These connectivity patterns within the floodplain network are central to the setting of river flows that will meet environmental requirements for biota that use floodplain wetlands during their life history. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献