Radio observations of the planetary nebula around the OH/IR star OH 354.88-0.54 (V1018 Sco)     

Martin Cohen  Jessica M. Chapman  Rachel M. Deacon †  Robert J. Sault  Quentin A. Parker  Anne J. Green 《Monthly notices of the Royal Astronomical Society》2006,369(1):189-196

We present radio observations of the unique, recently formed, planetary nebula (PN) associated with a very long-period OH/IR variable star V1018 Sco that is unequivocally still in its asymptotic giant branch phase. Two regions within the optical nebula are clearly detected in non-thermal radio continuum emission, with radio spectral indices comparable to those seen in colliding-wind Wolf–Rayet binaries. We suggest that these represent shocked interactions between the hot, fast stellar wind and the cold nebular shell that represents the PN's slow wind moving away from the central star. This same interface produces both synchrotron radio continuum and the optical PN emission. The fast wind is neither spherical in geometry nor aligned with any obvious optical or radio axis. We also report the detection of transient H₂O maser emission in this nebula.  相似文献   

Quantitative analysis of net-transgressive shoreline trajectories and stratigraphic architectures: mid-to-late Jurassic of the North Sea rift basin     

Gary J. Hampson  Peter J. Sixsmith  Rachel L. Kieft  Christopher A. -L. Jackson  Howard D. Johnson 《Basin Research》2009,21(5):528-558

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Poroelastic two‐phase material modeling: theoretical formulation and embedded finite element method implementation          下载免费PDF全文

Nathan Benkemoun  Rachel Gelet  Emmanuel Roubin  Jean‐Baptiste Colliat 《国际地质力学数值与分析法杂志》2015,39(12):1255-1275

This paper presents the formulation of FEMs for the numerical modeling of a poroelastic two‐phase (aggregates/mixture phase) solid. The displacement and pressure fields are decomposed, following the Enhanced Assumed Strain (EAS) method, into a regular part and an enhanced part. This leads to discontinuous strain and pressure gradient fields allowing to capture the jump in mechanical and hydrical properties passing through the interface between the aggregates and the mixture phase. All these enhanced fields are treated in the context of the embedded FEM through a local enhancement of the finite element interpolations as these jumps appear. The local character of these interpolations leads after a static condensation of the enhanced fields to a problem exhibiting the same structure as common poroelastic finite element models but incorporating now the mechanical and hydrical properties of a two‐phase solid. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Thermal recovery from a fractured medium in local thermal non‐equilibrium     

Rachel Gelet  Benjamin Loret  Nasser Khalili 《国际地质力学数值与分析法杂志》2013,37(15):2471-2501

Thermal recovery from a hot dry rock (HDR) reservoir viewed as a deformable fractured medium is investigated with a focus on the assumption of local thermal non‐equilibrium (LTNE). Hydraulic diffusion, thermal diffusion, forced convection and deformation are considered in a two‐phase framework, the solid phase being made by impermeable solid blocks separated by saturated fractures. The finite element approximation of the constitutive and field equations is formulated and applied to obtain the response of a generic HDR reservoir to circulation tests. A change of time profile of the outlet fluid temperature is observed as the fracture spacing increases, switching from a single‐step pattern to a double‐step pattern, a feature which is viewed as characteristic of established LTNE. A dimensionless number is proposed to delineate between local thermal equilibrium (LTE) and non‐equilibrium. This number embodies local physical properties of the mixture, elements of the geometry of the reservoir and the production flow rate. All the above properties being fixed, the resulting fracture spacing threshold between LTNE and LTE is found to decrease with increasing porosity or fluid velocity. The thermally induced effective stress is tensile near the injection well, illustrating the thermal contraction of the rock, while the pressure contribution of the fracture fluid is negligible during the late period. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Burning through organizational boundaries? Examining inter-organizational communication networks in policy-mandated collaborative bushfire planning groups     

Rachel F. Brummel  Kristen C. Nelson  Pamela J. Jakes 《Global Environmental Change》2012,22(2):516-528

Collaboration can enhance cooperation across geographic and organizational scales, effectively “burning through” those boundaries. Using structured social network analysis (SNA) and qualitative in-depth interviews, this study examined three collaborative bushfire planning groups in New South Wales, Australia and asked: How does participation in policy-mandated collaboration affect bushfire communication networks amongst organizational representatives? Inter-organizational communication networks became more active, less centralized, and more closely connected during planning than they had been prior. However, efforts to institutionalize collaboration were intrinsically biased towards placing administrative power and influence in public agencies. Further, collaborative planning groups did not maintain “during planning” levels of network activity and structure after planning was completed. In one case, the mandated planning process had a negative impact on inter-agency communication networks. Contextual aspects such as group size, history of inter-organizational conflict and fire occurrence, and process management were important in the development of inter-organizational networks. Though communication diminished after planning was completed, participation in the collaborative planning effort may serve as an important basis for the continuation of inter-organizational relationships beyond the scope of the planning process.  相似文献   

Optical extinction due to aerosols in the upper haze of Venus: Four years of SOIR/VEX observations from 2006 to 2010     

Valérie Wilquet  Rachel Drummond  Arnaud Mahieux  Séverine Robert  Ann Carine Vandaele  Jean-Loup Bertaux 《Icarus》2012,217(2):875-881

The variability of the aerosol loading in the mesosphere of Venus is investigated from a large data set obtained with SOIR, a channel of the SPICAV instrument suite onboard Venus Express. Vertical profiles of the extinction due to light absorption by aerosols are retrieved from a spectral window around 3.0 μm recorded in many solar occultations (～200) from September 2006 to September 2010. For this period, the continuum of light absorption is analyzed in terms of spatial and temporal variations of the upper haze of Venus. It is shown that there is a high short-term (a few Earth days) and a long-term (～80 Earth days) variability of the extinction profiles within the data set. Latitudinal dependency of the aerosol loading is presented for the entire period considered and for shorter periods of time as well.  相似文献   

Characterization of volatile organic compound emission sources in Fort Saskatchewan,Alberta using principal component analysis     

Rachel Mintz  Robert D. McWhinney 《Journal of Atmospheric Chemistry》2008,60(1):83-101

Volatile organic compounds (VOCs) were measured at two sites in a highly industrialized zone in western Canada from September 2004 to March 2006. Principal component analysis (PCA) with varimax rotation was performed on 30 VOCs to identify the pollution sources. Aliphatics, aromatics, and halogenated aliphatics were studied. The two monitoring sites were 11 km apart, with site 1 closer to the city of Fort Saskatchewan and site 2 predominantly down wind from the industrial sources. PCA results provided the basis for interpreting the relationship between the ambient 24-h integrated VOC samples and the emission sources in the region. Challenges existed in interpreting the PCA results in such a highly industrialized region; however a unique feature to this study was the fact that the region was home to the only 1,2-dichloroethane emitting facility in Canada. Other specific industry related VOCs in the region were vinyl chloride, styrene and HCFC-22. Making use of these specific VOCs in the PCA allowed for easy identification of an industrial contribution. For factors that were not easily distinguishable, further PCA tests were conducted using carbon monoxide concentrations, wind direction data and seasonal splitting of the samples. The analysis found that five factors accounted for 82% of the variance at site 1 and five factors accounted for 81% of the variance at site 2. The factor accounting for the highest variability (∼40%) at the two sites was the most difficult to interpret, but showed contributions from both industry and vehicle related emissions. Specific industrial sources were identified using 1,2-dichloroethane as a chemical tracer or by corroborating wind speed with known industry VOC emissions. Both sites had two factors identified as specific industry sources and these factors totaled to over 20% of the variance. Long range transport of stable halogenated compounds accounted for greater than 10% of the variance, and seasonal effects accounted for 5% of the variance.  相似文献   

Paleo-climate of the Boise area, Idaho from the last glacial maximum to the present based on groundwater δH and δO compositions     

Melissa E. Schlegel  Steve Nelson  Rachel Henderson 《Quaternary Research》2009,71(2):172-214

A 30 ka paleo-climate record of the Boise area, Idaho, USA has been delineated using groundwater stable isotopic compositions. Groundwater ages are modern (cold batholith), 5-15 ka (thermal batholith) , 10-20 ka (frontal fault) , and 20-30 ka (Snake River plain thermal). The stable isotopic composition of groundwaters have been used as a surrogate for the stable isotopic composition of precipitation. Using δ²H and δ¹⁸O compositions, local groundwater lines (LGWL's) were defined for each system. Each LGWL has been evaluated with defined slopes of 6.94 and 8, respectively, and resulting deuterium excess values (d) were found for each groundwater system for each slope. Time dependent changes in moisture source humidity and temperature, and Boise area recharge temperatures, calculated from stable isotopic data and the deuterium excess factors, agree with previous paleo-climate studies. Results indicate that from the last glacial maximum to the present time the humidity over the ocean moisture source increased by 9%, sea surface temperature at the moisture source increased 6-7°C, and local Boise temperature increased by 4-5°C. A greater increase of temperature at the moisture source as compared to the Boise area may impart be due to a shift in the moisture source area.  相似文献   

Direct Fourier transform mass spectral analysis of natural waters with low dissolved organic matter     

Rachel L. Sleighter  Georgina A. McKee  Patrick G. Hatcher 《Organic Geochemistry》2009,40(1):119-125

A major obstacle for characterizing dissolved organic matter (DOM) with ultrahigh resolution mass spectrometry has been its low concentrations in natural waters. Many previous mass spectrometric studies of both terrestrial and marine DOM typically have isolated and concentrated the DOM using solid phase C₁₈ extraction disks, ultrafiltration, or XAD resins, all of which are known to discriminate against many different classes of compounds. We have, for the first time, developed an approach to directly analyze natural water samples with less than 6 mg/l DOC (dissolved organic carbon), using electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICR-MS). We demonstrate the sensitivity and ability of sequential selective ion accumulation (SSIA) to detect the thousands of components in a single freshwater DOM sample without any significant pretreatment. By utilizing SSIA, the baseline noise decreases while signal to noise ratios of the peaks increase, allowing for approximately 40% more formulas to be assigned to peaks in the mass spectra.  相似文献   

The many manifestations of downsizing: hierarchical galaxy formation models confront observations     

Fabio Fontanot  Gabriella De Lucia  Pierluigi Monaco  Rachel S. Somerville  Paola Santini 《Monthly notices of the Royal Astronomical Society》2009,397(4):1776-1790

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