Line-driven disc wind models with an improved line force     

Daniel Proga  †  James M. Stone  Janet E. Drew 《Monthly notices of the Royal Astronomical Society》1999,310(2):476-482

We describe an efficient method of calculating the radiation pressure resulting from spectral lines, including all the terms in the velocity gradient tensor. We apply this method to calculate the two-dimensional, time-dependent structure of winds from luminous discs. Qualitative features of our new models are very similar to those we calculated including only the dominant terms in the tensor. In particular, we find that models which displayed unsteady behaviour in our earlier paper are also unsteady with the new method, and gross properties of the winds, such as mass-loss rate and characteristic velocity, are not changed by the more accurate approach. The largest change caused by the new method is in the disc-wind opening angle: winds driven only by the disc radiation are more polar with the new method, whilst winds driven by the disc and central object radiation are typically more equatorial. In the closing discussion, we provide further insight into the way the geometry of the radiation field and consequent flow determine the time properties of the flow.  相似文献   

Multidisciplined investigation to locate the Kentucky shipwreck     

Janet E. Simms  Paul E. Albertson 《Geoarchaeology》2000,15(5):441-468

A local artifact collector contacted the U.S. Army Engineer District, Vicksburg in the fall of 1994 concerning timbers from a ship protruding from the west bank of the Red River, Louisiana, during the summer of 1994. From historical records it was determined that the shipwreck is that of the Kentucky, which sank in 1865. An investigation integrating archaeological, geological, and geophysical methods was undertaken to determine the location, orientation, and depth of the wreckage. Based on site geology, the shipwreck is expected to lie within a silty sand deposit within 4–8.5 m below the ground surface. The results of probe investigations performed by the archaeologists and borehole data orient the long axis of the ship N57.5E. This orientation conflicts with the geophysical data, which suggest an orientation of N116W. The geophysical surveys identified an anomalous region, approximately 31 m long and 10 m wide, that borders the Red River and an abandoned channel of the Red River. The magnetometer data suggests that the bow of the ship is pointed toward the abandoned channel. This orientation contradicts historical records which have the bow pointing toward the modern Red River. A subsequent underwater investigation by the archaeological contractor discovered a rudder‐related mechanism protruding from the bank of the Red River, confirming the geophysical prediction. All three scientific surveys agree that the wreckage is at a depth 3.8–8.5 m below ground surface and at an inclined position, with a downward slope from the bank of the Red River to the abandoned channel. © 2000 John Wiley & Sons, Inc.*  相似文献   

Use of terrestrial photogrammetry for monitoring and measuring bank erosion     

Rachel Barker  Lawrence Dixon  Janet Hooke 《地球表面变化过程与地形》1997,22(13):1217-1227

This paper examines the use of terrestrial photogrammetry as a technique for measuring bank erosion in a rapidly changing fluvial environment. It has been recognized that there are a number of advantages when applying photogrammetric techniques to geomorphological situations. In this study the enhancement of spatial sampling combined with the ability to capture additional information, such as soil moisture, on film, is of particular importance in enabling the identification of specific processes involved in bank erosion as well as detailed volumetric analysis of losses. Metric terrestrial photography was taken of the river bank on several dates, and data were abstracted by the use of analytical photogrammetry. This enabled the generation of digital terrain models from which morphological and volumetric changes could be assessed. © 1997 John Wiley & Sons, Ltd.  相似文献   

Long-Term Evaluation of Mulch Biowall Performance to Treat Chlorinated Solvents     

Kenneth L. Walker Jr.  Travis M. McGuire  David T. Adamson  R. Hunter Anderson 《Ground Water Monitoring & Remediation》2020,40(1):35-46

Permeable reactive barriers (PRBs), such as mulch biowalls, have been installed at numerous groundwater cleanup sites, and laboratory and field studies have demonstrated biotic and abiotic processes that degrade chlorinated volatile organic compounds (CVOCs) in groundwater passing through these engineered remedies. However, the longevity of mulch biowalls remains a fundamental research question. Soil and groundwater sampling at seven mulch biowalls at Altus Air Force Base (AFB) approximately 10 years after installation demonstrated the ongoing degradation of CVOCs. Trichloroethene was not detected in five of seven groundwater samples collected from the biowall despite upgradient detections above federal drinking water standards. Microbial sampling established the presence of key dechlorinating bacteria and the abundance of genes encoding specific enzymes for degradation, high methane concentrations, low sulfate concentrations, and negative oxidation-reduction potential, all indicative of highly reducing conditions within the biowalls and favorable conditions for CVOC destruction via microbial reductive dechlorination. High cellulose content (>79%) of the mulch, elevated total organic carbon (TOC) content in groundwater, and elevated potentially bioavailable organic carbon (PBOC) measurements in soil samples further supports an ongoing, long-lived source of carbon. These results demonstrate the ongoing and long-term efficacy of the mulch biowalls at Altus AFB. In addition, concentrations of bacteria, TOC, PBOC, and other geochemical parameters suggest a modest impact of the biowalls downgradient. The continued presence of CVOCs downgradient may be attributable to back diffusion from low-permeability shale. However, the biowalls continue to provide benefits by removing CVOCs in groundwater, thus reducing further CVOC loading to the downgradient, low-permeability strata.  相似文献   

On‐Site Vapor‐Phase Analysis as a Novel Approach for Monitoring Groundwater Wells     

David T. Adamson  Thomas E. McHugh  Michal W. Rysz  Roberto Landazuri  Mir Ahmad Seyedabbasi  Patrick E. Haas  Charles J. Newell 《Ground Water Monitoring & Remediation》2014,34(2):42-59

The results of comprehensive field testing of on‐site vapor‐phase‐based groundwater monitoring methods are presented to demonstrate their utility as a robust and cost‐effective approach for rapidly obtaining volatile organic compounds (VOCs) concentration data from a monitoring well. These methods—which rely on sensitive, commercially available field equipment to analyze vapor in equilibrium with groundwater—proved easy to implement and can be tailored to site‐specific needs, including multilevel sampling. During field testing, low‐flow groundwater concentrations could be reasonably estimated using submerged passive vapor diffusion samplers or field equilibration of collected groundwater (R² = 0.85 to 0.96). These two methods are not as reliant on in‐well mixing to overcome vertical stratification within wells as simpler headspace methods. The importance of well and aquifer‐specific factors on concentration data (and therefore method selection) is highlighted, including the effect of changing in‐well patterns due to seasonal temperature gradients. Results indicated that vertical stratification was relatively limited within the set of wells included in these studies, resulting in similar performance for short depth‐discrete passive vapor diffusion samplers (constructed from 40‐mL vials) and longer samplers (2.5 to 5 feet in length) designed to cover a larger portion of the screened interval. A year‐long, multi‐event evaluation demonstrated that vapor‐phase‐based monitoring methods are no more variable than conventional groundwater monitoring methods, with both types subject to similar spatial and temporal variability that can be difficult to reduce. Vapor sampling methods represent a promising approach for estimation of groundwater concentrations by reducing the cost liabilities associated with monitoring while providing a more sustainable approach.  相似文献   

Pfiesteria shumwayae (Pfiesteriaceae) in New Zealand     

Lesley L. Rhodes  Joann M. Burkholder  Howard B. Glasgow  Parke A. Rublee  Coy Allen  Janet E. Adamson 《新西兰海洋与淡水研究杂志》2013,47(3):621-630

Pfiesteria shumwayae Steidinger et Burkholder is now known to be present in New Zealand and occurs in estuaries around the country. The presence of Pfiesteria was initially determined by a polymerase chain reaction (PCR)‐based detection assay, using oligonucleotide primers targeted at ribosomal DNA extracted from estuarine water and sediments. Presence was confirmed by isolation from fresh sediments in the presence offish (Oreochromis mossambicus), followed by identification by scanning electron microscopy. The New Zealand isolates of P. shumwayae were ichthyotoxic in bioassays, but there is no historic evidence offish kills in New Zealand associated with the dinoflagellate.  相似文献   

Aetideus and Euaetideus (copepoda: Calanoida) from the Atlantic and Pacific Oceans     

Janet M. Bradford 《新西兰海洋与淡水研究杂志》2013,47(1):12-40

The genus Euaetideus Sars, 1925 is here merged with Aetideus Brady, 1883 (Copepoda : Calanoida : Aetideidae). Three new species of the genus Aetideus are described from the Pacific as well as the males of three other known species. A key is given to the known males and females in the genus Aetideus. The closely related genera Paivella and Snelliaetideus are compared with Aetideus.  相似文献   

New and little‐known species of Heterorhabdidae (Copepoda: Calanoida) from the southwest pacific     

Janet M. Bradford 《新西兰海洋与淡水研究杂志》2013,47(1):120-140

Three new species of calanoid copepods are described: two in Heterorhabdus and one in Disseta. The males of H. pustulifer and H. caribbeanensis are described and the identities of H. proximus, H. norvegicus and H. austrinus are clarified. H. spinifer is recorded for the second time. A key to the subgenus Heterorhabdus is provided.  相似文献   

Records of pelagic copepods off Kaikoura,New Zealand   总被引：1，自引：1，他引：0  

Janet M. Bradford 《新西兰海洋与淡水研究杂志》2013,47(4):351-363

Additions to the pelagic copepod fauna of Kaikoura, New Zealand, include 20 species previously unrecorded and the males of 8 species for which females only had been recorded; further information concerning 2 other species is added.  相似文献   

The genus Pseudo-nitzschia (Bacillariophyceae) in New Zealand: analysis of the last decade's monitoring data     

L Rhodes  W Jiang  B Knight  J Adamson  K Smith  V Langi 《新西兰海洋与淡水研究杂志》2013,47(4):490-503

The diatom genus Pseudo-nitzschia blooms throughout New Zealand's coastal waters. More than a decade of monitoring data were analysed in this study and seasonality was a significant factor in the appearance of Pseudo-nitzschia blooms. Austral spring and summer were the main bloom periods, although there were regional differences. Between January 2000 and August 2011, 8.4% of 29,000 seawater samples analysed for Pseudo-nitzschia exceeded the voluntary trigger level for biotoxin testing (10×10⁴ cells l^?1), and these were analysed by fluorescent in situ hybridisation (FISH) assays. Pseudo-nitzschia fraudulenta and P. pseudodelicatissima (low domoic acid [DA] producers) were the dominant bloom formers throughout New Zealand (each contributing 25%) followed by the highly toxic P. australis (10%). Shellfish flesh testing for DA was triggered on 8477 occasions between 2000 and 2011, but no samples exceeded the regulatory limit (20 mg/kg); the maximum concentration was 13 mg/kg (Marlborough Sounds, mid-winter 2010).  相似文献