Simultaneous optical polarimetry and X-ray observations of the magnetic CV CP Tuc (AX J2315−592)     

Gavin Ramsay  S. B. Potter  David A. H. Buckley  Peter J. Wheatley 《Monthly notices of the Royal Astronomical Society》1999,306(4):809-814

CP Tuc (AX J2315–592) shows a dip in X-rays which lasts for approximately half the binary orbit and is deeper in soft X-rays compared with hard X-rays. It has been proposed that this dip is due to the accretion stream obscuring the accretion region from view. If CP Tuc were a polar, as has been suggested, then the length of such a dip would make it unique amongst polars since in those polars in which a dip is seen in hard X-rays the dip lasts for only 0.1 of the orbit. We present optical polarimetry and RXTE observations of CP Tuc which show circular polarization levels of ∼10 per cent and find evidence for only one photometric period. These data confirm CP Tuc as a polar. Our modelling of the polarization data implies that the X-ray dip is due to the bulk of the primary accretion region being self-eclipsed by the white dwarf. The energy dependence of the dip is due to a combination of this self-eclipse and also the presence of an X-ray temperature gradient over the primary accretion region.  相似文献   

Magnetostratigraphy of Palaeocene basalts from the Vaigat Formation of West Greenland   总被引：1，自引：0，他引：1  

Peter Riisager  & Niels Abrahamsen 《Geophysical Journal International》1999,137(3):774-782

A palaeomagnetic study comprising the directional results from 289 individual lava flows, sampled along eight sections in the Palaeocene basalts of West Greenland, is reported. The eight individual sections are correlated using lithostratigraphical marker horizons to form a single composite profile. Generally, the lithological correlation is in good agreement with the record of geomagnetic secular variation.
  The total composite palaeomagnetic profile represents a stratigraphic thickness of 1.6  km through the Vaigat Formation, which is the lowermost of the two volcanic formations formed during the main stage of plateau volcanism. Only two polarity zones are found in the composite profile, suggesting a very short duration for the West Greenland main plateau-building volcanism. ⁴⁰Ar/³⁹Ar dates support a high extrusion rate and also indicate that the lower normal polarity zone is Chron C27n and that the upper reverse polarity zone is Chron C26r.
  The C27n–C26r transition is fully recorded along one of the sections (Nuusap Qaqqarsua), with intermediate directions covering a 200  m thick succession of lavas. A combined palaeomagnetic, field and geochemical study along this profile showed good agreement; that is, geochemically and geologically derived single magmatic events show groupings of the palaeomagnetic directions. Supposing a duration for the geomagnetic transition of 5000 years, the eruption frequency during this period was as high as one flow every 80 years.  相似文献   

Mass Diving Tourism – A New Dimension Calls for New Management Approaches     

Peter van Treeck  Helmut Schuhmacher 《Marine pollution bulletin》1999,37(8-12):499-504

Diving has become a booming branch of the tourism business. The economies of many countries with reef-lined coasts depend on high numbers of tourist divers; the resultant degradation of reefs by mechanical damage is accepted due to the short-term gain from the tourism business. Many activities of recreational diving do not particularly require coral reefs – any varied three-dimensional structure (e.g. a wreck) may be sufficiently attractive. The conflict between the needs of nature conservation and the economic interests of diving tourism can be mitigated by the formation of artificial underwater attractions as reef substitutes. Based on experiments in the northern Red Sea, we propose to deposit calcium minerals from the seawater in situ by electrolysis on a template of any desired shape. After transplantation of living coral fragments, a diverse community will develop. With this method different modules can be designed and formed on the seabed which can serve different needs such as diver training, environmental education and recreation as well as reef rehabilitation. By a combination of such modules, a recreational underwater park can be formed well suited to function as a DAD (diver aggregation device) and therefore, divert diver pressure from the natural reef.  相似文献   

Participation in higher education: A geodemographic perspective on the potential for further expansion in student numbers     

Peter Batey  Peter Brown  Mark Corver 《Journal of Geographical Systems》1999,1(3):277-303

Higher education in England has expanded rapidly in the last ten years with the result that currently more than 30% of young people go on to university. Expansion is likely to continue following the recommendations of a national committee of inquiry (the Dearing Committee). The participation rate is known to vary substantially among social groups and between geographical areas. In this paper the participation rate is calculated using a new measure, the Young Entrants Index (YEI), and the extent of variation by region, gender and residential neighbourhood type established. The Super Profiles geodemographic system is used to facilitate the latter. This is shown to be a powerful discriminator and to offer great potential as an alternative analytical approach to the conventional social class categories, based on parental occupation, that have formed the basis of most participation studies to date. Received: 20 October 1998/Accepted: 5 May 1999  相似文献   

W. J. Bouma, G. I. Pearman and M. R. Manning (eds.), GREENHOUSE: Coping with Climatic Change     

Peter Tyson 《Climatic change》1999,41(1):131-132

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Mapping Submerged Aquatic Vegetation with GIS in the Caloosahatchee Estuary: Evaluation of Different Interpolation Methods     

Weihe Guan  Robert H. Chamberlain  Bruce M. Sabol  Peter H. Doering 《Marine Geodesy》1999,22(2):69-91

This article evaluates different spatial interpolation methods for mapping submerged aquatic vegetation (SAV) in the Caloosahatchee Estuary, Florida. Data used for interpolation were collected by the Submersed Aquatic Vegetation Early Warning System (SAVEWS). The system consists of hydro-acoustic equipment, which operates from a slow-moving boat and records bottom depth, seagrass height, and seagrass density. This information is coupled with geographic location coordinates from a Global Positioning System (GPS) and stored together in digital files, representing SAV status at points along transect lines. Adequate spatial interpolation is needed to present the SAV information, including density, height, and water depth, as spatially continuous data for mapping and for comparison between seasons and years. Interpolation methods examined in this study include ordinary kriging with five different semivariance models combined with a variable number of neighboring points, the inverse distance weighted (IDW) method with different parameters, and the triangulated irregular network (TIN) method with linear and quintic options. Interpolation results were compared with survey data at selected calibration transects to examine the suitability of different interpolation methods. Suitability was quantified by the determination coefficient (R2) and the root-mean-square error (RMSE) between interpolated and observed values. The most suitable interpolation method was identified as the one yielding the highest R2 value and/or the lowest RMSE value. For different geographic conditions, seasons, and SAV parameters, different interpolation methods were recommended. This study identified that kriging was more suitable than the IDW or TIN method for spatial interpolation of all SAV parameters measured. It also suggested that transect data with irregular spatial distribution patterns such as SAV parameters are sensitive to interpolation methods. An inappropriate interpolation method such as TIN can lead to erroneous spatial representation of the SAV status. With a functional geographic system and adequate computing power, the evaluation and selection of interpolation methods can be automated and quantitative, leading to a more efficient and accurate decision.  相似文献   

Naturnahe Abwasserreinigung: Interdisziplinäre Zusammenarbeit von Naturwissenschaftler und Ingenieur     

Tanja Gschlssl  Peter Schleypen  Christian Steinmann  Arnulf Melzer 《Limnologica》1999,29(1):103-104

Sewage from scattered villages is often treated in septic tanks whose removal efficiency of biodegradable components amounts to about 35%. Viewed from the standpoint of water protection such a performance provides an insufficient prevention of water pollution. It is worth aspiring to more extensive sewage treatment, i.e. oxidation of organic matter and nitrogen compounds. This particularly applies to rural regions if scattered villages are situated in ecologically sensitive regions such as watersheds of small brooks. Here, it is resonable to emply natural methods of treating sewage such as constructed wetlands and lagoons up to a size of 1,000 population equivalents. Constructed wetlands and lagoons provide an excellent field of cooperation between biologist and engineer, because the complexity of the microbial communities and the influence of the physico-chemical and geological conditions upon the microorganisms are not yet well understood. Further interdisciplinary research work has to be done for instance in regard to the relationship between helophytes and bacteria in the biofilm on the rhizomes of the need or focussing upon effluent polishing of lagoons.  相似文献   

Automatic data acquisition and modeling of the greifswalder bodden ecosystem     

Axel Kob  Peter Eschholz  Maria-Luise Hubert  Ulrich Vietinghoff 《Limnologica》1999,29(3):314

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DNA tracers with information capacity and high detection sensitivity tested in groundwater studies   总被引：1，自引：0，他引：1  

I. H. Sabir  Jacob Torgersen  Sylvi Haldorsen  Peter Aleström 《Hydrogeology Journal》1999,7(3):264-272

 In order to investigate the usefulness of unique synthetic DNA tracers in groundwater, a field experiment was conducted in Norway. DNA tracers and a sodium-chloride tracer were injected into an aquifer. The transport of DNA molecules was interpreted by comparing with the plume of chloride ions under forced-gradient steady-state flow conditions. Spatial concentration moments described the migration of conservative tracers. Mobility and migration of DNA in groundwater demonstrate that DNA tracers can be detected by using the polymerase chain reaction (PCR) and DNA sequence analysis. The results indicate that DNA tracers can be valuable tools as tracers in groundwater investigations. Received, June 1997 / Revised, July 1998, December 1998 / Accepted, January 1999  相似文献   

Trace metals and radionuclides reveal sediment sources and accumulation rates in Jordan Cove, Connecticut     

Gaboury Benoit  Tim F. Rozan  Peter C. Patton  Chester L. Arnold 《Estuaries and Coasts》1999,22(1):65-80

Many small estuaries are influenced by flow restrictions resulting from transportation rights-of-way and other causes. The biogeochemical functioning and history of such systems can be evaluated through study of their sediments. Ten long and six short cores were collected from the length of Jordan Cove, Connecticut, a Long Island Sound subestuary, and analyzed for stratigraphy, radionuclides (¹⁴C, ²¹⁰Pb, ²²⁶Ra, ¹³⁷Cs, and ⁶⁰Co), and metals (Ag, Cd, Cu, Pb, Zn, Fe, and Al). For at least 3,800 yr, rising sea level has gradually inundated Jordan Cove, filling it with mud similar to that currently being deposited there. Long-term sediment accumulation in the cove averaged close to 0.1 cm yr⁻¹ over the last three millennia. Recent sediment accumulation rates decrease inland from 0.84 cm yr⁻¹ to 0.40 cm yr⁻¹, and are slightly faster than relative sea-level rise at this site (0.3 cm yr⁻¹). Similarity of depth distributions of trace metals was used to confirm relative sediment accumulation rates. ⁶⁰Co and Ag are derived from sources outside the cove and its watershed, presumably the Millstone nuclear power plant and regional contaminated sediments, respectively. The combined data suggest that Long Island Sound is an important source of sediment to the cove; a minor part of total sediment is supplied from the local watershed. Trace metal levels are strongly correlated with Fe but not with either organic matter or Al. Sediment quality has declined in the cove over the past 60 yr, but only slightly. Cu, Pb, and Zn data correlate strongly with Fe but not with either organic matter or aluminum. Ratios of Ag to Fe and to trace metals suggest that Ag in the cove is derived almost entirely from Long Island Sound. This result supports the notion that Fenormalized Ag can serve as a better tracer of some kinds of contamination than more common and abundant metals, like Cu, Pb, and Zn. *** DIRECT SUPPORT *** A01BY085 00008  相似文献