Results from the first ballast water sampling study in the Mediterranean Sea - the Port of Koper study     

David M  Gollasch S  Cabrini M  Perkovic M  Bosnjak D  Virgilio D 《Marine pollution bulletin》2007,54(1):53-65

The ongoing transfer of harmful organisms by shipping, especially via ballast water transport, may result in a change of biodiversity, alteration of ecosystems, negative impacts on human health and economic loss. Species introductions which cause irreversible consequences to receiving environments and economies call for particular attention. One critical issue is a need to evaluate the quantities and processes of species introductions. Consequently ballast water was sampled on 15 ships calling at the Port of Koper, Slovenia. This was the first ballast water sampling study in the Mediterranean Sea. This paper summarises the sampling results. Samples were analysed for all types of aquatic organisms including bacteria. The results may be considered as background information for an initial risk assessment of future species introductions - an important tool for the implementation of ballast water management measures.  相似文献   

Analytical models for the groundwater tidal prism and associated benthic water flux     

Jeffrey N. King  Ashish J. Mehta  Robert G. Dean 《Hydrogeology Journal》2010,18(1):203-215

The groundwater tidal prism is defined as the volume of water that inundates a porous medium, forced by one tidal oscillation in surface water. The pressure gradient that generates the prism acts on the subterranean estuary. Analytical models for the groundwater tidal prism and associated benthic flux are presented. The prism and flux are shown to be directly proportional to porosity, tidal amplitude, and the length of the groundwater wave; flux is inversely proportional to tidal period. The duration of discharge flux exceeds the duration of recharge flux over one tidal period; and discharge flux continues for some time following low tide. Models compare favorably with laboratory observations and are applied to a South Atlantic Bight study area, where tide generates an 11-m³ groundwater tidal prism per m of shoreline, and drives 81 m³ s?^?1 to the study area, which describes 23% of an observational estimate. In a marine water body, the discharge component of any oscillatory benthic water flux is submarine groundwater discharge. Benthic flux transports constituents between groundwater and surface water, and is a process by which pollutant loading and saltwater intrusion may occur in coastal areas.  相似文献   

Recent progress on reservoir history matching: a review   总被引：3，自引：0，他引：3  

Dean S. Oliver  Yan Chen 《Computational Geosciences》2011,15(1):185-221

History matching is a type of inverse problem in which observed reservoir behavior is used to estimate reservoir model variables that caused the behavior. Obtaining even a single history-matched reservoir model requires a substantial amount of effort, but the past decade has seen remarkable progress in the ability to generate reservoir simulation models that match large amounts of production data. Progress can be partially attributed to an increase in computational power, but the widespread adoption of geostatistics and Monte Carlo methods has also contributed indirectly. In this review paper, we will summarize key developments in history matching and then review many of the accomplishments of the past decade, including developments in reparameterization of the model variables, methods for computation of the sensitivity coefficients, and methods for quantifying uncertainty. An attempt has been made to compare representative procedures and to identify possible limitations of each.  相似文献   

An unexpected outburst from A0535+262     

A. B. Hill  A. J. Bird  A. J. Dean  V. A. McBride  V. Sguera †  D. J. Clark  M. Molina  S. Scaringi  S. E. Shaw 《Monthly notices of the Royal Astronomical Society》2007,381(3):1275-1279

A0535+262 is a transient Be/X-ray binary system which was in a quiescent phase from 1994 to 2005. In this paper we report on the timing and spectral properties of the INTEGRAL detection of the source in 2003 October. The source is detected for ∼6000 s in the 18–100 keV energy band at a luminosity of  ∼3.8 × 10³⁵ erg s⁻¹  ; this is compatible with the high end of the range of luminosities expected for quiescent emission. The system is observed to be outside of the centrifugal inhibition regime and pulsations are detected with periodicity,   P = 103.7 ± 0.1 s  . An examination of the pulse history of the source shows that it had been in a constant state of spin-down since it entered the quiescent phase in 1994. The rate of spin-down implies the consistent presence of an accretion disc supplying torques to the pulsar. The observations show that the system is still active and highly variable even in the absence of recent Type I or Type II X-ray outbursts.  相似文献   

The velocity dispersion and mass profile of the Milky Way     

Walter Dehnen  Dean E. McLaughlin  Jalpesh Sachania 《Monthly notices of the Royal Astronomical Society》2006,369(4):1688-1692

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Evaluating the potential of a blended passive microwave‐interactive multi‐sensor product for improved mapping of snow cover and estimations of snow water equivalent     

Cezar Kongoli  Charles A. Dean  Sean R. Helfrich  Ralph R. Ferraro 《水文研究》2007,21(12):1597-1607

The retrieval of Snow Water Equivalent (SWE) from remote sensing satellites continues to be a very challenging problem. In this paper, we evaluate the accuracy of a new SWE product derived from the blending of a passive microwave SWE product based on the Advanced Microwave Sounding Unit (AMSU) with a multi‐sensor snow cover extent product based on the Interactive Multi‐sensor Snow and Ice Mapping System (IMS). The microwave measurements have the ability to penetrate the snow pack, and thus, the retrieval of SWE is best accomplished using the AMSU. On the other hand, the IMS maps snow cover more reliably due to the use of multiple satellite and ground observations. The evolution of global snow cover from the blended, the AMSU and the IMS products was examined during the 2006 snow season. Despite the overall good inter‐product agreement, it was shown that the retrievals of snow cover extent in the blended product are improved when using IMS, with implications for improved microwave retrievals of SWE. In a separate investigation, the skill of the microwave SWE product was also examined for its ability to correctly estimate SWE globally and regionally. Qualitative evaluation of global SWE retrievals suggested dependence on land surface temperature: the lower the temperature, the higher the SWE retrieved. This temperature bias was attributed in part to temperature effects on those snow properties that impact microwave response. Therefore, algorithm modifications are needed with more dynamical adjustments to account for changing snow cover. Quantitative evaluation over Slovakia in central Europe, for a limited period in 2006, showed reasonably good performance for SWE less than 100 mm. Sensitivity to deeper snow decreased significantly. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Phase correlations in cosmic microwave background temperature maps     

Peter Coles  Patrick Dineen  John Earl  Dean Wright 《Monthly notices of the Royal Astronomical Society》2004,350(3):989-1004

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Ablated tektite from the central Indian Ocean     

B. P. Glass  Dean R. Chapman  M. Shyam Prasad 《Meteoritics & planetary science》1996,31(3):365-369

Abstract A well-preserved ablated (button-shaped) tektite recovered from the surface sediments of the central Indian Ocean lacks flow ridges and has apparently undergone ablation of 6.9 to 7.9 mm. The lack of flow ridges and amount of ablation indicate that, if it originated in Southeast Asia, it must have had a very shallow trajectory (only a few degrees) and a velocity on the order of 7 km/s as it re-entered the atmosphere. The central Indian Ocean tektite is compositionally similar to high-magnesium (HMg) australites found at Serpentine Lakes and Lake Wilson, Australia, and to some HMg microtektites found in deep-sea sediments from the central Indian Ocean. This discovery supports a previous conclusion that the Australasian tektite strewn field covers most of the Indian Ocean.  相似文献   

Approximations to composite GPS protection levels for aircraft precision approach and landing   总被引：1，自引：1，他引：0  

Dean Bruckner  Frank van Graas  Trent Skidmore 《GPS Solutions》2011,15(4):333-344

Persistent pseudorange biases constitute a serious potential integrity problem for differential GPS systems used in aircraft precision approach and landing. Various approaches to solve this problem are documented in the literature, including composite protection levels (PLs) that incorporate an explicit bias term in their mathematical expressions. A statistical characterization for such a PL was previously presented in this journal. Modeling GPS error in the position domain as multivariate normal with nonzero mean resulted in the definition of vertical, horizontal, and radial composite PLs, termed VPL_c, HPL_c, and RPL_c, respectively. In the present effort, approximations to these computationally intensive PLs are presented for possible use in real time. Two of these are shown to be over-bounding approximations to exact quantities VPL_c and HPL_c. An approximation to RPL_c is also presented, as well as a method of quantitative evaluation for each of these composite PLs. Monte-Carlo simulations for a single GPS measurement epoch are then developed to illustrate the exact PLs and their approximations and demonstrate that the approximations to VPL_c and HPL_c over-bound the exact PLs. The approximation to RPL_c is shown to be far simpler computationally than the exact PL, but demonstrating that the approximation is an over-bound is left to future research. This paper makes available to the reader both the methods and the Matlab^? simulation code needed to evaluate computationally efficient PL approximations. Thus, it fosters further research into the use of GPS in safety critical applications.  相似文献   

Optimal Routefinding with Unlimited Possible Directions of Movement     

Denis J. Dean 《Transactions in GIS》2011,15(1):87-107

Finding optimal paths through raster databases is limited by the very nature of the raster data itself. This limitation restricts the possible directions of movement through the database from the infinite possibilities found in the real world to a finite number of possibilities defined by the cell‐to‐cell movement that characterizes raster databases. A Triangulated Irregular Network (TIN)‐based alternative optimization model that allows unlimited possible directions of movement is presented. While not without its own limitations, this new approach offers a viable alternative to raster‐based optimal routefinding.  相似文献