Weighted merge context for clustering and quantizing spatial data with self-organizing neural networks     

Julian Hagenauer 《Journal of Geographical Systems》2016,18(1):1-15

This publication presents a generalization of merge context, named weighted merge context (WMC), which is particularly useful for clustering and quantizing spatial data with self-organizing neural networks. In contrast to merge context, WMC does not depend on a predefined (sequential) ordering of the data; distance is evaluated by recursively taking neighboring observations into account. For this purpose, WMC utilizes a weight matrix that describes the neighborhood relationships between observations. This property distinguishes WMC from existing approaches like contextual neural gas (NG) or the GeoSOM, which force spatially close observations to be represented by similar prototypes, but neglected the similarity of the observations’ neighborhoods. For practical studies, WMC is combined with the NG algorithm to obtain weighted merging NG (WMNG). The properties of WMNG and its usefulness for clustering and quantizing spatial data are investigated on two different case studies which utilize an simulated binary grid and a real-world continuous data set.  相似文献   

The two basic components of the interstellar neutral hydrogen and its relation with the galactic structure     

Ramon Julian Quiroga 《Astrophysics and Space Science》1975,35(1):67-80

The two basic components of the neutral hydrogen, cool dense clouds merged in a hotter tenuous medium, are studied using 21 cm absorption data of the Parkes Survey. The mean parameters obtained for the typical clouds next to the galactic plane are τ_p = 1.7, velocity half-width=3.3 km s^?1. Their temperatures areT _sc ≥40 K with a meanT _sc =63±12 K and the obtained hot gas density isn _HH=(0.15±0.05) atom cm^?3. Theoretical analysis following Giovanelli and Brown (1973) reveals that the pressure equilibrium condition (n _HH+2n _e )·T _SH≈n _HC·T _sc is compatible with the quoted values if it is assumed that the cosmic abundances in the interstellar medium are below the adopted normal solar abundance. This lack of heavy elements suggests accretion to grains which is consistent with the observed narrow concentration of the dark matter on the galactic layer (≤100 pc halfwidth). The same pressure condition leads to a mean cool cloud density ofn _HC～30 atom cm^?3 and a hot gas temperature ofT _SH～10 500 K. Comparison with data from Hii regions suggests that the cool clouds are somewhat denser and less extensive than such regions. An explanation for it is the expansion that the Hii regions went through in their origin. Comparison with 21 cm emission data shows that the cloud galactic layer is only about a quarter as thick as the hot gas layer. All the present results suggest that only such clouds can be spatially related with the typical I population associated with the spiral structure.  相似文献   

Bioavailability of heavy metals bound to sediments affected by a mining spill using Solea senegalensis and Scrobicularia plana     

Riba I  Casado-Martínez MC  Blasco J  DelValls TA 《Marine environmental research》2004,58(2-5):395-399

After the Aznalcóllar mining spill (April, 1998) different ecosystems along the Guadiamar river and the Guadalquivir estuary were impacted by high concentrations of metals. The concentration of metals Zn, Cd, Pb, Cu and As has been detected as a good tracer of the pathway of the toxic spill. Different individuals of the fish Solea senegalensis and the clam Scrobicularia plana were exposed to contaminated sediments after the accidental spill in the south-west Spain. The induction of metallothioneins in fish and the bioaccumulation of metals in clams were determined in different tissues to determine the biological adverse effect associated with the heavy metals from the spill. A relationship between the enrichment of metals in the tissues and the induction of metallothioneins was determined for those assays performed using contaminated sediments. The bioaccumulation of metals indicates that the risk associated with the spill should be continuously evaluated to establish the sublethal effects related to the accident.  相似文献   

A four-component ecosystem model of biological activity in the Arabian Sea   总被引：1，自引：0，他引：1  

Julian P. McCreary  Jr  Kevin E. Kohler  Raleigh R. Hood  Donald B. Olson 《Progress in Oceanography》1996,37(3-4)

A coupled, physical-biological model is used to study the processes that determine the annual cycle of biological activity in the Arabian Sea. The physical model is a system with a surface mixed layer imbedded in the upper layer, and fluid is allowed to move between layers via entrainment, detrainment and mixing processes. The biological model consists of a set of advective-diffusive equations in each layer that determine the nitrogen concentrations in four compartments: nutrients, phytoplankton, zooplankton and detritus. Coupling is provided by the horizontal-velocity, layer-thickness, entrainment and detrainment fields from the physical solution. Surface forcing fields (such as wind stress and photosynthetically active radiation) are derived from monthly climatological data, and the source of nitrogen for the system is upward diffusion of nutrients from the deep ocean into the lower layer. Our main-run solution compares favorably with observed physical and biological fields; in particular, it is able to simulate all the prominent phytoplankton blooms visible in the CZCS data. Three bloom types develop in response to the physical processes of upwelling, detrainment and entrainment. Upwelling blooms are strong, long-lasting events that continue as long as the upwelling persists. They occur during the Southwest Monsoon off Somalia, Oman and India as a result of coastal alongshore winds, and at the mouth of the Gulf of Aden through Ekman pumping. Detrainment blooms are intense, short-lived events that develop when the mixed layer thins abruptly, thereby quickly increasing the depth-averaged light intensity available for phytoplankton growth. They occur during the fall in the central Arabian Sea, and during the spring throughout most of the basin. In contrast to the other bloom types, entrainment blooms are weak because entrainment steadily thickens the mixed layer, which in turn decreases the depth-averaged light intensity. There is an entrainment bloom in the central Arabian Sea during June in the solution, but it is not apparent in the CZCS data. Bloom dynamics are isolated in a suite of diagnostic calculations and test solutions. Some results from these analyses are the following. Entrainment is the primary nutrient source for the offshore bloom in the central Arabian Sea, but advection and recycling also contribute. The ultimate cause for the decay of the solution's spring (and fall) blooms is nutrient deprivation, but their rapid initial decay results from grazing and self shading. Zooplankton grazing is always an essential process, limiting phytoplankton concentrations during both bloom and oligotrophic periods. Detrital remineralization is also important: in a test solution without remineralization, nutrient levels drop markedly in every layer of the model and all blooms are severely weakened. Senescence, however, has little effect: in a test solution without senescence, its lack is almost completely compensated for by increased grazing. Finally, the model's detrainment blooms are too brief and intense in comparison to the CZCS data; this difference cannot be removed by altering biological parameters, which suggests that phytoplankton growth in the model is more sensitive to mixed-layer thickness than it is in the real ocean.  相似文献   

Bioavailability of heavy metals bound to sediments affected by a mining spill using Solea senegalensis and Scrobicularia plana     

I. Riba  M. C. Casado-Martínez  J. Blasco  T. A. DelValls 《Marine environmental research》2004,58(2-5):395

After the Aznalcóllar mining spill (April, 1998) different ecosystems along the Guadiamar river and the Guadalquivir estuary were impacted by high concentrations of metals. The concentration of metals Zn, Cd, Pb, Cu and As has been detected as a good tracer of the pathway of the toxic spill. Different individuals of the fish Solea senegalensis and the clam Scrobicularia plana were exposed to contaminated sediments after the accidental spill in the south-west Spain. The induction of metallothioneins in fish and the bioaccumulation of metals in clams were determined in different tissues to determine the biological adverse effect associated with the heavy metals from the spill. A relationship between the enrichment of metals in the tissues and the induction of metallothioneins was determined for those assays performed using contaminated sediments. The bioaccumulation of metals indicates that the risk associated with the spill should be continuously evaluated to establish the sublethal effects related to the accident.  相似文献   

The effect of salinity on growth and weight loss of juvenile plaice (Pleuronectes platessa, L): An experimental test     

Julian Augley  Mark Huxham  Teresa F. Fernandes  Alastair R. Lyndon 《Journal of Sea Research》2008,60(4):292-296

Previous population estimates of the 0+ plaice (Pleuronectes platessa L.) in the Firth of Forth, east central Scotland, did not take account of the Forth estuary west of the Forth bridges. Previous work found plaice in the estuary grew as fast as, or faster than, the outer firth plaice. It was hypothesised that salinity may affect growth rates of early 0+ plaice. This hypothesis was tested in a laboratory experiment, by exposing juvenile plaice to three different, but naturally — experienced by the juveniles, salinities; 25, 30 and 35. Plaice fed a minimum ration did not grow in length. Mean weight decreased at all three salinities, however, the lowest weight loss was found at the lowest salinity (25) and the highest weight loss was found at the highest salinity (35). The minimum feeding ration was halted and plaice were then fed ad libitum. Consumption rates were not significantly different during the ad libitum feeding, while significant differences in mean weight change were found between the highest and lowest salinities.  相似文献   

International legal options for the control of biofouling on international vessels   总被引：1，自引：0，他引：1  

Julian Roberts  Martin Tsamenyi   《Marine Policy》2008,32(4):559-569

Shipping represents a threat as a vector for the transfer of non-indigenous marine species through the discharge of ballast water and biofouling of vessels’ external structures and internal piping. While considerable attention has been given to the management of ballast water, there currently exists no international legal instrument with which to control biofouling.A number of existing legal mechanisms may be applicable in the context of coastal States’ rights under international law. However, existing mechanisms are insufficient to regulate all aspects of the biofouling problem to ensure comprehensive management of the issue. There is, therefore, a need for the development of a comprehensive international agreement to address this gap. The issue of biofouling on international vessels has now been included on the work programme of the International Maritime Organisation (IMO). As a contribution to discussions on how to address this particular issue at an international level, this article provides an analysis of the options available through the IMO to address this issue.Having defined the specific “threat scenario” with regard to hull fouling, the article will consider: (i) the international legal framework that has been established to regulate the harmful impacts of international shipping; (ii) the range of practical measures that are available to manage biofouling on vessels; and (iii) international legal options available to States to address the threat of biofouling posed by international shipping.  相似文献   

Is delta-aminolevulinic acid dehydratase activity in bivalves from south-west Iberian Peninsula a good biomarker of lead exposure?     

Kalman J  Riba I  Blasco J  DelValls TA 《Marine environmental research》2008,66(1):38-40

The coast of Huelva is considered as a heavily contaminated area where the Tinto and Odiel rivers discharge after running through a metalliferous mining area in the Iberian Pyrite Belt and end in common estuary called Ría of Huelva. Lead is a highly toxic and widely distributed element in the aquatic environment; therefore there is a great interest in assessing the impact of this contaminant on aquatic organisms. To study the bioavailability and sources of lead, the bivalve species Chamelea gallina was collected from six sampling sites along the coast of Huelva. Besides the effect of this metal on the enzyme activity, delta-aminolevulinic acid dehydratase (ALA-D) was determined in the whole tissue. Results show the inverse relationship between the lead concentration and the activity of ALA-D measured in whole tissues (r2=0.7). Individuals collected from the Ría of Huelva estuary had the highest levels of total lead concentrations and the lowest activity of ALA-D. Lead isotope analyses demonstrated the different sources of lead contamination and also confirmed the influence of Ría of Huelva on the metal input to the marine environment.  相似文献   

Multi-attribute machine learning analysis for weak BSR detection in the Pegasus Basin,Offshore New Zealand     

Chenin  Julian  Bedle  Heather 《Marine Geophysical Researches》2020,41(4):1-15

Marine Geophysical Research - Much of our knowledge of gas hydrate in the Dongsha area of the South China Sea has been gained through intensive geophysical surveys and drilling. However, many...  相似文献   

Holocene vegetation and fire dynamics in the supra‐mediterranean belt of the Nebrodi Mountains (Sicily,Italy)     

Martina Bisculm  Daniele Colombaroli  Elisa Vescovi  Jacqueline F. N. van Leeuwen  Paul D. Henne  Julian Rothen  Giovanni Procacci  Salvatore Pasta  Tommaso La Mantia  Willy Tinner 《第四纪科学杂志》2012,27(7):687-698

High‐resolution pollen, macrofossil and charcoal data, combined with accelerator mass spectrometry ¹⁴C dating and multivariate analysis, were used to reconstruct Holocene vegetation and fire dynamics at Urio Quattrocchi, a small lake in the supra‐mediterranean belt in the Nebrodi Mountains of Sicily (Italy). The data suggest that after 10 000 cal a BP increasing moisture availability supported closed forests with deciduous (Quercus cerris, Fagus sylvatica and Fraxinus spp.) and evergreen (Quercus ilex) species. Species‐rich closed forest persisted until 6850 cal a BP, when Neolithic activities caused a forest decline and affected plant diversity. Secondary forest with abundant Ilex aquifolium recovered between 6650 and 6000 cal a BP, indicating moist conditions. From 5000 cal a BP, agriculture and pastoralism led to the currently fragmented landscape with sparse deciduous forests (Quercus cerris). The study suggests that evergreen broadleaved species were more important at elevations above 1000 m a.s.l. before ca. 5000 cal a BP than subsequently, which might reflect less human impact or warmer‐than‐today climatic conditions between 10 000 and 5000 cal a BP. Despite land use since Neolithic times, deciduous supra‐mediterranean forests were never completely displaced from the Nebrodi Mountains, because of favourable moist conditions that persisted throughout the Holocene. Reconstructed vegetation dynamics document the absence of any pronounced mid‐ or late‐Holocene ‘aridification’ trend at the site, an issue which is controversially debated in Italy and the Mediterranean region. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献