Multiobjective analysis of a public wellfield using artificial neural networks   总被引：3，自引：0，他引：3  

Coppola EA  Szidarovszky F  Davis D  Spayd S  Poulton MM  Roman E 《Ground water》2007,45(1):53-61

As competition for increasingly scarce ground water resources grows, many decision makers may come to rely upon rigorous multiobjective techniques to help identify appropriate and defensible policies, particularly when disparate stakeholder groups are involved. In this study, decision analysis was conducted on a public water supply wellfield to balance water supply needs with well vulnerability to contamination from a nearby ground water contaminant plume. With few alternative water sources, decision makers must balance the conflicting objectives of maximizing water supply volume from noncontaminated wells while minimizing their vulnerability to contamination from the plume. Artificial neural networks (ANNs) were developed with simulation data from a numerical ground water flow model developed for the study area. The ANN-derived state transition equations were embedded into a multiobjective optimization model, from which the Pareto frontier or trade-off curve between water supply and wellfield vulnerability was identified. Relative preference values and power factors were assigned to the three stakeholders, namely the company whose waste contaminated the aquifer, the community supplied by the wells, and the water utility company that owns and operates the wells. A compromise pumping policy that effectively balances the two conflicting objectives in accordance with the preferences of the three stakeholder groups was then identified using various distance-based methods.  相似文献   

Effect of a varying gravitational constant on the SN Ia Hubble diagram,AGN luminosity evolution,and X-ray source counts     

Roman Tomaschitz 《Astrophysics and Space Science》2010,325(2):259-275

The impact of a cosmic time evolution of the gravitational constant on SN Ia luminosity and AGN/QSO luminosity functions is studied. The gravitational constant scales linearly with the Hubble parameter, its present-day variation being \(\dot{G}_{0}/G_{0}\approx 1.9\times 10^{-4}\)?Gyr^?1, compatible with current bounds from lunar laser ranging. Distance moduli of Type Ia supernovae are fitted with a cosmic expansion factor derived from temperature variations of planetary paleoclimates, and a luminosity dependence on look-back time proportional to the varying gravitational constant is inferred from the Hubble diagram. A fit is performed to the comoving space density of X-ray-selected active galactic nuclei (AGNs) and optically selected quasars (QSOs) extending to redshifts z≈6. The initial steep increase of the AGN space density is reproduced by a redshift evolution depending solely on the Hubble parameter as scaling variable. The AGN luminosity scales with the Hubble parameter, and the scaling exponents of the luminosity function, composed of two competing power laws with exponential cutoff, are obtained. Based on the AGN luminosity function, flux-limited X-ray source counts are investigated. The counting functions are derived and put to test by fitting cumulative number counts of soft X-ray point sources compiled from ROSAT, XMM-Newton, and Chandra surveys.  相似文献   

How the capacity of bedrock to collect dust and produce soil affects phosphorus bioavailability in the northern Appalachian Mountains of Pennsylvania     

Virginia Marcon  Beth Hoagland  Xin Gu  Wenjing Liu  Jason Kaye  Roman A. DiBiase  Susan L. Brantley 《地球表面变化过程与地形》2021,46(14):2807-2823

More above-ground biomass (kg m⁻²) grows in the northern Appalachian Mountains (USA) in forests on shale than on sandstone at all landscape positions other than ridgetops. This has been tentatively attributed to physical (rather than chemical) attributes of the substrates, such as elevation, particle size, and water capacity. However, shales have generally similar phosphorus (P) concentrations to sandstones and, in the Valley and Ridge province, they erode more quickly. This led us to hypothesize that faster replenishment of the lithogenic nutrient P in shale soils through erosion + soil production could instead control the differences in biomass. To test this, soils and foliage from 10 sites on shales and sandstones in the northern Appalachians from roughly the same elevation and aspect were analysed. We discovered that, when controlling for location, concentrations of bioavailable P in soils and P in foliage were higher and P resorbed from senescing red oak leaves was lower on slower-eroding sandstone than on faster-eroding shale. Lower resorption generally can be attributed to lower P limitation for trees. Further investigation of weathering and erosion on one of the sandstone–shale pairs within a larger, paired watershed study revealed that the differences in P concentrations in biomass and foliage between lithologies likely developed because sandstones act as ‘collectors’ that trap nutrients from residual and exogenous sources, while shales erode quickly and thus promote production of soil from bedrock that releases P to ecosystems. We concluded that the combined effects of differential rates of dust collection and erosion results in roughly equal biomass growing on sandstone and shale ridgetops. This work emphasizes the balance between a landscape's capacity to collect dust versus produce soil in controlling bioavailability of nutrients.  相似文献   

Accounting for velocity jitter in planet search surveys     

Roman V. Baluev 《Monthly notices of the Royal Astronomical Society》2009,393(3):969-978

The role of radial velocity (RV) jitter in extrasolar planet search surveys is discussed. Based on the maximum-likelihood principle, improved statistical algorithms for RV fitting and period search are developed. These algorithms incorporate a built-in jitter determination, so that resulting estimations of planetary parameters account for this jitter automatically. This approach is applied to RV data for several extrasolar planetary systems. It is shown that many RV planet search surveys suffer from periodic systematic errors which increase effective RV jitter and can lead to erroneous conclusions. For instance, the planet candidate HD 74156 d may be a false detection made due to annual systematic errors.  相似文献   

Basalt generation at the Apollo 12 site,Part 1: New data,classification, and re-evaluation     

Clive R. Neal  Matthew D. Hacker  Gregory A. Snyder  Lawrence A. Taylor  Yun-Gang Liu  Roman A. Schmitt 《Meteoritics & planetary science》1994,29(3):334-348

Abstract— New data are reported from five previously unanalyzed Apollo 12 mare basalts that are incorporated into an evaluation of previous petrogenetic models and classification schemes for these basalts. This paper proposes a classification for Apollo 12 mare basalts on the basis of whole-rock Mg# [molar 100*(Mg/(Mg+Fe))] and Rb/Sr ratio (analyzed by isotope dilution), whereby the ilmenite, olivine, and pigeonite basalt groups are readily distinguished from each other. Scrutiny of the Apollo 12 feldspathic “suite” demonstrates that two of the three basalts previously assigned to this group (12031, 12038, 12072) can be reclassified: 12031 is a plagioclase-rich pigeonite basalt (Nyquist et al, 1979); and 12072 is an olivine basalt Only basalt 12038 stands out as a unique sample (Nyquist et al., 1981) to the Apollo 12 she, but whether this represents a single sample from another flow at the Apollo 12 site or is exotic to this site is equivocal. The question of whether the olivine and pigeonite basalt suites are co-magmatic is addressed by incompatible trace-element chemistry: the trends defined by these two suites when Co/Sm and Sm/Eu ratios are plotted against Rb/Sr ratio demonstrate that these two basaltic types cannot be co-magmatic. Crystal fractionation/accumulation paths have been calculated and show that neither the pigeonite, olivine, or ilmenite basalts are related by this process. Each suite requires a distinct and separate source region. This study also examines sample heterogeneity and the degree to which whole-rock analyses are representative, which is critical when petrogenetic interpretation is undertaken. Sample heterogeneity has been investigated petrographically (inhomogeneous mineral distribution) with consideration of duplicate analyses, and whether a specific sample (using average data) plots consistently upon a fractionation trend when a number of different compositional parameters are considered. Using these criteria, four basalts have been identified where reported analyses are not representative of the whole-rock composition: 12005, an ilmenite basalt; 12006 and 12036, olivine basalts; and 12031 previously classified as a feldspathic basalt, but reclassified as part of the pigeonite suite (Nyquist et al., 1979).  相似文献   

Carbon production and export from Biscayne Bay,Florida. I. Temporal patterns in primary production,seston and zooplankton     

Michael R. Roman  M.R. Reeve  J.L. Froggatt 《Estuarine, Coastal and Shelf Science》1983,17(1):45-59

Five stations along a transect from the western shore of Biscayne Bay, Florida to the Florida Current were sampled monthly for one year. The variability and amount of seston particulate organic carbon, adenosine triphosphate, chlorophyll a, primary production and zooplankton decreased along the seaward transect. The greater inshore biomass and variability of seston were the result of the allochthonous input of detritus and inorganic nutrients via terrestrial runoff. Annual primary production in this subtropical coastal lagoon ranged from 13 to 46 g C m^?2 yr^?1. Chlorophyll a in the bay ranged from 1 to 3 mg chlorophyll a m^?2. In contrast, chlorophyll a in the surface centimetre of the sediment ranged from 50 to 300 mg chlorophyll a m^?2. In this clear, shallow (2 to 3 m), oligotrophic lagoon, over 90% of total primary production is by submerged macrophytes and benthic algae. The high zooplankton biomass in the bay is most likely sustained by macrophyte detritus and the resuspension of benthic diatoms by the high winds associated with summer squalls and winter cold fronts.  相似文献   

The influence of selenium on photosynthesis and "light-enhanced dark respiration" (LEDR) in the flagellate Euglena gracilis after exposure to ultraviolet radiation     

Nils G.A. Ekelund  Roman A. Danilov 《Aquatic Sciences - Research Across Boundaries》2001,63(4):457-465

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近百年里海海平面的升降与伏尔加三角洲的发育     

李从先  V·依万诺夫  范代读  V·科洛达也夫  刘曙光  R·恰洛夫  杨守业 《海洋地质与第四纪地质》2002,22(3):1-9

位于里海北部的伏尔加三角洲属河控型三角洲，其水下坡度极度平缓。近百年来里海海平面升降幅度达3．46m，其变化可分为3个阶段：1900－1929年缓慢下降期，平均下降速率为1.1cm/a；1930－1977年快速下降期，平均速率为6.3cm/a；1978－1999年为快速上升期，平均上升速率达到8.8cm/a。在海平面下降阶段，伏尔加三角洲增长幅度达到每年2－180km^2，这是由于河流泥沙的沉积和浅水区出露水面而造成。海平面上升之时，较浅水下三角洲部分成为“缓冲带”，降低了海平面上升对三角洲的影响。尽管近20多年来海平面迅速上升，伏尔加三角洲并未发现海岸侵蚀、湿地损失、盐水入侵、海岸洪涝灾害等一般大河三角洲常见的现象。对比其它三角洲可以发现，各个大河三角洲各以不同的方式响应海平面的上升。  相似文献   

Changes in plankton community structure and function in response to variable freshwater flow in two tributaries of the Chesapeake Bay   总被引：1，自引：0，他引：1  

Matthew L. Reaugh  Michael R. Roman  Diane K. Stoecker 《Estuaries and Coasts》2007,30(3):403-417

The biomass of phytoplankton, microzooplankton, copepods, and gelatinous zooplankton were measured in two tributaries of the Chesapeake Bay during the springs of consecutive dry (below average freshwater flow), wet (above average freshwater flow), and average freshwater flow years. The potential for copepod control of microzooplankton biomass in the dry and wet years was evaluated by comparing the estimated grazing rates of microzooplankton by the dominant copepod species (Acartia spp. andEurytemora affinis) to microzooplankton growth rates and by calculating the percent of daily microzooplanton standing stock removed through copepod grazing. There were significant increases in phytoplankton and copepod biomass, but not for microzooplankton biomass in the wet year as compared to the dry year. The ctenophoreMnemiopsis leidyi was present during the dry year but was absent during the sampling period of the wet and average freshwater flow years. Grazing pressure on microzooplankton was greatest in the wet year, withAcartia spp. andE. affinis ingesting 0.21–2.64 μg of microzooplankton C copepod⁻¹ d⁻¹ and removing up to 60% of the microzooplankton standing stock per day. In the dry year, these copepod species ingested 0.10–0.73 μg of microzooplankton C copepod⁻¹ d⁻¹ with a maximum daily removal of approximately 3% of the microzooplankton standing stock. Potential copepod grazing pressure was significantly less than microzooplankton growth in the dry year, but was equivalent to microzooplankton growth in the wet year, implying strong top-down control of the microzooplankton community in the wet year. These results suggest that increased grazing control of microzooplankton populations by more copepods in the wet year released top-down control of phytoplankton. Reduced microzooplankton grazing, in conjunction with increased nutrient availability, resulted in large increases in phytoplankton biomass in the wet year. Increased freshwater flow has the potential to influence trophic cascades and the partitioning of plankton production in estuarine systems.  相似文献   

Extreme rainfalls in Eastern Himalaya and southern slope of Meghalaya Plateau and their geomorphologic impacts   总被引：3，自引：0，他引：3  

Roman Soja  Leszek Starkel   《Geomorphology》2007,84(3-4):170

This paper presents the detailed rainfall characteristics of 3 key areas located in the eastern monsoon India: the margin of Darjeeling Himalaya, the margin of Bhutanese Himalaya and the Cherrapunji region at the southern slope of Meghalaya Upland. All these areas are sensitive to changes but differ in annual rainfall totals (2000–4000 mm, 4000–6000 m and 6000–23,000 mm respectively) and in the frequency of extreme rainfalls. Therefore the response of geomorphic processes is different, also due to various human impact. In the Darjeeling Himalaya the thresholds may be passed 2–3 times in one century and the system may return to the former equilibrium. At the margin of western Bhutanese Himalaya in 1990s, the clustering of three events caused an acceleration in the transformation and formation of a new trend of evolution, especially in the piedmont zone. In the Cherrapunji of Meghalaya region in the natural conditions the effects of dozens of extreme rainfalls every year were checked by the dense vegetation cover. After deforestation and extensive land use the fertile soil was removed and either the exposed bedrock or armoured debris top layer protect the surface against degradation and facilitate only rapid overland flow. A new “sterile” system has been formed.  相似文献