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21.
Antonio Tovar-Snchez Sergio A. Saudo-Wilhelmy A. Russell Flegal 《Estuarine, Coastal and Shelf Science》2004,60(4):717-728
Despite the fact that Co is an essential trace element for the growth of marine phytoplankton, there is very limited information on the cycling of this trace metal in the marine environment. We report here the distribution of dissolved (<0.4 μm) and particulate (>0.4 μm) Co in surface waters of the Hudson River Estuary (HRE) and San Francisco Bay (SFB). Samples were collected during several cruises (from 1990 to 1995 in SFB and from 1995 to 1997 in the HRE) along the whole salinity gradient. Dissolved Co concentrations (mean±1 standard deviation) were nearly identical in magnitude in both estuaries despite differences in climate, hydrography, riverine-flow conditions and land-usage (HRE=0.91±0.61 nM; SFB=1.12±0.69 nM). Dissolved Co levels in each system showed non-conservative distributions when plotted as a function of salinity, with increasing concentrations downstream from the riverine end-members. Desorption from suspended particulates and sewage inputs, therefore, seems to be the major processes responsible for the non-conservative behavior of Co observed. Mass balance estimates also indicated that most of the estuarine Co is exported out of both estuaries, indicating that they and other estuarine systems are principal sources of this essential trace element to the open ocean. 相似文献
22.
Alessandro Morbidelli Antonio Giorgilli 《Celestial Mechanics and Dynamical Astronomy》1993,55(2):131-159
We revisit some results of perturbation theories by a method of successive elimination of harmonics inspired by some ideas of Delaunay. On the one hand, we give a connection between the KAM theorem and the Nekhoroshev theorem. On the other hand, we support in a quantitative fashion a semi-numerical method of analysis of a perturbed system recently introduced by one of the authors. 相似文献
23.
Lambert problem solution in the hill model of motion 总被引:1,自引:0,他引:1
Alexander Sukhanov Antonio F. Bertachini A. Prado 《Celestial Mechanics and Dynamical Astronomy》2004,90(3-4):331-354
The goal of this paper is obtaining a solution of the Lambert problem in the restricted three-body problem described by the
Hill equations. This solution is based on the use of pre determinate reference orbits of different types giving the first
guess and defining the sought-for transfer type. A mathematical procedure giving the Lambert problem solution is described.
This procedure provides step-by-step transformation of the reference orbit to the sought-for transfer orbit. Numerical examples
of the procedure application to the transfers in the Sun–Earth system are considered. These examples include transfer between
two specified positions in a given time, a periodic orbit design, a halo orbit design, halo-to-halo transfers, LEO-to-halo
transfer, analysis of a family of the halo-to-halo transfer orbits. The proposed method of the Lambert problem solution can
be used for the two-point boundary value problem solution in any model of motion if a set of typical reference orbits can
be found. 相似文献
24.
We present a new model for the chemical evolution of elliptical galaxies taking into account SN feedback, detailed nucleosynthesis
and galactic winds. We discuss the effect of galactic winds on the chemical enrichment of the ICM and compute the energy per
particle injected by the galaxies into the ICM.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
25.
Annual Variation of Benthic Nutrient Fluxes in Shallow Coastal Waters (Gulf of Trieste, Northern Adriatic Sea) 总被引:5,自引:0,他引:5
Abstract. Benthic fluxes of dissolved N. Si and P nutrients, alkalinity, dissolved inorganic C (DIC), and O2 from sediments in the Gulf of Trieste (northern Adriatic, Italy) were measured monthly for 16 months, using laboratory incubated flux chambers at in siru temperatures in the dark. The annual average fluxes were: 02 = -19.3 ± 8.2, DIC = 13.7 ± 9.6, NO3 = -0.04 ± 0.16, NH4 = 0.3 ± 0.4. PO4= 4.001 ± 0.01, Si = 0.9 ± 0.1 mmol m-2 d-1, with strong temporal fluctuations. The highest effluxes of all nutrients and DIC were observed in the summer. Small effluxes of DIC and NH4 and influxes of Si and PO4 were observed in late winter. Only NH4 (ca. 50%) and Si (ca. 70%) fluxes were significantly correlated with temperature. This correlation suggests that the rate of downward input and the quality of sedimented organic matter (autochthonous and allochthonous) were superimposed on the temperature fluctuations. High DIC, NH4 and Si effluxes observed in May 1993 during low temperature were due to the degradation of sedimentary organic matter produced by an early spring bloom of benthic microalgae which occurred about 6 weeks earlies while the autumn phytoplankton bloom was simultaneously reflected in enhanced benthic fluxes due to higher temperature. The role of benthic biological advection in this transport across the sediment-water interface, evaluated by comparison between measured benthic and calculated diffusive fluxes from nutrient pore water concentrations, was of minor importance. This is probably due to low infaunal activity throughout the year it was localized mostly in the narrow surficial layer. The annual average diffusive fluxes of NH4 and PO4 were higher than those measured, probably due to the presence of nitrificationdenitrifi-cation processes and redox-dependent chemical reactions at the oxic sediment-water interface, respectively. Only during bottom-water hypoxia in September 1993 did strong PO4 effluxes prevail. Calculations based on the Redfield stoichiometry of oxic decomposition of organic N to NH4 and NO3, and differences between diffusive and measured NH4 fluxes showed that denitrifkation averaged 0.8 mmol m-2 d-1. Significant correlations between NH4 and PO4 DIC and Si, and NH4 and Si fluxes suggested their parallel regeneration and utilization at the sediment-water interface. The nutrient fluxes observed were not significantly linked to O2 consumption, suggesting also that anaerobic oxidation processes were important at the sediment-water interface in the gulf. The N, P and Si nutriqnts released from sediment pore waters are probably utilized in benthic microalgal and bottorn-hater primary production. This indicates that pelagic and benthic communities in the central part of the Gulf of Trieste function relatively independently of each other. 相似文献
26.
José Antonio Belinchón 《Astrophysics and Space Science》2009,323(3):307-315
We study a massive cosmic strings with BII symmetries cosmological models in two contexts. The first of them is the standard
one with a barotropic equation of state. In the second one we explore the possibility of taking into account variable “constants”
(G and Λ). Both models are studied under the self-similar hypothesis. We put special emphasis in calculating the numerical values
for the equations of state. We find that for ω∈(0,1], G, is a growing time function while Λ, behaves as positive decreasing time function. If ω=0, both “constants”, G and Λ, behave as true constants. 相似文献
27.
Antonio Alfonso-Faus 《Astrophysics and Space Science》2012,337(1):367-372
Combining the kinematical definitions of the two dimensionless parameters, the deceleration q(x) and the Hubble t
0
H(x), we get a differential equation (where x=t/t
0 is the age of the universe relative to its present value t
0). First integration gives the function H(x). The present values of the Hubble parameter H(1) [approximately t
0
H(1)≈1], and the deceleration parameter [approximately q(1)≈−0.5], determine the function H(x). A second integration gives the cosmological scale factor a(x). Differentiation of a(x) gives the speed of expansion of the universe. The evolution of the universe that results from our approach is: an initial
extremely fast exponential expansion (inflation), followed by an almost linear expansion (first decelerated, and later accelerated).
For the future, at approximately t≈3t
0 there is a final exponential expansion, a second inflation that produces a disaggregation of the universe to infinity. We
find the necessary and sufficient conditions for this disaggregation to occur. The precise value of the final age is given
only with one parameter: the present value of the deceleration parameter [q(1)≈−0.5]. This emerging picture of the history of the universe represents an important challenge, an opportunity for the
immediate research on the Universe. These conclusions have been elaborated without the use of any particular cosmological
model of the universe. 相似文献
28.
Abdul Jawad Antonio Pasqua Surajit Chattopadhyay 《Astrophysics and Space Science》2013,344(2):489-494
In this paper, we discuss cosmological application of holographic Dark Energy (HDE) in the framework of f(G) modified gravity. For this purpose, we construct f(G) model with the inclusion of HDE and a well-known power law form of the scale factor a(t). The reconstructed f(G) is found to satisfy a sufficient condition for a realistic modified gravity model. We find quintessence behavior of effective equation of state (EoS) parameter ω DE through energy conditions in this context. Moreover, we observe that the squared speed of sound $v_{s}^{2}$ remains negative, which indicates the instability of HDE f(G) model. 相似文献
29.
Elisa Lopez Capel Jos Maria de la Rosa Arranz Francisco J. Gonzlez-Vila Jos Antonio Gonzlez-Perez David A.C. Manning 《Organic Geochemistry》2006,37(12):1983
Analysis of river, estuary and marine sediments from the Atlantic coast of Spain using thermogravimetry–differential scanning calorimetry–quadrupole mass spectrometry–isotope ratio mass spectrometry (TG–DSC–QMS–IRMS) was used to (a) distinguish bulk chemical hosts for C within a sediment and humic acid fraction, (b) track C pools with differing natural C isotope ratios and (c) observe variation with distance from the coast. This is the first application of such a novel method to the characterisation of organic matter from marine sediments and their corresponding humic acid fractions. Using thermal analysis, a labile, a recalcitrant and a refractory carbon pool can be distinguished. Extracted humic fractions are mainly of recalcitrant nature. The proportion of refractory carbon is greatest in marine sediments and humic acid fractions. Quadrupole mass spectrometry confirmed that the greatest proportion of m/z 44 (CO2) and m/z 18 (H2O) were detected at temperatures associated with recalcitrant carbon (510–540 °C). Isotope analysis detected progressive enrichment in δ13C for the sediment samples with an increase in marine influence. Isotopic heterogeneity in the refractory organic matter in marine sediments could be due to products of anthropogenic origin or natural combustion products. Isotope homogeneity of humic acids confirms the presence of terrigenous C in marine sediments, allowing the terrestrial input to be characterised. 相似文献
30.
Résumé Nous appliquons dans ce mémoire la théorie des perturbations, développée antérieuremet par l'un de nous, à la déduction des principales caractéristiques normales des perturbations compatibles avec un champ moyen donné de pression et de température. Cette deduction comprend la détermination: 1) de la configuration moyenne des perturbations dans les différentes régions étudiées; 2) des zones de creusement et de comblement et en particulier des foyers de formation et de disparition des perturbations; 3) des trajectoires, vitesses, fréquences et amplitudes moyennes des perturbations. C'est à l'ensemble de ces propriétés moyennes que nous donnons le nom de «climatologie dynamique» d'une période donnée.Après une première partie théorique, nous donnons des exemples d'application des résultats généraux à la climatologie dynamique des mois de Janvier et de Juillet pour l'Amérique du Nord, l'Atlantique Nord et l'Europe.
à ce mémoire a été assigné le Prix 1956 de la « Società Italiana di Geofisica e Meteorologia ». 相似文献
Summary In this paper we apply the theory of perturbations, previously developed by one of us, to the deduction of the main normal characteristics of the perturbations that are compatible with a given mean field of pressure and temperature. This deduction comprises the determination: 1) of the mean configuration of the perturbations for the different regions under examination; 2) of the normal deepening and filling regions of the perturbations, and particularly their formation and vanishing focuses; 3) of the mean paths, speeds, frequencies and amplitudes of the perturbations. The «dynamical climatology» we are contemplating here is concerned with all these mean properties of the perturbations for a given period.After a first theoretical part, we give some examples of the application of the general results to the dynamical climatology of January and July for North America, North Atlantic and Europe.
à ce mémoire a été assigné le Prix 1956 de la « Società Italiana di Geofisica e Meteorologia ». 相似文献