Analysis of rotation curves in the framework of Rⁿ gravity     

C. Frigerio Martins  P. Salucci 《Monthly notices of the Royal Astronomical Society》2007,381(3):1103-1108

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Blind Estimation of the Ocean Acoustic Channel by Time–Frequency Processing     

Nelson E. Martins Srgio M. Jesus 《Oceanic Engineering, IEEE Journal of》2006,31(3):646-656

A blind estimator of the ocean acoustic channel impulse response envelope is presented. The signal model is characterized by a deterministic multipath channel excited by a highly nonstationary deterministic source signal. The time-frequency (TF) representation of the received signal allows for the separation between the channel and the source signal. The proposed estimator proceeds in two steps: First, the unstable initial arrivals allow for the estimation of the source signal instantaneous frequency (IF) by maximization of the radially Gaussian kernel distribution; then, the Wigner-Ville distribution (WV) is sequentially windowed and integrated, where the window is defined by the previously estimated IF. The integral gives the channel impulse response envelope, which turns to be an approximation to the blind conventional matched filter (MF). The blind channel estimator (CE) is applicable upon the following conditions: that the multipath channel contains at least one dominant arrival well separated from the others, and that the IF of the source signal is a one-to-one function. Results obtained on real data from the INternal TIde Measurements with Acoustic Tomography Experiments (INTIMATE'96), where the acoustic channel was driven by an linear frequency modulation signal, show that the channel's envelope detailed structure could be accurately and consistently recovered, with the correlation of the estimates ranging from 0.796 to 0.973, as compared to the MF result  相似文献   

Amino acid composition,petrology, geochemistry, 14C terrestrial age and oxygen isotopes of the Shişr 033 CR chondrite     

Z. Martins  B. A. Hofmann  E. Gnos  R. C. Greenwood  A. Verchovsky  I. A. Franchi  A. J. T. Jull  O. Botta  D. P. Glavin  J. P. Dworkin  P. Ehrenfreund 《Meteoritics & planetary science》2007,42(9):1581-1595

Abstract— We have analyzed Shi?r 033, a CR chondrite from the Omani desert, using several different analytical techniques designed to study the degree of terrestrial alteration of this meteorite and also its petrologic classification. Bulk chemical analyses (including organic carbon and mean total H₂O content) are consistent with a CR classification. Additionally, oxygen isotope analysis on a bulk sample indicates that Shi?r 033 is of type CR2. Amino acid analysis using liquid chromatography with UV fluorescence detection (HPLC‐FD) and liquid chromatography‐time of flight‐mass spectrometry (LC‐ToF‐MS) show that the absolute and the relative amino acid content of Shi?r 033 is distinct from other carbonaceous chondrites. Oxygen isotope analysis of a phyllosilicate‐rich dark inclusion shows that this inclusion is closer to CV3 or CO3 chondrites. The effects of terrestrial weathering in Shi?r 033 are evident from the dark inclusion carbon isotopic data, bulk chemistry (through the elevated concentrations of Sr and Ba), and amino acid data, which suggests extensive amino acid contamination of the meteorite from the fall site soil. Nevertheless, Shi?r 033 contains a small fraction of indigenous components, as indicated by the presence of the extraterrestrial amino acid α‐aminoisobutyric acid (AIB) that was not detected in the Shi?r soils. Finally, the terrestrial age of Shi?r 033 was determined and is discussed in the context of high levels of contamination.  相似文献   

Solute concentrations in the lower niger river and the source rock contribution     

O. Martins 《水文研究》1988,2(1):19-29

Water quality analyses for the Niger River for the 1980/81 hydrological year are presented. The samples were collected from the main river at Lokoja, and from two main tributaries, the Kaduna and the Benue Rivers. Different water types were distinguished by the concentrations of major ions. The type Ca > Na > Mg > K - HCO₃ > SO₄ > Cl was represented at all stations during at least part of the year. Chloride was found to dominate the sulphate ion in the Kaduna and Niger, while the Benue maintained a higher concentration of sulphate relative to chloride all year round. Distinct patterns of seasonal variation in the ion concentrations were observed, particularly for the samples collected at Lokoja. Low ion concentrations were prominent during periods of high discharge, while low flow periods coincided with high dissolved ion concentrations. The contribution of rainwater to the total dissolved solids in the river waters was assessed indirectly using rainwater chemistry data from the Gulf of Guinea. The estimated rainwater contribution to the Lower Niger amounts to 5.15 mg 1^?1. Geochemical weathering calculations involving reactions of the four major minerals of granitic rocks - anorthite, biotite, albite, and K-feldspar - with carbon dioxide and water, can account for the average water composition of the Lower Niger. The proportion of the ionic components was also related to the occurrence of the respective element in the minerals.  相似文献   

Trace metals in sediment cores from Deception and Penguin Islands (South Shetland Islands, Antarctica)     

Guerra R  Fetter E  Ceschim LM  Martins CC 《Marine pollution bulletin》2011,62(11):2571-2575

This paper presents information on the levels of trace elements in sediments collected at Deception and Penguin Islands and tracks the sources of natural and anthropogenic inputs of metals into this sub-Antarctic region. The results suggest that natural processes, such as volcanic activity, hydrothermal processes and sediment transport, are more important than anthropogenic inputs in accounting for the metal concentrations measured in sediments at Deception Island. The higher levels of trace metals recorded in sediments at Penguin Island seem to reflect the composition of the source rocks of the island, which are dominated by the olivine-basalt group. Our findings show that human activities in the study areas may contribute to negligible levels of trace metals associated with anthropogenic inputs (e.g., Cr and Zn) in sediments, and these results can be used in the future as background levels related to low anthropogenic impacts.  相似文献   

Coda wave attenuation in the Parecis Basin,Amazon Craton,Brazil: sensitivity to basement depth     

Lucas Vieira Barros  Marcelo Assumpção  Ronnie Quintero  Vinicius Martins Ferreira 《Journal of Seismology》2011,15(2):391-409

Small local earthquakes from two aftershock sequences in Porto dos Gaúchos, Amazon craton—Brazil, were used to estimate the coda wave attenuation in the frequency band of 1 to 24 Hz. The time-domain coda-decay method of a single backscattering model is employed to estimate frequency dependence of the quality factor (Q _c) of coda waves modeled using Q_c = Q₀ f^hQ_{\rm c} =Q_{\rm 0} f^\eta , where Q ₀ is the coda quality factor at frequency of 1 Hz and η is the frequency parameter. We also used the independent frequency model approach (Morozov, Geophys J Int, 175:239–252, 2008), based in the temporal attenuation coefficient, χ(f) instead of Q(f), given by the equation c(f)=g+\fracpfQ_e \chi (f)\!=\!\gamma \!+\!\frac{\pi f}{Q_{\rm e} }, for the calculation of the geometrical attenuation (γ) and effective attenuation (Q_e^-1 )(Q_{\rm e}^{-1} ). Q _c values have been computed at central frequencies (and band) of 1.5 (1–2), 3.0 (2–4), 6.0 (4–8), 9.0 (6–12), 12 (8–16), and 18 (12–24) Hz for five different datasets selected according to the geotectonic environment as well as the ability to sample shallow or deeper structures, particularly the sediments of the Parecis basin and the crystalline basement of the Amazon craton. For the Parecis basin Q_c = (98±12)f^(1.14±0.08)Q_{\rm c} =(98\pm 12)f^{(1.14\pm 0.08)}, for the surrounding shield Q_c = (167±46)f^(1.03±0.04)Q_{\rm c} =(167\pm 46)f^{(1.03\pm 0.04)}, and for the whole region of Porto dos Gaúchos Q_c = (99±19)f^(1.17±0.02)Q_{\rm c} =(99\pm 19)f^{(1.17\pm 0.02)}. Using the independent frequency model, we found: for the cratonic zone, γ = 0.014 s^− 1, Q_e^-1 = 0.0001Q_{\rm e}^{-1} =0.0001, ν ≈ 1.12; for the basin zone with sediments of ~500 m, γ = 0.031 s^− 1, Q_e^-1 = 0.0003Q_{\rm e}^{-1} =0.0003, ν ≈ 1.27; and for the Parecis basin with sediments of ~1,000 m, γ = 0.047 s^− 1, Q_e^-1 = 0.0005Q_{\rm e}^{-1} =0.0005, ν ≈ 1.42. Analysis of the attenuation factor (Q _c) for different values of the geometrical spreading parameter (ν) indicated that an increase of ν generally causes an increase in Q _c, both in the basin as well as in the craton. But the differences in the attenuation between different geological environments are maintained for different models of geometrical spreading. It was shown that the energy of coda waves is attenuated more strongly in the sediments, Q_c = (78±23)f^(1.17±0.14)Q_{\rm c} =(78\pm 23)f^{(1.17\pm 0.14)} (in the deepest part of the basin), than in the basement, Q_c = (167±46)f^(1.03±0.04)Q_{\rm c} =(167\pm 46)f^{(1.03\pm 0.04)} (in the craton). Thus, the coda wave analysis can contribute to studies of geological structures in the upper crust, as the average coda quality factor is dependent on the thickness of sedimentary layer.  相似文献   

Arsenic and trace metal contents in sediment profiles from the Admiralty Bay, King George Island, Antarctica     

Ribeiro AP  Figueira RC  Martins CC  Silva CR  França EJ  Bícego MC  Mahiques MM  Montone RC 《Marine pollution bulletin》2011,62(1):192-196

Admiralty Bay (Antarctica) hosts three scientific stations (Ferraz, Arctowski and Macchu Picchu), which require the use of fossil fuel as an energy source. Fossil fuels are also considered the main source of pollution in the area, representing important inputs of major pollutants (organic compounds) and trace metals and metalloids of environmental interest. Accordingly, this work presents the results of As, Cd, Cr, Cu, Ni, Pb and Zn in sediment profiles from Admiralty Bay. The sediment results from Ferraz station were slightly higher than the other sampling sites. The highest contents were observed for Cu and Zn (from 44 to 89 mg kg⁻¹). Otherwise, by using enrichment factors and geochronology analysis, the most relevant enrichment was observed for As in the samples collected close to the Ferraz station, indicating that increasing As content may be associated with the activities associated with this site.  相似文献   

Petrophysical characterization of the South Georgia Rift Basin for supercritical CO2 storage: a preliminary assessment     

Olusoga Martins Akintunde  Camelia Knapp  James Knapp 《Environmental Earth Sciences》2013,70(7):2971-2985

The Triassic–Jurassic South Georgia Rift (SGR) Basin, buried beneath Coastal Plain sediments of southern South Carolina, southeastern Georgia, western Florida, and southern Alabama, consists of an assemblage of continental rift deposits (popularly called red beds), and mafic igneous rocks (basalt flows and diabase sills). The red beds are capped by basalts and/or diabase sills, and constitute the target for supercritical CO₂ storage as part of a Department of Energy funded project to study the feasibility for safe and permanent sequestration. The purpose of this research is to evaluate subsurface suitability for underground CO₂ storage in terms of the local and regional distribution of porous and permeable reservoirs. In addition, unlike shale-capped CO₂ reservoirs, very little is known about the ability of basalts and diabase sills to act as viable seals for CO₂ storage. New results demonstrate the presence of confined porous rocks that may be capable of storing significant quantities of supercritical CO₂. Reservoir thicknesses as high as 420 m and an average porosity as high as 14 % were obtained. The SGR Basin manifests distinct porosity–permeability regimes that are influenced by the depositional environments. These are: a high-porosity, medium/low-permeability zone associated with lacustrine deposits, a medium/low-porosity, low-permeability zone dominated by fluvial fine- to very fine-grained sandstone, and an extremely low porosity and permeability zone characterized by fluvial and alluvial-fan deposits. Analyses further show that the basalt flows and diabase sills are characterized by low porosity as well as high seismic velocities and densities that are favorable to caprock integrity.  相似文献   

Macrobenthos and multi-molecular markers as indicators of environmental contamination in a South American port (Mar del Plata,Southwest Atlantic)     

Mariano J. Albano  Paulo da Cunha Lana  Claudia Bremec  Rodolfo Elías  César C. Martins  Natalia Venturini  Pablo Muniz  Silvia Rivero  Eduardo A. Vallarino  Sandra Obenat 《Marine pollution bulletin》2013

We evaluated benthic habitat quality along a presumed contamination gradient in the Mar del Plata port (Southwestern Atlantic) by coupling biological and chemical proxies in a multidisciplinary approach. Organic matter and photosynthetic pigment contents were higher in silty-clay bottoms of the inner port sites. Levels of all fecal steroids decreased from the inner sites to the port inlet. High concentrations of coprostanol in the inner sites seemed to derive from a permanent population of sea lions rather than from sewage outfalls due to coprostanol/epicoprostanol ratio (IV) values <2.5. PAHs levels were also higher in the inner sector, related to both biomass combustion and petroleum combustion associated to local marine traffic. High disturbance and low ecological status were reflected in low benthic diversity and high AMBI values in the inner sites.  相似文献   

Optical dating of clastic deposits generated by an extreme marine coastal flood: The 1755 tsunami deposits in the Algarve (Portugal)     

P.P. Cunha  J.P. Buylaert  A.S. Murray  C. Andrade  M.C. Freitas  F. Fatela  J.M. Munhá  A.A. Martins  S. Sugisaki 《Quaternary Geochronology》2010,5(2-3):329-335

Identification of past tsunamis is important for risk assessment and management of coastal areas. Obtaining accurate and precise ages of sediments originating from such extreme marine coastal floods is crucial for a reliable estimation of the recurrence interval of these often devastating events. We present here the results of quartz optical dating and ¹⁴C dating of two sites (Boca do Rio and Martinhal) on the Algarve coast (southern Portugal). These sites contain deposits of the great tsunami of November 1, 1755. The sections were described using sedimentological techniques; at both sites tsunami-laid sands and gravels were identified, intercalated between estuarine muds. Quartz luminescence ages from these sedimentary successions were derived using standard SAR-OSL dating using multi-grain sub-samples. A multiple sampling strategy was employed with several samples taken from the AD 1755 tsunami deposit and from the sediments bracketing the tsunami layer. Our SAR-OSL protocol was shown to be appropriate using dose recovery measurements (measured/given dose ratio of 1.004 ± 0.007, n = 165). The several OSL ages from the 1755 tsunamigenic deposits are internally reproducible but yield age overestimates of between 20 and 125% (60–310 years respectively); this is in agreement with values reported in the literature for similar deposits. The age overestimation of the tsunami-laid sands is presumably due to the rapid erosion and deposition of older sediments, with insufficient light exposure for complete bleaching during the tsunami event itself. The absence of significant bleaching during the tsunami is also suggested by the shape of the dose distributions based on sub-samples made up of only about 100 grains. Analysis of the distributions with the minimum-age model seems to yield the expected age for two of the three distributions. It is important to note that age offsets of a few tens of years to a few hundred years rapidly become insignificant when dating older (>1 to few ka) tsunami layers.  相似文献