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81.
Luis Eduardo Antunes Vieira Walter D. Gonzalez Ezequiel Echer Bruce T. Tsurutani 《Solar physics》2004,223(1-2):245-258
In this paper we discuss the main-phase evolution of intense magnetic storms, associated with the passage of different interplanetary magnetic structures. It is shown that their evolution, driven by intense magnetic fields in the sheath region just behind interplanetary shocks, evolves faster (implying physically different magnetospheric configurations) than that associated with intense magnetic fields in the ejecta itself and in corotating streams. The estimated ring-current injection rate for the main phase of intense magnetic storms caused by sheath fields is ∼10 times greater than the estimated injection rate for N–S magnetic clouds. Based on these results, we propose storm-intensity criteria for several classes of the driving interplanetary structures. The time necessary to reach a Dst/SYM index threshold level is an important parameter for a space weather forecast. 相似文献
82.
83.
A reconstruction of sunspot numbers for the last 1000 years was obtained using a sum of sine waves derived from spectral analysis of the time series of sunspot number R
z for the period 1700–1999. The time series was decomposed in frequency levels using the wavelet transform, and an iterative regression model (ARIST) was used to identify the amplitude and phase of the main periodicities. The 1000-year reconstructed sunspot number reproduces well the great maximums and minimums in solar activity, identified in cosmonuclides variation records, and, specifically, the epochs of the Oort, Wolf, Spörer, Maunder, and Dalton Minimums as well the Medieval and Modern Maximums. The average sunspot number activity in each anomalous period was used in linear equations to obtain estimates of the solar radio flux F
10.7, solar wind velocity, and the southward component of the interplanetary magnetic field. 相似文献
84.
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 Qc = Q0 fhQ_{\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+\fracpfQe \chi (f)\!=\!\gamma \!+\!\frac{\pi f}{Q_{\rm e} }, for the calculation of the geometrical attenuation (γ) and effective attenuation (Qe-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 Qc = (98±12)f(1.14±0.08)Q_{\rm c} =(98\pm 12)f^{(1.14\pm 0.08)}, for the surrounding shield Qc = (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 Qc = (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, Qe-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, Qe-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, Qe-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, Qc = (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, Qc = (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
85.
86.
Valfredo A. Lemos Emanuel V. dos Santos Vieira Eldevan dos Santos Silva Liz O. dos Santos 《洁净——土壤、空气、水》2012,40(3):268-271
A method for the determination of nickel in water was developed. The procedure involves preconcentration of nickel by using dispersive liquid–liquid microextraction. The Ni(II) ions were extracted in chloroform in the form of complex with the reagent 2‐(2′‐benzothiazolylazo)‐p‐cresol. Ethanol was used as the disperser solvent. After injection of the extracting mixture in a solution of nickel, a cloudy mixture was observed. A quick centrifugation induces phase separation and thus the settling of rich phase. The nickel content in the rich phase is measured by flame atomic absorption spectrometry. Under optimal conditions, the limit of detection and quantification obtained were 1.4 and 4.7 µg L?1, respectively. Some parameters used to characterize preconcentration systems, such as enrichment factor and consumption index were calculated and resulted in 29 and 0.34 mL, respectively. After optimization of variables and determination of analytical characteristics, the method was used for the analysis of certified reference materials (BCR‐713: wastewater, effluent and BCR‐414: plankton) and real water samples. 相似文献
87.
Matthew McQuinn Adam Lidz Matias Zaldarriaga Lars Hernquist Suvendra Dutta 《Monthly notices of the Royal Astronomical Society》2008,388(3):1101-1110
We show that near-infrared observations of the red side of the Lyα line from a single gamma-ray burst (GRB) afterglow cannot be used to constrain the global neutral fraction of the intergalactic medium (IGM), , at the GRB's redshift to better than . Some GRB sightlines will encounter more neutral hydrogen than others at fixed owing to the patchiness of reionization. GRBs during the epoch of reionization will often bear no discernible signature of a neutral IGM in their afterglow spectra. We discuss the constraints on from the z = 6.3 burst, GRB050904, and quantify the probability of detecting a neutral IGM using future spectroscopic observations of high-redshift, near-infrared GRB afterglows. Assuming an observation with signal-to-noise ratio similar to the Subaru FOCAS spectrum of GRB050904 and that the column density distribution of damped Lyα absorbers is the same as measured at lower redshifts, a GRB from an epoch when can be used to detect a partly neutral IGM at 97 per cent confidence level ≈10 per cent of the time (and, for an observation with three times the sensitivity, ≈30 per cent of the time). 相似文献
88.
89.
Mauricio da Rocha Fragoso Gabriel Vieira de Carvalho Felipe Lobo Mendes Soares Daiane Gracieli Faller Luiz Paulo de Freitas Assad Raquel Toste Lívia Maria Barbosa Sancho Elisa Nóbrega Passos Carina Stefoni Böck Bruna Reis Luiz Landau Hernan G. Arango Andrew M. Moore 《Ocean Dynamics》2016,66(3):419-434
90.
本文介绍中、西双方在西班牙莱斯诺德(LANZAROTE)火山与地球动力学地下实验室共同进行静力水准仪、水平应变伸缩仪、岩体和空气测温计等仪器的合作研究实验以及分析所得的首批成果。 相似文献