On the ability to estimate narrow-band signal parameters usingtowed arrays     

Edelson  G.S. Tufts  D.W. 《Oceanic Engineering, IEEE Journal of》1992,17(1):48-61

Using the Cramer-Rao lower bound (CRLB) as an indicator of potential performance, the limits on the estimation and resolution capabilities of a towed line array of uniformly spaced hydrophones to provide frequency and bearing information about narrowband signals are examined. It is assumed that a monochromatic plane wave arrives at the array for each source. Several versions of the bounds are computed using different assumptions about which parameters have known values and about the way in which the samples are taken in space and in time. It is shown that the CRLB values for different situations can be compared to provide information about the effective use of a moving aperture for estimation of the parameters of narrowband signals arriving at the array. It is also shown that adding at least one hydrophone occupying a fixed position in space can improve the bearing estimates of a towed array by supplying additional frequency information if both the bearings and frequencies of the sources are unknown  相似文献   

Provenance of High Arsenic Holocene Sediment and Low Arsenic Pleistocene Sediment in Bangladesh Aquifers: A Preliminary Assessment     

ZHENG Yan  YANG Qiang  Alan M. SELTZER  N. Gary HEMMING  Sidney R. HEMMING 《《地质学报》英文版》2013,87(Z1):667-668

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The influence of quark anomalous magnetic moment in the Nambu–Jona-Lasinio model with different regularizations     

William R. Tavares  Rodrigo M. Nunes  Sidney S. Avancini  Ricardo L. S. Farias 《Astronomische Nachrichten》2024,345(2-3):e230168

The Nambu–Jona-Lasinio model is known for its simplicity and capacity to reproduce some of the basic characteristics of the quantum chromodynamics phase diagram. However, since it is a nonrenormalizable model, there are regularization issues that should be treated conveniently. This is the case when considering the quark anomalous magnetic moment (AMM) when external constant magnetic fields are present. Regularization procedures based on entangled functions between the magnetic field and the cutoff of the model can predict first-order phase transitions for chiral symmetry restoration at finite values of magnetic fields and inverse magnetic catalysis. The strengths of magnetic fields explored in NJL model and lattice QCD do not show first-order phase transition. In the present work, we show that some of the previous results are regularization-dependent effects and how to handle the divergences using the vacuum magnetic regularization scheme.  相似文献   

Base metals and other minor elements in the manganese deposits of west-central Arkansas     

G.H. Wagner  Ronald H. Konig  Sidney Vogelpohl  Michael D. Jones 《Chemical Geology》1979,27(4):309-327

Manganese oxides from deposits in west-central Arkansas were analyzed by X-ray diffraction for mineralogy and by atomic absorption spectroscopy for Mn, Fe, Co, Cu, Ni, Zn, V, Al, Li, Na, K, Mg, Ca, Sr and Ba. We report on 42 samples from 25 sites with more than 25 wt.% Mn and less than 7 wt.% Fe. Most samples were mixtures of two or more of the following minerals, many with concentric deposition: cryptomelane, lithiophorite, psilomelane and pyrolusite. In the purer samples of single minerals, lithiophorite contained the higher concentrations of total base metals (Co + Cu + Ni + Zn) than other minerals. In atom % of Mn these concentrations were: 9.51% in lithiophorite; 0.432% in psilomelane; and 0.275% in cryptomelane. The relative concentration of base metals in the pure minerals, proceeding from highest to lowest concentration, were: lithiophorite (Co = Cu > Ni > Zn); psilomelane (Co > Cu > Zn > Ni) and cryptomelane (Zn > Co = Cu > Ni).The concentration of Li correlates with the metals Al, Co, Cu, Ni and Zn, in the mineral samples containing measurable Li. Correlation coefficients (?) for Li with the various metals and sum of the base metals were: Al (? = 0.976); Co (? = 0.44); Ni (? = 0.954); Cu (? = 0.918); Zn (? = 0.875); and (Co + Cu + Ni + Zn) (? = 0.979). Li is believed to be a measure of lithiophorite. Correlation was found between Al content and base metal contents for all samples: Co (? = 0.354); Ni (? = 0.749); Cu (? = 0.808); Zn (? = 0.632); and (Co + Cu + Ni + Zn) (? = 0.884). The Al correlation extended to published values for these and the minerals hollandite and todorokite, except for Zn. Zn correlated with K in published analyses and in the eastern half of the study area where cryptomelane predominated.A mechanism is proposed to explain the enhancement by Al of base metal incorporation into manganese oxide minerals. The mechanism involves the isomorphous substitution of Al³⁺ for Mn⁴⁺ with charge neutralization by bivalent base metal ions.  相似文献   

Oscillator strengths for resonance lines of some silicon and sulfur ions     

Sidney O. Kastner 《Solar physics》1967,2(2):196-201

Oscillator strengths are calculated for resonance lines of some silicon and sulfur ions, which are present in the solar spectrum from about 160 Å to 380 Å. Spin-spin and spin-other orbit interactions are included. A comparison is made with Garstang's results for Six; agreement is good.  相似文献   

Globular clusters and galactic evolution (invited review)     

Sidney van den Bergh 《Astrophysics and Space Science》1986,118(1-2):435-438

Observations of the frequency with which globular clusters surround galaxies are reviewed. With a single exception the data do not favour the view that elliptical galaxies are formed from merging disc systems. Attention is also drawn to the unusually high frequency of globular clusters in central galaxies of rich clusters.  相似文献   

The conference on supply and demand of water transport, organized by the Stockholm school of economics on the occasion of the retirement of Professor Thomas Thorburn : Stockholm, Sweden, 18–19 June 1979     

Sidney Gilman 《Marine Policy》1979,3(4):322-324

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Whale mining,whale saving     

Sidney Holt 《Marine Policy》1985,9(3):192-213

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Oscillating glacial northern and southern deep water formation from combined neodymium and carbon isotopes     

Alexander M. Piotrowski  Steven L. Goldstein  Sidney  R. Hemming  Richard G. Fairbanks  David R. Zylberberg 《Earth and Planetary Science Letters》2008,272(1-2):394-405

While ocean circulation is driven by the formation of deep water in the North Atlantic and the Circum-Antarctic, the role of southern-sourced deep water formation in climate change is poorly understood. Here we address the balance of northern- and southern-sourced waters in the South Atlantic through the last glacial period using neodymium isotope ratios of authigenic ferromanganese oxides in thirteen deep sea cores from throughout the South Atlantic. The data indicate that northern-sourced water did not reach the Southern Ocean during the late glacial, and was replaced by southern-derived intermediate and deep waters. The high-resolution neodymium isotope record (~ 300 yr sample spacing) from two spliced deep Cape Basin sites indicates that over the last glacial period northern-sourced water mass export to the Southern Ocean was stronger during the major Greenland millennial warming intervals (and Southern Hemisphere cool periods), and particularly during the major interstadials 8, 12, and 14. Northern-sourced water mass export was weaker during Greenland stadials and reached minima during Heinrich Events. The benthic foraminiferal carbon isotopes in the same Cape Basin core reflect a partial control by Southern Hemisphere climate changes and indicate that deep water formation and ventilation occurred in the Southern Ocean during major Greenland cooling intervals (stadials). Together, neodymium isotopes and benthic carbon isotopes provide new information about water mass sourcing and circulation in deep Southern Ocean waters during rapid glacial climate changes. Combining carbon and neodymium isotopes can be used to monitor the relative proportion of northern- and southern-sourced waters in the Cape Basin to gain insight into the processes which control the carbon isotopic composition of deep waters. In this study we show that deep water formation and circulation was more important than biological productivity and nutrient regeneration changes for controlling the carbon isotope chemistry of Antarctic Bottom Water during millennial-scale glacial climate cycles. This observation also lends support to the hypothesis that ocean circulation is linked to interhemispheric climate changes on short timescales, and that ventilation in the glacial ocean rapidly switched between the northern and Southern Hemisphere on millennial timescales.  相似文献   

Evidence for an ionized disc in the narrow-line Seyfert 1 galaxy Ark 564     

S. Vaughan  K. A. Pounds  J. Reeves  R. Warwick  R. Edelson 《Monthly notices of the Royal Astronomical Society》1999,308(4):L34-L38

We present simultaneous ASCA and RXTE observations of Ark 564, the brightest known 'narrow-line' Seyfert 1 in the 2–10 keV band. The measured X-ray spectrum is dominated by a steep (Γ≈2.7) power-law continuum extending to at least 20 keV, with imprinted Fe K-line and edge features and an additional 'soft excess' below ∼1.5 keV. The energy of the iron K-edge indicates the presence of highly ionized material, which we identify in terms of reflection from a strongly irradiated accretion disc. The high reflectivity of this putative disc, together with its strong intrinsic O  viii Ly α and O  viii recombination emission, can also explain much of the observed soft excess flux. Furthermore, the same spectral model also provides a reasonable match to the very steep 0.1–2 keV spectrum deduced from ROSAT data. The source is much more rapidly variable than 'normal' Seyfert 1s of comparable luminosity, increasing by a factor of ∼50 per cent in 1.6 h, with no measurable lag between the 0.5–2 keV and 3–12 keV bands, consistent with much of the soft excess flux arising from reprocessing of the primary power-law component in the inner region of the accretion disc. We note, finally, that if the unusually steep power-law component is a result of Compton cooling of a disc corona by an intense soft photon flux, then the implication is that the bulk of these soft photons lie in the unobserved extreme ultraviolet.  相似文献