Interpretation of the magnetic field from a sphere in the wavenumber domain     

B. Holm Jacobsen  L. Børsting Pedersen 《Pure and Applied Geophysics》1980,118(2):1155-1169

A Fourier transformation of the magnetic field from a magnetized sphere allows a particularly simple interpretation of the parameters of the sphere. The depth to the centre and total magnetic moments of the sphere are related to the intercept and slope of the power spectrum. The horizontal centre and direction of magnetization are related to slope and intercept of the phase spectra in two perpendicular, horizontal directions. Examples with artificial data contaminated by various noise components are presented.  相似文献   

Resolving the Holocene alluvial record in southeastern Australia using luminescence and radiocarbon techniques     

Michael D. Cheetham  Annabelle F. Keene  Wayne D. Erskine  Richard T. Bush  Kathryn Fitzsimmons  Geraldine E. Jacobsen  Stewart J. Fallon 《第四纪科学杂志》2010,25(7):1160-1168

A previous assessment of radiocarbon (¹⁴C) dates from alluvial units in southeastern Australia revealed a gap in the geochronological record that coincides with the Holocene climatic optimum. This gap in the alluvial record can be further refined using optically stimulated luminescence (OSL). The chronology of Holocene river terraces on Widden Brook, a sandy alluvial stream in southeastern Australia, was established using ¹⁴C and OSL techniques. Combined use of these independent techniques allows for a more rigorous assessment of the alluvial record. The robust chronology, consisting of 38 ¹⁴C and 11 OSL samples, permitted identification of significant depositional variation within the catchment, resulting from localised geomorphic processes. The three terrace sequences identified yielded distinct chronologies, suggesting alluvial deposition at different times. The sequences exhibited a continuous chronology, which indicated continuous deposition throughout the Holocene. The chronology of terrace sequences within this catchment suggests that terrace formation can be attributed to localised geomorphic processes rather than climatic forcing. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Pedotransfer functions estimating soil hydraulic properties using different soil parameters   总被引：1，自引：0，他引：1  

Christen D. Børgesen  Bo V. Iversen  Ole H. Jacobsen  Marcel G. Schaap 《水文研究》2008,22(11):1630-1639

Estimates of soil hydraulic properties using pedotransfer functions (PTF) are useful in many studies such as hydrochemical modelling and soil mapping. The objective of this study was to calibrate and test parametric PTFs that predict soil water retention and unsaturated hydraulic conductivity parameters. The PTFs are based on neural networks and the Bootstrap method using different sets of predictors and predict the van Genuchten/Mualem parameters. A Danish soil data set (152 horizons) dominated by sandy and sandy loamy soils was used in the development of PTFs to predict the Mualem hydraulic conductivity parameters. A larger data set (1618 horizons) with a broader textural range was used in the development of PTFs to predict the van Genuchten parameters. The PTFs using either three or seven textural classes combined with soil organic mater and bulk density gave the most reliable predictions of the hydraulic properties of the studied soils. We found that introducing measured water content as a predictor generally gave lower errors for water retention predictions and higher errors for conductivity predictions. The best of the developed PTFs for predicting hydraulic conductivity was tested against PTFs from the literature using a subdata set of the data used in the calibration. The test showed that the developed PTFs gave better predictions (lower errors) than the PTFs from the literature. This is not surprising since the developed PTFs are based mainly on hydraulic conductivity data near saturation and sandier soils than the PTFs from the literature. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Fatal ingestion of floating net debris by two sperm whales (Physeter macrocephalus)     

Jeff K. Jacobsen  Liam Massey 《Marine pollution bulletin》2010,60(5):765-767

In 2008 two male sperm whales (Physeter macrocephalus) stranded along the northern California coast with large amounts of fishing net scraps, rope, and other plastic debris in their stomachs. One animal had a ruptured stomach, the other was emaciated, and gastric impaction was suspected as the cause of both deaths. There were 134 different types of nets in these two animals, all made of floating material, varying in size from 10 cm² to about 16 m². The variability in size and age of the pieces suggests the material was ingested from the surface as debris rather than bitten off from active gear. These strandings demonstrate that ingestion of marine debris can be fatal to large whales, in addition to the well documented entanglements known to impact these species.  相似文献   

Transition metals in the transition zone: partitioning of Ni,Co, and Zn between olivine,wadsleyite, ringwoodite,and clinoenstatite     

Li?ZhangEmail author  Joseph?R.?Smyth  Takaaki?Kawazoe  Steven?D.?Jacobsen  Shan?Qin 《Contributions to Mineralogy and Petrology》2018,173(7):52

Ni, Co, and Zn are widely distributed in the Earth’s mantle as significant minor elements that may offer insights into the chemistry of melting in the mantle. To better understand the distribution of Ni²⁺, Co²⁺, and Zn²⁺ in the most abundant silicate phases in the transition zone and the upper mantle, we have analyzed the crystal chemistry of wadsleyite (Mg₂SiO₄), ringwoodite (Mg₂SiO₄), forsterite (Mg₂SiO₄), and clinoenstatite (Mg₂Si₂O₆) synthesized at 12–20 GPa and 1200–1400 °C with 1.5–3 wt% of either NiO, CoO, or ZnO in starting materials. Single-crystal X-ray diffraction analyses demonstrate that significant amounts of Ni, Co, and Zn are incorporated in octahedral sites in wadsleyite (up to 7.1 at%), ringwoodite (up to 11.3 at%), olivine (up to 2.0 at%), and clinoenstatite (up to 3.2 at%). Crystal structure refinements indicate that crystal field stabilization energy (CFSE) controls both cation ordering and transition metal partitioning in coexisting minerals. According to electron microprobe analyses, Ni and Co partition preferentially into forsterite and wadsleyite relative to coexisting clinoenstatite. Ni strongly prefers ringwoodite over coexisting wadsleyite with \({D}_{\text{Ni}}^{\text{Rw}/\text{Wd}}\)?=?4.13. Due to decreasing metal–oxygen distances with rising pressure, crystal field effect on distribution of divalent metal ions in magnesium silicates is more critical in the transition zone relative to the upper mantle. Analyses of Ni partitioning between the major upper-mantle phases implies that Ni-rich olivine in ultramafic rocks can be indicative of near-primary magmas.  相似文献   

Correction to: Transition metals in the transition zone: partitioning of Ni,Co, and Zn between olivine,wadsleyite, ringwoodite,and clinoenstatite     

Li?ZhangEmail author  Joseph?R.?Smyth  Takaaki?Kawazoe  Steven?D.?Jacobsen  Shan?Qin 《Contributions to Mineralogy and Petrology》2018,173(7):60

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