Fractal velocity models in refraction seismology   总被引：4，自引：0，他引：4  

David J. Crossley  Oliver G. Jensen 《Pure and Applied Geophysics》1989,131(1-2):61-76

The introduction of noise components to a simple crustal velocity model is shown to markedly affect the appearance of synthetic seismograms calculated according to ray theory applied to refraction experiments. Here we simulate noise by a self-similar process with a power spectral density which falls off as inverse wavenumber to a simple power (0–2). The major effect is to destroy the coherency of the arrival branches normally expected from deterministic velocity models; the arrival amplitudes also show large trace-to-trace variations and considerable sensitivity to shot position. Some of these differences can be ascribed to the variety of noise model chosen (i.e., white noise, flicker noise and brown noise). It is argued that there is no clear distinction between coherent noise and geological structure.  相似文献   

Products and mechanisms of the gas phase reactions of NO3 with CH3SCH3, CD3SCD3, CH3SH and CH3SSCH3     

N. R. Jensen  J. Hjorth  C. Lohse  H. Skov  G. Restelll 《Journal of Atmospheric Chemistry》1992,14(1-4):95-108

Products and mechanisms of the reaction between the nitrate radical (NO₃) and three of the most abundant reduced organic sulphur compounds in the atmosphere (CH₃SCH₃, CH₃SH and CH₃SSCH₃), have been studied in a 480 L reaction chamber using in situ FT-IR and ion chromatography as analytical techniques. In the three reactions, methanesulphonic acid was found to be the most abundant sulphur containing product. In addition the stable products SO₂, H₂SO₄, CH₂O, and CH₃ONO₂ were identified and quantified and thionitric acid-S-methyl ester (CH₃SNO₂) was observed in the i.r. spectrum from all of the three reactions. Deuterated dimethylsulphide (CD₃SCD₃) showed an isotope effect on the reaction Deuterated dimethylsulphide (CD₃SCD₃) showed an isotope effect on the reaction rate constant (k_H/k_D) of 3.8±0.6, indicating that hydrogen abstraction is the first step in the NO₃+CH₃SCH₃ reaction, probably after the formation of an inital adduct.Based on the products and intermediates identified, reaction mechanisms are proposed for the three reactions.  相似文献   

Magma influx and mixing in the Bjerkreim-Sokndal layered intrusion, South Norway: evidence from the boundary between two megacyclic units at Storeknuten     

J.C. Jensen  F.M. Nielsen  J.C. Duchesne  D. Demaiffe  J.R. Wilson   《Lithos》1993,29(3-4):311-325

The Bjerkreim-Sokndal layered intrusion belongs to the Proterozoic anorthositic province in the Rogaland area of southern Norway. The northwestern part of the intrusion comprises a ca. 6 km-thick Layered Series made up of megacyclic units (MCU) arranged in a syncline; each megacyclic unit reflects the influx of fresh magma into the chamber. The boundary between megacyclic units III and IV has been studied in detail at Storeknuten on the southern flank of the syncline. The megacyclic units can be subdivided into a series of cumulate stratigraphic zones; the interval from the top of zone IIIe to the base of zone IVd is exposed in the Storeknuten area. Modally layered plagioclase-hypersthene-ilmenite-magnetite-augite-apatite cumulates belonging to zone IIIe are overlain by 30 m of massive plagioclase-rich rocks (commonly containing ilmenite and/or hypersthene) constituting zone IVa. The entry of cumulus olivine defines the base of zone IVb (dominantly plagioclase-olivine-ilmenite cumulates) which is about 100 m thick. Many of the olivines are partly or completely replaced by Ca-poor pyroxene/Fe---Ti oxide symplectites. This massive leucotroctolitic zone is overlain by modally layered, laminated plagioclase-hypersthene-ilmenite cumulates of zone IVc. The successive entry of magnetite, apatite (accompanied by Ca-rich pyroxene) and inverted pigeonite defines zones IVd, e and f respectively. The entry of K-feldspar (accompanied by Fe-rich olivine) defines the base of a jotunitic transition zone which passes upwards into mangerites and quartz mangerites.

There is a compositional regression through zone IVa. The upper part of zone IIIe has Ca-poor pyroxene with about En68, plagioclase with An44–48 and a Sr-isotope ratio of about 0.7062, while the base of zone IVb has olivine with Fo75 together with En78, An53 and 0.7050 respectively. Similar reversals are shown by the minor element compositions of plagioclase and Fe---Ti oxides. Sr-isotope ratios increase systematically up through zone IVb (reaching 0.7058 in zone IVd) while An% and Sr in plagioclase and Ni and Cr in Fe---Ti oxides decrease. Olivine compositions vary unsystematically and are believed to have changed their Fe:Mg ratios as a result of trapped liquid shift.

The magma residing in the chamber when the influx at the base of megacyclic unit IV took place was compositionally zoned, and assimilation of gneissic country rock at the roof had resulted in the Sr-isotope ratio increasing up through the magma column. The new magma had a Sr-isotope ratio of about 0.7050 while the resident magma had a ratio of 0.7062 at the floor, increasing upwards. The new magma mixed with the basal layer(s) of the compositionally zoned resident magma and crystallization of this hybrid magma during influx and mixing produced the compositional regression in zone IVa. When magma influx ceased, olivine-bearing rocks began to crystallize at the base of zone IVb. The leucotroctolites at the base of this zone are the most primitive rocks in the entire intrusion. The systematic increase in Sr-isotope ratios up through zone IVb resulted from progressive mixing between new and resident magma. This mixing either took place during magma influx or by the progressive mixing of overlying resident magma layers during crystallization.

Calculations based on geochemical modelling, the thickness of cumulate stratigraphy repeated and Sr-isotope ratios indicate that the new magma influx had a thickness of 350–500 m in the Storeknuten section and that the leucotroctolites of zone IVb represent about 20–30% crystallization of this influx.  相似文献   

On the interaction of geology, measurement, and statistical analysis of small-scale permeability measurements   总被引：1，自引：0，他引：1  

J.L. Jensen  C.A. Glasbey  P.W.M. Corbett 《地学学报》1994,6(4):397-403

Sedimentary rocks exhibit small-scale (mm) permeability variations which can be detected with a probe permeameter. The structure of the laminations may provide evidence about the characteristics of the measurement device. The statistical interpretation of these measurements using averages and variograms is enhanced when the geological character of the rock is taken into consideration. The three aspects of rock characterization, namely geology, measurement, and statistical analysis, are best assessed in concert. This theme is illustrated using probe data taken from sections of the Rannoch and Etive Formations, Northern North Sea.  相似文献   

The Askervein Hill Project: Vertical profiles of wind and turbulence     

R. E. Mickle  N. J. Cook  A. M. Hoff  N. O. Jensen  J. R. Salmon  P. A. Taylor  G. Tetzlaff  H. W. Teunissen 《Boundary-Layer Meteorology》1988,43(1-2):143-169

This is one of a series of papers on the Askervein Hill Project. It presents results from the Askervein 1982 and 1983 experiments in the form of vertical profiles of mean wind and turbulence integral statistics at upwind reference locations and at two hilltop sites. The data were obtained from a variety of sensors including sonic, Gill UVW and cup anemometers mounted on 50, 30, 17 and 10 m towers and TALA kite systems. Comparisons with numerical-model predictions are discussed.  相似文献   

The 2nd international workshop on waves,storm surges and coastal hazards incorporating the 16th international workshop on wave hindcasting and forecasting     

Swail  Val  Alves  Jose-Henrique  Brown  Jennifer  Greenslade  Diana  Jensen  Robert 《Ocean Dynamics》2021,71(9):957-961

  相似文献   

A contribution to the crystal chemistry of the voltaite group: solid solutions, Mössbauer and infrared spectra, and anomalous anisotropy     

Juraj Majzlan  Hannes Schlicht  Maria Wierzbicka-Wieczorek  Gerald Giester  Herbert Pöllmann  Beatrix Brömme  Stephen Doyle  Gernot Buth  Christian Bender Koch 《Mineralogy and Petrology》2013,107(2):221-233

Voltaite is a mineral of fumaroles, solfatares, coal-fire gas vents, and acid-mine drainage systems. The nominal composition is K₂Fe₅ ²⁺Fe₃ ³⁺Al(SO₄)₁₂·18H₂O and the nominal symmetry is cubic, $Fd\overline{3}c$ . The tetragonal (I4₁/acd) superstructure of voltaite is known as the mineral pertlikite. In this study, we investigated 22 synthetic voltaite samples in which Fe²⁺ was partially or completely replaced by Mg, Zn, Mn, or Cd, by single-crystal and powder X-ray diffraction (both in-house and synchrotron). Two samples contained NH₄ ⁺ instead of K⁺. The structure of voltaite is based on a framework defined by kröhnkite-like heteropolyhedral chains which host both M³⁺ and M²⁺ in octahedral coordination. Unit cell dimensions of the end-members scale almost linearly with the size of M²⁺. In the Fe²⁺-Mg-Zn solid solutions, the Fe²⁺-Mg and Fe²⁺-Zn solutions are linear (ideal) in terms of their lattice-parameter variations. The Mg-Zn solid solution, however, is strongly non-ideal. A detailed analysis of the topology of the chains showed that this behavior originates in expansion and contraction of individual M²⁺-O bonds within the chains. In the Mg-Zn solid solution, some of the M²⁺-O bonds expand while none contract. In the other solid solutions, expansion of some M²⁺-O bonds is always compensated by contraction of the other ones. Parts of the nominally cubic crystals are optically anisotropic and their symmetry is found to be tetragonal by single crystal X-ray diffraction measurements. The coexistence of cubic and tetragonal sectors within a single crystal without any detectable difference in their chemical composition is difficult to explain in terms of growth of such composite crystals. Mössbauer and infrared spectra collected on our synthetic crystals conform with previously published data.  相似文献   

The COVID-19 pandemic and global environmental change: Emerging research needs     

Robert Barouki  Manolis Kogevinas  Karine Audouze  Kristine Belesova  Ake Bergman  Linda Birnbaum  Sandra Boekhold  Sebastien Denys  Celine Desseille  Elina Drakvik  Howard Frumkin  Jeanne Garric  Delphine Destoumieux-Garzon  Andrew Haines  Anke Huss  Genon Jensen  Spyros Karakitsios  Jana Klanova  Paolo Vineis 《Chemie der Erde / Geochemistry》2013

The outbreak of COVID-19 raised numerous questions on the interactions between the occurrence of new infections, the environment, climate and health. The European Union requested the H2020 HERA project which aims at setting priorities in research on environment, climate and health, to identify relevant research needs regarding Covid-19. The emergence and spread of SARS-CoV-2 appears to be related to urbanization, habitat destruction, live animal trade, intensive livestock farming and global travel. The contribution of climate and air pollution requires additional studies. Importantly, the severity of COVID-19 depends on the interactions between the viral infection, ageing and chronic diseases such as metabolic, respiratory and cardiovascular diseases and obesity which are themselves influenced by environmental stressors. The mechanisms of these interactions deserve additional scrutiny. Both the pandemic and the social response to the disease have elicited an array of behavioural and societal changes that may remain long after the pandemic and that may have long term health effects including on mental health. Recovery plans are currently being discussed or implemented and the environmental and health impacts of those plans are not clearly foreseen. Clearly, COVID-19 will have a long-lasting impact on the environmental health field and will open new research perspectives and policy needs.  相似文献   

Using Low‐Resolution Satellite Data to Quantify Terrestrial Carbon in Tropical Areas     

Ryan R. Jensen  Michael W. Binford 《国际地球制图》2013,28(2):19-24

Abstract

The ability to map and monitor terrestrial carbon is important in tropical regions where land conversion is intense and tropical moist forests store much of Earth's terrestrial carbon. The release of terrestrial carbon in the form of carbon dioxide could alter local, regional, and global weather, and enhance the greenhouse effect. This study analyzed the ability of coarse‐resolution Advanced Very High Resolution Radiometer (AVHRR) remote sensor data to quantify carbon stored in the Guaporé / Itenez River Basin in Bolivia and Brazil. This area was selected because of the amount of land conversion that has occurred there relative to other areas of the Amazon Basin. A supervised vegetation classification map was created with training sites acquired through fieldwork done in the area in summer 1998. Image pixels were classified as tropical moist forest, degraded tropical moist forest, cerrado, grasslands, degraded savanna, or bare ground. Estimated above and below‐ground carbon values of the different land cover types were applied to each class to calculate total carbon values. It was concluded that data such as AVHRR may be used to calculate the amount of carbon in terrestrial ecosystems in regional scale areas.  相似文献   

spatialCopula: A Matlab toolbox for copula-based spatial analysis     

Hannes Kazianka 《Stochastic Environmental Research and Risk Assessment (SERRA)》2013,27(1):121-135

The spatialCopula toolbox contains a set of Matlab functions that provides utilities for copula-based analysis of spatially referenced data, a topic which has re cently attracted much attention in spatial statistics. These tools have been developed to support the work flow in parameter estimation, spatial interpolation and visualization. They offer flexible and user-friendly software for dealing with non-Gaussian and extreme value data that possibly contain a spatial trend or geometric anisotropy. The objective of this paper is to give an introduction to the concept behind the software and to outline the functionality of the toolbox. We illustrate its usefulness by analyzing a data set here referred to as the Gomel data set, which includes moderately skewed radioactivity measurements in the region of Gomel, Belarus. The source codes are freely available in Matlab language on the author’s website (fam.tuwien.ac.at/~hakazian/software.html).  相似文献