Non-monotone spectral projected gradient method applied to full waveform inversion   总被引：1，自引：0，他引：1  

Noam Zeev  Olga Savasta  Debora Cores 《Geophysical Prospecting》2006,54(5):525-534

The seismic inversion problem is a highly non‐linear problem that can be reduced to the minimization of the least‐squares criterion between the observed and the modelled data. It has been solved using different classical optimization strategies that require a monotone descent of the objective function. We propose solving the full‐waveform inversion problem using the non‐monotone spectral projected gradient method: a low‐cost and low‐storage optimization technique that maintains the velocity values in a feasible convex region by frequently projecting them on this convex set. The new methodology uses the gradient direction with a particular spectral step length that allows the objective function to increase at some iterations, guarantees convergence to a stationary point starting from any initial iterate, and greatly speeds up the convergence of gradient methods. We combine the new optimization scheme as a solver of the full‐waveform inversion with a multiscale approach and apply it to a modified version of the Marmousi data set. The results of this application show that the proposed method performs better than the classical gradient method by reducing the number of function evaluations and the residual values.  相似文献   

Effects of heavy metals on some soil biological parameters   总被引：11，自引：0，他引：11  

Olga Mikanova 《Journal of Geochemical Exploration》2006,88(1-3):220

The soils most polluted by heavy metals are probably alluvial soils. One of them is the alluvium of the Litavka River. The heavy metal content was much higher in some cases than the threshold values, allowed by the Czech standards. The effect of soil contamination on enzyme activity is presented. Generally, the values of enzymatic activities were highest in the soil above the source of contamination and they decrease as they approach the source of contamination. All measured parameters were affected by heavy metal concentrations. Our results demonstrate that several parameters of microbial activity could be used as good indicators of increasing concentrations of Cd, Pb and Zn in soil.  相似文献   

Phosphate Lu–Hf geochronology     

Gry H. Barfod  Olga Otero  Francis Albarde 《Chemical Geology》2003,200(3-4):241-253

Igneous, metamorphic and biogenic apatite contains Lu and Hf in proportions that make this mineral suitable for dating by the ¹⁷⁶Lu–¹⁷⁶Hf method. We present a new method for separation of Lu and Hf from apatite that involves a single extraction column step for Hf and a second exchange column step for Lu. This procedure allows rapid sample processing prior to analysis by MC-ICP-MS. Results from the igneous Gardiner, Skaergaard and Khibina Intrusions indicate that the closure temperature for the Lu–Hf isotopic system in apatite is relatively high. The Lu–Hf isochron age of 60 Ma for the Skaergaard Intrusion, East Greenland, is older than the generally accepted emplacement age, but does not appear to be a product of mixing. A centimeter-sized apatite from the Otter Lake area, Grenvillian Province, yields high and variable ¹⁷⁶Lu/¹⁷⁷Hf ratios showing that metamorphic apatite may, in some cases, allow for mono-mineral dating. The most important application of the method is undoubtedly its potential use for dating sedimentary formations. Although we find biogenic apatite in porous matrix highly susceptible to post-depositional resetting of the Lu–Hf isotopic system, the preservation of a near-depositional age for a shark tooth from the impermeable London Clay and recent work on crystalline authigenic phosphorites [Earth Planet. Sci. Lett. 201 (2002) 203] show the Lu–Hf system to be a promising tool for direct dating of sedimentary formations.  相似文献   

Foreword     

Olga Gritsai  Herman van der Wusten 《GeoJournal》1997,41(4):291-292

  相似文献   

Identifying Critical Locations in a Spatial Network with Graph Theory   总被引：2，自引：0，他引：2  

Ur&#;ka Dem&#;ar  Olga &#;patenková  Kirsi Virrantaus 《Transactions in GIS》2008,12(1):61-82

Effective management of infrastructural networks in the case of a crisis requires a prior analysis of the vulnerability of spatial networks and identification of critical locations where an interdiction would cause damage and disruption. This article presents a mathematical method for modelling the vulnerability risk of network elements which can be used for identification of critical locations in a spatial network. The method combines dual graph modelling with connectivity analysis and topological measures and has been tested on the street network of the Helsinki Metropolitan Area in Finland. Based on the results of this test the vulnerability risk of the network elements was experimentally defined. Further developments are currently under consideration for eventually developing a risk model not only for one but for a group of co‐located spatial networks.  相似文献   

Complexation of Gold(III)-Chloride at the Surface of Hematite     

Olga N. Karasyova  Lyudmila I. Ivanova  Leonid Z. Lakshtanov  Lars Lövgren  Staffan Sjöberg 《Aquatic Geochemistry》1998,4(2):215-231

The acid/base properties of the hematite/water interface and surfacecomplexation with gold has been studied by potentiometric titrations in thefour component system H⁺ – FeOH –AuCl ₄ ^- – Cl^-. Equilibrium measurementswere performed in NaCl media at 298.2 K. In the evaluation of equilibriummodel from experimental data the constant capacitance model was applied. Theacid/base properties were investigated in 0.1 M NaCl in the range 2.6 pH 7.4. The resulting intrinsic constants for protonation anddeprotonation of hydroxyl groups at the surface were log _1,1,0,0(int) ^s = 7.10 ± 0.06 andlog _{-1,1,0,0(int)} ^s = - 7.80 ±0.06. The density of proton active surface sites was 2.85nm^-2 and the specific capacitance 2.5 C V^-1 m^-2. In the investigation of surface complexation of gold, thepotentiometric titrations were performed in the range 2.0 pH 10.2.Titration data was supplemented with analysis of Au in the aqueous phase byatomic absorbance spectrometry. The equilibrium model proposed consists ofthe following monodentate surface complexes: FeOHAuCl₃(log _0,1,1,-1 ^s = 1.45 ± 0.03),FeOHAuCl₂OH (log _-1,1,1,-2 ^s = -3.89 ± 0.02), FeOHAu(OH)₃ (log _-3,1,1,-4 ^s = -21.94 ± 0.05). Aslightly better fit could be obtained by assuming formation of a bidentatecomplex with the composition(FeO)₂Au(OH)H₂O. However, based onstructural arguments this complex was rejected.  相似文献   

Russian human geography in the 'wonderland' of globalization     

Olga Gritsai 《GeoJournal》1998,45(1-2):77-83

  相似文献   

Millennium scale environment changes of the Okhotsk Sea during last 80 kyr and their phase relationship with global climate changes     

Sergey Alexandrovich Gorbarenko  Evgenia L’vovich Goldberg  Michaele Kashgarian  Tat’yana Alekseevna Velivetskaya  Sergey Petrovich Zakharkov  Vladimir Stepanovich Pechnikov  Alexandr Anatol’evich Bosin  Olga Yur’evna Psheneva  Elena Diamilevna Ivanova 《Journal of Oceanography》2007,63(4):609-623

The paper presents the records of several paleoproductivity proxies (PP) (biogenic opal and Ba (Si_bio, Ba_bio), organic carbon (C_org) and carbonate Ca_carb, chlorin and benthic foraminifera abundance (BFA)) in sediments of the Okhotsk Sea for the last 80 kyr with a resolution of ∼100–300 years. The sediment age model was based on the AMS ¹⁴C data, records of benthic foraminifera δ¹⁸O, paleointensity of the Earth’s geomagnetic field and magnetic susceptibility. PP values demonstrate series of severe prolonged productivity drops in the Okhotsk Sea followed by a sharp increase during the last glaciation. On the basis of quantitative estimations of the paleoproductivity in the Okhotsk Sea during the cold MIS 2 and warm Holocene (Gorbarenko and Goldberg, 2005), it is suggested that the millennium scale relationship in productivity-climate changes of this basin was similar: an increase in the sea’s productivity was related with regional climate warming and vice-versa. The PP records of productivity/climate oscillations in the Okhotsk Sea during MIS 2–4 occurred contemporaneously with the North Atlantic cold Heinrich events (HE) and Greenland Dansgaard-Oyeshger interstadial (DOI). Observed successions of prolonged climate cooling events followed by rapid, abrupt warming are similar to climate and environmental oscillations in the N. Atlantic and Greenland, that confirms the millennium-scale climate changes synchronicities in the Northern Hemisphere including the far NW Pacific, the hydrology and climate conditions of which are close to those of the Okhotsk Sea. Synchronism of the N. Hemisphere severe cooling (including the Okhotsk Sea) with the Antarctic warming suggests that mechanisms of the “seesaw” effect (Blunier and Brook, 2001) in the low latitude heat redistribution between high latitudes of both hemispheres were more complicated than direct NADW formation forcing and encompasses the global atmospheric reorganization. Within the PP used a closer connection in the Okhotsk Sea millennium oscillations was observed for the C_org, BFA and chlorin; Ba_bio increases more closely to DOI. Si_bio variability does not show any evident correlation with productivity changes.  相似文献   

Subcellular Distribution of Heavy Metals in Organs of BivalveModiolus Modiolus Living Along a Metal Contamination Gradient     

Olga V. Podgurskaya  Victor Ya. Kavun 《Ocean Science Journal》2006,41(1):43-51

Concentration and distribution of Fe, Zn, Cu, Cd, Mn, Pb, Ni among subcellular fractions (cellular membrane structures and cytosol) and Zn, Cu, Cd among cytoplasmic proteins in the kidney and digestive gland of musselModiolus modiolus living along a polymetallic concentration gradient were studied. It was found in the kidney ofM. modiolus from contaminated sites that the Fe percent increased in the “membrane” fraction, whereas Zn, Pb, Ni and Mn percent increased in the cytosol compared to the kidney of the control mussel. Note kidney cytosol ofM. modiolus from clean and contaminated sites sequestered major parts of Cu and Cd. In the digestive gland ofM. modiolus from contaminated sites Fe, Zn, Cd, Mn, Ni percent increased in the “membrane” fraction, whereas Cu, Pb percent increased in the cytosol compared to digestive gland of control mussel. Gel-filtration chromatography shows kidney ofM. modiolus contains increased metallothionein-like protein levels irrespective of ambient dissolved metal concentrations. It was shown that the metal detoxification system in the kidney and digestive gland ofM. modiolus was efficient under extremely high ambient metal levels. However, under complex environmental contamination in the kidney ofM. modiolus, the metal detoxification capacity of metallothionein-like proteins was damaged.  相似文献   

Community Structure of Free-living Marine Nematodes in the Area of Agar-Producing Alga Ahnfeltia To b u c h i e n s i s Field (Starka Strait,Peter the Great Bay,East Sea)     

Olga Pavlyuk  Yulia Trebukhova 《Ocean Science Journal》2007,42(3):165-170

The structure of the nematodes communities has been studied in the sediments on two sites located outside and under the layer ofAhnfeltia tobuchiensis (Kanno and Matsubara 1932; Makijenko 1970). Bottom sediments at the stations were represented by sands with a different degree of silting. Specific structure of nematodes at the stations was significantly different under the similar environmental conditions (water depth, dissolved oxygen saturation, salinity, temperature of the bottom layer and organic carbon content inside of the sediment). Nematodes dominated (75.7 %) in meiobenthos community under the layer of A.tobuchiensis where concentration of silt particles was 12 %. Representatives of the family Comesomatidae were dominant. Low index of species diversity and high Simpson domination index were detected in this community. Under a layer ofA. tobuchiensis with the thickness of 30 cm concentration of the silt particles was 5.39 %; nematodes density was low and made 32.1 % of the general density of meiobenthos. Species of the families Xyalidae and Monoposthiidae were dominant. Outside of A.tobuchiensis, field percentage of silt particles was minimal (3.1 %) and representatives of families Cyatholaimidae and Axonolaimidae dominated. The specific structure of nematodes in this type of the ground is characterized by high index of species diversity and low level of domination.  相似文献