Influence of electron nongyrotropy and anisotropy on parallel wave propagation: Numerical solution of dispersion relation     

F.J.R. Simões  M.V. Alves  F.R. Cardoso  E. Costa 《Journal of Atmospheric and Solar》2011,73(11-12):1511-1519

This work investigates the influence of a nongyrotropic electron beam on the coupling between the electromagnetic modes of parallel propagation in a background gyrotropic plasma. We explore the importance of the relevant parameters in driving instabilities: the ratio of electron plasma frequency to electron cyclotron frequency, the gyrophase angle, and the temperature anisotropy. We confirm previous results that nongyrotropy can lead to mode coupling for specific values of relevant parameters. More important was to observe that when the anisotropy in the system provides sufficient free energy to start instabilities, the electron nongyrotropy plays an important role to change the growth rate.  相似文献   

Antioxidant Enzymes Response in Vetiver Grass: A Greenhouse Study for Chelant‐Assisted Phytoremediation of Lead‐Contaminated Residential Soils     

Syam S. Andra  Rupali Datta  Ramana Reddy  Sumathi K. M. Saminathan  Dibyendu Sarkar 《洁净——土壤、空气、水》2011,39(5):428-436

In a previous study we have demonstrated the suitability of using vetiver grass (Vetiveria zizanioides L.) for the phytostabilization of lead‐based paint contaminated residential soils. Vetiver did not show any growth retardation or toxicity symptoms despite high soil Pb levels. Antioxidant enzymes like superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) reportedly allow plants to combat metal stress. Thus, we hypothesized that in vetiver, these antioxidant enzymes can play an important role in combating Pb induced stress, and that chelant‐bound Pb is less toxic to vetiver compared to free Pb in soil. The response of antioxidant enzymes was studied in vetiver grass grown in Pb paint‐contaminated residential soils collected from San Antonio, Texas and Baltimore, Maryland. Chelating agents such as ethylenediaminetetraacetic acid (EDTA) and ethylenediaminedisuccinic acid (EDDS) were used to mobilize Pb from bound fractions to the labile pool, facilitating Pb uptake by vetiver. Although the Pb concentration in vetiver from these treatments was significantly higher than those grown in the absence of a chelant, the antioxidant enzymes activities were lower compared to the latter. Antioxidant enzymes activity of vetiver plants grown in the presence of chelants is lower compared to those in without chelant treatment, while they tended to increase with dose in treatments with varying chelant concentrations. Data obtained support the proposed hypothesis.  相似文献   

A Potential Global Standard Stratotype-Section and Point of the Moscovian Stage (Carboniferous)     

WANG Xiangdong  QI Yuping  Lance LAMBERT  WANG Zhihao  WANG Yue  HU Keyi  LIN Wei  CHEN Bo 《《地质学报》英文版》2011,85(2):366-372

Conodonts and fusulinids are the two most widely used biotic groups for subdividing and correlating Bashkirian and Moscovian strata. The definition of the base of the Global Moscovian Stage is undecided because there are many disagreements among existing boundary definition proposals, each of which has disadvantages. Declinognathodus donetzianus is easily recognized but somewhat limited in its paleogeographic distribution. Idiognathoides postsulcatus is slightly more widespread, but it is less easily identified and its occurrences may be diachronous from region to region. Diplognathodus ellesmerensis is easily recognized and even more widespread, but it is usually rare and its ancestry is not adequately known. The Naqing Section of South Guizhou, South China contains diverse conodont evolutionary lineages among different taxa, including Idiognathoides, Idiognathodus, Diplognathodus, Neognathodus, Gondolella and Mesogondolella. There are numerous transitional forms in almost every lineage of the Naqing section, which shows that the prospects for South China to play a critical role in determining the basal Moscovian Stage definition are good.  相似文献   

Surface layer variability in the Ross Sea,Antarctica as assessed by in situ fluorescence measurements     

Walker O. Smith  Vernon Asper  Sasha Tozzi  Xiao Liu  Sharon E. Stammerjohn 《Progress in Oceanography》2011,88(1-4):28-45

Phytoplankton fluorescence, temperature and salinity were measured from December through February using in situ instruments deployed at two locations in the southern Ross Sea, Antarctica during the austral summers of three consecutive years (2003–2004, 2004–2005, and 2005–2006) to assess the short-term, seasonal and interannual variations in phytoplankton biomass and oceanographic conditions. The seasonal climatologies of physical forcing variables were also determined from satellite measurements, and the data from the two sites compared to the 2000–2009 mean. In situ fluorometers were deployed at three depths at 77°S, 172.7°E and 77.5°S, 180°. Significant differences between the two sites were consistently observed, confirming the anticipated high level of spatial and temporal heterogeneity. Chlorophyll fluorescence was maximal in late December, and generally decreased rapidly to modest levels in January and February. However, during 1 year (2003–2004) a secondary bloom was found, with summer maxima being similar to those observed during spring. Fluorescence displayed a strong diel cycle, with strong quenching during periods of maximum irradiance. The magnitude of this reduction was large (the minimum average fluorescence was 25% of the daily mean) and decreased with depth. Fluorescence varied interannually, with the absolute levels and temporal patterns being different among years. The two sites had different temperature/salinity properties as measured at 24 m, and both variables changed with time. During 2004–2005 we were able to continuously measure the photosynthetic quantum efficiency of PSII (F_v/F_m) at 11 m, which revealed a minimum in December, and an increase in January, whereas the absolute fluorescence (F_o) decreased simultaneously. We suggest that this reflected a mixing event, whereby available irradiance increased, allowing a short period of growth in a more favorable optical environment. While substantial variations from the mean physical forcing were observed, the linkage of these physical variations with fluorescence was not always clear. Short-term (over 24-h) changes in fluorescence occurred, and were likely related to advective events. Wind events altered fluorescence in the surface layer, and these redistributed phytoplankton in the surface. The variability in chlorophyll fluorescence and physical forcing over a variety of scales in the Ross Sea provides insights into temporal–spatial coupling of phytoplankton.  相似文献   

Effects of soil types and forms of arsenical pesticide on rice growth and development   总被引：1，自引：1，他引：0  

S. Quazi Ph.D.  R. Datta Ph.D.  D. Sarkar Ph.D. 《International Journal of Environmental Science and Technology》2011,8(3):445-460

For decades, repeated and widespread use of arsenical pesticides has significantly contributed to arsenic contamination in soils. Residues from the overuse of these arsenicals may result in phytotoxicity to crops, which will depend on soil types, plant species and the toxicity of arsenical pesticides. A greenhouse column study was conducted to evaluate the effect of two pesticides, i.e. one organic (dimethylarsinic acid) and one inorganic (sodium arsenate), on the vegetative response of rice as a function of soil properties. Four soils with varying arsenic retention capabilities at two different pesticide amendment rates (675 and 1500 mg/kg) representing the worst case scenarios in superfund sites were used. Results showed that arsenic availability to rice was mainly influenced by soil physicochemical properties. The soil with the lowest arsenic retention capacity had the highest arsenic concentration in the leachate as well as in the plant tissue. In contrast, for soils with higher arsenic retention capacity, higher concentrations of arsenic were found in the surface soil which resulted in the inhibition of plant growth. There was no significant difference between labile arsenic / plant-available arsenic irrespective of the form of arsenical pesticide used. Plant growth parameters such as biomass, shoot height, root length decreased with increased arsenic concentrations in all soils. A significant negative correlation (P<0.05) was observed between the phytoavailable arsenic and plant growth response. Interestingly, the form of arsenical pesticide used did not impact arsenic uptake or shoot growth but significantly impacted root growth.  相似文献   

A fully implicit and consistent finite element framework for modeling reservoir compaction with large deformation and nonlinear flow model. Part I: theory and formulation   总被引：2，自引：0，他引：2  

Zhijun Liu  Ruijie Liu 《Computational Geosciences》2018,22(3):623-637

Reservoir depletion results in rock failure, wellbore instability, hydrocarbon production loss, oil sand production, and ground surface subsidence. Specifically, the compaction of carbonate reservoirs with soft rocks often induces large plastic deformation due to rock pore collapse. On the other hand, following the compaction of reservoirs and failure of rock formations, the porosity and permeability of formations will, in general, decrease. These bring a challenge for reservoir simulations because of high nonlinearity of coupled geomechanics and fluid flow fields. In this work, we present a fully implicit, fully coupled, and fully consistent finite element formulation for coupled geomechanics and fluid flow problems with finite deformation and nonlinear flow models. The Pelessone smooth cap plasticity model, an important material model to capture rock compaction behavior and a challenging material model for implicit numerical formulations, is incorporated in the proposed formulation. Furthermore, a stress-dependent permeability model is taken into account in the formulation. A co-rotational framework is adopted for finite deformation, and an implicit material integrator for cap plasticity models is consistently derived. Furthermore, the coupled field equations are consistently linearized including nonlinear flow models. The physical theories, nonlinear material and flow models, and numerical formulations are the focus of part I of this work. In part II, we verify the proposed numerical framework and demonstrate the performance of our numerical formulation using several numerical examples including a field reservoir with soft rocks undergoing serious compaction.  相似文献   

The March–April 2014 sequence of earthquakes in North Chile     

《Journal of South American Earth Sciences》2015

During March–April 2014 a series of earthquakes occurred around the Iquique city located in the northern Chile region. The two largest events of this sequence are the Mw8.2, April 1, 2014 and Mw7.7, April 4, 2014 quakes. Here we computed the nodal planes of eight of the large and well teleseismically recorded events of this series based on grid search, teleseismic moment tensors inversion, empirical Green's function deconvolution and its stack to average the deconvolutions for the Mw = 8.2, April 1, 2014, synthetic Green's function deconvolution and its stack to average the deconvolutions for the same event and 3D static deformation analysis of the above mentioned events based on the AK135 model. Grid search nodal planes and moment tensors suggest the dominance of reverse faulting. Almost all of the calculated teleseismic moment tensors represent a considerable amount of DC (usually more than 90%) and lower amount of CLVD for this sequence of events. Empirical and synthetic Green's function deconvolution showing down dip rupture propagation and 3D static deformation representing higher amount of vertical deformation in comparison with horizontal deformation components plus the existence of uplift and subsidence. According to the aftershocks distribution there is a bilateral distribution of the aftershocks around the first large event of this sequence that occurred March 16, 2014 (Mw6.7) so that they are approximately limited between the Mw8.2 (at north) and Mw7.7 (at south) quakes. Moreover there exist two bands of regional seismicity during early-mid 2014: a shallow off-shore band between the trench and coast and a deeper inland band under the active volcanic chain (both nearly parallel to the trench).  相似文献   

PATRONAGE RATES OF SUPERMARKET SHOPPING CENTERS,SAN ANTONIO,TEXAS*     

Richard C. Jones 《The Professional geographer》1991,43(3):345-355

The neighborhood supermarket shopping center is an increasingly important element of the suburban retail landscape. An analysis of patronage differentials for such centers in San Antonio, TX, reveals that both competitive share and retail mix factors are important. Correlation analysis of a patronage density index with locational and management variables indicates that center and store visibility, distance from a regional mall, retail mix (offering of goods appropriate to a small center), and size of center (smaller is better) were the most important explanatory factors in center viability.  相似文献   

Reply to the discussion by Charollais et al. on “Reconciling strontium-isotope and K–Ar ages with biostratigraphy: the case of the Urgonian platform, Early Cretaceous of the Jura mountains, Western Switzerland” by Godet et al. (2011), Swiss Journal of Geosciences, 104, 147–160     

Alexis Godet  Karl B. Föllmi  Stéphane Bodin  Thierry Adatte 《Swiss Journal of Geoscience》2013,106(3):569-580

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图像检索技术研究进展     

周文罡  李厚强  田奇 《南京气象学院学报》2017,9(6):613-634

近年来,互联网上视觉数据呈现出爆炸式的增长,越来越多的研究工作围绕图像搜索或图像检索技术而展开.早期的搜索技术仅采用文本信息,忽视了视觉内容作为排序的线索,导致搜索文本和视觉内容不一致.基于内容的图像检索（CBIR）技术充分利用视觉内容识别相关图像,在近几年来获得了广泛关注.在图像检索中,最根本的问题是意图鸿沟和语义鸿沟,围绕该问题,近年涌现出大量的基于内容的图像检索的技术.本文主要对2003-2016年间提出的相关图像检索方法进行总结、分类和评估,并对未来的潜在研究方向进行讨论.  相似文献