8,402 research outputs found
Assessment of in situ immobilization of Lead (Pb) and Arsenic (As) in contaminated soils with phosphate and iron: solubility and bioaccessibility
No full textThe effect of in situ immobilization of lead (Pb) and arsenic (As) in soil with respectively phosphate and iron is well recognized. However, studies on combined Pb and As-contaminated soil are fewer, and assessment of the effectiveness of the immobilization on mobility and bioaccessibility is also necessary. In this study, a Pb and As-contaminated soil was collected from an abandoned lead/zinc mine in Shaoxing, Zhejiang province of China, which has been treated with three phosphates, i.e., calcium magnesium phosphate (CMP), phosphate rock, and single super-phosphate (SSP) for 6 months in a field study. The ferrous sulfate (FeSO4) at 20 g kg-1 was then amended to the soil samples and incubated for 8 weeks in a greenhouse. The solubility and bioaccessibility tests were used to assess the effectiveness of the in situ immobilization. The result showed that phosphates addition decreased the concentrations of CaCl2-extractable Pb; however, the concentrations of water-soluble As increased upon CMP and SSP addition. With the iron addition, the water-soluble As concentrations decreased significantly, but CaCl2-extractable Pb concentrations increased. The bioaccessibility of As and Pb measured in artificial gastric and small intestinal solutions decreased with phosphate and iron application except for the bioaccessibility of As in the gastric phase with SSP addition. Combined application of phosphates and iron can be an effective approach to lower bioaccessibility of As and Pb, but has opposing effects on mobility of As and Pb in contaminated soil
Sr-Nd-Pb-Hf isotope results from ODP Leg 187: Evidence for mantle dynamics of the Australian-Antarctic Discordance and origin of the Indian MORB source
No full textNew high precision PIMMS Hf and Pb isotope data for 14–28 Ma basalts recovered during ODP Leg 187 are compared with zero-age dredge samples from the Australian-Antarctic Discordance (AAD). These new data show that combined Nd-Hf isotope systematics can be used as an effective discriminant between Indian and Pacific MORB source mantle domains. In particular, Indian mantle is displaced to lower εNd and higher εHf ratios compared to Pacific mantle. As with Pb isotope plots, there is almost no overlap between the two mantle types in Nd-Hf isotope space. On the basis of our new Nd-Hf isotope data, we demonstrate that Pacific MORB-source mantle was present near the eastern margin of the AAD from as early as 28 Ma, its boundary with Indian MORB-source mantle coinciding with the eastern edge of a basin-wide arcuate depth anomaly that is centered on the AAD. This observation rules out models requiring rapid migration of Pacific MORB mantle into the Indian Ocean basin since separation of Australia from Antarctica. Although temporal variations in isotopic composition can be discerned relative to the fracture zone boundary of the modern AAD at 127°E, the distribution of different compositional groups appears to have remained much the same relative to the position of the residual depth anomaly for the past 30 m.y. Thus significant lateral flow of mantle along the ridge axis toward the interface appears unlikely. Instead, the dynamics that maintain both the residual depth anomaly and the isotopic boundary between Indian and Pacific mantle are due to eastward migration of the Australian and Antarctic plates over a stagnated, but slowly upwelling, slab oriented roughly orthogonal to the ridge axis. Temporal and spatial variations in the compositions of Indian MORB basalts within the AAD can be explained by progressive displacement of shallower Indian MORB-source mantle by deeper mantle having a higher εHf composition ascending ahead of the upwelling slab. Models for the origin of the distinctive composition of the Indian MORB-source based on recycling of a heterogeneous enriched component that consist of ancient altered ocean crust plus<10% pelagic sediment are inconsistent with Nd-Hf isotope systematics. Instead, the data can be explained by a model in which Indian mantle includes a significant proportion of material that was processed in the mantle wedge above a subduction zone and was subsequently mixed back into unprocessed upper mantle
Microscopia de força piezoeléctrica de relaxors ferroeléctricos
No full textDoutoramento em Ciência e Engenharia de MateriaisNesta tese, ferroeléctricos relaxor (I dont know uf the order is correct) de base
Pb das familias (Pb,La)(Zr,Ti)O3 (PLZT), Pb(Mg1/3,Nb2/3)O3-PbTiO3 (PMN-PT),
Pb(Zn1/3,Nb2/3)O3-PbTiO3 (PZN-PT) foram investigados e analisados. As
propriedades ferroeléctricas e dieléctricas das amostras foram estudadas por
métodos convencionais de macro e localmente por microscopia de força
piezoeléctrica (PFM).
Nos cerâmicos PLZT 9.75/65/35 o contraste da PFM à escala nanometrica _
foi investigado em função do tamanho e orientação dos grãos. Apurou-se que
a intensidade do sinal piezoeléctrico das nanoestruturas diminui com o
aumento da temperatura e desaparece a 490 K (La mol. 8%) e 420 K (9,5%).
Os ciclos de histerese locais foram obtidos em função da temperatura. A
evolução dos parâmetros macroscópicos e locais com a temperatura de
superfície sugere um forte efeito de superfície nas transições de fase
ferroeléctricas do material investigado. A rugosidade da parede de domínio é
determinada por PFM para a estrutura de domínio natural existente neste
ferroeléctrico policristalino. Além disso, os domínios ferroeléctricos artificiais
foram criados pela aplicação de pulsos eléctricos à ponta do condutor PFM e o
tamanho de domínio in-plane foi medido em função da duração do pulso.
Todas estas experiências levaram à conclusão de que a parede de domínio
em relaxors do tipo PZT é quase uma interface unidimensional. O mecanismo
de contraste na superfície de relaxors do tipo PLZT é medido por PFMAs estruturas de domínio versus evolução da profundidade foram estudadas
em cristais PZN-4,5%PT, com diferentes orientações através da PFM. Padrões
de domínio irregulares com tamanhos típicos de 20-100 nm foram observados
nas superfícies com orientação das amostras unpoled?. Pelo contrário,
os cortes de cristal exibem domínios regulares de tamanho mícron
normal, com os limites do domínio orientados ao longo dos planos
cristalográficos permitidos. A existência de nanodomínios em cristais com
orientação está provisoriamente (wrong Word) atribuída à natureza
relaxor de PZN-PT, onde pequenos grupos polares podem formar-se em
coindições de zero-field-cooling (ZFC). Estes nanodomínios são considerados
como os núcleos do estado de polarização oposta e podem ser responsáveis
pelo menor campo coercitivo para este corte de cristal em particular. No
entanto, a histerese local piezoelétrica realizada pelo PFM à escala
nanométrica indica uma mudança de comportamento de PZN-PT semelhante
para ambas as orientações cristalográficas investigadas. A evolução das
estruturas de domínio com polimento abaixo da superfície do cristal foi
investigada. O domínio de ramificações e os efeitos de polarização de triagem
após o polimento e as medições de temperatura têm sido estudados pela PFM
e pela análise SEM. Além disso, verificou-se que a intensidade do sinal
piezoeléctrico a partir das estruturas de nanodomínio diminui com o aumento
da temperatura, acabando por desaparecer aos 430 K (orientaçáo ) e
470 K (orientação ). Esta diferença de temperatura nas transições de
fase local em cristais de diferentes orientações é explicada pelo forte efeito de
superfície na transição da fase ferroelétrica em relaxors.A comutação da polarização em relaxor ergódico e nas fases ferroeléctricas do
sistema PMN-PT foram realizadas pela combinação de três métodos,
Microscopia de Força Piezoeléctrica, medição de um único ponto de
relaxamento eletromecânico e por ultimo mapeamento de espectroscopia de
tensão. A dependência do comportamento do relaxamento na amplitude e
tempo da tensão de pulso foi encontrada para seguir um comportamento
logarítmico universal com uma inclinação quase constante. Este
comportamento é indicativo da progressiva população dos estados de
relaxamento lento, ao contrário de uma relaxação linear na presença de uma
ampla distribuição do tempo de relaxamento. O papel do comportamento de
relaxamento, da não-linearidade ferroeléctrica e da heterogeneidade espacial
do campo na ponta da sonda de AFM sobre o comportamento do ciclo de
histerese é analisada em detalhe. Os ciclos de histerese para ergódica PMN-
10%PT são mostrados como cineticamente limitados, enquanto que no PMN,
com maior teor de PT, são observados verdadeiros ciclos de histerese
ferroeléctrica com viés de baixa nucleação.In this thesis, Pb-based relaxor ferroelectrics of the (Pb,La)(Zr,Ti)O3 (PLZT),
Pb(Mg1/3,Nb2/3)O3-PbTiO3 (PMN-PT), Pb(Zn1/3,Nb2/3)O3-PbTiO3 (PZN-PT)
families were investigated and analyzed. Ferroelectric and dielectric properties
of the samples were studied by conventional macroscopic methods and locally
by piezoresponse force microscopy (PFM).
In PLZT 9.75/65/35 ceramics the nanoscale PFM contrast was investigated as
a function of grain size and grain orientation. It was found that the intensity of
piezoresponse signal from nanodomain structure decreases with temperature
and it disappears at 490 K (La mol. 8%) and 420 K (9.5%). Local hysteresis
loops were obtained as a function of temperature. The evolution of the
macroscopic and local parameters with temperature suggests strong surface
effect on ferroelectric phase transition in the investigated materials. The domain
wall roughness is determined with PFM for the natural domain structure
existing in this polycrystalline ferroelectric. Besides, artificial ferroelectric
domains were created by application of voltage pulses to the conducting PFM
tip, and the in-plane domain size was measured as a function of pulse duration.
All these experiments result in the conclusion that the domain wall in PZT-type
relaxors is quasi one-dimensional interface. The mechanism of the surface
contrast in PLZT-type relaxors is uncovered by PFM.
Domain structures vs. depth evolution was studied in PZN-4.5%PT crystals
with different orientation via PFM. Irregular domain patterns with the typical
sizes 20-100 nm were observed on the (001)-oriented surfaces of unpoled
samples. On the contrary, (111) crystal cuts exhibit normal micron-size regular
domains with the domain boundaries directed along allowed crystallographic
planes. The existence of nanodomains in (001)-oriented crystals is tentatively
attributed to the relaxor nature of PZN-PT where small polar clusters may form
under zero-field-cooling (ZFC) conditions. These nanodomains are considered
as the nuclei of the opposite polarization state and can be responsible for the
smaller coercive field for this particular crystal cut. However, local piezoelectric
hysteresis performed by PFM on the nanometer scale indicates similar
switching behavior of PZN-PT for both investigated crystallographic
orientations. Evolution of the domain structures with polishing below the crystal
surface has been investigated. The domain branching and polarization
screening effects after polishing and temperatures measurements have been
studied by PFM and SEM analysis. In addition, it was found what the intensity
of piezoresponse signal from nanodomain structures decreases with
temperature and finally disappears at 430 K ( orientation) and 470 K
( orientation). This difference of the temperature of local phase
transitions for crystals of different orientaions is explained by strong surface
effect on ferroelectric phase transition in relaxors.
Polarization switching in ergodic relaxor and ferroelectric phases in the PMNPT
system is studied using Piezoresponse Force Microscopy, single point
electromechanical relaxation measurements, and voltage spectroscopy
mapping. The dependence of relaxation behavior on voltage pulse amplitude
and time was found to follow a universal logarithmic behavior with a nearly
constant slope. This behavior is indicative of the progressive population of
slow relaxation states, as opposed to a linear relaxation in the presence of a
broad relaxation time distribution. The role of relaxation behavior,
ferroelectric non-linearity, and the spatial inhomogeneity of the tip field on
hysteresis loop behavior is analyzed in detail. The hysteresis loops for
ergodic PMN-10%PT are shown to be kinetically limited, while in PMN with
larger PT content, true ferroelectric hysteresis loops with low nucleation
biases are observed.FCT - SFRH/BD/22391/200
Terminal suturing of Gondwana along the southern margin of South China Craton : evidence from detrital zircon U-Pb ages and Hf isotopes in Cambrian and Ordovician strata, Hainan Island
No full textThis work was supported by the National Natural Science Foundation of China (grants 41472086 and 41272120), “111” Project (B08030), the fundamental Research Funds for the Central Universities, China University of Geosciences (Wuhan) (CUG2012019240 and CUG2013019137). The first author also acknowledges China Scholarship Council (grant 201208420001) for supporting his research in the University of St. Andrews. Date of Acceptance: 20/11/2014Hainan Island, located near the southern end of mainland South China, consists of the Qiongzhong Block to the north and the Sanya Block to the south. In the Cambrian, these blocks were separated by an intervening ocean. U-Pb ages and Hf isotope compositions of detrital zircons from the Cambrian succession in the Sanya Block suggest that the unit contains detritus derived from late Paleoproterozoic and Mesoproterozoic units along the western margin of the West Australia Craton (e.g., Northampton Complex) or the Albany-Fraser-Wilkes orogen, which separates the West Australia and Mawson cratons. Thus, in the Cambrian the Sanya Block was not part of the South China Craton but rather part of the West Australian Craton and its environs. In contrast, overlying Late Ordovician strata display evidence for input of detritus from the Qiongzhong Block, which constituted part of the southeastern convergent plate margin of the South China Craton in the early Paleozoic. The evolving provenance record of the Cambrian and Ordovician strata suggests that the juxtaposition of South China and West Australian cratons occurred during the early to mid-Ordovician. The event was linked with the northern continuation of Kuungan Orogeny, with South China providing a record of final assembly of Gondwana.Peer reviewe
Effect of Pb-Polluted soil on soybean growth and associated toxicological risk
No full textGlycine max (L.) Merr. (soybean) has been mentioned as a potential accumulator of hazardous metals, such as Pb. The main route of human exposure to heavy metals is consumption. This study evaluates Pb accumulation in soybean at different growth stages. The aim was to determine the period of the crop development when absorption and distribution mostly occur. Soybean plants were grown in control and Pb-polluted soils in a greenhouse experiment. Morpho-physiological parameters and Pb content in organs were analyzed. Results showed that Pb affected the biomass of roots and plant height, with the highest Pb accumulation occurring in the roots and with low translocation to aerial organs. Moreover, Pb accumulation and distribution occurred before grain filling, the crop critical period. Soybean seeds accumulated Pb above permissible values, but with no associated toxicological risk. Furthermore, pods showed higher Pb values than seeds, suggesting a protective effect.Fil: Blanco, Andrés. Universidad Nacional de Córdoba; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto Multidisciplinario de Biología Vegetal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto Multidisciplinario de Biología Vegetal; ArgentinaFil: Pignata, Maria Luisa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto Multidisciplinario de Biología Vegetal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto Multidisciplinario de Biología Vegetal; Argentina. Universidad Nacional de Córdoba; ArgentinaFil: Rodriguez, Judith Hebelen. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto Multidisciplinario de Biología Vegetal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto Multidisciplinario de Biología Vegetal; Argentina. Universidad Nacional de Córdoba; Argentin
Trace Analysis of Heavy Metals (Cd, Pb, Hg) Using 3D Printed graphene/PLA Composite Electrodes
No full textHere we investigate the use of 3D printed graphene/PLA electrodes for quantifying trace amounts of Hg, Pb, and Cd. We prepared cylindrical electrodes by sealing a 600 µm diameter graphene/PLA filament in a pipette tip filled with epoxy. We characterized the electrodes using scanning electron microscopy, Raman spectroscopy, and cyclic voltammetry in ferrocene methanol. The physical characterization showed a significant amount of disorder in the carbon structure and the electrochemical characterization showed quasi-reversible behavior without any electrode pretreatment. We then used unmodified graphene/PLA electrode to quantify Hg, and Pb and Cd in 0.01 M HCl and 0.1 M acetate buffer using square wave anodic stripping voltammetry. We were able to quantify Hg with a limit of detection (LOD) of 6.1 nM (1.2 ppb), but Pb and Cd did not present measurable peaks at concentrations below ~400 nM. We improved the LODs for Pb and Cd by depositing Bi microparticles on the graphene/PLA and, after optimization, achieved clear stripping peaks at the 20 nM level for both ions (4.1 and 2.2 ppb for Pb2+ and Cd2+, respectively). The results obtained for all three metals allowed quantification below the EPA action limits in drinking water
O processo de verticalização e seus problemas no bairro de Manaíra, João Pessoa-PB.
No full textThe work traces the verticalization process in District Manaíra in João Pessoa-PB. To fulfill its purpose broke the concept, causes, and consequences of this process mainly the problems caused by such a process. Reports related to the process of urban verticalization in order to understand the process and support research studies. "Was taken as a base study dissertation titled The study Manaíra neighborhood in João Pessoa, Paraíba," Nobrega (2011). Additionally, consultation to planning legislation relating to the theme. Research upgraded the empirical survey and mapping by the cited author. Thus, in addition to consulting government institutions such as the Water and Sewerage Company of Paraíba, the core of the research corresponds to the empirical survey of land use studied in the neighborhood that was recorded by consignment types of buildings. This survey maps of land use were developed. Finally, the article discusses the problems caused by the process of verticalization in District Manaíra located on the edge of João Pessoa-PB.O trabalho traça um panorama do processo de verticalização, no Bairro de Manaíra na cidade de João Pessoa-PB. Para cumprir seu propósito partiu-se do conceito, causas, consequências resultantes deste processo e principalmente, os problemas ocasionados por tal processo. Reporta-se a estudos relacionados ao processo de verticalização urbana, no intuito de compreender o processo e fundamentar a pesquisa. “Tomou-se como estudo base a dissertação de mestrado intitulada O estudo do bairro de Manaíra em João Pessoa, Paraíba”, de Nóbrega (2011). Além disso, consulta-se a legislação urbanística referente à temática. A pesquisa atualizou o levantamento empírico e o mapeamento realizado pela autora citada. Desta forma, além da consulta as instituições governamentais como a Companhia de Águas e Esgotos da Paraíba, IBGE, Corpo de Bombeiros e etc., o cerne da pesquisa corresponde ao levantamento empírico do uso do solo do bairro estudado em que se registrou lote por lote o tipo de edificação. Deste levantamento foram elaborados mapas do uso do solo. Por fim, foram identificados e abordados os problemas ocasionados pelo processo de verticalização no Bairro de Manaíra localizado na orla de João Pessoa-PB
Searches for transverse momentum dependent flow vector fluctuations in Pb-Pb and p-Pb collisions at the LHC
No full textThe measurement of azimuthal correlations of charged particles is presented for Pb-Pb collisions at sNN=2.76 TeV and p-Pb collisions at sNN=5.02 TeV with the ALICE detector at the CERN Large Hadron Collider. These correlations are measured for the second, third and fourth order flow vector in the pseudorapidity region |η| < 0.8 as a function of centrality and transverse momentum pT using two observables, to search for evidence of pT-dependent flow vector fluctuations. For Pb-Pb collisions at 2.76 TeV, the measurements indicate that pT-dependent fluctuations are only present for the second order flow vector. Similar results have been found for p-Pb collisions at 5.02 TeV. These measurements are compared to hydrodynamic model calculations with event-by-event geometry fluctuations in the initial state to constrain the initial conditions and transport properties of the matter created in Pb–Pb and p–Pb collisions
Vector boson production in p+Pb and Pb+Pb collisions measured with ATLAS at the LHC
No full textElectroweak boson production processes (W, Z and photon) provide access to the earliest moments of heavy ion collisions. Furthermore, because they do not undergo strong interactions, they are sensitive to the initial-state geometry of the collision and potentially the details of the nuclear parton distribution functions (PDF). ATLAS results on vector boson yields have demonstrated binary collision scaling in Pb+Pb collisions. In p+Pb collisions, the measurement of vector bosons provides possible constraints on the nuclear PDF and insights into the details of the initial collision geometry. We report on the latest results of vector boson production in p+Pb collisions at sqrt(sNN)=5.02 TeV and Pb+Pb collisions at sqrt(sNN)=2.76 TeV. In p+Pb collisions, production yields and lepton charge asymmetry of W bosons are presented as a function of pseudorapidity of the charged lepton and centrality. Photon and Z yields are presented differentially as a function of transverse momentum, rapidity and centrality. The vector boson yields are compared to calculations incorporating different PDF sets, as well as different centrality calculations
Gene expression of Ntann12 in Nicotiana tabacum to Pb treatment
No full textPlants are sessile organisms that are unable to move away from adverse environmental conditions. In order to survive or adapt their growth to environmental stresses, plants undergo physiological, biochemical and molecular changes. Lead (Pb), on the other hand, is a widespread heavy metal pollutant that is commonly found in the environment. It is highly persistent and causes toxicity to plants, animals, and human. To advance our understanding in Pb tolerance in plants and subsequently develop phytoremediation technology, there is a need to identify genes associated with Pb stress.
Nicotiana tabacum has the characteristics of a plant ideal for phytoremediation. It has deep and highly branched root system, is tolerant to Pb pollutant, and repulsive to herbivores. Recent studies have shown that annexins participate in abiotic stress responses. Ntann12 is an annexin in Nicotiana tabacum. It was found to be upregulated upon Rhodoccocus fascians infection, salt and abscisic acid treatments. It is likely that Ntann12 could be involved in the response of plants to Pb stress and play a role to defend plants against Pb-induced oxidative damage
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