9,145 research outputs found
Anomalous thickness dependence of the Hall effect in ultrathin Pb layers on Si(111)
No full textThe magnetoconductive properties of ultrathin Pb films deposited on Si(111) are measured and compared with density-functional electronic band-structure calculations on two-dimensional, free-standing, 1 to 8 monolayers thick Pb(111) slabs. A description with free-standing slabs is possible because it turned out that the Hall coefficient is independent of the substrate and of the crystalline order in the film. We show that the oscillations in sign of the Hall coefficient observed as a function of film thickness can be explained directly from the thickness dependent variations of the electronic band-structure at the Fermi energy. © 2002 The American Physical Society
Optimizing the Managerial Decision in Energetic Industry
No full textMaking a decision is a complex process which must be based upon a method that is able to establish the optimum criteria in choosing an alternative, in evaluating the main effects of implementing the decision which was taken and in estimating the risks involved. The optimizing methods and techniques fall into several groups. Thus, judging by the number of criteria that was taken into consideration when making decisions, the optimization methods and techniques can be identified as uni-criterial decisions and multi-criterial decisions; considering the objective condition state which affects the problem that needs decisional solution, there can be decisional methods and techniques used in optimizing decisions in conditions of certainty, decisional methods and techniques used in optimizing decisions in conditions of uncertainty and decisional methods and techniques used in optimizing decisions in risky conditions. The continuous improvement of the decisional subsystem - an important component of the firm’s management - represents a necessity under the circumstances that the latest decades reveal a development of the decisional elements, both in the theoretic-methodological field and in the application field. The decisional methods and techniques must be found in the managers’ decisional processes at different hierarchical levels (individual managers or group managers), so that a high scientific materialization level of the methods should be ensured.decision; variant; optimizing methods and techniques; decisional tree; certainty; uncertainty; risk
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
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
Multiphysics Coupling for PB-FHRs
No full textPebble-bed fuelled, molten salt-cooled nuclear reactors (PB-FHRs) involve interactions between a fluid coolant phase, solid particle fuel phase and neutron interactions enabling fission of nuclear fuel for heat production. As these three aspects are highly interdependent, this work presents a three-way coupled methodology for simulation of PB-FHRs to provide a robust analysis tool for detailed analysis of such reactor designs.
Computational fluid dynamics (CFD) techniques are implemented for simulation of the coolant fluid’s flow and temperature fields. Discrete element methods (DEM) are used to model individual pebble fuel elements present within the core, focusing on particle-particle interactions and structures formed within packed beds of mono-sized spheres. Modelling of the interaction between these two phases is realised through a two-way coupled methodology and open-source codes. Additional to the interaction of the fluid and pebble phases, consideration of the neutronic interactions resulting in nuclear heating of the fuel pebbles is included. The Monte Carlo neutron transport method is employed for determination of the fission rate distribution for PB-FHR geometries. Inclusion of the neutronics results within the CFD and DEM solvers, and vice versa, results in three-way coupled multiphysics simulations for PB-FHRs.
This work has been built up over successively more complex simulations, starting with CFD-DEM replication of an isothermal pebble re-circulation experiment and culminating in the three-way coupled simulation of a true PB-FHR design. Additional analysis focusing on the neutronic behaviour of the PB-FHR geometry for various geometric and material property configurations is also presented. It was found that the multiplication factor of PB-FHRs with a free surface of pebbles within the core region are highly influenced on the shape of this free surface.
The three-way coupling methodology was shown to provide detailed representations of PB-FHR geometries in a timely manner without the need for simplification of the geometry or material properties. This allowed for detailed analysis of coolant, fuel pebble and neutronic properties throughout the core region. The results obtained demonstrate the suitability for use as an accurate design tool
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
Behavior and toxic effects of Pb in a waterfowl model with oral exposure to Pb shots : Investigating Pb exposure in wild birds
No full textAmong wild birds, lead (Pb) exposure caused by ingestion of ammunition is a worldwide problem. We aimed to reveal the behavior and toxic effect of Pb caused by ingesting Pb shots in waterfowl. Four male, eight-week old Muscovy ducks (Cairina moschata) were given three Pb shots (approximately 240 mg in total) orally and then fed for 29 days after exposure, simulating a low-dose Pb exposure in wild waterfowl. During the breeding period, blood samples were collected 10 times, and fecal samples every day. Additionally, 22 fresh tissue and 6 bone samples were obtained from each duck through the dissection. Although there were no gross abnormalities, the maximum blood Pb concentration of each duck ranged from 0.6 to 3.7 mg/L, reaching a threshold concentration indicative of clinical symptoms (>0.5 mg/L). delta-aminolevulinic acid dehydratase declined one day after exposure and remained low throughout the feeding period. Hematocrit also tended to decrease, indicating signs of anemia. The highest Pb accumulation was observed in the bones, followed by the kidneys, intestinal tracts, and liver. High Pb accumulation in the bones, which are known to have a long Pb half-life, suggested that Pb would remain in the body and possibly affect bird health beyond 28 days after exposure. Gene expression analysis showed a significant increase in the expression of the toll-like receptor-3 gene, which is involved in virus discrimination in the liver, suggesting a disruption of the immune system. Microbiota analyses showed a correlation between the blood Pb concentration and the abundances of Lachnospiraceae and Ruminococcaceae, suggesting that Pb affects lipid metabolism. These results provide fundamental data on Pb exposure in wild birds and a new perspective on the damage such exposure causes
Jet shapes in pp and Pb-Pb collisions at ALICE
No full textThe aim of this work is to explore possible medium modifications to the substructure of inclusive charged jets in Pb-Pb relative to proton-proton collisions by measuring a set of jet shapes. The set of shapes includes the radial moment, , and the momentum dispersion D. They provide complementary information on the fragmentation and can help to discriminate between two different scenarios: intra-jet broadening or collimation as a result of jet quenching. \noindent The shapes are measured in Pb--Pb collisions at = 2.76 TeV with a constituent cutoff of 0.15 GeV/c and jet resolution 0.2. New techniques for background subtraction are applied and a two-dimensional unfolding is performed to correct the shapes to particle level. The corrected jet shapes for jet GeV/c are presented and discussed. The observed jet shape modifications suggest that the in-medium fragmentation is harder and more collimated than vacuum fragmentation as obtained by a PYTHIA calculation. The PYTHIA calculation is validated with proton-proton data at 7 TeV.The aim of this work is to explore possible medium modifications to the substructure of inclusive charged jets in Pb-Pb relative to proton-proton collisions by measuring a set of jet shapes. The set of shapes includes the radial moment, g , and the momentum dispersion p T D . They provide complementary information on the fragmentation and can help to discriminate between two different scenarios: intra-jet broadening or collimation as a result of jet quenching. The shapes are measured in Pb–Pb collisions at sNN=2.76 TeV with a constituent cutoff of 0.15 GeV/ c and jet resolution R=0.2 . New techniques for background subtraction are applied and a two-dimensional unfolding is performed to correct the shapes to particle level. The corrected jet shapes for jet pT 40≤pT,jet≤60 GeV/c are presented and discussed. The observed jet shape modifications suggest that the in-medium fragmentation is harder and more collimated than vacuum fragmentation as obtained by a PYTHIA calculation. The PYTHIA calculation is validated with proton-proton data at 7 TeV.The aim of this work is to explore possible medium modifications to the substructure of inclusive charged jets in Pb-Pb relative to proton-proton collisions by measuring a set of jet shapes. The set of shapes includes the radial moment, , and the momentum dispersion D. They provide complementary information on the fragmentation and can help to discriminate between two different scenarios: intra-jet broadening or collimation as a result of jet quenching. \noindent The shapes are measured in Pb--Pb collisions at = 2.76 TeV with a constituent cutoff of 0.15 GeV/c and jet resolution 0.2. New techniques for background subtraction are applied and a two-dimensional unfolding is performed to correct the shapes to particle level. The corrected jet shapes for jet GeV/c are presented and discussed. The observed jet shape modifications suggest that the in-medium fragmentation is harder and more collimated than vacuum fragmentation as obtained by a PYTHIA calculation. The PYTHIA calculation is validated with proton-proton data at 7 TeV
Precipitation studies of Pb in single crystal PbTe
No full textA study of the kinetics of precipitation of excess Pb in PbTe was made by the use of Hall measurements. The objective was to find how excess Pb precipitated
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