Estudos sobre a nutrição mineral do arroz: XVI, absorção radicular e foliar do rádio fósforo por diversas variedades

Excised roots obtained from 8 varieties of rice (IAC-164, 165 and 1246, Batatais, Caqui, Dourado Precoce, 90 Dias and Senbon) were used to study the kinetics of P uptake. Three cultivars (IAC-164, 90 Dias and Senbon) were employed in an experiment designed to compare root and leaf uptake and to evaluate the long distance transport. The main conclusions were as follows: a) after 180 minutes of contact with the external solution the uptake reached a maximum in the case of varieties IAC-164 and 165 , 90 Dias and Dourado Precoce; the same took place with the remaining cultivars after 240 minutes; b) the best fitting for individual varieties was obtained by using eiter potential or exponential models of adjustment wherein time was the independent variable and rate of uptake was the dependent one. c) IAC-164 and IAC-165 showed the highest efficiency of absorption while Dourado Precoce and 90 dias showed the lowest one. d) some evidence for the operation of a dual uptake mechanism was obtained when data from all varieties were put together; e) root absorption was usually higher than foliar uptake.Estudando-se a absorção do rádio fósforo por raízes destacadas das variedades IAC-164, 165 e 1246, Batatais, Caqui, Dourado precoce, 90 dias e Senbon (as primeiras nacionais, a última japonesa) verificou-se diferença entre as mesmas na cinética de absorção. Nas condições experimentais, obteve-se evidência de um padrão duplo de absorção do anion fosfato. A absorção radicular mostrou-se mais eficiente que a foliar em termos de quantidade absorvida e de transporte a longa distânci

Estudos sobre a nutrição mineral do arroz: XX - marcha de absorção de micronutrientes pelas variedades IAC-164 e IAC-165

Rice plants were grown in nutrient solution till the end of their life cycle. At given stages of development plant samples harvested for the determination of dry matter and micronutrient contents in the various organs. The following conclusions were drawn: only Fe accumulation showed some degree of positive relation with dry matter production; the pattern of distribution of the elements among the plant parts was essentially the same, for both varieties; B, Cu and Fe tend to concentrate in the root system; no clear cut pattern of variation in leaf composition could be described throughout the plant life cycle; maximum rate of uptake took place between full tillering and panicle formation.Plantas de arroz, variedades IAC-164 e IAC-165 foram cultivadas em solução nutritiva até o fim do ciclo. Em estádios determinados do seu desenvolvimento foram colhidas amostras que depois de secas foram analisadas determinando-se B, Cu, Fe, Mn e Zn nos diversos órgãos. Os dados obtidos permitiram verificar que: somente a acumulação do Fe quando um para lelismo com a de matéria seca; o padrão da distribuição porcentual nos vários órgãos dos elementos analisados durante o ciclo foi o mesmo nas duas variedades verificando-se que B, Cu e Fe tendem a acumular-se mais nas raízes que na parte aérea o oposto acontecendo com o Mn e o Zn; não foram observadas variações consistentes nos teores foliares dos elementos durante o experimento; no período que vai do perfilhamento pleno até a formação da panícula foi em geral maior a velocidade de acumulação dos macronutrientes

Structural and spectroscopic investigation of the charge-ordered, short-range ordered, and disordered phases of the Co3O2BO3 ludwigite

Charge ordering is prone to occur in crystalline materials with mixed-valence ions. It is presumably accompanied by a structural phase transition, with possible exceptions in compounds that already present more than one inequivalent site for the mixed-valence ions in the charge-disordered phase. In this work, we investigate the representative case of the homometallic Co ludwigite Co2+2Co3+O2BO3 (Pbam space group) with four distinct Co crystallographic sites [M1–M4] surrounded by oxygen octahedra. The mixed-valent character of the Co ions up to at least T=873 K is verified through x-ray absorption near-edge structure (XANES) experiments. Single crystal x-ray diffraction (XRD) and neutron powder diffraction (NPD) confirm that the Co ions at the M4 site are much smaller than the others at low temperatures, consistent with a Co3+ oxidation state at M4 and Co2+ at the remaining sites. The size difference between the Co ions in the M4 and M2 sites is continuously reduced upon warming above ≈370 K, indicating a gradual charge redistribution within the M4−M2−M4 (424) ladder in the average structure. Minor structural anomalies with no space group modification are observed near 475 and 495 K, where sharp phase transitions were previously revealed by calorimetry and electrical resistivity data. An increasing structural disorder, beyond a conventional thermal effect, is noted above ≈370 K, manifested by an anomalous increment of XRD Debye-Waller factors and broadened vibrational modes observed by Raman scattering. The local Co-O distance distribution, revealed by Co K-edge extended x-ray absorption fine structure (EXAFS) data and analyzed with an evolutionary algorithm method, is similar to that inferred from the XRD crystal structure below ≈370 K. At higher temperatures, the local Co-O distance distribution remains similar to that found at low temperatures, at variance with the average crystal structure obtained with XRD. We conclude that the oxidation states Co2+ and Co3+ are instantaneously well defined in a local atomic level at all temperatures, however the thermal energy promotes local defects in the charge-ordered configuration of the 424 ladders upon warming. These defects coalesce into a phase-segregated state within a narrow temperature interval (475<T<495 K). Finally, a transition at ≈500 K revealed by differential scanning calorimetry (DSC) in the iron ludwigite Fe3O2BO3 is discussed

Strange particle production in proton-proton collisions at s=0.9\sqrt{s}=0.9 TeV with ALICE at the LHC

The production of mesons containing strange quarks (K$^0_s$, $\phi$) and both singly and doubly strange baryons ($\Lambda$, Anti-$\Lambda$, and $\Xi$+Anti-$\Xi$) are measured at central rapidity in pp collisions at $\sqrt{s}$ = 0.9 TeV with the ALICE experiment at the LHC. The results are obtained from the analysis of about 250 k minimum bias events recorded in 2009. Measurements of yields (dN/dy) and transverse momentum spectra at central rapidities for inelastic pp collisions are presented. For mesons, we report yields () of 0.184 $\pm$ 0.002 stat. $\pm$ 0.006 syst. for K$^0_s$ and 0.021 $\pm$ 0.004 stat. $\pm$ 0.003 syst. for $\phi$. For baryons, we find = 0.048 $\pm$ 0.001 stat. $\pm$ 0.004 syst. for $\Lambda$, 0.047 $\pm$ 0.002 stat. $\pm$ 0.005 syst. for Anti-$\Lambda$ and 0.0101 $\pm$ 0.0020 stat. $\pm$ 0.0009 syst. for $\Xi$+Anti-$\Xi$. The results are also compared with predictions for identified particle spectra from QCD-inspired models and provide a baseline for comparisons with both future pp measurements at higher energies and heavy-ion collisions.Comment: 33 pages, 21 captioned figures, 10 tables, authors from page 28, published version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/387

Two-pion Bose-Einstein correlations in central Pb-Pb collisions at sNN\sqrt{s_{\rm NN}} = 2.76 TeV

The first measurement of two-pion Bose-Einstein correlations in central Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 2.76$ TeV at the Large Hadron Collider is presented. We observe a growing trend with energy now not only for the longitudinal and the outward but also for the sideward pion source radius. The pion homogeneity volume and the decoupling time are significantly larger than those measured at RHIC.Comment: 17 pages, 5 captioned figures, 1 table, authors from page 12, published version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/388

Suppression of charged particle production at large transverse momentum in central Pb-Pb collisions at sNN=2.76\sqrt{s_{\rm NN}} = 2.76 TeV

Inclusive transverse momentum spectra of primary charged particles in Pb-Pb collisions at $\sqrt{s_{_{\rm NN}}}$ = 2.76 TeV have been measured by the ALICE Collaboration at the LHC. The data are presented for central and peripheral collisions, corresponding to 0-5% and 70-80% of the hadronic Pb-Pb cross section. The measured charged particle spectra in $|\eta|<0.8$ and $0.3 < p_T < 20$ GeV/$c$ are compared to the expectation in pp collisions at the same $\sqrt{s_{\rm NN}}$, scaled by the number of underlying nucleon-nucleon collisions. The comparison is expressed in terms of the nuclear modification factor $R_{\rm AA}$. The result indicates only weak medium effects ($R_{\rm AA} \approx$ 0.7) in peripheral collisions. In central collisions, $R_{\rm AA}$ reaches a minimum of about 0.14 at $p_{\rm T}=6$-7GeV/$c$ and increases significantly at larger $p_{\rm T}$. The measured suppression of high-$p_{\rm T}$ particles is stronger than that observed at lower collision energies, indicating that a very dense medium is formed in central Pb-Pb collisions at the LHC.Comment: 15 pages, 5 captioned figures, 3 tables, authors from page 10, published version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/98

Learning from multimedia and hypermedia

Computer-based multimedia and hypermedia resources (e.g., the world wide web) have become one of the primary sources of academic information for a majority of pupils and students. In line with this expansion in the field of education, the scientific study of learning from multimedia and hypermedia has become a very active field of research. In this chapter we provide a short overview with regard to research on learning with multimedia and hypermedia. In two review sections, we describe the educational benefits of multiple representations and of learner control, as these are the two defining characteristics of hypermedia. In a third review section we describe recent scientific trends in the field of multimedia/hypermedia learning. In all three review sections we will point to relevant European work on multimedia/hypermedia carried out within the last 5 years, and often carried out within the Kaleidoscope Network of Excellence. According to the interdisciplinary nature of the field this work might come not only from psychology, but also from technology or pedagogy. Comparing the different research activities on multimedia and hypermedia that have dominated the international scientific discourse in the last decade reveals some important differences. Most important, a gap seems to exist between researchers mainly interested in a “serious” educational use of multimedia/ hypermedia and researchers mainly interested in “serious” experimental research on learning with multimedia/hypermedia. Recent discussions about the pros and cons of “design-based research” or “use-inspired basic research” can be seen as a direct consequence of an increasing awareness of the tensions within these two different cultures of research on education