Arquivos PDF do Prof. C.A. dos Santos

Instituto de Física - UFRGS

ATENÇÃO: as novidades encontram-se no final do arquivo!

, críticas e comentários
são bem-vindos!!!

  Inverted and Crossed Hysteresis Loops in Ag/Ni Multilayers
C.A. dos Santos and B. Rodmacq
Journal of Magnetism and Magnetic Materials 147 (1995) L250-2522
We report on the observation of inverted and crossed magnetic hysteresis loops in Ag/Ni multilayers. The samples were prepared by triode dc sputtering, at 100 K, with nickel layer thickness of about 8 Å and Ag layer thicknesses ranging from about 5 to 40 Å. The phenomenon was observed in all the samples measured at temperatures larger than 90 K.
Keywords: Inverted hysteresis, Multilayer, Thin film, Ag, Ni
Veja o texto completo(see the full text)
  Mössbauer Study of the Planar Antiferromagnetic FeTa2O6: A Mössbauer and X-ray Study
Luci I. Zawislak, J.B.M. da Cunha, A. Vasquez and C.A. dos Santos  
Solid State Communication 94 (1995) 345-348
We report on Mössbauer spectroscopy study of magnetic ordering in FeTa2O6. At temperatures abov 10 K, the compound is paramagnetic; the spectrum obtained at 10 K shows a very asymmetric doublet, suggesting the onset of the magnetic ordering; between 9.75 K and 4.2 K the spectra consist of magnetic components. The temperature dependence of the sublattice magnetization, as determined from Mössbauer measurements, qualitatively resembles that calculated for the two-dimensional Ising Model.
Keywords: A. magnetically ordered materials, B. chemical synthesis, D. phase transitions, E. nuclear resonances.
Veja o texto completo (see the full text)
  Magnetic behaviour of the antiferromagnet FeTa2O6
L I Zawislak, G L F Fraga, J B Marimon da Cunha, D Schmitt, A S Carriço and C A dos Santos
Journal of Physics: Condensed Matter 9 (1997) 2295-2302
The magnetic behaviour of the antiferromagnet FeTa2O6 was investigated through heat capacity, magnetic susceptibility and magnetization measurements. The broad magnetic susceptibility curve (peak at 15 K) presents an inflection typical of two-dimensional systems. This inflection is observed near 10 K, the temperature where early reported Mössbauer measurements indicate the onset of magnetic order. Heat capacity measurements have shown a clear transition at 8.7 K, where Mössbauer measurements show complete ordering. Magnetization curves, for temperatures between 1.4 K and 5 K, display a noticeable change in slope suggesting a spin-flop transition induced by a field higher than 10 Tesla. It is argued that this transition, which disappears for T>6 K, is an evidence of two-dimensional behaviour.
PACS numbers: 75.40.Cx, 75.50.Ee, 75.50.Bb
Veja o texto completo (see the full text)
  Cation Ordering Observed on (Mn0.9Fe0.1)(Ta0.8Nb0.2)2O6: A Mössbauer and X-ray Study
Luci I. Zawislak, V. Antonietti, J.B.M. da Cunha and C.A. dos Santos  
Solid State Communication 101 (1997) 767-770
Mössbauer spectroscopy and powder X-ray diffraction are used to show cation ordering on a natural manganotantalite sample. By using electron microprobe analysis the chemical composition (Mn0.9Fe0.1)(Ta0.8Nb0.2)2O6 has been determined. The as-received sample is partially ordered, as suggested by the low intensities of the super-structure reflections in the X-ray diffration pattern and by the existence of two dou-blets in the Mössbauer spectrum. Heat treatment in vaccum (P@10-5 Pa) at temperature T@1320 K induces cation ordering as clearly suggested by the Mössbauer spectrum. The effect on the X-ray diffraction pattern is evident but less pronounced.
Keywords: C. X-ray scattering, D. order-disorder effects, E. nuclear resonances.
Veja o texto completo (see the full text)
  Effects of argon irradiation on a plasma nitrided carbon steel
G. Simon, M.A.Z. Vasconcellos and C.A. dos Santos
Surface and Coatings Technology 102 (1998) 90-96
We report on the effects of Ar irradiation on a plasma nitrided steel. Samples of AISI 1010 steel were nitrided in a mixture of H2-20% N2 under a total pressure of 5 mbar. The current was adjusted to maintain the cathode temperature at 720 K. The nitrided samples were submitted to the following treatments: (a) Ar irradiation forming a plateau from near surface down to about 150 nm; (b) after each irradiation the samples were submitted to 1 hour thermal annealing in high vacuum at temperatures between 523 and 973 K. X-ray diffraction and conversion electron Mössbauer spectroscopy measurements show that Ar irradiation induces the precipitation of finely dispersed e- Fe2+x(N,C), which are unstable at temperatures as low as 523 K. Further annealing at higher temperatures promote the dissolution of the e carbonitrides and the increasing of the amount of g'-Fe4N, up to temperatures about 800 K, after which all the nitrides and carbonitrides are unstable. Our results show clearly that Ar bombardment can induce the transformation g'>e3.2 + e2+x, which is consistent with the instability of small g' precipitates at room temperature.
Veja o texto completo(see the full text)
  Near-surface composition and microhardness profile of plasma nitrided H-12 tool steel
E.J. Miola S. D. de Souza, M. Olzon-Dionysio, D. Spinelli, M. R. F. Soares, M. A. Z. Vasconcellos and C.A. dos Santos
Materials Science and Engineering, A256 (1998) 60-68
Samples of AISI H-12 tool steel were plasma nitrided at 500 °C in a mixture of H2-20% N2 under a total pressure of 6 mbar, by using DC and pulsed glow discharges. The treatment time varied from 1 h to 6 h. X-ray diffraction (glancing angle and q-2q geometry), conversion electron Mössbauer spectroscopy, conversion X-ray Mössbauer spectroscopy, electron probe microanalysis, optical micrograph and Vickers microhardness were used as analytical techniques. The obtained results suggest that, under the present experimental conditions: (i) The near-surface compound layer consists of a mixture of g'-Fe4N and e-Fex(N,C); (ii) the near-diffusion zone compound layer consists of a mixture of g'-Fe4N, e-Fex(N,C), a"-Fe16N2 and g-austenite; (iii) the dependence of compound layer thickness on nitriding time violates the parabolic behavior and emphasizes effects from cathode sputtering and radiation-enhanced diffusion.
Keywords: Plasma nitriding; H-12 tool steel; Mössbauer spectroscopy; x-ray diffraction; microhardness.
Veja o texto completo (see the full text)
  Nitriding of H-12 tool steel by direct-current and pulsed plasma
E.J. Miola, S. D. de Souza, M. Olzon-Dionysio, D. Spinelli and C.A. dos Santos
Surface and Coatings Technology 116-119 (1999) 347-351
Direct-current and pulsed plasma were used to nitride samples of AISI H-12 tool steel with treatment time varying from 1 h to 6 h. X-ray diffraction (glancing angle and q-2q geometry), conversion electron Mössbauer spectroscopy, conversion X-ray Mössbauer spectroscopy and Vickers microhardness were used as analytical techniques. The near-surface compound layer consists of a mixture of g'-Fe4N and e-Fex(N,C), while the near-diffusion zone compound layer consists of a mixture of g '-Fe4N, e-Fex(N,C), a"- Fe16N2 and g-austenite. For DC plasma the dependence of compound layer thickness on nitriding time obeys the parabolic law, but for pulsed plasma this dependence violates the parabolic law.
Keywords: Plasma nitriding; H-12 tool steel; Mössbauer spectroscopy; x-ray diffraction; microhardness.
Veja o texto completo (see the full text)
  X-ray diffraction measurements of plasma nitrided Ti-6Al-4V
S.L.R. da Silva, L.O. Kerber, L. Amaral and C.A. dos Santos
Surface and Coatings Technology 116-119 (1999) 342-346
A systematic study was undertaken with samples of commercial Ti-6Al-4V nitrided in a conventional dc plasma equipment. As treatment parameter we have used: nitriding time (from 15 to 360 min); nitriding atmosphere (H2-20% N2 and H2-60% N2); total pressure (from 10 mPa to 1 kPa) and cathode temperature (from 673 K to 943 K). X-ray diffraction measurements show that the effect of nitriding on the near-surface composition of (a+b)-Ti-6Al-4V is a very complex function of the process parameters. Among these it appears that the sample temperature plays the more dramatic role. For temperatures below 773 K, e-Ti2N and d-TiN are clearly present only for long treatment in N/H=3/2 atmosphere. For the N/H=1/4 atmosphere, these nitrides are not present in the XRD pattern of samples treated at 773 K, even for long treatment time as 240 min. On the other hand, samples treated at 943 K show well-resolved e-Ti2N and d-TiN reflections even for small treatment times as 15 min.
Keywords: Plasma nitriding; Ti-6Al-4V; X-ray diffraction.
Veja o texto completo (see the full text)
  Structure and magnetic properties of layered (FexCo1-x)Ta2O6 compounds
V. D. Mello, L. I. Zawislak, J. B. Marimon da Cunha, E. J. Kinast, J. B. Soares and C. A. dos Santos
Journal of Magnetism and Magnetic Materials 196-197 (1999) 846-847
Samples of (FexCo1-x)Ta2O6 were prepared from pure FeTa2O6 and CoTa2O6. From X-ray diffraction (XRD) measurements followed by Rietveld refinement, it is demonstrated that the solid solution obeys the Vegard's law. Mössbauer spectroscopy (MS) measurements at 4.2 K and 300 K show that for x>=0.8 the Fe-Co substitution have no apparent effect on the hyperfine parameters.
Keywords: Antiferromagnet, Rietveld refinement, Mössbauer spectroscopy.
Materials: FeTa2O6, CoTa2O6, FeCoTa2O6, tapiolite
Veja o texto completo (see the full text)
  Iron oxidation and order-disorder in the (Fe2+,Mn)(Ta,Nb)2O6-(Fe2+,Mn)Fe3+ (Ta,Nb)2O8 transition
C A dos Santos, L I Zawislak, V Antonietti, E J Kinast and J B M da Cunha
Journal of Physics: Condensed Matter 11 (1999) 7021-7033
Heat treatments in air and in vacuum have been performed on crystal and powder of the natural sample (Mn2+0.88Fe2+ 0.09)(Ta5+0.86Nb5+0.14)2O2- 6, as well as on powder of synthetic Fe2+(Nb5+0.6 Ta5+0.4)2O6. Crystal parameters and hyperfine interactions were obtained by use of X-ray diffraction and Mössbauer spectroscopy. It is shown that the partially ordered natural sample is completely ordered after heat treatment in vacuum. Conversely, heat treatment in air induced the (Mn2+0.88Fe2+ 0.09)(Ta5+0.86Nb5+0.14)2O2- 6 - wodginite (Mn2+,Fe2+)Fe3+ (Ta,Nb)2O8 transformation on the powdered sample. When applied to the crystal sample, the heat treatment in air produced a mixture of two phases: that one in large amount is the ordered (Mn2+0.88Fe2+ 0.09)(Ta5+0.86Nb5+0.14)2O2- 6, the other, in minor amount, is (Mn2+,Fe2+)Fe3+ (Ta,Nb)2O8. The former arrives from cation ordering in the bulk portion of the sample, while the latter results from the near-surface oxidation. The Mn content as well as the oxidant atmosphere appears to play an important role on the transition mechanism. The same heat treatment applied to the synthetic ferrocolumbite induces a different reaction: ferrocolumbite is transformed into Fe3+(Nb0.6Ta0.4)O4 with minor amount of (Nb,Ta)2O5.
PACS numbers: 81.40.-z, 82.80.Ej, 91.60.-x
Veja o texto completo (see the full text)
  Some structure and magnetic effects of Ga incorporation on a-FeOOH
C.A. dos Santos, A.M.C. Horbe, C.M.O. Barcellos and J.B. Marimon da Cunha
Solid State Communication 118 (2001) 449-452
The effects of Ga incorporation on goethite were investigated by using X-ray diffractometry (XRD), particle-induced X-ray emission (PIXE), susceptibility measurements and Mössbauer spectroscopy (MS). Samples GaxFe1-xOOH were prepared with x=0.00, 0.01, 0.03, 0.05, 0.10, 0.35 and 0.70. All the samples are single-phase and an accurate observation of the structure refinement procedure makes clear the sample-dependent structural behaviour. A model is proposed in which the main effect of Ga incorporation is to reduce the crystallite dimensions.
Keywords: A. Oxides; B. Chemical synthesis; C. Mössbauer spectroscopy; C. X-ray diffraction
PACS numbers: 81.20.Ev, 82.80.Ej, 75.50.-y
Veja o texto completo (see the full text)
  Structure refinement of mixed oxides FexCo1-xTa2O6
V. Antonietti, E.J. Kinast, L.I. Zawislak, J.B.M. da Cunha and C.A. dos Santos
Journal of Physics and Chemistry of Solids 62 (2001) 1239-1242
We report X-ray powder diffraction measurements performed on synthetic samples of the tapiolite-like FexCo1-xTa2O6 solid solution. The crystal structure has been refined by the Rietveld method, by using the program Fullprof. All the samples are tetragonal and were indexed to the space group P42/mnm. The end-members (FeTa2O6 and CoTa2O6) have unit-cell parameters quite similar to those previously published. The unit-cell parameters a and c for the mixed samples vary linearly with the cation substitution (Co-Fe) according to the Vegard's law in all the range of substitution.
Keywords: A. Oxides; B. Chemical synthesis; C.X-ray diffraction; D. Crystal structure
PACS numbers: 81.20.Ev, 82.80.Ej, 75.50.-y
Veja o texto completo (see the full text)
  Crystal Chemistry and Structure of the Orthorhombic (Fe,Mn)(Ta,Nb)2O6 Family of Compounds
C. A. dos Santos, L. I. Zawislak, E. J. Kinast, V. Antonietti and J. B. M. da Cunha
Brazilian Journal of Physics 31 (2001) 616-631
In this paper we review the crystal chemistry and structure data from the literature and our results reported in the last decade for natural and synthetic samples of the tantalite-columbite series. Order-disorder transitions and oxidation reactions on the ixiolite-columbite-wodginite system are reported for two Brazilian samples. It is shown that reports on these subjects are sometimes dubious and incomplete. In addition to the reaction atmosphere (air or vacuum), order-disorder and oxidation are strongly dependent on the physical state of the samples (powdered or crystal). Structure and chemical composition have been investigated in our laboratory using X-ray diffraction (XRD), electron probe microanalysis (EPMA) and Mössbauer spectroscopy (MS).
PACS numbers: 75.40.Cx, 75.50.Ee, 81.40.-z, 82.80.Ej, 91.60.-x
Keywords: Tantalite, columbite, tapiolite, Mössbauer spectroscopy, X-ray diffraction, antiferromagnetism.
Veja o texto completo (see the full text)
  Coexistence of Rutile and Trirutile Phases in a Natural Tapiolite Sample
E.J. Kinast, L.I. Zawislak, J.B.M. da Cunha, V. Antonietti, M.A.Z. de Vasconcellos and C.A. dos Santos
Journal of Solid State Chemistry 163 (2002) 218-222
We report X-ray powder diffraction (XRD), electron probe microanalysis (EPMA) and Mössbauer spectroscopy (MS) measurements performed on a natural tapiolite with composition Fe0.57Mn0.37Ti0.10Ta 1.27Nb0.67O6. XRD and MS suggest that besides partially ordered the as-collected sample is a mixture of trirutile (P42/mnm, a=4.7532(9) Å, c=9.228(7) Å) and Nb-rich rutile (P42/mnm, a=4.856(2) Å, c=3.098(1) Å) structures. The Mössbauer spectra of the rutile (Fe,Mn,Ta,Nb)O2 were fitted to D=1.72±0.05 mm/s and d=1.10±0.03 mm/s at 300 K and to D=2.10±0.06 mm/s and d=1.18±0.03 mm/s at 80 K. The present results suggest that cation ordering in compounds of the tapiolite series can be easily assessed by Mössbauer spectroscopy in a similar way as previously demonstrated for the columbite series.
Keywords: Tapiolite, Rutile, Trirutile, order-disorder, oxidation, Mössbauer spectroscopy, X-ray diffraction, Electron probe microanalysis
Veja o texto completo (see the full text)
  Indicadores de Qualidade da Atividade Científica
L. Strehl, C.A. dos Santos
Ciência Hoje 31 (2002) 34-39
O uso de indicadores bibliométricos vem sendo progressivamente adotado para avaliação da qualidade da produção científica, bem como para o estabelecimento de políticas de aquisição de periódicos. Dentre os indicadores, o fator de impacto (FI) tem sido o mais utilizado. Demonstra-se que para a aplicação do FI como critério de identificação da qualidade de uma produção científica, deve-se levar em consideração não apenas a sua condição relativa, como sua mutabilidade temporal. Caso contrário, pode-se incorrer em injusti-ças no momento da comparação das publicações de pesquisadores de áreas distintas, cujos valores de FI não possuem a mesma significação.
Veja o texto completo
  Bohr, Heisenberg e a bomba atômica.
C.A. dos Santos
Voz do Paraná, n. 1750, 27/3/2002
Em setembro de 1941, o físico alemão Werner Heisenberg visita o físico dinamarquês Niels Bohr. Não se trata de uma visita comum, entre colegas de profissão, entre um ex-aluno (Heisenberg) e seu ex-professor. Há mais de um ano a Dinamarca estava sob a ocupação de tropas alemãs, e Heisenberg ocupava o importante cargo de coordenador científico do programa nuclear alemão. As motivações para o encontro e o conteúdo da conversa continuam sob o manto da controvérsia. A primeira versão de Heisenberg foi publica em 1956, no livro de Robert Jungk, Brighter than a thousand suns (Mais brilhante que mil sóis). Recentemente a família de Bohr resolveu tornar público parte das anotações de Bohr, nas quais ele reage à versão de Heisenberg.
Veja o texto completo
  O Centenário da Academia Olímpia
C.A. dos Santos
Voz do Paraná, n. 1769, 9/4/2003
Na páscoa de 1902, Moritz Solovine leu um anúncio num jornal de Berna segundo o qual Albert Einstein dava aulas particulares de matemática e física por três francos a hora. No terceiro dia de aula, Einstein desistiu de cobrar e sugeriu que eles tivessem apenas reuniões diárias para discutir o que bem entendessem. Algumas semanas depois Conrad Habicht começou a participar das discussões. Para ridicularizar as verdadeiras academias científicas passaram a se autodenominar Akademie Olympia. Foi com esses dois colegas e com Michele Besso que Einstein discutiu as idéias científicas que redundaram nos extraordinários trabalhos publicados em 1905
Veja o texto completo
  Surface Modification of Titanium by Plasma Nitriding
Myriam Pereira Kapczinski, Carlos Gil, Eder Julio Kinast, Carlos Alberto dos Santos
Materials Research, Vol. 6, No. 2, 265-271, 2003.
A systematic investigation was undertaken on commercially pure titanium submitted to plasma nitriding. Thirteen different sets of operational parameters (nitriding time, sample temperature and plasma atmosphere) were used. Surface analyses were performed using X-ray diffraction, nuclear reaction and scanning electron microscopy. Wear tests were done with stainless steel Gracey scaler, sonic apparatus and pin-on-disc machine. The obtained results indicate that the tribological performance can be improved for samples treated with the following conditions: nitriding time of 3 h; plasma atmosphere consisting of 80%N2+20%H2 or 20%N2+80%H2; sample temperature during nitriding of 600 or 800 °C. Keywords: plasma nitriding, tribology, titanium, dental implants
Veja o texto completo
  Thermal behavior of supersolidus bronze powder compacts during heating by hollow cathode discharge
C. Alves Jr., V. Hajek, C.A. dos Santos
Materials Science and Engineering, A348 (2003) 84-89.
Porous aluminum./bronze compacts formed from prealloyed metastable (supersolidus) powder were heated either by plasma or by a resistive furnace technique. The plasma heating was performed in two different setups: (i) Hollow Cathode Discharge (HCD) method and (ii) Shielded Cathode Discharge (SCD) method. All experiments were carried out for 12 min in hydrogen at temperatures ranging from 673 to 1323 K. In HCD, for temperatures above 773 K, a fully filled, non-porous region was obtained in the center of the compacts, exhibiting a quite different behavior than that obtained using either SCD or resistive techniques. In these cases, uniformly dispersed condensed micro-regions were detected in samples treated at temperatures higher than 1223 K. These observations are discussed in terms of the heating mechanism, mass transfer and behavior of supersolidus powder particles. A simple physical model for the creation of the central fully filled region obtained by HCD is introduced. Keywords: Supersolidus powder; Aluminum./bronze; Hollow cathode; Plasma heating
Veja o texto completo
  Near-surface composition and tribological behaviour of plasma nitrided titanium
M P Kapczinski, E J Kinast and C A dos Santos
J. Phys. D: Appl. Phys., 36 (2003) 1858?1863.
Near-surface composition and tribological behaviour of plasma nitrided commercially pure (CP) Ti have been investigated using x-ray diffraction, nuclear reaction analysis, scanning electron microscopy, wear assays with stainless steel Gracey scaler and sonic apparatus, and friction coefficient measurements. The total wear behaviour can be divided into two steps. The first step is the growth of an oxynitride layer. The second step is the breakdown of the oxynitride layer during which debris is produced, increasing the friction coefficient. Each sample exhibits features that correlate with the near-surface composition. For instance, the presence of thin layers of e-Ti2N and d-TiN precipitating on the near-surface region control the transition from the first to the second step.
Veja o texto completo
  Bicriticality in FexCo1-xTa2O6
E. J. Kinast, V. Antonietti, D. Schmitt, O. Isnard, J. B. M. da Cunha, M. A. Gusmão, and C. A. dos Santos
Phys. Rev. Lett., 91 (2003) 197208-4.
X-ray and neutron-diffraction, dc magnetic susceptibility, magnetization, and specific-heat measurements are reported for FexCo1.xTa2O6 mixed oxides. X-ray refinement indicates homogeneous samples for all the reported concentrations. The neutron-diffraction measurements reveal magnetic structures with double propagation vectors ..1=4; 1=4; 1=4. for CoTa2O6, and .1=2; 0; 1=2. and .0; 1=2; 1=2. for FeTa2O6. The latter remain unchanged in the Fe-rich samples, for 0:46 . x< 1:00, while the Co-rich samples show propagation vectors ..1=4; 1=4; 0. for 0:09 . x< 0:46. The temperature vs x phase diagram exhibits a bicritical point at about T . 4:9 K and x . 0:46. For this concentration, and at low temperatures, the system shows coexistence of both magnetic structures. This novel bicritical behavior is interpreted as induced by competition between the different magnetic and crystallographic structures. PACS numbers: 75.30.Kz, 64.75.+g, 83.85.Hf
Veja o texto completo
  Einstein apaixonado: A ciência mal-contada de um mito bem-traçado
C. A. dos Santos
Revista Brasileira de Ensino de Física, v. 26, n.1, p.87-88 (2004).
O parágrafo de abertura de Einstein Apaixonado, livro recentemente publicado por Dennis Overbye, é um magnífico prenúncio de que o mito Albert Einstein será revelado em toda a sua complexidade psicológica. Overbye manipula bem as palavras e constrói frases bem acabadas. A maravilhosa construção do primeiro capítulo deixa o leitor sedento pela continuidade da leitura. Overbye mantém esta expectativa em bom ritmo até o início do quarto capítulo, quando ele se desvia do caminho sugerido e toma o rumo das biografias clássicas, com soluções perturbadoras. Em suma, Einstein Apaixonado nos brinda com maravilhosos trechos isolados, sobretudo aqueles nos quais vislumbramos o bem-traçado perfil de um mitológico Einstein. Por outro lado, o autor não conseguiu manter o mesmo nível de qualidade quando investiu nas discussões de conceitos físicos.
Veja o texto completo
C. A. dos Santos e Mara Figueira
Ciência Hoje das Crianças, Ano 17, n.145, p.2-5, abril de 2004.
Ossos, sorriam! A história dos raios-X. Com a descoberta dos raios X, muita gente passou a achar que, lançando-os contra uma pessoa, era possível vê-la nua, quando, no máximo, se veria o esqueleto. Também havia quem acreditasse que, jogando raios X sobre o crânio de alguém, dava para ler seus pensamentos, outra idéia sem fundamento! um jornal alertou a população dizendo que qualquer pessoa, com um aparelho de raios X, poderia ver o que ocorria em uma casa. Essa foi só uma das muitas notícias erradas publicadas a partir de 1895, ano em que Wilhelm Conrad Roentgen descobriu os raios X. Em 1896, o físico inglês Sir George Stokes demonstrou que os raios X são produzidos quando partículas com carga elétrica são desaceleradas!
Veja o texto completo
  Tutorial básico para o uso do Moodle

Tutorial destinado a alunos da UFRGS. Portanto, trata apenas das ferramentas disponíveis na interface do aluno, de acordo com a configuração instalada no Moodle Institucional da UFRGS.
Veja o tutorial