|
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 |
|
| Raios-X
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. |
|