515 research outputs found
Associação da seringueira com a cultura do café, no município de Ouro Preto D'Oeste em Rondônia.
bitstream/item/56619/1/PA-1540-0001.pd
Relevance of pseudospin symmetry in proton-nucleus scattering
The manifestation of pseudospin-symmetry in proton-nucleus scattering is
discussed. Constraints on the pseudospin-symmetry violating scattering
amplitude are given which require as input cross section and polarization data,
but no measurements of the spin rotation function. Application of these
constraints to p-58Ni and p-208Pb scattering data in the laboratory energy
range of 200 MeV to 800 MeV, reveals a significant violation of the symmetry at
lower energies and a weak one at higher energies. Using a schematic model
within the Dirac phenomenology, the role of the Coulomb potential in
proton-nucleus scattering with regard to pseudospin symmetry is studied. Our
results indicate that the existence of pseudospin-symmetry in proton-nucleus
scattering is questionable in the whole energy region considered and that the
violation of this symmetry stems from the long range nature of the Coulomb
interaction.Comment: 22 pages including 9 figures, correction of 1 reference, revision of
abstract and major modification of chapter 4, Fig. 6, and Fig. 7; addition of
Fig. 8 and Fig.
New insight on pseudospin doublets in nuclei
The relevance of the pseudospin symmetry in nuclei is considered. New insight
is obtained from looking at the continuous transition from a model satisfying
the spin symmetry to another one satisfying the pseudospin symmetry. This study
suggests that there are models allowing no missing single-particle states in
this transition, contrary to what is usually advocated. It rather points out to
an association of pseudospin partners different from the one usually assumed,
together with a strong violation of the corresponding symmetry. A comparison
with results obtained from some relativistic approaches is made.Comment: 27 pages, 18 figure
Unusual magnetic relaxation behavior in La0.5Ca0.5MnO3 and Nd0.5Sr0.5MnO3
We have carried out a systematic magnetic relaxation study, measured after
applying and switching off a 5 T magnetic field to polycrystalline samples of
La0.5Ca0.5MnO3 and Nd0.5Sr0.5MnO3. The long time logarithmic relaxation rate
(LTLRR), decreased from 10 K to 150 K and increased from 150 K to 195 K in
La0.5Ca0.5MnO3. This change in behavior was found to be related to the complete
suppression of the antiferromagnetic phase above 150 K and in the presence of a
5 T magnetic field. At 195 K, the magnetization first decreased, and after a
few minutes increased slowly as a function of time. Moreover, between 200 K and
245 K, the magnetization increased throughout the measured time span. The
change in the slope of the curves, from negative to positive at about 200 K was
found to be related to the suppression of antiferromagnetic fluctuations in
small magnetic fields. A similar temperature dependence of the LTLRR was found
for the Nd0.5Sr0.5MnO3 sample. However, the temperature where the LTLRR reached
the minimum in Nd0.5Sr0.5MnO3 was lower than that of La0.5Ca0.5MnO3. This
result agrees with the stronger ferromagnetic interactions that exist in
Nd0.5Sr0.5MnO3 in comparison to La0.5Ca0.5MnO3. The above measurements
suggested that the general temperature dependence of the LTLRR and the
underlying physics were mainly independent of the particular charge ordering
system considered. All relaxation curves could be fitted using a logarithmic
law at long times. This slow relaxation was attributed to the coexistence of
ferromagnetic and antiferromagnetic interactions between Mn ions, which
produced a distribution of energy barriers.Comment: Accepted to PRB as a regular article, 10 figures, Scheduled Issue: 01
June 200
Associação da seringueira com a cultura do cafeeiro no Estado de Rondonia.
Tema Central: Sistemas Agroflorestais no Desenvolvimento Sustentavel. v.2 Trabalhos voluntarios. Editores Luciano J. Montoya e Moacir J.S. Medrado
Specific heat and magnetic measurements in Nd0.5Sr0.5MnO3, Nd0.5Ca0.5MnO3 and Ho0.5Ca0.5MnO3 samples
We studied the magnetization as a function of temperature and magnetic field
in the compounds Nd0.5Sr0.5MnO3, Nd0.5Ca0.5MnO3 and Ho0.5Ca0.5MnO3. It allowed
us to identify the ferromagnetic, antiferromagnetic and charge ordering phases
in each case. The intrinsic magnetic moments of Nd3+ and Ho3+ ions experienced
a short range order at low temperatures. We also did specific heat measurements
with applied magnetic fields between 0 and 9 T and temperatures between 2 and
300 K in all three samples. Close to the charge ordering and ferromagnetic
transition temperatures the specific heat curves showed peaks superposed to the
characteristic response of the lattice oscillations. Below 10 K the specific
heat measurements evidenced a Schottky-like anomaly for all samples. However,
we could not successfully fit the curves to either a two level nor a
distribution of two-level Schottky anomaly. Our results indicated that the peak
temperature of the Schottky anomaly was higher in the compounds with narrower
conduction band.Comment: submitted to PR
Análise Morfométrica de Bacia Hidrográfica: Subsídio à Gestão Territorial Estudo de Caso no Alto e Médio Mamanguape.
Para esta análise, foram criados os mapas da drenagem e hipsométrico, levando em conta que o relevo é um dos aspectos mais importantes deste estudo, pois permite compreender a disposição da drenagem e tem aplicação direta para a gestão territorial. A análise da morfometria utilizou 17 índices morfométricos entre os mais de 50 existentes na literatura, dentre os quais podem-se destacar: fator de forma; índice de circularidade; coeficiente de compacidade; índice de rugosidade; padrão de drenagem; canais de drenagem; amplitude altimétrica; densidade de drenagem; textura topográfica; e coeficiente de manutenção. Com base na análise dos resultados, pode-se concluir que o fator de forma (0,44), o índice de circularidade (0,78), o coeficiente de compacidade (1,12) e o índice de rugosidade (0,72) demonstraram que a bacia hidrográfica em estudo exibe um formato alongado contribuindo, dessa forma, para o processo de escoamento e apresentando, portanto, baixa suscetibilidade à ocorrência de enchentes. Enfim, esses parâmetros podem ser utilizados para comparação entre os diversos tipos de áreas como microbacias, fazendas ou municípios, auxiliando, no monitoramento, análise e gestão territorial.bitstream/item/84896/1/0000010346-BPD-Analise-morfometrica.pd
Reproducible k-means clustering in galaxy feature data from the GAMA survey
A fundamental bimodality of galaxies in the local Universe is apparent in many of the features used to describe them. Multiple sub-populations exist within this framework, each representing galaxies following distinct evolutionary pathways. Accurately identifying and characterizing these sub-populations requires that a large number of galaxy features be analysed simultaneously. Future galaxy surveys such as LSST and Euclid will yield data volumes for which traditional approaches to galaxy classification will become unfeasible. To address this, we apply a robust k-means unsupervized clustering method to feature data derived from a sample of 7338 local-Universe galaxies selected from the Galaxy And Mass Assembly (GAMA) survey. This allows us to partition our sample into k clusters without the need for training on pre-labelled data, facilitating a full census of our high-dimensionality feature space and guarding against stochastic effects. We find that the local galaxy population natively splits into 2, 3, 5, and a maximum of six sub-populations, with each corresponding to a distinct ongoing evolutionary mechanism. Notably, the impact of the local environment appears strongly linked with the evolution of low-mass (M* \u3c 1010 M⊙) galaxies, with more massive systems appearing to evolve more passively from the blue cloud on to the red sequence. With a typical run time of ~3 min per value of k for our galaxy sample, we show how k-means unsupervized clustering is an ideal tool for future analysis of large extragalactic data sets, being scalable, adaptable, and providing crucial insight into the fundamental properties of the local galaxy population
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