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991.
E. K. Lenzi B. F. de Oliveira N. G.C. Astrath L. C. Malacarne R. S. Mendes M. L. Baesso L. R. Evangelista 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,62(2):155-158
We consider nonlocal effects, obtained by incorporating fractional
derivatives in the kinetic energy of a conventional Hamiltonian, to analyze physical properties of
non-crystalline
solids at very low temperature. By using thermal Green functions,
we deduce some experimentally observable quantities such as the
particle momentum distribution function, the particle energy
distribution function, and the specific heat. The
agreement between the results obtained for the specific heat and
the experimental data suggests that the approach presented here may
be useful as a phenomenological model to investigate thermal properties of
non-crystalline solids at low temperature. 相似文献
992.
Nanocomposites consisting of metallic Fe particles and a nonmagnetic oxide were prepared by reducing MgFe2O4 with Al or Mg in a ball mill. The reaction takes place as a fast self-propagating process sometime between 0.5 and 1 h of milling. Combining XRD and Mössbauer spectroscopy reveals that the bcc Fe phase contains a few percents of dissolved Al, it has a high defect concentration, and the surface tension of the ultrafine (about 15 nm) grains results in local compressive strains. The magnetization is 25% less than expected for pure ferromagnetic Fe. 相似文献
993.
In this paper, a new high sensitivity potentiometric pH-electrode with a response in the acid region is proposed. It consists of a PbO2-paraffin matrix deposited on graphite. Its simple construction and studies of some variables at 0.5 mol L−1 ionic strength are reported. A direct relationship between the electric potential difference and the solution pH was observed for pH values ranging from 1.2 to 7.5. A slope greater than 100 mV/decade and a conditional electric potential of about 1250 mV were obtained. The results presented a high correlation with those from a conventional glass pH-electrode in complex matrix samples. 相似文献
994.
Nunes FM Barros-Filho BA de Oliveira MC Mafezoli J Andrade-Neto M de Mattos MC Silveira ER Pirani JR 《Magnetic resonance in chemistry : MRC》2005,43(2):180-183
One- and two-dimensional NMR experiments were used for the unambiguous assignment of the 1H and 13C NMR chemical shifts of 3,3-diisopentenyl-N-methyl-2,4-quinoldione and five novel reaction derivatives. 相似文献
995.
G. N. de Oliveira 《Numerische Mathematik》1970,15(4):345-347
Summary Given an arbitraryn ×n real matrixA andn real numberss
1, ...,s
n
, we study the problem of the existence of a diagonal matrixM such that the characteristic values ofA +M bes
1, ...,s
n
. 相似文献
996.
V.M. de Oliveira 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,31(2):259-263
We do an analytical study of the statistical properties of an ecosystem composed of species that are coupled via pairwise interactions that are given by the Hebb rule and have deterministic self-interactions u. In the model each species is characterized by an infinite set of p = αN traits. As one of our main results, we observe that the ecosystem becomes less cooperative as the complexity of species (number
of traits) is increased.
Received 23 September 2002 Published online 4 February 2003
RID="a"
ID="a"e-mail: viviane@if.sc.usp.br 相似文献
997.
998.
Rubinger RM da Silva RL de Oliveira AG Ribeiro GM Albuquerque HA Rodrigues WN Moreira MV 《Chaos (Woodbury, N.Y.)》2003,13(2):457-466
We have observed low frequency current oscillations in a semi-insulating GaAs sample grown by low temperature molecular beam epitaxy. For this, an experimental setup proper to measure high impedance samples with small external noise was developed. Spontaneous oscillations in the current were observed for some bias conditions. Although measurements were carried out from room temperature down to liquid helium, the dynamical analysis was carried out around 200 K where the signal to noise ratio was fairly favorable. To increase the data quality we have also used a noise reduction algorithm suitably developed for nonlinear systems. We observed attractors having low embedding dimension, limit cycle bifurcations, and chaotic behavior characteristic of nonlinear dynamical processes in route to chaos. Attractor reconstruction, Poincare sections, Lyapunov exponents, and correlation dimension were also analyzed. 相似文献
999.
A clock reaction produced by mixing chlorate and iodine solutions in perchloric acid media is reported. This is the first example of a clock reaction using chlorate as a reagent. Increasing chlorate and acid concentration reduces the induction period. Changing the initial iodine concentration does not affect the length of the induction period. The discovery of this clock reaction opens the possibility that a new family of oscillation reactions can be built using chlorate as reagent. 相似文献
1000.
Silva BM Andrade PB Ferreres F Seabra RM Oliveira MB Ferreira MA 《Natural product research》2005,19(3):275-281
Phenolic compounds, organic acids and free amino acids of quince seeds were determined by HPLC/DAD, HPLC/UV and GC/FID, respectively. Quince seeds presented a phenolic profile composed of 3-O-caffeoylquinic, 4-O-caffeoylquinic, 5-O-caffeoylquinic and 3,5-dicaffeoylquinic acids, lucenin-2, vicenin-2, stellarin-2, isoschaftoside, schaftoside, 6-C-pentosyl-8-C-glucosyl chrysoeriol and 6-C-glucosyl-8-C-pentosyl chrysoeriol. Six identified organic acids constituted the organic acid profile of quince seeds: citric, ascorbic, malic, quinic, shikimic and fumaric acids. The free amino acid profile was composed of 21 identified free amino acids and the three most abundant were glutamic and aspartic acids and asparagine. 相似文献