Biomedical subjects

L R da Silva

Publications and source records attributed to L R da Silva.

7 recordsLinked to original sources

PubMed2006

Non-Markovian Fokker-Planck equation: solutions and first passage time distribution.

We investigate the solutions and first passage time distribution for an anomalous diffusion process governed by a generalized non-Markovian Fokker-Planck equation. In our analysis, we also consider the presence of external forces and absorbent (source) terms. In addition, we show that a rich class of diffusive processes, including normal and anomalous ones, can be obtained from the solutions found here.

Journal Article↗

PubMed2005

N-dimensional fractional diffusion equation and Green function approach: spatially dependent diffusion coefficient and external force.

We investigate an N-dimensional fractional diffusion equation with radial symmetry by using the Green function approach. We consider, in our analysis, the spatial dependence on the diffusion coefficient and the presence of an external force. In particular, we employ boundary conditions in a finite interval and after we extend it to a semi-infinite interval. We also show that a rich class of diffusive processes, including normal and anomalous ones, can be obtained from the solutions found here.

Journal Article↗

PubMed2003

Exact solutions to nonlinear nonautonomous space-fractional diffusion equations with absorption.

We analyze a nonlinear fractional diffusion equation with absorption by employing fractional spatial derivatives and obtain some more exact classes of solutions. In particular, the diffusion equation employed here extends some known diffusion equations such as the porous medium equation and the thin film equation. We also discuss some implications by considering a diffusion coefficient D(x,t)=D(t)/x/(-theta) (theta in R) and a drift force F=-k(1)(t)x+k(alpha)x/x/(alpha-1). In both situations, we relate our solutions to those obtained within the maximum entropy principle by using the Tsallis entropy.

Journal Article↗

PubMed2001

Specific heat of multifractal energy spectra.

Motivated by the self-similar character of energy spectra demonstrated for quasicrystals, we investigate the case of multifractal energy spectra, and compute the specific heat associated with simple archetypal forms of multifractal sets as generated by iterated maps. We considered the logistic map and the circle map at their threshold to chaos. Both examples show nontrivial structures associated with the scaling properties of their respective chaotic attractors. The specific heat displays generically log-periodic oscillations around a value that characterizes a single exponent, the "fractal dimension," of the distribution of energy levels close to the minimum value set to 0. It is shown that when the fractal dimension and the frequency of log oscillations of the density of states are large, the amplitude of the resulting log oscillation in the specific heat becomes much smaller than the log-periodic oscillation measured on the density of states.

Journal Article↗

PubMed1999

Antimicrobial peptides from the Brazilian frog Phyllomedusa distincta.

Different peptides were purified by chromatographic procedures from the skin-secretory glands of the frog Phyllomedusa distincta. These are the first peptides reported from this frog species. Their primary structure was determined by a combination of automated Edman degradation and mass spectrometry. Peptide Q2 contains 25 amino acid residues, peptide Q1 and L have 28 each, peptide M contains 31, and peptide K has 33 amino acid residues. They all showed potent antimicrobial activity against Gram-negative and Gram-positive bacteria, presenting minimal inhibitory concentrations from 0.6 to 40 microM, when tested against Enterococcus faecalis, Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa. Peptides K, L, and Q1 were chemically synthesized and shown to be active.

Amino Acid Sequence↗

PubMed1978

[Not Available].

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Brazil↗

PubMedDate not supplied

[Carcinosarcoma of the esophagus: diagnostic importance of partial endoscopic polypectomy].

The clinical and pathological manifestations of a case of carcinosarcoma of the esophagus are reported. Barium swallow and endoscopy revealed a polypoid mass in mid esophagus. The tumor was large, pedunculated, covered by smooth mucosa with some erosions. Histologically the tumor was composed of a mixture of invasion keratinizing cells and intermingled bundle of spindle shaped cells resembling fibrosarcoma. The tumor was removed with surgery and did not show submucosa infiltration. It was not detected any metastasis or local recurrence during the 12 months follow-up period. The diagnosis was made by an endoscopic partial polypectomy. We conclude that partial polypectomy may be of value in preoperative diagnosis of esophageal polypoid mass.

Carcinosarcoma↗