Histopathology and laser autofluorescence of ischemic kidneys of rats

The purpose of this research was to evaluate the severity of renal ischemia/reperfusion injury as determined by histology and by laser-induced fluorescence (LIF) with excitation wavelengths of 442 nm and 532 nm. Wistar rats (four groups of six animals) were subjected to left renal warm ischemia for 20, 40, 60 and 80 min followed by 10 min of reperfusion. Autofluorescence was determined before ischemia (control) and then every 5-10 min thereafter. Tissue samples for histology were harvested from the right kidney (control) and from the left kidney after reperfusion. LIF and ischemia time showed a significant correlation (p < 0.0001 and r (2)=0.47, and p=0.006 and r (2)=0.25, respectively, for the excitation wavelengths of 442 nm and 532 nm). Histological scores showed a good correlation with ischemia time (p < 0.0001). The correlations between optical spectroscopy values and histological damage were: LIF at 442 nm p < 0.0001, LIF at 532 nm p=0.001; IFF (peak of back scattered light/LIF) at 442 nm p > 0.05, and IFF at 532 nm p > 0.05. After reperfusion LIF tended to return to preischemic basal levels which occurred in the presence of histological damage. This suggests that factors other than morphological alterations may have a more relevant effect on changes observed in LIF. In conclusion, renal ischemia/reperfusion changed tissue fluorescence induced by laser. The excitation light of 442 nm showed a better correlation with the ischemia time and with the severity of tissue injury.

Hopf Bifurcations in a Watt Governor with a Spring

This paper pursues the study carried out in [ 10], focusing on the codimension one Hopf bifurcations in the hexagonal Watt governor system. Here are studied Hopf bifurcations of codimensions two, three and four and the pertinent Lyapunov stability coefficients and bifurcation diagrams. This allows to determine the number, types and positions of bifurcating small amplitude periodic orbits. As a consequence it is found an open region in the parameter space where two attracting periodic orbits coexist with an attracting equilibrium point.

Bifurcation analysis of a model for biological control

In this paper we study the Lyapunov stability and Hopf bifurcation in a biological system which models the biological control of parasites of orange plantations. (c) 2007 Elsevier Ltd. All rights reserved.

Stability and Hopf bifurcation in an hexagonal governor system

In this paper we study the Lyapunov stability and the Hopf bifurcation in a system coupling an hexagonal centrifugal governor with a steam engine. Here are given sufficient conditions for the stability of the equilibrium state and of the bifurcating periodic orbit. These conditions are expressed in terms of the physical parameters of the system, and hold for parameters outside a variety of codimension two. (C) 2007 Elsevier Ltd. All rights reserved.

New classes of spatial central configurations for the n+3-body problem

In this paper, we show the existence of new families of spatial central configurations for the n + 3-body problem, n >= 3. We study spatial central configurations where n bodies are at the vertices of a regular n-gon T and the other three bodies are symmetrically located on the straight line that is perpendicular to the plane that contains T and passes through the center of T. The results have simple and analytic proofs. (c) 2010 Elsevier Ltd. All rights reserved.

Stacked central configurations for the spatial six-body problem

In this paper we show the existence of three new families of stacked spatial central configurations for the six-body problem with the following properties: four bodies are at the vertices of a regular tetrahedron and the other two bodies are on a line connecting one vertex of the tetrahedron with the center of the opposite face. (c) 2009 Elsevier B.V. All rights reserved.