6 research outputs found
Self-trapped bidirectional waveguides in a saturable photorefractive medium
We introduce a time-dependent model for the generation of joint solitary
waveguides by counter-propagating light beams in a photorefractive crystal.
Depending on initial conditions, beams form stable steady-state structures or
display periodic and irregular temporal dynamics. The steady-state solutions
are non-uniform in the direction of propagation and represent a general class
of self-trapped waveguides, including counterpropagating spatial vector
solitons as a particular case.Comment: 4 pages, 5 figure
Effect of degree of lipomobilization on results of glucose test in dairy cows in heat stress
Cows exposed to heat stress exhibit a decreased ability to mobilize lipids
due to increased sensitivity to insulin, which is expressed in a decreased
concentration of NEFA. However, certain cows can preserve the level of lipid
mobilization after adapting to heat stress. We assumed that cows that have a
preserved ability to mobilize lipids are less sensitive to insulin and that
they have a lower tolerance for glucose. The aim of this work was to compare
the results of an intravenous glucose tolerance test in cows that exhibited,
in prolonged heat stress, a decreased (NEFA<0.20 mmol/l) or preserved
(NEFA>0.30 mmol/l) ability for lipid mobilization. Glucose concentration and
NEFA concentration were measured following intravenous application of
glucose. The mean glycaemic index value did not differ statistically
significantly between the two groups of cows at 10, 15 and 20 minutes after
glucose application (p>0.05), but there was a tendency at 10 and 15 minutes
for the glycaemia to be higher in cows with preserved lipomobilization
(p<0.1). At 30, 60 and 90 minutes after glucose application, glycaemia was
statistically significantly higher (p<0.01; p<0.05 and p<0.05) in the group
of cows with preserved lipomobilization. The glycaemic index values (mmol/l)
shown in the same order (30, 60 and 90 minutes) were as follows 9.91Ā±0.21:
9.23Ā±0.41; 5.41Ā±0.5: 4.67Ā±0.33 and 4.31Ā±0.39: 3.47Ā±0.37. The mean value for
NEFA concentration in samples originating from the two experimental groups of
cows did not differ statistically significantly following glucose
application. The NEFA concentration showed a tendency to be higher in cows
with preserved lipid mobilization in comparison with cows with decreased
lipomobilization at 20 and 30 minutes after glucose application (p<0.1).
Following the intravenous glucose tolerance test, NEFA and glucose
concentrations were in a significant negative correlation, and that
correlation was more expressed in cows with decreased lipomobilization. Cows
with preserved lipomobilization have a lower tolerance for glucose than cows
with a decreased lipomobilization during heat stress. [Projekat Ministarstva
nauke Republike Srbije, br. TR 31062
Spatiotemporal instabilities of counterpropagating beams in nematic liquid crystals
We investigate the behavior of counterpropagating self-trapped optical beam structures in nematic liquid crystals. We treat numerically a time-dependent model for the beam propagation and the director reorientation in a nematic liquid crystal, in (2 + 1) spatial dimensions. The formation of stable solitons in a narrow threshold region of control parameters is displayed. Spatiotemporal instabilities are observed as the input intensity, the propagation distance, and the birefringence are increased. Transverse displacement, filamentation, and dynamical instabilities of counterpropagating beams are demonstrated