8 research outputs found
Composite multi-vortex diffraction-free beams and van Hove singularities in honeycomb lattices
We find diffraction-free beams for graphene and MoS-type honeycomb
optical lattices. The resulting composite solutions have the form of
multi-vortices, with spinor topological charges (, ). Exact solutions
for the spinor components are obtained in the Dirac limit. The effects of the
valley degree of freedom and the mass are analyzed. Passing through the
van-Hove singularity the topological structure of the solutions is modified.
Exactly at the singularity the diffraction-free beams take the form of strongly
localized one-dimensional stripes.Comment: 4 pages, 6 figures, accepted for publication in Optics Letter
Nonlinear magnetoinductive transmission lines
Power transmission in one-dimensional nonlinear magnetic metamaterials driven
at one end is investigated numerically and analytically in a wide frequency
range. The nonlinear magnetic metamaterials are composed of varactor-loaded
split-ring resonators which are coupled magnetically through their mutual
inductances, forming thus a magnetoiductive transmission line. In the linear
limit, significant power transmission along the array only appears for
frequencies inside the linear magnetoinductive wave band. We present
analytical, closed form solutions for the magnetoinductive waves transmitting
the power in this regime, and their discrete frequency dispersion. When
nonlinearity is important, more frequency bands with significant power
transmission along the array may appear. In the equivalent circuit picture, the
nonlinear magnetoiductive transmission line driven at one end by a relatively
weak electromotive force, can be modeled by coupled
resistive-inductive-capacitive (RLC) circuits with voltage-dependent
capacitance. Extended numerical simulations reveal that power transmission
along the array is also possible in other than the linear frequency bands,
which are located close to the nonlinear resonances of a single nonlinear RLC
circuit. Moreover, the effectiveness of power transmission for driving
frequencies in the nonlinear bands is comparable to that in the linear band.
Power transmission in the nonlinear bands occurs through the linear modes of
the system, and it is closely related to the instability of a mode that is
localized at the driven site.Comment: 11 pages, 11 figures, submitted to International Journal of
Bifurcation and Chao
A diagrammatic approach to triplet supercurrents in ferromagnetic Josephson junctions
We present a numerical study of ferromagnetic Josephson junctions with one intermediate layer and spin active interfaces in the ballistic regime, comparing the behaviour of one, two and three dimensional junctions. We find that in two and three dimensional junctions the geometries which lack spin flip scattering at one of the interfaces have a critical current that decays to zero, as we increase the magnetization of the intermediate layer towards the half metal limit. As known, magnetization direction inhomogeneity produces a long range supercurrent with width variation, even when spin flip scattering exists in one of the interfaces only, although of lower characteristic decay length, compared to junctions with spin flip scattering at both interfaces. In the case of a single spin-flip interface and large thickness of the junction, we find a dominant second harmonic in the current-phase relation, in agreement with earlier work. We apply a diagrammatic approach, which explains the strong second harmonic and the long range property of the supercurrent. We find that in the three dimensional junction case the main contribution to both the long range supercurrent and the second harmonic in thick Josephson junctions with one spin flip interface comes from diagrammatic terms that correspond to scattering loops inside the junction which are subject to anomalous Andreev reflections on the spin flip interface and normal Andreev reflections at the non spin flip interface, thus exhibiting the triplet nature of the phenomenon. We also find the emergence of the strong first harmonic for small variation of the magnetization geometry and comment on the effect of normal interface scattering and temperature on the second harmonic
Acute resistance exercise results in catecholaminergic rather than hypothalamic-pituitary-adrenal axis stimulation during exercise in young men
Exercise is a paradigm of a stress situation. The adaptive response to
stressors comprises the activation of the hypothalamic-pituitary-adrenal
(HPA) axis and components of the autonomic sympathetic system. An
aseptic inflammatory reaction is triggered by exercise, involving the
stimulation of the so-called proinflammatory cytokines, such as tumor
necrosis factor a (TNF alpha), interleukin-1 (IL-1), and IL-6. The
anti-inflammatory cytokines IL-2, IL-8, and IL-10 increase moderately
during resistance exercise. To investigate the effect of a short bout of
resistance exercise on components of the stress and inflammatory
responses during the exercise period, 17 healthy, young, untrained male
volunteers were studied during 3 equal consecutive cycles of resistance
exercises of 30 min total duration. Blood sampling was performed at
baseline and at the end of each cycle. Lactate, cortisol, catecholamines
(epinephrine, norepinephrine), IL-1 alpha, IL-1 beta, IL-2, IL-6, IL-8,
IL-10, epidermal growth factor (EGF), and monocyte chemotactic protein-1
(MCP-1) were measured at all time-points. Circulating levels of
catecholamines and lactate increased significantly (P < 0.05) whereas
cortisol did not. During the time course of the exercise, circulating
levels of TNF alpha, IL-2, and EGF increased, whereas MCP-1 decreased
significantly. IL-1 alpha, IL-1 beta, IL-6, IL-8, and IL-10 levels did
not change significantly. Statistically significant positive linear
correlations were found between areas under the curve for increases in
levels of IL-2 and TNF alpha, TNF alpha and cortisol, as well as
epinephrine and norepinephrine. We conclude that acute resistance
exercise results in catecholaminergic, but not HPA axis stimulation
during exercise, in parallel with a mild inflammatory reaction. The
absence of a major inflammatory reaction and of a cortisol increase
during acute resistance exercise makes this a good candidate for the
exercise of sedentary individuals