1,368 research outputs found
Transversal-rotational and zero group velocity modes in tunable magneto-granular phononic crystals
We report on the design and operation of a 1D magneto-granular phononic
crystal composed of a chain of steel spherical beads on top of permanent
magnets. The magnetic field of the permanent magnets induces forces in the
granular structure. By changing its strength, we can tune the dynamic response
of the granular structure. We present experimental results with evidence of
coupled transversal-rotational modes, and zero group velocities modes. These
observations are well supported by a proposed model taking into account the
mechanical coupling between the beads and the magnets by linear stiffnesses and
including all degrees of freedom in translations and rotations
Principles and experience of justification of ecological representativeness of Emerald network potential sites
The article presents the results of the multi-method research to provide justification of Emerald network potential site, which meets the requirements of environmental representativeness. Flora and vegetation of the core natural habitat, species composition and prevalence of the species of European importance and from the Red books of the country and region, as well as the habitats of European importance were systematized with the use of methods of botanical and geobotanical studie
Photocurrent in nanostructures with asymmetric antidots
The steady current induced by electromagnetic field in a 2D system with
asymmetric scatterers is studied. The scatterers are assumed to be oriented
cuts with one diffusive and another specular sides. Besides, the existence of
isotropic impurity scatterers is assumed. This simple model simulates the
lattice of half-disk which have been studied numerically recently. The model
allows the exact solution in the framework of the kinetic equation. The static
current response in the second order of electric field is obtained. The
photogalvanic tensor contains both responses to linear and circular
polarization of electromagnetic field. The model possesses non-analyticity with
regards to the rate of impurity scattering.Comment: 9 pages, 6 figure
Acoustic Probing of the Jamming Transition in an Unconsolidated Granular Medium
Experiments with acoustic waves guided along the mechanically free surface of
an unconsolidated granular packed structure provide information on the
elasticity of granular media at very low pressures that are naturally
controlled by the gravitational acceleration and the depth beneath the surface.
Comparison of the determined dispersion relations for guided surface acoustic
modes with a theoretical model reveals the dependencies of the elastic moduli
of the granular medium on pressure. The experiments confirm recent theoretical
predictions that relaxation of the disordered granular packing through
non-affine motion leads to a peculiar scaling of shear rigidity with pressure
near the jamming transition corresponding to zero pressure. Unexpectedly, and
in disagreement with the most of the available theories, the bulk modulus
depends on pressure in a very similar way to the shear modulus
Two-dimensional effective action for matter fields coupled to the dilaton
We revise the calculation of the one-loop effective action for scalar and
spinor fields coupled to the dilaton in two dimensions. Applying the method of
covariant perturbation theory for the heat kernel we derive the effective
action in an explicitly covariant form that produces both the conformally
invariant and the conformally anomalous terms.For scalar fields the conformally
invariant part of the action is nonlocal. The obtained effective action is
proved to be infrared finite. We also compute the one-loop effective action for
scalar fields at finite temperature.Comment: LaTeX, 25 page
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