1,515 research outputs found
Topologically protected elastic waves in phononic metamaterials
Topological states of quantum matter exhibit unique disorder-immune surface
states protected by underlying nontrivial topological invariants of the bulk.
Such immunity from backscattering makes topological surface or edge states
ideal carriers for both classical and quantum information. So far, topological
matters have been explored only in the realms of electronics and photonics,
with limited range of bulk properties and largely immutable materials. These
constraints thus impose severe performance trade-offs in experimentally
realizable topologically ordered states. In contrast, phononic metamaterials
not only provide access to a much wider range of material properties, but also
allow temporal modulation in the non-adiabatic regime. Here, from the
first-principles we demonstrate numerically the first phononic topological
metamaterial in an elastic-wave analogue of the quantum spin Hall effect. A
dual-scale phononic crystal slab is used to support two effective spins of
phonon over a broad bandwidth, and strong spin-orbit coupling is realized by
breaking spatial mirror symmetry. By preserving the spin polarization with an
external load or spatial symmetry, phononic edge states are shown to be robust
against scattering from discrete defects as well as disorders in the continuum.
Our system opens up the possibility of realizing topological materials for
phonons in both static and time-dependent regimes.Comment: 19 pages, 6 figure
Quantum Dynamics in a Time-dependent Hard-Wall Spherical Trap
Exact solution of the Schr\"{o}dinger equation is given for a particle inside
a hard sphere whose wall is moving with a constant velocity. Numerical
computations are presented for both contracting and expanding spheres. The
propagator is constructed and compared with the propagator of a particle in an
infinite square well with one wall in uniform motion.Comment: 6 pages, 4 figures, Accepted by Europhys. Let
Trapping and guiding surface plasmons in curved graphene landscapes
We demonstrate that graphene placed on top of structured substrates offers a
novel approach for trapping and guiding surface plasmons. A monolayer graphene
with a spatially varying curvature exhibits an effective trapping potential for
graphene plasmons near curved areas such as bumps, humps and wells. We derive
the governing equation for describing such localized channel plasmons guided by
curved graphene and validate our theory by the first-principle numerical
simulations. The proposed confinement mechanism enables plasmon guiding by the
regions of maximal curvature, and it offers a versatile platform for
manipulating light in planar landscapes. In addition, isolated deformations of
graphene such as bumps are shown to support localized surface modes and
resonances suggesting a new way to engineer plasmonic metasurfaces.Comment: 6 pages, 4 figure
Comparative investigation of methods for determining the lateral stiffness of coupled RC shears walls
In this study, the lateral stiffness of coupled RC shear walls is studied using the continuum method, equivalent frame and finite element methods. For this purpose, asix-story coupled shear walls with typical dimensions are considered and the lateral displacements of system are calculated under a variety of lateral loads such as: uniform, triangular distributed and concentrated loads, then the results are compared with together. The results show that under the rectangular and concentrated loadings, equivalent frame and continuum indicate more displacements compared finite element approach; therefore, these methods approximate less lateral stiffness for coupled RC shear walls. In addition, equivalent frame technique in most cases, except triangular loading, compared with continuous medium method determines more soft behavior for the structure.Keywords: 1-Coupled RC shear wall 2-Lateral stiffness 3-Equivalent frame 4-Continuum method 5-finite elemen
Erratum to: Mechano-Transduction Signals Derived from Self-Assembling Peptide Nanofibers Containing Long Motif of Laminin Influence Neurogenesis in In-Vitro and In-Vivo (Mol Neurobiol, 10.1007/s12035-016-9836-z)
Astroglial scaring and limited neurogenesis are two problematic issues in recovery of spinal cord injury (SCI). In the meantime, it seems that mechanical manipulations of scaffold to inhibit astroglial scarring and improve neurogenesis is worthy of value. In the present investigation, the effect of nanofiber (gel) concentration as a mechanical-stimuli in neurogenesis was investigated. Cell viability, membrane damage, and neural differentiation derived from endometrial stem cells encapsulated into self-assembling peptide nanofiber containing long motif of laminin were assessed. Then, two of their concentrations that had no significant difference of neural differentiation potential were selected for motor neuron investigation in SCI model of rat. MTT assay data showed that nanofibers at the concentrations of 0.125 and 0.25 % w/v induced higher and less cell viability than others, respectively, while cell viability derived from higher concentrations of 0.25 % w/v had ascending trend. Gene expression results showed that noggin along with laminin motif over-expressed TH gene and the absence of noggin or laminin motif did not in all concentrations. Bcl2 over-expression is concomitant with the decrease of nanofiber stiffness, NF+ cells increment, and astrogenesis inhibition and dark neuron decrement in SCI model. It seems that stiffness affects on Bcl2 gene expression and may through β-Catenin/Wnt signaling pathway and BMP-4 inhibition decreases astrogenesis and improves neurogenesis. However, stiffness had a significant effect on upregulation of GFAP+ cells and motor neuron recovery in in vivo. It might be concluded that eventually there is a critical definitive point concentration that at less or higher than of it changes cell behavior and neural differentiation through different molecular pathways
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