9,231 research outputs found
Deployable Tensegrity Reflectors for Small Satellites
Future small satellite missions require low-cost, precision reflector structures with large aperture that can be packaged in a small envelope. Existing furlable reflectors form a compact package which, although narrow, is too tall for many applications.An alternative approach is proposed, consisting of a deployable “tensegrity” prism forming a ring structure that deploys two identical cable nets (front and rear nets) interconnected by tension ties; the reflecting mesh is attached to the front net. The geometric configuration of the structure has been optimized to reduce the compression in the struts of the tensegrity prism. A small-scale physical model has been constructed to demonstrate the proposed concept. A preliminary design of a 3-m-diam, 10-GHz reflector with a focal-length-to-diameter ratio of 0.4 that can be packaged within an envelope of 0.1 x 0.2 x 0.8 m^3 is presented
Spaceability in Banach and quasi-Banach sequence spaces
Let be a Banach space. We prove that, for a large class of Banach or
quasi-Banach spaces of -valued sequences, the sets , where is any subset of , and
contain closed infinite-dimensional subspaces of (if
non-empty, of course). This result is applied in several particular cases and
it is also shown that the same technique can be used to improve a result on the
existence of spaces formed by norm-attaining linear operators.Comment: 9 page
Resonant modes in strain-induced graphene superlattices
We study tunneling across a strain-induced superlattice in graphene. In
studying the effect of applied strain on the low-lying Dirac-like spectrum,
both a shift of the Dirac points in reciprocal space, and a deformation of the
Dirac cones is explicitly considered. The latter corresponds to an anisotropic,
possibly non-uniform, Fermi velocity. Along with the modes with unit
transmission usually found across a single barrier, we analytically find
additional resonant modes when considering a periodic structure of several
strain-induced barriers. We also study the band-like spectrum of bound states,
as a function of conserved energy and transverse momentum. Such a
strain-induced superlattice may thus effectively work as a mode filter for
transport in graphene
Dynamical polarization of graphene under strain
We study the dependence of the plasmon dispersion relation of graphene on
applied uniaxial strain. Besides electron correlation at the RPA level, we also
include local field effects specific for the honeycomb lattice. As a
consequence of the two-band character of the electronic band structure, we find
two distinct plasmon branches. We recover the square-root behavior of the
low-energy branch, and find a nonmonotonic dependence of the strain-induced
modification of its stiffness, as a function of the wavevector orientation with
respect to applied strain.Comment: Phys. Rev. B, accepte
Ballistic transport properties across nonuniform strain barriers in graphene
We study the effect of uniaxial strain on the transmission and the
conductivity across a strain-induced barrier in graphene. At variance with
conventional studies, which consider sharp barriers, we consider a more
realistic, smooth barrier, characterized by a nonuniform, continuous strain
profile. Our results are instrumental towards a better understanding of the
transport properties in corrugated graphene.Comment: High Press. Res., to appea
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