13,860 research outputs found
Two-dimensional heterogeneous photonic bandedge laser
We proposed and realized a two-dimensional (2D) photonic bandedge laser
surrounded by the photonic bandgap. The heterogeneous photonic crystal
structure consists of two triangular lattices of the same lattice constant with
different air hole radii. The photonic crystal laser was realized by
room-temperature optical pumping of air-bridge slabs of InGaAsP quantum wells
emitting at 1.55 micrometer. The lasing mode was identified from its spectral
positions and polarization directions. A low threshold incident pump power of
0.24mW was achieved. The measured characteristics of the photonic crystal
lasers closely agree with the results of real space and Fourier space
calculations based on the finite-difference time-domain method.Comment: 14 pages, 4 figure
Formation of Warped Disks by Galactic Fly-by Encounters. I. Stellar Disks
Warped disks are almost ubiquitous among spiral galaxies. Here we revisit and
test the `fly-by scenario' of warp formation, in which impulsive encounters
between galaxies are responsible for warped disks. Based on N-body simulations,
we investigate the morphological and kinematical evolution of the stellar
component of disks when galaxies undergo fly-by interactions with adjacent dark
matter halos. We find that the so-called `S'-shaped warps can be excited by
fly-bys and sustained for even up to a few billion years, and that this
scenario provides a cohesive explanation for several key observations. We show
that disk warp properties are governed primarily by the following three
parameters; (1) the impact parameter, i.e., the minimum distance between two
halos, (2) the mass ratio between two halos, and (3) the incident angle of the
fly-by perturber. The warp angle is tied up with all three parameters, yet the
warp lifetime is particularly sensitive to the incident angle of the perturber.
Interestingly, the modeled S-shaped warps are often non-symmetric depending on
the incident angle. We speculate that the puzzling U- and L-shaped warps are
geometrically superimposed S-types produced by successive fly-bys with
different incident angles, including multiple interactions with a satellite on
a highly elongated orbit.Comment: 16 pages, 13 figures, 3 tables. Accepted for publication in Ap
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