13,540 research outputs found
Isotropic photonic band gap and anisotropic structures in transmission spectra of two-dimensional 5-fold and 8-fold symmetric quasiperiodic photonic crystals
We measured and calculated transmission spectra of two-dimensional
quasiperiodic photonic crystals (PCs) based on a 5-fold (Penrose) or 8-fold
(octagonal) symmetric quasiperiodic pattern. The photonic crystal consisted of
dielectric cylindrical rods in air placed normal to the basal plane on vertices
of tiles composing the quasiperiodic pattern. An isotropic photonic band gap
(PBG) appeared in the TM mode, where electric fields were parallel to the rods,
even when the real part of a dielectric constant of the rod was as small as
2.4. An isotropic PBG-like dip was seen in tiny Penrose and octagonal PCs with
only 6 and 9 rods, respectively. These results indicate that local multiple
light scattering within the tiny PC plays an important role in the PBG
formation. Besides the isotropic PBG, we found dips depending on the incident
angle of the light. This is the first report of anisotropic structures clearly
observed in transmission spectra of quasiperiodic PCs. Based on rod-number and
rod-arrangement dependence, it is thought that the shapes and positions of the
anisotropic dips are determined by global multiple light scattering covering
the whole system. In contrast to the isotropic PBG due to local light
scattering, we could not find any PBGs due to global light scattering even
though we studied transmission spectra of a huge Penrose PC with 466 rods.Comment: One tex file for manuscript and 12 PNG files for figures consisting
of Fig.1a-d, 2,3, ...
How to construct a coordinate representation of a Hamiltonian operator on a torus
The dynamical system of a point particle constrained on a torus is quantized
\`a la Dirac with two kinds of coordinate systems respectively; the Cartesian
and toric coordinate systems. In the Cartesian coordinate system, it is
difficult to express momentum operators in coordinate representation owing to
the complication in structure of the commutation relations between canonical
variables. In the toric coordinate system, the commutation relations have a
simple form and their solutions in coordinate representation are easily
obtained with, furthermore, two quantum Hamiltonians turning up. A problem
comes out when the coordinate system is transformed, after quantization, from
the Cartesian to the toric coordinate system.Comment: 17 pages, LaTeX, 1 Figure included as a compressed uuencoded
postscript fil
Subaru Deep Survey VI. A Census of Lyman Break Galaxies at z=4 and 5 in the Subaru Deep Fields: Clustering Properties
We investigate the clustering properties of 2,600 Lyman Break Galaxies (LBGs)
at z=3.5-5.2 in two large blank fields, the Subaru Deep Field and the
Subaru/XMM Deep Field (600arcmin^2 each). The angular correlation functions of
these LBGs show a clear clustering at both z~4 and 5. The correlation lengths
are r_0= 4.1^{+0.2}_{-0.2} and 5.9^{+1.3}_{-1.7} h_{100}^{-1} Mpc (r_0=
5.1^{+1.0}_{-1.1} and 5.9^{+1.3}_{-1.7} h_{100}^{-1} Mpc) for all the detected
LBGs (for L>L* LBGs) at z~4 and 5, respectively. These correlation lengths
correspond to galaxy-dark matter biases of b_g= 2.9^{+0.1}_{-0.1} and
4.6^{+0.9}_{-1.2} (b_g=3.5^{+0.6}_{-0.7} and 4.6^{+0.9}_{-1.2}), for all the
detected LBGs (for L>L^* LBGs) at z~4 and 5, respectively. These results,
combined with estimates for z~3 LBGs in the literature, show that the
correlation length of L>L^* LBGs is almost constant, ~5 h_{100}^{-1} Mpc, over
z~3-5, while the bias monotonically increases with redshift at z>3. We also
find that for LBGs at z~4 the clustering amplitude increases with UV-continuum
luminosity and with the amount of dust extinction. We estimate the mass of dark
halos hosting various kinds of high-z galaxies including LBGs with the analytic
model given by Sheth & Tormen (1999). We find that the typical mass of dark
halos hosting L>L^* LBGs is about 1x10^{12} h_{70}^{-1}Msol over z~3-5, which
is comparable to that of the Milky Way Galaxy. A single dark halo with ~10^{12}
h_{70}^{-1} Msol is found to host 0.1-0.3 LBG on average but host about four
K-band selected galaxies.Comment: 33 pages, 12 figures, ApJ in press. Paper with high resolution
figures is available at
http://hikari.astron.s.u-tokyo.ac.jp/~ouchi/work/astroph/SDS_V_VI/SDS_VI.pdf
(PDF) (The abstract was reduced by the revision.
Ab initio studies of the spin-transfer torque in tunnel junctions
We calculate the spin-transfer torque in Fe/MgO/Fe tunnel junctions and
compare the results to those for all-metallic junctions. We show that the
spin-transfer torque is interfacial in the ferromagnetic layer to a greater
degree than in all-metallic junctions. This result originates in the half
metallic behavior of Fe for the states at the Brillouin zone center;
in contrast to all-metallic structures, dephasing does not play an important
role. We further show that it is possible to get a component of the torque that
is out of the plane of the magnetizations and that is linear in the bias.
However, observation of such a torque requires highly ideal samples. In samples
with typical interfacial roughness, the torque is similar to that in
all-metallic multilayers, although for different reasons.Comment: 5 pages, 4 figure
A Comparison of Weak Lensing Measurements From Ground- and Space-Based Facilities
We assess the relative merits of weak lensing surveys, using overlapping
imaging data from the ground-based Subaru telescope and the Hubble Space
Telescope (HST). Our tests complement similar studies undertaken with simulated
data. From observations of 230,000 matched objects in the 2 square degree
COSMOS field, we identify the limit at which faint galaxy shapes can be
reliably measured from the ground. Our ground-based shear catalog achieves
sub-percent calibration bias compared to high resolution space-based data, for
galaxies brighter than i'~24.5 and with half-light radii larger than 1.8". This
selection corresponds to a surface density of ~15 galaxies per sq arcmin
compared to ~71 per sq arcmin from space. On the other hand the survey speed of
current ground-based facilities is much faster than that of HST, although this
gain is mitigated by the increased depth of space-based imaging desirable for
tomographic (3D) analyses. As an independent experiment, we also reconstruct
the projected mass distribution in the COSMOS field using both data sets, and
compare the derived cluster catalogs with those from X-ray observations. The
ground-based catalog achieves a reasonable degree of completeness, with minimal
contamination and no detected bias, for massive clusters at redshifts
0.2<z<0.5. The space-based data provide improved precision and a greater
sensitivity to clusters of lower mass or at higher redshift.Comment: 12 pages, 8 figures, submitted to ApJ, Higher resolution figures
available at http://www.astro.caltech.edu/~mansi/GroundvsSpace.pd
Crystal-field-induced magnetostrictions in the spin reorientation process of NdFeB-type compounds
Volume expansion associated with the spin reorientation
process of NdFeB-type compounds has been investigated in terms of
simple crystalline-electric-field (CEF) model. In this system,
is shown to be a direct measure of second order CEF energy. Calculated
anomalies in associated with the first-order magnetization
process of NdFeB are presented, which well reproduced the
observations.Comment: 2 pages, 2 figures, to appear in J. Magn. Magn. Mate
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