1,423 research outputs found
Exciton polaritons in two-dimensional photonic crystals
Experimental evidence of strong coupling between excitons confined in a
quantum well and the photonic modes of a two-dimensional dielectric lattice is
reported. Both resonant scattering and photoluminescence spectra at low
temperature show the anticrossing of the polariton branches, fingerprint of
strong coupling regime. The experiments are successfully interpreted in terms
of a quantum theory of exciton-photon coupling in the investigated structure.
These results show that the polariton dispersion can be tailored by properly
varying the photonic crystal lattice parameter, which opens the possibility to
obtain the generation of entangled photon pairs through polariton stimulated
scattering.Comment: 5 pages, 4 figure
ALMA imaging of SDP.81 - I. A pixelated reconstruction of the far-infrared continuum emission
We present a sub-50 pc-scale analysis of the gravitational lens system SDP.81
at redshift 3.042 using Atacama Large Millimetre/submillimetre Array (ALMA)
science verification data. We model both the mass distribution of the
gravitational lensing galaxy and the pixelated surface brightness distribution
of the background source using a novel Bayesian technique that fits the data
directly in visibility space. We find the 1 and 1.3 mm dust emission to be
magnified by a factor of u_tot = 17.6+/-0.4, giving an intrinsic total
star-formation rate of 315+/-60 M_sol/yr and a dust mass of 6.4+/-1.5*10^8
M_sol. The reconstructed dust emission is found to be non-uniform, but composed
of multiple regions that are heated by both diffuse and strongly clumped
star-formation. The highest surface brightness region is a ~1.9*0.7 kpc
disk-like structure, whose small extent is consistent with a potential
size-bias in gravitationally lensed starbursts. Although surrounded by extended
star formation, with a density of 20-30+/-10 M_sol/yr/kpc^2, the disk contains
three compact regions with densities that peak between 120-190+/-20
M_sol/yr/kpc^2. Such star-formation rate densities are below what is expected
for Eddington-limited star-formation by a radiation pressure supported
starburst. There is also a tentative variation in the spectral slope of the
different star-forming regions, which is likely due to a change in the dust
temperature and/or opacity across the source.Comment: MNRAS accepted 2015 April 1
ALMA imaging of SDP.81 - II. A pixelated reconstruction of the CO emission lines
We present a sub-100 pc-scale analysis of the CO molecular gas emission and
kinematics of the gravitational lens system SDP.81 at redshift 3.042 using
Atacama Large Millimetre/submillimetre Array (ALMA) science verification data
and a visibility-plane lens reconstruction technique. We find clear evidence
for an excitation dependent structure in the unlensed molecular gas
distribution, with emission in CO (5-4) being significantly more diffuse and
structured than in CO (8-7). The intrinsic line luminosity ratio is r_8-7/5-4 =
0.30 +/- 0.04, which is consistent with other low-excitation starbursts at z ~
3. An analysis of the velocity fields shows evidence for a star-forming disk
with multiple velocity components that is consistent with a
merger/post-coalescence merger scenario, and a dynamical mass of M(< 1.56 kpc)
= 1.6 +/- 0.6 x 10^10 M_sol . Source reconstructions from ALMA and the Hubble
Space Telescope show that the stellar component is offset from the molecular
gas and dust components. Together with Karl G. Jansky Very Large Array CO (1-0)
data, they provide corroborative evidence for a complex ~2 kpc-scale starburst
that is embedded within a larger ~15 kpc structure.Comment: MNRAS accepted, 6th July 201
Hydrogen mean force and anharmonicity in polycrystalline and amorphous ice
The hydrogen mean force from experimental neutron Compton profiles is derived
using deep inelastic neutron scattering on amorphous and polycrystalline ice.
The formalism of mean force is extended to probe its sensitivity to
anharmonicity in the hydrogen-nucleus effective potential. The shape of the
mean force for amorphous and polycrystalline ice is primarily determined by the
anisotropy of the underlying quasi-harmonic effective potential. The data from
amorphous ice show an additional curvature reflecting the more pronounced
anharmonicity of the effective potential with respect to that of ice Ih.Comment: 12 pages, 7 figures, original researc
Experimental perspectives of mineral dissolution and precipitation due to carbon dioxide-water-rock interactions
A Discussion on a Code Sound Reading System: a Case Study of I Can Read Greenville Language Center
Article described the code sound reading system applied in I Can Read (ICR) Greenville language center. The research was done qualitatively through the observation of teaching and learning process in three different classes of ICR 1 level at the center. A pre-test and post-test for reading were taken from Book 2 of ICR 1. Participants were three classes with three different teachers having different working experiences. The results of the research were: (1) the use of code sounds in reading was useful to improve students\u27 reading skill which was shown by the increasing of correctly pronounced code sounds; (2) the students\u27 reading skill and reading comprehension had improved, regardless the teachers\u27 teaching style. In conclusion, a code sound reading system is successful in helping students to improve their reading skill and reading comprehension, regardless the teachers\u27 teaching style
Simulations of Galactic Cosmic Rays Impacts on the Herschel/PACS Photoconductor Arrays with Geant4 Code
We present results of simulations performed with the Geant4 software code of
the effects of Galactic Cosmic Ray impacts on the photoconductor arrays of the
PACS instrument. This instrument is part of the ESA-Herschel payload, which
will be launched in late 2007 and will operate at the Lagrangian L2 point of
the Sun-Earth system. Both the Satellite plus the cryostat (the shield) and the
detector act as source of secondary events, affecting the detector performance.
Secondary event rates originated within the detector and from the shield are of
comparable intensity. The impacts deposit energy on each photoconductor pixel
but do not affect the behaviour of nearby pixels. These latter are hit with a
probability always lower than 7%. The energy deposited produces a spike which
can be hundreds times larger than the noise. We then compare our simulations
with proton irradiation tests carried out for one of the detector modules and
follow the detector behaviour under 'real' conditions.Comment: paper submitted to Experimental Astronomy in March 200
Effective t-J Hamiltonian for the Copper Oxides
Starting from the Emery model, which is assumed to describe the copper oxygen
planes, and including direct oxygen hopping matrix elements, we have been able
to derive the effective t-J Hamiltonian for the copper orbitals using the
Linked Cluster Expansion Method up to fourth order in the hybridization matrix
element.Comment: (ps version of the dvi file, resubmitted because previous
uucompressed version was corrupted), 9 page
Far-infrared line spectra of active galaxies from the Herschel/PACS Spectrometer: the complete database
We present a coherent database of spectroscopic observations of far-IR
fine-structure lines from the Herschel/PACS archive for a sample of 170 local
AGN, plus a comparison sample of 20 starburst galaxies and 43 dwarf galaxies.
Published Spitzer/IRS and Herschel/SPIRE line fluxes are included to extend our
database to the full 10-600 spectral range. The observations are
compared to a set of CLOUDY photoionisation models to estimate the above
physical quantities through different diagnostic diagrams. We confirm the
presence of a stratification of gas density in the emission regions of the
galaxies, which increases with the ionisation potential of the emission lines.
The new [OIV]25.9/[OIII]88 vs [NeIII]15.6/[NeII]12.8 diagram is proposed as the best diagnostic to separate: AGN activity
from any kind of star formation; and low-metallicity dwarf galaxies from
starburst galaxies. Current stellar atmosphere models fail to reproduce the
observed [OIV]25.9/[OIII]88 ratios, which are much higher when
compared to the predicted values. Finally, the ([NeIII]15.6 +
[NeII]12.8)/([SIV]10.5 + [SIII]18.7) ratio is proposed as
a promising metallicity tracer to be used in obscured objects, where optical
lines fail to accurately measure the metallicity. The diagnostic power of mid-
to far-infrared spectroscopy shown here for local galaxies will be of crucial
importance to study galaxy evolution during the dust-obscured phase at the peak
of the star formation and black-hole accretion activity (). This
study will be addressed by future deep spectroscopic surveys with present and
forthcoming facilities such as JWST, ALMA, and SPICA.Comment: Accepted for publication in the ApJ
Magnetooptical effects in quantum wells irradiated with light pulses
The method of detection and investigation of the magnetopolaron effect in the
semiconductor quantum wells (QW) in a strong magnetic field, based on pulse
light irradiation and measuring the reflected and transmitted pulses, has been
proposed. It has been shown that a beating amplitude on the frequencies,
corresponding to the magnetopolaron energy level splitting, depends strongly
from the exciting pulse width. The existence of the time points of the total
reflection and total transparency has been predicted. The high orders of the
perturbation theory on electron-electromagnetic field interaction have been
taken into account.Comment: 5 pages, 5 figures with captions, corrected typos, figures are
reedeted to improve their quality in accordance with the Referee requirement;
Phys. Rev. B, Brief Reports, submitted for publicatio
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