32,421 research outputs found
Surface acoustic wave modulation of single photon emission from GaN/InGaN nanowire quantum dots
On-chip quantum information processing requires controllable quantum light
sources that can be operated on-demand at high-speeds and with the possibility
of in-situ control of the photon emission wavelength and its optical
polarization properties. Here, we report on the dynamic control of the optical
emission from core-shell GaN/InGaN nanowire (NW) heterostructures using radio
frequency surface acoustic waves (SAWs). The SAWs are excited on the surface of
a piezoelectric lithium niobate crystal equipped with a SAW delay line onto
which the NWs were mechanically transferred. Luminescent quantum dot (QD)-like
exciton localization centers induced by compositional fluctuations within the
InGaN nanoshell were identified using stroboscopic micro-photoluminescence
(micro-PL) spectroscopy. They exhibit narrow and almost fully linearly
polarized emission lines in the micro-PL spectra and a pronounced anti-bunching
signature of single photon emission in the photon correlation experiments. When
the nanowire is perturbed by the propagating SAW, the embedded QD is
periodically strained and its excitonic transitions are modulated by the
acousto-mechanical coupling, giving rise to a spectral fine-tuning within a
~1.5 meV bandwidth at the acoustic frequency of ~330 MHz. This outcome can be
further combined with spectral detection filtering for temporal control of the
emitted photons. The effect of the SAW piezoelectric field on the QD charge
population and on the optical polarization degree is also observed. The
advantage of the acousto-optoelectric over other control schemes is that it
allows in-situ manipulation of the optical emission properties over a wide
frequency range (up to GHz frequencies).Comment: arXiv admin note: text overlap with arXiv:1902.0791
Experimental analysis of lateral impact on planar brittle material: spatial properties of the cracks
The breakup of glass and alumina plates due to planar impacts on one of their
lateral sides is studied. Particular attention is given to investigating the
spatial location of the cracks within the plates. Analysis based on a
phenomenological model suggests that bifurcations along the cracks' paths are
more likely to take place closer to the impact region than far away from it, i.
e., the bifurcation probability seems to lower as the perpendicular distance
from the impacted lateral in- creases. It is also found that many observables
are not sensitive to the plate material used in this work, as long as the
fragment multiplicities corresponding to the fragmentation of the plates are
similar. This gives support to the universal properties of the fragmentation
process reported in for- mer experiments. However, even under the just
mentioned circumstances, some spatial observables are capable of distinguishing
the material of which the plates are made and, therefore, it suggests that this
universality should be carefully investigated
Nonlinear viscosity and velocity distribution function in a simple longitudinal flow
A compressible flow characterized by a velocity field is
analyzed by means of the Boltzmann equation and the Bhatnagar-Gross-Krook
kinetic model. The sign of the control parameter (the longitudinal deformation
rate ) distinguishes between an expansion () and a condensation ()
phenomenon. The temperature is a decreasing function of time in the former
case, while it is an increasing function in the latter. The non-Newtonian
behavior of the gas is described by a dimensionless nonlinear viscosity
, that depends on the dimensionless longitudinal rate . The
Chapman-Enskog expansion of in powers of is seen to be only
asymptotic (except in the case of Maxwell molecules). The velocity distribution
function is also studied. At any value of , it exhibits an algebraic
high-velocity tail that is responsible for the divergence of velocity moments.
For sufficiently negative , moments of degree four and higher may diverge,
while for positive the divergence occurs in moments of degree equal to or
larger than eight.Comment: 18 pages (Revtex), including 5 figures (eps). Analysis of the heat
flux plus other minor changes added. Revised version accepted for publication
in PR
Aging to non-Newtonian hydrodynamics in a granular gas
The evolution to the steady state of a granular gas subject to simple shear
flow is analyzed by means of computer simulations. It is found that, regardless
of its initial preparation, the system reaches (after a transient period
lasting a few collisions per particle) a non-Newtonian (unsteady) hydrodynamic
regime, even at strong dissipation and for states where the time scale
associated with inelastic cooling is shorter than the one associated with the
irreversible fluxes. Comparison with a simplified rheological model shows a
good agreement.Comment: 6 pages, 4 figures; v2: improved version to be published in EP
Third and fourth degree collisional moments for inelastic Maxwell models
The third and fourth degree collisional moments for -dimensional inelastic
Maxwell models are exactly evaluated in terms of the velocity moments, with
explicit expressions for the associated eigenvalues and cross coefficients as
functions of the coefficient of normal restitution. The results are applied to
the analysis of the time evolution of the moments (scaled with the thermal
speed) in the free cooling problem. It is observed that the characteristic
relaxation time toward the homogeneous cooling state decreases as the
anisotropy of the corresponding moment increases. In particular, in contrast to
what happens in the one-dimensional case, all the anisotropic moments of degree
equal to or less than four vanish in the homogeneous cooling state for .Comment: 15 pages, 3 figures; v2: addition of two new reference
The AKARI 2.5-5 Micron Spectra of Luminous Infrared Galaxies in the Local Universe
We present AKARI 2.5-5um spectra of 145 local luminous infrared galaxies in
the Great Observatories All-sky LIRG Survey. In all of the spectra, we measure
the line fluxes and EQWs of the polycyclic aromatic hydrocarbon (PAH) at 3.3um
and the hydrogen recombination line Br-alpha, with apertures matched to the
slit sizes of the Spitzer spectrograph and with an aperture covering ~95% of
the total flux in the AKARI 2D spectra. The star formation rates (SFRs) derived
from Br-alpha measured in the latter aperture agree well with SFRs(LIR), when
the dust extinction correction is adopted based on the 9.7um absorption
feature. Together with the Spitzer spectra, we are able to compare the 3.3 and
6.2um PAH features, the two most commonly used near/mid-IR indicators of
starburst (SB) or active galactic nucleus (AGN) dominated galaxies. We find
that the 3.3 and 6.2um PAH EQWs do not follow a linear correlation and at least
1/3 of galaxies classified as AGN-dominated using 3.3um PAH are classified as
starbursts based on 6.2um PAH. These galaxies have a bluer continuum slope than
galaxies that are indicated to be SB-dominated by both PAH features. The bluer
continuum emission suggests that their continuum is dominated by stellar
emission rather than hot dust. We also find that the median Spitzer spectra of
these sources are remarkably similar to the pure SB-dominated sources indicated
by high PAH EQWs in both 3.3 and 6.2um. We propose a revised SB/AGN diagnostic
diagram using 2-5um data. We also use the AKARI and Spitzer spectra to examine
the performance of our new diagnostics and to estimate 3.3um PAH fluxes using
the JWST photometric bands in 0<z<5. Of the known PAH features and mid-IR high
ionization emission lines used as SB/AGN indicators, only the 3.3um PAH feature
is observable with JWST at z>3.5, because the rest of the features at longer
wavelengths fall outside the JWST wavelength coverage.Comment: 13 pages (without appendices), 12 figures, Accepted for publication
in A&
Agricultura irrigada no Ceará: recursos físicos, humanos e produção técnico-científica.
Agricultura Irrigada no Ceara; Recursos fisicos; Solos irrigaveis; Aerea implantada com irrigacao e culturas irrigadas; Aerea experimental com agricultura irrigada; Sistemas de irrigacao utilizados; Recursos humanos; Producao tecnico-cientifica por linha de pesquisa; Manejo de irrigacao; Desenvolvimento e avaliacao de equipamento e sistemas de irrigacao; Parametros basicos do solo para irrigacao e drenagem; Informatica na irrigacao e drenagem; Avaliacao socio-economica da irrigacao.bitstream/item/35433/1/Dc-025.pd
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