4,972 research outputs found
Tunneling effects on impurity spectral function in coupled asymmetric quantum wires
The impurity spectral function is studied in coupled double quantum wires at
finite temperatures. Simple anisotropy in the confinement direction of the
wires leads to finite non-diagonal elements of the impurity spectral function
matrix. These non-diagonal elements are responsible for tunneling effects and
result in pronounced extra peak in the impurity spectral function up to
temperatures as high as 20 K.Comment: Accepted in Phys. Rev.
Shape acquisition of rotating objects based on Laser Line Scanning
The present work proposes a methodology for 3D shape acquisition of objects through rotation-based Laser Line Scanning. This
enables the acquisition of an object's 3D shape from multiple views,
which leads to a more complete and accurate model
Parasitic infections in two Benthopelagic fish from Amazon: the Arowana Osteoglossum bicirrhosum (Osteoglossidae) and Oscar Astronotus ocellatus (Cichlidae).
The parasitic fauna of wild Osteoglossum bicirrhosum from central Amazon (Brazil) and wild Astronotus ocellatus from eastern Amazon (Brazil) as well as the host-parasite relationship were evaluated. 87.5% O. bicirrhosum were parasitized only by Gonocleithrum aruanae (Monogenoidea). 92.8% A. ocellatus were parasitized by Ichthyophthirius multifiliis (Ciliophora), Gussevia asota (Monogenoidea), Posthodiplostomum sp. metacercariae (Diplostomidae), Procamallanus inopinatus adults and Contracaecum larvae (Anisakidae). High levels of infection by G. aruanae occurred in O. bicirrhosum while in A. ocellatus the highest levels of infection were caused by helminthes ectoparasites such as G. asota, and endoparasites such as Posthodiplostomum sp., P. inopinatus and Contracaecum sp. There was a significant (p>0.05) negative correlation between the intensity of helminthes species and the relative condition factor (Kn) from A. ocellatus, indicating that these parasites are pathogenic for hosts. The parasite fauna of O. bicirrhosum was scarce, while the parasites for A. ocellatus were mainly helminthes species, including adults and larval forms. Such differences on parasites fauna of both omnivore hosts may due to their history life as well as environmental and biological factors
Protozoários e metazoários parasitos do cardinal Paracheirodon axelrodi Schultz, 1956 (Characidae), peixe ornamental proveniente de exportador de Manaus, Estado do Amazonas, Brasil.
Os estudos sobre a parasitofauna de peixes ornamentais cultivados são de grande relevância para o conhecimento das espécies de parasitos, permitindo interferência em sua proliferação para evitar epizootias e, consequentemente, perdas econômicas na criação. O presente estudo investigou a prevalência e intensidade de parasitos protozoários e metazoários em cardinal Paracheirodon axelrodi (N = 89), mantidos em tanques de um exportador de Manaus, Estado do Amazonas, Brasil. Dos espécimes de P. axelrodi necropsiados, 65,2% (N = 58) estavam parasitados pelos Protozoa Piscinoodiniutn pillulare (3,4%) e Ichthyophthirius mult!filiis (7,9%), Monogenoidea Gyrodactylus sp. (42,7%), Nematoda Procamallanus sp. (23,6%) e Trematoda (1,1%). Gyrodactylus sp. e Procamallanus sp., porém, foram os parasitos de maior prevalência e intensidade. Apesar da elevada prevalência de parasitismo em P. axelrodi durante a sua permanência no exportador, a intensidade de protozoários e metazoários foi baixa pelo manejo profilático nos tanques. Os resultados demonstram que os cuidados com tratamento e profilaxia são de extrema importância na aquicultura de peixes ornamentais
Carrier relaxation due to electron-electron interaction in coupled double quantum well structures
We calculate the electron-electron interaction induced energy-dependent
inelastic carrier relaxation rate in doped semiconductor coupled double quantum
well nanostructures within the two subband approximation at zero temperature.
In particular, we calculate, using many-body theory, the imaginary part of the
full self-energy matrix by expanding in the dynamically RPA screened Coulomb
interaction, obtaining the intrasubband and intersubband electron relaxation
rates in the ground and excited subbands as a function of electron energy. We
separate out the single particle and the collective excitation contributions,
and comment on the effects of structural asymmetry in the quantum well on the
relaxation rate. Effects of dynamical screening and Fermi statistics are
automatically included in our many body formalism rather than being
incorporated in an ad-hoc manner as one must do in the Boltzman theory.Comment: 26 pages, 5 figure
The Expanding Nebular Remnant of the Recurrent Nova RS Ophiuchi (2006): II. Modeling of Combined Hubble Space Telescope Imaging and Ground-based Spectroscopy
We report Hubble Space Telescope imaging, obtained 155 and 449 days after the
2006 outburst of the recurrent nova RS Ophiuchi, together with ground-based
spectroscopic observations, obtained from the Observatorio Astron\'omico
Nacional en San Pedro M\'artir, Baja California, M\'exico and at the
Observatorio Astrof\'isico Guillermo Haro, at Cananea, Sonora, M\'exico. The
observations at the first epoch were used as inputs to model the geometry and
kinematic structure of the evolving RS Oph nebular remnant. We find that the
modeled remnant comprises two distinct co-aligned bipolar components; a
low-velocity, high-density innermost (hour glass) region and a more extended,
high-velocity (dumbbell) structure. This overall structure is in agreement with
that deduced from radio observations and optical interferometry at earlier
epochs. We find that the asymmetry observed in the west lobe is an instrumental
effect caused by the profile of the HST filter and hence demonstrate that this
lobe is approaching the observer. We then conclude that the system has an
inclination to the line of sight of 39 degrees. This is in
agreement with the inclination of the binary orbit and lends support to the
proposal that this morphology is due to the interaction of the outburst ejecta
with either an accretion disk around the central white dwarf and/or a
pre-existing red giant wind that is significantly denser in the equatorial
regions of the binary than at the poles. The second epoch HST observation was
also modeled. However, as no spectra were taken at this epoch, it is more
difficult to constrain any model. Nevertheless, we demonstrate that between the
two HST epochs the outer dumbbell structure seems to have expanded linearly.Comment: 33 pages, 9 figures, 1 table, accepted for publication in Ap
Criticality in strongly correlated fluids
In this brief review I will discuss criticality in strongly correlated
fluids. Unlike simple fluids, molecules of which interact through short ranged
isotropic potential, particles of strongly correlated fluids usually interact
through long ranged forces of Coulomb or dipolar form. While for simple fluids
mechanism of phase separation into liquid and gas was elucidated by van der
Waals more than a century ago, the universality class of strongly correlated
fluids, or in some cases even existence of liquid-gas phase separation remains
uncertain.Comment: Proceedings of Scaling Concepts and Complex Systems, Merida, Mexic
River sediment yield classification using remote sensing imagery
The monitoring of water quality is essencial to the mankind, since we strongly depend on such resource for living and working. The presence of sediments in rivers usually indicates changes in the land use, which can affect the quality of water and the lifetime of hydroelectric power plants. In countries like Brazil, where more than 70% of the energy comes from the water, it is crucial to keep monitoring the sediment yield in rivers and lakes. In this work, we evaluate some stateof- the-art supervised pattern recognition techniques to classify different levels of sediments in Brazilian rivers using satellite images, as well as we make available an annotated dataset composed of two images to foster the related research
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