5,921 research outputs found
Diffusion-limited deposition of dipolar particles
Deposits of dipolar particles are investigated by means of extensive Monte
Carlo simulations. We found that the effect of the interactions is described by
an initial, non-universal, scaling regime characterized by orientationally
ordered deposits. In the dipolar regime, the order and geometry of the clusters
depend on the strength of the interactions and the magnetic properties are
tunable by controlling the growth conditions. At later stages, the growth is
dominated by thermal effects and the diffusion-limited universal regime
obtains, at finite temperatures. At low temperatures the crossover size
increases exponentially as T decreases and at T=0 only the dipolar regime is
observed.Comment: 5 pages, 4 figure
Structural and insulator-to-metal phase transition at 50 GPa in GdMnO3
We present a study of the effect of very high pressure on the orthorhombic
perovskite GdMnO3 by Raman spectroscopy and synchrotron x-ray diffraction up to
53.2 GPa. The experimental results yield a structural and insulator-to-metal
phase transition close to 50 GPa, from an orthorhombic to a metrically cubic
structure. The phase transition is of first order with a pressure hysteresis of
about 6 GPa. The observed behavior under very high pressure might well be a
general feature in rare-earth manganites.Comment: 4 pages, 3 figures and 2 table
Community ecology of parasites in four species of Corydoras (Callichthyidae), ornamental fish endemic to the eastern Amazon (Brazil).
This study compared the parasites community in Corydoras ephippifer, Corydoras melanistius, Corydoras amapaensis and Corydoras spilurus from tributaries from the Amapari River in State of Amapá (Brazil). A total of 151 fish of these four ornamental species were examined, of which 66.2% were parasitized by one or more species, and a total of 732 parasites were collected. Corydoras ephippifer (91.2%) and C. spilurus (98.8%) were the most parasitized hosts, while C. amapaensis (9.6%) was the least parasitized. A high similarity (approximately equals 75%) of parasite communities was found in the host species. Hosts were parasitized by Procamallanus (Spirocamallanus) inopinatus, Camallanus sp. and metacercariae of digeneans. The parasites had an aggregated dispersion pattern, but in C. ephippifer a random dispersion of P. (S.) inopinatus was found. The parasite community was characterized by a low species richness (1-4 parasites per host), low diversity and low evenness, and consisted mainly of endoparasites with high prevalence and low abundance. An important component in the determination of the helminth parasite community composition was the dominance of species that use these fish species as secondary intermediate or paratenic hosts. This was the first study on the parasite community for these four hosts. A checklist of parasite species in wild populations of Corydoras spp. from different localities was also reported here
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.
Desperfilhador por roto-compressão: novo equipamento para desperfilhar bananeiras.
O trabalho foi conduzido para desenvolver um novo equipamento para a eliminação de perfilhos, com redução de mão de obra e maior praticidade de uso
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
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
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