Kinetic modelling of epitaxial film growth with up- and downward step barriers

The formation of three-dimensional structures during the epitaxial growth of films is associated to the reflection of diffusing particles in descending terraces due to the presence of the so-called Ehrlich-Schwoebel (ES) barrier. We generalize this concept in a solid-on-solid growth model, in which a barrier dependent on the particle coordination (number of lateral bonds) exists whenever the particle performs an interlayer diffusion. The rules do not distinguish explicitly if the particle is executing a descending or an ascending interlayer diffusion. We show that the usual model, with a step barrier in descending steps, produces spurious, columnar, and highly unstable morphologies if the growth temperature is varied in a usual range of mound formation experiments. Our model generates well-behaved mounded morphologies for the same ES barriers that produce anomalous morphologies in the standard model. Moreover, mounds are also obtained when the step barrier has an equal value for all particles independently if they are free or bonded. Kinetic roughening is observed at long times, when the surface roughness w and the characteristic length $\xi$ scale as $w ~ t^\beta$ and $\xi ~ t^\zeta$ where $\beta \approx 0.31$ and $\zeta \approx 0.22$, independently of the growth temperature.Comment: 15 pages, 7 figure

A redução de antihelmínticos no controle da verminose em caprinos e ovinos.

bitstream/item/32417/1/Reducao.pd

Magnetic fields around evolved stars: further observations of H2_2O maser polarization

We aim to detect the magnetic field and infer its properties around four AGB stars using H$_2$O maser observations. The sample we observed consists of the following sources: the semi-regular variable RT Vir and the Mira variables AP Lyn, IK Tau, and IRC+60370. We observed the 6$_{1,6}-5_{2,3}$ H$_2$O maser rotational transition, in full-polarization mode, to determine its linear and circular polarization. Based on the Zeeman effect, one can infer the properties of the magnetic field from the maser polarization analysis. We detected a total of 238 maser features, in three of the four observed sources. No masers were found toward AP Lyn. The observed masers are all located between 2.4 and 53.0 AU from the stars. Linear and circular polarization was found in 18 and 11 maser features, respectively. We more than doubled the number of AGB stars in which magnetic field has been detected from H$_2$O maser polarization, as our results confirm the presence of fields around IK Tau, RT Vir and IRC+60370. The strength of the field along the line of sight is found to be between 47 and 331 mG in the H$_2$O maser region. Extrapolating this result to the surface of the stars, assuming a toroidal field ($\propto$ r$^{-1}$), we find magnetic fields of 0.3-6.9 G on the stellar surfaces. If, instead of a toroidal field, we assume a poloidal field ($\propto$ r$^{-2}$), then the extrapolated magnetic field strength on the stellar surfaces are in the range between 2.2 and $\sim$115 G. Finally, if a dipole field ($\propto$ r$^{-3}$) is assumed, the field strength on the surface of the star is found to be between 15.8 and $\sim$1945 G. The magnetic energy of our sources is higher than the thermal and kinetic energy in the H$_2$O maser region of this class of objects. This leads us to conclude that, indeed, magnetic fields probably play an important role in shaping the outflows of evolved stars. (abridged)Comment: 15 pages, 5 figures, 7 tables. Accepted for publication in A&

Typology and evolution of the new mineralogy developed at the mine waste dump of Valdarcas (Vila Nova de Cerveira - N Portugal) - Environmental Implications

[Abstract] The abandoned waste dump of Valdarcas tungsten skarn deposit — Vila Nova de Cerveira, N Portugal, represents a key site, appropriate to study the environmental problems related to deactivated sulfide tails. The tungsten mineralization which occurs in coexistence with metallic sulfide minerals, calcium silicates and carbonates, confers to this deposit special characteristics. The water-mineral interactions at the waste dump surface, leads to the generation of acid mine waters (AMD) with high content of metals and sulfate (ASW), related to the sulfide minerals alteration. Consequently occurs the contamination of the Coura river system Simultaneously the alteration of calcium silicates and carbonates produces neutralization reactions, and the development of a new mineralogy - soluble salts, iron crusts and clay minerals. The new paragenesis reflects the occurrence of wet-dry cycles, related to the seasonal variations of rainfall. These geochemical trends and their role in the process evolution of the waste dump surface to the stabilization are the main subject of this work.The soluble salts, iron crusts and the clay minerals have different capacities and mechanisms to fixate the chemical potential associated to the AMD/ASW. The instability of the salt minerals leads only to a temporary fixation of the contaminant elements. On the other hand, the crusts are capable of fixate efficiently these elements, specially the iron oxides, furthermore, they isolate the reactive minerals from the weathering agents. Consequently they limit the aquatic contamination, the dispersion area of the environmental impact and contribute to the chemical stabilization of the waste dum

A blessed endoscopy

info:eu-repo/semantics/publishedVersio

Living bacteria rheology: population growth, aggregation patterns and cooperative behaviour under different shear flows

The activity of growing living bacteria was investigated using real-time and in situ rheology -- in stationary and oscillatory shear. Two different strains of the human pathogen Staphylococcus aureus -- strain COL and its isogenic cell wall autolysis mutant -- were considered in this work. For low bacteria density, strain COL forms small clusters, while the mutant, presenting deficient cell separation, forms irregular larger aggregates. In the early stages of growth, when subjected to a stationary shear, the viscosity of both strains increases with the population of cells. As the bacteria reach the exponential phase of growth, the viscosity of the two strains follow different and rich behaviours, with no counterpart in the optical density or in the population's colony forming units measurements. While the viscosity of strain COL keeps increasing during the exponential phase and returns close to its initial value for the late phase of growth, where the population stabilizes, the viscosity of the mutant strain decreases steeply, still in the exponential phase, remains constant for some time and increases again, reaching a constant plateau at a maximum value for the late phase of growth. These complex viscoelastic behaviours, which were observed to be shear stress dependent, are a consequence of two coupled effects: the cell density continuous increase and its changing interacting properties. The viscous and elastic moduli of strain COL, obtained with oscillatory shear, exhibit power-law behaviours whose exponent are dependent on the bacteria growth stage. The viscous and elastic moduli of the mutant have complex behaviours, emerging from the different relaxation times that are associated with the large molecules of the medium and the self-organized structures of bacteria. These behaviours reflect nevertheless the bacteria growth stage.Comment: 9 pages, 10 figure

A granular cell tumor: an unusual colon polyp

We read with interest the article by Sevilla Ribota et al1 that described an unexpected finding of a granular cell tumour (GCT) of the rectum, which was removed by band ligation-assisted mucosectomy. We present a similar case of a GCT of the cecum, which was resected using a different endoscopic procedure.info:eu-repo/semantics/publishedVersio

Chagas disease reactivation in a heart transplant patient infected by domestic Trypanosoma cruzi discrete typing unit I (TcIDOM)

Background Trypanosoma cruzi, causative agent of Chagas disease, displays high intraspecific genetic diversity: six genetic lineages or discrete typing units (DTUs) are currently recognized, termed TcI through TcVI. Each DTU presents a particular distribution pattern across the Americas, and is loosely associated with different transmission cycles and hosts. Several DTUs are known to circulate in Central America. It has been previously suggested that TcI infection is benign and does not lead to chronic chagasic cardiomyopathy (CCC). Findings In this study, we genotyped T. cruzi parasites circulating in the blood and from explanted cardiac tissue of an El Salvadorian patient who developed reactivation Chagas disease while on immunosuppressive medications after undergoing heart transplant in the U.S. as treatment for end-stage CCC. Parasite typing was performed through molecular methods (restriction fragment length polymorphism of polymerase reaction chain amplified products, microsatellite typing, maxicircle sequence typing and low-stringency single primer PCR, [LSSP-PCR]) as well as lineage-specific serology. We show that the parasites infecting the patient belong to the TcI DTU exclusively. Our data indicate that the parasites isolated from the patient belong to a genotype frequently associated with human infection throughout the Americas (TcI DOM ). Conclusions Our results constitute compelling evidence in support of TcI DTU’s ability to cause end-stage CCC and help dispel any residual bias that infection with this lineage is benign, pointing to the need for increased surveillance for dissemination of this genotype in endemic regions, the USA and globally