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

Fine structure of the age-chromospheric activity relation in solar-type stars I: The Ca II infrared triplet: Absolute flux calibration

Strong spectral lines are useful indicators of stellar chromospheric activity. They are physically linked to the convection efficiency, differential rotation, and angular momentum evolution and are a potential indicator of age. However, for ages > 2 Gyr, the age-activity relationship remains poorly constrained thus hampering its full application. The Ca II infrared triplet (IRT lines) has been poorly studied compared to classical chromospheric indicators. We report in this paper absolute chromospheric fluxes in the three Ca II IRT lines, based on a new calibration tied to up-to-date model atmospheres. We obtain the Ca II IRT absolute fluxes for 113 FGK stars from high signal-to-noise ratio and high-resolution spectra covering an extensive domain of chromospheric activity levels. We perform an absolute continuum flux calibration for the Ca II IRT lines anchored in atmospheric models calculated as an explicit function of effective temperatures, metallicity, and gravities avoiding the degeneracy present in photometric continuum calibrations based solely on color indices. The internal uncertainties achieved for continuum absolute flux calculations are 2\% of the solar chromospheric flux, one order of magnitude lower than photometric calibrations. We gauge the impact of observational errors on the final chromospheric fluxes due to the absolute continuum flux calibration and find that $T_{\rm eff}$ uncertainties are properly mitigated by the photospheric correction leaving [Fe/H] as the dominating factor in the chromospheric flux uncertainty. Across the FGK spectral types, the Ca II IRT lines are sensitive to chromospheric activity. The reduced internal uncertainties reported here enable us to build a new chromospheric absolute flux scale and explore the age-activity relation from the active regime down to very low activity levels and a wide range of $T_{\rm eff}$, mass, [Fe/H], and age.Comment: 12 pages, 12 figures, 6 tables, Accepted for publication on A&A. Abstract edited to comply with arXiv standards regarding the number of character

The detection of viable vegetative cells of Bacillus sporothermodurans using propidium monoazide with semi-nested PCR

AbstractBacillus sporothermodurans produces highly heat-resistant spores that can survive ultra-high temperature (UHT) treatment in milk. Therefore, we developed a rapid, specific and sensitive semi-nested touchdown PCR assay combined with propidium monoazide (PMA) treatment for the detection of viable B. sporothermodurans vegetative cells. The semi-nested touchdown PCR alone proved to be specific for B. sporothermodurans, and the achieved detection limit was 4 CFU/mL from bacterial culture and artificially contaminated UHT milk. This method combined with PMA treatment was shown to amplify DNA specifically from viable cells and presented a detection limit of 102 CFU/mL in UHT milk. The developed PMA-PCR assay shows applicability for the specific detection of viable cells of B. sporothermodurans from UHT milk. This method is of special significance for applications in the food industry by reducing the time required for the analysis of milk and dairy products for the presence of this microorganism

Improving the vacuum-infusion process to manufacture high quality structural composite for the aeronautic market

In last years, the vacuum-infusion processing method is being replacing successfully autoclave technologies to manufacture advanced composite structures, namely, the carbon-fibre reinforced plastic (CFRP) ones, for aeronautical and aerospace applications. The high investment associated with autoclave “prepreg” manufacturing has prompted interest in the use of alternative vacuum-infusion technologies that proven to be much more cost-effective processing methods. The present work presents, describes and discusses improvements and developments made on an existing vacuum-infusion process to obtained high quality and reliable CRFP structural components to the aircraft industry. The first aim is to use the developed technology to produce wing elevators for an unmanned aerial vehicle (UAV), commonly known as “drone”, expected to be used in firefighting and policing civilian operations. An additional heating stage was enhanced to the initial standard vacuum process to increase the quality and reliability of the final manufactured composite parts, namely in terms of void reduction and control of fibre content and orientation. A prototype part was manufactured by using this improved vacuum-infusion process to be tested and validate the developed technology. This paper will present and discuss the results obtained in the manufacturing and characterization tests made on the produced prototypes.FCT projeto UID/CTM/50025/201

Análise de dois métodos de quantificação de DNA em amostras de diferentes populações de açaizeiro.

Em reações PCR faz-se necessário trabalhar com DNA de boa qualidade. E conhecer a eficiência de cada processo na análise de DNA, tais como a extração e a quantificação do DNA. A quantificação envolve a estimativa da concentração do DNA obtida, que depende do tipo e quantidade de amostra disponível. Dentre os métodos disponíveis para quantificação tem-se a eletroforese em gel de agarose, que permite a resolução de ácidos nuciéicos, um método comparativo, e a utilização do fluorímetro, um equipamento que trabalha com alterações nas caracteristicas de f1uorescência na presença de DNA, um método quantitativo. O objetivo deste trabalho foi analisar esses dois métodos na quantificação de amostras de DNA de açaizeiro verificando a eficácia e a praticidade. Foram extraídos DNA's de folíolos de 87 matrizes de açaizeiro de três populações. A concentração do DNA genômico foi estimada de duas formas: em gel de agarose a 1,0% utilizando a comparação do DNA total com três concentrações do DNA lambda (50, 100 e 200 ng/ IJL) e em fluorímetro, marca Hoefer DyNA Quant 200, por meio da média de duas ou três leituras, conforme a variação de 10% para mais ou para menos da amostra quantificada. O método mais eficaz foi escolhido através de estatística simples, envolvendo média, valores mínimos e máximos e coeficiente de variação para cada população e para amostra total. A quantificação na agarose detectou 87,76; 64,4 e 61,03 ng para as populações de Breves, São Sebastião da Boa Vista e BRS- Pa. A variação ficou entre O e 200ng. No f1uorímetro as quantificações foram 82,06; 82,24 e 49,85 ng para as populações de Breves, São Sebastião da Boa Vista e BRS-Pa. Ficando a variação entre 8 e 335,5ng. A análise desses métodos mostra que os dois métodos são considerados eficientes, sendo a agarose o método mas prático

Finite-size scaling considerations on the ground state microcanonical temperature in entropic sampling simulations

In this work we discuss the behavior of the microcanonical temperature $\frac{\partial S(E)}{\partial E}$ obtained by means of numerical entropic sampling studies. It is observed that in almost all cases the slope of the logarithm of the density of states $S(E)$ is not infinite in the ground state, since as expected it should be directly related to the inverse temperature $\frac{1}{T}$. Here we show that these finite slopes are in fact due to finite-size effects and we propose an analytic expression $a\ln(bL)$ for the behavior of $\frac{\varDelta S}{\varDelta E}$ when $L\rightarrow\infty$. To test this idea we use three distinct two-dimensional square lattice models presenting second-order phase transitions. We calculated by exact means the parameters $a$ and $b$ for the two-states Ising model and for the $q=3$ and $4$ states Potts model and compared with the results obtained by entropic sampling simulations. We found an excellent agreement between exact and numerical values. We argue that this new set of parameters $a$ and $b$ represents an interesting novel issue of investigation in entropic sampling studies for different models

Analytical results for long time behavior in anomalous diffusion

We investigate through a Generalized Langevin formalism the phenomenon of anomalous diffusion for asymptotic times, and we generalized the concept of the diffusion exponent. A method is proposed to obtain the diffusion coefficient analytically through the introduction of a time scaling factor $\lambda$. We obtain as well an exact expression for $\lambda$ for all kinds of diffusion. Moreover, we show that $\lambda$ is a universal parameter determined by the diffusion exponent. The results are then compared with numerical calculations and very good agreement is observed. The method is general and may be applied to many types of stochastic problem