Soil respiration, microbial respiration and mineralisation in soils of montane rainforests of Southern Ecuador: influence of altitude

Impacts of land use and climate change in tropical forests on the global carbon budget are of principal interest in the recent research, as these forests amount to about 48 % of the world’s forested area. Interest has been focused on lowland tropical forests mainly, but tropical montane forests occupy about 20 % of all tropical forests. Soils of tropical montane forests are frequently waterlogged and characterised by high soil organic carbon stocks. Furthermore, along altitudinal gradients, changes in stand structure and net primary production can be observed that have not been fully explained yet. As causes reduced microbial activity and nitrogen turnover in soils of tropical montane forests have been suggested. Against the background of climate change, carbon turnover mechanisms in soils of these forests are of special interest. The present study therefore aimed at determining and quantifying relevant carbon and nitrogen pools as well as nitrogen mineralisation potentials. Furthermore, size, activity, and structure of microbial biomass were characterised. The collected data was supposed to provide basic knowledge on carbon and nitrogen cycling in tropical montane forest soils. Thus, evaluation of the susceptibility of their carbon stocks for climate change as well as nitrogen and carbon limitation of microbial organic matter decomposition was possible. Field work of this study was conducted during 2003–2005 at an altitudinal transect that in- cluded five study sites between 1 050 and 3 060 m amsl. Total soil respiration was recorded biweekly over two years, the contribution of roots to total soil CO2 efflux over one year. Soils of the study sites were sampled twice and biochemical and microbial parameters were determined

Détermination de la ténacité de matériaux fragiles ou ductiles à partir de l’essai d’indentation

Les différentes méthodes qui utilisent l’essai d’indentation pour estimer la ténacité sont revues et commentées. Pour les matériaux fragiles, les formules sont principalement basées sur la mesure des fissures formées par l’indenteur ou, si l’essai est instrumenté, sur les décrochements (pop-in) observés sur la courbe charge-déplacement. D’autres méthodes moins connues peuvent utiliser la mesure de l’ouverture en fond de fissure, une équivalence entre la longueur de fissure formée et l’accroissement de pénétration de l’indenteur ou le clivage provoqué par une indentation proche du bord du matériau étudié. Pour les matériaux ductiles aucune fissure n’est visible à la surface, même pour les fortes charges appliquées. Dans ce cas la ténacité est reliée par la mécanique continue du dommage à un dommage critique mis en évidence par la diminution du module d’élasticité avec l’augmentation de la profondeur d’indentation. Toutes ces méthodes permettent de calculer la ténacité avec une incertitude pouvant aller au maximum à 50 %

A numerical method to calculate the Abbott parameters: A wear application

A numerical technique was proposed to plot the Abbott curve and to compute its associated parameters defined by the DIN 4776 and ISO 13565 norms. These parameters were then extended and applied to non-sigmoid Abbott curves. By studying the discretisation errors, we show that a minimum of 200 intercepts, with parabolic interpolations between discretised data profiles, have to be taken into consideration to calculate the parameters as accurately as possible. Experimental profiles were eroded by means of a numerical wear model, and it was shown that the Abbott parameters correlate well with the wear model parameters. Our numerical estimations of Abbott parameters were performed for electro-eroded, tool machined, polished, worn and sandblasted surfaces. Manual measures were compared with our algorithmic method and it was shown that the difference is lower than 1% for Mr1 and Mr2 Abbott parameters, but the numerical technique leads to a lower dispersion

Efeito da radiação UV-B na germinação de conídios de Trichoderma obtidos de produtos comerciais.

Resumo: O efeito da radiação UV-B foi avaliada na germinação de conídios de Trichoderma spp. obtidos de produtos comerciais (Trichodermil® - Itaforte Bioprodutos; Trichodermax® SP – Turfal; Quality® WG – Laboratório de Biocontrole Farroupilha). Uma alíquota de 20 ?L de suspensões de conídios (105 conídios/ml), de cada produto, foi plaqueada em triplicata em meio BDA + oxgall e imediatamente expostas à radiação UV-B por 1, 2, 3, 4 e 5 h. Placas controle foram envoltas em papel alumínio e mantidas na câmara durante toda a exposição. Após a exposição, as placas foram mantidas no escuro a 25°C± 1. A germinação foi avaliada após 16 h e 24 h para a testemunha e para os conídios irradiados, respectivamente. De cada placa foram avaliados 300 conídios e a porcentagem de germinação foi calculada comparando-se com o controle. O aumento da radiação UV-B reduziu a germinação de conídios para todos os isolados de Trichoderma. Para os três isolados, a média de germinação dos conídios para o controle foi de 91,3%. Para os irradiados por 1, 2, 3, 4 e 5 h as médias de germinação foram de 78,1%, 47,6%, 38,4%, 28,0% e 17,4%, respectivamente. Todos os isolados apresentaram a mesma sensibilidade à radiação UV-B. Esses resultados demonstram a sensibilidade de isolados de Trichoderma ao UV-B e sugerem a necessidade de formulações com protetores anti-UV-B ou recomendação de aplicação em períodos ou condições adequadas

Multiscale measures of equilibrium on finite dynamic systems

This article presents a new method for the study of the evolution of dynamic systems based on the notion of quantity of information. The system is divided into elementary cells and the quantity of information is studied with respect to the cell size. We have introduced an analogy between quantity of information and entropy, and defined the intrinsic entropy as the entropy of the whole system independent of the size of the cells. It is shown that the intrinsic entropy follows a Gaussian probability density function (PDF) and thereafter, the time needed by the system to reach equilibrium is a random variable. For a finite system, statistical analyses show that this entropy converges to a state of equilibrium and an algorithmic method is proposed to quantify the time needed to reach equilibrium for a given confidence interval level. A Monte-Carlo simulation of diffusion of A* atoms in A is then provided to illustrate the proposed simulation. It follows that the time to reach equilibrium for a constant error probability, te, depends on the number, n, of elementary cells as: te∝n2.22±0.06. For an infinite system size (n infinite), the intrinsic entropy obtained by statistical modelling is a pertinent characteristic number of the system at the equilibrium

Physical Interpretations of the Numerical Instabilities in Diffusion Equations Via Statistical Thermodynamics

The aim of this paper is to analyze the physical meaning of the numerical instabilities of the parabolic partial differential equations when solved by finite differences. Even though the explicit scheme used to solve the equations is physically well posed, mathematical instabilities can occur as a consequence of the iteration errors if the discretisation space and the discretisation time satisfy the stability criterion. To analyze the physical meaning of these instabilities, the system is divided in sub-systems on which a Brownian motion takes place. The Brownian motion has on average some mathematical properties that can be analytically solved using a simple diffusion equation. Thanks to this mesoscopic discretisation, we could prove that for each half sub-cell the equality stability criterion corresponds to an inversion of the particle flux and a decrease in the cell entropy in keeping with time as criterion increases. As a consequence, all stability criteria defined in literature can be used to define a physical continuous 'time-length' frontier on which mesoscopic and microscopic models join

Statistical artefacts in the determination of the fractal dimension by the slit island method

This paper comments upon some statistical aspects of the slit island method which is widely used to calculate the fractal dimension of fractured surfaces or of materials’ features like grain geometry. If a noise is introduced when measuring areas and perimeters of the islands (experimental errors), it is shown that errors are made in the calculation of the fractal dimension and more than a false analytical relation between a physical process parameter and the fractal dimension can be found. Moreover, positive or negative correlation with the same physical process parameter can be obtained whether the regression is performed by plotting the variation of the noisy area versus the noisy perimeter of the considered islands or vice versa. Monte-Carlo simulations confirm the analytical relations obtained under statistical considerations

DEAD-box RNA helicases in Escherichia coli

In spite of their importance in RNA metabolism, the function of DExD/H-box proteins (including DEAD-box proteins) is poorly understood at the molecular level. Here, we present recent progress achieved with the five DEAD-box proteins from Escherichia coli, which have been particularly well studied. These proteins, which have orthologues in many bacteria, participate, in particular, in specific steps of mRNA decay and ribosome assembly. In vitro, they behave as poorly processive RNA helicases, presumably because they only unwind a few base pairs at each cycle so that stable duplexes can reanneal rather than dissociate. Except for one of them (DbpA), these proteins lack RNA specificity in vitro, and specificity in vivo is likely conferred by partners that target them to defined substrates. Interestingly, at least one of them is multifunctional, presumably because it can interact with different partners. Altogether, several aspects of the information gathered with these proteins have become paradigms for our understanding of DEAD-box proteins in general

Perimeter analysis of the Von Koch island, application to the evolution of grain boundaries during heating

This paper introduces an analyse of the fractal dimension by Richardson’s method. Two different ways to calculate the fractal dimension are presented with their related calculation errors and applied the Von Koch curves. A Monte-Carlo simulation of the evolution of the grains’ boundaries when heating shows that the interfaces lose their fractal characteristics as reported in experimental work. This result is interpreted by dissipation of the energy during the evolution of the grain boundary