H-theorem and trend to equilibrium of chemically reacting mixture of gases

The trend to equilibrium of a quaternary mixture of monatomic gases undergoing a reversible reaction of bimolecular type is studied in a quite rigorous mathematical picture within the framework of Boltzmann equation extended to chemically reacting mixture of gases. The H-theorem and entropy inequality allow to prove two main results under the assumption of uniformly boundedness and equicontinuity of the distribution functions. One of the results establishes the tendency of a reacting mixture to evolve to an equilibrium state as time becomes large. The other states that the solution of the Boltzmann equation for chemically reacting mixture of gases converges in strong L1-sense to its equilibrium solution.Universidade Nova de Lisboa. Centro de Matemática(CMA-UNL)Brazilian Research Council (CNPq)Universidade do Minho. Centro de Matemática(CMat)Fundação para a Ciência e a Tecnologia (FCT) - PTDC/MAT/68615/200

Near-Exact Distributions for Likelihood Ratio Statistics Used in the Simultaneous Test of Conditions on Mean Vectors and Patterns of Covariance Matrices

The authors address likelihood ratio statistics used to test simultaneously conditions on mean vectors and patterns on covariance matrices. Tests for conditions on mean vectors, assuming or not a given structure for the covariance matrix, are quite common, since they may be easily implemented. But, on the other hand, the practical use of simultaneous tests for conditions on the mean vectors and a given pattern for the covariance matrix is usually hindered by the nonmanageability of the expressions for their exact distribution functions. The authors show the importance of being able to adequately factorize the c.f. of the logarithm of likelihood ratio statistics in order to obtain sharp and highly manageable near-exact distributions, or even the exact distribution in a highly manageable form. The tests considered are the simultaneous tests of equality or nullity of means and circularity, compound symmetry, or sphericity of the covariance matrix. Numerical studies show the high accuracy of the near-exact distributions and their adequacy for cases with very small samples and/or large number of variables. The exact and near-exact quantiles computed show how the common chi-square asymptotic approximation is highly inadequate for situations with small samples or large number of variables

Modeling of chemical wear in ferrous alloys/silicon nitride contacts during high speed cutting

The wear resistance of SisN4 in machining of iron alloys can be surprisingly low due to chemical affinity for dissolution in the metal. This limits the use of SisN4 inserts in high speed machining of steels, while Si3N4 retains the best performance of all cutting materials in turning of grey cast iron, a different ferrous alloy. The chemical wear of several ceramics has been investigated on the basis of dissolution in pure iron by Kramer and Suh. Nevertheless, the influence of alloy elements was not studied. In the present work, solid solution thermodynamics is applied to predict chemical wear of S&N4 by setting the influence of interaction coefficients of the alloy elements in the Henrian activity of Si and N in austenite. The model predicts the relative order of magnitude of the crater wear of SisN4 inserts in machining of tool steels, carbon steels and grey cast iron

The effect of hydrodynamic conditions in Corynebacterium glutamicum growth

[Excerpt] Corynebacterium glutamicum is a facultative anaerobic, gram-positive bacterium with a GRAS status that grows fast and achieves high cell densities. C. glutamicum is commonly used in amino acids production, and is also able to convert sugars in organic acids (OA) and alcohols in specific conditions: anaerobic and limited-oxygen environments. In these conditions, the carbon metabolism is modified, namely the flux shifts from the pentose phosphate pathway to glycolysis and the TCA cycle flux decreases and consequently bacterial growth is strongly affected [1,2]. (...

The mobile context framework: providing context to mobile applications

The spread of mobile devices in modern societies has forced the industry to create software paradigms to meet the new challenges it faces. Some of these challenges are the huge heterogeneity of devices or the quick changes of users’ context. In this scenario, context becomes a key element, enabling mobile applications to be user centric and adapt to user requirements. The Mobile Context Framework, proposed in this paper, is a contribution to solve some of these challenges. Using Web servers running on the devices, context data can be provided to web applications. Besides the framework’s architecture, a prototype is presented as proof of concept of the platform’s potential.This work is funded by ERDF - European Regional Development Fund through the COMPETE Programme (operational programme for competitiveness) and by National Funds through the FCT - Fundação para a Ciência e a Tecnologia (Portuguese Foundation for Science and Technology) within project FCOMP-01-0124-FEDER- 015095

An in vitro dynamic model of catheter-associated urinary tract infections to investigate the role of uncommon bacteria on the Escherichia coli microbial consortium

About 9% of nosocomial infections are attributed to catheter-associated urinary tract infections (CAUTIs). Uncommon bacteria (Delftia tusurhatensis) have been isolated in CAUTIs in combination with wellestablished pathogenic bacteria such as E. coli. Nonetheless, the reason why E. coli coexists with other bacteria instead of outcompeting and completely eliminating them are unknown. As such, a flow cell reactor simulating the hydrodynamic conditions found in CAUTIs (shear rate of 15 s-1) was used to characterize the microbial physiology of E. coli and D. tsuruhatensis individually and in consortium, in terms of growth kinetics and substrate uptake. Single-species biofilms showed that up to 48 h the CFU counts significantly increased for both species (p<0.05). After 48 h, both species stabilized with similar CFU values reaching log 6.24 CFU.cm2 for E. coli and log 6.31 CFU.cm2 for D. tsuruhatensis (p>0.05). The assessment of spatial distribution of dual-species biofilms by LNA/2´OMe-FISH revealed that E. coli and D. tsuruhatensis coexist and tend to co-aggregate over time, which implies that bacteria are able to cooperate synergistically. Substrate uptake measurements revealed that in artificial urine medium the bacteria metabolized lactic acid, uric acid (E. coli and D. tsuruhatensis) and citric acid (D. tsuruhatensis). In the consortium, D. tsuruhatensis consumed citric acid more rapidly, presumably leaving more uric acid available in the medium to be used by E. coli. In conclusion, metabolic cooperation between E. coli and uncommon species seems to occur when these species share the same environment, leading to the formation of a stable microbial community

The effect of substrate availability on behavioural and physiological indicators of welfare in the African cichlid (Oreochromis mossambicus)

Male African cichlids (Oreochromis mossambicus) establish territories on the substrate upon which spawning pits are dug, thus attracting females. The substrate, therefore, plays a very significant role in its lifecycle. The effects of substrate access on behaviour and physiology in captivity were assessed. Mixed-sex, all-male and all-female groups were observed for five days, with and without substrate. Social patterns, behaviour directed towards the substrate, locomotor activity and spatial behaviour were recorded, and haematocrit, plasma cortisol and glucose levels were measured. Substrate inclusion saw a significant increase in behavioural diversity, sexual behaviour of dominant males in mixed groups, pit digging and territoriality whereas a lack of substrate was characterised by increased chafing and inactivity. Vacuum-pit digging was also observed. Frequency of aggression did not differ significantly and female behaviour was not affected by the presence of substrate. For both sexes, no differences in cortisol and glucose levels were found between the two treatments, but haematocrit increased with substrate. The key role played by substrate in territorial males is consistent with the behavioural and physiological data reported. In the absence of substrate, decreased territorial behaviour is contrasted with similar levels of aggression, cortisol and glucose; all of which are suggestive of a stress-related context. Moreover, the exhibition of vacuum activities is a signal that behavioural needs are not being met and may be some form of coping mechanism. These findings, taken in conjunction with the variations in behavioural diversity and inactivity, suggest that the welfare of male cichlids may be adversely affected by the absence of substrate