Ruthenium supported on new TiO2–ZrO2 systems as catalysts for the partial oxidation of methane

The partial oxidation of methane is studied at 673–873 K over new Ru-based catalysts supported on TiO₂–ZrO₂ with different TiO₂ content. Supports were prepared by a sol–gel method, and RuCl₃ and RuNO(NO₃)₃ were used as ruthenium precursors to prepare the catalysts (1–2 wt% Ru). The effect of the reaction temperature on the catalytic behavior is analyzed, along with the support composition and the Ru precursor used.     

Coverage extension by means of non-conventional multi-hop communications

This paper analyzes the benefits that can be obtained by using opportunistic multi-hop extensions in terms of coverage extension of traditional network deployments. We assume that there are some devices acting as relaying entities, so as to allow others reaching an Access Element, in those situations in which a direct connection is not possible. Two different network deployments are used for this analysis: in the first one, an a priori planning is not assumed and, therefore, the Access Elements are randomly deployed, thus leading to a rather poor connectivity; on the other hand, in the second case, the Access Elements are placed according to an array deployment, thus maximizing the covered area. The paper finds analytical expressions for the probability of a user to be disconnected, i.e. she is not able to reach an Access Element, or the outage probability, for both scenarios, when either one or two hop paths can be used. These results are assessed, first, and complemented later, by means of an extensive simulation-based analysis, which brings about the possibility of extending the results when more than two hops are considered. The results provide helpful insights for aiding network dimensioning processes, since they allow establishing sensible bounds on the maximum number of hops which should be used to connect to the network; in the two complementary deployments which are used throughout the paper, there was not much additional benefit for paths longer than three/four hops, regardless of the probability for a user terminal to behave as a forwarding node.     

Optimum Selection of Access Networks Within Heterogeneous Wireless Environments Based on Linear Programming Techniques

In this work we analyze the possibilities which are brought about by the use of linear programming techniques in the framework of access selection procedures within heterogeneous wireless network environments. We present a tool which has been designed and implemented (based on the GLPK package) to tackle this problem. This tool can be used to retrieve the optimum assignment of access elements of a particular network deployment. To fulfil this goal, we introduce a flexible cost (utility) function, which allows modulating the relevance given to the different aspects which could be taken into consideration while deciding the access alternative to be used: connection with a preferred operator, minimizing the number of handovers, or selecting the link with the best quality, amongst others. Afterwards, the tool is used to study a set of access selection strategies, so as to establish the combination of parameters which might lead to optimum performances.     

Optimizing Internet flows over IEEE 802.11b wireless local areanetworks: a performance-enhancing proxy based on forward errorcorrection

The success of the IP and its associated technologies has led to new challenges as we try to use it more widely in everyday communications. In particular, the drive toward wireless and highly heterogeneous infrastructures supporting IP services transparently and independent of the underlying physical layer is a challenge. In this context, this article focuses on introducing an implementation of a generic performance-enhancing proxy, called the wireless adaptation layer, and particularly its forward error control enhancement module. The error control module is a potentially important tool for achieving better UDP and TCP performance over the inherently unreliable wireless channels, and providing some adaptation for that. In order to assess the benefits and drawbacks of the selected design, we have also conducted some performance measurements over IEEE 802.11b WLANs     

The putative effects of prebiotics as immunomodulatory agents

The gradual increase of degenerative diseases observed in the last decades has been raising morbidity, incapacitation and mortality. The occurrence of these kinds of diseases is related to the aging of humanity as well as the unhealthy choices of individuals, particularly those dwelling in large urban centers, which are closely linked with poor nutrition, obesity, and tobacco and alcohol consumption. The introduction of functional compounds in the diet seems to be an attractive alternative to ameliorate the quality of life of all age groups. The prebiotics stand out because of their beneficial effects, favoring the growth of colonic microbiota, helping the gastrointestinal metabolism, and regulating the serum cholesterol and mineral absorption. Experimental data indicates that prebiotics could reduce the severity or incidence of degenerative diseases, such as neoplasias, diabetics, coronary diseases, and infectious diseases. They also seem to promote a positive modulation of the immune system. Their effects on the immune system could even be associated to increase of resistance to infection and microbicide capability, as well as to a decrease in allergic reactions. This article's goal is to analyze the immunomodulatory potential of prebiotics observed in experimental and trial studies.     

Study of ruthenium supported on Ta2O5–ZrO2 and Nb2O5–ZrO2 as catalysts for the partial oxidation of methane

Ru-based catalysts supported on Ta₂O₅–ZrO₂ and Nb₂O₅–ZrO₂ are studied in the partial oxidation of methane at 673–873 K. Supports with different Ta₂O₅ or Nb₂O₅ content were prepared by a sol–gel method, and RuCl₃ and RuNO(NO₃)₃ were used as precursors to prepare the catalysts (ca. 2 wt.% Ru). At 673 K high selectivity to CO₂ was found. An increase of temperature up to 773 K produced an increase in the selectivity to syngas (H₂/CO = 2.2–3.1), and this is related with the transformation of RuO₂ to metallic Ru as was determined from XRD and XPS results. At 873 K and with co-fed CO₂ an increase of the catalytic activity and CO selectivity was found. A TOF value of 5.7 s⁻¹ and H₂/CO ratio ca. 1 was achieved over Ru(Cl)/6TaZr. Catalytic results are discussed as a function of the support composition and characteristics of Ru-based phases.     

Immunomodulatory effects of fructans

According to the Pan-American Health Organization (PAHO), there is a growing increase of degenerative diseases in countries of the Americas, bringing on disability and death of the population. As eating properly is the most effective way to reduce the risk of diseases, food scientists are seeking alternatives for more nutritional foods, mainly through the investigation of functional compounds in natural foods. Among the functional compounds, fructans stand out for their beneficial effects on the animal body, favoring the growth of bifidobacteria in the colon that improve gastrointestinal metabolism, as well as regulating the levels of serum cholesterol and the absorption of minerals. Besides, fructans seem to be involved in the positive modulation of the immune system, mainly in an increased resistance to infections and microbicidal activity as well as by the reduction of allergic reactions and cancer in experimental models. This paper aims to analyze literature data concerning the benefits of consuming the fructans contained in natural food, especially their immunomodulatory actions in both animals and humans.     

Distribution Transformer Modeling for Application in Three-Phase Power Flow Algorithm

In this paper, it is presented a methodology for three-phase distribution transformer modeling, considering several types of transformer configuration, to be used in algorithms of power flow in three-phase radial distribution networks. The paper provides a detailed discussion about the models and the results from an implementation of the power flow algorithm. The results, taken from three different networks, are presented for several transformer configurations and for voltage regulators as well.