Modifying Crystallinity,Morphology, and Photophysical Properties of Carbon Nitride by Using Crystals as Reactants

Here we show a general method to improve the crystallinity of carbon nitride nanosheets by using melamine crystals as reactants for the high temperature synthesis. Additionally, the crystals were calcined in a sealed ampoule, which provides a pressurized environment, yielding crystalline carbon nitride nanosheets that display altered morphology and photophysical properties compared to the reference materials. Electronic microscopy, optical and photoelectrochemical measurements prove the modifications of parameters such like band structure, charge recombination or inter-layer distance. The new growth strategy presented here opens many opportunities for the design of crystalline materials with tailored properties for different applications.     

Association of cyclists’ age and sex with risk of involvement in a crash before and after adjustment for cycling exposure

This study aimed to estimate the association of cyclists’ age and sex with the risk of being involved in a crash with and without adjustment for their amount of exposure. We used the distribution of the entire population and cyclists (total and non-responsible) involved in road crashes in Spain between 1993 and 2009 held by the Spanish National Institute of Statistics and the Spanish General Traffic Directorate to calculate rates of exposure and involvement in a crash. Males aged 45–49 years were used as the reference category to obtain exposure rate ratios (ERR) and unadjusted crash rate ratios (URR). We then used these values in decomposition analysis to calculate crash rate ratios adjusted for exposure (ARR). The pattern of ARR was substantially different from URR. In both sexes the highest values were observed in the youngest age groups, and the values decreased as age increased except for a slight increase in the oldest age groups. In males, a slight increase in the lowest and highest age categories was observed for crashes resulting in severe injury or death, and a decrease was observed for the youngest cyclists who were wearing a helmet. The large differences between age and sex groups in the risk of involvement in a cycling crash are strongly dependent on differences in their exposure rates. Taking exposure rates into account, cyclists younger than 30 years and older than 65 years of age had the highest risk of being involved in a crash.     

Maximum power point tracker based on maximum power point resistance modeling

This paper presents a new, simple, accurate, and inexpensive practical methodology and experimental solution for the modeling of conventional (domestic and commercial facilities) photovoltaic generators (PVG), so that they can work at their maximum power point (MPP). The PVG may be a panel, an array of panels, or a photovoltaic field. As a starting restriction (actual) it has to be assumed that it is not possible to isolate the PVG variables dependence (mainly current, voltage, and hence power) with solar radiation and temperature, because they are highly correlated. This methodology proposes the modeling facility on its MPP by its MPP resistance (R_MPP = V_MPP/I_MPP), being V_MPP and I_MPP the voltage and current of the PVG, respectively, at its MPP. The analysis shows, by simulation first and then experimentally, that R_MPP does not present significant temperature dependencies, at least in the usual range. This important result allows us to model the PVG only in terms of solar radiation. From a set of experimental data, different models to estimate R_MPP are proposed. The obtained results are very accurate. These models allow an immediate practical application that it is also developed in the paper: MPP tracker (MPPT) design by the calculation of the DC/DC converter duty cycle which places the PVG at its MPP directly and continuously. This new methodology and experimental system has been registered in the Spanish Patent and Trademark Office with the number P201530352. Copyright © 2015 John Wiley & Sons, Ltd.     

Water�CGas Shift and CO Methanation Reactions over Ni�CCeO2(111) Catalysts

X-ray and ultraviolet photoelectron spectroscopies were used to study the interaction of Ni atoms with CeO₂(111) surfaces. Upon adsorption on CeO₂(111) at 300 K, nickel remains in a metallic state. Heating to elevated temperatures (500?C800 K) leads to partial reduction of the ceria substrate with the formation of Ni²⁺ species that exists as NiO and/or Ce_1?xNi_xO_2?y. Interactions of nickel with the oxide substrate significantly reduce the density of occupied Ni 3d states near the Fermi level. The results of core-level photoemission and near-edge X-ray absorption fine structure point to weakly bound CO species on CeO₂(111) which are clearly distinguishable from the formation of chemisorbed carbonates. In the presence of Ni, a stronger interaction is observed with chemisorption of CO on the admetal. When the Ni is in contact with Ce⁺³ cations, CO dissociates on the surface at 300 K forming NiC_x compounds that may be involved in the formation of CH₄ at higher temperatures. At medium and large Ni coverages (>0.3 ML), the Ni/CeO₂(111) surfaces are able to catalyze the production of methane from CO and H₂, with an activity slightly higher than that of Ni(100) or Ni(111). On the other hand, at small coverages of Ni (<0.3 ML), the Ni/CeO₂(111) surfaces exhibit a very low activity for CO methanation but are very good catalysts for the water?Cgas shift reaction.     

A non-parametric method for estimating enthalpy-temperature functions of shape-stabilized phase change materials

A method for thermodynamic characterization of shape-stabilized phase change materials (PCM) based on one-single sample and one-single experiment has been proposed. The simplicity of the experimental device is comparable to that of the T-History method. However, instead of simple energy balances as in T-History method, a numerical heat transfer model is used to retrieve the whole set of parameters/functions characterizing the PCM from temperature measurements at one-single point within the PCM. An efficient inversion technique has been proposed for that. Its most striking feature is that it allows non-parametric identification of the enthalpy-temperature function in an easy way. Such a function is retrieved by solving a problem of nonhomogeneous heat source term estimation by inversion of a linear heat conduction model.     

Confined melting in deformable porous media: A first attempt to explain the graphite/salt composites behaviour

This paper deals with phase change in composite materials made of graphite and a phase-change material (PCM). The composites are manufactured by compressing a solid mixture of salt and graphite particles. In previous works, the interest of such materials for thermal energy storage at high temperature has been highlighted. They are characterized by quite high energy storage capacity as well as high thermal conductivity. However, first melting/crystallization of these composites could lead to significant salt leakage and shows some a priori unexpected features like melting over a range of temperature instead of at constant temperature and significant loss of heat storage capacity. A poro-thermo-elastic analysis is carried out in this paper for understanding salt melting within the graphite matrices and for proposing reliable ways for composite materials improvement. An intentionally simple think-model, based on mass and energy conservation equations, pressure-dependent liquid–crystal equilibriums, linear elasticity laws and Poiseuille-like flow, is proposed. In spite of the simplicity, the model turns out to be apt to explain main macroscopic features of materials melting as observed in calorimetric tests. The influence on melting dynamics of parameters like the heating rate, the pore-wall rigidity and thickness, the salt volume expansion and the pore connectivity is investigated and several ways for composite materials improvements are discussed.     

Susceptibility and resistance to ethanol in Saccharomyces strains isolated from wild and fermentative environments

In this work, we apply statistical modelling techniques to study the influence of increasing concentrations of ethanol on the overall growth of 29 yeast strains belonging to different Saccharomyces and non‐Saccharomyces species. A modified Gompertz equation for decay was used to objectively estimate the noninhibitory concentration (NIC) and minimum inhibitory concentration (MIC) for the assayed strains to ethanol, which are related to the susceptibility and resistance of yeasts to this compound, respectively. A first ANOVA analysis, grouping strains as a function of their respective Saccharomyces species, revealed that S. cerevisiae was the yeast with the highest, and statistically significant, ethanol resistance value. Then, a second factorial ANOVA analysis, using the origin of strains (wild or fermentative) and their taxonomic classification (S. cerevisiae, S. paradoxus or S. bayanus var. uvarum) as categorical predictor variables, showed that no significant differences for the NIC and MIC parameters were found between both ecological niches within the same species, indicative that these physiological characteristics were presumably not modified throughout the adaptation to human‐manipulated fermentative environments. Finally, differences among selected strains with respect to ethanol tolerance were correlated to the initial contents of unsaturated fatty acids, mainly oleic acid. Copyright © 2010 John Wiley & Sons, Ltd.     

Glycerol acetals, kinetic study of the reaction between glycerol and formaldehyde

The acetalization reaction between glycerol and formaldehyde using Amberlyst 47 acidic ion exchange resin was studied. These acetals can be obtained from renewable sources (bioalcohols and bioalcohol derived aldehydes) and seem to be good candidates for different applications such as oxygenated diesel additives. A preliminary kinetic study was performed in a batch stirred tank reactor studying the influence of different process parameters like temperature, feed composition and the stirring speed. A pseudo homogenous kinetic model able to explain the reaction mechanism was adjusted. Thus, the corresponding order of reaction was determined. Amberlyst 47 acidic ion exchange resin showed a fairly good behavior allowing 100% of selectivity towards acetals formation. However, the studied acetalization reaction showed high thermodynamic limitations achieving glycerol conversions around 50% using a stoichiometric feed ratio at 353 K. The product is a mixture of two isomers (1,3-Dioxan-5-ol and 1,3-dioxolane-4-methanol) and the conversion of 1,3-dioxolane-4-methanol into 1,3-Dioxan-5-ol was also observed.     

Modelling opinion formation driven communities in social networks

In a previous paper we proposed a model to study the dynamics of opinion formation in human societies by a co-evolution process involving two distinct time scales of fast transaction and slower network evolution dynamics. In the transaction dynamics we take into account short range interactions as discussions between individuals and long range interactions to describe the attitude to the overall mood of society. The latter is handled by a uniformly distributed parameter α, assigned randomly to each individual, as quenched personal bias. The network evolution dynamics is realised by rewiring the societal network due to state variable changes as a result of transaction dynamics. The main consequence of this complex dynamics is that communities emerge in the social network for a range of values in the ratio between time scales. In this paper we focus our attention on the attitude parameter α and its influence on the conformation of opinion and the size of the resulting communities. We present numerical studies and extract interesting features of the model that can be interpreted in terms of social behaviour.