Grand canonical Monte Carlo simulation study of methane adsorption at an open graphite surface and in slitlike carbon pores at 273 K

Grand canonical Monte Carlo (GCMC) simulation was used for the systematic investigation of the supercritical methane adsorption at 273 K on an open graphite surface and in slitlike micropores of different sizes. For both considered adsorption systems the calculated excess adsorption isotherms exhibit a maximum. The effect of the pore size on the maximum surface excess and isosteric enthalpy of adsorption for methane storage at 273 K is discussed. The microscopic detailed picture of methane densification near the homogeneous graphite wall and in slitlike pores at 273 K is presented with selected local density profiles and snapshots. Finally, the reliable pore size distributions, obtained in the range of the microporosity, for two pitch-based microporous activated carbon fibers are calculated from the local excess adsorption isotherms obtained via the GCMC simulation. The current systematic study of supercritical methane adsorption both on an open graphite surface and in slitlike micropores performed by the GCMC summarizes recent investigations performed at slightly different temperatures and usually a lower pressure range by advanced methods based on the statistical thermodynamics.

Interpretation of the temperature dependence of rate constants in biosensor studies

A comparison is made between Arrhenius and transition-state analyses of the temperature dependence of rate constants reported in four published biosensor studies. Although the Eyring transition-state theory seemingly affords a more definitive solution to the problem of characterizing the activation energetics, the analysis is equivocal because of inherent assumptions about reaction mechanism and the magnitude of the transmission coefficient. In view of those uncertainties it is suggested that a preferable course of action entails reversion to the empirical Arrhenius analysis with regard to the energy of activation and a preexponential factor. The former is essentially equivalent to the enthalpy of activation, whereas the magnitude of the latter indicates directly the extent of disparity between the frequency of product formation and the universal frequency factor (temperature multiplied by the ratio of the Boltzmann and Planck constants) and hence the likelihood of a more complicated kinetic mechanism than that encompassed by the Eyring transition-state theory. (C) 2004 Elsevier Inc. All rights reserved.

Canonical solution groups of a homomorphism : manipulator kinematics, nonparametric regression and distributed object systems

The kinematic mapping of a rigid open-link manipulator is a homomorphism between Lie groups. The homomorphisrn has solution groups that act on an inverse kinematic solution element. A canonical representation of solution group operators that act on a solution element of three and seven degree-of-freedom (do!) dextrous manipulators is determined by geometric analysis. Seven canonical solution groups are determined for the seven do! Robotics Research K-1207 and Hollerbach arms. The solution element of a dextrous manipulator is a collection of trivial fibre bundles with solution fibres homotopic to the Torus. If fibre solutions are parameterised by a scalar, a direct inverse funct.ion that maps the scalar and Cartesian base space coordinates to solution element fibre coordinates may be defined. A direct inverse pararneterisation of a solution element may be approximated by a local linear map generated by an inverse augmented Jacobian correction of a linear interpolation. The action of canonical solution group operators on a local linear approximation of the solution element of inverse kinematics of dextrous manipulators generates cyclical solutions. The solution representation is proposed as a model of inverse kinematic transformations in primate nervous systems. Simultaneous calibration of a composition of stereo-camera and manipulator kinematic models is under-determined by equi-output parameter groups in the composition of stereo-camera and Denavit Hartenberg (DH) rnodels. An error measure for simultaneous calibration of a composition of models is derived and parameter subsets with no equi-output groups are determined by numerical experiments to simultaneously calibrate the composition of homogeneous or pan-tilt stereo-camera with DH models. For acceleration of exact Newton second-order re-calibration of DH parameters after a sequential calibration of stereo-camera and DH parameters, an optimal numerical evaluation of DH matrix first order and second order error derivatives with respect to a re-calibration error function is derived, implemented and tested. A distributed object environment for point and click image-based tele-command of manipulators and stereo-cameras is specified and implemented that supports rapid prototyping of numerical experiments in distributed system control. The environment is validated by a hierarchical k-fold cross validated calibration to Cartesian space of a radial basis function regression correction of an affine stereo model. Basic design and performance requirements are defined for scalable virtual micro-kernels that broker inter-Java-virtual-machine remote method invocations between components of secure manageable fault-tolerant open distributed agile Total Quality Managed ISO 9000+ conformant Just in Time manufacturing systems.

Improvement of the mechanical properties of 2124 Al/SiCp MMC plate by optimisation of the solution treatment

Static mechanical properties of 2124 Al/SiCp MMC have been measured as a function of solution temperature and time. An optimum solution treatment has been established which produces significant improvements in static mechanical properties and fatigue crack growth resistance over conventional solution treatments. Increasing the solution treatment parameters up to the optimum values improves the mechanical properties because of intermetallic dissolution, improved solute and GPB zone strengthening and increased matrix dislocation density. Increasing the solution treatment parameters beyond the optimum values results in a rapid reduction in mechanical properties due to the formation of gas porosity and surface blisters. The optimum solution treatment improves tensile properties in the transverse orientation to a greater extent than in the longitudinal orientation and this results in reduced anisotropy. © 1996 Elsevier Science Limited.

Measurement and correlation of the solubility of telmisartan (form A) in nine different solvents from 277.85 to 338.35 K

The solubility of telmisartan (form A) in nine organic solvents (chloroform, dichloromethane, ethanol, toluene, benzene, 2-propanol, ethyl acetate, methanol and acetone) was determined by a laser monitoring technique at temperatures from 277.85 to 338.35 K. The solubility of telmisartan (form A) in all of the nine solvents increased with temperature as did the rates at which the solubility increased except in chloroform and dichloromethane. The mole fraction solubility in chloroform is higher than that in dichloromethane, which are both one order of magnitude higher than those in the other seven solvents at the experimental temperatures. The solubility data were correlated with the modified Apelblat equation and λh equations. The results show that the λh equation is in better agreement with the experimental data than the Apelblat equation. The relative root mean square deviations (σ) of the λh equation are in the range from 0.004 to 0.45 %. The dissolution enthalpies, entropies and Gibbs energies of telmisartan in these solvents were estimated by the Van’t Hoff equation and the Gibbs equation. The melting point and the fusion enthalpy of telmisartan were determined by differential scanning calorimetry.

Gas Solubility and Vapor Pressure of Electrolytes Based on Alkylcarbonates Containing Litfsi, Lifap, and LiPF6 Lithium Salt: Measurement and Prediction

Most liquid electrolytes used in commercial lithium-ion batteries are composed by alkylcarbonate mixture containing lithium salt. The decomposition of these solvents by oxidation or reduction during cycling of the cell, induce generation of gases (CO2, CH4, C2H4, CO …) increasing of pressure in the sealed cell, which causes a safety problem [1]. The prior understanding of parameters, such as structure and nature of salt, temperature pressure, concentration, salting effects and solvation parameters, which influence gas solubility and vapor pressure of electrolytes is required to formulate safer and suitable electrolytes especially at high temperature.

We present in this work the CO2, CH4, C2H4, CO solubility in different pure alkyl-carbonate solvents (PC, DMC, EMC, DEC) and their binary or ternary mixtures as well as the effect of temperature and lithium salt LiX (X = LiPF6, LiTFSI or LiFAP) structure and concentration on these properties. Furthermore, in order to understand parameters that influence the choice of the structure of the solvents and their ability to dissolve gas through the addition of a salt, we firstly analyzed experimentally the transport properties (Self diffusion coefficient (D), fluidity (h-1), and conductivity (s) and lithium transport number (tLi) using the Stock-Einstein, and extended Jones-Dole equations [2]. Furthermore, measured data for the of CO2, C2H4, CH4 and CO solubility in pure alkylcarbonates and their mixtures containing LiPF6; LiFAP; LiTFSI salt, are reported as a function of temperature and concentration in salt. Based on experimental solubility data, the Henry’s law constant of gases in these solvents and electrolytes was then deduced and compared with values predicted by using COSMO-RS methodology within COSMOthermX software. From these results, the molar thermodynamic functions of dissolution such as the standard Gibbs energy, the enthalpy, and the entropy, as well as the mixing enthalpy of the solvents and electrolytes with the gases in its hypothetical liquid state were calculated and discussed [3]. Finally, the analysis of the CO2 solubility variations with the salt addition was then evaluated by determining specific ion parameters Hi by using the Setchenov coefficients in solution. This study showed that the gas solubility is entropy driven and can been influenced by the shape, charge density, and size of the anions in lithium salt.

References

[1] S.A. Freunberger, Y. Chen, Z. Peng, J.M. Griffin, L.J. Hardwick, F. Bardé, P. Novák, P.G. Bruce, Journal of the American Chemical Society 133 (2011) 8040-8047.

[2] P. Porion, Y.R. Dougassa, C. Tessier, L. El Ouatani, J. Jacquemin, M. Anouti, Electrochimica Acta 114 (2013) 95-104.

[3] Y.R. Dougassa, C. Tessier, L. El Ouatani, M. Anouti, J. Jacquemin, The Journal of Chemical Thermodynamics 61 (2013) 32-44.

Production of bioplastics from hydrolysates of paper industry by Haloferax mediterranei

The biorefinery concept has attracted much attention over the last decade due to increasing concerns about the use of fossil resources. In this context emerged the use of bioplastics, namely polyhydroxyalkanoates (PHA). PHA are biocompatible and biodegradable plastics that can be obtained from renewable raw materials and can constitute an alternative solution to conventional plastics. In this work, hydrolysed cellulose pulp, coming from Eucalyptus globulus wood cooking, was used as substrate to the PHA-storing bacteria Haloferax mediterranei. The hydrolysed pulp is rich in simple sugars, mainly glucose (81.96 g.L-1) and xylose (20.90 g.L-1). Tests were made in defined medium with glucose and xylose and in hydrolysate supplemented with salts and yeast extract. Different concentrations of glucose were tested, namely 10, 15, 20, 30 and 40 g.L-1. The best accumulation results (27.1 % of PHA) were obtained in hydrolysate medium with 10 g.L-1. Using this concentration, assays were performed in fed-batch and sequencing batch reactor conditions in order to determine the best feeding strategy. The strategy that led to the best results was fed-batch assay with 24.7 % of PHA. An assay without sterile conditions was performed, in which was obtained the same growth than in sterilization test. Finally it was performed an assay in a bioreactor and a fast growth (0.14 h-1) with high glucose and xylose consumption rates (0.368 g.L-1.h-1 and 0.0947 g.L-1.h-1, respectively) were obtained. However 1.50 g.L-1 of PHA, corresponding to 16.1 % (92.52 % of 3HB and 3HV of 7.48 %) of % PHA were observed. The polymer was further characterized by DSC with a glass transition temperature of -6.07 °C, a melting temperature of 156.3 °C and a melting enthalpy of 63.07 J.g-1, values that are in accordance with the literature. This work recognizes for the first time the suitability of the pulp paper hydrolysate as a substrate for PHA production by H. mediterranei.

Impact of the cation symmetry on the mutual solubilities between water and imidazolium-based ionic liquids

Aiming at the evaluation of the impact of the ionic liquids (ILs) cation symmetry on their phase behaviour, in this work, novel mutual solubilities with water of the symmetric series of [C(n)C(n)im][NTf2] (with n=1-5) were determined and compared with their isomeric forms of the asymmetric [C(n)C(1)im][NTf2] group. While the solubility of isomeric ILs in water was found to be similar, the solubility of water in ILs follows the same trend up to a maximum cation alkyl side chain length. For n >= 4 in [C(n)C(n)im][NTf2] the solubility of water in the asymmetric ILs is slightly higher than that observed in the symmetric counterparts. The thermodynamic properties of solution and solvation derived from the experimental solubility data of ILs in water at infinite dilution, namely the Gibbs energy, enthalpy and entropy were used to evaluate the cation symmetry effect on the ILs solvation. It is shown that the solubility of ILs in water is entropically driven and highly influenced by the cation size. Accordingly, it was found that the ILs solubility in water of both symmetric and asymmetric series depends on their molecular volume. Based on these findings, a linear correlation between the logarithm of the solubility of ILs in water and their molar volume is here proposed for the [NTf2]-based ILs at a fixed temperature.

Interactions of pyridinium, pyrrolidinium or piperidinium based ionic liquids with water: measurements and COSMO-RS modelling

Looking for a better knowledge concerning water and ionic liquids (ILs) interactions, a systematic study of the activity coefficients of water in pyridinium, pyrrolidinium and piperidinium-based ILs at 298.2 K is here presented based on water activity measurements. Additionally, the study of the structural effects of the pyridinium-based cation is also pursued. The results show that non-aromatic ILs are interacting more with water than aromatic ones, and among the ortho, meta and para isomers of 1-butyl-methylpyridinium chloride, the ortho position confers a more hydrophilic character to that specific IL. The physicalchemistry of the solutions was interpreted based on dissociation constants, natural bond orbitals and excess enthalpies providing a sound basis for the interpretation of the experimental observations. These results show that hydrogen bonding controls the behavior of these systems, being the anion-water one of the most relevant interactions, but modulated by the anionecation interactions.

Perception Of Oral And Maxillofacial Surgeons, Orthodontists And Laypersons In Relation To The Harmony Of The Smile.

Harmony is one of the main objectives in surgical and orthodontic treatment and this harmony must be present in the smile, as well as in the face. The aim of the present study was to assess the perceptions of professionals and laypersons in relation to the harmony of the smile of patients with or without vertical maxillary alterations. Sixty observers (oral and maxillofacial surgeons, orthodontists and laypersons) reported the degree of harmony of six smiles using an objective questionnaire and the participants indicated if there was a need for corrective surgery or not. The classification of observers was recorded on a Likert scale from 1 to 5. Mixed regression was used to determine differences between the three groups. Statistically significant differences were found only for the harmony of the smile between the oral and maxillofacial surgeons and laypersons, with laypersons being more critical when assessing the smile. There was no statistical difference between the other groups for the harmony of the smile or the indication of corrective surgery. The patterns of greater or lesser harmony determined by observers during the smile were similar to those found in the literature as the ideal standard in relation to vertical maxillary positioning. Laypersons had a tendency to be more critical in relation to facial harmony than surgeons, although no statistical differences were found in the other groups in relation to the harmony of the smile or indication for the corrective surgery. In addition, the patterns of greater or lesser harmony of the smile determined by the participants were similar to those found in the literature as the ideal standard in relation to vertical maxillary positioning. Overall, the present study demonstrates that adequate interaction between surgeons, orthodontists and laypersons is essential in order to achieve facial harmony with orthodontic and/or surgical treatment. Opinion of specialists and laypersons about the smile in relation to the vertical positioning of the maxilla.

O emprego de quitosana quimicamente modificada com anidrido succínico na adsorção de azul de metileno

The adsorption capacity of alpha-chitosan and its modified form with succinic anhydride was compared with the traditional adsorbent active carbon by using the dye methylene blue, employed in the textile industry. The isotherms for both biopolymers were classified as SSA systems in the Giles model, more specifically in L class and subgroup 3. The dye concentration in the supernatant in the adsorption assay was determined through electronic spectroscopy. By calorimetric titration thermodynamic data of the interaction between methyene blue and the chemically modified chitosan at the solid/liquid interface were obtained. The enthalpy of the dye/chitosan interaction gave 2.47 ± 0.02 kJ mol-1 with an equilibrium constant of 7350 ± 10 and for the carbon/dye interaction this constant gave 5951 ± 8. The spontaneity of these adsorptions are reflected by the free Gibbs energies of -22.1 ± 0.4 and -21.5 ± 0.2 kJ mol-1, respectively, found for these systems. This new adsorbent derived from a natural polysaccharide is as efficient as activated carbon. However 97% of the bonded dye can be eluted by sodium chloride solution, while this same operation elutes only 42% from carbon. Chitosan is efficient in dye removal with the additional advantage of being cheap, non-toxic, biocompatible and biodegradable.

Characterization of dynamic solid phase DNA extraction from blood with magnetically controlled silica beads

A novel solid phase extraction technique is described where DNA is bound and eluted from magnetic silica beads in a manner where efficiency is dependent on the magnetic manipulation of the beads and not on the flow of solution through a packed bed. The utility of this technique in the isolation of reasonably pure, PCR-amplifiable DNA from complex samples is shown by isolating DNA from whole human blood, and subsequently amplifying a fragment of the beta-globin gene. By effectively controlling the movement of the solid phase in the presence of a static sample, the issues associated with reproducibly packing a solid phase in a microchannel and maintaining consistent flow rates are eliminated. The technique described here is rapid, simple, and efficient, allowing for recovery of more than 60% of DNA from 0.6 mu L of blood at a concentration which is suitable for PCR amplification. In addition, the technique presented here requires inexpensive, common laboratory equipment, making it easily adopted for both clinical point-of-care applications and on-site forensic sample analysis.

Influence of land-use change on near-surface hydrological processes: Undisturbed forest to pasture

Soil compaction that follows the clearing of tropical forest for cattle pasture is associated with lower soil hydraulic conductivity and increased frequency and volume of overland flow. We investigated the frequency of perched water tables, overland flow and stormflow in an Amazon forest and in an adjacent 25-year-old pasture cleared from the same forest. We compared the results with the frequencies of these phenomena estimated from comparisons of rainfall intensity and soil hydraulic conductivity. The frequency of perched water tables based on rainfall intensity and soil hydraulic conductivity was expected to double in pasture compared with forest. This corresponded closely with an approximate doubling of the frequency of stormflow and overland flow in pasture. In contrast, the stormflow volume in pasture increased 17-fold. This disproportional increase of stormflow resulted from overland flow generation over large areas of pasture, while overland flow generation in the forest was spatially limited and was observed only very near the stream channel. In both catchments, stormflow was generated by saturation excess because of perched water tables and near-surface groundwater levels. Stormflow was occasionally generated in the forest by rapid return flow from macropores, while slow return flow from a continuous perched water table was more common in the pasture. These results suggest that deforestation for pasture alters fundamental mechanisms of stormflow generation and may increase runoff volumes over wide regions of Amazonia. (C) 2009 Elsevier B.V. All rights reserved.

Montmorillonite as a component of polysulfone nanocomposite membranes

Nanocomposite membranes containing polysulfone (PSI) and sodium montmorillonite from Wyoming (MMT) were prepared by a combination of solution dispersion and the immersion step of the wet-phase inversion method. The purpose was to study the MMT addition with contents of 0.5 and 3.0 mass% MMT in the preparation of nanocomposite membranes by means of morphology, thermal, mechanical and hydrophilic properties of nanocomposite membranes and to compare these properties to the pure PSf membrane ones. Small-angle X-ray diffraction patterns revealed the formation of intercalated clay mineral layers in the PSf matrix and TEM images also presented an exfoliated structure. A good dispersion of the clay mineral particles was detected by SEM images. Tensile tests showed that both elongation at break and tensile strength of the nanocomposites were improved in comparison to the pristine PSf. The thermal stability of the nanocomposite membranes, evaluated by onset and final temperatures of degradation, was also enhanced. The hydrophilicity of the nanocomposite membranes, determined by water contact angle measurements, was higher; therefore, the MMT addition was useful to produce more hydrophilic membranes. (C) 2009 Elsevier B.V. All rights reserved.

Electron theoretical investigation of the stability of the B2-TiFe compound

The metastable phase diagram of the BCC-based ordering equilibria in the Ti-Fe system has been calculated using a truncated cluster expansion, through the combination of FP-LAPW and cluster variation method (CVM) in the irregular tetrahedron cluster approximation. The results are compared with phenomenological CVM assessments of the system and suggest that the value for the experimental formation enthalpy of the B2-TiFe compound should be significantly more negative than the currently assessed value. (C) 2008 Elsevier B.V. All rights reserved.