Search results for "THERMODYNAMICS"
showing 10 items of 2774 documents
Linear instability of mixed convection of cold water in a porous layer induced by viscous dissipation
2009
Accepted version of an article published in the journal: International Journal of Thermal Sciences, Elsevier Published version available on Science Direct: http://dx.doi.org/10.1016/j.ijthermalsci.2008.06.012 An analysis of linear stability of the stationary laminar Darcy flow in a horizontal porous layer is performed. The porous layer is saturated with cold water. The upper plane boundary is assumed to be subject to heat transfer with finite conductance to an environment at the temperature of maximum density of cold water. The lower plane boundary is adiabatic. Convective instabilities are caused by flow viscous dissipation, inducing a basic temperature distribution that decreases in the u…
Complete-active-space second-order perturbation theory (CASPT2//CASSCF) study of the dissociative electron attachment in canonical DNA nucleobases ca…
2015
Low-energy (0-3 eV) ballistic electrons originated during the irradiation of biological material can interact with DNA/RNA nucleobases yielding transient-anion species which undergo decompositions. Since the discovery that these reactions can eventually lead to strand breaking of the DNA chains, great efforts have been dedicated to their study. The main fragmentation at the 0-3 eV energy range is the ejection of a hydrogen atom from the specific nitrogen positions. In the present study, the methodological approach introduced in a previous work on uracil [I. González-Ramírez et al., J. Chem. Theory Comput. 8, 2769-2776 (2012)] is employed to study the DNA canonical nucleobases fragmentations…
Adsorbents and columns in analytical high-performance liquid chromatography: A perspective with regard to development and understanding
2012
A brief historical survey is presented on the evaluation of silica adsorbents in analytical HPLC. The theory of analytical HPLC is mostly still being based on the height equivalent to a theoretical plate concept and the van Deemter equation that was derived from gas phase adsorption involving a linear adsorption isotherm and fast mass transfer kinetics. One can obviously wonder whether the use of the van Deemter equation is relevant and valid for the evaluation of the performance of HPLC systems, where most often the liquid solutes involve charged molecules in electrolytes and in very many cases the adsorbates are macromolecules having diffusion coefficients of small magnitude. Instead of t…
Simultaneous optimization of mobile phase composition, column nature and length to analyse complex samples using serially coupled columns
2013
Abstract The combination of the selectivity of different columns serially coupled improves the separation expectancies with regard to the separation offered by each single column. In the reported approaches, either a pre-selected isocratic mobile phase composition or gradient program, giving rise to acceptable retention, is used. In previous work (JCA 1281 (2013) 94), we showed that the approach succeeds with conventional columns, assembled through zero-dead volume couplers. In this work, the simultaneous interpretive optimization of mobile phase composition and column nature and length, based on a limited number of experimental data, is demonstrated. This approach allows an impressive redu…
Prediction of Peak Shape and Characterization of Column Performance in Liquid Chromatography as a Function of Flow Rate
2015
Traditionally, column performance in liquid chromatography has been studied using information from the elution of probe compounds at different flow rates through van Deemter plots, which relate the column plate height to the linear mobile phase velocity. A more recent approach to characterize columns is the representation of the peak widths (or the right and left peak half-widths) for a set of compounds versus their retention times, which, for isocratic elution, give rise to almost linear plots. In previous work, these plots have been shown to facilitate the prediction of peak profiles (width and asymmetry) with optimization purposes. In this work, a detailed study on the dependence of the …
Phase coexistence in finite van der Waals systems
1999
Phase coexistence in finite systems obeying van der Waals equation of state is studied by minimizing a model free energy function for a spherical liquid droplet and a gaseous phase around it. Phase diagrams are calculated for finite systems with a large range of sizes. According to this model, the highest temperature where a droplet and vapour can exist in equilibrium decreases as N −0.4, where N is the number of particles in the system. The model predicts higher equilibrium vapour pressures than molecular dynamics simulations.
Organic solvent vapor effects on phase transition of α and β tegafur upon grinding with solvent additives.
2012
Abstract Solvent effects on α tegafur (5-fluoro-1-(tetrahydro-2-furyl)uracil) phase transition to β tegafur during grinding with solvent additive, as well as phase transition in samples exposed to 95% relative solvent vapor pressure has been studied in this research. Samples containing 0.5% and 0.1% of β tegafur in α and β tegafur mixture, as well as samples of pure α tegafur were ground with different solvent additives, and conversion degrees depending on the solvent were determined using PXRD method. Samples with α and β tegafur weight fraction of 1:1 were exposed to 95% relative solvent vapor pressure, and phase transition rates were determined. Solubility of α tegafur, solvent sorption …
(Vapour + liquid) equilibria of (water + dimethylformamide): application of the headspace-gas chromatography for the determination of thermodynamic i…
1998
Abstract Isothermal measurements of the partial vapour pressures have been carried out on {water + dimethylformamide (DMF)} at temperatures betweenT=305.15 K andT=323.15 K using an apparatus composed of a headspace sampler and a normal gas chromatograph. These data were simultaneously evaluated in one step with respect to the (composition dependent, integral) Flory-Huggins interaction parametergby means of a new method which minimizes the Gibbs energy of mixing and does not require chemical potentials. The expression forggiven by Koningsveld and Kleintjens, originally designed for polymer solutions, describes the present results best.
A second strain gradient elasticity theory with second velocity gradient inertia – Part I: Constitutive equations and quasi-static behavior
2013
Abstract A multi-cell homogenization procedure with four geometrically different groups of cell elements (respectively for the bulk, the boundary surface, the edge lines and the corner points of a body) is envisioned, which is able not only to extract the effective constitutive properties of a material, but also to assess the “surface effects” produced by the boundary surface on the near bulk material. Applied to an unbounded material in combination with the thermodynamics energy balance principles, this procedure leads to an equivalent continuum constitutively characterized by (ordinary, double and triple) generalized stresses and momenta. Also, applying this procedure to a (finite) body s…
A coupled cluster study of the 1 1A1g and 1 1B2u states of benzene
1998
A theoretical investigation of the equilibrium structures and harmonic frequencies of the 1 1A1g and 1 1B2u states of benzene is presented. The performance of coupled cluster singles (CCS), the recently proposed CC2 model, and coupled cluster singles and doubles (CCSD) is compared. The CC2 ground and excited states frequencies are a significant improvement of the CCS results and are relatively close to the CCSD results. A comparative analysis of the vibrations in the two electronic states of both C6H6 and C6D6 is presented. The reliability of predicted shifts in harmonic frequencies between the two states and isotopic shifts is estimated on the basis of the convergence in the CCS, CC2, and …