1,721,211 research outputs found
Floris F, graaf van Holland en Zeeland, heer van Friesland (1256- 1296), door Henri Obreen
No full textLemaitre Henri. Floris F, graaf van Holland en Zeeland, heer van Friesland (1256- 1296), door Henri Obreen. In: Bibliothèque de l'école des chartes. 1908, tome 69. pp. 675-676
Mathematical modeling on gas turbine blades/vanes under variable convective and radiative heat flux with tentative different laws of cooling
Full text linkIn the last twenty years the modeling of heat transfer on gas turbine cascades has been based on computational fluid dynamic and turbulence modeling at sonic transition. The method is called Conjugate Flow and Heat Transfer (CHT). The quest for higher Turbine Inlet Temperature (TIT) to increase electrical efficiency makes radiative transfer the more and more effective in the leading edge and suction/ pressure sides. Calculation of its amount and transfer towards surface are therefore needed. In this paper we decouple convection and radiation load, the first assumed from convective heat transfer data and the second by means of emissivity charts and analytical fits of heteropolar species as CO2 and H2O. Then we propose to solve the temperature profile in the blade through a quasi-two-dimensional power balance in the form of a second order partial differential equation which includes radiation and convection. Real cascades are cooled internally trough cool compressed air, so that we include in the power balance the effect of a heat sink or law of cooling that is up to the designer to test in order to reduce the thermal gradients and material temperature. The problem is numerically solved by means of the Finite Element Method (FEM) and, subsequently, some numerical simulations are also presented
On the effect of solute-solvent Pauli repulsion on n → π* transition for acrolein in water solution
Full text linkIn this work, we present a method to compute the Pauli repulsion contribution to the solute-solvent interaction that exploits solute electronic configurations sampled by Quantum Monte Carlo simulations. Starting from the inspiring model of Amovilli and Mennucci, the discreteness of the solvent is recovered by the definition of molecular domains and the concept of probe molecule. The method can be calibrated on the solute ground state but it offers the advantage of being able to be applied also to electronic-excited states. We show the results for the formaldehyde-water intermolecular pair, here used for the calibration, and two clusters containing acrolein surrounded by 11 and 19 water molecules simulating the solvation shell. In these systems, hydrogen bonds are formed between the solute and the water molecules and we found that, in such case, the Pauli repulsion contribution gives a red shift in the n → π* vertical transition energy
Intermolecular Pauli repulsion: a QMC study of molecules in ground and excited state in free space and in solution
Full text linkIn this work we present a method to compute the Pauli repulsion interaction energy between two molecules and for a molecule solvated by a discrete medium. The method of Amovilli and Mennucci, that has been developed within a continuum solvent model approach, is here revised in order to treat the solvation environment with a discrete number of solvent molecules. In our model, one of the two interacting systems, and the solvent in the case of solvation, acts as ‘probe’. A probe has a volume domain defined by the atomic spheres centred on the nuclei of the relevant molecule. The probe measures the fraction of electrons of the solute molecule falling in its domain leading to the evaluation of Pauli repulsion energy. To this end, Quantum Monte Carlo calculations are used to sample the electronic configurations of the solute. The method has been designed to be applied also to excited states. We show results for test systems in the ground state and for the ground and the (Formula presented.) excited states of acetone in a cluster with 14 water molecules
How increasing pressure affects the ion hydration structure and shell properties at ambient temperature
Full text linkThis work deals with the effect of increasing pressure at 298.15 K on the structure and hydration shell properties of ions in infinitely diluted solutions. Results were obtained from NPT Monte Carlo simulations at various pressures, from 1 atm up to 8000 atm, for some alkali metal, alkaline earth and halide ions in TIP4P water. As pressure increases, the ion-O and the ion-H radial distribution functions (rdfs) are subjected to changes to differing extents depending on both the charge and the size of the ion. The first peak of the ion-O rdf is shifted to a shorter distance from the ion for Cs+, Br− and I−, while in the other cases there is no evidence of shortening. In contrast, for the alkaline earth ions, the most prominent effect is the decrease in the height of the first peak. Minima positions of the ion-O rdfs were used to define the first and the second hydration shells at a given pressure. Water dipole orientation with respect to the radial direction was examined, showing that at higher pressures the ion-dipole interaction becomes less attractive than at 1 atm. A much less favorable orientation was found for waters in the first shell of halide ions. Shell properties were computed from definite integrals of the ion-O rdfs, such as the coordination number and the shell contribution to the excess volume. For the first hydration shell, apart from Ca2+, there is a significant increase in the coordination number upon increasing pressure. This effect becomes more important the larger the ion size is and this is very significant for alkali metal and halide ions. In the case of I− the gap observed between 4 katm and 5 katm reflects the striking effect of increasing pressure on the shell definition. The coordination number remains almost constant when using an alternative boundary for the shell. This was suggested by the radial distribution of water-dipole orientations. Shell excess volume contributions are discussed by examining their dependence on pressure. Electrostriction is shown for the first shell, while the second shell's contribution to the excess volume is positive. At a higher pressure, the shell electrostrictive volume per water molecule is always less than at 1 atm. The greatest effect is shown for the first shell of alkaline earth. The effect of a different shell boundary is examined on the shell quantities of halide ions
Ionic hydration at ambient and higher pressures: Computed chemical potentials from simulations and finite-size effects
No full textFor the chemical potential of a hydrated mono-atomic ion,
finite- size effects on simulation results obtained using molecular potential truncation are investigated. Free energy perturbation (FEP) calculations
were carried out by scaling in two processes the Lennard-Jones (LJ) ion-water parameters and the ion-charge (q) for Br-, K+ and Ca2+ interacting with TIP4P water. Corrections which scale with q2 enable us to reduce finite-size effects.
However, at ambient conditions, discrepancies which depend on q are shown by the corrected values when comparison is made with the experimental data
of the Marcus compilation. Similar behavior was observed
by extrapolating the original FEP results to an infinitely large system.
Hence, these errors were assumed to depend on water density and corrected at high pressures. Consistency, within statistical uncertainties, is shown when comparing with results derived from computed volumetric quantities.
Results are also compared with those derived from experimental values of excess volumes at ambient conditions
Calculation of potential energy surfaces with quantum Monte Carlo as a useful tool for the design of green chemical syntheses: The HOCO radical test case.
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AUTOEFFICACIA E BENESSERE PSICOLOGICO E LAVORATIVO DEGLI INSEGNANTI IN TEMPO DI COVID-19
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