86,170 research outputs found
Joint Formation of QSOs and Spheroids: QSOs as clocks of star formation in Spheroids
Direct and indirect observational evidence leads to the conclusion that high
redshift QSOs did shine in the core of early type proto-galaxies during their
main episode of star formation. Exploting this fact, we derive the rate of
formation of this kind of stellar systems at high redshift by using the QSO
Luminosity Function. The elemental proportions in elliptical galaxies, the
descendents of the QSO hosts, suggest that the star formation was more rapid in
more massive objects. We show that this is expected to occur in Dark Matter
haloes, when the processes of cooling and heating is considered. This is also
confirmed by comparing the observed sub-mm counts to those derived by coupling
the formation rate and the star formation rate of the spheroidal galaxies with
a detailed model for their SED evolution. In this scenario SCUBA galaxies and
Lyman Break Galaxies are early type proto-galaxies forming the bulk of their
stars before the onset of QSO activity.Comment: 13 pages, 8 figures, accepted by MNRAS, major revision of the
formalis
Doubly-periodic array of bubbles in a Hele-Shaw cell
Exact solutions are presented for a doubly-periodic array of steadily moving
bubbles in a Hele-Shaw cell when surface tension is neglected. It is assumed
that the bubbles either are symmetrical with respect to the channel centreline
or have fore-and-aft symmetry, or both, so that the relevant flow domain can be
reduced to a simply connected region. By using conformal mapping techniques, a
general solution with any number of bubbles per unit cell is obtained in
integral form. Several examples are given, including solutions for multi-file
arrays of bubbles in the channel geometry and doubly-periodic solutions in an
unbounded cell.Comment: 15 pages, 12 figure
Liquid mixtures involving fluorinated alcohols: The equation of state (p, r, T, x) of (Ethanol + Trifluoroethanol) Experimental and Simulation
Liquid mixtures involving fluorinated alcohols:
The equation of state (p, r, T, x) of (Ethanol + Trifluoroethanol)
Experimental and Simulation
Pedro Duartea, Djêide Rodriguesa, Marcelo Silvaa, Pedro Morgadoa,
Luís Martinsa,b and Eduardo J. M. Filipea*
aCentro de Química Estrutural, Instituto Superior Técnico, 1049-001 Lisboa, Portugal
bCentro de Química de Évora, Universidade de Évora, 7000-671 Évora, Portugal
Fluorinated alcohols are substances with unique properties and high technological value in the pharmaceutical and chemical industries. Trifluoroethanol (TFE), in particular, displays a number of unusual properties as a solvent. For example, it dissolves nylon at room temperature and is effectively used as solvent in bioengineering. The presence of the three fluorines atoms gives the alcohol a high ionization constant, strong hydrogen bonding capability and stability at high temperatures.
In the pharmaceutical industry, TFE finds use as the major raw material for the production of inhalation anesthetics. Mixtures of TFE and water (known as Fluorinols®) are used as working fluids for Rankine cycle heat engines for terrestrial and space applications, as a result of a unique combination of physical and thermodynamic properties such as high thermal efficiency and excellent turbine expansion characteristics.
Environmentally, TFE is a CFC substitute with an acceptable short lifetime and with small ozone depletion potential. Additionally, TFE is known to induce conformational changes in proteins and it is used as a co-solvent to analyze structural features of partially folded states.
The (ethanol + TFE) system displays an interesting and peculiar behaviour, combining a negative azeotrope with high positive excess volumes.
In this work, liquid mixtures of (ethanol + TFE) were investigated. The densities of the mixtures were measured as a function of composition between 278K and 338K and at pressures up to 700 bar. The corresponding excess volumes as a function of temperature and pressure, the isothermal compressibilities and thermal expansivities were calculated from the experimental results. The mixtures are highly non-ideal with excess volumes ranging from 0.8 - 1.0 cm3mol-1.
Finally, molecular dynamic simulations were performed to model and interpret the experimental results. The Trappe force field was used to simulate the (TFE + ethanol) mixtures and calculate the corresponding excess volumes. The simulation results are able to reproduce the correct sign and order of magnitude of the experimental VE without fitting to the experimental data. Furthermore, the simulations suggest the presence of a particular type of hydrogen bridge between ethanol and TFE, that can help to rationalize the experimental results
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