The Effects of radial inflow of gas and galactic fountains on the chemical evolution of M31

Galactic fountains and radial gas flows are very important ingredients in modeling the chemical evolution of galactic disks. Our aim here is to study the effects of galactic fountains and radial gas flows in the chemical evolution of the disk of M31. We adopt a ballistic method to study the effects of galactic fountains on the chemical enrichment of the M31 disk. We find that the landing coordinate for the fountains in M31 is no more than 1 kpc from the starting point, thus producing negligible effect on the chemical evolution of the disk. We find that the delay time in the enrichment process due to fountains is no longer than 100 Myr and this timescale also produces negligible effects on the results. Then, we compute the chemical evolution of the M31 disk with radial gas flows produced by the infall of extragalactic material and fountains. We find that a moderate inside-out formation of the disk coupled with radial flows of variable speed can very well reproduce the observed gradient. We discuss also the effects of other parameters such a threshold in the gas density for star formation and an efficiency of star formation varying with the galactic radius. We conclude that the most important physical processes in creating disk gradients are the inside-out formation and the radial gas flows. More data on abundance gradients both locally and at high redshift are necessary to confirm this conclusion.Comment: Accepted by A&

The Fountains of Łódź: Their Relevance to the Lives of its Inhabitants

This paper presents the characteristics of the fountains of Łódź, their location in the public spaces of the city and changes in various time periods. Special attention is drawn to the function of fountains in contemporary cities and their social perception. Moreover, in the last part, the presumed reasons for their present distribution and typological variety are given

On turbulent particle fountains

We describe new experiments in which particle-laden turbulent fountains with source Froude numbers 20>Fr_{0}>6 are produced when particle-laden fresh water is injected upwards into a reservoir filled with fresh water. We find that the ratio $U$ of the particle fall speed to the characteristic speed of the fountain determines whether the flow is analogous to a single-phase fountain ($U\ll 1$) or becomes a fully separated flow ($U\geqslant 1$). In the single-phase limit, a fountain with momentum flux $M$ and buoyancy flux $B$ oscillates about the mean height, $h_{m}=(1.56\pm 0.04)M^{3/4}B^{-1/2}$, as fluid periodically cascades from the maximum height, $h_{t}=h_{m}+{\rm\Delta}h$, to the base of the tank. Experimental measurements of the speed $u$ and radius $r$ of the fountain at the mean height $h_{m}$, combined with the conservation of buoyancy, suggest that $Fr(h_{m})=u(g^{\prime }r)^{-1/2}\approx 1$. Using these values, we find that the classical scaling for the frequency of the oscillations, ${\it\omega}\sim BM^{-1}$, is equivalent to the scaling $u(h_{m})/r(h_{m})$ for a fountain supplied at $z=h_{m}$ with $Fr=1$ (Burridge &amp; Hunt, J. Fluid Mech., vol. 728, 2013, pp. 91–119). This suggests that the oscillations are controlled in the upper part of the fountain where $Fr\leqslant 1$, and that they may be understood in terms of a balance between the upward supply of a growing dense particle cloud, at the height where $Fr=1$, and the downward flow of this cloud. In contrast, in the separated flow regime, we find that particles do not reach the height at which $Fr=1$: instead, they are transported to the level at which the upward speed of the fountain fluid equals their fall speed. The particles then continuously sediment while the particle-free fountain fluid continues to rise slowly above the height of particle fallout, carried by its momentum.</jats:p

Galactic fountains and gas accretion

Star-forming disc galaxies such as the Milky Way need to accrete \gsim 1 $M_{\odot}$ of gas each year to sustain their star formation. This gas accretion is likely to come from the cooling of the hot corona, however it is still not clear how this process can take place. We present simulations supporting the idea that this cooling and the subsequent accretion are caused by the passage of cold galactic-fountain clouds through the hot corona. The Kelvin-Helmholtz instability strips gas from these clouds and the stripped gas causes coronal gas to condense in the cloud's wake. For likely parameters of the Galactic corona and of typical fountain clouds we obtain a global accretion rate of the order of that required to feed the star formation.Comment: 2 pages, 1 figure, to appear in "Hunting for the Dark: The Hidden Side of Galaxy Formation", Malta, 19-23 Oct. 2009, eds. V.P. Debattista & C.C. Popescu, AIP Conf. Se

Progress in Atomic Fountains at LNE-SYRTE

We give an overview of the work done with the Laboratoire National de M\'etrologie et d'Essais-Syst\`emes de R\'ef\'erence Temps-Espace (LNE-SYRTE) fountain ensemble during the last five years. After a description of the clock ensemble, comprising three fountains, FO1, FO2, and FOM, and the newest developments, we review recent studies of several systematic frequency shifts. This includes the distributed cavity phase shift, which we evaluate for the FO1 and FOM fountains, applying the techniques of our recent work on FO2. We also report calculations of the microwave lensing frequency shift for the three fountains, review the status of the blackbody radiation shift, and summarize recent experimental work to control microwave leakage and spurious phase perturbations. We give current accuracy budgets. We also describe several applications in time and frequency metrology: fountain comparisons, calibrations of the international atomic time, secondary representation of the SI second based on the 87Rb hyperfine frequency, absolute measurements of optical frequencies, tests of the T2L2 satellite laser link, and review fundamental physics applications of the LNE-SYRTE fountain ensemble. Finally, we give a summary of the tests of the PHARAO cold atom space clock performed using the FOM transportable fountain.Comment: 19 pages, 12 figures, 5 tables, 126 reference