System-Size Dependence in Grand Canonical and Canonical Ensembles

The thermodynamics for a system with given temperature, density, and volume is described by the Canonical ensemble. The thermodynamics for a corresponding system with the same temperature, volume, and average density is described by the Grand Canonical ensemble. In general a chosen thermodynamic potential (e.g., free energy) is different in the two cases. Their relationship is considered here as a function of the system size. Exact expressions relating the fundamental potential for each (free energy and pressure, respectively) are identified for arbitrary system size. A formal asymptotic analysis for large system size gives the expected equivalence, but without any characterization of the intermediate size dependence. More detailed evaluation is provided for the simple case of a homogeneous, non-interacting Fermi gas. In this case, the origin of size dependence arises from only two length scales, the average inter-particle distance and quantum length scale (thermal deBroglie or Fermi length). The free energies per particle calculated from each ensemble are compared for particle numbers $2\le N\le 64$ for a range of temperatures above and below the Fermi temperature. The relevance of these results for applications of density functional theory is discussed briefly.Comment: 13 pages, 8 figure

A Spreading Danger: Time for a New Policy towards Chechnya. CEPS Policy Briefs No. 68, 1 April 2005

The ongoing conflict in and around Chechnya is helping to feed the wider international jihadi movement, and is endangering the West as well as Russia. The next “soft target” of North Caucasian terrorism could be a Western one. Mutual recriminations over the conflict have badly damaged relations between Russia and the West. While most of the blame for this lies with Russian policies, the Western approach to the issue has often been unhelpful and irresponsible. Denunciations of Russian behaviour have not been matched by a real understanding of the Chechen conflict or a real commitment to help. In their own interest, Western countries need urgently to address the crisis in the North Caucasus. This requires them to recognize the seriousness of the threat, to open a real dialogue on cooperation with Russia rather than simply making criticisms, and to make a serious economic contribution to the region

Transportation of water-based slurry in an open furrow, launder or stream

The transport of large boulders in a furrow from a mining area to a nearby pond was considered. The furrow is filled with a mixture of water and soil particles flowing down to the pond at a very high velocity. Due to operating constraints, the slope of the furrow is reduced progressively. A formula is derived, relating the slope of the furrow and the composition of the fluid to the maximum size and shape of the transported boulders. The characteristics of the boulders carried all the way down to the pond may then be determined

Density PDFs of diffuse gas in the Milky Way

The probability distribution functions (PDFs) of the average densities of the diffuse ionized gas (DIG) and the diffuse atomic gas are close to lognormal, especially when lines of sight at |b|5 degree are considered separately. Our results provide strong support for the existence of a lognormal density PDF in the diffuse ISM, consistent with a turbulent origin of density structure in the diffuse gas.Comment: 4 pages, 1 figure. To be published in the proceedings of the August 2008 conference (held in Eapinho, Portugal) "The Role of Disk-Halo Interaction in Galaxy Evolution: Outflow vs Infall?", Ed. M. A. de Avillez, EAS Publications Serie

The AMBRE Project: Parameterisation of FGK-type stars from the ESO:HARPS archived spectra

The AMBRE project is a collaboration between the European Southern Observatory (ESO) and the Observatoire de la Cote d'Azur (OCA). It has been established to determine the stellar atmospheric parameters (effective temperature, surface gravity, global metallicities and abundance of alpha-elements over iron) of the archived spectra of four ESO spectrographs. The analysis of the ESO:HARPS archived spectra is presented. The sample being analysed (AMBRE:HARPS) covers the period from 2003 to 2010 and is comprised of 126688 scientific spectra corresponding to 17218 different stars. For the analysis of the spectral sample, the automated pipeline developed for the analysis of the AMBRE:FEROS archived spectra has been adapted to the characteristics of the HARPS spectra. Within the pipeline, the stellar parameters are determined by the MATISSE algorithm, developed at OCA for the analysis of large samples of stellar spectra in the framework of galactic archaeology. In the present application, MATISSE uses the AMBRE grid of synthetic spectra, which covers FGKM-type stars for a range of gravities and metallicities. We first determined the radial velocity and its associated error for the ~15% of the AMBRE:HARPS spectra, for which this velocity had not been derived by the ESO:HARPS reduction pipeline. The stellar atmospheric parameters and the associated chemical index [alpha/Fe] with their associated errors have then been estimated for all the spectra of the AMBRE:HARPS archived sample. Based on quality criteria, we accepted and delivered the parameterisation of ~71% of the total sample to ESO. These spectra correspond to ~10706 stars; each are observed between one and several hundred times. This automatic parameterisation of the AMBRE:HARPS spectra shows that the large majority of these stars are cool main-sequence dwarfs with metallicities greater than -0.5 dex

Helioseismic Ring Analysis of CME Source Regions

We apply the ring diagram technique to source regions of halo coronal mass ejections (CMEs) to study changes in acoustic mode parameters before, during, and after the onset of CMEs. We find that CME regions associated with a low value of magnetic flux have line widths smaller than the quiet regions implying a longer life-time for the oscillation modes. We suggest that this criterion may be used to forecast the active regions which may trigger CMEs.Comment: Accepted for publication in J. Astrophys. Astr. Also available at http://www2.nso.edu/staff/sushant/paper.htm