The Static Dielectric Constant of a Colloidal Suspension

We derive an expression for the static dielectric constant of the colloidal susp ensions based on the electrokinetic equations. The analysis assumes that the ions have the same diffusivity, and that the double layer is much thinner than the radius of curvature of the particles. It is shown that the dielectric increment of the double layer polarization mechanism is originated from the free energy stored in the salt concentration inhomogeniety. We also show that the dominant polarization charges in the theory are at the electrodes, rather than close to the particles.Comment: 15 pages, 1 figur

Mitchell Ohriner, "Flow: The Rhythmic Voice in Rap Music"

Review of Mitchell Ohriner's Flow: The Rhythmic Voice In Rap Musi

‘Wot do u call it? Doof doof’: Articulations of glocality in Australian grime music

Grime music emerged at the turn of the millennium in the United Kingdom. While grounded and street-level at its outset, the form has since become global in reach. This article focuses on performance practice in the East Australian grime scene and its development over time. Principally, it attends to how MCs and DJs articulate a sense of belonging to both the UK and their local communities in Melbourne and Sydney, through lyrical and musical signification. These articulations are shown to be an example of ‘glocal’ performance practice, which is locally situated yet globally rendering. The article also demonstrates how these artists’ conceptions of legitimate practice are heavily mediated by YouTube videos of canonical UK practice, owing to their geographical dislocation from the genre’s initial point of origin. As a result, radio performances – known as ‘sets’ – and live shows are often prioritized over recorded releases. These findings are supported by interviews with Australian artists, and musical analysis of two key performances: a radio set on Australian broadcaster Triple J from November 2018 and a global grime showcase on London’s Rinse FM from January 2019

Pirate mentality: How London radio has shaped creative practice in grime music

Grime music is an Afrodiasporic performance form originating in London. While artists such as Stormzy and Skepta are now international stars, its gestation took place within a grounded network of record shops, radio stations and raves. This article argues for grime pirate radio’s role as both an oppositional channel and site of creative practice. Based on empirical work undertaken from 2017 to 2019 in London’s grime scene, it demonstrates how artists harness radio’s communicative power to engender a Black counterpublic, before outlining a framework for creative agency: afforded by a network of stations and practitioners; made meaningful through its community of listeners; and realized through improvisatory practice. Existing studies focusing on pirate radio often present these fora as domains for dissemination. In grime, however, its creative function highlights the potentiality of radio as a performance medium: a space for quotidian belonging and co-presence, but also for musical development and grassroots practice

Interplay of shear and bulk viscosity in generating flow in heavy-ion collisions

We perform viscous hydrodynamic calculations in 2+1 dimensions to investigate the influence of bulk viscosity on the viscous suppression of elliptic flow in non-central heavy-ion collisions at RHIC energies. Bulk and shear viscous effects on the evolution of radial and elliptic flow are studied with different model assumptions for the transport coefficients. We find that the temperature dependence of the relaxation time for the bulk viscous pressure, especially its critical slowing down near the quark-hadron phase transition at T_c, partially offsets effects from the strong growth of the bulk viscosity itself near T_c, and that even small values of the specific shear viscosity eta/s of the fireball matter can be extracted without large uncertainties from poorly controlled bulk viscous effects.Comment: 13 pages, 7 figures, 1 table. Submitted to Physical Review C. v2: corrected typos in several entries in Table

Nickel-iron-selenium hydrogenases - An overview

[NiFeSe] hydrogenases are a subgroup of the large family of [NiFe] hydrogenases in which a selenocysteine ligand coordinates the Ni atom at the active site. As observed for other selenoproteins, the [NiFeSe] hydrogenases display much higher catalytic activities than their Cys-containing homologues. Here, we review the biochemical, catalytic, spectroscopic and structural properties of known [NiFeSe] hydrogenases, namely from the Hys (group 1 [NiFeSe] hydrogenase), Fru (F420-reducing [NiFeSe] hydrogenases) and Vhu families (F420-non-reducing [NiFeSe] hydrogenases). A survey of new [NiFeSe] hydrogenases present in the databases showed that all enzymes belong to either group 1 periplasmic uptake hydrogenases (Hys) or to group 3 cytoplasmic hydrogenases (Fru and Vhu) and are present in either sulfate-re-ducing or methanogenic microorganisms. In both kinds of organisms, the [NiFeSe] hydrogenases are preferred over their Cys-containing homologues if selenium is available. Since no structural information is available for the Vhu and Fru enzymes, we have modelled the large subunit of these enzymes and analyzed the area surrounding the active site. Three [NiFeSe] hydrogenases of the Hys and Vhu types were identified in which the selenocysteine residue is found in a different location in the sequence, which could result in a different coordination to the Ni atom. The high activity and fast reactivation, together with a degree of oxygen tolerance for the H2-production activity, make the Hys hydrogenases attractive catalysts for technological applications. © 2011 Wiley-VCH Verlag GmbH & Co. KGaA.This work was supported by research grants PTDC/BIAPRO/70429/2006 funded by Fundação para a Ciência e Tecnologia (FCT, MCES, Portugal) and European Union FEDER program, and CTQ2006-12097 funded by the Ministerio de Ciencia e Innovacion (Spain).Peer Reviewe

Triggering the Formation of Halo Globular Clusters with Galaxy Outflows

We investigate the interactions of high-redshift galaxy outflows with low-mass virialized (Tvir < 10,000K) clouds of primordial composition. While atomic cooling allows star formation in larger primordial objects, such "minihalos" are generally unable to form stars by themselves. However, the large population of high-redshift starburst galaxies may have induced widespread star formation in these objects, via shocks that caused intense cooling both through nonequilibrium H2 formation and metal-line emission. Using a simple analytic model, we show that the resulting star clusters naturally reproduce three key features of the observed population of halo globular clusters (GCs). First, the 10,000 K maximum virial temperature corresponds to the ~ 10^6 solar mass upper limit on the stellar mass of GCs. Secondly, the momentum imparted in such interactions is sufficient to strip the gas from its associated dark matter halo, explaining why GCs do not reside in dark matter potential wells. Finally, the mixing of ejected metals into the primordial gas is able to explain the ~ 0.1 dex homogeneity of stellar metallicities within a given GC, while at the same time allowing for a large spread in metallicity between different clusters. To study this possibility in detail, we use a simple 1D numerical model of turbulence transport to simulate mixing in cloud-outflow interactions. We find that as the shock shears across the side of the cloud, Kelvin-Helmholtz instabilities arise, which cause mixing of enriched material into > 20% of the cloud. Such estimates ignore the likely presence of large-scale vortices, however, which would further enhance turbulence generation. Thus quantitative mixing predictions must await more detailed numerical studies.Comment: 21 pages, 11 figures, Apj in pres

Merging Rates of the First Objects and the Formation of First Mini-Filaments in Models with Massive Neutrinos

We study the effect of massive neutrinos on the formation and evolution of the first filaments containing the first star-forming halos of mass M~10^{6}M_sun at z~20. With the help of the extended Press-Schechter formalism, we evaluate analytically the rates of merging of the first star-forming halos into zero-dimensional larger halos and one-dimensional first filaments. It is shown that as the neutrino mass fraction f_{\nu} increases, the halo-to-filament merging rate increases while the halo-to-halo merging rate decreases sharply. For f_{\nu}<=0.04, the halo-to-filament merging rate is negligibly low at all filament mass scales, while for f_{\nu}>=0.07 the halo-to-filament merging rate exceeds 0.1 at the characteristic filament mass scale of ~10^{9}M_sun. The distribution of the redshifts at which the first filaments ultimately collapse along their longest axes is derived and found to have a sharp maximum at z~8. We also investigate the formation and evolution of the second generation filaments which contain the first galaxies of mass 10^{9}M_sun at z=8 as the parent of the first generation filaments. A similar trend is found: For f_{\nu}>= 0.07 the rate of clustering of the first galaxies into the second-generation filaments exceeds 0.3 at the characteristic mass scale of ~10^{11}M_sun. The longest-axis collapse of these second-generation filaments are found to occur at z~3. The implications of our results on the formation of massive high-z galaxies and the early metal enrichment of the intergalactic media by supernova-driven outflows, and possibility of constraining the neutrino mass from the mass distribution of the high-z central blackholes are discussed.Comment: Accepted for publication in ApJ, mistakes in the calculation of the merging rates corrected, feasibility study of constraining neutrino mass with high-z quasar luminosity function presented, discussion improved, 7 figure