39 research outputs found
The Iκεα model of feedback-regulated galaxy formation
We present the Iκεα model of galaxy formation, in which a galaxy’s star formation rate is set by the balance between energy injected by feedback from massive stars and energy lost by the deepening of the potential of its host dark matter halo due to cosmological accretion. Such a balance is secularly stable provided that the star formation rate increases with the pressure in the star forming gas. The Iκεα model has four parameters that together control the feedback from star formation and the cosmological accretion rate onto a halo. Iκεα reproduces accurately the star formation rate as a function of halo mass and redshift in the EAGLE hydrodynamical simulation, even when all four parameters are held constant. It predicts the emergence of a star forming main sequence along which the specific star formation rate depends weakly on stellar mass with an amplitude that increases rapidly with redshift. We briefly discuss the emerging mass-metallicity relation, the evolution of the galaxy stellar mass function, and an extension of the model that includes feedback from active galactic nuclei (AGN). These self-regulation results are independent of the star formation law and the galaxy’s gas content. Instead, star forming galaxies are shaped by the balance between stellar feedback and cosmological accretion, with accurately accounting for energy losses associated with feedback a crucial ingredient
Systematic review on applicability of magnetic iron-oxides integrated photocatalysts for degradation of organic pollutants in water
Owing to biocompatibility, abundance, and low cost, magnetic iron oxides are well suited for the design of efficient and magnetically separable photocatalysts for water treatment. This review presents a detailed survey of magnetic iron oxide–integrated photocatalysts (MIOIPs), in which we have discussed essential conditions needed for designing of efficient MIOIPs for water purification. The synthesis methods and detailed experimental setups for fabrication of MIOIPs were discussed, and the integration manners of iron oxides (Fe2O3, Fe3O4, FeO, and ferrites) with binary, ternary, and quaternary non-magnetic photocatalysts have been categorized. The mechanistic view of enhanced photocatalytic activity caused by different MIOIPs under various light sources was also elaborately argued. The role of various reactive species in photocatalytic oxidative degrading of organic pollutants was investigated. Altogether, this review article has compressively considered and discussed various signs of advancements made toward the synthesis of MIOIPs and their stability, recyclability, and catalytic efficacy for wastewater treatment
Supernovae and AGN driven galactic outflows
We present analytical solutions for winds from galaxies with NFW dark matter
halo. We consider winds driven by energy and mass injection from multiple
supernovae, as well as momentum injection due to radiation from a central black
hole. We find that the wind dynamics depends on three velocity scales: (a)
v_star \sim (\dot{E} / 2 \dot{M})^{1/2} describes the effect of starburst
activity, with \dot{E}, \dot{M} as energy and mass injection rate in a central
region of radius R; (b) \vbh ~ (G\mbh / 2 R)^{1/2} for the effect of a central
black hole of mass \mbh on gas at distance R and (c) v_{s} =(GM_h/ 2Cr_s)^{1/2}
which is closely related to the galaxy circular velocity, with C as a function
of halo concentration parameter. We find the wind terminal speed to be 2
(v_star^2 +1.5(\Gamma -1) \vbh^2 -v_s^2)^{1/2}, where \Gamma is the ratio of
force due to radiation pressure to gravity of the central black hole. We also
find that: (a) winds from quiescent star forming galaxies cannot escape from
10^{11.5} \le M_h \le 10^{12.5}Msun galaxies, (b) circumgalactic gas at large
distances should be present for galaxies in this mass range, (c) for an
escaping wind, the wind speed in low to intermediate mass galaxies is ~
400--1000 km/s, consistent with observed X-ray temperatures; (d) winds from
massive galaxies with AGN have speeds \gtrsim 1000 km/s. We also find that the
ratio [2 v_star ^2 -(1 -\Gamma) \vbh^2]/ v_c^2 dictates the amount of gas lost.
Used in conjunction with an appropriate relation between \mbh and M_h, and an
appropriate opacity of dust grains in IR (K band), this ratio becomes minimum
at a certain halo mass scale (M_h ~ 10^{12--12.5} Msun) that signifies the
cross-over of AGN domination in outflow properties from starburst activity at
lower masses. We find that stellar mass for massive galaxies scales as M_star
\propto M_h^{0.26},and for low mass galaxies, M_star \propto M_h^{5/3}.Comment: 20 pages, 6 figures, Accepted in ApJ, Comments Welcom
Simulation of radiation driven wind from disc galaxies
We present 2-D hydrodynamic simulation of rotating galactic winds driven by
radiation. We study the structure and dynamics of the cool and/or warm
component( K) which is mixed with dust. We have taken into
account the total gravity of a galactic system that consists of a disc, a bulge
and a dark matter halo. We find that the combined effect of gravity and
radiation pressure from a realistic disc drives the gas away to a distance of
kpc in Myr for typical galactic parameters. The outflow
speed increases rapidly with the disc Eddington parameter ) for . We find that the rotation speed of
the outflowing gas is km s. The wind is confined in a
cone which mostly consist of low angular momentum gas lifted from the central
region.Comment: 10 pages, 11 figures, Accepted for publication in MNRA
Optimization of Lignocellulose Degrading Enzyme Laccase from Basidiomycetes Using One Variable at a Time Approach
ABSTRACT Present study deals with the screening of few species of basidiomycetes for the production of laccase. Ten samples of basidiomycetes were collected from different lignocellulosic sources and best four fungal species viz., Schizophyllum sp., Polyporus sp., Phanerochaete sp. & Trametes sp. were screened for production of laccase. One Variable at a Time approach (OVAT) was used to study different parameters namely, pH, carbon and nitrogen sources, solid to liquid ratio and surfactants on the activity of laccase enzyme. Schizophyllum sp. showed maximum laccase activity (1060.5 IU ml -1 ) at pH 6.5 amongst all other parameters investigated. It showed maximum laccase activity of 10.5 IU ml -1 with NaNO 3 and Peptone
Ferroelectric and magnetic properties of Nd-doped Bi4 − xFeTi3O12 nanoparticles prepared through the egg-white method
Multiferroic behavior of Bi(4 − x)Nd(x)FeTi(3)O(12) (0.0 ≤ × ≤ 0.25, × = 0.05) ceramic nanoparticles prepared through the egg-white method was investigated. The dielectric properties of the samples show normal behavior and are explained in the light of space charge polarization. Room temperature polarization-electric field (P-E) curves show that the samples are not saturated with maximum remanence polarization, P(r) = 0.110 μC/cm(2), and a relatively low coercive field, E(c) = of 7.918 kV/cm, at an applied field of 1 kV/cm was observed for 5% Nd doping. The room temperature M-H hysteresis curve shows that the samples exhibit intrinsic antiferromagnetism with a weak ferromagnetism. These properties entitle the grown nanoparticles of BNFT as one of the few multiferroic materials that exhibit decent magnetization and electric polarization