Generation of rotationally dominated galaxies by mergers of pressure-supported progenitors

Through the analysis of a set of numerical simulations of major mergers between initially non-rotating, pressure supported progenitor galaxies with a range of central mass concentrations, we have shown that: (1) it is possible to generate elliptical-like galaxies, with v/sigma > 1 outside one effective radius, as a result of the conversion of orbital- into internal-angular momentum; (2) the outer regions acquire part of the angular momentum first; (3) both the baryonic and the dark matter components of the remnant galaxy acquire part of the angular momentum, the relative fractions depend on the initial concentration of the merging galaxies. For this conversion to occur the initial baryonic component must be sufficiently dense and/or the encounter should take place on a orbit with high angular momentum. Systems with these hybrid properties have been recently observed through a combination of stellar absorption lines and planetary nebulae for kinematic studies of early-type galaxies. Our results are in qualitative agreement with such observations and demonstrate that even mergers composed of non-rotating, pressure-supported progenitor galaxies can produce early-type galaxies with significant rotation at large radii.Comment: 5 pages, 6 figures, 2 tables. Accepted for publication in A&A Letter

Two-fluid gravitational instabilities in a galactic disk

We forlulate and solve the hydrodynamic equations describing an azimuthally symmetric galactic disk as a. two-fluid system. The stars and the gas are treated as two different isothermal fluids of different velocity dispersions (Cs >> Cg ), which interact gravitationally with each other. The disk is supported by rotation and random motion. The formulation of the equations closely follows the one-fluid treatment by Toomre. We solve the lineraized perturbation equations by the method of modes, and study the stability of the galactic disk agaInst the growth of axisymmetric two-fluid gravitational instabilities. We find that even when both the fluids in a two-fluid system are separately stable, the joint two-fluid system, because of the gravitational interaction between the two fluids, may be unstable. The ratio of the gas contnbution to the stellar contribution toward the formation of two-fluid instabilities is substantially greater than μg/μs, the ratio of their respective surface densities; this is due to the lower gas velocity dispersion as compared to the stellar velocity dispersion (Cg << Cs). The two contributions are comparable when the gas fraction (μg/μs) IS only ~ 0.10-0.25. Therefore, a galactic disk is a meaningful two-fluid system even when the gas constitutes only 1O %-20 % of the total surface density. The ratio of the amplitude in the gas to the amplItude In the stars is an increasIng function of the wavenumber of the two-fluid perturbation. The wavelength and the time of growth of a typical two-fluid instability in the inner galaxy, for μg/μs = 0.1-0.2, and ~2-3 kpc and ~2-4 × 107 years, respectively, and each of these contains gas of mass 4 × 107-108 M. The two-fluid analysis presented here is applocable to any general disk galaxy consisting of stars and gas

Patterns in abundance and diversity of faecally dispersed parasites of tiger in Tadoba National Park, central India

BACKGROUND: Importance of parasites in ecological and evolutionary interactions is being increasingly recognized. However, ecological data on parasites of important host species is still scanty. We analyze the patterns seen in the faecal parasites of tigers in the Tadoba National Park, India, and speculate on the factors and processes shaping the parasite community and the possible implications for tiger ecology. RESULTS: The prevalence and intensities were high and the parasite community was dominated by indirect life cycle parasites. Across all genera of parasites variance scaled with the square of the mean and there was a significant positive correlation between prevalence and abundance. There was no significant association between different types of parasites. CONCLUSIONS: The 70 samples analyzed formed 14 distinct clusters. If we assume each of the clusters to represent individual tigers that were sampled repeatedly and that resident tigers are more likely to be sampled repeatedly, the presumed transient tigers had significantly greater parasite loads than the presumed resident ones

Ecology of ficus religiosa accounts for its association with religion

While many plants and trees in specific areas acquire cult significance, very few such as Ficus religiosa L. have acquired a universal status. This hemiepiphyte, Ficus religiosa L., is of dual interest since it venerated by a quarter of the present mankind (Hindus and Buddhists, largely Asian) on one hand and also since these plants are blamed for destruction of buildings due to their ability to grow on buildings. Divergence in views exists whether epiphytic plants exert a destructive influence on buildings. A focused survey of the coastal forts on land and sea has shown uniformly that the naturally growing plants of certain Ficus sp., notably Ficus religiosa L., grow exclusively on the vertical sheer side of rock faces and not either on the ground or on the top surface of these 8-10 centuries old rock structures; also seen on the side of rock piles as recent as 4-5 years as well as in sacred groves of several centuries to millennia old. We could trace the roots through these structures from beginning to the end in many parts of these forts, especially when there are overhanging structures at entrances. The root tips, the point of growth, would be far too insignificant to account for destruction in any of these large rock-and-lime masonry structures while vibration per se was insignificant as the tree was seen in all forts on land or sea. The association with religion of the distinctive Ficus religiosa itself appears to be self-evident from its socio-anthropological association with rock piles, hitherto not visualized for any flora and logically appears to pre-date both Hinduism and Buddhism

Co-Localization of DNA i-Motif-Forming Sequences and 5-Hydroxymethyl-cytosines in Human Embryonic Stem Cells

G-quadruplexes (G4s) and i-motifs (iMs) are tetraplex DNA structures. Sequences capable of forming G4/iMs are abundant near the transcription start sites (TSS) of several genes. G4/iMs affect gene expression in vitro. Depending on the gene, the presence of G4/iMs can enhance or suppress expression, making it challenging to discern the underlying mechanism by which they operate. Factors affecting G4/iM structures can provide additional insight into their mechanism of regulation. One such factor is epigenetic modification. The 5-hydroxymethylated cytosines (5hmCs) are epigenetic modifications that occur abundantly in human embryonic stem cells (hESC). The 5hmCs, like G4/iMs, are known to participate in gene regulation and are also enriched near the TSS. We investigated genomic co-localization to assess the possibility that these two elements may play an interdependent role in regulating genes in hESC. Our results indicate that amongst 15,760 G4/iM-forming locations, only 15% have 5hmCs associated with them. A detailed analysis of G4/iM-forming locations enriched in 5hmC indicates that most of these locations are in genes that are associated with cell differentiation, proliferation, apoptosis and embryogenesis. The library generated from our analysis is an important resource for investigators exploring the interdependence of these DNA features in regulating expression of selected genes in hESC

Deposition of polymer bilayer configuration by pulsed laser ablation and its use for study of polymer-polymer interface

Thin films of polyphenylene sulphide (PPS) and polyethylene (PE) polymers have been deposited in a bilayer configuration using pulsed excimer laser ablation. Such bilayer specimens have been annealed at different temperatures, up to a maximum of 120°C, and for different time intervals, up to a maximum of 110 min, to investigate the evolution of the interface. By employing the technique of spectroscopic ellipsometry, the nature and the degree of thermally induced polymeric transport across the interface are brought out