The growth of galaxies in cosmological simulations of structure formation

We use hydrodynamic simulations to examine how the baryonic components of galaxies are assembled, focusing on the relative importance of mergers and smooth accretion in the formation of ~L_* systems. In our primary simulation, which models a (50\hmpc)^3 comoving volume of a Lambda-dominated cold dark matter universe, the space density of objects at our (64-particle) baryon mass resolution threshold, M_c=5.4e10 M_sun, corresponds to that of observed galaxies with L~L_*/4. Galaxies above this threshold gain most of their mass by accretion rather than by mergers. At the redshift of peak mass growth, z~2, accretion dominates over merging by about 4:1. The mean accretion rate per galaxy declines from ~40 M_sun/yr at z=2 to ~10 M_sun/yr at z=0, while the merging rate peaks later (z~1) and declines more slowly, so by z=0 the ratio is about 2:1. We cannot distinguish truly smooth accretion from merging with objects below our mass resolution threshold, but extrapolating our measured mass spectrum of merging objects, dP/dM ~ M^a with a ~ -1, implies that sub-resolution mergers would add relatively little mass. The global star formation history in these simulations tracks the mass accretion rate rather than the merger rate. At low redshift, destruction of galaxies by mergers is approximately balanced by the growth of new systems, so the comoving space density of resolved galaxies stays nearly constant despite significant mass evolution at the galaxy-by-galaxy level. The predicted merger rate at z<~1 agrees with recent estimates from close pairs in the CFRS and CNOC2 redshift surveys.Comment: Submitted to ApJ, 35 pp including 15 fig

Effect of the Milky Way on Magellanic Cloud structure

A combination of analytic models and n-body simulations implies that the structural evolution of the Large Magellanic Cloud (LMC) is dominated by its dynamical interaction with the Milky Way. Although expected at some level, the scope of the involvement has significant observational consequences. First, LMC disk orbits are torqued out of the disk plane, thickening the disk and populating a spheroid. The torque results from direct forcing by the Milky Way tide and, indirectly, from the drag between the LMC disk and its halo resulting from the induced precession of the LMC disk. The latter is a newly reported mechanism that can affect all satellite interations. However, the overall torque can not isotropize the stellar orbits and their kinematics remains disk-like. Such a kinematic signature is observed for nearly all LMC populations. The extended disk distribution is predicted to increase the microlensing toward the LMC. Second, the disk's binding energy slowly decreases during this process, puffing up and priming the outer regions for subsequent tidal stripping. Because the tidally stripped debris will be spatially extended, the distribution of stripped stars is much more extended than the HI Magellanic Stream. This is consistent with upper limits to stellar densities in the gas stream and suggests a different strategy for detecting the stripped stars. And, finally, the mass loss over several LMC orbits is predicted by n-body simulation and the debris extends to tens of kiloparsecs from the tidal boundary. Although the overall space density of the stripped stars is low, possible existence of such intervening populations have been recently reported and may be detectable using 2MASS.Comment: 15 pages, color Postscript figures, uses emulateapj.sty. Also available from http://www-astro.phast.umass.edu/~weinberg/weinberg-pubs.htm

Bifurcations, Chaos, Controlling and Synchronization of Certain Nonlinear Oscillators

In this set of lectures, we review briefly some of the recent developments in the study of the chaotic dynamics of nonlinear oscillators, particularly of damped and driven type. By taking a representative set of examples such as the Duffing, Bonhoeffer-van der Pol and MLC circuit oscillators, we briefly explain the various bifurcations and chaos phenomena associated with these systems. We use numerical and analytical as well as analogue simulation methods to study these systems. Then we point out how controlling of chaotic motions can be effected by algorithmic procedures requiring minimal perturbations. Finally we briefly discuss how synchronization of identically evolving chaotic systems can be achieved and how they can be used in secure communications.Comment: 31 pages (24 figures) LaTeX. To appear Springer Lecture Notes in Physics Please Lakshmanan for figures (e-mail: [email protected]

The Magellanic Stream and the density of coronal gas in the Galactic halo

The properties of the Magellanic Stream constrain the density of coronal gas in the distant Galactic halo. We show that motion through ambient gas can strongly heat Stream clouds, driving mass loss and causing evaporation. If the ambient gas density is too high, then evaporation occurs on unreasonably short timescales. Since heating dominates drag, tidal stripping appears to be responsible for producing the Stream. Requiring the survival of the cloud MS IV for 500 Myr sets an upper limit on the halo gas density n_H< 10^{-5} cm^{-3} at 50 kpc, roughly a factor of 10 lower than that estimated from the drag model of Moore & Davis (1994). Implications for models of the evolution of gas in galaxy halos are discussed.Comment: 4 pages, 1 figure, in press, ApJ

Ultrasound-Assisted PSA Catalyzed One-Pot Green Synthesis of Pyrazolyl Pyrrole Derivatives

A fast, efficient and environmentally benign synthesis of pyrazolyl pyrrole derivatives has been developed by the one-pot multicomponent reaction of an aldehyde, nitroalkane, amine, and enolizable reactant with active C-H group, using Phosphosulfonic acid (PSA) as reusable solid acid catalyst under mild, solvent-free, ultra-sonication conditions. In comparison to the existing conventional methods, this green and efficient protocol provides remarkable advantages such as good to excellent yields, lower reaction time, less cost, easy work-up and solvent-free. © 2020 Author(s).The authors are thankful to Prof. C. Devendranath Reddy, Department of Chemistry, S.V. University, Tirupati for his helpful discussions and acknowledge DST-PURSE 2nd Phase Programme in S.V. University, Tirupati funded by DST-New Delhi, India for providing instrumentation facility and funding to Mr. Gundluru Mohan through SRF (File No: 17118-UGC-III (3)/ DST-PURSE 2nd Phase/2017, Dt: 23-08-2018)

The Efficiency of Globular Cluster Formation

(Abridged): The total populations of globular cluster systems (GCSs) are discussed in terms of their connection to the efficiency of globular cluster formation---the mass fraction of star-forming gas that was able to form bound stellar clusters rather than isolated stars or unbound associations---in galaxy halos. Observed variations in GCS specific frequencies (S_N=N_gc/L_gal), both as a function of galactocentric radius in individual systems and globally between entire galaxies, are reviewed in this light. It is argued that trends in S_N do not reflect any real variation in the underlying efficiency of cluster formation; rather, they result from ignoring the hot gas in many large ellipticals. This claim is checked and confirmed in each of M87, M49, and NGC 1399, for which existing data are combined to show that the volume density profile of globular clusters, rho_cl, is directly proportional to the sum of (rho_gas+rho_stars) at large radii. The constant of proportionality is the same in each case: epsilon=0.0026 +/- 0.0005 in the mean. This is identified with the globular cluster formation efficiency. The implication that epsilon might have had a universal value is supported by data on the GCSs of 97 early-type galaxies, on the GCS of the Milky Way, and on the ongoing formation of open clusters. These results have specific implications for some issues in GCS and galaxy formation, and they should serve as a strong constraint on more general theories of star and cluster formation.Comment: 36 pages with 11 figures; accepted for publication in The Astronomical Journa

One-step simultaneous liquid phase exfoliation-induced chirality in graphene and their chirality-mediated microRNA delivery

Graphene (G) has established itself as an exciting prospect for a broad range of applications owing to its remarkable properties. Recent innovations in chiral nanosystems have led to sensors, drug delivery, catalysis, etc. owing to the stereospecific interactions between various nanosystems and enantiomers. As the molecular structure of G itself is achiral introducing chirality in G by simple attachment of a functional group (a chiral ligand) on the G nanosheet may result in more diverse applications. Herein, we demonstrate direct liquid phase exfoliation and chiral induction in G nanosheets abbreviated as L-graphene and D-graphene in the presence of chiral L-tyrosine and D-tyrosine and by applying high-temperature sonication. The obtained exfoliated nanosheets demonstrated stable chirality confirmed by circular dichroism. Fourier transform infrared (FTIR) spectra, Raman spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and differential scanning calorimetry (DSC) showed functional, structural, morphological, surface, and thermal characteristics of L-graphene and D-graphene. The hemo-compatibility of these chiral graphenes was evaluated for the very first time utilizing human red blood cells. Lastly, for the very first time, an attempt was made to explore enantiomeric binding between chiral L-graphene and D-graphene with microRNA (miR-205) and their possibility towards chirality-mediated gene delivery in prostate cancerous cells

Green Synthesis of 2-amino-3-cyano-4H-chromen-4-ylphosphonates

A facile and highly efficient and green synthetic protocol is developed for the bioactive 2-amino-3-cyano-4H-chromen-4-ylphosphonates by the one-pot reaction of various salicylaldehydes, malononitrile, and diethyl phosphite using sulfamic acid as an efficient, reusable and heterogeneous solid acid catalyst. All the synthesized compounds were characterized by their 1H-NMR, 13C-NMR, 31P-NMR, and Mass spectral studies. © 2020 Author(s).The authors are thankful to Prof. C. Devendranath Reddy, Department of Chemistry, S.V. University, Tirupati for his helpful discussions and acknowledge DST-PURSE 2nd Phase Programme in S.V. University, Tirupati funded by DST-New Delhi, India for providing instrumentation facility and funding to Mr. Gundluru Mohan through SRF (File No: 17118-UGC-III(3)/ DST-PURSE 2nd Phase/2017, Dt: 23-08-2018)

Genotoxic and antibacterial nature of biofabricated zinc oxide nanoparticles from Sida rhombifolia linn

Phyto-assisted synthesis of zinc oxide nanoparticles (ZnO-NPs) has gained importance because of their stable and eco-friendly nature with significant biological properties compared to chemically synthesized NPs. In the present study biofabrication of ZnO-NPs were carried out using aqueous leaf extract of Sida rhombifolia Linn. The biofabricated ZnO-NPs showed an absorption peak at 307 nm and bandgap energy of 3.51 eV with an average size of similar to 30 nm. The XRD analysis revealed stiff narrow peaks confirming the particles were of no impurities, which were in agreement with EDS analysis. The biofabricated ZnO-NPs exhibited significant antibacterial activity with a MIC of 0.25 mg mL(-1) against E. coli, while it was 0.5 mg mL(-1) against B. subtilis and S. typhi. The live and dead cell analysis of the nanoparticles confirmed that the antibacterial activity was due to damage in the cell walls of the test pathogens. Further, the nanoparticles also offered significant antioxidant and genotoxic properties with an IC50 of 974.5 mu g mL(-1) and 548.4 mu g mL(-1), respectively