Cosmological Shock Waves in the Large Scale Structure of the Universe: Non-gravitational Effects

Cosmological shock waves result from supersonic flow motions induced by hierarchical clustering of nonlinear structures in the universe. These shocks govern the nature of cosmic plasma through thermalization of gas and acceleration of nonthermal, cosmic-ray (CR) particles. We study the statistics and energetics of shocks formed in cosmological simulations of a concordance $\Lambda$CDM universe, with a special emphasis on the effects of non-gravitational processes such as radiative cooling, photoionization/heating, and galactic superwind feedbacks. Adopting an improved model for gas thermalization and CR acceleration efficiencies based on nonlinear diffusive shock acceleration calculations, we then estimate the gas thermal energy and the CR energy dissipated at shocks through the history of the universe. Since shocks can serve as sites for generation of vorticity, we also examine the vorticity that should have been generated mostly at curved shocks in cosmological simulations. We find that the dynamics and energetics of shocks are governed primarily by the gravity of matter, so other non-gravitational processes do not affect significantly the global energy dissipation and vorticity generation at cosmological shocks. Our results reinforce scenarios in which the intracluster medium and warm-hot intergalactic medium contain energetically significant populations of nonthermal particles and turbulent flow motions.Comment: Submitted to ApJ. Pdf with full resolution figures can be downloaded from http://canopus.cnu.ac.kr/ryu/krco.pd

Massive and Red Objects predicted by a semianalytical model of galaxy formation

We study whether hierarchical galaxy formation in a concordance $\Lambda$CDM universe can produce enough massive and red galaxies compared to the observations. We implement a semi-analytical model in which the central black holes gain their mass during major mergers of galaxies and the energy feedback from active galaxy nuclei (AGN) suppresses the gas cooling in their host halos. The energy feedback from AGN acts effectively only in massive galaxies when supermassive black holes have been formed in the central bulges. Compared with previous models without black hole formation, our model predicts more massive and luminous galaxies at high redshift, agreeing with the observations of K20 up to $z\sim 3$. Also the predicted stellar mass density from massive galaxies agrees with the observations of GDDS. Because of the energy feedback from AGN, the formation of new stars is stopped in massive galaxies with the termination of gas cooling and these galaxies soon become red with color $R-K>$5 (Vega magnitude), comparable to the Extremely Red Objects (EROs) observed at redshift $z\sim$1-2. Still the predicted number density of very EROs is lower than observed at $z\sim 2$, and it may be related to inadequate descriptions of dust extinction, star formation history and AGN feedback in those luminous galaxies.Comment: Accepted for Publication in ApJ, added reference

Translated points and Rabinowitz Floer homology

We prove that if a contact manifold admits an exact filling then every local contactomorphism isotopic to the identity admits a translated point in the interior of its support, in the sense of Sandon [San11b]. In addition we prove that if the Rabinowitz Floer homology of the filling is non-zero then every contactomorphism isotopic to the identity admits a translated point, and if the Rabinowitz Floer homology of the filling is infinite dimensional then every contactmorphism isotopic to the identity has either infinitely many translated points, or a translated point on a closed leaf. Moreover if the contact manifold has dimension greater than or equal to 3, the latter option generically doesn't happen. Finally, we prove that a generic contactomorphism on $\mathbb{R}^{2n+1}$ has infinitely many geometrically distinct iterated translated points all of which lie in the interior of its support.Comment: 13 pages, v2: numerous corrections, results unchange

State space collapse and diffusion approximation for a network operating under a fair bandwidth sharing policy

We consider a connection-level model of Internet congestion control, introduced by Massouli\'{e} and Roberts [Telecommunication Systems 15 (2000) 185--201], that represents the randomly varying number of flows present in a network. Here, bandwidth is shared fairly among elastic document transfers according to a weighted $\alpha$-fair bandwidth sharing policy introduced by Mo and Walrand [IEEE/ACM Transactions on Networking 8 (2000) 556--567] [$\alpha\in (0,\infty)$]. Assuming Poisson arrivals and exponentially distributed document sizes, we focus on the heavy traffic regime in which the average load placed on each resource is approximately equal to its capacity. A fluid model (or functional law of large numbers approximation) for this stochastic model was derived and analyzed in a prior work [Ann. Appl. Probab. 14 (2004) 1055--1083] by two of the authors. Here, we use the long-time behavior of the solutions of the fluid model established in that paper to derive a property called multiplicative state space collapse, which, loosely speaking, shows that in diffusion scale, the flow count process for the stochastic model can be approximately recovered as a continuous lifting of the workload process.Comment: Published in at http://dx.doi.org/10.1214/08-AAP591 the Annals of Applied Probability (http://www.imstat.org/aap/) by the Institute of Mathematical Statistics (http://www.imstat.org

Visualizing Quantum Well State Perturbations of Metallic Thin Films near Stacking Fault Defects

We demonstrate that quantum well states (QWS) of thin Pb films are highly perturbed within the proximity of intrinsic film defects. Scanning Tunneling Spectroscopy (STM/STS) measurements indicate that the energy of these states have a strong distance dependence within 4 nm of the defect with the strongest energetic fluctuations equaling up to 100 meV. These localized perturbations show large spatially-dependent asymmetries in the LDOS around the defect site for each corresponding quantum well state. These energetic fluctuations can be described by a simple model which accounts for fluctuations in the confinement potential induced by topographic changes.Comment: Updated Versio

Gauge/String-Gravity Duality and Froissart Bound

The gauge/string-gravity duality correspondence opened renewed hope and possibility to address some of the fundamental and non-perturbative QCD problems in particle physics, such as hadron spectrum and Regge behavior of the scattering amplitude at high energies. One of the most fundamental and long-standing problem is the high energy behavior of total cross-sections. According to a series of exhaustive tests by the COMPETE group, (1). total cross-sections have a universal Heisenberg behavior in energy corresponding to the maximal energy behavior allowed by the Froissart bound, i.e., $A + B ln^2 (s/s_0)$ with $B \sim 0.32 mb$ and $s_0 \sim 34.41 GeV^2$ for all reactions, and (2). the factorization relation among $\sigma_{pp, even}, \sigma_{\gamma p}, and \sigma_{\gamma \gamma}$ is well satisfied by experiments. I discuss the recent interesting application of the gauge/string-gravity duality of $AdS/CFT$ correspondence with a deformed background metric so as to break the conformal symmetry that can lead to the Heisenberg behavior of rising total cross-sections, and present some preliminary results on the high energy QCD from Planckian scattering in $AdS$ and black-hole production.Comment: 10 pages, Presented to the Coral Gables Conference 2003, Launching of BelleE\'poque in High Energy Physics and Cosmology, 17 - 21 December 2003, Fort Lauderdale, Florid

Modelling spatially regulated B-catenin dynamics & invasion in intestinal crypts

Experimental data (e.g., genetic lineage and cell population studies) on intestinal crypts reveal that regulatory features of crypt behavior, such as control via morphogen gradients, are remarkably well conserved among numerous organisms (e.g., from mouse and rat to human) and throughout the different regions of the small and large intestines. In this article, we construct a partial differential equation model of a single colonic crypt that describes the spatial distribution of Wnt pathway proteins along the crypt axis. The novelty of our continuum model is that it is based upon assumptions that can be directly related to processes at the cellular and subcellular scales. We use the model to predict how the distributions of Wnt pathway proteins are affected by mutations. The model is then extended to investigate how mutant cell populations can invade neighboring crypts. The model simulations suggest that cell crowding caused by increased proliferation and decreased cell loss may be sufficient for a mutant cell population to colonize a neighboring healthy crypt