Local-Group tests of dark-matter Concordance Cosmology: Towards a new paradigm for structure formation

(abridged) Predictions of the Concordance Cosmological Model (CCM) of the structures in the environment of large spiral galaxies are compared with observed properties of Local Group galaxies. Five new most probably irreconcilable problems are uncovered. However, the Local Group properties provide hints that may lead to a solution of the above problems The DoS and bulge--satellite correlation suggest that dissipational events forming bulges are related to the processes forming phase-space correlated satellite populations. Such events are well known to occur since in galaxy encounters energy and angular momentum are expelled in the form of tidal tails, which can fragment to form populations of tidal-dwarf galaxies (TDGs) and associated star clusters. If Local Group satellite galaxies are to be interpreted as TDGs then the sub-structure predictions of CCM are internally in conflict. All findings thus suggest that the CCM does not account for the Local Group observations and that therefore existing as well as new viable alternatives have to be further explored. These are discussed and natural solutions for the above problems emerge.Comment: A and A, in press, 25 pages, 9 figures; new version contains minor text adjustments for conformity with the published version and additional minor changes resulting from reader's feedback. The speculation on a dark force has been added. Also, the Fritz Zwicky Paradox is now included to agree with the published versio

Mass-loss and expansion of ultra compact dwarf galaxies through gas expulsion and stellar evolution for top-heavy stellar initial mass functions

(abridged) The dynamical V-band mass-to-light ratios of ultra compact dwarf galaxies (UCDs) are higher than predicted by simple stellar population models with the canonical stellar initial mass function (IMF). One way to explain this finding is a top-heavy IMF, so that the unseen mass is provided by additional remnants of high-mass stars. A possible explanation for why the IMF in UCDs could be top-heavy while this is not the case in less massive stellar systems is that encounters between proto-stars and stars become probable in forming massive systems. However, the required number of additional stellar remnants proves to be rather high, which raises the question of how their progenitors would affect the early evolution of a UCD. We have therefore calculated the first 200 Myr of the evolution of the UCDs, using the particle-mesh code Superbox. It is assumed that the stellar populations of UCDs were created in an initial starburst, which implies heavy mass loss during the following approximately 40 Myr due to primordial gas expulsion and supernova explosions. We find at the end of the simulations for various initial conditions and (tabulated) mass-loss histories objects that roughly resemble UCDs. Thus, the existence of UCDs does not contradict the notion that their stellar populations formed rapidly and with a top-heavy IMF. We find tentative evidence that the UCDs may have had densities as high as 10^8 M_sun/pc^3 at birth.Comment: 19 pages, 16 figures. Figure 4 has been modified in this version; it now shows the quantities that were actually used in the paper. This modification therefore does not imply any further changes to the paper, but there are a few other, very minor changes (typos corrected, formulations changed)

High-resolution simulations of galaxy mergers: Resolving globular cluster formation

Massive star clusters observed in galaxy mergers are often suggested to be progenitors of globular clusters. To study this hypothesis, we performed the highest resolution simulation of a gas-rich galaxy merger so far. The formation of massive star clusters of 10^5 to 10^7 Mo, triggered by the galaxy interaction, is directly resolved in this model. We show that these clusters are tightly bound structures with little net rotation, due to evolve into compact long-lived stellar systems. Massive clusters formed in galaxy mergers are thus robust candidates for progenitors of long-lived globular clusters. The simulated cluster mass spectrum is consistent with theory and observations. Tidal dwarf galaxies of 10^8-9 Mo can form at the same time, and appear to be part of a different class of objects, being more extended and rotating.Comment: MNRAS letters accepted. Version with high-resolution figures available at http://aramis.obspm.fr/~bournaud/GC.pd

Dense Stellar Populations: Initial Conditions

This chapter is based on four lectures given at the Cambridge N-body school "Cambody". The material covered includes the IMF, the 6D structure of dense clusters, residual gas expulsion and the initial binary population. It is aimed at those needing to initialise stellar populations for a variety of purposes (N-body experiments, stellar population synthesis).Comment: 85 pages. To appear in The Cambridge N-body Lectures, Sverre Aarseth, Christopher Tout, Rosemary Mardling (eds), Lecture Notes in Physics Series, Springer Verla

Syndromics: A Bioinformatics Approach for Neurotrauma Research

Substantial scientific progress has been made in the past 50 years in delineating many of the biological mechanisms involved in the primary and secondary injuries following trauma to the spinal cord and brain. These advances have highlighted numerous potential therapeutic approaches that may help restore function after injury. Despite these advances, bench-to-bedside translation has remained elusive. Translational testing of novel therapies requires standardized measures of function for comparison across different laboratories, paradigms, and species. Although numerous functional assessments have been developed in animal models, it remains unclear how to best integrate this information to describe the complete translational “syndrome” produced by neurotrauma. The present paper describes a multivariate statistical framework for integrating diverse neurotrauma data and reviews the few papers to date that have taken an information-intensive approach for basic neurotrauma research. We argue that these papers can be described as the seminal works of a new field that we call “syndromics”, which aim to apply informatics tools to disease models to characterize the full set of mechanistic inter-relationships from multi-scale data. In the future, centralized databases of raw neurotrauma data will enable better syndromic approaches and aid future translational research, leading to more efficient testing regimens and more clinically relevant findings

Development of Brain Targeting Peptide Based MMP-9 Inhibiting Nanoparticles for the Treatment of Brain Diseases with Elevated MMP-9 Activity.

Latent and active levels of cerebral matrix metalloproteinase 9 (MMP-9) are elevated in neurological diseases and brain injuries, contributing to neurological damage and poor clinical outcomes. This study aimed developing peptide-based nanoparticles with ability to cross the blood-brain-barrier (BBB) and inhibit MMP-9. Three amphiphilic peptides were synthesised containing brain-targeting ligands (HAIYPRH or CKAPETALC) conjugated with MMP-9 inhibiting peptide (CTTHWGFTLC) linked by glycine (spacer) at the N-terminus, and the peptide sequences were conjugated at the N- terminus to cholesterol. 19F NMR assay was developed to measure MMP-9 inhibition. Cell toxicity was evaluated by the LDH assay, and dialysis studies were conducted with/without fetal bovine serum. An in vitro model was employed to evaluate the ability of nanoparticles crossing the BBB. The amphiphilic peptide (Cholesterol-GGGCTTHWGFTLCHAIYPRH) formed nanoparticles (average size of 202.8 nm) with ability to cross the BBB model. MMP-9 inhibiting nanoparticles were non-toxic to cells, and reduced MMP-9 activity from kobs of 4.5 × 10-6s-1 to complete inhibition. Dialysis studies showed that nanoparticles did not disassemble by extreme dilution (40 folds), but gradually hydrolysed by serum enzymes. In conclusion, the MMP-9 inhibiting nanoparticles reduced the activity of MMP-9, with acceptable serum stability, minimal cell toxicity and ability to cross the in vitro BBB model