199 research outputs found
Formation and evolution of galaxy dark matter halos and their substructure
We use the ``Via Lactea'' simulation to study the co-evolution of a Milky
Way-size LambdaCDM halo and its subhalo population. While most of the host halo
mass is accreted over the first 6 Gyr in a series of major mergers, the
physical mass distribution [not M_vir(z)] remains practically constant since
z=1. The same is true in a large sample of LambdaCDM galaxy halos. Subhalo mass
loss peaks between the turnaround and virialization epochs of a given mass
shell, and declines afterwards. 97% of the z=1 subhalos have a surviving bound
remnant at the present epoch. The retained mass fraction is larger for
initially lighter subhalos: satellites with maximum circular velocities Vmax=10
km/s at z=1 have today about 40% of their mass back then. At the first
pericenter passage a larger average mass fraction is lost than during each
following orbit. Tides remove mass in substructure from the outside in, leading
to higher concentrations compared to field halos of the same mass. This effect,
combined with the earlier formation epoch of the inner satellites, results in
strongly increasing subhalo concentrations towards the Galactic center. We
present individual evolutionary tracks and present-day properties of the likely
hosts of the dwarf satellites around the Milky Way. The formation histories of
``field halos'' that lie today beyond the Via Lactea host are found to strongly
depend on the density of their environment. This is caused by tidal mass loss
that affects many field halos on eccentric orbits.Comment: 20 pages, 18 figures. Figures 6,7 and 8 corrected in this version,
for details see the erratum in ApJ 679, 1680 and
http://www.ucolick.org/~diemand/vl/publ/vlevolerr.pdf. Data, movies and
images are available at http://www.ucolick.org/~diemand/vl
Density Profiles of Cold Dark Matter Substructure: Implications for the Missing Satellites Problem
The structural evolution of substructure in cold dark matter (CDM) models is
investigated combining ``low-resolution'' satellites from cosmological N-body
simulations of parent halos with N=10^7 particles with high-resolution
individual subhalos orbiting within a static host potential. We show that, as a
result of mass loss, convergence in the central density profiles requires the
initial satellites to be resolved with N=10^7 particles and parsec-scale force
resolution. We find that the density profiles of substructure halos can be well
fitted with a power-law central slope that is unmodified by tidal forces even
after the tidal stripping of over 99% of the initial mass and an exponential
cutoff in the outer parts. The solution to the missing-satellites problem
advocated by Stoehr et al. in 2002 relied on the flattening of the dark matter
(DM) halo central density cusps by gravitational tides, enabling the observed
satellites to be embedded within DM halos with maximum circular velocities as
large as 60 km/s. In contrast, our results suggest that tidal interactions do
not provide the mechanism for associating the dwarf spheroidal satellites
(dSphs) of the Milky Way with the most massive substructure halos expected in a
CDM universe. We compare the predicted velocity dispersion profiles of Fornax
and Draco to observations, assuming that they are embedded in CDM halos. Models
with isotropic and tangentially anisotropic velocity distributions for the
stellar component fit the data only if the surrounding DM halos have maximum
circular velocities in the range 20-35 km/s. If the dSphs are embedded within
halos this large then the overabundance of satellites within the concordance
LCDM cosmological model is significantly alleviated, but this still does not
provide the entire solution.Comment: Accepted for publication in ApJ, 17 pages, 9 figures, LaTeX (uses
emulateapj5.sty
Coupling site-directed mutagenesis with high-level expression: large scale production of mutant porins from E. coli
Combination of an origin repair mutagenesis system with a new mutS host strain increased the efficiency of mutagenesis from 46% to 75% mutant clones. Overexpression with the T7 expression system afforded large quantities of proteins from mutant strains. A series of E. coli BE host strains devoid of major outer membrane proteins was constructed, facilitating the purification of mutant porins to homogeneity. This allowed preparation of 149 porin mutants in E. coli used in detailed explorations of the structure and function of this membrane protein to high resolutio
Insights into Gene Modulation by Therapeutic TNF and IFNγ Antibodies: TNF Regulates IFNγ Production by T Cells and TNF-Regulated Genes Linked to Psoriasis Transcriptome
Therapeutic antibodies against tumor necrosis factor (TNF) (infliximab) and IFNγ (fontolizumab) have been developed to treat autoimmune diseases. While the primary targets of these antibodies are clearly defined, the set of inflammatory molecules, which is altered by use of these inhibitors, is poorly understood. We elucidate the target genes of these antibodies in activated human peripheral blood mononuclear cells from healthy volunteers. While genes suppressed by fontolizumab overlap with known IFNγ-induced genes, majority of genes suppressed by infliximab have previously not been traced to TNF signaling. With this approach we were able to extrapolate new TNF-associated genes to be upregulated in psoriasis vulgaris, an “autoimmune” disease effectively treated with TNF antagonists. These genes represent potential therapeutic targets of TNF antagonists in psoriasis. Furthermore, these data establish an unexpected effect of TNF blockade on IFNγ synthesis by T cells. Synthesis of IFNγ, a cytokine of Th1-polarized T cells, is suppressed by 8.1-fold (P<0.01) at the mRNA level, while synthesis of IFNγ is eliminated in >60% of individual T cells. These data suggest that TNF blockade with infliximab can suppress a major pathway of the adaptive immune response and this observation provides a key rationale for targeting TNF in “Type-1” T-cell-mediated autoimmune diseases
Towards reducing DBP formation potential of drinking water by favouring direct ozone over hydroxyl radical reactions during ozonation
When ozonation is employed in advanced water treatment plants to produce drinking water, dissolved organic matter reacts with ozone (O) and/or hydroxyl radicals (OH) affecting disinfection byproduct (DBP) formation with subsequently used chlorine-based disinfectants. This study presents the effects of varying exposures of O and OH on DBP concentrations and their associated toxicity generated after subsequent chlorination. DBP formation potential tests and in vitro bioassays were conducted after batch ozonation experiments of coagulated surface water with and without addition of tertiary butanol (t-BuOH, 10 mM) and hydrogen peroxide (HO, 1 mg/mg O), and at different pH (6-8) and transferred ozone doses (0-1 mg/mg TOC).Although ozonation led to a 24-37% decrease in formation of total trihalomethanes, haloacetic acids, haloacetonitriles, and trihaloacetamides, an increase in formation of total trihalonitromethanes, chloral hydrate, and haloketones was observed. This effect however was less pronounced for samples ozonated at conditions favoring molecular ozone (e.g., pH 6 and in the presence of t-BuOH) over OH reactions (e.g., pH 8 and in the presence of HO). Compared to ozonation only, addition of HO consistently enhanced formation of all DBP groups (20-61%) except trihalonitromethanes. This proves that OH-transformed organic matter is more susceptible to halogen incorporation. Analogously, adsorbable organic halogen (AOX) concentrations increased under conditions that favor OH reactions. The ratio of unknown to known AOX, however, was greater at conditions that promote direct O reactions. Although significant correlation was found between AOX and genotoxicity with the p53 bioassay, toxicity tests using 4 in vitro bioassays showed relatively low absolute differences between various ozonation conditions
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