103 research outputs found
Bulgeless Galaxies and their Angular Momentum Problem
The specific angular momentum of Cold Dark Matter (CDM) halos in a
CDM universe is investigated. Their dimensionless specific angular
momentum with and
the virial velocity and virial radius, respectively depends strongly
on their merging histories. We investigate a set of CDM simulations
and explore the specific angular momentum content of halos formed through
various merging histories. Halos with a quiet merging history, dominated by
minor mergers and accretion until the present epoch, acquire by tidal torques
on average only 2% to 3% of the angular momentum required for their rotational
support (). This is in conflict with observational data for a
sample of late-type bulgeless galaxies which indicates that those galaxies
reside in dark halos with exceptionally high values of . Minor mergers and accretion preserve or slowly increase the
specific angular momentum of dark halos with time. This mechanism is however
not efficient enough in order to explain the observed spin values for late-type
dwarf galaxies. Energetic feedback processes have been invoked to solve the
problem that gas loses a large fraction of its specific angular momentum during
infall. Under the assumption that dark halos hosting bulgeless galaxies acquire
their mass via quiescent accretion, our results indicate yet another serious
problem: the specific angular momentum gained during the formation of these
objects is not large enough to explain their observed rotational
properties,even if no angular momentum would be lost during gas infall.Comment: 4 pages, 3 figures. To appear in September 1, 2004, issue of ApJ
Letter
Sustainable and printable nanocellulose-based ionogels as gel polymer electrolytes for supercapacitors
A new gel polymer electrolyte (GPE) based supercapacitor with an ionic conductivity up to 0.32-0.94 mS cm has been synthesized from a mixture of an ionic liquid (IL) with nanocellulose (NC). The new NC-ionogel was prepared by combining the IL 1-ethyl-3-methylimidazolium dimethyl phosphate (EMIMP) with carboxymethylated cellulose nanofibers (CNFc) at different ratios (CNFc ratio from 1 to 4). The addition of CNFc improved the ionogel properties to become easily printable onto the electrode surface. The new GPE based supercapacitor cell showed good electrochemical performance with specific capacitance of 160 F g and an equivalent series resistance (ESR) of 10.2 Ω cm at a current density of 1 mA cm. The accessibility to the full capacitance of the device is demonstrated after the addition of CNFc in EMIMP compared to the pristine EMIMP (99 F g−1 and 14.7 Ω cm−2)
The Evolution of the Dark Halo Spin Parameters lambda and lambda' in a LCDM Universe: The Role of Minor and Major Mergers
The evolution of the spin parameter of dark halos and the dependence on the
halo merging history in a set of dissipationless cosmological LCDM simulations
is investigated. Special focus is placed on the differences of the two commonly
used versions of the spin parameter, namely lambda=J*E^1/2/(G*M^5/2) (Peebles
80) and lambda'=J/(sqrt(2)*M_vir*R_vir*V_vir) (Bullock et al. 01). Though the
distribution of the spin transfer rate defined as the ratio of the spin
parameters after and prior to a merger is similar to a high degree for both,
lambda and lambda', we find considerable differences in the time evolution:
while lambda' is roughly independent of redshift, lambda turns out to increase
significantly with decreasing redshift. This distinct behaviour arises from
small differences in the spin transfer during accretion events. The evolution
of the spin parameter is strongly coupled with the virial ratio
eta:=2*E_kin/|E_pot| of dark halos. Major mergers disturb halos and increase
both their virial ratio and spin parameter for 1-2 Gyrs. At high redshifts
(z=2-3) many halos are disturbed with an average virial ratio of eta = 1.3
which approaches unity until z=0. We find that the redshift evolution of the
spin parameters is dominated by the huge number of minor mergers rather than
the rare major merger events.Comment: 10 pages, 11 figures, submitted to MNRA
A correlation between central supermassive black holes and the globular cluster systems of early-type galaxies
Elliptical, lenticular, and early-type spiral galaxies show a remarkably
tight power-law correlation between the mass M_BH of their central supermassive
black hole (SMBH) and the number N_GC of globular clusters:
M_BH=m*N_GC^(1.08+/-0.04) with m=1.7*10^5 solar masses. Thus, to a good
approximation the SMBH mass is the same as the total mass of the globular
clusters. Based on a limited sample of 13 galaxies, this relation appears to be
a better predictor of SMBH mass (rms scatter 0.2 dex) than the M_BH-sigma
relation between SMBH mass and velocity dispersion sigma. The small scatter
reflects the fact that galaxies with high globular cluster specific frequency
S_N tend to harbor SMBHs that are more massive than expected from the
M_BH-sigma relation.Comment: 14 pages, 3 figures, to appear in ApJ 720, 516 (2010
Hard and transparent films formed by nanocellulose-TiO2 nanoparticle hybrids
T he formation of hybrids of nanofibrillated cellulose and titania nanoparticles in aqueous media has been studied. Their transparency and mechanical behavior have been assessed by spectrophotometry and nanoindentation. The results show that limiting the titania nanoparticle concentration below 16 vol% yields homogeneous hybrids with a very high Young's modulus and hardness, of up to 44 GPa and 3.4 GPa, respectively, and an optical transmittance above 80%. Electron microscopy shows that higher nanoparticle contents result in agglomeration and an inhomogeneous hybrid nanostructure with a concomitant reduction of hardness and optical transmittance. Infrared spectroscopy suggests that the nanostructure of the hybrids is controlled by electrostatic adsorption of the titania nanoparticles on the negatively charged nanocellulose surfaces
Peculiarities in Velocity Dispersion and Surface Density Profiles of Star Clusters
Based on our recent work on tidal tails of star clusters (Kuepper et al.
2009) we investigate star clusters of a few 10^4 Msun by means of velocity
dispersion profiles and surface density profiles. We use a comprehensive set of
-body computations of star clusters on various orbits within a realistic
tidal field to study the evolution of these profiles with time, and ongoing
cluster dissolution From the velocity dispersion profiles we find that the
population of potential escapers, i.e. energetically unbound stars inside the
Jacobi radius, dominates clusters at radii above about 50% of the Jacobi
radius. Beyond 70% of the Jacobi radius nearly all stars are energetically
unbound. The velocity dispersion therefore significantly deviates from the
predictions of simple equilibrium models in this regime. We furthermore argue
that for this reason this part of a cluster cannot be used to detect a dark
matter halo or deviations from Newtonian gravity. By fitting templates to the
about 10^4 computed surface density profiles we estimate the accuracy which can
be achieved in reconstructing the Jacobi radius of a cluster in this way. We
find that the template of King (1962) works well for extended clusters on
nearly circular orbits, but shows significant flaws in the case of eccentric
cluster orbits. This we fix by extending this template with 3 more free
parameters. Our template can reconstruct the tidal radius over all fitted
ranges with an accuracy of about 10%, and is especially useful in the case of
cluster data with a wide radial coverage and for clusters showing significant
extra-tidal stellar populations. No other template that we have tried can yield
comparable results over this range of cluster conditions. All templates fail to
reconstruct tidal parameters of concentrated clusters, however. (abridged)Comment: 23 pages, 13 figures, accepted for publication in MNRA
Bayesian and frequentist analysis of an Austrian genome-wide association study of colorectal cancer and advanced adenomas
Most genome-wide association studies (GWAS) were analyzed using single marker tests in combination with stringent correction procedures for multiple testing. Thus, a substantial proportion of associated single nucleotide polymorphisms (SNPs) remained undetected and may account for missing heritability in complex traits. Model selection procedures present a powerful alternative to identify associated SNPs in high-dimensional settings. In this GWAS including 1060 colorectal cancer cases, 689 cases of advanced colorectal adenomas and 4367 controls we pursued a dual approach to investigate genome-wide associations with disease risk applying both, single marker analysis and model selection based on the modified Bayesian information criterion, mBIC2, implemented in the software package MOSGWA. For different case-control comparisons, we report models including between 1-14 candidate SNPs. A genome-wide significant association of rs17659990 (P=5.43x10(-9), DOCK3, chromosome 3p21.2) with colorectal cancer risk was observed. Furthermore, 56 SNPs known to influence susceptibility to colorectal cancer and advanced adenoma were tested in a hypothesis-driven approach and several of them were found to be relevant in our Austrian cohort. After correction for multiple testing (alpha=8.9x10(-4)), the most significant associations were observed for SNPs rs10505477 (P=6.08x10(-4)) and rs6983267 (P=7.35x10(-4)) of CASC8, rs3802842 (P=8.98x10(-5), COLCA1,2), and rs12953717 (P=4.64x10(-4), SMAD7). All previously unreported SNPs demand replication in additional samples. Reanalysis of existing GWAS datasets using model selection as tool to detect SNPs associated with a complex trait may present a promising resource to identify further genetic risk variants not only for colorectal cancer
Supplementation with Small-Quantity Lipid-Based Nutrient Supplements Does Not Increase Child Morbidity in a Semiurban Setting in Ghana: A Secondary Outcome Noninferiority Analysis of the International Lipid-Based Nutrient Supplements (iLiNS)–DYAD Randomized Controlled Trial
Background
Adequate knowledge about the safety of consumption of small-quantity lipid-based nutrient supplements (SQ-LNSs) is needed. Objective
We aimed to test the hypothesis that SQ-LNS consumption is noninferior to control with respect to child morbidity. Methods
Women (n = 1320) ≤20 wk pregnant were assigned to iron and folic acid until delivery with no supplementation for offspring; or multiple micronutrient supplements until 6 mo postpartum with no supplementation for offspring; or SQ-LNSs until 6 mo postpartum, and SQ-LNSs for offspring (6 mg Fe/d) from 6 to 18 mo of age [the lipid-based nutrient supplement (LNS) group]. We assessed noninferiority (margin ≤20%) between any 2 groups during 0–6 mo of age, and between the non-LNS and LNS groups during 6–18 mo of age for caregiver-reported acute respiratory infection, diarrhea, gastroenteritis, fever/suspected malaria, poor appetite, and “other illnesses.” Results
During 0–6 mo of age, 1197 infants contributed 190,503 infant-days. For all morbidity combined, overall mean incidence (per 100 infant-days) was 3.3 episodes, overall mean prevalence (percentage of infant-days) was 19.3%, and the 95% CIs of the incidence rate ratio (IRR) and longitudinal prevalence rate ratio (LPRR) between any 2 groups were ≤1.20. During 6–18 mo, there were 240,097 infant-days for the non-LNS group and 118,698 for the LNS group. For all morbidity combined, group mean incidences were 4.3 and 4.3, respectively (IRR: 1.0; 95% CI: 1.0, 1.1), and mean prevalences were 28.2% and 29.3%, respectively (LPRR: 1.0; 95% CI: 1.0, 1.1). Noninferiority was inconclusive for diarrhea, fever/suspected malaria, and poor appetite. Conclusions
SQ-LNS consumption does not increase reported overall child morbidity in this population compared with the 2 other treatments.
This trial was registered at clinicaltrials.gov as NCT00970866
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