38 research outputs found
Are the nearby groups of galaxies gravitationally bound objects?
We have compared numerical simulations to observations for the nearby (< 40
Mpc) groups of galaxies (Huchra & Geller 1982 and Ramella et al. 2002). The
group identification is carried out using a group-finding algorithm developed
by Huchra and Geller (1982). Using cosmological N-body simulation code with the
LambdaCDM cosmology, we show that the dynamical properties of groups of
galaxies identified from the simulation data are, in general, in a moderate,
within 2sigma, agreement with the observational catalogues of groups of
galaxies. As simulations offer more dynamical information than observations, we
used the N-body simulation data to calculate whether the nearby groups of
galaxies are gravitationally bound objects by using their virial ratio. We show
that in a LambdaCDM cosmology about 20 per cent of nearby groups of galaxies,
identified by the same algorithm as in the case of observations, are not bound,
but merely groups in a visual sense. This is quite significant, specifically
because estimations of group masses in observations are often based on an
assumption that groups of galaxies found by the friends-of-friends algorithm
are gravitationally bound objects. Simulations with different resolutions show
the same results. We also show how the fraction of gravitationally unbound
groups varies when the apparent magnitude limit of the sample and the value of
the cosmological constant is changed. In general, a larger value of the
Omega_Lambda generates slightly more unbound groups.Comment: 13 figures and 7 tables, Accepted 2007 September 19. Received 2007
September 19; in original form 2007 April
Computing secular motion under slowly rotating quadratic perturbation
We consider secular perturbations of nearly Keplerian two-body motion under a
perturbing potential that can be approximated to sufficient accuracy by
expanding it to second order in the coordinates. After averaging over time to
obtain the secular Hamiltonian, we use angular momentum and eccentricity
vectors as elements. The method of variation of constants then leads to a set
of equations of motion that are simple and regular, thus allowing efficient
numerical integration. Some possible applications are briefly described.Comment: 3 pages, 0 figures accepted for publicatio
NMR protocol for determination of oxidation susceptibility of serum lipids and application of the protocol to a chocolate study
A protocol for determination of oxidation susceptibility of serum lipids based on proton nuclear magnetic resonance (1H NMR) spectroscopy is presented and compared to the commonly used spectrophotometric method. Even though there are methodological differences between these two methods, the NMR-based oxidation susceptibility correlates well (r2 = 0.73) with the lag time determined spectrophotometrically. In addition to the oxidizability of serum lipids, the NMR method provides also information about the lipid profile. The NMR oxidation assay was applied to the chocolate study including fasting serum samples (n = 45) from subjects who had consumed white (WC), dark (DC) or high-polyphenol chocolate (HPC) daily for 3 weeks. The oxidation susceptibility of serum lipids decreased in the HPC group, and there was a significant difference between the WC and HPC groups (P = 0.031). According to the random forest analysis, the consumption of the HPC chocolate induced changes to the amounts of HDL, phosphatidylcholine, sphingomyelin, and nervonic, docosahexaenoic and myristic acids. Furthermore, arachidonic, docosahexaenoic, docosapentaenoic and palmitic acids, gamma-glutamyl transferase, hemoglobin, HDL, phosphatidylcholine and choline containing phospholipids explained about 60% of the oxidation susceptibility values
Natural Transfer of Viable Microbes in Space from Planets in the Extra-Solar Systems to a Planet in our Solar System and Vice-Versa
We investigate whether it is possible that viable microbes could have been
transported to Earth from the planets in extra-solar systems by means of
natural vehicles such as ejecta expelled by comet or asteroid impacts on such
planets. The probabilities of close encounters with other solar systems are
taken into account as well as the limitations of bacterial survival times
inside ejecta in space, caused by radiation and DNA decay. The conclusion is
that no potentially DNA/RNA life-carrying ejecta from another solar system in
the general Galactic star field landed on Earth before life already existed on
Earth, not even if microbial survival time in space is as long as tens of
millions of years. However, if the Sun formed initially as a part of a star
cluster, as is commonly assumed, we cannot rule out the possibility of transfer
of life from one of the sister systems to us. Likewise, there is a possibility
that some extra-solar planets carry life that originated in our solar system.
It will be of great interest to identify the members of the Sun's birth cluster
of stars and study them for evidence for planets and life on the planets. The
former step may be accomplished by the GAIA mission, the latter step by the SIM
and DARWIN missions. Therefore it may not be too long until we have
experimental knowledge on the question whether the natural transfer of life
from one solar system to another has actually taken place.Comment: 25 pages, 1 table, accepted to Ap
The Corona Borealis supercluster: connectivity, collapse, and evolution
We present a study of the Corona Borealis (CB) supercluster. We determined
the high-density cores of the CB and the richest galaxy clusters in them, and
studied their dynamical state and galaxy content. We determined filaments in
the supercluster to analyse the connectivity of clusters. We compared the mass
distribution in the CB with predictions from the spherical collapse model and
analysed the acceleration field in the CB. We found that at a radius
around clusters in the CB (A2065, A2061, A2089, and Gr2064)
(corresponding to the density contrast ), the galaxy
distribution shows a minimum. The values for individual clusters lie
in the range of Mpc. The radii of the clusters (splashback
radii) lie in the range of .
The projected phase space diagrams and the comparison with the spherical
collapse model suggest that regions have passed turnaround
and are collapsing. Galaxy content in clusters varies strongly. The cluster
A2061 has the highest fraction of galaxies with old stellar populations, and
A2065 has the highest fraction of galaxies with young stellar populations. The
number of long filaments near clusters vary from one at A2089 to five at A2061.
During the future evolution, the clusters in the main part of the CB may merge
and form one of the largest bound systems in the nearby Universe. Another part
of the CB, with the cluster Gr2064, will form a separate system. The structures
with a current density contrast have passed turnaround
and started to collapse at redshifts . The comparison of
the number and properties of the most massive collapsing supercluster cores
from observations and simulations may serve as a test for cosmological models.Comment: 24 pages, 17 figures, accepted for publication in A&