97 research outputs found
Lifetime of magnetic excitations in supported ferromagnetic and antiferromagnetic spin-1/2 Heisenberg chains
The lifetime of magnetic excitations in finite 1D-supported Heisenberg chains of magnetic atoms is studied theoretically for a model system formed of S = 1/2 spins. Both ferromagnetic and antiferromagnetic cases are considered as well as open chains and rings of atoms. Different chain lengths are considered allowing extrapolation to infinite chains. All the excited magnetic states in the finite chains and rings are studied, not only the spin-wave mode. The magnetic excitations decay by electron-hole pair creation in the substrate. As the main result, for all the systems considered, the decay rate appears to vary approximately proportionally to the excitation energy of the state, with a proportionality constant independent of the strength of the Heisenberg exchange term. In certain finite systems, a stable state is evidenced at low energy, associated with a special spin coupling structure. © 2012 American Physical Society.Peer Reviewe
Chemically peculiar stars in the Large Magellanic Cloud
The detection of magnetic chemically peculiar (CP2) stars in open clusters of
extragalactic systems can give observational answers to many unsolved
questions. The mean percentage of CP2 stars in the Milky Way is of the order of
5% for the spectral range from early B- to F-type, luminosity class V objects.
The origin of the CP2 phenomenon seems to be closely connected to the overall
metallicity and global magnetic field environment. The theoretical models are
still only tested by observations in the Milky Way. It is therefore essential
to provide high quality observations in rather different global environments.
The young clusters NGC 2136/7 were observed in the Delta a photometric system.
This intermediate band photometric system samples the depth of the 520nm flux
depression by comparing the flux at the center with the adjacent regions with
bandwidths of 11nm to 23nm. The Delta a photometric system is most suitable for
detecting CP2 stars with high efficiency, but is also capable of detecting a
small percentage of non-magnetic CP objects. We present high precision
photometric Delta a observations of 417 objects in NGC 2136/7 and its
surrounding field, of which five turned out to be bona fide magnetic CP stars.
In addition, we discovered two Be/Ae stars. From our investigations of NGC
1711, NGC 1866, NGC 2136/7, their surroundings, and one independent field of
the LMC population, we derive an occurrence of classical chemically peculiar
stars of 2.2(6)% in the LMC, which is only half the value found in the Milky
Way. The mass and age distribution of the photometrically detected CP stars is
not different from that of similar objects in galactic open clusters.Comment: 5 pages, 4 figures, accepted by A&
Signatures of accretion events in the halos of early-type galaxies from comparing PNe and GCs kinematics
We have compared the halo kinematics traced by globular clusters (GCs) and
planetary nebulae (PNe) for two elliptical galaxies in the Fornax and Virgo
clusters NGC 1399 and NGC 4649, and for the merger remnant NGC 5128 (Centaurus
A). We find differences in the rotational properties of the PN, red GC, and
blue GC systems in all these three galaxies. NGC 1399 PNe and GCs show line of
sight velocity distributions in specific regions that are significantly
different, based on Kolmogorov-Smirnov tests. The PN system shows multi-spin
components, with nearly opposite direction of rotation in the inner and the
outer parts. The GCs velocity field is not point-symmetric in the outer regions
of the galaxy, indicating that the system has not reached dynamical equilibrium
yet. In NGC 4649 PNe, red and blue GCs have different rotation axes and
rotational velocities. Finally, in NGC 5128 both PNe and GCs deviate from
equilibrium in the outer regions of the galaxy, and in the inner regions the PN
system is rotationally supported, whereas the GC system is dominated by
velocity dispersion. The observed different kinematic properties, including
deviations from point-symmetry, between PNe and GCs suggest that these systems
are accreted at different times by the host galaxy, and the most recent
accretion took place only few Gyr ago.We discuss two scenarios which may
explain some of these differences: i) tidal stripping of loosely-bound GCs, and
ii) multiple accretion of low luminosity and dwarf galaxies. Because these two
mechanisms affect mostly the GC system, differences with the PNe kinematics can
be expected.Comment: 14 pages, 13 figures, Accepted for publication in MNRAS. This new
version contains an improved analysis, which includes the study of
point-symmetry in the velocity fields and its implications for dynamical
equilibriu
Bupleurum chinense Roots: a Bioactivity-Guided Approach toward Saponin-Type NF-κB Inhibitors
The roots of Bupleurum chinense have a long history in traditional medicine to treat infectious diseases and inflammatory disorders. Two major compounds, saikosaponins A and D, were reported to exert potent anti-inflammatory activity by inhibiting NF-κB. In the present study, we isolated new saikosaponin analogues from the roots of B. chinese interfering with NF-κB activity in vitro. The methanol-soluble fraction of the dichloromethane extract of Radix Bupleuri was subjected to activity-guided isolation yielding 18 compounds, including triterpenoids and polyacetylenes. Their structures were determined by spectroscopic methods as saikogenin D (1), prosaikogenin D (2), saikosaponins B2 (3), W (4), B1 (5), Y (6), D (7), A (8), E (9), B4 (10), B3 (11), and T (12), saikodiyne A (13), D (14), E (15) and F (16), falcarindiol (17), and 1-linoleoyl-sn-glycero-3-phosphorylcholine (18). Among them, 4, 15, and 16 are new compounds, whereas 6, previously described as a semi-synthetic compound, is isolated from a natural source for the first time, and 13–17 are the first reports of polyacetylenes from this plant. Nine saponins/triterpenoids were tested for inhibition of NF-κB signaling in a cell-based NF-κB-dependent luciferase reporter gene model in vitro. Five of them (1, 2, 4, 6, and 8) showed strong (> 50%, at 30 µM) NF-κB inhibition, but also varying degrees of cytotoxicity, with compounds 1 and 4 (showing no significant cytotoxicity) presenting IC50 values of 14.0 µM and 14.1 µM in the cell-based assay, respectively
Measuring the non-thermal pressure in early type galaxy atmospheres: A comparison of X-ray and optical potential profiles in M87 and NGC1399
We compare the gravitational potential profiles of the elliptical galaxies
NGC 4486 (M87) and NGC 1399 (the central galaxy in the Fornax cluster) derived
from X-ray and optical data. This comparison suggests that the combined
contribution of cosmic rays, magnetic fields and micro-turbulence to the
pressure is ~10% of the gas thermal pressure in the cores of NGC 1399 and M87,
although the uncertainties in our model assumptions (e.g., spherical symmetry)
are sufficiently large that the contribution could be consistent with zero. In
the absence of any other form of non-thermal pressure support, these upper
bounds translate into upper limits on the magnetic field of ~10-20 muG at a
distance of 1'-2' from the centers of NGC1399 and M87. We show that these
results are consistent with the current paradigm of cool cluster cores, based
on the assumption that AGN activity regulates the thermal state of the gas by
injecting energy into the intra-cluster medium. The limit of ~10-20% on the
energy density in the form of relativistic protons applies not only to the
current state of the gas, but essentially to the entire history of the
intra-cluster medium, provided that cosmic ray protons evolve adiabatically and
that their spatial diffusion is suppressed.Comment: Accepted for MNRAS. 19 pages; 14 figures; expanded version in
response to comments from the refere
Mass-to-light ratio gradients in early-type galaxy haloes
Since the near future should see a rapidly expanding set of probes of the
halo masses of individual early-type galaxies, we introduce a convenient
parameter for characterising the halo masses from both observational and
theoretical results: \dML, the logarithmic radial gradient of the mass-to-light
ratio. Using halo density profiles from LCDM simulations, we derive predictions
for this gradient for various galaxy luminosities and star formation
efficiencies . As a pilot study, we assemble the available \dML\
data from kinematics in early-type galaxies - representing the first unbiassed
study of halo masses in a wide range of early-type galaxy luminosities - and
find a correlation between luminosity and \dML, such that the brightest
galaxies appear the most dark-matter dominated. We find that the gradients in
most of the brightest galaxies may fit in well with the LCDM predictions, but
that there is also a population of fainter galaxies whose gradients are so low
as to imply an unreasonably high star formation efficiency .
This difficulty is eased if dark haloes are not assumed to have the standard
LCDM profiles, but lower central concentrations.Comment: 17 pages, 13 figures. Accepted for publication on MNRA
Polyacetylenes from Notopterygium incisum–New Selective Partial Agonists of Peroxisome Proliferator-Activated Receptor-Gamma
Peroxisome proliferator-activated receptor gamma (PPARγ) is a key regulator of glucose and lipid metabolism and therefore an important pharmacological target to combat metabolic diseases. Since the currently used full PPARγ agonists display serious side effects, identification of novel ligands, particularly partial agonists, is highly relevant. Searching for new active compounds, we investigated extracts of the underground parts of Notopterygium incisum, a medicinal plant used in traditional Chinese medicine, and observed significant PPARγ activation using a PPARγ-driven luciferase reporter model. Activity-guided fractionation of the dichloromethane extract led to the isolation of six polyacetylenes, which displayed properties of selective partial PPARγ agonists in the luciferase reporter model. Since PPARγ activation by this class of compounds has so far not been reported, we have chosen the prototypical polyacetylene falcarindiol for further investigation. The effect of falcarindiol (10 µM) in the luciferase reporter model was blocked upon co-treatment with the PPARγ antagonist T0070907 (1 µM). Falcarindiol bound to the purified human PPARγ receptor with a Ki of 3.07 µM. In silico docking studies suggested a binding mode within the ligand binding site, where hydrogen bonds to Cys285 and Glu295 are predicted to be formed in addition to extensive hydrophobic interactions. Furthermore, falcarindiol further induced 3T3-L1 preadipocyte differentiation and enhanced the insulin-induced glucose uptake in differentiated 3T3-L1 adipocytes confirming effectiveness in cell models with endogenous PPARγ expression. In conclusion, we identified falcarindiol-type polyacetylenes as a novel class of natural partial PPARγ agonists, having potential to be further explored as pharmaceutical leads or dietary supplements
Antifungal, anti-inflammatory and cytotoxicity activities of three varieties of Labisia pumila benth : from microwave obtained extracts.
Background: Labisia pumila, locally known as Kacip Fatimah, is a forest-floor plant that has tremendous potential in the herbal industry. It is one of the five herbal plants identified by the government as one of the national key economic areas to be developed for commercial purposes. There are three varieties of L. pumila namely, L. pumila var. pumila, L. pumila var. alata and L. pumila var. lanceolata and each has its own use.Methods: The leaves and roots of the three varieties of L. pumila Benth. were extracted using microwave assisted extraction (MAE). Antifungal activity of all plant extracts were characterized against Fusarium sp., Candida sp. and Mucor using the agar diffusion disc. Anti-inflammatory assays were performed using NO production by macrophage RAW 264.7 cell lines induced by LPS/IFN-g and cytotoxic activity was determined using several cancer cell lines and one normal cell line.Results: The overall result demonstrated that leaf and root extracts of all three varieties of L. pumila exhibited moderate to appreciable antifungal activity against Fusarium sp., Candida sp. and Mucor compared to streptomycin used as positive control. Leaf and root extracts of all varieties significantly decreased NO release. However, the root extracts showed higher activity compared to the leaf extracts. Cytotoxic activity against MCF-7, MDA-MB-231 and Chang cell lines were observed with all extracts.Conclusions: These findings suggest the potential use of L. pumila Benth. as a natural medicine and indicated the possible application of this medicinal plant such anti inflammatory activity and cytotoxic agents
The Globular Cluster System of NGC 1399. II. Kinematics of a Large Sample of Globular Clusters
We study the kinematics and dynamics of the globular cluster system of NGC
1399, the central galaxy of the Fornax cluster. The observational data consists
of medium resolution spectra, obtained at the Very Large Telescope. Our sample
comprises 468 radial velocities in the magnitude range 20 < m_R < 23. This is
the largest sample of globular cluster velocities around any galaxy obtained so
far. The radial range is 2 arcmin < r < 9 arcmin, corresponding to 11 kpc to 50
kpc of galactocentric distance. There is the possibility that unbound clusters
and/or objects in the foreground contaminate the NGC 1399 cluster sample. Under
strong error selection, practically no objects are found with velocities lower
than 800 km/s or higher than 2000 km/s. Since the extreme velocities influence
the velocity dispersion considerably, uncertainty regarding the exact value of
the dispersion remains. Within the above velocity limits, we derive a projected
velocity dispersion for the total sample of 274+-9 km/s which within the
uncertainties remains constant over the entire radial range. Without any
velocity restriction, it increases to 325 km/s. Blue and red clusters show
different dispersions corresponding to their different surface density
profiles. Spherical models point to a circular velocity of 415+-30$ km/s,
assuming isotropy for the red clusters. This value is constant out to 40 kpc.
The inferred dark halo potential can be well represented by a logarithmic
potential. Also a halo of the NFW type fits well to the observations. Some mass
profiles derived from X-ray analyses do not agree with a constant circular
velocity within our radial range, irrespective of its exact value.Comment: 38 pages, 20 figures, accepted by A
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