122 research outputs found
Dark matter dominated dwarf disc galaxy Segue 1
Several observations reveal that dwarf galaxy Segue 1 has a dark matter (DM)
halo at least ~ 200 times more massive than its visible baryon mass of only ~
103 solar masses. The baryon mass is dominated by stars with perhaps an
interstellar gas mass of < 13 solar masses. Regarding Segue 1 as a dwarf disc
galaxy by its morphological appearance of long stretch, we invoke the dynamic
model of Xiang-Gruess, Lou & Duschl (XLD) to estimate its physical parameters
for possible equilibria with and without an isopedically magnetized gas disc.
We estimate the range of DM mass and compare it with available observational
inferences. Due to the relatively high stellar velocity dispersion compared to
the stellar surface mass density, we find that a massive DM halo would be
necessary to sustain disc equilibria. The required DM halo mass agrees grossly
with observational inferences so far. For an isopedic magnetic field in a gas
disc, the ratio f between the DM and baryon potentials depends strongly on the
magnetic field strength. Therefore, a massive DM halo is needed to counteract
either the strong stellar velocity dispersion and rotation of the stellar disc
or the magnetic Lorentz force in the gas disc. By the radial force balances,
the DM halo mass increases for faster disc rotation.Comment: 5 pages, 2 figures, accepted for publication in MNRA
Diffuse X-ray Emissions from Dynamic Planetary Nebulae
We present theoretical results of a piecewise isothermal shock wind model
devised for predicting the luminosity and surface brightness profile of diffuse
X-ray emissions primarily from the inner shocked downstream wind zone of a
planetary nebula (PN) surrounded by self-similar shocked dense shell and outer
slow AGB wind envelope involving self-gravity and compare/fit our computational
model results with available observations of a few grossly spherical X-ray
emitting PNe. Matching shocked piecewise isothermal self-similar void (ISSV)
solutions with self-gravity of Lou & Zhai (LZ) for the outer zone and a
stationary isothermal fast tenuous wind with a reverse shock for the inner zone
across an expanding contact discontinuity, we can consistently construct
dynamic evolution models of PNe with diffuse X-ray emissions. On the basis of
such a chosen dynamic wind interaction model, both X-ray luminosity and radial
X-ray brightness profile are determined by three key parameters, namely the
so-called X-ray parameter , two radii and of the reverse
shock and the contact discontinuity. We find that morphologies of X-ray
emissions would appear in the forms of either a central luminous sphere or a
bright ring embedded within optically bright shells. In contrast to previous
adiabatic models, the X-ray brightness peaks around the reverse shock, instead
of the contact discontinuity surface just inside the outer shocked dense shell.
Diffuse X-ray emissions of a few observed PNe appear to support this wind-wind
dynamic interaction scenario.Comment: 13 pages, 8 figures, accepted by Mon. Not. R. Astron. Soc. Accepted
2010 June 2. Received 2010 May 28; in original form 2010 May
Microbiology, ecology, and application of the nitrite-dependent anaerobic methane oxidation process
Nitrite-dependent anaerobic methane oxidation (n-damo), which couples the anaerobic oxidation of methane to denitrification, is a recently discovered process mediated by “Candidatus Methylomirabilis oxyfera.” M. oxyfera is affiliated with the “NC10” phylum, a phylum having no members in pure culture. Based on the isotopic labeling experiments, it is hypothesized that M. oxyfera has an unusual intra-aerobic pathway for the production of oxygen via the dismutation of nitric oxide into dinitrogen gas and oxygen. In addition, the bacterial species has a unique ultrastructure that is distinct from that of other previously described microorganisms. M. oxyfera-like sequences have been recovered from different natural habitats, suggesting that the n-damo process potentially contributes to global carbon and nitrogen cycles. The n-damo process is a process that can reduce the greenhouse effect, as methane is more effective in heat-trapping than carbon dioxide. The n-damo process, which uses methane instead of organic matter to drive denitrification, is also an economical nitrogen removal process because methane is a relatively inexpensive electron donor. This mini-review summarizes the peculiar microbiology of M. oxyfera and discusses the potential ecological importance and engineering application of the n-damo process
Global non-axisymmetric perturbation configurations in a composite disc system with an isopedic magnetic field: relation between dark matter halo and magnetic field
We study global non-axisymmetric stationary perturbations of aligned and
unaligned logarithmic spiral configurations in an axisymmetric composite
differentially rotating disc system of scale-free stellar and isopedically
magnetized gas discs coupled by gravity. The gas disc is threaded across by a
vertical magnetic field with a constant dimensionless isopedic ratio
of surface gas mass density
to with being the gravitational constant. Our
exploration focuses on the relation between and the dark matter
amount represented by a ratio in order to sustain
stationary perturbation configurations, where is the gravitational
potential of a presumed axisymmetric halo of dark matter and is the
gravitational potential of the composite disc matter. High and low
values correspond to relatively weak and strong magnetic fields given the same
gas surface mass density, respectively. The main goal of our model analysis is
to reveal the relation between isopedic magnetic fields and dark matter halo in
spiral galaxies with globally stationary perturbation configurations. Our
results show that, fairly strong yet realistic magnetic fields require a
considerably larger amount of dark matter in aligned and unaligned cases than
weak or moderate magnetic field strengths. We discuss astrophysical and
cosmological implications of our findings. For examples, patterns and pattern
speeds of galaxies may change during the course of galactic evolution.
Multiple-armed galaxies may be more numerous in the early Universe. Flocculent
galaxies may represent the transitional phase of pattern variations in
galaxies.Comment: 21 pages, 5 figures, accepted for publication in MNRA
Dynamic Evolution Model of Isothermal Voids and Shocks
We explore self-similar hydrodynamic evolution of central voids embedded in
an isothermal gas of spherical symmetry under the self-gravity. More
specifically, we study voids expanding at constant radial speeds in an
isothermal gas and construct all types of possible void solutions without or
with shocks in surrounding envelopes. We examine properties of void boundaries
and outer envelopes. Voids without shocks are all bounded by overdense shells
and either inflows or outflows in the outer envelope may occur. These
solutions, referred to as type void solutions, are further
divided into subtypes and
according to their characteristic behaviours across the sonic critical line
(SCL). Void solutions with shocks in envelopes are referred to as type
voids and can have both dense and quasi-smooth edges.
Asymptotically, outflows, breezes, inflows, accretions and static outer
envelopes may all surround such type voids. Both cases of
constant and varying temperatures across isothermal shock fronts are analyzed;
they are referred to as types and
void shock solutions. We apply the `phase net matching procedure' to construct
various self-similar void solutions. We also present analysis on void
generation mechanisms and describe several astrophysical applications. By
including self-gravity, gas pressure and shocks, our isothermal self-similar
void (ISSV) model is adaptable to various astrophysical systems such as
planetary nebulae, hot bubbles and superbubbles in the interstellar medium as
well as supernova remnants.Comment: 24 pages, 13 figuers, accepted by ApS
Retigeric Acid B Exhibits Antitumor Activity through Suppression of Nuclear Factor-κB Signaling in Prostate Cancer Cells in Vitro and in Vivo
Previously, we reported that retigeric acid B (RB), a natural pentacyclic triterpenic acid isolated from lichen, inhibited cell growth and induced apoptosis in androgen-independent prostate cancer (PCa) cells. However, the mechanism of action of RB remains unclear. In this study, we found that using PC3 and DU145 cells as models, RB inhibited phosphorylation levels of IκBα and p65 subunit of NF-κB in a time- and dosage-dependent manner. Detailed study revealed that RB blocked the nuclear translocation of p65 and its DNA binding activity, which correlated with suppression of NF-κB-regulated proteins including Bcl-2, Bcl-xL, cyclin D1 and survivin. NF-κB reporter assay suggested that RB was able to inhibit both constitutive activated-NF-κB and LPS (lipopolysaccharide)-induced activation of NF-κB. Overexpression of RelA/p65 rescued RB-induced cell death, while knockdown of RelA/p65 significantly promoted RB-mediated inhibitory effect on cell proliferation, suggesting the crucial involvement of NF-κB pathway in this event. We further analyzed antitumor activity of RB in in vivo study. In C57BL/6 mice carrying RM-1 homografts, RB inhibited tumor growth and triggered apoptosis mainly through suppressing NF-κB activity in tumor tissues. Additionally, DNA microarray data revealed global changes in the gene expression associated with cell proliferation, apoptosis, invasion and metastasis in response to RB treatment. Therefore, our findings suggested that RB exerted its anti-tumor effect by targeting the NF-κB pathway in PCa cells, and this could be a general mechanism for the anti-tumor effect of RB in other types of cancers as well
Notolutesins A–J, Dolabrane-Type Diterpenoids from the Chinese Liverwort Notoscyphus lutescens
Ten new dolabrane-type diterpenoids, notolutesins A–J (1–10), were isolated from the Chinese liverwort Notoscyphus lutescens, along with four known compounds. The structures of the new compounds were established on the basis of extensive spectroscopic data, and that of 1 was confirmed by single-crystal X-ray crystallography. The absolute configuration of 1 was determined by comparing its experimental and calculated electronic circular dichroism spectra. All of the isolates were evaluated for their cytotoxicity against a small panel of human cancer cell lines, and compound 1 exhibited an IC50 value of 6.2 μM against the PC3 human prostate cancer cell line
Finishing the euchromatic sequence of the human genome
The sequence of the human genome encodes the genetic instructions for human physiology, as well as rich information about human evolution. In 2001, the International Human Genome Sequencing Consortium reported a draft sequence of the euchromatic portion of the human genome. Since then, the international collaboration has worked to convert this draft into a genome sequence with high accuracy and nearly complete coverage. Here, we report the result of this finishing process. The current genome sequence (Build 35) contains 2.85 billion nucleotides interrupted by only 341 gaps. It covers ∼99% of the euchromatic genome and is accurate to an error rate of ∼1 event per 100,000 bases. Many of the remaining euchromatic gaps are associated with segmental duplications and will require focused work with new methods. The near-complete sequence, the first for a vertebrate, greatly improves the precision of biological analyses of the human genome including studies of gene number, birth and death. Notably, the human enome seems to encode only 20,000-25,000 protein-coding genes. The genome sequence reported here should serve as a firm foundation for biomedical research in the decades ahead
Preferential Recruitment of Th17 Cells to Cervical Cancer via CCR6-CCL20 Pathway
<div><p>Our previous studies suggest that Th17 cells accumulate within tumor tissues and correlate with recurrence of cervical cancer patients. However, the source of the increased tumor-infiltrating Th17 cells remains poorly understood. We investigated the prevalence, phenotype and trafficking property of Th17 cells in patients with cervical cancer. Our results showed that Th17 cells highly aggregated within tumor tissues in an activated phenotype with markedly increased expression of CCR6. Correspondingly, level of CCL20 in the tumor tissues was significantly higher than that in non-tumor and normal control tissues, and strongly positively associated with Th17 cells. Further, in vitro migration assay showed CCL20 had effective chemotaxis to circulating Th17 cells. In conclusion, Th17 cells are recruited into tumor tissues preferentially through CCR6-CCL20 pathway, which can serve as a novel therapeutic target for cervical cancer.</p></div
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