14,165 research outputs found
The Carnegie-Irvine Galaxy Survey. III. The Three-Component Structure of Nearby Elliptical Galaxies
Motivated by recent developments in our understanding of the formation and
evolution of massive galaxies, we explore the detailed photometric structure of
a representative sample of 94 bright, nearby elliptical galaxies, using
high-quality optical images from the Carnegie-Irvine Galaxy Survey. The sample
spans a range of environments and stellar masses, from M* = 10^{10.2} to
10^{12.0} solar mass. We exploit the unique capabilities of two-dimensional
image decomposition to explore the possibility that local elliptical galaxies
may contain photometrically distinct substructure that can shed light on their
evolutionary history. Compared with the traditional one-dimensional approach,
these two-dimensional models are capable of consistently recovering the surface
brightness distribution and the systematic radial variation of geometric
information at the same time. Contrary to conventional perception, we find that
the global light distribution of the majority (>75%) of elliptical galaxies is
not well described by a single Sersic function. Instead, we propose that local
elliptical galaxies generically contain three subcomponents: a compact (R_e < 1
kpc) inner component with luminosity fraction f ~ 0.1-0.15; an
intermediate-scale (R_e ~ 2.5 kpc) middle component with f ~ 0.2-0.25; and a
dominant (f = 0.6), extended (R_e ~ 10 kpc) outer envelope. All subcomponents
have average Sersic indices n ~ 1-2, significantly lower than the values
typically obtained from single-component fits. The individual subcomponents
follow well-defined photometric scaling relations and the stellar mass-size
relation. We discuss the physical nature of the substructures and their
implications for the formation of massive elliptical galaxies.Comment: To appear in The Astrophysical Journal; 36 pages, 2 tables, 38
figures; For the full resolution version, see:
http://users.obs.carnegiescience.edu/shuang/PaperIII.pdf ; For the atlas of
all selected models, see
http://users.obs.carnegiescience.edu/shuang/AppendixE.pd
The Carnegie-Irvine Galaxy Survey. IV. A Method to Determine the Average Mass Ratio of Mergers That Built Massive Elliptical Galaxies
Many recent observations and numerical simulations suggest that nearby
massive, early-type galaxies were formed through a "two-phase" process. In the
proposed second phase, the extended stellar envelope was accumulated through
many dry mergers. However, details of the past merger history of present-day
ellipticals, such as the typical merger mass ratio, are difficult to constrain
observationally. Within the context and assumptions of the two-phase formation
scenario, we propose a straightforward method, using photometric data alone, to
estimate the average mass ratio of mergers that contributed to the build-up of
massive elliptical galaxies. We study a sample of nearby massive elliptical
galaxies selected from the Carnegie-Irvine Galaxy Survey, using two-dimensional
analysis to decompose their light distribution into an inner, denser component
plus an extended, outer envelope, each having a different optical color. The
combination of these two substructures accurately recovers the negative color
gradient exhibited by the galaxy as whole. The color difference between the two
components ( ~ 0.10 mag; ~ 0.14 mag), based on the
slope of the M_stellar-color relation for nearby early-type galaxies, can be
translated into an estimate of the average mass ratio of the mergers. The rough
estimate, 1:5 to 1:10, is consistent with the expectation of the two-phase
formation scenario, suggesting that minor mergers were largely responsible for
building up to the outer stellar envelope of present-day massive ellipticals.
With the help of accurate photometry, large sample size, and more choices of
colors promised by ongoing and future surveys, the approach proposed here can
reveal more insights into the growth of massive galaxies during the last few
Gyr.Comment: Accepted by ApJ; 20 pages, 11 figures, 1 table; The high resolution
figures and the full table can be downloaded from here:
https://github.com/dr-guangtou/cgs_colorgra
Determination of a set of constitutive equations for an al-li alloy at SPF conditions
© 2015 The Authors.Uniaxial tensile tests of aluminium-lithium alloy AA1420wereconducted at superplastic forming conditions. The mechanical properties of this Al-Li alloy were then modelled by a set of physicallybased constitutive equations. The constitutive equations describe the isotropic work hardening,recovery and damage by dislocation density changes and grain size evolution. Based on a recent upgraded optimisation technique, the material constants for these constitutive equations were determined
Arsenic trioxide-induced cytotoxicity in small cell lung cancer via altered redox homeostasis and mitochondrial integrity.
Arsenic trioxide (ATO) has demonstrated anticancer activity in different malignancies, especially acute promyelocytic leukemia, with a wide array of putative mechanisms. In this study, we aimed to elucidate the activity and mechanisms of ATO in small cell lung cancer (SCLC). A panel of SCLC cell lines (H841, DMS79, H526, H69 and H187) was employed to demonstrate the activity of ATO. Cell viability, apoptosis and mitochondrial membrane depolarization were assessed. Western blotting was performed to determine the alteration of pro-apoptotic and anti-apoptotic mediators. Reactive oxygen species (ROS) (hydrogen peroxide and superoxide) and intracellular glutathione (GSH) were measured. Antioxidants, N-acetyl-L-cysteine (NAC) and butylated hydroxyanisole (BHA), were applied to restore GSH content and reduce production of ROS. All SCLC cell lines were relatively sensitive to ATO with IC50 values below 10 µM. ATO induced cell death mainly through apoptosis in H841 cells in a dose-dependent manner. Hydrogen peroxide was the major ROS in SCLC cells induced by ATO. Along with GSH depletion and Bcl-2 downregulation, mitochondrial membrane permeabilization was enhanced, followed by release of AIF and SMAC from mitochondria to initiate different cell death pathways. NAC reversed cell death and molecular changes induced by ATO via restoring GSH and reducing ROS content. BHA inhibited hydrogen peroxide production completely and partially restored GSH content accounting for partial reversal of cell inhibition and mitochondrial dysfunction. Nonetheless, ATO reduced both reduced and oxidized form of thioredoxin 1 (Trx1) with no effect on Trx1 redox potential. ATO led to cell death in SCLC mainly through mitochondrial dysfunction, resulting from altered cellular redox homeostasis, namely, hydrogen peroxide generation, GSH depletion and Trx1 downregulation.published_or_final_versio
Numerical simulation of transient force and eddy current loss in a 720-MVA power transformer
Author name used in this publication: S. L. HoAuthor name used in this publication: H. C. WongVersion of RecordPublishe
A 3-D study of eddy current field and temperature rises in a compact bus duct system
Author name used in this publication: S. L. HoAuthor name used in this publication: H. C. WongAuthor name used in this publication: K. W. E. Cheng2005-2006 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe
Calculations of transient eddy current field and dynamic short circuit forces in a large power transformer
Author name used in this publication: S. L. HoAuthor name used in this publication: S. Y. YangAuthor name used in this publication: H. C. WongRefereed conference paper2005-2006 > Academic research: refereed > Refereed conference paperVersion of RecordPublishe
Calculation of eddy current field in the ascending flange for the bushings and tank wall of a large power transformer
Author name used in this publication: S. L. HoAuthor name used in this publication: K. W. E. Cheng2007-2008 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe
Accretion-modified Stars in Accretion Disks of Active Galactic Nuclei: the Low-luminosity Cases and an Application to Sgr A\!^{*}
In this paper, we investigate the astrophysical processes of stellar-mass
black holes (sMBHs) embedded in advection-dominated accretion flows (ADAFs) of
supermassive black holes (SMBHs) in low-luminosity active galactic nuclei
(AGNs). The sMBH is undergoing Bondi accretion at a rate lower than the SMBH.
Outflows from the sMBH-ADAF dynamically interact with their surroundings and
form a cavity inside the SMBH-ADAF, thereby quenching the accretion onto the
SMBH. Rejuvenation of the Bondi accretion is rapidly done by turbulence. These
processes give rise to quasi-periodic episodes of sMBH activities and create
flickerings from relativistic jets developed by the Blandford-Znajek mechanism
if the sMBH is maximally rotating. Accumulating successive sMBH-outflows
trigger viscous instability of the SMBH-ADAF, leading to a flare following a
series of flickerings. Recently, the similarity of near-infrared flare's orbits
has been found by GRAVITY/VLTI astrometric observations of Sgr A\!^{*}: their
loci during the last 4-years consist of a ring in agreement with the
well-determined SMBH mass. We apply the present model to Sgr A\!^{*}, which
shows quasi-periodic flickerings. A SMBHH of is preferred
orbiting around the central SMBH of Sgr A\!^{*} from fitting radio to X-ray
continuum. Such an extreme mass ratio inspiraling (EMRI) provides an excellent
laboratory for LISA, Taiji and Tianqin detection of mHz gravitational waves
with strains of , as well as their polarization.Comment: 16 pages, 3 figures, accepted by ApJ
Prevention of colitis-associated colon cancer using a vaccine to target abnormal expression of the MUC1 tumor antigen
Association between chronic inflammation and cancer development is exemplified by inflammatory bowel disease (IBD) where patients with chronic uncontrolled colitis have a significantly increased risk of developing colitis-associated colorectal cancer (CACC). CACC appears to progresses through the inflammation-dysplasia-carcinoma sequence. This highlights the need to identify targets and interventions that reduce inflammation and prevent development of dysplasia in the context of IBD. Using the dextran sulfate sodium (DSS) mouse model of chronic colitis and CACC, we show that an important target of intervention in human disease would be the epithelial cell molecule MUC1 that is aberrantly expressed on inflamed colonocytes and promotes inflammation and progression to CACC. We show that a MUC1 vaccine can ameliorate chronic colitis and prevent development of dysplasia in the colon and thus extend survival in human MUC1 transgenic mice. This study supports the potential of prophylactic vaccines to target antigens that become aberrantly expressed in chronic inflammation (e.g., IBD) and continue to be expressed on the associated cancers (e.g., colon cancer), to prevent and/or treat both diseases
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