425 research outputs found
The progenitors of Type Ia supernovae with long delay times
The nature of the progenitors of Type Ia supernovae (SNe Ia) is still
unclear. In this paper, by considering the effect of the instability of
accretion disk on the evolution of white dwarf (WD) binaries, we performed
binary evolution calculations for about 2400 close WD binaries, in which a
carbon--oxygen WD accretes material from a main-sequence star or a slightly
evolved subgiant star (WD + MS channel), or a red-giant star (WD + RG channel)
to increase its mass to the Chandrasekhar (Ch) mass limit. According to these
calculations, we mapped out the initial parameters for SNe Ia in the orbital
period--secondary mass () plane for various WD
masses for these two channels, respectively. We confirm that WDs in the WD + MS
channel with a mass as low as can accrete efficiently and reach
the Ch limit, while the lowest WD mass for the WD + RG channel is . We have implemented these results in a binary population synthesis
study to obtain the SN Ia birthrates and the evolution of SN Ia birthrates with
time for both a constant star formation rate and a single starburst. We find
that the Galactic SN Ia birthrate from the WD + MS channel is according to our standard model, which is higher than
previous results. However, similar to previous studies, the birthrate from the
WD + RG channel is still low (). We also
find that about one third of SNe Ia from the WD + MS channel and all SNe Ia
from the WD + RG channel can contribute to the old populations (\ga1 Gyr) of
SN Ia progenitors.Comment: 11 pages, 9 figures, 1 table, accepted for publication in MNRA
Tissue specific induction of p62/sqstm1 by farnesoid X receptor
Background: Farnesoid X Receptor (FXR) is a member of the nuclear receptor superfamily and is a ligand-activated transcription factor essential for maintaining liver and intestinal homeostasis. FXR is protective against carcinogenesis and inflammation in liver and intestine as demonstrated by the development of inflammation and tumors in the liver and intestine of FXR knock-out mice. However, mechanisms for the protective effects of FXR are not completely understood. This study reports a novel role of FXR in regulating expression of Sqstm1, which encodes for p62 protein. p62 plays an important role in maintaining cellular homeostasis through selective autophagy and activating signal transduction pathways, such as NF-κB to support cell survival and caspase-8 to initiate apoptosis. FXR regulation of Sqstm1 may serve as a protective mechanism. Methods and Results: This study showed that FXR bound to the Sqstm1 gene in both mouse livers and ileums as determined by chromatin immunoprecipitation. In addition, FXR activation enhanced transcriptional activation of Sqstm1 in vitro. However, wild-type mice treated with GW4064, a synthetic FXR ligand, showed that FXR activation induced mRNA and protein expression of Sqstm1/p62 in ileum, but not in liver. Interestingly, FXR-transgenic mice showed induced mRNA expression of Sqstm1 in both liver and ileum compared to wild-type mice. Conclusions: Our current study has identified a novel role of FXR in regulating the expression of p62, a key factor in protein degradation and cell signaling. Regulation of p62 by FXR indicates tissue-specific and gene-dosage effects. Furthermore, FXR-mediated induction of p62 may implicate a protective mechanism of FXR. © 2012 Williams et al
The rotation of surviving companion stars after type Ia supernova explosions in the WD+MS scenario
In the SD scenario of SNe Ia the companion survives the SN explosion and thus
should be visible near the center of the SN remnant and may show some unusual
features. A promising approach to test progenitor models of SNe Ia is to search
for the companion in SNRs. Here we present the results of 3D hydrodynamics
simulations of the interaction between the SN Ia blast wave and a MS companion
taking into consideration its orbital motion and spin. The primary goal of this
work is to investigate the rotation of surviving companions after SN Ia
explosions in the WD+MS scenario. We use Eggleton's code including the
optically thick accretion wind model to obtain realistic models of companions.
The impact of the SN blast wave on these companions is followed in 3D
hydrodynamic simulations employing the SPH code GADGET3. We find that the
rotation of the companion does not significantly affect the amount of stripped
mass and the kick velocity caused by the SN impact. However, in our
simulations, the rotational velocity of the companion is significantly reduced
to about 14% to 32% of its pre-explosion value due to the expansion of the
companion and the fact that 55%-89% of the initial angular momentum is carried
away by the stripped matter. Compared with the observed rotational velocity of
the presumed companion star of Tycho's SN, Tycho G, of 6 km/s the final
rotational velocity we obtain is still higher by at least a factor of two.
Whether this difference is significant, and may cast doubts on the suggestion
that Tycho G is the companion of SN 1572, has to be investigated in future
studies. Based on binary population synthesis results we present, for the first
time, the expected distribution of rotational velocities of companions after
the explosion which may provide useful information for the identification of
the surviving companion in observational searches in other historical SNRs.Comment: 13 pages, 15 figures, accepted for publication by Astronomy and
Astrophysic
Not All Instances Contribute Equally: Instance-adaptive Class Representation Learning for Few-Shot Visual Recognition
Few-shot visual recognition refers to recognize novel visual concepts from a
few labeled instances. Many few-shot visual recognition methods adopt the
metric-based meta-learning paradigm by comparing the query representation with
class representations to predict the category of query instance. However,
current metric-based methods generally treat all instances equally and
consequently often obtain biased class representation, considering not all
instances are equally significant when summarizing the instance-level
representations for the class-level representation. For example, some instances
may contain unrepresentative information, such as too much background and
information of unrelated concepts, which skew the results. To address the above
issues, we propose a novel metric-based meta-learning framework termed
instance-adaptive class representation learning network (ICRL-Net) for few-shot
visual recognition. Specifically, we develop an adaptive instance revaluing
network with the capability to address the biased representation issue when
generating the class representation, by learning and assigning adaptive weights
for different instances according to their relative significance in the support
set of corresponding class. Additionally, we design an improved bilinear
instance representation and incorporate two novel structural losses, i.e.,
intra-class instance clustering loss and inter-class representation
distinguishing loss, to further regulate the instance revaluation process and
refine the class representation. We conduct extensive experiments on four
commonly adopted few-shot benchmarks: miniImageNet, tieredImageNet, CIFAR-FS,
and FC100 datasets. The experimental results compared with the state-of-the-art
approaches demonstrate the superiority of our ICRL-Net
Dichlorido[N-(2-pyridylmethylidene)benzene-1,4-diamine]zinc(II)
In the title compound, [ZnCl2(C12H11N3)], the ZnII atom is four-coordinated by two N atoms from an N-(2-pyridylmethylene)benzene-1,4-diamine ligand and two Cl atoms in a distorted tetrahedral geometry. In the crystal, the complex molecules are connected by N—H⋯Cl and C—H⋯Cl hydrogen bonds into a two-dimensional layer structure parallel to (110)
WD+RG systems as the progenitors of Type Ia supernovae
Type Ia supernovae (SNe Ia) play an important role in the study of cosmic
evolution, especially in cosmology. There are several progenitor models for SNe
Ia proposed in the past years. In this paper, by considering the effect of
accretion disk instability on the evolution of white dwarf (WD) binaries, we
performed detailed binary evolution calculations for the WD + red-giant (RG)
channel of SNe Ia, in which a carbon-oxygen WD accretes material from a RG star
to increase its mass to the Chandrasekhar mass limit. According to these
calculations, we mapped out the initial and final parameters for SNe Ia in the
orbital period--secondary mass plane for various WD masses for this channel. We
discussed the influence of the variation of the duty cycle value on the regions
for producing SNe Ia. Similar to previous studies, this work also indicates
that the long-period dwarf novae offer a possible ways for producing SNe Ia.
Meanwhile, we find that the surviving companion stars from this channel have a
low mass after SN explosion, which may provide a means for the formation of the
population of single low-mass WDs (<0.45Msun).Comment: 5 pages, 3 figure
Synergistic effects of Yiqi Huazhuo Gushen herbal formula and valsartan on metabolic syndrome complicated with microalbuminuria
Purpose: To study the effects of a combination of Yiqi Huazhuo Gushen formula and valsartan on metabolic syndrome (MetS) complicated with microalbuminuria.Methods: Patients with MetS (100), recruited from Department of the Traditional Chinese Medicine, Shanghai Jiao Tong University Affiliated Sixth People’s Hospital; Department of Integrated Traditional Chinese and Western Medicine, Huashan Hospital, Fudan University; and Department of Endocrinology, Hospital of Integrated Traditional Chinese and Western Medicine in Yueyang, Shanghai University of Traditional Chinese Medicine, were randomly divided into two sets: control group (n = 50) given valsartan treatment, and Chinese herbal medicine (CHF) group (n = 50) given Yiqi Huazhuo Gushen formula in addition to valsartan. Both therapeutic regimens were given once a day for 12 weeks. The parameters measured were conversion rate of microalbuminuria (MA), ratio of urinary albumin to creatinine (UACR), 24- h total volume of urinary protein (24hTP), urinary transferrin, urinary β2 microglobulin, constitutional index (CI), and waist-hip ratio (WHR). Other indices assessed were peak systolic and diastolic pressure (SBP and DBP), mean arterial blood pressure (MABP), fasting plasma glucose (FPG), postprandial 2 h blood glucose (2hPG), glycosylated hemoglobin (GH), steadystate model for insulin resistance (HOMA-IR), total cholesterol (TC), glycerin trilaurate (TG), low density lipoprotein (LDL), and high-density lipoprotein (HDL).Results: All 100 subjects completed the clinical study. The outcome revealed that compared with 10.00 % in controls, the negative conversion of MA reached 28.00 % in the CHF group (p < 0.050). CHF produced reductions in MA, UACR, BMI, 24hTP and urinary β2 microglobulin (p < 0.05). It also led to marked increases in BMI, WHR, SBP, MAP, FPG, 2hPPG, HbA1c and HOMA-IR, and significant decreases in TG (p < 0.05).Conclusion: These results suggest that CHF treatment results in alleviation of microalbuminuria and multiple cardiovascular risk factors in metabolic syndrome complicated with microalbuminuria. These effects correlate with improvements in insulin sensitivity and rectification of abnormal fat distribution.Keywords: Metabolic syndrome, Microalbuminuria, Yiqi Huazhuo Gushen formula, Insulin resistance, Central obesit
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