4,014 research outputs found
Further Study On U(1) Gauge Invariance Restoration
To further investigate the applicability of the projection scheme for
eliminating the unphysical divergence due to U(1) gauge invariance
violation, we study the process which possesses
advantages of simplicity and clearness. Our study indicates that the projection
scheme can indeed eliminate the unphysical divergence caused by the
U(1) gauge invariance violation and the scheme can apply to very high energy
region.Comment: Latex, 13 pages, 4 EPS fiure
The mechanism of dietary cholesterol effects on lipids metabolism in rats
<p>Abstract</p> <p>Background</p> <p>Cholesterol administration has been reported to influence hepatic lipid metabolism in rats. In the present study, the effect of dietary cholesterol on hepatic activity and mRNA expression of the enzymes involved in lipid metabolism were investigated. Fourteen male Wistar rats were randomly divided into 2 groups and fed 1% cholesterol or cholesterol free AIN76 diets for 4 weeks.</p> <p>Results</p> <p>The serum triglyceride and high density lipoprotein cholesterol levels were significantly decreased but the total cholesterol and non high density lipoprotein cholesterol levels were significantly increased in the cholesterol-fed rats compared with the control rats. And the concentrations of the hepatic total cholesterol and triglyceride increased about 4-fold and 20-fold separately by dietary cholesterol. The activities of hepatic malic enzyme, glucose-6-phosphate dehydrogenase, fatty acid synthase, phosphatidate phophatase and carnitine palmitoyl transferase were depressed by the cholesterol feeding (40%, 70%, 50%, 15% and 25% respectively). The results of mRNA expression showed that fatty acid synthase, carnitine palmitoyl transferase 1, carnitine palmitoyl transferase 2, and HMG-CoA reductase were down-regulated (35%, 30%, 50% and 25% respectively) and acyl-CoA: cholesterol acyltransferase and cholesterol 7Ī±-hydroxylase were up regulated (1.6 and 6.5 folds) in liver by the cholesterol administration.</p> <p>Conclusions</p> <p>The dietary cholesterol increased the triglyceride accumulation in liver, but did not stimulate the activity and the gene expression of hepatic enzymes related to triglyceride and fatty acid biosynthesis.</p
Comparison of Cloud Base Height Derived from a Ground-Based Infrared Cloud Measurement and Two Ceilometers
The cloud base height (CBH) derived from the whole-sky infrared cloud-measuring system (WSIRCMS) and two ceilometers (Vaisala CL31 and CL51) from November 1, 2011, to June 12, 2012, at the Chinese Meteorological Administration (CMA) Beijing Observatory Station are analysed. Significant differences can be found by comparing the measurements of different instruments. More exactly, the cloud occurrence retrieved from CL31 is 3.8% higher than that from CL51, while WSIRCMS data shows 3.6% higher than ceilometers. More than 75.5% of the two ceilometersā differences are within Ā±200ām and about 89.5% within Ā±500ām, while only 30.7% of the differences between WSIRCMS and ceilometers are within Ā±500ām and about 55.2% within Ā±1000ām. These differences may be caused by the measurement principles and CBH retrieval algorithm. A combination of a laser ceilometer and an infrared cloud instrument is recommended to improve the capability for determining cloud occurrence and retrieving CBHs
Thermal and nonthermal emission from a peculiar long-duration GRB 211211A
Long-duration GRB 211211A that lacks a supernova emission even down to very
stringent limits at such a low redshift and is associated with
kilonova emission, suggests that its physical origin is from a binary compact
star merger. By reanalyzing its data observed with the Gamma-Ray Burst Monitor
on board the Fermi mission, we find that both time-integrated and time-resolved
spectra can be fitted well by using a 2SBPL plus blackbody (2SBPL+BB) model in
the prompt emission. The bulk Lorentz factors () of the
outflow can be inferred by invoking the observed thermal emission at the
photosphere radius within a pure fireball model, and we find out that the
temporal evolution of seems to be tracking with the light
curve. The derived values of are also consistent with the
-/ correlations that
had been found in other bursts. Moreover, we also calculate the magnetization
factor in the central engine and at the
photosphere radius within the framework of a hybrid jet model, and find that
the values of both and are larger than 1
for different time slices. It suggests that at least the Poynting-flux
component is indeed existent in the outflow. If this is the case, one possible
physical interpretation of thermal and nonthermal emissions in GRB 211211A is
from the contributions of both annihilation and the
Blandford-Znajek mechanisms in the relativistic jet when a stellar mass black
hole resides in the central engine.Comment: 12 pages, 6 figures, and 4 tables. ApJ in press, and matched with the
published veriso
Molecular Beam Epitaxy Growth of Superconducting LiFeAs Film on SrTiO3(001) Substrate
The stoichiometric "111" iron-based superconductor, LiFeAs, has attacted
great research interest in recent years. For the first time, we have
successfully grown LiFeAs thin film by molecular beam epitaxy (MBE) on
SrTiO3(001) substrate, and studied the interfacial growth behavior by
reflection high energy electron diffraction (RHEED) and low-temperature
scanning tunneling microscope (LT-STM). The effects of substrate temperature
and Li/Fe flux ratio were investigated. Uniform LiFeAs film as thin as 3
quintuple-layer (QL) is formed. Superconducting gap appears in LiFeAs films
thicker than 4 QL at 4.7 K. When the film is thicker than 13 QL, the
superconducting gap determined by the distance between coherence peaks is about
7 meV, close to the value of bulk material. The ex situ transport measurement
of thick LiFeAs film shows a sharp superconducting transition around 16 K. The
upper critical field, Hc2(0)=13.0 T, is estimated from the temperature
dependent magnetoresistance. The precise thickness and quality control of
LiFeAs film paves the road of growing similar ultrathin iron arsenide films.Comment: 7 pages, 6 figure
Crossover between Weak Antilocalization and Weak Localization of Bulk States in Ultrathin Bi2Se3 Films
We report transport studies on the 5 nm thick Bi2Se3 topological insulator
films which are grown via molecular beam epitaxy technique. The angle-resolved
photoemission spectroscopy data show that the Fermi level of the system lies in
the bulk conduction band above the Dirac point, suggesting important
contribution of bulk states to the transport results. In particular, the
crossover from weak antilocalization to weak localization in the bulk states is
observed in the parallel magnetic field measurements up to 50 Tesla. The
measured magneto-resistance exhibits interesting anisotropy with respect to the
orientation of B// and I, signifying intrinsic spin-orbit coupling in the
Bi2Se3 films. Our work directly shows the crossover of quantum interference
effect in the bulk states from weak antilocalization to weak localization. It
presents an important step toward a better understanding of the existing
three-dimensional topological insulators and the potential applications of
nano-scale topological insulator devices
Dietary saponins of sea cucumber alleviate orotic acid-induced fatty liver in rats via PPARĪ± and SREBP-1c signaling
<p>Abstract</p> <p>Background</p> <p>Nonalcoholic fatty liver disease is the most common chronic liver disease in the world, and is becoming increasingly prevalent. Saponins of sea cucumber (SSC) are proven to exhibit various biological activities. Therefore, the present study was undertaken to examine the effect of saponins extracted from sea cucumber (Pearsonothuria graeffei) on the preventive activity of fatty liver in rats.</p> <p>Methods</p> <p>Male Wistar rats were randomly divided into five groups, including normal control group, fatty liver model group, SSC-treated group with SSC at levels of 0.01%, 0.03% and 0.05%. Model rats were established by administration with 1% orotic acid (OA). After the experiment period, serum total cholesterol (TC), triglyceride (TG), and hepatic lipid concentrations were determined. To search for a possible mechanism, we examined the changes of key enzymes and transcriptional factors involved in hepatic lipids biosynthesis, fatty acid Ī²-oxidation.</p> <p>Results</p> <p>Both 0.03% and 0.05% SSC treatment alleviated hepatic steatosis and reduced serum TG and TC concentration significantly in OA fed rats. Hepatic lipogenic enzymes, such as fatty acid synthase (FAS), malic enzyme (ME), and glucose-6-phosphate dehydrogenase (G6PDH) activities were inhibited by SSC treatment. SSC also decreased the gene expression of FAS, ME, G6PDH and sterol-regulatory element binding protein (SREBP-1c). Otherwise, the rats feeding with SSC showed increased carnitine palmitoyl transferase (CPT) activity in the liver. Hepatic peroxisome proliferator-activated receptor (PPARĪ±), together with its target gene CPT and acyl-CoA oxidase (ACO) mRNA expression were also upregulated by SSC.</p> <p>Conclusions</p> <p>According to our study, the lipids-lowering effect of dietary SSC may be partly associated with the enhancement of Ī²-oxidation via PPARĪ± activation. In addition, the inhibited SREBP-1c- mediated lipogenesis caused by SSC may also contribute to alleviating fatty liver.</p
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