16,180 research outputs found
The Physical Connections Among IR QSOs, PG QSOs and Narrow-Line Seyfert 1 Galaxies
We study the properties of infrared-selected QSOs (IR QSOs),
optically-selected QSOs (PG QSOs) and Narrow Line Seyfert 1 galaxies (NLS1s).
We compare their properties from the infrared to the optical and examine
various correlations among the black hole mass, accretion rate, star formation
rate and optical and infrared luminosities. We find that the infrared excess in
IR QSOs is mostly in the far infrared, and their infrared spectral indices
suggest that the excess emission is from low temperature dust heated by
starbursts rather than AGNs. The infrared excess is therefore a useful
criterion to separate the relative contributions of starbursts and AGNs. We
further find a tight correlation between the star formation rate and the
accretion rate of central AGNs for IR QSOs. The ratio of the star formation
rate and the accretion rate is about several hundred for IR QSOs, but decreases
with the central black hole mass. This shows that the tight correlation between
the stellar mass and the central black hole mass is preserved in massive
starbursts during violent mergers. We suggest that the higher Eddington ratios
of NLS1s and IR QSOs imply that they are in the early stage of evolution toward
classical Seyfert 1's and QSOs, respectively.Comment: 32 pages, 6 figures, accepted by Ap
Gas explosion analysis of safety gap effect on the innovating FLNG vessel with a cylindrical platform
© 2016 Elsevier LtdAfter investigating gas dispersion on a cylindrical Floating Liquefied Natural Gas (FLNG) platform (Li et al, 2016), this second article focuses on assessment of gas explosion by using Computational Fluid Dynamics (CFD). Gas explosion simulations are carried out to evaluate the explosion overpressure mitigating effect of safety gap. The Data-dump technique, which is an effective tool in resetting turbulence length scale in gas explosion overpressure calculation, is applied to ensure simulation accuracy for the congestion scenario with safety gap. Two sets of different safety gaps are designed to investigate the safety gap on the cylindrical FLNG platform, the overall results indicate that the safety gap is effective in reducing overpressure in two adjacent congestions. However, for the explosion scenario where the flame is propagating through several safety gaps to the far field congestion, the safety gap mitigates overpressure only in certain explosion protecting targets. Two series of artificial configurations are modeled to further investigate the explosion scenarios with more than two safety gaps in one direction. It is concluded that the optimal safety gap design in overpressure mitigation for the cylindrical FLNG platform is to balance the safety gap distance ratio in the congested regions
Observation of an in-plane magnetic-field-driven phase transition in a quantum Hall system with SU(4) symmetry
In condensed matter physics, the study of electronic states with SU(N)
symmetry has attracted considerable and growing attention in recent years, as
systems with such a symmetry can often have a spontaneous symmetry-breaking
effect giving rise to a novel ground state. For example, pseudospin quantum
Hall ferromagnet of broken SU(2) symmetry has been realized by bringing two
Landau levels close to degeneracy in a bilayer quantum Hall system. In the past
several years, the exploration of collective states in other multi-component
quantum Hall systems has emerged. Here we show the conventional pseudospin
quantum Hall ferromagnetic states with broken SU(2) symmetry collapsed rapidly
into an unexpected state with broken SU(4) symmetry, by in-plane magnetic field
in a two-subband GaAs/AlGaAs two-dimensional electron system at filling factor
around . Within a narrow tilting range angle of 0.5 degrees, the
activation energy increases as much as 12 K. While the origin of this puzzling
observation remains to be exploited, we discuss the possibility of a
long-sought pairing state of electrons with a four-fold degeneracy.Comment: 13 pages, 4 figure
First-principles study of native point defects in Bi2Se3
Using first-principles method within the framework of the density functional
theory, we study the influence of native point defect on the structural and
electronic properties of BiSe. Se vacancy in BiSe is a double
donor, and Bi vacancy is a triple acceptor. Se antisite (Se) is always
an active donor in the system because its donor level ((+1/0))
enters into the conduction band. Interestingly, Bi antisite(Bi) in
BiSe is an amphoteric dopant, acting as a donor when
0.119eV (the material is typical p-type) and as an acceptor when
0.251eV (the material is typical n-type). The formation energies
under different growth environments (such as Bi-rich or Se-rich) indicate that
under Se-rich condition, Se is the most stable native defect independent
of electron chemical potential . Under Bi-rich condition, Se vacancy
is the most stable native defect except for under the growth window as
0.262eV (the material is typical n-type) and
-0.459eV(Bi-rich), under such growth windows one
negative charged Bi is the most stable one.Comment: 7 pages, 4 figure
Study on cementitious properties of steel slag
The converter steel slag chemical and mineral components in China’s main steel plants have been analysed in the present paper. The electronic microscope, energy spectrum analysis, X-ray diffraction analysis confirmed the main mineral compositions in the converter slag. Converter slag of different components were grounded to obtain a powder with specific surface area over 400m2/kg, making them to take place some part of the cement in the concrete as the admixture and carry out the standard tests. The results indicate that the converter slag can be used as cementitious materials for construction. Furthermore, physical mechanic and durability tests on the concrete that certain amount of cement be substituted by converter steel slag powder from different steel plants are carried out, the results show that the concrete with partial substitution of steel slag powder has the advantages of higher later period strength, better frost resistance, good wear resistance and lower hydration heat, etc. This study can be used as the technical basis for “Steel Slag Powder Used For Cement And Concrete”, “Steel Slag Portland Cement”, “Low Heat Portland Steel Slag Cement”, “Steel Slag Road Cement” in China, as well as a driving force to the works of steel slag utilization with high-value addition, circular economy, energy conservation and discharge reduction in the iron and steel industry
Probing Quantum Hall Pseudospin Ferromagnet by Resistively Detected NMR
Resistively Detected Nuclear Magnetic Resonance (RD-NMR) has been used to
investigate a two-subband electron system in a regime where quantum Hall
pseudo-spin ferromagnetic (QHPF) states are prominently developed. It reveals
that the easy-axis QHPF state around the total filling factor can be
detected by the RD-NMR measurement. Approaching one of the Landau level (LL)
crossing points, the RD-NMR signal strength and the nuclear spin relaxation
rate enhance significantly, a signature of low energy spin
excitations. However, the RD-NMR signal at another identical LL crossing point
is surprisingly missing which presents a puzzle
Can Changing Breeding Structure Serve as a Climate Adaptation Strategy? Evidence from a Comparative Study of China and Mongolia
Under the influence of climate change, the vulnerability of grassland ecosystems in the Mongolian Plateau has increased. Correspondingly, herdsmen need to adopt more livelihood adaptation strategies to cope with changes in climate and grassland environment. The purpose of this study is to analyze the impact of breeding structure on grassland quality in Mongolian plateau. We select 20 border provinces/banners of Mongolia and Inner Mongolia Autonomous Region for research, and combined statistical data with remote sensing data of 2007-2016. The Normalized Difference Vegetation Index (NDVI) is used to quantify the grassland vegetation quality. Results show that there are differences in livestock dynamics and grassland quality between Mongolia and Inner Mongolia, and higher sheep proportion leads to grassland degradation, and the impact varied in regions with different livestock carrying capacity. The initial grassland conditions could alleviate the negative impact of the sheep proportion on the grassland quality. The results of the mediation effect show that the primary industry GDP has a masking effect, i.e., the primary industry GDP can alleviate the negative influence of sheep proportion on grassland quality. The results of heterogeneity analysis showed that there were differences in the effect of sheep proportion on grassland quality under different livestock carrying capacity. In addition, after distinguishing countries, Mongolia did not show significant results due to its relatively stable breeding structure. While the breeding structure of Inner Mongolia had a greater negative impact on the grassland quality, which further indicated that the decline of sheep proportion has played a stronger ecological benefit
cDNA, genomic sequence cloning and overexpression of ribosomal protein S16 gene (RPS16) from the Giant Panda
RPS16 of eukaryote is a component of the 40S small ribosomal subunit encoded by RPS16 gene and is also a homolog of prokaryotic RPS9. The cDNA and genomic sequence of RPS16 was cloned successfully for the first time from the Giant Panda (Ailuropoda melanoleuca) using reverse transcription-polymerase chain reaction (RT-PCR) technology and Touchdown-PCR, respectively, which were both sequenced and analyzed preliminarily. The cDNA of the RPS16 gene was overexpressed in Escherichia coli BL21. The length of cDNA fragment cloned is 448 bp containing an open reading frame of 441 bp encoding 146 amino acids and the length of the genomic sequence is 2510 bp, containing five exons and four introns. Alignment analysis indicates that the nucleotide sequence share a high homology with those of Bos taurus, Homo sapiens, Mus musculus, Rattus norvegicus and Danio rerio by 95.46, 92.97, 89.80, 89.80 and 82.54%, respectively. The deduced amino acid sequence is entirely identical compared with the first four animals and share a high homology with that of D. rerio by 96.58%. Topology prediction shows that there is one cAMP- and cGMP-dependent protein kinase phosphorylation site, three protein kinase C phosphorylation sites, one casein kinase II phosphorylation site, two N-myristoylation sites, one amidation site and one ribosomal protein S9 signature in the RPS16 protein of the Giant Panda . The RPS16 gene can be readily expressed in E. coli and it fused with the N-terminally GST-tagged protein which gave rise to the accumulation of an expected 20.095 kDa polypeptide, in good agreement with the predicted molecular weight. The expression product obtained could be used for purification and further study of its function
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