888 research outputs found
Study of multiband disordered systems using the typical medium dynamical cluster approximation
We generalize the typical medium dynamical cluster approximation to multiband
disordered systems. Using our extended formalism, we perform a systematic study
of the non-local correlation effects induced by disorder on the density of
states and the mobility edge of the three-dimensional two-band Anderson model.
We include inter-band and intra-band hopping and an intra-band disorder
potential. Our results are consistent with the ones obtained by the transfer
matrix and the kernel polynomial methods. We apply the method to
KFeSe with Fe vacancies. Despite the strong vacancy disorder
and anisotropy, we find the material is not an Anderson insulator. Our results
demonstrate the application of the typical medium dynamical cluster
approximation method to study Anderson localization in real materials.Comment: 10 pages, 8 figure
Pressure-induced melting of magnetic order and emergence of new quantum state in alpha-RuCl3
Here we report the observation of pressure-induced melting of
antiferromagnetic (AFM) order and emergence of a new quantum state in the
honeycomb-lattice halide alpha-RuCl3, a candidate compound in the proximity of
quantum spin liquid state. Our high-pressure heat capacity measurements
demonstrate that the AFM order smoothly melts away at a critical pressure (Pc)
of 0.7 GPa. Intriguingly, the AFM transition temperature displays an increase
upon applying pressure below the Pc, in stark contrast to usual phase diagrams,
for example in pressurized parent compounds of unconventional superconductors.
Furthermore, in the high-pressure phase an unusual steady of magnetoresistance
is observed. These observations suggest that the high-pressure phase is in an
exotic gapped quantum state which is robust against pressure up to ~140 GPa.Comment: 20 pages, 4 figure
Unusually stronger quantum fluctuation with larger spins: Novel phenomena revealed by emergent magnetism in pressurized high-temperature superconductor FeSe
A counter-intuitive enhancement of quantum fluctuation with larger spins,
together with a few novel physical phenomena, is discovered in studying the
recently observed emergent magnetism in high-temperature superconductor FeSe
under pressure. Starting with experimental crystalline structure from our
high-pressure X-ray refinement, we analyze theoretically the stability of the
magnetically ordered state with a realistic spin-fermion model. We find
surprisingly that in comparison with the magnetically ordered Fe-pnictides, the
larger spins in FeSe suffer even stronger long-range quantum fluctuation that
diminishes their ordering at ambient pressure. This "fail-to-order" quantum
spin liquid state then develops into an ordered state above 1GPa due to
weakened fluctuation accompanying the reduction of anion height and carrier
density. The ordering further benefits from the ferro-orbital order and shows
the observed enhancement around 1GPa. We further clarify the controversial
nature of magnetism and its interplay with nematicity in FeSe in the same
unified picture for all Fe-based superconductors. In addition, the versatile
itinerant carriers produce interesting correlated metal behavior in a large
region of phase space. Our study establishes a generic exceptional paradigm of
stronger quantum fluctuation with larger spins that complements the standard
knowledge of insulating magnetism.Comment: 7 pages, 4 figure
A global transcriptional network connecting noncoding mutations to changes in tumor gene expression.
Although cancer genomes are replete with noncoding mutations, the effects of these mutations remain poorly characterized. Here we perform an integrative analysis of 930 tumor whole genomes and matched transcriptomes, identifying a network of 193 noncoding loci in which mutations disrupt target gene expression. These 'somatic eQTLs' (expression quantitative trait loci) are frequently mutated in specific cancer tissues, and the majority can be validated in an independent cohort of 3,382 tumors. Among these, we find that the effects of noncoding mutations on DAAM1, MTG2 and HYI transcription are recapitulated in multiple cancer cell lines and that increasing DAAM1 expression leads to invasive cell migration. Collectively, the noncoding loci converge on a set of core pathways, permitting a classification of tumors into pathway-based subtypes. The somatic eQTL network is disrupted in 88% of tumors, suggesting widespread impact of noncoding mutations in cancer
The AI-2/luxS Quorum Sensing System Affects the Growth Characteristics, Biofilm Formation, and Virulence of Haemophilus parasuis
Haemophilus parasuis (H. parasuis) is a kind of opportunistic pathogen of the upper respiratory tract of piglets. Under certain circumstances, virulent strains can breach the mucosal barrier and enter the bloodstream, causing severe Glässer's disease. Many virulence factors are found to be related to the pathogenicity of H. parasuis strain, but the pathogenic mechanism remains unclear. LuxS/AI-2, as a kind of very important quorum sensing system, affects the growth characteristics, biofilm formation, antibiotic production, virulence, and metabolism of different strains. In order to investigate the effect of luxS/AI-2 quorum sensing system on the virulence of H. parasuis, a deletion mutant strain (ΔluxS) and complemented strain (C-luxS) were constructed and characterized. The results showed that the luxS gene participated in regulating and controlling stress resistance, biofilm formation and virulence. Compared with wild-type strain, ΔluxS strain decreased the production of AI-2 molecules and the tolerance toward oxidative stress and heat shock, and it reduced the abilities of autoagglutination, hemagglutination, and adherence, whereas it increased the abilities to form biofilm in vitro. In vivo experiments showed that ΔluxS strain attenuated its virulence about 10-folds and significantly decreased its tissue burden of bacteria in mice, compared with the wild-type strain. Taken together, the luxS/AI-2 quorum sensing system in H. parasuis not only plays an important role in growth and biofilm formation, but also affects the pathogenicity of H. parasuis
BAs and boride III-V alloys
Boron arsenide, the typically-ignored member of the III-V arsenide series
BAs-AlAs-GaAs-InAs is found to resemble silicon electronically: its Gamma
conduction band minimum is p-like (Gamma_15), not s-like (Gamma_1c), it has an
X_1c-like indirect band gap, and its bond charge is distributed almost equally
on the two atoms in the unit cell, exhibiting nearly perfect covalency. The
reasons for these are tracked down to the anomalously low atomic p orbital
energy in the boron and to the unusually strong s-s repulsion in BAs relative
to most other III-V compounds. We find unexpected valence band offsets of BAs
with respect to GaAs and AlAs. The valence band maximum (VBM) of BAs is
significantly higher than that of AlAs, despite the much smaller bond length of
BAs, and the VBM of GaAs is only slightly higher than in BAs. These effects
result from the unusually strong mixing of the cation and anion states at the
VBM. For the BAs-GaAs alloys, we find (i) a relatively small (~3.5 eV) and
composition-independent band gap bowing. This means that while addition of
small amounts of nitrogen to GaAs lowers the gap, addition of small amounts of
boron to GaAs raises the gap (ii) boron ``semi-localized'' states in the
conduction band (similar to those in GaN-GaAs alloys), and (iii) bulk mixing
enthalpies which are smaller than in GaN-GaAs alloys. The unique features of
boride III-V alloys offer new opportunities in band gap engineering.Comment: 18 pages, 14 figures, 6 tables, 61 references. Accepted for
publication in Phys. Rev. B. Scheduled to appear Oct. 15 200
Cloning and Characterization of a Putative TAC1 Ortholog Associated with Leaf Angle in Maize (Zea mays L.)
BACKGROUND: Modifying plant architecture to increase photosynthesis efficiency and reduce shade avoidance response is very important for further yield improvement when crops are grown in high density. Identification of alleles controlling leaf angle in maize is needed to provide insight into molecular mechanism of leaf development and achieving ideal plant architecture to improve grain yield. METHODOLOGY/PRINCIPAL FINDINGS: The gene cloning was done by using comparative genomics, and then performing real-time polymerase chain reaction (RT-PCR) analysis to assay gene expression. The gene function was validated by sequence dissimilarity analysis and QTL mapping using a functional cleaved amplified polymorphism (CAP). CONCLUSIONS: The leaf angle is controlled by a major quantitative trait locus, ZmTAC1 (Zea mays L. Leaf Angle Control 1). ZmTAC1 has 4 exons encoding a protein with 263 amino acids, and its domains are the same as those of the rice OsTAC1 protein. ZmTAC1 was found to be located in the region of qLA2 by using the CAP marker and the F(2:3) families from the cross between Yu82 and Shen137. Real-time PCR analysis revealed ZmTAC1 expression was the highest in the leaf-sheath pulvinus, less in the leaf and shoot apical meristem, and the lowest in the root. A nucleotide difference in the 5'-untranslated region (UTR) between the compact inbred line Yu82 ("CTCC") and the expanded inbred line Shen137 ("CCCC") influences the expression level of ZmTAC1, further controlling the size of the leaf angle. Sequence verification of the change in the 5'-UTR revealed ZmTAC1 with "CTCC" was present in 13 compact inbred lines and ZmTAC1 with "CCCC" was present in 18 expanded inbred lines, indicating ZmTAC1 had been extensively utilized in breeding with regard to the improvement of the maize plant architecture
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