13 research outputs found
Unconventional Integer Quantum Hall effect in graphene
Monolayer graphite films, or graphene, have quasiparticle excitations that
can be described by 2+1 dimensional Dirac theory. We demonstrate that this
produces an unconventional form of the quantized Hall conductivity with , that notably distinguishes graphene from
other materials where the integer quantum Hall effect was observed. This
unconventional quantization is caused by the quantum anomaly of the
Landau level and was discovered in recent experiments on ultrathin graphite
films.Comment: 4 pages, RevTeX4, 2 EPS figures; version accepted for publication in
Physical Review Letter
Transport of Dirac quasiparticles in graphene: Hall and optical conductivities
The analytical expressions for both diagonal and off-diagonal ac and dc
conductivities of graphene placed in an external magnetic field are derived.
These conductivities exhibit rather unusual behavior as functions of frequency,
chemical potential and applied field which is caused by the fact that the
quasiparticle excitations in graphene are Dirac-like. One of the most striking
effects observed in graphene is the odd integer quantum Hall effect. We argue
that it is caused by the anomalous properties of the Dirac quasiparticles from
the lowest Landau level. Other quantities such as Hall angle and Nernst signal
also exhibit rather unusual behavior, in particular when there is an excitonic
gap in the spectrum of the Dirac quasiparticle excitations.Comment: 25 pages, RevTeX4, 8 EPS figures; final version published in PR
Multifractality of the quantum Hall wave functions in higher Landau levels
To probe the universality class of the quantum Hall system at the
metal-insulator critical point, the multifractality of the wave function
is studied for higher Landau levels, , for various range of
random potential. We have found that, while the multifractal spectrum
(and consequently the fractal dimension) does vary with , the
parabolic form for indicative of a log-normal distribution of
persists in higher Landau levels. If we relate the multifractality with
the scaling of localization via the conformal theory, an asymptotic recovery of
the single-parameter scaling with increasing is seen, in agreement
with Huckestein's irrelevant scaling field argument.Comment: 10 pages, revtex, 5 figures available on request from
[email protected]
Localization and conductance fluctuations in the integer quantum Hall effect: Real--space renormalization group approach
We consider the network model of the integer quantum Hall effect transition.
By generalizing the real--space renormalization group procedure for the
classical percolation to the case of quantum percolation, we derive a closed
renormalization group (RG) equation for the universal distribution of
conductance of the quantum Hall sample at the transition. We find an
approximate solution of the RG equation and use it to calculate the critical
exponent of the localization length and the central moments of the conductance
distribution. The results obtained are compared with the results of recent
numerical simulations.Comment: 17 pages, RevTex, 7 figure
Signature-Tagged Mutagenesis in a Chicken Infection Model Leads to the Identification of a Novel Avian Pathogenic Escherichia coli Fimbrial Adhesin
The extraintestinal pathogen, avian pathogenic E. coli (APEC), known to cause systemic infections in chickens, is responsible for large economic losses in the poultry industry worldwide. In order to identify genes involved in the early essential stages of pathogenesis, namely adhesion and colonization, Signature-tagged mutagenesis (STM) was applied to a previously established lung colonization model of infection by generating and screening a total of 1,800 mutants of an APEC strain IMT5155 (O2:K1:H5; Sequence type complex 95). The study led to the identification of new genes of interest, including two adhesins, one of which coded for a novel APEC fimbrial adhesin (Yqi) not described for its role in APEC pathogenesis to date. Its gene product has been temporarily designated ExPEC Adhesin I (EA/I) until the adhesin-specific receptor is identified. Deletion of the ExPEC adhesin I gene resulted in reduced colonization ability by APEC strain IMT5155 both in vitro and in vivo. Furthermore, complementation of the adhesin gene restored its ability to colonize epithelial cells in vitro. The ExPEC adhesin I protein was successfully expressed in vitro. Electron microscopy of an afimbriate strain E. coli AAEC189 over-expressed with the putative EA/I gene cluster revealed short fimbrial-like appendages protruding out of the bacterial outer membrane. We observed that this adhesin coding gene yqi is prevalent among extraintestinal pathogenic E. coli (ExPEC) isolates, including APEC (54.4%), uropathogenic E. coli (UPEC) (65.9%) and newborn meningitic E. coli (NMEC) (60.0%), and absent in all of the 153 intestinal pathogenic E. coli strains tested, thereby validating the designation of the adhesin as ExPEC Adhesin I. In addition, prevalence of EA/I was most frequently associated with the B2 group of the EcoR classification and ST95 complex of the multi locus sequence typing (MLST) scheme, with evidence of a positive selection within this highly pathogenic complex. This is the first report of the newly identified and functionally characterized ExPEC adhesin I and its significant role during APEC infection in chickens
The Size, Shape, and Scattering of Sagittarius A* at 86GHz: First VLBI with ALMA
Contains fulltext :
200904.pdf (preprint version ) (Open Access)
Contains fulltext :
200904.pdf (publisher's version ) (Open Access