16 research outputs found
Scaling Behavior of the Activated Conductivity in a Quantum Hall Liquid
We propose a scaling model for the universal longitudinal conductivity near
the mobility edge for the integer quantum Hall liquid. We fit our model with
available experimental data on exponentially activated conductance near the
Landau level tails in the integer quantum Hall regime. We obtain quantitative
agreement between our scaling model and the experimental data over a wide
temperature and magnetic field range.Comment: 9 pages, Latex, 2 figures (available upon request), #phd0
Criticality in the two-dimensional random-bond Ising model
The two-dimensional (2D) random-bond Ising model has a novel multicritical
point on the ferromagnetic to paramagnetic phase boundary. This random phase
transition is one of the simplest examples of a 2D critical point occurring at
both finite temperatures and disorder strength. We study the associated
critical properties, by mapping the random 2D Ising model onto a network model.
The model closely resembles network models of quantum Hall plateau transitions,
but has different symmetries. Numerical transfer matrix calculations enable us
to obtain estimates for the critical exponents at the random Ising phase
transition. The values are consistent with recent estimates obtained from
high-temperature series.Comment: minor changes, 7 pages LaTex, 8 postscript figures included using
epsf; to be published Phys. Rev. B 55 (1997
Spectral Properties of the Chalker-Coddington Network
We numerically investigate the spectral statistics of pseudo-energies for the
unitary network operator U of the Chalker--Coddington network. The shape of the
level spacing distribution as well the scaling of its moments is compared to
known results for quantum Hall systems. We also discuss the influence of
multifractality on the tail of the spacing distribution.Comment: JPSJ-style, 7 pages, 4 Postscript figures, to be published in J.
Phys. Soc. Jp
Universal Scaling of Strong-Field Localization in an Integer Quantum Hall Liquid
We study the Landau level localization and scaling properties of a disordered
two-dimensional electron gas in the presence of a strong external magnetic
field. The impurities are treated as random distributed scattering centers with
parameterized potentials. Using a transfer matrix for a finite-width strip
geometry, we calculate the localization length as a function of system size and
electron energy. The finite-size localization length is determined by
calculating the Lyapunov exponents of the transfer matrix. A detailed
finite-size scaling analysis is used to study the critical behavior near the
center of the Landau bands. The influence of varying the impurity
concentration, the scattering potential range and its nature, and the Landau
level index on the scaling behavior and on the critical exponent is
systematically investigated. Particular emphasis is put on studying the effects
of finite range of the disorder potential and Landau level coupling on the
quantum localization behavior. Our numerical results, which are carried out on
systems much larger than those studied before, indicate that pure
-function disorder in the absence of any Landau level coupling gives
rise to non-universal localization properties with the critical exponents in
the lowest two Landau levels being substantially different. Inclusion of a
finite potential range and/or Landau level mixing may be essential in producing
universality in the localization.Comment: 28 pages, Latex, 17 figures (available upon request), #phd0
SARS-CoV-2 genomic characterization and evolution in China
The pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) affected global health worldwide due to its high contagiousness. During the viral spread, many mutations occurred within the virus genome. China has adopted nonpharmaceutical intervention (NPI) to contain COVID-19 outbreaks. In order to understand the evolution and genomic variation of SARS-CoV-2 in China under this policy, a total of 524 sequences downloaded from Global Initiative on Sharing All Influenza Data (GISAID) between 2019 and 2022 were included in this study. The time-scaled evolutionary analysis showed that these sequences clustered in three groups (Group A-C). Group B and C accounted for the majority of the sequences whose divergence times were around 2020 and distributed in multiple regions. Group A was mainly composed of G variants, which were mainly isolated from several regions. Moreover, we found that 191 sites had mutations with no less than 3 times, including 30 amino acids that were deleted. Finally, we found that spike and nucleocapsid genes underwent positive selection evolution, indicating that the mutations within spike and nucleocapsid genes increased the SARS-CoV-2 contagiousness. Hence, this study preliminarily elucidates the evolutionary characteristics and genomic mutations of SARS-CoV-2 under the implementation of the NPI policy in China, providing scientific basis for further understanding the control effect of the NPI policy on the epidemic
The complete chloroplast genome of Vaccinium duclouxii, an endemic species in China
Vaccinium duclouxii is an endemic species in China, which is distributed in Sichuan and Yunnan province of China. The chloroplast (cp) genome of V. duclouxii is 168,953 bp in size containing 123 unique genes, including 8 rRNA genes, 38 tRNA genes, and 77 protein-coding genes (PCGs). Phylogenetic analysis exhibited that V. duclouxii and V. macrocarpon were most related to Arbutus unedo
Redox-Enhanced Photoelectrochemical Activity in PHV/CdS Hybrid Film
Semiconductive photocatalytic materials have received increasing attention recently due to their ability to transform solar energy into chemical fuels and photodegrade a wide range of pollutants. Among them, cadmium sulfide (CdS) nanoparticles have been extensively studied as semiconductive photocatalysts in previous studies on hydrogen generation and environmental purification due to their suitable bandgap and sensitive light response. However, the practical applications of CdS are limited by its low charge separation, which is caused by its weak ability to separate photo-generated electron-hole pairs. In order to enhance the photoelectrochemical activity of CdS, a polymer based on viologen (PHV) was utilized to create a series of PHV/CdS hybrid films so that the viologen unit could work as the electron acceptor to increase the charge separation. In this work, various electrochemical, spectroscopic, and microscopic methods were utilized to analyze the hybrid films, and the results indicated that introducing PHV can significantly improve the performance of CdS. The photoelectrochemical activities of the hybrid films were also evaluated at various ratios, and it was discovered that a PHV-to-CdS ratio of 2:1 was the ideal ratio for the hybrid films. In comparison with CdS nanoparticles, the PHV/CdS hybrid film has a relatively lower band gap, and it can inhibit the recombination of electrons and holes, enhancing its photoelectrochemical activities. All of these merits make the PHV/CdS hybrid film as a strong candidate for photocatalysis applications in the future