3,478 research outputs found
Bond distortion effects and electric orders in spiral multiferroic magnets
We study in this paper bond distortion effect on electric polarization in
spiral multiferroic magnets based on cluster and chain models. The bond
distortion break inversion symmetry and modify the - hybridization.
Consequently, it will affect electric polarization which can be divided into
spin-current part and lattice-mediated part. The spin-current polarization can
be written in terms of and
the lattice-mediated polarization exists only when the M-O-M bond is distorted.
The electric polarization for three-atom M-O-M and four-atom M-O-M
clusters is calculated. We also study possible electric ordering in three kinds
of chains made of different clusters. We apply our theory to multiferroics
cuprates and find that the results are in agreement with experimental
observations.Comment: 14 pages, 11 figure
Landau-Zener transition of a two-level system driven by spin chains near their critical points
The Landau-Zener(LZ) transition of a two-level system coupling to spin chains
near their critical points is studied in this paper. Two kinds of spin chains,
the Ising spin chain and XY spin chain, are considered. We calculate and
analyze the effects of system-chain coupling on the LZ transition. A relation
between the LZ transition and the critical points of the spin chain is
established. These results suggest that LZ transitions may serve as the
witnesses of criticality of the spin chain. This may provide a new way to study
quantum phase transitions as well as LZ transitions.Comment: 5 pages, 4 figures. European Physical Journals D accepte
Graphite Nanoeraser
We present here a method for cleaning intermediate-size (5~50nm)
contamination from highly oriented pyrolytic graphite. Electron beam deposition
causes a continuous increase of carbonaceous material on graphene and graphite
surfaces, which is difficult to remove by conventional techniques. Direct
mechanical wiping using a graphite nanoeraser is observed to drastically reduce
the amount of contamination. After the mechanical removal of contamination, the
graphite surfaces were able to self-retract after shearing, indicating that van
der Waals contact bonding is restored. Since contact bonding provides an
indication of a level of cleanliness normally only attainable in a high-quality
clean-room, we discuss potential applications in preparation of ultraclean
surfaces.Comment: 10 pages, two figure
Multi-Player and Multi-Choice Quantum Game
We investigate a multi-player and multi-choice quantum game. We start from
two-player and two-choice game and the result is better than its classical
version. Then we extend it to N-player and N-choice cases. In the quantum
domain, we provide a strategy with which players can always avoid the worst
outcome. Also, by changing the value of the parameter of the initial state, the
probabilities for players to obtain the best payoff will be much higher that in
its classical version.Comment: 4 pages, 1 figur
Chalcogenide Glass-on-Graphene Photonics
Two-dimensional (2-D) materials are of tremendous interest to integrated
photonics given their singular optical characteristics spanning light emission,
modulation, saturable absorption, and nonlinear optics. To harness their
optical properties, these atomically thin materials are usually attached onto
prefabricated devices via a transfer process. In this paper, we present a new
route for 2-D material integration with planar photonics. Central to this
approach is the use of chalcogenide glass, a multifunctional material which can
be directly deposited and patterned on a wide variety of 2-D materials and can
simultaneously function as the light guiding medium, a gate dielectric, and a
passivation layer for 2-D materials. Besides claiming improved fabrication
yield and throughput compared to the traditional transfer process, our
technique also enables unconventional multilayer device geometries optimally
designed for enhancing light-matter interactions in the 2-D layers.
Capitalizing on this facile integration method, we demonstrate a series of
high-performance glass-on-graphene devices including ultra-broadband on-chip
polarizers, energy-efficient thermo-optic switches, as well as graphene-based
mid-infrared (mid-IR) waveguide-integrated photodetectors and modulators
A new multivariate empirical mode decomposition method for improving the performance of SSVEP-based brain–computer interface
Objective: Accurate and efficient detection of steady-state visual evoked potentials (SSVEP) in electroencephalogram (EEG) is essential for the related brain–computer interface (BCI) applications. Approach: Although the canonical correlation analysis (CCA) has been applied extensively and successfully to SSVEP recognition, the spontaneous EEG activities and artifacts that often occur during data recording can deteriorate the recognition performance. Therefore, it is meaningful to extract a few frequency sub-bands of interest to avoid or reduce the influence of unrelated brain activity and artifacts. This paper presents an improved method to detect the frequency component associated with SSVEP using multivariate empirical mode decomposition (MEMD) and CCA (MEMD-CCA). EEG signals from nine healthy volunteers were recorded to evaluate the performance of the proposed method for SSVEP recognition. Main results: We compared our method with CCA and temporally local multivariate synchronization index (TMSI). The results suggest that the MEMD-CCA achieved significantly higher accuracy in contrast to standard CCA and TMSI. It gave the improvements of 1.34%, 3.11%, 3.33%, 10.45%, 15.78%, 18.45%, 15.00% and 14.22% on average over CCA at time windows from 0.5 s to 5 s and 0.55%, 1.56%, 7.78%, 14.67%, 13.67%, 7.33% and 7.78% over TMSI from 0.75 s to 5 s. The method outperformed the filter-based decomposition (FB), empirical mode decomposition (EMD) and wavelet decomposition (WT) based CCA for SSVEP recognition. Significance: The results demonstrate the ability of our proposed MEMD-CCA to improve the performance of SSVEP-based BCI
Presence of qnr gene in Escherichia coli and Klebsiella pneumoniae resistant to ciprofloxacin isolated from pediatric patients in China
<p>Abstract</p> <p>Background</p> <p>Quinolone resistance in <it>Enterobacteriaceae </it>results mainly from mutations in type II DNA topoisomerase genes and/or changes in the expression of outer membrane and efflux pumps. Several recent studies have indicated that plasmid-mediated resistance mechanisms also play a significant role in fluoroquinolone resistance, and its prevalence is increasing worldwide. In China, the presence of the <it>qnr </it>gene in the clinical isolates of <it>Enterobacteriaceae </it>has been reported, but this transmissible quinolone resistance gene has not been detected in strains isolated singly from pediatric patients. Because quinolones associated with a variety of adverse side effects on children, they are not authorized for pediatric use. This study therefore aimed to investigate the presence of the <it>qnr </it>gene in clinical isolates of <it>E. coli </it>and <it>K. pneumoniae </it>from pediatric patients in China.</p> <p>Methods</p> <p>A total 213 of non-repetitive clinical isolates resistant to ciprofloxacin from <it>E. coli </it>and <it>K. pneumoniae </it>were collected from hospitalized patients at five children's hospital in Beijing, Shanghai, Guangzhou, and Chongqing. The isolates were screened for the plasmid-mediated quinolone resistance genes of <it>qnrA</it>, <it>qnrB</it>, and <it>qnrS </it>by PCR. Transferability was examined by conjugation with the sodium azide-resistant <it>E. coli </it>J53. All <it>qnr</it>-positive were analyzed for clonality by enterobacterial repetitive intergenic consensus (ERIC)-PCR.</p> <p>Results</p> <p>The study found that 19 ciprofloxacin-resistant clinical isolates of <it>E. coli </it>and <it>K. pneumoniae </it>were positive for the <it>qnr </it>gene, and most of the <it>qnr </it>positive strains were ESBL producers. Conjugation experiments showed that quinolone resitance could be transferred to recipients. Apart from this, different DNA banding patterns were obtained by ERIC-PCR from positive strains, which means that most of them were not clonally related.</p> <p>Conclusion</p> <p>This report on transferable fluoroquinolone resistance due to the <it>qnr </it>gene among <it>E. coli </it>and <it>K. pneumoniae </it>strains indicated that plasmid-mediated quinolone resistance has emerged in pediatric patients in China.</p
RNAi-mediated silencing of the Bmi-1 gene causes growth inhibition and enhances doxorubicin-induced apoptosis in MCF-7 cells
The oncogene Bmi-1 is a member of the Polycomb group gene family. Its expression is found to be greatly increased in a number of malignant tumors including breast cancer. This could suggest Bmi-1 as a potent therapeutic target. In this study, RNAi was introduced to down-regulate the expression of Bmi-1 in a highly malignant breast adenocarcinoma cell line, MCF-7. A thorough study of the biological behavior and chemosensitivity changes of the MCF-7 cells was carried out in context to the therapeutic potential of Bmi-1. The results obtained indicated that siRNA targeting of Bmi-1 could lead to an efficient and specific inhibition of endogenous Bmi-1 activity. The mRNA and protein expression of Bmi-1 were determined by RT-PCR and Western blot, respectively. Furthermore, silencing of Bmi-1 resulted in a drastic inhibition of the growth of MCF-7 cells as well as G1 /S phase transition. The number of target cells was found to increase in phase G 0 /G 1 and decrease in the S phase, but no increase in the basal level of apoptosis was noticed. On the other hand, a reduction in the expression of cyclin D1 and an increase in the expression of p21 were also noticed. Silencing of Bmi-1 made the MCF-7 cells more sensitive to the chemotherapeutic agent doxorubicin and induced a significantly higher percentage of apoptotic cells. Here, we report on a study regarding the RNAi-mediated silencing of the Bmi-1 gene in breast cancer
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