2,613 research outputs found
The dynamically induced Fermi arcs and Fermi pockets in two dimensions: a model for underdoped cuprates
We investigate the effects of the dynamic bosonic fluctuations on the Fermi
surface reconstruction in two dimensions as a model for the underdoped
cuprates. At energies larger than the boson energy , the dynamic
nature of the fluctuations is not important and the quasi-particle dispersion
exhibits the shadow feature like that induced by a static long range order. At
lower energies, however, the shadow feature is pushed away by the finite
. The detailed low energy features are determined by the bare
dispersion and the coupling of quasi-particles to the dynamic fluctuations. We
present how these factors reconstruct the Fermi surface to produce the Fermi
arcs or the Fermi pockets, or their coexistence. Our principal result is that
the dynamic nature of the fluctuations, without invoking a
yet-to-be-established translational symmetry breaking hidden order, can produce
the Fermi pocket centered away from the towards the zone center
which may coexist with the Fermi arcs. This is discussed in comparison with the
experimental observations.Comment: Some comments and references were added and typos were corrected. The
published version. 9 page
In vitro antioxidative activity of moss extract, and effect of moss on serum lipid level of mice fed with high-fat diet
Purpose: To evaluate the potential of active compounds derived from moss in the prevention and treatment of various diseases.Methods: Three species of moss were extracted with deionized water at 95 °C, and with 70.5 % ethanol at 85 °C. Analysis of total phenolic contents (TPC) of the extracts were performed by Folin- Ciocalteu (FC) method. The antioxidant activity of the extracts were determined using three methods, namely, by 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic) acid (ABTS), 1,1-diphenyl-2-picrylhydrazyl (DPPH) and ferric reducing antioxidant power (FRAP). In vivo effects were evaluated in mice fed high fat diet (HFD) supplemented with 20 % ground moss. Cholesterol levels in HFD were evaluated by ophthalaldehyde method. Serum triglyceride levels were measured using triglyceride (TG) kit, while blood insulin level and leptin concentration were measured by enzyme-linked immunosorbent assay (ELISA) kit.Results: The moss extracts exhibited antioxidative effects, as evidenced of . TPC of 47.20 ± 11.20 to 119.87 ± 11.51 mg GAE/mg, respectively. ABTS scavenging activity was 1078.11 ± 18.95 to 2587.33 ± 46.19 μmol Trolox/mg, DPPH scavenging activity of were 42.11 ± 8.22 to 298.78 ± 20.02 μmol Trolox/mg, and FRAP value of 393.19 ± 24.64 to 1070.14 ± 17.92 μmol Trolox/mg, respectively. Mice fed with 20 % ground moss did not show any significant effect (p < 0.05) on visceral weight and blood lipid levels of HFD, while leptin concentrations reduced significantly to 4.74 ± 0.00 and 0.20 ± 0.00 ng/dL) relative to HFD alone (26.72 ± 6.53 ng/dL).Conclusion: Moss can potentially be used as an antioxidative ingredient, for the improvement of overall human health, suggesting that important medical benefits associated with moss consumption. However, further investigations are required to ascertain this.Keywords: Moss, total phenolic content, antioxidant activity, insulin, lepti
Highly oxygen-stable CO2 reductase-catalyzed bioconversion of carbon dioxide into formate in electrochemical reactor
Electrochemical reduction of carbon dioxide (CO2) into value-added chemicals have been one of promising issues to utilize greenhouse gas for the storage of hydrogen, bioplastic, fuel cell et al. Among many potential candidates such as formate, alcohols, ethylene, etc., formate was known one of most promising chemicals through the addition of two elections and one proton during electro-catalytic reduction of CO2.
Here, our group has developed efficient CO2 reductase-catalyzed conversion of CO2 into formate in electrochemical reactor. Electro-biocatalytic reduction of CO2 into formate have three main challenges. Formate dehydrogenase(FDH) have been one of potential CO2 reductase candidates but the activity of many FDHs for formate oxidation was superior than that of CO2 reduction. However, recombinant MeFDH1 in our study showed significantly higher preference for CO2 reduction with 209 (±10.66) s-1 of turnover rate than that of formate oxidation with 85.62 (± 5.76) s-1. In addition, the value of kinetic equilibrium constant (Keq), which determines the direction of reaction in reversible catalysis, implied that kinetic preference for CO2 reduction is 62.3-folds higher than that for formate oxidation. This kinetics analysis allowed MeFDH1 to be referred to as the CO2 reductase. As another challenge, Mo- or W-containing formate dehydrogenase was known vulnerable against oxygen molecule. As contrasted with the high oxygen-sensitivity of FDHs from other strains, MeFDH1 was not deactivated even under 0.13 mM of dissolved oxygen. At a range of oxygen level (0.1 % to 4 %) in the composition of Carbon Capture and Storage (CCS) gas, MeFDH1 was consequently stable without considerable decreased activity. Lastly, the long-term stability of CO2 reduction reaction system has been indispensable issue in both biocatalysts and chemical catalysts. Through the immobilization of MeFDH1, the enhanced stability for long-term operation leaded the formate formation over 500 mM with high volumetric productivity for several days
Comparative Genomics Platform and Phylogenetic Analysis of Fungal Laccases and Multi-Copper Oxidases
Abstract Laccases (EC 1.10.3.2), a group of multi-copper oxidases (MCOs), play multiple biological functions and widely exist in many species. Fungal laccases have been extensively studied for their industrial applications, however, there was no database specially focused on fungal laccases. To provide a comparative genomics platform for fungal laccases, we have developed a comparative genomics platform for laccases and MCOs (http://laccase.riceblast.snu.ac.kr/). Based on protein domain profiles of characterized sequences, 3,571 laccases were predicted from 690 genomes including 253 fungi. The number of putative laccases and their properties exhibited dynamic distribution across the taxonomy. A total of 505 laccases from 68 genomes were selected and subjected to phylogenetic analysis. As a result, four clades comprised of nine subclades were phylogenetically grouped by their putative functions and analyzed at the sequence level. Our work would provide a workbench for putative laccases mainly focused on the fungal kingdom as well as a new perspective in the identification and classification of putative laccases and MCOs.Peer reviewe
Adaptive channel estimation in WCDMA STTD systems
The receiver performance with the use of a space
time transmit diversity (STTD) scheme is more susceptible to
the accuracy of channel estimate than that without the use of
the STTD scheme since the despreading signals suffer from the
effect of crosstalk and the transmit power is equally divided
into multiple transmit antennas. As a result, the efficiency of
channel estimation in the WCDMA STTD system becomes an
important issue more than that in the non-STTD system. In this
paper, an adaptive channel estimator (ACE) is designed to
mitigate the performance degradation due to inaccurate
channel estimation. Numerical results show that the
performance improvement significantly increases with the use
of the proposed ACE, particularly when the channel condition
becomes worse
Optimum pilot pattern for channel estimation in OFDM systems
The performance of channel estimation in orthogonal frequency division multiplexing (OFDM) systems significantly depends on the pilot signal, which is usually scattered in time and frequency domains. For a given pilot density, the authors optimally design the pilot pattern so as to minimize the mean squared error (MSE) of the channel estimate with the use of a general interpolator. The analytic results are verified by computer simulation
Design of a Channel-Aware OFDM Transceiver
The transmission performance of an OFDM system can significantly be improved by exploiting the channel characteristics. In this paper, we consider the design of a channel-aware OFDM transceiver whose parameters are adjusted in response to the change of channel condition. To this end, we first estimate the channel state information (CSI), such as the signal to interference power ratio, low order moments of Doppler spectrum and power-delay profile of the channel. The proposed CSI estimator can estimate these CSI parameters altogether in a unique manner by exploiting the autocorrelation properties of the channel impulse response (CIR). Then, we design a CIR estimator and adaptive OFDM modulator that adjust their parameters according to the estimated CSI. Finally, we verify the performance of the proposed OFDM transceiver by computer simulation.This work was in part supported by the Ministry of Information &
Communications, Korea, under the Information Technology Research Center
(ITRC) Support Program
FE implementation of HAH model using FDM-based stress update algorithm for springback prediction of AHSS sheets
The homogeneous anisotropic hardening (HAH) model was implemented into a finite element (FE) code in order to predict springback for an advanced high strength steel (AHSS) sheet sample after double-stage U-draw bending. The finite difference method (FDM) was utilized as an alternative way to calculate the derivatives of this advanced distortional plasticity model allowing the update of the equivalent plastic strain and stress tensor at each time step in the user-material subroutines (UMAT and VUMAT). The FDM makes it easier to derive the stress gradient of complex yield surfaces. The proposed FDM-based stress update algorithm was verified by comparing the springback profiles after the single- and double-stage U-draw bending tests for a DP980 sheet sample predicted with analytical and numerical approaches. In addition, the springback measurement parameters and computational efficiencies depending on both approaches were also compared. The results indicate that the computational efficiency and accuracy of the FE simulations with the FDM-based stress update algorithm were similar to those of the analytical method. © 2018 Institute of Physics Publishing. All rights reserved.11Ysciescopu
Optimum pilot pattern for MMSE channel estimation in single-carrier MIMO systems
The minimum mean squared error (MMSE)
channel estimator (CE) can provide receiver performance better
than the least square (LS) CE. However, the MMSE CE usually
uses a pilot pattern optimally designed for the LS CE. In this
paper, we derive an optimum pilot pattern for the MMSE CE in
single-carrier MIMO systems assuming that both the transmitter
and receiver know the average channel information, such as the
channel correlation matrix and signal to interference and noise
power ratio. Analytic and simulation results show that the
MMSE CE with the use of the proposed pilot pattern can reduce
the MSE compared to the use of one optimized for the LS CEThis work was supported (in part) by the Ministry of Information
& Communications, Korea, under the Information Technology
Research Center (ITRC) Support Program
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