self-consistent theory for graphene transport Adam, Shaffique; Hwang, E.H; Galitski, V.M ...
Proceedings of the National Academy of Sciences - PNAS,
11/2007, Letnik:
104, Številka:
47
Journal Article
Recenzirano
Odprti dostop
We demonstrate theoretically that most of the observed transport properties of graphene sheets at zero magnetic field can be explained by scattering from charged impurities. We find that, contrary to ...common perception, these properties are not universal but depend on the concentration of charged impurities nimp. For dirty samples (250 x 10¹⁰ cm⁻² < nimp < 400 x 10¹⁰ cm⁻²), the value of the minimum conductivity at low carrier density is indeed 4e²/h in agreement with early experiments, with weak dependence on impurity concentration. For cleaner samples, we predict that the minimum conductivity depends strongly on nimp, increasing to 8e²/h for nimp almost equal to 20 x 10¹⁰ cm⁻². A clear strategy to improve graphene mobility is to eliminate charged impurities or use a substrate with a larger dielectric constant.
MicroRNAs (miRNAs) are involved in tumorigenecity by regulating specific oncogenes and tumor suppressor genes, and their roles in breast cancer stem cells (BCSCs) are becoming apparent. Distinct from ...the CD44(+)/CD24(-/low) sub-population, we have isolated a novel PROCR(+)/ESA(+) BCSC sub-population. To explore miRNA-regulatory mechanisms in this sub-population, we performed miRNA expression profiling and found miR-495 as the most highly upegulated miRNA in PROCR(+)/ESA(+) cells. Coincidently, high upregulation of miR-495 was also found in CD44(+)/CD24(-/low) BCSCs, reflecting its potential importance in maintaining common BCSC properties. Ectopic expression of miR-495 in breast cancer cells promoted their colony formation in vitro and tumorigenesis in mice. miR-495 directly suppressed E-cadherin expression to promote cell invasion and inhibited REDD1 expression to enhance cell proliferation in hypoxia through post-transcriptional mechanism. miR-495 expression was directly modulated by transcription factor E12/E47, which itself is highly expressed in BCSCs. These findings reveal a novel regulatory pathway centered on miR-495 that contributes to BCSC properties and hypoxia resistance.
We investigate collective modes in three dimensional (3D) gapless multi-Weyl semimetals with anisotropic energy band dispersions (i.e., with a positive integer J). For comparison, we also consider ...the gapless semimetals with the isotropic band dispersions (i.e. E ~ k
). We calculate analytically long-wavelength plasma frequencies incorporating interband transitions and chiral properties of carriers. For both the isotropic and anisotropic cases, we find that interband transitions and chirality lead to the depolarization shift of plasma frequencies. For the isotropic parabolic band dispersion the long-wavelength plasmons do not decay via Landau damping, while for the higher-order band dispersions the long-wavelength plasmons experience damping below a critical density. For systems with the anisotropic dispersion the density dependence of the long-wavelength plasma frequency along the direction of non-linear dispersion behaves like that of the isotropic linear band model, while along the direction of linear dispersion it behaves like that of the isotropic non-linear model. Plasmons along both directions remain undamped over a broad range of densities due to the chirality induced depolarization shift. Our results provide a comprehensive picture of how band dispersion and chirality affect plasmon behaviors in 3D gapless chiral systems with the arbitrary band dispersion.
The propensity for synchronization of complex networks with directed and weighted links is considered. We show that a weighting procedure based upon the global structure of network pathways enhances ...complete synchronization of identical dynamical units in scale-free networks. Furthermore, we numerically show that very similar conditions hold also for phase synchronization of nonidentical chaotic oscillators.
Background and purpose: Lipid rafts and caveolae are membrane microdomains with important roles in cell survival signalling involving the Akt pathway. Cholesterol is important for the structure and ...function of these microdomains. The ginsenoside Rh2 exhibits anti‐tumour activity. Because Rh2 is structurally similar to cholesterol, we investigated the possibility that Rh2 exerted its anti‐tumour effect by modulating rafts and caveolae.
Experimental approach: A431 cells (human epidermoid carcinoma cell line) were treated with Rh2 and the effects on cell apoptosis, raft localization and Akt activation measured. We also examined the effects of over‐expression of Akt and active‐Akt on Rh2‐induced cell death.
Key results: Rh2 induced apoptosis concentration‐ and time‐dependently. Rh2 reduced the levels of rafts and caveolae in the plasma membrane and increased their internalization. Furthermore, Akt activity was decreased and consequently, Akt‐dependent phosphorylation of Bad, a pro‐survival protein, was decreased whereas the pro‐apoptotic proteins, Bim and Bax, were increased upon Rh2 treatment. Unlike microdomain internalization induce by cholesterol depletion, Rh2‐mediated internalization of rafts and caveolae was not reversed by cholesterol addition. Also, cholesterol addition did not restore Akt activation or rescue cells from Rh2‐induced cell death. Rh2‐induced cell death was attenuated in MDA‐MB‐231 cells over‐expressing either wild‐type or dominant‐active Akt.
Conclusions and implications: Rh2 induced internalization of rafts and caveolae, leading to Akt inactivation, and ultimately apoptosis. Because elevated levels of membrane rafts and caveolae, and Akt activation have been correlated with cancer development, internalization of these microdomains by Rh2 could potentially be used as an anti‐cancer therapy.
Early childhood caries is a severe oral disease that results in aggressive tooth decay. Particularly, a synergistic association between a fungus,
, and a cariogenic bacterium,
, promotes the ...development of hard-to-remove and highly acidic biofilms, exacerbating the virulent damage. These interactions are largely mediated via glucosyltransferases (GtfB) binding to mannans on the cell wall of
Here, we present an enzymatic approach to target GtfB-mannan interactions in this cross-kingdom consortium using mannan-degrading exo- and endo-enzymes. These exo- and endo-enzymes are highly effective in reducing biofilm biomass without killing microorganisms, as well as alleviating the production of an acidic pH environment conducive to tooth decay. To corroborate these results, we present biophysical evidence using single-molecule atomic force microscopy, biofilm shearing, and enamel surface topography analyses. Data show a drastic decrease in binding forces of GtfB to
(∼15-fold reduction) following enzyme treatment. Furthermore, enzymatic activity disrupted biofilm mechanical stability and significantly reduced human tooth enamel demineralization without cytotoxic effects on gingival keratinocytes. Our results represent significant progress toward a novel nonbiocidal therapeutic intervention against pathogenic bacterial-fungal biofilms by targeting the interkingdom receptor-ligand binding interactions.
Biofilm formation is a key virulence factor responsible for various infectious diseases. Particularly, interactions between a fungus,
, and a bacterium,
, have been known to play important roles in the pathogenesis of dental caries. Although some antimicrobials have been applied to treat fungal-involved biofilm-associated diseases, these often lack targeting polymicrobial interactions. Furthermore, these may not be appropriate for preventive measures because these antimicrobials may disrupt ecological microbiota and/or induce the prevalence of drug resistance over time. By specifically targeting the interaction mechanism whereby mannoproteins on the
surface mediate the cross-kingdom interaction, we demonstrated that mannoprotein-degrading enzymes can effectively disrupt biofilm interactions without microbiocidal effects or causing cytotoxicity to human cells. This suggests a potential application as a targeted approach for intervening a pathogenic cross-kingdom biofilm associated with a costly and unresolved oral disease.
We review the physics of charged impurities in the vicinity of graphene. The long-range nature of Coulomb impurities affects both the nature of the ground state density profile and graphene’s ...transport properties. We discuss the screening of a single Coulomb impurity and the ensemble averaged density profile of graphene in the presence of many randomly distributed impurities. Finally, we discuss graphene’s transport properties due to scattering off charged impurities both at low and high carrier density.
The oral cavity, a unique ecosystem harboring diverse microorganisms, maintains health through a balanced microflora. Disruption may lead to disease, emphasizing the protective role of gingival ...epithelial cells (GECs) in preventing harm from pathogenic oral microbes. Shifting GECs’ response from proinflammatory to antimicrobial could be a novel strategy for periodontitis. Photobiomodulation therapy (PBMT), a nonpharmacologic host modulatory approach, is considered an alternative to drugs. While the host cell response induced by a single type of pathogen-associated molecular patterns (PAMPs) was widely studied, this model does not address the cellular response to intact microbes that exhibit multiple PAMPs that might modulate the response. Inspired by this, we developed an in vitro model that simulates direct interactions between host cells and intact pathogens and evaluated the effect of PBMT on the response of human gingival keratinocytes (HGKs) to challenge viable oral microbes at both the cellular and molecular levels. Our data demonstrated that LED pretreatment on microbially challenged HGKs with specific continuous wavelengths (red: 615 nm; near-infrared: 880 nm) induced the production of various antimicrobial peptides, enhanced cell viability and proliferation, promoted reactive oxygen species scavenging, and down-modulated proinflammatory activity. The data also suggest a potential explanation regarding the superior efficacy of near-infrared light treatment compared with red light in enhancing antimicrobial activity and reducing cellular inflammation of HGKs. Taken together, the findings suggest that PBMT enhances the overall barrier function of gingival epithelium while minimizing inflammation-mediated breakdown of the underlying structures.
Exposure to polycyclic aromatic hydrocarbons (PAHs) during pregnancy is known to increase oxidative stress, which may influence pregnancy outcomes and health of the child.
This study investigated ...whether fruit and vegetable intake modifies the relationship between exposure to PAHs and oxidative stress status during pregnancy. Urinary levels of 2-naphthol and 1-hydroxypyrene (biomarkers of exposure to PAHs), and malondialdehyde (MDA; a biomarker of oxidative stress) were analyzed in 715 pregnant women at 12-28 weeks of gestation. The dietary antioxidant intake during pregnancy was estimated using the 24-h recall method. Urinary 2-naphthol, 1-hydroxypyrene and MDA levels were analyzed by high-performance liquid chromatography-fluorescence detection.
The urinary MDA level was positively correlated with the 2-naphthol level (r=0.255, P<0.001) and 1-hydroxypyrene level (r=0.240, P<0.001). Multiple regression analysis after adjustment for covariates revealed that the urinary 1-hydroxypyrene level was positively associated with the MDA level; these positive associations only existed in pregnant women, with either the fruit and vegetable intake or the vitamin C intake in the first tertile (<390.1 g/day) or in the first and second tertiles (<141.5 mg/day), respectively.
These results suggest that an adequate maternal intake of fruit, vegetables and vitamin C is beneficial to the defense against the oxidative stress associated with exposure to PAHs in pregnant women.
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