3,853 research outputs found
Electronic Properties of Boron and Nitrogen doped graphene: A first principles study
Effect of doping of graphene either by Boron (B), Nitrogen (N) or co-doped by
B and N is studied using density functional theory. Our extensive band
structure and density of states calculations indicate that upon doping by N
(electron doping), the Dirac point in the graphene band structure shifts below
the Fermi level and an energy gap appears at the high symmetric K-point. On the
other hand, by B (hole doping), the Dirac point shifts above the Fermi level
and a gap appears. Upon co-doping of graphene by B and N, the energy gap
between valence and conduction bands appears at Fermi level and the system
behaves as narrow gap semiconductor. Obtained results are found to be in well
agreement with available experimental findings.Comment: 11 pages, 4 figures, 1 table, submitted to J. Nanopart. Re
Preferential regulation of stably expressed genes in the human genome suggests a widespread expression buffering role of microRNAs
In this study, we comprehensively explored the stably expressed genes (SE genes) and fluctuant genes (FL genes) in the human genome by a meta-analysis of large scale microarray data. We found that these genes have distinct function distributions. miRNA targets are shown to be significantly enriched in SE genes by using propensity analysis of miRNA regulation, supporting the hypothesis that miRNAs can buffer whole genome expression fluctuation. The expression-buffering effect of miRNA is independent of the target site number within the 3'-untranslated region. In addition, we found that gene expression fluctuation is positively correlated with the number of transcription factor binding sites in the promoter region, which suggests that coordination between transcription factors and miRNAs leads to balanced responses to external perturbations
Clar's Theory, STM Images, and Geometry of Graphene Nanoribbons
We show that Clar's theory of the aromatic sextet is a simple and powerful
tool to predict the stability, the \pi-electron distribution, the geometry, the
electronic/magnetic structure of graphene nanoribbons with different hydrogen
edge terminations. We use density functional theory to obtain the equilibrium
atomic positions, simulated scanning tunneling microscopy (STM) images, edge
energies, band gaps, and edge-induced strains of graphene ribbons that we
analyze in terms of Clar formulas. Based on their Clar representation, we
propose a classification scheme for graphene ribbons that groups configurations
with similar bond length alternations, STM patterns, and Raman spectra. Our
simulations show how STM images and Raman spectra can be used to identify the
type of edge termination
Etching and Narrowing of Graphene from the Edges
Large scale graphene electronics desires lithographic patterning of narrow
graphene nanoribbons (GNRs) for device integration. However, conventional
lithography can only reliably pattern ~20nm wide GNR arrays limited by
lithography resolution, while sub-5nm GNRs are desirable for high on/off ratio
field-effect transistors (FETs) at room temperature. Here, we devised a gas
phase chemical approach to etch graphene from the edges without damaging its
basal plane. The reaction involved high temperature oxidation of graphene in a
slightly reducing environment to afford controlled etch rate (\leq ~1nm/min).
We fabricated ~20-30nm wide GNR arrays lithographically, and used the gas phase
etching chemistry to narrow the ribbons down to <10nm. For the first time, high
on/off ratio up to ~10^4 was achieved at room temperature for FETs built with
sub-5nm wide GNR semiconductors derived from lithographic patterning and
narrowing. Our controlled etching method opens up a chemical way to control the
size of various graphene nano-structures beyond the capability of top-down
lithography.Comment: 18 pages, 4 figures, to appear in Nature Chemistr
Cancer cells exploit an orphan RNA to drive metastatic progression.
Here we performed a systematic search to identify breast-cancer-specific small noncoding RNAs, which we have collectively termed orphan noncoding RNAs (oncRNAs). We subsequently discovered that one of these oncRNAs, which originates from the 3' end of TERC, acts as a regulator of gene expression and is a robust promoter of breast cancer metastasis. This oncRNA, which we have named T3p, exerts its prometastatic effects by acting as an inhibitor of RISC complex activity and increasing the expression of the prometastatic genes NUPR1 and PANX2. Furthermore, we have shown that oncRNAs are present in cancer-cell-derived extracellular vesicles, raising the possibility that these circulating oncRNAs may also have a role in non-cell autonomous disease pathogenesis. Additionally, these circulating oncRNAs present a novel avenue for cancer fingerprinting using liquid biopsies
UHRF genes regulate programmed interdigital tissue regression and chondrogenesis in the embryonic limb
The primordium of the limb contains a number of progenitors far superior to those necessary to form the skeletal components of this appendage. During the course of development, precursors that do not follow the skeletogenic program are removed by cell senescence and apoptosis. The formation of the digits provides the most representative example of embryonic remodeling via cell degeneration. In the hand/foot regions of the embryonic vertebrate limb (autopod), the interdigital tissue and the zones of interphalangeal joint formation undergo massive degeneration that accounts for jointed and free digit morphology. Developmental senescence and caspase-dependent apoptosis are considered responsible for these remodeling processes. Our study uncovers a new upstream level of regulation of remodeling by the epigenetic regulators Uhrf1 and Uhrf2 genes. These genes are spatially and temporally expressed in the pre-apoptotic regions. UHRF1 and UHRF2 showed a nuclear localization associated with foci of methylated cytosine. Interestingly, nuclear labeling increased in cells progressing through the stages of degeneration prior to TUNEL positivity. Functional analysis in cultured limb skeletal progenitors via the overexpression of either UHRF1 or UHRF2 inhibited chondrogenesis and induced cell senescence and apoptosis accompanied with changes in global and regional DNA methylation. Uhrfs modulated canonical cell differentiation factors, such as Sox9 and Scleraxis, promoted apoptosis via up-regulation of Bak1, and induced cell senescence, by arresting progenitors at the S phase and upregulating the expression of p21. Expression of Uhrf genes in vivo was positively modulated by FGF signaling. In the micromass culture assay Uhrf1 was down-regulated as the progenitors lost stemness and differentiated into cartilage. Together, our findings emphasize the importance of tuning the balance between cell differentiation and cell stemness as a central step in the initiation of the so-called ?embryonic programmed cell death? and suggest that the structural organization of the chromatin, via epigenetic modifications, may be a precocious and critical factor in these regulatory events.Funding: We thank Montse Fernandez Calderon, Susana Dawalibi, and Sonia Perez Mantecon, for excellent technical assistance. This work was supported by a Grant (BFU2017-84046-P) from the Spanish Science and Innovation Ministry to J.A.M
6G Network AI Architecture for Everyone-Centric Customized Services
Mobile communication standards were developed for enhancing transmission and network performance by using more radio resources and improving spectrum and energy efficiency. How to effectively address diverse user requirements and guarantee everyone's Quality of Experience (QoE) remains an open problem. The Sixth Generation (6G) mobile systems will solve this problem by utilizing heterogenous network resources and pervasive intelligence to support everyone-centric customized services anywhere and anytime. In this article, we first coin the concept of Service Requirement Zone (SRZ) on the user side to characterize and visualize the integrated service requirements and preferences of specific tasks of individual users. On the system side, we further introduce the concept of User Satisfaction Ratio (USR) to evaluate the system's overall service ability of satisfying a variety of tasks with different SRZs. Then, we propose a network Artificial Intelligence (AI) architecture with integrated network resources and pervasive AI capabilities for supporting customized services with guaranteed QoEs. Finally, extensive simulations show that the proposed network AI architecture can consistently offer a higher USR performance than the cloud AI and edge AI architectures with respect to different task scheduling algorithms, random service requirements, and dynamic network conditions
Preparation of porous thin-film polymethylsiloxane microparticles in a W/O emulsion system
Porous thin-film polymethylsiloxane microparticles have been prepared successfully from octyltrichlorosilane and methyltrichlorosilane in (water/oil) W/O emulsion systems by using several oil phases and changing the amount of the silanes or of the surfactant Span 60. Hollow microspheres of various shell thicknesses (120-180 nm) and high surface area were prepared by using four types of nonpolar solvents as the oil phase of the W/O emulsion system. The diameter of the spheres can also be controlled (1-1.6 mu m) by using different oil phases. The results of thermal analysis, nitrogen adsorption isotherm, infrared spectra and X-ray diffraction data showed that hollow microspheres of amorphous polymethylsiloxane with high surface area (360-385 m(2)g(-1)) can be obtained by heating the spheres in air at 673 K; the polymethylsiloxane microspheres become nonporous silica particles after calcination at 873 K for 3 h. Cup-shape microparticles of polymethylsiloxane with nano-order thickness (20-120 nm) were prepared by reducing the amount of silanes in the mixture. Small hollow particles were prepared by replacing a portion of the octyltrichlorosilane with Span 60.ArticlePOLYMER JOURNAL. 47(6): 449-455 (2015)journal articl
Semiconducting Monolayer Materials as a Tunable Platform for Excitonic Solar Cells
The recent advent of two-dimensional monolayer materials with tunable
optoelectronic properties and high carrier mobility offers renewed
opportunities for efficient, ultra-thin excitonic solar cells alternative to
those based on conjugated polymer and small molecule donors. Using
first-principles density functional theory and many-body calculations, we
demonstrate that monolayers of hexagonal BN and graphene (CBN) combined with
commonly used acceptors such as PCBM fullerene or semiconducting carbon
nanotubes can provide excitonic solar cells with tunable absorber gap,
donor-acceptor interface band alignment, and power conversion efficiency, as
well as novel device architectures. For the case of CBN-PCBM devices, we
predict the limit of power conversion efficiencies to be in the 10 - 20% range
depending on the CBN monolayer structure. Our results demonstrate the
possibility of using monolayer materials in tunable, efficient, polymer-free
thin-film solar cells in which unexplored exciton and carrier transport regimes
are at play.Comment: 7 pages, 5 figure
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