161 research outputs found
Raman spectroscopy and imaging of graphene
Graphene has many unique properties that make it an ideal material for
fundamental studies as well as for potential applications. Here we review the
recent results on the Raman spectroscopy and imaging of graphene. Raman
spectroscopy and imaging can be used as a quick and unambiguous method to
determine the number of graphene layers. Following, the strong Raman signal of
single layer graphene compared to graphite is explained by an interference
enhancement model. We have also studied the effect of substrates, the top layer
deposition, the annealing process, as well as folding (stacking order) on the
physical and electronic properties of graphene. Finally, Raman spectroscopy of
epitaxial graphene grown on SiC substrate is presented and strong compressive
strain on epitaxial graphene is observed. The results presented here are
closely related to the application of graphene on nano-electronic device and
help on the better understanding of physical and electronic properties of
graphene.Comment: 32 pages, 14 figure
Pathogen-origin horizontally transferred genes contribute to the evolution of Lepidopteran insects
<p>Abstract</p> <p>Background</p> <p>Horizontal gene transfer (HGT), a source of genetic variation, is generally considered to facilitate hosts' adaptability to environments. However, convincing evidence supporting the significant contribution of the transferred genes to the evolution of metazoan recipients is rare.</p> <p>Results</p> <p>In this study, based on sequence data accumulated to date, we used a unified method consisting of similarity search and phylogenetic analysis to detect horizontally transferred genes (HTGs) between prokaryotes and five insect species including <it>Drosophila melanogaster</it>, <it>Anopheles gambiae</it>, <it>Bombyx mori</it>, <it>Tribolium castaneum </it>and <it>Apis mellifera</it>. Unexpectedly, the candidate HTGs were not detected in <it>D. melanogaster</it>, <it>An. gambiae </it>and <it>T. castaneum</it>, and 79 genes in <it>Ap. mellifera </it>sieved by the same method were considered as contamination based on other information. Consequently, 14 types of 22 HTGs were detected only in the silkworm. Additionally, 13 types of the detected silkworm HTGs share homologous sequences in species of other Lepidopteran superfamilies, suggesting that the majority of these HTGs were derived from ancient transfer events before the radiation of Ditrysia clade. On the basis of phylogenetic topologies and BLAST search results, donor bacteria of these genes were inferred, respectively. At least half of the predicted donor organisms may be entomopathogenic bacteria. The predicted biochemical functions of these genes include four categories: glycosyl hydrolase family, oxidoreductase family, amino acid metabolism, and others.</p> <p>Conclusions</p> <p>The products of HTGs detected in this study may take part in comprehensive physiological metabolism. These genes potentially contributed to functional innovation and adaptability of Lepidopteran hosts in their ancient lineages associated with the diversification of angiosperms. Importantly, our results imply that pathogens may be advantageous to the subsistence and prosperity of hosts through effective HGT events at a large evolutionary scale.</p
Gold on graphene as a substrate for surface enhanced Raman scattering study
In this paper, we report our study on gold (Au) films with different
thicknesses deposited on single layer graphene (SLG) as surface enhanced Raman
scattering (SERS) substrates for the characterization of rhodamine (R6G)
molecules. We find that an Au film with a thickness of ~7 nm deposited on SLG
is an ideal substrate for SERS, giving the strongest Raman signals for the
molecules and the weakest photoluminescence (PL) background. While Au films
effectively enhance both the Raman and PL signals of molecules, SLG effectively
quenches the PL signals from the Au film and molecules. The former is due to
the electromagnetic mechanism involved while the latter is due to the strong
resonance energy transfer from Au to SLG. Hence, the combination of Au films
and SLG can be widely used in the characterization of low concentration
molecules with relatively weak Raman signals.Comment: 11 pages, 4 figure
Nonlinear graphene metamaterial
We demonstrate that the broadband nonlinear optical response of graphene can
be resonantly enhanced by more than an order of magnitude through hybridization
with a plasmonic metamaterial,while retaining an ultrafast nonlinear response
time of ~1 ps. Transmission modulation close to ~1% is seen at a pump uence of
~0.03 mJ/cm^2 at the wavelength of ~1600 nm. This approach allows to engineer
and enhance graphene's nonlinearity within a broad wavelength range enabling
applications in optical switching, mode-locking and pulse shaping.Comment: The following article has been submitted to Applied Physics Letters.
After it is published, it will be found at http://apl.aip.org
Burst expansion, distribution and diversification of MITEs in the silkworm genome
<p>Abstract</p> <p>Background</p> <p>Miniature inverted-repeat transposable elements (MITEs) are widespread in plants and animals. Although silkworm (<it>Bombyx mori</it>) has a large amount of and a variety of transposable elements, the genome-wide information of the silkworm MITEs is unknown.</p> <p>Results</p> <p>We used structure-based and homology approaches to search for MITEs in the silkworm genome. We identified 17 MITE families with a total of 5785 members, accounting for ~0.4% of the genome. 7 of 17 MITE families are completely novel based on the nucleotide composition of target site duplication (TSD) and/or terminal inverted repeats (TIR). Silkworm MITEs were widely and nonrandom distributed in the genome. One family named BmMITE-2 might experience a recent burst expansion. Network and diversity analyses for each family revealed different diversification patterns of the silkworm MITEs, reflecting the signatures of genome-shocks that silkworm experienced. Most silkworm MITEs preferentially inserted into or near genes and BmMITE-11 that encodes a germline-restricted small RNA might silence its the closest genes in silkworm ovary through a small RNA pathway.</p> <p>Conclusions</p> <p>Silkworm harbors 17 MITE families. The silkworm MITEs preferred to reside in or near genes and one MITE might be involved in gene silence. Our results emphasize the exceptional role of MITEs in transcriptional regulation of genes and have general implications to understand interaction between MITEs and their host genome.</p
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