1,452 research outputs found
A magnetorheological damper with embedded piezoelectric force sensor : experiment and modeling
2010-2011 > Academic research: refereed > Chapter in an edited book (author)Version of RecordPublishe
Facile Synthesis of High Quality Graphene Nanoribbons
Graphene nanoribbons have attracted attention for their novel electronic and
spin transport properties1-6, and because nanoribbons less than 10 nm wide have
a band gap that can be used to make field effect transistors. However,
producing nanoribbons of very high quality, or in high volumes, remains a
challenge. Here, we show that pristine few-layer nanoribbons can be produced by
unzipping mildly gas-phase oxidized multiwalled carbon nanotube using
mechanical sonication in an organic solvent. The nanoribbons exhibit very high
quality, with smooth edges (as seen by high-resolution transmission electron
microscopy), low ratios of disorder to graphitic Raman bands, and the highest
electrical conductance and mobility reported to date (up to 5e2/h and 1500
cm2/Vs for ribbons 10-20 nm in width). Further, at low temperature, the
nanoribbons exhibit phase coherent transport and Fabry-Perot interference,
suggesting minimal defects and edge roughness. The yield of nanoribbons was ~2%
of the starting raw nanotube soot material, which was significantly higher than
previous methods capable of producing high quality narrow nanoribbons1. The
relatively high yield synthesis of pristine graphene nanoribbons will make
these materials easily accessible for a wide range of fundamental and practical
applications.Comment: Nature Nanotechnology in pres
Laser-induced etching of few-layer graphene synthesized by Rapid-Chemical Vapour Deposition on Cu thin films
The outstanding electrical and mechanical properties of graphene make it very
attractive for several applications, Nanoelectronics above all. However a
reproducible and non destructive way to produce high quality, large-scale area,
single layer graphene sheets is still lacking. Chemical Vapour Deposition of
graphene on Cu catalytic thin films represents a promising method to reach this
goal, because of the low temperatures (T < 900 Celsius degrees) involved during
the process and of the theoretically expected monolayer self-limiting growth.
On the contrary such self-limiting growth is not commonly observed in
experiments, thus making the development of techniques allowing for a better
control of graphene growth highly desirable. Here we report about the local
ablation effect, arising in Raman analysis, due to the heat transfer induced by
the laser incident beam onto the graphene sample.Comment: v1:9 pages, 8 figures, submitted to SpringerPlus; v2: 11 pages,
PDFLaTeX, 9 figures, revised peer-reviewed version resubmitted to
SpringerPlus; 1 figure added, figure 1 and 4 replaced,typos corrected,
"Results and discussion" section significantly extended to better explain
etching mechanism and features of Raman spectra, references adde
Strain- and Adsorption-Dependent Electronic States and Transport or Localization in Graphene
The chapter generalizes results on influence of uniaxial strain and
adsorption on the electron states and charge transport or localization in
graphene with different configurations of imperfections (point defects):
resonant (neutral) adsorbed atoms either oxygen- or hydrogen-containing
molecules or functional groups, vacancies or substitutional atoms, charged
impurity atoms or molecules, and distortions. To observe electronic properties
of graphene-admolecules system, we applied electron paramagnetic resonance
technique in a broad temperature range for graphene oxides as a good basis for
understanding the electrotransport properties of other active carbons. Applied
technique allowed observation of possible metal-insulator transition and
sorption pumping effect as well as discussion of results in relation to the
granular metal model. The electronic and transport properties are calculated
within the framework of the tight-binding model along with the Kubo-Greenwood
quantum-mechanical formalism. Depending on electron density and type of the
sites, the conductivity for correlated and ordered adsorbates is found to be
enhanced in dozens of times as compared to the cases of their random
distribution. In case of the uniaxially strained graphene, the presence of
point defects counteracts against or contributes to the band-gap opening
according to their configurations. The band-gap behaviour is found to be
nonmonotonic with strain in case of a simultaneous action of defect ordering
and zigzag deformation. The amount of localized charge carriers (spins) is
found to be correlated with the content of adsorbed centres responsible for the
formation of potential barriers and, in turn, for the localization effects.
Physical and chemical states of graphene edges, especially at a uniaxial strain
along one of them, play a crucial role in electrical transport phenomena in
graphene-based materials.Comment: 16 pages, 10 figure
Improving the Energy-Conversion Efficiency of a PV-TE System with an Intelligent Power-Track Switching Technique and Efficient Thermal-Management Scheme
A photovoltaic-thermoelectric (PV-TE) hybrid system can be used for efficient thermal energy utilization from the generated waste heat in PV devices. In this article, an efficient PV-TE hybrid system with intelligent power-track switching technique and thermal management based on energy conversion is proposed. To make the output power of PV-TE system stable and normalized, an incorporated stable voltage circuit is designed based on energy conversion. In addition, a control-and-monitoring strategy is launched in the system to realize the normal collecting for the output power of PV-TE system. Finally, a battery protection circuit is performed to ensure that the energy converted by the entire system is effectively stored. The experimental results show that more electrical energy about 84 034 J was obtained with our energy harvesting system than that of a single photovoltaic (PV) cell. Besides, the thermal gradient of PV cells is indirectly reduced the operation of the whole system, which is automatically monitored due to the proposed intelligent power-track switching technique
Aharonov-Bohm interferences from local deformations in graphene
One of the most interesting aspects of graphene is the tied relation between
structural and electronic properties. The observation of ripples in the
graphene samples both free standing and on a substrate has given rise to a very
active investigation around the membrane-like properties of graphene and the
origin of the ripples remains as one of the most interesting open problems in
the system. The interplay of structural and electronic properties is
successfully described by the modelling of curvature and elastic deformations
by fictitious gauge fields that have become an ex- perimental reality after the
suggestion that Landau levels can form associated to strain in graphene and the
subsequent experimental confirmation. Here we propose a device to detect
microstresses in graphene based on a scanning-tunneling-microscopy setup able
to measure Aharonov-Bohm inter- ferences at the nanometer scale. The
interferences to be observed in the local density of states are created by the
fictitious magnetic field associated to elastic deformations of the sample.Comment: Some bugs fixe
Direct generation of intense extreme ultraviolet supercontinuum with 35 fs, 11 mJ pulses from a femtosecond laser amplifier
We report on the generation of intense extreme ultraviolet (EUV)
supercontinuum with photon energies spanning from 35 eV to 50 eV (i. e.,
supporting an isolated attosecond pulse with a duration of ~271 as) by loosely
focusing 35 fs, 11 mJ pulses from a femtosecond laser amplifier into a 10-mm
long gas cell filled with krypton gas. The dramatic change of spectral and
temporal properties of the driver pulses after passing through the gas cell
indicates that propagation effects play a significant role in promoting the
generation of the EUV supercontinuum.Comment: 14 pages, 4 figure
Quantum-squeezing effects of strained multilayer graphene NEMS
Quantum squeezing can improve the ultimate measurement precision by squeezing one desired fluctuation of the two physical quantities in Heisenberg relation. We propose a scheme to obtain squeezed states through graphene nanoelectromechanical system (NEMS) taking advantage of their thin thickness in principle. Two key criteria of achieving squeezing states, zero-point displacement uncertainty and squeezing factor of strained multilayer graphene NEMS, are studied. Our research promotes the measured precision limit of graphene-based nano-transducers by reducing quantum noises through squeezed states
Antimicrobial activity of apple cider vinegar against Escherichia coli, Staphylococcus aureus and Candida albicans; downregulating cytokine and microbial protein expression
The global escalation in antibiotic resistance cases means alternative antimicrobials are essential. The aim of this study was to investigate the antimicrobial capacity of apple cider vinegar (ACV) against E. coli, S. aureus and C. albicans. The minimum dilution of ACV required for growth inhibition varied for each microbial species. For C. albicans, a 1/2 ACV had the strongest effect, S. aureus, a 1/25 dilution ACV was required, whereas for E-coli cultures, a 1/50 ACV dilution was required (p < 0.05). Monocyte co-culture with microbes alongside ACV resulted in dose dependent downregulation of inflammatory cytokines (TNFα, IL-6). Results are expressed as percentage decreases in cytokine secretion comparing ACV treated with non-ACV treated monocytes cultured with E-coli (TNFα, 99.2%; IL-6, 98%), S. aureus (TNFα, 90%; IL-6, 83%) and C. albicans (TNFα, 83.3%; IL-6, 90.1%) respectively. Proteomic analyses of microbes demonstrated that ACV impaired cell integrity, organelles and protein expression. ACV treatment resulted in an absence in expression of DNA starvation protein, citrate synthase, isocitrate and malate dehydrogenases in E-coli; chaperone protein DNak and ftsz in S. aureus and pyruvate kinase, 6-phosphogluconate dehydrogenase, fructose bisphosphate were among the enzymes absent in C.albican cultures. The results demonstrate ACV has multiple antimicrobial potential with clinical therapeutic implications
Development of computations in bioscience and bioinformatics and its application: review of the Symposium of Computations in Bioinformatics and Bioscience (SCBB06)
The first symposium of computations in bioinformatics and bioscience (SCBB06) was held in Hangzhou, China on June 21–22, 2006. Twenty-six peer-reviewed papers were selected for publication in this special issue of BMC Bioinformatics. These papers cover a broad range of topics including bioinformatics theories, algorithms, applications and tool development. The main technical topics contain gene expression analysis, sequence analysis, genome analysis, phylogenetic analysis, gene function prediction, molecular interaction and system biology, genetics and population study, immune strategy, protein structure prediction and proteomics
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