2,280 research outputs found
Aperiodic conductivity oscillations in quasi-ballistic graphene heterojunctions
We observe conductivity oscillations with aperiodic spacing to only one side
of the tunneling current in a dual-gated graphene field effect transistor with
an n-p-n type potential barrier. The spacing and width of these oscillatoins
were found to be inconsistent with pure Farbry-Perot-type interferences, but
are in quantitative agreement with theoretical predictions that attribute them
to resonant tunneling through quasi-bound impurity states. This observation may
be understood as another signature of Klein tunneling in graphene
heterojunctions and is of importance for future development and modeling of
graphene based nanoelectronic devices.Comment: 3 pages, 3 figure
Localized States and Resultant Band Bending in Graphene Antidot Superlattices
We fabricated dye sensitized graphene antidot superlattices with the purpose
of elucidating the role of the localized edge state density. The fluorescence
from deposited dye molecules was found to strongly quench as a function of
increasing antidot filling fraction, whereas it was enhanced in unpatterned but
electrically back-gated samples. This contrasting behavior is strongly
indicative of a built-in lateral electric field that accounts for fluorescence
quenching as well as p-type doping. These findings are of great interest for
light-harvesting applications that require field separation of electron-hole
pairs.Comment: NanoLetters, 201
Transconductance and Coulomb blockade properties of in-plane grown carbon nanotube field effect transistors
Single electron transistors (SETs) made from single wall carbon nanotubes
(SWCNTs) are promising for quantum electronic devices operating with ultra-low
power consumption and allow fundamental studies of electron transport. We
report on SETs made by registered in-plane growth utilizing tailored nanoscale
catalyst patterns and chemical vapor deposition. Metallic SWCNTs have been
removed by an electrical burn-in technique and the common gate hysteresis was
removed using PMMA and baking, leading to field effect transistors with large
on/off ratios up to 10^5. Further segmentation into 200 nm short semiconducting
SWCNT devices created quantum dots which display conductance oscillations in
the Coulomb blockade regime. The demonstrated utilization of registered
in-plane growth opens possibilities to create novel SET device geometries which
are more complex, i.e. laterally ordered and scalable, as required for advanced
quantum electronic devices.Comment: 15 pages, 4 figure
(Glycol-κ2 O,O′)nitrosyl(η5-pentamethylcyclopentadienyl)ruthenium(II) bis(trifluoromethanesulfonate)
The title compound, [Ru(C10H15)(NO)(HOCH2CH2OH)](CF3SO3)2, possesses a three-legged piano-stool geometry around the Ru atom, with an average Ru—O distance of 2.120 (6) Å and an Ru—N—O angle of 159.45 (14)°. The ethyleneglycol ligand forms a non-planar metallacyclic ring by chelating the Ru atom via the O atoms. The O⋯O distances of 2.554 (2) and 2.568 (2) Å are indicative of hydrogen bonding between coordinated ethyleneglycol and outer-sphere trifluoromethanesulfonate fragments. The crystal packing is stabilized by ionic forces and several CH3⋯·F (2.585 and 2.640 Å) and CH3⋯O interactions (2.391, 2.678, 2.694 and 2.699 Å) between the pentamethylcyclopentadienyl ligand and trifluoromethanesulfonate anion. There is noticeable short intermolecular contact [2.9039 (16) Å], between an O atom of the SO3 group and a C atom of the pentamethylcyclopentadienyl ligand
Fractal boundary value problems for integral and differential equations with local fractional operators
In the present paper we investigate the fractal boundary value problems for the Fredholm and Volterra integral equations, heat conduction and wave equations by using the local fractional decomposition method. The operator is described by the local fractional operators. The four illustrative examples are given to elaborate the accuracy and reliability of the obtained results
Fractal boundary value problems for integral and differential equations with local fractional operators
In the present paper we investigate the fractal boundary value problems for the Fredholm and Volterra integral equations, heat conduction and wave equations by using the local fractional decomposition method. The operator is described by the local fractional operators. The four illustrative examples are given to elaborate the accuracy and reliability of the obtained results
Determination of Edge Purity in Bilayer Graphene Using micro-Raman Spectroscopy
Polarization resolved micro-Raman spectroscopy was carried out at the edges
of bilayer graphene. We find strong dependence of the intensity of the G band
on the incident laser polarization, with its intensity dependence being 90
degrees out of phase for the armchair and zigzag case, in accordance with
theoretical predictions. For the case of mixed-state edges we demonstrate that
the polarization contrast reflects the fractional composition of armchair and
zigzag edges, providing a monitor of edge purity, which is an important
parameter for the development of efficient nanoelectronic devices.Comment: 3 pages, 3 figures, to appear in Applied Physics Letter
Finite element analyses of FRP-strengthened concrete beams with corroded reinforcement
Existing deteriorated reinforced concrete (RC) structures need strengthening to extend service life. Fibre reinforced polymer (FRP) has been widely used to strengthen sound structures, but its application on damaged concrete structures still needs to be investigated. This paper presents non-linear finite element analyses conducted to assess the flexural behaviour of corrosion-damaged RC beams strengthened with externally bonded FRP. Beams in four different categories were analysed: a reference beam, a corroded but non-strengthened beam, and corroded beams strengthened with glass FRP (GFRP) and carbon FRP (CFRP) respectively. Furthermore, the strengthened beams were modelled with different modelling choices to investigate the effectiveness of FRP applied to the beam soffit and as U-jackets. Pre-loading and corrosion-induced cracks were incorporated by reducing the tensile strength of concrete elements at crack locations. Average and pitting corrosion were incorporated by reducing the cross-sectional area of the reinforcement corresponding to the measured corrosion levels. Interface elements were used to simulate the bond between FRP and concrete. The modelling methods were validated against experimental results. It was found that modelling of pitting corrosion, especially the location of pits, lengths and number of pits considered, were influential in predicting the load and deformation capacity of beams. A CFRP plate at the beam soffit, combined with inclined U-jackets at its ends of the CFRP plate provided sufficient flexural strengthening. Thus, intermediate U-jackets did not further increase the load-bearing capacity for the studied beam geometry and corrosion damages. However, with a GFRP sheet at the beam soffit, both inclined and intermediate U-jackets were needed to provide full utilisation of the GFRP sheet for the studied beam geometry. In further studies of the effectiveness of the strengthening methods, it is recommended to investigate beams of varying dimensions, corrosion patterns and levels, and FRP spacing and dimensions
Federated Linear Contextual Bandits with User-level Differential Privacy
This paper studies federated linear contextual bandits under the notion of
user-level differential privacy (DP). We first introduce a unified federated
bandits framework that can accommodate various definitions of DP in the
sequential decision-making setting. We then formally introduce user-level
central DP (CDP) and local DP (LDP) in the federated bandits framework, and
investigate the fundamental trade-offs between the learning regrets and the
corresponding DP guarantees in a federated linear contextual bandits model. For
CDP, we propose a federated algorithm termed as \robin and show that it is
near-optimal in terms of the number of clients and the privacy budget
by deriving nearly-matching upper and lower regret bounds when
user-level DP is satisfied. For LDP, we obtain several lower bounds, indicating
that learning under user-level -LDP must suffer a regret
blow-up factor at least { or
} under different conditions.Comment: Accepted by ICML 202
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