21,460 research outputs found
Effect of Electrolyte Concentration on the Capacitance and Mobility of Graphene
The use of graphene field-effect transistors as a biosensor is increasingly being used to study biological phenomena, due to the sensitivity and low reactivity of graphene. To further improve sensitivity in biological environments, we examined how different salt concentrations affect the mobility of capacitance of the graphene. Samples were also measured after an annealing process. We report on the positive correlation between sensitivity and electrolyte concentration and speculate on methods to improve future detectors. Mobility of the device was found to change from 1.07*103cm2/ (V*s) in de-ionized water to 2.78*103cm2/ (V*s) in a 500 mM potassium phosphate buffer solution
The solution space of metabolic networks: producibility, robustness and fluctuations
Flux analysis is a class of constraint-based approaches to the study of
biochemical reaction networks: they are based on determining the reaction flux
configurations compatible with given stoichiometric and thermodynamic
constraints. One of its main areas of application is the study of cellular
metabolic networks. We briefly and selectively review the main approaches to
this problem and then, building on recent work, we provide a characterization
of the productive capabilities of the metabolic network of the bacterium E.coli
in a specified growth medium in terms of the producible biochemical species.
While a robust and physiologically meaningful production profile clearly
emerges (including biomass components, biomass products, waste etc.), the
underlying constraints still allow for significant fluctuations even in key
metabolites like ATP and, as a consequence, apparently lay the ground for very
different growth scenarios.Comment: 10 pages, prepared for the Proceedings of the International Workshop
on Statistical-Mechanical Informatics, March 7-10, 2010, Kyoto, Japa
ESR theory for interacting 1D quantum wires
We compute the electron spin resonance (ESR) intensity for one-dimensional
quantum wires in semiconductor heterostructures, taking into account
electron-electron interactions and spin-orbit coupling. The ESR spectrum is
shown to be very sensitive to interactions. While in the absence of
interactions, the spectrum is a flat band, characteristic threshold
singularities appear in the interacting limit. This suggests the practical use
of ESR to reveal spin dynamics in a Luttinger liquid.Comment: 7 pages, 2 figures. To be published in Europhys. Let
On the strategy frequency problem in batch Minority Games
Ergodic stationary states of Minority Games with S strategies per agent can
be characterised in terms of the asymptotic probabilities with which
an agent uses of his strategies. We propose here a simple and general
method to calculate these quantities in batch canonical and grand-canonical
models. Known analytic theories are easily recovered as limiting cases and, as
a further application, the strategy frequency problem for the batch
grand-canonical Minority Game with S=2 is solved. The generalization of these
ideas to multi-asset models is also presented. Though similarly based on
response function techniques, our approach is alternative to the one recently
employed by Shayeghi and Coolen for canonical batch Minority Games with
arbitrary number of strategies.Comment: 17 page
On the transition to efficiency in Minority Games
The existence of a phase transition with diverging susceptibility in batch
Minority Games (MGs) is the mark of informationally efficient regimes and is
linked to the specifics of the agents' learning rules. Here we study how the
standard scenario is affected in a mixed population game in which agents with
the `optimal' learning rule (i.e. the one leading to efficiency) coexist with
ones whose adaptive dynamics is sub-optimal. Our generic finding is that any
non-vanishing intensive fraction of optimal agents guarantees the existence of
an efficient phase. Specifically, we calculate the dependence of the critical
point on the fraction of `optimal' agents focusing our analysis on three
cases: MGs with market impact correction, grand-canonical MGs and MGs with
heterogeneous comfort levels.Comment: 12 pages, 3 figures; contribution to the special issue "Viewing the
World through Spin Glasses" in honour of David Sherrington on the occasion of
his 65th birthda
Landau levels, edge states, and strained magnetic waveguides in graphene monolayers with enhanced spin-orbit interaction
The electronic properties of a graphene monolayer in a magnetic and a
strain-induced pseudo-magnetic field are studied in the presence of spin-orbit
interactions (SOI) that are artificially enhanced, e.g., by suitable adatom
deposition. For the homogeneous case, we provide analytical results for the
Landau level eigenstates for arbitrary intrinsic and Rashba SOI, including also
the Zeeman field. The edge states in a semi-infinite geometry are studied in
the absence of the Rashba term. For a critical value of the magnetic field, we
find a quantum phase transition separating two phases with spin-filtered
helical edge states at the Dirac point. These phases have opposite spin current
direction. We also discuss strained magnetic waveguides with inhomogeneous
field profiles that allow for chiral snake orbits. Such waveguides are
practically immune to disorder-induced backscattering, and the SOI provides
non-trivial spin texture to these modes.Comment: 12 pages, 7 figures; v2: minor modifications, published versio
Spin-orbit coupling and spectral function of interacting electrons in carbon nanotubes
The electronic spin-orbit coupling in carbon nanotubes is strongly enhanced
by the curvature of the tube surface and has important effects on the
single-particle spectrum. Here, we include the full spin-orbit interaction in
the formulation of the effective low-energy theory for interacting electrons in
metallic single-wall carbon nanotubes and study its consequences. The resulting
theory is a four-channel Luttinger liquid, where spin and charge modes are
mixed. We show that the analytic structure of the spectral function is strongly
affected by this mixing, which can provide an experimental signature of the
spin-orbit interaction.Comment: 4+epsilon pages, 1 figure; published versio
Wavevector-dependent spin filtering and spin transport through magnetic barriers in graphene
We study the spin-resolved transport through magnetic nanostructures in monolayer and bilayer graphene. We take into account both the orbital effect of the inhomogeneous perpendicular magnetic field as well as the in-plane spin splitting due to the Zeeman interaction and to the exchange coupling possibly induced by the proximity of a ferromagnetic insulator. We find that a single barrier exhibits a wavevector-dependent spin filtering effect at energies close to the transmission threshold. This effect is significantly enhanced in a resonant double barrier configuration, where the spin polarization of the outgoing current can be increased up to 100% by increasing the distance between the barriers
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