1,482 research outputs found
Single-parameter adiabatic charge pumping in carbon nanotube resonators
Single-parameter adiabatic charge pumping, induced by a nearby
radio-frequency antenna, is achieved in suspended carbon nanotubes close to the
mechanical resonance. The charge pumping is due to an important dynamic
adjustment of the oscillating motion to the antenna signal and it is different
from the mechanism active in the two-parameter pumping. Finally, the second
harmonic oscillator response shows an interesting relationship with the first
harmonic that should be experimentally observed
Stochastic dynamics for a single vibrational mode in molecular junctions
We propose a very accurate computational scheme for the dynamics of a
classical oscillator coupled to a molecular junction driven by a finite bias,
including the finite mass effect. We focus on two minimal models for the
molecular junction: Anderson-Holstein (AH) and two-site Su-Schrieffer-Heeger
(SSH) models. As concerns the oscillator dynamics, we are able to recover a
Langevin equation confirming what found by other authors with different
approaches and assessing that quantum effects come from the electronic
subsystem only. Solving numerically the stochastic equation, we study the
position and velocity distribution probabilities of the oscillator and the
electronic transport properties at arbitrary values of electron-oscillator
interaction, gate and bias voltages. The range of validity of the adiabatic
approximation is established in a systematic way by analyzing the behaviour of
the kinetic energy of the oscillator. Due to the dynamical fluctuations, at
intermediate bias voltages, the velocity distributions deviate from a gaussian
shape and the average kinetic energy shows a non monotonic behaviour. In this
same regime of parameters, the dynamical effects favour the conduction far from
electronic resonances where small currents are observed in the infinite mass
approximation. These effects are enhanced in the two-site SSH model due to the
presence of the intermolecular hopping t. Remarkably, for sufficiently large
hopping with respect to tunneling on the molecule, small interaction strengths
and at intermediate bias (non gaussian regime), we point out a correspondence
between the minima of the kinetic energy and the maxima of the dynamical
conductance.Comment: 19 pages, 16 figures, submitted to Physical Review
Probing nonlinear mechanical effects through electronic currents: the case of a nanomechanical resonator acting as electronic transistor
We study a general model describing a self-detecting single electron
transistor realized by a suspended carbon nanotube actuated by a nearby
antenna. The main features of the device, recently observed in a number of
experiments, are accurately reproduced. When the device is in a low
current-carrying state, a peak in the current signals a mechanical resonance.
On the contrary, a dip in the current is found in high current-carrying states.
In the nonlinear vibration regime of the resonator, we are able to reproduce
quantitatively the characteristic asymmetric shape of the current-frequency
curves. We show that the nonlinear effects coming out at high values of the
antenna amplitude are related to the effective nonlinear force induced by the
electronic flow. The interplay between electronic and mechanical degrees of
freedom is understood in terms of an unifying model including in an intrinsic
way the nonlinear effects driven by the external probe.Comment: 7 pages, 3 figures, submitted to Physical Review
Noise-assisted Thouless pump in elastically deformable molecular junctions
We study a Thouless pump realized with an elastically \textit{deformable
quantum dot} whose center of mass follows a non-linear stochastic dynamics. The
interplay of noise, non-linear effects, dissipation and interaction with an
external time-dependent driving on the pumped charge is fully analyzed. The
results show that the quantum pumping mechanism not only is not destroyed by
the force fluctuations, but it becomes stronger when the forcing signal
frequency is tuned close to the resonance of the vibrational mode. The
robustness of the quantum pump with temperature is also investigated and an
exponential decay of the pumped charge is found when the coupling to the
vibrational mode is present. Implications of our results for
nano-electromechanical systems are also discussed.Comment: 2 Appendices and figures adde
Spectral, optical and transport properties of the adiabatic anisotropic Holstein model: Application to slightly doped organic semiconductors
Spectral, optical and transport properties of an anisotropic
three-dimensional Holstein model are studied within the adiabatic
approximation. The parameter regime is appropriate for organic semiconductors
used in single crystal based field effect transistors. Different approaches
have been used to solve the model: self-consistent Born approximation valid for
weak electron-phonon coupling, coherent potential approximation exact for
infinite dimensions, and numerical diagonalization for finite lattices. With
increasing temperature, the width of the spectral functions gets larger and
larger making the approximation of quasi-particle less accurate. On the
contrary, their peak positions are never strongly renormalized in comparison
with the bare ones. As expected, the density of states is characterized by an
exponential tail corresponding to localized states at low temperature. For weak
electron-lattice coupling, the optical conductivity follows a Drude behavior,
while, for intermediate electron-lattice coupling, a temperature dependent peak
is present at low frequency. For high temperatures and low particle densities,
the mobility always exhibits a power-law behavior as function of temperature.
With decreasing the particle density, at low temperature, the mobility shows a
transition from metallic to insulating behavior. Results are discussed in
connection with available experimental data.Comment: 9 pages, 7 figures, submitted to Phys. Rev.
Interplay of charge, spin and lattice degrees of freedom on the spectral properties of the one-dimensional Hubbard-Holstein model
We calculate the spectral function of the one dimensional Hubbard-Holstein
model using the time dependent Density Matrix Renormalization Group (tDMRG),
focusing on the regime of large local Coulomb repulsion, and away from
electronic half-filling. We argue that, from weak to intermediate
electron-phonon coupling, phonons interact only with the electronic charge, and
not with the spin degrees of freedom. For strong electron-phonon interaction,
spinon and holon bands are not discernible anymore and the system is well
described by a spinless polaronic liquid. In this regime, we observe multiple
peaks in the spectrum with an energy separation corresponding to the energy of
the lattice vibrations (i.e., phonons). We support the numerical results by
introducing a well controlled analytical approach based on Ogata-Shiba's
factorized wave-function, showing that the spectrum can be understood as a
convolution of three contributions, originating from charge, spin, and lattice
sectors. We recognize and interpret these signatures in the spectral properties
and discuss the experimental implications.Comment: 8 pages, 7 figure
Gender Differences in O2 Pulse During Single Set vs. Multiple-set Resistance Exercise
Please refer to the pdf version of the abstract located adjacent to the title
Deploy Energy-efficient Technologies in the Restoration of a Traditional Building in the Historical Center of Catania (Italy)☆
Abstract The policy about energy efficiency of buildings, including minimum energy requirements and energy performance certificate (EPC), have to be also applied to existing buildings in the case of energy retrofit. In this paper, the possible strategies that can be used to reduce the energy needs of traditional massive buildings, that are widespread in the old town of the Mediterranean cities, have been investigated. To this aim, this study evaluates the energy consumption of a massive building placed in Catania city, called "La Casa del Portuale", which was recently refurbished with the aim to host two local administrative centers. The energy needs of this building was evaluated through computer simulation both in the heating and cooling period, on a yearly basis. The activities research were developed analyzing different refurbishment solutions suitable to improve the thermal performance of most traditional buildings without adversely affecting their fabric and character. Therefore, the feasibility comparison has been performed between the examined refurbishment solutions. The results of the proposed research, considering the diffusion of this typology of buildings, could be assumed as reference to a significant portion of the traditional real estate
Evaluation of different methods to estimate the transfer of immunity in donkey foals fed with colostrum of good IgG quality: A preliminary study
The aims of the present study were to evaluate the correlation between IgG Serum Radial Immunodiffusion (SRID), Electrophoresis Gamma Globulins (EGG), Electrophoresis Total Protein (ETP) and the serum total protein (TP) analyzed by refractometry and by a dry chemistry analyzer (Biuret) and to estimate serum IgG concentrations using serum TP. A total of 36 samples collected at four different times (birth, 6, 12, 24 hours after birth) from nine Amiata donkey foals were evaluated with SRID, EGG, ETP, serum TP Biuret and refractometry. SRID IgG concentration increased significantly over time until T12. Serum TP analyzed with refractometry, electrophoresis and Biuret showed a statistically significant difference between T0 and T6 vs T12 and T24. A good or strong correlation was found between different tests performed. Equations to quantify serum IgG were created and can be used for estimating the donkey foals’ serum IgG in the first day of life. Serum TP refractometry showed a high correlation with SRID IgG (0.91) which may be a particularly useful and economic instrument to estimate the transfer of immunity in donkey foals during the first day of life
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