31,130 research outputs found
Structure and electronic properties of molybdenum monoatomic wires encapsulated in carbon nanotubes
Monoatomic chains of molybdenum encapsulated in single walled carbon
nanotubes of different chiralities are investigated using density functional
theory. We determine the optimal size of the carbon nanotube for encapsulating
a single atomic wire, as well as the most stable atomic arrangement adopted by
the wire. We also study the transport properties in the ballistic regime by
computing the transmission coefficients and tracing them back to electronic
conduction channels of the wire and the host. We predict that carbon nanotubes
of appropriate radii encapsulating a Mo wire have metallic behavior, even if
both the nanotube and the wire are insulators. Therefore, encapsulating Mo
wires in CNT is a way to create conductive quasi one-dimensional hybrid
nanostructures.Comment: 8 pages, 10 figure
Impact of dimerization and stretching on the transport properties of molybdenum atomic wires
We study the electrical and transport properties of monoatomic Mo wires with
different structural characteristics. We consider first periodic wires with
inter-atomic distances ranging between the dimerized wire to that formed by
equidistant atoms. We find that the dimerized case has a gap in the electronic
structure which makes it insulating, as opposed to the equidistant or
near-equidistant cases which are metallic. We also simulate two conducting
one-dimensional Mo electrodes separated by a scattering region which contains a
number of dimers between 1 and 6. The characteristics strongly depend on
the number of dimers and vary from ohmic to tunneling, with the presence of
different gaps. We also find that stretched chains are ferromagnetic.Comment: 8 pages, 7 figure
Non-equilibrium transport response from equilibrium transport theory
We propose a simple scheme that describes accurately essential
non-equilibrium effects in nanoscale electronics devices using equilibrium
transport theory. The scheme, which is based on the alignment and dealignment
of the junction molecular orbitals with the shifted Fermi levels of the
electrodes, simplifies drastically the calculation of current-voltage
characteristics compared to typical non-equilibrium algorithms. We probe that
the scheme captures a number of non-trivial transport phenomena such as the
negative differential resistance and rectification effects. It applies to those
atomic-scale junctions whose relevant states for transport are spatially placed
on the contact atoms or near the electrodes.Comment: 5 pages, 4 figures. Accepted in Physical Review
A model for conservative chaos constructed from multi-component Bose-Einstein condensates with a trap in 2 dimensions
To show a mechanism leading to the breakdown of a particle picture for the
multi-component Bose-Einstein condensates(BECs) with a harmonic trap in high
dimensions, we investigate the corresponding 2- nonlinear Schr{\"o}dinger
equation (Gross-Pitaevskii equation) with use of a modified variational
principle. A molecule of two identical Gaussian wavepackets has two degrees of
freedom(DFs), the separation of center-of-masses and the wavepacket width.
Without the inter-component interaction(ICI) these DFs show independent regular
oscillations with the degenerate eigen-frequencies. The inclusion of ICI
strongly mixes these DFs, generating a fat mode that breaks a particle picture,
which however can be recovered by introducing a time-periodic ICI with zero
average. In case of the molecule of three wavepackets for a three-component
BEC, the increase of amplitude of ICI yields a transition from regular to
chaotic oscillations in the wavepacket breathing.Comment: 5 pages, 4 figure
Structural instability of vortices in Bose-Einstein condensates
In this paper we study a gaseous Bose-Einstein condensate (BEC) and show
that: (i) A minimum value of the interaction is needed for the existence of
stable persistent currents. (ii) Vorticity is not a fundamental invariant of
the system, as there exists a conservative mechanism which can destroy a vortex
and change its sign. (iii) This mechanism is suppressed by strong interactions.Comment: 4 pages with 3 figures. Submitted to Phys. Rev. Let
Impact of Fano and Breit-Wigner resonances in the thermoelectric properties of nanoscale junctions
We show that the thermoelectric properties of nanoscale junctions featuring
states near the Fermi level strongly depend on the type of resonance generated
by such states, which can be either Fano or Breit-Wigner-like. We give general
expressions for the thermoelectric coefficients generated by the two types of
resonances and calculate the thermoelectric properties of these systems, which
encompass most nanoelectronics junctions. We include simulations of real
junctions where metalloporphyrin molecules bridge gold electrodes and prove
that for some metallic elements the thermoelectric properties show a large
variability. We find that the thermopower and figure of merit are largely
enhanced when the resonance gets close to the Fermi level and reach values much
higher than typical values found in other nanoscale junctions. The specific
value and temperature dependence are determined by a series of factors such as
the strength of the coupling between the state and other molecular states, the
symmetry of the state, the strength of the coupling between the molecule and
the leads and the spin filtering behavior of the junction.Comment: 9 pages, 11 figure
Intensity of physical education classes in adolescents
Se registrĂł la frecuencia cardiaca de 182 estudiantes (97 chicos y 85 chicas) de entre 12 y 18 años durante sus clases de EducaciĂłn FĂsica. Los resultados muestran una media del 21,62±14,33% del tiempo de clase en valores MVPA (moderate to vigorous physical activity). Respecto al gĂ©nero, pese a no ser significativo, los mayores valores corresponden a la chicas (23,47±14,45% vs 19,99±14,10%; p=0,106). No se ha observado efecto del tipo de sesiĂłn (deportes colectivos, deportes individuales, juegos tradicionales o bailes) sobre el tiempo en valores MVPA (p>0,05; TE0.05; ES<0.020), obtaining the highest values in team sports sessions. Results show that intensity and duration of analyzed classes do not comply with recommendations to become an adequate cardiovascular exercis
Is it possible to observe experimentally a metal-insulator transition in ultra cold atoms?
Kicked rotors with certain non-analytic potentials avoid dynamical
localization and undergo a metal-insulator transition. We show that typical
properties of this transition are still present as the non-analyticity is
progressively smoothed out provided that the smoothing is less than a certain
limiting value. We have identified a smoothing dependent time scale such that
full dynamical localization is absent and the quantum momentum distribution
develops power-law tails with anomalous decay exponents as in the case of a
conductor at the metal-insulator transition. We discuss under what conditions
these findings may be verified experimentally by using ultra cold atoms
techniques. It is found that ultra-cold atoms can indeed be utilized for the
experimental investigation of the metal-insulator transition.Comment: 7 pages, 3 figure
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