20,067 research outputs found
The role of contacts in molecular electronics
Molecular electronic devices are the upmost destiny of the miniaturization
trend of electronic components. Although not yet reproducible on large scale,
molecular devices are since recently subject of intense studies both
experimentally and theoretically, which agree in pointing out the extreme
sensitivity of such devices on the nature and quality of the contacts. This
chapter intends to provide a general theoretical framework for modelling
electronic transport at the molecular scale by describing the implementation of
a hybrid method based on Green function theory and density functional
algorithms. In order to show the presence of contact-dependent features in the
molecular conductance, we discuss three archetypal molecular devices, which are
intended to focus on the importance of the different sub-parts of a molecular
two-terminal setup.Comment: 17 pages, 8 figure
Innermost Stable Circular Orbits and Epicyclic Frequencies Around a Magnetized Neutron Star
A full-relativistic approach is used to compute the radius of the innermost
stable circular orbit (ISCO), the Keplerian, frame-dragging, precession and
oscillation frequencies of the radial and vertical motions of neutral test
particles orbiting the equatorial plane of a magnetized neutron star. The
space-time around the star is modelled by the six parametric solution derived
by Pachon et al. It is shown that the inclusion of an intense magnetic field,
such as the one of a neutron star, have non-negligible effects on the above
physical quantities, and therefore, its inclusion is necessary in order to
obtain a more accurate and realistic description of the physical processes
occurring in the neighbourhood of this kind of objects such as the dynamics of
accretion disk. The results discussed here also suggest that the consideration
of strong magnetic fields may introduce non-negligible corrections in, e.g.,
the relativistic precession model and therefore on the predictions made on the
mass of neutron stars.Comment: LaTeX file, 13 pages, 4 figure
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Ethics In Information Systems: Student Performance In Evaluating Ethical Dilemmas
The explosion in information technology in the last 20 years, and in particular, data communications networks, has had a major impact on ethical thinking and ethical issues. This has been manifested in the recent accounting and business scandals, as it is becoming apparent that the ethical dimensions of information systems-related business decisions cannot be safely ignored. It is important for business educators to introduce students to relevant ethical situations that they may face in the business world. This paper discusses the Information Systems ethical environment and students performance on business ethics cases in a telecommunications course. The results of this evaluation show that more exposure to ethical situations is needed, as students are not prepared to make sound ethical judgements
Fermion mass hierarchy and non-hierarchical mass ratios in SU(5) x U(1)_F
We consider a SU(5) x U(1)_F GUT-flavor model in which the number of effects
that determine the charged fermions Yukawa matrices is much larger than the
number of observables, resulting in a hierarchical fermion spectrum with no
particular regularities. The GUT-flavor symmetry is broken by flavons in the
adjoint of SU(5), realizing a variant of the Froggatt-Nielsen mechanism that
gives rise to a large number of effective operators. By assuming a common mass
for the heavy fields and universality of the fundamental Yukawa couplings, we
reduce the number of free parameters to one. The observed fermion mass spectrum
is reproduced thanks to selection rules that discriminate among various
contributions. Bottom-tau Yukawa unification is preserved at leading order, but
there is no unification for the first two families. Interestingly, U(1)_F
charges alone do not determine the hierarchy, and can only give upper bounds on
the parametric suppression of the Yukawa operators.Comment: 14 pages, one figure. Few typos correcte
Bias-dependent Contact Resistance in Rubrene Single-Crystal Field-Effect Transistors
We report a systematic study of the bias-dependent contact resistance in
rubrene single-crystal field-effect transistors with Ni, Co, Cu, Au, and Pt
electrodes. We show that the reproducibility in the values of contact
resistance strongly depends on the metal, ranging from a factor of two for Ni
to more than three orders of magnitude for Au. Surprisingly, FETs with Ni, Co,
and Cu contacts exhibits an unexpected reproducibility of the bias-dependent
differential conductance of the contacts, once this has been normalized to the
value measured at zero bias. This reproducibility may enable the study of
microscopic carrier injection processes into organic semiconductors.Comment: 4 pages, 4 figure
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