2,057 research outputs found
Gated combo nanodevice for sequential operations on single electron spin
An idea for a nanodevice in which an arbitrary sequence of three basic
quantum single qubit gates - negation, Hadamard and phase shift - can be
performed on a single electron spin. The spin state is manipulated using the
spin-orbit coupling and the electron trajectory is controlled by the electron
wave function self-focusing mechanism due to the electron interaction with the
charge induced on metal gates. We present results of simulations based on
iterative solution of the time dependent Schr\"odinger equation in which the
subsequent operations on the electron spin can be followed and controlled.
Description of the moving electron wave packet requires evaluation of the
electric field within the entire nanodevice in each time step
Stark effect on the exciton spectra of vertically coupled quantum dots: horizontal field orientation and non-aligned dots
We study the effect of an electric-field on an electron-hole pair in an
asymmetric system of vertically coupled self-assembled quantum dots taking into
account their non-perfect alignment. We show that the non-perfect alignment
does not qualitatively influence the exciton Stark effect for the electric
field applied in the growth direction, but can be detected by application of a
perpendicular electric field. We demonstrate that the direction of the shift
between the axes of non-aligned dots can be detected by rotation of a weak
electric field within the plane of confinement. Already for a nearly perfect
alignment the two-lowest energy bright exciton states possess antilocked
extrema as function of the orientation angle of the horizontal field which
appear when the field is parallel to the direction of the shift between the dot
centers
Accuracy of the Hartree-Fock method for Wigner molecules at high magnetic fields
Few-electron systems confined in two-dimensional parabolic quantum dots at
high magnetic fields are studied by the Hartree-Fock (HF) and exact
diagonalization methods. A generalized multicenter Gaussian basis is proposed
in the HF method. A comparison of the HF and exact results allows us to discuss
the relevance of the symmetry of the charge density distribution for the
accuracy of the HF method. It is shown that the energy estimates obtained with
the broken-symmetry HF wave functions become exact in the infinite
magnetic-field limit. In this limit the charge density of the broken-symmetry
solution can be identified with the classical charge distribution.Comment: to appear in EPJ
Very high energy gamma-ray follow-up observations of novae and dwarf novae with the MAGIC telescopes
In the last few years the Fermi-LAT instrument has detected GeV gamma-ray
emission from several novae. Such GeV emission can be interpreted in terms of
inverse Compton emission from electrons accelerated in the shock or in terms of
emission from hadrons accelerated in the same conditions. The latter might
reach much higher energies and could produce a second component in the
gamma-ray spectrum at TeV energies. We perform follow-up observations of
selected novae and dwarf novae in search of the second component in TeV energy
gamma rays. This can shed light on the acceleration process of leptons and
hadrons in nova explosions. We have performed observations with the MAGIC
telescopes of 3 sources, a symbiotic nova YY Her, a dwarf nova ASASSN-13ax and
a classical nova V339 Del, shortly after their outbursts. We did not detect TeV
gamma-ray emission from any of the objects observed. The TeV upper limits from
MAGIC observations and the GeV detection by Fermi constrain the acceleration
parameters for electrons and hadrons.Comment: Proceedings of the 34th International Cosmic Ray Conference, 30 July-
6 August, 2015, The Hague, The Netherlands. The content of this submission is
similar to our paper in the Fermi Symposium of novae observations with MAGIC,
which appeared as arXiv:1502.05853. arXiv admin note: substantial text
overlap with arXiv:1502.0585
The paradoxes of management
Funding text: this work was funded by national funds through FCT-Fundação para a Ciência e Tecnologia under the project ref. UID/ECO/00124/2013 and by POR Lisboa ubder the project LISBOA-01-0145-FEDER-007722.This paper explores paradox, a way of seeing organizations that emphasizes interdependence, opposition and persistence, as both a source of novelty and absurdity. Paradoxes are processes with a dual potential for organizational harm or good, depending on the way they are framed and tackled. We explore this dual side of paradox and discuss some of its implications for the management of organizations.publishersversionpublishe
Moonlighting function of Phytochelatin synthase1 in extracellular defense against fungal pathogens
Very high energy gamma-ray emission from X-ray transients during major outbursts
Context: Some high mass X-ray binaries (HMXB) have been recently confirmed as
gamma-ray sources by ground based Cherenkov telescopes. In this work, we
discuss the gamma-ray emission from X-ray transient sources formed by a Be star
and a highly magnetized neutron star. This kind of systems can produce variable
hadronic gamma-ray emission through the mechanism proposed by Cheng and
Ruderman, where a proton beam accelerated in the pulsar magnetosphere impacts
the transient accretion disk. We choose as case of study the best known system
of this class: A0535+26. Aims: We aim at making quantitative predictions about
the very high-energy radiation generated in Be-X ray binary systems with
strongly magnetized neutron stars. Methods: We study the gamma-ray emission
generated during a major X-ray outburst of a HMXB adopting for the model the
parameters of A0535+26. The emerging photon signal from the disk is determined
by the grammage of the disk that modulates the optical depth. The
electromagnetic cascades initiated by photons absorbed in the disk are
explored, making use of the so-called "Approximation A" to solve the cascade
equations. Very high energy photons induce Inverse Compton cascades in the
photon field of the massive star. We implemented Monte Carlo simulations of
these cascades, in order to estimate the characteristics of the resulting
spectrum. Results: TeV emission should be detectable by Cherenkov telescopes
during a major X-ray outburst of a binary formed by a Be star and a highly
magnetized neutron star. The gamma-ray light curve is found to evolve in
anti-correlation with the X-ray signal.Comment: 8 pages, 7 figures, accepted for publication in Astronomy and
Astrophysical journa
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