31 research outputs found
Two-Dimensional Electron Gas in InGaAs/InAlAs Quantum Wells
We designed and performed low temperature DC transport characterization
studies on two-dimensional electron gases confined in lattice-matched
InGaAs/InAlAs quantum wells grown by
molecular beam epitaxy on InP substrates. The nearly constant mobility for
samples with the setback distance larger than 50nm and the similarity between
the quantum and transport life-time suggest that the main scattering mechanism
is due to short range scattering, such as alloy scattering, with a scattering
rate of 2.2 ps. We also obtain the Fermi level at the
InGaAs/InAlAs surface to be 0.36eV above
the conduction band, when fitting our experimental densities with a
Poisson-Schr\"odinger model.Comment: Accepted in Applied Physics Letter
SU(1,1) symmetry of multimode squeezed states
We show that a class of multimode optical transformations that employ linear
optics plus two-mode squeezing can be expressed as SU(1,1) operators. These
operations are relevant to state-of-the-art continuous variable quantum
information experiments including quantum state sharing, quantum teleportation,
and multipartite entangled states. Using this SU(1,1) description of these
transformations, we obtain a new basis for such transformations that lies in a
useful representation of this group and lies outside the often-used restriction
to Gaussian states. We analyze this basis, show its application to a class of
transformations, and discuss its extension to more general quantum optical
networks
A Methodological Approach for Testing the Viability of Seeds Stored in Short-Term Seed Banks
[EN] Efficient management of `active¿ seed banks ¿ specifically aimed at the short-term storage at room temperature of seeds to be used locally in conservation/regeneration programmes of endemic or endangered plant species ¿ requires establishing the optimal storage time to maintain high seed viability, for each stored species. In this work, germination of seeds of the halophytes Thalictrum maritimum, Centaurea dracunculifolia and Linum maritimum has been investigated. The seeds had been stored for different periods of time in the seed bank of `La Albufera¿ Natural Park (Valencia, SE Spain) after collection in salt marshes of the Park, where small populations of the three species are present. Seeds of T. maritimum and C. dracunculifolia have a relatively short period of viability at room temperature, and should not be stored for more than three years. On the other hand, L. maritimum seeds maintain a high germination percentage and can be kept at room temperature for up to 10 years. T. maritimum seeds, in contrast to those of the other two species, did not germinate in in vitro tests nor when sown directly on a standard substrate, unless a pre-treatment of the seeds was applied, mechanical scarification being the most effective. These results will help to improve the management of the seed bank, to generate more efficiently new plants for reintroduction and reinforcement of populations of these species in their natural ecosystems within the Natural ParkForte Gil, J.; Yabor, L.; Bellido Nadal, A.; Collado Cerveró, F.; Ferrer-Gallego, P.; Vicente, O.; Boscaiu, M. (2017). A Methodological Approach for Testing the Viability of Seeds Stored in Short-Term Seed Banks. Notulae Scientia Biologicae. 9(4):563-570. doi:10.15835/nsb9410173S5635709
The Chevreton Tensor and Einstein-Maxwell Spacetimes Conformal to Einstein Spaces
In this paper we characterize the source-free Einstein-Maxwell spacetimes
which have a trace-free Chevreton tensor. We show that this is equivalent to
the Chevreton tensor being of pure-radiation type and that it restricts the
spacetimes to Petrov types \textbf{N} or \textbf{O}. We prove that the trace of
the Chevreton tensor is related to the Bach tensor and use this to find all
Einstein-Maxwell spacetimes with a zero cosmological constant that have a
vanishing Bach tensor. Among these spacetimes we then look for those which are
conformal to Einstein spaces. We find that the electromagnetic field and the
Weyl tensor must be aligned, and in the case that the electromagnetic field is
null, the spacetime must be conformally Ricci-flat and all such solutions are
known. In the non-null case, since the general solution is not known on closed
form, we settle with giving the integrability conditions in the general case,
but we do give new explicit examples of Einstein-Maxwell spacetimes that are
conformal to Einstein spaces, and we also find examples where the vanishing of
the Bach tensor does not imply that the spacetime is conformal to a -space.
The non-aligned Einstein-Maxwell spacetimes with vanishing Bach tensor are
conformally -spaces, but none of them are conformal to Einstein spaces.Comment: 22 pages. Corrected equation (12
Anisotropic Bose-Einstein condensates and completely integrable dynamical systems
A Gaussian ansatz for the wave function of two-dimensional harmonically
trapped anisotropic Bose-Einstein condensates is shown to lead, via a
variational procedure, to a coupled system of two second-order, nonlinear
ordinary differential equations. This dynamical system is shown to be in the
general class of Ermakov systems. Complete integrability of the resulting
Ermakov system is proven. Using the exact solution, collapse of the condensate
is analyzed in detail. Time-dependence of the trapping potential is allowed
Shortcuts to adiabaticity in a time-dependent box
A method is proposed to drive an ultrafast non-adiabatic dynamics of an
ultracold gas trapped in a box potential. The resulting state is free from
spurious excitations associated with the breakdown of adiabaticity, and
preserves the quantum correlations of the initial state up to a scaling factor.
The process relies on the existence of an adiabatic invariant and the inversion
of the dynamical self-similar scaling law dictated by it. Its physical
implementation generally requires the use of an auxiliary expulsive potential
analogous to those used in soliton control. The method is extended to a broad
family of many-body systems. As illustrative examples we consider the ultrafast
expansion of a Tonks-Girardeau gas and of Bose-Einstein condensates in
different dimensions, where the method exhibits an excellent robustness against
different regimes of interactions and the features of an experimentally
realizable box potential.Comment: 6 pp, 4 figures, typo in Eq. (6) fixe
Acceptance of near-natural greenspace management relates to ecological and socio-cultural assigned values among European urbanites
Grasslands are widespread elements of urban greenspace providing recreational, psychological and aesthetic benefits to city residents. Two urban grassland types of contrasting management dominate urban greenspaces: frequently mown, species-poor short-cut lawns and less intensively managed, near-natural tall-grass meadows. The higher conservation value of tall-grass meadows makes management interventions such as converting short-cut lawns into tall-grass meadows a promising tool for urban biodiversity conservation. The societal success of such interventions, however, depends on identifying the values urban residents assign to different types of urban grasslands, and how these values translate to attitudes towards greenspace management. Using 2027 questionnaires across 19 European cities, we identify the assigned values that correlate with people's personal greenspace use and their preferences for different types of urban grasslands to determine how these values relate to the agreement with a scenario of converting 50 of their cities� short-cut lawns into tall-grass meadows. We found that most people assigned nature-related values, such as wildness, to tall-grass meadows and utility-related values, such as recreation, to short-cut lawns. Positive value associations of wildness and species richness with tall-grass meadows, and social and nature-related greenspace activities, positively correlated with agreeing to convert short-cut lawns into tall-grass meadows. Conversely, disapproval of lawn conversion correlated with positive value associations of cleanliness and recreation potential with short-cut lawns. Here, people using greenspaces for nature-related activities were outstandingly positive about lawn conversion. The results show that the plurality of values assigned to different types of urban grasslands should be considered in urban greenspace planning. For example, tall-grass meadows could be managed to also accommodate the values associated with short-cut lawns, such as tidiness and recreation potential, to support their societal acceptance
Berry and Pancharatnam Topological Phases of Atomic and Optical Systems
Theoretical and experimental studies of Berry and Pancharatnam phases are
reviewed. Basic elements of differential geometry are presented for
understanding the topological nature of these phases. The basic theory analyzed
by Berry in relation to magnetic monopoles is presented. The theory is
generalized to nonadiabatic processes and to noncyclic Pancharatnam phases.
Different systems are discussed including polarization optics, n-level atomic
systems, neutron interferometry and molecular topological phases.Comment: Review article,72 pages, 186 reference
Recapturing Joaquín 'Chapo' Guzmán in the Mexican Press: An Analysis of the Front Page of El Universal, Reforma, Excélsior, and La Jornada in 2016
This article, whose aim is to know exactly how the headlines of Mexico's four main newspapers have reported on the recapture of Joaquín Guzmán, will show the results of an analysis of the journalistic content of these four Mexican newspapers. These are general papers, which published information on their front page regarding the recapture of the drug trafficker Joaquín 'Chapo' Guzmán. The events took place on January 8, 2016, six months after his escape from Altiplano prison in Mexico. If the escape was spectacular-being from a high-security prison and evidencing collusion of authorities and corruption of the system-the recapture was even more so. Well-known figures, such as actors Kate del Castillo and Sean Penn, were involved, together with a female politician of the Action Nacional Party, thus leading to questioning of the Mexican status quo. Coverage of the recapture was reduced, tending to minimize the impact of the criminal acts and contributing to both fictionalizing and rendering frivolous the figure of Guzmán. © 2018 The author(s)
Recapturing Joaquín 'Chapo' Guzmán in the Mexican Press: An Analysis of the Front Page of El Universal, Reforma, Excélsior, and La Jornada in 2016
This article, whose aim is to know exactly how the headlines of Mexico's four main newspapers have reported on the recapture of Joaquín Guzmán, will show the results of an analysis of the journalistic content of these four Mexican newspapers. These are general papers, which published information on their front page regarding the recapture of the drug trafficker Joaquín 'Chapo' Guzmán. The events took place on January 8, 2016, six months after his escape from Altiplano prison in Mexico. If the escape was spectacular-being from a high-security prison and evidencing collusion of authorities and corruption of the system-the recapture was even more so. Well-known figures, such as actors Kate del Castillo and Sean Penn, were involved, together with a female politician of the Action Nacional Party, thus leading to questioning of the Mexican status quo. Coverage of the recapture was reduced, tending to minimize the impact of the criminal acts and contributing to both fictionalizing and rendering frivolous the figure of Guzmán. © 2018 The author(s)