2,658 research outputs found
Numerical study of the localization length critical index in a network model of plateau-plateau transitions in the quantum Hall effect
We calculate numerically the localization length critical index within the
Chalker-Coddington (CC) model for plateau-plateau transitions in the quantum
Hall effect. Lyapunov exponents have been calculated with relative errors on
the order . Such high precision was obtained by considering the
distribution of Lyapunov exponents for large ensembles of relatively short
chains and calculating the ensemble average values. We analyze thoroughly
finite size effects and find the localization length critical index .Comment: 4 pages, 4 figure
Electrostatic tailoring of magnetic interference in quantum point contact ballistic Josephson junctions
The magneto-electrostatic tailoring of the supercurrent in quantum point
contact ballistic Josephson junctions is demonstrated. An etched InAs-based
heterostructure is laterally contacted to superconducting niobium leads and the
existence of two etched side gates permits, in combination with the application
of a perpendicular magnetic field, to modify continuously the magnetic
interference pattern by depleting the weak link. For wider junctions the
supercurrent presents a Fraunhofer-like interference pattern with periodicity
h/2e whereas by shrinking electrostatically the weak link, the periodicity
evolves continuously to a monotonic decay. These devices represent novel
tunable structures that might lead to the study of the elusive Majorana
fermions.Comment: 4.5 pages, 4 color figure
Mycobacterium bovis infections in Portugal: Spoligotyping and MIRU-VNTR typing of animal isolates
Tuberculosis is still one of the most important infectious diseases worldwide. Although human cases due to Mycobacterium bovis, the aetiological agent of bovine tuberculosis (bTB), considerably decreased in most industrialized countries, the possible zoonotic health hazard and the considerable economic losses it brings justify significant efforts to eradicate the disease in several countries. In Portugal, although a systematic slaughter policy of tuberculin reactive animals has been ongoing for several years, eradication is far from being achieved. In order to clarify possible infection sources and transmission routes, molecular typing of Portuguese M. bovis animal strains was undertaken. Two typing methods directed on potentially polymorphic genomic regions were chosen: Spoligotyping, a reverse line blot hybridization technique that evaluates the presence or absence of 43 oligonucleotide sequences in the Direct Repeat genomic region, and MIRU-VNTR (Mycobacterial Interspersed Repetitive Units- Variable Number Tandem Repeats) typing of 8 selected minisatellite like loci
Effective core potential ab initio calculations on main group heptoxides and large silicate systems
The ab initio molecular structures for several main group heptoxides (X2O7n-, n=0,2,4) are calculated using effective core potentials at the HF and DFT (B3LYP) levels. Particular attention is given to the X-O-X bond angle, as this structural parameter is a key feature for the study of both heptoxides and larger derivatives, such as polysilicate systems. The extent of the p-d interactions, which was found to be the main factor governing the magnitude of the X-O-X angle in transition metal heptoxides, does not play a significant role in the main group analogues.http://www.sciencedirect.com/science/article/B6TGT-40V4F3D-3/1/f26d56c6395122fcba007ed20f55868
Effect of a magnetic field on the two-phonon Raman scattering in graphene
We have studied, both experimentally and theoretically, the change of the
so-called 2D band of the Raman scattering spectrum of graphene (the two-phonon
peak near 2700 cm-1) in an external magnetic field applied perpendicular to the
graphene crystal plane at liquid helium temperature. A shift to lower frequency
and broadening of this band is observed as the magnetic field is increased from
0 to 33 T. At fields up to 5--10 T the changes are quadratic in the field while
they become linear at higher magnetic fields. This effect is explained by the
curving of the quasiclassical trajectories of the photo-excited electrons and
holes in the magnetic field, which enables us (i) to extract the electron
inelastic scattering rate, and (ii) to conclude that electronic scattering
accounts for about half of the measured width of the 2D peak.Comment: 11 pages, 7 figure
Tuning the electron-phonon coupling in multilayer graphene with magnetic fields
Magneto Raman scattering study of the E optical phonons in multi-layer
epitaxial graphene grown on a carbon face of SiC are presented. At 4.2K in
magnetic field up to 33 T, we observe a series of well pronounced avoided
crossings each time the optically active inter Landau level transition is tuned
in resonance with the E phonon excitation (at 196 meV). The width of the
phonon Raman scattering response also shows pronounced variations and is
enhanced in conditions of resonance. The experimental results are well
reproduced by a model that gives directly the strength of the electron-phonon
interaction.Comment: 4 pages, 3 figure
Rhodoliths and rhodolith beds
Rhodolith (maërl) beds, communities dominated by free living coralline algae, are
a common feature of subtidal environments worldwide. Well preserved as fossils, they have long
been recognized as important carbonate producers and paleoenvironmental indicators. Coralline
algae produce growth bands with a morphology and chemistry that record environmental variation.
Rhodoliths are hard but often fragile, and growth rates are only on the order of mm/yr. The
hard, complex structure of living beds provides habitats for numerous associated species not found
on otherwise entirely sedimentary bottoms. Beds are degraded locally by dredging and other anthropogenic
disturbances, and recovery is slow. They will likely suffer severe impacts worldwide
from the increasing acidity of the ocean. Investigations of rhodolith beds with scuba have enabled
precise stratified sampling that has shown the importance of individual rhodoliths as hot spots of
diversity. Observations, collections, and experiments by divers have revolutionized taxonomic studies
by allowing comprehensive, detailed collection and by showing the large effects of the environment
on rhodolith morphology. Facilitated by in situ collection and calibrations, corallines are now
contributing to paleoclimatic reconstructions over a broad range of temporal and spatial scales.
Beds are particularly abundant in the mesophotic zone of the Brazilian shelf where technical diving
has revealed new associations and species. This paper reviews selected past and present research on
rhodoliths and rhodolith beds that has been greatly facilitated by the use of scuba
New approach addressing sustainability in urban areas using sustainable city models
A brief analysis of the environmental, social and economic paradigm of nowadays cities, allows reaching a simple conclusion: current cities are not sustainable. Considering this, it is very important to study the causes of cities problems and to develop city models implementing sustainability practices. There are a limited number of studies developing sustainable city models, but the scientific community lacks even more studies about the rehabilitation of current cities to implement these models. This work emerges with the objective of analysing how it is possible to implement sustainability practices in cities through the development of a sustainable city model and an urban rehabilitation plan. The development of sustainable city models is a very complex topic and the analysis of the literature shows that it is necessary to consider the relation between environmental and social aspects in the development of sustainable cities, while taking special concerns when considering the economic issues. It was also concluded that sustainable city models and rehabilitation plans should be subject to sustainability assessments and should consider the active participation of its inhabitants. In fact, a city can only be sustainable if its population is in harmony with the city model and we can only assess results by predicting and measuring performance levels.(undefined
Comprehensive transient-state study for CARMENES-NIR high thermal stability
CARMENES has been proposed as a next-generation instrument for the 3.5m Calar
Alto Telescope. Its objective is finding habitable exoplanets around M dwarfs
through radial velocity measurements (m/s level) in the near-infrared.
Consequently, the NIR spectrograph is highly constraint regarding
thermal/mechanical requirements. As a first approach, the thermal stability has
been limited to \pm 0.01K (within year period) over a working temperature of
243K. This can be achieved by means of several temperature-controlled rooms.
The options considered to minimise the complexity of the thermal design are
here presented, as well as the transient-state thermal analyses realised to
make the best choice
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