39,725 research outputs found
Large cities are less green
We study how urban quality evolves as a result of carbon dioxide emissions as
urban agglomerations grow. We employ a bottom-up approach combining two
unprecedented microscopic data on population and carbon dioxide emissions in
the continental US. We first aggregate settlements that are close to each other
into cities using the City Clustering Algorithm (CCA) defining cities beyond
the administrative boundaries. Then, we use data on emissions at a
fine geographic scale to determine the total emissions of each city. We find a
superlinear scaling behavior, expressed by a power-law, between
emissions and city population with average allometric exponent
across all cities in the US. This result suggests that the high productivity of
large cities is done at the expense of a proportionally larger amount of
emissions compared to small cities. Furthermore, our results are substantially
different from those obtained by the standard administrative definition of
cities, i.e. Metropolitan Statistical Area (MSA). Specifically, MSAs display
isometric scaling emissions and we argue that this discrepancy is due to the
overestimation of MSA areas. The results suggest that allometric studies based
on administrative boundaries to define cities may suffer from endogeneity bias
Avaliação de cultivares de milho para silagem: resultados do ano agrÃcola 2001/2002.
bitstream/item/65238/1/CT-73-Cultiv-milho-silagem.pd
Fracturing the optimal paths
Optimal paths play a fundamental role in numerous physical applications
ranging from random polymers to brittle fracture, from the flow through porous
media to information propagation. Here for the first time we explore the path
that is activated once this optimal path fails and what happens when this new
path also fails and so on, until the system is completely disconnected. In fact
numerous applications can be found for this novel fracture problem. In the
limit of strong disorder, our results show that all the cracks are located on a
single self-similar connected line of fractal dimension .
For weak disorder, the number of cracks spreads all over the entire network
before global connectivity is lost. Strikingly, the disconnecting path
(backbone) is, however, completely independent on the disorder.Comment: 4 pages,4 figure
Developing a site-conditions map for seismic hazard Assessment in Portugal
The evaluation of site effects on a broad scale is a critical issue for seismic hazard and risk assessment, land use planning and emergency planning. As characterization of site conditions based on the shear-wave velocity has become increasingly important, several methods have been proposed in the literature to estimate its average over the first thirty meters (Vs30) from more extensively available data. These methods include correlations with geologic-geographic defined units and topographic slope. In this paper we present the first steps towards the development of a site–conditions map for Portugal, based on a regional database of shear-wave velocity data, together with geological, geographic, and lithological information. We computed Vs30 for each database site and classified it according to the corresponding geological-lithological information using maps at the smallest scale available (usually 1:50000). We evaluated the consistency of Vs30 values within generalized-geological classes, and assessed the performance of expedient methodologies proposed in the literature
Novel techniques in VUV high-resolution spectroscopy
Novel VUV sources and techniques for VUV spectroscopy are reviewed.
Laser-based VUV sources have been developed via non-linear upconversion of
laser pulses in the nanosecond (ns), the picosecond (ps), and femtosecond (fs)
domain, and are applied in high-resolution gas phase spectroscopic studies.
While the ns and ps pulsed laser sources, at Fourier-transform limited
bandwidths, are used in wavelength scanning spectroscopy, the fs laser source
is used in a two-pulse time delayed mode. In addition a Fourier-transform
spectrometer for high resolution gas-phase spectroscopic studies in the VUV is
described, exhibiting the multiplex advantage to measure many resonances
simultaneously.Comment: 17 Pages, 8 figures, Conference proceedings of the VUV/X-ray 2013 at
Hefei, Chin
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