249 research outputs found
Optimization of hybrid sol-gel coating for dropwise condensation of pure steam
We developed hybrid organic-inorganic sol-gel silica coatings with good durability in harsh environment (high temperatures, high vapor velocities) and with slightly hydrophobic behavior, sufficient to promote dropwise condensation (DWC) of pure steam. DWC is a very promising mechanism in new trends of thermal management and power generation systems to enhance the heat transfer during condensation as compared to film-wise condensation (FWC). The sol-gel coatings have been prepared from methyl triethoxy silane (MTES) and tetraethyl-orthosilicate (TEOS) and deposited on an aluminum substrate. The coatings were optimized in terms of precursor ratio and annealing temperature highlighting potentials and limits of such mixtures. A comprehensive surface characterization before and after saturated steam condensation tests has been performed and related to the thermal measurements for evaluating the heat transfer augmentation as compared to FWC obtained on untreated aluminum surfaces. The results showed that the developed hybrid organic-inorganic sol-gel silica coatings are promising DWC promoters
A multi-layer edge-on single photon counting silicon microstrip detector for innovative techniques in diagnostic radiology
A three-layer detector prototype, obtained by stacking three edge-on single photon counting silicon microstrip detectors, has been developed and widely tested. This was done in the framework of the Synchrotron Radiation for Medical Physics/Frontier Radiology (SYRMEP/FRONTRAD) collaboration activities, whose aim is to improve the quality of mammographic examinations operating both on the source and on the detector side. The active surface of the device has been fully characterized making use of an edge-scanning technique and of a well-collimated laminar synchrotron radiation beam. The obtained data (interlayer distances, channel correspondence, etc.) have then been used to combine information coming from each detector layer, without causing any loss in spatial and contrast resolution of the device. Contrast and spatial resolution have also been separately evaluated for each detector layer. Moreover, imaging techniques (phase contrast, refraction, and scatter imaging), resulting in an increased visibility of low absorbing details, have been implemented, and their effectiveness has been tested on a biological sample. Finally, the possibility of simultaneously acquiring different kind of images with the different detector layers is discussed. This would result in maximizing the information extracted from the sample, while at the same time the high absorption efficiency of the detector device would allow a low dose delivery
Geometry of River Networks I: Scaling, Fluctuations, and Deviations
This article is the first in a series of three papers investigating the
detailed geometry of river networks. Large-scale river networks mark an
important class of two-dimensional branching networks, being not only of
intrinsic interest but also a pervasive natural phenomenon. In the description
of river network structure, scaling laws are uniformly observed. Reported
values of scaling exponents vary suggesting that no unique set of scaling
exponents exists. To improve this current understanding of scaling in river
networks and to provide a fuller description of branching network structure, we
report here a theoretical and empirical study of fluctuations about and
deviations from scaling. We examine data for continent-scale river networks
such as the Mississippi and the Amazon and draw inspiration from a simple model
of directed, random networks. We center our investigations on the scaling of
the length of sub-basin's dominant stream with its area, a characterization of
basin shape known as Hack's law. We generalize this relationship to a joint
probability density and show that fluctuations about scaling are substantial.
We find strong deviations from scaling at small scales which can be explained
by the existence of linear network structure. At intermediate scales, we find
slow drifts in exponent values indicating that scaling is only approximately
obeyed and that universality remains indeterminate. At large scales, we observe
a breakdown in scaling due to decreasing sample space and correlations with
overall basin shape. The extent of approximate scaling is significantly
restricted by these deviations and will not be improved by increases in network
resolution.Comment: 16 pages, 13 figures, Revtex4, submitted to PR
An Analytical and Numerical Study of Optimal Channel Networks
We analyze the Optimal Channel Network model for river networks using both
analytical and numerical approaches. This is a lattice model in which a
functional describing the dissipated energy is introduced and minimized in
order to find the optimal configurations. The fractal character of river
networks is reflected in the power law behaviour of various quantities
characterising the morphology of the basin. In the context of a finite size
scaling Ansatz, the exponents describing the power law behaviour are calculated
exactly and show mean field behaviour, except for two limiting values of a
parameter characterizing the dissipated energy, for which the system belongs to
different universality classes. Two modified versions of the model,
incorporating quenched disorder are considered: the first simulates
heterogeneities in the local properties of the soil, the second considers the
effects of a non-uniform rainfall. In the region of mean field behaviour, the
model is shown to be robust to both kinds of perturbations. In the two limiting
cases the random rainfall is still irrelevant, whereas the heterogeneity in the
soil properties leads to new universality classes. Results of a numerical
analysis of the model are reported that confirm and complement the theoretical
analysis of the global minimum. The statistics of the local minima are found to
more strongly resemble observational data on real rivers.Comment: 27 pages, ps-file, 11 Postscript figure
Linking Community Participatory Research to Global Policymaking: Lessons Learned
The past two decades saw a proliferation of
opportunities for the perspectives of people
experiencing poverty and marginalisation to input into
global policymaking spaces. So far these efforts have
been contested, with attempts to embed participatory
methodologies facilitating only limited consultation
and falling into many pitfalls. While Participate
was built on learning from previous attempts
to influence global policy, we aimed to further
understand participatory processes, and advance
practical mechanisms for participation at every level
of decision-making, from local to national and global.
Participate emphasises the interactions between these
levels and the importance of impacting multiple levels
in order to create lasting, transformative change.
This chapter describes what has been learnt about
bringing the voices on the ground into global
policymaking. We examine how and by whom the
knowledge and evidence created were used, and the
barriers and challenges to embedding this knowledge
into global policy processes, through the following
questions:
• What have been the challenges to embedding
participatory processes into global policy spaces?
• What have these pathways of influence looked
like, and what are some of the key lessons learned
from these
Inventário Florístico Florestal de Santa Catarina: espécies da Floresta Estacional Decidual.
O presente trabalho visou apresentar e analisar a flora da Floresta Estacional Decidual em Santa Catarina, Brasil, tendo como fonte de dados os levantamentos realizados durante o Inventário Florístico Florestal de Santa Catarina. Foram avaliadas as espécies de indivíduos lenhosos de 79 unidades amostrais de 4.000 m². Foram feitas coletas extras de indivíduos férteis, no entorno e nas unidades amostrais, das demais formas de vida. Este esforço amostral registrou 420 espécies, abrangendo 90 famílias e 275 gêneros. Nas unidades amostrais, registrou-se 233 espécies, sendo 204 com diâmetro na altura do peito (DAP) ? 10 cm e 162 com diâmetro na altura do peito DAP ? 10 cm e altura ? 1,50 m, portanto com espécies em comuns. A coleta de material extra registrou 332 angiospermas e uma gimnosperma (Araucaria angustifolia), demonstrando a importância de coletas externas às áreas previamente delimitadas. Entre as ameaçadas de extinção foram registradas Ocotea odorifera e Araucaria angustifolia
Evidence for Supernova Signatures in the Spectrum of the Late-time Bump of the Optical Afterglow of GRB 021211
We present photometric and spectroscopic observations of the gamma-ray burst
GRB 021211 obtained during the late stages of its afterglow. The light curve
shows a rebrightening occurring ~25 days after the GRB. The analysis of a VLT
spectrum obtained during the bump (27 days after the GRB) reveals a suggestive
resemblance with the spectrum of the prototypical type-Ic SN 1994I, obtained
about ~10 days past maximum light. Particularly we have measured a strong,
broad absorption feature at 3770 A, which we have identified with Ca II
blueshifted by ~14400 km/s, thus indicating that a supernova (SN) component is
indeed powering the `bump' in the afterglow decay. Assuming SN 1994I as a
template, the spectroscopic and photometric data together indicate that the SN
and GRB explosions were at most separated by a few days. Our results suggest
that GRBs might be associated also to standard type-Ic supernovae.Comment: 6 pages, 4 color figures. Accepted for publication in A&A Letters.
Fig. 4 does not appair in the A&A version due to space restrictions. Includes
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Synchrotron based planar imaging and digital tomosynthesis of breast and biopsy phantoms using a CMOS active pixel sensor
The SYRMEP (SYnchrotron Radiation for MEdical Physics) beamline at Elettra is performing the first mammography study on human patients using free-space propagation phase contrast imaging. The stricter spatial resolution requirements of this method currently force the use of conventional films or specialized computed radiography (CR) systems. This also prevents the implementation of three-dimensional (3D) approaches. This paper explores the use of an X-ray detector based on complementary metal-oxide-semiconductor (CMOS) active pixel sensor (APS) technology as a possible alternative, for acquisitions both in planar and tomosynthesis geometry.Results indicate higher quality of the images acquired with the synchrotron set-up in both geometries. This improvement can be partly ascribed to the use of parallel, collimated and monochromatic synchrotron radiation (resulting in scatter rejection, no penumbra-induced blurring and optimized X-ray energy), and partly to phase contrast effects. Even though the pixel size of the used detector is still too large - and thus suboptimal - for free-space propagation phase contrast imaging, a degree of phase-induced edge enhancement can clearly be observed in the images
Unified View of Scaling Laws for River Networks
Scaling laws that describe the structure of river networks are shown to
follow from three simple assumptions. These assumptions are: (1) river networks
are structurally self-similar, (2) single channels are self-affine, and (3)
overland flow into channels occurs over a characteristic distance (drainage
density is uniform). We obtain a complete set of scaling relations connecting
the exponents of these scaling laws and find that only two of these exponents
are independent. We further demonstrate that the two predominant descriptions
of network structure (Tokunaga's law and Horton's laws) are equivalent in the
case of landscapes with uniform drainage density. The results are tested with
data from both real landscapes and a special class of random networks.Comment: 14 pages, 9 figures, 4 tables (converted to Revtex4, PRE ref added
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