25 research outputs found
Dynamic Community Detection into Analyzing of Wildfires Events
The study and comprehension of complex systems are crucial intellectual and
scientific challenges of the 21st century. In this scenario, network science
has emerged as a mathematical tool to support the study of such systems.
Examples include environmental processes such as wildfires, which are known for
their considerable impact on human life. However, there is a considerable lack
of studies of wildfire from a network science perspective. Here, employing the
chronological network concept -- a temporal network where nodes are linked if
two consecutive events occur between them -- we investigate the information
that dynamic community structures reveal about the wildfires' dynamics.
Particularly, we explore a two-phase dynamic community detection approach,
i.e., we applied the Louvain algorithm on a series of snapshots. Then we used
the Jaccard similarity coefficient to match communities across adjacent
snapshots. Experiments with the MODIS dataset of fire events in the Amazon
basing were conducted. Our results show that the dynamic communities can reveal
wildfire patterns observed throughout the year.Comment: 16 pages, 8 figure
Loop-Generated Bounds on Changes to the Graviton Dispersion Relation
We identify the effective theory appropriate to the propagation of massless
bulk fields in brane-world scenarios, to show that the dominant low-energy
effect of asymmetric warping in the bulk is to modify the dispersion relation
of the effective 4-dimensional modes. We show how such changes to the graviton
dispersion relation may be bounded through the effects they imply, through
loops, for the propagation of standard model particles. We compute these bounds
and show that they provide, in some cases, the strongest constraints on
nonstandard gravitational dispersions. The bounds obtained in this way are the
strongest for the fewest extra dimensions and when the extra-dimensional Planck
mass is the smallest. Although the best bounds come for warped 5-D scenarios,
for which the 5D Planck Mass is O(TeV), even in 4 dimensions the graviton loop
can lead to a bound on the graviton speed which is comparable with other
constraints.Comment: 18 pages, LaTeX, 4 figures, uses revte
Low-Energy Brane-World Effective Actions and Partial Supersymmetry Breaking
As part of a programme for the general study of the low-energy implications
of supersymmetry breaking in brane-world scenarios, we study the nonlinear
realization of supersymmetry which occurs when breaking N=2 to N=1
supergravity. We consider three explicit realizations of this supersymmetry
breaking pattern, which correspond to breaking by one brane, by one antibrane
or by two (or more) parallel branes. We derive the minimal field content, the
effective action and supersymmetry transformation rules for the resulting N=1
theory perturbatively in powers of kappa = 1/M_{Planck}. We show that the way
the massive gravitino and spin-1 fields assemble into N=1 multiplets implies
the existence of direct brane-brane contact interactions at order O(kappa).
This result is contrary to the O(kappa^2) predicted by the sequestering
scenario but in agreement with recent work of Anisimov et al. Our low-energy
approach is model independent and is a first step towards determining the
low-energy implications of more realistic brane models which completely break
all supersymmetries.Comment: Latex, 29 Page
Analysis of ecological thresholds in a temperate forest undergoing dieback.
Positive feedbacks in drivers of degradation can cause threshold responses in natural ecosystems. Though threshold responses have received much attention in studies of aquatic ecosystems, they have been neglected in terrestrial systems, such as forests, where the long time-scales required for monitoring have impeded research. In this study we explored the role of positive feedbacks in a temperate forest that has been monitored for 50 years and is undergoing dieback, largely as a result of death of the canopy dominant species (Fagus sylvatica, beech). Statistical analyses showed strong non-linear losses in basal area for some plots, while others showed relatively gradual change. Beech seedling density was positively related to canopy openness, but a similar relationship was not observed for saplings, suggesting a feedback whereby mortality in areas with high canopy openness was elevated. We combined this observation with empirical data on size- and growth-mediated mortality of trees to produce an individual-based model of forest dynamics. We used this model to simulate changes in the structure of the forest over 100 years under scenarios with different juvenile and mature mortality probabilities, as well as a positive feedback between seedling and mature tree mortality. This model produced declines in forest basal area when critical juvenile and mature mortality probabilities were exceeded. Feedbacks in juvenile mortality caused a greater reduction in basal area relative to scenarios with no feedback. Non-linear, concave declines of basal area occurred only when mature tree mortality was 3-5 times higher than rates observed in the field. Our results indicate that the longevity of trees may help to buffer forests against environmental change and that the maintenance of old, large trees may aid the resilience of forest stands. In addition, our work suggests that dieback of forests may be avoidable providing pressures on mature and juvenile trees do not pass critical thresholds
A novel scanning electrochemical microscopy strategy for the investigation of anomalous hydrogen evolution from AZ63 magnesium alloy
The evolution of hydrogen gas from corroding magnesium arises not exclusively from the cathodic half-cell reaction due to the consumption of the electrons released by the dissolving metal, but anodized magnesium generates significant amounts of H2 gas as well. In addition, the increase of the anodic overpotential enhances the rate of hydrogen gas generation. Therefore, spatially-resolved detection of the actual sites for hydrogen evolution related to anodically-activated sites is attempted using scanning electrochemical microscopy (SECM). This work describes a new experimental procedure for SECM based on a three-step (off-on-off) anodization operation sequence that was designed to obtain new insights into the behavior of magnesium and magnesium alloys when they are subjected to anodic polarization. Results obtained with scanning electrochemical microscopy (SECM) and scanning vibrating electrode technique (SVET) experiments presented here demonstrate the catalytic properties of the magnesium-oxide film for the hydrogen-evolution reaction
Contributions of Microelectrochemical Scanning Techniques for the Efficient Detection of Localized Corrosion Processes at the Cut Edges of Polymer-Coated Galvanized Steel
Spatially resolved information on corrosion reactions operating at the cut edges of coated metals can be obtained using microelectrochemical scanning techniques using a suitable selection of operation modes and scanning probes. The scanning vibrating electrode technique (SVET) provides current density maps with a spatial resolution of the order of the dimensions of the sample, which allows the temporal evolution of the corrosion reactions to be followed over time. This leads to the identification and localization of cathodic and anodic sites, although the technique lacks chemical specificity for the unequivocal identification of the reactive species. The application of scanning electrochemical microscopy (SECM) was previously limited to image cathodic reaction sites, either due to oxygen consumption in the amperometric operation or by the alkalinisation of the electrolyte in potentiometric operation. However, it is shown that anodic sites can be effectively monitored using an ion-selective microelectrode (ISME) as a probe. The ISME probes detected differences in the local concentrations of Zn2+ and OH− ions from the cut edges of a complete coil coating system compared to the same system after the polymeric layers were removed. In this way, it has been shown that the inhibitor loading in the polymer layers effectively contributes to reducing the corrosion rates at the cut edge, thus helping to extend the useful life of the sacrificial galvanized layer bonded directly to the steel matrix. Additionally, these two probe configurations can be integrated into a multi-electrode tip for potentiometric operation to simultaneously monitor localized changes in pH values and metal ion dissolution in a single scan. Spatial and temporal distributions were further investigated using different rastering procedures, and the potential of constructing pseudomaps for 2D-imaging is described
Improved potentiometric SECM imaging of galvanic corrosion reactions
The galvanic corrosion of Zn-Cu systems has been monitored in situ using scanning electrochemical microscopy in the potentiometric mode. Here, the initial studies performed using double-barrel microelectrodes for the simultaneous detection of local pH and Zn ion concentration changes in single lines scans, have been extended to the obtention of 2-D maps of Cu2+ and Zn2+ ions. The construction and calibration of a novel Cu2+ ion selective microelectrode is reported. New scanning algorithms and data evaluation tools have been explored for faster acquisition rates than those limited by the time constants associated to potentiometric response