438,875 research outputs found
Mapping Chestnut Stands Using Bi-Temporal VHR Data
This study analyzes the potential of very high resolution (VHR) remote sensing images and extended morphological profiles for mapping Chestnut stands on Tenerife Island (Canary Islands, Spain). Regarding their relevance for ecosystem services in the region (cultural and provisioning services) the public sector demand up-to-date information on chestnut and a simple straight-forward approach is presented in this study. We used two VHR WorldView images (March and May 2015) to cover different phenological phases. Moreover, we included spatial information in the classification process by extended morphological profiles (EMPs). Random forest is used for the classification process and we analyzed the impact of the bi-temporal information as well as of the spatial information on the classification accuracies. The detailed accuracy assessment clearly reveals the benefit of bi-temporal VHR WorldView images and spatial information, derived by EMPs, in terms of the mapping accuracy. The bi-temporal classification outperforms or at least performs equally well when compared to the classification accuracies achieved by the mono-temporal data. The inclusion of spatial information by EMPs further increases the classification accuracy by 5% and reduces the quantity and allocation disagreements on the final map. Overall the new proposed classification strategy proves useful for mapping chestnut stands in a heterogeneous and complex landscape, such as the municipality of La Orotava, Tenerife
Extracting Additional Information From Biotic Index Samples
Macroinvertebrates were collected from a small midwestern stream over a 3-year period as part of a non-point source pollution study. Temporal and spatial variability in standard biotic index values (BIs) were computed and compared with variability expressed by a series of additional community measurements, including the mean tolerance value of all taxa present in a sample, irrespective of the numerical abundance of individual taxa. The mean tolerance value exhibited lower spatial and temporal variability than the standard BI; therefore, mean tolerance values may be useful in estimating a stream\u27s long-term ambient water quality and its recovery potential. Computations of additional BI metrics are easily accomplished with no additional lab work required, and comparisons of mean tolerance values with standard BIs should aid investigators in interpreting changes in water quality
Competition of coarsening and shredding of clusters in a driven diffusive lattice gas
We investigate a driven diffusive lattice gas model with two oppositely
moving species of particles. The model is motivated by bi-directional traffic
of ants on a pre-existing trail. A third species, corresponding to pheromones
used by the ants for communication, is not conserved and mediates interactions
between the particles. Here we study the spatio-temporal organization of the
particles. In the uni-directional variant of this model it is known to be
determined by the formation and coarsening of ``loose clusters''. For our
bi-directional model, we show that the interaction of oppositely moving
clusters is essential. In the late stages of evolution the cluster size
oscillates because of a competition between their `shredding' during encounters
with oppositely moving counterparts and subsequent "coarsening" during
collision-free evolution. We also establish a nontrivial dependence of the
spatio-temporal organization on the system size
Capturing pattern bi-stability dynamics in delay-coupled swarms
Swarms of large numbers of agents appear in many biological and engineering
fields. Dynamic bi-stability of co-existing spatio-temporal patterns has been
observed in many models of large population swarms. However, many reduced
models for analysis, such as mean-field (MF), do not capture the bifurcation
structure of bi-stable behavior. Here, we develop a new model for the dynamics
of a large population swarm with delayed coupling. The additional physics
predicts how individual particle dynamics affects the motion of the entire
swarm. Specifically, (1) we correct the center of mass propulsion physics
accounting for the particles velocity distribution; (2) we show that the model
we develop is able to capture the pattern bi-stability displayed by the full
swarm model.Comment: 6 pages 4 figure
Dispersion in time and space: what propagating optical pulses in time (& not space) forces us to confront
I derive a temporally propagated uni-directional optical pulse equation valid
in the few cycle limit. Temporal propagation is advantageous because it
naturally preserves causality, unlike the competing spatially propagated
models. The exact coupled bi-directional equations that this approach generates
can be efficiently approximated down to a uni-directional form in cases where
an optical pulse changes little over one optical cycle. They also permit a
direct term-to-term comparison of the exact bi-directional theory with its
corresponding approximate uni-directional theory. Notably, temporal propagation
handles dispersion in a different way, and this difference serves to highlight
existing approximations inherent in spatially propagated treatments of
dispersion. Accordingly, I emphasise the need for future work in clarifying the
limitations of the dispersion conversion required by these types of approaches;
since the only alternative in the few cycle limit may be to resort to the much
more computationally intensive full Maxwell equation solvers.Comment: v3: updates and clarifications. arXiv admin note: text overlap with
arXiv:0810.568
Spatial and Temporal Hadron Correlators below and above the Chiral Phase Transition
Hadronic correlation functions at finite temperature in QCD, with four
flavours of dynamical quarks, have been analyzed both above and below the
chiral symmetry restoration temperature. We have used both point and extended
sources for spatial as well as temporal correlators. The effect of periodic
temporal boundary conditions for the valence quarks on the spatial meson
correlators has also been investigated. All our results are consistent with the
existence of individual quarks at high temperatures. A measurement of the
residual interaction between the quarks is presented.Comment: 19 pages HLRZ 54/93, BI-TP 93/76, TIFR/TH/94-1
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