547 research outputs found
A Novel Framework for Online Amnesic Trajectory Compression in Resource-constrained Environments
State-of-the-art trajectory compression methods usually involve high
space-time complexity or yield unsatisfactory compression rates, leading to
rapid exhaustion of memory, computation, storage and energy resources. Their
ability is commonly limited when operating in a resource-constrained
environment especially when the data volume (even when compressed) far exceeds
the storage limit. Hence we propose a novel online framework for error-bounded
trajectory compression and ageing called the Amnesic Bounded Quadrant System
(ABQS), whose core is the Bounded Quadrant System (BQS) algorithm family that
includes a normal version (BQS), Fast version (FBQS), and a Progressive version
(PBQS). ABQS intelligently manages a given storage and compresses the
trajectories with different error tolerances subject to their ages. In the
experiments, we conduct comprehensive evaluations for the BQS algorithm family
and the ABQS framework. Using empirical GPS traces from flying foxes and cars,
and synthetic data from simulation, we demonstrate the effectiveness of the
standalone BQS algorithms in significantly reducing the time and space
complexity of trajectory compression, while greatly improving the compression
rates of the state-of-the-art algorithms (up to 45%). We also show that the
operational time of the target resource-constrained hardware platform can be
prolonged by up to 41%. We then verify that with ABQS, given data volumes that
are far greater than storage space, ABQS is able to achieve 15 to 400 times
smaller errors than the baselines. We also show that the algorithm is robust to
extreme trajectory shapes.Comment: arXiv admin note: substantial text overlap with arXiv:1412.032
Optimal L\'{e}vy-flight foraging in a finite landscape
We present a simple model to study L\'{e}vy-flight foraging in a finite
landscape with countable targets. In our approach, foraging is a step-based
exploratory random search process with a power-law step-size distribution . We find that, when the termination is regulated by a finite
number of steps , the optimum value of that maximises the foraging
efficiency can vary substantially in the interval , depending on
the landscape features (landscape size and number of targets). We further
demonstrate that subjective returning can be another significant factor that
affects the foraging efficiency in such context. Our results suggest that
L\'{e}vy-flight foraging may arise through an interaction between the
environmental context and the termination of exploitation, and particularly
that the number of steps can play an important role in this scenario which is
overlooked by most previous work. Our study not only provides a new perspective
on L\'{e}vy-flight foraging, but also opens new avenues for investigating the
interaction between foraging dynamics and environment as well as offers a
realistic framework for analysing animal movement patterns from empirical data.Comment: 25 pages, 6 figure
Psyplot: Interactive data analysis and visualization with Python
The development, usage and analysis of climate models often requires the visualization of the data. This
visualization should ideally be nice looking, simple in application, fast, easy reproducible and flexible. There
exist a wide range of software tools to visualize model data which however often lack in their ability of being
(easy) scriptable, have low flexibility or simply are far too complex for a quick look into the data. Therefore, we
developed the open-source visualization framework psyplot that aims to cover the visualization in the daily work
of earth system scientists working with data of the climate system. It is build (mainly) upon the python packages
matplotlib, cartopy and xarray and integrates the visualization process into data analysis. This data can either be
stored in a NetCDF, GeoTIFF, or any other format that is handled by the xarray package. Due to its interactive
nature however, it may also be used with data that is currently processed and not already stored on the hard disk.
Visualizations of rastered data on the glob are supported for rectangular grids (following or not following the CF
Conventions) or on a triangular grid (following the CF Conventions (like the earth system model ICON) or the
unstructured grid conventions (UGRID)). Furthermore, the package visualizes scalar and vector fields, enables
to easily manage and format multiple plots at the same time. Psyplot can either be used with only a few lines of
code from the command line in an interactive python session, via python scripts or from through a graphical user
interface (GUI). Finally, the framework developed in this package enables a very flexible configuration, an easy
integration into other scripts using matplotlib
Efficient Branch-and-Bound Algorithms for Finding Triangle-Constrained 2-Clubs
In the Vertex Triangle 2-Club problem, we are given an undirected graph
and aim to find a maximum-vertex subgraph of that has diameter at most 2
and in which every vertex is contained in at least triangles in the
subgraph. So far, the only algorithm for solving Vertex Triangle 2-Club relies
on an ILP formulation [Almeida and Br\'as, Comput. Oper. Res. 2019]. In this
work, we develop a combinatorial branch-and-bound algorithm that, coupled with
a set of data reduction rules, outperforms the existing implementation and is
able to find optimal solutions on sparse real-world graphs with more than
100,000 vertices in a few minutes. We also extend our algorithm to the Edge
Triangle 2-Club problem where the triangle constraint is imposed on all edges
of the subgraph
Transseptal puncture without fluoroscopy using a radiofrequency needle: A case series
Background: The non-fluoroscopy approach with the use of a three-dimensional (3D) navigation system is increasingly recognized as a future technology in the treatment of arrhythmias. However, there are a limited number of articles published concerning transseptal puncture without the use of fluoroscopy.Methods: Presented in this paper is the first series of patients (n = 10) that have undergone transseptal puncture without the use of fluoroscopy under transesophageal echocardiography control using a radiofrequency transseptal needle and a 3D navigation system.Results: All patients were treated without complications. In 6 patients, re-pulmonary vein isolation was performed. In 5 cases, linear ablation of the left atrium for treatment of left atrial macro re-entry tachycardia was provided. In 2 patients, focal atrial tachycardia was treated, 1 patient underwent cavo tricuspidal isthmus (CTI) ablation and 1 patient, re-CTI ablation. The ablation of complex fragmented atrial electrograms was done in 2 patients. In 1 case, right atrial macro re-entry tachycardia was treated.Conclusions: Transseptal puncture without using fluoroscopy is safe and effective when using a radiofrequency needle, a 3D navigation system and transesophageal echocardiograph
Mass balance and area changes of glaciers in the Cordillera Real and Tres Cruces, Bolivia, between 2000 and 2016
Climate change has led to a significant shrinkage of glaciers in the Tropical Andes during the last decades. Recent multi-temporal quantifications of ice mass loss at mountain range to regional scale are missing. However, this is fundamental information for future water resource planning and glacier change projections. In this study, we measure temporally consistent glacier area changes and geodetic mass balances throughout the Bolivian Cordillera Real and Tres Cruces based on multi-sensor remote-sensing data. By analyzing multi-spectral satellite images and interferometric SAR data, a glacier recession of 81 ± 18 km2 (29%; 5.1 ± 1.1 km2 a−1), a geodetic mass balance of −403 ± 78 kg m−2 a−1 and a total ice mass loss of 1.8 ± 0.5 Gt is derived for 2000–2016. In the period 2013–2016, ice mass loss was 21% above the average rate. A retreat rate of 15 ± 5 km2 a−1 and a mass budget of −487 ± 349 kg m−2 a−1 are found in this more recent period. These higher change rates can be attributed to the strong El Niño event in 2015/16. The analyses of individual glacier changes and topographic variables confirmed the dependency of the mass budget and glacier recession on glacier aspect and median elevation
Changes of the tropical glaciers throughout Peru between 2000 and 2016 – mass balance and area fluctuations
Glaciers in tropical regions are very sensitive to climatic variations and thus strongly affected by climate change. The majority of the tropical glaciers worldwide are located in the Peruvian Andes, which have shown significant ice loss in the last century. Here, we present the first multi-temporal, region-wide survey of geodetic mass balances and glacier area fluctuations throughout Peru covering the period 2000–2016. Glacier extents are derived from Landsat imagery by performing automatic glacier delineation based on a combination of the NDSI and band ratio method and final manual inspection and correction. The mapping of debris-covered glacier extents is supported by synthetic aperture radar (SAR) coherence information. A total glacier area loss of km2 (−29 %, −34.3 km2 a−1) is obtained for the study period. Using interferometric satellite SAR acquisitions, bi-temporal geodetic mass balances are derived. An average specific mass balance of kg m−2 a−1 is found throughout Peru for the period 2000–2016. However, there are strong regional and temporal differences in the mass budgets ranging from 45±97 to kg m−2 a−1. The ice loss increased towards the end of the observation period. Between 2013 and 2016, a retreat of the glacierized area of km2 (−16 %, −101.9 km2 a−1) is mapped and the average mass budget amounts to kg m−2 a−1. The glacier changes revealed can be attributed to changes in the climatic settings in the study region, derived from ERA-Interim reanalysis data and the Oceanic Nino Index. The intense El Niño activities in 2015/16 are most likely the trigger for the increased change rates in the time interval 2013–2016. Our observations provide fundamental information on the current dramatic glacier changes for local authorities and for the calibration and validation of glacier change projections
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