2,677 research outputs found
Investigation on roof segmentation for 3D building reconstruction from aerial LIDAR point clouds
Three-dimensional (3D) reconstruction techniques are increasingly used to obtain 3D representations of buildings due to the broad range of applications for 3D city models related to sustainability, efficiency and resilience (i.e., energy demand estimation, estimation of the propagation of noise in an urban environment, routing and accessibility, flood or seismic damage assessment). With advancements in airborne laser scanning (ALS), 3D modeling of urban topography has increased its potential to automatize extraction of the characteristics of individual buildings. In 3D building modeling from light detection and ranging (LIDAR) point clouds, one major challenging issue is how to efficiently and accurately segment building regions and extract rooftop features. This study aims to present an investigation and critical comparison of two different fully automatic roof segmentation approaches for 3D building reconstruction. In particular, the paper presents and compares a cluster-based roof segmentation approach that uses (a) a fuzzy c-means clustering method refined through a density clustering and connectivity analysis, and (b) a region growing segmentation approach combined with random sample consensus (RANSAC) method. In addition, a robust 2.5D dual contouring method is utilized to deliver watertight 3D building modeling from the results of each proposed segmentation approach. The benchmark LIDAR point clouds and related reference data (generated by stereo plotting) of 58 buildings over downtown Toronto (Canada), made available to the scientific community by the International Society for Photogrammetry and Remote Sensing (ISPRS), have been used to evaluate the quality of the two proposed segmentation approaches by analysing the geometrical accuracy of the roof polygons. Moreover, the results of both approaches have been evaluated under different operating conditions against the real measurements (based on archive documentation and celerimetric surveys realized by a total station system) of a complex building located in the historical center of Matera (UNESCO world heritage site in southern Italy) that has been manually reconstructed in 3D via traditional Building Information Modeling (BIM) technique. The results demonstrate that both methods reach good performance metrics in terms of geometry accuracy. However, approach (b), based on region growing segmentation, exhibited slightly better performance but required greater computational time than the clustering-based approach
A Novel Predictive Tool in Nanoengineering: Straightforward Estimation of Superconformal Filling Efficiency
It is shown that the superconformal filling (SCF) efficiency
() of nano-scale cavities can be rationalized in terms of
relevant physical and geometric parameters. Based on extensive numerical
simulations and using the dynamic scaling theory of interface growth, it is
concluded that the relevant quantity for the evaluation of is
the so-called "physical" aspect ratio , where
() is the roughness (growth) exponent that governs the dynamic
evolution of the system and () is the typical depth (width) of the
cavity. The theoretical predictions are in excellent agreement with recently
reported experimental data for the SCF of electrodeposited copper and
chemically deposited silver in confined geometries, thus giving the basis of a
new tool to manage nanoengineering-related problems not completely resolved so
far.Comment: 3 pages, 2 figure
Numerical study of a first-order irreversible phase transition in a CO+NO catalyzed reaction model
The first-order irreversible phase transitions (IPT) of the Yaldran-Khan
model (Yaldran-Khan, J. Catal. 131, 369, 1991) for the CO+NO reaction is
studied using the constant coverage (CC) ensemble and performing epidemic
simulations. The CC method allows the study of hysteretic effects close to
coexistence as well as the location of both the upper spinodal point and the
coexistence point. Epidemic studies show that at coexistence the number of
active sites decreases according to a (short-time) power law followed by a
(long-time) exponential decay. It is concluded that first-order IPT's share
many characteristic of their reversible counterparts, such as the development
of short ranged correlations, hysteretic effects, metastabilities, etc.Comment: 17 pages, 10 figure
Critical behavior of a non-equilibrium interacting particle system driven by an oscillatory field
First- and second-order temperature driven transitions are studied, in a
lattice gas driven by an oscillatory field. The short time dynamics study
provides upper and lower bounds for the first-order transition points obtained
using standard simulations. The difference between upper and lower bounds is a
measure for the strength of the first-order transition and becomes negligible
small for densities close to one half. In addition, we give strong evidence on
the existence of multicritical points and a critical temperature gap, the
latter induced by the anisotropy introduced by the driving field.Comment: 12 pages, 4 figures; to appear in Europhys. Let
Geospatial methods and tools for natural risk management and communications
In the last decade, real-time access to data and the use of high-resolution spatial information have provided scientists and engineers with valuable information to help them understand risk. At the same time, there has been a rapid growth of novel and cutting-edge information and communication technologies for the collection, analysis and dissemination of data, re-inventing the way in which risk management is carried out throughout its cycle (risk identification and reduction, preparedness, disaster relief and recovery). The applications of those geospatial technologies are expected to enable better mitigation of, and adaptation to, the disastrous impact of natural hazards. The description of risks may particularly benefit from the integrated use of new algorithms and monitoring techniques. The ability of new tools to carry out intensive analyses over huge datasets makes it possible to perform future risk assessments, keeping abreast of temporal and spatial changes in hazard, exposure, and vulnerability. The present special issue aims to describe the state-of-the-art of natural risk assessment, management, and communication using new geospatial models and Earth Observation (EO)architecture. More specifically, we have collected a number of contributions dealing with: (1) applications of EO data and machine learning techniques for hazard, vulnerability and risk mapping; (2) natural hazards monitoring and forecasting geospatial systems; (3) modeling of spatiotemporal resource optimization for emergency management in the post-disaster phase; and (4) development of tools and platforms for risk projection assessment and communication of inherent uncertainties
An unified timing and spectral model for the Anomalous X-ray Pulsars XTE J1810-197 and CXOU J164710.2-455216
Anomalous X-ray pulsars (AXPs) and soft gamma repeaters (SGRs) are two small
classes of X-ray sources strongly suspected to host a magnetar, i.e. an
ultra-magnetized neutron star with $B\approx 10^14-10^15 G. Many SGRs/AXPs are
known to be variable, and recently the existence of genuinely "transient"
magnetars was discovered. Here we present a comprehensive study of the pulse
profile and spectral evolution of the two transient AXPs (TAXPs) XTE J1810-197
and CXOU J164710.2-455216. Our analysis was carried out in the framework of the
twisted magnetosphere model for magnetar emission. Starting from 3D Monte Carlo
simulations of the emerging spectrum, we produced a large database of synthetic
pulse profiles which was fitted to observed lightcurves in different spectral
bands and at different epochs. This allowed us to derive the physical
parameters of the model and their evolution with time, together with the
geometry of the two sources, i.e. the inclination of the line-of-sight and of
the magnetic axis with respect to the rotation axis. We then fitted the
(phase-averaged) spectra of the two TAXPs at different epochs using a model
similar to that used to calculate the pulse profiles ntzang in XSPEC) freezing
all parameters to the values obtained from the timing analysis, and leaving
only the normalization free to vary. This provided acceptable fits to
XMM-Newton data in all the observations we analyzed. Our results support a
picture in which a limited portion of the star surface close to one of the
magnetic poles is heated at the outburst onset. The subsequent evolution is
driven both by the cooling/varying size of the heated cap and by a progressive
untwisting of the magnetosphere.Comment: 15 pages, 12 figures, accepted for publication in Ap
Conchoidal transform of two plane curves
The conchoid of a plane curve is constructed using a fixed circle in
the affine plane. We generalize the classical definition so that we obtain a
conchoid from any pair of curves and in the projective plane. We
present two definitions, one purely algebraic through resultants and a more
geometric one using an incidence correspondence in \PP^2 \times \PP^2. We
prove, among other things, that the conchoid of a generic curve of fixed degree
is irreducible, we determine its singularities and give a formula for its
degree and genus. In the final section we return to the classical case: for any
given curve we give a criterion for its conchoid to be irreducible and we
give a procedure to determine when a curve is the conchoid of another.Comment: 18 pages Revised version: slight title change, improved exposition,
fixed proof of Theorem 5.3 Accepted for publication in Appl. Algebra Eng.,
Commun. Comput
Advanced radar absorbing ceramic-based materials for multifunctional applications in space environment
In this review, some results of the experimental activity carried out by the authors on advanced composite materials for space applications are reported. Composites are widely employed in the aerospace industry thanks to their lightweight and advanced thermo-mechanical and electrical properties. A critical issue to tackle using engineered materials for space activities is providing two or more specific functionalities by means of single items/components. In this scenario, carbon-based composites are believed to be ideal candidates for the forthcoming development of aerospace research and space missions, since a widespread variety of multi-functional structures are allowed by employing these materials. The research results described here suggest that hybrid ceramic/polymeric structures could be employed as spacecraft-specific subsystems in order to ensure extreme temperature withstanding and electromagnetic shielding behavior simultaneously. The morphological and thermo-mechanical analysis of carbon/carbon (C/C) three-dimensional (3D) shell prototypes is reported; then, the microwave characterization of multilayered carbon-filled micro-/nano-composite panels is described. Finally, the possibility of combining the C/C bulk with a carbon-reinforced skin in a synergic arrangement is discussed, with the aid of numerical and experimental analyses
Comment on Performance of Different Synchronization Measures in Real Data: A Case Study on Electroencephalographic Signals
Quian Quiroga [Phys. Rev. E 65, 041903 (2002)] reported a similar performance of several linear and nonlinear measures of synchronization when applied to the rat electrocorticogram (ECoG). However, they found that the mutual information measure did not produce robust estimates of synchronization when compared to other measures. We reexamined their data using a histogram method with adaptive partitioning and found the mutual information to be a useful measure of regional ECoG interdependence
Pituitary Adenylate Cyclase-Activating Polypeptide Orchestrates Neuronal Regulation Of The Astrocytic Glutamate-Releasing Mechanism System x\u3csub\u3ec\u3c/sub\u3e\u3csup\u3e−\u3c/sup\u3e
Glutamate signaling is achieved by an elaborate network involving neurons and astrocytes. Hence, it is critical to better understand how neurons and astrocytes interact to coordinate the cellular regulation of glutamate signaling. In these studies, we used rat cortical cell cultures to examine whether neurons or releasable neuronal factors were capable of regulating system xc-(Sxc), a glutamate-releasing mechanism that is expressed primarily by astrocytes and has been shown to regulate synaptic transmission. We found that astrocytes cultured with neurons or exposed to neuronal-conditioned media displayed significantly higher levels of Sxc activity. Next, we demonstrated that the pituitary adenylate cyclase-activating polypeptide (PACAP) may be a neuronal factor capable of regulating astrocytes. In support, we found that PACAP expression was restricted to neurons, and that PACAP receptors were expressed in astro-cytes. Interestingly, blockade of PACAP receptors in cultures comprised of astrocytes and neurons significantly decreased Sxc activity to the level observed in purified astrocytes, whereas application of PACAP to purified astrocytes increased Sxc activity to the level observed in cultures comprised of neurons and astrocytes. Collectively, these data reveal that neurons coordinate the actions of glutamate-related mechanisms expressed by astrocytes, such as Sxc, a process that likely involves PACAP
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