Mutual Visibility Research Articles

Three-dimensional pore-scale numerical simulation of methane-air combustion in inert porous media under the conditions of upstream and downstream combustion wave propagation through the media

Abstracts Porous media combustion of lean and ultra-rich methane-air mixtures was numerically studied using the approach when the process is simulated at the pore scale with explicit consideration of the three-dimensional porous structure and interstitial flow with thermal interaction between fluid and solid phases including the detailed chemical kinetics model and solid-to-solid radiation. The geometrical model of the packed bed was generated synthetically by simulation of particles falling under gravity force. A novel workflow for a randomly packed bed meshing at the pore scale was used to avoid the point contact problem. The results demonstrate that the model predicts a thermal nonequilibrium and heat recuperation mechanism in the combustion wave in the low-velocity regime correctly. The inhomogeneous structure of the porous media leads to large spatial variation of the process parameters such as velocity and temperature. It was shown that radiation makes a significant contribution to heat transfer in the region of a large temperature gradient. Radiative heat flux is transferred through the bed via radiation layer-by-layer due to restricted mutual visibility of the opaque particles. The mixture composition has a significant impact on the heat release rate and wave velocity and direction as well as thermal flame thickness and exhaust gas composition. At the macro scale, the mode of combustion wave propagation is quasi-steady whereas at the pore scale with little time steps the unsteady effects can be observed. Different subregions of the flame front propagate with not equal velocity, stand or accelerate depending on the local flow and porous matrix inhomogeneity. For the lean mixture the oscillatory regime of propagation was detected and analyzed.

Triadic time series motifs

We introduce the concept of time series motifs for time series analysis. Time series motifs consider not only the spatial information of mutual visibility but also the temporal information of relative magnitude between the data points. We study the profiles of the six triadic time series motifs. The six motif occurrence frequencies are derived for uncorrelated time series, which are approximately linear functions of the length of the time series. The corresponding motif profile thus converges to a constant vector. These analytical results have been verified by numerical simulations. For fractional Gaussian noises, numerical simulations unveil the nonlinear dependence of motif occurrence frequencies on the Hurst exponent. Applications of the time series motif analysis uncover that the motif occurrence frequency distributions are able to capture the different dynamics in the heartbeat rates of healthy subjects, congestive heart failure (CHF) subjects, and atrial fibrillation (AF) subjects and in the price fluctuations of bullish and bearish markets. Our method shows its potential power to classify different types of time series and test the time irreversibility of time series.

A Distinctly Rhetorical Space;Eusynoptosand the Greek Council-House

A Distinctly Rhetorical Space;<i>Eusynoptos</i>and the Greek Council-House

КОНЦЕПТУАЛЬНА СХЕМА СИСТЕМИ МОДЕЛЮВАННЯ ТАКТИЧНОЇ ОБСТАНОВКИ НА БАЗІ ГЕОІНФОРМАЦІЙНОЇ СИСТЕМИ

The analysis of the directions of geoinformation systems use in the military sphere indicates the need to develop domestic simulation systems for combat operations simulation and the creation of a system for a tactical military situation simulation using geoinformation systems for the Armed Forces of Ukraine. The article proposes a conceptual scheme of a system of simulation of a tactical situation on the basis of GIS technologies, which is proposed to be used for planning intelligence and special operations, the definition of objectives, the analysis of terrain and the mutual visibility of opposite sides, management of combat. Keywords: combat simulation system, geoinformation system, geospatial simulations.

Real-time global illumination by precomputed local reconstruction from sparse radiance probes

We present a direct-to-indirect transport technique that enables accurate real-time rendering of indirect illumination in mostly static scenes of complexity on par with modern games while supporting fully dynamic lights, cameras and diffuse surface materials. Our key contribution is an algorithm for reconstructing the incident radiance field from a sparse set of local samples --- radiance probes --- by incorporating mutual visibility into the reconstruction filter. To compute global illumination, we factorize the direct-to-indirect transport operator into global and local parts, sample the global transport with sparse radiance probes at real-time, and use the sampled radiance field as input to our precomputed local reconstruction operator to obtain indirect radiance. In contrast to previous methods aiming to encode the global direct-to-indirect transport operator, our precomputed data is local in the sense that it needs no long-range interactions between probes and receivers, and every receiver depends only on a small, constant number of nearby radiance probes, aiding compression, storage, and iterative workflows. While not as accurate, we demonstrate that our method can also be used for rendering indirect illumination on glossy surfaces, and approximating global illumination in scenes with large-scale dynamic geometry.

Three-dimensional visibility graph analysis and its application

Graph-based visibility analysis, developed from space syntax and social network theory, embraces mutual visibility between locations in a spatial system. It helps designers and researchers to decode spatial cognition and behavior, but methodological constraints limit its application to two-dimensional floor plans. In this study, we propose a new visibility graph analysis that can be used in three-dimensional built environments, such as multilevel atrium buildings or urban environments with canopies or overpass bridges. Furthermore, we draw a distinction between a generic visibility graph and a targeted visibility graph. In the former, an occupiable location is considered as both the origin and target of visibility lines. In the latter, we further take into account the visible space or specific targets in a system. Visible locations are spaces people can see but cannot necessarily physically occupy. With this differentiation, the visibility graph system is more amenable to new applications in three-dimensional architectural and urban design while retaining a mapping back to the original two-dimensional visibility graph method through the generic visibility graph. Four examples illustrate the application of the proposed visibility graph analysis in complex three-dimensional building and urban environments.

Применение электронного тахеометра для обследования конструкций металлических башен сотовой связи

The availability and stability of cellular communication can be achieved with areas coverage by base stations. Base station cellular (metal tower) is a complex and massive engineering structure which is usually installed on different buildings. Weight of tower with equipment exceeds 1000 kg. For security purposes of objects with installed cellular base stations you need constantly determine the operating characteristics of towers. One of the important characteristics is the deviation of the tower from the vertical. In the regulations for the operation of towers various ways of determining the deviation of the tower from the vertical are discussed. In the instructions it is proposed to determine the deviation of the tower based on observations with three or four starting points, between which there must be mutual visibility. After all dimensions processing we will receive a deviation of the tower from the vertical. The paper proposes a more simple method of determining deviations of the tower from the vertical with the use of electronic total station. The software of the instrument will improve the quality of the work. Measurements are performed from one point in topocentric coordinates system. Independent observations from a different point improve accuracy and serve as a control. Error of the results does not exceed 5–7 mm.

Sequentiality, Mutual Visibility, and Behavioral Matching: Body Sway and Pitch Register During Joint Decision Making

ABSTRACTWe studied behavioral matching during joint decision making. Drawing on motion-capture and voice data from 12 dyads, we analyzed body-sway and pitch-register matching during sequential transitions and continuations, with and without mutual visibility. Body sway was matched most strongly during sequential transitions in the conditions of mutual visibility. Pitch-register matching was higher during sequential transitions than continuations only when the participants could not see each other. These results suggest that both body sway and pitch register are used to manage sequential transitions, while mutual visibility influences the relative weights of these two resources. The conversational data are in Finnish with English translation.

Mutual visibility by luminous robots without collisions

We consider the Mutual Visibility problem for anonymous dimensionless robots with obstructed visibility moving in a plane: starting from distinct locations, the robots must reach, without colliding, a configuration where no three of them are collinear. We study this problem in the luminous robots model, in which each robot has a visible light that can assume colors from a fixed set.Among other results, we prove that Mutual Visibility can be solved in SSynch with 2 colors and in ASynch with 3 colors. If an adversary can interrupt and stop a robot moving to its computed destination, Mutual Visibility is still solvable in SSynch with 3 colors and, if the robots agree on the direction of one axis, also in ASynch.As a byproduct, we provide the first obstructed-visibility solutions to two classical problems for oblivious robots: collision-less convergence to a point (also known as near-gathering) and circle formation.

Learning Mutual Visibility Relationship for Pedestrian Detection with a Deep Model

Detecting pedestrians in cluttered scenes is a challenging problem in computer vision. The difficulty is added when several pedestrians overlap in images and occlude each other. We observe, however...

3D Beam Tracing Based on Visibility Lookup for Interactive Acoustic Modeling

We present a method for accelerating the computation of specular reflections in complex 3D enclosures, based on acoustic beam tracing. Our method constructs the beam tree on the fly through an iterative lookup process of a precomputed data structure that collects the information on the exact mutual visibility among all reflectors in the environment (region-to-region visibility). This information is encoded in the form of visibility regions that are conveniently represented in the space of acoustic rays using the Plücker coordinates. During the beam tracing phase, the visibility of the environment from the source position (the beam tree) is evaluated by traversing the precomputed visibility data structure and testing the presence of beams inside the visibility regions. The Plücker parameterization simplifies this procedure and reduces its computational burden, as it turns out to be an iterative intersection of linear subspaces. Similarly, during the path determination phase, acoustic paths are found by testing their presence within the nodes of the beam tree data structure. The simulations show that, with an average computation time per beam in the order of a dozen of microseconds, the proposed method can compute a large number of beams at rates suitable for interactive applications with moving sources and receivers.

A Unified Framework for Two-guard Walk Problem

We propose a unified framework to study the walk problem in a polygonal area by two collaborative guards. A walk is conducted by the two mobile guards on the area's boundary. They start at an initial boundary point, move along the boundary, and may possibly meet together again at an ending boundary point. It is required that the two guards maintain their mutual visibility at all times. Depending the geometric properties of the polygonal area, a walk may or may not be possible. In this work, three versions of the problem, namely, general polygon walk, room walk and street walk, are characterized in a unified manner in our framework. One additional merit of our framework is its simplicity. Applications of the walk problem by two guards include military rescue, area exploration, art gallery surveillance, etc.

Maintaining strong mutual visibility of an evader moving over the reduced visibility graph

In this paper, we address the problem of determining whether a mobile robot, called the pursuer, is able to maintain strong mutual visibility (a visibility notion between regions over a convex partition of the environment) of an antagonist agent, called the evader. We frame the problem as a non cooperative game. We consider the case in which the pursuer and the evader move at bounded speed, traveling in a known polygonal environment with or without holes, and in which there are no restrictions as to the distance that might separate the agents. Unlike our previous efforts (Murrieta-Cid et al. in Int J Robot Res 26:233---253, 2007), we give special attention to the combinatorial problem that arises when searching for a solution through visiting several locations in an environment with obstacles. In this paper we take a step further, namely, we assume an antagonistic evader who moves continuously and unpredictably, but with a constraint over its set of admissible motion policies, as the evader moves in the shortest-path roadmap, also called the reduced visibility graph (RVG). The pursuer does not know which among the possible paths over the RVG the evader will choose, but the pursuer is free to move within all the environment. We provide a constructive method to solve the decision problem of determining whether or not the pursuer is able to maintain strong mutual visibility of the evader. This method is based on an algorithm that computes the safe areas (areas that keep evader surveillance) at all times. We prove decidability of this problem, and provide a complexity measure to this evader surveillance game; both contributions hold for any general polygonal environment that might or not contain holes. All our algorithms have been implemented and we show simulation results.

On what happens in gesture when communication is unsuccessful

Previous studies found that repeated references in successful communication are often reduced, not only at the acoustic level, but also in terms of words and manual co-speech gestures. In the present study, we investigated whether repeated references are still reduced in a situation when reduction would not be beneficial for the communicative situation, namely after the speaker receives negative feedback from the addressee. In a director–matcher task (experiment I), we studied gesture rate, as well as the general form of the gestures produced in initial and repeated references. In a separate experiment (experiment II) we studied whether there might (also) be more gradual differences in gesture form between gestures in initial and repeated references, by asking human judges which of two gestures (one from an initial and one from a repeated reference following negative feedback) they considered more precise. In both experiments, mutual visibility was added as a between subjects factor. Results showed that after negative feedback, gesture rate increased in a marginally significant way. With regard to gesture form, we found little evidence for changes in gesture form after negative feedback, except for a marginally significant increase of the number of repeated strokes within a gesture. Lack of mutual visibility only had a significant reducing effect on gesture size, and did not interact with repetition in any way. However, we did find gradual differences in gesture form, with gestures produced after negative feedback being judged as marginally more precise than initial gestures. The results from the present study suggest that in the production of unsuccessful repeated references, a process different from the reduction process as found in previous studies in repeated references takes place, with speakers appearing to put more effort into their gestures after negative feedback, as suggested by the data trending towards an increased gesture rate and towards gestures being judged as more precise after feedback.

Numerical simulation of radiative heat transfer in indoor environments on programmable graphics hardware

The efficient use of energy for heating and cooling of indoor environments requires an accurate prediction and analysis of radiative heat transfer. Therefore it is necessary to use modern computer methods as otherwise the computational costs may become higher than for convective heat transfer, which is known to be a huge computational problem. A key problem in calculations of radiative heat transfer is the problem of mutual visibility arising in the determination of view factors. This is the same challenge that global illumination has to cope with which is one of the fundamental topics in computational graphics. The visibility problem is efficiently solved by modern graphics hardware. Therefore an OpenGL-based algorithm is developed to quickly and accurately calculate view factors for arbitrary, complex geometries. Theoretical and implementation details of the applied methods are given. We demonstrate the advantages of the developed computational method by a virtual test room for a tubular radiator, a heating of a warehouse by ceramic infrared heaters and the heat transfer in a car cabin.

Multi-view visualizations for emergency communities of volunteers

Information and communication technologies might empower emergency communities of volunteers by assisting community participation and improving their capacity to respond to unexpected events. However, designing technology for such purpose places unique visualization challenges that go beyond the current state of research on public participation tools and related technologies. Empowering these communities requires developing representations that enable collaborative reflection, promote mutual visibility of volunteers’ efforts and sustain a shared view of the community. Similarly, it is necessary to envision visualizations that facilitate sense making of large, simultaneous and distributed pieces of heterogeneous information with different levels of credibility and priority. Accordingly, this paper identifies and characterizes these challenges to propose a multi-view and multi-abstraction-level visualization approach for emergency communities of volunteers. In particular, it combines time-oriented visualizations, space-filling visualization techniques, interaction mechanisms and coordinated maps to support community participation as well as collaborative and individual sense making. The application of these visualization techniques is discussed through the development of a set of design prototypes.

Choosing the place for the installation of navigation system aerials on the ERS spacecraft body

The paper presents mathematical models, an algorithm and software for the assessment of the relative time spent by navigation satellites (NS) and Earth remote sensing (ERS) satellites under mutual visibility conditions. A method of choosing the place for the installation of navigation system aerials on the spacecraft body is proposed based on the criterion of maximum relative time of mutual visibility no less than a specified number of the NSs.

Reconciling the effects of mutual visibility on gesturing

Fourteen visibility experiments, which compared the overall rate of gesturing when participants could or could not see each other, have produced perfectly contradictory results: Seven found a significantly higher overall gesture rate in the visible condition, and seven found no significant difference. Experiments that used quasi-dialogues in which the addressees’ responses were experimentally constrained (e.g., using a confederate) found a significant difference; the experiments that used free dialogues did not. This review examined three possible explanations and found that (1) the use of quasi-dialogues did not ensure better experimental control, (2) the constrained addressees may have introduced a confound that could account for the significant difference, and (3) although mutual visibility did not affect the overall gesture rate in free dialogues, it significantly increased more specific features of gestures that are useful to addressees. These findings raise several issues about the utility of conventional visibility designs for understanding conversational gestures.

Probabilistic Visibility Evaluation for Direct Illumination

AbstractThe efficient evaluation of visibility in a three‐dimensional scene is a longstanding problem in computer graphics. Visibility evaluations come in many different forms: figuring out what object is visible in a pixel; determining whether a point is visible to a light source; or evaluating the mutual visibility between 2 surface points. This paper provides a new, experimental view on visibility, based on a probabilistic evaluation of the visibility function. Instead of checking the visibility against all possible intervening geometry the visibility between 2 points is now evaluated by testing only a random subset of objects. The result is not a Boolean value that is either 0 or 1, but a numerical value that can even be negative. Because we use the visibility evaluation as part of the integrand in illumination computations, the probabilistic evaluation of visibility becomes part of the Monte Carlo procedure of estimating the illumination integral, and results in an unbiased computation of illumination values in the scene. Moreover, the number of intersections tests for any given ray is decreased, since only a random selection of geometric primitives is tested. Although probabilistic visibility is an experimental and new idea, we present a practical algorithm for direct illumination that uses the probabilistic nature of visibility evaluations.

Does our speech change when we cannot gesture?

Do people speak differently when they cannot use their hands? Previous studies have suggested that speech becomes less fluent and more monotonous when speakers cannot gesture, but the evidence for this claim remains inconclusive. The present study attempts to find support for this claim in a production experiment in which speakers had to give addressees instructions on how to tie a tie; half of the participants had to perform this task while sitting on their hands. Other factors that influence the ease of communication, such as mutual visibility and previous experience, were also taken into account. No evidence was found for the claim that the inability to gesture affects speech fluency or monotony. An additional perception task showed that people were also not able to hear whether someone gestures or not.