Um die anderen Arten von Veröffentlichungen zu diesem Thema anzuzeigen, folgen Sie diesem Link: Geometric observers.
Zeitschriftenartikel zum Thema „Geometric observers“
Geben Sie eine Quelle nach APA, MLA, Chicago, Harvard und anderen Zitierweisen an
Machen Sie sich mit Top-50 Zeitschriftenartikel für die Forschung zum Thema "Geometric observers" bekannt.
Neben jedem Werk im Literaturverzeichnis ist die Option "Zur Bibliographie hinzufügen" verfügbar. Nutzen Sie sie, wird Ihre bibliographische Angabe des gewählten Werkes nach der nötigen Zitierweise (APA, MLA, Harvard, Chicago, Vancouver usw.) automatisch gestaltet.
Sie können auch den vollen Text der wissenschaftlichen Publikation im PDF-Format herunterladen und eine Online-Annotation der Arbeit lesen, wenn die relevanten Parameter in den Metadaten verfügbar sind.
Sehen Sie die Zeitschriftenartikel für verschiedene Spezialgebieten durch und erstellen Sie Ihre Bibliographie auf korrekte Weise.
1
Martínez-García, Edgar Alonso, Joaquín Rivero-Juárez, Luz Abril Torres-Méndez und Jorge Enrique Rodas-Osollo. „Divergent trinocular vision observers design for extended Kalman filter robot state estimation“. Proceedings of the Institution of Mechanical Engineers, Part I: Journal of Systems and Control Engineering 233, Nr. 5 (24.09.2018): 524–47. http://dx.doi.org/10.1177/0959651818800908.
Der volle Inhalt der QuelleAnnotation:
Here, we report the design of two deterministic observers that exploit the capabilities of a home-made divergent trinocular visual sensor to sense depth data. The three-dimensional key points that the observers can measure are triangulated for visual odometry and estimated by an extended Kalman filter. This work deals with a four-wheel-drive mobile robot with four passive suspensions. The direct and inverse kinematic solutions are deduced and used for the updating and prediction models of the extended Kalman filter as feedback for the robot’s position controller. The state-estimation visual odometry results were compared with the robot’s dead-reckoning kinematics, and both are combined as a recursive position controller. One observer model design is based on the analytical geometric multi-view approach. The other observer model has fundamentals on multi-view lateral optical flow, which was reformulated as nonspatial–temporal and is modeled by an exponential function. This work presents the analytical deductions of the models and formulations. Experimental validation deals with five main aspects: multi-view correction, a geometric observer for range measurement, an optical flow observer for range measurement, dead-reckoning and visual odometry. Furthermore, comparison of positioning includes a four-wheel odometer, deterministic visual observers and the observer–extended Kalman filter, compared with a vision-based global reference localization system.
2
Niethammer, M., P. A. Vela und A. Tannenbaum. „Geometric Observers for Dynamically Evolving Curves“. IEEE Transactions on Pattern Analysis and Machine Intelligence 30, Nr. 6 (Juni 2008): 1093–108. http://dx.doi.org/10.1109/tpami.2008.28.
Der volle Inhalt der Quelle
3
Wang, Yebin, und Kenji Utsunomiya. „From acceleration-based semi-active vibration reduction control to functional observer design“. at - Automatisierungstechnik 66, Nr. 3 (26.03.2018): 234–45. http://dx.doi.org/10.1515/auto-2017-0064.
Der volle Inhalt der QuelleAnnotation:
Abstract This work investigates a functional estimation problem for single input single output linear and nonlinear systems, motivated by its enabling role in acceleration-based semi-active control. Solvability of a linear functional estimation problem is studied from a geometric approach, where the functional dynamics are derived, decomposed, and transformed to expose structural properties. This approach is extended to solve a challenging nonlinear functional observer problem, combining with the exact error linearization. Existence conditions of nonlinear functional observers are established. Simulation verifies existence conditions and demonstrates the effectiveness of the proposed functional observer designs.
4
Lewis, F. L. „Geometric design techniques for observers in singular systems“. Automatica 26, Nr. 2 (März 1990): 411–15. http://dx.doi.org/10.1016/0005-1098(90)90138-8.
Der volle Inhalt der Quelle
5
Silver, Brian, Arturo Tamayo, Edward H. Wong, Bart Demaerschalk, Jose G. Merino und Vladimir Hachinski. „A reliable new method to estimate >1/3 middle cerebral artery infarction on early computed tomography scan“. Stroke 32, suppl_1 (Januar 2001): 325. http://dx.doi.org/10.1161/str.32.suppl_1.325-a.
Der volle Inhalt der QuelleAnnotation:
50 Objectives: To develop a reliable method of estimation of >1/3 involvement of the middle cerebral artery territory (MCAT) on early CT scan. Background: The European Cooperative Acute Stroke Study (ECASS) suggested that > 1/3 involvement of the MCAT on early CT scan was a risk factor for symptomatic intracerebral hemorrhage (SICH) following treatment with tissue plasminogen activator (tPA) for acute ischemic stroke (AIS). There are no published guidelines on how to perform such an evaluation. The ICE method was developed for the purpose of standardizing the approach of infarct size estimation. This method requires the observer of the CT scan to mentally: 1) Idealize the MCAT into an area approximating a trapezoid, 2) Close a geometric figure around the area(s) of hypodensity(ies), and 3) Estimate the ratio of the two geometric figures (C/I). Methods: Five stroke fellows (observers) were tested with 40 CT scans which had been performed within the first few hours of an acute neurological event. Observers were blinded to patient history. They were asked whether to treat the patient on the basis of the CT scan. The decision not to treat was predicated on the presence of hemorrhage or > 1/3 MCAT involvement. Results: Five scans showed evidence of hemorrhage. All observers detected the hemorrhages. The remaining scans were of patients with presumed ischemia. Six scans were thought to show > 1/3 MCAT involvement by all observers. For all scans, median interobserver agreement among 10 paired comparisons was 86% (range 73–93%). Median kappa was 0.72 (range 0.44–0.85, p<0.001). Conclusion: The ICE method has very good interobserver reliability. The method merits further investigation among non-stroke physicians.
6
Perdon, Anna Maria, und Maria Anderlucci. „GEOMETRIC DESIGN OF OBSERVERS FOR LINEAR TIME-DELAY SYSTEMS“. IFAC Proceedings Volumes 39, Nr. 10 (2006): 120–25. http://dx.doi.org/10.3182/20060710-3-it-4901.00021.
Der volle Inhalt der Quelle
7
Majid, H., und H. Abouaïssa. „Comparative Study of a Super-Twisting Sliding Mode Observer and an Extended Kalman Filter for a Freeway Traffic System“. Cybernetics and Information Technologies 15, Nr. 2 (01.06.2015): 141–58. http://dx.doi.org/10.1515/cait-2015-0034.
Der volle Inhalt der QuelleAnnotation:
Abstract Traffic state estimation represents one of the important ingredients for traffic prediction and forecasting. The work presented in this paper deals with the estimation of traffic state variables (density and speed), using the so called Super- Twisting Sliding Mode Observer (STSM). Several numerical simulations, using simulated and real data, show the relevance of the proposed approach. In addition, a comparative study with the Extended Kalman Filter (EKF) is carried-out. The comparison indices concern convergence and stability, dynamic performance and robustness. The design of the two observers is achieved using a nonlinear second order traffic flow model in the same highway traffic and geometric conditions.
8
Fraser, Ian H., und Denis M. Parker. „Visual Parsing and Priority Effects in Temporal Order Judgements of Line Drawn Patterns“. Perception 17, Nr. 4 (August 1988): 437–59. http://dx.doi.org/10.1068/p170437.
Der volle Inhalt der QuelleAnnotation:
Five experiments are reported in which the perception of the order of the components of line drawn patterns presented in rapid temporal sequence on a visual display unit was investigated. In experiments 1 and 2, respectively, a schematic face and an asymmetrical geometric design, and a realistic face and a symmetrical geometric design were each divided into four fragments consisting of outline and three internal features. These fragments were presented to observers in sequences in which the position of the outline in the sequence was systematically varied. Observers reported the perceived order of the fragments. If the order was misperceived the interfragment interval was increased until the sequence was correctly perceived. Analysis of the pattern of perceptual errors and the interfragment presentation interval at which the sequence was correctly perceived indicated that observers tended to perceive the sequence correctly when the outline was presented in first or last position, but had difficulty in doing this when it occupied an intermediate position. This effect was significantly stronger with facial than with geometric patterns. Furthermore, in the case of two face patterns, errors were of a form where observers reported the outline presented in positions two or three as occupying positions one or four respectively. In experiment 3 an identical procedure was used to compare the perception of temporally fragmented normal and inverted faces. The outline position effect was equally strong in both cases. In experiment 4 the relative strength of the tendency to move the outline towards first or final position was assessed by dividing each of two patterns, a face and a house, into three fragments consisting of outline and two groups of internal features. Order perception was significantly better with outline in first or third position, but where it was presented in the intermediate position it was reported as being presented in first position. In experiment 5 the general pattern of results obtained in experiments 1, 2, and 3 was verified with the use of a methodology in which pattern fragment sequences and interfragment intervals were both randomised from trial to trial and the observer's task was to specify the position of the outline in the sequence. Four patterns—a normal face, a face with inverted internal features (INF face), a face outline with irrelevant internal features (IRF face), and a geometric design—were each divided into four fragments consisting of outline and three internal features. Results indicated that for the normal and the INF face, detection of the outline position was significantly better in first and last position, whereas for the other two patterns detection was significantly better in first than in any of the other three positions. It is argued that the results of the five experiments emphasise the special importance of the outline in pattern recognition and support the existence of two processes in visual perception; a high-level parsing process and an outline priority effect. Both processes are probably precognitive in nature.
9
Bukaros, A., A. Herega, V. Sergeiev, T. Obnyavko und K. Konkov. „STATE OBSERVER OF THE COMBAT VEHICLE ELECTRIC DRIVES“. Collection of scientific works of Odesa Military Academy, Nr. 17 (31.08.2022): 116–24. http://dx.doi.org/10.37129/2313-7509.2022.17.116-124.
Der volle Inhalt der QuelleAnnotation:
The paper substantiates the use of adaptive state observers of combat vehicles guiding electric drives instead of imperfect rotation speed sensors of executive motors, as which tachogenerators are traditionally used. The synthesis is carried out, the structure and mathematical description of the Luenberger observer of the direct current executive motor with independent excitation by the modal method are obtained. The performance of the synthesized observer is confirmed by checking the fulfillment of the observability condition. An expression for determining the geometric mean root, which makes it possible to simplify the structure of the observer and to evaluate not only the rotation speed, but also the load torque on the motor shaft is proposed. For definite structure of the observer, expressions for the coefficients of the Luenberger matrix are obtained. The modernized Luenberger observer was studied by simulation in the Matlab/Simulink environment. The parameters of the DC executive motor D-135 of the vertical guidance system of the 9K35 anti-aircraft missile system were used as the initial data of the model. The simulation results with the accepted binomial distribution of the roots of the characteristic polynomial proved the efficiency of the proposed structure of the observer. The estimation of the electric drive coordinates occurred aperiodically, without fluctuations, however, it had a relatively large error due to the underestimated speed of the observer. To eliminate this shortcoming, the distribution of the roots of the characteristic polynomial of the observer according to the Chebyshev linear form was proposed. With this distribution of roots, the performance of the Luenberger observer increased significantly, which limited the error in tracking the coordinates of the electric drive to 4%. The prospects for further research of the proposed method for the synthesis of state observers of the executive motors of the combat vehicles guidance systems are outlined. Keywords: Luenberger observer, executive motor, guidance system, combat vehicle.
10
Estévez, Oscar. „Interindividual Receptor Variability of Normal Colour Observers: Analysis of the 2-Deg Stiles and Burch Data“. Perception 15, Nr. 6 (Dezember 1986): 677–87. http://dx.doi.org/10.1068/p150677.
Der volle Inhalt der QuelleAnnotation:
Examination of the interobserver variability among the ten observers of the 2-deg Stiles and Burch colorimetric study reveals an interesting pattern: the chromaticities of the matches made by different normal subjects fall approximately on straight lines and these lines appear to converge. Because of a geometric relationship that holds between the normal, anomalous, and dichromatic colour spaces, it can be argued that part of the variability must be due to actual differences in the shape or spectral position of the receptor sensitivities of different normal observers.
11
Gharechahi, Razieh, Mohammad Nouri-Zonoz und Alireza Tavanfar. „A tale of two velocities: Threading versus slicing“. International Journal of Geometric Methods in Modern Physics 15, Nr. 03 (20.02.2018): 1850047. http://dx.doi.org/10.1142/s0219887818500470.
Der volle Inhalt der QuelleAnnotation:
One of the important quantities in cosmology and astrophysics is the 3-velocity of an object. Specifically, when the gravitational fields are strong, one should require the employment of general relativity both in its definition and measurement. Looking into the literature for GR-based definitions of 3-velocity, one usually finds different ad hoc definitions applied according to the case under consideration. Here, we introduce and analyze systematically the two principal definitions of 3-velocity assigned to a test particle following the timelike trajectories in stationary spacetimes. These definitions are based on the [Formula: see text] (threading) and [Formula: see text] (slicing) spacetime decomposition formalisms and defined relative to two different sets of observers. After showing that Synge’s definition of spatial distance and 3-velocity is equivalent to those defined in the [Formula: see text] (threading) formalism, we exemplify the differences between these two definitions by calculating them for particles in circular orbits in axially symmetric stationary spacetimes. Illustrating its geometric nature, the relative linear velocity between the corresponding observers is obtained in terms of the spacetime metric components. Circular particle orbits in the Kerr spacetime, as the prototype and the most well known of stationary spacetimes, are examined with respect to these definitions to highlight their observer-dependent nature. We also examine the Kerr-NUT spacetime in which the NUT parameter, contributing to the off-diagonal terms in the metric, is mainly interpreted not as a rotation parameter but as a gravitomagnetic monopole charge. Finally, in a specific astrophysical setup which includes rotating black holes, it is shown how the local velocity of an orbiting star could be related to its spectral line shifts measured by distant observers.
12
Dresp-Langley, Birgitta. „Generic Properties of Curvature Sensing through Vision and Touch“. Computational and Mathematical Methods in Medicine 2013 (2013): 1–7. http://dx.doi.org/10.1155/2013/634168.
Der volle Inhalt der QuelleAnnotation:
Generic properties of curvature representations formed on the basis of vision and touch were examined as a function of mathematical properties of curved objects. Virtual representations of the curves were shown on a computer screen for visual scaling by sighted observers (experiment 1). Their physical counterparts were placed in the two hands of blindfolded and congenitally blind observers for tactile scaling. The psychophysical data show that curvature representations in congenitally blind individuals, who never had any visual experience, and in sighted observers, who rely on vision most of the time, are statistically linked to the same mathematical properties of the curves. The perceived magnitude of object curvature, sensed through either vision or touch, is related by a mathematical power law, with similar exponents for the two sensory modalities, to the aspect ratio of the curves, a scale invariant geometric property. This finding supports biologically motivated models of sensory integration suggesting a universal power law for the adaptive brain control and balance of motor responses to environmental stimuli from any sensory modality.
13
van Paasschen, Jorien, Elisa Zamboni, Francesca Bacci und David Melcher. „Consistent Emotions Elicited by Low-Level Visual Features in Abstract Art“. Art & Perception 2, Nr. 1-2 (2014): 99–118. http://dx.doi.org/10.1163/22134913-00002012.
Der volle Inhalt der QuelleAnnotation:
It is often assumed that works of art have the ability to elicit emotion in their observers. An emotional response to a visual stimulus can occur as early as 120 ms after stimulus onset, before object categorisation can take place. This implies that emotions elicited by an artwork may depend in part on bottom-up processing of its visual features (e.g., shape, colour, composition) and not just on object recognition or understanding of artistic style. We predicted that participants are able to judge the emotion conveyed by an artwork in a manner that is consistent across observers. We tested this hypothesis using abstract paintings; these do not provide any reference to objects or narrative contexts, so that any perceived emotion must stem from basic visual characteristics. Nineteen participants with no background in art rated 340 abstract artworks from different artistic movements on valence and arousal on a Likert scale. An intra-class correlation model showed a high consistency in ratings across observers. Importantly, observers used the whole range of the rating scale. Artworks with a high number of edges (complex) and dark colours were rated as more arousing and more negative compared to paintings containing clear lines, bright colours and geometric shapes. These findings provide evidence that emotions can be captured in a meaningful way by the artist in a set of low-level visual characteristics, and that observers interpret this emotional message in a consistent, uniform manner.
14
BINI, DONATO, CHRISTIAN CHERUBINI, GIANLUCA CRUCIANI und ROBERT T. JANTZEN. „GEOMETRIC TRANSPORT ALONG CIRCULAR ORBITS IN STATIONARY AXISYMMETRIC SPACETIMES“. International Journal of Modern Physics D 13, Nr. 09 (Oktober 2004): 1771–803. http://dx.doi.org/10.1142/s0218271804005237.
Der volle Inhalt der QuelleAnnotation:
Parallel transport along circular orbits in orthogonally transitive stationary axisymmetric spacetimes is described explicitly relative to Lie transport in terms of the electric and magnetic parts of the induced connection. The influence of both the gravito-electromagnetic fields associated with the zero angular momentum observers and of the Frenet–Serret parameters of these orbits as a function of their angular velocity is seen on the behavior of parallel transport through its representation as a parameter-dependent Lorentz transformation between these two inner-product preserving transports which is generated by the induced connection. This extends the analysis of parallel transport in the equatorial plane of the Kerr spacetime to the entire spacetime outside the black hole horizon, and helps give an intuitive picture of how competing "central attraction forces" and centripetal accelerations contribute with gravitomagnetic effects to explain the behavior of the 4-acceleration of circular orbits in that spacetime.
15
Koehl, Patrice, und Joel Hass. „Landmark-free geometric methods in biological shape analysis“. Journal of The Royal Society Interface 12, Nr. 113 (Dezember 2015): 20150795. http://dx.doi.org/10.1098/rsif.2015.0795.
Der volle Inhalt der QuelleAnnotation:
In this paper, we propose a new approach for computing a distance between two shapes embedded in three-dimensional space. We take as input a pair of triangulated genus zero surfaces that are topologically equivalent to spheres with no holes or handles, and construct a discrete conformal map f between the surfaces. The conformal map is chosen to minimize a symmetric deformation energy E sd ( f ) which we introduce. This measures the distance of f from an isometry, i.e. a non-distorting correspondence. We show that the energy of the minimizing map gives a well-behaved metric on the space of genus zero surfaces. In contrast to most methods in this field, our approach does not rely on any assignment of landmarks on the two surfaces. We illustrate applications of our approach to geometric morphometrics using three datasets representing the bones and teeth of primates. Experiments on these datasets show that our approach performs remarkably well both in shape recognition and in identifying evolutionary patterns, with success rates similar to, and in some cases better than, those obtained by expert observers.
16
Baldi, P., M. Blanke, P. Castaldi, N. Mimmo und S. Simani. „Fault diagnosis for satellite sensors and actuators using nonlinear geometric approach and adaptive observers“. International Journal of Robust and Nonlinear Control 29, Nr. 16 (02.04.2018): 5429–55. http://dx.doi.org/10.1002/rnc.4083.
Der volle Inhalt der Quelle
17
Dobias, Joshua, und Wm Stine. „Dynamic Cancellation of Perceived Rotation from the Venetian Blind Effect“. Vision 3, Nr. 2 (03.04.2019): 14. http://dx.doi.org/10.3390/vision3020014.
Der volle Inhalt der QuelleAnnotation:
Geometric differences between the images seen by each eye enable the perception of depth. Additionally, depth is produced in the absence of geometric disparities with binocular disparities in either the average luminance or contrast, which is known as the Venetian blind effect. The temporal dynamics of the Venetian blind effect are much slower (1.3 Hz) than those for geometric binocular disparities (4–5 Hz). Sine-wave modulations of luminance and contrast disparity, however, can be discriminated from square-wave modulations at 1 Hz, which suggests a non-linearity. To measure this non-linearity, a luminance or contrast disparity modulation was presented at a particular frequency and paired with a geometric disparity modulation that cancelled the perceived rotation induced by the luminance or contrast modulation. Phases between the luminance or contrast and the geometric modulation varied in 50 ms increments from −200 and 200 ms. When phases were aligned, observers perceived little or no rotation. When not aligned, a perceived rotation was induced by a contrast or luminance disparity that was then cancelled by the geometric disparity. This causes the perception of a slight jump. The Generalized Difference Model, which is linear in time, predicted a minimal probability in cases when luminance or contrast disparities occurred before the geometric disparities due to the slower dynamics of the Venetian blind effect. The Gated Generalized Difference Model, which is non-linear in time, predicted a minimal probability for offsets of 0 ms. Results followed the Gated model, which further suggests a non-linearity in time for the Venetian blind effect.
18
Vinogradova, M., A. Kanatnikov und O. Tkacheva. „State Observer for the Pacemaker Model Based on the Van der Pol Equation“. Mathematics and Mathematical Modeling, Nr. 1 (09.06.2020): 16–32. http://dx.doi.org/10.24108/mathm.0120.0000216.
Der volle Inhalt der QuelleAnnotation:
A Dutch physiologist and a founder of electrocardiography V. Einthoven [10] proposed the first known model of the cardiac electrical activity. Later, van der Pol and van der Mark [11] developed a model of the heart, where the heartbeat is considered as a relaxation oscillation. From this point of view, to model the operation of pacemakers, the van der Pol equation [14,15,19] can be useful. The paper offers modeling of only one heart node that is the S-A (sinoatrial) node, which is the main heart pacemaker [20].Many control algorithms for dynamic systems are based on feedback, which involves the full state vector of a dynamic system. However, in practice, the full state vector is not always known. So, in the case of cardiac electrical activity, the potentials of the nodes rather than their changing rates are measured. To restore the full state vector from existing measurements, state observers are often used.In this paper, we solve the task of constructing an observer with linear error dynamics [22.25]. A necessary condition for the existence of such an observer is the system observability. The sufficient conditions can be formulated in the framework of the differential-geometric approach [25] using the ideas of duplicity [25,26]. Within this approach, an algorithm for observer construction can be developed. In the paper, a general problem to construct an observer for two-dimensional systems is solved and the results obtained are applied to the pacemaker model based on the Van der Pol oscillator. The numerical simulation enables us to illustrate operation of the observer developed.
19
Wang, Liping, Hailong Pei und Zihuan Cheng. „Geometric Attitude Fault-Tolerant Control of Quadrotor Unmanned Aerial Vehicles with Adaptive Extended State Observers“. Machines 12, Nr. 1 (10.01.2024): 47. http://dx.doi.org/10.3390/machines12010047.
Der volle Inhalt der QuelleAnnotation:
This paper is concerned with the attitude tracking problem of quadrotor unmanned aerial vehicles (UAVs) with respect to endogenous uncertainties, exogenous disturbances and actuator failures. Two different control methods are proposed to solve this problem. First, an adaptive extended state observer (AESO)-based control framework is devised to tackle the difficulties caused by model uncertainties and external disturbances. A fault-tolerant control method is proposed to cope with the occurrence of actuator failure, which is modeled as a constant loss of effectiveness. Another method employs AESOs to compensate for lumped disturbances, which include endogenous uncertainties, exogenous disturbances and actuator failures. Then, the error can exponentially converge to a bounded set. Finally, simulations are performed to ensure the feasibility of the designed technique.
20
Dvorsky, Richard. „A Scale Invariant Fully Conformal Cosmological Model and Its Support by Astrophysical Data“. Universe 11, Nr. 2 (21.01.2025): 30. https://doi.org/10.3390/universe11020030.
Der volle Inhalt der QuelleAnnotation:
According to general relativity, the cosmological redshift may be caused by other mechanisms than the source moving away from the observer. It can occur on a global scale, similar to the gravitational redshift near massive stars. In principle, these are differences in the time-dependent global metric field between the source in the past and the observer in the present. In this paper we attempt a new interpretation of the simple solution of Einstein’s equations within a fully conformal metric for the case of a time-independent energy-momentum tensor. The scaling factor here acts identically on all four space-time coordinates and the speed of light is independent of the conformal time. The fully conformal metric is interpreted here as a universal geometric background which is scale invariant and acts universally on all objects, including gauges and clocks, regardless of their dimensions and internal interactions. The associated scale invariant exponential expansion is thus only relative and all observers at different times are completely equal. The model introduces the concept of the appearent age of the universe, which is the limiting consequence of time dilation into the past, and corresponds to the present value of the age of the universe H−1 according to the standard model. This appearent age is the same for all observers, and the Hubble constant is thus a true universal constant, invariant to time translations. The motivation of this work was to test the possibility of the above cosmological redshift mechanism in confrontation with astrophysical data. Probably the most important consequence is the generalized formulation and interpretation of the Hubble-Lemaître law z(r) = (eHr/c − 1), which shows good agreement with astrophysical data even for the most distant supernovae. Confronting the conformal metric model with some astrophysical data shows an interesting agreement with the observed spatial distribution of astrophysical sources such as γ-ray bursts and quasars. On a cosmological scale, the above fully conformal metric naturally determines the global energy density, spatial flatness, and solves the horizon problem and Olbers’ paradox in infinite spacetime.
21
Koehl, Patrice. „Minimum action principle and shape dynamics“. Journal of The Royal Society Interface 14, Nr. 130 (Mai 2017): 20170031. http://dx.doi.org/10.1098/rsif.2017.0031.
Der volle Inhalt der QuelleAnnotation:
In this paper, we propose a new method for computing a distance between two shapes embedded in three-dimensional space. Instead of comparing directly the geometric properties of the two shapes, we measure the cost of deforming one of the two shapes into the other. The deformation is computed as the geodesic between the two shapes in the space of shapes. The geodesic is found as a minimizer of the Onsager–Machlup action, based on an elastic energy for shapes that we define. Its length is set to be the integral of the action along that path; it defines an intrinsic quasi-metric on the space of shapes. We illustrate applications of our method to geometric morphometrics using three datasets representing bones and teeth of primates. Experiments on these datasets show that the variational quasi-metric we have introduced performs remarkably well both in shape recognition and in identifying evolutionary patterns, with success rates similar to, and in some cases better than, those obtained by expert observers.
22
Puhachov, Ivan, Cedric Martens, Paul G. Kry und Mikhail Bessmeltsev. „Reconstruction of Machine-Made Shapes from Bitmap Sketches“. ACM Transactions on Graphics 42, Nr. 6 (05.12.2023): 1–16. http://dx.doi.org/10.1145/3618361.
Der volle Inhalt der QuelleAnnotation:
We propose a method of reconstructing 3D machine-made shapes from bitmap sketches by separating an input image into individual patches and jointly optimizing their geometry. We rely on two main observations: (1) human observers interpret sketches of man-made shapes as a collection of simple geometric primitives, and (2) sketch strokes often indicate occlusion contours or sharp ridges between those primitives. Using these main observations we design a system that takes a single bitmap image of a shape, estimates image depth and segmentation into primitives with neural networks, then fits primitives to the predicted depth while determining occlusion contours and aligning intersections with the input drawing via optimization. Unlike previous work, our approach does not require additional input, annotation, or templates, and does not require retraining for a new category of man-made shapes. Our method produces triangular meshes that display sharp geometric features and are suitable for downstream applications, such as editing, rendering, and shading.
23
Yuan, Jiangping, Hua Li, Baohui Xu und Guangxue Chen. „Impact of Geometric Features on Color Similarity Perception of Displayed 3D Tablets“. Journal of Imaging Science and Technology 64, Nr. 5 (01.09.2020): 50404–1. http://dx.doi.org/10.2352/j.imagingsci.technol.2020.64.5.050404.
Der volle Inhalt der QuelleAnnotation:
Abstract To explore the effects of geometric features on the color similarity perception of displayed three-dimensional (3D) tablets designed by color 3D modeling techniques or printed by color 3D printing techniques, two subjective similarity scaling tasks were conducted for color tablets with four shape features (circular, oval, triangular-columnar, and rounded-cuboid shapes) and four notch features (straight V, straight U, crisscross V, and crisscross U shapes) displayed on a calibrated monitor using the nine-level category judgement method. Invited observers were asked to assort all displayed samples into tablet groups using six surface colors (aqua blue, bright green, pink, orange yellow, bright red, and silvery white), and all perceived similarity values were recorded and compared to original samples successively. The results showed that the similarity perception of tested tablets was inapparently affected by the given shape features and notch features, and it should be judged by a flexible interval rather than by a fixed color difference. This research provides practical insight into the visualization of color similarity perception for displayed personalized tablets to advance precision medicine by 3D printing.
24
Cardall, Christian. „Minkowski and Galilei/Newton Fluid Dynamics: A Geometric 3 + 1 Spacetime Perspective“. Fluids 4, Nr. 1 (26.12.2018): 1. http://dx.doi.org/10.3390/fluids4010001.
Der volle Inhalt der QuelleAnnotation:
A kinetic theory of classical particles serves as a unified basis for developing a geometric 3 + 1 spacetime perspective on fluid dynamics capable of embracing both Minkowski and Galilei/Newton spacetimes. Parallel treatment of these cases on as common a footing as possible reveals that the particle four-momentum is better regarded as comprising momentum and inertia rather than momentum and energy; and, consequently, that the object now known as the stress-energy or energy-momentum tensor is more properly understood as a stress-inertia or inertia-momentum tensor. In dealing with both fiducial and comoving frames as fluid dynamics requires, tensor decompositions in terms of the four-velocities of observers associated with these frames render use of coordinate-free geometric notation not only fully viable, but conceptually simplifying. A particle number four-vector, three-momentum (1, 1) tensor, and kinetic energy four-vector characterize a simple fluid and satisfy balance equations involving spacetime divergences on both Minkowski and Galilei/Newton spacetimes. Reduced to a fully 3 + 1 form, these equations yield the familiar conservative formulations of special relativistic and non-relativistic fluid dynamics as partial differential equations in inertial coordinates, and in geometric form will provide a useful conceptual bridge to arbitrary-Lagrange–Euler and general relativistic formulations.
25
van der Zee, Tim J., und Arthur D. Kuo. „TimTrack: A drift-free algorithm for estimating geometric muscle features from ultrasound images“. PLOS ONE 17, Nr. 3 (24.03.2022): e0265752. http://dx.doi.org/10.1371/journal.pone.0265752.
Der volle Inhalt der QuelleAnnotation:
Ultrasound imaging is valuable for non-invasively estimating fascicle lengths and other features of pennate muscle, especially when performed computationally. Effective analysis techniques to date typically use optic flow to track displacements from image sequences, but are sensitive to integration drift for longer sequences. We here present an alternative algorithm that objectively estimates geometric features of pennate muscle from ultrasound images, without drift sensitivity. The algorithm identifies aponeuroses and estimates fascicle angles to derive fascicle lengths. Length estimates of human vastus lateralis and gastrocnemius fascicles in healthy subjects (N = 9 and N = 17 respectively) compared well (overall root-mean-square difference, RMSD = 0.52 cm) to manual estimates by independent observers (n = 3), with overall coefficient of multiple correlation (CMC) of 0.98. Our tests yielded accuracy (CMC, RMSD) and processing speed similar to or exceeding that of state-of-the-art algorithms. The algorithm requires minimal manual intervention and can optionally extrapolate fascicle lengths that extend beyond the image frame. It thus facilitates automated analysis of ultrasound images without drift.
26
Igamberdiev, Abir. „Time and Life in the Relational Universe: Prolegomena to an Integral Paradigm of Natural Philosophy“. Philosophies 3, Nr. 4 (16.10.2018): 30. http://dx.doi.org/10.3390/philosophies3040030.
Der volle Inhalt der QuelleAnnotation:
Relational ideas for our description of the natural world can be traced to the concept of Anaxagoras on the multiplicity of basic particles, later called “homoiomeroi” by Aristotle, that constitute the Universe and have the same nature as the whole world. Leibniz viewed the Universe as an infinite set of embodied logical essences called monads, which possess inner view, compute their own programs and perform mathematical transformations of their qualities, independently of all other monads. In this paradigm, space appears as a relational order of co-existences and time as a relational order of sequences. The relational paradigm was recognized in physics as a dependence of the spatiotemporal structure and its actualization on the observer. In the foundations of mathematics, the basic logical principles are united with the basic geometrical principles that are generic to the unfolding of internal logic. These principles appear as universal topological structures (“geometric atoms”) shaping the world. The decision-making system performs internal quantum reduction which is described by external observers via the probability function. In biology, individual systems operate as separate relational domains. The wave function superposition is restricted within a single domain and does not expand outside it, which corresponds to the statement of Leibniz that “monads have no windows”.
27
Cosson, Philip, und Zenghai Lu. „Geometric validation of a computer simulator used in radiography education“. BJR|Open 2, Nr. 1 (November 2020): 20190027. http://dx.doi.org/10.1259/bjro.20190027.
Der volle Inhalt der QuelleAnnotation:
Objectives: The radiographical process of projection of a complex human form onto a two-dimensional image plane gives rise to distortions and magnifications. It is important that any simulation used for educational purposes should correctly reproduce these. Images generated using a commercially available computer simulation widely used in radiography education (ProjectionVRTM) were tested for geometric accuracy of projection in all planes. Methods: An anthropomorphic skull phantom was imaged using standard projection radiography techniques and also scanned using axial CT acquisition. The data from the CT was then loaded into the simulator and the same projection radiography techniques simulated. Bony points were identified on both the real radiographs and the digitally reconstructed radiographs (DRRs). Measurements sensitive to rotation and magnification were chosen to check for rotation and distortion errors. Results: The real radiographs and the DRRs were compared by four experienced observers and measurements taken between the identified bony points on each of the images obtained. Analysis of the mean observations shows that the measurement from the DRR matches the real radiograph +1.5 mm/−1.5 mm. The Bland Altman bias was 0.55 (1.26 STD), with 95% limits of agreement 3.01 to −1.91. Conclusions: Agreement between the empirical measurements is within the reported error of cephalometric analysis in all three anatomical planes. The image appearances of both the real radiographs and DRRs compared favourably. Advances in knowledge: The commercial computer simulator under test (ProjectionVRTM) was able to faithfully recreate the image appearances of real radiography techniques, including magnification and distortion. Students using this simulation for training will obtain feedback likely to be useful when lessons are applied to real-world situations.
28
Bressloff, Paul C., Jack D. Cowan, Martin Golubitsky, Peter J. Thomas und Matthew C. Wiener. „What Geometric Visual Hallucinations Tell Us about the Visual Cortex“. Neural Computation 14, Nr. 3 (01.03.2002): 473–91. http://dx.doi.org/10.1162/089976602317250861.
Der volle Inhalt der QuelleAnnotation:
Many observers see geometric visual hallucinations after taking hallucinogens such as LSD, cannabis, mescaline or psilocybin; on viewing bright flickering lights; on waking up or falling asleep; in “near-death” experiences; and in many other syndromes. Klüver organized the images into four groups called form constants: (I) tunnels and funnels, (II) spirals, (III) lattices, including honeycombs and triangles, and (IV) cobwebs. In most cases, the images are seen in both eyes and move with them. We interpret this to mean that they are generated in the brain. Here, we summarize a theory of their origin in visual cortex (area V1), based on the assumption that the form of the retino–cortical map and the architecture of V1 determine their geometry. (A much longer and more detailed mathematical version has been published in Philosophical Transactions of the Royal Society B, 356 [2001].) We model V1 as the continuum limit of a lattice of interconnected hypercolumns, each comprising a number of interconnected iso-orientation columns. Based on anatomical evidence, we assume that the lateral connectivity between hypercolumns exhibits symmetries, rendering it invariant under the action of the Euclidean group E(2), composed of reflections and translations in the plane, and a (novel) shift-twist action. Using this symmetry, we show that the various patterns of activity that spontaneously emerge when V1's spatially uniform resting state becomes unstable correspond to the form constants when transformed to the visual field using the retino-cortical map. The results are sensitive to the detailed specification of the lateral connectivity and suggest that the cortical mechanisms that generate geometric visual hallucinations are closely related to those used to process edges, contours, surfaces, and textures.
29
Friedenberg, Jay. „The Perceived Beauty of Regular Polygon Tessellations“. Symmetry 11, Nr. 8 (02.08.2019): 984. http://dx.doi.org/10.3390/sym11080984.
Der volle Inhalt der QuelleAnnotation:
Beauty judgments for regular polygon tessellations were examined in two experiments. In experiment 1 we tested the three regular and eight semi-regular tilings characterized by a single vertex. In experiment 2 we tested the 20 demi-regular tilings containing two vertices. Observers viewed the tessellations at different random orientations inside a circular aperture and rated them using a numeric 1–7 scale. The data from the first experiment show a peak in preference for tiles with two types of polygons and for five polygons around a vertex. Triangles were liked more than other geometric shapes. The results from the second experiment demonstrate a preference for tessellations with a greater number of different kinds of polygons in the overall pattern and for tiles with the greatest difference in the number of polygons between the two vertices. Ratings were higher for tiles with circular arrangements of elements and lower for those with linear arrangements. Symmetry group p6m was liked the most and groups cmm and pmm were liked the least. Taken as a whole the results suggest a preference for complexity and variety in terms of both vertex qualities and symmetric transformations. Observers were sensitive to both the underlying mathematical properties of the patterns as well as their emergent organization.
30
Castellano, T., L. Doyle und D. McIntosh. „The Visibility of Earth Transits“. Symposium - International Astronomical Union 202 (2004): 445–47. http://dx.doi.org/10.1017/s0074180900218457.
Der volle Inhalt der QuelleAnnotation:
The recent photometric detection of planetary transits of the solar-like star HD 209458 at a distance of 47 parsecs suggest that transits can reveal the presence of Jupiter-size planetary companions in the solar neighborhood (Charbonneau et al. 2000; Henry et al. 2000). Recent space-based transit searches have achieved photometric precision within an order of magnitude of that required to detect the much smaller transit signal of an earth-size planet across a solar-size star. Laboratory experiments in the presence of realistic noise sources have shown that CCDs can achieve photometric precision adequate to detect the 9.6 E-5 dimming of the Sun due to a transit of the Earth (Borucki et al. 1997; Koch et al. 2000). Space-based solar irradiance monitoring has shown that the intrinsic variability of the Sun would not preclude such a detection (Borucki, Scargle, Hudson 1985). Transits of the Sun by the Earth would be detectable by observers that reside within a narrow band of sky positions near the ecliptic plane, if the observers possess current Earth epoch levels of technology and astronomical expertise. A catalog of solar-like stars that satisfy the geometric condition for Earth transit visibility are presented.
31
Ramzan, M. „Decoherence dynamics of geometric measure of quantum discord and measurement induced nonlocality for noninertial observers at finite temperature“. Quantum Information Processing 12, Nr. 8 (10.03.2013): 2721–38. http://dx.doi.org/10.1007/s11128-013-0558-0.
Der volle Inhalt der Quelle
32
Unterstrasser, S., und K. Gierens. „Numerical simulations of contrail-to-cirrus transition – Part 1: An extensive parametric study“. Atmospheric Chemistry and Physics Discussions 9, Nr. 4 (09.07.2009): 14901–53. http://dx.doi.org/10.5194/acpd-9-14901-2009.
Der volle Inhalt der QuelleAnnotation:
Abstract. Simulations of contrail-to-cirrus transition over up to 6 h were performed using a LES-model. The sensitivity of microphysical, optical and geometric contrail properties on relative humidity RHi, temperature T and vertical wind shear s was investigated in an extensive parametric study. The dominant parameter for contrail evolution is relative humidity. Substantial spreading is only visible for RHi≳120%. Vertical wind shear has a smaller effect on most contrail properties than human observers might expect from the visual impression. Our model shows that after a few hours the water vapour removed by falling ice crystals from the contrail layer can be several times higher than the ice mass that is actually present in the contrail at any instance.
33
Peatt, Megan J., und Noel D. Richardson. „Optical Photometry of WR140 as the Dust Formed During the 2016 Periastron Passage“. Research Notes of the AAS 6, Nr. 1 (17.01.2022): 20. http://dx.doi.org/10.3847/2515-5172/ac4af7.
Der volle Inhalt der QuelleAnnotation:
Abstract The colliding wind binary WR140 produces dust in its shocked gas every periastron passage. While the infrared light curve is very repeatable, there are noticeable changes every cycle in the optical time-series photometry. In the phases following periastron, there are optical dips in the light curve that were postulated to be caused by localized clumps in the dust produced in our line of sight. We report on the B- and V-band light curves that were recorded by the American Association of Variable Star Observers after the 2016 periastron event and briefly discuss comparisons to geometric models of the dust production to infer that these features are likely caused by localized dust clumps in the new dust shell.
34
Unterstrasser, S., und K. Gierens. „Numerical simulations of contrail-to-cirrus transition – Part 1: An extensive parametric study“. Atmospheric Chemistry and Physics 10, Nr. 4 (19.02.2010): 2017–36. http://dx.doi.org/10.5194/acp-10-2017-2010.
Der volle Inhalt der QuelleAnnotation:
Abstract. Simulations of contrail-to-cirrus transition over up to 6 h were performed using a LES-model. The sensitivity of microphysical, optical and geometric contrail properties to relative humidity RHi, temperature T and vertical wind shear s was investigated in an extensive parametric study. The dominant parameter for contrail evolution is relative humidity. Substantial spreading is only visible for RHi≳120%. Vertical wind shear has a smaller effect on optical properties than human observers might expect from the visual impression. Our model shows that after a few hours the water vapour removed by falling ice crystals from the contrail layer can be several times higher than the ice mass that is actually present in the contrail at any instance.
35
Chaudhry, M. L., und U. C. Gupta. „Performance analysis of the discrete-time GI/Geom/1/N queue“. Journal of Applied Probability 33, Nr. 1 (März 1996): 239–55. http://dx.doi.org/10.2307/3215281.
Der volle Inhalt der QuelleAnnotation:
This paper presents an analysis of the single-server discrete-time finite-buffer queue with general interarrival and geometric service time, GI/Geom/1/N. Using the supplementary variable technique, and considering the remaining interarrival time as a supplementary variable, two variations of this model, namely the late arrival system with delayed access (LAS-DA) and early arrival system (EAS), have been examined. For both cases, steady-state distributions for outside observers as well as at random and prearrival epochs have been obtained. The waiting time analysis has also been carried out. Results for the Geom/G/1/N queue with LAS-DA have been obtained from the GI/Geom/1/N queue with EAS. We also give various performance measures. An algorithm for computing state probabilities is given in an appendix.
36
Chaudhry, M. L., und U. C. Gupta. „Performance analysis of the discrete-time GI/Geom/1/N queue“. Journal of Applied Probability 33, Nr. 01 (März 1996): 239–55. http://dx.doi.org/10.1017/s0021900200103894.
Der volle Inhalt der QuelleAnnotation:
This paper presents an analysis of the single-server discrete-time finite-buffer queue with general interarrival and geometric service time,GI/Geom/1/N. Using the supplementary variable technique, and considering the remaining interarrival time as a supplementary variable, two variations of this model, namely the late arrival system with delayed access (LAS-DA) and early arrival system (EAS), have been examined. For both cases, steady-state distributions for outside observers as well as at random and prearrival epochs have been obtained. The waiting time analysis has also been carried out. Results for theGeom/G/1/Nqueue with LAS-DA have been obtained from theGI/Geom/1/Nqueue with EAS. We also give various performance measures. An algorithm for computing state probabilities is given in an appendix.
37
OBRIST, DOMINIK. „Directivity of acoustic emissions from wave packets to the far field“. Journal of Fluid Mechanics 640 (10.11.2009): 165–86. http://dx.doi.org/10.1017/s0022112009991297.
Der volle Inhalt der QuelleAnnotation:
We investigate the acoustic emission from wave packets to the far field. To this end, we develop a theory for one- and two-dimensional source fields in the shape of wave packets with Gaussian envelopes. This theory is based on an approximation to Lighthill's acoustic analogy for distant observers. It is formulated in the spectral domain in which a Gaussian wave packet is represented again by a Gaussian. This allows us to determine the directivity of the acoustic emission (e.g. superdirectivity and Mach waves) by simple geometric constructions in the spectral domain. It is shown that the character of the acoustic emission is mainly governed by the aspect ratio and the Mach number of the wave packet source. To illustrate the relevance of this theory we use it to study two prominent problems in subsonic jet aeroacoustics.
38
Lu, Jiajun, Fangyan Dong und Kaoru Hirota. „Location Detection of Informative Bright Region in Tunnel Scenes Using Lighting and Traffic Lane Cues“. Journal of Advanced Computational Intelligence and Intelligent Informatics 19, Nr. 2 (20.03.2015): 255–63. http://dx.doi.org/10.20965/jaciii.2015.p0255.
Der volle Inhalt der QuelleAnnotation:
To locate Informative Bright Region (IBR) in which visual information is missing owing to limited dynamic range of image sensor, an algorithm is proposed that combines the geometric properties of visual cues into a confidence map. The location of an IBR in a road tunnel scene is estimated in real-time under the condition in which most of the vision information inside the IBR is lost. The algorithm is evaluated by comparing the estimated location of IBR with that annotated by multiple human observers in a self-built tunnel scene video dataset recorded by a car-mounted camera, and the algorithm achieves a running time of 10 ms for each frame. The algorithm aims to provide control timing of imaging sensor on a low-cost platform such as a vehicle driving recorder to enhance the visual contents captured in over-exposed regions.
39
Metaxas, Vasileios I., Gerasimos A. Messaris, George D. Gatzounis und George S. Panayiotakis. „OPTIMISATION OF PATIENT DOSE AND IMAGE QUALITY IN FLUOROSCOPICALLY GUIDED CERVICAL SPINE SURGERY: A PHANTOM-BASED STUDY“. Radiation Protection Dosimetry 184, Nr. 2 (01.12.2018): 237–47. http://dx.doi.org/10.1093/rpd/ncy205.
Der volle Inhalt der QuelleAnnotation:
Abstract The purpose of the current study was to provide useful data, which may help neurosurgeons to manage the patient dose and image quality in spinal surgery procedures, utilising a phantom and a test object. The kerma area product, cumulative dose (CD) and entrance surface dose (ESD) rate on the phantom and image intensifier were measured, for selectable fields of view (FOVs), fluoroscopy modes, two geometric magnifications and various phantom thicknesses. The images were subjectively evaluated regarding low-contrast detectability and high-contrast resolution. Signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), high-contrast spatial resolution (HCSR) and figure of merit (FOM) values were also estimated. The ESD rates increased with increasing phantom thickness, when using electronic or geometric magnification, continuous or high-definition fluoroscopy (HDF). The observers’ evaluation showed relatively slight changes in image quality when pulsed fluoroscopy was used. SNR, CNR and HCSR values decreased with increasing phantom thicknesses, while remained almost constant when using pulsed fluoroscopy. SNR and HCSR improved in HDF, while the CNR remained almost constant only for the FOVs 23 and 17 cm. By applying electronic magnification, this resulted in improved HCSR. FOM values decreased in HDF, with increasing phantom thickness and using electronic magnification. For the ‘thinnest’ patients, CD may overestimate skin dose by 25% than the actual values. Geometric magnification resulted in improved FOM, especially for low-dose fluoroscopy and FOV 23 cm. The knowledge of the increments in dose values, image quality and FOM indices concerning phantom thickness may help neurosurgeons to optimise spinal surgery procedures by selecting the appropriate operational parameters, which could contribute toward the establishment of a radiation protection culture.
40
Taylor, Nicola, David Giles, Micha Panáčková, James Mitchell, Joel Chidley und Nick Draper. „A Novel Tool for the Assessment of Sport Climbers’ Movement Performance“. International Journal of Sports Physiology and Performance 15, Nr. 6 (01.07.2020): 795–800. http://dx.doi.org/10.1123/ijspp.2019-0311.
Der volle Inhalt der QuelleAnnotation:
Purpose: To assess the validity and reliability of a novel movement-performance assessment tool for climbing/sport climbing. Methods: First, salient climbing movement-performance factors were identified through an iterative consultation process with 10 expert climbing coaches; the resulting Climber’s Movement Performance Assessment Tool (CM-PAT) contained 14 items in 5 categories. Second, 61 intermediate to advanced climbers ascended a single route, which was video recorded. Subsequently, 4 experienced (>10 y coaching) coaches used the CM-PAT to observe and score the climbers’ performance. Interrater reliability and comparisons with existing measures of climbing performance (6-mo self-reported ability, success and failure, climbing pace [m·min−1], and geometric entropy) were made. Results: Intraclass correlation coefficient (2,k) for the 4 raters demonstrated excellent reliability (>.81) between observers and good to excellent test–retest reliability (.71–.91). Pearson correlations between self-reported ability and CM-PAT scores explained 61% of the variance in self-reported climbing performance compared with 16% for geometric entropy and 52% for climbing pace. Considering differences in successful and unsuccessful climbers, the CM-PAT (P < .0005; d = 2.14), geometric entropy (P = .014; d = 0.67), and pace (P < .0005; d = 1.88) were able to differentiate between groups. Conclusions: The CM-PAT is the first sport climbing performance observational instrument to be developed through a thorough iterative process with expert coaches. Excellent interrater and test–retest reliability and excellent agreement with self-reported ability and with existing quantitative measures of performance support its recommendation for use in coaching and research contexts. Notably, a key advantage over existing measures is the identification of coachable elements of performance.
41
Trugenberger, Carlo A. „Combinatorial Quantum Gravity and Emergent 3D Quantum Behaviour“. Universe 9, Nr. 12 (29.11.2023): 499. http://dx.doi.org/10.3390/universe9120499.
Der volle Inhalt der QuelleAnnotation:
We review combinatorial quantum gravity, an approach that combines Einstein’s idea of dynamical geometry with Wheeler’s “it from bit” hypothesis in a model of dynamical graphs governed by the coarse Ollivier–Ricci curvature. This drives a continuous phase transition from a random to a geometric phase due to a condensation of loops on the graph. In the 2D case, the geometric phase describes negative-curvature surfaces with two inversely related scales: an ultraviolet (UV) Planck length and an infrared (IR) radius of curvature. Below the Planck scale, the random bit character survives; chunks of random bits of the Planck size describe matter particles of excitation energy given by their excess curvature. Between the Planck length and the curvature radius, the surface is smooth, with spectral and Hausdorff dimension 2. At scales larger than the curvature radius, particles see the surface as an effective Lorentzian de Sitter surface, the spectral dimension becomes 3, and the effective slow dynamics of particles, as seen by co-moving observers, emerges as quantum mechanics in Euclidean 3D space. Since the 3D distances are inherited from the underlying 2D de Sitter surface, we obtain curved trajectories around massive particles also in 3D, representing the large-scale gravity interactions. We thus propose that this 2D model describes a generic holographic screen relevant for real quantum gravity.
42
Pfeifer, Christian. „Finsler spacetime geometry in physics“. International Journal of Geometric Methods in Modern Physics 16, supp02 (November 2019): 1941004. http://dx.doi.org/10.1142/s0219887819410044.
Der volle Inhalt der QuelleAnnotation:
Finsler geometry naturally appears in the description of various physical systems. In this review, I divide the emergence of Finsler geometry in physics into three categories: dual description of dispersion relations, most general geometric clock and geometry being compatible with the relevant Ehlers–Pirani–Schild axioms. As Finsler geometry is a straightforward generalization of Riemannian geometry there are many attempts to use it as generalized geometry of spacetime in physics. However, this generalization is subtle due to the existence of non-trivial null directions. I review how a pseudo-Finsler spacetime geometry can be defined such that it provides a precise notion of causal curves, observers and their measurements as well as a gravitational field equation determining the Finslerian spacetime geometry dynamically. The construction of such Finsler spacetimes lays the foundation for comparing their predictions with observations, in astrophysics as well as in laboratory experiments.
43
Lages, Martin, und Suzanne Heron. „On the Aperture Problem of Binocular 3D Motion Perception“. Vision 3, Nr. 4 (19.11.2019): 64. http://dx.doi.org/10.3390/vision3040064.
Der volle Inhalt der QuelleAnnotation:
Like many predators, humans have forward-facing eyes that are set a short distance apart so that an extensive region of the visual field is seen from two different points of view. The human visual system can establish a three-dimensional (3D) percept from the projection of images into the left and right eye. How the visual system integrates local motion and binocular depth in order to accomplish 3D motion perception is still under investigation. Here, we propose a geometric-statistical model that combines noisy velocity constraints with a spherical motion prior to solve the aperture problem in 3D. In two psychophysical experiments, it is shown that instantiations of this model can explain how human observers disambiguate 3D line motion direction behind a circular aperture. We discuss the implications of our results for the processing of motion and dynamic depth in the visual system.
44
Barabanschikov, V. A. „Configurational relations of a face as a source of information about personality“. Experimental Psychology (Russia) 12, Nr. 3 (2019): 28–46. http://dx.doi.org/10.17759/exppsy.2019120303.
Der volle Inhalt der QuelleAnnotation:
The possibilities of obtaining information about the identity of a third party were studied in different ways of depicting a face. The results of two series of experiments were compared, in which the same configuration relations were included in the context of either a schematic face made up of abstract geometric figures or photographic portraits of specific people. Stimulus material was based on the figures of E. Brunswick (1956), demonstrating the dependence of induced expressions (joy/gust) on the spatial organization of the face. Assessment of individual psychological features of the sitter and self-assessment of observers were performed using the Personal Differential method. As a result of the analysis the general regularities of perception of a person in the created conditions are revealed: polarization of estimations of features and their asymmetry defined by impressions about the state of modelers — real or imaginary. Two nonspecific phenomena of interpersonal perception related to transformations of the configuration relations of the face have been revealed: (1) inversion of the attractiveness of the person shown in the photo, and (2) doubling of the personality of the virtual sitter. It is shown that the influence of the observer’s self-esteem on the modeler’s assessment depends both on the type of the face image and on the direction of configuration transformations. The obtained results are interpreted in terms of the dynamics of constellation of features, the mechanism of super generation of emotional manifestations and halo-effect of attractiveness. The methodology of general psychological research of interpersonal perception based on the variation of configuration relations of the face is substantiated.
45
Powell, James L. „Field Measurement of Signalized Intersection Delay for 1997 Update of the Highway Capacity Manual“. Transportation Research Record: Journal of the Transportation Research Board 1646, Nr. 1 (Januar 1998): 79–86. http://dx.doi.org/10.3141/1646-10.
Der volle Inhalt der QuelleAnnotation:
The 1997 update of the Highway Capacity Manual changes the basis of delay for level-of-service determination at signalized intersections from stopped delay to conceptually more appealing total delay. Total delay is made up of components including volume, control, and geometric delay. Level of service is now defined in terms of control delay, which provides a more stable and tractable relation to total delay, but the issue of field measurement remains in any case. A combined theoretical and empirical approach to measuring field delay on the basis of typical vehicle deceleration and acceleration profiles is taken in this paper. The profiles are related to the relatively easily surveyed quantity of vehicles in queue, which is equivalent to estimating time in queue of all vehicles stopped by the traffic signal. The results indicate that after vehicles in queue are sampled, correction factors can account, in practical terms, for the unsurveyed deceleration and acceleration delay. The corrections are simple additive factors that are a function of free-flow speed and average number of vehicles stopped in queue. Another adjustment is included for the consistent tendency of human observers to overestimate vehicles in queue. All of these factors are included in the new 1997 HCM procedure for measuring signalized intersection delay in the field. Further identified work includes the need to fully develop the total delay concept to account for geometric delay consistently over a variety of interrupted- and uninterrupted-flow facilities. Such resolution should be included in HCM 2000 preparation currently in progress.
46
Bonnen, Kathryn, Alexander C. Huk und Lawrence K. Cormack. „Dynamic mechanisms of visually guided 3D motion tracking“. Journal of Neurophysiology 118, Nr. 3 (01.09.2017): 1515–31. http://dx.doi.org/10.1152/jn.00831.2016.
Der volle Inhalt der QuelleAnnotation:
The continuous perception of motion-through-depth is critical for both navigation and interacting with objects in a dynamic three-dimensional (3D) world. Here we used 3D tracking to simultaneously assess the perception of motion in all directions, facilitating comparisons of responses to motion-through-depth to frontoparallel motion. Observers manually tracked a stereoscopic target as it moved in a 3D Brownian random walk. We found that continuous tracking of motion-through-depth was selectively impaired, showing different spatiotemporal properties compared with frontoparallel motion tracking. Two separate factors were found to contribute to this selective impairment. The first is the geometric constraint that motion-through-depth yields much smaller retinal projections than frontoparallel motion, given the same object speed in the 3D environment. The second factor is the sluggish nature of disparity processing, which is present even for frontoparallel motion tracking of a disparity-defined stimulus. Thus, despite the ecological importance of reacting to approaching objects, both the geometry of 3D vision and the nature of disparity processing result in considerable impairments for tracking motion-through-depth using binocular cues. NEW & NOTEWORTHY We characterize motion perception continuously in all directions using an ecologically relevant, manual target tracking paradigm we recently developed. This approach reveals a selective impairment to the perception of motion-through-depth. Geometric considerations demonstrate that this impairment is not consistent with previously observed spatial deficits (e.g., stereomotion suppression). However, results from an examination of disparity processing are consistent with the longer latencies observed in discrete, trial-based measurements of the perception of motion-through-depth.
47
Yudianto, Erfan, Susanto Susanto und Sinta Priciliya. „Etnomatematika pada Batik Lukis Daun Singkong di Rumah Produksi Daweea Batik Bondowoso“. Jurnal Elemen 6, Nr. 2 (31.07.2020): 199–210. http://dx.doi.org/10.29408/jel.v6i2.2002.
Der volle Inhalt der QuelleAnnotation:
Ethnomathematics is the relationship between culture and mathematics found in society's habits, where people have unconsciously applied mathematical concepts in their culture or habits. The custom referred to in this study is what is done by batik in making one batik sheet every time. The purpose of this study was to describe ethnomathematics on cassava leaves in the production house Daweea Batik Bondowoso East Java. This research is qualitative research with an ethnographic approach. The subject of this study was the craftsmen in the Daweea Bondowoso Batik production house. Data collection methods used are observation, interviews, and documentation. The observation was carried out by the researcher himself and assisted by two observers who were provided with observation guidelines. Interviews were conducted to artisans in Daweea Bondowoso batik production house, while the documentation was carried out by the researcher himself using a camera recorder. The results of this study indicate the existence of ethnomathematics in cassava leaves batik painting. Geometry concepts or elements found include points, lines, angles, flat shapes (rectangles, squares), congruence, concordance, equations, and geometric transformations (dilation).
48
Protonotarios, Emmanouil D., Buzz Baum, Alan Johnston, Ginger L. Hunter und Lewis D. Griffin. „An absolute interval scale of order for point patterns“. Journal of The Royal Society Interface 11, Nr. 99 (06.10.2014): 20140342. http://dx.doi.org/10.1098/rsif.2014.0342.
Der volle Inhalt der QuelleAnnotation:
Human observers readily make judgements about the degree of order in planar arrangements of points (point patterns). Here, based on pairwise ranking of 20 point patterns by degree of order, we have been able to show that judgements of order are highly consistent across individuals and the dimension of order has an interval scale structure spanning roughly 10 just-notable-differences (jnd) between disorder and order. We describe a geometric algorithm that estimates order to an accuracy of half a jnd by quantifying the variability of the size and shape of spaces between points. The algorithm is 70% more accurate than the best available measures. By anchoring the output of the algorithm so that Poisson point processes score on average 0, perfect lattices score 10 and unit steps correspond closely to jnds, we construct an absolute interval scale of order. We demonstrate its utility in biology by using this scale to quantify order during the development of the pattern of bristles on the dorsal thorax of the fruit fly.
49
Poulis, F. P., und J. M. Salim. „Weyl geometry and gauge-invariant gravitation“. International Journal of Modern Physics D 23, Nr. 11 (Oktober 2014): 1450091. http://dx.doi.org/10.1142/s0218271814500916.
Der volle Inhalt der QuelleAnnotation:
In this paper, we provide a gauge-invariant theory of gravitation in the context of Weyl Integrable Spacetimes. After making a brief review of the theory's postulates, we carefully define the observers' proper-time and point out its relation with spacetime description. As a consequence of this relation and the theory's gauge symmetry we recover all predictions of general relativity. This feature is made even clearer by a new exact solution we provide which reveals the importance of a well defined proper-time. The thermodynamical description of the source fields is given and we observe that each of the geometric fields have a certain physical significance, despite the gauge-invariance. This is shown by two examples, where one of them consists of a new cosmological constant solution. Our conclusions highlight the intimate relation among test particles trajectories, proper-time and spacetime description which can also be applied in any other situation, whether or not it recovers general relativity results and also in the absence of a gauge symmetry.
50
IVEZIĆ, TOMISLAV. „THE CONSTITUTIVE RELATIONS AND THE MAGNETOELECTRIC EFFECT FOR MOVING MEDIA“. International Journal of Modern Physics B 26, Nr. 08 (30.03.2012): 1250040. http://dx.doi.org/10.1142/s0217979212500403.
Der volle Inhalt der QuelleAnnotation:
In this paper the constitutive relations for moving media with homogeneous and isotropic electric and magnetic properties are presented as the connections between the generalized magnetization–polarization bivector [Formula: see text] and the electromagnetic field F. Using the decompositions of F and [Formula: see text], it is shown how the polarization vector P(x) and the magnetization vector M(x) depend on E, B and two different velocity vectors, u — the bulk velocity vector of the medium, and v — the velocity vector of the observers who measure E and B fields. These constitutive relations with four-dimensional geometric quantities, which correctly transform under the Lorentz transformations (LT), are compared with Minkowski's constitutive relations with the 3-vectors and several essential differences are pointed out. They are caused by the fact that, contrary to the general opinion, the usual transformations of the 3-vectors E, B, P, M, etc. are not the LT. The physical explanation is presented for the existence of the magnetoelectric effect in moving media that essentially differs from the traditional one.