Local Frame Research Articles

Relativistic contributions to the rotation of Mars

Context. The orientation and rotation of Mars can be described by a set of Euler angles (longitude, obliquity, and rotation angles) and estimated from radioscience data (tracking of orbiters and landers), which can then be used to infer the planet's internal properties. The data are analyzed using a modeling expressed within the barycentric celestial reference system (BCRS). This modeling includes several relativistic contributions that need to be properly taken into account to avoid any misinterpretation of the data. Aims. We provide new and more accurate (to the 0.1 mas level) estimations of the relativistic corrections to be included in the BCRS model of the orientation and rotation of Mars. Methods. There are two types of relativistic contributions with regard to Mars's rotation and orientation: (i) those that directly impact the Euler angles and (ii) those resulting from the time transformation between a local Mars reference frame and BCRS. The former contribution essentially corresponds to the geodetic effect, as well as to the smaller Lense-Thirring and Thomas precession effects, and we computed their values assuming that Mars evolves on a Keplerian orbit. As for the latter contribution, we computed the effect of the time transformation and compared the rotation angle corrections obtained, based on the assumption that the planets evolve on Keplerian orbits, with the corrections obtained, based on realistic orbits as described by the ephemerides. Results. The relativistic correction in longitude mainly comes from the geodetic effect and results in a geodetic precession (6.754 mas yr−1) and geodetic annual nutation (0.565 mas amplitude). For the rotation angle, the correction is dominated by the effect of the time transformation. The main annual, semiannual, and terannual terms display amplitudes of 166.954 mas, 7.783 mas, and 0.544 mas, respectively. The amplitude of the annual term differs by about 9 mas from the estimate usually considered by the community. We identified new terms at the Mars-Jupiter and Mars-Saturn synodic periods (0.567 mas and 0.102 mas amplitude) that are relevant considering the current level of uncertainty of the measurements, as well as a contribution to the rotation rate (7.3088 mas day−1). There is no significant correction that applies to the obliquity.

Anomalous compressible mode generation by global frame projections of pure Alfven mode

ABSTRACTAlfven wave is the single most important physical phenomenon of magneto-hydrodynamic (MHD) turbulence and has far-reaching impact to almost all studies related to astrophysical magnetic field. Yet the restoration of the Alfven wave fluctuations from a given magnetic field, aka the local Alfven wave problem, is never properly addressed in literature albeit its importance. Previous works model the Alfven wave fluctuation as the perturbation along a straight-line, constant magnetic field. However, Lazarian & Pogosyan (2012) suggested that the decomposition of Alfven wave along a straight line, aka. the global frame decomposition, has a factor of discrepancy to the true local Alfven wave fluctuation. Here, we provide a geometric interpretation on how the local Alfven wave is related to the global frame through the use of vector frame formulation. We prove both analytically and numerically that the local frame Alfven wave is an orthogonal transformation of that of the global frame and related by the local Alfvenic Mach number. In other words, when we observe Alfven wave in the global frame of reference, some of the Alfven wave will be mistaken as compressible waves. The importance of frame choices has a far-reaching impact to the analytical studies of MHD turbulence. Combining the frame formalism and the new techniques we can have accurate measurement to some of the fundamental turbulence properties like the inclination angle of mean magnetic field relative to the line of sight.

Sensor Fusion with Asynchronous Decentralized Processing for 3D Target Tracking with a Wireless Camera Network.

We present a method to acquire 3D position measurements for decentralized target tracking with an asynchronous camera network. Cameras with known poses have fields of view with overlapping projections on the ground and 3D volumes above a reference ground plane. The purpose is to track targets in 3D space without constraining motion to a reference ground plane. Cameras exchange line-of-sight vectors and respective time tags asynchronously. From stereoscopy, we obtain the fused 3D measurement at the local frame capture instant. We use local decentralized Kalman information filtering and particle filtering for target state estimation to test our approach with only local estimation. Monte Carlo simulation includes communication losses due to frame processing delays. We measure performance with the average root mean square error of 3D position estimates projected on the image planes of the cameras. We then compare only local estimation to exchanging additional asynchronous communications using the Batch Asynchronous Filter and the Sequential Asynchronous Particle Filter for further fusion of information pairs' estimates and fused 3D position measurements, respectively. Similar performance occurs in spite of the additional communication load relative to our local estimation approach, which exchanges just line-of-sight vectors.

The policy integration game? Congruence of outputs and implementation in policy integration

Researchers agree on the importance of policy integration in the analysis of responses to complex problems, yet they often use this concept to indicate integrated policy programmes (IPPs) as opposed to policy integration in practice (as performed by actors). Describing how IPPs are reshaped, while they are being implemented opens new research venues in the study of the policy integration process and its effects. This article theorises the ‘(in)congruent implementation' of IPPs and illustrates its theoretical contribution with the case study of the local implementation of the national ‘Security Decree' in the Italian cities of Bologna and Pesaro. The paper makes a theoretical contribution to the study of the political aspects of policy integration. In particular, it suggests that three factors—the misalignment of state and local policy frames, the incommensurability of different subsystems’ interests, and local politicians’ risk avoidance strategies—might be led to the process of reframing national integrative intentions from the bottom up.

Site-based description of R1ρ relaxation in local reference frames

Nuclear magnetic spin relaxation in the presence of an applied radiofrequency field depends critically on chemical exchange processes that transfer nuclear spins between chemical or conformational environments with distinct resonance frequencies. Characterization of chemical exchange processes in R1ρ relaxation dispersion, CEST, and DEST experiments provides powerful insights into chemical and conformational kinetics of biological macromolecules. The present work reformulates expressions for magnetization evolution and the R1ρ relaxation rate constant by focussing on the orientations of the tilted rotating frames of reference for magnetization components in different sites, by treating the spin-locking field strength as a perturbation to free-precession evolution, and by applying the Homotopy Analysis and Laplace transform methods to approximate solutions to the Bloch-McConnell equations. The results provide an expression for R1ρ that is invariant to the topology of the kinetic scheme, an approximate equation for evolution of spin-locked z-magnetization, and an approach for effective simplification of chemical exchange topologies for 2- and N-site chemical exchange processes. The theoretical approach also provides an accurate approximation for relaxation during a constant-amplitude radiofrequency field in the absence of exchange.

Event Camera and LiDAR based Human Tracking for Adverse Lighting Conditions in Subterranean Environments

In this article, we propose a novel LiDAR and event camera fusion modality for subterranean (SubT) environments for fast and precise object and human detection in a wide variety of adverse lighting conditions, such as low or no light, high-contrast zones and in the presence of blinding light sources. In the proposed approach, information from the event camera and LiDAR are fused to localize a human or an object-of-interest in a robot's local frame. The local detection is then transformed into the inertial frame and used to set references for a Nonlinear Model Predictive Controller (NMPC) for reactive tracking of humans or objects in SubT environments. The proposed novel fusion uses intensity filtering and K-means clustering on the LiDAR point cloud and frequency filtering and connectivity clustering on the events induced in an event camera by the returning LiDAR beams. The centroids of the clusters in the event camera and LiDAR streams are then paired to localize reflective markers present on safety vests and signs in SubT environments. The efficacy of the proposed scheme has been experimentally validated in a real SubT environment (a mine) with a Pioneer 3AT mobile robot. The experimental results show real-time performance for human detection and the NMPC-based controller allows for reactive tracking of a human or object of interest, even in complete darkness.

Cooperative Angles-Only Relative Navigation Algorithm for Multi-Spacecraft Formation in Close-Range

As to solve the collaborative relative navigation problem for near-circular orbiting small satellites in close-range under GNSS denied environment, a novel consensus constrained relative navigation algorithm based on the lever arm effect of the sensor offset from the spacecraft center of mass is proposed. Firstly, the orbital propagation model for the relative motion of multi-spacecraft is established based on Hill-Clohessy-Wiltshire dynamics and the line-of-sight measurement under sensor offset condition is modeled in Local Vertical Local Horizontal frame. Secondly, the consensus constraint model for the relative orbit state is constructed by introducing the geometry constraint between the spacecraft, based on which the consensus unscented Kalman filter is designed. Thirdly, the observability analysis is done and the necessary conditions of the sensor offset to make the state observable are obtained. Lastly, digital simulations are conducted to verify the proposed algorithm, where the comparison to the unconstrained case is also done. The results show that the estimated error of the relative position converges very quickly, the location error is smaller than 10 m under the condition of 10−3 rad level camera and 5 m offset.

Range-Only Bearing Estimator for Localization and Mapping

Navigation and exploration within unknown environments are typical examples in which simultaneous localization and mapping (SLAM) algorithms are applied. When mobile agents deploy only range sensors without bearing information, the agents must estimate the bearing using the online distance measurement for the localization and mapping purposes. In this paper, we propose a scalable dynamic bearing estimator to obtain the relative bearing of the static landmarks in the local coordinate frame of a moving agent in real-time. Using contraction theory, we provide convergence analysis of the proposed range-only bearing estimator and present upper and lower-bound for the estimator gain. Numerical simulations demonstrate the effectiveness of the proposed method.

Sustainable Ecology of the Metropolis and a Local Green Frame Involving Beneficial Insects on the Example of St. Petersburg

The article describes the results of design studies aimed at increasing the sustainability of the environment by attracting beneficial insects in the structure of the formation of a green frame. The work was carried out in 2021-2023, the vector of design research was formed on the basis of the St. Petersburg State University of Architecture and Civil Engineering (SPbGASU) undergraduate program and continues in the format of networking, including with the participation of Sevastopol State University (SevSU) undergraduate program ” directions “Landscape architecture”. The article describes both landscape and ideological practices that help attract beneficial insects to the territory of landscape objects, and also describes specific solutions on the example of the territory of the Petrogradsky and Kirovsky districts of the city of St. Petersburg, made with the participation of residents and the Improvement Committee. The importance of insects in the urban green network is described, the possibility of integrating special landscape zones into green infrastructure for this, the problem of creating a single ecological frame of the metropolis and a local green frame at the district level is considered. The author’s design methodology is presented in terms of the transition from the urban and town-planning level to specific design solutions at the masterplan level and, further, to the development of specific landscape niches with the landscaping species composition.

Autonomous coordinate establishment of local reference frames for ground-based positioning systems without known points

Autonomous coordinate establishment of local reference frames for ground-based positioning systems without known points

Mapping 3D grain and precipitate structure during in situ mechanical testing of open-cell metal foam using micro-computed tomography and high-energy X-ray diffraction microscopy

• 3D grain structure is mapped and tracked during loading of open-cell metal foam. • Challenges included sample size relative to beam size and large ligament motions. • X-ray CT and far-field HEDM measurements collected at incremental displacements. • New scanning and stitching methodology established for far-field HEDM measurements. • Ligament-tracking code used to express crystal orientation in local reference frame. Open-cell metal foams are ultra-low-density cellular metals with complex hierarchical structures that span bulk, cell, ligament, and sub-ligament scales and give rise to desirable properties such as high strength-to-weight ratio and excellent energy absorption. Although literature suggests that intrinsic material structures at sub-ligament length scales (e.g., grains and precipitates) play an important role in mechanical behavior of open-cell metal foams, there are very few experimental measurements of such structures in three dimensions and for meaningful volumes of foam. This study seeks to map and track the three-dimensional (3D) grain and precipitate structures of an intact volume of open-cell aluminum foam by advancing microstructural characterization techniques that leverage X-ray micro-computed tomography ( μ CT ) and far-field high-energy X-ray diffraction microscopy (FF-HEDM). A 6%-relative-density aluminum foam sample was mechanically tested in compression while μ CT and FF-HEDM measurements were collected at interrupted loading states at beamline 1-ID of the Advanced Photon Source. A new scanning strategy and reconstruction algorithm were established to enable characterization of a foam volume with diameter approximately four times wider than the nominal width of the X-ray beam. The result is a set of maps that detail both the 3D grain and precipitate structures throughout the foam volume at successive strain steps. A novel grain tracking procedure was developed to track individual grains within the foam volume by accounting for the large rigid-body motions that individual ligaments can undergo during mechanical loading. The ability to track grains and precipitate structures in three dimensions throughout large bulk deformation of ultra-low-density polycrystalline materials enables new possibilities for validating numerical models and investigating local failure mechanisms. Furthermore, the methods and procedures developed in this study could be applied to other ultra-low-density structures, such as additively manufactured lattices.

Vortex Lens: Interactive Vortex Core Line Extraction using Observed Line Integral Convolution.

This paper describes a novel method for detecting and visualizing vortex structures in unsteady 2D fluid flows. The method is based on an interactive local reference frame estimation that minimizes the observed time derivative of the input flow field v(x, t). A locally optimal reference frame w(x, t) assists the user in the identification of physically observable vortex structures in Observed Line Integral Convolution (LIC) visualizations. The observed LIC visualizations are interactively computed and displayed in a user-steered vortex lens region, embedded in the context of a conventional LIC visualization outside the lens. The locally optimal reference frame is then used to detect observed critical points, where v=w, which are used to seed vortex core lines. Each vortex core line is computed as a solution of the ordinary differential equation (ODE) · w(t)=w(w(t), t), with an observed critical point as initial condition (w(t0), t0). During integration, we enforce a strict error bound on the difference between the extracted core line and the integration of a path line of the input vector field, i.e., a solution to the ODE · v(t)=v(v(t), t). We experimentally verify that this error depends on the step size of the core line integration. This ensures that our method extracts Lagrangian vortex core lines that are the simultaneous solution of both ODEs with a numerical error that is controllable by the integration step size. We show the usability of our method in the context of an interactive system using a lens metaphor, and evaluate the results in comparison to state-of-the-art vortex core line extraction methods.

Bearing-Only Formation Control With Bounded Disturbances in Agents’ Local Coordinate Frames

Bearing-Only Formation Control With Bounded Disturbances in Agents’ Local Coordinate Frames

Multi-maneuver algorithms for multi-risk collision avoidance via nonconvex quadratic optimization

In this article, the problem of modeling and computing the optimal collision avoidance maneuvers for multiple short-term encounters is presented. Several metrics defining the overall collision risk are analyzed. These include imposing lower bounds on the miss-distance or the Mahalanobis distance at each corresponding time of closest approach (TCA) or upper-bounds on the collision probability. The avoidance maneuvers are modeled as impulsive ones in a single direction of the local frame and for a priori fixed dates for operational motivations. Station-keeping constraints are also imposed via linear inequalities on the relative states at each TCA. The specific nature of the imposed constraints is dictated by a practical framework provided by the French Space Agency (CNES). This results in formulating the maneuver design problem as an optimization problem with linear objective and non-convex quadratic constraints. Different algorithms are presented to solve this problem. Finally, the relative efficiency of the proposed approaches is evaluated and analyzed on a realistic conjunction built from data extracted from the CNES database and on academic random examples of higher complexity.

Tolerant Tea Shops: The Social Construction of Forbearance in Child Labor

Abstract: Urban expansion is associated with the emergence and transformation of marginal labor. In this context, labor migration from rural areas increasingly includes younger migrants, as generational agricultural vocations decline. This, in turn, challenges conceptions of child labor, where younger migrants are engaged in labor which is spatially remote from their families. In Mandalay, Myanmar's second largest city, urbanization has drawn in large numbers of children from rural areas. Many of those children supply labor in nonformal contexts. One such practice is the hospitality industry, where young children are sent to work in the many tea shops in the city, supplying labor in exchange for lodging, food, and nominal wages. In such settings, their labor is provided not only away from parental control but also outside of formal employment structures. The spatial arrangements of tea shops reflect an "in-betweenness" which occupies a liminal place between formal and informal, neither a home, nor a "restaurant," and where the boundaries of public and private space are blurred. This in-betweenness enables a context for tolerance and forbearance of child labor, which is viewed by patrons as a benevolent welfare arrangement, rather than as waged employment; the same patrons would view these children very differently if they saw them at work in a place classified as a restaurant. This example highlights how the contexts of space and place intersect with cultural values to give specific local framings of social issues.

Метафора как речевое действие в фреймовой модели

Introduction. Earlier studies of the frame organization of the artistic narrative allowed us to come to the conclusion that, firstly, ontological frames-determinants can predetermine the narrative structure of both extended fragments of the narrative text and small fragments limited by the semantics of the local frame; secondly, the semantic-syntactic frame can be considered as a standard linguistic unit with a standard integral structure and semantics, as well as stable naming. Materials and methods. In the proposed approach, a speech frame represents a linguistic expression as a speech action, the content and performance of which is described in a propositional aspect. The use of a metaphor in the text itself is a standard speech action that includes a metaphorical expression in the context, while the meaning of the metaphor is determined by the linguistic and pragmatic context. A metaphor (from a word to a detailed construction) can be considered as a speech action of the speaker by virtue of the fact that the act of metaphorical comparison itself, contained in a metaphor, can be described in terms of propositions. Plot-forming semantic-syntactic frames in an artistic narrative are considered as stable linguistic units with stable conventional meanings and corresponding stable names. Analysis. The semantic-syntactic frame should be considered as a standard semantic model of a typical situation (everyday, communicative), in which the structural and content elements of the semantics of the frame, namely propositions, their predicates and terms filling the terminals of the frame, correspond to certain language expressions for their representation in the surface structures of the narrative. The initial thesis is that from the point of view of the tasks of describing relevant parameters, it is advisable to present a metaphor as a model of a semantic-syntactic procedural frame. Results. Based on the results of the study, a model is proposed in which nuclear propositions describing the basic predications of metaphorical speech action are attributed to the first terminal of the frame; to the second one – the bases of metaphorical comparison; to the third one – the conditions of the linguistic context; to the fourth one – the conditions of the pragmatic context. It is concluded that the representation of a metaphor as a speech action in the form of a procedural semantic-syntactic frame allows analyzing its semantics, structure and functions as a result of performing the corresponding actions and semantic operations displayed in the proposed METAPHOR frame model.

Locality-Aware Transformer for Video-Based Sign Language Translation

Recently, the application of transformer makes significant progress in sign language translation. However, several characteristics of sign videos are neglected in existing transformer-based methods that hinder translation performance. Firstly, in sign videos, multiple consecutive frames represent a single sign gloss thus the local temporal relations are crucial. Secondly, the inconsistency between video and text demands the non-local and global context modeling ability of the model. To address these issues, a locality-aware transformer is proposed for sign language translation. Concretely, the multi-stride position encoding scheme assigns the same position index to adjacent frames with various strides to enhance the local dependency. Afterward, the adaptive temporal interaction module is utilized to capture non-local and flexible local frame correlation simultaneously. Moreover, a gloss counting task is designed to facilitate the holistic understanding of sign videos. Experimental results on two benchmark datasets demonstrate the effectiveness of the proposed framework.

Semantic Relevance Learning for Video-Query Based Video Moment Retrieval

The task of video-query based video moment retrieval (VQ-VMR) aims to localize the segment in the reference video, which matches semantically with a short query video. This is a challenging task due to the rapid expansion and massive growth of online video services. With accurate retrieval of the target moment, we propose a new metric to effectively assess the semantic relevance between the query video and segments in the reference video. We also develop a new VQ-VMR framework to discover the intrinsic semantic relevance between a pair of input videos. It comprises two key components: a Fine-grained Feature Interaction (FFI) module and a Semantic Relevance Measurement (SRM) module. Together they can effectively deal with both the spatial and temporal dimensions of videos. First, the FFI module computes the semantic similarity between videos at a local frame level, mainly considering the spatial information in the videos. Subsequently, the SRM module learns the similarity between videos from a global perspective, taking into account the temporal information. We have conducted extensive experiments on two key datasets which demonstrate noticeable improvements of the proposed approach over the state-of-the-art methods.

Research on Automatic Detection Algorithm for Pedestrians on the Road Based on Image Processing Method

Accurate detection of pedestrian targets can effectively improve the performance level of intelligent transportation and surveillance projects. In order to effectively enhance the accuracy of detecting pedestrian targets on the road, this paper first introduced the traditional pedestrian target detection algorithm, proposed the faster recurrent convolutional neural network (RCNN) algorithm to detect pedestrian targets, and improved it to make good use of the convolutional features at different scales. Finally, support vector machine (SVM), traditional Faster RCNN, and optimized Faster RCNN algorithms were compared by simulation experiments. The results showed that the optimized Faster RCNN algorithm had higher detection accuracy and recall rate, obtained a more accurate target localization frame, and detected faster than SVM and traditional Faster RCNN algorithms; the traditional Faster RCNN algorithm had higher detection accuracy and target frame localization accuracy than the SVM algorithm.

Cultivating the Past, Living the Modern: The Politics of Time in the Sultanate of Oman

Cultivating the Past, Living the Modern: The Politics of Time in the Sultanate of Oman