Global Rotation Research Articles

Multiple-stage ambiguity in motion perception reveals global computation of local motion directions.

The motion of a 1D image feature, such as a line, seen through a small aperture, or the small receptive field of a neural motion sensor, is underconstrained, and it is not possible to derive the true motion direction from a single local measurement. This is referred to as the aperture problem. How the visual system solves the aperture problem is a fundamental question in visual motion research. In the estimation of motion vectors through integration of ambiguous local motion measurements at different positions, conventional theories assume that the object motion is a rigid translation, with motion signals sharing a common motion vector within the spatial region over which the aperture problem is solved. However, this strategy fails for global rotation. Here we show that the human visual system can estimate global rotation directly through spatial pooling of locally ambiguous measurements, without an intervening step that computes local motion vectors. We designed a novel ambiguous global flow stimulus, which is globally as well as locally ambiguous. The global ambiguity implies that the stimulus is simultaneously consistent with both a global rigid translation and an infinite number of global rigid rotations. By the standard view, the motion should always be seen as a global translation, but it appears to shift from translation to rotation as observers shift fixation. This finding indicates that the visual system can estimate local vectors using a global rotation constraint, and suggests that local motion ambiguity may not be resolved until consistencies with multiple global motion patterns are assessed.

Test of source selection for constructing a more stable and uniform celestial reference frame

We aim to evaluate the possibility of improving the International Celestial Reference System realization starting from the ICRF2 catalogue by investigating the coordinate time series of radio sources observed by the very long baseline interferometry between 1979 and 2016. Sources with long observational history are selected as the candidates and the least-squares fits with special handling of the weights are performed to derive the linear drifts of the source coordinates. Then the sources are sorted, based on the normalized linear drift (i) over the whole sky, and (ii) in four homolographic areas divided by declinations. The axial stability of the reference system and sky distribution defined by the selected sources are evaluated, which are acted as the criterion for the final source lists. With our improved source selection scheme, two groups of sources are proposed and considered suitable for defining a more stable and homogeneous celestial reference system compared to the second version of the current International Celestial Reference Frame (ICRF2). The number of sources in the final lists are 323 and 294, respectively, and the global rotations of the axes derived from apparent motion of the sources are about two times better than the ICRF2.

Two-dimensionalization of the flow driven by a slowly rotating impeller in a rapidly rotating fluid

We characterize the two-dimensionalization process in the turbulent flow produced by an impeller rotating at a rate $\omega$ in a fluid rotating at a rate $\Omega$ around the same axis for Rossby number $Ro=\omega/\Omega$ down to $10^{-2}$. The flow can be described as the superposition of a large-scale vertically invariant global rotation and small-scale shear layers detached from the impeller blades. As $Ro$ decreases, the large-scale flow is subjected to azimuthal modulations. In this regime, the shear layers can be described in terms of wakes of inertial waves traveling with the blades, originating from the velocity difference between the non-axisymmetric large-scale flow and the blade rotation. The wakes are well defined and stable at low Rossby number, but they become disordered at $Ro$ of order of 1. This experiment provides insight into the route towards pure two-dimensionalization induced by a background rotation for flows driven by a non-axisymmetric rotating forcing.

KINEMATICS IN THE GALACTIC BULGE WITH APOGEE. II. HIGH-ORDER KINEMATIC MOMENTS AND COMPARISON TO EXTRAGALACTIC BAR DIAGNOSTICS

ABSTRACT Much of the inner Milky Way’s (MW) global rotation and velocity dispersion patterns can be reproduced by models of secularly evolved, bar-dominated bulges. More sophisticated constraints, including the higher moments of the line-of-sight velocity distributions (LOSVDs) and limits on the chemodynamical substructure, are critical for interpreting observations of the unresolved inner regions of extragalactic systems and for placing the MW in context with other galaxies. Here, we use SDSS-APOGEE data to develop these constraints, by presenting the first maps of the skewness and kurtosis of the LOSVDs of metal-rich and metal-poor inner MW stars (divided at [Fe/H] = −0.4), and comparing the observed patterns to those that are seen both in N-body models and in extragalactic bars. Despite closely matching the mean velocity and dispersion, the models do not reproduce the observed skewness patterns of the LOSVDs in different ways, which demonstrates that our understanding of the detailed orbital structure of the inner MW remains an important regime for improvement. We find evidence in the MW of the skewness–velocity correlation that is used as a diagnostic of extragalactic bars/bulges. This correlation appears in metal-rich stars only, providing further evidence for different evolutionary histories of chemically differentiated populations. We connect these skewness measurements to previous work on high-velocity “peaks” in the inner Galaxy, confirming the presence of that phenomenon, and we quantify the cylindrical rotation of the inner Galaxy, finding that the latitude-independent rotation vanishes outside l ∼ 7°. Finally, we evaluate the MW data in the light of selected extragalactic bar diagnostics and discuss the progress and challenges in using the MW as a resolved analog of unresolved stellar populations.

Structural behaviour and design of dowel groups Experimental and numerical identification of stress states and failure mechanisms of the surrounding timber matrix

Dowel-type fasteners in combination with steel plates are widely used in engineered timber structures. Since dowel groups are designed as semi-rigid connections subjected to an arbitrary set of internal forces, the corresponding structural behaviour of the surrounding timber matrix must be considered in the design process accordingly, including the effect of reinforcements. Corresponding stress states and failure mechanisms in the timber matrix of dowel groups are discussed herein. Surface strain fields from tests of dowel groups under complex loading situations were used to identify the sequence of cracking, as well as to assign the related failure modes. First cracking events were caused by stress peaks at the most loaded dowels and by a combination of shear stresses and stresses perpendicular to the grain, while later cracking events were associated with a predominant action of individual stress components. Thus, the non-linear global moment-relative rotation behaviour of dowel groups could be related to failure mechanisms in the surrounding timber matrix. The corresponding strain state was qualitatively as well as quantitatively reproduced by means of a numerical model, which gave access to stresses in the timber matrix and has potential to be implemented as a sub-model in engineering design software. The numerical model supported the feasibility of a decomposition of the stress state due to the global bending moment into stresses caused by a couple of equal forces parallel and perpendicular to the grain, which could be used in the design process. Based on experimental and numerical findings, essential aspects for a design procedure for the timber matrix in dowel groups loaded by a combination of internal forces are proposed.

Pairing Phase Transitions of Matter under Rotation.

The phases and properties of matter under global rotation have attracted much interest recently. In this Letter we investigate the pairing phenomena in a system of fermions under the presence of rotation. We find that there is a generic suppression effect on pairing states with zero angular momentum. We demonstrate this effect with the chiral condensation and the color superconductivity in hot dense QCD matter as explicit examples. In the case of chiral condensation, a new phase diagram in the temperature-rotation parameter space is found, with a nontrivial critical point.

Reversal cycle in square Rayleigh–Bénard cells in turbulent regime

We consider long-term data from direct numerical simulations of turbulent Rayleigh–Bénard convection inside two-dimensional (2-D) square cells. For the range of Rayleigh numbers $Ra=10^{7}{-}10^{8}$ and Prandtl numbers $Pr=3.0{-}4.3$ considered, two types of flow regimes are observed: a regime consisting of consecutive reversals, when the global rotation switches sign; and a regime consisting of an extended cessation, when global rotation is absent. A filtering method discriminates these two regimes and allows us to identify two characteristic time scales for the former regime. A time rescaling is then used to tune our records to a common duration, thus putting into evidence a generic reversal cycle. This cycle is composed of three successive phases: acceleration, accumulation and release including a rebound event. We complement this view in terms of a global angular impulse, available mechanical energy, global kinetic energy and their corresponding transfer rates. For a particular realisation of a reversal, each phase is described in terms of the flow patterns (large diagonal roll, counter-rotating corner flows and thermal plumes) and tied to the corresponding energy processes. We conclude by performing linear as well as nonlinear stability studies to account for the triggering mechanism of the release.

Building a Sustainable Global Surgical Program in an Academic Department of Surgery

BackgroundGlobal surgery and volunteerism in surgery has gained significant interest in recent years for general surgery residents across the country. However, there are few well-established long-term surgical programs affiliated with academic institutions. The present report discusses the implementation process and challenges facing an academic institution in building a long-term sustainable global surgery program. MethodsAs one of the pioneer programs in global surgery for residents, the Icahn School of Medicine at Mount Sinai global surgery rotation has been successfully running for the last 10 years in a small public hospital in the Dominican Republic. The present report details many key components of implementing a sustainable global surgery program and the evolution of this program over time. FindingsSince 2005, 80 general surgery residents have rotated through Juan Pablo Pina Hospital in the Dominican Republic. They have performed a total of 1239 major operations and 740 minor operations. They have also participated in 328 emergency cases. More importantly, this rotation helped shape residents' sense of social responsibility and ownership in their surgical training. Residents have also contributed to the training of local residents in laparoscopic skills and through cultural exchange. ConclusionsAs interest in global surgery grows among general surgery residents, it is essential that supporting academic institutions create sustainable and capacity-building rotations for their residents. These programs must address many of the barriers that can hinder maintenance of a sustainable global surgery experience for residents. After 10 years of sending our residents to the Dominican Republic, we have found that it is possible and valuable to incorporate a formal global surgery rotation into a general surgery residency.

Effect of a Global Surgery Resident Rotation on Physician Practices after Residency: The Mount Sinai Experience

Effect of a Global Surgery Resident Rotation on Physician Practices after Residency: The Mount Sinai Experience

Beyond the learning curve: length of global health electives.

Beyond the learning curve: length of global health electives.

Acoustic magnons in the long-wavelength limit: Investigating the Goldstone violation in many-body perturbation theory

Collective spin excitations in magnetic materials arise from the correlated motion of electron-hole pairs with opposite spins. The pair propagation is described by the transverse magnetic susceptibility, which we calculate within many-body perturbation theory from first principles employing the full-potential linearized augmented-plane-wave formalism. Ferromagnetic materials exhibit a spontaneously broken global rotation symmetry in spin space leading to the appearance of acoustic magnons (zero gap) in the long-wavelength limit. However, due to approximations used in the numerical scheme, the acoustic magnon dispersion exhibits a small but finite gap at $\mathrm{\ensuremath{\Gamma}}$. We analyze this violation of the Goldstone mode and present an approach that implements the magnetic susceptibility using a renormalized Green function instead of the Kohn-Sham one. This much more expensive approach shows substantial improvement of the Goldstone-mode condition. In addition, we discuss a possible correction scheme, which involves an adjustment of the Kohn-Sham exchange splitting, which is motivated by the spin-wave solution of the one-band Hubbard model. The new exchange splittings turn out to be closer to experiment. We present corrected magnon spectra for the elementary ferromagnets Fe, Co, and Ni.

Exploring the psychological effects of global health rotations on first year medical students through the analysis of student reflection.

Exploring the psychological effects of global health rotations on first year medical students through the analysis of student reflection.

International contagion through financial versus non-financial firms

The role of financial firms in the transmission of financial shocks across countries is well recognized in the literature. However, contagion through non-financial firms has not received much attention. This study examines the role of financial vis-à-vis non-financial firms in transmitting shocks across countries using a dynamic conditional correlation analysis. We provide empirical evidence from a sample of 49 countries. A novel finding of our study is that non-financial firms play a more pronounced role in the cross-market transmission of shocks than financial firms. Financial contagion is positively related to the level of equity market development and bilateral trade intensity. It is higher during periods of US economic downturns and financial crises. Given that the extent of international contagion varies across economic states and is more prevalent in the non-financial than in the financial sector, this study has implications for global sector rotation strategies.

A method based on point cloud sectioning to evaluate different sources of error on the shape of a manufactured object

ABSTRACTThis paper presents a method to evaluate the accuracy of a manufactured object with respect to its original CAD model. Different errors caused by the manufacturing process are assumed to come from global axis deformation and transverse sections rotation of the object with respect to its ideal CAD. Object and CAD shapes are given in form of point clouds, the former derived from a laser-scanning measurement, the latter from sampling the ideal surface by a dense and uniform point grid. Point clouds are sectioned in a finite number of thin blocks. This method has been applied to the analysis of a helical Darrieus blade prototype, parametrically designed and modelled with McNeel Rhinoceros and Grasshopper software, manufactured with a three-axes Computer Numerical Control machine. This procedure is able to check the conformity of the manufactured airfoil to the theoretical one and to establish the efficiency of the final prototype of the blade turbine.

CONVEX IMAGE ORIENTATION FROM RELATIVE ORIENTATIONS

Abstract. In this paper we propose a novel workflow for the estimation of global image orientations given relative orientations between pairs of overlapping images. Our approach is convex and independent on initial values. First, global rotations are estimated in a relaxed semidefinite program (SDP) and refined in an iterative least squares adjustment in the tangent space of SO(3). A critical aspect is the handling of outliers in the relative orientations. We present a novel heuristic graph based approach for filtering the relative rotations that outperforms state-of-the-art robust rotation averaging algorithms. In a second part we make use of point-observations, tracked over a set of overlapping images and formulate a linear homogeneous system of equations to transfer the scale information between triplets of images, using estimated global rotations and relative translation directions. The final step consists of refining the orientation parameters in a robust bundle adjustment. The proposed approach handles outliers in the homologous points and relative orientations in every step of the processing chain. We demonstrate the robustness of the procedure on synthetic data. Moreover, the performance of our approach is illustrated on real world benchmark data.

CONVEX IMAGE ORIENTATION FROM RELATIVE ORIENTATIONS

In this paper we propose a novel workflow for the estimation of global image orientations given relative orientations between pairs of overlapping images. Our approach is convex and independent on initial values. First, global rotations are estimated in a relaxed semidefinite program (SDP) and refined in an iterative least squares adjustment in the tangent space of SO(3). A critical aspect is the handling of outliers in the relative orientations. We present a novel heuristic graph based approach for filtering the relative rotations that outperforms state-of-the-art robust rotation averaging algorithms. In a second part we make use of point-observations, tracked over a set of overlapping images and formulate a linear homogeneous system of equations to transfer the scale information between triplets of images, using estimated global rotations and relative translation directions. The final step consists of refining the orientation parameters in a robust bundle adjustment. The proposed approach handles outliers in the homologous points and relative orientations in every step of the processing chain. We demonstrate the robustness of the procedure on synthetic data. Moreover, the performance of our approach is illustrated on real world benchmark data.

REFINED SATELLITE IMAGE ORIENTATION IN THE FREE OPEN-SOURCE PHOTOGRAMMETRIC TOOLS APERO/MICMAC

Abstract. This publication presents the RPC-based bundle adjustment implemented in the freeware open-source photogrammetric tool Apero/MicMac. The bundle adjustment model is based on some polynomial correction functions, enriched with a physical constraint that introduces the notion of a global sensor rotation into the model. The devised algorithms are evaluated against two datasets consisting of two stereo and a triplet pair of the Pleiades images. Two sets of correction functions and a number of GCPs configurations are examined. The obtained geo-referencing accuracy falls below the size of 1GSD.

REFINED SATELLITE IMAGE ORIENTATION IN THE FREE OPEN-SOURCE PHOTOGRAMMETRIC TOOLS APERO/MICMAC

This publication presents the RPC-based bundle adjustment implemented in the freeware open-source photogrammetric tool Apero/MicMac. The bundle adjustment model is based on some polynomial correction functions, enriched with a physical constraint that introduces the notion of a global sensor rotation into the model. The devised algorithms are evaluated against two datasets consisting of two stereo and a triplet pair of the Pleiades images. Two sets of correction functions and a number of GCPs configurations are examined. The obtained geo-referencing accuracy falls below the size of 1GSD.

Nonrigid Motion Correction With 3D Image-Based Navigators for Coronary MR Angiography.

To develop a retrospective nonrigid motion-correction method based on 3D image-based navigators (iNAVs) for free-breathing whole-heart coronary magnetic resonance angiography (MRA). The proposed method detects global rigid-body motion and localized nonrigid motion from 3D iNAVs and compensates them with an autofocusing algorithm. To model the global motion, 3D rotation and translation are estimated from the 3D iNAVs. Two sets of localized nonrigid motions are obtained from deformation fields between 3D iNAVs and reconstructed binned images, respectively. A bank of motion-corrected images is generated and the final image is assembled pixel-by-pixel by selecting the best focused pixel from this bank. In vivo studies with six healthy volunteers were conducted to compare the performance of the proposed method with 3D translational motion correction and no correction. In vivo studies showed that compared to no correction, 3D translational motion correction and the proposed method increased the vessel sharpness by 13% ± 13% and 19% ± 16%, respectively. Out of 90 vessel segments, 75 segments showed improvement with the proposed method compared to 3D translational correction. We have developed a nonrigid motion-correction method based on 3D iNAVs and an autofocusing algorithm that improves the vessel sharpness of free-breathing whole-heart coronary MRA. Magn Reson Med 77:1884-1893, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Rotating nanocomposite thin-walled beams undergoing large deformation

A computational model was developed to study the nonlinear steady state static response and free vibration of thin-walled carbon nanotubes/fiber/polymer laminated multiscale composite beams and blades. A set of nonlinear intrinsic equations describing the response of rotating cantilever composite beams undergoing large deformations was established. The main assumptions were small local strains and local rotations, large deflections and global rotations. Halpin–Tsai equations and fiber micromechanics were used to predict the bulk material properties of the multiscale nanocomposite. The carbon nanotubes (CNTs) were assumed to be uniformly distributed and randomly oriented through the epoxy resin matrix. Discretized by the Galerkin approximation, eigenvalues and vectors and nonlinear steady state static response of the nanocomposite beams and blades were calculated. The volume fraction of fibers, weight percentage of single-walled and multi-walled carbon nanotubes (SWCNTs and MWCNTs) and their aspect ratio were investigated through a detailed parametric study for their effects on the nonlinear response of nanotubes-reinforced moving beams. It was found that natural frequencies are significantly influenced by a small percentage of CNTs. It was also found that the SWCNTs reinforcement produces more pronounced effect in comparison with MWCNTs on the nonlinear steady state static response and natural frequencies of the composite beams.