Elliptical Object Research Articles

Sedimentation of an elliptical object in a two-dimensional foam

The sedimentation of an elliptical object in a dry two-dimensional, monodisperse foam is simulated. The calculations are quasi-static, allowing the identification and separation of the elastic, plastic and viscous response of the foam to the motion. In addition to its weight, the forces on the ellipse are due to the network of soap films and the pressures in the bubbles. These give rise to non-zero torque, lift and drag forces, causing the motion of the ellipse to deviate from a vertical path. Highly stretched films are formed in the wake of the ellipse and asymmetry in the flow field, with bubbles moving from the front to the back of the ellipse along only one side, causes it to rotate from a metastable state with its major axis perpendicular to gravity into a stable orientation with its major axis parallel to the direction of gravity. When the orientation is intermediate between these two limits, there is a significant lift force which causes the ellipse to move laterally. A larger, more eccentric, ellipse rotates more quickly.

Planning movements well in advance

It has been suggested that the metrics of grasping movements directed to visible objects are controlled in real time and are therefore unaffected by previous experience. We tested whether the properties of a visually presented distractor object influence the kinematics of a subsequent grasping movement performed under full vision. After viewing an elliptical distractor object in one of two different orientations participants grasped a target object, which was either the same object with the same orientation or a circular object without obvious orientation. When grasping the circular target, grip orientation was influenced by the orientation of the distractor. Moreover, as in classical visuomotor priming, grasping movements were initiated faster when distractor and target were identical. Results provide evidence that planning of visually guided grasping movements is influenced by prior perceptual experience, challenging the notion that metric aspects of grasping are controlled exclusively on the basis of real-time information.

Elliptical Object Detection by a Modified RANSAC with Sampling Constraint from Boundary Curves' Clustering

This paper proposes a method for detecting ellipses from an image despite (1) multiple colors within the ellipses, (2) partially occluded ellipses' boundaries, (3) noisy, locally deformed boundaries of ellipses, (4) presence of multiple objects other than the ellipses in the image, and (5) combinations of (1) through (4). After boundary curves are obtained by edge detection, by utilizing the first-order difference curves of the edge orientation of each pixel in the boundary curves, a segment-reconnect method obtains boundary clusters. Then, a modified RANSAC detects ellipses by choosing five pixels randomly from the boundary clusters, where overlapped ellipses are merged. Experimental results using synthesized images and real images demonstrate the effectiveness of the proposed method together with comparison with the Randomized Hough Transform, a well-known conventional method.

STRUCTURAL PARAMETERS OF SEVEN SMALL MAGELLANIC CLOUD INTERMEDIATE-AGE AND OLD STAR CLUSTERS

We present structural parameters for the seven intermediate-age and old star clusters NGC121, Lindsay 1, Kron 3, NGC339, NGC416, Lindsay 38, and NGC419 in the Small Magellanic Cloud. We fit King profiles and Elson, Fall, and Freeman profiles to both surface-brightness and star count data taken with the Advanced Camera for Surveys aboard the Hubble Space Telescope. Clusters older than 1 Gyr show a spread in cluster core radii that increases with age, while the youngest clusters have relatively compact cores. No evidence for post core collapse clusters was found. We find no correlation between core radius and distance from the SMC center, although consistent with other studies of dwarf galaxies, some relatively old and massive clusters have low densities. The oldest SMC star cluster, the only globular NGC121, is the most elliptical object of the studied clusters. No correlation is seen between ellipticity and distance from the SMC center. The structures of these massive intermediate-age (1-8 Gyr) SMC star clusters thus appear to primarily result from internal evolutionary processes.

Planning movements well in advance

It has been suggested that the metrics of grasping movements directed to visible objects are controlled in real time and are therefore unaffected by previous experience. We tested whether the properties of a visually presented distractor object influence the kinematics of a subsequent grasping movement performed under full vision. After viewing an elliptical distractor object in one of two different orientations participants grasped a target object, which was either the same object with the same orientation or a circular object without obvious orientation. When grasping the circular target, grip orientation was influenced by the orientation of the distractor. Moreover, as in classical visuomotor priming, grasping movements were initiated faster when distractor and target were identical. Results provide evidence that planning of visually guided grasping movements is influenced by prior perceptual experience, challenging the notion that metric aspects of grasping are controlled exclusively on the basis of real-time information.

Analysis of scattering from arbitrary configuration of elliptical obstacles using T -matrix representation

A new method of analysis of an arbitrary configuration of elliptical cylinders is presented. The treatment of such a problem is based on a combination of the cylindrical and elliptical coordinates systems. This approach is applied to the formulation of the scattered field at the surface of equivalent cylinder surrounding dielectric or metal elliptical object. To analyse the arbitrary set of elliptical cylinders, the iterative scattering procedure is used. A good agreement of the proposed method with the commercial FD simulator is achieved.

Optical identification of the 3C 58 pulsar wind nebula

Context. The Crab-like supernova remnant 3C 58 contains the young pulsar PSR J0295+6449, which powers a radio plerion and a compact torus-like pulsar wind nebula visible in X-rays. Aims. We have performed deep optical imaging of the 3C 58 field to detect the optical counterpart of the pulsar and its wind nebula. Methods. The imaging was carried out with the Nordic Optical Telescope. We also analyzed the archival images of the field obtained with the Chandra/ACIS-S and HRC-S in X-rays and with the Spitzer/IRAC in the mid-infrared. Results. We detect a faint extended elliptical optical object with B = 24. m 06 ± 0.08 and V = 23. 11 ± 0.04, whose center and peak brightness position are consistent at the sub-arcsecond level with the position of the pulsar. The morphology of the object and the orientation of its major axis are in excellent agreement with the torus region of the pulsar wind nebula seen almost edge on in the X-rays, although its extension is only about a half of what is in X-rays. This suggests that in the optical we see only the brightest central part of the torus nebula with the pulsar. The position and morphology of the object are also practically identical to the counterpart of the torus region recently detected in the mid-infrared bands. We do not resolve any point-like source within the nebula that could be identified with the pulsar and estimate that the contribution of the pulsar to the observed optical flux is <10%. Using the archival Chandra/ACIS-S data we analyzed the spectrum of the pulsar+nebula X-ray emission extracted from the spatial region constrained by the optical/infrared source position and extent and find that a single absorbed power law provides an acceptable spectral fit. Combining this fit with the optical and infrared fluxes of the detected candidate torus nebula counterpart, we compile a tentative multi-wavelength spectrum of the central part of the pulsar nebula. Within the uncertainties of the interstellar extinction towards 3C 58, it is reminiscent of either the Crab or PSR B0540-69 pulsar wind nebula spectra. Conclusions. The position, morphology, and spectral properties of the detected source strongly suggest that it is the optical/midinfrared counterpart of the 3C 58 pulsar + its wind nebula system. This makes 3C 58 the third member, together with the Crab and PSR B0540-69, of such a system as identified in the optical and mid-infrared.

Quantitative reconstruction from truncated projections in classical tomography

We prove that some kinds of truncation are entirely admissible for region-of-interest (ROI) reconstructions in classical tomography, contrary to the long-standing folklore that two-dimensional tomography is "all or nothing". The proof is based on a link between the Hilbert transforms of parallel beam and fanbeam projections, which was recently used by Noo et al. to achieve ROI image reconstruction from fanbeam data on less than a short scan, assuming no fanbeam truncation occurs. We extend the use of this link to achieve quantitative ROI reconstruction in the presence of truncated projections. Our results are illustrated with a specific example of a parallel-hole detector of length 24 cm and an elliptical object of 15- and 30-cm axes. The detector rotates 180/spl deg/ about a point on the long axis at 11.25 cm from the right-hand-side boundary. The right half of the ellipse, the ROI in this case, is not truncated, although the left side is truncated in many views. The ROI can be quantitatively reconstructed, as is verified by our simulation. We also show that under certain conditions, ROI reconstruction is possible with truncation on both sides of the field of view. These results bring new understanding to the fundamental mechanisms of tomography. Benefits of this new understanding can be anticipated in many classical tomography applications, particularly when the projections of the object are too wide for the available detector.

Morphological evolution of dwarf galaxies in the Local Group

The dwarf galaxies of the Local Group can be separated in three morphological groups: irregular, elliptical and spheroidal. As in the large galaxy clusters, there seems to be a morphology-position relationship: irregular galaxies are preferentially found in the outskirts (low density regions) of the Local Group, whereas dwarf ellipticals and spheroidals are more frequent in the central, high density regions. To cast light on the nature and origin of dwarf galaxies in the Local Group, Mayer et al. (2001a) have suggested that a dwarf irregular galaxy tidally interacting with a galaxy of much larger mass may be re-shaped into a dwarf spheroidal or elliptical object. In this paper we check by means of N-body Tree-SPH simulations whether this is possible for a selected sample of galaxies of the Local Group. Using the best data available in literature to fix the dynamical and kinematical status of a few dwarf galaxies in the Local Group, we follow the evolution of an ideal satellite, which supposedly started as an irregular object during its orbital motion around the Milky Way. We find that the tidal interactions with the Milky Way remove a large fraction of the mass of the dwarf irregular and gradually reshape it into a spherical object.

A simulation study of the degrees of freedom of movement in reaching and grasping

The question of independently controlled components in the act of reaching and grasping has attracted interest experimentally and theoretically. Data from 35 studies were recently found consistent with simulated kinematic finger and thumb trajectories optimised for minimum jerk. The present study closely reproduces those trajectories using a discrete-time model based on minimum acceleration. That model was further used to generate two-dimensional trajectories for finger and thumb to reach and grasp an elliptical object with varying position and/or orientation. Orthogonalisation of these four trajectories revealed one degree of freedom when direction of reach was constant and two degrees of freedom when direction of reach varied, irrespective of object distance and orientation. These simulations indicate that reach and grasp movements contain redundancy that is removable by formation of task-dependent synergies. As skilled movement can be planned and executed in a low dimension workspace, control of these independent components lessens central workload.

Effects of object ellipticity on strain, and implications for clast–matrix rocks

We examine the influence of object shape on strain, taking the example of an elliptical object in a matrix of different viscosity. The Eshelby–Bilby equation for the cross-sectional strain of circular cylindrical objects in a matrix of different viscosity is differentiated, to express the relationship of developing sectional ellipticity on incremental strain. This leads to an expression for the strain of initial elliptical objects whose axes are parallel or perpendicular to pure shearing. Graphs show that competent elliptical objects with axial ratios of R i =3 or more, will strain significantly more than circular objects of the same viscosity; less if the objects are incompetent. While the effect is likely to be insignificant for competent objects with initial ellipticity of <2, which is indicated from statistics for undeformed pebbles in conglomerates, any clast with greater ellipticity, such as R i =5 to 10, could deform significantly more than an equant clast, and thus appear to be materially less competent. These principles have implications for geological strain studies and for competence contrasts in rocks.

Inverse Scattering Image Reconstruction from Reflection and Transmission Data Obtained Using the Mirror Image Theory

The inverse scattering technique is expected to be useful to obtain quantitative acoustic parameter images of tissues in the human body. However, the difficulty of making observations around the 360° circumference of an object hinders the realization of the technique. In this paper, to mitigate the restrictions on observations, a reflection plate is placed behind an object and the problem of reconstructing an image from the reflection and transmission data at the half-circumference points around the object is considered. To this end, a technique is proposed based on the treatment of the conventional transmission inverse scattering problem using the mirror image theory. The validity of the method is tested using simulated data from an elliptical object. As a result, the precision of the reconstructed sound velocity image is verified to be almost satisfactory for the purposes of medical diagnostic applications.

On The Possibility of Identification of the Moving Celestial Objects Observed with the Space Astrometric Telescope

In connection with the creation of the scientific grounds of the Russian Project named “Struve” Space Astrometric System, the main principles of classification and identification of any celestial moving object observed with this System were formulated and basic algorithms were elaborated. These algorithms are invariable for a short or long observational arc, for a known or unknown heavenly body and for an artificial or natural celestial object.For classification of observed celestial bodies the angular velocities of motion are used. These values are calculated from the statistical treatment of the 5 nearest spherical celestial body positions with a time intervalbetween them near 7 seconds.For an identification of well known sky objects ordinary procedure may be used by means of traditional ephemeris calculations. For an identification of unknown natural celestial bodies a special algorithm was developed. Ituses a calculated angular velocity of moving object from one scan to another close scan of observations. Then, having several accurate positions of fixed object during 5-10 hours per day, we can determine an initial elliptical object’s orbit by the Apparent Motion Parameters Method created at Pulkovo Observatory. It deals with a position of object, its angular velocity and acceleration, position’s angle and a curvature of trajectory on a short observational arc. These last four quantities are named the Apparent Motion Parameters.In spite of a preliminary character of the AMP-method orbits we can identify an observed object through a large interval of time, for example over 2-4 months after orbit determination. In this problem the observed and calculated angular velocities of the object’s motion are very useful. They are new and important ephemeris parameters at the epoch of Space Telescope astrometric positional observations. Examples of simulations of orbit determinations will be presented.

Toward accurate attenuation correction in SPECT without transmission measurements.

The current trend in attenuation correction for single photon emission computed tomography (SPECT) is to measure and reconstruct the attenuation coefficient map using a transmission scan, performed either sequentially or simultaneously with the emission scan. This approach requires dedicated hardware and increases the cost (and in some cases the scanning time) required to produce a clinical SPECT image. Furthermore, if short focal-length fan-beam collimators are used for transmission imaging, the projection data may be truncated, leading to errors in the attenuation coefficient map. Our goal is to obtain information about the attenuation distribution from only the measured emission data by exploiting the fact that only certain attenuation distributions are consistent with a given emission dataset. Ultimately this consistency information will either be used directly to compensate for attenuation or combined with the incomplete information from fan-beam transmission measurements to produce a more accurate attenuation coefficient map. In this manuscript the consistency conditions (which relate the measured SPECT data to the sinogram of the attenuation distribution) are used to find the uniform elliptical attenuation object which is most consistent with the measured emission data. This object is then used for attenuation correction during the reconstruction of the emission data. The method is tested using both simulated and experimentally acquired data from uniformly and nonuniformly attenuating objects. The results show that, for uniform elliptical attenuators, the consistency conditions of the SPECT data can be used to produce an accurate estimate of the attenuation map without performing any transmission measurements. The results also show that, in certain circumstances, the consistency conditions can prove useful for attenuation compensation with nonuniform attenuators.

A high-speed algorithm for elliptical object detection

A high-speed method for elliptical object location is proposed. Through the use of the geometric symmetry, it first locates the centers of elliptical objects and classifies the boundary points. Then, each point possible on an elliptical object boundary is used to obtain the remaining three parameters of the elliptical object. Since each boundary point is at most transformed to one point on the parameter space, the proposed method is very fast. Some experimental results are also given to show that the proposed method is better than some existing methods under the consideration of space and storage.

Elliptical object detection by using its geometric properties

A simple algorithm for ellipse detection in an image is proposed. The new method consists of three steps: (1) detect the elliptical center by using its symmetrical property; (2) identify the elliptical points by using a simple geometric property; and (3) estimate the five parameters ( x c , y c , A, B, θ) by using a least sum of squares fitting method. The new method has been tested on both the synthetic and real images. The experimental results show that the method is reliable and accurate.

The collapse and formation of galaxies. II - A control parameter for the Hubble sequence. III - The origin of the Hubble sequence

view Abstract Citations (27) References (25) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Collapse and Formation of Galaxies. II. A Control Parameter for the Hubble Sequence Lake, George ; Carlberg, R. G. Abstract We use N-body models of the dissipational formation of galaxies to relate final morphologies to initial conditions. The simulations have four basic control parameters: the mass ratio of gas to dark matter, the initial angular momentum, the amount of dissipation, and the initial velocity dispersion of the dark matter. As expected, the morphology of the final stellar object is strongly correlated with its angular momentum, disks having high angular momentum and spheroids low angular momentum. However, the final angular momentum of the stars can be greatly diminished from its initial value due to the angular- momentum transfer. All of the control parameters have some influence on the evolution and final state, but the most significant control parameter for the morphology is the initial velocity dispersion of the dark matter. In a "warm" collapse, the gas settles into circular orbits creating a disk. In a "cold" collapse, angular-momentum transfer and a greater tendency for stars to form out of low-angular-momentum material leads to a dense, slowly rotating, elliptical object. The borderline between warm and cold collapse is a velocity dispersion at turnaround equal to ~20% of the final value. Publication: The Astronomical Journal Pub Date: November 1988 DOI: 10.1086/114908 Bibcode: 1988AJ.....96.1581L Keywords: Disk Galaxies; Galactic Evolution; Gravitational Collapse; Hubble Diagram; Many Body Problem; Angular Momentum; Dark Matter; Elliptical Galaxies; Luminosity; Red Shift; Star Distribution; Velocity Distribution; Astrophysics; GALAXIES: FORMATION full text sources ADS | Related Materials (2) Part 1: 1975IAUS...69..247L Part 3: 1988AJ.....96.1587L