Range Of Eccentricities Research Articles

Analysis of the rub-impact forces between a controlled nonlinear rotating shaft system and the electromagnet pole legs

This article aimed to investigate the dynamical behaviours of a controlled asymmetric rotating shaft system when the rub-impact forces between the rotor and stator occur. A nonlinear position-velocity controller is proposed to control the system's lateral vibrations. The suggested control algorithm is integrated into the shaft system via four electromagnetic poles that are fixed on a fixed frame and act as active actuators. The dynamics of the asymmetric shaft, the electromagnetic coupling between the magnetic poles and the rotating shaft, and the rub-impact forces between the rotating shaft and the stator are included in the studied model. The derived dynamical model is firstly analyzed as a continuous nonlinear dynamical system utilizing the asymptotic analysis while neglecting the rub-impact forces. Different response curves are plotted to predict the conditions under which the rotating shaft may suffer from the rub-impact forces. Secondly, the whole system model is analyzed numerically as a discontinuous nonlinear dynamical system utilizing the bifurcation diagram, Poincaré map, and frequency spectrum. The main obtained results illustrated that the rub-impact forces occurrence between the uncontrolled rotating shaft and the stator induces unbounded oscillation that can destruct the rotating shaft. However, the suggested control algorithm has improved the vibratory behaviours of the considered system via minimizing the oscillation amplitudes and preventing the rub-impact forces for a wide range of the disk eccentricities. Moreover, it was found that the rotating shaft can whirl in a full annular rub mode with bounded oscillations if the proposed controller fails to prevent the rub-impact forces occurrence due to either the large disk eccentricity or the large asymmetric stiffness coefficients.

Rotor Active Magnetic Bearings System Control via a Tuned Nonlinear Saturation Oscillator

The proposed work focuses on improving the performance of the traditional nonlinear saturation controller (NSC) algorithm. In this work, a tuning mechanism can be implemented by providing the NSC control unit with the measured speed $\Omega $ of the rotor from a shaft encoder device in order to introduce a tuned NSC (TNSC). In other words, we are going to tune the NSC’s natural frequency ${\omega _{c}}$ at one half of $\Omega $ such that $\Omega =2{\omega _{c}}$ . This TNSC is adopted to reduce the vibratory amplitudes of a 16-pole constant-stiffness rotor-Active magnetic bearings AMBs) system for a wide range of speeds and eccentricities. The whole controlled system is studied mathematically to seek its approximate solutions via the multiple scales technique. Different relations between the rotor’s amplitudes and its parameters are plotted so as to verify the proposed tuning mechanism and its crucial role in improving the NSC’s performance.

Stochastic analysis of the rocking vulnerability of irregular anchored rigid bodies: application to soils of Mexico City

This paper focuses on the development and assessment of the expected damage for the rocking response of rigid anchored blocks, with irregular geometry and non-uniform mass distribution, considering the site conditions and the seismicity of Mexico City. The non-linear behavior of the restrainers is incorporated to evaluate the pure tension and tension-shear failure mechanisms. A probabilistic framework is performed covering a wide range of block sizes, slenderness ratios and eccentricities using physics-based ground motion simulation. In order to incorporate the uncertainties related to the propagation of far-field earthquakes with a significant contribution to the seismic hazard at study sites, it was simulated a set of scenarios using a stochastic summation methods of small-earthquakes records, considered as Empirical Green's Function (EGFs). As Engineering Demand Parameter (EDP), the absolute value of the maximum block rotation normalized by the body slenderness, as a function of the peak ground acceleration (PGA) is adopted. The results show that anchorages are more efficient for blocks with slenderness ratio between two and three, while slenderness above four provide a better stability when they are not restrained. Besides, there is a range of peak intensities where anchored blocks located in soft soils are less vulnerable with respect to those located in firm soils. The procedure used in here allows to take decisions about risk, reliability and resilience assessment of different types of contents, and it is easily adaptable to other seismic environments.

Eccentricity Driven Climate Effects in the Kepler-1649 System

Abstract The discovery of terrestrial exoplanets is uncovering increasingly diverse architectures. Of particular interest are those systems that contain exoplanets at a variety of star–planet separations, allowing direct comparison of exoplanet evolution (comparative planetology). The Kepler-1649 system contains two terrestrial planets similar both in size and insolation flux to Venus and Earth, although their eccentricities remain largely unconstrained. Here we present results of dynamical studies of the system and the potential effects on climate. The eccentricities of the Kepler-1649 system are poorly constrained, and we show that there are dynamically viable regions for further terrestrial planets in between the two known planets for a limited range of eccentricities. We investigate the effect of eccentricity of the outer planet on the dynamics of both planets and show that this results in high-frequency (1000–3000 years) eccentricity oscillations in long-term stable configurations. We calculate the resulting effect of these eccentricity variations on insolation flux and present the results of 3D climate simulations for the habitable zone planet. Our simulations demonstrate that, despite large eccentricity variations, the planet can maintain stable climates with relatively small temperature variations on the substellar hemisphere for a variety of initial climate configurations. Such systems thus provide key opportunities to explore alternative Venus/Earth climate evolution scenarios.

Spatial clustering of orientation preference in primary visual cortex of the large rodent agouti.

SummaryAll rodents investigated so far possess orientation-selective neurons in the primary visual cortex (V1) but – in contrast to carnivores and primates – no evidence of periodic maps with pinwheel-like structures. Theoretical studies debating whether phylogeny or universal principles determine development of pinwheels point to V1 size as a critical constraint. Thus, we set out to study maps of agouti, a big diurnal rodent with a V1 size comparable to cats'. In electrophysiology, we detected interspersed orientation and direction-selective neurons with a bias for horizontal contours, corroborated by homogeneous activation in optical imaging. Compatible with spatial clustering at short distance, nearby neurons tended to exhibit similar orientation preference. Our results argue against V1 size as a key parameter in determining the presence of periodic orientation maps. They are consistent with a phylogenetic influence on the map layout and development, potentially reflecting distinct retinal traits or interspecies differences in cortical circuitry.

Dynamics of retrograde $1/n$ mean motion resonances: the $1/{-2}$, $1/{-3}$ cases

In this paper, we investigate the dynamics of the exterior retrograde $1/n$ resonances within the framework of the planar circular restricted three-body problem (PCRTBP), taking the $1/{-2}$ and $1/{-3}$ resonances as examples. We prove that there is no asymmetric libration in retrograde $1/n$ resonances using analytical, numerical integrations, and semi-analytical methods, by mutual authenticating. For retrograde $1/n$ resonances, we calculate the magnitudes of the first- and second-harmonics of the expansion. The analytical results showed that the second-order harmonics in the expansion of the disturbing function can be neglected, which are the leading cause of the existence of the asymmetric libration in prograde $1/n$ resonances. Our results also conform to the latest qualitative criterion for the appearance of asymmetric libations proposed by Namouni and Morais (2016). And our analytical results are verified well by numerical integrations. By semi-analytical theory, we generate a series of phase-space portraits in the $e$ – $\phi $ polar plane for the full range of eccentricity to confirm the absence of the asymmetric librations in retrograde $1/n$ resonances. It is the first time the absence of the asymmetric librations in retrograde $1/n$ resonances is studied. We also analyze the dynamics of the pericentric and apocentric librations of the retrograde $1/n$ resonances. The stable resonant libration zones of the $1/{-2}$ , $1/{-3}$ , $1/{-4}$ and $1/{-5}$ resonances are illustrated in the $a$ – $e$ plane. Our research here reveals the differences between the dynamics of retrograde and prograde $1/n$ resonances.

A simplified FEM analysis on the static performance of aerostatic journal bearings with orifice restrictor

This paper puts forward a simplified FEM based on MATLAB PDE tool to investigate the static performance of aerostatic journal bearings. The pressure distribution equation is transformed into a standard elliptic equation, the boundary conditions and coefficients of the transformed equation are also confirmed by contrasting it with the standard elliptic equation. Then the effects of bearings structural parameters and external supply pressure on the film pressure distribution, load capacity and static stiffness are studied. The film pressure distribution changes significantly with the eccentricity ratio, and an eccentricity range corresponding to the optimal stiffness is also confirmed. Finally, an experimental platform with reversal structure is applied to reduce the measurement error, the maximum relative error between the results of simulation and experimental result is 11.54%.

Experimental and numerical studies of laser-welded stainless steel channel sections under combined compression and major axis bending moment

This paper presents an in-depth experimental and numerical investigation into the behaviour of laser-welded stainless steel channel sections under combined compression and bending moment about the major axis. Two laser-welded austenitic stainless steel plain channel sections were considered in the experimental investigation, and for each channel section, four eccentrically loaded stub column tests were conducted under various initial loading eccentricities. The experimental results were then adopted in a numerical investigation for the validation of finite element models, by means of which parametric studies were conducted to generate further structural performance data over a wider range of cross-section sizes and initial loading eccentricities. Both the obtained experimental and numerical results were carefully analysed and then used to evaluate the accuracy of the current codified design rules for welded stainless steel channel sections under combined compression and major axis bending. The evaluation results generally revealed that the codified design rules yield excessively conservative and scattered resistance predictions, owing to the neglect of the favourable material strain hardening of stainless steel and the beneficial stress redistribution within channel sections under combined loading. An improved design approach has been proposed through extension of the deformation-based continuous strength method (CSM) to the case of laser-welded stainless steel channel sections under combined compression and major axis bending. Quantitative evaluation of the new design approach was made through comparing the predicted resistances against the experimental and numerical failure loads, with the results revealing that the new design approach yields a much higher level of design accuracy and consistency than the current codified design rules. Finally, statistical analyses have been conducted to confirm the reliability of the new design approach according to EN 1990.

Eccentricity Parameters Identification for a Motorized Spindle System Based on Improved Maximum Likelihood Method

As a kind of rotor system, the electric spindle system is the core component of the precision grinding machine. The vibration caused by the mass imbalance is the main factor that causes the vibration of the grinding machine. Identifying the eccentricity parameters in an electric spindle system is a key issue in eliminating mass imbalances. It is difficult for engineers to understand the approximate range of eccentricity by experience; that is, it is difficult to obtain a priori information about eccentricity. At the same time, due to the geometric characteristics of the electrospindle system, the material factors and the randomness of the measurement response, these uncertain factors, even in a small case, are likely to cause large deviations in the eccentricity recognition results. The search algorithm used in the maximum likelihood method to identify the eccentricity parameters of the electrospindle system is computationally intensive, and the sensitivity in the iterative process brings some numerical problems. This paper introduces an Advance-Retreat Method (ARM) of the search interval to the maximum likelihood method, the unknown parameter increment obtained by the maximum likelihood method is used as the step size in the iteration, and the Advance-Retreat Method of the search interval is used to adjust the next design point so that the objective function value is gradually decreasing. The recognition results under the three kinds of measurement errors show that the improved maximum likelihood method improves the recognition effect of the maximum likelihood method and can reduce the influence of uncertainty factors on the recognition results, and the robustness is satisfactory.

Differential impact of exogenous and endogenous attention on the contrast sensitivity function across eccentricity.

Both exogenous and endogenous covert spatial attention enhance contrast sensitivity, a fundamental measure of visual function that depends substantially on the spatial frequency and eccentricity of a stimulus. Whether and how each type of attention systematically improves contrast sensitivity across spatial frequency and eccentricity are fundamental to our understanding of visual perception. Previous studies have assessed the effects of spatial attention at individual spatial frequencies and, separately, at different eccentricities, but this is the first study to do so parametrically with the same task and observers. Using an orientation discrimination task, we investigated the effect of attention on contrast sensitivity over a wide range of spatial frequencies and eccentricities. Targets were presented alone or among distractors to assess signal enhancement and distractor suppression mechanisms of spatial attention. At each eccentricity, we found that exogenous attention preferentially enhanced spatial frequencies higher than the peak frequency in the baseline condition. In contrast, endogenous attention similarly enhanced a broad range of lower and higher spatial frequencies. The presence or absence of distractors did not alter the pattern of enhancement by each type of attention. Our findings reveal how the two types of covert spatial attention differentially shape how we perceive basic visual dimensions across the visual field.

Measuring the eccentricity of binary black holes in GWTC-1 by using the inspiral-only waveform

ABSTRACT In this article, we estimate the eccentricity of 10 binary black holes (BBHs) in the Gravitational-Wave Transient Catalog GWTC-1 by using the inspiral-only BBH waveform template EccentricFD. First, we test our method with simulated eccentric BBHs. Afterwards we apply the method to real BBH gravitational-wave data. We find that the BBHs in GWTC-1, with the exception of GW151226, GW170608 and GW170729, show very small eccentricity. Their upper limits on eccentricity range from 0.033–0.084 with 90 per cent credible interval at a reference frequency of 10 Hz. For GW151226, GW170608 and GW170729, the upper limits are higher than 0.1. The relatively large eccentricity of GW151226 and GW170729 is probably due to ignoring χeff and the low signal-to-noise ratio, and GW170608 is worthy of follow-up research. We also point out the limitations of the inspiral-only non-spinning waveform template in eccentricity measurement. Measurement of BBH eccentricity helps us to understand its formation mechanism. With an increase in the number of BBH gravitational-wave events and a more complete eccentric BBH waveform template, this will become a viable method in the near future.

Cold-formed stainless steel CHS beam-columns – Testing, simulation and design

The present work was prompted by shortcomings identified in existing design provisions for stainless steel circular hollow section (CHS) beam-columns. First, addressing a lack of existing experimental data, a series of ferritic stainless steel CHS beam-column tests was undertaken at the cross-section and member levels. In total, 26 beam-column tests, including two section sizes (a non-slender class 3 and slender class 4 cross-section), two member slenderness values for each cross-section type and a wide range of loading eccentricities were carried out to investigate the interaction between local and global buckling. Following validation of finite element (FE) models, a numerical study was then undertaken to explore the buckling response of stainless steel CHS beam-columns, covering austenitic, duplex and ferritic grades with a wide range of local and global slendernesses and applied loading eccentricities. Over 2000 numerical results were generated and used to assess new design proposals for stainless steel beam-columns, featuring improved compression and bending end points and new interaction factors. The new proposals are more consistent and more accurate in their resistance predictions than the current EN 1993-1-4 (2015) design approach. The reliability of the new proposals has been verified by means of statistical analyses according to EN 1990 (2005).

Exogeneous Spatial Cueing beyond the Near Periphery: Cueing Effects in a Discrimination Paradigm at Large Eccentricities.

Although visual attention is one of the most thoroughly investigated topics in experimental psychology and vision science, most of this research tends to be restricted to the near periphery. Eccentricities used in attention studies usually do not exceed 20° to 30°, but most studies even make use of considerably smaller maximum eccentricities. Thus, empirical knowledge about attention beyond this range is sparse, probably due to a previous lack of suitable experimental devices to investigate attention in the far periphery. This is currently changing due to the development of temporal high-resolution projectors and head-mounted displays (HMDs) that allow displaying experimental stimuli at far eccentricities. In the present study, visual attention was investigated beyond the near periphery (15°, 30°, 56° Exp. 1) and (15°, 35°, 56° Exp. 2) in a peripheral Posner cueing paradigm using a discrimination task with placeholders. Interestingly, cueing effects were revealed for the whole range of eccentricities although the inhomogeneity of the visual field and its functional subdivisions might lead one to suspect otherwise.

Chaos in the inert Oort cloud

Context. Distant trans-Neptunian objects are subject to planetary perturbations and galactic tides. The former decrease with the distance, while the latter increase. In the intermediate regime where they have the same order of magnitude (the “inert Oort cloud”), both are weak, resulting in very long evolution timescales. To date, three observed objects can be considered to belong to this category. Aims. We aim to provide a clear understanding of where this transition occurs, and to characterise the long-term dynamics of small bodies in the intermediate regime: relevant resonances, chaotic zones (if any), and timescales at play. Methods. The different regimes are explored analytically and numerically. We also monitored the behaviour of swarms of particles during 4.5 Gyrs in order to identify which of the dynamical features are discernible in a realistic amount of time. Results. There exists a tilted equilibrium plane (Laplace plane) about which orbits precess. The dynamics is integrable in the low and high semi-major axis regimes, but mostly chaotic in between. From about 800 to 1100 astronomical units (au), the chaos covers almost all the eccentricity range. The diffusion timescales are large, but not to the point of being indiscernible in a 4.5 Gyrs duration: the perihelion distance can actually vary from tens to hundreds of au. Orbital variations are damped near the ecliptic (where previous studies focussed), but favoured in specific ranges of inclination corresponding to well-defined resonances. Moreover, starting from uniform distributions, the orbital angles cluster after 4.5 Gyrs for semi-major axes larger than 500 au, because of a very slow differential precession. Conclusions. Even if it is characterised by very long timescales, the inert Oort cloud mostly features chaotic regions; it is therefore much less inert than it appears. Orbits can be considered inert over 4.5 Gyrs only in small portions of the space of orbital elements, which include (90377) Sedna and 2012VP113. Effects of the galactic tides are discernible down to semi-major axes of about 500 au. We advocate including the galactic tides in simulations of distant trans-Neptunian objects, especially when studying the formation of detached bodies or the clustering of orbital elements.

A 3PN Fourier domain waveform for non-spinning binaries with moderate eccentricity

While current gravitational wave observations with ground based detectors have been consistent with compact binaries in quasi-circular orbits, eccentric binaries may be detectable by ground-based and space-based instruments in the near future. Eccentricity significantly complicates the gravitational wave signal, and we currently lack fast and accurate models that are valid in the moderate to large eccentricity range. In a previous paper, we built a Fourier domain, eccentric waveform model at leading order in the post-Newtonian approximation, i.e. as an expansion in small velocities and weak fields. Here we extend this model to 3rd post-Newtonian order, incorporating the effects of periastron precession and higher post-Newtonian order effects that qualitatively change the waveform behavior. Our 3PN model combines the stationary phase approximation, a truncated sum of harmonics of combinations of two orbital frequencies (an azimuthal one and a radial one), and a bivariate expansion in the orbital separation and the eccentricity. We validate the model through comparisons with a fully-numerical, time domain post-Newtonian model, and find good agreement (matches between ) in much of the parameter space. We estimate in what regions of parameter space eccentric effects are important by exploring the signal to noise ratio of eccentric corrections. We also examine the effects of higher post-Newtonian order terms in the waveform amplitude, and the agreement between different PN-consistent, numerical, time-domain models. In an effort to guide future improvements to the model, we gauge the error in our 3PN model incurred by the different analytic approximations used to construct it. This model is useful for preliminary data analysis investigations and it could allow for a phenomenological hybrid that incorporates eccentricity into an inspiral-merger-ringdown model.

Depositional process and astronomical forcing model of lacustrine fine-grained sedimentary rocks: A case study of the early Paleogene in the Dongying Sag, Bohai Bay Basin

Abstract The Paleogene strata of the Bohai Bay Basin include multiple sets of lacustrine fine-grained sediments, which provide a detailed record of the climate changes that occurred in the lake basin. Early Paleogene fine-grained sedimentary rocks are the main target layers of continental shale oil exploration in eastern China. Therefore, studies of the geological responses to astronomical factors have important theoretical and practical significance for understanding the depositional process of lacustrine fine-grained sedimentary rocks. In this paper, we focus on the lower Es3 (Es3l)-upper Es4 (Es4u) units in four shale oil wells in the Dongying Sag of the Bohai Bay Basin. Based on the previous establishment of a high-resolution astronomical time scale in this area, we have further studied the petrological characteristics and lithofacies of the fine-grained sedimentary rocks. Then the geological responses to astronomical cycles on different scales are investigated, and the models for the depositional process of fine-grained sedimentary rocks under the control of astronomical factors are revealed. The results indicate that the cyclic changes in mineral content and lithofacies in fine-grained sedimentary rocks in the Dongying Sag are controlled by short eccentricity and precession cycles. Periods near the maximum short eccentricity range had large precession amplitudes, humid climates, and the development of organic-rich laminated calcareous mudstone lithofacies. In contrast, periods near the minimum short eccentricity range had small precession amplitudes, a dry climates, and the development of organic-containing layered muddy limestone lithofacies. This study explores the depositional process of fine-grained sedimentary rocks from the perspective of astronomical cycles, which is conducive to the comprehensive prediction of favorable shale oil layers.

The HD 181433 Planetary System: Dynamics and a New Orbital Solution

Abstract We present a detailed analysis of the orbital stability of the HD 181433 planetary system, finding it to exhibit strong dynamical instability across a wide range of orbital eccentricities, semimajor axes, and mutual inclinations. We also analyze the behavior of an alternative system architecture, proposed by Campanella, and find that it offers greater stability than the original solution, as a result of the planets being trapped in strong mutual resonance. We take advantage of more recent observations to perform a full refit of the system, producing a new planetary solution. The best-fit orbit for HD 181433 d now places the planet at a semimajor axis of 6.60 ± 0.22 au, with an eccentricity of 0.469 ± 0.013. Extensive simulations of this new system architecture reveal it to be dynamically stable across a broad range of potential orbital parameter space, increasing our confidence that the new solution represents the ground truth of the system. Our work highlights the advantage of performing dynamical simulations of candidate planetary systems in concert with the orbital fitting process, as well as supporting the continuing monitoring of radial velocity planet search targets.

Looking at the Road When Driving Around Bends: Influence of Vehicle Automation and Speed.

When negotiating bends car drivers perform gaze polling: their gaze shifts between guiding fixations (GFs; gaze directed 1–2 s ahead) and look-ahead fixations (LAFs; longer time headway). How might this behavior change in autonomous vehicles where the need for constant active visual guidance is removed? In this driving simulator study, we analyzed this gaze behavior both when the driver was in charge of steering or when steering was delegated to automation, separately for bend approach (straight line) and the entry of the bend (turn), and at various speeds. The analysis of gaze distributions relative to bend sections and driving conditions indicate that visual anticipation (through LAFs) is most prominent before entering the bend. Passive driving increased the proportion of LAFs with a concomitant decrease of GFs, and increased the gaze polling frequency. Gaze polling frequency also increased at higher speeds, in particular during the bend approach when steering was not performed. LAFs encompassed a wide range of eccentricities. To account for this heterogeneity two sub-categories serving distinct information requirements are proposed: mid-eccentricity LAFs could be more useful for anticipatory planning of steering actions, and far-eccentricity LAFs for monitoring potential hazards. The results support the idea that gaze and steering coordination may be strongly impacted in autonomous vehicles.

RAC-CNN: multimodal deep learning based automatic detection and classification of rod and cone photoreceptors in adaptive optics scanning light ophthalmoscope images.

Quantification of the human rod and cone photoreceptor mosaic in adaptive optics scanning light ophthalmoscope (AOSLO) images is useful for the study of various retinal pathologies. Subjective and time-consuming manual grading has remained the gold standard for evaluating these images, with no well validated automatic methods for detecting individual rods having been developed. We present a novel deep learning based automatic method, called the rod and cone CNN (RAC-CNN), for detecting and classifying rods and cones in multimodal AOSLO images. We test our method on images from healthy subjects as well as subjects with achromatopsia over a range of retinal eccentricities. We show that our method is on par with human grading for detecting rods and cones.

Connexin-36 distribution and layer-specific topography in the cat retina

Connexin-36 (Cx36) is the major constituent of mammalian retinal gap junctions positioned in key signal pathways. Here, we examined the laminar and large-scale topographical distribution of Cx36 punctate immunolabels in the retina of the cat, a classical model of the mammalian visual system. Calretinin-immunoreactive (CaR-IR) cell populations served to outline the nuclear and plexiform layers and to stain specific neuronal populations. CaR-IR cells included horizontal cells in the outer retina, numerous amacrine cells, and scattered cells in the ganglion cell layer. Cx36-IR plaques were found among horizontal cell dendrites albeit without systematic colocalization of the two labels. Diffuse Cx36 immunoreactivity was found in the cytoplasm of AII amacrine cells, but no colocalization of Cx36 plaques was observed with either the perikarya or the long varicose dendrites of the CaR-IR non-AII amacrine cells. Cx36 puncta were seen throughout the entire inner plexiform layer showing their highest density in the ON sublamina. The densities of AII amacrine cell bodies and Cx36 plaques in the ON sublamina were strongly correlated across a wide range of eccentricities suggesting their anatomical association. However, the high number of plaques per AII cell suggests that a considerable fraction of Cx36 gap junctions in the ON sublamina is formed by other cell types than AII amacrine cells drawing attention to extensive but less studied electrically coupled networks.