Angular Configuration Research Articles

Misalignment-Induced Micro-Elastohydrodynamic Lubrication in Rotary Lip Seals

In literature the lubrication of rotary lip seals is explained by hydrodynamic action on a microscopic scale. This theory assumes perfect concentricity between the seal and the shaft which in reality seldomly occurs. Focusing on the stern tube seals application, an analysis is performed on the phenomena distorting the axisymmetric operation of rotary lip seals. Radial and angular shaft misalignments together with pressure and temperature gradients have been modelled. The model predictions are validated using a dedicated setup. Additionally, applying the soft-EHL film thickness expressions at the asperity level, an equivalent film thickness along the circumferential direction is estimated. The Reynolds PDE is solved to predict the misalignment-induced hydrodynamic pressure build-up. The film thickness variation derived and accompanying non-uniform contact pressure distribution was shown to be sufficient for hydrodynamic action and, depending on the minimum film thickness, the hydrodynamic pressure build-up can exceed the static contact pressure. Additionally, significant differences were observed between the radial and angular misalignment configurations.

Sincronización de sistemas activos en procesos de manejo de materiales

The present work proposes an application of automata’s language and control systems in discrete events theory in a prototype of material handling system to ensure the continuity in the sequence that a transferred piece will have to execute between two points of a productive process. Also guaranteeing the synchronization of its active elements, in this case, a robot in angular configuration and a conveyor belt, for the fulfillment of its specific task without errors. We describe the development of the prototype for testing, the programming of the digital process controllers based on the theoretical methodology suggested, and finally, the integration of a graphical monitoring and control interface that allows the visualization of the system state to the user. The results suggest the adequate performance of the developed algorithms, the graphical interface and, in general, of the active elements that make up the material handling system.

Contribution to Sandy Site Characterization: Spectro-Directional Signature, Grain Size Distribution and Mineralogy Extracted from Sand Samples

The characterization of sands detailed in this paper has been performed in order to support the in-flight radiometric performance assessment of space-borne optical sensors over the so-called Pseudo-Invariant Calibration Sites (PICS). Although the physical properties of PICS surface are fairly stable in time, the signal measured from space varies with the illumination and the viewing geometries. Thus, there is a need to characterize the spectro-directional properties of PICS. This could be done on a broad scale, thanks to multi-spectral multi-directional space-borne sensors such as the POLDER instrument (with old data). However, interpolating or extrapolating the spectro-directional reflectance measured from space to spectral bands of another sensor is not straightforward. The hyperspectral characterization of sand samples collected within or nearby PICS could contribute to a solution. In this context, a set of 31 sand samples was compiled. The BiConical Reflectance Factor (BCRF), linked to Bidirectional Reflectance Distribution Function (BRDF), was measured between 0.4 and 2.5 µm, over a half hemisphere when the amount of sand in the sample was large enough and for only a single fixed angular configuration for small samples. These optical measurements were complemented by grain size distribution measurements and mineralogical analysis and compiled together with previously published measurements in the so-called PICSAND database, freely available online.

Active Perception Based Formation Control for Multiple Aerial Vehicles

Autonomous motion capture (mocap) systems for outdoor scenarios involving flying or mobile cameras rely on i) a robotic front-end to track and follow a human subject in real-time while he/she performs physical activities, and ii) an algorithmic back-end that estimates full body human pose and shape from the saved videos. In this paper we present a novel front-end for our aerial mocap system that consists of multiple micro aerial vehicles (MAVs) with only on-board cameras and computation. In previous work, we presented an approach for cooperative detection and tracking (CDT) of a subject using multiple MAVs. However, it did not ensure optimal view-point configurations of the MAVs to minimize the uncertainty in the person's cooperatively tracked 3D position estimate. In this article we introduce an active approach for CDT. In contrast to cooperatively tracking only the 3D positions of the person, the MAVs can now actively compute optimal local motion plans, resulting in optimal view-point configurations, which minimize the uncertainty in the tracked estimate. We achieve this by decoupling the goal of active tracking as a convex quadratic objective and non-convex constraints corresponding to angular configurations of the MAVs w.r.t. the person. We derive it using Gaussian observation model assumptions within the CDT algorithm. We also show how we embed all the non-convex constraints, including those for dynamic and static obstacle avoidance, as external control inputs in the MPC dynamics. Multiple real robot experiments and comparisons involving 3 MAVs in several challenging scenarios are presented (video link : https://youtu.be/1qWW2zWvRhA). Extensive simulation results demonstrate the scalability and robustness of our approach. ROS-based source code is also provided.

Robust Superlubricity of Gold–Graphite Heterointerfaces

AbstractNoncommensurate 2D interfaces hold great promise toward low friction and nanoelectromechanical applications. For identical constituents, the crystals interlock at specific rotational configurations leading to high barriers for slide. In contrast, nonidentical constituents comprising different lattice parameters should enable robust superlubricity for all rotational configurations. This is however not the case for gold–graphite interfaces, as both theory and experiments show scaling behavior of the sliding force as a function of the interface contact area. By simulating the sliding force for gold–graphite interfaces, this work shows that the origin for high force barriers at special angular configurations is a result of commensurability between the moiré structure and the contact geometry. Consequently, this paper suggests new geometries that can potentially overcome such commensurability effects to enable robust superlubricity.

Sincronización de sistemas activos en procesos de clasificación de objetos por tamaño

In this work, a study of control systems in discrete events is carried out through their representation using finite state machines, with the particularity of being applied in the management of a prototype that has been developed to performance tasks like handling and object classification by size. The present analysis gives continuity to a previous work, in which automaton theory totally based on mathematical formalism is approached, for its use in the control of a material handling process, whose active elements are a robot in angular configuration and a conveyor belt. Therefore, it is described the addition, to the test system, of sensors that allow the discernment of each piece entered into this process, of the own programming algorithms that lead to fulfill the established task, as well as of the graphic interface for management and presentation of process condition, through a computer. Results confirm the proper functioning of active elements used, as well as their appropriate synchronization in the assurance of the proposed object classification task, under analysis of the size characteristic.

The nonlinear ultrasound needle pulse.

Recent work has established an analytical formulation of broadband fields which extend in the axial direction and converge to a narrow concentrated line. Those unique (needle) fields have their origins in an angular spectrum configuration in which the forward propagating wavenumber of the field ( ) is constant across any plane for all of the propagated frequencies. A 3 MHz-based, finite amplitude distorted simulation of such a field is considered here in a water path scenario relevant to medical imaging. That nonlinear simulation had its focal features compared to those of a comparable Gaussian beam. The results suggest that the unique convergence of the needle pulse to a narrow but extended axial line in linear propagation is also inherited by higher harmonics in nonlinear propagation. Furthermore, the linear needle field's relatively short duration focal pulses, and the asymptotic declines of its radial profiles, also hold for the associated higher harmonics. Comparisons with the Gaussian field highlight some unique and potentially productive features of needle fields.

Biomechanical analysis of spino-pelvic postural configurations in spondylolysis subjected to various sport-related dynamic loading conditions.

To study the risks of spondylolysis due to extrinsic loading conditions related to sports activities and intrinsic spino-pelvic postural parameters [pelvic incidence (PI) and sacral slope (SS)]. A comprehensive osseo-disco-ligamentous L4-S1 finite element model was built for three cases with spondylolysis representing three different spino-pelvic angular configurations (SS = 32°, 47°, 59° and PI = 49°, 58°, 72°, respectively). After simulating the standing posture, 16 dynamic loading conditions were computationally tested for each configuration by combining four sport-related loads (compression, sagittal and lateral bending and axial torque). For each simulation, the Von Mises stress, L5-S1 facet contact force and resultant internal loads at the sacral endplate were computed. Significant effects were determined with an ANOVA. The maximal stress and volume of cancellous bone in the pars with stress higher than 75% of the ultimate stress were higher with 900N simulated compression (2.2MPa and 145mm3) compared to only the body weight (1.36MPa and 20.9mm3) (p < 0.001). Combined compression with 10Nm of flexion and an axial torque of 6Nm generated the highest stress conditions (up to 2.7MPa), and L5-S1 facet contact force (up to 430N). The maximal stress was on average 17% higher for the case with the highest SS compared to the one with lowest SS for the 16 tested conditions (p = 0.0028). Combined flexion and axial rotation with compression generated the highest stress conditions related to risks of spondylolysis. The stress conditions intensify in patients with higher PI and SS. These slides can be retrieved under Electronic Supplementary Material.

A new methodology for the estimation of wheel–rail contact forces at a high-frequency range

Online measurement of wheel–rail contact forces is nowadays in demand for evaluating safety and manoeuvring the condition in real time and in real operation. In this study, the wheel–rail contact forces are estimated using a novel indirect identification method based on the measured radial strain on the wheel web. Further, the strain response of the rolling wheel is derived using an analytical solution of the disk under a rotating load, and a scheme was prepared for the identification of the rolling wheel parameters and its corresponding characteristic matrix. An appropriate angular strain configuration is employed to eliminate the effect of wheel rotation. The Tikhonov regularization technique is employed to solve the ill-posed least square problem and to attenuate the effect of noisy measurement and numerical uncertainty during the estimation of the forces. A finite element model of the rotating load is then constructed to investigate the effectiveness and accuracy of the proposed methodology. The effects of the rotating speed, loading and measurement noise on the estimated normal force are studied. It is found that neglecting the effect of the rotating speed causes a notable error particularly in the high-speed range.

Neuromechanical Cost Functionals Governing Motor Control for Early Screening of Motor Disorders.

Developing a quantifier of the neural control of motion is extremely useful in characterizing motor disorders and personalizing the model equations using data. We approach this problem using a top-down optimal control methodology, with an aim that the quantity estimated from the collected data is representative of the underlying neural controller. For this purpose, we assume that during the flexion of an arm, human brain optimizes a functional. A functional is defined as a function of a function that returns a scalar. Generally, in forward problems, this functional is chosen to be a function of metabolic energy spent, jerkiness, variance of motion, etc., integrated throughout the trajectory of motion. Current states (angular configuration and velocity) and torque applied can approximately determine the motion of a joint. Therefore, any internal cost functional optimized by the brain has to have its effect in the control of the torque. In this work, we study the flexion of the arm in normals and patient groups and intend to find the cost functionals governing the motion. To achieve this, we parametrize the cost functional governing the motion into the variables θp and ωp, which are then estimated using marker data obtained from the subjects. These parameters are shown to vary significantly for the normal and patient populations. The θp values were shown to be significantly higher in the case of patients than in the case of normals and ωp values showed an exactly opposite trend. We also studied how these cost functionals govern the applied torques in both subject groups and how is it affected while perturbed with sinusoidal frequencies. A time frequency analysis of the resulting solutions revealed a distinguishing pattern for the normals compared with the patient groups.

Quantitative Assessment of Myocardial Perfusion SPECT Acquisition Parameters

Myocardial perfusion single photon emission computed tomography (SPECT) is invaluable diagnostic and prognostic tool in assessment of patients with coronary artery disease. Objective: The aim of the study was to look at the impact of different acquisition parameters and their quantitative influence on the quality of cardiac SPECT data in terms of contrast improvement, signal to noise ratio and contrast-to-noise ratio. Materials and Methods: A number of clinically relevant phantoms have been prepared and different acquisition parameters were implemented. These parameters were namely number of projections, time per projection, acquisition mode (S&S continuous, continuous rotation and conventional step and shot), rotation type, detectors configuration and single or dual detectors.Data evaluations were made using image contrast, signal to noise ratio, and contrast to noise ratio. Results: Time of projection showed an improvement in the figures of merit investigated as the time is increased. A time of 15 sec has reasonably provided comparable results when compared to 30 sec for NAC data set. When data were corrected for attenuation, longer acquisition time yielded the best image quality results. In terms of number of projections, data acquired with 64 projections were superior in all quantitative metrics. The acquisition mode results however were heavily dependent on whether AC or NAC was applied. When circular orbit was studied versus noncircular obit, most of image quality metrics were in favor of the noncircular rotation mode.An angular configuration of 76 degree was superior in most image quality aspects but some differences were noticed in AC and NAC data sets versus the 90 degree configuration. Data acquisition with one detector head was comparable but sometimes better than results obtained with dual head acquisitions. Conclusion: Image acquisition parameters are key elements of better diagnostic and improvedimage quality in myocardial perfusion SPECT imaging. Optimization of the acquisition parameters is a critical process especially when considered for every individual patient. We therefore recommend an on-site specific acquisition parameters might be the best approach to follow in routine activities provided substantial and several phantom and clinical trials.

Decay patterns of multi-quasiparticle bands—a model independent test of chiral symmetry

Nuclear chiral systems exhibit chiral symmetry bands, built on left-handed and right-handed angular momentum nucleon configurations. The experimental search for such chiral systems revealed a number of suitable candidates, however an unambiguous identification of nuclear chiral symmetry is still outstanding. In this work it is shown that the decay patterns of chiral bands built on multi-quasiparticle configurations are different from those involving different single-particle configurations. It is suggested to use the observed decay patterns of chiral candidates as a new model-independent test of chiral symmetry.

Orientational dynamics of fluctuating dipolar particles assembled in a mesoscopic colloidal ribbon.

We combine experiments and theory to investigate the dynamics and orientational fluctuations of ferromagnetic microellipsoids that form a ribbonlike structure due to attractive dipolar forces. When assembled in the ribbon, the ellipsoids display orientational thermal fluctuations with an amplitude that can be controlled via application of an in-plane magnetic field. We use video microscopy to investigate the orientational dynamics in real time and space. Theoretical arguments are used to derive an analytical expression that describes how the distribution of the different angular configurations depends on the strength of the applied field. The experimental data are in good agreement with the developed model for all the range of field parameters explored. Understanding the role of fluctuations in chains composed of dipolar particles is important not only from a fundamental point of view, but it may also help understanding the stability of such structures against thermal noise, which is relevant in microfluidics and laboratory-on-a-chip applications.

Robust Detection of Environmental Sounds in Binaural Auditory Scenes

In realistic acoustic scenes, the detection of particular types of environmental sounds is often impeded by the simultaneous presence of multiple sound sources. In this work, we use simulations to systematically investigate the impact of superimposed distractor sources on sound type classification in a binaural robotic system and suggest techniques for increasing the robustness under such conditions. First, we demonstrate that by superimposing target sounds with strongly varying general environmental sounds during training, sound type classifiers are less affected by the presence of a distractor source. Moreover, we show that generalization performance of such models depends on how similar the angular source configuration and the signal-to-noise ratio are to the conditions under which the models were trained. Based on these results, we demonstrate how robust models can be obtained by including a variety of different conditions in the training data, a procedure called multi-conditional training. We evaluate this technique training both with ambient sources as well as with point sources with varying angular configurations, and show that this is an effective approach to produce models with close-to-optimal performance under a wide range of conditions. Moreover, we investigate the impact of head orientation and find that it has a significant influence on classification performance.

DFT Study of Nitrous Oxide Adsorption on the Surface of Pt-Decorated Graphene

In the present study we search potential of Pt-decorated graphene (PtG) as a new nanostructure adsorbent for nitrous oxide (N2O) using density functional theory (DFT). After fully relaxation of different possible orientations of N2O-PtG complex, we distinguished two optimized configurations for this system; 1- terminal N-side of gas is oriented towards Pt so that the molecule axis is perpendicular to the surface (P1), and 2- O-side of the molecule is closing to Pt while the axis of molecule has an angular configuration to the surface (P2). Our results showed high adsorption of N2O on PtG, however there is a significant difference between the value of adsorption for P1 compared to that for P2 (-113.6 (-88.7 BSSE) vs. -41.2 (-32.0 BSSE) kJ mol-1). Results of the charge analyses reveled interesting net charge transfer; the direction of charge is from N2O to PtG for P1 configuration and the reverse is found for P2.

Communication: Cargo towing by artificial swimmers.

An active swimmer can tow a passive cargo by binding it to form a self-propelling dimer. The orientation of the cargo relative to the axis of the active dimer's head is determined by the hydrodynamic interactions associated with the propulsion mechanism of the latter. We show how the tower-cargo angular configuration greatly influences the dimer's diffusivity and, therefore, the efficiency of the active swimmer as a micro-towing motor.

Photon-assisted tunneling in a hybrid junction based on a quantum dot coupled to two ferromagnets and a superconductor

Photon-assisted transmission (PAT) through a three-terminal hybrid system based on a quantum dot coupled to two ferromagnetic (F) and one superconducting (S) electrodes is studied in the sub-gap regime. Linear conductance is calculated within the non-equilibrium Green function technique. The effect of PAT on the local and non-local conductances for arbitrary angles between the magnetic moments of the F electrodes is studied. A generalized formula for the Andreev reflection magnetoresistance (ARMR) is proposed and it is found that the linear conductance may be significantly modified by the photon-assisted tunneling, while ARMR remains practically unaffected by PAT. Also, the conditions for the ARMR inversion have been determined for an interplay between the transport processes occurring in the system, magnetic polarization of the F leads and the angular configuration of the magnetic moments in the F leads. It has been shown that by manipulating the a.c. amplitude and the photon angular frequency one may control the contributions to the total conductance originating from Andreev reflection, crossed Andreev reflection as well as electron tunneling between the F leads. The influence of the non-vanishing intradot Coulomb correlations on PAT in the considered three-terminal hybrid system is also discussed.

Short- and long-term outcomes following hallux-valgus correction: a modified Kramer osteotomy.

Short- and long-term assessments were performed of a modification to the Kramer osteotomy that developed to stabilize the metatarsal head using an angular implant, the LINK(®) internal hallux fixator (Waldemar LINK GmbH & Co. KG, Hamburg, Germany). For this retrospective study, radiological assessments were used to measure outcomes in 72 feet with hallux valgus treated from 2006 to 2011. The hallux-valgus angle, the intermetatarsal angle between the first and second intermetarsal shaft axes, and the distal metatarsal articular angle were measured at short- and long-term intervals. Long-term clinical assessments included results of the Foot Function Index and the American Orthopedic Foot and Ankle Society Forefoot Score. Of the 72 feet treated, 12 were done as bilateral operations. Fifty-five patients at a mean age of 52years (±12; range 22-78) were included in short-term assessments. Significant improvements in angular measurements were made (p<0.001) between baseline and 3month assessments. Three postoperative complications occurred and 40% (29/72) of the implants were eventually removed. Fifty-five of the 72 feet were available for long-term assessments at a median of 5years postoperatively (IQR 5-7; range 3-9). No significant loss of correction was detected (p=0.373). Clinical assessments indicated successful outcomes in 86% (47/55) of the feet, with slightly better results in older patients (p=0.033; OR 1.1, CI 95% 1.01-1.15). This technique can achieve normal angular configuration, even with severe deformities, without significant long-term loss of correction. Patients should be informed of potential discomfort necessitating hardware removal, although the likelihood of complications is low. Level III study.

The influence of angular configuration of two buildings on the local wind climate

Understanding flows in urban areas is important for a wide range of research areas. In this study the influence of different angular configurations of two buildings on the local wind climate is analysed. PIV (particle image velocimetry) measurements are conducted in an atmospheric boundary layer wind tunnel. Blocken et al. (2008a) showed that, counterintuitively, the wind speeds in the passage of diverging configurations is higher compared to converging configurations. Blocken et al. focused on the wind climate at pedestrian level. The results of this new study show that from the ground to the roof level the wind speeds in the passage are increasing with increasing angles between the buildings for the converging cases, while they are decreasing for the diverging cases. For all cases the highest turbulent kinetic energies can be found downstream of the passage. For the converging cases these regions are located downstream of the buildings and mostly above the pedestrian level, while for diverging cases these regions are located between the buildings at the pedestrian level, where the probability that pedestrians are present is higher.

Inverse Kinematics Based Human Mimicking System using Skeletal Tracking Technology

Humanoid robots needs to have human-like motions and appearance in order to be well-accepted by humans. Mimicking is a fast and user-friendly way to teach them human-like motions. However, direct assignment of observed human motions to robot's joints is not possible due to their physical differences. This paper presents a real-time inverse kinematics based human mimicking system to map human upper limbs motions to robot's joints safely and smoothly. It considers both main definitions of motion similarity, between end-effector motions and between angular configurations. Microsoft Kinect sensor is used for natural perceiving of human motions. Additional constraints are proposed and solved in the projected null space of the Jacobian matrix. They consider not only the workspace and the valid motion ranges of the robot's joints to avoid self-collisions, but also the similarity between the end-effector motions and the angular configurations to bring highly human-like motions to the robot. Performance of the proposed human mimicking system is quantitatively and qualitatively assessed and compared with the state-of-the-art methods in a human-robot interaction task using Nao humanoid robot. The results confirm applicability and ability of the proposed human mimicking system to properly mimic various human motions.