Motion Boundary Research Articles

Study on Atomization Mechanism of Oil Injection Lubrication for Rolling Bearing Based on Stratified Method

The atomization mechanism of lubrication fluid in rolling bearings under high-speed airflow between the rings was investigated. A simulation model of gas–liquid two-phase flow in angular contact ball bearings was developed, and the jet lubrication process between the bearing rings was simulated using FLUENT computational fluid dynamics software (Ansys 19.2). The complex motion boundary conditions of the rolling elements were addressed through a layered approach. We can obtain more accurate boundary layer flow field changes and statistics of the diameter of oil particles in lubricating oil atomization, which lays the foundation for analyzing the law of influence on lubricating oil atomization. The results show that as the number of boundary layer layers increases, the influence of the boundary layer flow field on the lubricating oil is more obvious. The oil particle size is excessively flat, and the concentration of large particles of oil appears to decrease. As the speed increases, the amount of oil in the cavity decreases, but the oil droplets are also fragmented, which intensifies the atomization and reduces the particle diameter. This reduces the Sauter Mean Diameter (SMD), which is not conducive to the lubrication of the bearing. Under different injection pressures, when the injection pressure is large, it is beneficial to the lubrication of the bearing.

Investigating landslide-induced tsunamis using a low-dissipation Riemann weakly compressible smoothed particle hydrodynamics model

In order to address the complex moving boundary problem and violent free-surface flows involved in the process of landslide tsunamis, this paper proposes a new low-dissipation Riemann-solver-based smoothed particle hydrodynamics (SPH) numerical model. In this model, the complex fluid-rigid slide interaction and friction effects on landslides are handled by an improved motion boundary approach based on a one-sided Riemann scheme. A weighted essentially non-oscillatory (WENO) reconstruction method is introduced to reduce excessive dissipation of the fluid caused by rigid landslide impact. The kernel gradient accuracy is assured by applying the corrected smoothed particle method (CSPM) into a continuity equation. Single-block and multi-block landslide tsunamis in two-dimensional (2D) or three-dimensional (3D) applications are simulated with different particle resolutions, and the results are compared to those of other numerical models and experimental results. The landslide trajectories obtained from the modified boundary model are in good agreements with the experimental values. Free-surface flows variations during the propagation are properly captured in the current simulations without introducing any artificial viscosity term, and the wave peaks exhibit deviations of −14%–10.5% from the experimental values, thus verifying the usability and robustness of the proposed Riemann-SPH model.

Investigation on the influence of temperature-variation clearance on the frequency of rolling bearing defects

The clearance between the inner ring (IR) of rolling bearing and rotor is directly proportional to the temperature rise. The increased friction between the IR and rotor, as well as changes in the frequency of rolling bearing defects, and the accuracy of bearing health monitoring decreases. Existing research cannot effectively solve this problem. In response to the above issues, in this paper, the clearance between the bearing IR and the rotor and the internal clearance of bearing were considered, and the clearance was considered as the motion boundary of the rotor inside the IR, dynamic models of the bearing IR, outer ring (OR), and rolling element defects were established, and the trend of rolling bearing defects frequencies with temperature was analyzed, then the rationality of the dynamic models were verified through experimental methods. The research results show that the friction between the rotor and the IR increases with increasing temperature, and the speed of the IR decreases accordingly. The characteristic frequencies of defects in the IR, OR, and rolling element of rolling bearings have decreased by approximately 6.42%, 8.07%, and 6.93% compared to the theoretical values without considering temperature, respectively. This indicates that when identifying the frequency of rolling bearing defects at different temperatures, the frequency deviation caused by the increase in clearance between the IR and the rotor should be considered. The research results may serve as an important basis for fault diagnosis and condition monitoring of rolling bearings.

Modeling Stiffness and Stress in Serpentine Flexures for Use in a Compliant Bone Plate

Abstract Serpentine flexures offer several advantages for use in linear motion mechanisms, including distributed compliance to reduce stress and increase range of motion. In this work, we develop an analytical model for predicting the moment, vertical deflection, and maximum stress experienced in serpentine flexures in response to an input vertical force. Two classes of serpentines are introduced and modeled with linear motion boundary conditions enforced. Finite element analysis demonstrates a mean model error of 0.86% for these metrics across many flexure topologies. Experimental testing is performed to validate the force–deflection response of three steel serpentine compliant mechanisms. The model is able to predict the experimental stiffness data with a mean error at yield of 5.3%, compared to 6.5% with finite element analysis. Large displacement simulations show the model could remain below 10% error for deflections 3–7 times beyond the mechanisms’ deflection at yield. Finally, the model’s utility is demonstrated in the design of a novel single-piece compliant fracture fixation plate that leverages serpentine flexures to deliver controlled axial motion for long bone secondary healing. Model-derived stress-equivalent flexures are compared in their transverse and torsional rigidity. The proposed model and specific findings can be leveraged to design linear motion mechanisms that incorporate serpentine flexures across a wide range of applications.

The Effect of a Moving Boundary on the Shear Strength of Granular Materials in a Direct Shear Test

The boundary state significantly influences the soil shear strength. Therefore, it is necessary to overcome the limitations of existing indoor test instruments and determine the differences in the shear properties of granular materials to ensure the economic feasibility and mechanical integrity of engineering structures. In this study, the core formula for the direct shear test was derived from the static balancing analysis of the shear box, the external force on the specimen, and the internal force on the shear surface. Three loading methods were then developed by the staggered state of the upper and lower boxes: the upper box moving shear loading method (UM), the lower box moving shear loading method (LM), and the bidirectional moving shear loading method (BM). Finally, by manipulating the motion boundary, the discrete element method (DEM) was employed to simulate the shear test of granular materials. Among the three loading methods, the order of the peak shear stresses was as follows: UM > BM > LM. Moreover, the order of the sample post-peak stress uniformities was as follows: LM > BM > UM. A shear strength conversion formula was then proposed. The findings of this study promote the advancement of the shear mechanics theory of granular materials in direct shear testing and can serve as a scientific basis for the design and manufacture of shear equipment.

Estimating Plate Tectonic Forces at the New Zealand Plate Boundary Using Strain Rates Derived From a Kinematic Model of Fault Slip

AbstractWe construct a model of forces at the New Zealand plate boundary from dynamical thin‐sheet modeling. Stress magnitudes estimated are 10–50 MPa and effective viscosities are 0.5–5 × 1021 Pa s within actively deforming regions. Models that include only far‐field forces and forces from variations in topography and bathymetry can fit observations in most of the plate boundary, but basal tractions are required to fit extension in Havre Trough. For models that include nontopographic forces, we specify a rheology to acquire a unique solution for each of three rheologies: power‐law rheology with n = 3, power law with n = 5, and a pseudo‐plastic equal‐stress rheology. The inclusion of nontopographic forces allows these models to fit observations very well. We predict forces in Havre Trough equivalent to basal tractions of 7–10 MPa at 20‐km depth. Models with n = 3 and n = 5 require antiparallel forces on opposite sides of the plate boundary to drive deformation in South Island which would imply a plate boundary zone that is more localized at depth. The equal‐stress pseudo‐plastic model drives deformation with plate motion boundary conditions and localizes it with variations in effective viscosity. The effective rheology of South Island is most realistically modeled by an equal‐stress pseudo‐plastic rheology. The n = 3 or n = 5 power‐law rheology models require a highly localized boundary zone in the lower lithosphere, but a broader zone in the upper lithosphere.

Unsupervised Hierarchical Domain Adaptation for Adverse Weather Optical Flow

Optical flow estimation has made great progress, but usually suffers from degradation under adverse weather. Although semi/full-supervised methods have made good attempts, the domain shift between the synthetic and real adverse weather images would deteriorate their performance. To alleviate this issue, our start point is to unsupervisedly transfer the knowledge from source clean domain to target degraded domain. Our key insight is that adverse weather does not change the intrinsic optical flow of the scene, but causes a significant difference for the warp error between clean and degraded images. In this work, we propose the first unsupervised framework for adverse weather optical flow via hierarchical motion-boundary adaptation. Specifically, we first employ image translation to construct the transformation relationship between clean and degraded domains. In motion adaptation, we utilize the flow consistency knowledge to align the cross-domain optical flows into a motion-invariance common space, where the optical flow from clean weather is used as the guidance-knowledge to obtain a preliminary optical flow for adverse weather. Furthermore, we leverage the warp error inconsistency which measures the motion misalignment of the boundary between the clean and degraded domains, and propose a joint intra- and inter-scene boundary contrastive adaptation to refine the motion boundary. The hierarchical motion and boundary adaptation jointly promotes optical flow in a unified framework. Extensive quantitative and qualitative experiments have been performed to verify the superiority of the proposed method.

Analysis of derrikingand slewing of the tower crane with consideration to driving mechanisms characteristics

The variational problem of the movement mode selection for the load outreach change mechanism during a steady-state tower crane slewing was formulated and solved in the paper, that ensures the minimization of the drive motor power. The variational problem is nonlinear, and so we used the modified PSO-Rot-Ring particle swarm met heuristic method for its solution. Low- and high-frequency oscillations of the outreach change mechanism elements during the start-up were detected in the optimization process. These oscillations are eliminated in the section of steady-state movement due to the selection of the motion boundary conditions.
 In order to increase the productivity during a tower crane exploitation the overlapping of the mechanisms operation is used. The article considers the overlapping of operations of the derriking and slewing mechanisms of the crane. To study the dynamic processes in the joint work of the derriking and slewing of the tower crane, a dynamic model was built. It takes into account the main movement of the derriking and slewing of the crane, as well as oscillation processes in the drive mechanisms and load oscillation on flexible suspension in two planes: in the plane of the derrikingand in the plane of slewing of the crane. The developed dynamic model takes into account the elastic-dissipative characteristics of the transfer mechanisms, as well as the dynamic mechanical characteristics of the drive motors, which describe the transient electromagnetic processes. On the basis of the developed dynamic model with the help of Lagrangeʼs equations six differential equations of the second order which describe a mechanical part of the mechanisms movement were found. In addition, the transient dynamic electromagnetic processes of each of the engines are described by four differential equations. As a result, a system of fourteen differential equations was obtained. It describes the common dynamics of the mechanical part of the crane mechanisms and electromagnetic processes in the electric engines of the derriking and slewing mechanisms. The obtained system of differential equations was solved by numerical methods with the help of developed computer program. For the actual construction of the tower crane in the overlapping work of the derriking and slewing mechanisms, kinematic, power, and energy characteristics were determined, which made it possible to estimate the actual loads in the elements of the construction and drive mechanisms. From the obtained results it was established that the elements of the construction and drive mechanisms are under significant dynamic and energy overloads.High-frequency oscillations of drive mechanisms at the beginning of the movement and low-frequency oscillations of elements of the construction and load were revealed. This significantly reduces the reliability of tower cranes, increases their energy losses, and affects the work of the crane operator and maintenance staff.

Attitude constraint-based recovery for under-actuated AUVs under vertical plane control during the capture stage

The landed docking method is one of the most widely used underwater recovery methods because it imposes fewer restrictions on AUV configuration and applies to a wide range of applications. During the capture stage, the AUV and the recovery device are in close proximity, and if the attitude of the AUV fluctuates significantly, a collision may occur and cause damage. Existing studies for the common underactuated AUV do not effectively constrain the non-directly controlled degrees of freedom, posing a significant safety risk to the underwater recovery in the capture stage. To address this issue, a vertical plane control strategy that considers the safety interval of non-direct controlled degrees of freedom is proposed to keep the attitude angle within the safety interval during the docking process. To begin, the non-directly controlled AUV's pitching motion is analyzed and simplified to demonstrate that it has input-to-state stability during the capture stage, and an estimate of its uniform ultimate bound is provided so that the motion boundary can be estimated. Then, based on the backstepping method, a thrust-gain-constrained vertical surface control strategy is proposed: for the directly controlled heaving motion and rolling motion, precise control is achieved through a reasonable configuration of control parameters; for the non-directly controlled pitching motion, the thrust-constrained gain is calculated through the ultimate bound so that the force applied to the pitch degrees of freedom of the thruster is constrained and the purpose of indirect control is achieved. Using this strategy, the pitch motion is guaranteed to be inside the safe interval, resulting in accurate, safe, and quick recovery control during the capture stage.

Cluster-based segmentation for tobacco plant detection and classification

Tobacco is one of the major economical crops in the agriculture sector. It is essential to detect tobacco plants using unmanned aerial vehicle (UAV) images for improved crop yield and plays an important role in the early treatment of tobacco plants. The proposed research work is carried out in three phases: In the first phase, we collect images from UAV’s and apply the French Commision Internationale de l'eclairage (CIE) L*a*b colour space model as pre-processing operations and segmentation. And then two prominent motion descriptors namely histogram of flow (HOF) and motion boundary histogram (MBH) are combined with the optimal histogram of oriented gradients (HOG) descriptor for exploring optimal motion trajectory and spatial measurements. And finally, the spatial variations with respect to the scale and illumination changes are incorporated using the optimal HOG descriptor. Here both dense motion patterns and HOG are refined using hierarchical feature selection using principal component analysis (PCA). The proposed model is trained and evaluated on different tobacco UAV image datasets and done a comparative analysis of different machine learning (ML) algorithms. The proposed model achieves good performance with 95% accuracy and 92% of sensitivity.

Instance Motion Tendency Learning for Video Panoptic Segmentation.

Video panoptic segmentation is an important but challenging task in computer vision. It not only performs panoptic segmentation of each frame, but also associates the same instance across adjacent frames. Due to the lack of temporal coherence modeling, most existing approaches often generate identity switches during instance association, and they cannot handle ambiguous segmentation boundaries caused by motion blur. To address these difficult issues, we introduce a simple yet effective Instance Motion Tendency Network (IMTNet) for video panoptic segmentation. It learns a global motion tendency map for instance association, and a hierarchical classifier for motion boundary refinement. Specifically, a Global Motion Tendency Module (GMTM) is designed to learn robust motion features from optical flows, which can directly associate each instance in the previous frame to the corresponding instance in the current frame. In addition, we propose a Motion Boundary Refinement Module (MBRM) to learn a hierarchical classifier to handle the boundary pixels of moving targets, which can effectively revise the inaccurate segmentation predictions. Experimental results on both Cityscapes and Cityscapes-VPS datasets show that our IMTNet outperforms most state-of-the-art approaches.

Experimental study on the wave-induced dynamic response and hydrodynamic characteristics of a submerged floating tunnel with elastically truncated boundary condition

Hydrodynamic load and motion response are the first considerations in the structural design of a submerged floating tunnel (SFT). Currently, most of the relevant studies have been based on a two-dimensional model test with a fixed or fully free boundary condition, which inhibits a deep investigation of the hydrodynamic characteristics with an elastic constraint. As a result, a series of difficulties exist in the structural design and analysis of an SFT. In this study, an SFT model with a one-degree-of-freedom vertical elastically truncated boundary condition was established to investigate the motion response and hydrodynamic characteristics of the tube under the wave action. The effect of several typical hydrodynamic parameters, such as the buoyancy-weight ratio, γ, the relative frequency, f/fN, the Keulegan–Carpenter (KC) number, the reduced velocity, Ur, the Reynolds number, Re, and the generalized Ursells number, on the motion characteristics of the tube, were selectively analyzed, and the reverse feedback mechanism from the tube's motion response to the hydrodynamic loads was confirmed. Finally, the critical hydrodynamic parameters corresponding to the maximum motion response at different values of γ were obtained, and a formula for calculating the hydrodynamic load parameters of the SFT in the motion state was established. The main conclusions of this study are as follows: (i) Under the wave action, the motion of the SFT shows an apparent nonlinearity, which is mainly caused by the intensive interaction between the tube and its surrounding water particles, as well as the nonlinearity of the wave. (ii) The relative displacement of the tube first increases and then decreases with increasing values of f/fN, Ur, KC number, Re, and the generalized Ursells number. (iii) γ is inversely proportional to the maximum relative displacement of the tube and the wave force on the tube in its motion direction. (iv) Under the motion boundary condition (as opposed to the fixed boundary condition), the peak frequency of the wave force on the SFT in its motion direction decreases and approaches the natural vibration frequency of the tube, whereas the wave force perpendicular to the motion direction increases. When the incident wave frequency is close to the natural vibration frequency of the tube, the tube resonates easily, leading to an increased wave force in the motion direction. (v) If the velocity in the Morison equation is substituted by the water particle velocity measured when the tube is at its equilibrium position, the inertia coefficient in the motion direction of the tube is linearly related to its displacement, whereas that in the direction perpendicular to the motion direction is logarithmically related to its displacement.

Drive power minimization of outreach change mechanism of tower crane during steady-state slewing mode

The variational problem of the movement mode selection for the load outreach change mechanism during a steady-state tower crane slewing was formulated and solved in the paper, that ensures the minimization of the drive motor power. We used a dynamic model of the outreach change mechanism for research work, which presented the mechanical system with three degrees of freedom. The formulated variational problem is nonlinear, and so we used the modified PSO-Rot-Ring particle swarm metaheuristic method for its solution. The analytical solution of another variational problem for the same model of the crane mechanism and an optimization criterion close in physical content was used as the solution initial approximation of the nonlinear variational problem to save calculated resources. The starting mode of the mechanism drive for the load outreach change was determined during the solution of the nonlinear variational problem, which ensures the root-mean-square value minimization of the drive motor power. Low- and high-frequency oscillations of the outreach change mechanism elements during the start-up were detected in the optimization process. The first oscillations are caused by the load rocking on the flexible suspension during the start-up, and the second – by the nature of the change in the driving moment and drive power. These oscillations are eliminated in the section of steady-state movement due to the selection of the motion boundary conditions, which are taken into account in the solution process of the variational problem.

Motion Video Recognition in Speeded-Up Robust Features Tracking

Motion video recognition has been well explored in applications of computer vision. In this paper, we propose a novel video representation, which enhances motion recognition in videos based on SURF (Speeded-Up Robust Features) and two filters. Firstly, the detector scheme of SURF is used to detect the candidate points of the video because it is an efficient faster local feature detector. Secondly, by using the optical flow field and trajectory, the feature points can be filtered from the candidate points, which enables a robust and efficient extraction of motion feature points. Additionally, we introduce a descriptor, called MoSURF (Motion Speeded-Up Robust Features), based on SURF (Speeded-Up Robust Features), HOG (Histogram of Oriented Gradient), HOF (Histograms of Optical Flow), MBH(Motion Boundary Histograms), and trajectory information, which can effectively describe motion information and are complementary to each other. We evaluate our video representation under action classification on three motion video datasets namely KTH, YouTube, and UCF50. Compared with state-of-the-art methods, the proposed method shows advanced results on all datasets.

Development of bony range of motion (B-ROM) boundary for total hip replacement planning

Background and objectivePre-operative surgical planning using computer simulation is increasingly standard practice before Total Hip Arthroplasty (THA), in order to determine the optimal implant positions, and thereby minimise post-operative complications such as dislocation, wear and leg length discrepancy. One of the limitations of current methods, however, is the lack of information on the subject-specific reference range of motion (ROM) that could be used as targets for surgical planning. Only a limited number of hip motions are considered, which are neither subject-specific, nor representative of all the hip motions associated with all the activities of daily livings (ADLs). In this paper, therefore, a method was developed to calculate subject-specific representative bony range of motion (B-ROM) that would cover all the possible joint motions and presented in terms of pure joint motions. MethodsOnly 3D bone geometries of femur and pelvis, constructed from personalised CT scan, were used as inputs for healthy hip joint whereas implant geometries and their positions on native bone geometries were required for planned treatment side or replaced side. Hip joint motion simulation was carried out using six different Tait-Bryan intrinsic rotation sequences of three pure joint motions - flexion-extension, abduction-adduction and internal-external rotation, and B-ROM was then identified for any of these six different sequences which caused earliest feasible impingement. The B-ROM could be used as a list of ROM data points or visualised as multiple 2D surface plots or a 3D envelop. Using the developed method, the B-ROM of a contralateral healthy hip joint of a patient can be used to define the subject-specific target ROM values to inform the surgical planning of the arthritic hip side so that the patient's natural ROM could be restored as closely as possible by the planned implant placements. This was demonstrated with a clinical verification study using ‘non-dislocating’ and ‘dislocating’ THA patients. ResultsThe results supported the study hypothesis that the percentage of intersected volume of the healthy and replaced side B-ROM was higher for the ‘Non-Dislocator’ patient (95%) compared to ‘Dislocator’ (78%). Also, the results showed that the only one sequence (first flexion-extension, then abduction-adduction and finally internal-external rotation) was not adequate to identify all the possible limiting B-ROM, and therefore, all the six rotation sequences should be considered. ConclusionsThe method encompasses every potential ADL, and as a result, more comprehensive surgical planning is possible, as the implant positions can be optimised in order to maximise impingement-free ROM, and consequently minimise clinical complications.

Coordinated Saturated Output-Feedback Control of an Autonomous Tractor-Trailer and a Combine Harvester in Crop-Harvesting Operation

This paper proposes a coordinated tracking controller for a tractor-trailer to keep a desired distance and heading angle relative to a combine harvester for the autonomous unloading of harvested crops in automatic agriculture operations. A coordinate transformation and the prescribed performance control (PPC) technique are employed to develop a second-order Euler-Lagrange formulation of the tracking errors. Then, a neural adaptive saturated velocity observer-based controller is proposed to force that the trailer center is exactly placed under the end point of the harvester unloading tube to collect cereal grains. By an effective application of the PPC technique and computing a safe motion boundary, controller non-singularity, collision avoidance and connectivity between two vehicles are preserved continuously. The model uncertainties including unknown vehicle parameters, variable trailer mass and moment of inertia during the crop collection, surface friction, climate and crop conditions and external disturbances are compensated by an effective combination of a neural network and an adaptive robust control law. Lyapunov’s direct method is employed to prove that the tracking errors are semi-globally uniformly ultimately bounded and converge to a neighborhood of the origin with a pre-specified maximum overshoot, convergence rate and steady-state accuracy. Finally, comparative simulation results are presented to demonstrate the effectiveness of the proposed controller for the crop harvesting operations in a practical perspective.

Microstructure and Mechanical Properties at Elevated Temperature of Powder Metallurgy Al-Zn-Mg-Cu Alloy Subjected to Hot Extrusion

In this work, Al-Zn-Mg-Cu powders containing 0.15 and 0.33 wt % oxygen were utilized to prepare high-strength aluminum alloys through the process of cold isostatic pressing, sintering, hot extrusion, and heat treatment. Microstructural and mechanical properties at elevated temperatures of 250, 350, and 450 °C were investigated by scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), transmission electron microscopy (TEM), and high-temperature tensile tests. Results showed that the tensile strengths of the obtained Al-Zn-Mg-Cu alloys with 0.15 wt % oxygen were 185, 46, and 18 MPa at 250, 350, and 450 °C, respectively. When the oxygen content of Al-Zn-Mg-Cu alloy rose to 0.33 wt %, the tensile strengths at the corresponding temperature reached up to 205, 68, and 25 MPa, respectively. The excellent high-temperature performance could be attributed to double hindrance to dislocation motion and grain boundary migration by a large amount of nano γ-Al2O3 created by the in-creased oxygen, thereby resulting in fine grains even at high temperatures.

Nonlinear thermal vibration of functionally graded non-uniform and imperfect micro-tube including the porosity in the thermal environment for different cross-section

In producing small-scale structures, having nonuniform geometrics and voids as the generation defect is the inevitable problem. However, in the mathematical simulations, the researchers have been more attentive to the perfect and uniform structures because of simple modeling. This article investigates the nonlinear free vibrational behavior of truncated conical imperfect functionally graded (FG) micro-scale tubes, including the porosity, including the various cross-section functions. The modified couple stress theory and Euler-Bernoulli beam theory coupled with the nonlinear Von-Kármán theory are employed based on Hamilton's principles to derive the general equation of motion and related boundary conditions. The cross-section is assumed on the basis of four different functions, involving the uniform section, linear section, convex section, and exponential section. The temperature-dependent materials were combined by ceramic and metal phases along the tube radius that this combination made a functionally graded tube. Furthermore, the nonlinear derived equations are finally solved via the generalized differential quadrature method (GDQM) as the numerical approach coupled with the iteration technique. Since thermal fins, fluid flow diffuser, fluid flow nozzle, etc., are designed for specific purposes with the non-uniform cross-section, the presented results have an excellent sight of developing and designing macro/- and micro-electromechanical systems (MEMS).

Self-casting and alter-casting: Healthcare professionals’ boundary work in response to peer workers

Within mental health services, the recovery model has been a guiding philosophy over the past decades. This model stresses ‘person-centred care’ and focuses on assisting service users to live a meaningful and hopeful life even if their illness has not been cured. As part of the recovery orientation, ‘peer workers’ (PWs), i.e. people with lived experiences of mental illness, are increasingly employed within mental health services. In this article, the authors explore how these changes open up frontiers and set in motion boundary work and identity discussions among healthcare professionals. Empirically, the article draws on qualitative data – interviews with healthcare professionals and observations of meetings – collected in mental healthcare services in Denmark. Theoretically, the article combines literature on professional boundary work with theories on ‘self-casting’, ‘alter-casting’ and ‘othering’. Analysing two sets of demarcations – those between healthcare professionals and PWs, and those between professionals and patients – the study shows how the recovery model leads to defensive boundary work as well as an opening up of boundaries.

Human Fall Detection in Surveillance Videos Using Fall Motion Vector Modeling

Representation of spatio-temporal properties of human body silhouette and human-to-ground relationship, significantly contribute to the fall detection process. So, we propose an approach to efficiently model the spatio-temporal features using fall motion vector. First, we construct a Gaussian mixture model (GMM) called fall motion mixture model (FMMM) using histogram of optical flow and motion boundary histogram features to implicitly capture motion attributes in both the fall and non-fall videos. The FMMM contains both fall and non-fall attributes resulting in a high-dimensional representation. In order to extract only the relevant attributes for a particular fall or non-fall videos, we perform factor analysis on FMMM to get a low dimensional representation known as fall motion vector. Using fall motion vector, we are able to efficiently identify fall events in varieties of scenarios, such as the narrow angle camera (Le2i dataset), wide angle camera (URFall dataset), and multiple cameras (Montreal dataset). In all these scenarios, we show that the proposed fall motion vector achieves better performance than the existing methods.