Precomputed ambient occlusion for character skins

Letter to the Editor: Joint Moments in the Joint Coordinate System, Euler or Dual Euler Basis

1. Human gastrocnemius medialis architecture was analysed in vivo, by ultrasonography, as a function of joint angle at rest and during voluntary isometric contractions up to the maximum force (MCV). maximum force (MVC). 2. At rest, as ankle joint angle increased from 90 to 150 deg, pennation increased from 15.8 to 27.7 deg, fibre length decreased from 57.0 to 34.0 mm and the physiological cross-sectional area (PCSA) increased from 42.1 to 63.5 cm2. 3. From rest to MVC, at a fixed ankle joint angle of 110 deg, pennation angle increased from 15.5 to 33.6 deg and fibre length decreased from 50.8 to 32.9 mm, with no significant change in the distance between the aponeuroses. As a result of these changes the PCSA increased by 34.8%. 4. Measurements of pennation angle, fibre length and distance between the aponeuroses of the gastrocnemius medialis were also performed by ultrasound on a cadaver leg and found to be in good agreement with direct anatomical measurements. 5. It is concluded that human gastrocnemius medialis architecture is significantly affected both by changes of joint angle at rest and by isometric contraction intensity. The remarkable shortening observed during isometric contraction suggests that, at rest, the gastrocnemius muscle and tendon are considerably slack. The extrapolation of muscle architectural data obtained from cadavers to in vivo conditions should be made only for matching muscle lengths.

The walking procedure of the cattle, Bostaurus, on a paddy field before spring plowing was captured with a high-speed video camera. The properties of the paddy soil used for tests and the geometrical configurations of the hooves of the cattle were examined. The geometrical configurations and motion postures of the cattle during walking on paddy field were analyzed, and the gait parameters were gained from the high-speed photographs. The changes of displacement, velocity, acceleration and force of the centre of mass (COM) of the cattle were analyzed. The changes of the joint angles and the orientations of all limbs were analyzed. It was shown that the changes of hip joint angle and shoulder joint angle were more remarkable, which provided the driving force for the body. The changes of the forelimb were more prominent compared with the hind-limb, moreover, the landing place of the hind-hooves were farther than the fore-hooves, which made the hind-limb have a larger movement space to prevent the interference between forelimb and hind-limb while the strides were increased. The movement of knee joint and elbow joint were very obvious after limb left the ground, the movements of hip joint and shoulder joint were steady to reduce the impact of the ground before limb touched down the ground. The results would provide some theoretical and practical references for biomimetic design for improving the reasonable motion of the walking robot on soft ground. This work may provide the basic theory in developing cattle-like robot in structural design. Besides, it provides an important reference to study the other bionic robots.

The purpose of this study was to identify and differentiate the motor strategies associated with sensory reweighting adapted during specific sensory integration tasks by healthy young adults. Thirty-six subjects (age range: 21–33 years) performed standing computerized dynamic posturography balance tasks across progressively increasing amplitudes of visual (VIS), somatosensory (SOM) and both (VIS+SOM) systems perturbation conditions. Adaptation in the motor strategy was measured as changes in electromyographic (EMG) activities and joint angles. The contribution of the perturbed sensory input in maintaining postural stability was calculated to determine the sensory reweighting. A multivariate design was used to model a linear combination of motor adaptation variables that discriminates specific sensory integration tasks. Results showed a significant progressive decrease in postural sway per unit amplitude of sensory perturbation in each condition, indicating dynamic sensory reweighting. Linear discriminant function analysis indicated that the adaptation in motor strategy during the VIS condition was associated with increased activity of EMG and joint angles in the upper body compared to the lower body. Conversely, during the SOM and VIS+SOM conditions, the adaptation in motor strategy was associated with decreased activity of EMG and joint angles in the lower body compared to the upper body. Therefore, the adaptation in motor strategies associated with sensory reweighting were different for different sensory integration tasks.

The primary sources of injuries in the workplace are improper manual material handling (MMH) motions, forklift collisions, slip, and fall. This research presents a Digital Twin (DT) framework to analyze fatigue in humans while performing lifting MMH activity in a laboratory environment for the purpose of reducing these types of injuries. The proposed methodology analyzes the worker’s body joints to detect biomechanical fatigue as a factor of change in back, elbow, and knee joint angles. Using the dynamic time warping (DTW) algorithm, the change in joint angles with time was analyzed. The variation in DTW parameters was evaluated using exponentially weighted moving average (EWMA) control charts for further analysis. A preliminary study considering two healthy male subjects performing seven experiments, each under an optical motion capture system was performed to test the model’s efficiency. Our contributions are twofold. First, we propose a model to detect biomechanical fatigue in the subjects performing MMH lifting activity as a change in joint angles. Secondly, the research also shows evidence that different individuals show signs of body fatigue via different body joints and showcases the need for a true personalized DT for an operator for fatigue assessment in an MMH environment.

This study aims to analyze the effect of mental fatigue on biomechanical variables of batting technique in softball. Good batting technique requires precise movement coordination, reaction speed, and high mental concentration. However, mental fatigue, which often occurs due to intensive cognitive activity or excessive mental load, is thought to affect biomechanical performance. This includes changes in joint angles, body rotation speed, and batted ball speed, which directly affect the effectiveness of batting in softball. This study involved 15 softball players from the Bumi Asri club with an average age of 20 ± 0.6 years. Data collection was carried out using a three-dimensional motion analysis device, ball speed radar, and heart rate sensor. Subjects will undergo a 15-minute warm-up session, followed by an intensive cognitive task designed to trigger mental fatigue. Biomechanical variables will be measured before and after mental fatigue, including analysis of changes in joint angles, body rotation speed, and batted ball speed. The data obtained will be analyzed using a paired sample t-test to evaluate significant differences. This study is expected to provide an important contribution in understanding the impact of mental fatigue on sports biomechanics, especially softball batting technique. In addition, the results of this study can be a basis for coaches to design more effective training strategies, so that athletes can maintain optimal performance even in challenging mental conditions.

Multi-view stereo can be used to rapidly create realistic virtual content, such as textured meshes or a geometric proxy for free-viewpoint Image-Based Rendering (IBR). These solutions greatly simplify the content creation process compared to traditional methods, but it is difficult to modify the content of the scene. We propose a novel approach to create scenes by composing (parts of) multiple captured scenes. The main difficulty of such compositions is that lighting conditions in each captured scene are different; to obtain a realistic composition we need to make lighting coherent. We propose a two-pass solution, by adapting a multi-view relighting network. We first match the lighting conditions of each scene separately and then synthesize shadows between scenes in a subsequent pass. We also improve the realism of the composition by estimating the change in ambient occlusion in contact areas between parts and compensate for the color balance of the different cameras used for capture. We illustrate our method with results on multiple compositions of outdoor scenes and show its application to multi-view image composition, IBR and textured mesh creation.

We present a novel geometry-based approach for the detection of small-scale cracks in a temporal series of 3D-reconstructions of concrete objects such as pillars and beams of bridges and other infrastructure. The detection algorithm relies on a geometry-derived coloration of the 3D surfaces for computing the optical flow between time steps. Our filtering technique identifies cracks based on motion discontinuities in the local crack neighborhood. This approach avoids using the material color which is likely to change over time due to weathering and other environmental influences. In addition, we detect and exclude regions with significant local changes in geometry over time e.g. due to vegetation. We verified our method with reconstructions of a horizontal concrete beam under increasing vertical load at the center. For this case, where the main crack direction is known and a precise registration of the beam geometries over time exists, this approach produces accurate crack detection regardless of substantial color variations and is also able to mask out regions with simulated growth of vegetation over time.

Human detection and tracking is an interesting field of research in computer vision and image processing areas. It is widely used in video surveillance, robotics, human machine interaction and other applications. The automated object detection and tracking is still a challenging task that needs to be addressed. Hence the main idea is to develop a system based on various image processing techniques to reliably detect and track people in video sequence from stationary cameras. The proposed method can be viewed as consisting of two stages namely detection and tracking. In detection stage, Histogram of Oriented Gradients popularly known as HOG is used as a feature descriptor. HOG features are robust to local changes in geometry and illumination but it is computationally expensive. This disadvantage of HOG is due to its exhaustive scanning approach over entire region of interest. The main contribution of this paper is to reduce the computational time of HOG by dynamically determining the region of interest and limiting the scan area. Further Principal component analysis is used to reduce the dimensionality of HOG features. The additional use of optical flow based tracking eliminates the need of HOG computation in every frame. Hence the person detected by HOG in initial frame is successfully tracked in subsequent frames and reduces HOG computation time. The proposed dynamic ROI selection method not only reduces detection time but also reduces the number of false positives and increases the efficiency. The experimental results show that the system efficiently detects and tracks people in videos without much of occlusion.

Abnormal blood flow patterns promoting inflammation, cellular proliferation, and thrombosis may be established by local changes in vessel geometry after stent implantation in bifurcation lesions. Our objective was to quantify altered hemodynamics due to main vessel (MV) stenting and subsequent virtual side branch (SB) angioplasty in a coronary bifurcation by using computational fluid dynamics (CFD) analysis. CFD models were generated from representative vascular dimensions and intravascular ultrasound images. Time-averaged wall shear stress (TAWSS), oscillatory shear index (OSI), and fractional flow reserve (FFR) were quantified. None of the luminal surface was exposed to low TAWSS (<4 dyn/cm(2)) in the nondiseased bifurcation model. MV stenting introduced eccentric areas of low TAWSS along the lateral wall of the MV. Virtual SB angioplasty resulted in a more concentric region of low TAWSS in the MV distal to the carina and along the lateral wall of the SB. The luminal surface exposed to low TAWSS was similar before and after virtual SB angioplasty (rest: 43% vs. 41%; hyperemia: 18% vs. 21%) and primarily due to stent-induced flow alterations. Sites of elevated OSI (>0.1) were minimal but more impacted by general vessel geometry established after MV stenting. FFR measured at a jailed SB was within the normal range despite angiographic stenosis of 54%. These findings indicate that the most commonly used percutaneous interventional strategy for a bifurcation lesion causes abnormal local hemodynamic conditions. These results may partially explain the high clinical event rates in bifurcation lesions.

The aim of this study is to realize a simplified gait analysis system using wearable sensors. In this paper, a joint angle measurement method using Kalman filter to correct gyroscope signals from accelerometer signals was examined in measurement of hip, knee and ankle joint angles with a wireless wearable sensor system, in which the sensors were attached on the body without exact positioning. The lower limb joint angles of three healthy subjects were measured during gait with the developed sensor system and a 3D motion measurement system in order to evaluate the measurement accuracy. Then, 10m walking measurement was performed under different walking speeds with a healthy subject in order to find the usefulness of the system as a simplified gait analysis system. The joint angles were measured with reasonable accuracy, and the system showed joint angle changes that were similar to those shown in a previous report as walking speed changed. It would be necessary to examine the influence of sensor attachment position and method for more stable measurement, and also to study other parameters for gait evaluation.

Replacement gilt feet and leg conformation traits are subjectively evaluated at early ages (150 d) in order to select acceptable replacements. The objectives of this study were to: 1) evaluate replacement gilt feet and leg conformation (FLC) using subjective and objective measurement methods, 2) estimate objective joint angle changes over two parities, and 3) evaluate the effect of three diets differing in standardized ileal digestible (SID) lysine concentrations on FLC traits using the objective evaluation method. Crossbred Large White × Landrace gilts (n = 641) were used. Gilts were moved to GDU at 77 days-of-age and randomly allotted to three ad libitum fed dietary treatments providing similar ME but differing in SID lysine concentrations (low, medium, and high) during the grow-finisher period. All animals received common gestation and lactation diets. Feet and leg conformation traits were evaluated at 100 d, 200 d, 1st litter (392 ± 25 d) and 2nd litter (548 ± 49 d) weaning events. Subjective evaluation was done on a scale from 1 to 5. Data were analyzed using mixed linear model methods. The majority of gilts received the intermediate score (i.e. 3) when joint angles were subjectively evaluated. No differences (P ≥ 0.05) were observed for knee, front pastern and hock objective joint angles between subjective scores assigned. Differences in subjectively evaluated rear pastern (P &lt; 0.05) were observed, where objective joint angles associated with scores of ≤ 2 and 3 were lower than score of ≥ 4. There was no interaction between dietary treatment and objective evaluation time-period for any FLC traits studied (P &gt; 0.05). Females with greater knee, hock, front and rear pastern objective joint angles at 100 d of age, continued to have greater joint angles (0.2 ± 0.04 degrees; P &lt; 0.001) later in life. Front and rear pastern joint angles decreased (P &lt; 0.001) and hock joint angles increased from 100 d to end of study (P &lt; 0.001).

A three-segment angle-driven model of dart throwing was developed to observe which joint angle of the upper limbs has most influence on the dart release speed. A subject performing 10 dart throwing trials were recorded using a motion analysis system. Subsequently, the joint angle time histories of individual trial were put in into the simulation model. The model calculated resultant dart release speed for each recorded trial and each trial was matched accurately. Systematically substituting a constant value to each joint angle, and observing the changes on dart release speed indicated that dart release speed was most susceptible to forearm extension/flexion. During coaching or performance, attention should be focused on this joint angle because any changes could have a substantial effect on the dart release speed.

A parametric model of muscle moment arm as a function of joint angle: Application to the dorsiflexor muscle group in mice

Physical exercise induces spatially heterogeneous adaptation in bone. However, it remains unclear where the changes in BMD and geometry have the greatest impact on femoral neck strength. The aim of this study was to determine the principal BMD-and-geometry changes induced by exercise that have the greatest effect on femoral neck strength. Pre- and post-exercise 3D-DXA images of the proximal femur were collected of male participants from the LIFTMOR-M exercise intervention trial. Meshes with element-by-element correspondence were generated by morphing a template mesh to each bone to calculate changes in BMD and geometry. Finite element (FE) models predicted femoral neck strength changes under single-leg stance and sideways fall load. Partial least squares regression (PLSR) models were developed with BMD-only, geometry-only, and BMD-and-geometry changes to determine the principal modes that explained the greatest variation in neck strength changes. The PLSR models explained over 90% of the strength variation with 3 PLS components using BMD-only (R2 > 0.92, RMSE < 0.06 N) and 8 PLS components with geometry-only (R2 > 0.93, RMSE < 0.06 N). Changes in the superior neck and distal cortex were most important during single-leg stance while the superior neck, medial head, and lateral trochanter were most important during a sideways fall. Local changes in femoral neck and head geometry could differentiate the exercise groups from the control group. Exercise interventions may target BMD changes in the superior neck, inferior neck, and greater trochanter for improved femoral neck strength in single-leg stance and sideways fall.