Body Translation Research Articles

A general mass lumping scheme for the variants of the extended finite element method

SummaryA new strategy for the mass matrix lumping of enriched elements for explicit transient analysis is presented. It is shown that to satisfy the kinetic energy conservation, the use of zero or negative masses for enriched degrees of freedom of lumped mass matrix may be necessary. For a completely cracked element, by lumping the mass of each side of the interface into the finite element nodes located at the same side and assigning zero masses to the enriched degrees of freedom, the kinetic energy for rigid body translations is conserved without transferring spurious energy across the interface. The time integration is performed by adopting an explicit‐implicit technique, where the regular and enriched degrees of freedom are treated explicitly and implicitly, respectively. The proposed method can be viewed as a general mass lumping scheme for the variants of the extended finite element methods because it can be used irrespective of the enrichment method. It also preserves the optimal critical time step of an intact finite element by treating the enriched degrees of freedom implicitly. The accuracy and efficiency of the proposed mass matrix are validated with several benchmark examples.

On jerk in the kinematic study of the rigid body

Jerk, as the derivative of acceleration, is used more and more in the kinematic study of the systems characterized by short travels and requiring a high precision of positioning, including elevators, CNC machine tools, and industrial robots. The acceleration modelling using jerk variation serve as a basis for generating the functioning tahogrames of the mechanical systems. Since peak values of jerk and acceleration are closely connected to safety and also to comfort in the mechanical systems where human presence is involved, a study concerning the positions of the systems where these values are reached will be performed in this paper. The position vector of the points where peak values of jerk are reached will be determined. Spatial motion as well as the particular motions of the rigid body (translation movement, rotation around a fixed axis, helical movement, the motion of planar mechanisms, spherical motion) will be considered. Since positioning is an important aim for the industrial robots, jerk variation in the various points of the robot’s parts may provide important information about peak values of acceleration, as well as about inertial forces involved in positioning. Also, jerk is currently used in speed modelling of elevators and robots, a study considering the positions corresponding to peak values of acceleration has not yet been performed.

Experimental evaluation of the strain intensity factor at the rigid line inclusion tip embedded in an epoxy matrix using digital image correlation

The strain intensity factor for a rigid line inclusion tip is experimentally determined using the digital image correlation (DIC) technique using multi-parameter displacement field equations. The multi-parameter displacement field equations for a rigid line inclusion are derived based on the Airy’s stress function approach and are reported here in an elegant manner. The unknown coefficients in the multi-parameter equation, inclusion tip location, rigid body translations and rotation are determined using a linear least squares method in an over-deterministic manner. A rigid line inclusion specimen is prepared using 0.1 mm steel strip embedded in an epoxy matrix. Experiments are performed for two inclusion configurations when the embedding matrix is subjected to a remote tensile field. In the first configuration, the inclusion is placed along the tensile loading direction. In the second configuration, the inclusion is kept inclined to the loading direction. The experimentally obtained strain intensity factor agrees well with the analytical estimates with an error less than 6% for the seven parameter solution for both the configuration, thereby confirming the accuracy of the proposed methodology.

Binocular 3D otolith-ocular reflexes: responses of normal chinchillas to tilt and translation.

Head rotation, translation, and tilt with respect to a gravitational field elicit reflexive eye movements that partially stabilize images of Earth-fixed objects on the retinas of humans and other vertebrates. Compared with the angular vestibulo-ocular reflex, responses to translation and tilt, collectively called the otolith-ocular reflex (OOR), are less completely characterized, typically smaller, generally disconjugate (different for the 2 eyes) and more complicated in their relationship to the natural stimuli that elicit them. We measured binocular 3-dimensional OOR responses of 6 alert normal chinchillas in darkness during whole body tilts around 16 Earth-horizontal axes and translations along 21 axes in horizontal, coronal, and sagittal planes. Ocular countertilt responses to 40-s whole body tilts about Earth-horizontal axes grew linearly with head tilt amplitude, but responses were disconjugate, with each eye's response greatest for whole body tilts about axes near the other eye's resting line of sight. OOR response magnitude during 1-Hz sinusoidal whole body translations along Earth-horizontal axes also grew with stimulus amplitude. Translational OOR responses were similarly disconjugate, with each eye's response greatest for whole body translations along its resting line of sight. Responses to Earth-horizontal translation were similar to those that would be expected for tilts that would cause a similar peak deviation of the gravitoinertial acceleration (GIA) vector with respect to the head, consistent with the "perceived tilt" model of the OOR. However, that model poorly fit responses to translations along non-Earth-horizontal axes and was insufficient to explain why responses are larger for the eye toward which the GIA vector deviates.NEW & NOTEWORTHY As the first in a pair of papers on Binocular 3D Otolith-Ocular Reflexes, this paper characterizes binocular 3D eye movements in normal chinchillas during tilts and translations. The eye movement responses were used to create a data set to fully define the normal otolith-ocular reflexes in chinchillas. This data set provides the foundation to use otolith-ocular reflexes to back-project direction and magnitude of eye movement to predict tilt axis as discussed in the companion paper.

Review on multi-stage incremental forming process to form vertical walled cup

Using incremental forming, forming of a vertical walled cup was impossible in a single-stage due to the reason that failure is followed by thinning at transition region (in between the wall & base of the cup). However in the recent years, forming of a cup with vertical wall or maximum wall angle compared to Single-stage Single Point Incremental Forming (SPIF) are being done successfully by many researchers using Multi-stage Single Point Incremental Forming (MSPIF) process. The reason behind the implementation of MSPIF process is that the thinning will be postponed even when the maximum wall angle is achieved, with number of intermediate stages during Incremental Forming. In the case of Single-stage Incremental Forming, wall angle beyond a certain limit can’t be obtained due to the reason that thinning will occur suddenly at transition region. In this paper, a review is presented on MSPIF process to form cup with vertical wall or maximum wall angle compared to Single-stage Incremental Forming. In addition, tool path design, different forming strategies, effect of forming direction & strategy, Rigid Body Translation (RBT) during intermediate stages, geometrical accuracy of formed part such as dimensional deviation & step formation at base, Formability using Forming Limit Stress Diagram (FLSD) and Thickness distribution and comparisons of MSPIF process are discussed. Further, works proposed for future to improve the process is also presented in this paper.

The lowest vibration modes of an elastic beam composed of alternating stiff and soft components

Harmonic vibrations of a strongly inhomogeneous elastic beam with piecewise uniform stiffnesses and densities are considered. The focus is on the lowest eigenmodes, which are often most harmful and unwanted. They are evaluated by perturbing the limiting rigid body translations and rotations of stiff beam components. The developed methodology is adapted for two particular configurations of a three-span beam. The derived approximate formulae are tested by comparison with the exact solution of a symmetric beam with two stiff outer components and free ends.

Addressing the need for a new generation of young translational researchers that focuses on societal impact: The Apollo Toronto Story

Translational research (TR) is a multidirectional and multidisciplinary integration of basic research, patient-oriented research and population-based research, with the long-term goal of improving human health. Unfortunately, the current scientific training system does not adequately align with the goals of TR. To address this issue, an organization called Apollo Toronto was established at the University of Toronto in Toronto, Ontario. Apollo Toronto is a medical student-run international collaborative project between the Eureka Institute for Translational Medicine and the University of Toronto (one of Eureka Institute’s partner universities), and provides a general overview of TR to interested medical and graduate students. Through local and international initiatives, the various Apollo chapters (including Apollo Toronto) aim to establish a network of trainees equipped to address systemic issues that impede the translation of an ever-growing body of scientific literature into health solutions.

Analysis of the Cervical Sagittal Alignment in Patients with Unstable Hangman Fracture Under C2∼3 Anterior Discectomy and Fusion

To investigate the changes in the sagittal parameters of the cervical spine and the clinical efficacy of C2∼3 anterior cervical discectomy and fusion (ACDF) combined with internal fixation for unstable hangman's fractures. The clinical data of 46 patients with unstable hangman's fractures treated with both C2∼3 ACDF combined with internal fixation between May 2012 and May 2017 were analyzed retrospectively. The upper cervical angle (C0∼2), the forward translation of the C2 vertebral body (C2-T), C2∼3 local kyphosis angle (C2∼3 LK), C2∼7 cervical curvature (C2∼7 CC), C2 sagittal vertical axis (C2-SVA), and T1 slope angle (T1S) were compared preoperatively, postoperatively, and at the last follow-up to evaluate the clinical therapeutic effects. A total of 46 patients were followed-up for an average of 16 months. No aggravation of the spinal cord, nerve injury, cerebrospinal fluid leakage, or other complications occurred. Six patients had American Spinal Injury Association (ASIA) grade C preoperatively; 4 improved to grade E, and 2 improved to grade D postoperatively. Twelve patients with ASIA grade D preoperatively improved to grade E postoperatively. C0∼2, C2-T, C2∼3 LK, C2∼7 CC, and C2-SVA measurements were significantly improved postoperatively and at the last follow-up, but there was no significant change in T1S between preoperative and postoperative values. For patients with unstable hangman's fractures, C2∼3 ACDF combined with internal fixation can achieve immediate stability of the upper cervical vertebrae, effectively correct the forward displacement and angulation of C2, and restore the sagittal balance of the cervical spine. The rate of osseous intervertebral fusion is high, and there are few complications. This method can effectively promote the recovery of spinal nerve function and preserve the motor function of the cervical vertebrae.

A numerical model for the time-dependent wake of a pedalling cyclist

A method for computing the wake of a pedalling cyclist is detailed and assessed through comparison with experimental studies. The large-scale time-dependent turbulent flow is simulated using the Scale Adaptive Simulation approach based on the Shear Stress Transport Reynolds-averaged Navier–Stokes model. Importantly, the motion of the legs is modelled by joining the model at the hips and knees and imposing solid body rotation and translation to the lower and upper legs. Rapid distortion of the cyclist geometry during pedalling requires frequent interpolation of the flow solution onto new meshes. The impact of numerical errors, that are inherent to this remeshing technique, on the computed aerodynamic drag force is assessed. The dynamic leg simulation was successful in reproducing the oscillation in the drag force experienced by a rider over the pedalling cycle that results from variations in the large-scale wake flow structure. Aerodynamic drag and streamwise vorticity fields obtained for both static and dynamic leg simulations are compared with similar experimental results across the crank cycle. The new technique presented here for simulating pedalling leg cycling flows offers one pathway for improving the assessment of cycling aerodynamic performance compared to using isolated static leg simulations alone, a practice common in optimising the aerodynamics of cyclists through computational fluid dynamics.

Transformation of vestibular signals for the decisions of hand choice during whole body motion.

In daily life, we frequently reach toward objects while our body is in motion. We have recently shown that body accelerations influence the decision of which hand to use for the reach, possibly by modulating the body-centered computations of the expected reach costs. However, head orientation relative to the body was not manipulated, and hence it remains unclear whether vestibular signals contribute in their head-based sensory frame or in a transformed body-centered reference frame to these cost calculations. To test this, subjects performed a preferential reaching task to targets at various directions while they were sinusoidally translated along the lateral body axis, with their head either aligned with the body (straight ahead) or rotated 18° to the left. As a measure of hand preference, we determined the target direction that resulted in equiprobable right/left-hand choices. Results show that head orientation affects this balanced target angle when the body is stationary but does not further modulate hand preference when the body is in motion. Furthermore, reaction and movement times were larger for reaches to the balanced target angle, resembling a competitive selection process, and were modulated by head orientation when the body was stationary. During body translation, reaction and movement times depended on the phase of the motion, but this phase-dependent modulation had no interaction with head orientation. We conclude that the brain transforms vestibular signals to body-centered coordinates at the early stage of reach planning, when the decision of hand choice is computed. NEW & NOTEWORTHY The brain takes inertial acceleration into account in computing the anticipated biomechanical costs that guide hand selection during whole body motion. Whereas these costs are defined in a body-centered, muscle-based reference frame, the otoliths detect the inertial acceleration in head-centered coordinates. By systematically manipulating head position relative to the body, we show that the brain transforms otolith signals into body-centered coordinates at an early stage of reach planning, i.e., before the decision of hand choice is computed.

Soil resistances for laterally loaded rigid piles in multi-layered elastic soil

ABSTRACTShort stubby piles like monopiles and large diameter drilled shafts undergo rigid body translation and rotation when subjected to a lateral force and/or a moment at the head. A method of analysis for these piles embedded in multi-layered elastic soil is developed using the variational principles of mechanics. Using this analysis, the soil resistance against pile movement can be rigorously related to the soil elastic constants, and the pile head displacement and rotation can be quickly calculated. The equilibrium equations for pile and soil displacements are obtained using the principle of virtual work and solved using an iterative algorithm. Pile responses obtained from the analysis match well with those obtained from three-dimensional finite element analyses in which the same inputs of loads, geometry, and material properties are given. Based on the new analysis, fitted equations for soil resistance parameters are developed, which can be used to directly calculate the pile head displacement and rotation without the use of the iterative algorithm. Numerical examples are provided that demonstrate how the method can be used to analyse practical problems.

Atomistic simulations of energies for arbitrary grain boundaries. Part II: Statistical analysis of energies for tilt and twist grain boundaries

The orientation-dependency of grain boundary (GB) energy in Al is investigated using a cutoff sphere molecular dynamics model presented in Part I, which is applicable to arbitrary GBs. A GB energy dataset is generated using the model with deletion of over-close atoms and without rigid body translations in building the candidate configurations for a given GB. The dataset includes 12,062 tilt GBs (TIGBs) and twist GBs (TWGBs) with a broad range of misorientation angle/axis (θ/O) and GB-plane orientation (n). Statistical analyses of the results show that the energies overall increase with θ in the low-θ range and then level off for higher θ, and that the energies for non-coincident site lattice GBs also follow the increasing trend in the low-θ range. The energies of TIGBs decrease with the variation of O from the central regions to the edge and then corners of the stereographic triangle, and the O-dependency of GB energy becomes more severe for TWGBs. The current energy dataset suggests that the n-dependency of GB energy is best correlated with the orientation-dependency of surface energy following the broken-bond model and it does not support the existing perspective of low energies for GBs terminated by low-index or dense planes. For both types of GBs, the energy suffers a stronger influence from θ than n.

Posterior short-segment fixation with transforaminal lumbar interbody fusion for the treatment of unstable lower lumbar fracture

Background: The objective of this study was to evaluate the clinical and radiographic results of posterior short-segment pedicle screw fixation and transforaminal lumbar interbody fusion (TLIF) in selected types of lower lumbar fractures. Methods: Twenty-seven patients with lower lumbar fractures were enrolled in this study. Demographic data, neurologic grade, anterior vertebral body heights, vertebral body translation, segmental Cobb angle, and management-related complications were assessed. The minimum follow-up period was 2 yr. Results: Twenty male patients and seven female patients underwent the procedure, with a mean operative time of 182 min. Mean blood loss was 588 mL. The mean preoperative local kyphotic angle was 9.5 degrees that improved to 2.5 degrees postoperatively. The loss of correction was insignificant at the final follow-up. The preoperative percentage of height lost improved from a mean of 52.5% to a mean of 89.05% postoperatively, and at last follow-up no loss of correction in height was noted compared to the postoperative results. No pseudarthrosis or metal failure was detected. All patients who were Frankle E on admission remained neurologically intact. Conclusions: Posterior short-segment fixation with pedicle screw fixation augmented with TLIF might be a possible choice for selected patients with unstable lower lumbar fractures, particularly in split fractures, burst fractures with a reversed cortex sign, and traumatic spondylolisthesis.

Modelling Rock Failure with a Novel Continuous to Discontinuous Method

The original discontinuous deformation and displacement (DDD) method is greatly refined using the statistical damage theory and contact mechanics. Next, a novel coupled method is proposed to model the continuous to discontinuous failure process of rocks. By hybridizing the finite element method (FEM) and discontinuous deformation analysis (DDA) method, the proposed method inherits the advantages of both and is able to provide a complete and unified description of rock deformation, crack initiation and propagation, and rock body translation, rotation and interaction. Moreover, to improve the deformation results and refine the stress distribution within the model blocks, finite elements are introduced into the blocks. The ability of an intact block to fracture is included as well, i.e., the deformable blocks that contain several finite elements may split into smaller blocks if the strength criteria are satisfied continuously. The boundaries of damaged elements represent newly formed joints, and sliding and opening may occur along these joints, i.e., mechanical interaction is allowed between adjacent blocks. The correctness and validity of the proposed method are verified through a series of benchmark tests. The simulated results are consistent with the analytical solutions, previous studies and experimental observations. Overall, the coupled method is an effective and reliable approach for modelling the entire rock failure process with satisfactory accuracy and shows considerable potential in geotechnical engineering.

Atomistic simulations of energies for arbitrary grain boundaries. Part I: Model and validation

Grain boundary (GB) energies are important data for understanding and predictive modeling of thermal and mechanical behaviors in polycrystalline materials. In this study, a cutoff sphere molecular dynamics model is proposed to calculate the energies of arbitrary GBs. This model eliminates the effect of interaction between free surface and GB in a bicrystal cell by excluding the surface region in the energy computation. The model is tested for four groups of coincident site lattice (CSL) GBs with low-to-medium coincidence index and non-CSL GBs in aluminum. The results show that, at a fraction of computation time as of the original sphere model, the cutoff sphere model without rigid body translation (RBT) provides approximate energy predictions that agree with experimental results and those of the classical block model adopting periodic boundary conditions. The good performance of the cutoff sphere model for non-CSL GBs lies in its faithful reproduction of characteristic structure units and resulting quasi-periodicity in the GB structures. The applicability to arbitrary GBs renders the model an attractive tool to construct energy datasets useful for material behavior simulations. Further improvement in the accuracy of energy predictions is shown to be possible by incorporating RBT at the expense of significantly-increased computational cost.

On a geometrically exact Euler‐Bernoulli beam element

AbstractIn this work, a geometrically exact, fully nonlinear Euler‐Bernoulli beam formulation is presented. Herewith a special case of Timoshenko rod models, discussed in various publications such as [2] or [4], is considered. Following the basic assumptions of transversal shear rigidity and plane cross sections, the formulation is based on displacements, their derivatives and a torsional rotation angle, in order to cover finite deformations and rotations. A straight reference configuration is considered, whereas the possibility for initially curved configurations is discussed in [1]. Within the Euler‐Bernoulli theory a cross section undergoes ridged body translation and rotation. While the translation is described by the motion of the beam axis only, the rotation is accounted within a rotational field, see e.g. [3]. In the present formulation, the rotational field is parametrized by the rotation tensor based on Rodrigues formula, which yields a simple update scheme as shown in [5], and is the first of its kind for Euler‐Bernoulli beam models. Using this parametrization an ansatz is presented, that allows for consistent connection of structural members, even in cases of physical discontinuities. On the element level C1 continuous Hermite polynomials are used to interpolate the displacements an their derivatives, while a Lagrangian interpolation scheme is chosen for the torsional rotation. A numerical Benchmark problems is presented to demonstrate the performance of the finite element formulation.

Vestibular System and Self-Motion.

Detection of the state of self-motion, such as the instantaneous heading direction, the traveled trajectory and traveled distance or time, is critical for efficient spatial navigation. Numerous psychophysical studies have indicated that the vestibular system, originating from the otolith and semicircular canals in our inner ears, provides robust signals for different aspects of self-motion perception. In addition, vestibular signals interact with other sensory signals such as visual optic flow to facilitate natural navigation. These behavioral results are consistent with recent findings in neurophysiological studies. In particular, vestibular activity in response to the translation or rotation of the head/body in darkness is revealed in a growing number of cortical regions, many of which are also sensitive to visual motion stimuli. The temporal dynamics of the vestibular activity in the central nervous system can vary widely, ranging from acceleration-dominant to velocity-dominant. Different temporal dynamic signals may be decoded by higher level areas for different functions. For example, the acceleration signals during the translation of body in the horizontal plane may be used by the brain to estimate the heading directions. Although translation and rotation signals arise from independent peripheral organs, that is, otolith and canals, respectively, they frequently converge onto single neurons in the central nervous system including both the brainstem and the cerebral cortex. The convergent neurons typically exhibit stronger responses during a combined curved motion trajectory which may serve as the neural correlate for complex path perception. During spatial navigation, traveled distance or time may be encoded by different population of neurons in multiple regions including hippocampal-entorhinal system, posterior parietal cortex, or frontal cortex.

Causal inference for spatial constancy across whole body motion.

The brain uses self-motion information to internally update egocentric representations of locations of remembered world-fixed visual objects. If a discrepancy is observed between this internal update and reafferent visual feedback, this could be either due to an inaccurate update or because the object has moved during the motion. To optimally infer the object's location it is therefore critical for the brain to estimate the probabilities of these two causal structures and accordingly integrate and/or segregate the internal and sensory estimates. To test this hypothesis, we designed a spatial updating task involving passive whole body translation. Participants, seated on a vestibular sled, had to remember the world-fixed position of a visual target. Immediately after the translation, the reafferent visual feedback was provided by flashing a second target around the estimated "updated" target location, and participants had to report the initial target location. We found that the participants' responses were systematically biased toward the position of the second target position for relatively small but not for large differences between the "updated" and the second target location. This pattern was better captured by a Bayesian causal inference model than by alternative models that would always either integrate or segregate the internally updated target location and the visual feedback. Our results suggest that the brain implicitly represents the posterior probability that the internally updated estimate and the visual feedback come from a common cause and uses this probability to weigh the two sources of information in mediating spatial constancy across whole body motion. NEW & NOTEWORTHY When we move, egocentric representations of object locations require internal updating to keep them in register with their true world-fixed locations. How does this mechanism interact with reafferent visual input, given that objects typically do not disappear from view? Here we show that the brain implicitly represents the probability that both types of information derive from the same object and uses this probability to weigh their contribution for achieving spatial constancy across whole body motion.

Knowledge-transfer-based cost-effective search for interface structures: A case study on fcc-Al [110] tilt grain boundary

Determining the atomic configuration of an interface is one of the most important issues in materials science research. Although theoretical simulations are effective tools, an exhaustive search is computationally prohibitive due to the high degrees of freedom of the interface structure. In the interface structure search, multiple energy surfaces created by a variety of orientation angles need to be explored, and the necessary computational costs for different angles vary substantially owing to significant variations in the supercell sizes. In this paper, we introduce two machine-learning concepts, called transfer learning and cost-sensitive search, to the interface-structure search. As a case study, we demonstrate the effectiveness of our method, called cost-sensitive multitask Bayesian optimization, using the fcc-Al [110] tilt grain boundary. Four microscopic parameters, the three-dimensional rigid body translation, and the number of atomic columns, are optimized by transferring knowledge of energy surfaces among different orientation angles. We show that transferring knowledge of different energy surfaces can accelerate the structure search, and that considering the cost variations further improves the total efficiency.

히브리어 고대 시가의 번역 : ‘모세의 축복’의 서두(신 33:2-3)

In many cultures, old traditions and memories are often transmitted in the form of hymns and songs. It is the same in the Old Testament. The oldest records in the Old Testament are mainly songs, which are usually referred to as ancient Hebrew poetry. These include the Blessing of Jacob (Gen 49), the Song of Moses (Exo 15), the Prophecies of Balaam (Num 23-24), the Blessing of Moses (Deu 33), the Song of Deborah (Jdg 5), the Song of Habakkuk (Hab 3), 2 Samuel 22 (= Psa 18), and Psalms 68.BR Translating these ancient Hebrew songs is a difficult and challenging task. There are several reasons for this. First of all, since these songs are very old, it is not easy to restore or reconstruct the contents of the original text where the text is seriously damaged. There are also cases where the classical Hebrew grammar and spelling, which we are familiar with, do not apply to these poems. These early forms of Hebrew should be understood through comparison with other Semitic languages such as Akkadian, Ugaritic, and Hebrew inscriptions.BR Ancient Hebrew poetry has linguistic features that are not found in the classical biblical Hebrew. For example, (1) t-prefixed form is used instead of y-prefixed form for an imperfect third person plural; (2) the frequent use of the so-called nun energicum in all imperfect forms; (3) תי is used for a perfect second person feminine singular; (4) the use of enclitic ט (mem); and (4) the disappearance of the nota accusativi –ta.BR Apart from the difficulty of translation, there is another important reason to study ancient Hebrew poetry. Since these poems are from the earliest period of Israel, they preserve the information about the early traditions of the origin and development of the religion of Israel and the faith of Yahwism.BR This study attempts to translate introductory part of the so-called “Blessing of Moses” (Deu 33:2-3). The result of this study reconstructs verses 2 and 3 as three stanzas of three lines each (2a, 2b, 2c/2d, 2e, 3a/3b, 3c, 3d).BR The most divergent part of my translation is that it sees the “holy ones” in 3b as heavenly beings whereas other previous Korean versions translate it as “the faithful.”BR This study further requires the translation of the main body of the Blessing of Moses as well as of other ancient Hebrew songs.