The Application of Quaternions to Strap-Down MEMS Sensor Data

We describe the mathematical transformations required to convert the data recorded using typical 6-axis microelectromechanical systems (MEMS) sensor packages (3-axis rate gyroscopes and 3-axis accelerometers) when attached to an object undergoing a short duration loading event, such as blast loading, where inertial data alone are sufficient to track the object motion. By using the quaternion description, the complex object rotations and displacements that typically occur are translated into the more convenient earth frame of reference. An illustrative example is presented where a large and heavy object was thrown by the action of a very strong air blast in a complex manner. The data conversion process yielded an accurate animation of the object’s subsequent motion.

Progression or Stagnancy? Portraying Native Americans in Michael Apted’s Thunderheart (1992)

Progression or Stagnancy? Portraying Native Americans in Michael Apted’s Thunderheart (1992) As argued by Wilcomb Washburn, no other ethnic group has been misrepresented in media and popular culture to such extent as the Native Americans (2010). Movies that shaped their image did so by crystallizing stereotypes and misconceptions, through which indigenous peoples have been perceived until the present day. Thomas Edison’s vignettes, early westerns, as well as subsequent motion pictures of the 1960s and 1970s strengthened the stereotypes of the vanishing Indians, bloodthirsty savages, and their noble alter ego. The 1990s brought about a revival of the western in its new, revisionist form, mainly due to the achievements of the American Indian Movement. This paper argues that the movie Thunderheart (1992) by Michael Apted — albeit belonging to that ostensibly revolutionary current — continues to reproduce various well established stereotypes in the portrayal of the Native Americans . It examines significantachievements of this partly liberal motion picture, as well as its failures and faults. Thisarticle argues that Thunderheart departs from traditional, dualistic portrayals of Native Americans as bloodthirsty and noble savages and manages to present a revisionist version of historical events; at the same time, it fails to omit numerous Hollywood clichés, such as stereotypical representation of native spirituality, formation of an “Indian identity”, and “othering” of the Native Americans, which contributes to their further alienation and cultural appropriation. This paper provides an insightful analysis of the movie, drawing on scholarship in the field of cultural and indigenous studies in order to lay bare the ambivalence towards indigenous people in the United States, that is reflected in the movie industry. Moreover, it indicates towards the commodification of native culture, as well as the perception of Native Americans as primitive and inferior, allowing to classify Thunderheartas an unfortunate product of colonialism.

Objective assessments of human motor ability of the upper limb: A systematic review

BACKGROUND: Most of the patients who survive stroke, spinal cord or others nervous system injuries, must face different challenges for a complete recovery of physical functional impairment. An accurate and recurrent assessment of the patient rehabilitation progress is very important. So far, wearable sensors (e.g. accelerometers, gyroscopes) and depth cameras have been used in medical rehabilitation for the automation of traditional motor assessments. Combined with machine learning techniques, these sensors are leading to novel metric systems for upper limb mobility assessment. OBJECTIVE: Review current research for objective and quantitative assessments of the upper limb movement, analyzing sensors used, health issues examined, and data processes applied such as: selected features, feature engineering approach, learning models and data processing techniques. METHOD: A systematic review conducted according to the PRISMA guidelines. EBSCOHOST discovery service was queried for relevant articles published from January 2014 to December 2018 with English language and scholarly peer reviewed journals limits. RESULTS: Of the 568 articles identified, 75 were assessed for eligibility and 43 were finally included and weighed for an in-depth analysis according to their ponderation. The reviewed studies show a wide use of sensors to capture raw data for subsequent motion analysis. CONCLUSION: As the volume of the data captured via these sensors increase, it makes sense to extract useful information about them such as prediction of performance scores, detection of movement impairments and measured progression of recovery.

A motion aftereffect from viewing other people’s gaze

SummaryRecent work suggests that our brains may generate subtle, false motion signals streaming from other people to the objects of their attention, aiding social cognition. For instance, brief exposure to static images depicting other people gazing at objects made subjects slower at detecting subsequent motion in the direction of gaze, suggesting that looking at someone else’s gaze caused a directional motion adaptation. Here we confirm, using a more stringent method, that viewing static images of another person gazing in a particular direction, at an object, produced motion aftereffects in the opposite direction. The aftereffect was manifested as a change in perceptual decision threshold for detecting left versus right motion. The effect disappeared when the person was looking away from the object. These findings suggest that the attentive gaze of others is encoded as an implied agent-to-object motion that is sufficiently robust to cause genuine motion aftereffects, though subtle enough to remain subthreshold.

A framework for hadronic rescattering in pp collisions

In this article, a framework for hadronic rescattering in the general-purpose Pythia event generator is introduced. The starting point is the recently presented space–time picture of the hadronization process. It is now extended with a tracing of the subsequent motion of the primary hadrons, including both subsequent scattering processes among them and decays of them. The major new component is cross-section parameterizations for a range of possible hadron–hadron combinations, applicable from threshold energies upwards. The production dynamics in these collisions has also been extended to cope with different kinds of low-energy processes. The properties of the model are studied, and some first comparisons with LHC $$\mathrm {p}\mathrm {p}$$ p p data are presented. Whereas it turns out that approximately half of all final particles participated in rescatterings, the net effects in $$\mathrm {p}\mathrm {p}$$ p p events are still rather limited, and only striking in a few distributions. The new code opens up for several future studies, however, such as effects in $$\mathrm {p}$$ p A and AA collisions.

Detachment in capillary adhesion: the relative roles of tilting and separation

We study the dynamics of detachment in 2D capillary adhesion by considering a plate that is initially attached to a flat, rigid substrate via the surface tension of a bridging liquid droplet. In particular, we focus on the effect of allowing the plate to tilt freely during its subsequent motion. A linear stability analysis shows that small perturbations from equilibrium decouple into two modes: one in which the plate separates from the substrate, remaining parallel, and another in which it tilts, simultaneously causing the bridging droplet to migrate. If the initial tilt perturbation is of a similar magnitude to (or bigger than) the separation perturbation, then the presence of this second tilting mode can significantly alter the dynamics. Indeed, this tilting mechanism changes the ultimate fate of the plate: depending on the size of the plate and the initial perturbation, the plate may anomalously detach. We discuss this observation in relation to previous experiments on a 3D system that showed a qualitatively similar anomalous detachment.

Stiffness as a control factor for object manipulation

During manipulation, force is exerted with the expectation that an object will move in an intended manner. This prediction is a learned coordination between force and movement. Mechanically, impedance is a way to describe this coordination, and object interaction could be anticipated by setting impedance before the hand moves the object. This strategy would be especially important at the end of a reach, because feedback is ineffective for rapid force changes. Since mechanical impedance is not subject to the time delays of feedback, it can, if set properly, produce the desired motion on impact. We examined this possibility by instructing subjects to move a handle to a specific target position along a track. The handle was locked in place until the subject exerted enough force to cross a threshold; the handle was then released abruptly to move along the track. We hypothesized that this ballistic release task would encourage subjects to modify impedance in anticipation of the upcoming movement and found that one component of impedance, stiffness, varied in a way that matched the behavioral demands of the task. Analysis suggests that this stiffness was set before the handle moved and governed the subsequent motion. We also found separate components of muscle activity that corresponded to stiffness and to changes in force. Our results show that subjects used a robust and efficient strategy to coordinate force and displacement by modulating muscle activity in a way that was behaviorally relevant in the task. NEW & NOTEWORTHY The arm can behave like a spring, and this mechanical behavior can be advantageous in situations requiring rapid changes in force and/or displacement. Selection of a proper “virtual” spring before the occurrence of a rapid transient could facilitate a desired responsive movement. We show that these spring-like arm mechanics, set in anticipation of an instantaneous force change, function as an efficient strategy to control movement when feedback is ineffective.

Launching a projectile to cover maximal area

The launch and subsequent motion of a projectile provide a context for several quantities that yearn to be optimised. Most notable is the horizontal range of the projectile, a problem dating back to Galileo and still studied in modern times; see, for example [1], [2], [3], [4]. In a different direction, the articles [5] and [6] provide a solution to the problem of finding the angle of launch that results in the trajectory of longest arc length.

Could Chalk Hopping Be Caused by Reverse Chatter?

Anyone who has ever used a chalkboard is probably familiar with the phenomenon of “chalk hopping,” where the chalk unexpectedly skips across the chalkboard, leaving a dotted line in its wake. Such behavior is ubiquitous to mechanical systems with moving parts in contact, where it is almost always undesirable. It is widely believed that hopping behavior is a physical manifestation of either the classical Painlevé paradox or a related phenomenon called dynamical jam. The present paper poses the question of whether chalk hopping might be caused by a different, and much more recently discovered, instability called “reverse chatter,” in which two bodies initially in sustained contact can lose contact through a sequence of impacts with increasing amplitude. Previous simulations of reverse chatter have considered only constant external loads, which do not adequately model the forces exerted on a piece of chalk. The current work presents simulation results for a model system in the presence of a control algorithm that mimics the human hand by attempting to keep the chalk in contact with the chalkboard. The simulations reveal that there exist physically realistic parameter values for which a loss of contact occurs that cannot be attributed to either the classical Painlevé paradox or dynamical jam, but which can only be attributed to reverse chatter. Furthermore, the subsequent motion of the system after losing contact is found to be strikingly similar to that of chalk hopping on a chalkboard, to a hitherto unparalleled degree. These results show that neither the classical Painlevé paradox nor dynamical jam is necessary for hopping behavior, and suggest that reverse chatter may be the most plausible explanation for chalk hopping.

Why Continuous Motions Cannot Be Composed of Sub-motions: Aristotle on Change, Rest, and Actual and Potential Middles

I examine the reasons Aristotle presents in Physics VIII 8 for denying a crucial assumption of Zeno’s dichotomy paradox: that every motion is composed of sub-motions. Aristotle claims that a unified motion is divisible into motions only in potentiality (δυνάμει). If it were actually divided at some point, the mobile would need to have arrived at and then have departed from this point, and that would require some interval of rest. Commentators have generally found Aristotle’s reasoning unconvincing. Against David Bostock and Richard Sorabji, inter alia, I argue that Aristotle offers a plausible and internally consistent response to Zeno. I defend Aristotle’s reasoning by using his discussion of what to say about the mobile at boundary instants, transitions between change and rest. There Aristotle articulates what I call the Changes are Open, Rests are Closed Rule: what is true of something at a boundary instant is what is true of it over the time of its rest. By contrast, predications true of something over its period of change are not true of the thing at either of the boundary instants of that change. I argue that this rule issues from Aristotle’s general understanding of change, as laid out in Phys. III. It also fits well with Phys. VI, where Aristotle maintains that there is a first boundary instant included in the time of rest, but not a “first in which the mobile began to change.” I then show how this rule underlies Aristotle’s argument that a continuous motion cannot be composed of actual sub-motions. Aristotle distinguishes potential middles, points passed through en route to a terminus, from actual middles. The Changes are Open, Rests are Closed Rule only applies to actual middles, because only they are boundaries of change that the mobile must arrive at and then depart from. On my reading, Aristotle argues that the instant of arrival, the first instant at which the mobile has come to be at the actual middle, cannot belong to the time of the subsequent motion. If it did, the mobile would already be moving towards the next terminus and thus, per Phys. VI 6, would have already left. But it cannot have moved away from the midpoint at the very same moment it has arrived there. This means that the instant of arrival must be separated from the time of departure by an interval of rest. I show how Aristotle’s reasoning applies generally to rule out any continuous reflexive motion or continuous complex rectilinear motion. On my interpretation, however, the argument does not apply to every change of direction. When, as in the case of projectile motion, multiple movers and their relative powers explain why the mobile changes directions, distinct sub-motions are not involved. Aristotle holds that such motions cannot be continuous, not because they involve intervals of rest, but because they involve multiple causes of motion. My interpretation of the Changes are Open, Rests are Closed Rule allows us to make better sense of Aristotle’s argument than any previous interpretation.