Overcoming a 'forbidden phenotype': The parrot's head supports, propels, and powers tripedal locomotion

No vertebrate, living or extinct, is known to have possessed an odd number of limbs. Despite this ″forbidden phenotype″, gaits that utilize odd numbers of limbs (e.g., tripedalism or pentapedalism) have evolved in both avian and mammalian lineages. Tripedal locomotion is commonly employed by parrots during climbing, who utilize their beaks as an additional support. However, it is unclear whether the beak functions simply as a stabilizing hook, or as a propulsive limb. Here, we present data on kinetics of tripedal climbing in six rosy –faced lovebirds (Agapornis rosiecollis). Our findings demonstrate that parrots utilize cyclical tripedal gaits when climbing and the beak and hindlimbs generate comparable propulsive and tangential substrate reaction forces and power. Propulsive and tangential forces generated by the beak are of equal or greater magnitudes to those forces generated by the forelimbs of humans and non –human primates during vertical climbing. We conclude that the feeding apparatus and neck musculature of parrots has been co–opted to function biomechanically as a third limb during vertical climbing. We hypothesize that this exaptation required substantive alterations to the neuromuscular system including enhanced force–generating capabilities of the neck musculature and modifications to limb central pattern generators.

Study of the strengthened state near the forces for the semi-plan

Many of the engineering applications have faced the delicate contact problem in the area close to the forces where it is very difficult to experimentally carry out various measurements and draw important conclusions on the condition of the contact points. In this paper the forced state in the vicinity of the forces for the half-plane will be studied. Furthermore, the qualities displayed by the half-plane under the action of normal forces, tangential forces and the moment caused by a pair of forces will be analyzed, as well as changes in the elastic characteristics for the forced plane state and the deformed plane state.

Effect of Graphene nanoplatelets (GNP) reinforcement on grindability of zirconium diboride ceramics

The grindability of graphene nanoplatelets (GNP) reinforced ZrB2 was studied using resin bonded diamond grinding wheel under dry and wet conditions. A comparative study of grinding forces was performed at selected wheel surface speeds and depth of cuts for surface grinding. ZrB2-GNP showed lower normal grinding forces due to the reduced hardness. The presence of GNP reinforcement in ZrB2 resulted in lower tangential forces and reduced specific grinding energy due to the role of GNP as solid lubricant. The measured forces showed good correlation with the micro cutting model for ZrB2 and ZrB2-GNP under dry condition. The tangential forces showed same trend as normal forces at different depth of cuts and wheel surface speeds for both ZrB2 and ZrB2-GNP with average force ratios of 0.3 and 0.35 respectively. The presence of porosity in ZrB2 increased the normal grinding forces during wet grinding. Scanning Electron Microscope (SEM) images of the grinding chips indicated a mixture of both the ductile mode and the brittle mode of material removal with predominantly brittle fractured chips. Energy Dispersive Spectroscopy (EDS) confirmed the presence of GNPs in ZrB2-GNP grinding chips. The topography of the grinding wheel showed higher wheel loading after the dry grinding than that of wet grinding. The wet grinding resulted in relatively lower surface roughness (Ra values) compared to that of dry grinding.

Investigation of the Emission Higher Harmonics into the Generator Grid

The article considers a section of the grid with generator voltage busbars (GRU-10 kV) of one of the hydroelectric power plants HPP-I of a large cascade HPP, which supplies electricity to an aluminium plant via two busbars. It is described that the plant load includes converter units, including: transformers, bridge rectifier blocks and saturation chokes, which are powerful sources of harmonic disturbances. An overview of the developed model and the principles of its construction for studying the influence a powerful non-linear load on the generator is given. Analysis of the results calculations on the model showed that the load of an industrial enterprise creates current and voltage distortions in the electrical s not only of the plant itself, but also in urban grids, and on the busbars of the generator voltage HPP-I. The article analyzes the influence of the current effects of a large industrial enterprise load in asymmetric modes on hydrogenerators by evaluating torsional vibrations and tangential vibrations in generators. It is shown that tangential forces of double frequency (100 Hz) practically do not create significant vibration displacements when the natural frequency of the frontal parts basket is adjusted.

Theoretical and Experimental Study of Changes in the Structure of the Intermediate Layer during Friction between Contacting Bodies

Friction is often accompanied by local fracture at the boundary of contacting bodies. The space between contacting bodies usually contains moving particles of a different nature, and a change in the effective friction conditions can be associated with a change in the structure of the contact area. This paper presents a new series of experiments where balls simulated the particles of the intermediate layer interacting with an elastic layer of different thickness. The effects of regularization when the balls approached each other were investigated considering different initial configurations (line and spatial structure). The balls simulated the particles of the intermediate layer interacting with the elastic layer of different thickness. The opposite effects of convergence and separation of the balls were observed in different experiments. A model of mutual effect during the contact of two balls with a two-layered elastic half-space was developed. An analysis of tangential forces due to the mutual effect was performed for different layer thicknesses, its relative compliance, and different distances between the balls. It was found that the input parameters defined the sign of the tangential force, which led to the convergence or the separation of the balls. The results can be used to create structures controlling the motion in the intermediate layer.

Self-Excited Full-Vehicle Oscillations Caused by Tire–Road Interaction: Virtual and Real-World Experimental Investigation

ABSTRACT In this article, self-excited full-vehicle oscillations (power-hops) are introduced. Initially, results of full-vehicle measurements are shown followed by the presentation of a specially build test rig (longitudinal dynamics test rig). Subsequently, these oscillations are investigated by using simulation-based tools within multibody simulation–related full-vehicle modeling. Tire–road interaction is evaluated in this process either by characteristic curves or by a proprietary quasistatic tire model that returns overall tangential forces by evaluating the state of every discretized element within the footprint area.

Normal and Tangential Forces Combine to Convey Contact Pressure during Dynamic Tactile Stimulation

Humans need to accurately process the contact forces that arise as they perform everyday haptic interactions, but the mechanisms by which the forces on the skin are represented and integrated remain little understood. In this study, we used a force-controlled robotic platform and simultaneous ultrasonic modulation of the finger-surface friction to briefly and independently manipulate the normal and tangential forces during passive haptic stimulation by a flat surface. When participants were asked whether the contact pressure on their finger had briefly increased or decreased, they could not distinguish the normal force from the tangential force. Instead, they integrated the normal and tangential components of the force vector into a multidimensional computation of the contact force. We additionally investigated whether participants relied on three common contact-force metrics. Interestingly, the change in the amplitude of the force vector predicted participants’ responses better than the change of the coefficient of dynamic friction and the change of the angle of the contact force vector. Thus, intensive cues related to the amplitude of the applied force may be meaningful for the sensing of contact pressure during haptic stimulation by a moving surface.

Design of a Wearable Haptic Device for Hand Palm Cutaneous Feedback

This study describes the main design and prototyping steps of a novel haptic device for cutaneous stimulus of a hand palm. This part of the hand is fundamental in several grasping and manipulation tasks, but is still less exploited in haptics applications than other parts of the hand, as for instance the fingertips. The proposed device has a parallel tendon-based mechanical structure and is actuated by three motors positioned on the hand’s back. The device is able to apply both normal and tangential forces and to render the contact with surfaces with different slopes. The end-effector can be easily changed to simulate the contact with different surface curvatures. The design is inspired by a smaller device previously developed for the fingertips; however, in the device presented in this study, there are significant differences due to the wider size, the different form-factor, and the structure of hand palm. The hand palm represents the support for the fingers and is connected to the arm through the wrist. The device has to be developed taking into account fingers’ and wrist’s motions, and this requirement constrains the number of actuators and the features of the transmission system. The larger size of the palm and the higher forces challenge the device from a structural point of view. Since tendons can apply only tensile forces, a spring-based support has been developed to keep the end-effector separated from the palm when the device is not actuated or when the force to be rendered is null. The study presents the main design guidelines and the main features of the proposed device. A prototype has been realized for the preliminary tests, and an application scenario with a VR environment is introduced.

High Precision Contact Model for Ball Bearings With Waviness

Studying high precision ball bearings requires the development of predictive models. In presence of waviness on the rings, geometrical and also mechanical parameters will vary according to the angular position. To consider these modifications, a nonlinear contact model is proposed with normal and tangential forces calculation using Hertz and Dahl’s models. To solve the static equilibrium of the bearing, a highly modular energy method is developed. It allows the determination of both local and global parameters using the same equation. The 2D developed approach can be used to study different waviness orders and magnitudes to get a better understanding on how this affects the bearing behavior (contact load, balls gaping, pointing defects...). The presented results show that even small contact direction reorientation can create tangential forces. This modifies the bearing deflections and induces a residual moment. These phenomena can only be observed when the contact is accurately modeled.