Cat's Paw Research Articles

Hierarchical Voronoi Structure Inspired by Cat Paw Pads Substantially Enhances Landing Impact Energy Dissipation

Hierarchical Voronoi Structure Inspired by Cat Paw Pads Substantially Enhances Landing Impact Energy Dissipation

Influence of the Side Branch Structure Pattern of the Imitation Cat's Claw Function on the Vibration and Noise of Tires

To study the method of reducing the low-frequency vibration noise of the tire, a passenger car tire(205/55R16) is taken as the research object. The dynamic grounding characteristics and vibration reduction mechanism of the cat's paw pad are analyzed. The research showed that the swing deformation characteristics of paw pads during the walking process of cats is one of the main ways to reduce the impact from the ground and achieve vibration reduction and silencing. To analyze the influence of tire grounding on noise, the tire grounding is divided into five areas, and the characteristics of ten tire grounding areas are analyzed through tests. Pearson correlation analysis is used to obtain the characteristics of the eight most relevant grounding areas with tire noise, and multiple linear regression is conducted between the characteristics of the eight grounding areas. The product of the correlation coefficient and the average value of the characteristics of the ground contact area shows that the central area of the tire tread contributes the most to the tire noise. The swing deformation characteristics of the bionic cat paw pad are realized by setting the staggered side branch pipe groove in the center of the tire, and the vibration reduction characteristics of the bionic tire are analyzed by using the finite element method. The results showed that when the tire rolls, the amplitude and fluctuation range of the ground radial excitation force acting on the bionic tire are reduced compared with the original tire, and the vibration and noise characteristics of the tire are improved.

The Application of Neural Networks to Modular Arrangements of Predetermined Time Standards

To study the method of reducing the low-frequency vibration noise of tires, a passenger car tire (205/55R16) is taken as the research object. The dynamic grounding characteristics and vibration reduction mechanism of the cat’s paw pad are analysed. The research showed that the swing deformation characteristics of paw pads during the walking process of cats are one of the main ways to reduce the impact from the ground and achieve vibration reduction and silencing. To analyse the influence of tire grounding on noise, tire grounding is divided into five areas, and the characteristics of ten tire grounding areas are analysed through tests. Pearson correlation analysis is used to obtain the characteristics of the eight most relevant grounding parameters with tire noise, and multiple linear regression is conducted between the characteristics of the eight grounding areas. The product of the correlation coefficient and the average value of the characteristics of the ground contact area shows that the central area of the tire tread contributes the most to the tire noise. The swing deformation characteristics of the bionic cat paw pad are realized by setting the staggered side branch pipe groove in the centre of the tire, and the vibration reduction characteristics of the bionic tire are analysed using the finite element method. The results showed that when the tire rolls, the amplitude and fluctuation range of the ground radial excitation force acting on the bionic tire are reduced compared with the original tire, and the vibration and noise characteristics of the tire are improved.

A space crawling robotic bio-paw (SCRBP) enabled by triboelectric sensors for surface identification

With the rapid development of space crawling robotics technology, tactile perception, a significant source for the robot to sense the external environment, has become the preferred solution to gather information in space. Sensors embedded in the robotic end-effector unit can collect and encode the large tactile data, allowing the robot to feel and perceive the real surroundings. Therefore, a space crawling robotic bio-paw (SCRBP) inspired by a cat paw, which performs as a compliant device and can flat the impulse force during the robot’s contact process to the target surface, is proposed in this paper. Meanwhile, a touch-sensing system embedded on SCRBP with self-powered sensors based on the triboelectric nanogenerator (TENG) technology is proposed which can provide the multi-dimensional sensation information in real time. By combining with machine learning (ML), the sensory system can be used for surface identification from the footfall process to the robot’s controller hub. In conclusion, SCRBP device proposed in this paper has obvious advantages in surface information acquisition, space adaptability, power consumption, cost, reliable signal and minimized data. Accordingly, SCRBP system shows fabulous potential in space robotics.

A 3D-Printed Sole Design Bioinspired by Cat Paw Pad and Triply Periodic Minimal Surface for Improving Paratrooper Landing Protection.

Paratroopers are highly susceptible to lower extremity impact injuries during landing. To reduce the ground reaction force (GRF), inspired by the cat paw pad and triply periodic minimal surface (TPMS), a novel type of bionic cushion sole for paratrooper boots was designed and fabricated by additive manufacturing. A shear thickening fluid (STF) was used to mimic the unique adipose tissue with viscoelastic behavior found in cat paw pads, which is formed by a dermal layer encompassing a subcutaneous layer and acts as the primary energy dissipation mechanism for attenuating ground impact. Based on uniaxial compression tests using four typical types of cubic TPMS specimens, TPMSs with Gyroid and Diamond topologies were chosen to fill the midsole. The quasi-static and dynamic mechanical behaviors of the bionic sole were investigated by quasi-static compression tests and drop hammer tests, respectively. Then, drop landing tests at heights of 40 cm and 80 cm were performed on five kinds of soles to assess the cushioning capacity and compare them with standard paratrooper boots and sports shoes. The results showed that sports shoes had the highest cushioning capacity at a height of 40 cm, whereas at a height of 80 cm, the sole with a 1.5 mm thick Gyroid configuration and STF filling could reduce the maximum peak GRF by 15.5% when compared to standard paratrooper boots. The present work has implications for the design of novel bioinspired soles for reducing impact force.

Emergence of Extreme Paw Accelerations During Cat Paw Shaking: Interactions of Spinal Central Pattern Generator, Hindlimb Mechanics and Muscle Length-Depended Feedback.

Cat paw shaking is a spinal reflex for removing an irritating stimulus from paw by developing extremely high paw accelerations. Previous studies of paw shaking revealed a proximal-to-distal gradient of hindlimb segmental velocities/accelerations, as well as complex inter-joint coordination: passive motion-dependent interaction moments acting on distal segments are opposed by distal muscle moments. However, mechanisms of developing extreme paw accelerations during paw shaking remain unknown. We hypothesized that paw-shaking mechanics and muscle activity might correspond to a whip-like mechanism of energy generation and transfer along the hindlimb. We first demonstrated in experiments with five intact, adult, female cats that during paw shaking, energy generated by proximal muscle moments was transmitted to distal segments by joint forces. This energy transfer was mostly responsible for the segmental velocity/acceleration proximal-to-distal gradient. Distal muscle moments mostly absorbed energy of the distal segments. We then developed a neuromechanical model of hindlimb paw shaking comprised a half-center CPG, activating hip flexors and extensors, and passive viscoelastic distal muscles that produced length/velocity-depended force. Simulations reproduced whip-like mechanisms found experimentally: the proximal-to-distal velocity/acceleration gradient, energy transfer by joint forces and energy absorption by distal muscle moments, as well as atypical co-activation of ankle and hip flexors with knee extensors. Manipulating model parameters, including reversal of segmental inertia distal-to-proximal gradient, demonstrated important inertia contribution to developing the segmental velocity/acceleration proximal-to-distal gradient. We concluded that extreme paw accelerations during paw shaking result from interactions between a spinal CPG, hindlimb segmental inertia, and muscle length/velocity-depended feedback that tunes limb viscoelastic properties.

CAT PAW: Combinatorial Algorithm to Test all Possible Assortments of Weights

<h2>Abstract</h2> Group-based multi-criteria decision-making (MCDM) is a challenging and time-consuming process often rich with subjectivity. This paper outlines an algorithm created in Python to evaluate every possible criterion weighting combination to assist in making an objective decision. Implications of this study include increased efficiency and reduced subjectivity in group-based MCDM.

Hierarchical network structural composites for extraordinary energy dissipation inspired by the cat paw

The proverbial “nine lives” of cats are attributed to the capacity of the felines to withstand jumps and falls from a high-rise without being fatally wounded, and this is due in large part to their impact-resistant paw pads. The pads possess a complex architecture of multiscale collagen fiber networks and adipose mass chambers. We propose in this paper the concept of a hierarchical composite made of porous polyurethane (PU) main network skeletons coated with graphene oxide (GO)/multiwalled carbon nanotubes (MWCNTs), freeze-dry constructed secondary membrane network configurations with GO/MWCNTs, and embedded in a polyborondimethylsiloxane (PBDMS) matrix. The design of the composite is inspired by the architectures of collagens present in the cat paw and the composites provide significant creep resistance, load bearing, shape recovery and also stiffness tailoring. More importantly, the hierarchical composites possess remarkable high energy dissipations during quasi-static cyclic compression and dynamic mechanical loadings as vibration (damping capacity: 160% increase compared to the pure matrix) and impact (impacting energy absorption: ∼100%). The multiscale deformation mechanisms are analyzed and discussed with the support of finite element simulations. The main fibrous and secondary membranous networks generated during the manufacturing of the composite act as multiscale confinements to the lipid-like matrix, so that the matrix with reversible B-O bonds can significantly contribute to the unusual energy dissipation characteristics. Similar to the cat paws, the hierarchical composites are also soft, flexible and show significant potential for safety wearing devices in sport and broad engineering applications.

The Future of Progressive Politics in a Post-Fordist World

The Future of Progressive Politics in a Post-Fordist World

Research on Vibration Reduction Method of Nonpneumatic Tire Spoke Based on the Mechanical Properties of Domestic cat's Paw Pads.

Although there is no risk of puncture, the vibration problem caused by discontinuous structures limits nonpneumatic tire development (NPT). The vibration reduction of nonpneumatic tires is a solvable urgent problem. This current study analyzed the dynamic grounding characteristics and the vibration reduction mechanism of the cat's paw pads and then applied the mechanical properties to the bionic design of nonpneumatic tire spokes to solve the vibration problem. Domestic cats' paw pads' dynamic grounding characteristics were determined using the pressure-sensitive walkway, high-speed camera, and VIC-2D. The results indicated that the mechanical characteristics of swing deformation of paw pads during the grounding process attenuated the grounding stress and buffered the energy storage to achieve the vibration reduction effect. According to the similarity transformation, a finite element model of NPT that could accurately reconstruct the structure and realistically reflect the load deformation was employed. The structure design of asymmetric arcs on the spokes' side edges was proposed, and it can effectively reduce the radial excitation force of NPT. The three parameters, the asymmetric arc, the thickness, and the curvature of spokes, were used as design variables to maximize the vibration reduction. The orthogonal experimental, the Kriging approximate model, and the genetic algorithm were carefully selected for optimal solutions. Compared with the original tire, the results showed that peak amplitude 1, peak amplitude 2, and the root square of the optimized tire's amplitudes were reduced by 76.07%, 52.88%, and 51.65%, respectively. These research results offer great potential guidance in the design of low-vibration NPT.

Design of Two-Wheeled Motorcycle Tire Crown Contour Bioinspired by Cat Paw Pads

The grip force of tires is crucial for vehicle security and drivability under different driving conditions. A small contact area and stress concentration in the contact patch of two-wheeled motorcycle (TWM) tires result in a reduction in grip performance and wear resistance. Even worse, improving the grip and wear resistance together is difficult to achieve. The purpose of the current study is to analyze the dynamic grounding characteristics and geometry of a cat paw pad and then apply its structure to the TWM tire to improve the contact area and wear resistance under different operating conditions. A nonlinear finite element tire model that could accurately reconstruct the tire structure and realistically reflect the mechanical response to different loads was employed. Then, the accuracy of the tire model was validated by a static test with a control tire. For cats, the dynamic grounding characteristics and topology of paw pads were determined using a pressure-sensitive walkway and a three-dimensional (3D) laser scanner. The results indicated that the cat forepaw third pad (CFTP) exhibited excellent grip capacity. According to similarity transformation, a bionic tire crown was designed according to the lateral fitting curve of the CFTP. Comparative results showed the enlargement of the contact area and decreases in peak pressure and frictional energy rate for the bionic tire under different conditions. With these improvements, the grip performance was improved, and the service life was extended synchronously. These research results can be applied for the design of TWM tires, especially cross-country motorcycle tires.

Comprehensive Biomechanism of Impact Resistance in the Cat's Paw Pad.

Cats are able to jump from a high-rise without any sign of injury, which is attributed in large part to their impact-resistant paw pads. The biomechanical study of paw pads may therefore contribute to improving the impact resistance of specific biomimetic materials. The present study is aimed at investigating the mechanics of the paw pads, revealing their impact-resistant biomechanism from macro- and microscopic perspectives. Histological and micro-CT scanning methods were exploited to analyze the microstructure of the pads, and mechanical testing was conducted to observe the macroscopic mechanical properties at different loading frequencies. Numerical micromodels of the ellipsoidal and cylindrical adipose compartments were developed to evaluate the mechanical functionality as compressive actions. The results show that the stiffness of the pad increases roughly in proportion to strain and mechanical properties are almost impervious to strain rate. Furthermore, the adipose compartment, which comprises adipose tissue enclosed within collagen septa, in the subcutaneous tissue presents an ellipsoid-like structure, with a decreasing area from the middle to the two ends. Additionally, the finite element results show that the ellipsoidal structure has larger displacement in the early stage of impact, which can absorb more energy and prevent instability at touchdown, while the cylindrical structure is more resistant to deformation. Moreover, the Von Mises of the ellipsoidal compartment decrease gradually from both ends to the middle, making it change to a cylindrical shape, and this may be the reason why the macroscopic stiffness increases with increasing time after contact. This preliminary investigation represents the basis for biomechanical interpretation and can accordingly provide new inspirations of shock-absorbing composite materials in engineering.

Caught by the Cat's Paw

Federal employment discrimination law is enamored with court-created doctrines with catchy names. A fairly recent addition to the canon is the concept of the “cat’s paw,” formally recognized by the Supreme Court in Staub v. Proctor Hospital. With its name coined by Judge Richard Posner and drawn from a fable, the concept of cat’s paw has taken ground quickly, discussed in hundreds of cases. This Article argues that the cat’s paw doctrine is a mistake, and the courts should abolish it. Before the Supreme Court recognized it as a separate doctrine, the Supreme Court decided numerous cases with facts that could now be called “cat’s paw” cases. The Supreme Court did not need or even mention the need for a new doctrine to adjudicate those cases. Strangely, the Supreme Court does not cite to any of these cases in Staub. Indeed, these Supreme Court cases are going to cause a judicial headache as lower courts try to reconcile pre-Staub jurisprudence with the court-created cat’s paw doctrine. The current cat’s paw doctrine muddles rather than elucidates complex concepts of intent, causation, and agency liability. Before cat’s paw doctrine becomes further entrenched, this Article provides a new and more complete history of the doctrine. This new history shows that courts did not need the cat’s paw doctrine prior to its creation. Even the Seventh Circuit decision that coined the phrase “cat’s paw” did not rely on cat’s paw to resolve the case. Importantly, there is only one way to reconcile Staub with several other canonical Supreme Court cases — to read it as simply recognizing one set of facts under which a plaintiff could prevail under federal discrimination law. Some lower courts are interpreting Staub to place significant limits on the scope of discrimination law. However, using cat’s paw to limit the scope is inconsistent with numerous Supreme Court cases, as well as the text and purposes of the discrimination statutes. Cat’s paw doctrine should be abolished while it is in its infancy because it is not needed and will likely lead to decades of confusion in employment discrimination jurisprudence.

Discrimination in the Age of Social Media: The New Dangers of Cat's Paw Liability

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A Sketchbook for the City to Come: The Pop‐Up as R&amp;D

Dan Hill, an Executive Director at Future Cities Catapult, is not content to accept that architecture is willy‐nilly the carapace for the desires of the society that constructs it. He argues that pop‐ups – all too often the tools of corporate branding or the cat's paw of gentrification – should be used to implement overt social initiatives, presaging an architecture of positive change in cities. A member of the Finnish Innovation Fund Sitra's Strategic Design Unit from 2011 to 2012, he helped lead the Open Kitchen initiative featured here.

Alpha Actinin-1 Regulates Cell-Matrix Adhesion Organization in Keratinocytes: Consequences for Skin Cell Motility

The migration of keratinocytes in wound healing requires coordinated activities of the motility machinery of a cell, the cytoskeleton and matrix adhesions. In this study we assessed the role of alpha actinin-1 (ACTN1), one of the two alpha actinin isoforms expressed in keratinocytes, in skin cell migration via an shRNA-mediated knockdown approach. Keratinocytes deficient in ACTN1 exhibit changes in their actin cytoskeleton organization, a loss in front-rear polarity and impaired lamellipodial dynamics. They also display aberrant directed motility and move slower than their wild-type counterparts. Moreover, they have abnormally arranged matrix adhesion sites. Specifically, the focal adhesions in ACTN1 knockdown keratinocytes are not organized as distinct entities. Rather, focal adhesion proteins are arranged in a circle subjacent to cortical fibers of actin. In the same cells, hemidesmosome proteins arrange in cat paw patterns, more typical of confluent, stationary cells and β4 integrin dynamics are reduced in knockdown cells compared with control keratinocytes. In summary, our data suggest a mechanism by which ACTN1 determines the motility of keratinocytes by regulating the organization of the actin cytoskeleton, focal adhesion and hemidesmosome proteins complexes, thereby modulating cell speed, lamellipodial dynamics and directed migration.

Task-dependent inhibition of slow-twitch soleus and excitation of fast-twitch gastrocnemius do not require high movement speed and velocity-dependent sensory feedback.

Although individual heads of triceps surae, soleus (SO) and medial gastrocnemius (MG) muscles, are often considered close functional synergists, previous studies have shown distinct activity patterns between them in some motor behaviors. The goal of this study was to test two hypotheses explaining inhibition of slow SO with respect to fast MG: (1) inhibition occurs at high movement velocities and mediated by velocity-dependent sensory feedback and (2) inhibition depends on the ankle-knee joint moment combination and does not require high movement velocities. The hypotheses were tested by comparing the SO EMG/MG EMG ratio during fast and slow motor behaviors (cat paw shake responses vs. back, straight leg load lifting in humans), which had the same ankle extension-knee flexion moment combination; and during fast and slow behaviors with the ankle extension-knee extension moment combination (human vertical jumping and stance phase of walking in cats and leg load lifting in humans). In addition, SO EMG/MG EMG ratio was determined during cat paw shake responses and walking before and after removal of stretch velocity-dependent sensory feedback by self-reinnervating SO and/or gastrocnemius. We found the ratio SO EMG/MG EMG below 1 (p < 0.05) during fast paw shake responses and slow back load lifting, requiring the ankle extension-knee flexion moment combination; whereas the ratio SO EMG/MG EMG was above 1 (p < 0.05) during fast vertical jumping and slow tasks of walking and leg load lifting, requiring ankle extension-knee extension moments. Removal of velocity-dependent sensory feedback did not affect the SO EMG/MG EMG ratio in cats. We concluded that the relative inhibition of SO does not require high muscle velocities, depends on ankle-knee moment combinations, and is mechanically advantageous for allowing a greater MG contribution to ankle extension and knee flexion moments.

Charles Dickens and the Cat Paw Letter Opener

This article explores the sensory expectations around Victorian taxidermy, beginning with Charles Dickens’s letter opener made from the paw of his favourite cat and moving to a discussion of <em>Our Mutual Friend</em>. I suggest that in a mid-Victorian moment in which work and laziness are polarized as the available moral, economic, and social categories, a desire for stillness, a space that is neither work nor laziness, exists in the encounter with taxidermied animals. The taxidermied animal allows energy and stillness to coexist.

Stabilization of cat paw trajectory during locomotion.

We investigated which of cat limb kinematic variables during swing of regular walking and accurate stepping along a horizontal ladder are stabilized by coordinated changes of limb segment angles. Three hypotheses were tested: 1) animals stabilize the entire swing trajectory of specific kinematic variables (performance variables); and 2) the level of trajectory stabilization is similar between regular and ladder walking and 3) is higher for forelimbs compared with hindlimbs. We used the framework of the uncontrolled manifold (UCM) hypothesis to quantify the structure of variance of limb kinematics in the limb segment orientation space across steps. Two components of variance were quantified for each potential performance variable, one of which affected it ("bad variance," variance orthogonal to the UCM, VORT) while the other one did not ("good variance," variance within the UCM, VUCM). The analysis of five candidate performance variables revealed that cats during both locomotor behaviors stabilize 1) paw vertical position during the entire swing (VUCM > VORT, except in mid-hindpaw swing of ladder walking) and 2) horizontal paw position in initial and terminal swing (except for the entire forepaw swing of regular walking). We also found that the limb length was typically stabilized in midswing, whereas limb orientation was not (VUCM ≤ VORT) for both limbs and behaviors during entire swing. We conclude that stabilization of paw position in early and terminal swing enables accurate and stable locomotion, while stabilization of vertical paw position in midswing helps paw clearance. This study is the first to demonstrate the applicability of the UCM-based analysis to nonhuman movement.

Cute and Monstrous Furbys in Online Fan Production

Cute and Monstrous Furbys in Online Fan Production