Singular Position Research Articles

Study on the Thermodynamic–Kinetic Coupling Characteristics of Free-Piston Stirling Air Conditioning

Unlike traditional free-piston Stirling heat engines or heat pumps, the free piston Stirling air conditioning (FPSAC) is specifically designed for electric vehicle air conditioning under ambient room temperature conditions. In the FPSAC system, the displacer and the power piston are coupled through gas forces, emphasizing the importance of investing the thermodynamic–kinetic coupling characteristics. This study analyzed the damping terms within the dynamic equations of the FPSAC model and solved these equations to reveal system dynamics. By linearizing the working chamber’s pressure, the study examined the machine’s dynamic behavior, presenting solutions for amplitude and phase angle. Derived expressions for the displacement and acceleration of both the power piston and the displacer further support this analysis. The research evaluates the influence of driving force on amplitude and phase angle, alongside the impact of damping coefficients, thereby isolating thermodynamic–dynamic coupling characteristics. Control equations integrating dynamics and thermodynamics were developed, and a comprehensive system model was constructed using MATLAB(2020a)/Simulink to simulate acceleration and displacement variation in the pistons. Key findings include: (1) a positive correlation between driving force and displacer, where increased force leads to higher amplitudes; (2) a frequency of 65 Hz reveals a singularity occurs in displacer amplitude, resulting in system instability; (3) phase angle between pistons reduces to below 10° when the driving force exceeds 150 N; and (4) the power piston’s amplitude decreases with an increase in damping C1, while changes in damping C2 primarily affect the displacer’s singularity position around 65 Hz, with higher C2 values shifting the singularity to lower frequencies.

The Self-Liberated Slave Periquillo Saves the Missionary Juan Pobre: Blackness, Indigeneity, and the Origins of the Black Pacific

ABSTRACT Seeking to chart the depth of the history of the Black Pacific, this article utilizes a contemporaneous Spanish chronicle to interrogate an episode from 1602 in Luta (Mariana Islands), where a former slave named Periquillo negotiated with CHamorus to spare the life of the missionary Juan Pobre de Zamora. I demonstrate that Indigenous CHamoru notions of community, the singular position of diasporic Africans in the Pacific (which made possible their role as go-betweens), and awareness of both groups of Spanish inhumanity drove the course of events. Resurrecting this episode draws backward the timeline of studies of the Black Pacific, which tend to focus on the second half of the 20th century.

Defect pairs in nematic cell alignment on doubly connected domains

We consider the orientational order that arises from the alignment of anisotropic biological cells confined in bounded domains. Especially, it is known that topological defects, where the orientation angles are not well-defined, play an important role in the global pattern formation of cell alignment. Hence, it is important to investigate the relationship between the shape of the region and the location of the defects. The orientational order of cells is theoretically modelled as a harmonic function achieving the minimum elastic energy state of the nematic liquid crystal, and an analytical formula in simply connected domains is given by Miyazako & Nara (Miyazako, Nara 2022 R. Soc. Open Sci . 9, 211663 ( doi:10.1098/rsos.211663 )). In this paper, we extend this study to construct an analytic formula of cell angle in the doubly connected domains, where topological defects and boundary shapes are represented as the positions of logarithmic singularities and as conformal maps from a given region to a standard annular region, respectively. In addition, using this analytical formula, we propose a numerical algorithm to minimize elastic energy, from which we investigate cell alignment in doubly connected domains with anisotropic quadrilateral boundaries. Our numerical simulations suggest that pairs of topological defects tend to be located around corners of the boundaries, which will be a design principle of the boundary geometry for controlling the defect positions and cell alignment.

Evolution of the polarization singularities in partially coherent beams on propagation through turbulence

In recent years, topological singularities of wavefields have been considered as structures that can improve a variety of optical technologies, including remote sensing and free-space optical communications. However, atmospheric turbulence can distort the features of singularities over long propagation distances, limiting their use in many cases. One solution being considered is the reduction of spatial coherence of light, as partially coherent beams have shown increased resistance to turbulence under a broad range of situations. In this paper, we look at the evolution of polarization singularities that arise in a particular projection of a partially coherent vector beam, and how the position and number of singularities are affected by atmospheric turbulence. We find that there are projections where the singularities persist on propagation, suggesting their possible use in applications.

A replaceable-component method to construct single-degree-of-freedom multi-mode planar mechanisms with up to eight links

Abstract. The multi-mode planar mechanisms (MMPMs) are excellent-performance reconfigurable mechanisms, which not only inherit structural characteristics of planar mechanisms but also have the multi-task, multi-working-condition application advantages of multi-mode mechanisms. However, lacking common bifurcation analysis and construction methods, their industrial application and development are seriously hindered. This paper presents a replaceable-component method to construct a set of single-degree-of-freedom (single-DOF) MMPMs based on the branch graphs of the corresponding planar mechanisms and the proposed multi-mode modules (MMMs). First, according to the established loop equations, all the kinematic information of the original planar mechanism is obtained by the branch graphs and singularity points using Maple. Then, compared to the relationship between the concepts of the branch and motion mode, the number and continuity of branches are taken as the index to identify the potential bifurcation and mode conversion ability for the corresponding planar mechanisms. Subsequently, the MMM is presented to help the planar mechanisms break the singularity positions to form the corresponding MMPMs, and the steps of constructing single-DOF MMPMs are summarized. Finally, a single-DOF Stephenson six-bar three-mode planar mechanism, a Watt six-bar three-mode planar mechanism, and an eight-bar four-mode planar mechanism are constructed for the first time, and the corresponding multi-mode motion analyses are made. The results can give the available configuration for the design of corresponding MMPMs. The proposed method will provide strong guidance for the configuration design of MMPMs.

Walls, bubbles and doom — the cosmology of HEFT

As experiment charts new territory at the electroweak scale, the enterprise to characterise all possible theories becomes all the more necessary. In the absence of new particles, this ambitious enterprise is attainable and has led to the Higgs Effective Field Theory (HEFT) as the most general characterising framework, containing the Standard Model Effective Field Theory (SMEFT) as a subspace. The characterisation of this theory space led to the dichotomy SMEFT vs. HEFT SMEFT as the two possible realisations of symmetry breaking. The criterion to distinguish these two possibilities is non-local in field space, and phenomena which explore field space beyond the neighbourhood of the vacuum manifold are in a singular position to tell them apart. Cosmology allows for such phenomena, and this work focuses on HEFT SMEFT, the less explored of the two options, to find that first order phase transitions with detectable gravitational wave remnants, domain wall formation and vacuum decay in the far, far distant future can take place and single out HEFT SMEFT. Results in cosmology are put against LHC constraints, and the potential of future ground- and space-based experiments to cover parameter space is discussed.

Élever la bizarrerie à la dignité du style. Pour une éthique de l’accompagnement des patients autistes

ObjectivesThis article aims to identify how the analytical framework can lead an autistic subject to create an artisanal solution that allows him to enter the world. MethodThe Lacanian theoretical conceptualization is based on clinical observations collected during the treatment of a young autistic boy. ResultsWe argue that engaging in therapeutic work with an autistic patient can offer him a potential environment – which we distinguish from potential space – in which his particular quirks can be elevated to the dignity of a style that the autistic child will himself shape and that will allow him a certain social bond. DiscussionWe qualify the therapeutic space offered by the analytical framework as a potential environment, which we define as the coordinates of the encounter set up by the clinician bringing into existence a Stimmung from which the child can experience his or her instinctual movements. Stimmung is to be understood as the phenomenological quality of the potential environment, simultaneously including tuning, invocative address, disposition, and atmosphere, i.e. a possible relationship with the Other. Clinical intervention would allow the child not to represent himself in this potential environment – which is the nature of potential space –, but to present himself to the world. It is the clinician's responsibility to bring into existence an Other who can isolate and put into circulation the subject's oddity – which could be considered a failure – bringing forth a singularizing sign and elevating it to the dignity of style that the autistic child will shape. ConclusionThe style, thus obtained, corresponds to the possibility of a singular enunciative position – inscribing a presence in the world by tempering the weight of the subject –, which, in autism, always requires a certain amount of tinkering in order to arrive at a solution.

A Kinematic Synthesis Methodology for P-Drivable Spatial Single Degree-of-Freedom Mechanisms to Avoid Singularities

Abstract For a single degree-of-freedom spatial mechanism, a reference frame attached to any of its links produces a continuous motion of this frame. Given the progression of this frame from the start through the end of the mechanism’s motion, this paper seeks to identify specific points relative to this moving reference frame. The points of interest are those that can be coupled with a second point determined in the fixed frame to act as the end joint locations for a spherical–prismatic–spherical (SPS) driving chain. If the selection of the point pair is made such that the change in distance between them as the mechanism moves is strictly monotonic, then the SPS chain they define is potentially capable of driving the mechanism over the desired range of motion. This motion is referred to as locally P-drivable because a global solution is not ensured by the process proposed herein. This synthesis process can avoid singularities encountered by actuating the mechanism at one of its original joints. The proposed approach enables the dimensional synthesis of a single degree-of-freedom mechanism to focus on creating circuit-defect-free solutions without concern for potential singular positions. The actuating chain can then be determined as a separate step in the synthesis process. This paper also considers motions that are not P-drivable and the specialization to planar systems with the synthesis of a P-drivable revolute–prismatic–revolute (RPR) chain.

Cucker–Smale type flocking models on a sphere

Cucker–Smale type flocking models on a sphere

Design and development of a novel Four-Links rotational hybrid Energy-Harvesting suspension system compatible with conventional suspension technologies

This study introduces a novel rotational Energy Harvesting Shock Absorber (EHSA), specifically designed for use alongside existing vehicle suspension systems. Addressing issues faced by standalone EHSAs, this design incorporates a four-bar mechanism coupled to a rotary energy recovery system. The proposed EHSA system, dubbed the FL-EHSA (Four Links Energy Harvesting Shock Absorber), is based on link connections and is highly versatile. It has the potential to significantly improve vehicle efficiency by harnessing energy usually wasted by traditional shock absorbers. Using a geometric definition process influenced by various factors such as vehicle suspension type and commercial availability of components, the FL-EHSA system was modeled, and bench-tested to validate the system’s energy recovery potential and performance. The movement of the mechanism was analyzed to achieve the target damping value matching the value of a conventional suspension and to maximize efficiency through DOE analysis and to avoid mechanical locking (singular positions). It explains the effect of backlash in mechanical components through simulation and highlights the importance of using dedicated gearboxes for energy recovery. In addition, this work highlights the untapped potential of four-bar mechanisms in automotive energy recovery applications. Moreover, the proposed design is easily integrated into any vehicle, making it a promising solution for EHSA systems.

Shaping of a reflective microjet via the addition of a metal mask onto a dielectric scatterer

The method of shaping a reflective microjet (MJ) via the addition of a metal mask onto a dielectric scatterer is proposed. The study focuses on the effects of size, shape of metal mask, and shape of scatterer on the performance of the MJ. The results show that the mask size is a vital factor in tailoring the characteristic parameters of the MJ, especially the focal length (FL). With a properly designed mask size, the FL can increase by 0.51λ, as much as 4 times the FL of a MJ generated without a metal mask. The mask size dependence of MJ parameters is related to the change of number and position of phase singularity in Poynting vector distribution. And the shapes of the mask and scatterer only slightly affect the optimal mask size at which the FL maximizes. In addition, the MJ generated by the presently proposed scattering system can work in the frequency range of 0.1 THz–1.4 THz. The effect of frequency on MJ properties is related to the dispensation and absorption of material. The proposed method can be used to effectively tailor the FL of the reflective MJ to meet the requirements set by various applications.

Research on a Biomimetic Flexible Ball Joint With Variable Stiffness for Robots

Abstract The human ball joint is a compact and flexible 3-degree-of-freedom (DOF) composite joint. The ball joints commonly used in robot design lack active driving capability. Ball joints with active drive generally consist of three single-degree-of-freedom joints connected in series, which is a noncompacted structure and easily leads to singular postures. In order to meet the demand for high-performance composite joint modules for service robots, this article designs a flexible biomimetic spherical robot joint with variable stiffness characteristics: the mechanism of muscle parallel antagonistic drive and ligament wrapping constraint is simulated; three parallel branch chains are used to drive three composite degrees-of-freedom; ropes, soft airbags, and series elastic drive gears are used to form a flexible transmission system; the contour of the rope winch has been optimized with the aim of transmission stability; and a pneumatic variable stiffness soft structure has been designed and fabricated. A compliance control algorithm for joints was developed based on the principle of impedance control. The research results indicate that the biomimetic ball-and-socket joint has a compact structure, a wide range of motion and good motion tracking performance, variable stiffness performance, and flexible interaction ability.

Parametrization Effects of the Non-Linear Unsteady Vortex Method with Vortex Particle Method for Small Rotor Aerodynamics

The aim of this article is to investigate the parameter sensitivity of the (Non-Linear) Unsteady Vortex Lattice Method-Vortex Particle Method [(NL-)UVLM-VPM] with Particle Strength Exchange-Large Eddy Simulations (PSE-LES) method on a lower Reynolds number rotor. The previous work detailed the method, but introduced parameters whose influence were not investigated. Most importantly, the Vreman model coefficient was chosen arbitrarily and was not suitable to ensure stability for this lower Reynolds number rotor simulation. In addition, the previous work presented a consistency study where geometry and time discretization were refined simultaneously. The present article starts with a comparative literature review of potential methods used to solve the aerodynamics of an isolated hovering rotor. This review highlights the differences in modeling, discretizations, sensitivity analysis, validation cases, and the results chosen by the different studies. Then, a transparent and thorough parametric study of the method is presented alongside discussions of the observed results and their physical interpretation regarding the flow. The sensitivity analysis is performed for the three free parameters of UVLM, namely Vatistas core size, the geometry and the temporal discretizations, and then for the three additional parameters introduced by UVLM-VPM, which are the Vreman model coefficient, the particle spacing, and the conversion time. The effect of different databases in the non-linear coupling is also shown. The method is shown to be consistent with both geometry and temporal refinements. It is also consistent with the expected behavior of the different parameters change, including the numerical stability that depends on the strength of the LES diffusion controlled by the Vreman model coefficient. The effect of discretization refinement presented here not only shows the integrated coefficients where different errors can cancel each other, but also looks at their convergence and where relevant, the distributed loads and tip singularity position. Finally, the aerodynamics results of the method are compared for different databases and with higher fidelity Unsteady Reynolds Averaged Navier–Stokes (URANS) 3D results on a lower Reynolds number rotor.

Chemical effect on the Van Hove singularity in superconducting kagome metal AV3Sb5 (A = K, Rb, and Cs).

To understand the alkali-metal-dependent material properties of recently discovered AV3Sb5 (A = K, Rb, and Cs), we conducted a detailed electronic structure analysis based on first-principles density functional theory calculations. Contrary to the case of A = K and Rb, the energetic positions of the low-lying Van Hove singularities are reversed in CsV3Sb5, and the characteristic higher-order Van Hove point gets closer to the Fermi level. We found that this notable difference can be attributed to the chemical effect, apart from structural differences. Due to their different orbital compositions, Van Hove points show qualitatively different responses to the structure changes. A previously unnoticed highest lying point can be lowered, locating close to or even below the other ones in response to a reasonable range of bi- and uni-axial strain. Our results can be useful in better understanding the material-dependent features reported in this family and in realizing experimental control of exotic quantum phases.

Study on Singularity Passing Method for Large Industrial Robot Based on Proper Element Improvement of Inverse Matrix

Singularity has become a limitation to the expected diversification of industrial robot applications in production. Here, we propose a novel solution for the inverse kinematics of a 6-DOF manipulator that suppresses rapid joint rotation when passing through a singularity. The proposed method is based on the optimization of the inverse Jacobi cofactor matrix utilized in the inverse kinematics calculation. By optimizing only the elements related to the four and six joints of the cofactor matrix in the inverse matrix, we were able to suppress the divergence of the joint velocities and achieve smooth robot motion when the robot entered a singular posture at the wrist. The developed system application range and tuning gain that minimize the position and orientation error were also determined. Hence, the position and orientation errors were improved by approximately 76%, and rapid rotation of the joints was almost completely suppressed. The method did not require consideration of tools attached to the hand tip, and the hand tip position, orientation, and velocity were all maintained.

Kinematic Analysis of 3-PRPPS Spatial Parallel Manipulator with Circularly Guided Base for Singularity-Free Robotic Motions

Robot manipulators are classified as serial manipulators and parallel manipulators. Parallel manipulators are classified into planar and spatial parallel manipulators (SPMs). The parallel manipulators have moved and fixed platforms connected with serial chains. The parallel manipulators have many linkages, which create a singularity problem. The singular positions of SPMs have also gained substantial attention in various industrial applications due to their intrinsic advantages in precision, flexibility, and load-bearing capabilities. The 3-PRPPS SPM has three prismatic joints, one spherical joint, and one revolute joint. This work changed the fixed base with a circular guided base to avoid singularity issues. The manipulator was modeled with direct kinematic relations. The Jacobian matrix for position and orientation was derived. The workspace was taken as the common area of the three circles, whose radius was the maximum arm length. The position and orientation of the end effector were traced. In the form of the end effector traces, no singularities in the mechanism were observed. The path of the robot manipulator was observed in all the possible positions and orientations. The multi-body simulation was also conducted on the 3-PRPPS manipulator, the main findings of which are presented in this article.

Monitoring and Path Avoiding Method of Singular Position of the Redundant Manipulator

Monitoring and Path Avoiding Method of Singular Position of the Redundant Manipulator

THz hooks generated on the basis of hollow reflection mirror

THz hook (TH) is a curved beam in THz frequency region, which is characterized additionally by the bending angle θ besides focal length, intensity and transverse size. Here, we study paired THs generated by two cuboid scatterers placed on a hollow mirror. The study focuses on the effects of hollow geometry and polarization state of incident wave on the THs performance. The results show that the hollow geometry affects mainly the bending angle θ, which can change by two fold. The effect is associated with the hollow geometry induced changes of number and position of phase singularity in Poynting vector distribution. The polarization state of incident wave affects considerably both bending angle and focal length. As the polarization state is changed, the FL (focal length) can change by ∼26 fold and the θ by ∼9° due to the interactions of the polarized electric field with scatterers and with the hollow mirror. It implies that the use of hollow mirror results in significant enhancement of polarization effect on the TH performance. Present study allows to conclude that the bending angle and focal length of paired THs generated on the basis of the hollow mirror can be efficiently tailored by the hollow geometry and polarization state.

Effect of van-Hove singularities in single-walled carbon nanotube leads on transport through T-shaped double quantum dot system

The T-shaped double quantum dot system with single-walled metallic armchair carbon nanotube leads has been studied using Green functions obtained by the equation of motion method. The effect of relative spacing between the energy levels of the dots, interdot tunneling matrix-element, interdot Coulomb interaction, and van-Hove singularities in density of states characteristics of quasi-one-dimensional carbon nanotube leads on the conductance of the double quantum dot system has been studied. The conductance and dot occupancies are calculated at finite temperatures. The density of states of the carbon nanotube leads is observed to play a significant role in determining the conductance profile. In particular, whenever the chemical potential of the isolated double quantum dot system is aligned with the position of a van-Hove singularity in the density of states of armchair carbon nanotube leads, the height of the corresponding conductance peak falls considerably. It is further observed that the suppression in the heights of the alternate peaks depends on the relative positions of the energy levels of the dots and their magnitude of separation.

Body and mind: Decoding the dynamics of pedestrians and the effect of smartphone distraction by coupling mechanical and decisional processes

Pedestrians are able to anticipate, which gives them an edge in avoiding collisions and navigating in cluttered spaces. However, these capabilities are impaired by digital distraction through smartphones, a growing safety concern. To capture these features, we put forward a continuous agent-based model (dubbed ANDA) hinging on a transparent delineation of a decision-making process, wherein a desired velocity is selected as the optimum of a perceived cost, and a mechanical layer that handles contacts and collisions. Altogether, the model includes less than a dozen parameters, many of which are fit using independent experimental data. The versatility of ANDA is demonstrated by numerical simulations that successfully replicate empirical observations in a very wide range of scenarios. These scenarios vary from collision avoidance involving one, two, or more agents, to collective flow properties in unidirectional and bidirectional settings, and to the dynamics of evacuation through a bottleneck, where contact forces are directly accessible. Remarkably, the model is able to replicate the enhanced chaoticity of the flow observed experimentally in ’smartphone-walking’ pedestrians, by reducing the frequency of decisional updates, replicating the digital distraction effect. The conceptual transparency of the model makes it easy to pinpoint the origin of its current limitations and to clarify the singular position of pedestrian crowds amid active-matter systems.