Artificial Force Research Articles

Formation control for autonomous robots with collision and obstacle avoidance using a rotational and repulsive force–based approach

In this article, we address a formation control problem for a group of autonomous robots to track a moving target in the presence of obstacles. In the proposed method, desired formations, which consist of virtual nodes arranged in specific shapes, are first generated. Then, autonomous robots are driven toward these virtual nodes without collisions with each other using a novel control scheme, which is based on artificial force fields. The convergence analysis is shown based on Lyapunov’s stability. The novelty of the proposed approach lies in a new combination of rotational force field and repulsive force field to design a mechanism so that robots can avoid and escape complex obstacle shapes. The effectiveness of the proposed method is illustrated with numerical examples using V-shape and circular shape formations.

Iridium-Catalyzed Asymmetric Borylation of Unactivated Methylene C(sp3)-H Bonds.

Herein, we show the highly enantioselective borylation of unactivated methylene C(sp3)-H bonds in 2-alkylpyridines and 2-alkyl-1,3-azole derivatives using an iridium-BINOL-based chiral monophosphite catalyst system. Quantum chemical calculations using the artificial force induced reaction (AFIR) method suggested that a monophosphite-Ir-tris(boryl) complex generates a narrow chiral reaction pocket where the differentiation of the enantiotopic methylene C-H bonds is accomplished through an assembly of multiple noncovalent interactions.

Computational Study on the Mechanism and Origin of the Regioselectivity and Stereospecificity in Pd/SIPr-Catalyzed Ring-Opening Cross-Coupling of 2-Arylaziridines with Arylboronic Acids

The mechanism, regioselectivity, and stereospecificity of Pd/NHC-catalyzed ring-opening cross-coupling of 2-arylaziridines with arylboronic acids (Takeda et al. J. Am. Chem. Soc. 2014, 136, 8544−8547) is rationalized from density functional theory calculations. Pd(0)SIPr complex, the active species, can be formed through the reduction of (η3-cinnamyl)(Cl)Pd(II)SIPr complex, where arylboronic acid in solution plays a key role. Then the Pd(0)SIPr complex acts as the active species of the catalytic cycle that consists of the regioselective and stereospecific oxidative addition, proton transfer, rate-determining transmetalation, and reductive elimination. Transition states for the oxidative addition were systematically determined from a multicomponent artificial force induced reaction search and explained the regioselectivity and stereospecificity of the reaction. An energy decomposition analysis on the key transition states suggested that the interactions between Pd(0)SIPr and 2-arylaziridines are important to the selectivity. The computed mechanism of the full catalytic cycle is consistent with the experimental data. Our detailed mechanistic survey provides important mechanistic insights for enantiospecific and regioselective ring-opening reactions of 2-arylaziridines.

A model-based bone milling state identification method via force sensing for a robotic surgical system.

This paper presents a model-based bone milling state identification method that provides intraoperative bone quality information during robotic bone milling. The method helps surgeons identify bone layer transitions during bone milling. On the basis of a series of bone milling experiments with commercial artificial bones, an artificial neural network force model is developed to estimate the milling force of different bone densities as a function of the milling feed rate and spindle speed. The model estimations are used to identify the bone density at the cutting zone by comparing the actual milling force with the estimated one. The verification experiments indicate the ability of the proposed method to distinguish between one cortical and two cancellous bone densities. The significance of the proposed method is that it can be used to discriminate a set of different bone density layers for a range of the milling feed rate and spindle speed.

On Benchmarking of Automated Methods for Performing Exhaustive Reaction Path Search.

In recent years, the importance of computational chemistry approaches has grown rapidly because of recent advances in computational software and hardware. Automated reaction path search is one of the promising techniques which would allow exploration of unknown chemistry using computers. Several methods have been developed so far, and comparison of the performance of existing methods would be a subject of interest to many chemists. In this paper, we present the performance of our single-component artificial force induced reaction method (SC-AFIR) to rectify the result shown in a recent report [ Grambow et al. J. Am. Chem. Soc. 2018 , 140 , 1035 - 1048 ] on the performance of the SC-AFIR method compared to four other methods. We discuss the flaws in their benchmark procedure and our thoughts on benchmarking of automated reaction path search methods.

Stabilisation and drag reduction of pipe flows by flattening the base profile

Recent experimental observations (Kühnen et al., Nat. Phys., vol. 14, 2018b, pp. 386–390) have shown that flattening a turbulent streamwise velocity profile in pipe flow destabilises the turbulence so that the flow relaminarises. We show that a similar phenomenon exists for laminar pipe flow profiles in the sense that the nonlinear stability of the laminar state is enhanced as the profile becomes more flattened. The flattening of the laminar base profile is produced by an artificial localised body force designed to mimic an obstacle used in the experiments of Kühnen et al. (Flow Turbul. Combust., vol. 100, 2018a, pp. 919–943) and the nonlinear stability measured by the size of the energy of the initial perturbations needed to trigger transition. Significant drag reduction is also observed for the turbulent flow when triggered by sufficiently large disturbances. In order to make the nonlinear stability computations more efficient, we examine how indicative the minimal seed – the disturbance of smallest energy for transition – is in measuring transition thresholds. We first show that the minimal seed is relatively robust to base profile changes and spectral filtering. We then compare the (unforced) transition behaviour of the minimal seed with several forms of randomised initial conditions in the range of Reynolds numbers $Re=2400$–$10\,000$ and find that the energy of the minimal seed after the Orr and oblique phases of its evolution is close to that of a critical localised random disturbance. In this sense, the minimal seed at the end of the oblique phase can be regarded as a good proxy for typical disturbances (here taken to be the localised random ones) and is thus used as initial condition in the simulations with the body force. The enhanced nonlinear stability and drag reduction predicted in the present study are an encouraging first step in modelling the experiments of Kühnen et al. and should motivate future developments to fully exploit the benefits of this promising direction for flow control.

A Theoretical Study on the Mechanism of the Oxidative Deborylation/C-C Coupling Reaction of Borepin Derivatives.

One-electron oxidation of borepin derivatives that consists of a boron-containing seven-membered ring has been reported to cause deborylation/C-C coupling, yielding aromatic compounds. The reaction can be achieved not only by transition metal compounds but also by oxidants without transition metal such as O2 and other organic compounds. Despite numerous experimental attempts, the mechanism of this peculiar reaction as well as the fate of the BCl part eliminated from borepin remain unclear to date. Based on theoretical approaches using the artificial force induced reaction method, here we address the mechanism of the unusual boron-mediated C-C coupling. For this purpose, two borepin derivatives (1 and 35), bearing ethyl and phenyl groups, respectively, were used as reactants, and FeCl3/MeNO2 and O2 were chosen as oxidants. The calculations revealed reaction pathways that provided an overall picture of the mechanism of the target reaction, which features four key steps, namely, (i) quaternization of the boron atom by the coordination of oxidant, (ii) intersystem crossing, (iii) skeletal rearrangement to form a six-membered ring, and (iv) elimination of a boron moiety. The intrinsic nature of boron, i.e., a strong tendency to accept a coordination ligand even under oxidative conditions, is responsible for the oxidative deborylation/C-C coupling of borepin.

A Reaction Path Network for Wöhler's Urea Synthesis

We theoretically studied reaction paths of Wohler's urea synthesis using the artificial force induced reaction method and the rate constant matrix contraction method. The systematic search resulted...

Artificial and Virtual Impedance Interaction Force Reflection-Based Bilateral Shared Control for Miniature Unmanned Aerial Vehicle

In this paper, we propose artificial and virtual-impedance interaction force reflection-based shared control strategy for bilateral telemanipulation of miniature aerial vehicle (MAV). The shared input for the master is designed by combining the velocity of the slave–MAV system with the scaled position–velocity of the master manipulator. The master input also uses the reflected interaction force between the slave and remote environment. The interaction force between environment and MAV is modeled by using two different approaches as the artificial and virtual impedance force field. The reflected interaction force applies to the human operators' hand through the haptic manipulator. The interaction force provides a situational awareness about the remote environment, guiding the operator to navigate and control the MAV for a safe and stable interaction with the remote environment. The shared control input for the slave is designed by combining the velocity of the MAV with the scaled position–velocity of the master manipulator. The convergence analysis of the closed-loop bilateral shared control system is shown by using the Lyapunov method. The analysis shows that the closed-loop system is input-to-state stable and ultimately bounded in the presence of passive and nonpassive interaction with the environment and the human operator. The design is implemented and evaluated on a quadrotor MAV with both artificial and virtual impedance force field based interaction interfaces to demonstrate the effectiveness for the real-time interaction with the environment.

Understanding CO oxidation on the Pt(111) surface based on a reaction route network.

Analysis of a reaction on a solid surface is an important task for understanding the catalytic reaction mechanism. In this study, we studied CO oxidation on the Pt(111) surface by using the artificial force induced reaction (AFIR) method. A systematic reaction path search was done, and the reaction route network was created. This network included not only bond rearrangement paths but also migration paths of adsorbed species. Then, the obtained network was analyzed using a kinetics method called rate constant matrix contraction (RCMC). It is found that the bottleneck of the overall reaction is the CO2 generation step from an adsorbed CO molecule and an O atom. This result is consistent with the Langmuir-Hinshelwood (LH) mechanism with O2 dissociation discussed in previous studies. The present procedure, i.e., construction of the reaction route network by the AFIR method followed by application of the RCMC kinetics method to the resultant reaction route network, was fully systematic and uncovered two aspects: the impact of the existence of multiple paths in each bond rearrangement step and an entropic contribution arising from short-range migration of adsorbed species.

Vehicle Reference Generator for Collision-free Paths

This paper presents a reference generator for ground vehicles. The generated trajectories avoid collisions with obstacles, and can be used for vehicle autonomous driving or for active control of manned vehicles. This generator integrates artificial forces of potential fields of the object surrounding the vehicle. The potential fields are adapted to the vehicular environment on a road. The reference generator is used with a dynamic controller to ensure the tracking of the accident-free reference. The performance of the proposed generator-based controller is tested on a simulated road scenario.

Zn(OTf)2-mediated annulations of N-propargylated tetrahydrocarbolines: divergent synthesis of four distinct alkaloidal scaffolds.

Intramolecular hydroarylations of N-propargylated tetrahydrocarbolines were efficiently mediated using a unique combination of Zn(OTf)2 with t-BuOH under neutral conditions. Use of the artificial force induced reaction method in the global reaction route mapping strategy provided insights into the Zn(OTf)2-mediated hydroarylations and the associated intriguing solvent effects of t-BuOH facilitating a protodezincation process without a Brønsted acid activator. We systematically implemented three distinct hydroarylations as well as an unanticipated α-alkenylation of a carbonyl group to obtain the four alkaloidal scaffolds 2-4, and 18. Zn(OTf)2-mediated annulation of 1c proceeded through kinetic formation of the spiroindole 3c followed by an alkenyl shift and concomitant retro-Mannich-type fragmentation to furnish azepino[4,5-b]indole 2 framework. Substituents on substrate 1 in the vicinity of the reaction sites substantially affected the mode of the divergent annulations. Judicious choices of the substituents, solvent and reaction conditions enabled programmable divergent synthesis of the four distinct skeletons.

Collision Avoidance for Cooperative Formation Control of a Robot Group

Abstract In order to fulfill any objective, a group of mobile robots has to ensure avoidance of collisions between each other at all times. This paper will present an integration of a collision avoidance scheme based on artificial force fields into cooperative formation control for ground robots which leads to implications for airborne robots. The focus will rest on the aspects required to use the control algorithms on an existing system of given mobile robots together with a measurement and communication system and give implications on the usability and stability of the formation control. The presented results show that the control algorithms can achieve formations while avoiding a collision for a group of mecanum wheeled robots in simulation as well as in an experiment. There are still divergences between the simulation and experimental data which lead to the conclusion that the simulation is not accurate considering used assumptions.

Combined Automated Reaction Pathway Searches and Sparse Modeling Analysis for Catalytic Properties of Lowest Energy Twins of Cu13.

In nanocatalysis, growing attention has recently been given to investigation of energetically low-lying structural isomers of atomic clusters, because some isomers can demonstrate better catalytic activity than the most stable structures. In this study, we present a comparative investigation of catalytic activity for NO dissociation of a pair of the energetically degenerated isomers of Cu13 cluster having C2 and C s symmetries. It is shown that although these isomers have similar structural, electronic, and optical properties, they can possess very different catalytic activities. The effect of isomerization between cluster isomers is considered using state-of-the-art automated reaction pathway search techniques such as an artificial force induced reaction (AFIR) method as a part of a global reaction route mapping (GRRM) strategy. This method allows effectively to locate a large number of possible reaction pathways and transition states (TSs). In total, 12 TSs for NO dissociation were obtained for Cu13, of C2, C s, as well as I h isomers. Sparse modeling analysis shows that LUMO is strongly negatively correlated with total energy of TSs. For most TSs, LUMO has the antibonding character of NO, consisting of the interaction between π* of NO and SOMO of Cu13. Therefore, an increase in the strength of interaction between NO molecule and Cu13 cluster causes the rise in energy of the LUMO, resulting in lowering of the TS energy for NO dissociation. The combination of the automated reaction pathway search technique and sparse modeling represents a powerful tool for analysis and prediction of the physicochemical properties of atomic clusters, especially in the regime of structural fluxionality, where traditional methods based on random geometry search analyses are difficult.

Excited-State Reactivity of [Mn(im)(CO)3 (phen)]+ : A Structural Exploration.

The electronic excited state reactivity of [Mn(im)(CO)3 (phen)]+ (phen = 1,10-phenanthroline; im = imidazole) ranging between 420 and 330 nm have been analyzed by means of relativistic spin-orbit time-dependent density functional theory and wavefunction approaches (state-average-complete-active-space self-consistent-field/multistate CAS second-order perturbation theory). Minimum energy conical intersection (MECI) structures and connecting pathways were explored using the artificial force induced reaction (AFIR) method. MECIs between the first and second singlet excited states (S1 /S2 -MECIs) were searched by the single-component AFIR (SC-AFIR) algorithm combined with the gradient projection type optimizer. The structural, electronic, and excited states properties of [Mn(im)(CO)3 (phen)]+ are compared to those of the Re(I) analogue [Re(im)(CO)3 (phen)]+ . The high density of excited states and the presence of low-lying metal-centered states that characterize the Mn complex add complexity to the photophysics and open various dissociative channels for both the CO and imidazole ligands. © 2018 Wiley Periodicals, Inc.

On the boundary conditions in Lagrangian particle methods and the physical foundations of continuum mechanics

This paper aims to discuss the boundary conditions techniques employed in the solution of physical and engineering problems using the Lagrangian particle approach in continuum mechanics. Simulations using different boundary treatment techniques have been performed, and in addition, a review of the literature on the techniques commonly employed in SPH simulations was also performed. The fictitious (virtual/ghost), the dynamic particles and the artificial repulsive forces are widely employed in problem-solving, mixing concepts of molecular and continuum scales, being inadequate for the use in continuum scale (considering the disrespect of the classical physics laws). On the other hand, the reflective boundary conditions, based on fundamentals of Physics (Newton’s restitution law) and analytic geometry, are in accordance with the continuum hypothesis and their use is recommended in continuum mechanics problems, out of the molecular scale. In many boundary conditions employed in particle methods, models of repulsive molecular forces in conjunction with virtual particles are being used without theoretical foundation in continuum mechanics and classical Physics. Purely computational solutions employing fictitious particles and artificial molecular forces should be avoided, and methods that respect the continuum theory, such as the reflective boundary conditions, should be employed on the macroscopic scale. Both hydrostatic and hydrodynamics analysis have been performed. An excellent agreement with the analytical solution or experimental results have been achieved. From the results found, the applicability of the reflexive boundary technique in the continuum domain, discretized by particles, was verified.

Aerial Camera Network for Observing Moving Targets

This paper considers a network of camera-equipped quad-rotors (aerial cameras) as aerial camera network (ACN) where each aerial camera is smart in the sense that it is mobile and can process, store, and wirelessly communicate information. This paper then presents an algorithm for decentralized and cooperative motion planning of these aerial cameras in 3-D environment to observe multiple targets moving on the ground. The proposed algorithm enables the ACN to observe targets from different elevations with the objective of jointly maximizing duration and quality (resolution) of observation for each target. This multi-scale observation depends on the field-of-view (FOV) of aerial camera and the quality of observation depends on the elevation and/or zoom level of aerial camera. The algorithm uses a quad-tree data structure to model not only the discrete movement decisions of aerial cameras in a 3-D environment but also the variations in the FOVs and qualities of observations. The use of artificial forces in the algorithm allows the aerial cameras to avoid collisions and to share the workload of assigning locations and targets to themselves. Simulation results present the effectiveness and performance evaluation of the proposed algorithm by comparison with the existing approaches of multi-target cooperative observation.

Designing the Backbone of Hexasilabenzene Derivatives with a High Unimolecular Kinetic Stability.

It is an important subject to theoretically predict the kinetic stability of transient species. In this study, we have studied the kinetic stability of hexasilabenzene Si6 H6 and its derivatives, that is, decasilanaphthalene Si10 H8 and Li-substituted hexasilabenzene Si6 Li6 , theoretically by the artificial force induced reaction (AFIR) method combined with the rate constant matrix contraction (RCMC) method. Molecular design was further conducted to extend the unimolecular lifetime of hexasilabenzene derivatives. Although both Si10 H8 and Si6 Li6 were shown to possess shorter lifetimes than Si6 H6 , we found that the lifetimes of Si6 Li6 changed depending on arrangements of Li atoms around the monocyclic Si6 backbone. Based on this knowledge, we found that a compound of an atomic composition Si6 H4 Li2 with a planar, monocyclic Si6 backbone has a relatively long unimolecular lifetime. Moreover, substitution of the two Li atoms by Na atoms further increased the lifetime.

Turbulent structure of stably stratified inhomogeneous flow

Effects of buoyancy force stabilizing disturbances are investigated on the inhomogeneous flow where disturbances are dispersed from the turbulent to non-turbulent field in the direction perpendicular to the gravity force. Attaching the fringe region, where disturbances are excited by the artificial body force, a Fourier spectral method is used for the inhomogeneous flow stirred at one side of the cuboid computational box. As a result, it is found that the turbulent kinetic energy is dispersed as layered structures elongated in the streamwise direction through the vibrating motion. A close look at the layered structures shows that they are flanked by colder fluids at the top and hotter fluids at the bottom, and hence vertically compressed and horizontally expanded by the buoyancy related to the countergradient heat flux, though they are punctuated by the vertical expansion of fluids at the forefront of the layered structures, which is related to the downgradient heat flux, indicating that the layered structures are gravity currents. However, the phase between temperature fluctuations and vertical velocity is shifted by π/2 rad, indicating that temperature fluctuations are generated by the propagation of internal gravity waves.

An improved reaction path optimization method using a chain of conformations

The efficient fast path optimization (FPO) method is proposed to optimize the reaction paths on energy surfaces by using chains of conformations. No artificial spring force is used in the FPO method to ensure the equal spacing of adjacent conformations. The FPO method is applied to optimize the reaction path on two model potential surfaces. The use of this method enabled the optimization of the reaction paths with a drastically reduced number of optimization cycles for both potentials. It was also successfully utilized to define the MEP of the isomerization of the glycine molecule in water by FPO method.