General Force Research Articles

Microscopic field theory for structure formation in systems of self-propelled particles with generic torques.

We derive a dynamical field theory for self-propelled particles subjected to generic torques and forces by explicitly coarse-graining their microscopic dynamics, described by a many-body Fokker-Planck equation. The model includes both intrinsic torques inducing self-rotation, as well as interparticle torques leading to, for instance, the local alignment of particles' orientations. Within this approach, although the functional form of the pairwise interactions does not need to be specified, one can directly map the parameters of the field theory onto the parameters of particle-based models. We perform a linear stability analysis of the homogeneous solution of the field equations and find both long-wavelength and short-wavelength instabilities. The former signals the emergence of a macroscopic structure, which we associate with motility-induced phase separation, while the second one signals the growth of a finite structure with a characteristic size. Intrinsic torques hinder phase separation, pushing the onset of the long-wavelength instability to higher activities. Furthermore, they generate finite-sized structures with a characteristic size proportional to both the self-propulsion velocity and the inverse of the self-rotation frequency. Our results show that a general mechanism might explain why chirality tends to suppress motility-induced phase separation but instead promotes the formation of non-equilibrium patterns.

An adaptive sparse general regression neural network-based force observer for teleoperation system

Restricted by factors such as small robot size and harsh operating environment, the inability to obtain the interaction force between the robot arm and the environment through force sensors has become problematic in promoting the application of teleoperation systems in minimally invasive surgery, nuclear waste cleanup, and other fields. To accurately obtain the interaction force without the force sensors, a force observer based on an adaptive sparse general regression neural network (ASGRNN) is proposed in this paper. The proposed force observer uses a machine learning-based approach to obtain estimated force, thus eliminating the need for the dynamic parameters of the robot arm. Also, an innovative feature selection method incorporating the wrapper method and sparse regularization is proposed to select the input features of the force observer. Secondly, two new criteria are defined to eliminate the useless support vectors in the model. In addition, an improved antlion optimization algorithm (IALO) is proposed to optimize the bandwidth parameters of the model. To verify the performance of the proposed force observer, a 6-degree-of-freedom teleoperation robot experimental platform is built and compared with three existing force estimation models. The results show that the proposed force observer outperforms the existing model in terms of estimation accuracy, and the mean square error (MSE) is at least 35.79% lower than the existing model. In conclusion, this paper provides a feasible and effective force observer for a teleoperation system where force sensors are not applicable and dynamic parameters are non-knowable.

Four-point bending piezoelectric energy harvester with uniform surface strain toward better energy conversion performance and material usage

Improving the energy conversion efficiency of piezoelectric energy harvesters is of great importance, and one approach is to make more uniform use of the working material by ensuring a uniform strain state. To achieve better performance, this paper presents a four-point bending piezoelectric energy harvester with extensive investigation and modeling to identify the influential parameters. An electromechanical analytical model is presented and verified by experimental data. The frequency-domain method extracts the solutions for a general time-variable force and impact. Four-point bending is compared with the standard cantilever harvesters regarding voltage generation, mechanical strain, and figure of merit. Strain contours are analyzed and interpreted for this innovative approach, and the power generation by the optimal resistance load is studied. Dimensionless parameters are introduced and investigated to find the optimal operating conditions for the four-point bending harvester. Finally, the four-point bending performance and the best figure of merit are discussed with a view to the long-term fatigue life of the harvester. The results show that in the best four-point bending energy conversion conditions; the energy conversion coefficient is more than three times higher than that of typical cantilever energy harvesters. The results also illustrate that the axial strain experienced in a standard cantilever harvester is more than three times higher than that of the four-point bending harvester, suggesting the latter device may have favorable fatigue performance. Overall, the presented piezoelectric harvester has improved energy conversion efficiency and experiences a reduced and uniform surface strain, making it appropriate for high-efficiency energy harvesting systems.

Analysis and Optimization Based on Factors Affecting the Spiral Climbing Locomotion of Snake-like Robot

The snake-like robot is a limbless bionic robot widely used in unstructured environments to perform tasks with substantial functional flexibility and environmental adaptability in complex environments. In this paper, the spiral climbing motion of a snake-like robot on the outer surface of a cylindrical object was studied based on the three-dimensional motion of a biological snake, and we carried out the analysis and optimization of the motion-influencing factors. First, the spiral climbing motion of the snake-like robot was implemented by the angle control method, and the target motion was studied and analyzed by combining numerical and environmental simulations. We integrated the influence of kinematics and dynamics factors on the spiral climbing motion. Based on this, we established a multi-objective optimization function that utilized the influence factors to optimize the joint module. In addition, through dynamics simulation analysis, the change of the general clamping force of the snake-like robot’s spiral climbing motion was transformed into the analysis of the contact force between the joint module and the cylinder. On the basis of the results, the effect of the control strategy adopted in this paper on the motion and change rule of the spiral climbing motion was analyzed. This paper presents the analysis of the spiral climbing motion, which is of great theoretical significance and engineering value for the realization of the three-dimensional motion of the snake-like robot.

Stability Research of a Triangular Tethered Satellite Formation: Dynamics, Filtering, and Control

This article investigates the stability of a triangular tethered satellite formation (TTSF) and the performance improvement by filtering and the virtual control of general force. The equation of motion is formulated by Lagrangian equation, and the state space equation (SSE) is derived with the second-order terms decoupled. Then the stability of SSE is discussed with the tethers nonstretched and stretched, respectively, where the existence of a stable orbit arounthe equilibrium is explored and the effect of initial conditions on the stability of the system around a stable orbit is discussed. To smooth the system response, a steepest descent-based state filter for TTSF system is designed, which provides the optimized state information. Moreover, to get the expected system response, a virtual control law is acted on the system with hysteresis relay property employed to strengthen its robustness. Finally, simulation results are shown to validate the theoretical analyses.

A Car-Following Model with the Acceleration Generalized Force Coupled with External Resistance and the Temporal-Spatial Distribution of Battery Decline

A novel energy storage mode based on the vehicle-to-grid (V2G) and vehicle-to-vehicle (V2V) concept will be greatly researched and applied as a new green solution to energy and environmental problems. However, the existing research on battery capacity decline in V2G applications has mainly focused on modeling the battery capacity to investigate its decline during vehicle charging and discharging, in order to reduce the battery capacity decline and evaluate its economics. A car-following model with the acceleration generalized force coupled with external resistance is proposed in the paper. A linear stability analysis was used to analyze the stability of the model. The stability of the traffic flow was improved when the value of the resistance coefficient increases. Then, the currents of different vehicles were also calculated according to the velocities. Moreover, the effect of different physical characteristics of driving on the decline of distributed energy storage batteries in the Internet of Vehicles (IoV) was investigated. The results suggest that in different road types and road slopes, vehicles which are at the end of the platoon position have less battery capacity degradation and better battery condition. It provides a reference for subsequent research related to V2G energy storage in the context of vehicle networking.

Varying-G gravity: physical properties, asymptotic regimes, and Green’s functions, an event horizon, the vacuum energy density, and the external pressure that modifies Jeans stability

ABSTRACT We study varying-G gravity and we add the necessary proofs (general force law, asymptotic forms, and Green’s functions, vacuum and external pressures, linearization of perturbations leading to a new Jeans stability criterion, and a physical origin) to elevate this novel idea to the status of a classical theory. The theory we lay out is not merely a correction to Newtonian gravity, it is a brand-new theory of gravity that encompasses the Newtonian framework and weak-field Weyl gravity in the limit of high accelerations, as well as Modified Newtonian Dynamics (MOND) in the opposite limit. In varying-G gravity, the source of the potential of a spherical mass distribution M(x) is σ(dG/dx) + (G/x2)(dM/dx), where x is the dimensionless radial coordinate and σ(x) = M(x)/x2 is the surface density away from the center x = 0. We calculate the potential $\Phi (x)=\int {G(x)\, \sigma (x)\, dx}$ from Poisson’s equation and the radial acceleration $a(x) = G(x)\, \sigma (x)$. Furthermore, a non-linear scaling transformation of the radial coordinate $x\in (0, \infty)\longmapsto \xi \in (0, 1)$ with scale factor ξ/x ∝ 1/G produces a finite space, in which the spherical surface ξ = 1 is an event horizon. In this classical context, it is the coupling of σ(x) to the gradient dG/dx in the above source that modifies the dynamics at all astrophysical scales, including empty space (where dG/dx ≠ 0). In vacuum, the source σ(dG/dx) supports an energy density distribution that supplies a repelling pressure gradient outside of discrete isolated massive systems. Surprisingly, the same source becomes attractive in linearized perturbations, and its linear pressure gradient opposes the kinetic terms in the Jeans stability criterion.

General Analytical Nuclear Forces and Molecular Potential Energy Surface from Full Configuration Interaction Quantum Monte Carlo.

The full configuration interaction quantum Monte Carlo (FCIQMC) is a state-of-the-art stochastic electronic structure method, providing a methodology to compute FCI-level state energies of molecular systems within a quantum chemical basis. However, especially to probe dynamics at the FCIQMC level, it is necessary to devise more efficient schemes to produce nuclear forces and potential energy surfaces (PES) from FCIQMC. In this work, we derive the general formula for nuclear forces from FCIQMC, and clarify different contributions of the total force. This method to obtain FCIQMC forces eliminates previous restrictions and can be used with frozen core approximation and free selection of orbitals, making it promising for more efficient nuclear forces calculations. After some numerical checks of this procedure on the binding curve of N2 molecule, we use the FCIQMC energy and force to obtain the full-dimensional ground state PES of the water molecule via Gaussian processes regression. The new water FCIQMC PES can be used as the basis for H2O ground state nuclear dynamics, structure optimization, and rotation-vibrational spectrum calculation.

Reduced surface accumulation of swimming bacteria in viscoelastic polymer fluids

Surface-associated bacterial communities flourish in nature and in the body of animal hosts with abundant macromolecular polymers. It is unclear how the endowed viscoelasticity of polymeric fluids influences bacterial motile behavior in such environments. Here, we combined experiment and theory to study near-surface swimming of flagellated bacteria in viscoelastic polymer fluids. In contrast to the swimming behavior in Newtonian fluids, we discovered that cells swim in less curved trajectories and display reduced near-surface accumulation. Using a theoretical analysis of the non-Newtonian hydrodynamic forces, we demonstrated the existence of a generic lift force acting on a rotating filament near a rigid surface, which arises from the elastic tension generated along curved flow streamlines. This viscoelastic lift force weakens the hydrodynamic interaction between flagellated swimmers and solid surfaces and contributes to a decrease in surface accumulation. Our findings reveal previously unrecognized facets of bacterial transport and surface exploration in polymer-rich environments that are pertinent to diverse microbial processes and may inform the design of artificial microswimmers capable of navigating through complex geometries.

Statistical dynamics of driven systems of confined interacting particles in the overdamped-motion regime

Systems consisting of confined, interacting particles doing overdamped motion admit an effective description in terms of nonlinear Fokker-Planck equations. The behavior of these systems is closely related to the S power-law entropies and can be interpreted in terms of the S-based thermostatistics. The connection between overdamped systems and the S measures provides valuable insights on diverse physical problems, such as the dynamics of interacting vortices in type-II superconductors. The S-thermostatistical approach to the study of many-body systems described by nonlinear Fokker-Planck equations has been intensively explored in recent years, but most of these efforts were restricted to systems affected by time-independent external potentials. Here, we extend this treatment to systems evolving under time-dependent external forces. We establish a lower bound on the work done by these forces when they drive the system during a transformation. The bound is expressed in terms of a free energy based on the S entropy and is satisfied even if the driving forces are not derivable from a potential function. It constitutes a generalization, for systems governed by nonlinear Fokker-Planck equations involving general time-dependent external forces, of the H-theorem satisfied by these systems when the external forces arise from a time-independent potential.

Reticular chemistry for the rational design of mechanically robust mesoporous merged-net metal-organic frameworks

Reticular chemistry for the rational design of mechanically robust mesoporous merged-net metal-organic frameworks

Inter-epidemic Rift Valley fever virus infection incidence and risks for zoonotic spillover in northern Tanzania.

Rift Valley fever virus (RVFV) is a mosquito-borne pathogen that has caused epidemics involving people and animals across Africa and the Arabian Peninsula. A number of studies have found evidence for the circulation of RVFV among livestock between these epidemics but the population-level incidence of infection during this inter-epidemic period (IEP) is rarely reported. General force of infection (FOI) models were applied to age-adjusted cross-sectional serological data to reconstruct the annual FOI and population-level incidence of RVFV infection among cattle, goats, and sheep in northern Tanzania from 2009 through 2015, a period without reported Rift Valley fever (RVF) cases in people or animals. To evaluate the potential for zoonotic RVFV spillover during this period, the relationship between village-level livestock RVFV FOI and human RVFV seropositivity was quantified using multi-level logistic regression. The predicted average annual incidence was 72 (95% Credible Interval [CrI] 63, 81) RVFV infections per 10,000 animals and 96 (95% CrI 81, 113), 79 (95% CrI 62, 98), and 39 (95% CrI 28, 52) per 10,000 cattle, sheep, and goats, respectively. There was variation in transmission intensity between study villages, with the highest estimated village-level FOI 2.49% (95% CrI 1.89, 3.23) and the lowest 0.12% (95% CrI 0.02, 0.43). The human RVFV seroprevalence was 8.2% (95% Confidence Interval 6.2, 10.9). Human seropositivity was strongly associated with the village-level FOI in livestock, with the odds of seropositivity in an individual person increasing by around 1.2 times (95% CrI 1.1, 1.3) for each additional annual RVFV seroconversion per 1,000 animals. A history of raw milk consumption was also positively associated with human seropositivity. RVFV has circulated at apparently low levels among livestock in northern Tanzania in the period since the last reported epidemic. Although our data do not allow us to confirm human RVFV infections during the IEP, a strong association between human seropositivity and the FOI in cattle, goats, and sheep supports the hypothesis that RVFV circulation among livestock during the IEP poses a risk for undetected zoonotic spillover in northern Tanzania. We provide further evidence for the likely role of raw milk consumption in RVFV transmission from animals to people.

The effect of an educational training curriculum on receiving and delivering the stick in the modern way and the achievement of (4 x 100) mail runners

The evolution of the level of sport achievement in recent years in sports and general games special forces where I started sports teams of a very small achievement and this is due to the use of all scientific methods regarding sports training and contain athletics on a series of events that are less than the one from the other in terms of importance from points or get gold medals and there are individual games and other mass is effective (4X100) of the only collective events in athletics The importance of research has demonstrated the knowledge of the role of the conditions to achieve maximum speed of the runners as well as the impact on achievement. The research problem is the weakness of the completion of the difference in this event as a result of using the old method, the objective of this research is teaching runners Technique delivery and receipt of the stick of the modern situation Ramming search is modern role in the arrival of hostilities early maximum speed of the technique, the research methodology, the researcher used the experimental method, The research sample were runners Faculty of Physical Education, the statistical methods, the researcher used statistical pouch (spss).

Molecular dynamics modeling of cracks in dry clay sheets at the nanoscale

Clay is a nanomaterial by nature. The cracking in clay at the nanoscale can provide significant insight into the cracking mechanism in clay at the continuum scale. This article is devoted to understanding the atomic-scale mechanism of the formation of cracks in a dry clay sheet through molecular dynamics with a general force field for clay. We simulate the formations of mode I and mode II cracks in intact dry clay sheets under tension and shear loading conditions, respectively. The numerical results show that the mode I and II cracking in a clay sheet is brittle and strain-rate dependent. The notion of critical bond stretch is adopted to model the breakage of bonds between atoms in clay. The critical bond length for crack formation is determined by the radial distribution function and the force curve between a pair of atoms. We investigate the crack initiation under mode I and mode II loading conditions from the bond breakage analysis. We interpret the cracking mechanism in terms of the type and number of broken bonds in mode I and mode II cracking. We present the stress intensity factor and cracking energy release rate under both cracking modes. The numerical results of the stress intensity factor and cracking energy release rate are quantitatively comparable to the experimental and numerical data in the literature.

Stability of Multidegree of Freedom Potential Systems to General Infinitesimal Positional Perturbation Forces

Abstract The stability of general linear multidegree of freedom stable potential systems that are perturbed by general arbitrary positional forces, which may be neither conservative nor purely circulatory/conservative, is considered. It has been recently recognized that such perturbed potential systems with multiple frequencies of vibration are susceptible to instability, and this paper is centrally concerned with the situation when potential systems have such multiple natural frequencies. An approach based on perturbation theory that includes nonlinear terms in the expansions of the perturbed eigenvalues is developed. Explicit conditions under which the system either remains stable or becomes unstable due to flutter are provided. These results show that the stability/instability picture that emerges is far subtler and more complex than what might be intuitively inferred. The manner in which prior results related to narrower classes of perturbation matrices, like circulatory matrices, get included in the more general results obtained here is pointed out. Several numerical examples illustrate the applicability of the analytical results. An engineering application is provided demonstrating the power of the analytical results.

Some Consequences of Mathematical Inaccuracies in Mechanics

The article is devoted to the study of some violations of the known laws of mathematics and classical mechanics in continuum mechanics and kinetics. The most common is open non-stationary systems. From the equations formulated earlier and some experiments, a connection traced between the gradients of physical quantities and the angular momentum (force). The use of Hamilton's formalism and the dependence of force only on the distance between particles limits the study. In the collision integral, for example, for a rarefied gas, the Lennard-Jones potential, which not related to the type under consideration, is often used. Hamilton's formalism traces the behavior of closed systems. The general form of boundary conditions and forces changes the theory proposed in the works of N.N. Bogolyubov. The results of the reformulation discussed. Even in the classical theory, after taking into account the moments, we come to the absence of symmetric stress tensor in Boltzmann theory. The symmetric tensor obtains after assumption of small influence from absence of symmetry at the condition of the forces balance. No symmetric tensor leads to the existence of two solutions. New examples of solving problems on hydromechanics, elasticity theory and kinetic theory are given. A correspondence between the terms of the Liouville equation with more general and traditional forces established for continues mechanics. Previously considered boundary layer problems, jet problems and the simplest problems of elasticity theory. The paper proposes a method for finding the second solution for no symmetric problems, if the solution of the symmetric problem we know. The mathematical inaccuracies of the theory of continuum mechanics and kinetics discussed.

The global distribution of known and undiscovered ant biodiversity.

Invertebrates constitute the majority of animal species and are critical for ecosystem functioning and services. Nonetheless, global invertebrate biodiversity patterns and their congruences with vertebrates remain largely unknown. We resolve the first high-resolution (~20-km) global diversity map for a major invertebrate clade, ants, using biodiversity informatics, range modeling, and machine learning to synthesize existing knowledge and predict the distribution of undiscovered diversity. We find that ants and different vertebrate groups have distinct features in their patterns of richness and rarity, underscoring the need to consider a diversity of taxa in conservation. However, despite their phylogenetic and physiological divergence, ant distributions are not highly anomalous relative to variation among vertebrate clades. Furthermore, our models predict that rarity centers largely overlap (78%), suggesting that general forces shape endemism patterns across taxa. This raises confidence that conservation of areas important for small-ranged vertebrates will benefit invertebrates while providing a “treasure map” to guide future discovery.

Redundant Parallel Beam Multiaxis Force Sensor—Accuracy Space

The principle of the redundant parallel beam multi-axis force sensor is a transformation from displacement domain to force domain. This paper proposed a general force error model of a distributed force measurement system with redundant multi-axis force sensors based on the measurement <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$/$ </tex-math></inline-formula> surveying adjustment method to transform displacement sensor errors to force errors. The optimum accuracy space is defined according to the error model. According to the accuracy space, the torque error increase sharply when the measuring point is far away from the optimum accuracy space, but the force error remains constant. A long-distance arrangement of displacement sensors can increase the size of the optimum accuracy space and a high-precision displacement sensor can increase the measurement accuracy in the whole space. A deformation filter can minimize the affection of the loading platform deformation on the measurement accuracy. A dual-measurement system is recommended to increase both the force accuracy and the torque accuracy when the measuring point is far from the optimum accuracy space of the main multi-axis force sensing system. The error point cloud is used to verify the proposed error model.

Migrant Identity and Culture Maintenance: The Welsh in Johnstown, Cambria County, Pennsylvania, 1870–1930

Abstract Welsh immigrants and their children comprised a distinct ethnolinguistic community in Johnstown, Pennsylvania, during the late nineteenth and early twentieth centuries. This article analyzes the nature of that community and suggests that while ethnic integrity was initially maintained due to linguistic ability, religious adherence, and the creation of popular cultural institutions, it was ultimately undermined, not only by the general forces of acculturation, but also by specifically Welsh factors. While the Welsh experience in Johnstown differed sharply from that undergone by the English, it did not simply mirror that of other non-Anglophone groups.

Multiple-order vertical vortex-induced vibration mechanism of a typical streamlined closed-box girder

Multiple-order vertical vortex-induced vibrations (VIVs) have been frequently observed in prototype bridges as well as tested models in wind tunnels, but VIV excitation and VIV suppression mechanisms need further investigation. In this study, a simplified vortex model (SVM) derived from the spatial distribution characteristics of the wind pressure around the girder surface was developed to elucidate the multiple-order vertical VIV phenomena of a typical streamlined closed-box girder with additional attachments. The results showed that there are three potential lock-in ranges of vertical VIVs. The 1st lock-in range is excited and sustained by the separated vortex formation at the trailing edge, which is referred to as trailing-edge-vortex-dominated VIV. In the 2nd and 3rd lock-in ranges, the contribution of local aerodynamic forces to the general vortex-excited forces (VEFs) over the upper surface varies with the local positions in the form of simple harmonic curves. Therefore, the local aerodynamic force can be simplified by a concentrated force with an approximately constant loading amplitude and drift velocity, which is illustrated as a simplified moving vortex; based on this, an SVM can be established and utilized to associate the vortex-drift pattern with multiple vertical VIVs in terms of Strouhal number of the separated vortex. With the help of the SVM, the 2nd and 3rd lock-in ranges are excited and sustained by the separated vortex formation at the leading edge and then by a regular vortex drift pattern over the upper surface of the bridge girder, referred to as impinging-edge-vortex-dominated VIVs. Spoilers installed on the handrails can effectively suppress the separated vortex formation both at the trailing edge and leading edge; thus, vertical VIVs in all lock-in ranges can be mitigated.