Mutual Force Research Articles

Chemical-mechanical dispersing behavior of a nanoceria abrasive

The authors studied dispersing behavior of a nanoceria abrasive under joint actions of mechanical ultra-sonication and chemical dispersants, to explore effective approaches and methods for dispersing it and manifesting its functions of nanometric scale. It was found that mechanical ultra-sonication solely could not disperse the nanoceria abrasive effectively, while dispersants such as sodium hexametaphosphate (SHP) and sodium dodecylbenzenesulfonate (SDBS) could help to disperse the nanoceria abrasive. SHP and SDBS were found to increase value of zeta potential of the nanoceria abrasive markedly and decrease level of apparent viscosity of its slurry observably. It was deduced by analysis that the dispersants increased inter-particles mutual repulsive force by forming steric hindrance between particles and augmenting zeta potential of particle surfaces, which could overcome van der Waals attracting force to some extent, reduce agglomeration and flocculation of the nanoceria particles, thus improve dispersibility and stability of the nanoceria particles in slurries.

Calculation of Cogging Force in Permanent Magnet Linear Motor Using Analytical and Finite Element Methods

In a permanent magnet (PM) linear motor, there is a force ripple which is detrimental to positioning. This force ripple is mainly due to a cogging force and a mutual force ripple. These forces are affected by the geometric parameters of a brushless PM motor, such as the width of the magnet, the height of the magnet, the shifted length of the magnetic pole, the length and height of the armature and the slot width. The optimal design can be found by considering force ripple as a cost function and the geometric parameters as design variables. In this paper, we calculate the flux density distribution in the air gap using the analytic solution of Laplace and Possion equations in the function of geometric parameters. The cogging force is obtained by integrating the Maxwell stress tensor, which is described by the flux density distribution on the slot face and end face of the iron core of an armature. Finally, a finite element method is presented in order to compare with the previous method.

Overlapping two self-avoiding polymers in a closed cylindrical pore: Implications for chromosome segregation in a bacterial cell

We study the spatial organization and segregation of two self-avoiding polymers trapped inside a closed cylindrical pore. Using molecular-dynamics simulations, we show how confinement shapes the chains, especially their mutual (entropic) force, chain miscibility, and segregation dynamics. Under strong confinement, the chains are shown to repel more strongly and thus segregate better if they are shorter and the confining space is more asymmetric, in contrast to the spherically confined case, where nonlinear chain topology is required for chain partitioning in equilibrium. When applied to bacterial chromosomes, our results imply that chromosome miscibility depends on how they are compacted and structured inside the cell (by proteins and supercoiling). Finally, longitudinal confinement is shown to have nontrivial effects on segregation dynamics by randomizing and thus slowing down the segregation process, which would otherwise be assisted with entropic forces.

Magnetohydrodynamics of superfluid and superconducting neutron star cores

Mature neutron stars are cold enough to contain a number of superfluid and superconducting components. These systems are distinguished by the presence of additional dynamical degrees of freedom associated with superfluidity. In order to consider models with mixtures of condensates we need to develop a multifluid description that accounts for the presence of rotational neutron vortices and magnetic proton fluxtubes. We also need to model the forces that impede the motion of vortices and fluxtubes, and understand how these forces act on the condensates. This paper concerns the development of such a model for the outer core of a neutron star, where superfluid neutrons co-exist with a type II proton superconductor and an electron gas. We discuss the hydrodynamics of this system, focusing on the role of the entrainment effect, the magnetic field, the vortex/fluxtube tension and the dissipative mutual friction forces. Out final results can be directly applied to a number of interesting astrophysical scenarios, e.g. associated with neutron star oscillations or the evolution of the large scale magnetic field.

Molecular Dynamics Simulations on High-Performance Reconfigurable Computing Systems

The acceleration of molecular dynamics (MD) simulations using high-performance reconfigurable computing (HPRC) has been much studied. Given the intense competition from multicore and GPUs, there is now a question whether MD on HPRC can be competitive. We concentrate here on the MD kernel computation: determining the short-range force between particle pairs. In one part of the study, we systematically explore the design space of the force pipeline with respect to arithmetic algorithm, arithmetic mode, precision, and various other optimizations. We examine simplifications and find that some have little effect on simulation quality. In the other part, we present the first FPGA study of the filtering of particle pairs with nearly zero mutual force, a standard optimization in MD codes. There are several innovations, including a novel partitioning of the particle space, and new methods for filtering and mapping work onto the pipelines. As a consequence, highly efficient filtering can be implemented with only a small fraction of the FPGA's resources. Overall, we find that, for an Altera Stratix-III EP3ES260, 8 force pipelines running at nearly 200 MHz can fit on the FPGA, and that they can perform at 95% efficiency. This results in an 80-fold per core speed-up for the short-range force, which is likely to make FPGAs highly competitive for MD.

Packing and melting of mesoscopically confined two-dimensional Coulomb crystals in straight narrow channels

The microstructure and melting dynamics of the two-dimensional mesoscopic Coulomb crystal with 1/r-type mutual interaction force and parabolic transverse confining potential, under different degrees of incommensurability, are investigated through molecular-dynamics simulation. To tune the degree of incommensurability, N(a) extra particles are added into the commensurate uniform triangular lattice which has seven-layer structure and 40 particles in each layer with the periodic longitudinal boundary condition, until the system reaches another commensurate packing with eight-layer structure at N(a)=40. It is found that the increasing incommensurability with the increasing N(a) or 40-N(a) gradually deteriorates the structural order with the presence of intrinsic defects and the anisotropic bond-length distribution, except for the defect-free configurations at a few magic N(a)'s. The system prefers the seven- and the eight-layer single structures through the entire crystal for the low- and the high-N(a) regimes, respectively, and the configurations with seven- and eight-layer domain mixtures for 18≤N(a)≤24. The increasing strain or the worse local particle interlocking around the intrinsic defects with the increasing incommensurability also causes the easier structural rearrangement associated with the easier particle hopping and the earlier onset of melting transition. The transverse confinement suppresses the transverse motion, induces nonuniform melting, and sustains the layered structure after melting.

Hydrodynamic equations of anisotropic, polarized and inhomogeneous superfluid vortex tangles

We include the effects of anisotropy and polarization in the hydrodynamics of inhomogeneous vortex tangles, thus generalizing the well known Hall–Vinen–Bekarevich–Khalatnikov equations, which do not take them in consideration. These effects contribute to the mutual friction force F n s between normal and superfluid components and to the vortex tension force ρ s T . These equations are complemented by an evolution equation for the vortex line density L , which takes into account these contributions. These equations are expected to be more suitable than the usual ones for rotating counterflows, or turbulence behind a cylinder, or turbulence produced by a grid of parallel thin cylinders towed across a superfluid, because in these situations polarization is expected to play a relevant role.

Study on lignin coverage of masson pine fiber

In order to obtain the adhesion force of fiber in a paper sheet easily, the relationships between internal bonding strength (IBS) and surface lignin content of masson pine CTMP treated with peracetic acid (PAA) have been investigated with XPS technique, and the surface morphology of fibers was also imaged by AFM. The results showed that the extent of lignin covered on the fiber surface was two times as high as that of whole pulp lignin, and the IBS was inversely proportional to surface lignin. The relationship between IBS and lignin coverage was formulated based on the experimental data. The mutual adhesion forces, cellulose-to-cellulose and lignin-to-lignin, were calculated using these equations, and the results were 28.69 mN/m and 2.487mN/m, respectively.

Effects of a high magnetic field on the coarsening of MnBi grains solidified from isothermal annealed semi-solid melt

With the imposition of a high magnetic field up to 11.5 T, the morphologic transition of the MnBi phase and the magnetic properties of the Bi–4.36 wt.% and 8.25 wt.% Mn alloy specimens solidified from a semi-solid state were investigated. Compared with the irregular shape and unequal dimensions of MnBi grains under 0 T, the coarsened MnBi grains were connected together and tended to be parallel to the direction of the external field of 11.5 T. The changes might be attributed to the Ostwald ripening of ferromagnetic grains in the isothermal holding stage and subsequent aggregation along the direction of external field driven by mutual magnetic force among the grains. The uniform orientation of the ferromagnetic MnBi grains obtained in the microstructures effectively improves the saturation magnetization of the Bi/MnBi composite materials, but the oversized grains and the defects in grains make the coercivity decrease.

Stability and dynamics of two-soliton molecules

The problem of soliton-soliton force is revisited. From the exact two-soliton solution of a nonautonomous Gross-Pitaevskii equation, we derive a generalized formula for the mutual force between two solitons. The force is given for arbitrary soliton amplitude difference, relative speed, phase, and separation. The latter allows for the investigation of soliton molecule formation, dynamics, and stability. We reveal the role of the time-dependent relative phase between the solitons in binding them in a soliton molecule. We derive its equilibrium bond length, spring constant, frequency, effective mass, and binding energy of the molecule. We investigate the molecule's stability against perturbations such as reflection from surfaces, scattering by barriers, and collisions with other solitons.

The dynamics of pulsar glitches: contrasting phenomenology with numerical evolutions

In this paper we consider a simple two-fluid model for pulsar glitches. We derive the basic equations that govern the spin evolution of the system from two-fluid hydrodynamics, accounting for the vortex mediated mutual friction force that determines the glitch rise. This leads to a simple "bulk" model that can be used to describe the main properties of a glitch event resulting from vortex unpinning. In order to model the long term relaxation following the glitch our model would require additional assumptions regarding the repinning of vortices, an issue that we only touch upon briefly. Instead, we focus on comparing the phenomenological model to results obtained from time-evolutions of the linearised two-fluid equations, i.e. a "hydrodynamic" model for glitches. This allows us to study, for the first time, dynamics that was "averaged" in the bulk model, i.e. consider the various neutron star oscillation modes that are excited during a glitch. The hydro-results are of some relevance for efforts to detect gravitational waves from glitching pulsars, although the conclusions drawn from our rather simple model are pessimistic as far as the detectability of these events is concerned.

A Vector Control Method of LPMBDCM Considering Effects of PM Flux Linkage Harmonic and Cogging Force

This paper presents a general vector control principle of surface-mounted permanent magnet (SPM) motors with arbitrary back-electromotive-force (back-EMF) waveform, then applies it to minimize the force pulsation of three-phase linear permanent magnet brushless dc motors (LPMBDCMs). The principle is derived from the force equation in the dot product form of the current vector and the permanent magnet (PM) flux linkage derivative vector. It indicates that the mutual force is proportional to the amplitude of current vector, and the ohmic loss is at the minimum when the current vector is aligned with the PM flux linkage derivative vector. Based on a d'q' asynchronously rotating reference frame considering the effects of PM flux linkage harmonic, a new id' = 0 vector control method with the cogging force compensation is proposed according to the principle. From the results of simulation with an accurate finite element (FE) based phase variable model, the validity of the proposed control method is verified compared with the conventional PWM current control for a LPMBDCM.

MUTUAL INDUCTANCE AND FORCE EXERTED BETWEEN THICK COILS

We present exact three-dimensional semi-analytical ex- pressions of the force exerted between two coaxial thick coils with rect- angular cross-sections. Then, we present a semi-analytical formulation of their mutual inductance. For this purpose, we have to calculate six and seven integrations for calculating the force and the mutual induc- tance respectively. After mathematical manipulations, we can obtain semi-analytical formulations based on only two integrations. It is to be noted that such integrals can be evaluated numerically as they are smooth and derivable. Then, we compare our results with the flla- ment and the flnite element methods. All the results are in excellent agreement.

A Study of Super Nonlinear Motion of Electrostatically Coupled Two-Particle System

We consider a pair of nonidentical mechanical pendulums. The bob of each pendulum in addition to its own mass electrically is charged. The pendulums are hung from a common pivot in a vertical plane forming a slanted asymmet-ric ??shaped figure. For arbitrary initial swings that are not necessarily confined to small angles, we analyze the dy-namics of each bob under the influence of gravity’s pull as well as the mutual repulsive Coulombian internal force. The equations describing the motion of the system are a set of highly, supper nonlinear coupled differential equations. Applying Mathematica we solve the equations numerically. For nonidentical parameters describing the pendulums, namely, we show the system behaves chaotically; i.e. the angular position of each pendulum leaves a non-repeatable, chaotic pattern in time. For this coupled two-particle interactive system we show also by folding the time axis, the angular position of one of the pendulums vs. the other traces a Lissajous type curve. Our report includes various traditional phase diagrams and a set of newly designed, useful, phase-type diagrams as well. For a comprehensive understanding about the dynamics of the problem at hand, we provide Mathematica codes conducive to animating the chaotic motion of the system. The generic format of the codes allows adjusting the relevant pa-rameters at will and addressing the “what-if” scenarios.

Numerical and experimental motion simulations of nonsymmetric ship collisions

A calculation model to simulate nonsymmetric ship collisions, implying an arbitrary impact location and collision angle, is described in the paper. The model that is introduced is based on the time integration of twelve equations of motion, six for each ship. The motions of the ships are linked together by a mutual contact force. The contact force is evaluated as an integral over the surface tractions at the contact interface. The calculation model provides full time histories of the ship motions and the acting forces. Physical understanding of the underlying phenomena was obtained by a series of model-scale experiments in which a striking ship collided with an initially motionless struck ship. In this paper, numerical simulations of four nonsymmetric collisions are presented and the calculations are validated with the results of the experiments.

Motion of three viscoelastic planets in the field of their mutual attraction forces

Translational-rotational motion of three planets modeled by viscoelastic balls in the gravitational field of mutual attraction is studied in this paper. The system of equations of motion for the mechanical system under consideration is deduced from the d’Alembert-Lagrange variational principle. Using the method of separation of motions, an approximate system of ordinary differential equations, describing the translational-rotational motion of the planets, is obtained with taking into account perturbations caused by elasticity and dissipation. The found steady-state motion of the system is an analog to triangular libration points in the classical three-body problem.

A parametric simulation method for discrete dislocation dynamics

A new computer simulation method employed in discrete dislocation dynamics is presented. The article summarizes results of an application of the method to elementary interactions among glide dislocations and dipolar dislocation loops. The glide dislocations are represented by parametrically described curves moving in glide planes whereas the dipolar loops are treated as rigid objects. All mutual force interactions are considered in the models. As a consequence, the computational complexity rapidly increases with the number of objects considered. This difficulty is treated by advanced computational techniques such as suitable accurate numerical methods and parallel implementation of the algorithms. Therefore the method is able to simulate particular phenomena of dislocation dynamics which occur in crystalline solids deformed by single slip: generation of glide dislocations from the Frank-Read source, interaction of glide dislocations with obstacles, their encounters in channels of the bands, sweeping of dipolar loops by glide dislocations and a loop clustering.

Oscillations of dissipative superfluid neutron stars

We investigate the oscillations of slowly rotating superfluid stars, taking into account the vortex-mediated mutual friction force that is expected to be the main damping mechanism in mature neutron star cores. Working to linear order in the rotation of the star, we consider both the fundamental $f$-modes and the inertial $r$-modes. In the case of the (polar) $f$-modes, we work out an analytic approximation of the mode which allows us to write down a closed expression for the mutual friction damping time scale. The analytic result is in good agreement with previous numerical results obtained using an energy integral argument. We extend previous work by considering the full range of permissible values for the vortex drag, e.g. the friction between each individual vortex and the electron fluid. This leads to the first ever results for the $f$-mode in the strong drag regime. Our estimates provide useful insight into the dependence on, and relevance of, various equation of state parameters. In the case of the (axial) $r$-modes, we confirm the existence of two classes of modes. However, we demonstrate that only one of these sets remains purely axial in more realistic neutron star models. Our analysis lays the foundation for companion studies of the mutual friction damping of the $r$-modes at second order in the slow-rotation approximation, the first time evolutions for superfluid neutron star perturbations and also the first detailed attempt at studying the dynamics of superfluid neutron stars with both a relative rotation between the components and mutual friction.

Rethinking Atlantic History

[First paragraph]Shaping the Stuart World 1603-1714: The Atlantic Connection. Allan I. Macinnes & Arthur H. Williamson (eds.). Leiden: Brill Academic Publishers, 2006. xiv + 389 pp. (Cloth US$ 135.00)Slavery and the British Empire: From Africa to America. Kenneth Morgan. New York: Oxford University Press, 2007. x + 221 pp. (Paper US$ 32.00)Although an important debate continues about the concept itself, the use of “the Atlantic” has embedded itself in scholarly vernacular. The scholarly output directly spawned by an engagement with the concept continues apace. That ocean, and the peoples who lived and traded along its edges, and who finally moved across it, have provided an important geographical focus for some major reconsiderations of modern history. Prompted by the Macinnes/Williamson volume, I returned to my own undergraduate and graduate notes and essays from courses on Stuart Britain: the Atlantic was totally absent – not even present as a distant speck on our intellectual map. We studied, and debated, the formal histories of migrations to the Americas (i.e. Europeanmigrations) but there was no mention of Africa or Africans. And no sense was conveyed that the European engagement with the Americas (in their totality – as opposed to North America) was a two-way, mutual force: that the European world was influenced, indeed shaped in many critical regards,by the Americas: by the land, the products, the peoples, and by the markets of that hemisphere. At its most obvious in the ebb and flow of peoples, even that eluded the historians I encountered as a student. It was as if we were talking about a different cosmos; few moved beyond the conventions of European migrations westwards and little attention was paid to that most dominant of migrations – the enforced African migrations to the Americas.

Mechanical Modelling of a Bent Axis Pump

AbstractIn the technical literature numerous studies are found focused on the mathematical modelling of mechanical aspects of swash plate axial piston pumps. Instead, bent axis pumps are rarely considered despite their widespread use in mobile and fixed applications. This research paper presents the mechanical model of a bent axis pump that simulates the dynamic behaviour of the main measurable quantities (e.g. the shaft torque) and the mutual forces in interacting components. The model is parametric and thus apt in predicting the influence of geometric design variables on pumps mechanical characteristics. A number of simulation analyses grounded on the presented model and on an ADAMS multi- body approach are considered and contrasted one another and with experimental torque data for validation purposes.