External Force Field Research Articles

Self-assembly and ion transport behaviour of liquid-crystalline graphene oxide multilayer sandwich nanopapers

ABSTRACT The controllability of ion channel size is critical for ion transport and sieving. Graphene oxide (GO) has a planar two-dimensional structure and a rich functional group as a binding site, and the liquid crystal material generally undergoes an orientation change under the action of an external force field. Therefore, this property can be incorporated into GO, and the distance between the layers of GO can be controlled by designing the liquid crystal cell which meets the requirements and adjusting the external force field, thereby controlling the transport of ions. In this paper, multilayer sandwich nanopapers were fabricated by liquid crystals and GO via hydrogen bonding, and the controlled ion transport behaviour was investigated. In the presence of external electric or magnetic field, ion channels in the interlayer distance of sandwich GO nanopapers can be adjusted due to the changes of mesogen orientation; therefore, ion conductivity can be adjusted when a lithium-ion solution pass through the nanopapers. Such nano-paper materials show promise in many fields such as ion transport, separation systems, ion battery and capacitor devices.

Robot Path Planning Method Based on Level Set

For the problem of robot path planning under the action of external force field, the directionality of outward force can promote and hinder the movement of the robot. The continuous path planning method can break through the traditional robot path planning algorithm based on grid search. Limit, effectively utilize the external force field existing in the space, and improve the numerical implementation method to ensure the feasibility of the planned path in the strong external force field. Based on the Level Set method, the path planning problem is defined. The particle tracking of the robot is transformed into the numerical evolution of the curve. The optimal time path is obtained by solving the Hamilton-Jacques equation. The numerical calculation accuracy of the improved backward path tracking is guaranteed. The feasibility of planning the path. The simulation results show that the algorithm can effectively deal with a variety of complex external force fields and maintain the path in a strong external force field.

Enhanced electromagnetic interference shielding and mechanical properties of segregated polymer/carbon nanotube composite via selective microwave sintering

Formation of segregated structure in conductive polymer composites (CPCs) is an efficient strategy to achieve high electrical conductivity at relatively low filler loading. Nevertheless, not every polymer can meet the requirements for the conventional hot compression molding (CM), and it will always result in the weak interfacial bonding among the polymer domains. Herein, a clean and energy-saving approach based on selective microwave sintering (SMS) was proposed to fabricate the segregated poly(ethylene-co-octene) (POE)/carbon nanotube (CNT) composites with significantly enhanced electromagnetic interference (EMI) shielding and mechanical performance. CNT nanoparticles were selectively dispersed and coated on the surface of POE granules under an external force field. The coated CNT layer served as the microwave absorber, thus inducing the local melting and welding of the neighboring POE domains without destroying the original CNT segregated network. In this way, the intense inter-diffusion and entanglement of POE chains occurred in the interface regions to ensure high-quality sintering among POE granules. The prepared conductive POE/CNT composites were endowed with the significantly enhanced mechanical properties, showing nearly 2 times of tensile strength and over 10 times of elongation at break than the samples prepared by hot compaction. Also, the SMS composites with only 2.10 vol% CNT exhibited the excellent electrical conductivity of 26.0 S/m and EMI SE of 34.7 dB at the frequency of 12.0 GHz, respectively. What's more, the sintering process, reinforcement mechanism, and fusion behavior among neighboring polymer granules were intensively investigated via infrared thermography and COMSOL simulation.

Positivity preserving schemes for the fractional Klein-Kramers equation with boundaries

The fractional Klein-Kramers equation describes the process of subdiffusion in the presence of an external force field in phase space and incorporates a fractional operator in time of order α, 0 < α < 1. We present a family of finite volume schemes for the fractional Klein-Kramers equation, that includes first or second-order schemes in phase space, and implicit or explicit schemes in time with an order of accuracy that can change between α and 2−α. It is proved, for the open domain, that the schemes satisfy the positivity preserving property. The positivity preserving property for the explicit schemes imposes a strong condition in the relation between time step, space step and phase step, for small values of α, highlighting the advantage of using implicit schemes in these cases. For a bounded domain in space, two types of boundary conditions are considered, absorbing boundary conditions and reflecting boundary conditions. The inclusion of boundary conditions leads to some technical complications that require changes in the schemes near the boundary. The positivity preserving property holds for the new formulation and the overall accuracy is ensured with the use of non-uniform meshes. Numerical tests are presented in the end to show the convergence of the finite volume schemes.

Effect of Differential Rotation of Oscillating Inner Core on Steady Flow Instability in a Rotating Sphere

A comparative analysis of steady flow excited by an oscillating core in a rotating spherical cavity with a liquid is carried out in different cases: when the core is free and performs differential rotation, and when the core differential rotation is absent. In the cavity reference frame the core, whose density is less than the density of the liquid, oscillates near the cavity center under the action of transverse to the rotation axis external force field. In both cases, the oscillations lead to the appearance of almost two-dimensional axisymmetric azimuthal steady flow, with several inflection points in the velocity profile. An increase in the amplitude of core oscillations leads to a loss of stability of the axisymmetric flow. In the supercritical region, there is a series of threshold transitions associated with various instability modes. The instability manifests itself in the development of an azimuthal periodic system of vortices elongated parallel to the rotation axis. The modes differ in an azimuthal wavenumber, the location of the vortices (distance from the axis of rotation), and the azimuthal drift rate of the vortex system relative to the cavity. It is shown that the core differential rotation modifies the azimuthal velocity profile, resulting in a change in the instability thresholds. Due to an additional azimuthal flow, the drift velocity of the same type vortices in the two cases is different. The effect of the core differential rotation on the dispersion relations for various instability modes has been investigated.

A hybrid thermostatted kinetic framework for the modeling of a hybrid multisource system with storage

The planning and development of a hybrid energy source network is based on an optimal analysis which takes into account the connection costs and the production facilities. This paper aims at modeling a hybrid multisource system by employing the methods of the thermostatted kinetic theory. Specifically a network of energy sources is allocated into a geographical domain, which is divided into different regions each of them containing different energy sources. A hybrid kinetic theory framework is proposed where the energy source is identified by a quality parameter which can attain discrete values, whereas the energy supplied by the source is modeled by defining a continuous variable. The mathematical framework consists into a system of partial integro-differential equations with quadratic type nonlinearities whose parameters are interaction rates and probability density functions. The storage system is also modeled by introducing an external force field coupled with a mathematical thermostat for ensuring the conservation of the activation energy of the energy network. The existence and uniqueness of the solution is investigated by employing fixed point arguments and integration along the characteristic curves. A critical analysis and research perspectives conclude the paper showing that the proposed thermostatted kinetic theory frameworks can be considered as general paradigms for the derivation of specific models.

THRESHOLD EFFECTS IN THE SPECTRUM OF THE ONE-PARTICLE SCHRÖDINGER OPERATOR ON A LATTICE

We consider a wide class of Schrödinger operators HV = H0 V describing a particle in an external force field vˆ in the d -dimensional cubic integer lattice d , d  3 . We study the existence or absence of bound states of the one-particle Schrödinger operator HV depending on the potential vˆ and the dimension of the lattice d , d  3, as well as threshold effects in its spectrum. We establish that the appearance of bound states of the operator HV depends on whether the threshold of the essential spectrum of HV is a regular point or a singular point: namely, if the lower threshold of the essential spectrum of HV is a regular point of the essential spectrum, then it does not create any eigenvalues below the essential spectrum under small perturbations, but if the lower threshold of the essential spectrum of the operator HV is a singular point, then it creates eigenvalues below the essential spectrum under perturbations.

Thermal conductivity of emulsion with anisotropic microstructure induced by external field

The structure formation influence on various macroscopic properties of disperse systems is poorly investigated in respect to emulsion systems. The present work deals with the experimental and theoretical study of the heat transfer in emulsions whose dispersed phase droplets are arranged into chain-like structures under the action of external force field. The studied emulsions are of water-in-oil and oil-in-water types; they are based on ferrofluid and contain dispersed phase droplets in a size range of the order of several tens of micrometers. It is demonstrated that the emulsion thermal conductivity grows notably under the effect of external magnetic field parallel to the heat flux and provoking structure formation. It is revealed that the maximal response of thermal conductivity on the magnetic field action takes place at the dispersed phase volume fraction of about 20–30%. The structure formation in magnetic field has been simulated, and the magnetic interactions of emulsion droplets with each other and with the sample boundaries have been considered and discussed. The macroscopic thermal conductivity of structured emulsions has been numerically calculated and compared with experimental data. The obtained results may be of interest in the development of potential applications of controlling the properties of colloids by magnetic field.

Exploring disturbance as a force for good in motor learning.

Disturbance forces facilitate motor learning, but theoretical explanations for this counterintuitive phenomenon are lacking. Smooth arm movements require predictions (inference) about the force-field associated with a workspace. The Free Energy Principle (FEP) suggests that such ‘active inference’ is driven by ‘surprise’. We used these insights to create a formal model that explains why disturbance might help learning. In two experiments, participants undertook a continuous tracking task where they learned how to move their arm in different directions through a novel 3D force field. We compared baseline performance before and after exposure to the novel field to quantify learning. In Experiment 1, the exposure phases (but not the baseline measures) were delivered under three different conditions: (i) robot haptic assistance; (ii) no guidance; (iii) robot haptic disturbance. The disturbance group showed the best learning as our model predicted. Experiment 2 further tested our FEP inspired model. Assistive and/or disturbance forces were applied as a function of performance (low surprise), and compared to a random error manipulation (high surprise). The random group showed the most improvement as predicted by the model. Thus, motor learning can be conceptualised as a process of entropy reduction. Short term motor strategies (e.g. global impedance) can mitigate unexpected perturbations, but continuous movements require active inference about external force-fields in order to create accurate internal models of the external world (motor learning). Our findings reconcile research on the relationship between noise, variability, and motor learning, and show that information is the currency of motor learning.

Electrical Conductivity of Field-Structured Emulsions

The structure formation influence on various macroscopic properties of fluid–fluid disperse systems is poorly investigated. The present work deals with the experimental study of the charge transfer in emulsions whose dispersed phase droplets are arranged into chainlike structures under the action of an external force field. The emulsions studied are the fluid system in which water droplets are dispersed in a hydrocarbon-based magnetic fluid. Under the effect of an external uniform magnetic field, anisotropic aggregates form from the emulsion dispersed phase drops. The low-frequency electrical conductivity of emulsions has been measured. It is demonstrated that the emulsions’ conductivity grows several times under the effect of magnetic field parallel to the measuring electrical field. The anisotropic character of the emulsion electrical conductivity in the presence of magnetic field has been demonstrated. It is revealed that the maximal response of conductivity on the magnetic field action takes place at the dispersed phase volume fraction of about 20%. The dynamics of the conductivity variation is analyzed in dependence on the magnetic field strength and the dispersed phase volume fraction. The obtained results may be of interest in the development of potential applications of disperse systems with magnetic-field-controllable properties.

Structure of the Hydrophobic Core Determines the 3D Protein Structure-Verification by Single Mutation Proteins.

Four de novo proteins differing in single mutation positions, with a chain length of 56 amino acids, represent diverse 3D structures: monomeric 3α and 4β + α folds. The reason for this diversity is seen in the different structure of the hydrophobic core as a result of synergy leading to the generation of a system in which the polypeptide chain as a whole participates. On the basis of the fuzzy oil drop model, where the structure of the hydrophobic core is expressed by means of the hydrophobic distribution function in the form of a 3D Gaussian distribution, it has been shown that the composition of the hydrophobic core in these two structural forms is different. In addition, the use of a model to determine the structure of the early intermediate in the folding process allows to indicate differences in the polypeptide chain geometry, which, combined with the construction of a common hydrophobic nucleus as an effect of specific synergy, may indicate the reason for the diversity of the folding process of the polypeptide chain. The results indicate the need to take into account the presence of an external force field originating from the water environment and that its active impact on the formation of a hydrophobic core whose participation in the stabilization of the tertiary structure is fundamental.

Optimal transport with discrete long-range mean-field interactions

We study an optimal transport problem where, at some intermediate time, the mass is either accelerated by an external force field or self-interacting. We obtain the regularity of the velocity potential, intermediate density, and optimal transport map, under the conditions on the interaction potential that are related to the so-called Ma–Trudinger–Wang condition from optimal transport [X.-N. Ma, N. S. Trudinger and X.-J. Wang, Regularity of potential functions of the optimal transportation problems, Arch. Ration. Mech. Anal. 177 (2005) 151–183.].

3D printed cellulose-based high-efficiency oil-water separation mesh

In this study, a high-performance oil-water separation mesh based on cellulose was fabricated by Direct Ink Writing (DIW) 3D printing technology. The 3D printing process can be undergo in a natural environment by using a cellulose acetate/ethyl acetate solution as a DIW printing ink. This oil-water separation mesh prepared has various advantages, such as uniform size, controllable aperture, simple and easy printing process, and rapid prototyping. The super high separation efficiency of 96 % and the high flux of 400 000 L·m−2·h−1 can be realized when the average pore size of the 3D printed super-hydrophilic cellulose mesh is 280 μm or less. Moreover, oil-water separation mesh prepared based on highly hydrophilic cellulose are chemically resistant to extreme acidity and alkalinity. It is also capable of separating oils of various viscosities. In addition, the cellulose mesh can cope with the mechanical force caused by high-frequency vibration, and maintain excellent oil-water separation efficiency in the external force field. Therefore, this highly efficient oil-water separation mesh can be used in oil-water separation processes in a variety of applications.

A Review of Secondary Flow in Inertial Microfluidics.

Inertial microfluidic technology, which can manipulate the target particle entirely relying on the microchannel characteristic geometry and intrinsic hydrodynamic effect, has attracted great attention due to its fascinating advantages of high throughput, simplicity, high resolution and low cost. As a passive microfluidic technology, inertial microfluidics can precisely focus, separate, mix or trap target particles in a continuous and high-flow-speed manner without any extra external force field. Therefore, it is promising and has great potential for a wide range of industrial, biomedical and clinical applications. In the regime of inertial microfluidics, particle migration due to inertial effects forms multiple equilibrium positions in straight channels. However, this is not promising for particle detection and separation. Secondary flow, which is a relatively minor flow perpendicular to the primary flow, may reduce the number of equilibrium positions as well as modify the location of particles focusing within channel cross sections by applying an additional hydrodynamic drag. For secondary flow, the pattern and magnitude can be controlled by the well-designed channel structure, such as curvature or disturbance obstacle. The magnitude and form of generated secondary flow are greatly dependent on the disturbing microstructure. Therefore, many inventive and delicate applications of secondary flow in inertial microfluidics have been reported. In this review, we comprehensively summarize the usage of the secondary flow in inertial microfluidics.

Learning New Feedforward Motor Commands Based on Feedback Responses.

Learning a new motor task modifies feedforward (i.e., voluntary) motor commands and such learning also changes the sensitivity of feedback responses (i.e., reflexes) to mechanical perturbations [1-9]. For example, after people learn to generate straight reaching movements in the presence of an external force field or learn to reduce shoulder muscle activity when generating pure elbow movements with shoulder fixation, evoked stretch reflex responses to mechanical perturbations reflect the learning expressed during self-initiated reaching. Such a transfer from feedforward motor commands to feedback responses is thought to take place because of shared neural circuits at the level of the spinal cord, brainstem, and cerebral cortex [10-13]. The presence of shared neural resources also predicts the transfer from feedback responses to feedforward motor commands. Little is known about such a transfer presumably because it is relatively hard to elicit learning in reflexes without engaging associated voluntary responses following mechanical perturbations. Here, we demonstrate such transfer by leveraging two approaches to elicit stretch reflexes while minimizing engagement of voluntary motor responses in the learning process: applying very short mechanical perturbations [14-19] and instructing participants to not respond to them [20-26]. Taken together, our work shows that transfer between feedforward and feedback control is bidirectional, furthering the notion that these processes share common neural circuits that underlie motor learning and transfer.

Tunable DNA Origami Motors Translocate Ballistically Over μm Distances at nm/s Speeds

AbstractInspired by biological motor proteins, that efficiently convert chemical fuel to unidirectional motion, there has been considerable interest in developing synthetic analogues. Among the synthetic motors created thus far, DNA motors that undertake discrete steps on RNA tracks have shown the greatest promise. Nonetheless, DNA nanomotors lack intrinsic directionality, are low speed and take a limited number of steps prior to stalling or dissociation. Herein, we report the first example of a highly tunable DNA origami motor that moves linearly over micron distances at an average speed of 40 nm/min. Importantly, nanomotors move unidirectionally without intervention through an external force field or a patterned track. Because DNA origami enables precise testing of nanoscale structure‐function relationships, we were able to experimentally study the role of motor shape, chassis flexibility, leg distribution, and total number of legs in tuning performance. An anisotropic rigid chassis coupled with a high density of legs maximizes nanomotor speed and endurance.

Tunable DNA Origami Motors Translocate Ballistically Over μm Distances at nm/s Speeds.

Inspired by biological motor proteins, that efficiently convert chemical fuel to unidirectional motion, there has been considerable interest in developing synthetic analogues. Among the synthetic motors created thus far, DNA motors that undertake discrete steps on RNA tracks have shown the greatest promise. Nonetheless, DNA nanomotors lack intrinsic directionality, are low speed and take a limited number of steps prior to stalling or dissociation. Herein, we report the first example of a highly tunable DNA origami motor that moves linearly over micron distances at an average speed of 40 nm/min. Importantly, nanomotors move unidirectionally without intervention through an external force field or a patterned track. Because DNA origami enables precise testing of nanoscale structure-function relationships, we were able to experimentally study the role of motor shape, chassis flexibility, leg distribution, and total number of legs in tuning performance. An anisotropic rigid chassis coupled with a high density of legs maximizes nanomotor speed and endurance.

Transition between coherent and incoherent chirping mechanisms in electron-positron pair creation

We examine the effect of a frequency-chirped external force field on the final energy that has been absorbed by two classical mechanical oscillators, by quantum mechanical two- and three-level systems, and by electron-positron pairs that were created from the quantum field theoretical Dirac vacuum. By comparing the final dynamical responses to the original force field with that associated with the corresponding time-reversed field, we can test the sensitivity of each of these five systems to the temporal phase information contained in the field. We predict that the linear oscillator, the two-level atom, and the pair-creation process triggered by a spatially homogeneous field are remarkably immune to this phase, whereas the quartic oscillator, the three-level atom, or the pair-creation process caused by a space-time field absorb the provided energy differently depending on the temporal details of the external field.

Deformable microswimmer in an external force field

External forces, such as gravity, influence swimming microorganisms. For flagellar microorganisms, such as Chlamydomonas, gravitactic swimming has been attributed to back-heaviness. Using a simple bead-spring microswimmer model, we show that back-heaviness is not necessary for the gravitactic swimming of flagellar microorganisms. The hydrodynamic interaction among beads results in the alignment of swimming direction with external force. By modulating flagellar beating patterns a microorganism can also change its swimming direction. This understanding can aid in the design of robotic swimmers.

On the modeling of a solar, wind and fossil fuel energy source by means of the thermostatted kinetic theory

This paper is devoted to the modeling of a hybrid energy distribution network with storage, within the thermostatted kinetic theory framework. The network consists of a non-renewable energy source and a renewable energy source. The energy storage is modeled by the introduction of the external force field coupled to the thermostat term. The activation parameters of the energy sources are assumed time-dependent in order to mimic the time-dependent efficiency of different specific energy sources. In particular a solar energy source, a wind energy source and a fossil fuel energy source are modeled. A computational analysis is performed to show the effects of the intermittent activation on the plan of quality improvement of the energy provided to the customers and on the construction of the energy storage. Discussions and future research perspectives are proposed in the last section of the paper.