Force Field Strength Research Articles

Effect of noninertial acceleration on heat transfer by Rayleigh–Bénard magnetoconvection: Exploring nonlinear dynamics

AbstractBuoyancy‐driven Rayleigh–Bénard convection in the presence of a magnetic field, rotation, and temperature‐dependent viscosity has applications in the field of crystal growth, space laboratory experiments, and atmospheric convection. It also has potential applications in heat transfer and magnetohydrodynamics, which can occur in planetary and stellar interiors. The present work aims to study the combined effect of magnetic fields and rotation on the onset of Rayleigh–Bénard convection in temperature‐dependent viscosity Newtonian liquids with internal heat sources/sinks. Both linear and weak nonlinear stability analyses of convection are performed in the problem. The minimal representation of the Fourier series for the stream function and the magnetic potential allows us to derive the analytical expression for the thermal Rayleigh number () and the generalized Lorenz model. In linear theory, the critical Rayleigh number and the wave number are tabulated for different values of the Chandrasekhar number (), the Taylor number (), and the thermorheological parameter (), and the onset of stability is analyzed. It is found that the instability manifests at when for stress‐free and isothermal boundaries. In nonlinear theory, the generalized Lorenz model obtained is not amenable to analytical treatment; therefore, the classical fourth‐order Runge–Kutta method is applied to solve the Lorenz model. It is found that the internal Rayleigh number, the thermorheological parameter, and the Taylor number influence the onset of convection and heat transfer coefficient. It is also demonstrated that the joint increase in rotational force and magnetic field strength stabilizes the system strongly, thereby reducing heat transfer. However, increasing the heat source and the variable viscosity parameter have antagonistic influences.

Adsorption and dynamics in cylindrical pore: Molecular dynamics and classical density functional theory study

In this work, we investigate the adsorption of single-component and binary neutral fluids in cylindrical pore using molecular dynamics simulations combined with classical density functional theory (cDFT). For the binary case, we also consider scenarios where one component exhibits a non-spherical structure. We investigated the density distribution curves of fluid components in the pore and found that the cDFT calculations without any adjustable parameter yielded results consistent with molecular dynamics simulations. This consistency becomes more pronounced as the temperature increases. At lower temperatures, the theoretical accuracy declines, but it still remains quantitatively reliable. We have developed a method for calculating diffusion coefficient in porous media involving exchange of particles between the exterior and interior of the pores, and applied the method to compute the diffusion coefficients for molecules from outside to inside the pore, as well as within the pore itself. Based on the calculated diffusion coefficients, we can draw several main conclusions: intrapore diffusion along the axial direction always decreases with increasing pore radius; increasing the surface force field strength enhances diffusion in narrow pores while reducing it in wider pores. Moreover, increasing the attraction strength between particles consistently leads to slower diffusion. These findings provide valuable insights into the factors affecting the diffusion process and can be used to optimize porous materials for various applications.

The relationship between teachers’ enacted pedagogical content knowledge and student learning in fundamental concepts of electrostatics

ABSTRACT Background It is commonly understood that teachers’ effectiveness is reflected by the performances of their students. On the other hand, teachers’ effectiveness is commonly associated with pedagogical content knowledge (PCK). Purpose This paper reports a mixed method study exploring the relationship between teachers’ PCK and evidence of student learning in fundamental concepts of electrostatics. Sample Two in-service and two pre-service teachers as well as 133 students participated in the present study. Design and methods Data reflecting teachers’ PCK was collected using classroom observations and interviews whereas evidence of student learning was explored using a performance test designed for this research. The PCK and the evidence of student learning were studied in terms of the concepts of electrostatic force, electric field, and electric field strength. The refined consensus model of PCK served as the conceptual framework for the study while the components of the topic-specific PCK model served as the analytical framework. Guided by the components, we developed a rubric to score teachers’ PCK on a four-point scale, separately for each concept. Students’ performance was also separately averaged for each concept. Quantitatively, correlation coefficients were calculated for each concept. Qualitatively, in-depth analysis of students’ test responses in the fundamental concepts was conducted in relation to teachers’ engagements with the corresponding concepts. Results The results revealed moderate correlations in terms of the concepts of electrostatic force and electric field strength whereas the correlation was weak in terms of the electric field. Furthermore, we found that the test responses of students often matched the way they were taught by their teachers, supporting the quantitative results. Conclusion Teachers’ PCK and student learning showed weak and moderate correlations that were positive and significant, suggesting that there are other factors beyond PCK that influence student learning.

Assistance control strategy for upper-limb rehabilitation robot based on motion trend

Abstract. Robot-assisted rehabilitation has proven to improve a subject's upper-extremity motor function. However, it is still challenging to control the robot to provide minimal assistance based on the subject's performance. This paper proposes a motion-trend-based assistance control strategy to solve this problem. The control strategy provides the corresponding normal and tangential forces by constructing an adaptive virtual assistance force field around a predetermined training trajectory. In the normal direction, a performance function based on the position-tracking error and normal motion trend is established to adjust the normal assistance force field strength in real time; in the tangential direction, a performance function based on the tangential interaction force and tangential motion trend is established to adjust the tangential assistance force field strength in real time. Additionally, good motion trends can quickly reduce the assistance force field. The normal motion trend represents the state of the subject moving toward the target trajectory, and the tangential motion trend represents the state of increasing tangential interaction force. Finally, the performance of this control strategy was evaluated by training experiments with eight healthy subjects. Preliminary experiments showed that the normal assist force in the active movement phase was 92.48 % smaller than that in the poor phase, and the tangential assist force was 90.73 % smaller than that in the slack phase. And the normal assist force and tangential assist force will become zero within 0.2 s when the subject has a good tendency to move. This shows that the control strategy proposed in this paper can quickly adjust the assistance according to the subject's motor performance. In addition, the assistance can be quickly reduced when the subject has a good movement trend. Future work will incorporate OpenSim (muscle and bone simulation software) to develop a pathway suitable for the subject's arm rehabilitation.

Exploring dynamic pedagogical content knowledge across fundamental concepts of electrostatics

This paper reports a case study that explored teachers’ dynamic pedagogical content knowledge (PCK) across three big ideas of electrostatics namely the electrostatic force, electric field, and electric field strength. Two pre-service and two in-service teachers participated in the study. The refined consensus model of PCK was adopted as the theoretical framework for the study. We studied PCK as enacted during classroom teaching using observations and interviews. Data was analyzed alongside a four-point scale grand PCK rubric used to score the competence of the teachers for every big idea. The results showed that PCK of the teachers varied across the big ideas, which is attributed to the nature of concepts, as well as teachers’ content knowledge in each. The findings imply that pre-service teacher education programs should involve focus on teaching specific concepts to support the development of holistic PCK for a topic.

Dynamic design of a magnetic-enhanced nonlinear energy sink

In order to improve the reliability of the nonlinear energy sink (NES), a nonlinear, non-contact magnetic force is proposed to limit the large vibration of the NES oscillator in this paper. Based on the magnetic force expression of permanent magnets, a dynamic equation of a linear oscillator (LO) equipped with the magnetic-enhanced NES (ME-NES) is established. The dynamic characteristics of the ME-NES are analyzed by approximate analytical and numerical simulations. Moreover, the experiment of the ME-NES is carried out to verify the theoretical results. The transient response and steady-state response of the LO with the ME-NES are investigated. The effects of nonlinear magnetic force, magnetic spacing, and magnetic field strength on the vibration of the NES oscillator and the LO are summarized. The results show that the limiting effect of nonlinear magnetic force is better than that of linear force. The vibration of the NES mass is evidently reduced, and the vibration suppression of the NES is significantly enhanced by the limitation of the nonlinear magnetic force. In a word, the proposed non-contact ME-NES is a reliable and efficient vibration reduction strategy, which is helpful to the design of the NES in engineering practice.

An energy-saving anti-inclined lifting permanent magnet

ABSTRACT The lifting permanent magnet is a new type of magnetic transport device consisting of a mechanical driving mechanism and a permanent magnet system. It can reduce power consumption as opposed to lifting electromagnet. However, the single-drive mechanism could not be used in the inclined condition, and how to calculate the balance working point of the magnetic circuit with several permanent magnet limits its application and development. In this paper, an anti-inclined mechanism with double drive mechanism was designed and implemented. The concentric shafts and the reversing gear were adopted to realise synchronous rotation. For the permanent magnet system, the iteration method for multi-magnets balance working point analysis is proposed and implemented. Based on the prototype experiment, the anti-inclined lifting permanent magnet hoisted a 1 ton weight workpiece successfully at an inclination angle of 30 degrees. And the measurement experiment proved that the iteration method is more precise than the conventional isolated method and is a better preparation for analysing the magnetic force and residual magnetic field strength.

Novel Magnetic Attachment System Manufactured Using High-Frequency Heat Treatment and Stamp Technique: Introduction and Basic Performance

Recently, a novel magnetic attachment with extremely low cost and high performance was developed. This article aims to introduce a novel magnetic attachment and to evaluate its basic eligibility for denture retention in clinical practice. The novel magnetic attachment system used in this study was the direct-bonding root-keeper-type Magteeth™ MT800 (MagneDesign, Nagoya, Japan). The retentive force without displacement (position 0) and after horizontal displacement to positions 0.5, 1, 1.5, 2, 2.5, and 3 mm were measured. The values relative to the retentive force without displacement were gradually decreased to 82.7 ± 16.3%, 68.8 ± 17.1%, 62.4 ± 15%, 47.2 ± 13.1%, 35.7 ± 9.9%, and 20.7 ± 6.5%, respectively. The retentive force and magnetic field strength did not change significantly after the load test (100 N load, 10,000 times). No new gap between the metal and resin was found in the root keeper- and magnet assembly-embedded blocks after the load test. Some scratches on magnetic assembly and root keeper surface, while no change in the resin texture after the load test were observed. Based on the findings of this preliminary study, this novel low-cost magnetic attachment exhibited favorable retention, strength, and durability for clinical use.

Effects of electron spatial inertia and magnetic field gradient on transport across magnetic filter

This work investigates, via particle-in-cell with Monte Carlo collision simulations, electron transport across magnetic filter (MF) in obstructed-drift plasma sources. The studied source consists of three stages, namely: the ionization stage where power is coupled to the plasma, the magnetic filter stage where the magnetic field strength is maximal and impedes electron transport, and the diffusion stage where most of the charged particles come from the first stage. The plasma source is schematized by a square whose walls (sides) are dielectric, except for the wall at the exhaust plane which is metallic and simulates a biased screen grid. As expected, our results show that as the plasma passes through the MF, electron density and temperature decrease. The electron flux and fluid velocity spatial distributions present an S-shaped path through which these plasma properties are significant. These high flux and fluid velocity are due to the superimposition of E×B and diamagnetic drifts that are enhanced by the walls. Moreover, at the entrance and exhaust of this S-shaped path, i.e., in the vicinity of the walls, the magnitude of the spatial inertia is significant in comparison to acceleration induced by an electric field and pressure gradient. The analytical analysis of this inertia shows that its magnitude and direction are mainly controlled by the gradients of the electric field, pressure force, electron density, and magnetic field strength. Therefore, the control of the spatial inertia, and thus, of electron flux across the magnetic filter, can be achieved by controlling the spatial distribution of the magnetic field strength.

Entropy generation effect of a buoyancy force on hydromagnetic heat generating couple stress fluid through a porous medium with isothermal boundaries

This investigation addresses the influence of a buoyancy force on the flow of a couple stress hydromagnetic heat generating fluid across a porous channel with isothermal boundaries. The analytical formulations for the momentum and energy equations are derived to seek the solutions for the rate of fluid momentum, heat transfer and the rate of entropy generation with the use of a well known and efficient series solution of Adomian decomposition method (ADM). The findings are compared with earlier acquired findings for validation and hereby showed the speedy convergence of the series solution. The results showed the substantial influence of inward warmth inside the stream and buoyancy force on the motion and thermal energy of the flow system. Also, the activities of entropy generation generally occur maximally at the centreline of the flow stream with significant reduction with respect to buoyancy force and magnetic field strength.

Comparing Pedagogical Content Knowledge Across Fundamental Concepts of Electrostatics: A Case of Three Pre-service Teachers

It has recently been suggested that pedagogical content knowledge (PCK) has a concept-specific nature, beyond the topic-specific level of PCK. This paper reports a case study of three pre-service teachers’ reported PCK about three fundamental concepts within the topic of electrostatics, namely electrostatic force, electric field and electric field strength. The aim of the study was to compare the quality of the PCK of each of the individual participants across these fundamental concepts. Data was collected using a content representation tool and a lesson planning form prescribed by the participants’ teacher training institution. A topic-specific PCK model was adopted as the framework for this study. The model asserts that the content of a particular topic is transformed for instruction through five components, namely learners’ prior knowledge, curricular saliency, what is difficult to teach, representations including analogies and conceptual teaching strategies. Guided by the model, we designed a rubric to assess the concept-specific PCK of the participants on a four-point scale. The results of the study indicated that the PCK of the participants varied across the fundamental concepts of electrostatics, with each participant reporting better PCK for a different concept. The results of the study imply that describing PCK at concept level is appropriate and recommend that PCK should be strengthened at concept level during teacher training to ensure that it develops across all of the concepts within a topic.

Studies of force field effects on thermal conductivity of complex plasmas

The plasma thermal conductivity of three-dimensional (3D) strongly coupled Yukawa fluids (SCYFs) has been investigated under the influence of varying external force fields through the recently improved homogenous nonequilibrium molecular dynamics (MD) approach. The effects of external field strength (F*) have been calculated along with various combinations of plasma coupling (Γ) and screening parameter (κ) on the plasma thermal conductivity of SCYFs using homogenous nonequilibrium MD (HNEMD) simulations. New investigations show that the plasma thermal conductivity of complex plasmas decreases with an increase of external force field strength and plasma coupling (Γ). Our calculations show that the decreasing behavior is noted for plasma thermal conductivity with increasing screening parameter and system size. The HNEMD simulation results under different force field strengths are in satisfactory agreement with previous numerical results of nonequilibrium MD and equilibrium MD simulations and with reference data points and it showed that the deviations are within less than ±20% for the presented results. It has been shown that our numerical results extended the range of external force field strength up to 0.001 ≤ F* ≤ 0.1 exercised in the previous work in order to establish the size of the linear regimes and to clarify the nature of linearity of 3D SCYFs.

A Computational Study of Density of Some High Energy Molecules

AbstractThe detonation pressure depends quadratically on the loading density of the explosives. A precise estimate of the density is thus crucial to decide if a novel energetic material is worth pursuing. In this work we investigate theoretically the crystal densities of the energetic compounds RDX, TNT, NTO, DNAM, CL‐20, DADNE, and HMX. We calculate the crystal densities by using Materials Studio 7.0 Polymorph Predictor, employing force fields and exploring molecular packing arrangements with minima in total energy. Geometry optimized molecular structures computed by density functional theory (DFT) are used as input to the density predictions. In an additional DFT study we apply two functionals, B3LYP and M06 with the 6‐31G(d) and the 6‐31G(d,p) basis sets, and the program package GAUSSIAN09. In this part of the work crystal densities are calculated by using the molecular isosurface volume (defined by the volume within a surface with an electron density of 0.001 electrons per Bohr3) alone or combined with the variance of the electrostatic potential (ESP). The Polymorph Predictor seems to overestimate the densities, but the values are very dependent on the force field strength determined by charges assigned to atoms. In the GAUSSIAN09 DFT study the densities derived by using the M06 functional are in similar agreement with experimental data as what we experienced for the B3LYP results, although both functionals appear to give slightly lower densities than reported experimentally for the majority of the molecules. On average, the densities derived by the ESP method correlate equally well with measured values as the results obtained by the isosurface method.

Calculations of thermal conductivity of complex (dusty) plasmas using homogenous nonequilibrium molecular simulations

The heat conductivity of three-dimensional Yukawa dusty plasma liquids (YDPLs) has been investigated by employing a homogenous nonequilibrium molecular dynamics (HNEMD) technique at a low normalized force field strength (F*). The obtained results for plasma heat conductivity with suitable normalizations are measured over a wide range of various plasma states of the Coulomb coupling (Γ) and screening length (κ) in a canonical ensemble (NVT). The calculations for lattice correlations (Ψ) show that our YDPLs system remains in a nonideal strongly coupled regime for a complete range of Γ. It has been shown that the presented Yukawa system obeys a simple analytical temperature demonstration of λ0 with a normalized Einstein frequency. The employed HNEMD algorithm is found to have a more efficient method than that of different earlier numerical methods and it gives more satisfactory results for lower to intermediate Γ with small system sizes at low F*. The obtained simulation results at nearly equilibrium F* (= 0.002) are in reasonable agreement with different earlier numerical results and with the present reference set of data showed deviations within less than ±15% for most of the present data points and generally underpredicted the λ0 by 2–22%, depending on (Γ, κ).

Nonlinear Effects of Dusty Plasmas using Homogenous Nonequilibrium Molecular Dynamics Simulations

Three-dimensional strongly coupled complex (dusty) plasma (SCCDP) is modeled using homogenous nonequilibrium molecular dynamics (HNEMD) simulations. The thermal conductivity (λ0) and the effects of external force field (F*) strength on the λ0 of SCCDP are calculated at higher screening strengths (κ) from generalized Evan’s algorithm. It has been shown that the presented investigations exhibit a non-Newtonian effect that the λ0(Γ) increases with increasing force field strength that represents interaction contributions in Yukawa conductivity. It is also verified that the results obtained with different external force filed strengths are in satisfactory agreement with earlier numerical results and with reference set of data showed deviations within less than ± 10% for most of the present data point. Our very recently computed thermal conductivity at lower &kappa is validated by comparing the results of λ0(Γ) at higher κ that also extended the range of force field strength (0.001≤F*≤ 0.1) which explains the nature of nonlinearity of SCCDP.

Molecular dynamics simulations of thermal conductivity in 2D complex Yukawa liquids

The thermal conductivity in strongly coupled complex dusty plasma liquids (SCCDPLs) has been investigated through an improved homogenous nonequilibrium molecular simulation (HNEMS) method, for the first time. The HNEMS method has been employed for two-dimensional (2D) Yukawa systems in a canonical ensemble. The thermal conductivities with suitable normalizations (plasma and Einstein frequencies), in the value of low force field strength, have been computed for a wide range of plasma state points of Coulomb coupling (Γ) and screening strength (κ). The new simulation results are found to obey the simple analytical temperature scaling law. The present HNEMS results are in generally with parts of earlier HNEMS, equilibrium molecular dynamics (EMD) and experimental data in the literature for the 2D and there-dimensional (3D) SCCDPLs. It is shown that the HNEMS method can be used to estimate the thermal conductivity very effectively and to understand the fundamental behaviours in 2D Yukawa systems.

Dynamic Linear Response Theory for Conformational Relaxation of Proteins

Dynamic linear response theory is adapted to the problem of computing the time evolution of the atomic coordinates of a protein in response to the unbinding of a ligand molecule from a binding pocket within the protein. When the ligand dissociates from the molecule, the protein molecule finds itself out of equilibrium and its configuration begins to change, ultimately coming to a new stable configuration corresponding to equilibrium in a force field that lacks the ligand-protein interaction terms. Dynamic linear response theory (LRT) relates the nonequilibrium motion of the protein atoms that ensues after the ligand molecule dissociates to equilibrium dynamics in the force field, or equivalently, on the potential energy surface (PES) relevant to the unliganded protein. In general, the connection implied by linear response theory holds only when the ligand-protein force field is small. However, in the case where the PES of the unliganded protein system is a quadratic (harmonic oscillator) function of the coordinates, and the force of the ligand upon the protein molecule in the ligand-bound conformation is constant (the force on each atom in the protein is independent of the location of the atom), dynamic LRT is exact for any ligand-protein force field strength. An analogous statement can be made for the case where the atoms in the protein are subjected to frictional and random noise forces in accord with the Langevin equation (to account for interaction of the protein with solvent, for example). We numerically illustrate the application of dynamic LRT for a simple harmonic oscillator model of the ferric binding protein, and for an analogous model of T4 lysozyme. Using a physically appropriate value of the viscosity of water to guide the choice of friction parameters, we find relaxation time scales of residue-residue distances on the order of several hundred ps. Comparison is made to relevant experimental measurements.

Dependence of A-RNA simulations on the choice of the force field and salt strength

We present an extensive molecular dynamics study (0.6 micros in total) on three A-RNA duplexes. The dependence of the A-RNA geometry on force fields (Parm99 and Parmbsc0) and salt strength conditions (approximately 0.18 M net-neutralizing Na(+) and approximately 0.3 M KCl) was investigated. The Parmbsc0 force field makes the A-RNA duplex more compact in comparison to the Parm99 by preventing temporary alpha/gamma t/t flips common in Parm99 simulations. Nevertheless, since the alpha/gamma t/t sub-state occurs to certain extent in experimental A-RNA structures, we consider both force fields as viable. The stabilization of the A-RNA helices caused by the Parmbsc0 force field includes visible reduction of the major groove width, increase of the base pair roll, larger helical inclination and small increases of twist. Therefore, the Parmbsc0 shifts the simulated duplexes more deeply into the A-form. Further narrowing of the deep major groove is observed in excess salt simulations, again accompanied by larger roll, inclination and twist. The cumulative difference between Parm99/lower-salt and Parmbsc0/higher-salt simulations is approximately 4-8 A for the average PP distances, and -0.7 to -2.5 degrees, -2.0 to -5.4 degrees, -2.6 to -8.6 degrees and 1.7 to 7.0 degrees for the twist, roll, inclination and propeller, respectively. The effects of the force field and salt condition are sequence-dependent. Thus, the compactness of A-RNA is sensitive to the sequence and the salt strength which may, for example, modulate the end-to-end distance of the A-RNA helix. The simulations neatly reproduce the known base pair roll re-distribution in alternating purine-pyrimidine A-RNA helices.

Rapid Adaptation to Scaled Changes of the Mechanical Environment

We investigated adaptation to simple force field scaling to determine whether the same strategy is used as during adaptation to more complex changes in the mechanical environment. Subjects initially trained in a force field, consisting of a rightward lateral force with a parabolic spatial profile (PF). The field strength was then unexpectedly increased or decreased (DeltaPF) for repeated sets of five consecutive trials, with intervening PF trials. Stiff elastic walls, which prevented lateral movement of the arm, randomly replaced 25% of DeltaPF trials. Lateral deviation on DeltaPF trials and lateral force against the elastic walls were used to assess the extent to which feedforward adaptations could be attributed to changes in lateral force or increased stiffness of the arm. When force field strength was increased or decreased hand paths were perturbed to the right or left, respectively. Performance error was significantly reduced between the first and second DeltaPF trial positions of the set, whereas the lateral force impulse exerted against the elastic walls did not change until the third trial position. The lateral force was scaled upward or downward in response to the change in force field strength, suggesting a gradual change in the internal model. The results support a dual strategy of cocontraction (increased stiffness) and internal model modification. The development of an accurate internal model is a slower process than cocontraction and error reduction. This may explain the need to represent motor learning as two parallel processes with varying timescales, as recently proposed by Smith and colleagues.

Blood progenitor cell separation from clinical leukapheresis product by magnetic nanoparticle binding and magnetophoresis

Positive selection of CD34+ blood progenitor cells from circulation has been reported to improve patient recovery in applications of autologous transplantation. Current magnetic separation methods rely on cell capture and release on solid supports rather than sorting from flowing suspensions, which limits the range of therapeutic applications and the process scale up. We tested CD34+ cell immunomagnetic labeling and isolation from fresh leukocyte fraction of peripheral blood (leukapheresis) using the continuous quadrupole magnetic flow sorter (QMS), consisting of a flow channel (SHOT, Greenville, IN) and a quadrupole magnet with a maximum field intensity (B(o)) of 1.42 T and a mean force field strength (S(m)) of 1.45 x 10(8) TA/m(2). Both the sample magnetophoretic mobility (m) and the inlet and outlet flow patterns highly affect the QMS performance. Seven commercial progenitor cell labeling reagent combinations were quantitatively evaluated by measuring magnetophoretic mobility of a high CD34 expression cell line, KG-1a, using the cell tracking velocimeter (CTV). The CD34 Progenitor Cell Isolation Kit (Miltenyi Biotec, Bergisch Gladbach, Germany) showed the strongest labeling of KG-1a cells and was selected for progenitor cell enrichment from 11 fresh and 11 cryopreserved clinical leukapheresis samples derived from different donors. The CD34+ cells were isolated with a purity of 60-96%, a recovery of 18-60%, an enrichment rate of 12-169, and a throughput of (1.7-9.3) x 10(4) cells/s. The results also showed a highly regular dependence of the QMS performance on the flow conditions that agreed with the theoretical predictions based on the CD34+ cell magnetophoretic mobility.