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The Lamb shift, one of the most fundamental interactions in atomic physics, arises from the interaction of H atoms with the electromagnetic fluctuations of the quantum vacuum. The energy shift has been computed in a variety of ways. The energy shift, as Feynman, Power, and Milonni demonstrated, equals the change in the vacuum energy in the volume containing the H atoms due to the change in the index of refraction arising from the presence of the H atoms. Using this result and a group theoretical calculation of the contribution to the Lamb shift from each frequency of the vacuum fluctuations, in this paper we obtain an expression for the region of the vacuum energy for each frequency ω around the H atom due to the Lamb shift. This same field plays an essential role in the van der Waals force. We show the ground state atom is surrounded by a region of positive vacuum energy that extends well beyond the atom for low frequencies. This region can be described as a steady state cloud of vacuum fluctuations. For energies E = ℏ ω less than 1 eV, where ℏ is the reduced Planck constant and ω is frequency, the radius of the positive energy region is shown to be approximately 14.4/E Å. For a vacuum fluctuation of wavelength, λ , the radius is (α / 2 π) λ , where α is the fine-structure constant. Thus, for long wavelengths, the region has macroscopic dimensions. The energy–time uncertainty relation predicts a maximum possible radius that is larger than the radius based on the radiative shift calculations by a factor of 1 / 4 α . [ABSTRACT FROM AUTHOR]

This paper proposes a hybrid algorithm based on the ant colony and Physarum Polycephalum algorithms. The positive feedback mechanism is used to find the globally optimal path. The crossover and mutation operations of the genetic algorithm are introduced into the path search mechanism for the first time. The Van der Waals force is applied to the pheromone updating mechanism. Simulation results show that the improved algorithm has advantages in quality and speed of solution compared with other mainstream algorithms. This paper provides fast and accurate route methods for solving the Traveling Salesman Problem first and a delivery scheme is also presented for UAVs to realize "contactless delivery" to users in the Changchun Mingzhu District during the COVID-19 epidemic, which confirms the practicability and robustness of the algorithm. [ABSTRACT FROM AUTHOR]

Casimir–van der Waals forces are important in the self-assembly processes of nanoparticles. In this paper, using a hybrid approach based on Lifshitz theory of Casimir–van der Waals interactions and corrections due to the shape of the nanoparticles, it is shown that for non-spherical nanoparticles, the usual Hamaker approach overestimates the magnitude of the interaction. In particular, the study considers nanoplates of different thicknesses, nanocubes assembled with their faces parallel to each other, and tilted nanocubes, where the main interaction is between edges. [ABSTRACT FROM AUTHOR]

The coal deformation was induced by the gas adsorption of N2, CH4, and CO2. However, the differences between different gas adsorption performances and the deformation mechanism of coal need to be further studied. In this study, the experiments were conducted using self‐developed equipment to reveal the adsorption characteristics of different gases. The results showed that the gas adsorption capacity followed the sequence of CO2 > CH4 > N2. The gas adsorption capacity was negatively correlated with temperature. The maximum decrease in adsorption capacity (23.70%) was N2. The gas adsorption capacity was positively correlated with gas pressure. The maximum increase in gas adsorption capacity (232.79%) was N2. Correspondingly, the coal deformation of CO2 was the largest, and that of N2 was the smallest. The maximum decrease in deformation (31.09%) was CO2 during the temperature increase. The initial coal deformation rates of N2, CH4, and CO2 were 0.060, 0.091, and 0.042 mm·h−1, respectively. The maximum increase of deformation (234.65%) was CH4 with the gas pressure increase. The initial coal deformation rates of N2, CH4, and CO2 were 0.024, 0.045, and 0.016 mm·h−1, respectively. This work guided further clarifying the mechanism of different gases' adsorption capacity and coal deformation. [ABSTRACT FROM AUTHOR]

Recent studies have revealed the importance of powder transport by gas-phase flows in the laser-interaction zone in laser powder bed additive manufacturing. The understanding of such a mass transfer mechanism is necessary for developing and optimizing laser-assisted processes of additive manufacturing. Powder bed surface relief around the remelted track is experimentally characterized by metallography and laser scanning profilometry in single-track experiments with powders of various materials and various particle sizes. Denudation zones with sharp irregular boundaries containing particle agglomerates are observed for finer powders with smaller particles. Denudation zones without well-defined boundaries containing single particles are observed for coarser powders. The balance of forces applied to a particle is theoretically analyzed to understand powder rearrangement in the laser-interaction zone. The drag force is estimated by a similarity point-source model of the entrainment flow with a correction for the finite size of the evaporation spot. The adhesion force appears to be greater than the gravity one for the fine powders and lower than the gravity for the coarse powders, thus explaining the observed difference in the denudation zone morphology. The measured variation of the denudation width with the material properties and the particle size is consistent with the theoretical predictions. [ABSTRACT FROM AUTHOR]

Investigation on the adhesion effect of lunar dust particles on contacting interface improves in lunar dust protection and prolongs the equipment service life. In this work, the contact mathematical adhesion model between an ultra-fine lunar dust particle and the aluminum-based rough surface is established based on the fractal theory. The research shows that the van der Waals force dominates adhesion force for ultra-fine lunar dust particles in space environment and is directly related to the rough surface fractal parameters, namely the fractal dimension parameter D , fractal roughness G as well as root-mean-square roughness(rms). Based on van der Waals adhesion model, the optimum rough surface fractal parameters are obtained through model optimization when the van der Waals force is minimal. The van der Waals forces reaches the minimum for lunar dust particle with diameters of 500 nm and 2.5 μm when the rms is 2.689 nm and 4.7 nm respectively. To validate the effectiveness of using fractal theory to the surface topography in van der Waals force calculation, the dust residual rates have been compared with the aluminum surfaces prepared using chemical etching method, electrochemical etching method, and combined chemical method. Based on the AFM topography of the surfaces, the van der Waals forces have been calculated between the lunar dust particles and the surfaces prepared using different etching methods. The centrifugal experiments suggest that van der Waals force is positively related to the dust residual rates. In summary, the fractal theory is effective in describing the surface roughness in lunar dust adhesion problems and it can be used in future lunar dust protection surface design and applications. [ABSTRACT FROM AUTHOR]

[Display omitted] Analytical expressions for calculating Hamaker constant (HC) and van der Waals (VDW) energy/force for interaction of a particle with a solid water interface has been reported for over eighty years. This work further developed novel analytical expressions and numerical approaches for determining HC and VDW interaction energy/force for the particle approaching and penetrating air–water interface (AWI), respectively. The expressions of HC and VDW interaction energy/force before penetrating were developed through analysis of the variation in free energy of the interaction system with bringing the particle from infinity to the vicinity of the AWI. The surface element integration (SEI) technique was modified to calculate VDW energy/force after penetrating. We explain why repulsive VDW energy exists inhibiting the particle from approaching the AWI. We found very significant VDW repulsion for a particle at a concave AWI after penetration, which can even exceed the capillary force and cause strong retention in water films on a solid surface and at air–water-solid interface line. The methods and findings of this work are critical to quantification and understanding of a variety of engineered processes such as particle manipulation (e.g., bubble flotation, Pickering emulsion, and particle laden interfaces). [ABSTRACT FROM AUTHOR]

[Display omitted] • CsPbBr 3 with quantum-limited domain effects have reversible hydrochromic properties. • Different Organic solvents cause polarity-related discoloration of composites. • A detection model was developed for all-organic solvent polarity detection. Hydrochromic materials have received much attention in anticounterfeiting due to their reversible photoemission properties toward water. However, existing hydrochromic materials usually suffer from slow hydrochromic response and limited stability, repeatability, and color tunability. This paper found for the first time that CsPbBr 3 /Cs 4 PbBr 6 composites with quantum-limited domain effects had reversible hydrochromism. CsPbBr 3 /Cs 4 PbBr 6 composites were successfully synthesized in molecular sieve MCM-41 using an improved mechanochemical method. The composites underwent a reversible phase transition from Cs 4 PbBr 6 /CsPbBr 3 to CsPbBr 3 upon treatment with a trace amount of water, the photoluminescence colors underwent a change from blue to green, and reversion occurred due to heating. Mechanistic investigation revealed that quantum dots underwent soft agglomeration due to van der Waals forces in polar solvent environments, affecting the action of quantum domain-limiting effects. Therefore, organic solvents with different polarities can cause different degrees of reversible discoloration of the material. This study provides new ideas for understanding the phase transition and agglomeration of metal halide perovskite quantum dots in polar solvent environments. Additionally, it offered new options for aqueous color-changing materials and organic solvent polar detection materials. [ABSTRACT FROM AUTHOR]

[Display omitted] Wettability effect has long been a concern in various aqueous lubrication systems including biological and industrial applications. The wettability may affect lubrication performance by changing interfacial viscosity or hydration force. The key point to reveal the mechanism is to design an ideal experimental system to exclude other bulk factors other than surface wettability. In this work, silicon surfaces with different treatments were used to study the single factor effect of wettability on aqueous lubrication. The normal and friction forces of these surfaces were quantified by atomic force microscopy (AFM) in water environment. The interfacial viscosity was evaluated according to the probe dynamic approaching process. Macroscale and microscale lubrication experiments of other materials were also conducted as verification and supplement. A semi-quantitative relationship between friction and wettability was revealed and attributed to the competition between the attractive van der Waals interactions and wettability-dependent repulsive hydration interaction, which determined the strength of the adhesive interaction and dominated the sliding energy dissipation. The contribution of viscous effect of water was considered to be relatively minor. The findings provide an in-depth understanding of aqueous lubrication and outline important guidelines for tuning adhesion and friction. [ABSTRACT FROM AUTHOR]

We developed a method of measuring microscopic ζ potential (ZP) from force vs distance (FD) curves observed by atomic force microscope (AFM). ZP in microscopic regions on wafer surfaces may be one of the most important design guides of chemical mechanical polishing slurries applicable to ultrafine patterned wafers, while ZP is generally observed as an average information for a wide area. Our method is based on the linear correlation between jump-in loads in FD curves observed by the AFM for the blanket wafers (SiO2, SiN and poly-Si) in water systems and ZP of each wafer surface measured by the flow potential method. In the applications of our AFM-based measurement method, material-dependency of ZP on the SiO2/SiN patterned wafer surface and an additive material in a slurry (anionic polymer) adsorbing selectively on the SiN surface of the SiO2/SiN patterned wafer were observed. [ABSTRACT FROM AUTHOR]

• Stable Pickering emulsion stabilized by pristine TiO 2 nanoparticles was developed. • Emulsions were stabilized by van der Waals force of hydrophilic TiO 2 nanoparticles. • New composite beads were prepared with the obtained vdW -Pickering emulsion. • The composite materials showed high UV blocking ability and enhanced photostability. • Pickering emulsion stabilizing method developed here is simple, general and green. Highly hydrophilic nanoparticles are generally considered not suitable for stabilizing Pickering emulsions, since they could not be effectively wetted by the oil phase at the water-oil interface. However, highly hydrophilic nanoparticles with good dispersity are possibly absorbed and packed onto the surface of the oil droplets in water via the van der Waals attraction between the nanoparticles and the oil droplets. Hence, a novel " van der Waals emulsion" should be possible to be stabilized by highly hydrophilic nanoparticles. Oil-in-water emulsions solely stabilized by pristine TiO 2 nanoparticles (i.e., TiO 2 without any modification or additives) were prepared. The emulsification behavior under varying pH value, oil fraction, particle content and temperature of the emulsion were explored. Composite wax-based beads which encapsulated chemical sunscreen and was coated by TiO 2 nanoparticles, was also fabricated using the obtained emulsion as the templates. The emulsions displayed the highest stability near the isoelectric points of the TiO 2 nanoparticles, which was attributed to the van der Waals attraction between TiO 2 nanoparticles and oil droplets. Such mechanism was supported by a theoretical analysis based on calculation of the Hamaker constants and experimental evidences. Therefore, this work presents a simple, general and green method for preparing particle-stabilized emulsions. [ABSTRACT FROM AUTHOR]

Thin polymeric coatings are commonly used for altering surface properties and modulating the interfacial performance of materials. Possible contributions from the substrate to the interfacial forces and effects are, however, usually ignored and are not well understood, nor is it established how the coating thickness modulates and eventually eliminates contributions from substrates to the van der Waals (vdW) interfacial force. In this study we quantified, by colloid-probe atomic force microscope (AFM) and by theoretical calculations, the interfacial vdW contributions from substrates acting through ethanol plasma polymer (EtOHpp) coatings of a range of thicknesses on Au and Si bulk materials. In approach force curves against EtOHpp-coated Au substrates the magnitude of the vdW force decreased as the EtOHpp coating thickness increased to 18 nm and then plateaued with further increases in coating thickness, providing direct evidence for a contribution to the total interfacial vdW force from the Au substrate acting through thin coatings. The experimental observations accord with theoretical calculations of the thickness dependence of Hamaker coefficients derived from rigorous simulation using the Lifshitz theory. In addition, the measured forces agree well with theoretical predictions including correction for finite roughness. Thus, our experimental and theoretical results establish how the thickness of polymer thin film coatings modulates the total interfacial vdW force and how this can be used to tune the net vdW force so as to either contain a large substrate contribution or arise predominantly from the polymeric overlayer. Our findings enable rational design of coating thickness to tailor interfacial interactions and material performance. [ABSTRACT FROM AUTHOR]

• The SPH method is developed to model the van der Waals force. • We utilize SPH to simulate the rupture of thin liquid film without resort to lubrication theory. • We introduce the coordinate transformation in SPH to handle the rupture of thin liquid films. • Both van der Waals force and surface tension are imposed on the outmost layer of SPH particles. The rupture of thin liquid films driven by the van der Waals force is of significance in many engineering processes, and most previous studies have relied on the lubrication approximation. In this paper, we develop a smoothed particle hydrodynamics (SPH) representation for the van der Waals force and simulate the rupture of thin liquid films without resort to lubrication theory. The van der Waals force in SPH is only imposed on one layer, i.e., the outermost layer of fluid particles, where a weighting function is deployed to evaluate the contributions of particles on or near the interface. However, to obtain an accurate hydrostatic pressure in reaction to the van der Waals force, a smaller smoothing length is used for the calculation of the weighting function than that used for SPH discretizations of the bulk fluid. The same surface particles are also used to model the surface tension. To deal with the rupture of a thin liquid film with a very small aspect ratio ε (ε = thickness/length), a coordinate transformation is introduced to shrink the length of the liquid film to achieve accurate numerical resolution with a manageable number of particles. As verifications of our physical model and numerical algorithm, we simulate the hydrostatic pressure in a stationary film and the relaxation of an initially square droplet and compare the SPH results with the analytical solutions. The method is then applied to simulate the rupture of thin liquid films with moderate and small aspect ratios (ε = 0.5 and 0.005). The convergence of the method is verified by refining particle spacing to four different levels. The effect of the capillary number on the rupture process is analyzed. [ABSTRACT FROM AUTHOR]

In this work, nonlinear vibration and frequency response analysis of a double-walled piezoelectric nanoresonator based on a cylindrical nanoshell is performed using the Gurtin–Murdoch surface/interface theory. The piezoelectric nanoresonator is simultaneously subjected to the visco-Pasternak medium and nonlinear van der Waals and electrostatic forces. It is found that the electrostatic and piezoelectric voltages, length to radius ratio, nanoresonator gap width, linear and nonlinear van der Waals coefficients and other parameters can effectively change the flexural rigidity of the system, which in turn affects the nonlinear frequency response. Also, increasing or decreasing of some parameters leads to increase or decrease in the resonance amplitude, resonant frequency, instability of the system, nonlinear behavior and bandwidth. [ABSTRACT FROM AUTHOR]

• The mechanical behavior of a clamped–clamped microbeam with middle paddle is analyzed. • The pull in voltage declines and the deflection enlarges as the intermolecular forces increase. • Presence of the electrostatic force accelerated the instability resulting from the capillary force. • Fringing field effect considerably affected determination of the bifurcation points. The present study is aimed to investigate pull-in instability, static deformation, natural frequency, primary and subharmonic resonances in the clamped–clamped microbeam with middle T-shaped paddle in presence of electrostatic force, Casimir force, van der Waals force and fringing field effect; besides, it is focused on investigating the effect of capillary force on instability and adhesion considering the effects of middle layer elongation and axial force. The microbeam is modeled as an Euler Bernoulli beam. In order to solve the nonlinear equations, the Galerkin-based rank reduction method was used. The discretized equations are solved by the perturbation theory in the neighborhood of primary and subharmonic resonances. The obtained results showed that the van der Waals and Casimir forces had attractive nature and led to the increased static deformation as well as occurrence of the pull-in at lower voltages; besides, the effects of attraction in Casimir was more than that in van der Waals. Results showed that with increase in the dimensionless length, which is influenced by the capillary force, the maximum static deformation was increased as well, leading to instability in capillary coefficients. Furthermore, presence of the electrostatic force also accelerated the instability resulting from the capillary force. Effects of the axial force and elongation in the clamped state resulted in the reduced static deformation as well as delayed instability. It is shown that changing the Casimir and Van der Waals forces as well as the fringing field effect, in addition to causing changes in the voltage and range, considerably affected determination of the bifurcation points. To validate the analytical results, numerical simulation is performed. [ABSTRACT FROM AUTHOR]

Four polyacrylate resins (PARs) with different side chain were successfully prepared, which can selectively adsorb organics with moderate polarity (dielectric constant ranging from 2.21 to 21). PARs can also selectively remove low concentration of toluene (5 ppm) and chloroform (1 ppm) in water with maximum removal efficiencies of 98.16% and 95.65%, and the treated wastewater meet the requirements of world health organization (WHO). [Display omitted] • Four polyacrylate resins (PARs) with different side chain were prepared. • PARs can selectively adsorb organics with moderate polarity. • PARs can selectively remove dissolved organics with moderate polarity in water. • Van der Waals interaction is the main driving force of PARs for organic adsorption. Efficient removal of trace amounts of dissolved organics with moderate polarity (DOMP) in water via adsorption method is a challenge. Most typical adsorption materials such as activated carbon exhibits poor selectivity and few polymers can remove DOMP in water. Herein, four polyacrylate resin (PAR)-based materials with different side chain are successfully fabricated, which can selectively adsorb pure organics with moderate polarity (dielectric constant ranging from 2.21 to 21). Interestingly, PARs can also selectively remove low concentration of toluene (5 ppm) and chloroform (1 ppm) in water with maximum removal efficiencies of 98.16% and 95.65%, respectively. Molecular dynamic (MD) simulations reveals that the driving force and selectivity of the adsorption behaviors can be attributed to the van der Waals interactions between the side chain of PARs and organics. Our study provides a designing strategy and novel material for efficient removal of organic pollutants with trace amounts in water. [ABSTRACT FROM AUTHOR]

3D printing or assembly techniques in the micro/nano-world enable production of micro-parts for building small machines or structures for biomedicine applications, such as cultivation of living cells in the field of Tissue Engineering. Micro-sized assembly requires automated manipulation procedures and methods for determination of suitable objects for assembly. The latter is possible by van der Waals force measurement and determination of distance at the van der Waals peak between two objects in contact. They are dependent not only on the Hamaker coefficients of the materials in contact and their geometries, but also on the nano-roughness asperities and crystal structure asperities of the contact surfaces. A method is presented for measuring van der Waals force and determining micro-objects' (sizes between 10-100 μm) distances between materials in contact at the van der Waals peak in the presence of nano-roughness and crystal structure roughness. The proposed model was validated by experimental lab results between various materials and shapes (glass and polystyrene beads, metallic wires). [ABSTRACT FROM AUTHOR]

Quinone outside inhibitors (QoIs), which inhibit the mitochondrial respiratory system by binding to the Qo site of Complex III in fungi, are widely used as pesticides with broad spectrum antifungal activity. However, excessive use of QoIs leads to pesticide resistance through mutation of amino acid residues in the Qo site. Recently, metyltetraprole, a novel QoI that is effective against wild-type and resistant mutant fungi, was developed. Interestingly, metyltetraprole has a very similar structure to other QoIs, azoxystrobin and pyraclostrobin, which do not act on resistant mutants. However, it is unknown how slight structural differences in these inhibitors alter their effectiveness towards fungi with amino acid mutations in the Qo site of Complex III. Therefore, we studied the features of interactions of inhibitors effective towards resistant mutants by quantitatively comparing the interaction profiles of three QoIs at the atomic level. First, we reproduced the binding affinity by the thermodynamic integration (TI) method, which treated explicitly environmental molecules and considered the pseudo-binding pathway. As such, a good correlation (R2 = 0.74) was observed between the binding free energy calculated using the TI method and experimentally observed pIC50 value in 12 inhibitor-target pairs, including wild-type and mutant Complex III in two fungal species, Zymoseptoria tritici and Pyrenophora teres. Trajectory analysis of this TI calculation revealed that the effectiveness against resistant mutant fungi strongly depended on the interaction of constituent parts of the inhibitor disposed near the active center of the target protein. Specifically, the key in the effectiveness against resistant mutant fungi is that the corresponding component part, tetrazolinone moiety of metyltetraprole, traded off Coulomb and van der Waals interactions in response to subtle changes in the binding pose. [ABSTRACT FROM AUTHOR]

With the development of NEMSs (nano-electro-mechanical systems), the size-dependent behavior has been an active topic. The scale parameter seems an essential factor dominating mechanical behavior at nanoscale. However, is it always dominant? This is a question deserving careful investigation. For this reason, the buckling of a bi-layered PE (piezoelectric) nanobeam is analyzed. The main purpose is to reveal and compare the effects of the nonlocal scale, imperfect interface, interlaminar van der Waals force and loading ratio. The imperfect interface is modeled by normal and shear springs, and the van der Waals force is represented by the Hamaker formula. Based on the principle of virtual work, the analytical solution of the critical buckling loading is derived by using the trigonometric shear deformation theory. After the verification in some degenerated cases, parametric studies are conducted. It is indicated that if the nonlocal parameter varies in the typical range [0, 4 nm^2], it only has quite limited effect on the buckling behavior, as compared with the other three factors. In this case, although the buckling relies on the nonlocal scale, it is far more dependent on the conventional non-nanoscale factors. The conclusions can provide references for optimal design of NEMSs. [ABSTRACT FROM AUTHOR]

This paper investigates the mechanical properties of CNT-reinforced composites via meshless method, and material nonlinearity of its constituents is considered. An equivalent continuum simulation is employed to evaluate the microstructure of CNTs, based on that, both two-dimensional simplified and three-dimensional models are introduced separately. A plasticity model is adopted in the interface between reinforcement and matrix. The effect of van der Waals forces between CNTs is also considered by uniformly aligned transverse springs, which are continuously connected to nanotubes along their length. Parametric studies of the mechanical properties with varying spring stiffness are carried out to prove the suitability of Winkler’s multi-spring model. The governing equations of motion are obtained by establishing energy functional, and displacement fields in the spatial domain are discretized by the moving least-squares (MLS) approximation. The effects of length of reinforcement, node distribution and influence domain are also investigated, and the stability and precision of the presented meshless method are validated by convergence and comparison studies. [ABSTRACT FROM AUTHOR]

A number of experiments on fluid flow at the micro/nano-scale have demonstrated that flow velocity obviously deviates from the classical Poiseuille's law due to the micro forces between the wall and the fluid. Based on an oil--water two-phase network simulation model, a three-dimensional pore-scale micro network model with solid--liquid interfacial effects was established. The influences of solid--liquid interface effects including van der Waals force and wettability on the residual oil distribution and relative permeability were investigated through microscopic simulation. The effects of pore radius, pore--throat size ratio, shaping factor, and coordination number on the residual oil distribution were analyzed at the same time. The results showed that the oil recovery would be overestimated by about 4% without van der Waals force in a water-wet reservoir. The impact of van der Waals force on water-wet reservoirs was significantly obvious in contrast with oil-wet reservoirs. In addition, the residual oil distribution was significantly influenced by pore radius in water-wet reservoir, comparatively influenced by pore--throat size ratio in oil-wet reservoir. The present study illustrates the successful application of three-dimensional micro network models considering solid--liquid interfacial effects, and provides new insights for oil recovery enhancement. [ABSTRACT FROM AUTHOR]

This paper aims at investigating free vibrations and stability of double-walled carbon nanotube (DWCNT)-based spinning nanobearings. The so-called nanobearing consists of two coaxial carbon nanotubes (CNTs) where either of the two CNTs can be a rotor while the other takes the role of stator. Euler-Bernoulli beam model along with the Eringen's nonlocal theory of elasticity are employed to obtain governing equations of transverse vibrations for the CNTs. The coupling of the two CNTs originates from the van-der-Waals (vdW) forcing present in the interface of the two CNTs. The coupling is taken into account as distributed spring foundation with an equivalent elastic stiffness. Based on the obtained model, effects of small-scale parameter, vdW interaction between CNTs and the diameter ratio of CNTs on the critical spinning speed are investigated. Finally, the stability margins of the nanobearings are determined and some general conclusions are drawn. [ABSTRACT FROM AUTHOR]

This research is on the dynamics of electrostatically actuated radial-contour mode microring resonators. The governing equation of motion is derived by the minimization of the Hamiltonian and generalized to include the viscous damping effect. The Galerkin method is used to discretize the distributed-parameter model of the considered ring resonator. The periodic solutions in the vicinity of fundamental natural frequency are determined by means of shooting method; the stability of the periodic orbits are investigated by determining the well-known Floquet exponents of the perturbed motions. The influences of intermolecular forces such as van der Waals and Casimir on the dynamic behavior of the resonator are investigated. The natural frequencies and mode shapes of the ring are calculated for various values of ratio of radii (β). The effect of the design parameters including ring radius, electrostatic voltage and quality factor on the dynamic responses, is discussed. The results of present study can be used in the design of novel MEMS resonators, RF filters and channelizers. [ABSTRACT FROM AUTHOR]

There are great opportunities in the manipulation of bacterial mechanosensitive (MS) ion channels for specific and targeted drug delivery purposes. Recent research has shown that these ion channels have the potential to be converted into nanovalves through clever use of magnetic nanoparticles and magnetic fields. Using a combination of molecular dynamics (MD) simulations and the finite element (FE) modelling, this study investigates the theoretical feasibility of opening the MscL channel (MS channel of large conductance of E. coli) by applying mechanical force directly to its N-terminus. This region has already been reported to function as a major mechanosensor in this channel. The stress-strain behaviour of each MscL helix was obtained using all atom MD simulations. Using the same method, we simulated two models, the wild-type (WT) MscL and the G22N mutant MscL, both embedded in a POPE lipid bilayer. In addition to indicating the main interacting residues at the hydrophobic pore, their pairwise interaction energies were monitored during the channel gating. We implemented these inputs into our FE model of MscL using curve-fitting codes and continuum mechanics equations. In the FE model, the channel could be fully opened via pulling directly on the N-terminus and bottom of TM1 by mutating dominant van der Waals interactions in the channel pore; otherwise the stress generated on the channel protein can irreversibly unravel the N-secondary structure. This is a significant finding suggesting that applying force in this manner is sufficient to open an MscL nanovalve delivering various drugs used, for example, in cancer chemotherapy. More importantly, the FE model indicates that to fully operate an MscL nanovalve by pulling directly on the N-terminus and bottom of TM1, gain-of-function (GOF) mutants (e.g., G22N MscL) would have to be employed rather than the WT MscL channel. [ABSTRACT FROM AUTHOR]

In this paper we derive explicit expressions for the Green’s functions in the case of an anisotropic elastic half-space and bimaterial subjected to a line force and a line dislocation. In contrast to previous studies in this area, our analysis includes the contributions of both anisotropic surface elasticity and surface van der Waals interaction forces. By means of the Stroh sextic formalism, analytical continuation and the state-space approach, the corresponding boundary value problem is reduced to a system of six (for a half-space) or 12 (for a bimaterial) coupled first-order differential equations. By employing the orthogonality relations among the corresponding eigenvectors, the coupled system of differential equations is further decoupled to six (for a half-space) or 12 (for a bimaterial) independent first-order differential equations. The latter is solved analytically using exponential integrals. In addition, we identify four and seven non-zero intrinsic material lengths for a half-space and a bimaterial, respectively, due entirely to the incorporation of the surface elasticity and surface van der Waal forces. We prove that these material lengths can be only either real and positive or complex conjugates with positive real parts. [ABSTRACT FROM AUTHOR]

Phonons (collective atomic vibrations in solids) are more effective in transporting heat than photons. This is the reason why the conduction mode of heat transport in nonmetals (mediated by phonons) is dominant compared to the radiation mode of heat transport (mediated by photons). However, since phonons are unable to traverse a vacuum gap (unlike photons), it is commonly believed that two bodies separated by a gap cannot exchange heat via phonons. Recently, a mechanism was proposed [J. B. Pendry, K. Sasihithlu, and R. V. Craster, Phys. Rev. B 94, 075414 (2016)] by which phonons can transport heat across a vacuum gap - through the Van der Waals interaction between two bodies with gap less than the wavelength of light. Such heat transfer mechanisms are highly relevant for heating (and cooling) of nanostructures; the heating of the flying heads in magnetic storage disks is a case in point. Here, the theoretical derivation for modelling phonon transmission is revisited and extended to the case of two bodies made of different materials separated by a vacuum gap. Magnitudes of phonon transmission, and hence the heat transfer, for commonly used materials in the micro- and nano-electromechanical industry are calculated and compared with the calculation of conduction heat transfer through air for small gaps as well as the heat transfer calculation due to photon exchange. [ABSTRACT FROM AUTHOR]

In this work, discrete element method (DEM) is used to study the effect of particle size and aspect ratio on packing structure of fine ellipsoids. It shows that porosity and coordination number significantly change with particle size and shape. The porosity-aspect ratio curve has minima at around 0.5 for oblate spheroids and 1.5 for prolate spheroids, but the cusp at 1.0 varies from convex to concave when particle size reduces as a result of the increasing role of the cohesive forces between particles. The coordination number-aspect ratio curves change from a strong to weak “M” shape when particle size reduces. Based on the results, equations are formulated to describe the correlation between bed porosity, aspect ratio, and particle size or force ratio. Microscopically, the radial distribution function is also affected by both particle size and shape. Fine particles have more disordered structure than coarse particles, and the packing of fine spheres is more ordered than fine ellipsoids. For coarse ellipsoids, majority of particles tend to orient horizontally, but the preferred orientation become worse when reducing particle size. [ABSTRACT FROM AUTHOR]

Parkinson’s disease (PD) is characterized by the progressive degeneration of the dopaminergic neurons in the substantia nigra (SN) region. Acteoside has displayed multiple biological functions. Its potential role against PD and the underlying signaling mechanisms are largely unknown. Here, we showed that oral administration of acteoside significantly attenuated parkinsonism symptoms in rotenone-induced PD rats. Further, acteoside inhibited rotenone-induced α-synuclein, caspase-3 upregulation and microtubule-associated protein 2 (MAP2) downregulation in PD rats. The molecular docking and molecular dynamics (MD) simulation results indicated that acteoside may directly bind to and inhibit caspase-3. Acteoside formed hydrogen bonds with at least six residues of caspase-3: ThrA177, SerA178, GlyA238, SerB339, ArgB341 and TrpB348. In addition, a pi-pi interaction was formed between acteoside and caspase-3’s HisA237, which might further stabilize the complex. MD simulation results demonstrated that the binding affinity of the caspase-3-acteoside complex was higher than that of caspase-3 and its native ligand inhibitor. Together, we show that acteoside binds to caspase-3 and exerts neuroprotection in the rotenone rat model of PD. [ABSTRACT FROM AUTHOR]

Detachment of a surface from a viscoelastic layer, such as a film of glue, engenders bridges between the surfaces until separation. Such surface instabilities arising during contact and detachment of viscoelastic films with rigid contactors have been theoretically explored by linear stability analysis and nonlinear simulations. The contact instabilities of viscoelastic materials are found to manifest in either a ‘critical’ or a ‘dominant’ mode in which the former is preferred when the contactor is slowly brought near the film while the latter manifests when the film is ‘hard-pressed’ against it. The nonlinear analysis considers the movement of contactor during adhesion-debonding cycle, which uncovers that the kinetic parameters can overshadow the thermodynamically predicted area of contact, average force for pull-off, energy of contactor-film separation, and pathways of debonding. Three distinct pathways of debonding – peeling, catastrophic column collapse, and column coalescence, are found to manifest with the variation in the ratio of the elastic to viscous compliances of the viscoelastic film. The study also reveals that in the dominant mode of instability, a smaller length scale with a larger area contact between the contactor and film can develop patterns having aspect ratio ∼10 times larger than the same obtained from elastic film. [ABSTRACT FROM AUTHOR]

The van der Waals force is significant for the formation of microstructures of wind-blown deposits, such as loess soil. However, it is difficult to observe the effect of the van der Waals force in the natural environment and laboratory. The conventional DDA model, which simplifies contact as compressed elastic springs, has been successfully applied in simulating blocky rock behaviors, but it is incapable of simulating tension forces. In this paper, we modified the conventional DDA model by considering blocks as soil particles and by applying the van der Waals force among the particles to investigate the micro-behavior of fine soil. The modified DDA is validated by simulating two ideal experiments. Then, the falling process of fine grains (<65 μm), similar to wind-blown dust, is simulated by the modified and conventional DDA models separately. The simulated deposits of the falling grains by the two models show significant differences in microstructure. The microstructure generated by the modified DDA model is much closer to the loose structure of a real loess specimens, while that generated by the conventional DDA model is much more compact. This verifies that the van der Waals force is crucial for the formation of the loose microstructure of loess. [ABSTRACT FROM AUTHOR]

Si surfaces were functionalized by anodization to create nanoneedles. Such surfaces allow Velcro-like bonding at room temperature with large bond strength for such functionalized surfaces. In addition, Velcro-like bonding has a capability of multiple bonding and debonding of the same surfaces analogous to the Velcro principle. To employ such surfaces and the bonding technique in wafer or chip bonding or in integrated circuit packaging applications, understanding the fabrication and the bonding mechanism between such surfaces is very crucial. This paper presents a simple silicon-based technology to generate Velcro-like surfaces using the anodization of Si wafer in a hydrofluoric acid-based electrolyte, and describes the bond strength between such surfaces using the van der Waals force approach. The capability of the technique and the validity of the proposed van der Waals force model are shown by comparison with the experimental results. [2015-0308] [ABSTRACT FROM PUBLISHER]

Electromechanical buckling (EMB) of beam-type nanoelectromechanical systems (NEMSs) is investigated based on modified strain gradient theory. The system is modeled as a clamped-guided nanobeam which is under compressive or tensile axial loads as well as the effect of nonlinear electrostatic and van der Waals symmetric transverse forces. In addition, the beam is considered to be made of axially and transverse functionally graded materials. Here, FGM is Poly-SiGe, of which the general properties change gradually from silicon to germanium based on a simple power-law method. Considering the Euler–Bernoulli beam theory and using the principle of minimum potential energy, the governing equations and corresponding boundary conditions are established. After validation of results, the effects of power law index, variation of size effect parameters, length-thickness ratio and the distance between the two fixed and movable electrodes on the buckling response of the system are discussed. [ABSTRACT FROM AUTHOR]

This paper presents the results on interaction behaviour between spinnable multiwall carbon nanotube bundles. Spinnable carbon nanotube webs were used as test specimens. Mechanical peel tests were performed to investigate the effect of average orientation angles on interactions between nanotube bundles. Thus, in the absence of any binding agents, the effect of orientation directions on Van Der Waals forces between the nanotube bundles was revealed. The experimental results obtained from this study are consistent with theoretical calculations from published literature. It was found that the interaction force of the spinnable nanotube bundles is inversely related to their average orientation angle. It is shown that the force for parallel nanotube bundles at 0° angle is higher than the force for crossed nanotube bundles at 90° angle. [ABSTRACT FROM AUTHOR]

Considering recent applications of electrophoresis conduced in nanoscaled devices, where particle–particle interaction can play a role, we studied for the first time the electrophoresis of two rigid spheres along their center line, taking account of the hydrodynamic, electric, and van der Waals interactions between them. Under the conditions of constant surface potential and surface charge density, the influences of the level of surface potential/charge density, the bulk salt concentration, and the particle–particle distance on their electrokinetic behaviors are examined. Numerical simulation reveals that these behaviors are much more complicated and interesting than those of isolated particles. In particular, we show that care must be taken in choosing an appropriate particle concentration in relevant experiment to avoid obtaining unreliable mobility data. [ABSTRACT FROM AUTHOR]

Experimental observations reveal that the physical response of nano-structures is size-dependent. Herein, modified strain gradient theory in conjunction with Euler–Bernoulli beam theory have been used for mathematical modeling of the size dependent instability of nanostructures. Effect of van der Waals intermolecular force has been included in the mathematical model. Two common beam-type systems including double-clamped nano-bridge and clamped-free nano-cantilever have been investigated. Three approaches including using an approximated differential transformation method (DTM), applying iterative numerical method and developing a simple lumped parameter model have been employed to solve the governing equations of the systems. The obtained results have been compared with those obtained via numerical method. Furthermore a lumped parameter model has been developed to simply explain the physical performance of the systems without mathematical complexity. The pull-in parameters of the nanostructures as basic design parameters have been calculated. Effect of the size dependency on the pull-in performance has been discussed for both nano-structures. [ABSTRACT FROM AUTHOR]

The van der Waals force (vdW force) between particulate matters at low humid condition and short distance contact is of great scientific importance in surface science. Due to the conventional theory for the van der Waals force between particles in single (vacuum or water) medium can not be directly applied in the humid condition, we present a mathematical model to calculate the van der Waals force between particle and surface linked by a liquid bridge in atmospheric humidity based on the surface integration method. In our model, the integration calculated the vdW force is divided into a wetting and a dry integrating region, and their boundary point is the radius of the wetting portion of the particle which is expressed as a function of relative humidity, contact angles and separation distance between the particle surface and the plane. For three basic contact geometries (sphere, cone and cylinder), the computational expressions of van der Waals force derived from our model are consistent with that by Butt. Moreover, our calculation results of the parabola particle model agree well with the published experimental data, which validated the rationality of the proposed model. In addition, our model can accurately calculate the vdW force between arbitrary-shaped particle and a plane surface in humidity environment. [ABSTRACT FROM AUTHOR]

Here, we describe peptide aggregation, which is also known as enzymatic protein resynthesis. Whey protein hydrolysate (WPH) is the starting material for assembling peptides. Analyses of the involved amino acids, intrinsic fluorescence, fluorescence phase diagram, secondary structure, turbidity, and surface hydrophobicity were performed to investigate the reaction process. The aggregation mechanism consists of two parts: 1) formation and 2) aggregation of the building blocks that form the ordered secondary β-sheet structure. Constructing the building blocks requires at least one intermediate state, which is formed after 0.5 hours. Non-synergistic changes in the secondary and tertiary structures then allow the intermediate state to emerge. [ABSTRACT FROM AUTHOR]

[Display omitted] • Blue-shift in the absorption maximum of 7MCA in the presence of aromatic diamine indicates complex formation. • 1H NMR and FT-IR analysis confirms H bonding between OPD and 7MCA. • The magnitude of the quenching rate parameter for 7MCA-PPD is more than 7MCA-OPD in protic solvents whereas in aprotic solvents, it is more for 7MCA-OPD compared to 7MCA-PPD. • The nature of interacting force for 7MCA-OPD and 7MCA-PPD systems is hydrophobic in methanol whereas it is weak van der Waals force in DMF. The Influence of substituent position in aromatic diamines such as ortho -phenylenediamine (OPD) and para -phenylenediamine (PPD) on 7-methoxy-4-azido methyl coumarin (7MCA) has been studied in different solvents. A hypsochromic shift in the absorption maximum of 7MCA in the presence of aromatic diamine indicates the formation of the complex. From the 1H NMR study, it is understood that there is an H-bonding between the NH 2 proton of OPD and 7MCA. A shift in the N–H stretching band of OPD observed in FT-IR spectra towards lower frequency indicates H-bonding between 7MCA and OPD. But the nature of the interaction between PPD and 7MCA cannot be determined from NMR and FT-IR study. Non-linear S-V plots obtained from the fluorescence quenching study reveals the involvement of both static and dynamic quenching processes. The value of the quenching rate parameter for para -phenylenediamine is more than ortho -phenylenediamine in protic solvents. But the value of the quenching rate parameter for ortho -phenylenediamine is more than its para isomer in aprotic solvents. Electrochemical analysis reveals that there is no electron transfer from these amino anilines to coumarin derivatives. The Nature of force between 7MCA and aromatic diamine (OPD and PPD) is hydrophobic in methanol since the change in enthalpy and entropy are positive but these thermodynamic parameters have negative values in DMF solvent indicating, a weak van der Waals force between 7MCA and amino anilines. [ABSTRACT FROM AUTHOR]

Contact adhesive force (Fa) scaling is critical for relay miniaturization, since the actuation area and/or actuation voltage must be sufficiently large to overcome the spring restoring force (Fk) in order to turn on the relay and Fk must be larger than Fa in order to turn off the relay. In this work, contact adhesive force is investigated in MEM logic relays with contact dimple regions as small as 100 nm in lateral dimension. The results indicate that van der Waals force is predominant. An adhesive force of 0.02 nN/nm2 is extracted for tungsten-to-tungsten contact. Fa reduction should be possible with contact dimple size reduction and contact surface coating. [ABSTRACT FROM AUTHOR]

Highlights: [•] Forces between microparticles in a solution of charged nanoparticles are calculated. [•] The forces first increase and then decrease as nanoparticle concentration increases. [•] Nanoparticles stabilize the microparticle dispersion at intermediate concentrations. [ABSTRACT FROM AUTHOR]

Highlights: [•] A model based on the van der Waals force is established using a cohesive method. [•] A cohesive law for nanograined metal–ceramic interfaces is proposed for the first time. [•] The atomic forces play a part in metal–ceramic interfaces based on this model. [•] The strength of metal–ceramic interfaces is described quantitatively. [ABSTRACT FROM AUTHOR]

Abstract: The grains of lunar regolith are characterized with rough surfaces, angular shapes and mutual adhesions due to short-range interactions. These features control the macroscopic mechanical behavior of lunar regolith but have not been completely captured by contact models in previous Discrete Element Method (DEM) analyses. In this paper, a simplified two-dimensional microscopic contact model is proposed for high efficiency DEM analyses of lunar regolith. The model consists of three components in the normal, tangential and rolling directions respectively, plus two new parameters. A shape parameter is used to control the rolling resistance ability at the contact area between two particles to capture the features of grain shape and interlocking. The second parameter, micro-separation, which denotes the nominal minimum distance between the molecules of the two contacting particles, is introduced to account for van der Waals force as the major component of the short-range interactions that contribute to the adhesion of regolith grains in lunar environment conditions. The novel model has been implemented in a two-dimensional DEM code for numerical simulations of biaxial compression tests on lunar regolith. The effects of interparticle friction, grain shape, lunar environment conditions and void ratio on the strength of lunar regolith were numerically investigated. The results show that soils in the simulated lunar environment exhibit greater strength and more apparent strain-softening and shear dilatancy than on the Earth. The proposed model can capture the main features of the mechanical behavior of lunar regolith (apparent cohesion and high peak friction angle) and a wide range of strength indices can be obtained by the contact model. [Copyright &y& Elsevier]

Highlights: [•] We developed a simple and extendible boundary model for granular flow simulations. [•] Practical systems were modeled easily with the signed distance functions (SDF). [•] A new potential-based particle interaction model was developed for the SDF. [•] The cohesive force was introduced into the new SDF model. [•] The new model was shown to be applicable to various practical systems. [ABSTRACT FROM AUTHOR]

Abstract: In this work, buckling and post-buckling analysis of fluid conveying multi-walled carbon nanotubes are investigated analytically. The nonlinear governing equations of motion and boundary conditions are derived based on Eringen nonlocal elasticity theory. The nanotube is modeled based on Euler–Bernoulli and Timoshenko beam theories. The Von Karman strain–displacement equation is used to model the structural nonlinearities. Furthermore, the Van der Waals interaction between adjacent layers is taken into account. An analytical approach is employed to determine the critical (buckling) fluid flow velocities and post-buckling deflection. The effects of the small-scale parameter, Van der Waals force, ends support, shear deformation and aspect ratio are carefully examined on the critical fluid velocities and post-buckling behavior. [Copyright &y& Elsevier]

Abstract: In this paper we solve the common nonlinear boundary value problems (BVPs) of cantilever-type micro-electromechanical system (MEMS) and nano-electromechanical system (NEMS) using the distributed parameter model by the Duan–Rach modified Adomian decomposition method (ADM). The nonlinear BVPs that are investigated include the cases of the single and double cantilever-type geometries under the influence of the intermolecular van der Waals force and the quantum Casimir force for appropriate distances of separation. The new Duan–Rach modified ADM transforms the nonlinear BVP consisting of a nonlinear differential equation subject to appropriate boundary conditions into an equivalent nonlinear Fredholm–Volterra integral equation before designing an efficient recursion scheme to compute approximate analytic solutions without resort to any undetermined coefficients. The new approach facilitates parametric analyses for such designs and the pull-in parameters can be estimated by combining with the Padé approximant. We also consider the accuracy and the rate of convergence for the solution approximants of the resulting Adomian decomposition series, which demonstrates an approximate exponential rate of convergence. Furthermore we show how to easily achieve an accelerated rate of convergence in the sequence of the Adomian approximate solutions by applying Duan''s parametrized recursion scheme in computing the solution components. Finally we compare the Duan–Rach modified recursion scheme in the ADM with the method of undetermined coefficients in the ADM for solution of nonlinear BVPs to illustrate the advantages of our new approach over prior art. [Copyright &y& Elsevier]

The effect of magnetic fields on water is still a highly controversial topic despite the vast amount of research devoted to this topic in past decades. Enhanced water evaporation in a magnetic field, however, is less disputed. The underlying mechanism for this phenomenon has been investigated in previous studies. In this paper, we present an investigation of the evaporation of water in a large gradient magnetic field. The evaporation of pure water at simulated gravity positions (0 gravity level (ab. g), 1 g, 1.56 g and 1.96 g) in a superconducting magnet was compared with that in the absence of the magnetic field. The results showed that the evaporation of water was indeed faster in the magnetic field than in the absence of the magnetic field. Furthermore, the amount of water evaporation differed depending on the position of the sample within the magnetic field. In particular, the evaporation at 0 g was clearly faster than that at other positions. The results are discussed from the point of view of the evaporation surface area of the water/air interface and the convection induced by the magnetization force due to the difference in the magnetic susceptibility of water vapor and the surrounding air. [ABSTRACT FROM AUTHOR]

Abstract: We present a new approach, which can be considered as a generalization of the Derjaguin approximation, that provides exact means to determine the force acting between a three-dimensional body of any shape and a half-space mutually interacting via pairwise potentials. Using it, in the cases of the Lennard-Jones, standard and the retarded (Casimir) van der Waals interactions we derive exact expressions for the forces between a half-space or a slab of finite thickness and an ellipsoid in a general orientation, which in the simplest case reduces to a sphere, a tilted fully elliptic torus, and a body obtained via rotation of a single loop generalized Cassini oval, a particular example of which mimics the shape of a red blood cell. The results are obtained for the case when the object is separated from the plane via a non-polar continuous medium that can be gas, liquid or vacuum. Specific examples of biological objects of various shapes interacting with a plate like substrates are also considered. [Copyright &y& Elsevier]

The collision efficiency of two nanoparticles with different diameters in the Brownian coagulation is investigated. The collision equations are solved to obtain the collision efficiency for the dioctyl phthalate nanoparticle with the diameter changing from 100 nm to 750 nm in the presence of the van der Waals force and the elastic deformation force. It is found that the collision efficiency decreases as a whole with the increase of both the particle diameter and the radius ratio of two particles. There exists an abrupt increase in the collision efficiency when the particle diameter is equal to 550 nm. Finally, a new expression is presented for the collision efficiency of two nanoparticles with different diameters. [ABSTRACT FROM AUTHOR]

Abstract: The oblique collision efficiency of nanoparticles at different colliding angles in Brownian coagulation is investigated. A model of central oblique collision between two nanoparticles is presented to derive equations which are solved to get the collision efficiency by considering van der Waals force and elastic deformation force. Based on the calculated data of collision efficiency under different colliding angles and particle diameters, a new expression relating central oblique collision efficiency at different colliding angles to particle diameter is brought forward. [Copyright &y& Elsevier]

Abstract: An elastic beam suspended horizontally over a substrate in liquid electrolyte was subjected to electric, osmotic, and van der Waals forces. The problem, which is governed by four non-dimensional parameters, was solved using the finite element method. The sum of the electric and osmotic forces, the electrochemical force, is usually attractive. However, the electrochemical force can be repulsive for a narrow range of the ion concentration, the initial separation and surface potentials. Furthermore, the beam deflection is not a monotonic function of the applied surface potentials, the bulk ion concentration, or the initial separation between the beam and the substrate. As these parameters are increased monotonically, the beam bends up and then down. The pull-in voltage increases as the bulk ion concentration increases. The pull-in voltage of a double-wall carbon nanotube suspended over a graphite substrate in liquid can be less than or greater than the pull-in voltage in air, depending on the bulk ion concentration. The critical separation between the DWCNT and the substrate increases with the bulk ion concentration. However, for a given bulk ion concentration, the critical separation is independent of the electric potentials. Furthermore, the critical separation is approximately equal in liquid and air. [Copyright &y& Elsevier]