Repulsive Components Research Articles

Tuning the Adhesion of Silica Microparticles to a Poly(2-vinyl pyridine) Brush: An AFM Force Measurement Study

AFM force measurements have been performed to study the influence of the pH value and salt concentration on the interactions between poly(2-vinyl pyridine) brushes and microsized silica spheres, focusing on attractive and adhesion forces. It was found that the interaction was composed of a repulsive component reflecting the conformation of the brush and an additional attractive force. It can therefore be switched reversibly between purely repulsive at pH 2.5 to strong and medium adhesion by changing the pH value to pH 4 and 6, respectively. Addition of KCl showed different effects: at pH 2.5 high salt concentrations induced an attractive force; at pH 4 the interaction changed from strong attraction in the osmotic brush regime to repulsion and weaker adhesion in the salted brush regime; at pH 6 increase of the KCl concentration weakened the attractive force. These effects could partly be explained by the theory of polyelectrolyte brushes; under some conditions the mechanism of the attractive force is still unclear.

Studies on free energies of solution and its components of thiazole amine derivatives

The polarizable continuum model (PCM) is employed to investigate theoretically the solvation of two heterocyclic compounds containing halogens. The PCM analysis has been carried out for 4-(4-chlorophenyl)-1,3-thiazol-2-amine and 4-(4-bromophenyl)-1,3-thiazol-2-amine in ten solvents with wide range of dielectric constants. In this paper, we report the results obtained in the computation of electrostatic interaction, repulsive component of Gibb's free energy of solvation, cavitation enthalpy and entropy of solvation for the two thiazole amines in various solvents. The dipole moments of the two amine molecules are calculated theoretically by AM1, PM3, MNDO and ab initio methods. The induced dipole moments of these two thiazoles are also calculated in these solvents. The thermodynamic properties of the systems, such as free energies, electrostatic interaction, cavitation enthalpy and dipole moment are discussed in terms of the physical properties such as dielectric constant, index of refraction, surface tension and molecular size of the solvents.

Adhesion of a Compliant Cylindrical Shell Onto a Rigid Substrate

The mechanical deformation of an ideal thin-walled cylindrical shell is investigated in the presence of intersurface interactions with a planar rigid substrate. A Dugdale–Barenblatt–Maugis (DBM) cohesive zone approximation is introduced to simulate the convoluted surface force potential. Without loss of generality, the repulsive component of the surface forces is approximated by a linear soft-repulsion, and the attractive component is described by two essential variables, namely, surface force range and magnitude, which are allowed to vary. The nonlinear problem is solved numerically to generate the pressure distribution within the contact, the deformed membrane profiles, and the adhesion-delamination mechanics, which are distinctly different from the classical solid cylinder adhesion models. The model has wide applications in cell adhesion and nanostructures.

A comprehensive modeling and vibration analysis of AFM microcantilevers subjected to nonlinear tip-sample interaction forces

Precise and accurate representation of an Atomic Force Microscopy (AFM) system is essential in studying the effects of boundary interaction forces present between the probe's tip and the sample. In this paper, a comprehensive analytical model for the AFM system utilizing a distributed-parameters based approach is proposed. More specifically, we consider two important attributes of these systems; namely the rotary inertia and shear deformation when compared with the Euler-Bernoulli beam theory. Moreover, a comprehensive nonlinear interaction force is assumed between probe's and sample in order to reveal the response of the system more realistically. This nanoscale interaction force is based on a general form consisting of both attractive and repulsive components as well as a function of the tip-sample distance and the microcantilever's base and sample oscillations. Mechanical properties of the sample could interact with the nanomechanical coupling field between the probe' tip and sample and be implemented in studying the composition information of the sample and the ultra-small features inside it. Therefore, by modulating the dynamics of the AFM system such as the driving amplitude of the microcantilever the procedure for the subsurface imaging is described. The presented approach here could be implemented for designing the AFM probes by examining the tip-sample interaction forces dominant by the van der Waals forces. Several numerical case studies are presented and the force-distance diagram reveals that the proposed nonlinear nanomechanical force along with the distributed-parameters model for the microcantilever is able to fulfill the mechanics of the Lennard-Jones potential.

Mass predictions of atomic nuclei in the infinite nuclear matter model

We present here the mass excesses, binding energies, one- and two-neutron, one- and two-proton and α-particle separation energies of 6727 nuclei in the ranges 4≤Z≤120 and 8≤A≤303 calculated in the infinite nuclear matter model. Compared to our predictions of 1999 mass table, the present ones are obtained using larger data base of 2003 mass table of Wapstra and Audi and resorting to higher accuracy in the solutions of the η-differential equations of the INM model. The local energy η’s supposed to carry signature of the characteristic properties of nuclei are found to possess the predictive capability. In fact η-systematics reveal new magic numbers in the drip-line regions giving rise to new islands of stability supported by relativistic mean field theoretic calculations. This is a manifestation of a new phenomenon where shell-effect overcomes the instability due to repulsive components of the nucleon–nucleon force broadening the stability peninsula. The two-neutron separation energy-systematics derived from the present mass predictions reveal a general new feature for the existence of islands of inversion in the exotic neutron-rich regions of nuclear landscape, apart from supporting the presently known islands around 31Na and 62Ti. The five global parameters representing the properties of infinite nuclear matter, the surface, the Coulomb and the pairing terms are retained as per our 1999 mass table. The root-mean-square deviation of the present mass-fit to 2198 known masses is 342 keV, while the mean deviation is 1.3 keV, reminiscent of no left-over systematic effects. This is a substantive improvement over our 1999 mass table having rms deviation of 401 keV and mean deviation of 9 keV for 1884 data nuclei.

Free Energy Difference in Indolicidin Attraction to Eukaryotic and Prokaryotic Model Cell Membranes

We analyzed the thermodynamic and structural determinants of indolicidin interactions with eukaryotic and prokaryotic cell membranes using a series of atomistically detailed molecular dynamics simulations. We used quartz-supported bilayers with two different compositions of zwitterionic and anionic phospholipids as model eukaryotic and prokaryotic cell membranes. Indolicidin was preferentially attracted to the model prokaryotic cell membrane in contrast to the weak adsorption on the eukaryotic membrane. The nature of the indolicidin surface adsorption depended on an electrostatic guiding component, an attractive enthalpic component derived from van der Waals interactions, and a balance between entropic factors related to peptide confinement at the interface and counterion release from the bilayer surface. Thus, whereas we attributed the specificity of the indolicidin/membrane interaction to electrostatics, these interactions were not the sole contributors to the free energy of adsorption. Instead, a balance between an attractive van der Waals enthalpic component and a repulsive entropic component determined the overall strength of indolicidin adsorption.

Dispersion, static correlation, and delocalisation errors in density functional theory: An electrostatic theorem perspective

Dispersion, static correlation, and delocalisation errors in density functional theory are considered from the unconventional perspective of the force on a nucleus in a stretched diatomic molecule. The electrostatic theorem of Feynman is used to relate errors in the forces to errors in the electron density distortions, which in turn are related to erroneous terms in the Kohn-Sham equations. For H(2), the exact dispersion force arises from a subtle density distortion; the static correlation error leads to an overestimated force due to an exaggerated distortion. For H(2)(+), the exact force arises from a delicate balance between attractive and repulsive components; the delocalisation error leads to an underestimated force due to an underestimated distortion. The net force in H(2)(+) can become repulsive, giving the characteristic barrier in the potential energy curve. Increasing the fraction of long-range exact orbital exchange increases the distortion, reducing delocalisation error but increasing static correlation error.

Role of Three-Body Forces in Proton and Heavy-Ion Scatterings

The three-body forces (TBF) effect is known to play an important role on the nuclear saturation property, which can be demonstrated typically in the Brueckner (G-matrix) theory. Recently, we have proposed new complex G-matrix interactions CEG07, from which nucleon-nucleus (NA) and nucleus-nucleus (AA) folding potentials are obtained. The CEG07 G-matrices are derived from the free-space nucleon-nucleon interaction, the Extended Soft Core (ESC) model, including the TBF contributions composed of the three-body repulsive (TBR) and attractive (TBA) components. Using CEG07, we have analyzed the elastic scattering of NA and AA systems. For NA systems, we have tested the optical potentials obtained by the single-folding procedure with CEG07 in the cases of the proton elastic scattering. We have further applied the CEG07 G-matrix to the AA systms in the framework of the double-folding model and analyzed the elastic scattering of complex nuclei systems at E/A = 70 ∼ 135 MeV. The TBF (especially TBR) effect is clearly seen in all cases investigated.

Polarizability-based equation of state: Application to CO, N 2 and O 2

The description of dense gases and liquids still remains a challenge in thermodynamics. Recently, our group developed a new equation of state that is described by an attractive exponential contribution and a repulsive component that both are a function of polarizability volume and macroscopic volume. In this Letter, we apply this equation of state to moderately dense gases of CO, N 2 and O 2 over a broad temperature range. Literature data is excellently reproduced with the new equation of state and in comparison to the Ideal Gas Law or the original van der Waals equation of state gives substantial improvement.

A Comparative Study of Four Parallel and Distributed PSO Methods

We present four new parallel and distributed particle swarm optimization methods consisting in a genetic algorithm whose individuals are co-evolving swarms, an “island model”-based multi-swarm system, where swarms are independent and interact by means of particle migrations at regular time steps, and their respective variants enriched by adding a repulsive component to the particles. We study the proposed methods on a wide set of problems including theoretically hand-tailored benchmarks and complex real-life applications from the field of drug discovery, with a particular focus on the generalization ability of the obtained solutions. We show that the proposed repulsive multi-swarm system has a better optimization ability than all the other presented methods on all the studied problems. Interestingly, the proposed repulsive multi-swarm system is also the one that returns the most general solutions.

Selective Americium(III) Complexation by Dithiophosphinates: A Density Functional Theoretical Validation for Covalent Interactions Responsible for Unusual Separation Behavior from Trivalent Lanthanides

The separation of trivalent actinides and lanthanides is a challenging task for chemists because of their similar charge and chemical behavior. Soft donor ligands like Cyanex-301 were found to be selective for the trivalent actinides over the lanthanides. Formation of different extractable species for Am(3+) and various lanthanides (viz. La(3+), Eu(3+), and Lu(3+)) was explained on the basis of their relative stabilities as compared to their corresponding trinitrato complexes calculated using the density functional method. Further, the metal-ligand complexation energy was segregated into electrostatic, Pauli repulsion, and orbital interaction components. Higher covalence in the M-S bond in the dithiophosphinate complexes as compared to the M-O bond in the nitrate complexes was reflected in the higher orbital and lower electrostatic interactions for the complexes with increasing number of dithiophosphinate ligands. Higher affinity of the dithiophosphinate ligands for Am(3+) over Eu(3+) was corroborated with higher covalence in the Am-S bond as compared to the Eu-S bond, which was reflected in shorter bond length in the case of the former and higher ligand to metal charge transfer in Am(III)-dithiophosphinate complexes. The results were found to be consistent in gas phase density functional theory (DFT) calculations using different GGA functional. More negative complexation energies in the case of Eu(3+) complexes of Me(2)PS(2)(-) as compared to the corresponding Am(3+) complexes in spite of marginally higher covalence in the Am-S bond as compared to the Eu-S bond might be due to higher ionic interaction in the Eu(3+) complexes in the gas phase calculations. The higher covalence in the Am-S bond obtained from the gas phase studies of their geometries and electronic structures solely cannot explain the selectivity of the dithiophosphinate ligands for Am(3+) over Eu(3+). Presence of solvent may also play an important role to control the selectivity as observed from higher complexation energies for Am(3+) in the presence of solvent. Thus, the theoretical results were able to explain the experimentally observed trends in the metal-ligand complexation affinity.

Communication: Free-energy analysis of hydration effect on protein with explicit solvent: Equilibrium fluctuation of cytochrome c

The relationship between the protein conformation and the hydration effect is investigated for the equilibrium fluctuation of cytochrome c. To elucidate the hydration effect with explicit solvent, the solvation free energy of the protein immersed in water was calculated using the molecular dynamics simulation coupled with the method of energy representation. The variations of the protein intramolecular energy and the solvation free energy are found to compensate each other in the course of equilibrium structural fluctuation. The roles of the attractive and repulsive components in the protein-water interaction are further examined for the solvation free energy. The attractive component represented as the average sum of protein-water interaction energy is dominated by the electrostatic effect and is correlated to the solvation free energy through the linear-response-type relationship. No correlation with the (total) solvation free energy is seen, on the other hand, for the repulsive component expressed as the excluded-volume effect.

S165013 粗視化分子動力学法によるナノ厚さ潤滑膜を介した固体二面間の凝着シミュレーション([S16501]ヘッド・ディスク・インターフェイス)

Using coarse-grained molecular dynamics, we simulated behavior of 1.8-nm-thick perfluoropolyether films coated on a solid substrate with respect to the approach and withdrawal of a solid probe. Similar to typical force-distance curves measured with atomic force microscopy, the simulation results showed that the adhesive force acting on the solid probe reached a maximum and then decreased gradually as the solid-solid spacing increased during the withdrawal. We also found that the adhesive force increased with the withdrawal speed of the solid probe, possibly due to the rapid decrease of the repulsive component of the adhesive force.

Improved Incompressible Smoothed Particle Hydrodynamics method for simulating flow around bluff bodies

In this article, we present numerical solutions for flow over an airfoil and a square obstacle using Incompressible Smoothed Particle Hydrodynamics (ISPH) method with an improved solid boundary treatment approach, referred to as the Multiple Boundary Tangents (MBT) method. It was shown that the MBT boundary treatment technique is very effective for tackling boundaries of complex shapes. Also, we have proposed the usage of the repulsive component of the Lennard-Jones Potential (LJP) in the advection equation to repair particle fractures occurring in the SPH method due to the tendency of SPH particles to follow the stream line trajectory. This approach is named as the artificial particle displacement method. Numerical results suggest that the improved ISPH method which is consisting of the MBT method, artificial particle displacement and the corrective SPH discretization scheme enables one to obtain very stable and robust SPH simulations. The square obstacle and NACA airfoil geometry with the angle of attacks between 0° and 15° were simulated in a laminar flow field with relatively high Reynolds numbers. We illustrated that the improved ISPH method is able to capture the complex physics of bluff-body flows naturally such as the flow separation, wake formation at the trailing edge, and the vortex shedding. The SPH results are validated with a mesh-dependent Finite Element Method (FEM) and excellent agreements among the results were observed.

Site-Selective Solvation in Supercritical CO2Observed by Raman Spectroscopy: Phenyl Group Leads to Greater Attractive Energy than Chloro Group

Vibrational Raman spectra of the C=C stretching modes of cis-stilbene and cis-1,2-dichloroethylene (C(2)H(2)Cl(2)) were measured in supercritical CO(2) in a density range of 0.08 < ρ(r) = ρ/ρ(c) < 1.5 at an isotherm of T(r) = T/T(c) = 1.02. As the fluid density increased, the peak frequencies of cis-stilbene and cis-C(2)H(2)Cl(2) shifted toward the low-energy side. The shifted frequencies of cis-stilbene were consistently greater than those of cis-C(2)H(2)Cl(2) in all density regions, by a factor of 4. By analyzing these density dependencies using the perturbed hard-sphere theory, the shifted frequencies were decomposed into attractive and repulsive components. By quantifying these components as a function of fluid density, we investigated how each solute is solvated in supercritical CO(2). The results indicate that the attractive energy between cis-stilbene and CO(2) is twice that between cis-C(2)H(2)Cl(2) and CO(2). A local density augmentation around the solute molecule was not observed in the cis-C(2)H(2)Cl(2)/CO(2) system, but it was observed in the cis-stilbene/CO(2) system because of site-selective solvation around the phenyl group of cis-stilbene. To the best of our knowledge, this is the first time that the site-selective solvation of a solute molecule has been observed using Raman spectral measurements of a solution system. Based on theoretical calculations and Raman spectral measurements of cis-stilbene in the supercritical fluid of dipolar CHF(3), it is concluded that a driving force for site-selective solvation is the dispersion force.

A JKR-based dynamic model for the impact of micro-particle with a flat surface

A JKR-based dynamic model, with energy dissipation through both irreversible snap-on/snap-off process and viscoelastic effect, is developed to simulate the dynamics of low-velocity normal impact of micro-sized particle with a flat surface. The first-contact energy loss because of the incompletely reversible, quasi-static loading/unloading is incorporated in the dissipation model. The damping forces corresponding to both the attractive and repulsive components of the JKR contact forces are introduced to account for the hysteresis related to material viscoelasticity. The predicted particle behaviors for the impacts with incident velocities below or above the critical velocity are discussed. The predictions of both the critical velocity and the variation of restitution coefficient vs. incident velocity are compared with experiments in literature where reasonable agreement is obtained. The dependence of restitution coefficient on incident velocity is analyzed. Finally, the model sensitivity analysis such as the effect of the damping coefficient variation is discussed. The work provides a solid basis for the development of discrete-element-method approach of micro-sized particulate system.

Attractive and repulsive forces of ferromagnetic materials in time-varying electromagnetic fields

Electromagnetic forces of ferromagnetic materials consist of attractive and repulsive components, which can be introduced from the Lorentz force formula and the Kelvin force formula. In harmonic fields, the attractive and the repulsive forces both have DC and AC components and they cancel out with each other to reduce the total average force. The contributions or influences of the frequency, magnetic permeability and electric conductivity of the material to attractive and repulsive forces in time-varying fields are analyzed and simulated by the numerical experiments using FEM methods. Results show that the total time average electromagnetic forces can be reduced greatly, even to zero in certain states, which is useful to control the vibration problem.

Derivation of enhanced potentials for uranium dioxide and the calculation of lattice and intrinsic defect properties

Previously reported forms of the cation–anion Buckingham potential provide a significantly greater contribution than the repulsive Coulombic component at short-range thus predicting an unphysical attraction between the pair of ions. A detailed reappraisal of the computer modelling of uranium dioxide (UO 2) employing atomistic simulation techniques is presented. An improved set of interatomic potentials is derived in order to describe the lattice correctly under conditions subsequent to radiation damage with the creation of Frenkel pair defects. Novel methodology is employed in the derivation of potentials ensuring applicability over the entire region of interest. The cation–anion potential is obtained via a combination of empirical fitting to crystal structural data and parametric fitting to additional physical properties. These potentials are subsequently verified and validated by calculation of additional bulk lattice properties, whose values agree favourably with those measured experimentally. Atomistic computer simulation techniques are then used to investigate the defect properties of UO 2. The theoretical techniques are based upon efficient energy minimization procedures and Mott–Littleton methodology for accurate defect modelling and employed to calculate intrinsic defect formation energies and enable predictions of the expected type of intrinsic disorder to be made.

Intra-sex vocal interactions in two hybridizing seabird species (Puffinus sp.)

Hybridization between two closely related species breeding in sympatry depends on the effectiveness of both inter-sex (sexual attraction) and intra-sex (competitors’ repulsion) components of communication. As birds primarily communicate acoustically, several studies have investigated interspecific vocal interactions between the sexes and their consequences on sympatric zones with a focus on songbird species. Here, we investigate these issues on intra-sex vocal interactions occurring during incubation in two non-songbird sister species, the Yelkouan Puffinus yelkouan and the Balearic Puffinus mauretanicus shearwaters. We compared the acoustical structure of calls and the behaviors obtained in response to same-sex Yelkouan and Balearic calls across allopatric parental populations from each species and a sympatric-hybridized population. Acoustic analyses showed that, for both sexes, calls have species-specific characteristics while hybrids have intermediate acoustic features compared to their parental species. Playback experiments showed that despite their vocal differences, both species interact and reply to each other. Remarkably, incubating Yelkouan and hybrid individuals resulted in equal intra-sex responses to either species while incubating Balearic birds led to lower territorial responses to Yelkouan than to conspecific calls. Moreover, incubating Balearic males less readily responded to same-sex Yelkouan calls than Balearic females. These results may have fitness consequences: Yelkouan birds, and especially males, would be more likely to win same-sex disputes against Balearic incubating birds than against Yelkouan incubating birds.

Solute−Solvent Intermolecular Interactions in Supercritical Xe, SF6, CO2, and CHF3Investigated by Raman Spectroscopy: Greatest Attractive Energy Observed in Supercritical Xe

Vibrational Raman spectra of the C=C stretching modes of cis- and trans-1,2-dichloroethylene (C(2)H(2)Cl(2)) were measured in supercritical Xe, SF(6), CO(2), and CHF(3). The spectra were collected over a wide range of densities of supercritical fluids at a fixed solute mole fraction and isotherm of T(r) = T/T(c) = 1.02. In all fluids, as the density increased, the peak frequencies of the C=C stretching modes shifted toward the low-energy side. By analyzing these density dependencies using the perturbed hard-sphere theory, the shifted amounts were characterized into attractive and repulsive components. The attractive shifts of both isomers were almost equivalent in supercritical CHF(3), CO(2), and SF(6), whereas they were significantly larger in supercritical Xe. The attractive shifts obtained experimentally were compared with the ones calculated on the basis of dispersion, dipole-dipole, dipole-induced-dipole, and dipole-quadrupole interactions between solute and solvent molecules. The experimental attractive shifts in supercritical Xe were 2-3 times greater than the calculated shifts. The large attractive shifts were ascribed to both an anisotropic solvation structure and to a strong interaction (charge transfer) between Xe and C(2)H(2)Cl(2) molecules.