Short-range Forces Research Articles

Structural short-range forces between solid-melt interfaces

We predict the structural interaction of crystalline solid-melt interfaces using amplitude equations which are derived from classical density functional theory or phase-field-crystal modeling. The solid ordering decays exponentially on the scale of the interface thickness at solid-melt interfaces; the overlap of two such profiles leads to a short range interaction, which is mainly carried by the longest-range density waves, which can facilitate grain boundary premelting. We calculate the tail of these interactions, depending on the relative translation of the two crystals fully analytically and predict the interaction potential, and compare it to numerical simulations. For grain boundaries the interaction is predicted to decay twice faster as for two crystals without misorientation.

Large-scale solar magnetic field mapping: I.

This article focuses on mapping the Sun’s large-scale magnetic fields. In particular, the model considers how photospheric fields evolve in time. Our solar field mapping method uses Netlogo’s cellular automata software via algorithms to carry out the movement of magnetic field on the Sun via agents. This model's entities consist of two breeds: blue and red agents. The former carry a fixed amount of radially outward magnetic flux: 1023 Mx, and the latter, the identical amount of inward directed flux. The individual agents are distinguished, for clarity, by various shades of blue and red arrows whose orientation indicates the direction the agents are moving, relative to the near-steady bulk fluid motions. The fluid motions generally advect the field with the well known meridional circulation and differential rotation. Our model predominantly focuses on spatial and temporal variations from the bulk fluid motions owing to magnetic interactions. There are but a few effects that agents have on each other: i) while at the poles, field agents are connected via the Babcock - Leighton (B - L) subsurface field to other latitudes. This allows them to undertake two duties there: A) the B - L subsurface field spawns the next generation of new magnetic field via new agents, and B) the B - L subsurface field attracts lower-latitude fields via the “long-range” magnetic stress tension; ii) nearby agents affect each other’s motion by short-range interactions; and iii) through annihilation: when opposite field agents get too close to each other, they disappear in pairs. The behavior of the agents’ long- and short-range magnetic forces is discussed within this paper as well as the model's use of internal boundary conditions. The workings of the model may be seen in the accompanying movies and/or by using the software available via SpringerPlus’ website, or on the NetlogoTM community website, where help is readable available, and should all these fail, some help from the author.Electronic supplementary materialThe online version of this article (doi:10.1186/2193-1801-2-21) contains supplementary material, which is available to authorized users.

Ciliary contact interactions dominate surface scattering of swimming eukaryotes

Interactions between swimming cells and surfaces are essential to many microbiological processes, from bacterial biofilm formation to human fertilization. However, despite their fundamental importance, relatively little is known about the physical mechanisms that govern the scattering of flagellated or ciliated cells from solid surfaces. A more detailed understanding of these interactions promises not only new biological insights into structure and dynamics of flagella and cilia but may also lead to new microfluidic techniques for controlling cell motility and microbial locomotion, with potential applications ranging from diagnostic tools to therapeutic protein synthesis and photosynthetic biofuel production. Due to fundamental differences in physiology and swimming strategies, it is an open question of whether microfluidic transport and rectification schemes that have recently been demonstrated for pusher-type microswimmers such as bacteria and sperm cells, can be transferred to puller-type algae and other motile eukaryotes, because it is not known whether long-range hydrodynamic or short-range mechanical forces dominate the surface interactions of these microorganisms. Here, using high-speed microscopic imaging, we present direct experimental evidence that the surface scattering of both mammalian sperm cells and unicellular green algae is primarily governed by direct ciliary contact interactions. Building on this insight, we predict and experimentally verify the existence of optimal microfluidic ratchets that maximize rectification of initially uniform Chlamydomonas reinhardtii suspensions. Because mechano-elastic properties of cilia are conserved across eukaryotic species, we expect that our results apply to a wide range of swimming microorganisms.

A numerical study of nanoscale electrohydrodynamic patterning in a liquid film

A computational model is developed to study the manufacturing of micro/nanostructures by electrohydrodynamic (EHD) patterning processes. The computational methodology is based on the iterative coupling of the discontinuous boundary element method for electric field with the finite element method for free surface deformation. The model is capable of modeling fully nonlinear free surface deformations induced by an electric field. Geometric discontinuity resulting from the contact of the liquid film with the template is fully accounted for by introducing the short-range molecular forces. The critical voltage for liquid film instability is found by tracing the asymptote of the structural height vs. applied voltage curve, followed by a confirmation by the existence of an internal minimum of the total free energy. Computer codes are verified using the analytical solutions and available measurements. An important finding from the numerical simulations is that steady state structures can be electrohydrodynamically patterned when the applied voltage is either below or above a critical value. While linear analyses are useful, they may significantly over-predict the critical voltage, a crucial parameter for an EHD patterning process. The highly nonlinear phenomena of wetting the template above the critical voltage were considered to be unstable within the framework of linear perturbation. However, these phenomena can be very well predicted by the nonlinear boundary/finite element model enhanced by the short-range molecular forces. Finally, the computational model is flexible and may be modified with ease to analyze an EHD-patterning process for an air–polymer–polymer tri-layered system or other multiple-layered films for fabricating more complex nanostructures.

Interactions of High-Affinity Cationic Blockers with the Translocation Pores of B. Anthracis, C. Botulinum, and C. Perfringens Binary Toxins

Cationic β-cyclodextrin derivatives were recently introduced as highly effective, potentially universal blockers of binary bacterial toxins: anthrax toxin of Bacillus anthracis, C2 toxin of Clostridium botulinum, and iota toxin of Clostridium perfringens. The binary toxins are made of two separate components: the enzymatic A component and the binding/translocation B component, which forms oligomeric channels in the target cell membrane. Here we studied the voltage and salt dependence of the rate constants of binding and dissociation reactions of two structurally different β-cyclodextrins (AmPrβCD and AMBnTβCD) in the PA63, C2IIa, and Ib channels. With all three channels, the blocker carrying extra hydrophobic aromatic groups, AMBnTβCD, demonstrated stronger binding compared with AmPrβCD. This effect is seen as an increased residence time of the blocker in the channels, whereas the time between blockages stays practically unchanged. Surprisingly, the voltage sensitivity, expressed as a slope of the logarithm of the blocker residence time as a function of voltage, was practically the same for all six cases studied, suggesting structural similarities among the three channels. Also, the more-effective AMBnTβCD blocker shows weaker salt dependence of the binding and dissociation rate constants compared with AmPrβCD. By estimating the relative contributions of the applied transmembrane field, long-range Coulomb, and salt-concentration-independent, short-range forces, we found that the latter represent the leading interaction, which accounts for the high efficiency of blockage. In a search for the putative groups in the channel lumen that are responsible for the short-range forces, we performed measurements with the F427A mutant of PA63. We found that the on-rates of the blockage were virtually conserved, but the residence times dropped by more than an order of magnitude, reducing the difference between the efficiencies of the two blockers.

Magnetic field directed assembly of two-dimensional fractal colloidal aggregates

The anisotropy of dipolar interactions can sometimes be a hindrance when assembling colloids, as it limits the diversity of structures that can be manufactured. Here we demonstrate that a mixture of paramagnetic and diamagnetic colloids in a ferrofluid can be used to create a variety of fractal aggregates in the presence of a field. These aggregates exhibit growth both parallel and perpendicular to the field, a distinct departure from the linear chains that are typical of dipolar assembly. The fractal dimension of these aggregates displays a parabolic character as the ferrofluid concentration is increased and varies between 0.94 ± 0.03 and 1.54 ± 0.03—a wider range than that which is seen when colloids are assembled using short-range forces. This behavior is explained by examining how the ferrofluid concentration affects the relative strength of the dipolar interactions between each type of particle. These dipolar fractal aggregates may find use in the study of gelation via long-range forces or the preparation of gels that can be activated using an external field.

INTERATOMIC INTERACTIONS AND ZONE CENTRE PHONONS IN MULTIFERROIC BiFeO3 CERAMICS

The existence of an epitaxially stabilized tetragonal-like (“T -like”) monoclinic phase in BiFeO 3 thin films with high levels of compressive strain has been reported recently. While their structural and ferroelectric properties are different from those of rhombohedral-like (“R-like”) films with lower levels of strain, little information exists on magnetic properties. In this study we have applied a short range force constant model by using normal coordinates to investigate the Raman and the infrared wavenumbers in tetragonal BiFeO 3 having space group P4mm (C4v1). The calculation of zone center phonons has been made by using three stretching and six bending force constants. The calculated Raman and infrared wavenumbers are in very good agreement with the observed ones. The potential energy distribution has also been investigated for determining the significance of contribution from each force constant toward the Raman and the infrared wavenumbers.

Study of zone center phonons in wolframite ZnWO_4

A short-range force constant model was applied to investigate the phonons in wolframite ZnWO_4 crystals in their monoclinic phase having space group P2/c and symmetry C_{2h}. The normal symmetry coordinates for the monoclinic wolframite were computed. The zone center phonons were calculated by using 8 stretching and 6 bending force constants. The calculated results are in very good agreement with the observed ones. The infrared frequencies were assigned for the first time. The potential energy distribution was also investigated for determining the significance of the contribution from each force constant toward the Raman and infrared wavenumbers.

A Numerical Technique for Preserving the Topology of Polymer Knots: The Case of Short-range Attractive Interactions

The statistical mechanics of single polymer knots is studied using Monte Carlo simulations. The polymers are considered on a cubic lattice and their conformations are randomly changed with the help of pivot transformations. After each transformation, it is checked if the topology of the knot is preserved by means of a method called pivot algorithm and excluded area (in short PAEA) and described in a previous publication of the authors. As an application of this method the specific energy, the radius of gyration and heat capacity of a few types of knots are computed. The case of attractive short-range forces is investigated. The sampling of the energy states is performed by means of the Wang-Landau algorithm. The obtained results show that the specific energy and heat capacity increase with increasing knot complexity as in the case of repulsive interactions. The data about the gyration radius allow to estimate the size of the polymer knots at different temperatures.

Research Progress in Atomic Resolution Microscopy

Tremendous progress has been made in non-contact atomic force microscopy (NC-AFM) recently. The spatial resolution of NC-AFM imaging and spectroscopy of individual molecules on surfaces has reached true atomic resolution and bond differentiation level. Combination of NC-AFM with other scanning probe techniques can open a new way for materials, physics, chemistry, and biochemistry studies. In this review, we first introduce the basic principle of NC-AFM and qPlus sensor. The interaction force at atomic scale and precise measurement of short-range force are discussed. We summarize the recent advances in structural determination of organic molecules, chemical identification, electronic structure, and atomic manipulation at the atomic scale. In addition, we also discuss the application of Kelvin probe force microscopy (KPFM) in measurement of local contact potential difference (LCPD). Finally, perspectives and challenges in NC-AFM techniques are presented.

LATTICE DYNAMICAL INVESTIGATIONS FOR RAMAN AND THE INFRARED FREQUENCIES OF Cs2HgCl4

A short-range force constant model has been applied in investigating the Raman and infrared modes in insulating Cs2HgCl4 in orthorhombic phase having space group Pnam using normal coordinate analysis. Calculations on zone centre phonons have been made with twelve stretching and three bending force constants. The calculated Raman and infrared wave numbers are in good agreement with the available experimental results. The potential energy distribution has also been investigated for determining the significance of contribution from each force constant towards the Raman and the infrared wave numbers.

Function ofTiO2Lattice Defects toward Photocatalytic Processes: View of Electronic Driven Force

Oxygen vacancies and Ti-related defects (OTDs) are the main lattice defects ofTiO2, which have great influence on its photocatalytic activity. To understand the relationship between the defects and photocatalytic activities, detailed discussions based on the electronic driven force provided by these defects are carried out during the three commonly accepted processes in photocatalytic reactions. It is found that these defects inevitably (i) influence the energy structure of the pristineTiO2as the isolate acceptor/donor level or hybrid with the original orbital, (ii) provide a disordered short-range force that confuses the charge carriers transferring to surface active sites, (iii) act not only as the surface active sites for trapping the charge carriers but also as the main chemisorption sites forO2,H2O, and organic species. These effects of the defects make them one of the key factors that determine the efficiency of heterogeneous photocatalysis. Clarifying the role of the defects will further facilitate the exploration and the construction of high-performance photocatalysts for practical applications.

Universal three-body recombination via resonantd-wave interactions

For a system of three identical bosons interacting via short-range forces, when two of the atoms are about to form a two-body s-wave dimer, there exists an infinite number of three-body bound states. This effect is the well-known Efimov effect. These three-body states (Efimov states) are found to be universal for ultracold atomic gases and the lowest Efimov state crosses the three-body break-up threshold when the s-wave two-body scattering length is $a \approx -9.73 r_{\rm vdW}$, $r_{\rm vdW}$ being the van der Waals length. This article focuses on a generalized version of this Efimov scenario, where two of the atoms are about to form a two-body d-wave dimer, which leads to strong d-wave interactions. In a recent paper [B. Gao, Phys. Rev. A. {\bf 62}, 050702(R) (2000)], Bo Gao has predicted that for broad resonances the d-wave dimer is always formed near $a \approx 0.956 r_{\rm vdW}$. Here we find that a single universal three-body state associated with the d-wave dimer is also formed near the three-body break-up threshold at $a \approx 1.09 r_{\rm vdW}$ and its signature can be found through enhancement of the three-body recombination. The three-body effective potential curves that are crucial for understanding the recombination dynamics are also calculated and analyzed. An improved method to calculate the couplings, effective potential curves, and recombination rate coefficients is presented.

Complexity of quantum states in the two-dimensional pairing model

It is known that many-fermion systems, such as complex atoms and nuclei, reveal (at some level of excitation energy) local signatures of quantum chaos similar to the predictions of random matrix theory. Here, we study the gradual development of such signatures in a model system of up to 16 fermions interacting through short-range pairing-type forces in a two-dimensional harmonic trap. We proceed from the simplest characteristics of the level spacing distribution to the complexity of eigenstates, strength, and correlation functions. For increasing pairing strength, at first, chaotic signatures gradually appear. However, when the pairing force dominates the Hamiltonian, we see a regression towards regularity. We introduce a "phase correlator" that allows us to distinguish the complexity of a quantum state that originates from its collective nature, from the complexity originating from quantum chaos.

Effect of Short-Range and Tensor Force Correlations on High-Density Behavior of Symmetry Energy

The effect of short-range and tensor correlations on nuclear symmetry energy is investigated by using realistic nuclear momentum distribution n(k). For finite nuclei, the n(k) is discussed in detail within an analytical model that allows inclusion of both short-range and tensor correlation effects in a physically very transparent way. The equation of state of symmetric nuclear matter is calculated by using realistic n(k) parameterization. The tensor-force induced short-range correlations are shown to have a significant impact on the behavior of symmetry energy.

Classical rotons in cold atomic traps

We predict the emergence of a roton minimum in the dispersion relation of elementary excitations in cold atomic gases in the presence of diffusive light. In large magneto-optical traps, multiple scattering of light is responsible for the collective behavior of the system, which is associated to an effective Coulomb-like interaction between the atoms. In optically thick clouds, the rescattered light undergoes diffusive propagation, which is responsible for a stochastic short-range force acting on the atoms. We show that the dynamical competition between these two forces is by the appearance of a roton minimum in the dispersion relation. Making use of the fluctuation-dissipation theorem, we show that the roton minimum is related to classical long-range order in the system.

Integral relations and the adiabatic expansion method for1+2reactions above the breakup threshold: Helium trimers with soft-core potentials

The integral relations formalism introduced in \cite{bar09,rom11}, and designed to describe 1+$N$ reactions, is extended here to collision energies above the threshold for the target breakup. These two relations are completely general, and in this work they are used together with the adiabatic expansion method for the description of 1+2 reactions. The neutron-deuteron breakup, for which benchmark calculations are available, is taken as a test of the method. The s-wave collision between the $^4$He atom and $^4$He$_2$ dimer above the breakup threshold and the possibility of using soft-core two-body potentials plus a short-range three-body force will be investigated. Comparisons to previous calculations for the three-body recombination and collision dissociation rates will be shown.

On the fundamental derivative of gas dynamics in the vapor–liquid critical region of single-component typical fluids

This document describes the results of an investigation on the variation of the so-called fundamental derivative of gas dynamics, Γ, in the vapor–liquid critical region of well-measured substances, namely methane, carbon dioxide and water, for which accurate, scaled fundamental equations are available. The results demonstrate that for a pure fluid in the single-phase thermodynamic regime, Γ diverges to +∞ independent of the direction of approach of the vapor–liquid critical point. Furthermore, in the two-phase thermodynamic regime, Γ diverges to −∞ independent of the direction of approach of the vapor–liquid critical point. These two qualitative results, as well as the value of the exponent giving the power-law dependence of Γ along the critical isochore as a function of |T−TC|/T (T is the temperature and “C” indicates its critical point value), namely ≈−0.89, are similar for all pure, non-ionized fluids belonging to the class of 3-dimensional Ising-like systems, i.e., systems governed by short-range forces.

P.2.c.023 Long-term safety and tolerability of the multimodal antidepressant Lu AA21004 in subjects with major depressive disorder

Rovibrational absorption spectra of methyl chloride in the spectral region between 2800 and 3200 cm−1 were recorded with a high-resolution Fourier transform spectrometer. A multispectrum fitting procedure was used to analyze 527 transitions of the ν1 band and to retrieve the self-broadening coefficients for various J- and K-values with an estimated accuracy around 8%. Pure rotational transitions of CH3Cl in the submillimeter/terahertz region (0.2–1.4 THz) were also investigated using two complementary techniques of frequency-multiplication and continuous-wave photomixing. Forty-three pure rotational self-broadening coefficients were extracted with the accuracy between 3 and 5%. The whole set of measured values was used to model the J- and K-rotational dependences of the self-broadening coefficients by second-order polynomials. In addition, semi-classical calculations were performed, based on the real symmetric-top geometry of the active molecule, an intermolecular potential model including not only the dominant electrostatic but also the short-range forces, as well as on an exact classical treatment of the relative translational motion of the colliding partners. Comparison of all experimental and theoretical results shows similar rotational dependences and no significant vibrational dependence, so that extrapolations to other spectral regions should be straightforward.

Analysis of self-broadened pure rotational and rovibrational lines of methyl chloride at room temperature

Rovibrational absorption spectra of methyl chloride in the spectral region between 2800 and 3200cm−1 were recorded with a high-resolution Fourier transform spectrometer. A multispectrum fitting procedure was used to analyze 527 transitions of the ν1 band and to retrieve the self-broadening coefficients for various J- and K-values with an estimated accuracy around 8%. Pure rotational transitions of CH3Cl in the submillimeter/terahertz region (0.2–1.4THz) were also investigated using two complementary techniques of frequency-multiplication and continuous-wave photomixing. Forty-three pure rotational self-broadening coefficients were extracted with the accuracy between 3 and 5%. The whole set of measured values was used to model the J- and K-rotational dependences of the self-broadening coefficients by second-order polynomials. In addition, semi-classical calculations were performed, based on the real symmetric-top geometry of the active molecule, an intermolecular potential model including not only the dominant electrostatic but also the short-range forces, as well as on an exact classical treatment of the relative translational motion of the colliding partners. Comparison of all experimental and theoretical results shows similar rotational dependences and no significant vibrational dependence, so that extrapolations to other spectral regions should be straightforward.