Anisotropic Dipoles Research Articles

Spontaneous Orientation Polarization of Anisotropic Equivalent Dipoles Harnessed by Entropy Engineering for Ultra-Thin Electromagnetic Wave Absorber

HighlightsThe strengthening mechanism of spontaneous orientation polarization of anisotropic equivalent dipoles within high-entropy alloys (HEAs) is proposed for enhancing dielectric attenuation of HEAs.The source of carbon supporter is expanded to the biomass category, which can construct the shell-core heterointerfaces with HEAs by means of a reformative carbothermal shock method.The sample carbonized cellulose paper/HEAs-Mn2.15 achieves efficient electromagnetic wave absorption of -51.35 dB at an ultra-thin thickness of 1.03 mm.This work combines theoretical calculations and electromagnetic simulations to propose feasible strategies for the design and application of electromagnetic functional devices such as ultra-wideband bandpass filter.

Epitaxial growth of perovskite oxide films facilitated by oxygen vacancies

Anisotropic elastic dipoles of oxygen vacancies interact with substrate-induced misfit strain in epitaxial oxide films. This interaction leads to specific spatial alignment of the dipoles that facilitates coherent growth.

Ultrafast, accurate, and robust localization of anisotropic dipoles

The resolution of single molecule localization imaging techniques largely depends on the precision of localization algorithms. However, the commonly used Gaussian function is not appropriate for anisotropic dipoles because it is not the true point spread function. We derived the theoretical point spread function of tilted dipoles with restricted mobility and developed an algorithm based on an artificial neural network for estimating the localization, orientation and mobility of individual dipoles. Compared with fitting-based methods, our algorithm demonstrated ultrafast speed and higher accuracy, reduced sensitivity to defocusing, strong robustness and adaptability, making it an optimal choice for both two-dimensional and three-dimensional super-resolution imaging analysis.

Enhanced performance of polymer solar cells using solution-processed tetra-n-alkyl ammonium bromides as electron extraction layers

We investigate solution-processed tetra-n-alkyl ammonium bromides (TAABs) as electron extraction layers (EELs) in bulk heterojunction (BHJ) solar cells based on poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61 butyric acid methyl ester (PCBM). The EELs of TAABs lead to simultaneous increases in open-circuit voltage (VOC), short-circuit current density, and fill factor, enhancing the power conversion efficiency of BHJ solar cells from 2.38% to 4.02–4.19%. It is interesting that the same increase in VOC of about 0.14 V is obtained for devices with Al, Ag, and Au cathodes by using the EEL of TOAB. The self-assembly of TOAB into the lamellar structure stacked upright atop P3HT:PCBM is corroborated by synchrotron X-ray diffraction. The surface morphologies of TAABs atop P3HT:PCBM, explored by atomic force microscopy, show that there are ultrathin layers of TAABs in the regions beside large island clusters. The underlying mechanism is inferred that the TAAB molecules introduce anisotropic dipoles toward P3HT:PCBM which significantly elevate the vacuum level of the metal cathode for the efficient electron extraction. Our results provide a simple method to fabricate high performance BHJ solar cells by solution processing.

Microscopic model of Purcell enhancement in hyperbolic metamaterials

We study theoretically a dramatic enhancement of spontaneous emission in metamaterials with the hyperbolic dispersion modeled as a cubic lattice of anisotropic resonant dipoles. We analyze the dependence of the Purcell factor on the source position in the lattice unit cell and demonstrate that the optimal emitter position to achieve large Purcell factors and Lamb shifts are in the local field maxima. We show that the calculated Green function has a characteristic cross-like shape, spatially modulated due to structure discreteness. Our basic microscopic theory provides fundamental insights into the rapidly developing field of hyperbolic metamaterials.

Spatial coordination between cell and nuclear shape within micropatterned endothelial cells

Growing evidence suggests that cytoplasmic actin filaments are essential factors in the modulation of nuclear shape and function. However, the mechanistic understanding of the internal orchestration between cell and nuclear shape is still lacking. Here we show that orientation and deformation of the nucleus are regulated by lateral compressive forces driven by tension in central actomyosin fibres. By using a combination of micro-manipulation tools, our study reveals that tension in central stress fibres is gradually generated by anisotropic force contraction dipoles, which expand as the cell elongates and spreads. Our findings indicate that large-scale cell shape changes induce a drastic condensation of chromatin and dramatically affect cell proliferation. On the basis of these findings, we propose a simple mechanical model that quantitatively accounts for our experimental data and provides a conceptual framework for the mechanistic coordination between cell and nuclear shape.

Mechanism of excitation energy transfer between ring‐shaped aggregates of pigments

AbstractWe theoretically study the mechanism of excitation energy transfer (EET) between two ring‐shaped aggregates of pigments. Dynamics of the pigment system and the light field are described by a Markovian quantum master equation and the Maxwell's equations, respectively. Self‐consistently solving these equations, we investigate the interplay between light and aggregates of pigments. From our calculation, it is revealed that the isotropic property gives two coupling constants, which prevents the deterioration of the EET rate between anisotropic dipoles. The distance dependence of the coupling strengths is also calculated for all excited states of the aggregate, which shows that each excited state has a different distance dependence of the coupling strength.

Elastic interactions of active cells with soft materials

Anchorage-dependent cells collect information on the mechanical properties of the environment through their contractile machineries and use this information to position and orient themselves. Since the probing process is anisotropic, cellular force patterns during active mechanosensing can be modeled as anisotropic force contraction dipoles. Their buildup depends on the mechanical properties of the environment, including elastic rigidity and prestrain. In a finite sized sample, it also depends on sample geometry and boundary conditions through image strain fields. We discuss the interactions of active cells with an elastic environment and compare it to the case of physical force dipoles. Despite marked differences, both cases can be described in the same theoretical framework. We exactly solve the elastic equations for anisotropic force contraction dipoles in different geometries (full space, half space, and sphere) and with different boundary conditions. These results are then used to predict optimal position and orientation of mechanosensing cells in soft material.

Elastic interactions of cells.

Biological cells in soft materials can be modeled as anisotropic force contraction dipoles. The corresponding elastic interaction potentials are long ranged (approximately 1/r3 with distance r) and depend sensitively on elastic constants, geometry, and cellular orientations. On elastic substrates, the elastic interaction is similar to that of electric quadrupoles in two dimensions and for dense systems leads to aggregation with herringbone order on a cellular scale. Free and clamped surfaces of samples of finite size introduce attractive and repulsive corrections, respectively, which vary on the macroscopic scale. Our theory predicts cell reorientation on stretched elastic substrates.

Influence of boundary conditions on the ordering of elastic dipoles

AbstractWe consider elastic dipoles in several two‐dimensional geometries. Using Cauchy integral techniques and the image method, the state of elastic equilibrium under different boundary conditions can be determined. The results are used to find the ground state of systems of anisotropic dipoles via the simulated annealing method. Only in the case of fixed boundaries the ordering depends on the boundary condition.

23] Studies of nucleic acids and their protein interactions by 19F NMR

This chapter discusses the studies of nucleic acids and their protein interactions, by 19F nuclear magnetic resonance (NMR). Application of 19F NMR spectroscopy for macromolecular complexes is most useful in instances where co-crystal structures are unavailable and where the large size or the complex nature of intermolecular associations severely restricts the application of 1H NMR. Dissection of protein-nucleic acid complexes, by standard 1H NMR methods, has been substantially hampered by overlapping resonances and is only successful when restricted to small proteins (subunit size of about 12 kD) and short or symmetric nucleic acid targets (about 20 base pairs). One would like to extend NMR to extract structural information from larger complexes, with simplified spectra, limited to a preselected local neighborhood of a probe site. The density, distribution, and symmetry of the orbital electrons about a given nucleus determine the sensitivity and the orientation dependence of the resulting chemical shift. A large, intrinsic sensitivity of the covalently bound fluorine atom stems from the anisotropic distribution of the electrons in the three 2-p orbitals. The fluorine nucleus sensitivity to its micro-environment is, therefore, large and highly orientation dependent. The observed chemical shift change, induced by a new chemical environment, is a linear combination of shielding contributions from: (a) van der Waals interactions, (b) ring current shielding, (c) electronically anisotropic groups, (d) dipoles, and (e) fluorine hydrogen bonding.

Thermal fluctuations in a pair of magnetostatically coupled particles

The influence of the thermal agitation on the switching dynamics for a pair of identical uniaxially anisotropic dipoles is studied for the case of the applied field parallel to the bond direction and the common anisotropy axis. A set of Langevin equations was derived from the micromagnetic energy expression and solved numerically. The switching behavior resembles a random walk over the energy barrier arising from the anisotropy of the system. The relaxation time is computed as a function of temperature, applied field, and coupling strength. The temperature dependence of the maximum energy of the fluctuations provides a method of evaluating the energy barrier of reversal. The thermal agitation is shown to reduce the symmetry of the ‘‘fanning’’ reversal mode.

Measurements of the London penetration depth in Bi-based high-T c compounds

The muon spin relaxation was measured in the high-T c superconductors Bi2Sr1.3Ca0.7 CuO6.15, Bi2Sr2CaCu2O8 and Bi2Pb x Sr2Ca2Cu3O10. We present our method to determine the London penetration depth perpendicular toc-axis λ⊥ (0) taking also contributions from the anisotropic magnetization and nuclear dipoles to the muon frequency spectrum into account.

Evaluation of the scattering matrix of an arbitrary particle using the coupled dipole approximation

The coupled dipole approximation is applied to the calculation of the scattering matrix of an arbitrary particle. Both isotropic and anisotropic dipoles are used in the calculations. The forms of the matrices obtained for several types of scatterers are found to be in exact agreement with those predicted by symmetry. The method is tested quantitatively by comparison with Mie predictions for solid and coated spheres and good agreement is observed. This comparison is also used to establish appropriate magnitudes for anisotropic dipolar polarizabilities.

ChemInform Abstract: CALCULATION OF MOLECULAR POLARIZABILITIES USING AN ANISOTROPIC ATOM POINT DIPOLE INTERACTION MODEL WHICH INCLUDES THE EFFECT OF ELECTRON REPULSION

AbstractDas von Applequist, Carl und Fung vorgeschlagene Modell wird durch Ersatz von isotropen durch anisotrope Atompunktdipole modifiziert.

Calculation of molecular polarizabilities using an anisotropic atom point dipole interaction model which includes the effect of electron repulsion

The point dipole interaction model for molecular polarizability recently proposed by Applequist, Carl, and Fung is modified by replacing isotropic atomic point dipoles with anisotropic atomic point dipoles. The modified formalism, which is invariant to coordinate transformations, requires an additional empirical parameter for each atom type (ξA, the atomic anisotropy constant) and a single, global parameter applicable to all nonconjugated systems (κ, the repulsion exponent). The atomic polarizability tensor in the molecular environment is evaluated as a function of interatomic electron repulsion. This latter quantity is shown to be related to the degree to which bonding diminishes the polarizability of an atomic center in the direction (s) of the covalent bond (s). The anisotropic atom point dipole interaction model generates identical mean molecular polarizabilities as in the isotropic procedures of Applequist et al., while reducing the average error in the calculated molecular polarizability components to ∼7%. This error is comparable to experimental uncertainty.

Switching behaviour of interacting magnetic particles

The magnetostatic properties of particulate magnetic media depend strongly on the packing density because of the magnetic interactions of the particles. To investigate the influence of these interactions we considered two models. One was a dipole model consisting of anisotropic dipoles and dealing with only one component of the magnetic moment. The other model consisted of two interacting Stoner-Wohlfarth particles, where the magnetic moments might rotate. We observed that in the latter model the coercive force decreases under practical conditions with the strength of the interaction, while in the first model it increases.

Change of crystal dimensions due to the alignment of anisotropic elastic dipoles

A method is proposed to determine the elastic dipole tensor of a lattice defect. The length change of a crystal was measured, when the defect orientation in the lattice is changed.

Exact Energy of Interaction Between Nonpolar Molecules Represented as Dipoles

A new non-perturbative method is developed for deriving the energy of interaction between molecules represented as polarizable dipoles. The method is applied to obtain the exact energy of interaction for two anisotropic electric dipoles and for three dipoles in the isotropic case. The results of London and of Casimir and Polder are special limiting cases. Deviations of the London energy from the exact result are investigated. A new feature which emerges is that the potential energy becomes repulsive at very small distances of separation.

Exact interaction energy between two anisotropic polarizable dipoles

The interaction energy between the two arbitrarily oriented anisotropic non-polar molecules represented as dipoles is derived using a new nonperturbative method valid for all separations. The results of London, Casimir and Polder, and Craig and Power emerge as special cases.