Analysis of dispersions of coupled asymmetric subwavelength-diameter wires

We propose a novel waveguide based on a structure of coupled asymmetric subwavelength-diameter wires to realize a high negative dispersion. The waveguide consists of an optical nanofiber and a GaAs nanowire. The properties of the supermodes are calculated using finite elements method. The results show that the symmetric supermode in the coupled structure can exhibit a giant negative dispersion up to −4.5 × 10⁶ ps/nm/km.     

Effective parameter extraction of 3D metamaterial arrays via first-principles homogenization theory

In this paper, the effective parameters of diverse single-negative bulk structures are extracted in terms of first-principles homogenization techniques. Each metamaterial unit-cell is initially considered to be an electrically small scatterer, and under this assumption, its polarizabilities are derived via a dynamic approach. Also, the wavenumber of a normally incident propagating plane wave through the aforementioned single-negative structures is obtained by means of several algorithms. The retrieved polarizabilities of a single scatterer and the wavenumber of the periodic medium are, finally, incorporated in the homogenization formulas to compute the desired effective parameters. Numerical verification addressing the analysis of two different resonators and comparisons with the results of a popular homogenization method, reveals the merits of the proposed formulation and proves its overall efficiency.     

Approximate Theoretical Study on the Characteristic of a Femtosecond KLM Laser

The conclusion that the pulse-width is proportional to the square root of the third order dispersion coefficient is obtained by using the modified higher-order nonlinear Schr?dinger equation with concurrent actions of third order dispersion and self-steepen effect when a femtosecond pulse propagates steadily in a laser. This result is in agreement with the experimental result. Besides, the action of second order dispersion term is also discussed in the realization of mode locking process of a laser.     

Thermal dispersion driven by the spontaneous imbibition process

In this work, we have theoretically analyzed the thermal dispersion process under the influence of the spontaneous imbibition of a liquid trapped in a capillary element, considering the presence of a uniform temperature gradient. The capillary element is represented by a porous medium which is initially found at temperature T₀ and pressure P₀. Suddenly, the lower part of the porous medium touches a liquid reservoir at temperature T_l and pressure P₀. This contact between both phases, in turn causes spontaneously the imbibition process. Using a one-dimensional formulation of the average conservation laws, we derive the corresponding nondimensional momentum and energy equations. The numerical solutions permit us to evaluate the position and velocity of the imbibition front as well as the temperature profiles and Nusselt numbers. The above results are shown by taking into account the influence of three dimensionless parameters: the ratio of the characteristic thermal time to the characteristic imbibition time, β, the ratio of the hydrostatic head of the imbibed liquid to the characteristic pressure difference for the imbibition front, α, and the ratio of the dispersive thermal diffusivity to the effective thermal diffusivity of the medium, Ω. The predictions show that temperature profiles and the heat transfer process are strongly dependent on thermal dispersion effects, indicating a clear deviation in comparison with the case of Ω = 0 that represents the absence of the thermal dispersion.     

Nonlinear Comparison of High-order and Optimized Finite-difference Schemes

The effect of reducing the formal order of accuracy of a finite-difference scheme in order to optimize its high-wavenumber performance, is investigated using the 1-D nonlinear unsteady inviscid Burgers' equation. Both explicit and compact schemes are compared to schemes wilh various levels of optimization. Results are given for the absolute and L2 errors as a function of time. It is found that the benefits of optimization do carry over into nonlinear applications.     

Simultaneous determination and qualitative analysis of six types of components in Naoxintong capsule by miniaturized matrix solid‐phase dispersion extraction coupled with ultra high‐performance liquid chromatography with photodiode array detection and quadrupole time‐of‐flight mass spectrometry

A simple and effective sample preparation process based on miniaturized matrix solid‐phase dispersion was developed for simultaneous determination of phenolic acids (gallic acid, chlorogenic acid, ferulic acid, 3,5‐dicaffeoylqunic acid, 1,5‐dicaffeoylqunic acid, rosmarinic acid, lithospermic acid, and salvianolic acid B), flavonoids (kaempferol‐3‐O‐rutinoside, calycosin, and formononetin), lactones (ligustilide and butyllidephthalide), monoterpenoids (paeoniflorin), phenanthraquinones (cryptotanshinone), and furans (5‐hydroxymethylfurfural) in Naoxintong capsule by ultra high‐performance liquid chromatography. The optimized condition was that 25 mg Naoxintong powder was blended homogeneously with 100 mg Florisil PR for 4 min. One milliliter of methanol/water (75:25, v/v) acidified by 0.05% formic acid was selected to elute all components. It was found that the recoveries of the six types of components ranged from 61.36 to 96.94%. The proposed miniaturized matrix solid‐phase dispersion coupled with ultra high‐performance liquid chromatography was successfully applied to simultaneous determination of the six types of components in Naoxintong capsules. The results demonstrated that the proposed miniaturized matrix solid‐phase dispersion coupled with ultra high‐performance liquid chromatography could be used as an environmentally friendly tool for the extraction and determination of multiple bioactive components in natural products.     

M-indeterminate distributions in quantum mechanics and the non-overlapping wave function paradox

We consider the non-overlapping wave function paradox of Aharanov et al., wherein the relative phase between two wave functions cannot be measured by the moments of position or momentum. We show that there is an unlimited number of other expectation values that depend on the phase. We further show that the Wigner distribution is M-indeterminate, that is, a distribution whose moments do not uniquely determine the distribution. We generalize to more than two non-overlapping functions. We consider arbitrary representations and show there is an unlimited number of M-indeterminate distributions. The dual case of non-overlapping momentum functions is also considered.     

Electron inelastic mean free path (IMFP) values of Kapton,polyethylene (PE), polymethylmethacrylate (PMMA), polystyrene (PS) and polytetrafluoroethylene (PTFE) measured with elastic peak electron spectroscopy (EPES)

Elastic peak electron spectroscopy (EPES) was employed to measure the inelastic mean free path (IMFP) for energies between 500 and 1600 eV for five insulating organic compounds: Kapton, polyethylene (PE), poly(methyl methacrylate) (PMMA), polystyrene (PS) and polytetrafluoroethylene (PTFE). A Ni and a Si sample were used as reference materials to avoid measurement of the elastic reflection coefficient in absolute units. Correction of experimental elastic peak intensities for surface excitations was performed which turned out to be essential. The results are compared with recent evaluations of optical constants to yield the IMFP in the literature giving satisfactory agreement, with deviations generally below 20%. Investigation of the kinematics in an electron reflection experiment shows that the dispersion coefficient used in REELS data analysis cannot be identified with the true plasmon dispersion.     

Hydrocarbon Soluble Alkali-Metal-Aluminium Hydride Surrog[ATES]

A series of group 1 hydrocarbon-soluble donor free aluminates [AM(^tBuDHP)(TMP)Al(ⁱBu)₂] (AM=Li, Na, K, Rb) have been synthesised by combining an alkali metal dihydropyridyl unit [(2-^tBuC₅H₅N)AM)] containing a surrogate hydride (sp³ C−H) with [(ⁱBu)₂Al(TMP)]. These aluminates have been characterised by X-ray crystallography and NMR spectroscopy. While the lithium aluminate forms a monomer, the heavier alkali metal aluminates exist as polymeric chains propagated by non-covalent interactions between the alkali metal cations and the alkyldihydropyridyl units. Solvates [(THF)Li(^tBuDHP)(TMP)Al(ⁱBu)₂] and [(TMEDA)Na(^tBuDHP)(TMP)Al(ⁱBu)₂] have also been crystallographically characterised. Theoretical calculations show how the dispersion forces tend to increase on moving from Li to Rb, as opposed to the electrostatic forces of stabilization, which are orders of magnitude more significant. Having unique structural features, these bimetallic compounds can be considered as starting points for exploring unique reactivity trends as alkali-metal-aluminium hydride surrog[ATES].     

An Incremental System To Predict the Effect of Different London Dispersion Donors in All-meta-Substituted Azobenzenes

Predictive models based on incremental systems exist for many chemical phenomena, thus allowing easy estimates. Despite their low magnitude in isolated systems London dispersion interactions are ubiquitous in manifold situations ranging from solvation to catalysis or in biological systems. Based on our azobenzene system, we systematically determined the London dispersion donor strength of the alkyl substituents Me, Et, iPr up to tBu. Based on this data, we were able to implement an incremental system for London dispersion for the azobenzene scheme. We propose an equation that allows the prediction of the effect of change of substituents on London dispersion interactions in azobenzenes, which has to be validated in similar molecular arrangements in the future.