On the limits of quasi-static theory in plasmonic nanostructures

The approximated analytical approach of Quasi-Static Theory (QST) is widely used in modelling the optical response of plasmonic nanoparticles. It is well known that its accuracy is remarkable provided that the particle is much smaller than the wavelength of the interacting radiation and that the field induced inside the structure is approximately uniform. Here, we investigate the limits of QST range of validity for gold nanostructures freestanding in air. First, we compare QST predictions of scattering spectra of nanospheres and cylindrical nanowires of various sizes with the exact results provided by Mie scattering theory. We observe a non-monotonic behaviour of the error of QST as a function of the characteristic length of the nanostructures, revealing a non-trivial scaling of its accuracy with the scatterer size. Second, we study nanowires with elliptical section upon different excitation conditions by performing finite element numerical analysis. Comparing simulation results with QST estimates of the extinction cross-section, we find that QST accuracy is strongly dependent on the excitation conditions, yielding good results even if the field is highly inhomogeneous inside the structure.

Computer Simulation of a Radial Contactless Magnetic Suspension on a Permanent Magnet System

The distributions of magnetic induction and magnetic field strength are obtained. It was found that with a parallel arrangement of toroidal rings of elliptical cross-section in a magnetic suspension, the magnetic induction is 1.7 times higher than with a perpendicular arrangement of the same rings. The calculation of the ponderomotive and magnetomotive forces between two toroidal annular permanent magnets with a radial magnetization of an elliptical section in a contactless magnetic suspension system is carried out. Quasi-elastic stiffness coefficients and static load capacity were calculated for both models. It is shown that the rigidity of the suspension decreases monotonically with a decrease in the size of the gap, regardless of the model.

Substantiation of the Parameters of Universal Scatterer for Bulk Materials

In the paper it is noted that the even distribution of seed and granules of mineral fertilizers inside the soil allows increasing their efficiency and obtaining a potential crop yield. For an even distribution of seeds of grain crops, herbs and fertilizer granules inside the soil, the use of a universal conical scatterer is proposed. The purpose of the study is to substantiate the parameters of a universal conical scatterer, which ensures an even distribution of metered bulk and hard-flowing materials, in particular, seed and granules of mineral fertilizers inside the soil. The results of studies of the conical scatterer of an opener allow to establish that to obtain an even distribution of materials in the direction transverse to the translational speed it is necessary to cut an elliptical section of the scatterer. The cutting plane should be perpendicularto the translational speed (movement direction) at an angle between it and the central axis of the cone, lower than Π 2. The optimal parameters of the conical scatterer are calculated on the basis of the evenness of the particle descending along the conegeneratrix. The revealed dependence of the particle falling time on the initial dimensions of the scatterer made it possible to establish its optimal parameters: the height of the cut-section 6-14 mm; the cone base diameter 100-140 mm. The universal conical scatterer can be used in any industry that requires even scattering of metered bulk and hard-flowing materials.

Controlling Shapes in a Coaxial Flow Focusing Microfluidic Device: Experiments and Theory

A coaxial flow focusing PDMS (polydimethylsiloxane) microfluidic device has been designed and manufactured by soft lithography in order to experimentally study a miscible inner flow. We studied a coaxially focused inner flow (formed by an aqueous fluorescein solution) which was fully isolated from all microchannel surfaces by an additional water outer flow. Different flow rates were used to produce a variety of flow ratios and a 3D reconstruction of the cross-section was performed using confocal microscope images. The results showed an elliptical section of the coaxially focused inner flow that changes in shape depending on the flow rate ratio applied. We have also developed a mathematical model that allows us to predict and control the geometry of the coaxially focused inner flow.

Experiment on Pressure Characteristics of Submerged Floating Tunnel with Different Section Types Under Wave Condition

Submerged floating tunnel (SFT for short) is a special underwater traffic structure, and wave load is one of the main environmental loads of SFT structure. In this paper, the 1:60 physical model test of three kinds of SFT in a two-dimensional wave flume is tested. The effects of random irregular waves on the SFT structure under different wave heights and periods are discussed. The study shows that: (1) Compared with circular and polygonal sections, there are multiple local peaks in the elliptical section during the period. with the increase of wave height, the number of local peaks also increases. It suggests that the rotational moment plays an important role in the elliptical section which has a relatively small depth-width ratio. (2) The position of the maximum and minimum pressure in the three kinds of SFT sections is consistent. Their vertical wave forces are all larger than their horizontal wave forces. The increase of vertical wave force relative to horizontal wave force in polygon section is larger than that in elliptical section, and the difference in the circular section is the smallest. (3) Under the same traffic condition, the wave force of the elliptical and polygon section is smaller, but they are more sensitive to the change of wave height, and the increase is obvious. The distribution of wave force in the circular section is more uniform.