U-shaped Particles Research Articles

Terahertz wave front manipulation based on Pancharatnam-Berry coding metasurface

We design a coding metasurface based on Pancharatnam-Berry (PB) phase to manipulate terahertz waves, which is simple and flexible. Compared with the previous design of the coding metasurface, the present coding particles can be obtained by using a same size meta-particle with various orientations instead of designing multiple structures or changing specific size parameters. The PB coding metasurfaces composed of U-shaped particles with pre-designed coding sequences can generate multi-bit coding in the terahertz frequencies and control the reflected terahertz waves to the various directions. Both simulation and theoretical calculation scattering patterns of the designed PB coding metasurfaces demonstrate the expected manipulations. Additionally, the bandwidth of radar cross section (RCS) reduction of approaching −15 dB is 1.05THz (range from 0.9THz to 1.95THz). We believe that the proposed design provides a more flexible way for the manipulation of reflected terahertz waves.

Freestanding loadbearing structures with Z-shaped particles

Architectural structures such as masonry walls or columns exhibit a slender verticality, in contrast to the squat, sloped forms obtained with typical unconfined granular materials. Here we demonstrate the ability to create freestanding, weight-bearing, similarly slender and vertical structures by the simple pouring of suitably shaped dry particles into a mold that is subsequently removed. Combining experiments and simulations we explore a family of particle types that can entangle through their non-convex, hooked shape. We show that Z-shaped particles produce granular aggregates which can either be fluid and pourable, or solid and rigid enough to maintain vertical interfaces and build freestanding columns of large aspect ratio ( $$>$$ 10) that support compressive loads without external confinement. We investigate the stability of such columns with uniaxial compression, bending, and vibration tests and compare with other particle types including U-shaped particles and rods. We find a pronounced anisotropy in the internal stress propagation together with strong strain-stiffening, which stabilizes rather than destabilizes the structures under load.

Compact Feeding Network for Array Radiations of Spoof Surface Plasmon Polaritons.

We propose a splitter feeding network for array radiations of spoof surface plasmon polaritons (SPPs), which are guided by ultrathin corrugated metallic strips. Based on the coupled mode theory, SPP fields along a single waveguide in a certain frequency range can be readily coupled into two adjacent branch waveguides with the same propagation constants. We propose to load U-shaped particles anti-symmetrically at the ends of such two branch waveguides, showing a high integration degree of the feeding network. By controlling linear phase modulations produced by the U-shaped particle chain, we demonstrate theoretically and experimentally that the SPP fields based on bound modes can be efficiently radiated to far fields in broadside direction. The proposed method shows that the symmetry of electromagnetic field modes can be exploited to the SPP transmission network, providing potential solutions to compact power dividers and combiners for microwave and optical devices and systems.

Compression- and shear-driven jamming of U-shaped particles in two dimensions

We carry out numerical simulations of soft, U-shaped, frictionless particles in $d=2$ dimensions in order to explore the effects of complex particle shape on the jamming transition. We consider both cases of uniform compression-driven and shear-driven jamming as packing fraction $\phi$ and compression or shear rate is varied. Upon slow compression, jamming is found to occur when the isostatic condition is satisfied. Under driven steady state shearing, jamming occurs at a higher packing fraction $\phi_J$ than observed in compression. A growing relaxation time and translational correlation length is found as $\phi$ increases towards $\phi_J$. We consider the orientational ordering and rotation of particles induced by the shear flow. Both nematic and tetratic ordering are found, but these decrease as $\phi$ increases to $\phi_J$. At the jamming transition, the nematic ordering further decreases, while the tetratic ordering increases, but the orientational correlation lengths remain small throughout. The average angular velocity of the particles is found to increase as $\phi$ increases, saturating to a plateau just below $\phi_J$, but then increasing again as $\phi$ increases above $\phi_J$.

Transmission of an electromagnetic wave through a bianisotropic metafilm

Transmittance and reflectance are analytically calculated for the light of arbitrary polarization incident on the two-dimensional lattice (metafilm) composed of bianisotropic particles with the known polarizability matrix. The results of calculating the coefficients for metafilms composed of U-shaped particles are presented.

Visualization and analysis of unfolded nucleosomes associated with transcribing chromatin.

We have characterized the structure of transcriptionally active nucleosome subunits using electron spectroscopic imaging. Individual nucleosomes were analyzed in terms of total mass, DNA and protein content, while the ensemble of images of active nucleosomes was used to calculate a three-dimensional reconstruction. Transcriptionally active nucleosomes were separated from inactive nucleosomes by mercury-affinity chromatography thus making it possible to compare their structures. The chromatographic results combined with electron spectroscopic imaging confirm that active nucleosomes unfold to form extended U-shaped particles. Phosphorus mapping indicated that the nucleosomal DNA also underwent a conformational change consistent with particle unfolding. The three-dimensional structure of the Hg-affinity purified nucleosomes determined using quaternion-assisted angular reconstitution methods unites and resolves the different electron microscopic views of the particle and is concordant with a sulphydryl-exposing disruption of the H3-H4 tetramer.

Ultrastructure of transcriptionally competent chromatin

We have examined a salt-soluble, transcriptionally competent gene-enriched fraction of chicken erythrocyte chromatin and compared it to bulk chromatin using the unique microanalytical capabilities of Electron Spectroscopic Imaging (ESI). The salt-soluble fraction is enriched 48 fold in beta-globin gene sequences and is also enriched in histones that are post-synthetically modified, including acetylation and ubiquitination. Differences between the two fractions are also apparent in the distribution of the two major forms of nucleoprotein structures, including (1) particles which present a circular profile and possess protein and DNA content nearly identical to that of the canonical nucleosome and account for 89% of particles in the bulk fraction but account for only 66% of the particles in the competent fraction, and (2) u-shaped particles which possess about 20% less protein mass than particles of circular profile and are about 10x more prevalent in the transcriptionally competent fraction than in the bulk. Additionally, elongated particles with protein and DNA content similar to the u-shaped objects are also seen in the competent fraction.