The specific-heat difference between the O:H van der Waals bond and the H-O polar-covalent bond and the Coulomb repulsion between electron pairs on adjacent oxygen atoms determine the angle-length-stiffness relaxation dynamics of the hydrogen bond (O:H-O), which is responsible for the density and phonon-stiffness oscillation of water ice over the full temperature range. Cooling shortens and stiffens the part of relatively lower specific-heat, and meanwhile lengthens and softens the other part of the O:H-O bond via repulsion. Length contraction/elongation of a specific part always stiffens/softens its corresponding phonon. In the liquid and in the solid phase, the O:H bond contracts more than the H-O elongates, hence, an O:H-O cooling contraction and the seemingly "regular" process of cooling densification take place. During freezing, the H-O contracts less than the O:H elongates, leading to an O:H-O elongation and volume expansion. At extremely low temperatures, the O:H-O angle stretching lowers the density slightly as the O:H and the H-O lengths change insignificantly. In ice, the O-O distance is longer than it is in water, resulting in a lower density, so that ice floats.
Five new hydroanthraquinone derivatives, tetrahydroaltersolanols C-F (1-4) and dihydroaltersolanol A (5), and five new alterporriol-type anthranoid dimers, alterporriols N-R (12-16), along with seven known analogues (6-11 and 17), were isolated from the culture broth and the mycelia of Alternaria sp. ZJ-2008003, a fungus obtained from a Sarcophyton sp. soft coral collected from the South China Sea. Their structures and the relative configurations were elucidated using comprehensive spectroscopic methods including 1D and 2D NOE spectra as well as single-crystal X-ray crystallography. Compound 13 represents the first isolated alterporriol dimer with a C-4-C-4' linkage, and the absolute configuration of 4 was determined using the modified Mosher's method. Compounds 1 and 15 exhibited antiviral activity against the porcine reproductive and respiratory syndrome virus (PRRSV), with IC₅₀ values of 65 and 39 μM, respectively. Compound 14 showed cytotoxic activity against PC-3 and HCT-116 cell lines, with IC₅₀ values of 6.4 and 8.6 μM, respectively.
In modern integrated circuits and wireless communication devices or systems, three key features need to be solved simultaneously to reach higher performance and more compact size: signal integrity, interference suppression, and miniaturization. However, the above-mentioned requests are almost contradictory using the traditional techniques. To overcome this challenge, here we propose time-domain spoof surface plasmon polaritons (SPPs) as the carrier of signals. By designing a special plasmonic waveguide constructed by printing two narrow corrugated metallic strips on the top and bottom surfaces of a dielectric substrate with mirror symmetry, we show that spoof SPPs are supported from very low frequency to the cutoff frequency with strong subwavelength effects, which can be converted to the time-domain SPPs. When two such plasmonic waveguides are tightly packed with deep-subwavelength separation, which commonly happens in integrated circuits and wireless communications due to limited space, we demonstrate theoretically and experimentally that SPP signals on such two plasmonic waveguides have better propagation performance and much less mutual coupling than the conventional signals on two traditional microstrip lines with the same size and separation. Hence the proposed method can achieve significant interference suppression in very compact space, providing a potential solution to break the challenge of signal integrity. KEYWORDS: surface plasmon polaritons, time domain, signal integrity, interference suppression S ignal interference suppression and signal integrity are two of the most challenging topics in physics and electrical engineering. Especially, the rapid developments of super-largescale integration of high-speed circuits and wireless communication systems/devices have brought forward higher requirements for signal interference suppression and signal integrity in the past decades. 1−3 Some special circuit strategies have been proposed to improve the signal quality, such as the equalization technique 4 and differential microstrip lines. 5 However, in the above techniques, additional areas of circuits and power consumptions are required, which make them rather difficult to utilize in high-frequency and/or high-speed circuits and systems. In fact, signal integrity, signal interference suppression, and miniaturization are three key features to be solved simultaneously to achieve higher performance and smaller size of complicated circuits and systems. But these factors are almost contradictory using the traditional transmission lines. To solve the challenges, we are forced to find new physics models beyond traditional transmission lines, and the surface plasmon polariton (SPP) approach is one of the possibilities due to its strong subwavelength effects.At optical frequencies, because of the negative permittivity behavior of the metal and positive permittivity of the dielectric, SPPs are formed by the interaction between free electrons and the electromagnetic field 6,7 and propagate in parallel to the metal−diele...
In past decades, terahertz radiation, which locates between microwave and far‐infrared light in the electromagnetic spectrum, has attracted more and more attention. Various passive and active components such as absorbers, filters, polarizers, and focusing lenses have been developed for manipulating terahertz radiation. With the further evolution of metamaterials and metasurfaces, unprecedented freedom is gained for flexibly controlling terahertz waves, including focusing, deflection, beam steering, polarization conversion, and generation of orbit angular momentum. Among them, terahertz beam steering has become the focus of considerable interest owing to its significance for wireless communication, high‐resolution imaging, and radar applications. In this paper, first the conventional terahertz beam steering technologies are reviewed, including mechanical scanning, phased array, frequency scanning antennas, and multibeam switching technology. Then, the reconfigurable metasurface routes based on semiconductor active components, phase transition materials, electrically tunable materials, and micro‐electromechanical technology are summarized and the respective performances for terahertz beam steering are discussed. Moreover, programmable metasurfaces with digitalized description of metasurfaces and real‐time manipulations of radiation patterns are also illustrated in detail. Finally, a summary of the present terahertz beam steering technologies is provided and an outlook for the future is discussed.
The second harmonic generation is one of the most important applications of nonlinear effect, which has attracted great interests in nonlinear optics and microwave in the past decades. To the best of our knowledge, however, generating the second harmonics of surface plasmon polaritons (SPPs) has not been reported. Here, we propose to generate the second harmonics of spoof SPPs with high efficiency at microwave frequencies using subwavelength-scale nonlinear active device integrated on specially designed plasmonic waveguides, which are composed of two ultrathin corrugated metallic strips printed on the top and bottom surfaces of a thin dielectric slab anti-symmetrically. We show that the plasmonic waveguide supports broadband propagations of spoof SPPs with strong subwavelength effect, whose dispersion property can be controlled by changing the geometrical parameters. By loading the nonlinear device made from semiconductors to the intersection of two plasmonic waveguides with different corrugation depths, we experimentally demonstrate the efficient generation of second-harmonic SPPs in broad frequency band. The proposed second-harmonic generator can be directly used as SPP frequency multiplier, and the proposed method can be extended to achieve high-order harmonics and produce SPP mixers, which are essential to SPP integrated circuits and systems.
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