A Dual/Single Wideband Switchable Metamaterial Absorber at Low Frequency

Based on PIN diode and resistive film, a dual/single wideband switchable metamaterial absorber at low frequency is presented in this paper. Its absorption is over 90% from 0.8GHz to 1.5GHz and from 4.2GHz to 5.2GHz while the PIN diode operates in forward biased condition. On the contrary, with the PIN diode acting in reverse biased condition, the above 90% absorption occurs from 1.1GHz to 3.2GHz. The surface current distributions at the absorption frequencies are monitored to explain the reason of wideband absorption. The simulation results show that the absorption property of the metamaterial absorber is polarization-sensitive. The metamaterial absorber possesses the advantages of simple structure, wideband, dual/single band, and switchable performance.

Functional divergence and spectral tuning of microbial rhodopsins from an ancestral proton pump

For billions of years, life has continuously adapted to dynamic physical conditions near the Earth s surface. Fossils and other preserved biosignatures in the paleontological record are the most direct evidence for reconstructing the broad historical contours of this adaptive interplay. However, biosignatures dating to Earth s earliest history are exceedingly rare. Here, we combine phylogenetic inference of primordial rhodopsin proteins with modeled spectral features of the Precambrian Earth environment to reconstruct the paleobiological history of this essential family of photoactive transmembrane proteins. Our results suggest that ancestral microbial rhodopsins likely acted as light-driven proton pumps, and were spectrally tuned toward the absorption of green light, which would have enabled their hosts to occupy depths in a water column or biofilm where UV wavelengths were attenuated. Subsequent diversification of rhodopsin functions and peak absorption frequencies track the diversification of surface ecological niches induced by the accumulation of atmospheric oxygen. Inferred ancestors retain distinct associations between extant functions and peak absorption frequencies. Our findings suggest that novel information encoded by biomolecules can be used as paleosensors for conditions of ancient, inhabited niches of host organisms not represented elsewhere in the paleontological record. The coupling of functional diversification and spectral tuning of this pervasive protein family underscores the utility of rhodopsins as universal testbeds for inferring remotely detectable biosignatures on inhabited planetary bodies.

Understanding the structural, optical, and dielectric characteristics of SrLaLiTe1−xMnxO6 perovskites

In electronic applications, good dielectric permittivity material has huge potential in the capacitive energy storage devices. Herein, in the present work the dielectric study of SrLaLiTe1−xMnxO6 (x = 0.02, 0.04, 0.06, 0.08, and 0.10) double perovskites has been studied and discussed. These compounds were prepared through solid-state reaction method. All of the prepared compounds were confirmed to crystallized in monoclinic structure of P21/n space symmetry with better crystallization when dopant concentrations increased until x = 0.08. The formation of Li–O–Te/Mn bonds in octahedral structures in all compounds were confirmed in this study. The existence of peaks at specific wavenumbers indicated vibrations of B–site cations’ bonds. When dopant amounts were increased from x = 0.02 to x = 0.08, there was an increasing trend of grains sizes formation in the compounds. The discussions on effects of grain sizes towards dielectric properties were included in this paper. Other important results and discussions comprised of the significant effects of dopant on the optical band gap (Eopt) and absorption frequencies of the compounds. The decreasing trend of Eopt towards semiconductor range indicated the compounds’ promising potentials for optoelectronic device application.

Preparation, Structural Analysis, and Tunability of Optical and Dielectric Characteristics of Mn–modified SrLaLiTeO6 Double Perovskite

SrLaLiTe 1- x Mn x O 6 ( x = 0.02, 0.04, 0.06, 0.08, 0.10) double perovskites have been prepared using solid state method. Studies on structural by applying X–ray diffraction (XRD) characterization found that all compounds formed in monoclinic, P2 1 /n symmetry with reduction of lattice parameters and unit cell volume as dopant concentration increased. The formation of Te 6+ /Mn 6+ –O–Li + octahedral structure can be confirmed with the presence of peaks at certain wavenumbers indicating vibrations of Te – O or Mn – O bonds. As dopant concentration increased, field emission scanning electron microscope (FESEM) characterization found that the increasing trend of formation in grains sizes from x = 0.02 to x = 0.08, and its effects towards dielectric properties which were conducted by electrochemical impedance spectroscopy (EIS) studies were discussed in this paper. Other discussions included were regarding the significant effect of dopant towards optical band gap, E opt and absorption frequencies of prepared compounds compared to pristine compound indicating its promising potential for optoelectronic device application.

NOISE-ABSORBING ACOUSTIC SCREEN BASED ON A HELMHOLTZ RESONATOR

The paper aims at studying the noise protection potential of an acoustic screen based on a Helmholtz resonator to solve the problem of noise reduction level in the area in front of the screen. For experimental analysis, a modular acoustic screen has been made. Replaceable modules are made on the basis of a wooden frame with stiffening ribs, one side of the module is blind, another has slotted holes, which ensures the formation of noise absorbers on a Helmholtz resonator principle. Changing the position of the modules in the support racks provides the ability to change the screen reflexive surface nature. The main problem solved in this work is to experimentally determine the decrease magnitude in the sound pressure level in the area in front of the screen. The results of sound pressure level measurements at various frequencies are provided, the comparison of the reflected noise obtained values with the results obtained in the sound pressure level analysis in the case of a solid screen is given. The coincidence of the calculated values of the active sound absorption frequencies with the measured values is shown. It is concluded that there is a possibility to solve the nose reduction level problem when using such screens in areas where people can be.

Исследование спектров комплексного показателя преломления пленок мононуклеотидов на кремнии в терагерцевом диапазоне

The possibility of obtaining spectra of the complex refractive index of mononucleotide films deposited on a polished silicon substrate in the terahertz (THz) range has been shown for the first time. The transmission of biopolymer samples with a THz spectrometer was measured. The natural absorption frequencies and refractive index spectrum of adenosine in the THz range were defined.

Spurious Absorption Frequency Appearance Due to Frequency Conversion Processes in Pulsed THz TDS Problems

The appearance of the spurious absorption frequencies caused by the frequency conversion process at the broadband THz pulse propagation in a medium is theoretically and experimentally discussed. The spurious absorption frequencies appear due to both the frequency doubling and generation of waves with sum or difference frequency. Such generation might occur because of the nonlinear response of a medium or its non-instantaneous response. This phenomenon is confirmed by the results of a few physical experiments provided with the THz CW signals and broadband THz pulses that are transmitted through the ordinary or dangerous substances. A high correlation between the time-dependent spectral intensities for the basic frequency and generated frequencies is demonstrated while using the computer simulation results. This feature of the frequency conversion might be used for the detection and identification of a substance.

Effect of a Magnetic Field on Photocatalytic Degradation of Rhodamine B Over g-C3N4

Magnetic fields have potential applications in photocatalysis. However, there is limited research on the effect of magnetic fields on heterogeneous photocatalysis, and the action mechanism remains unclear. In this study, the photocatalytic degradation of rhodamine B over g-C3N4 in an aqueous solution was investigated, and the adsorption and photocatalytic activity were analyzed in the absence and presence of a magnetic field. Furthermore, the infrared absorption frequency of the bending vibration of water was measured in real-time. The results show that the adsorption and photocatalytic efficiencies were positively correlated with the magnetic field intensity in the range of 0∼2 T, while high-intensity magnetic fields (4∼8 T) played an inhibitory role. In addition, the infrared absorption frequencies of water exhibited a red-shift under 1 T and 2 T magnetic fields at 37 °C, while the absorption frequencies under 4 T and 8 T magnetic fields were the same as that in the absence of magnetic fields. The effects of the magnetic field on the g-C3N4 photocatalytic efficiency and water infrared absorption frequency were similar, suggesting that the effect of the magnetic field on the water structure may be one factor affecting the g-C3N4 photocatalytic efficiency.