Different from conventional-phased arrays providing only angle-dependent beampatterns, frequency diverse arrays (FDAs) produce angle-range-dependent and time-variant transmit beampatterns. Recently, ...time-invariant range focusing beampatterns have been reported in some works, which could not be achieved by traditional antenna arrays. However, this paper shows that these papers neglected the time-range or frequency-phase relationship and led to erroneous simulation results and conclusions. The formulas of time-invariant FDA are carefully reviewed, and the unnoticed misconceptions are analyzed. By reestablishing the correct signal models, a set of numerical examples are presented to demonstrate that the beampatterns of FDA arrays are actually time variant in free space.
A high-gain low-profile reflector antenna with dual-band radiation ability is presented in this paper. The antenna achieves a relative 2 dB gain bandwidth of 10% around
, and a relative 2 dB gain ...bandwidth of 20%, around
, where
and
are the center operating frequencies of the frequency bands of 29.4~32.4 GHz and 142~174 GHz, respectively. To achieve the dual-band radiation ability, a composite dual-band feed with an
/
ratio of around 5 is proposed as the feed for the reflector antenna, which includes a higher-band circular waveguide and a lower-band coaxial horn. The metallic elliptical surface serves as the subreflector (SR) in the higher band, while the SR is the planar reflectarray in the lower band. Due to the design of the dual reflector, the dual-band reflector antenna features a low focal-to-diameter (F/D) ratio of approximately 0.2. According to the simulated results, the proposed reflector antenna achieves efficiencies of 59.0% and 42.9% at
and
, respectively. For verification purposes, a Ku/E-band scaled prototype is manufactured. The measured VSWRs, radiation patterns, and gains are in reasonable agreement with the simulated ones, proving the correctness of the proposed design method.
High-gain and beam-scanning antennas are extremely important in the applications of millimeter-wave (MMW) and terahertz (THz) technologies. Dielectric lens is a suitable candidate for this purpose, ...because it has no metal and quite small feeding loss. In this paper, discrete dielectric lenses are studied in which periodic antireflection (AR) structures are added to reduce impedance mismatch at the air-dielectric interfaces, leading to higher directivity. Meanwhile, a multifrequency phase matching method is proposed to realize a beam-scanning lens in both MMW and THz regions. The design concept of the beam-scanning lens is applicable to other frequency ranges as well, which opens new opportunities for future lens design. Moreover, three-dimensional (3-D) printing technology is employed to simplify the manufacturing process and reduce the cost. Experiments are done in both MMW and THz regions, and the results verify the concept of lens design. The 3-D printed MMW and THz lenses with fixed and scanning beams demonstrated in this work could be an important step toward MMW and THz communications, radar, and imaging systems for practical applications.
Cadmium (Cd) is a toxic metal, targeting the lung, liver, kidney, and testes following acute intoxication, and causing nephrotoxicity, immunotoxicity, osteotoxicity and tumors after prolonged ...exposures. Reactive oxygen species (ROS) are often implicated in Cd toxicology. This minireview focused on direct evidence for the generation of free radicals in intact animals following acute Cd overload and discussed the association of ROS in chronic Cd toxicity and carcinogenesis. Cd-generated superoxide anion, hydrogen peroxide, and hydroxyl radicals
in vivo have been detected by the electron spin resonance spectra, which are often accompanied by activation of redox sensitive transcription factors (e.g., NF-κB, AP-1 and Nrf2) and alteration of ROS-related gene expression. It is generally agreed upon that oxidative stress plays important roles in acute Cd poisoning. However, following long-term Cd exposure at environmentally-relevant low levels, direct evidence for oxidative stress is often obscure. Alterations in ROS-related gene expression during chronic exposures are also less significant compared to acute Cd poisoning. This is probably due to induced adaptation mechanisms (e.g., metallothionein and glutathione) following chronic Cd exposures, which in turn diminish Cd-induced oxidative stress. In chronic Cd-transformed cells, less ROS signals are detected with fluorescence probes. Acquired apoptotic tolerance renders damaged cells to proliferate with inherent oxidative DNA lesions, potentially leading to tumorigenesis. Thus, ROS are generated following acute Cd overload and play important roles in tissue damage. Adaptation to chronic Cd exposure reduces ROS production, but acquired Cd tolerance with aberrant gene expression plays important roles in chronic Cd toxicity and carcinogenesis.
Abstract
The frustrated magnet
α
-RuCl
3
constitutes a fascinating quantum material platform that harbors the intriguing Kitaev physics. However, a consensus on its intricate spin interactions and ...field-induced quantum phases has not been reached yet. Here we exploit multiple state-of-the-art many-body methods and determine the microscopic spin model that quantitatively explains major observations in
α
-RuCl
3
, including the zigzag order, double-peak specific heat, magnetic anisotropy, and the characteristic M-star dynamical spin structure, etc. According to our model simulations, the in-plane field drives the system into the polarized phase at about 7 T and a thermal fractionalization occurs at finite temperature, reconciling observations in different experiments. Under out-of-plane fields, the zigzag order is suppressed at 35 T, above which, and below a polarization field of 100 T level, there emerges a field-induced quantum spin liquid. The fractional entropy and algebraic low-temperature specific heat unveil the nature of a gapless spin liquid, which can be explored in high-field measurements on
α
-RuCl
3
.
Nucleus accumbens (NAc) is involved in behaviors that depend on heightened wakefulness, but its impact on arousal remains unclear. Here, we demonstrate that NAc dopamine D1 receptor (D1R)-expressing ...neurons are essential for behavioral arousal. Using in vivo fiber photometry in mice, we find arousal-dependent increases in population activity of NAc D1R neurons. Optogenetic activation of NAc D1R neurons induces immediate transitions from non-rapid eye movement sleep to wakefulness, and chemogenetic stimulation prolongs arousal, with decreased food intake. Patch-clamp, tracing, immunohistochemistry, and electron microscopy reveal that NAc D1R neurons project to the midbrain and lateral hypothalamus, and might disinhibit midbrain dopamine neurons and lateral hypothalamus orexin neurons. Photoactivation of terminals in the midbrain and lateral hypothalamus is sufficient to induce wakefulness. Silencing of NAc D1R neurons suppresses arousal, with increased nest-building behaviors. Collectively, our data indicate that NAc D1R neuron circuits are essential for the induction and maintenance of wakefulness.
High-selective bandpass filters (BPFs) based on novel multiple-mode substrate-integrated waveguide (SIW) cavities are proposed in this article. The multiple-mode SIW cavities are realized by a method ...of folded SIW (FSIW) structure, and its characteristics are analyzed in detail. Dual modes TE<inline-formula> <tex-math notation="LaTeX">_{102}</tex-math> </inline-formula> and TE<inline-formula> <tex-math notation="LaTeX">_{201}</tex-math> </inline-formula> in the normal SIW as well as modes TE<inline-formula> <tex-math notation="LaTeX">_{\mathrm{1/2,0,1/2}}</tex-math> </inline-formula>, TE<inline-formula> <tex-math notation="LaTeX">_{\mathrm{1/2,0,3/2}}</tex-math> </inline-formula>, and TE<inline-formula> <tex-math notation="LaTeX">_{\mathrm{3/2,0,1/2}}</tex-math> </inline-formula> in the FSIW can be exploited to realize multiple-mode cavities for BPFs' design because their resonant frequencies can be controlled flexibly. To demonstrate the multiple-mode SIW filters' design, two single-band triple-mode SIW BPFs with three finite-transmission zeros (FTZs) are proposed first. Then, dual-band and single-band quad-mode SIW BPFs with four FTZs are proposed. FTZs' locations of the proposed filters can be controlled well, and their controllability is analyzed. Finally, three SIW filters are designed, fabricated, and measured to verify the proposed filters and method. The proposed multiple-mode SIW filters have the advantages of high selectivity, compact size, and flexibly controllable FTZs' locations and bandwidth (BW).
Abstract
A switched‐beam circular array with ultra‐wideband ridged horn elements is proposed in this letter. To obtain stable radiation patterns in a broadband as well as in a large coverage in the ...elevation plane, the electromagnetic fields in the ridged horn antenna are analyzed by the mode decomposition method. Based on the analysis, the rear of the ridged horn is cut. Besides, the ridge extension, out of the horn aperture, serves as a transformer from the horn to the free space for the downward radiation caused by the horn aperture asymmetry. The simulated results show that the circular array can obtain omnidirectional beam coverage in the range of
θ
= 50°–100° from 2.2 to 5.9 GHz, with the
S
11
below −10 dB and the gain higher than 5 dBi. The performance of the proposed antenna is validated by experiments.
A novel wide-angle beam-scanning phase synthesis method, namely, multibeam phase matching method is introduced in this paper. It takes full advantage of angle sensitivity characteristic of ...reflectarray elements to improve the beam-scanning performance of reflectarrays. In the process of reflectarray aperture synthesis, the beam deviation factors and reference phases are optimized to minimize the total phase error, and the geometries of each element are optimized to match the desired phase shifts at multiple beam-scanning angles after taking into account the real incident angles. Then, a <inline-formula> <tex-math notation="LaTeX">16 \times 16 </tex-math></inline-formula>-element reflectarray antenna with square patch elements operating at 12 GHz has been designed, simulated, and fabricated. The measured results show that a gain variation less than 1.7 dB across the scan coverage from −45° to +45° can be achieved by mechanically rotating the feed antenna, which shows a considerable improvement in beam-scanning performance as compared to the reflectarrays designed using conventional single-focus and bifocal methods.
A wideband linearly polarized transmitarray antenna operating in 7-16 GHz is presented in this paper. First, a wideband element with three metallic layers is proposed, which is composed of a split ...circular ring connected by a narrow strip in the middle layer, and two polarizers in the upper and bottom layers. This element features a low transmission loss and approximately linear phase curves in a wide frequency band over one octave. Then, an optimization method is introduced to design the transmitarray that follows the bandwidth definition of 1 dB gain drop. The first key point of this method is determining the transmitarray element distribution with the weighted reference phases. The second is realizing wideband performances by controlling the calculated directivities and radiation patterns of the modified wideband transmitarray model at all operating frequencies. In the experiment, a <inline-formula> <tex-math notation="LaTeX">25\times 25 </tex-math></inline-formula>-element horn-fed transmitarray with a <inline-formula> <tex-math notation="LaTeX">240 \times 240 </tex-math></inline-formula> mm 2 aperture area is designed and fabricated. The simulated results show that its bandwidths of 0.5, 1.5, and 3 dB gain drop are 41%, 56%, and 71%, respectively. Moreover, a peak aperture efficiency of 40.7% is achieved. Measured results agree reasonably well with the simulated ones. These results validate the proposed wideband element and the optimization method.
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