A multibeam beam-forming network (BFN) for generating 2-D multibeam array antenna (MAA) is proposed using single-layer substrate integrated waveguide (SIW) technology. Firstly, a new topology for ...building <inline-formula> <tex-math notation="LaTeX">16\times 16 </tex-math></inline-formula> BFNs is proposed, which successfully transforms the traditional topology from a 3-D configuration to a 2-D (or uniplanar) one. Two major challenges are tackled during this transformation, namely, the planarization of basic components and the reduction of excessive intersections between multiple paths. To this end, a novel design of eight-port hybrid couplers, as critical components of this BFN, is developed to transform a 3-D to a 2-D structure. Furthermore, a new design of eight-port crossover, which can address four path intersections simultaneously, is proposed to reduce the total number of path intersections from 16 to only 4. The proposed topology for <inline-formula> <tex-math notation="LaTeX">16\,\times \,16 </tex-math></inline-formula> BFNs allows all the basic components, including eight-port hybrid couplers, eight-port crossovers, and phase shifters, to be placed within a single-layer configuration. Fed by the proposed uniplanar <inline-formula> <tex-math notation="LaTeX">16\times 16 </tex-math></inline-formula> BFN, a 2-D MAA with 16 (<inline-formula> <tex-math notation="LaTeX">4\,\times \,4 </tex-math></inline-formula>) beams, which is capable of switching the beams in both elevation and azimuth directions, is realized. Compared with the previous 2-D Butler matrix (BM) designs using multilayer technology, it is for the first time that a uniplanar design of <inline-formula> <tex-math notation="LaTeX">16\times16 </tex-math></inline-formula> BFN is proposed and realized, which significantly simplifies the design and fabrication complexity.
A wideband dual-layer Huygens' unit cell based on offset electric dipole pair (OEDP) is proposed. Different from traditional designs with a combination of electric and magnetic polarizabilities, the ...proposed Huygens' unit cell exclusively employs electric polarizabilities. By doing so, it practically avoids the unbalanced resonant frequencies between the two polarizabilities, thereby achieving wideband transmission. Based on the proposed unit cell, a wideband and high-gain multibeam array antenna is developed. First, a Rotman lens is designed by using a substrate-integrated waveguide (SIW) technology. Then a parallel-fed slot antenna array is connected to the Rotman lens to generate multiple beams. Without using a series-fed slot antenna array, the multibeam array antenna based on Rotman lens can operate within a relatively wide bandwidth (28-32 GHz). Second, a wideband dual-layer Huygens' metasurface is developed that serves as a superstrate of the multibeam array antenna for increasing the antenna gain further. A wideband and high-gain multibeam array antenna is finally realized, which is comprised of a Rotman lens, a parallel-fed slot antenna array, and a Huygens' metasurface. To verify the performance of this design, a prototype is fabricated and its measured results are compared to the simulated counterparts.
A novel three-layer substrate-integrated waveguide (SIW) <inline-formula> <tex-math notation="LaTeX">9\times9 </tex-math></inline-formula> Butler matrix (BM) that can produce a broadside beam and ...wide-angle coverage is presented in this article. Unlike the traditional <inline-formula> <tex-math notation="LaTeX">8\times8 </tex-math></inline-formula> BM, the proposed BM is realized by cascading three-way couplers. Connecting to the radiation structure and feeding the center input port, a phase difference of 0° is observed and a broadside beam can be produced. When exciting the side input ports, a maximum phase difference of ±160° is obtained and wide-angle side beams are generated. The operation principle and design development of the <inline-formula> <tex-math notation="LaTeX">9\times9 </tex-math></inline-formula> BM are illustrated in detail to determine the topology and the phase shifters. With the desired phase differences and amplitude distributions, a three-layer topology of the <inline-formula> <tex-math notation="LaTeX">9\times9 </tex-math></inline-formula> BM is developed to reduce the footprint and improve the compactness, which is subsequently realized in SIW technology. To realize wide-angle coverage, a new endfire metasurface antenna derived from the traditional Vivaldi antenna is proposed, which achieves a fractional 10-dB impedance bandwidth of 72% and a half-power beamwidth (HPBW) of 128° at 28 GHz. By integrating the three-layer SIW <inline-formula> <tex-math notation="LaTeX">9\times9 </tex-math></inline-formula> BM with an endfire metasurface antenna array, a wide-angle endfire multibeam metasurface antenna is obtained, which achieves a wide HPBW coverage of ±113° and a maximum gain of 12.1 dBi. The topology of an extended single-layer <inline-formula> <tex-math notation="LaTeX">18\times18 </tex-math></inline-formula> BM based on the designed <inline-formula> <tex-math notation="LaTeX">9\times9 </tex-math></inline-formula> BM is presented, and multilayer solutions are adopted to demonstrate the possibility of realizing higher order BMs.
A parallel-plate Luneburg lens (LL) based on all-metal metamaterial is presented in this paper. To achieve the required refractive index distribution of the LL, an all-metal unit cell with a ...separated cuboid is proposed, whose height is related to its refractive index. This inserted cuboid is attached to neither the top plate nor the bottom plate of the parallel plate. Compared with traditional bed of nail design, the proposed metamaterial unit cell exhibits a wider bandwidth. The operation principle of such a unit cell is investigated using the transverse resonance technique. To construct the all-metal metamaterial LL into one body, a cruciform cuboid is added to each unit cell such that adjacent unit cells can connect to each other. Based on the designed metamaterial LL, a multibeam antenna is developed by providing seven inputs, which can generate seven predefined beams. Several parts of the prototype are separately fabricated and assembled, and good agreement is observed between simulation and measurement. The designed LL based multibeam antenna has several advantages, including wide bandwidth, high aperture efficiency, and high radiation efficiency.
A multibeam array antenna (MAA) fed by a Rotman lens with a reduced sidelobe level (SLL) is designed using a substrate integrate waveguide (SIW) technology. The designed MAA is composed of a Rotman ...lens and a 12 × 8 slot array, which functions as the beamforming network and the radiation part, respectively. To reduce the SLL in E-plane, dual-port excitations (DPEs) are applied, instead of single-port excitations (SPEs), at each feeding port of the Rotman lens. By using DPEs, a more tapered amplitude distribution can be obtained on the array elements as compared to using SPEs; therefore, the SLL is reduced from about -11 to -18 dB. The SLL in H-plane is controlled by introducing a Chebyshev distribution to the designed eight-element slot array. Based on the designed MAA, a fabricated prototype is measured to test the discrepancy between simulation and experiment.
Fungi play an irreplaceable role in drug discovery in the course of human history, as they possess unique abilities to synthesize diverse specialized metabolites with significant medicinal potential.
...Trichoderma
are well-studied filamentous fungi generally observed in nature, which are widely marketed as biocontrol agents. The secondary metabolites produced by
Trichoderma
have gained extensive attention since they possess attractive chemical structures with remarkable biological activities. A large number of metabolites have been isolated from
Trichoderma
species in recent years. A previous review by Reino et al. summarized 186 compounds isolated from
Trichoderma
as well as their biological activities up to 2008. To update the relevant list of reviews of secondary metabolites produced from
Trichoderma
sp., we provide a comprehensive overview in regard to the newly described metabolites of
Trichoderma
from the beginning of 2009 to the end of 2020, with emphasis on their chemistry and various bioactivities. A total of 203 compounds with considerable bioactivities are included in this review, which is worth expecting for the discovery of new drug leads and agrochemicals in the foreseeable future. Moreover, new strategies for discovering secondary metabolites of
Trichoderma
in recent years are also discussed herein.
Many positive-strand RNA viruses, including all known coronaviruses, employ programmed −1 ribosomal frameshifting (−1 PRF) to regulate the translation of polycistronic viral RNAs. However, only a few ...host factors have been shown to regulate −1 PRF. Through a genome-wide CRISPR-Cas9 knockout screen, we have identified host factors that either suppress or enhance severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) –1 PRF. Among them, eukaryotic translation initiation factor 2A (eIF2A) specifically and directly enhances −1 PRF independent of changes in initiation. Consistent with the crucial role of efficient −1 PRF in transcriptase/replicase expression, loss of eIF2A reduces SARS-CoV-2 replication in cells. Furthermore, transcriptome-wide analysis shows that eIF2A preferentially binds CG-rich RNA motifs, including a region within 18S ribosomal RNA near the contacts between the SARS-CoV-2 frameshift-stimulatory element (FSE) and the ribosome. Thus, our results indicate a role for eIF2A in modulating the translation of specific RNAs independent of its role during initiation.
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•CRISPR-Cas9 screens identify modulators of SARS-CoV-2 –1 PRF•eIF2A enhances −1 PRF independent of its previously described role in initiation•Loss of eIF2A reduces SARS-CoV-2 replication in cells•eIF2A preferentially binds CG-rich RNA motifs
A translation recoding event known as programmed −1 ribosomal frameshifting is critical for SARS-CoV-2 replication. Through CRISPR-based genetic screens, Wei et al. identify an unexpected role of noncanonical translation factor eIF2A in promoting this process. As a result, deleting eIF2A reduces SARS-CoV-2 replication in cells.
A new topology for 2-D scanning multibeam array antenna (MAA) design is proposed. Different from the traditional 2-D scanning scheme, this new design approach is composed of a 1-D beam-forming ...network (BFN) and a set of 1-D pattern-reconfigurable antennas, which can together realize 2-D multibeam scanning. Compared with traditional schemes, the proposed topology has advantages of uniplanar configuration and better flexibility in scaling up the array. To demonstrate the validity of the proposed topology, a high-gain 2-D scanning leaky-wave MAA operating at 10 GHz is designed. A horn BFN and a fixed-frequency leaky-wave antenna (LWA) are designed as the feeding part and radiation part, respectively. A number of new techniques are also developed for the design. For the horn BFN, a new phase-compensation method to reduce the gain drop is presented and phase inverters are introduced to provide an extra 180° of phase shift. Meanwhile, some modification of the LWA is conducted for better compatibility between the horn BFN and the LWA. A substrate integrated waveguide (SIW) to half-mode SIW (HMSIW) transition is introduced between the horn BFN and the LWA. The LWAs are terminally shorted to avoid the usage of matched loads. The width of the LWA is investigated to achieve suitable beam coverage and S-parameters. Finally, the antenna is fabricated and experiments are conducted to verify the agreement between simulation and measurement.
This letter presents a multibeam antenna array fed by a substrate integrated waveguide 8 × 8 dual-layer Butler matrix within the band from 28 to 31 GHz. The dual-layer structure is adopted aiming to ...achieve miniature, so that the size of the structure is reduced by more than 50% compared with similar single-layer design. The utilization of dual-layer structure also decreases the complexity of the whole Butler matrix. A 2 × 8 slot antenna array is used as the radiating portion to obtain high gains and relatively low side lobe levels. The proposed multibeam antenna array is fabricated and tested to verify the performances.
The dynamic recrystallization behavior of a medium carbon vanadium microalloyed steel was systematically investigated at the temperatures from 900°C to 1100°C and strain rates from 0.01s−1 to 10s−1 ...on a Gleeble-1500 thermo-simulation machine. The flow stress constitutive equation of hot deformation for this steel was developed with the activation energy Q being about 273kJ/mol, which is in reasonable agreement with those reported before. Activation energy analysis showed that vanadium addition in microalloyed steels seemed not to affect the activation energy much. The effect of Zener–Hollomon parameter on the characteristic points of flow curves was studied using the power law relation, and the dependence of critical strain (stress) on peak strain (stress) obeyed a linear equation. Dynamic recrystallization is the most important softening mechanism for the experimental steel during hot compression. The dynamic recrystallization kinetics model of this steel was established based on flow stress and a frequently-used dynamic recrystallization kinetics equation. Dynamic recrystallization microstructure under different deformation conditions was also observed and the dependence of steady-state grain size on the Zener–Hollomon parameter was plotted.
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