Two-Dimensional Transceiver Beamforming for Mainlobe Jamming Suppression with FDA-MIMO Radar

With the rapid development of electronic warfare technology, the airborne electronic counter measures (ECM) system can generate mainlobe jamming using range gate pull-off (RGPO) strategy, which brings serious performance degradation of target tracking for the tracking and guidance radar. In this study, a two-dimensional transceiver beamforming approach is proposed to suppress the mainlobe jamming with frequency diverse array using multiple-input multiple-output (FDA-MIMO) radar. The mainlobe jamming signal differs from the real target echo in the joint transmit and receive domain due to the range dependence of FDA beampattern. The amplitude of RGPO signal is greater than the amplitude of real target echo. Thus, the transceiver beampattern can be designed to null out the jamming while maintaining the real target. The jamming suppression performance is studied in consideration of practical range constraint of RGPO. Simulation results are provided to verify the effectiveness of the proposed approach

The Spatially Separated Polarization Sensitive FDA-MIMO Radar: A New Antenna Structure for Unambiguous Parameter Estimation

Joint DOA-range-polarization estimation with a novel radar system, i.e., spatially separated polarization sensitive random frequency diverse array based on multiple-input multiple-output (SS-PSRFDA-MIMO) radar, is discussed. The proposed array can obtain not only unambiguous range estimation but also polarization parameter estimation. Firstly, the signal model of SS-PSRFDA-MIMO radar is constructed. Secondly, dimension reduction multiple signal classification (DR-MUSIC) algorithm is extended to parameter estimation with the proposed array. Last, simulations demonstrate the proposed algorithm is effective to estimate parameter, and the performance of proposed array is better than that of polarization sensitive frequency diverse array based on MIMO radar. It is worth mentioning that the Cramér–Rao lower bound (CRLB) of range estimation with the proposed array is much lower than that of PSFDA-MIMO radar

Raman Spectral and Density Functional Theory Analyses of the CsB₃O₅ Melt Structure

Melt structures are essential to understand a variety of crystal growth phenomena of alkali-metal triborates, but have not been fully explored. In this work, Raman spectroscopy, coupled with the density functional theory (DFT) method, has been used to solve the CsB₃O₅ (CBO) melt structure. When the CBO crystal melts, the extra-ring B₄–Ø bonds (the B–Ø bonds of BØ₄ groups, Ø = bridging oxygen atom) that connect two B₃O₃Ø₄ rings (the basic boron–oxygen unit in the CBO crystal structure) break. As a result, the three-dimensional boron–oxygen network collapses to unique polymer-like [B₃O₄Ø₂]_<i>n</i> chains. On the basis of the optimized [B₃O₄Ø₂]_<i>n</i> chain model, the CBO melt Raman spectrum was calculated by the DFT method for the first time and the calculated results confirm that the [B₃O₄Ø₂]_<i>n</i> chain is the primary species in the CBO melt. These results also demonstrate the capability of the combined Raman spectral and DFT method for analyzing borate melt structures

Raman and Density Functional Theory Studies of Li₂Mo₄O₁₃ Structures in Crystalline and Molten States

The Li₂Mo₄O₁₃ melt structure and its Raman spectral characteristics are the key for establishing the composition–structure relationship of lithium molybdate melts. In this work, Raman spectroscopy, factor group analysis, and density functional theory (DFT) were applied to investigate the structural and spectral details of the <i>H</i>-Li₂Mo₄O₁₃ crystal and a Li₂Mo₄O₁₃ melt. Factor group analysis shows that the crystal has 171 vibrational modes (84A_g + 87A_u), including three acoustic modes (3A_u), six librational modes (2A_g + 4A_u), 21 translational modes (7A_g + 14A_u), and 141 internal modes (75A_g + 66A_u). All of the A_g modes are Raman-active and were assigned by the DFT method. The Li₂Mo₄O₁₃ melt structure was deduced from the <i>H</i>-Li₂Mo₄O₁₃ crystal structure and demonstrated by the DFT method. The results show that the Li₂Mo₄O₁₃ melt is made up of Li⁺ ions and Mo₄O₁₃^2– groups, each of which is formed by four corner-sharing MoO₃Ø/MoO₂Ø₂ tetrahedra (Ø = bridging oxygen). The melt has three acoustic modes (3A) and 54 optical modes (54A). All of the optical modes are Raman-active and were accurately assigned by the DFT method

Investigation on the Structure of a LiB₃O₅–Li₂Mo₃O₁₀ High-Temperature Solution for Understanding the Li₂Mo₃O₁₀ Flux Behavior

LiB₃O₅ is the most widely used nonlinear optical crystal. Li₂Mo₃O₁₀ (a nominal composition) is a typical flux used to produce large-sized and high-quality LiB₃O₅ crystals. The structure of the LiB₃O₅–Li₂Mo₃O₁₀ high-temperature solution is essential to understanding the flux behavior of Li₂Mo₃O₁₀ but still remains unclear. In this work, high-temperature Raman spectroscopy combined with density functional theory (DFT) was applied to study the LiB₃O₅–Li₂Mo₃O₁₀ solution structure. Raman spectra of a LiB₃O₅–Li₄Mo₅O₁₇–Li₂Mo₄O₁₃ polycrystalline mixture were recorded at different temperatures until the mixture melted completely. The solution structure was deduced from the spectral changes and verified by DFT calculations. When the mixture began to melt, its molybdate component first changed into the Li₂Mo₃O₁₀ melt; meanwhile, the complicated molybdate groups existing in the crystalline state transformed into Mo₃O₁₀^2– groups, which are formed by three corner-sharing MoO₃Ø^–/MoO₂Ø₂ (Ø = bridging oxygen atom) tetrahedra. When LiB₃O₅ dissolved in the Li₂Mo₃O₁₀ melt, the crystal structure collapsed into polymeric chains of [B₃O₄Ø₂^–]_<i>n</i>. Its basic structural unit, the B₃O₄Ø₂^– ring, coordinated with the Mo₃O₁₀^2– group to form a MoO₃·B₃O₄Ø₂^– complex and a Mo₂O₇^2– group. On the basis of the LiB₃O₅–Li₂Mo₃O₁₀ solution structure, we discuss the LiB₃O₅ crystal growth mechanism and the compositional dependence of the solution viscosity

Discovery of SHR9352: A Highly Potent G Protein-Biased μ‑Opioid Receptor Agonist

Recently, targeting the G protein-biased signaling has emerged as an attractive therapeutic strategy for treating severe acute pain with the potential to reduce the side effect of the traditional opioid drug. Herein, we describe the discovery of a highly potent G protein-biased μ-opioid receptor (MOR) agonist, SHR9352. This novel molecule exhibited excellent MOR activity and limited β-arrestin recruitment, as well as a high selectivity over κ-opioid receptor and δ-opioid receptor demonstrated robust in vivo efficacy and displayed favorable pharmacokinetic properties across species