This paper investigates the downlink (DL) transmit design for massive multiple-input multiple-output (MIMO) low-earth-orbit (LEO) satellite communication systems, where only the slow-varying ...statistical channel state information is exploited at the transmitter. The channel model for the DL massive MIMO LEO satellite system is established, in which both the satellite and the user terminals (UTs) are equipped with uniform planar arrays. Observing the rank-one property of the channel matrices, we show that the single-stream precoding for each UT is the optimal choice that maximizes the ergodic sum rate. This favorable result simplifies the complicated design of transmit covariance matrices into that of precoding vectors without any loss of optimality. Then, an efficient algorithm is devised to compute the precoding vectors. Furthermore, we formulate an approximate transmit design based on the upper bound on the ergodic sum rate, for which the optimality of single-stream precoding still holds. We show that, in this case, the design of precoding vectors can be simplified into that of scalar variables, for which an effective algorithm is developed. In addition, a low-complexity learning framework is proposed for optimizing the scalar variables. Simulation results demonstrate that the proposed approaches can achieve significant performance gains over the existing schemes.
With the development of digital technology, digital dance movement recognition and correction has become a hot research topic. This study focuses on a movement recognition system that incorporates ...human skeletal information and aims to improve dance movements’ accuracy and correction efficiency. This study develops a digital dance movement recognition and correction system that combines human lean information. This system can recognize and correct dance movements accurately by improving the spatio-temporal graph convolutional network (ST-GCN). The study employs a spatio-temporal graph representation of the human skeleton and spatial graph convolution technique, and enhances the system’s movement recognition capability through an adaptive graph convolution module. The experimental results show that the system achieves an average accuracy of 99.3% in dance movement recognition, 82% and 92% on the publicly available datasets UTKinect and MSRAction3D, respectively, and 95% on the dance movement dataset ETHDance constructed in this study. In addition, by introducing channel, spatial and temporal attention mechanisms, the system also shows high efficiency in dance movement correction. For the correction test of 10 basic dance movements, the correction accuracy is more than 95%, significantly higher than the 69.91% of the traditional method. This study improves the accuracy of dance movement recognition and provides adequate technical support for dance teaching and practicing.
Recently, by taking advantage of evolutionary multiobjective optimization techniques in diversity preservation, the means of multiobjectivization has attracted increasing interest in the studies of ...multimodal optimization (MMO). While most existing work of multiobjectivization aims to find all optimal solutions simultaneously, in this paper, we propose to approximate multimodal fitness landscapes via multiobjectivization, thus providing an estimation of potential optimal areas. To begin with, an MMO problem is transformed into a multiobjective optimization problem (MOP) by adding an adaptive diversity indicator as the second optimization objective, and an approximate fitness landscape is obtained via optimization of the transformed MOP using a multiobjective evolutionary algorithm. Then, on the basis of the approximate fitness landscape, an adaptive peak detection method is proposed to find peaks where optimal solutions may exist. Finally, local search is performed inside the detected peaks on the approximate fitness landscape. To assess the performance of the proposed algorithm, extensive experiments are conducted on 20 multimodal test functions, in comparison with three state-of-the-art algorithms for MMO. Experimental results demonstrate that the proposed algorithm not only shows promising performance in benchmark comparisons, but also has good potential in assisting preference-based decision-making in MMO.
We report the synthesis, crystal structures, and spectral, thermal, and magnetic properties of a family of metal–organic perovskite ABX3, C(NH2)3MII(HCOO)3, in which A=C(NH2)3 is guanidinium, B=M is ...a divalent metal ion (Mn, Fe, Co, Ni, Cu, or Zn), and X is the formate HCOO−. The compounds could be synthesized by either diffusion or hydrothermal methods from water or water‐rich solutions depending on the metal. The five members (Mn, Fe, Co, Ni, and Zn) are isostructural and crystallize in the orthorhombic space group Pnna, while the Cu member in Pna21. In the perovskite structures, the octahedrally coordinated metal ions are connected by the anti–anti formate bridges, thus forming the anionic NaCl‐type M(HCOO)3− frameworks, with the guanidinium in the nearly cubic cavities of the frameworks. The Jahn–Teller effect of Cu2+ results in a distorted anionic Cu–formate framework that can be regarded as Cu–formate chains through short basal CuO bonds linked by the long axial CuO bonds. These materials show higher thermal stability than other metal–organic perovskite series of AmineHM(HCOO)3 templated by the organic monoammonium cations (AmineH+) as a result of the stronger hydrogen bonding between guanidinium and the formate of the framework. A magnetic study revealed that the five magnetic members (except Zn) display spin‐canted antiferromagnetism, with a Néel temperature of 8.8 (Mn), 10.0 (Fe), 14.2 (Co), 34.2 (Ni), and 4.6 K (Cu). In addition to the general spin‐canted antiferromagnetism, the Fe compound shows two isothermal transformations (a spin‐flop and a spin‐flip to the paramagnetic phase) within 50 kOe. The Co member possesses quite a large canting angle. The Cu member is a magnetic system with low dimensional character and shows slow magnetic relaxation that probably results from the domain dynamics.
Nice cubes: A family of metal–organic perovskite salts of C(NH2)3M(HCOO)3 for divalent Mn to Zn were synthesized from water or water‐rich solutions. They possess anionic NaCl‐type frameworks of M(HCOO)3 with guanidinium in the cubic cavities (see figure); the magnetic members show spin‐canted antiferromagnetism.
The synthesis of coupled resonator bandpass filters has been a classic theme of research for the past half century. Continuous efforts have been paid to explore new coupling topologies. Needless to ...say, the ultimate goal for filter synthesis is to find all the viable coupling topologies and their real-valued circuit models. In this article, a rigorous and straightforward framework for exhaustive search of not only all the viable coupling topologies but also all their real coupling matrices for a given filtering function is presented. The proposition that provides sufficient and necessary condition for a viable coupling topology with finite real coupling matrices is proved. The uniqueness of the folded coupling matrix is also proved and is used to establish the simultaneous equations for a well-behaved numerical solution search process. The special cases of the proposition are discussed with illustrative examples. Demonstration examples, including a prototyped filter in a novel "grid" coupling topology, have shown that the framework can systematically find all the viable coupling topologies and their real-valued solutions numerically, through which many new useful coupling configurations can be found, including the "trapezoid" configuration that is highly suitable for a dual-mode realization for a symmetric/asymmetric filter response.
In this article, a novel dual-mode monoblock dielectric resonator (MDR) for compact monoblock dielectric bandpass filters is presented and put into practical use for the first time. In the dual-mode ...resonator, two dissimilar TEM modes are generated by forming two perpendicular metalized blind holes in a silver-coated cuboid-shapes dielectric block. The resonator can maximize the space utilization with up to 50% volume reduction while maintaining a wide spurious-free frequency band. The coupling of the two modes in such a resonator can be effectively controlled by one or more partial-height metalized posts. A convenient input/output (I/O) coupling scheme for surface-mount applications is introduced, and versatile coupling arrangements for realizing various filter characteristics are presented. To demonstrate the proposed filter miniaturization technique, a six-pole inline bandpass filter with one pure imaginary transmission zero (TZ) in a 3.5-GHz band is electromagnetic (EM) designed, and a ten-pole symmetric bandpass filter with two pure imaginary TZs in a 2.6-GHz band of fifth-generation (5G) new radio (NR) frequency band is designed, prototyped, and tuned. Experimental results show that the proposed dual-mode MDR filter can obtain an acceptable RF performance for 5G applications with a significant volume reduction compared to existing single-mode solutions.
In this article, the comprehensive theory for synthesis of a dispersive box coupling section for full control of two transmission zeros (TZs) is presented and applied to the design of ...high-<inline-formula> <tex-math notation="LaTeX">Q</tex-math> </inline-formula> monoblock dielectric resonator (MDR) filters. Compared to the traditional cascaded quadruplet (CQ) MDR section, the dispersive box section provides high flexibility in controlling TZs, a wide spurious free high rejection band, simplicity in physical realization, and higher unloaded <inline-formula> <tex-math notation="LaTeX">Q</tex-math> </inline-formula>s. The analytic transformation for converting a traditional CQ section with diagonal cross coupling to a dispersive box is given to facilitate the direct synthesis and justifies the uniqueness of the realizable solution to all possible TZ arrangements. Circuit realizations of all possible TZ arrangements are discussed with synthesized coupling matrices. A practical eight-pole MDR filter with an asymmetric response is synthesized and prototyped. Excellent agreement between the synthesized and measured narrowband responses as well as the EM simulated and measured wideband responses affirms the great flexibility in controlling TZs and demonstrates a wide spurious-free high rejection band with the proposed dispersive box structure. The low in-band insertion loss demonstrates that the MDR filter using the dispersive box can be potentially applied in 5G and future wireless communication systems.
Shifting H bonds: Concerted hydrogen‐bond strengthening and weakening in different excited states can tune energy gaps between low‐lying electronic states and thus account for the photochemistry of ...thiocarbonyl chromophores in alcoholic solutions (see picture). Also, the relationship between electronic spectral shifts and the electronic excited‐state hydrogen‐bonding changes is clarified.
The time-dependent density functional theory (TDDFT) method was carried out to investigate the hydrogen-bonded intramolecular charge-transfer (ICT) excited state of 4-dimethylaminobenzonitrile ...(DMABN) in methanol (MeOH) solvent. We demonstrated that the intermolecular hydrogen bond Cidentical withN···H---O formed between DMABN and MeOH can induce the Cidentical withN stretching mode shift to the blue in both the ground state and the twisted intramolecular charge-transfer (TICT) state of DMABN. Therefore, the two components at 2091 and 2109 cm⁻¹ observed in the time-resolved infrared (TRIR) absorption spectra of DMABN in MeOH solvent were reassigned in this work. The hydrogen-bonded TICT state should correspond to the blue-side component at 2109 cm⁻¹, whereas not the red-side component at 2091 cm⁻¹ designated in the previous study. It was also demonstrated that the intermolecular hydrogen bond Cidentical withN···H---O is significantly strengthened in the TICT state. The intermolecular hydrogen bond strengthening in the TICT state can facilitate the deactivation of the excited state via internal conversion (IC), and thus account for the fluorescence quenching of DMABN in protic solvents. Furthermore, the dynamic equilibrium of these electronically excited states is explained by the hydrogen bond strengthening in the TICT state.
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