In this paper, we propose closed-form precoding schemes with optimal performance for constructive interference (CI) exploitation in the multiuser multiple-input single-output downlink, where the ...cases of both strict and non-strict phase rotation are considered. For optimization with strict phase rotation, we mathematically derive the optimal precoding structure with Lagrangian and Karush-Kuhn-Tucker conditions. By formulating its dual problem, the optimization problem is further shown to be equivalent to a quadratic programming over a simplex, which can be solved more efficiently. We then extend our analysis to the case of non-strict phase rotation, where it is mathematically shown that a K -dimensional optimization for non-strict phase rotation is equivalent to a 2K -dimensional optimization for strict phase rotation in terms of the problem formulation. The connection with the conventional zero-forcing precoding is also discussed. Based on the above-mentioned analysis, we further propose an iterative closed-form scheme to obtain the optimal precoding matrix, where within each iteration a closed-form solution can be obtained. Numerical results validate our analysis and the optimality of the proposed iterative closed-form algorithm, and further show that the proposed iterative closed-form scheme offers a flexible performance-complexity tradeoff by limiting the maximum number of iterations, which motivates the use of CI precoding in practical wireless systems.
In this letter, we propose a low-complexity hybrid precoding and combining design for the millimeter-wave MU-MIMO transmission, applicable to both fully connected and sub-connected structures. Analog ...precoding and combining schemes are first designed, where a joint approach, a decoupled approach, and a sub-optimal approach are proposed to harvest the array gain. Virtual path selection is performed to maximize the channel gain of the analog effective channel. Then, based on the effective channel, a low-dimensional zero-forcing precoding is applied in the baseband to manage the interference. The simulation results show that the proposed techniques offer an enhanced performance-complexity tradeoff compared with both existing hybrid schemes and fully digital schemes.
Photocatalysis is a promising route to convert solar energy into chemical energy directly, providing an alternative solution to environment and natural resource problems. Theoretically, all ...photocatalytic reactions are driven by charge carriers whose behavior can be divided into charge generation, separation, migration and surface reactions. Efficiencies of charge utilization in every step determine the overall performance of photocatalysis. Yolk-shell (YS) structures can provide an ideal platform for the efficient utilization of charge carriers. Typically, a YS structure is constructed from a hollow shell and an inner core, which can enhance light scattering in the hollow space and provide a large surface to create sufficient active sites, both of which can significantly improve the efficacy of charge utilization. Additionally, many strategies can be adopted to modify the YS structure for further enhancement of charge behaviors in every step. Existing reviews about YS structures mainly concentrate on the universality of the application of YSs, while the strategies to improve photocatalytic performance based on YSs have not been elaborately illustrated. This review describes the classification, synthesis, formation mechanism of YS structures and the rational regulation of the behaviors of photogenerated charge carriers, aiming at their effective utilization based on YS structures in heterogeneous photocatalytic reactions.
Yolk-shell structures provide an ideal platform for the rational regulation and effective utilization of charge carriers because of their void space and large surface areas. Furthermore, the efficiency of charge behavior in every step can be further improved by many strategies. This review describes the synthesis of yolk-shell structures and their effect for the enhancement of heterogeneous photocatalysis.
Simultaneous wireless information and power transfer (SWIPT) enables the transmission of information symbols and energy simultaneously. In this paper, we study the multiple-input-multiple-output ...SWIPT systems with limited RF chains at the base station. We focus on the scenario where there is one information decoder with a target signal-to-interference-plus-noise-ratio and several separate energy-harvesting receivers with harvested energy thresholds. To motivate our energy-efficient hybrid analog-digital beamforming strategy, the fully digital power minimization problem is first analyzed, where we mathematically show that the optimal beamformer consists of only the information beamformer, and derive closed-form beamformers for a number of special cases. Based on this result, we further consider hybrid beamforming and propose an iterative scheme where the analog and digital beamformers are alternately updated. For the proposed scheme, in each iteration we design the analog beamformer by minimizing the difference between the fully digital beamformer and the hybrid beamformer. Based on our above-mentioned analysis for fully digital case, the optimal solution for the analog beamformer can be obtained via a geometrical interpretation. We further design the robust beamformers for the proposed schemes, when only imperfect channel state information is available. The numerical results show that the proposed iterative designs achieve a close-to-optimal performance with significant gains in the total power consumption over fully digital SWIPT.
Abstract
We perform a Bayesian analysis of the maximum mass
M
TOV
of neutron stars with a quark core, incorporating the observational data from tidal deformability of the GW170817 binary neutron star ...merger as detected by LIGO/Virgo and the mass and radius of PSR J0030+0451 as detected by the Neutron Star Interior Composition Explorer. The analysis is performed under the assumption that the hadron–quark phase transition is of first order, where the low-density hadronic matter described in a unified manner by the soft QMF or the stiff DD2 equation of state (EOS) transforms into a high-density phase of quark matter modeled by the generic “constant-sound-speed” parameterization. The mass distribution measured for the 2.14
M
⊙
pulsar MSP J0740+6620 is used as the lower limit on
M
TOV
. We find the most probable values of the hybrid star maximum mass are
M
TOV
=
2.36
−
0.26
+
0.49
M
⊙
(
2.39
−
0.28
+
0.47
M
⊙
) for QMF (DD2), with an absolute upper bound around 2.85
M
⊙
, to the 90% posterior credible level. Such results appear robust with respect to the uncertainties in the hadronic EOS. We also discuss astrophysical implications of this result, especially on the postmerger product of GW170817, short gamma-ray bursts, and other likely binary neutron star mergers.
We present an ultra-compact single-shot spectrometer on silicon platform for sparse spectrum reconstruction. It consists of 32 stratified waveguide filters (SWFs) with diverse transmission spectra ...for sampling the unknown spectrum of the input signal and a specially designed ultra-compact structure for splitting the incident signal into those 32 filters with low power imbalance. Each SWF has a footprint less than 1 µm × 30 µm, while the 1 × 32 splitter and 32 filters in total occupy an area of about 35 µm × 260 µm, which to the best of our knowledge, is the smallest footprint spectrometer realized on silicon photonic platform. Experimental characteristics of the fabricated spectrometer demonstrate a broad operating bandwidth of 180 nm centered at 1550 nm and narrowband peaks with 0.45 nm Full-Width-Half-Maximum (FWHM) can be clearly resolved. This concept can also be implemented using other material platforms for operation in optical spectral bands of interest for various applications.
We study multi-user massive multiple-input single-output systems and focus on downlink transmission for PSK modulation, where the base station employs a large antenna array with low-cost 1-bit ...digital-to-analog converters (DACs). The direct combination of existing beamforming schemes with 1-bit DACs is shown to lead to an error floor at medium-to-high SNR regime, due to the coarse quantization of the DACs with limited precision. In this paper, based on the constructive interference, we consider both a quantized linear beamforming scheme where we analytically obtain the optimal beamforming matrix and a non-linear mapping scheme where we directly design the transmit signal vector. Due to the 1-bit quantization, the formulated optimization for the non-linear mapping scheme is shown to be non-convex. The non-convex constraints of the 1-bit DACs are first relaxed into convex, followed by an element-wise normalization to satisfy the 1-bit DAC transmission. We further propose a low-complexity symbol scaling scheme that consists of three stages, in which the quantized transmit signal on each antenna element is selected sequentially. Numerical results show that the proposed symbol scaling scheme achieves a comparable performance to the optimization-based non-linear mapping approach, while the corresponding performance-complexity tradeoff is more favorable for the proposed symbol scaling method.
High-performance lightweight architectures, such as metallic microlattices with excellent mechanical properties have been 3D printed, but they do not possess shape memory effect (SME), limiting their ...usages for advanced engineering structures, such as serving as a core in multifunctional lightweight sandwich structures. 3D printable self-healing shape memory polymer (SMP) microlattices could be a solution. However, existing 3D printable thermoset SMPs are limited to either low strength, poor stress memory, or non-recyclability. To address this issue, a new thermoset polymer, integrated with high strength, high recovery stress, perfect shape recovery, good recyclability, and 3D printability using direct light printing, has been developed in this study. Lightweight microlattices with various unit cells and length scales were printed and tested. The results show that the cubic microlattice has mechanical strength comparable to or even greater than that of metallic microlattices, good SME, decent recovery stress, and recyclability, making it the first multifunctional lightweight architecture (MLA) for potential multifunctional lightweight load carrying structural applications.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Thermal energy harvesting technologies based on composite phase change materials (PCMs) are capable of harvesting tremendous amounts of thermal energy
via
isothermal phase transitions, thus showing ...enormous potential in the design of state-of-the-art renewable energy infrastructure. Great progress has been recently made in terms of enhancing the thermal energy storage capability, transfer rate, conversion efficiency and utilization of composite PCMs. Although there are some recent reviews on composite PCMs, they are mainly concentrated on the thermal transfer enhancement and conventional utilization of PCMs. There are few systematic reviews concerning optimization strategies of PCM for thermal energy conversion. In particular, advanced multifunctional utilization of PCMs is still in its infancy. Herein, we systematically summarize the optimization strategies and mechanisms of recently reported composite PCMs for thermal energy storage, thermal transfer, energy conversion (solar-to-thermal, electro-to-thermal and magnetic-to-thermal conversion) and advanced utilization (fluorescence emission, infrared stealth technologies, drug release systems, thermotherapy and thermal protection), including some novel supporting materials (BN nanosheets and metal organic frameworks (MOFs)). Simultaneously, we provide in-depth and constructive insights into the correlations between the structural optimization strategies and thermal performances of composite PCMs. Finally, future research trends, alternative strategies and prospects are also highlighted according to up-to-date optimization strategies.
Thermal energy harvesting technologies based on composite phase change materials (PCMs) are capable of harvesting tremendous amounts of thermal energy
via
isothermal phase transitions, thus showing enormous potential in the design of state-of-the-art renewable energy infrastructure.
Beamforming techniques are proposed for a joint multi-input-multi-output (MIMO) radar-communication (RadCom) system, where a single device acts as radar and a communication base station (BS) by ...simultaneously communicating with downlink users and detecting radar targets. Two operational options are considered, where we first split the antennas into two groups, one for radar and the other for communication. Under this deployment, the radar signal is designed to fall into the null-space of the downlink channel. The communication beamformer is optimized such that the beampattern obtained matches the radar's beampattern while satisfying the communication performance requirements. To reduce the optimizations' constraints, we consider a second operational option, where all the antennas transmit a joint waveform that is shared by both radar and communications. In this case, we formulate an appropriate probing beampattern, while guaranteeing the performance of the downlink communications. By incorporating the SINR constraints into objective functions as penalty terms, we further simplify the original beamforming designs to weighted optimizations, and solve them by efficient manifold algorithms. Numerical results show that the shared deployment outperforms the separated case significantly, and the proposed weighted optimizations achieve a similar performance to the original optimizations, despite their significantly lower computational complexity.
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