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We reported an experimental and theoretical study on the promotion role of F doping in the improved catalytic performance of fluorinated graphene(F-GO) for ammonium perchlorate (AP) pyrolysis. F-GO was prepared by using graphite oxide (GO) as carbon sources and CF3COOH as fluorinating agent. Compared with other samples, the F-GO-180 with the highest F doping amounts, more C-F semi-ionic and C-F covalent bond amounts exhibit superior catalytic performance, as 10 wt% of catalyst added in AP, the exothermic peak temperature proceeded in just one step was even lower than the HTD peak temperature for pure AP and the released apparent specific heat of the thermal decomposition of AP catalyzed by F-GO-180 is 4261.2 J/g, which is almost sevenfold of that of pure AP (603.5 J/g). The doping of F atoms in graphene increased surface defects and the content of C-F semi-ionic and C-F covalent bond amounts of F-GO, which provided more active sites during the thermal decomposition of AP. The molecular simulation calculation results further confirmed that the F doping could react with the defect structure of graphene to form more C-F semi-ionic and C-F covalent bond, which could act as catalytic active sites and facilitate the electron transfer ability of the graphene to promote the formation of free radicals in the reaction. [ABSTRACT FROM AUTHOR]

Thermal stability of carbon based materials is crucial to their catalytic performance in oxidative dehydrogenation at high temperature. This work aims at exploring the mechanism for B doping to improve thermal stability and catalytic performance of N, B co-doped carbon (HC-N-B) for oxidative dehydrogenation of propane using CO2, which was prepared by using humic acids (HAs) extracted from Sheng Li lignite. Porous carbon (HC) from humic acids has low thermal stability in CO2 and N-doping resulted in the decreased thermal stability of HC. Interestingly, B doping HC-N showed very high thermal stability in CO2 (almost no weight-loss). Thus, HC-N-B could be used as considerable stable carbon catalysts with high catalytic activity for oxidative dehydrogenation of propane using CO2. Compared to porous carbon (HC) and N-doping porous carbon (HC-N) from HAs, the HC-N-B could remain the high catalytic dehydrogenation activity in 5 h. It was found that B doping on the defect structure in carbon skeleton structure of the HC-N could greatly increase the thermal stability of surface defects of N-doped porous carbon in CO2, and molecular simulation calculation results further confirmed that the existence of C-N-B and BC3 structure in the carbon skeleton defects could act as catalytic active sites in dehydrogenation reaction, which could slightly enhance the catalytic activity of the HC-N-B and largely improved its catalytic stability of the HC-N-B. [ABSTRACT FROM AUTHOR]

We propose a channel state information acquisition mechanism to reduce the training overhead in frequency-division duplexing (FDD) massive multiple-input multiple-output (MIMO) downlink (DL). While the massive MIMO has demonstrated the great potentials in many aspects, the carrier multiplexing designs in massive MIMO mostly adopt time-division duplexing (TDD) system, which stems from a stereotype that the uplink/DL channel reciprocity only holds for TDD. On the other hand, FDD massive MIMO is generally considered infeasible due to the unaffordable temporal overhead for sending training symbols at base station. Our proposed FDD with reverse training (FDD-RT) modifies the DL band training procedure in typical FDD system to reduce pilot overhead, where the DL band channel reciprocity is exploited in FDD-RT. FDD-RT contributes to providing a feasible and relatively low complexity method to implement massive MIMO in FDD system. Without FDD-RT, communication operators who currently use FDD system may be enforced to change to TDD system in the future to accommodate massive MIMO, where the cost is prohibitive. The most different property of FDD-RT from other solutions is that its training overhead does not scale with the number of antennas at base station. The detail analysis/comparison of FDD-RT will be given in this paper. [ABSTRACT FROM PUBLISHER]

In this paper, we propose coding-aided K-means clustering (CKMC) blind transceiver for space shift keying (SSK) multiple-input multiple-output (MIMO) systems, where the training of channel state information (CSI) is not required for detection. For the scenario where transmitter is with limited processing capability and limited power such as Internet Of Things (IOT) and wireless sensor network (WSN), SSK is preferable to typical MIMO due to its simplicity and improved energy efficiency. The proposed CKMC blind communication trades off receiver complexity for training overhead, which provides better spectral efficiency compared to training-based transceiver. In CKMC, the blind communication problem is converted to the problems of clustering and permutation; for the clustering problem, we propose K-means clustering (KMC) detector to reduce detection complexity; for the permutation problem, we propose to perform depermutation with the aid of channel decoding. The analysis of CKMC blind transceiver is conducted, and the verification of performance of CKMC is presented in the simulations section. The results show that the performance of CKMC blind communication can closely approach the performance of optimal receiver with perfect CSI under certain scenarios. [ABSTRACT FROM PUBLISHER]

We investigate the power allocation in generalized space-shift keying (GSSK) multiple-input–multiple-output (MIMO) systems. The maximum-likelihood detection with full channel state information (CSI) at the receiver is considered. The goal of the design is to allocate transmit power on GSSK antennas to minimize the symbol error rate (SER) under the total power constraint. An upper bound of SER conditioned on CSI is presented. We propose an algorithm, called the Euclidean distance-based power allocation scheme, to minimize the SER upper bound. Simulation results demonstrate the performance superiority in the proposed scheme compared with prior space-shift-keying-type schemes and the conventional MIMO schemes. [ABSTRACT FROM PUBLISHER]

Space shift keying (SSK) modulation and its extension, the generalized SSK (GSSK), present an attractive framework for the emerging large-scale MIMO systems in reducing hardware costs. In SSK, the maximum likelihood (ML) detector incurs considerable computational complexities. We propose a compressed sensing based detector, NCS, by formulating the SSK-type detection criterion as a convex optimization problem. The proposed NCS requires only O(n_tN_rN_t) complexity, outperforming the O(N_rN_t^n_t) complexity in the ML detector, at the cost of slight fidelity degradation. Simulations are conducted to substantiate the analytical derivation and the detection accuracy. [ABSTRACT FROM PUBLISHER]

Background: Patients with difficult weaning who undergo mechanical ventilation are more likely to be at risk of reintubation and the sequential use of oxygen therapy after extubation is a concern for clinicians. Therefore, the aim of the present study was to compare the effects of transnasal high-flow nasal cannula (HFNC) oxygen therapy and non-invasive positive-pressure ventilation (NIV) on respiratory mechanics in patients with difficult weaning., Methods: The present study was a single-center, retrospective, observational study. Twenty-nine patients with difficult weaning off invasive mechanical ventilation from the Department of Critical Care Medicine, The First Affiliated Hospital of Guangzhou Medical University, from December 2018 to April 2021, were included. Within 48 h after extubation, alternate respiratory support with HFNC and NIV was provided. Relevant indicators were recorded after each support mode had been maintained for at least 60 min. These included esophageal pressure (Pes), gastric pressure (Pga), transdiaphragmatic pressure (Pdi), pressure-time product of Pes (PTPes), pressure-time product of Pga (PTPga), pressure-time product of Pdi (PTPdi), ratio of the PTPdi to the PTPes (PTPdi/PTPes), and ratio of the Pes to the Pdi (Pes/Pdi), diaphragmatic electromyogram (EMGdi), percentage of esophageal pressure coefficient of variation (CVes%),diaphragmatic electromyogram coefficient of variation (CVEMG),inspiratory time (Ti), expiratory time (Te) and respiratory cycle time (Ttot)., Results: Of the 29 patients included, 22 were males and 7 were females [age: 63.97±15.34 years, Acute Physiological and Chronic Health Estimation II (APACHE II) score: 18.00±5.63]. The CVes% and the Pes/Pdi were significantly higher in patients with NIV than HFNC using 40 L/min, CVes%: 9 (-6, 20) vs. -7 (-23, 6) and Pes/Pdi: 0.17 (-0.1, 0.53), vs. -0.12 (-0.43, 0.08) (P<0.05). The remaining indicators were not statistically different., Conclusions: The sequential NIV and HFNC can be tolerated in patients with such difficult weaning off mechanical ventilation after extubation, and more patients tend to choose HFNC subjectively. Compared with HFNC, NIV reduces the work of adjunctive respiratory muscle, but the patient's Pes dispersion is high when NIV is used, and it is necessary to pay attention to patient-ventilator coordination in clinical practice. We recommend alternating HFNC and NIV during the sequential respiratory therapy after extubation., Competing Interests: Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://dx.doi.org/10.21037/atm-21-3408). The authors have no conflicts of interest to declare., (2021 Annals of Translational Medicine. All rights reserved.)