In frequency division duplex mode, the downlink channel state information (CSI) should be sent to the base station through feedback links so that the potential gains of a massive multiple-input ...multiple-output can be exhibited. However, such a transmission is hindered by excessive feedback overhead. In this letter, we use deep learning technology to develop CsiNet, a novel CSI sensing and recovery mechanism that learns to effectively use channel structure from training samples. CsiNet learns a transformation from CSI to a near-optimal number of representations (or codewords) and an inverse transformation from codewords to CSI. We perform experiments to demonstrate that CsiNet can recover CSI with significantly improved reconstruction quality compared with existing compressive sensing (CS)-based methods. Even at excessively low compression regions where CS-based methods cannot work, CsiNet retains effective beamforming gain.
Iron single atom catalysts (FeN4) hosted in the micropores of N‐doped carbons offer excellent performance for the oxygen reduction reaction (ORR). Achieving a high density of FeN4 sites accessible ...for ORR has proved challenging to date. Herein, a simple surface NaCl‐assisted method towards microporous N‐doped carbon electrocatalysts with an abundance of catalytically accessible FeN4 sites is reported. Powder mixtures of microporous zeolitic imidazolate framework‐8 and NaCl are first heated to 1000 °C in N2, with the melting of NaCl above 800 °C creating a highly porous N‐doped carbon product (NC‐NaCl). Ferric (Fe3+) ions are then adsorbed onto NC‐NaCl, with a second pyrolysis stage at 900 °C in N2 yielding a porous Fe/NC‐NaCl electrocatalyst (Brunauer–Emmett–Teller surface area, 1911 m2 g−1) with an excellent dispersion and high density of accessible surface FeN4 sites (26.3 × 1019 sites g−1). The Fe/NC‐NaCl electrocatalyst exhibits outstanding ORR performance with a high half‐wave potential of 0.832 V (vs reversible hydrogen electrode) in 0.1 m HClO4. When used as the ORR cathode catalyst in a 1.0 bar H2‐O2 fuel cell, Fe/NC‐NaCl offers a high peak power density of 0.89 W cm−2, ranking it as one of the most active M‐N‐C materials reported to date.
A molten NaCl‐assisted synthesis method is developed for the preparation of microporous Fe‐N‐C electrocatalysts rich in surface FeN4 active sites (26.3 × 1019 sites g−1). The obtained Fe/NC‐NaCl electrocatalyst offers outstanding performance for the oxygen reduction reaction, delivering a power density of 0.89 W cm−2 when applied as the cathode catalyst in a H2‐O2 proton exchange membrane fuel cell.
Abstract Research Summary Cost advantage helps a firm at the expense of its rivals, but may hurt some rivals worse than others. Conventional wisdom suggests that an advantaged firm will do more harm ...to closer competitors, but the opposite may occur if competitors can reposition themselves. Closer competitors have stronger incentives to reposition away from the advantaged firm, thereby potentially encroaching on rivals more distant from the advantaged firm and propagating the harm to them like the cue ball in billiards transfers energy from cue stick to target ball. Our formal model compares an advantaged firm's closer and farther competitors, when repositioning is allowed or prohibited, and demonstrates when its advantage hurts farther competitors worse than closer ones. We provide an illustrative case study from grocery retailing. Managerial Summary When Walmart brought its advantage in distribution efficiency to the low end of the grocery retailing industry, it displaced the inefficient downscale incumbent Winn‐Dixie in many geographic areas. One might have expected such increased efficiency at the low end of the market to hurt midscale supermarkets like Kroger more than premium grocers like Whole Foods, yet the opposite occurred. Why? In a word, repositioning. Midscale competitors retreated away from Walmart by repositioning upscale via renovations, which thereby transferred the impact to premium rivals who could not escape any further upscale. Our economic model of this “cue‐ball effect” predicts that the impact propagated onto upper‐end competitors is greater in markets with less income inequality, and our empirical results are consistent with this prediction.
The recent outbreak of COVID-19 in Wuhan turned into a public health emergency of international concern. With no antiviral drugs nor vaccines, and the presence of carriers without obvious symptoms, ...traditional public health intervention measures are significantly less effective. Here, we report the epidemiological and virological characteristics of the COVID-19 outbreak. Originated in bats, 2019-nCoV/ severe acute respiratory syndrome coronavirus (SARS-CoV)-2 likely experienced adaptive evolution in intermediate hosts before transfer to humans at a concentrated source of transmission. Similarities of receptor sequence binding to 2019-nCoV between humans and animals suggest a low species barrier for transmission of the virus to farm animals. We propose, based on the One Health model, that veterinarians and animal specialists should be involved in a cross-disciplinary collaboration in the fight against this epidemic.
The basic reproductive number (R0) of 2019-nCoV is higher than R0 of severe acute respiratory syndrome coronavirus (SARS-CoV) and Middle East respiratory syndrome coronavirus (MERS-CoV). COVID-19 presents with asymptomatic infections, with potential to propagate and perpetuate this epidemic.2019-nCoV isolated from patients shows limited sequence diversity, suggesting that the interspecies transmission event was very recent and that the source of the virus was focused, possibly a point-source event.The amino acid sequence in the ACE2 receptor responsible for 2019-nCoV binding in farm animals and cats has only a few exchanges compared with the human receptor, suggesting that the species barrier for virus transmission is small.
•Novel regularization method based on radial basis function discretization for calculating the DRT.•Improved estimation of DRT only when data collection range is truncated.•MATLAB GUI for computing ...the DRT.
The distribution of relaxation times (DRT) is an approach that can extract time characteristics of an electrochemical system from electrochemical impedance spectroscopy (EIS) measurements. Computing the DRT is difficult because it is an intrinsically ill-posed problem often requiring regularization. In order to improve the estimation of the DRT and to better control its error, a suitable discretization basis for the regularized regression needs to be chosen. However, this aspect has been invariably overlooked in the specialized literature. Pseudo-spectral methods using radial basis functions (RBFs) are, in principle, a better choice in comparison to other discretization basis, such as piecewise linear (PWL) functions, because they may achieve fast convergence. Furthermore, they can yield improved estimation by extending the estimated DRT to the entire frequency spectrum, if the underlying DRT decays to zero sufficiently fast outside the measured frequency range. Additionally, their implementation is relatively easier than other types of pseudo-spectral methods since they do not require ad hoc collocation point distributions. The as-developed novel RBF-based DRT framework was tested against controlled synthetic EIS spectra and real experimental data. Our results indicate that the RBF discretization performance is comparable with that of the PWL discretization at normal data collection range, and with improvement when the EIS acquisition is incomplete. In addition, we also show that applying RBF discretization for deconvolving the DRT problem can lead to faster numerical convergence rate as compared with that of PWL discretization only at error free situation. As a companion to this work we have developed a MATLAB GUI toolbox, which can be used to solve DRT regularization problems.
Ischemia-reperfusion injury is associated with serious clinical manifestations, including myocardial hibernation, acute heart failure, cerebral dysfunction, gastrointestinal dysfunction, systemic ...inflammatory response syndrome, and multiple organ dysfunction syndrome. Ischemia-reperfusion injury is a critical medical condition that poses an important therapeutic challenge for physicians. In this review article, we present recent advances focusing on the basic pathophysiology of ischemia-reperfusion injury, especially the involvement of reactive oxygen species and cell death pathways. The involvement of the NADPH oxidase system, nitric oxide synthase system, and xanthine oxidase system are also described. When the blood supply is re-established after prolonged ischemia, local inflammation and ROS production increase, leading to secondary injury. Cell damage induced by prolonged ischemia-reperfusion injury may lead to apoptosis, autophagy, necrosis, and necroptosis. We highlight the latest mechanistic insights into reperfusion-injury-induced cell death via these different processes. The interlinked signaling pathways of cell death could offer new targets for therapeutic approaches. Treatment approaches for ischemia-reperfusion injury are also reviewed. We believe that understanding the pathophysiology ischemia-reperfusion injury will enable the development of novel treatment interventions.
Hydrothermal liquefaction (HTL) is a thermochemical conversion technology that shows promising commercial potential for the production of biocrude oil from wet biomass. However, the inevitable ...production of the hydrothermal liquefaction aqueous phase (HTL-AP) acts as a double-edged sword: it is considered a waste stream that without additional treatment clouds the future scale-up prospects of HTL technology; on the other hand, it also offers potential as an untapped nutrient and energy resource that could be valorized. As more researchers turn to liquefaction as a means of producing renewable fuel, there is a growing need to better understand HTL-AP from a variety of vantage points. Specifically, the HTL-AP chemical composition, conversion pathways, energy valorization potential, and the interconnection of HTL-AP conversion with biofuel production technology are particularly worthy of investigation. This paper extensively reviews the impact of HTL conditions and the feedstock composition on the energy and elemental distribution of process outputs with specific emphasis on the HTL-AP. Moreover, this paper also compares and contrasts the current state of value-added products separation along with biological (biomass cultivation, anaerobic fermentation, and bioelectrochemical systems) and thermochemical (gasification and HTL) pathways to valorize HTL-AP. Furthermore, life cycle analysis (LCA) and techno-economic assessments (TEA) are performed to appraise the environmental sustainability and economic implications of these different valorization techniques. Finally, perspectives and challenges are presented and the integration approaches of HTL-AP valorization pathways with HTL and biorefining are explored.
Gasification is a promising technology for reducing the volume of biowaste feedstock. Further, with the incorporation of steam this thermochemical treatment technology also concomitantly produces H2, ...a high value energy. This paper aims to summarize the status of biowaste gasification technology and detail the benefits and limitations of different gasification processes, especially for biowaste. First, we compare steam with other gasification agents (oxygen and air) to understand the specific effects of gasification agents on the resulting gas quality and quantity. Second, influencing process factors (reactor configurations, temperature, steam to biomass ratio, and catalyst incorporation) are evaluated in terms of their impact on the resulting H2/CO ratio, gas heating value, gas yield, tar yield, and energy recovery. Third, commercial biowaste gasification applications are detailed and the economics and societal impacts are elucidated. Finally, the current challenges facing the field of gasification and the future outlooks of this technology for reducing biowaste are presented.
A series study of the ternary near–eutectoid Ti–Au–Cr shape memory alloys (SMA) at the Ti–rich corner was explored in this work towards the applications of biomedical materials. Fundamental analysis, ...such as microstructures, phase constitutions, lattice parameters, and mechanical properties of the specimens, were examined along with their functional properties, such as shape memory effect (SME) and superelasticity (SE). Most of the alloys possess good cold–workability except for those with great amounts of precipitates of the brittle Ti3Au at the high Au addition specimens. The Ti–4Au–8Cr alloy excelled in strength while the Ti–2Au–8Cr alloy surpassed other alloys in ductility. Most of the specimens possess SME as well as pseudoelasticity and/or superelasticity indicating the functionality of the Ti–Au–Cr alloys towards biomedical applications. The discrimination between the α′–martensite phase and the α′′–martensite phase was conducted by the TEM observation. The α′–martensite phase, which unexpectedly performed SME in this study was determined to locate exactly at the boundary of the α′–martensite regime and the α′′–martensite regime. The SME of the alloys, which were composed of the α′–martensite phase, were thus deduced to originate from the similarity of the α′–martensite and the α′′–martensite.
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•Near–eutectoid Ti–Au–Cr alloys were successfully synthesized by physical metallurgy.•Shape memory effect and superelastic effect of the Ti–Au–Cr alloys were investigated.•A diagram of phase constituents of various alloys in the Ti–Au–Cr was constructed.•Ti–2Au–8Cr and Ti–4Au–8Cr are superior to others indicating their practicability.•The discrimination of α′ and α′′ martensite phases were investigated by TEM.
Pre-existing immunity to seasonal endemic coronaviruses could have profound consequences for antibody responses to SARS-CoV-2, induced from natural infection or vaccination. A first step to establish ...whether pre-existing responses can impact SARS-CoV-2 infection is to understand the nature and extent of cross-reactivity in humans to coronaviruses. Here we compare serum antibody and memory B cell responses to coronavirus spike proteins from pre-pandemic and SARS-CoV-2 convalescent donors using binding and functional assays. We show weak evidence of pre-existing SARS-CoV-2 cross-reactive serum antibodies in pre-pandemic donors. However, we find evidence of pre-existing cross-reactive memory B cells that are activated during SARS-CoV-2 infection. Monoclonal antibodies show varying degrees of cross-reactivity with betacoronaviruses, including SARS-CoV-1 and endemic coronaviruses. We identify one cross-reactive neutralizing antibody specific to the S2 subunit of the S protein. Our results suggest that pre-existing immunity to endemic coronaviruses should be considered in evaluating antibody responses to SARS-CoV-2.
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