The first alkali‐metal vanadium iodate fluoride, CsVO2F(IO3), with a novel 3D anionic framework, has been rationally designed and hydrothermally synthesized. The 3D VO2F(IO3)− framework in ...CsVO2F(IO3) is built from 0D Λ‐shaped cis‐VO3F(IO3)24− polyanions via corner‐sharing of oxo anions and bridging of the iodate groups. CsVO2F(IO3) displays both a strong second‐harmonic generation (SHG) 1.1 times as strong as KTiOPO4 (KTP) under 2.05 μm laser radiation and high laser‐induced damage threshold (LIDT) of 107.9 MW cm−2. This work provides a new route to design SHG crystals with stable 3D anionic structures from low‐dimensional structural building units.
From zero to threero: CsVO2F(IO3) is the first example of a 3D VO2F(IO3)− anionic framework built from 0D Λ‐shaped cis‐VO3F(IO3)24− units. The system shows a strong second‐harmonic generation (SHG), 1.1 times as strong as KTiOPO4 under 2.05 μm laser radiation and a high laser‐induced damage threshold of 107.9 MW cm−2.
The modern ammonia synthesis industry founded by Haber-Bosch in 1913 has successfully altered the history of food production, fed explosive population growth, and laid the foundation of heterogeneous ...catalysis and chemical engineering as well. However, its reliance on fossil fuels for reactant H
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production consumes 1-3% of the world's electric energy and 2-5% of the world's natural gas, accompanied by more than 400 million tons of CO
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emission annually. Making use of water as the proton source and electric energy to drive the ammonia synthesis reaction will reduce the fossil fuel consumption and CO
2
emission and is thus regarded as a green and sustainable alternative to the conventional Haber-Bosch process. To date, some excellent reviews on electrochemical ammonia synthesis have been published, but most of them were organized according to the type of catalyst. A systematic summary of the performance-improving strategies of the electrocatalyst for ammonia synthesis is rarely reported and therefore highly desirable. In this review, the nitrogen reduction reaction mechanisms and recent theoretical advances are briefly outlined first. Then, strategies for both reactivity and selectivity enhancement of catalysts and catalytic systems are methodically discussed. Last, criteria for the electrochemical nitrogen reduction reaction, ammonia quantification methods, and an outlook for further research are also concluded. This review aims to provide systematic and concise guidance for the design of highly efficient and selective electrochemical ammonia synthesis systems.
A systematic summary of strategies to improve the performance of electrochemical NRR catalysts and NRR catalytic systems.
•Medical staff experience mental health disturb during the COVID-19 pandemic.•Direct and indirect exposure to COVID-19 affects the mental health profoundly.•Psychological materials and resources ...provide some protection.•Interventions with appropriate level are urgent.
The severe 2019 outbreak of novel coronavirus disease (COVID-19), which was first reported in Wuhan, would be expected to impact the mental health of local medical and nursing staff and thus lead them to seek help. However, those outcomes have yet to be established using epidemiological data. To explore the mental health status of medical and nursing staff and the efficacy, or lack thereof, of critically connecting psychological needs to receiving psychological care, we conducted a quantitative study. This is the first paper on the mental health of medical and nursing staff in Wuhan. Notably, among 994 medical and nursing staff working in Wuhan, 36.9% had subthreshold mental health disturbances (mean PHQ-9: 2.4), 34.4% had mild disturbances (mean PHQ-9: 5.4), 22.4% had moderate disturbances (mean PHQ-9: 9.0), and 6.2% had severe disturbance (mean PHQ-9: 15.1) in the immediate wake of the viral epidemic. The noted burden fell particularly heavily on young women. Of all participants, 36.3% had accessed psychological materials (such as books on mental health), 50.4% had accessed psychological resources available through media (such as online push messages on mental health self-help coping methods), and 17.5% had participated in counseling or psychotherapy. Trends in levels of psychological distress and factors such as exposure to infected people and psychological assistance were identified. Although staff accessed limited mental healthcare services, distressed staff nonetheless saw these services as important resources to alleviate acute mental health disturbances and improve their physical health perceptions. These findings emphasize the importance of being prepared to support frontline workers through mental health interventions at times of widespread crisis.
•Heat dissipation issues at near-junction region of GaN HEMT are reviewed comprehensively.•Phonon transport properties in GaN and GaN nanostructures are discussed based on both computations and ...experiments.•Phonon transport tuning mechanisms in perspectives of particle, wave, and topological nature of phonons for GaN and GaN nanostructures are introduced.
The heat dissipation issue has now become one of the most important bottlenecks for power electronics due to the rapid increase in power density and working frequency. Towards the wide bandgap semiconductor GaN high electron mobility transistors (HEMTs), near-junction thermal management is the breakthrough that mainly includes the accurate thermal modeling and effective thermal design for GaN and GaN HEMTs. In this review, we first offer a comprehensive understanding of phonon thermal transport in GaN and GaN HEMTs, including non-equilibrium transport of electrons and phonons in the heat generation process, phonon thermal conductivity, heat spreading, and interfacial thermal transport. Then, we review the current tuning mechanisms and methods for thermal transport in GaN and GaN HEMTs which are classified into three categories according to the particle nature, wave nature, and topological nature of phonons. At last, we conclude by providing our perspectives on challenges and opportunities in the research of phonon thermal transport and its tuning mechanisms in GaN HEMTs.
•A hybrid design using manifold arrangement and secondary channels for microchannel heat sink is proposed.•A Design Optimization Area (DOA) for the MMC-SOC is defined.•The pressure drop and thermal ...resistance can be both reduced in DOA.•The best hybrid design with geometrical parameters of (λ = 1, β = 1) is obtained.
The flow and heat transfer characteristics of a novel hybrid microchannel heat sink with manifold arrangement and secondary oblique channels (MMC-SOC) are numerically studied. Through the relationship between the total thermal resistance ratio (Rt/Rt0) and pressure drop ratio (ΔP/ΔP0), we define a region named Design Optimization Area (DOA), where the pressure drop ΔP and the total thermal resistance Rt can be both reduced due to the secondary channels. The numerical results show that the best heat sink can reduce ΔP by 1.91%, and simultaneously decrease Rt by 19.15% compared to the original MMC heat sink at Re = 295. In addition, the effects of secondary channel on ΔP are dependent on both the geometrical parameters and Reynolds numbers. On the one hand, it can reduce the pressure loss at small Reynolds numbers for most heat sinks. However, it can also increase the pressure loss at high Reynolds numbers for most heat sinks. As Re increases, the ratio (Rt/Rt0) becomes smaller and (ΔP/ΔP0) becomes larger, indicating a better thermal performance and a worse hydraulic performance. The secondary flow field analyses visually show the hydraulic and thermal performance enhancements due to thermal boundary layer re-development and flow mixing.
•A novel optimization approach is proposed to optimize the performance of a hybrid heat sink.•The Pareto-optimal set is obtained and verified by CFD results.•The optimized heat sink can reduce ...thermal resistance by 18.83% compared with manifold heat sink.•TOPSIS with entropy weight method is applied to select the best compromise solution from Pareto-optimal set.
A novel optimization approach, which combines optimal Latin hypercube design (Opt LHD), Pareto chart analysis, response surface methodology (RSM), the non-dominated sorting genetic algorithm II (NSGA-II) and technique for order preference by similarity ideal solution (TOPSIS), has been proposed and applied to optimize the performance of a hybrid microchannel heat sink combining manifold concept with secondary oblique channels. Four geometric parameters are selected as design variables and the optimization objective is to minimize the total thermal resistance Rt and pumping power Pp simultaneously. First, 160 sample points is generated by Opt LHD and the Pareto chart analysis is performed to identify the dominant design parameters influencing the objectives. Then, RSM is used to generate approximate models relating to the objectives and design parameters, and NSGA-II is selected to minimize Rt and Pp. 374 Pareto-optimal solutions are obtained and verified by CFD results, which indicates that the hybrid design can reduce Rt by 18.83% compared with manifold microchannel heat sink under the same Pp. Finally, the best compromise solution is obtained by TOPSIS combined with entropy weight method. The proposed optimization approach can also be applied to optimize the performance of other types of heat sinks.
Wuhan was the first epicentre of COVID-19 in the world, accounting for 80% of cases in China during the first wave. We aimed to assess household transmissibility of severe acute respiratory syndrome ...coronavirus 2 (SARS-CoV-2) and risk factors associated with infectivity and susceptibility to infection in Wuhan.
This retrospective cohort study included the households of all laboratory-confirmed or clinically confirmed COVID-19 cases and laboratory-confirmed asymptomatic SARS-CoV-2 infections identified by the Wuhan Center for Disease Control and Prevention between Dec 2, 2019, and April 18, 2020. We defined households as groups of family members and close relatives who did not necessarily live at the same address and considered households that shared common contacts as epidemiologically linked. We used a statistical transmission model to estimate household secondary attack rates and to quantify risk factors associated with infectivity and susceptibility to infection, accounting for individual-level exposure history. We assessed how intervention policies affected the household reproductive number, defined as the mean number of household contacts a case can infect.
27 101 households with 29 578 primary cases and 57 581 household contacts were identified. The secondary attack rate estimated with the transmission model was 15·6% (95% CI 15·2–16·0), assuming a mean incubation period of 5 days and a maximum infectious period of 22 days. Individuals aged 60 years or older were at a higher risk of infection with SARS-CoV-2 than all other age groups. Infants aged 0–1 years were significantly more likely to be infected than children aged 2–5 years (odds ratio OR 2·20, 95% CI 1·40–3·44) and children aged 6–12 years (1·53, 1·01–2·34). Given the same exposure time, children and adolescents younger than 20 years of age were more likely to infect others than were adults aged 60 years or older (1·58, 1·28–1·95). Asymptomatic individuals were much less likely to infect others than were symptomatic cases (0·21, 0·14–0·31). Symptomatic cases were more likely to infect others before symptom onset than after (1·42, 1·30–1·55). After mass isolation of cases, quarantine of household contacts, and restriction of movement policies were implemented, household reproductive numbers declined by 52% among primary cases (from 0·25 95% CI 0·24–0·26 to 0·12 0·10–0·13) and by 63% among secondary cases (from 0·17 0·16–0·18 to 0·063 0·057–0·070).
Within households, children and adolescents were less susceptible to SARS-CoV-2 infection but were more infectious than older individuals. Presymptomatic cases were more infectious and individuals with asymptomatic infection less infectious than symptomatic cases. These findings have implications for devising interventions for blocking household transmission of SARS-CoV-2, such as timely vaccination of eligible children once resources become available.
National Natural Science Foundation of China, Fundamental Research Funds for the Central Universities, US National Institutes of Health, and US National Science Foundation.
In humans, Interleukin-8 (IL-8 or CXCL8) is a granulocytic chemokine with multiple roles within the tumor microenvironment (TME), such as recruiting immunosuppressive cells to the tumor, increasing ...tumor angiogenesis, and promoting epithelial-to-mesenchymal transition (EMT). All of these effects of CXCL8 on individual cell types can result in cascading alterations to the TME. The changes in the TME components such as the cancer-associated fibroblasts (CAFs), the immune cells, the extracellular matrix, the blood vessels, or the lymphatic vessels further influence tumor progression and therapeutic resistance. Emerging roles of the microbiome in tumorigenesis or tumor progression revealed the intricate interactions between inflammatory response, dysbiosis, metabolites, CXCL8, immune cells, and the TME. Studies have shown that CXCL8 directly contributes to TME remodeling, cancer plasticity, and the development of resistance to both chemotherapy and immunotherapy. Further, clinical data demonstrate that CXCL8 could be an easily measurable prognostic biomarker in patients receiving immune checkpoint inhibitors. The blockade of the CXCL8-CXCR1/2 axis alone or in combination with other immunotherapy will be a promising strategy to improve antitumor efficacy. Herein, we review recent advances focusing on identifying the mechanisms between TME components and the CXCL8-CXCR1/2 axis for novel immunotherapy strategies.
•Full-band phonon Monte Carlo simulation is conducted to study thermal spreading resistance in GaN HEMTs.•Different simulation approaches for simulation phonon transport in GaN HEMTs are thoroughly ...compared.•Incorporating first-principle-calculated phonon properties in device thermal simulations is essential.
Accurate thermal simulation is essential for the near-junction thermal management and electro-thermal co-design of GaN HEMTs. While various methods have been employed to simulate phonon thermal transport in GaN, a comprehensive evaluation of their performance and reliability has yet to be conducted. In this work, first-principle-based steady-state full-band phonon tracing Monte Carlo (MC) simulations are conducted to study the thermal spreading resistance in GaN HEMTs. The results of full-band MC serve as a standard against which the applicability, accuracy, and computational efficiency of three widely-used approaches to simulate the near-junction phonon transport in GaN are thoroughly examined. The simulation techniques compared in this study include MC simulations with empirical isotropic phonon dispersion (isotropic MC), MC simulations with gray-medium approximation (gray MC), and finite-element methods (FEM) with effective thermal conductivities (FEM with keff). It is found that isotropic MC largely overestimates the thermal resistance due to the empirical model’s overestimation of phonon mean free path (MFP) distributions. By selecting an appropriate average MFP, gray MC can approximate the full-band results well, but due to its inability to reflect the contributions of different phonon modes, discrepancies are inevitable for some geometric parameters. For FEM-based analysis, although the diffusive nature of Fourier’s law precludes the reproduction of channel temperature distributions, the influence of phonon ballistic effects on the junction temperature can be accurately reflected in the well-chosen effective thermal conductivities. The comparison highlights the importance of directly incorporating first-principles-calculated phonon properties into device thermal simulations, and the paper can provide a clearer understanding of near-junction thermal transport in GaN and can be useful for thermal simulations of GaN-based devices.
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