Favorable Channel Research Articles

Reconfigurable Intelligent Surfaces: Potentials, Applications, and Challenges for 6G Wireless Networks

Reconfigurable intelligent surfaces (RISs), with the potential to realize smart radio environments, have emerged as an energy-efficient and a cost-effective technology to support the services and demands foreseen for coming decades. By leveraging a large number of low-cost passive reflecting elements, RISs introduce a phase-shift in the impinging signal to create a favorable propagation channel between the transmitter and the receiver. In this article, we provide a tutorial overview of RISs for sixth-generation (6G) wireless networks. Specifically, we present a comprehensive discussion on performance gains that can be achieved by integrating RISs with emerging communication technologies. We address the practical implementation of RIS-assisted networks and expose the crucial challenges, including the RIS reconfiguration, deployment and size optimization, and channel estimation. Furthermore, we explore the integration of RIS and non-orthogonal multiple access (NOMA) under imperfect channel state information (CSI). Our numerical results illustrate the importance of better channel estimation in RIS-assisted networks and indicate the various factors that impact the size of RIS. Finally, we present promising future research directions for realizing RIS-assisted networks in 6G communication.

Genesis of the Dawadi potassium nitrate deposit in Lop Nor, China

Nitrate deposits are rare worldwide, especially potassium nitrate deposits; furthermore, their genesis remains disputed. There is a rare salt-lake type potassium nitrate deposit in the Dawadi area of Lop Nor at the eastern margin of the Tarim Basin, and the ore bodies show coexisting solid and liquid phases. Additionally, there are large sulphate-type potash deposits in the adjoining Luobei Depression, south of the Dawadi area. To determine why there are two different types of potash deposits in adjacent depressions with similar climates, field geological surveys were conducted and samples collected. It was found that the Tertiary clastic layer at the periphery of the Dawadi deposit was rich in high-salinity brine, with nitrate contents of up to 495–16,719 mg/L, much higher than those in the Luobei Depression, 1–35 mg/L. Additionally, a type of deep hydrothermal (Ca–Cl) brine was found in the fault zones, with nitrate contents of up to 8044 mg/L, dozens of times greater than that of ordinary groundwater. Using comprehensive analysis and research, we concluded that the Dawadi and Luobei depressions belong to different hydrological systems with no connection between them; thus, the two deposits belong to different metallogenic systems. Furthermore, groundwater played an important role in the mineralization of the potassium nitrate deposit, and a deep source may have been an important source of the ore-forming materials. The fault system widely developed in Lop Nor provides favorable channels for deep hydrothermal recharge, and the groundwater and deep hydrothermal brine could provide the source for the nitrate mineralization in the Dawadi Depression through water–rock reactions.

Study on the Product Formation of the Reaction between Criegee Compound and Propargyl Radical

Mechanism of the reaction between Criegee compound (CH2OO) and Propargyl radical (C3H3) has been studied by using the density functional theory DFT/M06-2X in conjunction with the 6-311++G(3df,2p) basis set for both optimization and single-point energy calculations. The calculated results indicate that mechanism of the C3H3 + CH2OO reaction can occur in two different directions: H-atom abstraction and/or addition. As a result, 11 various products have been created from this reaction; in which, P10 (OCHCHCHCHO + H) is the most thermodynamically stable product and the reaction path leading to the P7 (CH2-[cyc-CCHCHOO] + H) product is the most energetically and kinetically favorable channel.

Mass spectroscopy and strong decays of excited open charm {D}_{J} mesons using relativistic Dirac formalism

The mass spectra for the heavy-light (c{bar{q}}) ;q = u or d charmed mesons are computed based on a relativistic framework. The low-lying 1P states are found to be in an excellent agreement with the PDG reported values. Using the computed mass spectra and following effective Lagrangian approach based on heavy quark and chiral symmetry, the OZI allowed two body strong decays are computed. The computed decay rates, ratios and branching fractions allow us to identify the proper spin-parity assignments of the newly observed charm states. Accordingly, we could identify D_J(2560) as 2^1S_0, D_J^*(2680) as 2^3S_1, D_J(2740) as 1^3D_2, D_J^*(2760) as 1^3D_3, D^*_J(3000) as 2^3P_0, D_J(3000) as 2^1P_1 and D^*_2(3000) as 1^3F_2 open charm states. The effective coupling constants, g_T, tilde{g_H}, g_Y, tilde{g_S} and g_Z extracted from the present study are found to be in accordance with the reported values. These coupling constants would be useful in further investigations. We found D^{*+} pi ^- as a favorable channel for the experimental search of the missing 1^1F_3 state.

Fusion dynamics of 12C with 92Zr and 194,198Pt targets at energies lying in the neighbourhood of Coulomb barrier

This work theoretically analyzed the role played by intrinsic degrees of freedom of the colliding partners and/or nucleon transfer channel in the fusion dynamics of [Formula: see text]C + [Formula: see text]Zr and [Formula: see text]C + [Formula: see text]Pt reactions. The theoretical calculations for the chosen reactions have been done by using symmetric–asymmetric Gaussian barrier distribution (SAGBD) model, coupled channel code CCFULL and one-dimensional Wong formula. The fusion excitation functions for these reactions are enhanced at energies lying in the sub-barrier regions with respect to calculations based on one-dimensional Wong formula. Such enhancement can be ascribed to the involvement of the low-lying inelastic surface excitations of the colliding systems and some other favored channels. The CCFULL calculations consider the couplings to low lying vibrational states of target isotopes and hence intimate the dominance of the collective excitations associated with the fusing partners. For all the studied reactions, the SAGBD model adequately addresses the sub-barrier fusion dynamics and thus the impacts of nuclear structure degrees of freedom associated with the collision partners are intrinsically incorporated via single Gaussian type of weight function. In the SAGBD approach, the nuclear structure effects are analyzed in terms of channel coupling parameter [Formula: see text] and percentage reduction of effective fusion barrier [Formula: see text] with reference to the Coulomb barrier. The larger values for [Formula: see text] and [Formula: see text] imply that the channel couplings due to internal structure of participants are significant at below barrier energies. The CCFULL calculations and SAGBD predictions consistently explain the fusion dynamics of chosen systems and hence reveal that both models have almost similar predictive power with respect to reported fusion data.

Theoretical study of the reaction mechanism between Criegee intermediates and hydroxyl radicals in the presence of ammonia and amine

Criegee intermediates (CIs), formed in the ozonolysis process of unsaturated hydrocarbons, play an important role in the formation of OH radicals, sulfuric acid, and aerosols. In this study, quantum chemical calculations were carried out to investigate the mechanism for the reaction of Criegee intermediates [involving CH2OO, CH3CHOO and (CH3)2COO] with OH radicals at the level of CCSD(T)/jun-cc-pVTZ//M06-2X/6-311 + G(2d,2p). A third component, such as water, ammonia, or amines, was introduced to the reaction of CIs with OH to evaluate their catalytic effect. The results show that the OH addition is the favorable channel among four channels involving cis-H abstraction, trans-H abstraction and O abstraction. The third component has a positively catalytic effect on the trans-H abstraction and O abstraction pathways. Moreover, for the trans-H abstraction of CH3CHOO and (CH3)2COO with OH, ammonia and amine exhibit more effectively catalytic ability than water. Furthermore, Born-Oppenheimer molecular dynamic simulation results show that the addition of third component to CIs and hydrogen abstraction from the third component by OH occur simultaneously.

Health messaging with Viber application on risk factors of non-communicable diseases among the rural population: community-based quasi-experimental study

Background: Mobile health and mobile phone technology have become increasingly noticed as favorable communication channels for the prevention of non-communicable diseases (NCDs) by reducing the unhealthy behaviors of NCDs. The study was carried out to assess the effect of the health messaging with the Viber application on modifiable risk factors of NCDs.Methods: A community-based quasi-experimental study was conducted among a total of 240 community members who were 30 to 60 years old selected from two villages in Twantay township with a one year intervention. Face-to-face interviews with all participants using the WHO STEP survey questionnaire and measurements of behavioral and metabolic risk factors of NCDs were carried out at baseline and after 12 months follow up. Changes in behavior and metabolic risk factors between the intervention and control group were analyzed using mixed-effects random-intercept linear regression modeling with propensity score adjustment. Because of the small sample in smoking, smokeless tobacco and alcohol users, the Wilcoxon rank-sum (Mann-Whitney) test was used to compare the changes between the two groups.Results: The amount of smoking and smokeless tobacco use among current users in the intervention group was reduced after the intervention (p<0.05). Of metabolic risk factors, participants in the intervention group had a significant net reduction in fasting blood sugar with a mean change relative to controls of -18.7 mg/dl 95% CI (-32.83, -4.56, p=0.010). No significant mean reduction was seen in other behavioral or metabolic risk factors.Conclusions: The study results showed that intervention affected a reduction in some behavioral and metabolic risk factors of NCDs.

A DFT+U study about agglomeration of Au atoms on reduced surface of rutile TiO2 (110)

The sintering deactivates CO oxidation in a single Au catalyst. Understanding the mechanism of sintering at a reduced atmosphere seems important for improving sintering resistance. Here, we employ the first principle calculations to evaluate the barrier energy of Au atoms on reduced rutile TiO2 (110) surface and to demonstrate a favorable channel for their diffusion at an early stage in sintering. In the current DFT + U calculations, 16 structural configurations with oxygen vacancies and Au atoms are considered. This shows that Au atoms prefer to mobilize on fivefold-coordinated Ti (Ti5c) row rather than moving perpendicularly from this Ti5c row to a twofold-coordinated O (O2c) row. We regard a trap center involving a complex of Au‒oxygen vacancy on an O2c row as the initial nucleation site during sintering. It will capture the unstable Au atom on a Ti5c row, and hence, a highly stable Au dimer would be produced as the primary nucleation pattern.

Computational Investigation on the Formation and Decomposition Reactions of the C4H3O Compound.

Gas-phase mechanism and kinetics of the formation and decomposition reactions of the C4H3O compound, a crucial intermediate of the atmospheric and combustion chemistry, were investigated using ab initio molecular orbital theory and the very expensive coupled-cluster CCSD(T)/CBS(T,Q,5)//B3LYP/6-311++G(3df,2p) method together with transition state theory and Rice–Ramsperger–Kassel–Macus kinetic predictions. The potential energy surface established shows that the C3H3 + CO addition reaction has four main entrances in which C3H3 + CO → IS1-cis (CHCCH2CO) is the most energetically favorable channel. The calculated results revealed that the bimolecular rate constants are positively dependent on both temperatures (T = 300–2000 K) and pressures (P = 1–76,000 Torr). Of these values, the k1 rate constant of the C3H3 + CO → IS1-cis addition channel is dominant over the 300–2000 K temperature range, increasing from 1.53 × 10–20 to 1.04 × 10–13 cm3 molecule–1 s–1 with the branching ratio reducing from 62% to 44%. The predicted unimolecular rate coefficients in the ranges of T = 300–2000 K and P = 1–76,000 Torr revealed that the intermediate products IS1-cis, IS1-trans, and IS2 are rather unstable and would rapidly decompose back to the reactants (C3H3 + CO), especially at high temperatures (T > 1000 K). The high-pressure limit rate constants for the C4H3O decomposition leading to products (C3H3 + CO), (CHCCHCO + H), and (CHCO + C2H2) have been found to be in excellent agreement with the available literature values proposed by Tian et al. (Combust. Flame, 2011,158, 756–773) without any adjustment from the ab initio calculations. Therefore, the predicted temperature- and pressure-dependent rate constants can be confidently used for modeling CO-related systems under atmospheric and combustion conditions.

NH4F-Induced Morphology Control of CoP Nanostructures to Enhance the Hydrogen Evolution Reaction.

Developing non-noble metal catalysts with superior catalytic activity and excellent durability is critically essential to promote electrochemical water splitting for hydrogen production. Morphology control as a promising and effective strategy is widely implemented to change the surface atomic coordination and thus enhance the intrinsic catalytic performance of current electrocatalysts. Herein, a series of cobalt phosphide (CoP) electrocatalysts with tunable morphologies of nanosheets, nanowires, nanorods, and nanoblocks have been prepared for the enhanced hydrogen evolution reaction (HER) by only adjusting the amount of ammonium fluoride (NH4F) in the hydrothermal process. Benefiting from the large active area, high surface activity, and favorable ion and gas diffusion channels, the clustered CoP nanorods obtained at a concentration of 0.15 M NH4F show the best HER performance with only an overpotential of 71 mV at a current density of 10 mA cm-2 and a low Tafel slope of 60.75 mV dec-1 in 1 M KOH. After 3000 CV cycles and 24 h durability tests, there is only a very slight degradation of performance owing to its outstanding stability and robust substrate adhesion.

Chronological and geochemical variations of the late Mesozoic granitoids in the Taihang Mountains and middle-southern Tan-Lu Fault: Implications for lithosphere destruction of the North China Craton

In the Late Mesozoic, the North China Craton (NCC) underwent significant lithospheric thinning and destruction, especially in the eastern part, but the mechanism and timing related to this process are still contentious. The Taihang Mountains (TH) are located in the western part of the eastern NCC and the Tan-Lu Fault (TLF) is in the eastern part, which are two essential magmatic areas that reveal deep processes of magma origin. We investigated the spatial-temporal distribution of igneous rocks from these two areas to constrain the tectonic setting and magmatic sources. SHRIMP zircon U-Pb ages of the granitoids within the Fangshan pluton in northern TH area range from 136 to 128 Ma. Their <i>ε</i>_Hf(t) values and δ¹⁸O values show ranges of −27.7 to −18.5 and 6.68 to 7.26 permil, respectively. Hence, we conclude that the rocks were formed by mixing between underplating magma and the melts from the lower crust. The O-Hf isotopic compositions of six granitoid samples from the Yunmengshan complex in northern TH are also reported. In combination with previous studies, we propose that the geochemical characteristics of the magmatic rocks from the TH area had insignificant changes during late Mesozoic time, but the rocks from the TLF area varied greatly. The difference between those two areas may reflect the diverse impact of the Paleo-Pacific subduction process. The high Mg# adakitic rocks (HMA) from TLF area have higher Mg# values than the HMA rocks from TH area. Our conclusion is that the HMA rocks in the TLF area were mainly formed by delaminated lower crust interacting with mantle materials and that the Paleo-Pacific subduction had limited impact on TH magmas. Based on chronology and geochemical characteristics, we recognize three stages: 1) ∼166 to 140 Ma, multi-directional compression resulted in crustal shortening and thickening in the NCC, accompanied by regional partial melting of the crust and underplating of mafic magmas, 2) 140 to 125 Ma, the TLF underwent left-lateral strike-slip movement. Subsequent delamination of the lower crust around the fault and the NCC evolved into an extensional tectonic environment, 3) after 125 Ma, a large-scale extension of the NCC occurred likely due to stress relaxation after delamination. The TLF acted as a favorable channel for transporting mantle material and fluids, which implies that the large-scale fault zone was a key factor of the NCC lithosphere destruction.

Hybrid Active/Passive Wireless Network Aided by Intelligent Reflecting Surface: System Modeling and Performance Analysis

Intelligent reflecting surface (IRS) is a new and promising paradigm to substantially improve the spectral and energy efficiency of wireless networks, by constructing favorable communication channels via tuning massive low-cost passive reflecting elements. Despite recent advances in the link-level performance optimization for various IRS-aided wireless systems, it still remains an open problem whether the large-scale deployment of IRSs in wireless networks can be a cost-effective solution to achieve their sustainable capacity growth in the future. To address this problem, we study in this paper a new hybrid wireless network comprising both active base stations (BSs) and passive IRSs, and characterize its achievable spatial throughput in the downlink as well as other pertinent key performance metrics averaged over both channel fading and random locations of the deployed BSs/IRSs therein based on <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">stochastic geometry</i> . Compared to prior works on characterizing the performance of wireless networks with active BSs only, our analysis needs to derive the power distributions of both the signal and interference reflected by distributed IRSs in the network under spatially correlated channels, which exhibit channel hardening effects when the number of IRS elements becomes large. Extensive numerical results are presented to validate our analysis and demonstrate the effectiveness of deploying distributed IRSs in enhancing the hybrid network throughput against the conventional network without IRS, which <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">significantly boosts the signal power</i> but results in only <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">marginally increased interference</i> in the network. Moreover, it is unveiled that there exists an <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">optimal IRS/BS density ratio</i> that maximizes the hybrid network throughput subject to a total deployment cost given their individual costs, while the conventional network without IRS (i.e., zero IRS/BS density ratio) is generally suboptimal in terms of throughput per unit cost.

Three-Dimensional Morphology and Connectivity of Organic Pores in Shale from the Wufeng and Longmaxi Formations at the Southeast Sichuan Basin in China

Organic pores play an important role in shale reservoirs. Organic pores occur where shale gas was produced and accumulated. However, there is little scientific understanding of the distribution and connectivity of organic pores. Organic pore types and their structural characteristics were studied using a total organic carbon (TOC), thin section, focused ion beam scanning electron microscope (FIB-SEM), and nano-CT. The samples were from the Wufeng Formation in the Upper Ordovician and Longmaxi Formations from the lower Silurian. The results show that organic matter is mainly concentrated in the Wufeng Formation and the bottom of the Longmaxi Formation and that the middle and upper parts of the Longmaxi Formation contain a low amount of organic matter. The shale of the Wufeng-Longmaxi Formation has high maturity, and its organic pores are well developed. There are three types of organic pores: algae, graptolite, and pyrobitumen pores. The pore connectivity of shale with a high organic content is better than that of shale with a low organic content. The volume of the organic pores accounts for more than 50% of the volume of the organic matter. Majority of the organic pores have an aperture smaller than 100 nm and are round, nearly circular, and elliptical in morphology. Most of the organic pores in a shale formation are developed in pyrobitumen, and most of the larger organic pores are concentrated at the center of solid pyrobitumen. The organic pores in pyrobitumen have the best connectivity and are the most favorable reservoir spaces and migration channels for shale gas, which is a crucial point of reference for future research of shale gas.

Boosted CO desorption behaviors induced by spatial dyadic heterostructure in polymeric carbon nitride for efficient photocatalytic CO2 conversion

In the present contribution, a highly crystalline nano-coral matrix on amorphous polymeric carbon nitride (PCN) nanosheets are structurally crafted and identified as an efficient photocatalyst for photocatalytic CO2 reduction reaction (CRR). The modified PCN presents a unique spatial dyadic heterostructure and favorable directional charge-transfer channel, resulting in improved charge separation for CRR. Notably, DFT calculations suggest that the modified PCN possesses reduced energy barrier for CO2 reduction into CO via facile accessible of COOH intermediate and boosted CO* desorption. The as-prepared functionalized PCN materials possess a remarkable photocatalytic CO2 reduction performance, yielding CO at a rate of 486.7 μmol h−1 g−1 (i.e. 34.0 folds’ higher than pristine PCN) with a high selectivity of 98.4 %. Our strategy of designing spatial dyadic heterostructure in polymeric carbon nitride provides new insights into the architecture engineering of CRR photocatalysts for efficient CO desorption and CO2 conversion.

Hybrid Iterative Detection and Decoding of Near-Instantaneously Adaptive Turbo-Coded Sparse Code Multiple Access

Reduced-complexity hybrid detection and decoding (HDD) schemes are conceived for turbo-coded sparse code multiple access (SCMA) by analysing its convergence behavior using extrinsic information transfer (EXIT) charts, which outperforms the state of the art joint detector and decoder (JDD). As a benefit of its carefully controlled complexity, the resultant system is eminently suitable for ultra-reliable low-latency communication (URLLC) in multiuser scenarios, since it requires a low number of turbo iterations between the detector and the decoder. In particular, a pair of HDD schemes are proposed. HDD-I and HDD-II achieve a complexity reduction of up to 25% and 36%, respectively, at a similar bit error rate (BER) performance as that of JDD. Additionally, we propose an adaptive turbo-coded SCMA system for mitigating the influence of multipath propagation so that the system's bits per symbol (BPS) throughput may be improved under favorable channel conditions by using the most appropriate near-instantaneous user load, modulation order and coding rate. Our adaptive system design principle can also be readily used for other channel coding schemes.

New Thermolysis Routes of Diaminodinitroethylene (DADNE)

AbstractPrimary steps of thermolysis of the promising high‐energy compound 1,1‐diamino‐2,2‐dinitroethylene (DADNE or FOX‐7) were studied by the quantum‐chemical methods using the PBE0 hybrid functional in the cc‐pVDZ basis set and the coupled‐cluster method at the CCSD/aug‐cc‐pVDZ level. A series of thermal decomposition reactions were studied. The reactions proceeding via hydrogen transfer from the amino group to carbon, along with four variants of transformations of the aci form of DADNE insufficiently studied earlier, are shown to be the most energetically favorable channels of the DADNE thermal decomposition. The activation enthalpies ΔHa of all these channels are close to the most reliable experimental values which are in the range of 190–200 kJ mol−1.

Glutarate Hydroxylation by the Carbon Starvation-Induced Protein D: A Computational Study into the Stereo- and Regioselectivities of the Reaction.

The carbon starvation-induced protein D (CsiD) is a recently characterized iron(II)/α-ketoglutarate-dependent oxygenase that activates a glutarate molecule as substrate at the C2 position to exclusively produce (S)-2-hydroxyglutarate products. This selective hydroxylation reaction by CsiD is an important component of the lysine biodegradation pathway in Escherichia coli; however, little is known on the details and the origin of the selectivity of the reaction. So far, experimental studies failed to trap and characterize any short-lived catalytic cycle intermediates. As no computational studies have been reported on this enzyme either, we decided to investigate the chemical reaction mechanism of glutarate activation by an iron(IV)-oxo model of the CsiD enzyme. In this work, we present a density functional theory study on a large active site cluster model of CsiD and investigate the glutarate hydroxylation pathways by a high-valent iron(IV)-oxo species leading to (S)-2-hydroxyglutarate, (R)-2-hydroxyglutarate, and 3-hydroxyglutarate. In agreement with experimental observation, the favorable product channel leads to pro-S C2-H hydrogen atom abstraction to form (S)-2-hydroxyglutarate. The reaction is stepwise with a hydrogen atom abstraction by an iron(IV)-oxo species followed by OH rebound from a radical intermediate. The work presented in this paper shows that despite the fact that the C-H bond strengths at the C2 and C3 positions of glutarate are similar in the gas phase, substrate binding and positioning guide the reaction to an enantioselective reaction process by destabilizing the hydrogen atom abstraction pathways for the pro-R C2-H and C3-H positions. Our studies predict the chemical properties of the iron(IV)-oxo species and its rate constants with glutarate and deuterated-glutarate. Moreover, the work shows little protein motions during the catalytic process, while the substrate entrance into the substrate binding pocket appears to be guided by three active site arginine residues that position the substrate for pro-S C2-H hydrogen atom abstraction. Finally, the calculations show that irrespective of the position of the substrate and what C-H bond is closest to the metal center, the lowest energy pathway is for a selective pro-S C2-H hydrogen atom abstraction.

Quantum Transport across Amorphous-Crystalline Interfaces in Tunnel Oxide Passivated Contact Solar Cells: Direct versus Defect-Assisted TunnelingSupported by the National Natural Science Foundation of China (Grant Nos. 61704083 and 61874060), the Natural Science Foundation of Jiangsu Province (Grant No. BK20181388), and NUPTSF (Grant No. NY219030).

Tunnel oxide passivated contact solar cells have evolved into one of the most promising silicon solar cell concepts of the past decade, achieving a record efficiency of 25%. We study the transport mechanisms of realistic tunnel oxide structures, as encountered in tunnel oxide passivating contact (TOPCon) solar cells. Tunneling transport is affected by various factors, including oxide layer thickness, hydrogen passivation, and oxygen vacancies. When the thickness of the tunnel oxide layer increases, a faster decline of conductivity is obtained computationally than that observed experimentally. Direct tunneling seems not to explain the transport characteristics of tunnel oxide contacts. Indeed, it can be shown that recombination of multiple oxygen defects in a-SiO x can generate atomic silicon nanowires in the tunnel layer. Accordingly, new and energetically favorable transmission channels are generated, which dramatically increase the total current, and could provide an explanation for our experimental results. Our work proves that hydrogenated silicon oxide (SiO x :H) facilitates high-quality passivation, and features good electrical conductivity, making it a promising hydrogenation material for TOPCon solar cells. By carefully selecting the experimental conditions for tuning the SiO x :H layer, we anticipate the simultaneous achievement of high open-circuit voltage and low contact resistance.

Catalytic mechanism of oxygen reduction on two types of CoN 4 ‐graphene : A density functional study

Co-coordinated nitrogen-doped carbons have been reported as highly active catalysts to oxygen reduction reaction (ORR) in fuel cell. Two CoN4-graphene catalysts with a hybrid structure of single Co atom embedded into pyridinic-N and pyrrolic-N doped graphenes, respectively, were studied. The detailed thermodynamic and kinetic behavior of the ORR on these two models was performed by DFT calculation. The results showed that both the two CoN4-G models possessed ORR activity. However, CoN4-G(A) catalyst showed higher catalytic activity but the CoN4-G(B) showed higher 4-electrons selectivity. On CoN4-G(A), both 2-electrons and 4-electrons pathways were feasible. Along the 4-electrons pathway, the OH reduction step was the thermodynamic and kinetic rate-determining step with the limiting potential of 0.43 V and a barrier of 0.42 eV. The formation barrier of H2O2(ads) was 0.61 eV which was easy to overcome. Then the 2-electrons pathway was also possible. On CoN4-G(B), only 4-electrons ORR pathway was favorable. The most favorable reaction channel was arranged as: O2 → OOH → 2OH → OH + H2O → 2H2O. The limiting potential of 4-electrons pathway was 0.35 V. The second step was the kinetic rate-determining step with the barrier of 0.86 eV.

Power allocation for video segment based caching strategy in F-RAN architecture

The concept of edge network caching has been proposed to alleviate the excessive pressure on the core networks. Furthermore, video segment caching technology, a method to cut the whole video into segments and cache them separately, has brought a novel idea to solve the caching problem in the smaller space for massive data. The adoption of segment caching in edge networks will divide the simple video transmission process into two coupling stages because of separate data caching, which leads to more complicated resource allocation. In this paper, this problem is discussed, and its mathematical model is established to minimize the energy consumption of video transmissions. By introducing an efficient prediction window of channel fading, an optimal dynamic scheduling algorithm based on Q-learning is proposed to minimize power consumption while ensuring smooth video streaming. The proposed Q-learning algorithm is simulated and the impacts of channel state, target video bit rate and large-scale channel parameter are evaluated. Simulation results show that the proposed method can effectively reduce the total power consumption while ensuring the smooth playback of video service, thanks to the fact that the proposed method is intelligent which can effectively utilize idle resources in favorable channel states.