In this paper, a flexible piezoelectric micromachined ultrasonic transducer (PMUT) based on Scandium (Sc)-doped Aluminum Nitride (AlN) film was designed and modeled by the three-dimensional finite ...element method (3D-FEM). The resonant frequency of 218.1 kHz was reported. It was noticeable that a high effective electromechanical coupling coefficient (k2eff) of 1.45% was obtained when a combination of a flexible PI and a thin Si layer was used as the PMUT supporting structure layer. Compared with a pure Si supporting layer counterpart, the coupling coefficient had been improved by 110.68%. Additionally, the increase of Sc doping concentration in AlN film further enhanced the device electromechanical coupling coefficient and resulted in an improvement for transmitting/receiving sensitivity of the proposed flexible PMUT. When the doping concentration of Sc reached 30%, the emission sensitivity was as large as 1.721 μm/V, which was 2.86 times greater than that of conventional AlN film-based PMUT. The receiving sensitivity was found to be 2.11 V/KPa, which was as high as 1.23 times the performance of an undoped device. Furthermore, the bending simulation result showed that the proposed flexible PMUT device can maintain a good mechanical stability when the bending radius is greater than 1.5 mm. The simulation of sound field characteristics demonstrated that the flexible PMUT based on AlScN could receive stable sound pressure signals under the bending radius of 1.5 cm.
The electronic properties, formation Helmholtz free energies, formation energies and the phase transition temperature Tc of M-doped (M = P, As, Bi atoms at the octahedral interstitial sites or in ...replacing of O or V sites) VO2 were studied using DFT calculations. Our results showed that the Tc of all M-doped VO2 could be reduced and Bi-doped VO2 could be a better one to obtain good thermochromic energy-saving materials.
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•M-doped (M = P, As, Bi) VO2 was studied using DFT calculations.•Tc of all M-doped (M = P, As, Bi) VO2 could be reduced and the band gaps of Eg2 were smaller than that of pure VO2.•Bi-doped VO2 could be a better one to obtain good thermochromic energy-saving materials.
The group VA elements (P, As, Bi) doped VO2 were thoroughly investigated using the DFT calculations to evaluate the electronic properties, formation Helmholtz free energy, formation energy and the phase transition temperature (Tc). The calculated results showed that these atoms (M = P, As, Bi) could be easily doped at the octahedral interstitial site or in replacing of V or O atoms to reduce the Tc of VO2. All M-doped VO2 could narrow the band gap of Eg2 where the Eg2 value of Bi-doped VO2 was the smallest (about 0.30 eV). The Tc for Bi@i, Bi@V, and Bi@O could be reduced to 85, 159, 23 K for the model of one M atom doped in the octahedral interstitial site or in replacing of one V or O atom of VO2 supercells containing 32 V atoms and 64 O atoms, respectively. It means that the Bi-doped VO2 could be a better promising candidate to obtain good thermochromic energy-saving foils. These results will give the experimental researchers a new possibility to regulate the phase transition of VO2.
The mechanisms of iron‐catalyzed regioselective anti‐Markovnikov addition of C‐H bonds in the aromatic ketones to alkenes are studied using Density Functional Theory (DFT) calculations with the ...B3LYP‐D3 method. Our results show that the overall catalytic cycle includes the initial generation of aromatic ketone C‐H activation, the coordination and insertion of a styrene, and finally C‐C reductive elimination. Two different alkylation products are obtained through the linear or branched formation via several different paths. The formation of the linear product is energetically favorable over that of the branched product, which is in agreement with the experimental observation. The rate‐limiting step for the whole catalytic cycle to obtain the main linear product is the reductive elimination step where the Gibbs free energy in solvent THF ΔGsol is 13.5 kcal/mol computed using the SMD method.
The mechanisms of iron‐catalyzed regioselective anti‐Markovnikov addition of CH bonds in the aromatic ketones to alkenes were studied using DFT (B3LYP‐D3) calculations. The results show that the rate‐limiting step for the whole catalytic cycle to obtain the main linear product is the reductive elimination step where the Gibbs free energy in solvent THF, ΔGsol is 13.5 kcal/mol.
First-principles density functional theory (DFT) electronic structure calculations were carried out for the model halogen-doped VO2 (M1 phase) to evaluate the effect of halogen (X = F, Cl, Br, I) ...doping on the band edges. The model structures of X-doped VO2 with X at V site or O site were constructed on the basis of 96-atom 2 × 2 × 2 supercell of monoclinic M1 phase of VO2. Our results showed that the band gap E g2 for Cl-doped VO2 at O1 site (0.51 eV) is smaller than that of F-doped VO2 at O1 site (0.61 eV) and that of pure VO2 (0.78 eV). We also investigated the substitution of chlorine, bromine, and iodine for vanadium in VO2, where the band gaps E g2 are 0.40, 0.45, and 0.37 eV for Cl-, Br-, and I-doped VO2 at V site, respectively. The Cl-doped VO2 at V site is the best one for achieving good VO2 thermochromic energy-saving foils.
Ni-catalyzed reductive cross-coupling reactions of electrophilic regents provide an important method to form C–C bonds. The present study explored several single electron transfer mechanisms for ...Ni-catalyzed reductive cross-coupling of aryl bromide and secondary alkyl bromide using Density Functional Theory (DFT) calculations. The results showed that two of the proposed mechanisms were feasible. One was a six-step catalytic cycle including oxidative addition, reduction, radical production, radical addition, reductive elimination and catalyst regeneration. The other was a five-step mechanism involving radical production, reduction, oxidative addition, radical addition, and reductive elimination. The rate-limiting step for both mechanisms was the radical addition step with the energy barrier of 10.42 kcal/mol. All DFT calculations were implemented in the gas phase.
Four of the proposed single electron transfer mechanisms in Ni-catalyzed reductive cross-coupling of aryl bromide and secondary alkyl bromide were studied using DFT calculations. The results showed that two of them were feasible in which the rate-limiting step was the radical addition step with the energy barrier of 10.42 kcal/mol. Display omitted
•We investigated mechanisms of the Ni-catalyzed reductive cross-coupling of aryl bromide and secondary alkyl bromide.•Two single electron transfer mechanisms are feasible.•The rate-limiting step is the radical addition step with the energy barrier of 10.42 kcal/mol.•We studied four possible single electron transfer mechanisms and two concerted mechanisms.
In mixed traffic with autonomous vehicles, the relationship between speed and lane-changing behavior is an important basis for mixed traffic control. In this study, we use empirical, simulation, and ...data-driven methods to study the relationship between speed and lane change rates in mixed traffic under different autonomous vehicle penetration rates. We use the empirical data to establish the corresponding road simulation models. Based on the simulation model, the traffic flow simulation experiments under the conditions of 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, and 90% penetration rate of autonomous vehicles were carried out. The analysis of the simulation results found that: (1) the penetration of autonomous vehicles into the road has a positive impact on the lanes far away from the entrance and exit, while the impact on the lanes closer to the entrance and exit is not obvious. (2) Lane-changing behavior has effectively decreased with the penetration of autonomous vehicles, but it is not obvious when the penetration rate exceeds 10%, and there is no significant drop in the lane connecting the entrance and exit. (3) There is a linear relationship between speed and lane-changing rate. Under different penetration rates, the data-driven analysis is used to perform multiple linear regressions, and the regression formula fits are all above 0.7. Based on the above findings, the linear formula of the fitting is proposed, and the value interval of the parameters in different states is given as well. Due to the small changes in the parameter values under different permeability conditions, the model has a certain degree of stability. The speed-lane change rate model proposed in this study can better describe the relationship between the speed of the ring-shaped urban expressway and the lane-changing behavior in the mixed traffic environment with the larger traffic flow.
•Synchronization signal is very essential for obtaining high precision control performance of thyristor power supply in tokamak.•The pulse generator with rectifier load make the output voltage ...waveform severe distortion and marked frequency variation in a wide range.•A real-time synchronization signal processing scheme is presented.•Based on Programmable Automation Controller (PAC) architecture the system is done and applied in HL-2A experiments.
In HL-2 M tokamak, three-phase thyristor power supplies are utilized to output a direct current to energize the device coil to control the plasma current and shape configuration. Phase-controlled is currently the most effective control method in thyristor power supply. The quality of the synchronization signal is directly related to the performance of the thyristor power supply control. HL-2 M device uses a pulse generator with rectifier load to supply power to the device coil, it makes the thyristor power supply AC input voltage not only have a wide frequency variation but also a severe waveform distortion, so it is difficult to obtain the accurate synchronization signal of the thyristor power supply. In this paper, a real-time tracking and processing method for variable frequency synchronization signals are proposed, which applied the digital filter with point-to-point to process varying frequency synchronization signal, calculated the real-time frequency of the filtered data, obtained the delay angles at different input frequencies according to the phase-frequency characteristics of Butterworth low-pass filter, and reconstructed the synchronization signal by phase compensation. The system has been built to achieve a wide range of real-time frequency tracking from 70 to 110 Hz, and provides multiple synchronization signal output with 15° interval. The performance of the system was verified in the HL-2A experiment.
The mechanisms of iron(II) bromide-catalyzed intramolecular C–H bond amination 1,2-shift tandem reactions of aryl azides have been studied using density functional theory calculations. The tandem ...reaction from R 1 , 1-azido-2-(1-methoxy-2-methylpropan-2-yl)benzene, to produce P 2 , 2,3-dimethyl-1H-indole, was calculated. Our results showed that the overall catalytic cycle includes the following steps: (I) extrusion of N2 to form iron nitrene; (II) C–H bond amination; (III) formation of the middle product P 1 , 2-methoxy-3,3-dimethylindoline; (IV) iminium ion formation ; (V) 1,2-shift process; and (VI) formation of indole P 2 . The rate-limiting step is the 1,2-shift process, where the energy barrier ΔE = 28.7 kcal/mol in the gas phase. Our calculated results also indicated that the preference for the 1,2-shift component of the tandem reaction is methyl < ethyl.
Flexible job-shop scheduling problem (FJSP) is an NP-hard puzzle which inherits the job-shop scheduling problem (JSP) characteristics. This paper presents a bee evolutionary guiding nondominated ...sorting genetic algorithm II (BEG-NSGA-II) for multiobjective FJSP (MO-FJSP) with the objectives to minimize the maximal completion time, the workload of the most loaded machine, and the total workload of all machines. It adopts a two-stage optimization mechanism during the optimizing process. In the first stage, the NSGA-II algorithm with T iteration times is first used to obtain the initial population N, in which a bee evolutionary guiding scheme is presented to exploit the solution space extensively. In the second stage, the NSGA-II algorithm with GEN iteration times is used again to obtain the Pareto-optimal solutions. In order to enhance the searching ability and avoid the premature convergence, an updating mechanism is employed in this stage. More specifically, its population consists of three parts, and each of them changes with the iteration times. What is more, numerical simulations are carried out which are based on some published benchmark instances. Finally, the effectiveness of the proposed BEG-NSGA-II algorithm is shown by comparing the experimental results and the results of some well-known algorithms already existed.
Iron-catalyzed direct arylations of unactivated arenes with aryl iodides provide an important method to form C-C bonds. The present study explored the mechanisms of iron(II)-catalyzed direct ...arylation of Iodobenzene with Benzene using Density Functional Theory (DFT) calculations at the B3LYP-D3 level, which included the halogen atom transfer (to produce aryl radical) mechanism, the single electron transfer mechanism, the σ–bond metathesis mechanism and the oxidative addition mechanism. The calculated results showed that the halogen atom transfer mechanism was favored. The rate-limiting step for the halogen atom transfer mechanism was the first step to produce the phenyl radical with the energy barrier of ΔE = 29.8 kcal/mol in the gas phase and the Gibbs free energy in solvent benzene ΔGsol = 37.7 kcal/mol. The substituent effects of phenyl iodide were also studied.
The mechanisms of iron-catalyzed direct arylation of Iodobenzene with Benzene were studied using DFT calculations. The results showed that halogen atom transfer mechanism was favored where the rate-limiting step was the first step to produce phenyl radical with the energy barrier of ΔE = 29.8 kcal/mol and ΔGsol = 37.7 kcal/mol. Display omitted
•We investigated the mechanisms of iron-catalyzed direct arylation of Iodobenzene with Benzene.•The halogen atom transfer mechanism was favored.•The rate-limiting step for the halogen atom transfer mechanism was the first step to produce the phenyl radical with the energy barrier of ΔE = 29.8 kcal/mol in the gas phase and the Gibbs free energy in solvent benzene ΔGsol = 37.7 kcal/mol.
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