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• Spark ignition of spray flames under altitude relight conditions. • Evolution and interactions of flow, spray and flame kernel motions. • Flame-tracking algorithm for identifying flame propagation behaviors. • A dipper-type propagation pattern of flame kernel and its formation mechanism. Altitude relight is an increasingly important issue limiting the development of low-emission combustors due to the current trend towards lean combustion. This paper experimentally investigates the flow field features and spark ignition processes inside a multi-swirl staged combustor to further reveal the internal mechanism leading to the deterioration of ignition performances under altitude conditions including sub-atmospheric pressures and low temperatures. Laser diagnostic technologies and high-speed imaging are applied to acquire the flow structures, droplet distributions, and detailed kernel motions under various inlet conditions. A flame-tracking algorithm is developed to capture the flame features (flame intensity-centroids and flame object edges) and provide the flame propagation trajectories during 10 ms following the spark. A typical "dipper-type propagation" pattern is summarized from numerous spark events and its formation mechanism can be clarified by statistical characteristics of flow and spray inside such staged combustors. The variation of ignition limits quantitatively characterizes the degree of ignition deterioration under sub-atmospheric pressures (10 ∼ 70 kPa) and low temperatures (253 ∼ 301 K). From the analysis of air to liquid ratio and Weber number, it is demonstrated that the increased droplet size and shrunken spray cone under altitude conditions are induced by three aspects, including the insufficient aerodynamic force, increased liquid viscosity force, and increased surface tension. The poor atomization quality is detrimental to the kernel generation and flame propagation and finally leads to the deterioration of ignition performances. [ABSTRACT FROM AUTHOR]

Degradation in the service or manufacturing tolerances can cause tip clearance variation, which adversely affects the stability and performance of compressors. In particular, for a miniature gas turbine, the size of the tip clearance ratio (the ratio of tip clearance to the tip chord length) is relatively large, thus it is more likely to operate at low Reynolds number. This study, therefore, numerically investigated the effect of tip clearance variation on the aerodynamic performance of a 1.5-stage transonic compressor at high and low Reynolds numbers using a 3D Reynolds averaged Navier-Stokes (RANS) solver that incorporates the SST k - ω turbulence model coupled with the γ - θ transition model. The results show that the aerodynamic performance and the tip flow field structure of the compressor change significantly with varying tip clearance. At high Reynolds number, the performance curves are essentially negatively linear with tip clearance, but the slopes sharply increase at medium tip clearance (0.9% C , C represents the tip chord length). At low Reynolds number, the varying trends of the sensitive curves for large tip clearances (0.9% C –1.8% C) are basically the same as that at high Reynolds number. However, for small tip clearances (0.3% C –0.9% C), the aerodynamic performance parameters fluctuate, namely, there is a peak aerodynamic performance at low Reynolds number. When considering the performance and surge margin of the compressor comprehensively, the best tip clearance is 0.6% C at high Reynolds number, but 0.9% C at low Reynolds number. [ABSTRACT FROM AUTHOR]

Accurate prediction of the unsteady flow mixing process and its effects on cooling performance in the turbine blade trailing edge (TE) is essential to improving TE cooling designs. This paper used high accuracy transient Scale Adaptive Simulation (SAS) method to investigate the unsteady flow and cooling characteristics of two novel turbine blades cutback TEs under blowing ratios BR s = 0.65 and 1.25. The two novel TEs have five rows of pin fins in the cooling slot and two rows of either cylindrical or fan-shaped film holes on the pressure side upstream of the cutback region. The results were compared against those of the baseline TE with only pin fins and the data obtained from Shear Stress Transport (SST) k- ω model. The results revealed that: 1) the coolant issued from upstream cylindrical or fan-shaped holes has significantly disturbed the Brown-Roshko vortices shedding off the lip of the top wall, but only largely reduced the magnitude of normal velocity fluctuation in the cutback region. The alternating vortices in the cutback region are stretched flat. The changes brought to the flow structures are more significant by the fan-shaped holes than the cylindrical holes; 2) Although increasing blowing ratio enhances flow unsteadiness in the cutback region of the three TEs, the differences in the magnitude of velocity fluctuations are much reduced among the three TEs; 3) The TE cutback with fan-shaped holes achieves a higher adiabatic wall cooling effectiveness η aw on the cutback wall at BR = 0.65 , and also a lower reduction in η aw at BR = 1.25 than the TE cutback with cylindrical holes; 4) Transient SAS method demonstrates a better agreement of η aw with the experimental data for the baseline TE on the cutback wall, and higher values of η aw than the results of the SST k- ω model on the top wall. [ABSTRACT FROM AUTHOR]

Based on the piezoelectric effect of piezoelectric materials, a new piezoelectric friction damper was designed by combining the piezoelectric ceramic with passive friction damper. The sliding friction damping force was changed between the friction plate by applying voltage, and real-time semi-active control to structure was realized. Working principle and construction method of the damper was analyzed and the corresponding damping force model was derived. Different numbers of piezoelectric friction damper layout optimization was researched for space truss structure by using genetic algorithm. And through adopting the semi-active control strategy based on LQR algorithm, different numbers of piezoelectric friction damper control effect of seismic response was analyzed at random layout and optimized layout of dampers. The results show that the piezoelectric friction damper has good mitigation effect to seismic response of the space truss model. After using genetic algorithm to optimize damper layout, the biggest control effect reaches 57%, and the control effect is improved by 8% compared with the random setting damper. [ABSTRACT FROM AUTHOR]

This study used large eddy simulation (LES) to investigate the control mechanism of a fluidic oscillator in the suppression of non-reattachment separation of a boundary layer from an ultra-high-lift, aft-loaded, low-pressure turbine under low Reynolds number. The internal flow characteristics of the fluidic oscillator were examined, with a focus on the influence mechanism of the pulse jet from the fluidic oscillator on boundary layer separation and transition. The effects of different jet angles (θ) on the suppression of separation bubbles were also compared in detail. Finally, the mechanism of interaction between the fluidic oscillator jet and the blade suction surface boundary layer was assessed. It was found that the pulse jet of the fluidic oscillator generated a streamwise vortex pair above the surface of the blade suction, which promoted an exchange of momentum between the boundary layer for the blade suction surface and the main flow, and clearly suppressed boundary layer separation. The streamwise vortex pair at θ = 30 ° showed the characteristics of higher strength, smaller size, slower decay, and longer penetration distance than the results at θ = 90 °, such that the momentum exchange between the low-energy fluid inside the boundary layer and the main flow is sustainable, which promoted the laminar boundary layer to produce bypass transition and significantly improved the aerodynamic performance of the turbine. [ABSTRACT FROM AUTHOR]

To further improve the thrust-to-weight ratio of turbofan engines, the flux capacity and core pressurization capacity of the fan should be enhanced. In the current study, detailed investigations are conducted to detect the effects on the aerodynamic performance of a wide-chord transonic fan and the underlying flow mechanism in the fan with a partial-height booster rotor (high-throughflow fan). The results show that the clocking arrangement of the tandem rotor in the high-throughflow fan determines the overall aerodynamic performance. At 20% clocking fraction arrangement (λ s = 20 %), compared with those of the baseline fan, the mass flow near the choke point (NC) and the total pressure ratio at the peak efficiency point (PE) of the high-throughflow fan are increased by 5.83% and 8.10%, respectively, whereas the casing diameter, peak efficiency, and stall margin nearly remain unchanged, and the increase in the total pressure ratio is mainly attributed to the increase in the core total pressure ratio. This study demonstrates that a high-throughflow fan can effectively improve the aerodynamic performance of the baseline fan, showing great potential in applications. [ABSTRACT FROM AUTHOR]

• A helical shaped dielectric barrier discharge actuator is developed as a plasma swirler. • Advantages of the plasma swirl injector with helical shaped actuators are demonstrated. • Actuators with different helical directions and electrode positions are assessed. • A central recirculation zone induced by the plasma actuation is observed. • The central recirculation zone dissipates the azimuthal velocity of the jet flow. In order to enhance the flow control effectiveness of the plasma swirl injector, dielectric barrier discharge (DBD) actuators with helical electrodes are developed and the performance is compared with that of straight actuators through flow field measurement. This new design can adjust the plasma distribution and increase the plasma intensity. More importantly, the design can be used to adjust the axial velocity besides the azimuthal velocity, therefore it can be used to mitigate flame blow-off or flashback. In addition, the plasma-induced flow can be aligned with the direction of flow moving out of the vane swirler accurately, which can reduce the pressure loss from the swirler. The helical shaped actuator is more suitable for working in conjunction with traditional mechanical swirlers, providing more flexibility in flow control. By changing the direction of the helical electrodes and their relative positions, four different plasma swirler configurations for flow control are considered, making flexible combinations with the vane swirler possible and providing more options for combustion control. Results of flow field measurement showed that a central recirculation zone (CRZ) appeared under the plasma actuation. Compared with that of the straight electrode actuation, the size of CRZ is increased and the back flow in CRZ is enhanced by the helical electrode actuation. Effect of CRZ on the azimuthal velocity dissipation is also observed. [ABSTRACT FROM AUTHOR]

The research on tandem impeller technology for centrifugal compressors has not been conducted in a systematic manner and remains incomplete. The lack of insight regarding the flow structure variations between tandem impellers with different meridional flow path profiles is considered to be the primary reason for the confusion. According to a detailed numerical investigation of a series of high-speed compressor stages with different impeller geometries, the secondary flow patterns were analyzed to determine the underlying physics of the impeller flow uniformity improvement, which is the main potential advantage of the tandem method. The impeller inlet/outlet radius ratio D 1 t /D 2 is critical to producing a superior tandem impeller application. The optimum D 1 t /D 2 range of 0.65–0.75 provided the maximum compressor efficiency gain of 1.5% due to the appropriate rearrangement of the impeller flow pattern. Outside of this optimum range, the impeller discharge flow uniformity could not be improved obviously and may even be reduced. The experimental results that were obtained by using centrifugal compressors with and without tandem impellers within the optimum D 1 t /D 2 range further demonstrate the performance gains achieved using the tandem impeller method. This study provides a valuable reference for tandem impeller technology applications and future advanced centrifugal compressor designs. [ABSTRACT FROM AUTHOR]

Experimental measurements were performed to study the influence of blade loading distribution on the aerodynamic performance of an ultra-high-lift low-pressure turbine cascade (Zw = 1.58) in the presence and absence of incoming wakes. The flow structures in front-loaded and aft-loaded blade passages were comprehensively compared at various Reynolds numbers. Furthermore, the flow mechanisms responsible for the effect of the blade loading distribution on the secondary flow were discussed in detail through numerical calculations. At the low Reynolds number of 25,000, weaker secondary flow was observed for the aft-loaded blade under steady conditions owing to the lower cross-passage pressure gradient compared to the front-loaded blade. Unsteady wakes clearly improved the throughflow characteristics of the cascade passage, increased the blade loading, and strengthened the secondary flow in the aft-loaded blade passage. At the high Reynolds number of 100,000, unsteady wakes delayed generation of the passage vortex in both the front-loaded and aft-loaded blade passages and clearly weakened the secondary flow. The experimental results revealed that the upstream wakes reduced the strength of the passage vortex core in the aft-loaded and front-loaded blade profiles by 21.6% and 17.5%, respectively. [ABSTRACT FROM AUTHOR]

In this paper, a 53 Gbps widely tunable transmitter is experimentally demonstrated for the first time, to our knowledge. An InGaAlAs/InP multiple-quantum-well (MQW) wafer is used with an identical layer structure for both the V-coupled cavity laser (VCL) and the electro-absorption modulator (EAM). The VCL uses a shallow-etched waveguide to reduce loss, while the EAM uses a deep-etched waveguide to increase the 3-dB modulation bandwidth. With the temperature varying from 19.5 to 30°C, the transmitter achieves wavelength tuning of 42 channels with a spacing of 100 GHz, corresponding to a tuning range of 32.6 nm from 1538.94 to 1571.54 nm. The static extinction ratio (ER) for all channels is higher than 14 dB. The measured 3-dB electro-optic (E0) bandwidth of the transmitter is over 40 GHz, which fits well with the calculated 3-dB bandwidth. At a fixed peak-to-peak driving voltage of 2.4 V, all channels exhibit clearly an open eye diagram with a 53 Gbps non-return-to-zero (NRZ) signal, while the dynamic ER is higher than 4.5 dB.

Two-dimensional transition metal dichalcogenides (TMDs), as flexible and stretchable materials, have attracted considerable attention in the field of novel flexible electronics due to their excellent mechanical, optical, and electronic properties. Among the various TMD materials, atomically thin MoS 2 has become the most widely used material due to its advantageous properties, such as its adjustable bandgap, excellent performance, and ease of preparation. In this work, we demonstrated the practicality of a stacked wafer-scale two-layer MoS 2 film obtained by transferring multiple single-layer films grown using chemical vapor deposition. The MoS 2 field-effect transistor cell had a top-gated device structure with a (PI) film as the substrate, which exhibited a high on/off ratio (10 8 ), large average mobility (∼8.56 cm 2 V -1 s -1 ), and exceptional uniformity. Furthermore, a range of flexible integrated logic devices, including inverters, NOR gates, and NAND gates, were successfully implemented via traditional lithography. These results highlight the immense potential of TMD materials, particularly MoS 2 , in enabling advanced flexible electronic and optoelectronic devices, which pave the way for transformative applications in future-generation electronics., (© 2023 IOP Publishing Ltd.)

This study was dedicated to introducing a new method for predicting the Sauter mean diameter (SMD) buildup in the swirl cup airblast fuel injector. There have been considerable difficulties with predicting SMD mainly because of complicated flow characteristics in a spray. Therefore, the backpropagation (BP) neural network-based machine learning was applied for the prediction of SMD as a function of geometry, condition parameters, and axial distance such as primary swirl number, secondary swirl number, venturi angle, mass flow rate of fuel, and relative air pressure. SMD was measured by a phase Doppler particle analyzer (PDPA). The results show that the prediction accuracy of the trained BP neural network was excellent with a coefficient of determination ( R 2 ) score of 0.9599, root mean square error (RMSE) score of 1.4613, and overall relative error within 20%. Through sensitivity analysis, the relative air pressure drop and primary swirl number were the largest and smallest factors affecting the value of SMD, respectively. Finally, the prediction accuracy of the BP neural network model is far greater than the current prediction correlations. Moreover, for the predicting target in the present study, the BP neural network shows the advantages of a simple structure and short running time compared with PSO-BP and GRNN. All these prove that the BP neural network is a novel and effective way to predict the SMD of droplets generated by a swirl cup airblast fuel injector., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

In today's information age, high performance nonvolatile memory devices have become extremely important. Despite their potential, existing devices suffer from limitations, such as low operation speed, low memory capacity, short retention time, and a complex preparation process. To overcome these limitations, advanced memory designs are required to improve speed, memory capacity, and retention time and reduce the number of preparation steps. Here, we present a nonvolatile floating-gate-like memory device based on a transistor that uses the polarization effect of ferroelectric material PZT (Pb[Zr 0.2 Ti 0.8 ]O 3 ) for regulating tunneling electrons for charging and discharging the MoS 2 channel layer. The transistor is defined as a polarized tunneling transistor (PTT) and does not require a tunnel layer or a floating-gate layer. The PTT demonstrates an ultrafast programming/erasing speed of 25/20 ns and a response time of 120/105 ns, which is comparable to the ultrafast flash memories based on van der Waals heterostructures. Additionally, the PTT has a high extinction ratio of 10 4 , a long retention time of 10 years, and a simple fabrication process. Our research provides future guidelines for the development of the next generation of ultrafast nonvolatile memory devices.

Two-dimensional InSe has been considered as a promising candidate for novel optoelectronic devices owing to large electron mobility and a near-infrared optical band gap. However, its widespread applications suffer from environmental instability. A lot of theoretical studies on the degradation mechanism of InSe have been reported whereas the experimental proofs are few. Meanwhile, the role of the extrinsic environment is still obscure during the degradation. As a common technique of studying the degradation mechanism of 2D materials, laser irradiation exhibits many unique advantages, such as being fast, convenient, and offering in situ compatibility. Here, we have developed a laser-treated method, which involves performing repeated measurements at the same point while monitoring the evolution of the resulting PL, to systematically study the photo-induced degradation process of InSe. Interestingly, we observe different evolution behavior of PL intensity under weak irradiation and strong irradiation. Our experimental results indicate the vacancy passivation and degrading effect simultaneously occurring in InSe under a weak laser irradiation, resulting in the PL increasing first and then decreasing during the measurement. Meanwhile we also notice that the passivation has a stronger effect on the PL than the degrading effect of weak oxidation. In contrast, under a strong laser irradiation, the InSe suffers serious destruction caused by excess heating and intense oxidation. This leads to a direct decrease of PL and corresponding oxidative products. Our work provides a reliable experimental supplement to the photo oxidation study of InSe and opens up a new avenue to regulate the PL of InSe., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

2D semiconductors, such as molybdenum disulfide (MoS 2 ), have attracted tremendous attention in constructing advanced monolithic integrated circuits (ICs) for future flexible and energy-efficient electronics. However, the development of large-scale ICs based on 2D materials is still in its early stage, mainly due to the non-uniformity of the individual devices and little investigation of device and circuit-level optimization. Herein, a 4-inch high-quality monolayer MoS 2 film is successfully synthesized, which is then used to fabricate top-gated (TG) MoS 2 field-effect transistors with wafer-scale uniformity. Some basic circuits such as static random access memory and ring oscillators are examined. A pass-transistor logic configuration based on pseudo-NMOS is then employed to design more complex MoS 2 logic circuits, which are successfully fabricated with proper logic functions tested. These preliminary integration efforts show the promising potential of wafer-scale 2D semiconductors for application in complex ICs., (© 2022 Wiley-VCH GmbH.)

Background: At present, many studies have described acute pulmonary embolism (PE) as a frequent and prognostically relevant complication of coronavirus disease 2019 (COVID-19) infection. Thus we performed the present analysis of 50 studies to evaluate the risk factors and mortality of PE in COVID-19 patients., Method: Databases including PubMed, Embase, Cochrane Library and Web of Science were searched to October, 2021. Odds ratio (OR), mean difference (MD) or standard MD was used to evaluate the outcomes. The primary outcomes were the difference of mortality between PE and non-PE COVID-19 patients as well as relevant risk factors of PE in COVID-19 patients. All statistical analyses were performed using the standard statistical procedures provided in Review Manager 5.2., Result: A total of 50 studies including 10053 patients were included in this meta-analysis. Our results indicated that COVID-19 patients with PE experienced significantly higher mortality than non-PE patients (21.9% vs. 10.7%), with a pooled OR of 2.21 (95% CI 1.30 - 3.76; P = .003). In addition, COVID-19 patients with PE also experienced more mechanical ventilation (MV) (OR 2.21; 95% CI 1.30 - 3.75; P = .003) and invasive mechanical ventilation (IMV) (OR 3.58; 95% CI 2.47 - 5.20; P < .0001) respectively. Univariate analysis (UVA) results indicated the Sequential Organ Failure Assessment (SOFA) score, time to deep venous thrombosis (DVT), nonintensive care unit (non-ICU) patients and no anticoagulation as risk factors of PE for COVID-19 patients. In addition, multivariate analysis also found that SOFA score, D-dimer, BMI > 30 kg/m2 and history of PE were risk factors of PE for COVID-19 patients., Conclusion: The present analysis indicated that PE increased the mortality of COVID-19 patients. Mechanical ventilation, especially invasive mechanical ventilation, is correlated with an increased incidence of PE in patients with COVID-19. The incidence of PE for COVID-19 patients may be multifactorial and further researches focused on risk factors were needed in the future., Competing Interests: The authors have no funding and conflict of interest to declare., (Copyright © 2022 the Author(s). Published by Wolters Kluwer Health, Inc.)

Organic-inorganic hybrid semiconducting (OIHS) materials, which can detect broader spectral regions, are highly desired in several applications including biomedical imaging, night vision, and optical communications. Although lead (Pb)-halide perovskites have reached a mature research stage, high toxicity of Pb hinders their large-scale viability. Tin (Sn)-based perovskites are the most common OIHS broadband light absorbers that replace toxic Pb; however, they are extremely unstable due to the notorious Sn 2+ oxidation. Herein, a novel, non-toxic, and solution-processed millimeter-sized OIHS single crystal [Ga(C 3 H 7 NO) 6 ](I 3 ) 3 has been grown at room temperature. Both the absorption measurement and density functional theory calculations have confirmed a narrow indirect band gap of 1.32 eV. The corresponding photodetector based on this single crystal demonstrated excellent performance including an ultraviolet-visible-near infrared (UV-vis-NIR) response between 325 and 1064 nm, fast response time ( t rise / t decay = 3.8 ms/5.4 ms), and profound air storage stability (41 h), thus outperforming most common photodetectors based on Sn-based perovskites. This work not only provides a profound understanding of this novel organic-inorganic single-crystal material but also demonstrates its great potential to realize the high-performance UV-vis-NIR broadband photodetectors.

A monolithic 6 × 6 transmitter-router with both port and wavelength switching at sub-nanosecond speed is proposed and experimentally demonstrated. Based on an intra-cavity cyclic echelle diffraction grating router (EDGR) and semiconductor optical amplifier (SOA) arrays, each selectable output port can realize a selected multi-wavelength laser (MWL) output. The measurement results show that all 36 input-output combinations have a single-mode emission spectrum with a sidemode suppression ratio (SMSR) over 30 dB. Simultaneous switching of six laser wavelengths is achieved together with the switching of the output port by a single electrode selection. The switching time is less than 1 ns. It can offer a cost-effective solution to multi-wavelength multi-port optical transmitter-routers for fast distributed optical switching in datacenters and high-performance computers (HPCs).