| 1. |
- Ding, Yu, et al.
(författare)
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Hydrogen-enhanced grain boundary vacancy stockpiling causes transgranular to intergranular fracture transition
- 2022
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Ingår i: Acta Materialia. - : Elsevier. - 1359-6454 .- 1873-2453. ; 239
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Tidskriftsartikel (refereegranskat)abstract
- The attention to hydrogen embrittlement (HE) has been intensified recently in the light of hydrogen as a carbon-free energy carrier. Despite worldwide research, the multifaceted HE mechanism remains a mat-ter of debate. Here we report an atomistic study of the coupled effect of hydrogen and deformation temperature on the pathway to intergranular fracture of nickel. Uniaxial straining is applied to nickel E5(210)[001] and E9(1-10)[22-1] grain boundaries with or without pre-charged hydrogen at various temperatures. Without hydrogen, vacancy generation at grain boundary is limited and transgranular frac-ture mode dominates. When charged, hydrogen as a booster can enhance strain-induced vacancy genera-tion by up to ten times. This leads to the superabundant vacancy stockpiling at the grain boundary, which agglomerates and nucleates intergranular nanovoids eventually causing intergranular fracture. While hy-drogen tends to persistently enhance vacancy concentration, temperature plays an intriguing dual role as either an enhancer or an inhibitor for vacancy stockpiling. These results show good agreement with recent positron annihilation spectroscopy experiments. An S-shaped quantitative correlation between the proportion of intergranular fracture and vacancy concentration was for the first time derived, highlight-ing the existence of a critical vacancy concentration, beyond which fracture mode will be completely intergranular.
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| 2. |
- Ding, Yu, et al.
(författare)
-
Hydrogen-induced transgranular to intergranular fracture transition in bi-crystalline nickel
- 2021
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Ingår i: Scripta Materialia. - : Elsevier. - 1359-6462 .- 1872-8456. ; 204
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Tidskriftsartikel (refereegranskat)abstract
- It is known that hydrogen can influence the dislocation plasticity and fracture mode transition of metallic materials, however, the nanoscale interaction mechanism between hydrogen and grain boundary largely remains illusive. By uniaxial straining of bi-crystalline Ni with a Σ5(210)[001] grain boundary, a transgranular to intergranular fracture transition facilitated by hydrogen is elucidated by atomistic modeling, and a specific hydrogen-controlled plasticity mechanism is revealed. Hydrogen is found to form a local atmosphere in the vicinity of grain boundary, which induces a local stress concentration and inhibits the subsequent stress relaxation at the grain boundary during deformation. It is this local stress concentration that promotes earlier dislocation emission, twinning evolution, and generation of more vacancies that facilitate nanovoiding. The nucleation and growth of nanovoids finally leads to intergranular fracture at the grain boundary, in contrast to the transgranular fracture of hydrogen-free sample.
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| 3. |
- Cui, Shaohua, 1995, et al.
(författare)
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Delay-throughput tradeoffs for signalized networks with finite queue capacity
- 2024
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Ingår i: Transportation Research Part B: Methodological. - 0191-2615. ; 180
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Tidskriftsartikel (refereegranskat)abstract
- Network-level adaptive signal control is an effective way to reduce delay and increase network throughput. However, in the face of asymmetric exogenous demand, the increase of network performance via adaptive signal control alone is at the expense of service fairness (i.e., phase actuation fairness and network resource utilization fairness). In addition, for oversaturated networks, arbitrary adaptive signal control seems to have little effect on improving network performance. Therefore, under the assumption that the mean routing proportions/turn ratios of vehicles at intersections are fixed, this study investigates the problem of optimally allocating input rates to entry links and simultaneously finding a stabilizing signal control policy with phase fairness. We model the stochastic optimization problem of maximizing network throughput subject to network stability (i.e., all queue lengths have finite means) and average phase actuation constraints to bridge the gap between stochastic network stability control and convex optimization. Moreover, we further propose a micro-level joint admission and bounded signal control algorithm to achieve network stability and throughput optimization simultaneously. Joint control is implemented in a fully decomposed and distributed manner. For any arrival rate, joint control provably achieves network throughput within O(1/V) of optimality while trading off average delay with O(V), where V is an adjusted control parameter. Through a comparative simulation of a real network with 256 O-D pairs, the proposed joint control keeps network throughput at maximum, guarantees service fairness, and fully utilizes network capacity (i.e., increases network throughput by 17.54%).
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| 4. |
- Fernández Schrunder, Alejandro, 1993-, et al.
(författare)
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A Bioimpedance Spectroscopy Interface for EIM Based on IF-Sampling and Pseudo 2-Path SC Bandpass ΔΣ ADC
- 2024
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Ingår i: IEEE Transactions on Biomedical Circuits and Systems. - : Institute of Electrical and Electronics Engineers (IEEE). - 1932-4545 .- 1940-9990. ; , s. 1-13
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a low-noise bioimpedance (bio-Z) spectroscopy interface for electrical impedance myography (EIM) over the 1 kHz to 2 MHz frequency range. The proposed interface employs a sinusoidal signal generator based on direct-digital-synthesis (DDS) to improve the accuracy of the bio-Z reading, and a quadrature low-intermediate frequency (IF) readout to achieve a good noise-to-power efficiency and the required data throughput to detect muscle contractions. The readout is able to measure baseline and time-varying bio-Z by employing robust and power-efficient low-gain IAs and sixth-order single-bit bandpass (BP) ΔΣ ADCs. The proposed bio-Z spectroscopy interface is implemented in a 180 nm CMOS process, consumes 344.3 - 479.3 μ W, and occupies 5.4 mm 2 area. Measurement results show 0.7 mΩ/√Hz sensitivity at 15.625 kHz, 105.8 dB SNR within 4 Hz bandwidth, and a 146.5 dB figure-of-merit. Additionally, recording of EIM in time and frequency domain during contractions of the bicep brachii muscle demonstrates the potential of the proposed bio-Z interface for wearable EIM systems.
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| 5. |
- Song, Kai, et al.
(författare)
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An Impedance Decoupling-Based Tuning Scheme for Wireless Power Transfer System under Dual-Side Capacitance Drift
- 2021
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Ingår i: IEEE Transactions on Power Electronics. - 0885-8993 .- 1941-0107. ; 36:7, s. 7526-7536
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Tidskriftsartikel (refereegranskat)abstract
- High performance of a wireless power transfer system is related to the resonance. However, the capacitance drift caused by temperature variation leads to detuning. In this article, a tuning scheme against dual-side capacitance drift using the impedance decoupling algorithm is investigated. First, the impact of the capacitance drift on transmission efficiency and output power are analyzed. Second, it is difficult to compensate for the dual-side capacitance drift quickly since the primary and secondary sides are coupled. Therefore, the impedance decoupling algorithm is introduced. The primary and secondary reactances are decoupled from the total impedance. The two independent reactances are only determined by the capacitance drift of the corresponding side. Then, by adjusting system frequency and the phase-shift angle of the semiactive rectifier, the reactances of both sides can be eliminated, respectively. Compared with the existing tuning methods focusing on total input impedance, the continuous adjustment on two sides is avoided, so the tuning time is significantly reduced. The experimental results prove that the proposed method can improve the system efficiency by 5%-40% and reduce the tuning time by 67% under different capacitance drift.
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| 6. |
- Wang, Ying, et al.
(författare)
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Epoxy composite with high thermal conductivity by constructing 3D-oriented carbon fiber and BN network structure
- 2021
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Ingår i: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 11:41, s. 25422-25430
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Tidskriftsartikel (refereegranskat)abstract
- As electronic devices tend to be integrated and high-powered, thermal conductivity is regarded as the crucial parameter of electronic components, which has become the main factor that limits the operating speed and service lifetime of electronic devices. However, constructing continuous thermal conductive paths for low content particle fillers and reducing interface thermal resistance between fillers and matrix are still two challenging issues for the preparation of thermally conductive composites. In this study, 3D-oriented carbon fiber (CF) thermal network structures filled with boron nitride flakes (BN) as thermal conductive bridges were successfully constructed. The epoxy composite was fabricated by thermal conductive material with a 3D oriented structure by the vacuum liquid impregnation method. This special 3D-oriented structure modified by BN (BN/CF) could efficiently broaden the heat conduction pathway and connected adjacent fibers, which leads to the reduction of thermal resistance. The thermal conductivity of the boron nitride/carbon fiber/epoxy resin composite (BN/CF/EP) with 5 vol% 10 mm CF and 40 vol% BN reaches up to 3.1 W m(-1) K-1, and its conductivity is only 2.5 x 10(-4) S cm(-1). This facile and high-efficient method could provide some useful advice for the thermal management material in the microelectronic field and aerospace industry.
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| 7. |
- Xue, Yanzhuo, et al.
(författare)
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A combined experimental and numerical approach to predict ship resistance and power demand in broken ice
- 2024
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Ingår i: Ocean Engineering. - 0029-8018. ; 292
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Tidskriftsartikel (refereegranskat)abstract
- Despite its remoteness and hostile environmental conditions, the Arctic holds significant shipping lanes, such as the Northern Sea Route (NSR) and the Northwest Passage (NWP). Typically, merchant ships operate along these routes in summer only, when the dominating type of ice is broken ice. A challenge of operating in such ice conditions is that there is no cost- and time-efficient method for predicting the resulting ice resistance, which makes route planning difficult, among others. To address this challenge, we present and analyze two complementary approaches to predict ship resistance in broken ice, of which one is experimental and the other numerical. The experimental approach makes use of a type of non-refrigerated synthetic model ice made of polypropylene, which makes it possible to test how a ship behaves in broken ice using a conventional non-refrigerated towing tank rather than an ice tank. The numerical approach, in turn, is based on the CFD-DEM method and can be used to consider fluid effects, such as the changes in fluid velocity and ship waves, while the ship is moving ahead. Validation calculations against established empirical approaches indicate that both approaches are reasonably accurate.
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| 8. |
- Yu, Cunming, et al.
(författare)
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Nature–Inspired self–cleaning surfaces: Mechanisms, modelling, and manufacturing
- 2020
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Ingår i: Chemical Engineering Research and Design. - : Elsevier BV. - 0263-8762 .- 1744-3563. ; 155, s. 48-65
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Tidskriftsartikel (refereegranskat)abstract
- Nature-inspired self-cleaning surfaces have attracted considerable attention from both fundamental research and practical applications. This review adopts a chemical-engineering point of view and focuses on mechanisms, modelling, and manufacturing (M3) of nature-inspired self-cleaning surfaces. We will introduce six nature-inspired self-cleaning mechanisms: The Lotus-effect, superhydrophobic-induced droplet jumping, superhydrophobic-induced unidirectional movement of water droplet, underwater-superoleophobic-based self-cleaning, slippery-based self-cleaning, and dry self-cleaning. These mechanisms of nature self-cleaning examples are popular and well-known as well as have been widely applied or exhibited potential applications in our daily life and industrial productions. The mathematical and numerical modelling of the identified self-cleaning mechanisms will be carefully introduced, which will contribute to the rational design and reproducible construction of these functional self-cleaning surfaces. Finally, we will discuss how these materials can be produced, with a focus on scalable manufacturing. We hope this review will strengthen the understanding on nature-inspired self-cleaning surfaces and stimulate interdisciplinary collaboration of material science, biology and engineering.
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| 9. |
- Zhong, Kai, et al.
(författare)
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Numerical study on the movement pattern of ice around the ship in the broken ice field
- 2023
-
Ingår i: Proceedings of the International Conference on Port and Ocean Engineering under Arctic Conditions, POAC. - 0376-6756 .- 2077-7841. ; 2023-June
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Konferensbidrag (refereegranskat)abstract
- Broken ice field is among the common type of ice conditions when ships operate in Arctic navigation, where ships face a significant increase in resistance and local structural safety threats due to the interaction between the ship's hull, water, and broken ice. The hull needs to remove a large amount of broken ice from its path and disturb the surrounding broken ice, and the extent to which can reflect the intensity of the ship-water-ice interaction. In this study, a coupled CFD-DEM approach to simulate ship-water-ice interaction-related phenomena. In the calculation process, rigid particles are considered as non-rebreakable broken ice, while the effect of ship wave variations on the movement of broken ice is taken into account. The "ice boundary layer" (IBL) is found in the numerical results, and distribution of the thickness of "IBL" along the ship's bow is derived and in good agreement with the formula proposed by Aboulazm (1989). After that, the relationship between ship speed on the movement of ice is also studied.
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| 10. |
- Huang, Yu-Kai, et al.
(författare)
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Noise Analysis and Design Methodology of Chopper Amplifiers With Analog DC-Servo Loop for Biopotential Acquisition Applications
- 2023
-
Ingår i: IEEE Transactions on Very Large Scale Integration (vlsi) Systems. - : Institute of Electrical and Electronics Engineers (IEEE). - 1063-8210 .- 1557-9999. ; , s. 1-13
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Tidskriftsartikel (refereegranskat)abstract
- Biopotential acquisition chopper instrumentation amplifiers require a dc-servo loop (DSL) in order to filter electrode dc offsets. However, the noise performance degradation due to the addition of the DSL is often overlooked despite that it can be very detrimental at the frequencies of interest. This article presents an in-depth noise analysis of biopotential acquisition chopper instrumentation amplifiers with analog DSLs. Analytical expressions that predict the noise of different DSL implementations are found and a design flow to minimize their noise contribution is proposed. The design methodology is demonstrated with example circuits targeting biopotential recording systems. These circuits are implemented using a standard 180 nm CMOS technology, and their performance is verified through postlayout simulations. The findings of this work provide a comprehensive understanding of the noise characteristics of a DSL, its impact on noise performance, and design strategies for noise optimization.
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