| 1. |
- Qi, Di, et al.
(author)
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Climate change drives rapid decadal acidification in the Arctic Ocean from 1994 to 2020
- 2022
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In: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 377:6614, s. 1544-1550
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Journal article (peer-reviewed)abstract
- The Arctic Ocean has experienced rapid warming and sea ice loss in recent decades, becoming the first open-ocean basin to experience widespread aragonite undersaturation [saturation state of aragonite (Warag) < 1]. However, its trend toward long-term ocean acidification and the underlying mechanisms remain undocumented. Here, we report rapid acidification there, with rates three to four times higher than in other ocean basins, and attribute it to changing sea ice coverage on a decadal time scale. Sea ice melt exposes seawater to the atmosphere and promotes rapid uptake of atmospheric carbon dioxide, lowering its alkalinity and buffer capacity and thus leading to sharp declines in pH and Warag. We predict a further decrease in pH, particularly at higher latitudes where sea ice retreat is active, whereas Arctic warming may counteract decreases in Warag in the future.
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| 2. |
- Deng, Zhang, et al.
(author)
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Using urban building energy modeling to quantify the energy performance of residential buildings under climate change
- 2023
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In: Building Simulation. - 1996-3599. ; 16:9, s. 1629-1643
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Journal article (peer-reviewed)abstract
- The building sector is facing a challenge in achieving carbon neutrality due to climate change and urbanization. Urban building energy modeling (UBEM) is an effective method to understand the energy use of building stocks at an urban scale and evaluate retrofit scenarios against future weather variations, supporting the implementation of carbon emission reduction policies. Currently, most studies focus on the energy performance of archetype buildings under climate change, which is hard to obtain refined results for individual buildings when scaling up to an urban area. Therefore, this study integrates future weather data with an UBEM approach to assess the impacts of climate change on the energy performance of urban areas, by taking two urban neighborhoods comprising 483 buildings in Geneva, Switzerland as case studies. In this regard, GIS datasets and Swiss building norms were collected to develop an archetype library. The building heating energy consumption was calculated by the UBEM tool-AutoBPS, which was then calibrated against annual metered data. A rapid UBEM calibration method was applied to achieve a percentage error of 2.7%. The calibrated models were then used to assess the impacts of climate change using four future weather datasets out of Shared Socioeconomic Pathways (SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5). The results showed a decrease of 22%-31% and 21%-29% for heating energy consumption, an increase of 113%-173% and 95%-144% for cooling energy consumption in the two neighborhoods by 2050. The average annual heating intensity dropped from 81 kWh/m 2 in the current typical climate to 57 kWh/m 2 in the SSP5-8.5, while the cooling intensity rose from 12 kWh/m 2 to 32 kWh/m 2. The overall envelope system upgrade reduced the average heating and cooling energy consumption by 41.7% and 18.6%, respectively, in the SSP scenarios. The spatial and temporal distribution of energy consumption change can provide valuable information for future urban energy planning against climate change.
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| 3. |
- Liu, Yixing, et al.
(author)
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Weight Distribution of a Knee Exoskeleton Influences Muscle Activities During Movements
- 2021
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In: IEEE Access. - : Institute of Electrical and Electronics Engineers (IEEE). - 2169-3536. ; 9, s. 91614-91624
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Journal article (peer-reviewed)abstract
- Lower extremity powered exoskeletons help people with movement disorders to perform daily activities and are used increasingly in gait retraining and rehabilitation. Studies of powered exoskeletons often focus on technological aspects such as actuators, control methods, energy and effects on gait. Limited research has been conducted on how different mechanical design parameters can affect the user. In this paper, we study the effects of weight distributions of knee exoskeleton components on simulated muscle activities during three functional movements. Four knee exoskeleton CAD models were developed based on actual motor and gear reducer products. Different placements of the motor and gearbox resulted in different weight distributions. One unilateral knee exoskeleton prototype was fabricated and tested on 5 healthy subjects. Simulation results were compared to observed electromyography signals. Muscle activities varied among weight distributions and movements, wherein no one physical design was optimal for all movements. We describe how a powered exoskeleton's core components can be expected to affect a user's ability and performance. Exoskeleton physical design should ideally take the user's activity goals and ability into consideration.
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| 4. |
- Mo, Jinyong, et al.
(author)
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Local lattice distortions, phase stability, and mechanical properties of NbMoTaWHfx alloys : A combined theoretical and experimental study
- 2023
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In: Computational materials science. - : Elsevier BV. - 0927-0256 .- 1879-0801. ; 217
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Journal article (peer-reviewed)abstract
- Refractory high-entropy alloys (RHEAs) are of growing interest due to their potentially superior mechanical performances at elevated temperatures. Inherent lattice distortions are believed to be a major contributor to strength in solid solution phases of RHEAs. Here, we investigate the NbMoTaWHfx alloy series (x = 0, 0.27, 0.57, 0.92, 1.33, 1.82) using first-principles simulations, thermodynamic modeling, and experimental techniques. The first-principles results suggest that Hf alloying is an effective means to enhance atomic-scale lattice distortions in BCC NbMoTaWHfx solid solutions. X-ray diffraction on prepared as-cast samples shows that the alloys with Hf content x <= 0.92 are single phase BCC alloys, whereas a dual BCC phase microstructure is observed for x = 1.33 and 1.82. Elemental mappings from scanning electron microscopy for the dual-phase alloys are checked with predictions from thermodynamic modeling for equilibrium and non-equilibrium solidifications. Room-temperature compressive mechanical tests reveal that yield and ultimate strengths increase strongly with the addition of Hf and saturate for x > 0.92, whereas the compressive plasticity is slightly improved by Hf but remains limited. We predict the compositional effects on poly-crystal elastic moduli for the constituent BCC phases and the dual-phase composites and find a linear behavior between modulus-normalized yield strength and lattice distortion on average.
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| 5. |
- Wan, Zhao-Yuan, et al.
(author)
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An Integrated Eye-Tracking and Motion Capture System in Synchronized Gaze and Movement Analysis
- 2023
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In: 2023 international conference on rehabilitation robotics, ICORR. - : Institute of Electrical and Electronics Engineers (IEEE).
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Conference paper (peer-reviewed)abstract
- Integrating mobile eye-tracking and motion capture emerges as a promising approach in studying visual-motor coordination, due to its capability of expressing gaze data within the same laboratory-centered coordinate system as body movement data. In this paper, we proposed an integrated eye-tracking and motion capture system, which can record and analyze temporally and spatially synchronized gaze and motion data during dynamic movement. The accuracy of gaze measurement were evaluated on five participants while they were instructed to view fixed vision targets at different distances while standing still or walking towards the targets. Similar accuracy could be achieved in both static and dynamic conditions. To demonstrate the usability of the integrated system, several walking tasks were performed in three different pathways. Results revealed that participants tended to focus their gaze on the upcoming path, especially on the downward path, possibly for better navigation and planning. In a more complex pathway, coupled with more gaze time on the pathway, participants were also found having the longest step time and shortest step length, which led to the lowest walking speed. It was believed that the integration of eye-tracking and motion capture is a feasible and promising methodology quantifying visual-motor coordination in locomotion.
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| 6. |
- Zhang, Longbin, et al.
(author)
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Modeling and Simulation of a Human Knee Exoskeleton's Assistive Strategies and Interaction
- 2021
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In: Frontiers in Neurorobotics. - : Frontiers Media SA. - 1662-5218.
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Journal article (peer-reviewed)abstract
- Exoskeletons are increasingly used in rehabilitation and daily life in patients with motor disorders after neurological injuries. In this paper, a realistic human knee exoskeleton model based on a physical system was generated, a human–machine system was created in a musculoskeletal modeling software, and human–machine interactions based on different assistive strategies were simulated. The developed human–machine system makes it possible to compute torques, muscle impulse, contact forces, and interactive forces involved in simulated movements. Assistive strategies modeled as a rotational actuator, a simple pendulum model, and a damped pendulum model were applied to the knee exoskeleton during simulated normal and fast gait. We found that the rotational actuator–based assistive controller could reduce the user's required physiological knee extensor torque and muscle impulse by a small amount, which suggests that joint rotational direction should be considered when developing an assistive strategy. Compared to the simple pendulum model, the damped pendulum model based controller made little difference during swing, but further decreased the user's required knee flexor torque during late stance. The trade-off that we identified between interaction forces and physiological torque, of which muscle impulse is the main contributor, should be considered when designing controllers for a physical exoskeleton system. Detailed information at joint and muscle levels provided in this human–machine system can contribute to the controller design optimization of assistive exoskeletons for rehabilitation and movement assistance.
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| 7. |
- Zhang, Xiaochen, et al.
(author)
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Multi-Objective-Based Human-in-the-Loop Optimization for Ankle Exoskeleton : A Preliminary Experimental Study
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Other publication (other academic/artistic)abstract
- Wearable robotic exoskeletons have been explored for their efficacy in physical rehabilitation and for assistance in daily activites in people with motor disorders. The concept of human-in-the-loop optimization has been used to identify ideal exoskeleton assistive torques based on measured individual performance metrics, for instance, metabolic cost, but few studies have attempted to optimize several performance metrics simultaneously.We have previously developed a cable-driven ankle exoskeleton that can provide assistance to the ankle in both sagittal and frontal planes, aimed for persons with dropfoot and excessive inversion. In this study, we propose a multi-objective human-in-the-loop optimization that identifies the ankle exoskeleton properties that improve gait quality, defined here as normal foot segment kinematics and step length symmetry. One able-bodied subject tested the feasibility of the proposed method. The subject wore the exoskeleton while walking on a treadmill. An extra weight was attached on the right foot to simulate the gait deviations associated with dropfoot and excessive inversion. The Pareto front, comprising six results, was sorted, which illustrated the improvement in both foot segment kinematics and step length symmetry. Within this set of results, each represents a unique compromise or balance between the two objectives, and it was observed that enhancing step length symmetry might lead to an increase in foot segment deviation, showcasing the inherent trade-off relationship between these two aspects.These results suggest that this method can potentially be useful in determining subject-specific exoskeleton control laws that improve several measures of gait in persons with gait disability.
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| 8. |
- Zhang, Xiaochen, et al.
(author)
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Soft Ankle Exoskeleton to Counteract Dropfoot and Excessive Inversion
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Other publication (other academic/artistic)abstract
- Wearable exoskeletons are emerging technologies for providing movement assistance and rehabilitation for people with motor disorders. In this study, we focus on the specific gait pathology dropfoot, which is common after a stroke. Dropfoot makes it difficult to achieve foot clearance during swing and heel contact at early stance and often necessitates compensatory movements. We developed a soft ankle exoskeleton consisting of actuation and transmission systems to assist two degrees of freedom simultaneously, dorsiflexion and eversion. The actuation system consists of two motors worn on a waist belt. The assistive force is transmitted to the medial and lateral sides of the forefoot via Bowden cables. The coupling design enables variable assistance of dorsiflexion and inversion at the same time. As a proof-of-concept study, we evaluated the performance of the exoskeleton on five able-bodied subjects in three movement cases - assisting dorsiflexion and eversion, controlling plantarflexion, and compensating for device resistance. In the first two cases, errors between the desired and the achieved ankle joints in two DoFs were low; errors of < 1.5° were achieved in assisting dorsiflexion and/or controlling plantarflexion, and of < 1.4° in assisting ankleeversion. The proposed force-free controller in case 3 significantly compensated for the device resistance during ankle joint plantarflexion. Our findings support the feasibility of the new ankle exoskeleton design in assisting two degrees of freedom at the ankle simultaneously.
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