| 1. |
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| 2. |
- Beal, Jacob, et al.
(författare)
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Robust estimation of bacterial cell count from optical density
- 2020
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Ingår i: Communications Biology. - : Springer Science and Business Media LLC. - 2399-3642. ; 3:1
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Tidskriftsartikel (refereegranskat)abstract
- Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data.
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| 3. |
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- 2019
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Tidskriftsartikel (refereegranskat)
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| 4. |
- Shang, Yuchen, et al.
(författare)
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Enhancement of short/medium-range order and thermal conductivity in ultrahard sp3 amorphous carbon by C70 precursor
- 2023
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Ingår i: Nature Communications. - : Springer Nature. - 2041-1723. ; 14:1
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Tidskriftsartikel (refereegranskat)abstract
- As an advanced amorphous material, sp3 amorphous carbon exhibits exceptional mechanical, thermal and optical properties, but it cannot be synthesized by using traditional processes such as fast cooling liquid carbon and an efficient strategy to tune its structure and properties is thus lacking. Here we show that the structures and physical properties of sp3 amorphous carbon can be modified by changing the concentration of carbon pentagons and hexagons in the fullerene precursor from the topological transition point of view. A highly transparent, nearly pure sp3−hybridized bulk amorphous carbon, which inherits more hexagonal-diamond structural feature, was synthesized from C70 at high pressure and high temperature. This amorphous carbon shows more hexagonal-diamond-like clusters, stronger short/medium-range structural order, and significantly enhanced thermal conductivity (36.3 ± 2.2 W m−1 K−1) and higher hardness (109.8 ± 5.6 GPa) compared to that synthesized from C60. Our work thus provides a valid strategy to modify the microstructure of amorphous solids for desirable properties.
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| 5. |
- Shang, Yuchen, et al.
(författare)
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Ultrahard bulk amorphous carbon from collapsed fullerene
- 2021
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Ingår i: Nature. - : Nature Publishing Group. - 0028-0836 .- 1476-4687. ; 599:7886, s. 599-604
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Tidskriftsartikel (refereegranskat)abstract
- Amorphous materials inherit short- and medium-range order from the corresponding crystal and thus preserve some of its properties while still exhibiting novel properties1,2. Due to its important applications in technology, amorphous carbon with sp2 or mixed sp2–sp3 hybridization has been explored and prepared3,4, but synthesis of bulk amorphous carbon with sp3 concentration close to 100% remains a challenge. Such materials inherit the short-/medium-range order of diamond and should also inherit its superior properties5. Here, we successfully synthesized millimetre-sized samples—with volumes 103–104 times as large as produced in earlier studies—of transparent, nearly pure sp3 amorphous carbon by heating fullerenes at pressures close to the cage collapse boundary. The material synthesized consists of many randomly oriented clusters with diamond-like short-/medium-range order and possesses the highest hardness (101.9 ± 2.3 GPa), elastic modulus (1,182 ± 40 GPa) and thermal conductivity (26.0 ± 1.3 W m−1 K−1) observed in any known amorphous material. It also exhibits optical bandgaps tunable from 1.85 eV to 2.79 eV. These discoveries contribute to our knowledge about advanced amorphous materials and the synthesis of bulk amorphous materials by high-pressure and high-temperature techniques and may enable new applications for amorphous solids.
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| 6. |
- Zhao, Sen, et al.
(författare)
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Expanding the mutation and phenotype spectrum of MYH3-associated skeletal disorders
- 2022
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Ingår i: NPJ genomic medicine. - : Nature Publishing Group. - 2056-7944. ; 7:1
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Tidskriftsartikel (refereegranskat)abstract
- Pathogenic variants in MYH3 cause distal arthrogryposis type 2A and type 2B3 as well as contractures, pterygia and spondylocarpotarsal fusion syndromes types 1A and 1B. These disorders are ultra-rare and their natural course and phenotypic variability are not well described. In this study, we summarize the clinical features and genetic findings of 17 patients from 10 unrelated families with vertebral malformations caused by dominant or recessive pathogenic variants in MYH3. Twelve novel pathogenic variants in MYH3 (NM_002470.4) were identified: three of them were de novo or inherited in autosomal dominant way and nine were inherited in autosomal recessive way. The patients had vertebral segmentation anomalies accompanied with variable joint contractures, short stature and dysmorphic facial features. There was a significant phenotypic overlap between dominant and recessive MYH3-associated conditions regarding the degree of short stature as well as the number of vertebral fusions. All monoallelic variants caused significantly decreased SMAD3 phosphorylation, which is consistent with the previously proposed pathogenic mechanism of impaired canonical TGF-β signaling. Most of the biallelic variants were predicted to be protein-truncating, while one missense variant c.4244T>G,p.(Leu1415Arg), which was inherited in an autosomal recessive way, was found to alter the phosphorylation level of p38, suggesting an inhibition of the non-canonical pathway of TGF-β signaling. In conclusion, the identification of 12 novel pathogenic variants and overlapping phenotypes in 17 affected individuals from 10 unrelated families expands the mutation and phenotype spectrum of MYH3-associated skeletal disorders. We show that disturbances of canonical or non-canonical TGF-β signaling pathways are involved in pathogenesis of MYH3-associated skeletal fusion (MASF) syndrome.
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| 7. |
- An, Rui, et al.
(författare)
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Photostability and Photodegradation Processes in Colloidal CsPbI3 Perovskite Quantum Dots
- 2018
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 10:45, s. 39222-39227
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Tidskriftsartikel (refereegranskat)abstract
- All-inorganic CsPbI3 perovskite quantum dots (QDs) have attracted intense attention for their successful application in photovoltaics (PVs) and optoelectronics that are enabled by their superior absorption capability and great photoluminescence (PL) properties. However, their photostability remains a practical bottleneck and further optimization is highly desirable. Here, we studied the photostability of as-obtained colloidal CsPbI3 QDs suspended in hexane. We found that light illumination does induce photodegradation of CsPbI3 QDs. Steady-state spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, and transient absorption spectroscopy verified that light illumination leads to detachment of the capping agent, collapse of the CsPbI3 QD surface, and finally aggregation of surface Pb0. Both dangling bonds containing surface and Pb0 serve as trap states causing PL quenching with a dramatic decrease of PL quantum yield. Our work provides a detailed insight about the correlation between the structural and photophysical consequences of the photodegradation process in CsPbI3 QDs and may lead to the optimization of such QDs toward device applications.
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| 8. |
- Cao, Qi, et al.
(författare)
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Jointly estimating the most likely driving paths and destination locations with incomplete vehicular trajectory data
- 2023
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Ingår i: Transportation Research, Part C: Emerging Technologies. - 0968-090X. ; 155
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Tidskriftsartikel (refereegranskat)abstract
- With an ever-increasing deployment density of probe and fixed sensors, massive vehicular trajectory data is available and show a promising foundation to improve the observability of dynamic traffic demand pattern. However, due to technical and privacy issues, the raw trajectories are not always complete and the paths and destinations between discontinuous trajectory nodes are usually missing. This paper proposes a probabilistic method to jointly reconstruct the missing driving path and destination location of vehicles with incomplete trajectory data. One problem-specific HMM-structured model incorporating spatial and temporal analysis (ST-HMM) is constructed to define the matching probability between observed data and possible movement. Two algorithms, namely candidate set generation and best-match search algorithms, are developed to seek the most possible one as matching result. It can implement end-to-end processing from incomplete trajectory data to complete and connective paths and destinations for the target vehicle. The proposed method is tested based on field-test data and city-wide road network. Compared with two benchmark methods, the proposed method improved the matching accuracy in terms of both path identification and destination inference. Additionally, sensitivity analyses on the size of training dataset and candidate set were performed. We believe that experiment results of these sensitivity analyses can help to provide guidance on data sensing and candidate generation.
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| 9. |
- Diuk-Wasser, Maria A., et al.
(författare)
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Monitoring Human Babesiosis Emergence through Vector Surveillance, New England, USA
- 2014
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Ingår i: Emerging Infectious Diseases. - : Centers for Disease Control and Prevention (CDC). - 1080-6040 .- 1080-6059. ; 20:2, s. 225-231
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Tidskriftsartikel (refereegranskat)abstract
- Human babesiosis is an emerging tick-borne disease caused by the intraerythrocytic protozoan Babesia microti. Its geographic distribution is more limited than that of Lyme disease, despite sharing the same tick vector and reservoir hosts. The geographic range of B. microti is expanding, but knowledge of its range is incomplete and relies exclusively on reports of human cases. We evaluated the utility of tick-based surveillance for monitoring disease expansion by comparing the ratios of the 2 infections in humans and ticks in areas with varying babesiosis endemicity. We found a close association between human disease and tick infection ratios in long-established babesiosis-endemic areas but a lower than expected incidence of human babesiosis on the basis of tick infection rates in new disease-endemic areas. This finding suggests that babesiosis at emerging sites is underreported. Vector-based surveillance can provide an early warning system for the emergence of human babesiosis.
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| 10. |
- Guo, Yuchen, et al.
(författare)
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Design Applicable 3D Microfluidic Functional Units Using 2D Topology Optimization with Length Scale Constraints
- 2020
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Ingår i: Micromachines. - : MDPI. - 2072-666X. ; 11:6
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Tidskriftsartikel (refereegranskat)abstract
- Due to the limits of computational time and computer memory, topology optimization problems involving fluidic flow frequently use simplified 2D models. Extruded versions of the 2D optimized results typically comprise the 3D designs to be fabricated. In practice, the depth of the fabricated flow channels is finite; the limited flow depth together with the no-slip condition potentially make the fluidic performance of the 3D model very different from that of the simplified 2D model. This discrepancy significantly limits the usefulness of performing topology optimization involving fluidic flow in 2D—at least if special care is not taken. Inspired by the electric circuit analogy method, we limit the widths of the microchannels in the 2D optimization process. To reduce the difference of fluidic performance between the 2D model and its 3D counterpart, we propose an applicable 2D optimization model, and ensure the manufacturability of the obtained layout, combinations of several morphology-mimicking filters impose maximum or minimum length scales on the solid phase or the fluidic phase. Two typical Lab-on-chip functional units, Tesla valve and fluidic channel splitter, are used to illustrate the validity of the proposed application of length scale control.
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| 11. |
- Han, Hedong, et al.
(författare)
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Utilization of Palliative Care for Patients Undergoing Hematopoietic Stem Cell Transplantation During Hospitalization : A Population-Based National Study
- 2019
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Ingår i: The American Journal of Hospice and Palliative Medicine. - : Sage Publications. - 1049-9091 .- 1938-2715. ; 36:10, s. 900-906
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVE: Patients undergoing hematopoietic stem cell transplantation (HSCT) have substantial physical and psychological symptoms. This study aimed to investigate the utilization of palliative care (PC) in patients undergoing HSCT during hospitalization.METHODS: The 2008-2014 National Inpatient Sample was queried for eligible participants. Demographics, hospital characteristics, comorbidities, posttransplantation complications, and inpatient procedures were compared between patients with and without PC. Multivariate logistic regression was performed to identify predictors associated with PC use.RESULTS: Among 21 458 patients undergoing HSCT during hospitalization, 278 (1.30%) received PC. The rate of PC use has significantly increased from 0.64% in 2008 to 1.95% in 2014. Patients receiving PC had more co-comorbidities, posttransplantation complications, inpatient procedures, and were more likely to carry a diagnosis of leukemia. In allogeneic HSCT, large bed size (odds ratio [OR] =2.80; 95% confidence interval [CI]: 1.17-6.70), stem cell source from cord blood (OR = 1.93; 95% CI: 1.15-3.24), and graft-versus-host disease (OR = 2.04; 95% CI: 1.36-3.06) were predictors of PC use. In a subset analysis of 783 patients who died during hospitalization, 166 (21.20%) received PC. Among the decedents, Hispanic race had lower odds of PC use (OR = 0.20; 95% CI: 0.05-0.82) in allogeneic HSCT and women had higher odds of PC (OR = 2.70; 95% CI: 1.35-5.41) in autologous HSCT.CONCLUSIONS: The rate of PC use has significantly increased among patients undergoing HSCT during hospitalization from 2008 to 2014 but still remains very low. Further investigation is warranted to verify and better understand the barriers toward PC use for HSCT patients.
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| 12. |
- Li, Yuchen, et al.
(författare)
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Public awareness, emotional reactions and human mobility in response to the COVID-19 outbreak in China : a population-based ecological study
- 2022
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Ingår i: Psychological Medicine. - : Cambridge University Press. - 0033-2917 .- 1469-8978. ; 52:9, s. 1793-1800
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Tidskriftsartikel (refereegranskat)abstract
- Background: The outbreak of COVID-19 generated severe emotional reactions, and restricted mobility was a crucial measure to reduce the spread of the virus. This study describes the changes in public emotional reactions and mobility patterns in the Chinese population during the COVID-19 outbreak.Methods: We collected data on public emotional reactions in response to the outbreak through Weibo, the Chinese Twitter, between January 1st and March 31st, 2020. Using anonymized location-tracking information, we analyzed the daily mobility patterns of approximately 90% of Sichuan residents.Results: There were three distinct phases of the emotional and behavioral reactions to the COVID-19 outbreak. The alarm phase (January 19th –26th) was a restriction-free period, characterized by few new daily cases, but enormous public negative emotions (the number of negative comments per Weibo post increased by 246.9 per day, 95%CI: 122.5–371.3), and a substantial increase in self-limiting mobility (from 45.6% to 54.5%, changing by 1.5% per day, 95%CI: 0.7%–2.3%). The epidemic phase (January 27th –February 15th) exhibited rapidly increasing numbers of new daily cases, decreasing expression of negative emotions (a decrease of 27.3 negative comments per post per day, 95%CI: −40.4–−14.2), and a stabilized level of self-limiting mobility. The relief phase (February 16th –March 31st) had a steady decline in new daily cases and decreasing levels of negative emotion and self-limiting mobility.Conclusions: During the COVID-19 outbreak in China, the public’s emotional reaction was strongest before the actual peak of the outbreak and declined thereafter. The change in human mobility patterns occurred before the implementation of restriction orders, suggesting a possible link between emotion and behavior.
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| 13. |
- Liu, Dongjie, et al.
(författare)
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Enhancing choice-set generation and route choice modeling with data- and knowledge-driven approach
- 2024
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Ingår i: Transportation Research, Part C: Emerging Technologies. - 0968-090X. ; 162
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Tidskriftsartikel (refereegranskat)abstract
- Two central and interconnected problems arise in the specification of a ‘‘complete’’ path-based route choice model: choice-set generation and choice from a choice set. Choice-set generation poses a significant challenge in personalization and the enumeration of the full choice set with large size. Despite the continued prevalence of classic econometric models for modeling choices within a given set, this requirement of knowledge-driven modeling necessitates explicit model structures and intricate domain knowledge, which may result in practical biases. In this study, a Conditional Variational AutoEncoder (CVAE)-based choice set generation model is developed, which approximates the probability distribution of the underlying choice set generation process conditional on individual and OD characteristics without relying on expert knowledge. In order to facilitate a friendly integration between knowledge-driven econometric and machine learning approaches, a neural-embedded route choice model (IAP-NERCM) with implicit availability/perception (IAP) of choice alternatives is proposed to automatically capture the heterogeneity of taste parameters without assuming any a priori relationship. Results based on synthetic data show that the proposed models are capable of reproducing the pre-defined coefficients. Field data of GPS data collected in Toyota City is used to future test the proposed models compared to classical statistical models. Results indicate that IAP-NERCM exhibits the ability to recover underlying taste function and achieves the best performance in terms of goodness-of-fit, predictability, and estimation time.
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| 14. |
- Liu, Xinyu, et al.
(författare)
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Vehicle trajectory prediction through manual setting and machine learning
- 2022
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Ingår i: ISCTT 2022 - 7th International Conference on Information Science, Computer Technology and Transportation. ; , s. 612-616
-
Konferensbidrag (refereegranskat)abstract
- The prediction of vehicle trajectory is an important step in safe driving. The relative positions or speeds of vehicles affect the interactions between them, which in turn produce predictions of trajectories. Through the trajectory prediction of each vehicle to form a complete safe driving environment. This paper will be divided into two parts for vehicle track, namely manual setting and machine learning. The advantage of manual setting is that it is convenient to observe the characteristics and then make other vehicles follow the corresponding behaviour. However, the disadvantage is that the characteristics that can be observed are incomplete, which makes the experimental error relatively large. The advantage of machine learning is that through previous experience to make all vehicles change in the corresponding situation. Through previous experience to make all vehicles change in the corresponding situation. An effective extraction and addition of the original data is helpful to reduce the final error. Our code base can be found in https://github.com/RR30/CIS_multi_vehicle_prediction/tree/Xinyu.
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| 15. |
- Liu, Yuchen, et al.
(författare)
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Effect of probe pulse duration in picosecond ultrasonics
- 2022
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 120:20
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Tidskriftsartikel (refereegranskat)abstract
- Picosecond ultrasonics is a powerful tool for nanoscale metrology, giving access to dimensions and mechanical, thermal, and optical properties of nanomaterials. By monitoring the temporal evolution of the interaction of light with coherent acoustic phonons, also known as Brillouin oscillations, phonon lifetime and optical absorption can be measured. However, the extraction of these quantities can be inaccurate due to the common assumption of the infinite coherence length of probe pulses. Here, we demonstrate the effect of probe pulse duration on picosecond ultrasonic measurements numerically and experimentally. We establish a model that shows how the probe coherence length affects the measured signal loss and how we can overcome this limitation and measure an upper limit of the acoustic attenuation factor. The model is verified experimentally on a GaAs bulk substrate by varying the probe pulse duration, showing a strong effect for sub-100 fs pulses. Finally, we applied to CH3NH3PbBr3, where we reveal a high acoustic attenuation factor, which is in line with recent claims of strong anharmonicity in halide perovskites.
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| 16. |
- Song, Yuchen, et al.
(författare)
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A state-based inverse reinforcement learning approach to model activity-travel choices behavior with reward function recovery
- 2024
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Ingår i: Transportation Research Part C. - : Elsevier BV. - 0968-090X .- 1879-2359. ; 158
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Tidskriftsartikel (refereegranskat)abstract
- Behaviorally oriented activity-travel choices (ATC) modeling is a principal part of travel demand analysis. Traditional econometric and rule-based methods require explicit model structures and complex domain knowledge. While several recent studies used machine learning models, especially adversarial inverse reinforcement learning (IRL) models, to learn potential ATC patterns with less expert-designed settings, they lack a clear representation of rational ATC behavior. In this study, we propose a data-driven IRL framework based on the maximum causal approach to minimize f-divergences between expert and agent state marginal distributions, which provides a more sample-efficient measurement. In addition, we specify a separate state-only reward function and derive an analytical gradient of the f-divergence objective with respect to reward parameters to ensure good convergences. The method can recover a stationary reward function, which assures the agent to get close to the expert behavior when training from scratch. We validate the proposed model using cellular signaling data from Chongqing, China by comparing with baseline models (behavior cloning, policy-based, and reward-based models) in aspects of policy performance comparison, reward recovery, and reward transfer tasks. The experiment results indicate that the proposed model outperforms existing methods and is relatively less sensitive to the number of expert demonstrations. Qualitative analyses are provided on the fundamental ATC preferences on different features given the reward function recovered from the observed mobility trajectories, and on the learning behaviors under different choices of f-divergence.
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| 17. |
- Wang, Yuchen, et al.
(författare)
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Field observations of C2 and C3 organosulfates and insights into their formation mechanisms at a suburban site in Hong Kong
- 2023
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Ingår i: SCIENCE OF THE TOTAL ENVIRONMENT. - 0048-9697 .- 1879-1026. ; 904
-
Tidskriftsartikel (refereegranskat)abstract
- Organosulfates (OSs) are formed from volatile organic compounds (VOCs) and their oxidation products in the presence of sulfate particles. While OSs represent an important component in secondary organic aerosol, the knowledge of their formation driving force, mechanisms, and environmental impact remain inadequately understood. In this study, we report ambient observations of C2-3 oxygenated VOCs derived OSs (C2-3 OSs) at a suburban location of Hong Kong during autumn 2016. The C2-3 OSs, including glycolaldehyde sulfate (GS), hydroxyacetone sulfate (HAS), glycolic acid sulfate (GAS), and lactic acid sulfate (LAS), were quantified/semiquantified using offline liquid chromatography-mass spectrometry analysis of aerosol filter samples. The average sum concentration of C2-3 OSs was 36 ng/m3. Correlation analysis revealed that sulfate, surface area, and liquid water content were important factors influencing C2-3 OS formation. Online measurement with an iodide High-Resolution Time-of-Flight Chemical-Ionization Mass Spectrometer (HR-ToF-CIMS) coupled with the Filter Inlet for Gases and AEROsols (FIGAERO) was also conducted to monitor C2-3 OSs, and their potential oxygenated VOC precursors in both gas-and particle-phase, and aerosol acidity tracer simultaneously. Our measurements support that glycolaldehyde/glyoxal, hydroxyacetone, glycolic acid/glyoxal, and lactic acid/ methylglyoxal are likely precursors for GS, HAS, GAS, and LAS, respectively. Additionally, we found strong correlation between C2-3 OSs and H3S2O8 , a marker for aerosol acidity, providing field observational evidence for acid-catalyzed formation of small OSs. Based on both online and offline measurements, acid-catalyzed formation mechanisms in particle/aqueous phase are proposed. Specifically, the unique structure of adjacent carbonyl and hydroxyl groups in the C2-3 oxygenated VOC precursors can facilitate the formation of (1) a five member ring intermediate via intramolecular hydrogen bond to react with sulfur trioxide through heterogenous reaction or (2) cyclic sulfate intermediate via particle-phase reaction with sulfuric acid to generate C2-3 OSs. These proposed mechanisms provide an alternative pathway for the liquid-phase production of C2-3 OSs.
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| 18. |
- Wang, Zhiqi, et al.
(författare)
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Topology Optimization of Passive Cell Traps
- 2021
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Ingår i: Micromachines. - : MDPI. - 2072-666X. ; 12:7
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Tidskriftsartikel (refereegranskat)abstract
- This paper discusses a flexible design method of cell traps based on the topology optimization of fluidic flows. Being different from the traditional method, this method obtains the periodic layout of the cell traps according to the cell trapping requirements by proposing a topology optimization model. Additionally, it satisfies the cell trapping function by restricting the flow distribution while taking into account the overall energy dissipation of the flow field. The dependence on the experience of the designer is reduced when this method is used to design a cell trap with acceptable trapping performance. By comparing the influence of the changes of various parameters on the optimization results, the flexibility of the topology optimization method for cell trap structure optimization is verified. The capability of this design method is validated by several performed comparisons between the obtained layouts and optimized designs in the published literature.
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| 19. |
- Yu, ChaoQing, et al.
(författare)
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Managing nitrogen to restore water quality in China
- 2019
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Ingår i: Nature. - : Nature Publishing Group. - 0028-0836 .- 1476-4687. ; 567:7749, s. 516-520
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Tidskriftsartikel (refereegranskat)abstract
- The nitrogen cycle has been radically changed by human activities(1). China consumes nearly one third of the world's nitrogen fertilizers. The excessive application of fertilizers(2,3) and increased nitrogen discharge from livestock, domestic and industrial sources have resulted in pervasive water pollution. Quantifying a nitrogen 'boundary'(4) in heterogeneous environments is important for the effective management of local water quality. Here we use a combination of water-quality observations and simulated nitrogen discharge from agricultural and other sources to estimate spatial patterns of nitrogen discharge into water bodies across China from 1955 to 2014. We find that the critical surface-water quality standard (1.0 milligrams of nitrogen per litre) was being exceeded in most provinces by the mid-1980s, and that current rates of anthropogenic nitrogen discharge (14.5 +/- 3.1 megatonnes of nitrogen per year) to fresh water are about 2.7 times the estimated 'safe' nitrogen discharge threshold (5.2 +/- 0.7 megatonnes of nitrogen per year). Current efforts to reduce pollution through wastewater treatment and by improving cropland nitrogen management can partially remedy this situation. Domestic wastewater treatment has helped to reduce net discharge by 0.7 +/- 0.1 megatonnes in 2014, but at high monetary and energy costs. Improved cropland nitrogen management could remove another 2.3 +/- 0.3 megatonnes of nitrogen per year-about 25 per cent of the excess discharge to fresh water. Successfully restoring a clean water environment in China will further require transformational changes to boost the national nutrient recycling rate from its current average of 36 per cent to about 87 per cent, which is a level typical of traditional Chinese agriculture. Although ambitious, such a high level of nitrogen recycling is technologically achievable at an estimated capital cost of approximately 100 billion US dollars and operating costs of 18-29 billion US dollars per year, and could provide co-benefits such as recycled wastewater for crop irrigation and improved environmental quality and ecosystem services.
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| 20. |
- Zhai, Chunguang, et al.
(författare)
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Molecular insertion regulates the donor-acceptor interactions in cocrystals for the design of piezochromic luminescent materials
- 2021
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Ingår i: Nature Communications. - : Nature Publishing Group. - 2041-1723. ; 12:1
-
Tidskriftsartikel (refereegranskat)abstract
- Developing a universal strategy to design piezochromic luminescent materials with desirable properties remains challenging. Here, we report that insertion of a non-emissive molecule into a donor (perylene) and acceptor (1,2,4,5-tetracyanobezene) binary cocrystal can realize fine manipulation of intermolecular interactions between perylene and 1,2,4,5-tetracyanobezene (TCNB) for desirable piezochromic luminescent properties. A continuous pressure-induced emission enhancement up to 3 GPa and a blue shift from 655 to 619 nm have been observed in perylene-TCNB cocrystals upon THF insertion, in contrast to the red-shifted and quenched emission observed when compressing perylene-TCNB cocrystals and other cocrystals reported earlier. By combining experiment with theory, it is further revealed that the inserted non-emissive THF forms blue-shifting hydrogen bonds with neighboring TCNB molecules and promote a conformation change of perylene molecules upon compression, causing the blue-shifted and enhanced emission. This strategy remains valid when inserting other molecules as non-emissive component into perylene-TCNB cocrystals for abnormal piezochromic luminescent behaviors.
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| 21. |
- Zhang, Fengying, et al.
(författare)
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Microscopic morphology independence in linear absorption cross-section of CsPbBr3 nanocrystalsMicroscopic morphology independence in linear absorption cross-section of CsPbBr3 nanocrystals
- 2021
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Ingår i: SCIENCE CHINA Materials. - : Springer Science and Business Media LLC. - 2095-8226 .- 2199-4501. ; 64:6, s. 1418-1426
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Tidskriftsartikel (refereegranskat)abstract
- Multiple morphologies of colloidal perovskite nanocrystals (NCs) diversify their optical and electronic properties. Among them, the linear absorption cross-section (σ) is a primary parameter to determine their intrinsic photophysical features, and consequently, application potential. Herein, three morphologies of all-inorganic hybrid colloidal perovskite CsPbBr3 NCs, nanocubes (NBs), nanoplatelets (NLs), and nanowires (NWs), were targeted, and their linear σ values were obtained through femtosecond transient absorption (TA) spectroscopy analysis. At high excitation energy well above the bandgap, the σ per particle of all CsPbBr3 NCs linearly increased with the particle volume (VNC) regardless of the morphology with the value of σ400 = 9.45 × 104 cm−1 × VNC (cm2). Density functional theory (DFT) calculation confirmed the negligible influence of shapes on the optical selection rules. The Einstein spontaneous emission coefficients calculated from the σ values define the intrinsic radiative recombination rate. However, reduced size dependence is observed when the excitation energy is close to the bandgap (i.e., at 460 nm) with the value of σ460 = 2.82 × 108 cm0.65 × (VNC)0.45 (cm2). This should be ascribed to the discrete energy levels as well as lower density of states close to the band edge for perovskite NCs. These results provide in-depth insight into the optical characteristics for perovskite NCs.
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| 22. |
- Zou, Xianshao, et al.
(författare)
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Carrier Recombination Processes in GaAs Wafers Passivated by Wet Nitridation
- 2020
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 12:25, s. 28360-28367
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Tidskriftsartikel (refereegranskat)abstract
- As one of the successful approaches to GaAs surface passivation, wet-chemical nitridation is applied here to relate the effect of surface passivation to carrier recombination processes in bulk GaAs. By combining time-resolved photoluminescence and optical pump-THz probe measurements, we found that surface hole trapping dominates the decay of photoluminescence, while photoconductivity dynamics is limited by surface electron trapping. Compared to untreated sample dynamics, the optimized nitridation reduces hole- and electron-trapping rate by at least 2.6 and 3 times, respectively. Our results indicate that under ambient conditions, recovery of the fast hole trapping due to the oxide regrowth at the deoxidized GaAs surface takes tens of hours, while it is effectively inhibited by surface nitridation. Our study demonstrates that surface nitridation stabilizes the GaAs surface via reduction of both electron- and hole-trapping rates, which results in chemical and electronical passivation of the bulk GaAs surface.
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