| 1. |
- 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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| 2. |
- Zhang, Xuning, et al.
(författare)
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On the understanding of energy loss and device fill factor trade-offs in non-fullerene organic solar cells with varied energy levels
- 2020
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Ingår i: Nano Energy. - : ELSEVIER. - 2211-2855 .- 2211-3282. ; 75
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Tidskriftsartikel (refereegranskat)abstract
- Fill factor (FF) is an important parameter governing the power conversion efficiency (PCE) in non-fullerene organic solar cells (NF-OSCs), which however is less studied than the other two parameters (short-circuit current J(sc) and open-circuit voltage V-oc). To understand how energy offsets, exciton and charge carrier dynamics impact the FF, four groups of bulk heterojunctions (BHJs) NF-OSCs are investigated with FFs varying from 0.61 to 0.78 under progressive changes of HOMO-HOMO offsets (Delta(HOMOs), from 0.09 to 0.24 eV). By pump-probe optical spectroscopy, we find that the FF exhibits a positive dependence on Delta(HOMO) and charge-separated state lifetime (tau(CS)) in the blends, a result of inhibited back charge transfers and recombination at the donor-acceptor interface under higher Delta(HOMO)s. Moreover, we observe a fast charge extraction with decreased sensitivity to internal electric-fields in high-FF devices. Despite these merits, the gains of FF are at the expense of increasing the voltage loss to non-radiative recombination in our studied systems. The combined results suggest that remaining appropriate energetic offsets is essential for controlling the carrier dynamics with longer-lived CS-states, restraining charge back transfer and reducing charge recombination toward high FFs and photovoltaic efficiencies.
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| 3. |
- Wang, Jianqiu, et al.
(författare)
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A Comparative Study on Hole Transfer Inversely Correlated with Driving Force in Two Non-Fullerene Organic Solar Cells
- 2019
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Ingår i: The Journal of Physical Chemistry Letters. - : AMER CHEMICAL SOC. - 1948-7185. ; 10:14, s. 4110-4116
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Tidskriftsartikel (refereegranskat)abstract
- We report a faster rate of hole transfer under a smaller AHomo in a comparative study of two group organic solar cells (OSCs) consisting of IT-4F as an acceptor and PBDBT and PBDBT-SF as donors. In the OSCs based on PBDBT. SF:IT-4F, a higher short-circuit current (J(SC)) was observed with a Delta(Homo) of 0.31 eV compared to a lower Jsc in PBDBT:IT-4F OSCs with a larger Delta(Homo) (0.45 eV). Intensive investigation indicates that the rate of transfer of a hole from IT-4F to PBDBT-SF or PBDBT is inversely proportional to the Delta(Homo) between IT-4F and donors. The larger Jsc in the PBDBT-SF:IT-4F device is attributed to a synergy of faster hole transfer, slower recombination, and rapid charge extraction enabled by desired morphology and balanced charge carrier mobilities with PBDBT-SF, suggesting that under a sufficiently high Delta(Homo), comprehensive considerations of the transport, film morphology, and energy levels are needed when designing new materials for high-performance OSCs.
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| 4. |
- Wang, Jianqiu, et al.
(författare)
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Fast Field-Insensitive Charge Extraction Enables High Fill Factors in Polymer Solar Cells
- 2020
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Ingår i: ACS Applied Materials and Interfaces. - : AMER CHEMICAL SOC. - 1944-8244 .- 1944-8252. ; 12:34, s. 38460-38469
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Tidskriftsartikel (refereegranskat)abstract
- Fill factor (FF) is a determining parameter for the power conversion efficiency (PCE) of organic solar cells (OSC). So far, nonfullerene (NF) OSCs with state-of-the-art PCEs exhibit FFs <0.8, lower than the values of Si or perovskite solar cells. The FFs directly display the dependence of photocurrent on bias, meaning that the competition between charge extraction and recombination is modulated by internal electric potential (V-in). Here, we report a study to understand key parameters/properties affecting the device FF based on seven groups of NF-OSCs consisting of widely used PBDBT-2F or PTB7-Th donors and representative NF-acceptors with FFs ranging from 0.60 to 0.78 and PCEs from 10.27 to 16.09%. We used field-dependent transient photocurrent measurements to reveal that fast and field-insensitive charge extraction at low V-in is an essential prerequisite for obtaining high FFs (0.75-0.8), which is enabled by balanced charge transport in steady and reduced bimolecular charge recombination in high purity phases. With bias-dependent quantum efficiency analysis, we further show that the recombination loss at low V-in in the devices with low FFs tends to be more significant involving excitons generated in the donor phase of blends. Our results provide relevance for how to improve the FF toward the boost of photovoltaic performance in NF-OSCs.
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| 5. |
- Liu, Sheng, et al.
(författare)
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An improved estimation of soil water and salt dynamics by considering soil bulk density changes under freeze/thaw conditions in arid areas with shallow groundwater tables
- 2023
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Ingår i: Science of the Total Environment. - : Elsevier BV. - 0048-9697. ; 859
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Tidskriftsartikel (refereegranskat)abstract
- Soil bulk density (BD) is a parameter dependent on soil texture, compositions of soil minerals and organic matter and the extent of soil compaction. Seasonal freeze/thaw in arid areas with shallow groundwater tables (AASGT) may significantly change BD and hence soil hydrothermal properties and water holding capacity. Therefore, quantifying soil bulk density changes (BDC) under freeze/thaw conditions can improve estimates of soil water-salt dynamics in AASGT. In this study, we conducted field experiments to investigate the soil water-salt dynamics under freeze/thaw conditions from three typical land-use types (i.e., farmland, woodland, and natural land) in the upper Yellow River basin, China. We proposed a method to estimate BDC, which can better describe the soil water-salt dynamics during the freeze/thaw period. Our results showed marked BDC occurred in all layers within the 0–100 cm profile in natural land, while mainly at the 20–80 cm profile in farmland. During the freezing period, BD in farmland and natural land first decreased rapidly and then remained relatively stable until the thawing period started. After that, BD gradually increased during the thawing period. The largest BDC in farmland and natural land were 0.48 g cm−3 (occurring at the 30–40 cm layer) and 0.43 g cm−3 (occurring at the 80–90 cm layer), respectively, close to 30 % of their initial values. The differences in BDC between the three land-use types were mainly owing to their differences in groundwater table depth, initial soil salt concentration, soil texture, and surface coverage conditions. Moreover, in farmland and natural land, ignoring BDC resulted in different degrees of overestimation or underestimation in soil water content, water fluxes, and soil hydrothermal properties in the selected soil layers. This study demonstrates that considering BDC can improve the accuracy of soil water-salt dynamics estimation in AASGT under freeze/thaw conditions.
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| 6. |
- Liu, Sheng, et al.
(författare)
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Improving soil hydrological simulation under freeze–thaw conditions by considering soil deformation and its impact on soil hydrothermal properties
- 2023
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Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694. ; 619
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Tidskriftsartikel (refereegranskat)abstract
- Traditional agricultural or eco-hydrological models usually ignore soil deformation and its impact on hydrothermal properties when simulating soil water, heat, and salt transport under freeze–thaw conditions. As a result, significant errors may occur when these models are used in areas with considerable frost heave, such as arid areas with shallow groundwater tables. In this study, the simultaneous heat and water model (SHAW model) was modified with considering soil deformation and its impact on hydrothermal properties during the freeze–thaw period. The modified SHAW model was then validated using the experimental data collected at the Hetao Irrigation District, in the upper Yellow River basin. Comparison between the simulated and observed data showed that the modified SHAW model performed well and obviously better than the original SHAW model in simulating the soil water, heat, and salt transport. As compared with the SHAW model, the modified SHAW model averagely decreased the RMSE value by 37.5% and 23% for soil water content and soil temperature, respectively. The modified model can be used as a decision tool for water management and salinity control of farmland in cold areas with significant frost heave.
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| 7. |
- Ou, Yangmei, et al.
(författare)
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Developing D-pi-D hole-transport materials for perovskite solar cells : the effect of the pi-bridge on device performance
- 2021
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Ingår i: Materials Chemistry Frontiers. - : Royal Society of Chemistry (RSC). - 2052-1537. ; 5:2, s. 876-884
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Tidskriftsartikel (refereegranskat)abstract
- Three cost-effective D-pi-D hole transport materials (HTMs) with different pi-bridges, including biphenyl (SY1), phenanthrene (SY2), and pyrene (SY3), have been synthesized via a one-pot reaction with cheap commercially available starting materials for application in organic-inorganic hybrid perovskite solar cells (PSCs). The effects of the various pi-bridges on the photophysical, electrochemical, and electrical properties, and film morphologies of the materials, as well as on the photovoltaic properties of the PSCs, have been systematically investigated accordingly. Our results clearly show that HTM-SY3 with pyrene as the pi-bridge exhibits higher hole mobility and better hole extraction/transport and film formation abilities than the other two HTMs. Devices that employed SY3 as the HTM show impressive power conversion efficiency (PCE) values of 19.08% and 13.41% in (FAPbI(3))(0.85)(MAPbBr(3))(0.15)- and CsPbI2Br-based PSCs, respectively, which are higher than those of the reference HTM-SY1- and SY2-based ones. Our studies demonstrate a promising strategy to rationally design and synthesize low-cost and efficient HTMs through structural engineering for use in PSCs.
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| 8. |
- Zhang, Dongyang, et al.
(författare)
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Source-code plagiarism in universities : a comparative study of student perspectives in China and the UK (Retracted article. See vol. 40, pg. 330, 2015)
- 2014
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Ingår i: Assessment & Evaluation in Higher Education. - : Routledge. - 0260-2938 .- 1469-297X. ; 39:6, s. 743-758
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Tidskriftsartikel (refereegranskat)abstract
- There has been much research and discussion relating to variations in plagiaristic activity observed in students from different demographic backgrounds. Differences in behaviour have been noted in many studies, although the underlying reasons are still a matter of debate. Existing work focuses mainly on textual plagiarism, and most often derives results by studying (small) groups of overseas students studying in a Western context. This study investigates understanding of source-code plagiarism (i.e. plagiarism of computer programmes) amongst university students in China. The survey instrument was a Chinese translation of a survey previously administered in English in the UK. This paper reports the results of the exploratory survey conducted in China, and compares these results to those from a parallel survey conducted in the UK. The results show that there is a significant difference in understanding between the respondents from the two surveys, and suggest topics which a future and more comprehensive study may focus on.
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