| 1. |
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- 2019
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Tidskriftsartikel (refereegranskat)
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| 2. |
- Chen, Fei'er, et al.
(författare)
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The effects of PM2.5 on asthmatic and allergic diseases or symptoms in preschool children of six Chinese cities, based on China, Children, Homes and Health (CCHH) project
- 2018
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Ingår i: Environmental Pollution. - : Elsevier BV. - 0269-7491 .- 1873-6424. ; 232, s. 329-337
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Tidskriftsartikel (refereegranskat)abstract
- The urbanization and industrialization in China is accompanied by bad air quality, and the prevalence of asthma in Chinese children has been increasing in recent years. To investigate the associations between ambient PM2.5 levels and asthmatic and allergic diseases or symptoms in preschool children in China, we assigned PM2.5 exposure data from the Global Burden of Disease (GBD) project to 205 kindergartens at a spatial resolution of 0.1° × 0.1° in six cities in China (Shanghai, Nanjing, Chongqing, Changsha, Urumqi, and Taiyuan). A hierarchical multiple logistical regression model was applied to analyze the associations between kindergarten-level PM2.5 exposure and individual-level outcomes of asthmatic and allergic symptoms. The individual-level variables, including gender, age, family history of asthma and allergic diseases, breastfeeding, parental smoking, indoor dampness, interior decoration pollution, household annual income, and city-level variable-annual temperature were adjusted. A total of 30,759 children (average age 4.6 years, 51.7% boys) were enrolled in this study. Apart from family history, indoor dampness, and decoration as predominant risk factors, we found that an increase of 10 μg/m3 of the annual PM2.5 was positively associated with the prevalence of allergic rhinitis by an odds ratio (OR) of 1.20 (95% confidence interval [CI] 1.11, 1.29) and diagnosed asthma by OR of 1.10 (95% CI 1.03, 1.18). Those who lived in non-urban (vs. urban) areas were exposed to more severe indoor air pollution arising from biomass combustion and had significantly higher ORs between PM2.5 and allergic rhinitis and current rhinitis. Our study suggested that long-term exposure to PM2.5 might increase the risks of asthmatic and allergic diseases or symptoms in preschool children in China. Compared to those living in urban areas, children living in suburban or rural areas had a higher risk of PM2.5 exposure.
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| 3. |
- Chen, Xiulai, et al.
(författare)
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DCEO Biotechnology: Tools to Design, Construct, Evaluate, and Optimize the Metabolic Pathway for Biosynthesis of Chemicals
- 2018
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Ingår i: Chemical Reviews. - : American Chemical Society (ACS). - 0009-2665 .- 1520-6890. ; 118:1, s. 4-72
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Forskningsöversikt (refereegranskat)abstract
- Chemical synthesis is a well established route for producing many chemicals on a large scale, but some drawbacks still exist in this process, such as unstable intermediates, multistep reactions, complex process control, etc. Biobased production provides an attractive alternative to these challenges, but how to make cells into efficient factories is challenging. As a key enabling technology to develop efficient cell factories, design-construction-evaluation-optimization (DCEO) biotechnology, which incorporates the concepts and techniques of pathway design, pathway construction, pathway evaluation, and pathway optimization at the systems level, offers a conceptual and technological framework to exploit potential pathways, modify existing pathways and create new pathways for the optimal production of desired chemicals. Here, we summarize recent progress of DCEO biotechnology and examples of its application, and provide insights as to when, what and how different strategies should be taken. In addition, we highlight future perspectives of DCEO biotechnology for the successful establishment of biorefineries.
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| 4. |
- Li, L., et al.
(författare)
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Divergence and plasticity shape adaptive potential of the Pacific oyster
- 2018
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Ingår i: Nature Ecology & Evolution. - : Springer Science and Business Media LLC. - 2397-334X. ; 2:11, s. 1751-1760
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Tidskriftsartikel (refereegranskat)abstract
- The interplay between divergence and phenotypic plasticity is critical to our understanding of a species' adaptive potential under rapid climate changes. We investigated divergence and plasticity in natural populations of the Pacific oyster Crassostrea gigas with a congeneric oyster Crassostrea angulata from southern China used as an outgroup. Genome re-sequencing of 371 oysters revealed unexpected genetic divergence in a small area that coincided with phenotypic divergence in growth, physiology, heat tolerance and gene expression across environmental gradients. These findings suggest that selection and local adaptation are pervasive and, together with limited gene flow, influence population structure. Genes showing sequence differentiation between populations also diverged in transcriptional response to heat stress. Plasticity in gene expression is positively correlated with evolved divergence, indicating that plasticity is adaptive and favoured by organisms under dynamic environments. Divergence in heat tolerance-partly through acetylation-mediated energy depression-implies differentiation in adaptive potential. Trade-offs between growth and survival may play an important role in local adaptation of oysters and other marine invertebrates.
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| 5. |
- Zhong, Jun, et al.
(författare)
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Climate Variability Controls on CO2 Consumption Fluxes and Carbon Dynamics for Monsoonal Rivers : Evidence From Xijiang River, Southwest China
- 2018
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Ingår i: Journal of Geophysical Research - Biogeosciences. - 2169-8953 .- 2169-8961. ; 123:8, s. 2553-2567
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Tidskriftsartikel (refereegranskat)abstract
- The feedbacks of climate variability on CO2 consumption fluxes and carbon dynamics are thought to play an important role in moderating the global carbon cycle. High-frequency sampling campaigns and analyses were conducted in this study to investigate temporal variations of river water chemistry and the impacts of climate variability on CO2 consumption fluxes and carbon dynamics for the Xijiang River, Southwest China. Physical processes modify biogeochemical processes, so major ions display different responses to changing discharge. The annual CO2 consumption rate is (6.8 +/- 0.2) x 10(6) ton/year by carbonate weathering and (2.4 +/- 0.3) x 10(6) ton/year by silicate weathering. The annual CO2 consumption flux is much higher than most world rivers, and strong CO2 consumption capacities are observed in catchments in Southwest China. Lower negative delta C-13(DIC) values are found in the high-flow season which corresponds with high temperatures compared to those in the low-flow season. High discharge will accelerate material transport, and high temperatures will increase primary production in the catchment, both of which can be responsible for the shift of delta C-13(DIC) values in the high-flow season. Increased mineral weathering and biological carbon influx in the catchment are the main factors controlling carbon dynamics. Overall, these findings highlight the sensitivity of CO2 consumption fluxes and carbon dynamics in response to climate variability in the riverine systems. Plain Language Summary There are feedbacks between climate variability and CO2 consumption fluxes by chemical weathering and carbon dynamics. Significant temporal variations of major ions and delta C-13(DIC) are observed in the Xijiang River. Multiple biogeochemical processes occur under various hydrological conditions, shifting major ions concentrations, and delta C-13(DIC). The annual CO2 consumption rate is (6.8 +/- 0.2) x 10(6) ton/year by carbonate weathering and (2.4 +/- 0.3) x 10(6) ton/year by silicate weathering. The annual CO2 consumption rates in the Xijiang River only account for a small fraction in the global CO2 consumption rates; the CO2 consumption capacity is much higher than the global average, while much lower than its source tributaries (Beipan and Nanpan Rivers). Slow subsurface flow paths with longer transit times switch to rapid near-surface flow paths with shorter transit times, as discharge increases. High temperatures increase reaction rates, and high discharge rates remove transport limitation, both of which would accelerate the chemical weathering rates. In the high-flow season, high discharge accompanying with high temperatures, large amounts of delta C-13-depleted biological carbon, flushes into the river, affecting the carbon dynamics.
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| 6. |
- Chen, Cheng, et al.
(författare)
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Cu(II) Complexes as p-Type Dopants in Efficient Perovskite Solar Cells
- 2017
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Ingår i: ACS Energy Letters. - : American Chemical Society (ACS). - 2380-8195. ; 2:2, s. 497-503
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Tidskriftsartikel (refereegranskat)abstract
- In this work, two Cu(II) complex compounds are designed and synthesized for applications as p-type dopants in solid-state perovskite solar cells (PSCs). Through the characterization of the optical and electrochemical properties, the complex Cu(bpcm)(2) is shown to be eligible for oxidization of the commonly used hole-transport material (HTM) SpiroOMeTAD. The reason is the electron-withdrawing effect of the chloride groups on the ligands. When the complex was applied as p-type dopant in PSCs containing Spiro-OMeTAD as HTM, an efficiency as high as 18.5% was achieved. This is the first time a Cu(II) pyridine complex has been used as p-type dopant in PSCs.
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| 7. |
- Gu, Enyao, et al.
(författare)
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A real-time Raman spectroscopy study of the dynamics of laser-thinning of MoS2 flakes to monolayers
- 2017
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Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226. ; 7:12
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Tidskriftsartikel (refereegranskat)abstract
- Transition metal dichalcogenides (TMDCs) in monolayer form have attracted a great deal of attention for electronic and optical applications. Compared to mechanical exfoliation and chemical synthesis, laser thinning is a novel and unique “on-demand” approach to fabricate monolayers or pattern desired shapes with high controllability and reproducibility. Its successful demonstration motivates a further exploration of the dynamic behaviour of this local thinning process. Here, we present an in-situ study of void formation by laser irradiation with the assistance of temporal Raman evolution. In the analysis of time-dependent Raman intensity, an empirical formula relating void size to laser power and exposure time is established. Void in thinner MoS2 flakes grows faster than in thicker ones as a result of reduced sublimation temperature in the two-dimensional (2D) materials. Our study provides useful insights into the laser-thinning dynamics of 2D TMDCs and guidelines for an effective control over the void formation.
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| 8. |
- Hu, Hai-Xi, et al.
(författare)
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Structural insights into HetR-PatS interaction involved in cyanobacterial pattern formation
- 2015
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 5
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Tidskriftsartikel (refereegranskat)abstract
- The one-dimensional pattern of heterocyst in the model cyanobacterium Anabaena sp. PCC 7120 is coordinated by the transcription factor HetR and PatS peptide. Here we report the complex structures of HetR binding to DNA, and its hood domain (HetR(Hood)) binding to a PatS-derived hexapeptide (PatS6) at 2.80 and 2.10 angstrom, respectively. The intertwined HetR dimer possesses a couple of novel HTH motifs, each of which consists of two canonical alpha-helices in the DNA-binding domain and an auxiliary alpha-helix from the flap domain of the neighboring subunit. Two PatS6 peptides bind to the lateral clefts of HetR(Hood), and trigger significant conformational changes of the flap domain, resulting in dissociation of the auxiliary alpha-helix and eventually release of HetR from the DNA major grove. These findings provide the structural insights into a prokaryotic example of Turing model.
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| 9. |
- Kristan, Matej, et al.
(författare)
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The Sixth Visual Object Tracking VOT2018 Challenge Results
- 2019
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Ingår i: Computer Vision – ECCV 2018 Workshops. - Cham : Springer Publishing Company. - 9783030110086 - 9783030110093 ; , s. 3-53
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Konferensbidrag (refereegranskat)abstract
- The Visual Object Tracking challenge VOT2018 is the sixth annual tracker benchmarking activity organized by the VOT initiative. Results of over eighty trackers are presented; many are state-of-the-art trackers published at major computer vision conferences or in journals in the recent years. The evaluation included the standard VOT and other popular methodologies for short-term tracking analysis and a “real-time” experiment simulating a situation where a tracker processes images as if provided by a continuously running sensor. A long-term tracking subchallenge has been introduced to the set of standard VOT sub-challenges. The new subchallenge focuses on long-term tracking properties, namely coping with target disappearance and reappearance. A new dataset has been compiled and a performance evaluation methodology that focuses on long-term tracking capabilities has been adopted. The VOT toolkit has been updated to support both standard short-term and the new long-term tracking subchallenges. Performance of the tested trackers typically by far exceeds standard baselines. The source code for most of the trackers is publicly available from the VOT page. The dataset, the evaluation kit and the results are publicly available at the challenge website (http://votchallenge.net).
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| 10. |
- Liu, Cong, et al.
(författare)
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Ambient Particulate Air Pollution and Daily Mortality in 652 Cities
- 2019
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Ingår i: New England Journal of Medicine. - Waltham : Massachusetts Medical Society. - 0028-4793 .- 1533-4406. ; 381:8, s. 705-715
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: The systematic evaluation of the results of time-series studies of air pollution is challenged by differences in model specification and publication bias.METHODS: We evaluated the associations of inhalable particulate matter (PM) with an aerodynamic diameter of 10 μm or less (PM10) and fine PM with an aerodynamic diameter of 2.5 μm or less (PM2.5) with daily all-cause, cardiovascular, and respiratory mortality across multiple countries or regions. Daily data on mortality and air pollution were collected from 652 cities in 24 countries or regions. We used overdispersed generalized additive models with random-effects meta-analysis to investigate the associations. Two-pollutant models were fitted to test the robustness of the associations. Concentration-response curves from each city were pooled to allow global estimates to be derived.RESULTS: On average, an increase of 10 μg per cubic meter in the 2-day moving average of PM10 concentration, which represents the average over the current and previous day, was associated with increases of 0.44% (95% confidence interval [CI], 0.39 to 0.50) in daily all-cause mortality, 0.36% (95% CI, 0.30 to 0.43) in daily cardiovascular mortality, and 0.47% (95% CI, 0.35 to 0.58) in daily respiratory mortality. The corresponding increases in daily mortality for the same change in PM2.5 concentration were 0.68% (95% CI, 0.59 to 0.77), 0.55% (95% CI, 0.45 to 0.66), and 0.74% (95% CI, 0.53 to 0.95). These associations remained significant after adjustment for gaseous pollutants. Associations were stronger in locations with lower annual mean PM concentrations and higher annual mean temperatures. The pooled concentration-response curves showed a consistent increase in daily mortality with increasing PM concentration, with steeper slopes at lower PM concentrations.CONCLUSIONS: Our data show independent associations between short-term exposure to PM10 and PM2.5 and daily all-cause, cardiovascular, and respiratory mortality in more than 600 cities across the globe. These data reinforce the evidence of a link between mortality and PM concentration established in regional and local studies. (Funded by the National Natural Science Foundation of China and others.).
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| 11. |
- Liu, Cong, et al.
(författare)
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Effects of nanocrystalline cellulose on the micro-creep properties of phenol formaldehyde resin
- 2018
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Ingår i: Materials Research Express. - : Institute of Physics Publishing. - 2053-1591. ; 5:12
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Tidskriftsartikel (refereegranskat)abstract
- The use of nanocrystalline cellulose (NCC) has become increasingly prevalent in recent years, with limited studies on the the time-dependent characteristics of wood-adhesive composite reinforced by it. To analyze the viscoelasticity of control phenol formaldehyde (PF) resin and wood-resin composites added with three types of NCC, the micro-creep properties of control phenol formaldehyde (PF) resin and PF resin with cellulose nanofibrils (CNF), cellulose microfibrils (CMF), and cellulose nanocrystals (CNC) were investigated by nanoindentation (NI). The sample creep curves proved that adding CNC, CMF, and CNF into the PF resin remarkably impacted the creep properties of the wood-resin sample interface. The cured resin sample had the lowest strength and the most deformation, and the pure wood sample performed slightly better. Among the three NCC-added wood-resin samples, the CNF-added wood-resin sample has the least deformation in the same load and the least permanent deformation after unloading followed by CMF-added and CNC-added wood-resin samples. In the derivative of creep curve function, the depth tendency of CNC-added and CNF-added wood-resin samples showed a gently increasing slope with time in contrast to CMF-added ones. Furthermore, scanning probe microscopy (SPM) images supported that PF resin had filled up the pores of the wood microstructures and strengthened the wood-resin sample in the company of NCC, which was then able to carry the load.
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| 12. |
- Mascher, Martin, et al.
(författare)
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A chromosome conformation capture ordered sequence of the barley genome
- 2017
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 544:7651, s. 427-433
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Tidskriftsartikel (refereegranskat)abstract
- Cereal grasses of the Triticeae tribe have been the major food source in temperate regions since the dawn of agriculture. Their large genomes are characterized by a high content of repetitive elements and large pericentromeric regions that are virtually devoid of meiotic recombination. Here we present a high-quality reference genome assembly for barley (Hordeum vulgare L.). We use chromosome conformation capture mapping to derive the linear order of sequences across the pericentromeric space and to investigate the spatial organization of chromatin in the nucleus at megabase resolution. The composition of genes and repetitive elements differs between distal and proximal regions. Gene family analyses reveal lineage-specific duplications of genes involved in the transport of nutrients to developing seeds and the mobilization of carbohydrates in grains. We demonstrate the importance of the barley reference sequence for breeding by inspecting the genomic partitioning of sequence variation in modern elite germplasm, highlighting regions vulnerable to genetic erosion.
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| 13. |
- Ning, Yuping, et al.
(författare)
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Effects of substrates, film thickness and temperature on thermal emittance of Mo/substrate deposited by magnetron sputtering
- 2016
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Ingår i: Vacuum. - : Elsevier BV. - 0042-207X .- 1879-2715. ; 128, s. 73-79
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Tidskriftsartikel (refereegranskat)abstract
- The thermal emittance of the Mo film, as an IR-refiector in solar selective absorbing coatings, is the most important property. The effects of the substrate material, the substrate surface roughness, the film thickness and the temperature on the thermal emittance of the Mo/substrate have been investigated. A series of Mo films with increasing film thickness were deposited on two types of substrate materials (glass and stainless steel). A saturated Mo thickness of 50 nm is found to produce the lowest thermal emittance. The thermal emittance of the Mo film is reduced by decreasing the substrate surface roughness. The emittance of the optimal Mo film remains 0.05 from 25 degrees C to 400 degrees C, which can meet the optical requirements for the IR-reflector.
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| 14. |
- Ning, Yuping, et al.
(författare)
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Investigation on low thermal emittance of Al films deposited by magnetron sputtering
- 2016
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Ingår i: Infrared physics & technology. - : Elsevier BV. - 1350-4495 .- 1879-0275. ; 75, s. 133-138
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Tidskriftsartikel (refereegranskat)abstract
- A series of Al films with different thicknesses were deposited on polished stainless steel by direct current (DC) magnetron sputtering as a metal IR-reflector layer in solar selective absorbing coating (SSAC). The effects of the film thickness and the temperature on the thermal emittance of the Al films are studied. An optimal thickness 78 nm of the Al film for the lowest total thermal emittance is obtained. The thermal emittance of the optimal Al film keeps close to 0.02 from 25 degrees C to 400 degrees C, which are low enough to satisfy the optical requirements in SSAC. The optical constants of the AI film are deduced by fitting the reflectance and transmission spectra using SCOUT software.
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| 15. |
- Sharmoukh, Walid, et al.
(författare)
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Molecular Engineering of D-D-pi-A-Based Organic Sensitizers for Enhanced Dye-Sensitized Solar Cell Performance
- 2018
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Ingår i: ACS Omega. - : American Chemical Society (ACS). - 2470-1343. ; 3:4, s. 3819-3829
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Tidskriftsartikel (refereegranskat)abstract
- A series of molecularly engineered and novel dyes WS1, WS2, WS3, and WS4, based on the D35 donor, 1-(4-hexylphenyl)-2,5-di(thiophen-2-yl)-1H-pyrrole and 4-(4-hexylphenyl)-4H-dithieno[3,2-b: 2', 3'-d] pyrrole as pi-conjugating linkers, were synthesized and compared to the well-known LEG4 dye. The performance of the dyes was investigated in combination with an electrolyte based on Co(II/III) complexes as redox shuttles. The electron recombination between the redox mediators in the electrolyte and the TiO2 interface decreases upon the introduction of 4-hexylybenzene entities on the 2,5-di(thiophen-2-yl)-1H-pyrrole and 4H-dithieno[3,2-b: 2', 3'-d] pyrrole linker units, probably because of steric hindrance. The open circuit photovoltage of WS1-, WS2-, WS3-, and WS4-based devices in combination with the Co(II/III)-based electrolyte are consistently higher than those based on a I-/I-3(-) electrolyte by 105, 147, 167, and 75 mV, respectively. The WS3-based devices show the highest power conversion efficiency of 7.4% at AM 1.5 G 100 mW/cm(2) illumination mainly attributable to the high open-circuit voltage (V-OC).
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| 16. |
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| 17. |
- Wang, Fangfang, et al.
(författare)
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Outward Foreign Direct Investment and Export Performance in China
- 2017
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Ingår i: Canadian public policy. - : University of Toronto Press Inc. (UTPress). - 0317-0861 .- 1911-9917. ; 43:S2, s. S72-S87
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Tidskriftsartikel (refereegranskat)abstract
- As one of the world's major exporters, China has witnessed a substantial increase in its outward foreign direct investment (OFDI). This article examines the effects of export-driven factors on China's OFDI through export-supporting and export platform. On the basis of 2003-2010 panel data from 144 countries and regions, including Canada, we find a strong effect of rising exports on China's OFDI. In addition, the export platform is an important part of China's OFDI, and this trend has strengthened in recent years. Moreover, markets of neighbouring host countries do not have a significant effect on the OFDI. China's OFDI has an obvious agglomeration effect in the host countries, particularly in high-income countries. The empirical results suggest that China should pay attention to the dual effects of its export-supporting and export platform on OFDI. The government should guide enterprises to implement a mixed international trade and investment strategy and build a platform of networking investment to protect firms' overseas investments.
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| 18. |
- Wu, Yongxin, et al.
(författare)
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Study on the thermal stability of Al/NbTiSiN/NbTiSiON/SiO2 solar selective absorbing coating
- 2015
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Ingår i: Solar Energy. - : Elsevier BV. - 0038-092X .- 1471-1257. ; 119, s. 18-28
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Tidskriftsartikel (refereegranskat)abstract
- In this work, the NbTiSiN and NbTiSiON layers are used instead of NbTiN and NbTiON layers to further improve the thermal stability of Al/NbTiN/NbTiON/SiO2 multilayer solar selective absorbing coating. The thermal stability of Si-doped individual layers and multilayer coatings are investigated. The X-ray diffraction (XRD) results show that Si incorporation into NbTiN (NbTiSiN) layer does not change its preferred orientation, and the Si-doped NbTiON (NbTiSiON) layer remains in amorphous phase. On the other hand, by introducing Si into NbTiN and NbTiON layers induce significant improvement of the oxidation resistance at 500 degrees C in air. After ageing in air at 500 degrees C for 2 h, the absorptance and emittance (at 400 degrees C) of Al/NbTiN/NbTiON/SiO2 and Al/NbTiSiN/NbTiSiON/SiO2 multilayer coatings change from 0.934/0.13 and 0.931/0.12 to 0.538/0.14 and 0.922/0.13, respectively. Meanwhile the surface roughness increases from 18.3 and 7.9 to 41.5 and 14.7 respectively, as atomic force microscopy (AFM) shows. The Al/NbTiSiN/NbTiSiON/SiO2 coating still has a high absorptance (0.910) and low emittance (0.13, at 400 degrees C) after ageing at 550 degrees C in vacuum for 100 h. It displays that Si-doping play an important role in the improvement of the thermal stability.
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| 19. |
- Zhang, Cong, et al.
(författare)
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Dependency- and similarity-aware caching for HTTP adaptive streaming
- 2018
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Ingår i: Multimedia tools and applications. - : Springer Science and Business Media LLC. - 1380-7501 .- 1573-7721. ; 77:1, s. 1453-1474
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Tidskriftsartikel (refereegranskat)abstract
- There has been significant interest in the use of HTTP adaptive streaming for live or on-demand video over the Internet in recent years. To mitigate the streaming transmission delay and reduce the networking overhead, an effective and critical approach is to utilize cache services between the origin servers and the heterogeneous clients. As the underlying protocol for web transactions, HTTP has great potentials to explore the resources within state-of-the-art CDNs for caching; yet distinct challenges arise in the HTTP adaptive streaming context. After examining a long-term and large-scale adaptive streaming dataset as well as statistical analysis, we demonstrate that the switching requests among the different qualities frequently emerge and constitute a significant portion in a per-day view. Consequently, they have substantially affected the performance of cache servers and Quality-of-Experience (QoE) of viewers. In this paper, we propose a novel cache model that captures the dependency among the segments in the cache server for adaptive HTTP streaming. Our work does not assume any specific selection algorithm on the client's side and hence can be easily incorporated into existing streaming cache systems. Its centralized nature is also well accommodated by the latest DASH specification. Moreover, we extend our work to the multi-server caching context and present a similarity-aware allocation mechanism to enhance the caching efficiency. The performance evaluation shows our dependency- and similarity-aware strategy can significantly improve the cache hit-ratio and QoE of HTTP streaming as compared to previous approaches.
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| 20. |
- Zhang, Cong, et al.
(författare)
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Dependency-Aware Caching for HTTP Adaptive Streaming
- 2016
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Ingår i: 2016 Digital Media Industry And Academic Forum (DMIAF). - 9781509010004 ; , s. 89-93
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Konferensbidrag (refereegranskat)abstract
- There has been significant interest in the use of HTTP adaptive streaming for live or on-demand video over the Internet in recent years. To mitigate the streaming transmission delay and reduce the networking overhead, an effective and critical approach is to utilize cache servers between the origin servers and the heterogeneous clients. As the underlying protocol for web transactions, HTTP has great potentials to explore the resources within state-of-the-art CDNs tor caching; yet distinct challenges arise in the HTTP adaptive streaming context. After examining a long-term and large-scale adaptive streaming dataset as well as statistical analysis, we demonstrate that the switching requests among the different qualities frequently emerge and constitute a significant portion in a per-day view. Consequently, they have substantially affected the performance of cache servers and Quality-of-Experience (QoE) of viewers. In this paper, we propose a novel cache model that captures the dependency among the segments in the cache server for adaptive HTTP streaming. Our work does not assume any specific selection algorithm on the client's side and hence can be easily incorporated into existing streaming cache system. Its centralized nature is also well accommodated by the latest DASH specification. The performance evaluation shows our dependency-aware strategy can significantly improved the cache hit-ratio and QoE of HTTP streaming as compared to previous methods.
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| 21. |
- Zhang, Fuguo, et al.
(författare)
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A facile route to grain morphology controllable perovskite thin films towards highly efficient perovskite solar cells
- 2018
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Ingår i: Nano Energy. - : Elsevier BV. - 2211-2855 .- 2211-3282. ; 53, s. 405-414
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Tidskriftsartikel (refereegranskat)abstract
- Perovskite photovoltaics have recently attracted extensive attention due to their unprecedented high power conversion efficiencies (PCEs) in combination with primitive manufacturing conditions. However, the inherent polycrystalline nature of perovskite films renders an exceptional density of structural defects, especially at the grain boundaries (GBs) and film surfaces, representing a key challenge that impedes the further performance improvement of perovskite solar cells (PSCs) and large solar module ambitions towards commercialization. Here, a novel strategy is presented utilizing a simple ethylammonium chloride (EACl) additive in combination with a facile solvent bathing approach to achieve high quality methyammonium lead iodide (MAPbI3) films. Well-oriented, micron-sized grains were observed, which contribute to an extended carrier lifetime and reduced trap density. Further investigations unraveled the distinctively prominent effects of EACl in modulating the perovskite film quality. The EACl was found to promote the perovskite grain growing without undergoing the formation of intermediate phases. Moreover, the EACl was also revealed to deplete at relative low temperature to enhance the film quality without compromising the beneficial bandgap for solar cell applications. This new strategy boosts the power conversion efficiency (PCE) to 20.9% and 19.0% for devices with effective areas of 0.126 cm2 and 1.020 cm2, respectively, with negligible current hysteresis and enhanced stability. Besides, perovskite films with a size of 10 × 10 cm2, and an assembled 16 cm2(5 × 5 cm2 module) perovskite solar module with a PCE of over 11% were constructed.
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| 22. |
- Zhang, Youwei, et al.
(författare)
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Competing Mechanisms for Photocurrent Induced at the Monolayer-Multilayer Graphene Junction
- 2018
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Ingår i: Small. - : WILEY-V C H VERLAG GMBH. - 1613-6810 .- 1613-6829. ; 14:24
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Tidskriftsartikel (refereegranskat)abstract
- Graphene is characterized by demonstrated unique properties for potential novel applications in photodetection operated in the frequency range from ultraviolet to terahertz. To date, detailed work on identifying the origin of photoresponse in graphene is still ongoing. Here, scanning photocurrent microscopy to explore the nature of photocurrent generated at the monolayer-multilayer graphene junction is employed. It is found that the contributing photocurrent mechanism relies on the mismatch of the Dirac points between the monolayer and multilayer graphene. For overlapping Dirac points, only photothermoelectric effect (PTE) is observed at the junction. When they do not coincide, a different photocurrent due to photovoltaic effect (PVE) appears and becomes more pronounced with larger separation of the Dirac points. While only PTE is reported for a monolayer-bilayer graphene junction in the literature, this work confirms the coexistence of PTE and PVE, thereby extending the understanding of photocurrent in graphene-based heterojunctions.
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| 23. |
- Zhang, Youwei, et al.
(författare)
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Extending the Spectral Responsivity of MoS2 Phototransistors by Incorporating Up-Conversion Microcrystals
- 2018
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Ingår i: Advanced Optical Materials. - : Wiley. - 2162-7568 .- 2195-1071. ; 6:21
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Tidskriftsartikel (refereegranskat)abstract
- Layered 2D semiconductors are characterized by unique photoelectric properties and, therefore, constitute a new class of basic building block for next‐generation optoelectronics. However, their wide bandgaps limit the spectral responsivity to a narrow range. Here, a facile approach is demonstrated by integrating β‐NaYF4:Yb3+, Er3+ up‐conversion microcrystals (UCMCs) with monolayer‐MoS2 phototransistors to break this bandgap‐imposed barrier and to drastically extend the responsivity range. In essence, the UCMCs up‐convert a near‐infrared excitation at 980 nm to visible light of photons with energy matching the large bandgap (i.e., 1.8 eV) of monolayer‐MoS2, thereby activating the phototransistor with remarkable photocurrent and minimum interference. This approach leads to preservation of the excellent electrical merits of monolayer‐MoS2 and simultaneous retention of its low dark current and high photoresponsivity to the above‐bandgap lights. Significantly, an enhancement by over 1000 times is achieved for both responsivity and specific detectivity at 980 nm excitation. Moreover, the rate of response is kept identical to that when the MoS2 phototransistor is excited by a visible light. Therefore, integrating with UCMCs can enable the emerging 2D semiconductors of wide bandgap to respond to infrared excitations with high efficacy and without sacrificing their performance in the visible region.
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