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- Allsopp, Benjamin, et al.
(författare)
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Towards improved cover glasses for photovoltaic devices
- 2020
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Ingår i: Progress in Photovoltaics. - : John Wiley and Sons Ltd. - 1062-7995 .- 1099-159X. ; 28, s. 1187-1206
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Tidskriftsartikel (refereegranskat)abstract
- For the solar energy industry to increase its competitiveness, there is a global drive to lower the cost of solar-generated electricity. Photovoltaic (PV) module assembly is material-demanding, and the cover glass constitutes a significant proportion of the cost. Currently, 3-mm-thick glass is the predominant cover material for PV modules, accounting for 10%–25% of the total cost. Here, we review the state-of-the-art of cover glasses for PV modules and present our recent results for improvement of the glass. These improvements were demonstrated in terms of mechanical, chemical and optical properties by optimizing the glass composition, including addition of novel dopants, to produce cover glasses that can provide (i) enhanced UV protection of polymeric PV module components, potentially increasing module service lifetimes; (ii) re-emission of a proportion of the absorbed UV photon energy as visible photons capable of being absorbed by the solar cells, thereby increasing PV module efficiencies and (iii) successful laboratory-scale demonstration of proof of concept, with increases of 1%–6% in Isc and 1%–8% in Ipm. Improvements in both chemical and crack resistance of the cover glass were also achieved through modest chemical reformulation, highlighting what may be achievable within existing manufacturing technology constraints. © 2020 The Authors.
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| 4. |
- Andersson-Gunnerås, Sara, et al.
(författare)
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Asymmetric expression of a poplar ACC oxidase controls ethylene production during gravitational induction of tension wood
- 2003
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Ingår i: The Plant Journal. - : Blackwell Publishing. - 0960-7412 .- 1365-313X. ; 34:3, s. 339-349
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Tidskriftsartikel (refereegranskat)abstract
- Ethylene is produced in wood-forming tissues, and when applied exogenously, it has been shown to cause profound effects on the pattern and rate of wood development. However, the molecular regulation of ethylene biosynthesis during wood formation is poorly understood. We have characterised an abundant 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase gene (PttACO1) in the wood-forming tissues of Populus tremula (L.) × P. tremuloides (Michx). PttACO1 is primarily expressed in developing secondary xylem, and is specifically upregulated during secondary wall formation. Nevertheless, according to GC–MS analysis combined with tangential cryosectioning, the distribution of ACC was found to be fairly uniform across the cambial-region tissues. Gravitational stimulation, which causes tension wood to form on the upper side of the stem, resulted in a strong induction of PttACO1 expression and ACC oxidase activity in the tension wood-forming tissues. The ACC levels increased in parallel to the PttACO1 expression. However, the increase on the upper (tension wood) side was only minor, whereas large amounts of both ACC and its hydrolysable conjugates accumulated on the lower (opposite) side of the stem. This suggests that the relatively low level of ACC on the tension wood side is a result of its conversion to ethylene by the highly upregulated PttACO1, and the concurrent accumulation of ACC on the opposite side of the wood is because of the low PttACO1 levels. We conclude that PttACO1 and ACC oxidase activity, but not ACC availability, are important in the control of the asymmetric ethylene production within the poplar stem when tension wood is induced by gravitational stimulation.
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- Björklund, Simon, et al.
(författare)
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Cross-talk between gibberellin and auxin in development of Populus wood: gibberellin stimulates polar auxin transport and has a common transcriptome with auxin
- 2007
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Ingår i: The Plant Journal. - : Wiley. - 0960-7412 .- 1365-313X. ; 52:3, s. 499-511
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Tidskriftsartikel (refereegranskat)abstract
- Both indole acetic acid (IAA) and gibberellins (GAs) stimulate cell and organ growth. We have examined GA/IAA cross-talk in cambial growth of hybrid aspen (Populus tremulaxtremuloides). Decapitated trees were fed with IAA and GA, alone and in combination. Endogenous hormone levels after feeding were measured, by mass spectrometry, in the stem tissues below the point of application. These stem tissues with defined hormone balances were also used for global transcriptome analysis, and the abundance of selected transcripts was measured by real-time reverse-transcription polymerase chain reaction. By feeding isotope-labeled IAA, we demonstrated that GA increases auxin levels in the stem by stimulating polar auxin transport. This finding adds a new dimension to the concept that the endogenous GA/IAA balance in plants is determined by cross-talk between the two hormones. We also show that GA has a common transcriptome with auxin, including many transcripts related to cell growth. This finding provides molecular support to physiological experiments demonstrating that either hormone can induce growth if the other hormone is absent/deficient because of mutations or experimental treatments. It also highlights the potential for extensive cross-talk between GA- and auxin-induced responses in vegetative growth of the intact plant. The role of endogenous IAA and GA in wood development is discussed.
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| 6. |
- Garcia, Johan, 1970-, et al.
(författare)
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Fine-Grained Starlink Throughput Variation Examined With State-Transition Modeling
- 2024
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Ingår i: 2024 19th Wireless On-Demand Network Systems and Services Conference (WONS). - : Institute of Electrical and Electronics Engineers (IEEE). - 9783903176614 - 9798350360622 ; , s. 69-76
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Konferensbidrag (refereegranskat)abstract
- Leveraging a data set of almost half a billion packets with high-precision packet times and sizes, we process it to extract characteristics of the bursts emitted over Starlink's Ethernet interface. The structure of these bursts directly reflect the physical layer receipt of OFDMA frames on the satellite link. We study these bursts by analyzing their rates, and by proxy the transition between different physical layer rates. The results highlight that there is definitive structure in the transition behavior, and we note specific behaviors such as particular transitionsteps associated with rate switching, and that rate switching occurs mainly to neighboring rates. We also study the joint burst rate and burst duration transitions, noting that transitions occur mainly within the same rate, and that changes in burst duration are often performed with an intermediate short burst in-between.Finally, we examine the configurations of the three factors burst rate, burst duration, and inter-burst silent time, which together determine the effective throughput of a Starlink connection.
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| 7. |
- Garcia, Johan, 1970-, et al.
(författare)
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Inferring Starlink Physical Layer Transmission Rates Through Receiver Packet Timestamps
- 2024
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Konferensbidrag (refereegranskat)abstract
- Although Starlink has been deployed for several years, a detailed understanding of system internals is still lacking. In this work we employ precise per-packet timestamps obtained from a hardware-timestamp capable NIC connected to a Starlink terminal.We find that Starlink frame timing details are readily observable at the network layer by analyzing the packet timing patterns.Based on a one-week measurement campaign we collect around half a billion of packet size and timing observations. Processing these observations yields 2.3 million transmission bursts. To learn details on the radio resource management we develop a methodology to infer the effective physical layer sending rate. Our findings show that although Starlink throughput can vary widely over multiple time-scales, there are a small number of fundamental physical layer transmission rates. We employ Gaussian Mixture Modeling to determine 14 such fundamental transmission rates, and relate the obtained rates to previous knowledge of the Starlink OFDMA frame structure. Our empirical observations provide an excellent match for a radio resource configuration where a Starlink frame employs 1000 subcarriers and 287 symbols per frame for user traffic transmission, which for uniform 4-QAM modulation yields a base rate of 430.5 Mbps. This physical layer base rate appears to mostly be varied by multiples of 27 Mbps, in several instances likely by modifying the modulation of a subset of the symbols in multiples of 18 symbols.
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| 8. |
- Garcia, Johan, 1970-, et al.
(författare)
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Interactions Between Train Velocity and Cellular Link Throughput - An Extensive Study
- 2019
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Ingår i: 2019 IEEE 30th Annual International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC). - : Institute of Electrical and Electronics Engineers (IEEE). - 9781538681107 - 9781538681114 ; , s. 1-7
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Konferensbidrag (refereegranskat)abstract
- Providing reliable internet connectivity to train passengers can be handled with onboard aggregation routers that use multiple external antennas to simultaneously convey user traffic over multiple links. This work studies the operational characteristics of a large-scale deployment of such a system. The examination focuses on how train velocity is associated with achieved link throughput, and how various interaction effects influence the relationship. A large data set collected over three years is analyzed, indicating that there is a systematic association between train velocity and link throughput that varies over the radio conditions and which is also linked to differences between operators.
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| 9. |
- Garcia, Johan, 1970-, et al.
(författare)
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LTE for Trains - Performance Interactions Examined with DL, ML and Resampling
- 2019
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Ingår i: 2019 IEEE Symposium on Computers and Communications (ISCC). - : IEEE. - 9781728129990 - 9781728130002 ; , s. 1-6
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Konferensbidrag (refereegranskat)abstract
- Current LTE networks provide a large fraction of the mobile communication needs. One recent application area that have attained additional interest is the provision of mobile communication services to train passengers. To allow more efficient use of network resources and better onboard communication experience, onboard traffic aggregation can be performed. In this work we examine a large-scale operational data set from a routerbased LTE traffic aggregation system mounted onboard more than 100 trains belonging to a major Swedish train operator. We use both deep learning (DL) with Deep Neural Networks and traditional machine learning (ML) with Random Forests to examine an observed association between train velocity and achieved throughput, which curiously varies over different radio conditions. More than 37000 train journeys are analyzed to explore for structure and learn potential explanatory features. The results indicate that the association has a limited presence on a per cell basis, and that there is only a limited amount of learnable structure per cell. A resampling evaluation shows that the association becomes apparent when cell measurements are aggregated at an order of tens to a hundred cells.
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| 10. |
- Garcia, Johan, 1970-, et al.
(författare)
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Multi-Timescale Evaluation of Starlink Throughput
- 2023
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Ingår i: LEO-NET '23. - : ACM Digital Library. - 9798400703324 ; , s. 31-36
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Konferensbidrag (refereegranskat)abstract
- Although Starlink has been rolled-out for several years, there is still a lack of knowledge regarding system details and performance characteristics. To address this, we perform a network layer measurement campaign utilizing precise times-Tamping to analyze throughput variations at multiple time scales, and infer system timing details. On larger timescales we quantify the diurnal variations where the throughput varies with the time of day. On the medium timescales we establish the likely frequency allocation and beam switching period to be 15 seconds. The associated connectivity disturbances contribute to severe link underutilization for single long-lived TCP flows, which typically reach only 46% of the estimated link capacity. On the sub-millisecond timescale our network layer measurements corroborate recent physical layer investigations of the Starlink frame timing, which is confirmed to be 1.33 ms. © 2023 Owner/Author(s).
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