| 1. |
- Aurelius, Andreas, et al.
(författare)
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How much of the bandwidth do we actually use? : An investigation of residential access traffic load
- 2012
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Ingår i: International Conference on Transparent Optical Networks. - : IEEE. - 9781467322270
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Konferensbidrag (refereegranskat)abstract
- Internet traffic from a fibre based residential access network is investigated concerning traffic volumes and link load. Also the cost of the services is analyzed. We show that 1 Mbps accesses subscribers maintain high loads, and that the price they pay per GB used is five times higher than the one paid by 100 Mbps access subscribers.
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| 2. |
- Ren, Zhihui, et al.
(författare)
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Temporal Scaling Characteristics of Sub-Daily Precipitation in Qinghai-Tibet Plateau
- 2024
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Ingår i: EARTHS FUTURE. - 2328-4277. ; 12:3
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Tidskriftsartikel (refereegranskat)abstract
- The Qinghai-Tibet Plateau (QTP) is highly susceptible to destructive rainstorm hazards and related natural disasters. However, the lack of sub-daily precipitation observations in this region has hindered our understanding of rainstorm-related hazards and their societal impacts. To address this data gap, a new approach is devised to estimate sub-daily precipitation in QTP using daily precipitation data and geographical information. The approach involves establishing a statistical relationship between daily and sub-daily precipitation based on data from 102 observation sites. This process results in a set of functions with six associated parameters. These parameters are then modeled using local geographical and climatic information through a machine learning algorithm called support vector regression. The results indicated that the temporal scaling characteristics of sub-daily precipitation can be accurately described using a logarithmic function. The uncertainty of the estimates is quantified using the coefficient of variance and coefficient of skewness, which are estimated using a logarithmic and linear curve, respectively. Additionally, the six parameters are found to be closely linked to geographical conditions, enabling the creation of a 1-km parameters data set. This data set can be utilized to quantitatively describe the probabilistic distribution and extract key information about maximum precipitation duration (from 1 to 12 hr). Overall, the findings suggest that the generated parameters data set holds significant potential for various applications, including risk analysis, forecasting, and early warning for rainstorm-related natural disasters in QTP. The innovative method developed in this study proves to be an effective approach for estimating sub-daily precipitation and assessing its uncertainty in ungauged regions. As one of famous hotspots for natural disaster studies on Earth, the Qinghai-Tibet Plateau (QTP) is highly vulnerable to destructive rainstorm hazard and related natural disasters, causing significant damage to property, infrastructure, agriculture, and resulting in extensive loss of life. Short-duration heavy precipitation at sub-daily scales is an important trigger for flash flood, debris flows and other disasters in QTP. However, it is a poorly gauged high mountain region, observed data for sub-daily precipitation is extremely limited. Although there have been several satellite products and reanalysis data for sub-daily precipitation in QTP, their quality has large bias and uncertainty compared to observations. It leaves a large data gap of sub-daily precipitation, hindering the studies of rainstorm-related natural disasters in the region. In this work, we develop a new strategy to quantify the temporal scaling characteristics of sub-daily precipitation, as a basis of temporal downscaling. Then we use the new strategy to generate a parameters data set, to fill the data gap of sub-daily precipitation in QTP. The parameters data set generated provides an effective way to estimate sub-daily precipitation and its uncertainty, which can effectively serve for the rainstorm-related natural disasters study in QTP. A high-resolution gridded parameters data set is generated to estimate sub-daily precipitation and its uncertainty in QTP The temporal scaling characteristics of sub-daily precipitation in QTP is well described by a logarithmic function Spatial heterogeneity in the temporal scaling characteristics of sub-daily precipitation in QTP is closely related to geographical conditions
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| 3. |
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| 4. |
- Yu, Hao, et al.
(författare)
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Association of an estrogen-sensitive Pax1-Col11a1-Mmp3 signaling axis with adolescent idiopathic scoliosis.
- 2023
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Adolescent idiopathic scoliosis (AIS) is a common and progressive spinal deformity in children that exhibits striking sexual dimorphism, with girls at more than five-fold greater risk of severe disease compared to boys. Despite its medical impact, the molecular mechanisms that drive AIS are largely unknown. We previously defined a female-specific AIS genetic risk locus in an enhancer near the PAX1 gene. Here we sought to define the roles of PAX1 and newly-identified AIS-associated genes in the developmental mechanism of AIS. In a genetic study of 9,161 individuals with AIS and 80,731 unaffected controls, significant association was identified with a variant in COL11A1 encoding collagen (α1) XI (rs3753841; NM_080629_c.4004C>T; p.(Pro1335Leu); P=7.07e -11 , OR=1.118). Using CRISPR mutagenesis we generated Pax1 knockout mice ( Pax1 -/- ). In postnatal spines we found that Pax1 and collagen (α1) XI protein both localize within the intervertebral disc (IVD)-vertebral junction region encompassing the growth plate, with less collagen (α1) XI detected in Pax1 -/- spines compared to wildtype. By genetic targeting we found that wildtype Col11a1 expression in growth plate cells (GPCs) suppresses expression of Pax1 and of Mmp3 , encoding the matrix metalloproteinase 3 enzyme implicated in matrix remodeling. However, this suppression was abrogated in the presence of the AIS-associated COL11A1 P1335L mutant. Further, we found that either knockdown of the estrogen receptor gene Esr2 , or tamoxifen treatment, significantly altered Col11a1 and Mmp3 expression in GPCs. These studies support a new molecular model of AIS pathogenesis wherein genetic variation and estrogen signaling increase disease susceptibility by altering a Pax1 - Col11a1 - Mmp3 signaling axis in the growth plate.
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| 5. |
- Yu, Hao, et al.
(författare)
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Association of genetic variation in COL11A1 with adolescent idiopathic scoliosis
- 2024
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Ingår i: eLIFE. - : eLife Sciences Publications, Ltd. - 2050-084X. ; 12
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Tidskriftsartikel (refereegranskat)abstract
- Adolescent idiopathic scoliosis (AIS) is a common and progressive spinal deformity in children that exhibits striking sexual dimorphism, with girls at more than fivefold greater risk of severe disease compared to boys. Despite its medical impact, the molecular mechanisms that drive AIS are largely unknown. We previously defined a female-specific AIS genetic risk locus in an enhancer near the PAX1 gene. Here, we sought to define the roles of PAX1 and newly identified AIS-associated genes in the developmental mechanism of AIS. In a genetic study of 10,519 individuals with AIS and 93,238 unaffected controls, significant association was identified with a variant in COL11A1 encoding collagen (α1) XI (rs3753841; NM_080629.2_c.4004C>T; p.(Pro1335Leu); p=7.07E-11, OR = 1.118). Using CRISPR mutagenesis we generated Pax1 knockout mice (Pax1-/-). In postnatal spines we found that PAX1 and collagen (α1) XI protein both localize within the intervertebral disc-vertebral junction region encompassing the growth plate, with less collagen (α1) XI detected in Pax1-/- spines compared to wild-type. By genetic targeting we found that wild-type Col11a1 expression in costal chondrocytes suppresses expression of Pax1 and of Mmp3, encoding the matrix metalloproteinase 3 enzyme implicated in matrix remodeling. However, the latter suppression was abrogated in the presence of the AIS-associated COL11A1P1335L mutant. Further, we found that either knockdown of the estrogen receptor gene Esr2 or tamoxifen treatment significantly altered Col11a1 and Mmp3 expression in chondrocytes. We propose a new molecular model of AIS pathogenesis wherein genetic variation and estrogen signaling increase disease susceptibility by altering a PAX1-COL11a1-MMP3 signaling axis in spinal chondrocytes.
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| 6. |
- Zhang, Yichi, 1995
(författare)
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Applicability of thermal energy storage in future district heating system - Design methodologies and performance evaluations
- 2021
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- District heating (DH) enables efficient and economical utilization of energy resources to satisfy the heat and hot water demands in buildings and is, thereby, well-established in Northern European countries. To achieve the future renewable energy system, the current DH systems are proved to undergo transitions towards the future DH systems, with major characteristics including renewable-based heat sources, low temperature networks, lower heating demands and smart controls. An important step is the coordination of heating and electricity sectors to achieve synergies and optimal solutions for the overall energy system, which is also known as the smart energy systems. Such goal could be achieved in a cost-effective manner by the flexibilities added from short-term thermal energy storage (TES) technologies. Despite the importance of TES has been demonstrated in previous studies, giving drastic changes compared to the current systems, the practical applicability of TES in the future DH systems remains unknown. The proposed benefits of TES might deviate from expectation considering the future characteristics, such as the low storage temperature levels and short space-heating period. Furthermore, the current studies about the TES applications have mostly focused on specific case studies. The findings are of limited applicability because they cannot be easily generalized and extrapolated to other future conditions. To explore the practical challenges and optimal applications of short-term TES units in the future, a systematic design framework that considers the diverse factors from top-level targets to bottom-level implementations is developed in this study. The top-level theoretical analysis method is developed to identify the load shifting potentials and associated storage capacities for the whole energy system, by comparing and matching energy supply and demand profiles. Compared to current bottom-up detailed system models, the proposed method requires only the energy profiles, which has resulted in much shorter analysis time. The method is further validated by complex system models, and because a good agreement has been achieved, it can be applied in various scenarios to efficiently pre-study the storage potentials. Then, the design of the practical TES capacity is derived from the theoretical result by considering performance indicators during realistic operations, such as power-to-heat conversion efficiency and heat loss efficiency. On bottom-level implementations, four typical short-term TES technologies were investigated including central water tank (CWT), district heating network inertia (DHNI), domestic hot water tank (DHWT), and building thermal mass (BTM). For this purpose, an integrated bottom-level model to simulate the operation dynamics of the district heating systems and to optimize the use of the TES units is developed. Techno-economic analysis and comparisons of TES technologies were performed on a variety of scenarios, which are representatives of the main characteristics of the current middle-temperature district heating system and future low-temperature district heating system. The changes in the source side, transportation networks and end-use building demands are considered. As a result, a performance map of the TES technologies indicating the strong links between the system characteristics and optimal TES applications has been identified. Based on that, the optimal combinations of TES technologies were proposed for a LTDH system. Consequently, combining this with top-level methods, the overall potentials and roles of short-term TES were identified by a systematic design framework.
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| 7. |
- Zhang, Yichi, 1995, et al.
(författare)
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Applicability of thermal energy storage in future low-temperature district heating systems – Case study using multi-scenario analysis
- 2021
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Ingår i: Energy Conversion and Management. - : Elsevier BV. - 0196-8904. ; 244
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Tidskriftsartikel (refereegranskat)abstract
- With the flexibilities added from thermal energy storage (TES) technologies, low temperature district heating (LTDH) system can coordinate the heat and electricity sectors in a cost-effective manner. Such combinations have therefore become an important step to achieve a 100% renewable energy system. Despite the importance of TES has been demonstrated in previous studies, giving drastic changes compared to the current systems, the practical applicability of TES in the LTDH systems remains unknown. Furthermore, the proposed benefits of TES might deviate from the expectations considering the development of future characteristics, such as the low temperature levels and small space-heating demand. This study investigates the performances and benefits of four typical short-term TES technologies, including the use of central water tank (CWT), district heating network inertia, domestic hot water tank (DHWT), and building thermal mass, based on a case LTDH system in Roskilde, Denmark. Techno-economic analysis is conducted on a variety of scenarios, based on future changes in operation of the heat sources to the end-users. An integrated model is also developed to simulate the operation dynamics of the district heating system with regards to optimizing the use of the TES units. This study provides a performance map of the TES technologies in accordance with the transitions from current to future LTDH systems, indicating the relationships between the system characteristics and optimal TES applications. The CWT is found to be most preferable for integrating the variable renewable energy due to its ability to store heat for long periods. In the end-use side, with the improved building performances and reduced space heating demand in the future, there is less potential for the use of building inertia. In contrary, the benefit of the DHWT, which mainly comes from the reduction of bypass loss during the non-space-heating period, is increased in the future. Furthermore, raising the network temperatures for active storage is found to be infeasible under all future LTDH scenarios because this measure significantly influences the heat source efficiency.
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| 8. |
- Zhang, Yichi, 1995, et al.
(författare)
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Assessment of district heating and cooling systems transition with respect to future changes in demand profiles and renewable energy supplies
- 2022
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Ingår i: Energy Conversion and Management. - : Elsevier BV. - 0196-8904. ; 268
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Tidskriftsartikel (refereegranskat)abstract
- District energy systems are about to shift towards closer temperature configurations, i.e. low-temperature district heating and high-temperature district cooling. Challenges and benefits of these transitions are mostly analyzed from a perspective of current energy demand and supply scenarios while the influence from future changes in these domains remains unknown. Based on a representative residential community in the Nordic district heating context, centralized district heating and cooling (DHC), ultra-low temperature district heating (ULTDH), and bi-directional fifth generation 5GDHC systems were assessed from technical, economical, and environmental aspects. Moreover, the applications of thermal energy storage (TES) and their roles in the future DHC systems were also investigated. The assessment was done by a generalized methodology framework, integrating the future changes, multiple operation scenarios modellings and system design optimizations. Results suggest that in the future low-energy building stock, the increased cooling demand makes the 5GDHC system the most economically attractive choice. In the supply side, with a 50% share of wind power in the future national grid, the electricity prices can make 5GDHC and ULTDHC either cost-saving or more expensive compared to the central DHC system dependent on if nuclear plants are decommissioned or not. Besides, with increasing power production from VRE, the limited application of TES for active shift of electricity demand is found when a system’s heat-to-power ratio is high. The methodology framework can be applied to similar systems to increase the understandings on system transitions.
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| 9. |
- Zhang, Yichi, 1995, et al.
(författare)
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Feasibilities of utilizing thermal inertia of district heating networks to improve system flexibility
- 2022
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Ingår i: Applied Thermal Engineering. - : Elsevier BV. - 1359-4311. ; 213
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Tidskriftsartikel (refereegranskat)abstract
- The use of district heating network inertia (DHNI) has been regarded as an efficient and cost-saving method to improve the flexibility of the energy systems. However, the acclaimed benefits in most studies are found in specific cases with traditional middle-temperature systems. The cases where DHNI is not feasible are unclear and the applicability of DHNI in future low-temperature district heating (LTDH) systems requires further investigations. Therefore, this study applied a top-down methodology where the practical storage potentials of DH networks are evaluated based on field investigations of 134 Swedish DH networks and 25 Chinese DH networks with various sizes and demand densities. Empirical relationships between the heat density and storage potentials are established and analyzed. Then, bottom-level analysis from technical and economical aspects are conducted on a variety of application scenarios for DHNI, including different temperature levels, heat sources, control strategies and renewable energy profiles. It is found that in LTDH system, by raising the network temperatures to actively use the DHNI, the heat source efficiency is reduced regardless the size and density of the network and, thereby, making the DHNI infeasible. This implies that the DHNI is only applicable in middle-temperature systems with combined heat and power plant (CHP) as a heat source in the extraction mode. Furthermore, the back-pressure mode is not economically attractive. In summary, the results from a multi-scenario analysis identified limited benefits of the DHNI, implying a proper consideration of its roles in future works.
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| 10. |
- Zhang, Yichi, 1995, et al.
(författare)
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Quantification of overlapping heating and cooling demand for the feasibility assessment of bi-directional systems over Europe
- 2023
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Ingår i: Energy and Buildings. - 0378-7788. ; 294
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Tidskriftsartikel (refereegranskat)abstract
- With warmer climate conditions, the growing need to cool down building environment in Europe calls for efficient solutions to solve the heating and cooling demand altogether. To meet such requirement, the bi-directional fifth generation district heating and cooling (5GDHC) system has been proposed in recent years, while having the capability of integrating the renewable and waste energy sources. The overlapping heating and cooling demand, or referred to as the simultaneous demand, is proved as the key pre-requisite to guide the application of 5GDHC through several case studies. However, how large is this overlapping part in the practical building stock and where are the feasible areas for 5GDHC remain unclear. To close the gap, this study assesses the quantities and geographical distributions of overlapping heating and cooling demand across Europe in EU 27, UK, and EFTA countries. Using GIS-based methods and data sources, the study region is split into 28 million hectare-sized units where the overlapping demand is specifically calculated. Moreover, the possible future changes to the heating and cooling demand alone brought by warmer climate, building renovations, and increased cooling area were investigated. The results from reference condition at year 2016 reveal that less than 0.1% of the building stock has DOC larger than 0.3, which is the threshold for 5GDHC being energy efficient. These potential areas are primarily found in city centres involving cooling demands from commercial and industrial processes. In the future scenarios of year 2050, while a better energy performance of buildings and warmer climate may decrease the heating and increase the cooling demand, the overlapping part is only slightly increased by around 5%. Accordingly, around 2500 ha-sized units from the entire study region are found to meet the DOC limit required by the 5GDHC while having large enough demand density to support district energy systems. The presented works geographically identified the potential areas for 5GDHC and can be extended with regional details to serve as the connection between top-level planning and bottom-level case studies.
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