The short-term variability impacts associated with high renewable energy sources (RESs) penetration in power system will significantly jeopardize the feasible and economically efficient operation of system while necessitating the enhancement of flexibility provision to guarantee the appropriate levels of reliability. To address these challenges, this paper introduces a unique unit commitment (UC) formulation with focus on the allocation and deployment of flexible ramp products. Alongside conventional generation units, emerging flexible resources have recently attracted much attention as desirable options to promote the flexibility degree in power system. Under this perspective, this paper develops a multi-resolution robust UC (RUC) incorporating flexible technologies in a co-optimized energy and reserve market. The proposed model not only optimizes the hourly commitment and dispatch scheduling of resources but also develops a novel nondeterministic flexible ramp product which can be adaptively adjusted into the net-load sudden variations based on intra-hourly intervals. To conquer the drawbacks of the conventional two-stage robust optimization including over-conservativeness, non-causality and heavy computational tractability, and to reduce the sub-optimality gaps brought by the conventional affinely adjustable robust (AAR) methodology, a novel augmented affinely adjustable robust (AAAR) strategy is recommended in the current paper. The superiority of the proposed approach upon the conventional AAR counterpart (AARC) is also investigated from both theoretical and practical aspects. Then, the merits of the coordinated operation of flexible resources are evaluated through the extensive comparisons. The applicability of the proposed model is validated by the results of the numerical tests conducted on both IEEE 24-bus reliability test system (RTS) and the IEEE 118-bus test system.
This paper tackles the topic of identifying and suppressing ineffective control actions in optimal power flow (OPF) and security-constrained OPF (SCOPF) problems. Conventional approaches offer transmission system operators (TSOs) low-transparency, purely academic solutions containing dozens of control actions; inferring their contribution to the overarching objective is challenging. Our 3-step methodology helps TSOs to understand the value of each control action. TSOs are informed of their ideal system costs (Step 1), plus the minimum number of required control actions (Step 2), thus gaining the ability to identify and subsequently suppress those deemed inefficient, i.e., whose elimination minimally impacts the objective (Step 3). Major contributions with respect to previous works include (a) the consideration of all types of contingencies and control actions, (b) the leveraging of the methodology to the SCOPF setting, including multiple suppression mentalities for identifying control actions, and (c) the further showcasing of the academia-industry gap in a topic that is relatively obscure in academia but crucial in industry. We prominently demonstrate that conventional solutions include dozens of redundant control actions which TSOs could reliably filter out. We adopt a predominantly industrial viewpoint, our end-goal being to provide results that are easier to interpret in real-world conditions.
It is known that the addition of Al in interstitial free steel has a positive influence on the normal direction fiber recrystallization texture. The location and role of Al in interstitial free steel are not yet clear. Current research shows the likely role of Al in precipitation and/or its location in the grain matrix/grain boundary (0.17 wt% Al) and its impact on the properties. Industrially processed hot-rolled steel subjected to cold rolling (90%) and isothermal annealing validated the formation of normal direction fiber recrystallization texture. Precipitation studies showed no Al-containing precipitates. High-resolution secondary ion mass spectrometry imaging confirmed the presence of Al more on certain grain boundaries in fully recrystallized steel. Molecular statics simulation studies using a large-scale atom/molecular massively parallel simulator showed a reduction in the grain boundary energy with Al addition, assisting the system to reach a minimum energy state.
Concentrated solar power (CSP) can be a flexible renewable resource on electric grids. Here we assess the direct and upstream socio-economic and environmental impacts of the projected deployment of CSP in China and Europe, using Input-Output Analysis. We first quantify the CSP experience curve, finding a learning rate of ∼16%, and combine this with future projections for installed capacity from China's National Development and Reform Commission and the International Energy Agency. We find employment intensities of 4.2 and 2.3 person-year/GWh in China and Europe, respectively (higher than PV and wind). The carbon emission intensity of CSP is currently higher than alternatives but this gap may narrow through learning. Carbon intensities are estimated at 129.7 and 99.8 gCO2eq/kWh in 2020 (in China and Europe, respectively) and could drop to 40.4 and 31.1 gCO2eq/kWh by 2050 given the projected expansion. We discuss the importance of including both environmental and socio-economic dimensions when assessing the impact of energy technologies and provide context for the role of CSP in the energy transition.
The Japanese perennial knotweed (Fallopia japonica) is a globally widespread neophyte whose usability is being investigated, e.g., to use knotweed for biogas plants and as a substitute for firewood. The present study investigates the potential of Japanese knotweed for material use. Morphological studies were carried out on the stem cell structures and arrangements (microstructure) and the external stem structure (macrostructure) and showed that Japanese knotweed is a plant species with several hierarchical morphological levels being a highly complex fibre-matrix composite with a low density. Mechanical properties were investigated using tensile, bending, compression and impact tests for fresh and dry specimens and then mathematically converted in density-related lightweight construction indices and compared with other materials using Ashby maps. Particularly under compression, properties are close to woods and wood composites, making the plant an interesting material for lightweight sandwich panels, where assembled slices of the stalk could serve as core elements. Fibre bundles, extracted from the stalk, show relatively low mechanical properties (tensile strength: 93 MPa; Young’s modulus: 4.77 GPa) compared to bast fibres such as hemp. The shredded stalks could be compounded into homogeneous granulates directly after harvesting without other separation processes. Therefore, the study presents a proof of concept for Japanese knotweed to apply the shredded stalks in injection-moulded PLA composites (tensile strength: mean = 54 MPa; Young’s modulus: mean = 5.61 GPa) comparable or even better than wood fibre-reinforced polymers.
Flow, suspended sediment transport and associated morphological changes in the Vietnamese Mekong Delta (VMD) are studied using field survey data and a two-dimensional (2D) depth-averaged hydromorphodynamic numerical model. The results show that approximately 61–81 % of the suspended sediment load in the Hau River during the flood seasons is diverted from the Tien River by a water and suspended sediment diversion channel. Tidal effects on flow and suspended sediment load are more pronounced in the Hau River than in the Tien River. The results show the formation of nine scour holes in the Tien River and seven scour holes in the Hau River from 2014 to 2017. Additional six scour holes are likely to form by the end of 2026 if the suspended sediment supply is reduced by 85 % due to damming. Notably, the scour holes are likely to form at locations of severe riverbank erosion. In the entire study area, the simulated total net incision volume in 2014–2017 is approximately 196 Mm³ (equivalent to 65.3 Mm³/yr). The predicted total net incision volumes from 2017 to 2026 are approximately 2472 and 3316 Mm³ under the 18 % and 85 % suspended sediment reduction scenarios, respectively, thereby likely threatening the delta sustainability. The methodology developed in this study is helpful in providing researchers and decision-makers with one way to predict numerically the scour hole formation and its association with riverbank stability in river deltas. Of equal importance, this research serves as a useful reference on the role of water and suspended sediment diversion channels in balancing landforms in river-delta systems, particularly where artificial diversion channels are planned.
Remote detection and monitoring of the vegetation responses to stress became relevant for sustainable agriculture. Ongoing developments in optical remote sensing technologies have provided tools to increase our understanding of stress-related physiological processes. Therefore, this study aimed to provide an overview of the main spectral technologies and retrieval approaches for detecting crop stress in agriculture. Firstly, we present integrated views on: i) biotic and abiotic stress factors, the phases of stress, and respective plant responses, and ii) the affected traits, appropriate spectral domains and corresponding methods for measuring traits remotely. Secondly, representative results of a systematic literature analysis are highlighted, identifying the current status and possible future trends in stress detection and monitoring. Distinct plant responses occurring under short-term, medium-term or severe chronic stress exposure can be captured with remote sensing due to specific light interaction processes, such as absorption and scattering manifested in the reflected radiance, i.e. visible (VIS), near infrared (NIR), shortwave infrared, and emitted radiance, i.e. solar-induced fluorescence and thermal infrared (TIR). From the analysis of 96 research papers, the following trends can be observed: increasing usage of satellite and unmanned aerial vehicle data in parallel with a shift in methods from simpler parametric approaches towards more advanced physically-based and hybrid models. Most study designs were largely driven by sensor availability and practical economic reasons, leading to the common usage of VIS-NIR-TIR sensor combinations. The majority of reviewed studies compared stress proxies calculated from single-source sensor domains rather than using data in a synergistic way. We identified new ways forward as guidance for improved synergistic usage of spectral domains for stress detection: (1) combined acquisition of data from multiple sensors for analysing multiple stress responses simultaneously (holistic view); (2) simultaneous retrieval of plant traits combining multi-domain radiative transfer models and machine learning methods; (3) assimilation of estimated plant traits from distinct spectral domains into integrated crop growth models. As a future outlook, we recommend combining multiple remote sensing data streams into crop model assimilation schemes to build up Digital Twins of agroecosystems, which may provide the most efficient way to detect the diversity of environmental and biotic stresses and thus enable respective management decisions.
Hemp (Cannabis sativa L.) is a promising crop for non-food agricultural production on soils contaminated by moderate doses of heavy metals, while silicon, as a beneficial element, is frequently reported to improve stressed plant behavior. Using a hydroponic system, plants of Cannabis sativa (cv. Santhica 27) were exposed for 1 week to 100 µM Zn in the presence or absence of 2 mM Si. Zinc accumulated in all plant organs but was mainly sequestered in the roots. Additional Si reduced Zn absorption but had no impact on Zn translocation. Zn accumulation had a slight negative impact on leaf number, stem length, and chlorophyll content, and additional Si did not mitigate these symptoms. Exogenous Si reduced the Zn-induced membrane lipid peroxidation (assessed by malondialdehyde quantification) and increased the total antioxidant activities estimated by the FRAP index. In the absence of Si, leaf phytochelatin and total glutathione were the highest in Zn-treated plants and Si significantly decreased their concentrations.
For the first time, random copolymers of styrene (St) and 1,3-butadiene (Bd) (poly(St n-r-Bd m), styrene butadiene rubber, SBR) were successfully prepared via solution reversible addition-fragmentation-transfer (RAFT) polymerization by employing dithio-and trithiocarbonate chain transfer agents (CTAs). The influence of various reaction parameters such as temperature and duration of polymerization, type of CTA, solvent and initiator, on molecular weight, molecular weight distribution (M w /M n) and the yield of the copolymers was investigated in detail. Determination of optimal reaction conditions allowed for the successful preparation of linear poly(St n-r-Bd m) having M n of up to 26 000 g/mol and Mw/Mn < 1.6, with an isolated yield of up to 39 wt%. According to NMR the obtained copolymers were random and did not contain any styrene blocks (more than 5 units in sequence). The composition of poly(St-r-Bd) was found to be nearly independent of reaction conditions and consisted of 19.6-24.0, 15.0-15.5 and 60.5-64.5 wt% of styrene, (1,2)-Bd and (1,4)-Bd units, respectively. The glass transition temperature (T g) of the copolymers (measured via DSC) varied between -55 and -62 oC, while T onset (measured via TGA) ranged between 385 and 390 oC. The optimized synthetic method for production of poly(St n-r-Bd m) copolymers was then extended to produce various poly[Xn-b-(Stm-r-Bdk)] block copolymers, where X represents different methacrylic or styrenic monomeric units. The molecular weight of the poly[X n-b-(St m-r-Bd k)] block copolymers was mainly dependent on the molar mass of the starting poly(X n) macro-CTA and reached as high as 72 000 g/mol, with the SBR segment varying between 11 800 and 39 600 g/mol. These materials, believed to be the first of their kind reported in the literature, show clear evidence of nanostructure formation via AFM and promise unique and attractive combinations of stiffness, toughness, thermomechanical performance and chemical reactivity. This work opens up new avenues for the synthesis of novel copolymers with exceptional levels of structural control, thus providing additional tools to the polymer research community as far as the design and creation of materials with new and useful properties is concerned.
Bacteriophages participate in soil life by influencing bacterial community structure and function, biogeochemical cycling and horizontal gene transfer. Despite their great abundance, diversity, and importance in microbial processes, they remain little explored in environmental studies. The influence of abiotic factors on the persistence of bacteriophages is now recognized; however, it has been mainly studied under experimental conditions. This study aimed to determine whether the abiotic factors well-known to influence bacteriophage persistence also control the natural distribution of the known DNA bacteriophage populations. To this end, soil from eight study sites including forests and grasslands located in the Attert River basin (Grand Duchy of Luxembourg) were sampled, covering different soil and land cover characteristics. Shotgun metagenomics, reference-based bioinformatics and statistical analyses allowed characterising the diversity of known DNA bacteriophage and bacterial communities. After combining soil properties with the identified DNA bacteriophage populations, our in-situ study highlighted the influence of pH and calcium cations on the diversity of the known fraction of the soil DNA bacteriophages. More interestingly, significant relationships were established between bacteriophage and bacterial populations. This study provides new insights into the importance of abiotic and biotic factors in the distribution of DNA bacteriophages and the natural ecology of terrestrial bacteriophages.
Alkali postdeposition treatments of Cu(In,Ga)Se2 absorbers with KF, RbF, and CsF have led to remarkable efficiency improvements for chalcopyrite thin film solar cells. However, the effect of such treatments on the electronic properties and defect physics of the chalcopyrite absorber surfaces are not yet fully understood. In this work, we use scanning tunneling spectroscopy and X-ray photoelectron spectroscopy to compare the surface defect electronic properties and chemical composition of RbF-treated and nontreated absorbers. We find that the RbF treatment is effective in passivating electronic defect levels at the surface by preventing surface oxidation. Our X-ray photoelectron spectroscopy (XPS) data points to the presence of chemisorbed Rb on the surface with a bonding configuration similar to that of a RbInSe2 bulk compound. Yet, a quantitative analysis indicates Rb coverage in the submonolayer regime, which is likely causing the surface passivation. Furthermore, ab initio calculations confirm that RbF-treated surfaces are less prone to oxidation (in the form of Ga, In, and Se oxides) than bare chalcopyrite surfaces. In addition, elemental diffusion of Rb along with Na, Cu, and Ga is found to occur when the samples are annealed under ultrahigh vacuum conditions. Magnetic sector secondary ion mass spectrometry measurements indicate that there is a homogeneous spatial distribution of Rb on the surface both before and after annealing, albeit with an increased concentration at the surface after heat treatment. Depth-resolved magnetic sector secondary ion mass spectrometry measurements show that Rb diffusion within the bulk occurs predominantly along grain boundaries. Scanning tunneling and XPS measurements after subsequent annealing steps demonstrate that the Rb accumulation at the surface leads to the formation of metallic Rb phases, involving a significant increase of electronic defect levels and/or surface dipole formation. These results strongly suggest a deterioration of the absorber-window interface because of increased recombination losses after the heat-induced diffusion of Rb toward the interface.
The Seebeck coefficient and electrical conductivity are two central quantities to be optimized simultaneously in designing thermoelectric materials, and they are determined by the dynamics of carrier scattering. Here a new regime is uncovered where the presence of multiple electron bands with different effective masses, crossing near the Fermi level, leads to strong energy‐dependent carrier lifetimes due to intrinsic electron–phonon scattering. In this anomalous regime, electrical conductivity decreases with carrier concentration, Seebeck coefficient reverses sign even at high doping, and power factor exhibits an unusual second peak. The origin and magnitude of this effect is explained using a general simplified model as well as first‐principles Boltzmann transport calculations in recently discovered half‐Heusler alloys. General design rules for using this paradigm to engineer enhanced performance in thermoelectric materials are identified. First principles calculations reveal that electron–phonon inter‐band scattering can cause anomalous reversal of the Seebeck effect and sharp increase in thermoelectric power factor of semiconductors, even at high doping concentrations. This opens a new design dimension for thermoelectric materials.
Background Food-grade titanium dioxide (TiO2), composed of nano- and submicron-sized particles, is used worldwide in various foodstuffs, toothpastes and pharmaceutical tablets as a whitening and opacifying agent. Its use as a food additive (E171 in EU) has raised concerns for human health regarding its systemic availability, tissue accumulation, genotoxicity and promotion of precancerous lesions. However, although the buccal mucosa is the first area exposed, oral transmucosal passage of TiO2 particles has not been documented. Here we analyzed TiO2 (E171) particle translocation in vivo through the pig buccal mucosa and in vitro on human buccal TR146 cells, and the effects of E171 on proliferating and differentiated human oral epithelial cells. Results Using transmission electronic microscopy (TEM) coupled to energy-dispersive X-ray spectroscopy (EDX), isolated TiO2 particles and small aggregates were observed in the buccal floor of pigs starting 30 min after the sublingual deposition of E171 suspended in water, and recovered in the submandibular lymph nodes at 4 h. In human TR146 cells exposed to E171, kinetic analyses using confocal microscopy, TEM and high-resolution secondary ion mass spectrometry (SIMS) imaging showed high uptake capacities of both the nano- and submicron-sized TiO2 particles. At 2 h, the cytotoxicity, genotoxicity and oxidative stress were investigated in both proliferating and differentiated TR146 cells exposed to E171 in comparison with two TiO2 size standards of 115 and 21 nm in diameter. All TiO2 samples were reported cytotoxic in proliferating cells, an effect almost abolished following differentiation. Genotoxicity (γH2AX or 53BP1 foci formation and comet assays) and oxidative stress (CellRox reagent) were only reported for the E171 and 115 nm TiO2 particles, and mainly in proliferating cells. Conclusions These data showed that the buccal mucosa is an important absorption route for the systemic passage of food-grade TiO2 particles. In human cells, TiO2 particles are cytotoxic and generate size-dependent oxidative and genotoxic stresses in proliferating cells, potentially impairing oral epithelium renewal. Altogether, these data emphasize that buccal exposure should be considered during toxicokinetic studies and for risk assessment of TiO2 in human when used as food additive, including in toothpastes and pharmaceutical formulations.
Software Defined Networking provides new functionalities to easily manage, configure, and optimize network resources by introducing a clear separation between the control entity and the forwarding devices. Such functionalities also help network operators detect and mitigate the security attacks to the network and provide better security level when compared to the traditional networks. However, some security threats, particularly distributed denial of service (DDoS) attacks, keep their effectiveness in degrading the availability of the networks even if the networking paradigm have changed. Existing DDoS attack detection approaches for SDN are mainly based on statistical (threshold-based) and Machine Learning-based (ML) approaches. Considering the dynamic characteristics of the network traffic, finding a dynamic threshold is somehow problematic. On the other hand, finding an appropriate feature that can discriminate DDoS attack from normal traffic is challenging for ML-based approaches. Therefore, to address the aforementioned issues, in this work, we propose a DDoS attack detection and countermeasure scheme based on discrete wavelet transform (DWT) and auto-encoder neural network for SDN. The proposed scheme extracts statistical features from the wavelet transform to be processed by an auto-encoder neural network to detect samples of DDoS attack traffic. Later, to reduce the computational burden imposed by the neural network model, the average hit rate in the flow table of the switches is used to activate the DDoS detection of the scheme. We also provide a detailed performance analysis by considering the computational cost complexity of the algorithms proposed in scheme and the evaluation of the successful detection rate with simulations. Our experimental results show that the proposed scheme achieves high detection rate against DNS amplification, Network Time Protocol and TCP SYN flood attacks with a remarkably low false alarm rate.
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