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Hydropower scheduling in day-ahead electricity markets is complex due to uncertainty in the electricity price. Internal cascade dependency of hydro power plants can also increase this complexity. One way to overcome this complexity is to replace the original hydropower system by an equivalent system, which provides simulation results sufficiently close to the ones of the original system. This paper presents a method to obtain multi-station equivalent models using a bilevel optimization problem, where the objective is to minimize the difference in outcomes between the original and the equivalent models. This bilevel problem is then transformed into a single-level optimization problem that can be solved using standard optimization techniques. Finally, the errors between the simulation results of the original and equivalent hydropower models are computed and analyzed for a Swedish system to show the accuracy of different multi-station equivalents. [ABSTRACT FROM PUBLISHER]

Presents a Norton approach for modeling electric power distribution networks where the system configuration is not fully known. Influence of capacitor switching on network harmonic generation; Measurement of the harmonic current or voltage source; Accuracy of modeling a distribution network as a current or voltage source.

It is sometimes difficult to explain how a power system works, especially for people who have not studied electrical engineering. This article shows how the interactions of a power system and its components can be explained using the parallel with a tandem bicycle. The active power balance in the power system is modeled by the parallel of keeping a constant speed of the bike, while the reactive power balance is represented with the fact that the bike has to be kept on the road without overturning. The parallel gives a good visualization of phenomena such as active power balance, frequency control, asynchronous machine slip, reactive power balance, and voltage control. [ABSTRACT FROM PUBLISHER]

The current study applies the cost-benefit analysis method to determine the optimal amount of spinning reserve. However, it is difficult for the method to handle large size problem, like large interconnected power systems with several control areas, directly. Therefore, this paper proposes a power system equivalent for the original system to reduce the complexity of the original problem. According to the proposed algorithm, each area of the system is first modeled by an equivalent system, obtained by the REI (radial – equivalent – independent) method, and an interconnected REI equivalent is obtained for the original interconnected system. A cost-benefit analysis is then performed to determine the spinning reserve requirements of both the original and equivalent systems. The cost-benefit algorithm considers either the SCUC (security constrained unit commitment) or the SCED (security constrained economic dispatch). Finally, the proposed interconnected REI equivalent is evaluated by comparing the spinning reserve of each control area in the original system with that in the equivalent system. Numerical studies are performed on two IEEE test systems. [ABSTRACT FROM AUTHOR]

Purpose: The clinical condition of a brain abscess is a potentially life-threatening disease. The combination of MRI-based imaging, surgical therapy and microbiological analysis is critical for the treatment and convalescence of the individual patient. The aim of this study was to evaluate brain tissue oxygenation measured with dynamic susceptibility contrast perfusion weighted imaging (DSC-PWI) in patients with brain abscess and its potential benefit for a better understanding of the environment in and around brain abscesses., Methods: Using a local database, 34 patients (with 45 abscesses) with brain abscesses treated between January 2013 and March 2021 were retrospectively included in this study. DSC-PWI imaging and microbiological work-up were key inclusion criteria. These data were analysed regarding a correlation between DSC-PWI and microbiological result by quantifying brain tissue oxygenation in the abscess itself, the abscess capsula and the surrounding oedema and by using six different parameters (CBF, CBV, CMRO2, COV, CTH and OEF)., Results: Relative cerebral blood flow (0.335 [0.18-0.613] vs. 0.81 [0.49-1.08], p = 0.015), relative cerebral blood volume (0.44 [0.203-0.72] vs. 0.87 [0.67-1.2], p = 0.018) and regional cerebral metabolic rate for oxygen (0.37 [0.208-0.695] vs. 0.82 [0.55-1.19], p = 0.022) were significantly lower in the oedema around abscesses without microbiological evidence of a specific bacteria in comparison with microbiological positive lesions., Conclusions: The results of this study indicate a relationship between brain tissue oxygenation status in DSC-PWI and microbiological/inflammatory status. These results may help to better understand the in vivo environment of brain abscesses and support future therapeutic decisions.

Background: Hyperdense lesions in CT after EVT of LVO are common. These lesions are predictors for haemorrhages and an equivalent of the final infarct. The aim of this study based on FDCT was the evaluation of predisposing factors for these lesions., Methods: Using a local database, 474 patients with mTICI ≥ 2B after EVT were recruited retrospectively. A postinterventional FDCT after recanalisation was analysed regarding such hyperdense lesions. This was correlated with a variety of items (demographics, past medical history, stroke assessment/treatment and short-/long-term follow-up)., Results: Significant differences were present in NHISS at admission, regarding time window, ASPECTS in initial NECT, location of the LVO, CT-perfusion (penumbra, mismatch ratio), haemostatic parameters (INR, aPTT), duration of EVT, number of EVT attempts, TICI, affected brain region, volume of demarcation and FDCT-ASPECTS. The ICH-rate, the volume of demarcation in follow-up NECT and the mRS at 90 days differed in association with these hyperdensities. INR, the location of demarcation, the volume of demarcation and the FDCT-ASPECTS could be demonstrated as independent factors for the development of such lesions., Conclusion: Our results support the prognostic value of hyperdense lesions after EVT. We identified the volume of the lesion, the affection of grey matter and the plasmatic coagulation system as independent factors for the development of such lesions.