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A computationally improved algorithm is presented to find the best transmission switching (TS) candidate for boosting resilience of electricity grids subject to (N‐2) contingencies. Here, resilience is computed as the reduction in load shed after the above‐mentioned (N‐2) contingencies. TS is a planned line outage, and past research shows that changing the transmission system's topology changes the power flow and removes post contingency violations. Finding the best TS candidate in a computationally suitable time for effectively boosting resilience is a challenge. The best TS candidate is found using a novel heuristic method by decreasing the search space based on proximity to the bus with the maximum load shedding (LSBmax). The LSBmax algorithm is faster than existing algorithms in the literature; and, it is compatible with both the AC and DC optimal power flow formulations. To validate the authors' claims of speedup and accuracy, two metrics are used to analyze the results from the IEEE 39‐bus and 118‐bus systems. Finally, the inherent parallelism of the LSBmax algorithm is leveraged on a high‐performance computing platform and applied to the large‐scale Polish 2383‐bus test system to validate scalability in both size and speedup in computation time.

For the corrective security-constrained optimal power flow (OPF) model, there exists a post-contingency stage due to the time delay of corrective measures. Line overflows in this stage may cause cascading failures. This paper proposes that the thermal inertia of transmission lines can be used to cope with post-contingency overflows. An enhanced security-constrained OPF model is established and line dynamic thermal behaviors are quantified. The post-contingency stage is divided into a response substage and a ramping substage and the highest temperatures are limited by thermal rating constraints. A solving strategy based on Benders decomposition is proposed to solve the established model. The original problem is decomposed into a master problem for preventive control and two subproblems for corrective control feasibility check and line thermal rating check. In each iteration, Benders cuts are generated for infeasible contingencies and returned into the master problem for adjusting the generation plan. Because the highest temperature function is implicit, an equivalent time method is presented to calculate its partial derivative in Benders cuts. The proposed model and approaches are validated on three test systems. Results show that the operation security is improved with a slight increase in total generation cost.

Corrective security-constrained optimal power flow (CSCOPF) considers the use of corrective control to remove system security violations in the post-contingency state. Its optimality not only depends on the pre-contingency state, but also the post-contingency state as well as the involved corrective control actions. This study first gives a comprehensive review on the relevant OPF models and then proposes a hybrid method to solve the CSCOPF problem. It makes use of the evolutionary algorithms to randomly search the maximum feasible region and state-of-the-art OPF solution technique (interior-point method) to provide deterministic solutions in the found region. The two interact iteratively to progressively approach the final solution. The proposed method is verified on the IEEE 14-bus and 118-bus systems. Comparison studies show that (i) CSCOPF can better balance the security and economy and (ii) the hybrid method is overall superior (in solution quality, robustness and convergence characteristic) over the single evolutionary algorithm. Parallel processing is applied to speed-up the computations.

This study deals with a new formulation for the direct current corrective optimal power flow. The formulation is based on the outage of generators and/or branches modelled as fictitious injections of active power. By including that fictitious injections in the optimisation problem, the injections are adjusted to the post-contingency state as a consequence of the corrective actions carried out to bring the system back to its normal state. So, when the analysis of contingencies is performed, the classical topological analysis and the subsequent analyses are avoided with this approach. This new formulation uses the sensitivity matrix between branch power flows and powers injected in a power system. An important feature of this matrix is to remain constant during the contingency analysis performed for the generation-load scenario (base case) of each period of time to be analysed. The approach proposed is illustrated in the IEEE-RTS of 24 buses. The results obtained in this distribution network demonstrate that the proposed methodology can assess the impact of contingencies with an acceptable accuracy and a short computation time.

This paper proposes an optimal dynamic reserve activation plan after the occurrence of an emergency situation (generator/transmission line outage, load increase or both). An optimal plan is developed to handle the emergency, using the coordinated action of fast and slow reserves, for secure operation with minimum overall cost. It considers the reserves supplied by the conventional thermal generators (spinning reserves), hydro power units and load demands (demand-side reserves). The optimal backing down of costly/fast reserves and bringing up of slow reserves in each sub-interval in an integrated manner is proposed. The proposed reserve activation approaches are solved using the genetic algorithm, and some of the simulation results are also compared using the Matlab optimization toolbox and the general algebraic modeling system (GAMS) software. The simulation studies are performed on the IEEE 30, 57 and 300 bus test systems. These results demonstrate the advantage of the proposed integrated/dynamic reserve activation plan over the conventional/sequential approach.

This study presents a novel stochastic multi-objective model for precise scheduling of energy and reserve services in day-ahead markets. This model is based on a security-constrained market clearing with an emphasis on preservation of system frequency. A frequency index that is derived from the total system frequency profile during post-contingency intervals has been defined as an extra objective function to control system frequency after the occurrence of a contingency. The model is capable of scheduling the tertiary regulation interval through appropriate generators’ reference power setting instructions made by the ISO based on participants’ bids for energy and reserve services. The reference power settings are obtained by an optimisation model and can be performed directly by the speed changers. The load dependency on frequency has also been analysed in the proposed model. This approach could be used by ISOs to make a trade-off concurrently between system frequency profile and total operating cost to operate the power system securely in an economically efficient manner. The developed multi-objective programming is analysed through two case studies; a three-bus system scheduled over 1 h and the IEEE 24-bus reliability test system over 24 h, solved by means of mixed-integer linear programming methods.

The global COVID-19 pandemic has placed tremendous physical and mental strain on the US healthcare system. Studies examining the effects of outbreaks have demonstrated both an increased prevalence and long-term development of Post-Traumatic Stress Disorder (PTSD) symptoms in healthcare providers. We sought to assess the impact of the COVID-19 pandemic on the psychological well-being of medical providers, medical trainees, and administrators at a large academic center to identify stressors and moderators to guide future mental health and hospital-system interventions. A 42-item survey examining specific stressors, grit, and resilience was widely distributed to physicians, residents, fellows, and administrators a large academic institution for departmental distribution. Survey results were analyzed using descriptive statistics, ANOVA, and multivariate linear regressions. A p-value <0.05 was considered statistically significant. A total of 785 participants completed the survey. The majority of respondents rated their stress to be significantly increased during the pandemic. Respondents’ fear of transmitting the virus to their family members was a significant stressor. Higher resilience was associated with lower stress, anxiety, fatigue, and sleep disturbances. Overall, respondents felt supported by their departments and institution and felt contingency plans and personal protective equipment were adequate. Healthcare workers have increased resilience in the face of heightened stress during a pandemic. Higher resilience and grit were protective factors in managing personal and system-level stressors at the peak of the COVID-19 pandemic in our institution. Implementing an intervention designed to enhance healthcare workers’ resilience in response to the COVID-19 pandemic is warranted. •Healthcare providers are experiencing higher levels of stress during the COVID-19 pandemic.•Healthcare providers have high resilience, which is protective against stress and other negative psychological factors resulting from this pandemic.•Future research should evaluate the efficacy of mental skills and resilience training in frontline workers to reduce symptoms of PTSD in future times of global crisis.

This commentary reflects on the influence of the post-political critique on urban studies. In this literature (e.g. Swyngedouw, 2014), the default position of contemporary democracies is postpolitics – the truly political is only rare, random and radical. The 'post-political trap' refers to the intuitively convincing, yet ultimately confining account it provides of contemporary urban governance. We identify three shortcomings. First, the binary understanding of the real political/politics as police negates the in-betweenness and contingency of actually existing urban politics. By so doing, secondly, political agency is reduced to the heroic and anti-heroic. Thus, the plurality of political agency in the urban sphere and multi-faceted forms of power lose their political quality. Third, the perceived omnipotence of the post-political order actually diminishes the possibilities of the urban as a political space of resistance and emancipation. On these grounds we argue not for a rejection of the notion of the post-political per se but for a more differentiated approach, one more alert to the contingencies of the political and of depoliticisation in the urban realm.

Scholarship engaging with (northern) urban theory from the south has troubled the core of urban studies. At this critical juncture, we argue that it is important to clarify core propositions and call attention to points of convergence and dissonance amongst advocates of ‘the southern urban critique’. We briefly review foundational arguments for this scholarly community, then outline three distinct iterations of the source of this critique: the south is empirically different; EuroAmerican hegemony works to displace a diversity of intellectual traditions; and the postcolonial encounter requires the critical interrogation of research practices. We then consider whether the southern urban critique is an argument for the study of a distinct southern urbanism, an ontological position about the socio-spatial contingency of all theorisation or a tactical strategy for calling attention to marginalised places and ideas to be superseded by an urban studies of a world of cities. We hope our efforts contribute to further conversation and greater analytical clarity, enabling more rigorous and robust articulations of the precise objects and objectives of the southern urban critique in particular, and urban studies more generally. 南方学界对（北方）城市理论研究的参与困扰了城市研究的核心。在这个关键时刻，我们认为澄清核心命题、并引起人们对“南方城市批评”倡导者的趋同点和不和谐之处的关注是很重要的。我们简要回顾了这个学术群体的基本论点，然后概述了这个批评来源的三个不同的迭代：南方在经验上是不同的；欧美霸权致力于取代多元化的知识传统；而后殖民时期的遭遇需要对研究实践进行批判性拷问。然后，我们探讨了南方城市批评到底是一种独特的南方城市化研究主张，一种关于所有理论的社会空间偶然性的本体论立场，亦或是一种战术策略，旨在将人们的注意力集中到将被对城市世界的研究取代的边缘化地方以及思想。我们希望我们的努力有助于进一步的对话和更大的分析清晰度，以便更加严格和有力地阐明南方城市批评（以及更普遍的城市研究）的精确对象和目标。

IntroductionThere is uncertainty surrounding the diagnosis, prevalence, phenotype, duration and treatment of Long COVID. This study aims to (A) describe the clinical phenotype of post-COVID symptomatology in children and young people (CYP) with laboratory-confirmed SARS-CoV-2 infection compared with test-negative controls, (B) produce an operational definition of Long COVID in CYP, and (C) establish its prevalence in CYP.Methods and analysisA cohort study of SARS-CoV-2-positive CYP aged 11–17 years compared with age, sex and geographically matched SARS-CoV-2 test-negative CYP. CYP aged 11–17 testing positive and negative for SARS-CoV-2 infection will be identified and contacted 3, 6, 12 and 24 months after the test date. Consenting CYP will complete an online questionnaire. We initially planned to recruit 3000 test positives and 3000 test negatives but have since extended our target. Data visualisation techniques will be used to examine trajectories over time for symptoms and variables measured repeatedly, separately by original test status. Summary measures of fatigue and mental health dimensions will be generated using dimension reduction methods such as latent variables/latent class/principal component analysis methods. Cross-tabulation of collected and derived variables against test status and discriminant analysis will help operationalise preliminary definitions of Long COVID.Ethics and disseminationResearch Ethics Committee approval granted. Data will be stored in secure Public Health England servers or University College London’s Data Safe Haven. Risks of harm will be minimised by providing information on where to seek support. Results will be published on a preprint server followed by journal publication, with reuse of articles under a CC BY licence. Data will be published with protection against identification when there are small frequencies involved.Trial registration numberISRCTN34804192; Pre-results.