A method for fault type discrimination and faulted phase identification using instantaneous local current measurements is proposed. Seven current components are obtained from the measured three-phase ...instantaneous currents through a transformation and band passed filtered to remove the fundamental components and high frequency content. Upon detecting a fault, nine fault discrimination indices are computed taking different ratios of the maximum rates of change of these filtered current components. The indices are used to (i) separate ground faults from the phase-to-phase and three-phase faults, (ii) discriminate phase-to-ground from phase-to-phase-to-ground faults, (iii) differentiate phase-to-phase faults from the three-phase faults, and (iv) identify the faulted phases. As the indices are ratios, decisions are less affected by the fault resistance. The algorithm was validated using a power system simulated in PSCAD/EMTDC. Extensive testing involving more than 10,000 fault scenarios showed that fault type and faulted phases can be successfully identified. The algorithm found some difficulty in identifying the phases involved in phase-to-phase-to-ground faults at certain fault inception angles, and one of the thresholds can be affected by the transposition scheme.
Since the onset of the coronavirus disease 2019 (COVID-19) pandemic, doctors and public authorities have demonstrated concern about the reduction in quality of care for other health conditions due to ...social restrictions and lack of resources. Using a population-based stroke registry, we investigated the impact of the onset of the COVID-19 pandemic in stroke admissions in Joinville, Brazil.
Patients admitted after the onset of COVID-19 restrictions in the city (defined as March 17, 2020) were compared with those admitted in 2019. We analyzed differences between stroke incidence, types, severity, reperfusion therapies, and time from stroke onset to admission. Statistical tests were also performed to compare the 30 days before and after COVID-19 to the same period in 2019.
We observed a decrease in total stroke admissions from an average of 12.9/100 000 per month in 2019 to 8.3 after COVID-19 (
=0.0029). When compared with the same period in 2019, there was a 36.4% reduction in stroke admissions. There was no difference in admissions for severe stroke (National Institutes of Health Stroke Scale score >8), intraparenchymal hemorrhage, and subarachnoid hemorrhage.
The onset of COVID-19 was correlated with a reduction in admissions for transient, mild, and moderate strokes. Given the need to prevent the worsening of symptoms and the occurrence of medical complications in these groups, a reorganization of the stroke-care networks is necessary to reduce collateral damage caused by COVID-19.
With widespread application of voltage source converter (VSC) as a key energy-conversion power electronic device by using the phase-locked loop (PLL) technique for synchronization, the system ...dynamics has become much complicated. In this paper, the nonlinear dynamics and transient stability of the PLL-based VSC system are investigated, within a unified framework of the (normalized) generalized swing equation. It is found that there are three different types of bifurcation, including the generalized saddle-node, Hopf, and homoclinic bifurcations. Within the coexistence parameter region, the basin boundary of the stable equilibrium point shows either a closed-loop or a fish-like pattern. With the help of the equal area criterion (EAC), the transient stabilities under different transient disturbances including short circuit, voltage dip, and power rise are analyzed. Because the equivalent damping of the VSC is state-dependent, the theoretical results based on the EAC are examined. Furthermore, based on the analytical results from the generalized swing equation, the principle for all major transient stability enhancement methods is uncovered. All these findings are well verified by extensive electromagnetic transient simulations. Therefore, the generalized swing equation provides a deeper physical insight and plays a crucial role in transient stability problems in power-electronic-dominated power systems, similar to the swing equation in traditional power systems.
Sterols are hydrophobic molecules, known to cluster signaling membrane-proteins in lipid rafts, while methyl-β-cyclodextrin (MβCD) has been a major tool for modulating membrane-sterol content for ...studying its effect on membrane proteins, including the transient receptor potential (TRP) channels. The Drosophila light-sensitive TRP channels are activated downstream of a G-protein-coupled phospholipase Cβ (PLC) cascade. In phototransduction, PLC is an enzyme that hydrolyzes phosphatidylinositol 4,5-bisphosphate (PIP2) generating diacylglycerol, inositol-tris-phosphate, and protons, leading to TRP and TRP-like (TRPL) channel openings. Here, we studied the effects of MβCD on Drosophila phototransduction using electrophysiology while fluorescently monitoring PIP2 hydrolysis, aiming to examine the effects of sterol modulation on PIP2 hydrolysis and the ensuing light-response in the native system. Incubation of photoreceptor cells with MβCD dramatically reduced the amplitude and kinetics of the TRP/TRPL-mediated light response. MβCD also suppressed PLC-dependent TRP/TRPL constitutive channel activity in the dark induced by mitochondrial uncouplers, but PLC-independent activation of the channels by linoleic acid was not affected. Furthermore, MβCD suppressed a constitutively active TRP mutant-channel, trpP365, suggesting that TRP channel activity is a target of MβCD action. Importantly, whole-cell voltage-clamp measurements from photoreceptors and simultaneously monitored PIP2-hydrolysis by translocation of fluorescently tagged Tubby protein domain, from the plasma membrane to the cytosol, revealed that MβCD virtually abolished the light response when having little effect on the light-activated PLC. Together, MβCD uncoupled TRP/TRPL channel gating from light-activated PLC and PIP2-hydrolysis suggesting the involvement of distinct nanoscopic lipid domains such as lipid rafts and PIP2 clusters in TRP/TRPL channel gating.
We present a measurement of the volumetric rate of "calcium-rich" optical transients in the local universe, using a sample of three events from the Palomar Transient Factory (PTF). This measurement ...builds on a detailed study of the PTF transient detection efficiencies and uses a Monte Carlo simulation of the PTF survey. We measure the volumetric rate of calcium-rich transients to be higher than previous estimates: events yr−1 Mpc−3. This is equivalent to 33%-94% of the local volumetric Type Ia supernova rate. This calcium-rich transient rate is sufficient to reproduce the observed calcium abundances in galaxy clusters, assuming an asymptotic calcium yield per calcium-rich event of ∼0.05 . We also study the PTF detection efficiency of these transients as a function of position within their candidate host galaxies. We confirm as a real physical effect previous results that suggest that calcium-rich transients prefer large physical offsets from their host galaxies.
A low quiescent current digital low-dropout (DLDO) voltage regulator with fast-transient response time is proposed for self-powered wireless sensor applications operating at near/subthreshold supply ...voltage. The D-LDO regulator incorporates both hill-climbing and binary search algorithms (HCBS) in the control logic, thus leveraging on each other's strengths to minimize the output voltage's ripple and the quiescent current during the steady-state period as well as output voltage's spike and response time during the transition period. Additional features such as hysteresis mode control and freeze mode control are incorporated into the system to improve the performance of the D-LDO regulator. A dynamic comparator is proposed for the near/subthreshold supply voltage operation, which minimizes the voltage error and improves the maximum operating frequency. Fabricated in 130-nm CMOS technology, the D-LDO regulator regulates the output voltage V OUT from 350 to 1150 mV, while the input supply voltage VIN ranges from 450 to 1200 mV. At a V OUT of 450 mV, V IN of 500 mV and an operating frequency of 10 MHz, the regulator delivers 1500-μA load current with I QUIESCENT of 8.9 μA and a transient response time of 1.6 μs. The maximum current and power efficiencies reach 99.9% and 89.9%, respectively. The measured line regulation and load regulation are 1.6 and 0.6 mV/mA, respectively.
Intracranial atherosclerotic disease (ICAD) is a major etiologic cause for acute ischemic stroke (AIS) and transient ischemic attack (TIA). The study was designed to investigate if differential ...morphological features exist in symptomatic atherosclerotic lesions between AIS and TIA patients.
The culprit plaques from 45 AIS patients and 42 TIA patients were analyzed for the degree of stenosis, vessel wall irregularity, normalized wall index (NWI), remodeling index, plaque-wall contrast ratio (CR), high signal intensity on T1-weighted images, plaque enhancement ratio and enhancement grade. These plaque features along with clinical characteristics were compared between AIS and TIA groups as well as between their stenosis degree-matched subgroups.
Overall, grade 2 enhancement (OR 3.85, 95%CI 1.42–10.46, p = 0.006) and hyperlipidemia (OR 3.04, 95%CI 1.13–8.22, p = 0.025) were independent indicators for AIS, whereas high NWI (OR 1.47, 95%CI 0.76–2.86, p = 0.004) was associated with TIA. In the comparison between the subgroups with moderate (30%–69%) stenosis, high plaque-wall CR (OR 5.38, 95%CI 1.39–20.75, p = 0.008) was associated with AIS, whereas high NWI (OR 2.50, 95%CI 0.61–10.00, p = 0.006) was associated with TIA.
Our study reveals differential morphological features in symptomatic ICAD lesions between AIS and TIA patients. Probing these features with MR vessel wall imaging may provide insights into the prognosis of patients with ICAD.
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•Differential plaque features were found between stroke and transient ischemic attack.•Grade 2 enhancement and high plaque-wall contrast ratio were associated with stroke.•High normalized wall index was associated with transient ischemic attack.
Resonant converters, especiallyLLC converters, are deployed in many applications thanks to their reliability and high efficiency. With the introduction of wide band gap (WBG) devices and the soft ...switching feature of the LLC converter, the switching frequency of the LLC can be pushed to the order of megahertz, to shrink the converter size and increase the power density. However, magnetic design and control challenges stand in the way of doing so. This article addresses the challenges of high-frequency magnetic design for the LLC converter, and presents an overview for the latest solutions on the magnetic design of the LLC transformer. The matrix transformer is suitable for an LLC converter where high output current at high frequency is required. Different integration methods for the matrix transformer are discussed and demonstrations of hardware prototypes are provided. The dynamic behavior of the LLC converter presents another significant challenge against deploying an LLC converter in applications where fast transient response is needed. This article discusses such challenges as well and provides an overview on the latest control techniques, including average current-mode control, charge control, and simplified optimal trajectory control, to improve the dynamic performance of an LLC converter. A 1 megahertz LLC converter with digital control is presented, using simplified optimal trajectory control with improved transient performance over a wide frequency range.
Affected by the current limitation, the operation of grid-forming (GFM) voltage source converters (VSCs) will be switched from a voltage source mode to a current source mode under grid faults. This ...mode switching may exacerbate the transient synchronization stability of GFM-VSCs. To enhance the transient synchronization stability under mode switching, a dynamic current limiting strategy is proposed in this article. By establishing the Lyapunov energy function, the transient synchronization stability criterion of GFM-VSCs under mode switching is obtained and the effect of different saturated currents is investigated. It reveals that the transient synchronization stability of GFM-VSCs can be improved by appropriately adjusting saturated current phases when the saturated current amplitude is fixed. Based on the stability criterion, the transient stability region is clearly described and the optimal saturated current phase of GFM-VSCs is derived. The investigation illustrates that the transient synchronization stability of GFM-VSCs can be guaranteed by designing active and reactive current limits with the optimal saturated current phase. Therefore, a dynamic current limiting strategy based on the optimal active and reactive current distribution is proposed. With this strategy, GFM-VSCs can not only avoid being damaged by the overcurrent under faults but also keep transient synchronization stability after mode switching. The effectiveness of the proposed dynamic current limiting strategy is verified by simulations and hardware-in-the-loop experiments.
With the wide application of inverter-fed motors (IFMs), it is necessary to monitor the groundwall (GW) insulation status to guarantee the reliable operation of motor drive system. This article first ...proposes a mathematical model of leakage current in IFM to analyze its time domain characteristics, and then an online GW insulation monitoring method is proposed based on the transient characteristics of leakage current. By using the initial oscillation amplitude, oscillation period, and attenuation time of leakage current, the phase, position, and severity of GW insulation degradation can be identified. The proposed method is validated using an IFM, and the experimental results agree well with theoretical analysis.
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