Time-domain science has undergone a revolution over the past decade, with tens of thousands of new supernovae (SNe) discovered each year. However, several observational domains, including SNe within ...days or hours of explosion and faint, red transients, are just beginning to be explored. Here we present the Young Supernova Experiment (YSE), a novel optical time-domain survey on the Pan-STARRS telescopes. Our survey is designed to obtain well-sampled griz light curves for thousands of transient events up to z 0.2. This large sample of transients with four-band light curves will lay the foundation for the Vera C. Rubin Observatory and the Nancy Grace Roman Space Telescope, providing a critical training set in similar filters and a well-calibrated low-redshift anchor of cosmologically useful SNe Ia to benefit dark energy science. As the name suggests, YSE complements and extends other ongoing time-domain surveys by discovering fast-rising SNe within a few hours to days of explosion. YSE is the only current four-band time-domain survey and is able to discover transients as faint as ∼21.5 mag in gri and ∼20.5 mag in z, depths that allow us to probe the earliest epochs of stellar explosions. YSE is currently observing approximately 750 deg2 of sky every 3 days, and we plan to increase the area to 1500 deg2 in the near future. When operating at full capacity, survey simulations show that YSE will find ∼5000 new SNe per year and at least two SNe within 3 days of explosion per month. To date, YSE has discovered or observed 8.3% of the transient candidates reported to the International Astronomical Union in 2020. We present an overview of YSE, including science goals, survey characteristics, and a summary of our transient discoveries to date.
With the increasing penetration of voltage source converters (VSC) in the modern power grid, the transient stability of grid-following converters has attracted extensive attention. During grid ...faults, instabilities of the grid-following converter might happen which mainly originates from the phase-locked loop (PLL) being not synchronized with the grid. In the existing research, current dynamics is considered to be very fast and its effect on the transient synchronization stability can be ignored. However, in the case of high-power converters used for large wind turbines, the bandwidth of the current loop cannot be designed too high due to low switching frequency. Neglecting the coupling effect on the synchronization stability will lead to wrong conclusions. This paper firstly proposes an improved equal-area criterion to show that the current dynamics change the accelerating and decelerating area and might deteriorate the stability, which reveals that the coupling effect of current and PLL is non-negligible. Accordingly, a refined fourth-order nonlinear model is proposed to describe the coupling effect of the current loop and PLL, which is utilized to give the bandwidth boundary whether the current dynamics can be ignored. Simulations and experiments are performed to verify the correctness of the proposed nonlinear model.
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.
This paper proposes a specifically designed parallel partial Gaussian process (PPGP) for large-scale probabilistic power system transient stability assessment (TSA). The differential and algebraic ...equations with uncertain resources are defined and reformulated regarding uncertainty quantification. The challenges of probabilistic TSA in large-scale systems are investigated and the necessity of introducing efficient modeling approaches is emphasized. PPGP inherits the advantages of Gaussian process modeling, including data-driven modeling that does not require the knowledge of input distribution and can effectively quantify the confidence interval of the estimate. It accelerates the model construction and evaluation by reducing the number of parameters to be estimated. In addition, thanks to the enhancement techniques via isotropic kernel, reparameterization, and composite likelihood, PPGP is able to achieve probabilistic TSA under high uncertainty conditions while maintaining very high computational efficiency. A theoretical analysis of the time complexity of PPGP is provided. Comparison results with the Latin hypercube sampling method, many single Gaussian processes, and sparse Gaussian process methods on the Texas 2000- bus system with 471 PVs and 470 wind generations highlight the significantly improved model efficacy and efficiency of the proposed method. Furthermore, experimental validation demonstrates the proposed method's efficacy in handling the co-existence of both stable and unstable cases.
This study presents the quantitative transient stability assessment and comparison for conventional synchronous generator (SG) and wind turbine generators (WTGs) by studying the impact of the fault ...clearing time, the grid coupling, the inertia constant, the generator terminal voltage sag and the slip on fault responses. The assessment and comparison is performed by evaluating the transient stability index through the modified transient energy function. Simulation results show WTGs exhibit different transient responses on the occurrence of faults as compared with conventional SG. This justifies the necessity of study in greater depth for reliable operation of conventional power systems with the integration of large wind power.
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.
Display omitted
•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.
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.
Data-driven transient stability assessment (TSA) models are usually sensitive to system scale changes and require dynamic information from time-domain simulation (TDS) as inputs. We propose a S ...ystem-sc A le- F re E T ransient C ontingency S creening (SAFE-TCS) scheme based on only the steady-state measurements. An analytical model is set up to estimate the state variation at fault occurrence (<inline-formula><tex-math notation="LaTeX">t_{0+}</tex-math></inline-formula>) snapshot, which forms multi-graph inputs together with the steady-state information. A novel pooling-ensemble multi-attention graph convolutional network (PE-MAGCN) realizes the spatio-temporal graph embedding, in which an inter-graph convolution link works for the temporal abstraction. Following a pooling-ensemble mechanism, PE-MAGCN derives a fixed-size expressive vector for task-specific networks. This promotes the robustness of the model against system extension. The advantages of SAFE-TCS also benefit from the coordination of various training tricks, including channel attention, category-balanced sampling and joint-decoupling learning, etc. Test results on IEEE 39 Bus system and IEEE 300 Bus system indicate the superiority of the proposed scheme over existing models and its adaptability under various scenarios.
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.
PDF
