With the increasing use of voltage source converters (VSCs) in power electronics dominated power systems, oscillation phenomena in DC-link voltage control (DVC) timescale (around 10 Hz) among ...multiple VSCs have occurred. Several studies have tried to analyze these oscillation problems, but all associated with the single VSC situation. To consider the dynamic interactions between VSCs in DVC timescale, especially in the weak grid condition, this paper presents a small-signal model to understand VSC external characteristics based on motion equation concept also featured in synchronous generator (SG). Comparisons of time-domain simulation responses and eigenvalues show that the proposed model can hold the main behaviors of concern. The form of the model is very similar to the rotor motion equation in SG, with which power engineers have been very familiar. In addition, by establishing the relationship between the unbalanced powers and state variables of internal voltage (viz., VSC output voltage), the modeling idea introduced in this paper can be applied to other power electronic devices.
The dynamics of coronavirus disease 2019 (COVID-19) transmissibility are yet to be fully understood. Better understanding of the transmission dynamics is important for the development and evaluation ...of effective control policies.
To delineate the transmission dynamics of COVID-19 and evaluate the transmission risk at different exposure window periods before and after symptom onset.
This prospective case-ascertained study in Taiwan included laboratory-confirmed cases of COVID-19 and their contacts. The study period was from January 15 to March 18, 2020. All close contacts were quarantined at home for 14 days after their last exposure to the index case. During the quarantine period, any relevant symptoms (fever, cough, or other respiratory symptoms) of contacts triggered a COVID-19 test. The final follow-up date was April 2, 2020.
Secondary clinical attack rate (considering symptomatic cases only) for different exposure time windows of the index cases and for different exposure settings (such as household, family, and health care).
We enrolled 100 confirmed patients, with a median age of 44 years (range, 11-88 years), including 44 men and 56 women. Among their 2761 close contacts, there were 22 paired index-secondary cases. The overall secondary clinical attack rate was 0.7% (95% CI, 0.4%-1.0%). The attack rate was higher among the 1818 contacts whose exposure to index cases started within 5 days of symptom onset (1.0% 95% CI, 0.6%-1.6%) compared with those who were exposed later (0 cases from 852 contacts; 95% CI, 0%-0.4%). The 299 contacts with exclusive presymptomatic exposures were also at risk (attack rate, 0.7% 95% CI, 0.2%-2.4%). The attack rate was higher among household (4.6% 95% CI, 2.3%-9.3%) and nonhousehold (5.3% 95% CI, 2.1%-12.8%) family contacts than that in health care or other settings. The attack rates were higher among those aged 40 to 59 years (1.1% 95% CI, 0.6%-2.1%) and those aged 60 years and older (0.9% 95% CI, 0.3%-2.6%).
In this study, high transmissibility of COVID-19 before and immediately after symptom onset suggests that finding and isolating symptomatic patients alone may not suffice to contain the epidemic, and more generalized measures may be required, such as social distancing.
Although the positive associations between social capital, household income and life satisfaction are well documented, little is known about how income actually shapes the relation between structural ...social capital and life satisfaction. This study investigates the roles of economic condition in determining the relationships between life satisfaction and three aspects of structural social capital, namely network size, neighborhood interaction and social participation. This study uses a random sample of 6002 adults nested in 2365 families from three regions in China: Beijing, Shanghai and Guangdong-province and applies multilevel linear regression models. The results firstly show that household income and structural social capital are positively associated with life satisfaction. Further analyses on the interaction effects find that household income substantively reduces the association between a social network size and life satisfaction but increases the relationship between social participation and life satisfaction. In addition, the differences between families explain about 25 % unexplained variances of life satisfaction.
A multiple resonance thermally activated delayed fluorescence (MR‐TADF) molecule with a fused, planar architecture tends to aggregate at high doping ratios, resulting in broad full width at half ...maximum (FWHM), redshifting electroluminescence peaks, and low device efficiency. Herein, we propose a mono‐substituted design strategy by introducing spiro‐9,9′‐bifluorene (SBF) units with different substituted sites into the MR‐TADF system for the first time. As a classic steric group, SBF can hinder interchromophore interactions, leading to high device efficiency (32.2–35.9 %) and narrow‐band emission (≈27 nm). Particularly, the shield‐like molecule, SF1BN, seldom exhibits a broadened FWHM as the doping ratio rises, which differs from the C3‐substituted isomer and unhindered parent emitter. These results manifest an effective method for constructing highly efficient MR‐TADF emitters through a spiro strategy and elucidate the feasibility for steric modulation of the spiro structure in π‐framework.
By incorporating a three‐dimensional spiro unit into multiple resonance thermally activated delayed fluorescence emitters, the device efficiency is increased to nearly 1.5 times that of the unhindered emitter. Notably, the linkage pattern with spatial interaction and hindrance can maintain the narrow FWHM and curb unfavorable redshifts at a high doping ratio.
Legislations for greenhouse gas and pollutant emissions from light-duty vehicles are pushing the spark ignition engine to be cleaner and more efficient. As one of the promising solutions, enhancing ...the ignition energy shows great potential in simultaneously mitigating combustion knock and enabling lean-burn operation. Featured with distributed ignition sites, pre-chamber ignition systems with large or small pre-chamber volumes, auxiliary or no auxiliary fueling, and large or small orifices have gained a surge of interest in decreasing the fuel consumption and pollutant emissions.
This paper aims at presenting a comprehensive review of recent progress and development trends of pre-chamber ignition systems adopted on future low-carbon and low-emission spark ignition engines. First, mechanisms behind this technology are discussed from the perspectives of the pre-chamber scavenging and combustion, jet ejection, main chamber combustion, and emission formations. Second, the design criteria of pre-chamber geometries are presented in detail, followed by a discussion on the fuel and air management for the main chamber. Next, recent numerical and experimental studies on the pre-chamber ignition system and its applications in conjunction with other complementary technologies are summarized. Finally, critical issues for commercialization and future research directions are discussed.
•The turbulent jet ignition applied on future gasoline engines was fully reviewed.•Mechanisms of scavenging and combustion in the pre- and main chambers were discussed.•Design criteria of pre-chamber geometries were presented in detail.•Recent numerical and experimental studies on the turbulent jet ignition were compared.•Critical issues in commercialization were summarized.
A potential concern is that their study only included cases that had a single exposure event and a 1-day exposure window. A more flexible case-selection approach might reduce bias, even though this ...approach would require methods to address uncertainty in actual infection timing. Using more comprehensive exposure windows, the estimated mean incubation period in Taiwan was 3.5 (95% CI 3.1–4.0) days, longer than Tanaka et al.’s estimates (1,2) but similar to estimates of 3.5 days from Italy (data collected during January 2022) (3) and South Korea (data collected during November–December 2021) (4) and estimates from a systematic review (3.6 days) (5).
This article investigates the event‐triggered consensus problem of general linear multiagent systems with denial‐of‐service (DoS) attacks. A distributed event‐triggered mechanism is presented to ...alleviate the limited communication resources, the designed mechanism is fully distributed owing to the introduction of some adaptive parameters. Moreover, since the DoS attacks have been considered in the event‐triggered rule design, a switching strategy for the adaptive parameters is adopted. A switching Lyapunov function is used to strictly demonstrate that secure consensus can be reached effectively under the proposed control mechanism. The quantitative relationship between the frequency of the DoS attacks and the consensus is also presented. Moreover, the Zeno behaviour can be excluded for the studied close‐looped systems. Finally, a numerical simulation example is given to demonstrate the validity of the designed control law.
This article investigates the event‐triggered consensus problem of general linear multiagent systems with denial‐of service attacks. Novel fully distributed control law and event‐triggered rule are designed without any usage of global information. Simulation examples are given to illustrate the validity of the designed control strategy.
Boron neutron capture therapy (BNCT) is a promising therapy for refractory cancer based on the cytotoxic reaction of 10B (n, α) 7Li. Although two BNCT agents are clinically available, they are ...quickly metabolized and show modest enrichment in tumor sites, partially limiting BNCT widespread application. Consequently, novel agents that perform active targeting and show good biocompatibility have to be developed. Herein, boronophenylalanine‐containing polydopamine (B‐PDA) nanoparticles are easily fabricated by encapsulating boronophenylalanine (BPA) in polydopamine via nitrogen‐boronate coordination. In this study, B‐PDA achieves increased tumor accumulation and prolonged retention effects in the tumor site and superior antitumor activity post neutron irradiation in the orthotopic xenograft glioma model. In brief, this study offers a novel strategy for BPA delivery and may broaden the perspective on nanomedicine design for BNCT.
The boronophenylalanine‐containing polydopamine (B‐PDA) nanoparticles developed in this study are a promising and favorable candidate for boron neutron capture therapy (BNCT) against glioma, which achieve sufficient tumor accumulation and retention for neutron irradiation. After irradiation, BNCT largely induced DNA double‐strand breaks to produce excellent antitumor effects. The B‐PDA nanoparticles are potential to be used for BNCT against glioma.
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