Increase in power consumption can cause serious stability problems in electric power systems if there are no ongoing or impending construction projects of new power plants or transmission lines. ...Additionally, such increase can result in large power losses of the system. In costly and environmentally effective manner to avoid constructing the new infrastructures such as power plants, transmission lines, etc., the distributed generation (DG) has been paid great attention so far as a potential solution for these problems. The beneficial effects of DG mainly depend on its location and size. Therefore, selection of optimal location and size of the DG is a necessary process to maintain the stability and reliability of existing system effectively before it is connected to a power grid. However, the systematic and cardinal rule for this issue is still an open question. In this paper, a method to determine the optimal locations of multiple DGs is proposed by considering power loss. Also, their optimal sizes are determined by using the Kalman filter algorithm.
This paper proposes a torque limit-based inertial control scheme of a doubly-fed induction generator (DFIG) that supports the frequency control of a power system. If a frequency deviation occurs, the ...proposed scheme aims to release a large amount of kinetic energy (KE) stored in the rotating masses of a DFIG to raise the frequency nadir (FN). Upon detecting the event, the scheme instantly increases its output to the torque limit and then reduces the output with the rotor speed so that it converges to the stable operating range. To restore the rotor speed while causing a small second frequency dip (SFD), after the rotor speed converges the power reference is reduced by a small amount and maintained until it meets the reference for maximum power point tracking control. The test results demonstrate that the scheme can improve the FN and maximum rate of change of frequency while causing a small SFD in any wind conditions and in a power system that has a high penetration of wind power, and thus the scheme helps maintain the required level of system reliability. The scheme releases the KE from 2.9 times to 3.7 times the Hydro-Québec requirement depending on the power reference.
This article proposes a new integrated dc-dc conversion system (IDCS) with dual-output phase-shift control for electric vehicles (EVs). The conventional dc-dc conversion system for EVs requires each ...dc-dc converter for on-board charger (OBC), traction converter (TC), and low-voltage dc-dc converter (LDC). It leads to the increase in the number of total components, overall volume, weight, and cost. Therefore, many studies on integrated power converter have been made to solve these problems. Nevertheless, they still need additional components and have drawbacks, such as high-voltage stress, nonisolation characteristics, and hard switching. To overcome these limitations, the new IDCS, which integrates the dc-dc converters of OBC, TC, and LDC at once is proposed. The proposed IDCS performs all functions of each dc-dc converter of OBC, LDC, and TC, while effectively reducing the total number of components and cost. In particular, it performs two simultaneous operations. One is to charge both the high-voltage battery and low-voltage battery (LVB) at the same time, and the other is to regulate the dc-link voltage, while charging the LVB. Moreover, the proposed IDCS increases the overall efficiency by synchronous rectification control. The featured characteristic and operational principles of proposed IDCS are first explained. Then, its design specifications are carefully investigated. Finally, the practical effectiveness is verified by experimental tests on the hardware prototype of 1.5 kW.
This paper presents an improved cascaded dual-buck AC-AC converter that requires fewer inductors, resulting in increased power density and reduced converter cost. By utilizing standard low-voltage ...rating devices, the proposed converter is capable of achieving a higher output voltage. In addition, the proposed converter is not affected by the current shoot-through and does not need dead-time. Furthermore, it does not need lossy snubber circuits or dedicated pulse width modulation (PWM) strategies. Moreover, the proposed converter enhances efficiency by utilizing MOSFETs and eliminates the loss of reverse recovery and related issues by disabling their body diodes.These features allow the proposed converter to be designed with a reduced level of control complexity, high reliability, high efficiency and obtain output waveforms with less distortion. To decrease the volume of inductors and capacitors, the cascaded units are operated using a phase-shifted PWM scheme. To confirm the practicability of the proposed converter, both the simulation and experimental results of the two-unit 2 kW cascaded AC-AC converter with 220 <inline-formula><tex-math notation="LaTeX">{{V}_{rms}}</tex-math></inline-formula> input voltage, and 350 <inline-formula><tex-math notation="LaTeX">{{V}_{rms}}</tex-math></inline-formula> output voltage is provided.
Introduction
The comparative efficacy of various bariatric procedures has not been completely elucidated. We aimed to evaluate efficacy and safety of various bariatric procedures comprehensively.
...Methods
We searched for randomized controlled trials investigating the efficacy of bariatric surgery. Network meta-analyses were performed to determine the percentage of excess weight loss (%EWL) and remission of diabetes mellitus (DM).
Results
Of 45 studies, 33 and 24 provided the data for %EWL and DM remission rates, respectively. Six months after surgery, biliopancreatic diversion with duodenal switch (BPD-DS), Roux-en-Y gastric bypass (RYGB), and sleeve gastrectomy (SG) showed superior efficacy for %EWL compared to the standard-of-care (mean difference MD, 95% confidence interval CI: BPD-DS, 38.2% 7.3%, 69.1%; RYGB, 32.1% 3.1%, 61.1%; SG, 32.5% 5.5%, 59.5%). However, adjustable gastric banding was not superior to standard-of-care (MD 95% CI = − 0.2% − 19.6%, 19.2%). At 1 year, all bariatric procedures were superior to standard-of-care. At 3 years, RYGB and SG showed superior efficacy when compared to standard-of-care (MD 95% CI: RYGB, 45.0% 21.8%, 68.2%; SG, 39.2% 15.2%, 63.3%). With respect to DM remission 3–5 years after surgery, BPD-DS, RYGB, and SG were superior to standard-of-care. Hernias, obstruction/stricture, bleeding, and ulcers were less common in patients who underwent SG than in those who underwent RYGB.
Conclusions
RYGB and SG had excellent long-term outcomes for both the %EWL and DM remission rates. Additionally, SG had a relatively lower risk of adverse events than RYGB.
Background and Aim
We conducted a nationwide validation study of diagnostic algorithms to identify cases of inflammatory bowel disease (IBD) within the Korea National Health Insurance System (NHIS) ...database.
Method
Using the NHIS dataset, we developed 44 algorithms combining the International Classification of Diseases (ICD)‐10 codes, codes for Rare and Intractable Diseases (RID) registration and claims data for health care encounters, and pharmaceutical prescriptions for IBD‐specific drugs.
For each algorithm, we compared the case identification results from electronic medical records data with the gold standard (chart‐based diagnosis). A multiple sampling test verified the validation results from the entire study population.
Results
A random nationwide sample of 1697 patients (848 potential cases and 849 negative control cases) from 17 hospitals were included for validation. A combination of the ICD‐10 code, ≥ 1 claims for health care encounters, and ≥ 1 prescription claims (reference algorithm) achieved excellent performance (sensitivity, 93.1% 95% confidence interval 91–94.7; specificity, 98.1% 96.9–98.8; positive predictive value, 97.5% 96.1–98.5; negative predictive value, 94.5% 92.8–95.8) with the lowest error rate (4.2% 3.3–5.3). The multiple sampling test confirmed that the reference algorithm achieves the best performance regarding IBD diagnosis. Algorithms including the RID registration codes exhibited poorer performance compared with that of the reference algorithm, particularly for the diagnosis of patients affiliated with secondary hospitals. The performance of the reference algorithm showed no statistical difference depending on the hospital volume or IBD type, with P‐value < 0.05.
Conclusions
We strongly recommend the reference algorithm as a uniform standard operational definition for future studies using the NHIS database.
The preparation of 2D layered SnS2 nanoplates with nanoscale lateral confinement (less than 150 nm) is described (see figure). Their unique nanoscale characteristics, including finite lateral 2D ...morphology, make the discharge capacity of Li ion batteries remarkably high‐almost close to the theoretical possible value.
This paper describes the development of a new buck cascaded buck-boost power factor correction (PFC) converter of 2 kW with a soft-switching technique. For its wide range of input voltage, it ...operates in both buck and boost modes. The parameters are properly selected to endure voltage and current stress in all operating ranges. In addition, the electromagnetic interference (EMI) filter is used to reduce the EMI noise and guarantee continuous input current in buck operation. Moreover, the zero-voltage-transient pulse-width-modulation (ZVT-PWM) method is applied to improve the overall efficiency of the converter. The performance of the proposed PFC converter with the widest range of input voltage is evaluated by the hardware experimental test including harmonics analysis based on the International Electrotechnical Commission standard in all operating ranges. Also, the variations of power factor are theoretically analyzed in both buck and boost modes to determine the widest input range of the proposed PFC converter of 2 kW with an EMI filter. These are strongly required to commercialize it in practice. Finally, the efficiency of proposed PFC converter is compared with that of a conventional buck cascaded buck-boost PFC converter under various conditions.
Although archaea, Gram-negative bacteria, and mammalian cells constitutively secrete membrane vesicles (MVs) as a mechanism for cell-free intercellular communication, this cellular process has been ...overlooked in Gram-positive bacteria. Here, we found for the first time that Gram-positive bacteria naturally produce MVs into the extracellular milieu. Further characterizations showed that the density and size of Staphylococcus aureus-derived MVs are both similar to those of Gram-negative bacteria. With a proteomics approach, we identified with high confidence a total of 90 protein components of S. aureus-derived MVs. In the group of identified proteins, the highly enriched extracellular proteins suggested that a specific sorting mechanism for vesicular proteins exists. We also identified proteins that facilitate the transfer of proteins to other bacteria, as well to eliminate competing organisms, antibiotic resistance, pathological functions in systemic infections, and MV biogenesis. Taken together, these observations suggest that the secretion of MVs is an evolutionally conserved, universal process that occurs from simple organisms to complex multicellular organisms. This information will help us not only to elucidate the biogenesis and functions of MVs, but also to develop therapeutic tools for vaccines, diagnosis, and antibiotics effective against pathogenic strains of Gram-positive bacteria.
