859 research outputs found
Real-Time Dynamic Simulation of Korean Power Grid for Frequency Regulation Control by MW Battery Energy Storage System
The aim of this study was to develop a real-time dynamic simulator of a power grid with power plant and battery model. The simulator was used to investigate the frequency control characteristics of a megawatt-scale high-capacity energy storage system connected to the electric power grid. In this study, a lithium-ion secondary battery was chosen as one of the batteries for a grid-connected model. The dynamics of the model was analysed in both steady and transient states. The frequency control system of the battery model plays a role in regulating the grid frequency by controlling the power of energy storage systems according to process variables and grid frequencies. The power grid model based on the current power network of South Korea, included power plants, substations and power demands. The power supply is classified by the type of turbine generator as thermal, nuclear, hydro power, pumped power storage, combined power plants and batteries, including high-capacity energy storage systems rated for a maximum of 500 MW. This study deals with an installed capacity of 87.17 GW and peak load of 77.30 GW in the Korean power grid. For 24 hours of operation, the maximum and minimum power outputs were simulated as 61.59 GW and 46.32 GW, respectively. The commercialized real-time dynamic simulation software ProTRAX was used. The simulation was conducted to observe the operation characteristics of the frequency control system during a breakdown of power plants, as well as under governor-free operation, auto generation control operation, and with the battery energy storage system connected. The results show that the model is valid for each power plant breakdown simulation. They also confirm that the output power and frequency controls of the battery operated well during simulations
Review of virtual power plant applications for power system management and vehicle-to-grid market development
The use of renewable energy sources and energy storage systems is increasing due to new policies in the energy industries. However, the increase in distributed generation hinders the reliability of power systems. In order to stabilize power systems, a virtual power plant has been proposed as a novel power grid management system. The virtual power plant plays includes different distributed energy resources and energy storage systems. We define a core virtual power plant technology related to demand response and ancillary service for the cases of Korea, America, and Europe. We also suggest applications of the proposed virtual power plant to the vehicle-to-grid market for restructuring national power industries in Korea
Angiolipoma of the Posterior Mediastinum with Extension into the Spinal Canal: A Case Report
Angiolipoma is a rare benign soft tissue tumor, an unusual variant of lipoma, consisting of fatty and vascular components and located in the subcutis, usually in the trunk and extremities. We report a case of posterior mediastinal angiolipoma extending into the spinal canal and showing both fat and angiomatous features on CT scan
Oxygen Partial Pressure during Pulsed Laser Deposition: Deterministic Role on Thermodynamic Stability of Atomic Termination Sequence at SrRuO3/BaTiO3 Interface
With recent trends on miniaturizing oxide-based devices, the need for
atomic-scale control of surface/interface structures by pulsed laser deposition
(PLD) has increased. In particular, realizing uniform atomic termination at the
surface/interface is highly desirable. However, a lack of understanding on the
surface formation mechanism in PLD has limited a deliberate control of
surface/interface atomic stacking sequences. Here, taking the prototypical
SrRuO3/BaTiO3/SrRuO3 (SRO/BTO/SRO) heterostructure as a model system, we
investigated the formation of different interfacial termination sequences
(BaO-RuO2 or TiO2-SrO) with oxygen partial pressure (PO2) during PLD. We found
that a uniform SrO-TiO2 termination sequence at the SRO/BTO interface can be
achieved by lowering the PO2 to 5 mTorr, regardless of the total background gas
pressure (Ptotal), growth mode, or growth rate. Our results indicate that the
thermodynamic stability of the BTO surface at the low-energy kinetics stage of
PLD can play an important role in surface/interface termination formation. This
work paves the way for realizing termination engineering in functional oxide
heterostructures.Comment: 27 pages, 6 figures, Supporting Informatio
Persistent Pain Is Dependent on Spinal Mitochondrial Antioxidant Levels
Reactive oxygen species (ROS) scavengers have been shown to relieve persistent pain; however, the mechanism is not clearly understood.
Superoxide produced from mitochondrial oxidative phosphorylation is considered the major source of ROS in neurons during excitation
where mitochondrial superoxide levels are normally controlled by superoxide dismutase (SOD-2). The present study hypothesizes that
capsaicin-induced secondary hyperalgesia is a consequence of superoxide build-up in spinal dorsal horn neurons and SOD-2 is a major
determinant. To test this hypothesis, the spinal levels of SOD-2 activity, inactivated SOD-2 proteins, and mitochondrial superoxide were
measured and correlated to the levels of capsaicin-induced secondary hyperalgesia in mice with and without SOD-2 manipulations. The
data suggest that superoxide accumulation is a culprit in the abnormal sensory processing in the spinal cord in capsaicin-induced
secondary hyperalgesia. Our studies also support the notion that SOD-2 nitration is a critical mechanism that maintains elevated
superoxide levels in the spinal cord after capsaicin treatment. Finally, our findings suggest a therapeutic potential for the manipulation
of spinal SOD-2 activity in pain conditions.This work was supported by National Institutes of Health Grants R01 NS31680 and P01 NS11255
Gravitating Self-dual Chern-Simons Solitons
Self-dual solitons of Chern-Simons Higgs theory are examined in curved
spacetime. We derive duality transformation of the Einstein Chern-Simons Higgs
theory within path integral formalism and study various aspects of dual
formulation including derivation of Bogomolnyi type bound. We find all possible
rotationally-symmetric soliton configurations carrying magnetic flux and
angular momentum when underlying spatial manifolds of these objects comprise a
cone, a cylinder, and a two sphere.Comment: 38 pages, 8 figures (Pslatex files are included in the text.) Two
references are added. To appear in Annals of Physic
IκB kinase (IKK)β, but not IKKα, is a critical mediator of osteoclast survival and is required for inflammation-induced bone loss
Transcription factor, nuclear factor κB (NF-κB), is required for osteoclast formation in vivo and mice lacking both of the NF-κB p50 and p52 proteins are osteopetrotic. Here we address the relative roles of the two catalytic subunits of the IκB kinase (IKK) complex that mediate NF-κB activation, IKKα and IKKβ, in osteoclast formation and inflammation-induced bone loss. Our findings point out the importance of the IKKβ subunit as a transducer of signals from receptor activator of NF-κB (RANK) to NF-κB. Although IKKα is required for RANK ligand-induced osteoclast formation in vitro, it is not needed in vivo. However, IKKβ is required for osteoclastogenesis in vitro and in vivo. IKKβ also protects osteoclasts and their progenitors from tumor necrosis factor α–induced apoptosis, and its loss in hematopoietic cells prevents inflammation-induced bone loss
Risk Factors for Recurrence of Symptomatic Common Bile Duct Stones after Cholecystectomy
Purpose. The recurrence of CBD stone is still observed in a considerable number of patients. The study was to evaluate the risk factors for recurrence of symptomatic CBD stone in patients who underwent cholecystectomy after the removal of CBD stone. Methods. The medical records of patients who underwent removal of CBD stone with subsequent cholecystectomy were reviewed. The risk factors for the recurrence of symptomatic CBD stone were compared between the recurrence and the nonrecurrence group. Results. The mean follow-up period was 40.6 months. The recurrence of symptomatic CBD stones was defined as the detection of bile duct stones no sooner than 6 months after complete clearance of CBD stones, based on symptoms or signs of biliary complication. 144 patients (68 males, 47.2%) were finally enrolled and their mean age was 59.8 (range: 26~86) years. The recurrence of CBD stone occurred in 15 patients (10.4%). The mean period until first recurrence was 25.9 months. The presence of type 1 or 2 periampullary diverticulum and multiple CBD stones were the independent risk factors. Conclusion. For the patients with type 1 or 2 periampullary diverticulum or multiple CBD stones, careful followup is needed for the risk in recurrence of symptomatic CBD stone
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