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A previously unidentified duality between buck and boost configured dc‐ac modular multilevel converters (MMCs) is firstly revealed. Armed with this insight, a new dual‐active‐bridge (DAB)‐MMC is proposed for high‐voltage dc (HVDC)‐to‐medium‐voltage dc (MVDC) power conversion that utilizes cascaded buck and boost dc–ac stages to obtain high dc step ratios. Single‐phase and three‐phase variants are presented. When compared with the conventional DAB‐MMC solution for the same dc step ratio, both the single‐phase and three‐phase topologies offer reduced MVDC side transformer winding current stresses, while the three‐phase topology also yields reduced MVDC side MMC submodule current stresses. The former is achieved by having the freedom to design the transformer with a lower turns ratio, and the latter is achieved due to the inherent paralleling of submodules on the MVDC side of the converter. Analysis of the three‐phase topology reveals its low‐voltage side transformer winding current stresses can be reduced by a factor of 3.27. A generalized mathematical model of the proposed buck–boost DAB‐MMC is derived and used to propose a dynamic controller for both the single‐phase and three‐phase topologies. Real‐time simulations obtained from a real‐time digital simulator system that incorporates an FPGA‐based controller for the valve firing controls validate the proposed buck–boost DAB‐MMC operation and dynamic controls.

High-voltage direct current (HVDC) is a proven technology for grid integration of renewable energy sources such as offshore wind farms and interconnecting distributed systems to main power grids. One economical solution for electrifying rural communities is to extract a small amount of power from existing HVDC transmission lines with power electronic converters, which is called tapping. This study analyses the feasibility and system performance of parallel tapping line-commutated converter (LCC)-HVDC systems with multiple full-bridge modular multilevel converters under various fault scenarios and operating conditions. Simulation results reveal that undesirable system disturbances such as DC-link voltage sags, DC-link current overshoots, and the transient reduction of inverter extinction angle are imposed on the LCC-HVDC system in the case of tap station AC side faults. Such disturbances would endanger the reliable operation of the entire LCC-HVDC system with the parallel taps. Furthermore, this study proposes two fault mitigating schemes, i.e. a tap station current modulation controller and three supplementary controller configurations, to reduce the impact of tap station AC side faults on the LCC-HVDC system. Both fault mitigating schemes are controller-based solutions, which are augmented to the existing controllers by utilising only local measurements. The proposed schemes are verified through simulations in PSCAD/EMTDC.

The treatment and prognosis for severe acute pancreatitis (SAP) is currently unsatisfactory showing a high incidence of morbidity and mortality. Here, we investigated the effect of bone marrow-derived mesenchymal stem cells (BMSCs) on SAP in rats and explored the possible mechanisms. The common bile duct of each model rat was occluded at the liver hilum, and the induction of SAP was achieved by retrograde perfusion of 3% sodium taurocholate (NaT). Prepared BMSCs were intravenously injected via the tail vein. Pancreatic acinar cells (PACs) were isolated from rat pancreas, and induced by TNF-α. In the present study, we found that necroptosis was activated in NaT-induced acute-necrotized pancreatitis, and transplanted BMSCs could inhibit necroptosis, repair pancreatic injury, and reduce systemic inflammatory response. In addition, necrostatin-1 (Nec-1), as the inhibitor of receptor-interacting protein kinase 1 (RIPK1), could also reduce SAP to some extent. Besides, we detected that BMSCs could also promote regeneration of damaged pancreatic tissues. Furthermore, in vitro, we also investigated that BMSCs could suppress TNF-α-induced necroptosis and improve the viability of PACs. In addition, Nec-1 and knockdown of receptor-interacting protein kinase 3 (RIPK3) or mixed lineage kinase domain-like protein (MLKL) could also inhibit necrosis of PACs induced by TNF-α. BMSCs ameliorated SAP and reduced injury of PACs by suppressing the activation of the necroptosis signaling pathway.

Aims Severe acute pancreatitis (SAP) is an acute disease of the digestive system accompanied by pancreatic necrosis. We have found that bone marrow-derived mesenchymal stem cells (BMSCs) can attenuate SAP, but the underlying mechanism remains unclear. The present study was conducted to explore the possible mechanisms by which BMSCs alleviate SAP. Main methods BMSCs and BMSCs engineered to overexpress microRNA (miR)-9 (miR-9-BMSCs) were transplanted into rat models of SAP via the tail vein. Pancreatic acinar cells (PACs) were isolated from rat pancreatic tissues and induced by tumor necrosis factor-α (TNF-α) in vitro. Key findings miR-9-BMSCs significantly reduced the systemic inflammatory response, impeded the necroptosis signaling pathway and promoted regeneration of damaged pancreas in vivo. miR-9-BMSCs secreted miR-9, which targeted the gene encoding receptor interacting protein kinase 1 in PACs induced by TNF-α, to inhibit necroptosis and ameliorate SAP. Significance miR-9-BMSCs can reduce SAP-induced injury to pancreatic tissues and PACs by regulating miR-9 to suppress necroptosis.

Background Severe acute pancreatitis (SAP) is a high mortality disease, for which there is a lack of effective therapies. Previous research has demonstrated that bone marrow-derived mesenchymal stem cells (BMSCs), which have immunomodulatory and antioxidant properties, have potential for the treatment of SAP. It remains unclear, however, whether the free radical scavenger N-acetylcysteine (NAC) can enhance the therapeutic efficacy of BMSC transplantation in SAP. In this study, we investigated the effect of combining treatment with NAC and BMSCs in a rat model of SAP. Methods SAP was induced by injection of sodium taurocholate into the pancreatic duct and, after successful induction of SAP, the rats were treated with BMSCs and NAC, either singly or in combination. Results After 3 days, serum levels of amylase, proinflammatory factors, malondialdehyde, and reactive oxygen species were significantly decreased in animals treated with BMSCs or NAC, compared with vehicle-treated animals. In contrast, total glutathione, superoxide dismutase and catalase were markedly increased after treatment with BMSCs or NAC. However, oxidative stress markers and inflammatory factors were significantly improved in the SAP + BMSCs + NAC group compared with those in the SAP + NAC group and the SAP + BMSCs group. Conclusions Combined NAC and BMSC therapy was found to alleviate oxidative stress damage to the pancreas and to inhibit the inflammatory response to a significantly greater extent than single therapy with either BMSCs or NAC. Because NAC enhances the therapeutic efficacy of BMSC transplantation in a rat model of SAP, combined therapy may provide a promising new approach for the treatment of SAP.

Background and aims It has been previously verified that mesenchymal stromal cells (MSCs) have a good therapeutic effect on severe acute pancreatitis (SAP) and the potential for regeneration of damaged pancreatic tissue, but the exact molecular mechanism remains unclear. In this study, we demonstrated the therapeutic effect of bone morrow MSCs (BMSCs) on SAP, probably by targeting heme oxygenase-1 (HO-1). Methods Six hours after SAP induction, either phosphate-buffered saline (PBS) or BMSCs were transfused into the caudal vein of rats, zinc protoporphyrin (ZnPP) was administered intraperitoneally. Pancreatic pathological scoring, serum levels of amylase and inflammatory factors, as well as levels of reactive oxygen species (ROS), malondialdehyde (MDA) and myeloperoxidase (MPO), superoxide dismutase (SOD) and catalase (CAT) activity in the pancreas were evaluated. Results Our data showed that BMSCs significantly reduce inflammation and oxidative stress, reduce apoptosis and promote angiogenesis of damaged pancreas. Moreover, BMSCs increased the level of HO-1 in the serum and pancreatic tissue in rats with SAP. In addition, the protective effect of BMSCs was partially neutralized by the HO-1 activity inhibitor ZnPP, suggesting a key role of HO-1 in the therapeutic effect of BMSCs on SAP. Conclusions BMSCs ameliorated SAP, probably by inducing expression of HO-1, which can exert anti-inflammatory and anti-oxidant effects, reduce apoptosis and promote angiogenesis.

Objective Bone marrow-derived mesenchymal stem cells (BMSCs) are effective in the treatment of severe acute pancreatitis (SAP), but their therapeutic effects could still be improved. In order to optimize the clinical application of BMSCs, we adopted the strategy of resveratrol (Res) pretreatment of BMSCs (Res-BMSCs) and applied it to a rat model of sodium taurocholate (NaT)-induced acute pancreatitis. Methods SAP was induced by injection of 3% NaT into the pancreatic duct and successful induction of SAP occurred after 12 h. Rats were treated with BMSCs, Res or BMSCs primed with Res at 40 mmol/L, Vandetanib (ZD6474) daily oral dosages of 50 mg/kg vandetanib. Results Res stimulated BMSCs to secrete vascular endothelial growth factor A (VEGFA), activated the downstream phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K)/protein kinase B (AKT) signaling pathway, and inhibited pancreatic cell apoptosis. In addition, conditioned medium (CM) from Res-BMSCs enhanced the proliferation of human umbilical vein endothelial cells (HUVECs) in vitro, increased resistance to apoptosis and promoted the expression of angiogenesis-related proteins CD31, VEGF and VEGFR2 in pancreatic tissue, but Vandetanib partly abolished these effects by blocking the VEGFA- mediated pathway. Conclusion Resveratrol-preprocessed BMSCs can activate the PI3K/AKT signaling pathway in pancreatic cells and HUVECs through paracrine release of VEGFA; thus, achieving the therapeutic effect of resisting apoptosis of pancreatic cells and promoting regeneration of damaged blood vessels. Res pretreatment may be a new strategy to improve the therapeutic effect of BMSCs on SAP.

Background The optimal methods for patients with difficult biliary stones remain under debate. The aim of this study was to evaluate the role of frequency-doubled double-pulse neodymium YAG (FREDDY) laser lithotripsy for removing difficult biliary stones during laparoscopic common bile duct exploration (LCBDE). Methods Between March 2013 and January 2015, 42 consecutive patients with difficult biliary stones who underwent LCBDE with FREDDY laser lithotripsy were included in this study. The clinical data of all patients were retrospectively collected and analysed. Results Bile ducts were completely cleared in all patients. The complications related to laser lithotripsy were not noted. A total of 38 patients (90.5%) underwent primary closure of common bile duct, and T-tube drainage was applied to four patients (9.5%). No bile duct injury, bleeding and perforation were observed. There were no post-operative surgery-related deaths. Bile leakage occurred in four patients (9.5%) with primary closure procedure, and all of them were managed successfully with conservative therapy. The median follow-up period was 42.8 months, with no evidence of bile duct stricture and stone recurrence in all patients. Conclusions The LCBDE combined with FREDDY laser lithotripsy appear to be effective and safe for the treatment of difficult biliary stones.

A generalized modular multilevel converter (MMC) chain-link structure is presented that allows independent power transfer between two dc systems and one ac system. This chain-link structure is shown to give rise to two new dc-dc-ac MMC topologies suitable for MVDC and HVDC applications. Simultaneous dc-dc and dc-ac conversion is achieved by exploiting a center-tap transformer connection where the windings can carry both dc and ac currents, without leading to increased transformer rating or size when compared to a conventional two-winding ac transformer for a standard dc-ac MMC. A unified control scheme is proposed to independently control dc and ac terminals power transfers while maintaining balanced capacitor voltages for both topologies. Converter operation and the proposed dynamic controls are validated by real-time simulations obtained from RTDS system using FPGA-based low-level valve firing control.

Patients with severe acute pancreatitis (SAP) represent a substantial challenge to medical practitioners due to the high associated rates of morbidity and mortality and a lack of satisfactory therapeutic outcomes. In a previous study, our group demonstrated that bone marrow-derived mesenchymal stem cells (BMSCs) can ameliorate SAP; however, the mechanisms of action remain to be fully understood. BMSCs were intravenously injected into SAP rats 12 h after experimental induction of SAP using sodium taurocholate (NaT). Histopathological changes and the levels of pro-inflammatory mediators were assessed by hematoxylin and eosin (H&E) staining and ELISA, respectively. Autophagy levels were assessed using qRT-PCR, western blotting, immunohistochemistry, immunofluorescence, and transmission electron microscopy. AR42J cells and human umbilical vein endothelial cells (HUVECs) were administered BMSC-conditioned media (BMSC-CM) after NaT treatment, and cell viability was measured using a Cell Counting Kit-8 (CCK-8) and flow cytometry. In vivo, BMSCs effectively reduced multiple systematic inflammatory responses, suppressed the activation of autophagy, and improved intestinal dysfunction. In vitro, BMSC-CM significantly improved the viability of injured cells, promoted angiogenesis, and decreased autophagy. We therefore propose that the administration of BMSCs alleviates SAP-induced multiple organ injury by inhibiting autophagy.

This paper concentrates on the image formation algorithm for TOP (Terrain Observation by Progressive Scans) mode data processing, which ensures both the quality of focusing and the phase accuracy. Based on the three-step processing schedule, the de-rotation operation is adopted to conquer the overlap in azimuth frequency domain, and the antenna sweep rate is discussed in tail. Moreover, the classic focusing kernel is applied for range and azimuth compressing. Furthermore, phase and compression-gain compensation function is given, which is implemented after deramp operation. Finally, the simulation results justify the effectiveness and precision of the proposed phase-preserving algorithm.

Mental workload research is important to people's health and work efficiency, Psychophysiological measures such as electroencephalography (EEG), ECG and respiration measures can be used to predict mental workload level. A Multi-channel phase-space reconstruction method is proposed in this paper which rearranges signal serials by the correlation coefficients and select time delay by signal determinism. The study of determinism and correlation dimension on simulative data exhibits a good performance. The result of EEG series shows a clearly consistency to workload level variety. The method is useful for multi-channel signals nonlinear analysis and mental workload detection.

Correct sleep scoring is the base of sleep studying; nonlinear features of EEG can represent different sleep stages. In this paper, correlation dimension (D2) and approximate entropy (ApEn) of sleep EEG have been calculated. The statistical results reveal that: D2 does not come to be saturated when the embedding dimension increases, but the relative value of D2 can effectively distinguish different sleep stages. ApEn has the advantage of calculating simply, steady result and representing preferably different sleep stages. ApEn and the relative value of D2 reveal, from different point of view, the same rule about EEG (brain) complexity changing, that is, both complexity and its fluctuation are maximal in the subject's awake hour, are decreasing with the deepening of sleep, but the complexity in REM is about the level between S1 and S2.

In this paper, a multi-channel reconstruction with correlation coefficients method is present for time series' determinism analysis. Nonlinear measures of determinism and D2 estimator for both single and multi-channel time series are calculated. It shows that the reconstruction method has well performance with noise and an obviously little variety to the selection of time delay and embedding dimension. Using this method, we demonstrate the multi-channels spontaneous EEG signals of five mental tasks exhibit a finite determinism structure which could be used for further nonlinear study. The method is applicable to online EEG analysis.

Mental EEG signal is contained by the background artifacts, the basic components of EEG rhythm and the components related to mental tasks. Many methods have been proposed to remove artifacts from EEG recordings, but there is limited when the artifacts are mixed and have comparable amplitudes with EEG, and is no helpful in separating the different components of EEG itself. Here we apply an optimized independent component analysis(ICA) method to separate these components with few channels of EEG. The result shows the separating performance is well, with components clustered and skull-projected, we also find some components related to mental tasks and their distribution. The research has some values in the cognition of mental activity and the function of brain.

Fluidized-bed processing is well-established in various branches of industry, which has found many applications in drying operation. But, in previous literatures, very few paper has been found on the drying of stick pullulan solution.

Pneumatically controlled downcomers which are free from bridging and spouting of solids have been developed and tested. The principle has been applied successfully to the development of new types of multi-stage fluidized beds, which have been tested up to the pilot-plant scale.