Fault-Tolerant Converter with a Modular Structure for HVDC Power Transmitting Applications

For the high-voltage direct-current (HVDC) power transmission system of offshore wind power, dc/dc converters are the potential solution to collect the power generated by off-shore wind farms to HVDC terminals. The converters operate with high-voltage gain, high efficiency, and fault tolerance over a wide range of operating conditions. In this paper, an isolated ultrahigh step-up dc/dc converter with a scalable modular structure is proposed for HVDC offshore wind power collection. A flyback-forward converter is employed as the power cell to form the expandable electrically isolated modular dc/dc converter. The duty ratio and phase-shift angle control are also developed for the proposed converter. Fault-tolerant characteristics of the converter are illustrated through the redundancy operation and fault-ride-through tests. Redundancy operation is designed to maintain high operation efficiency of the converters and fault-ride-through operation improves the converter reliability under harsh operating conditions. Analytical studies are carried out, and a 750-W prototype with three modular cells is built and experimentally tested to verify the performance of the proposed modular dc/dc converter

Biogenic production of DMSP and its degradation to DMS-their roles in the global sulfur cycle

Dimethyl sulfide (DMS) is the most abundant form of volatile sulfur in Earth's oceans, and is mainly produced by the enzymatic clevage of dimethylsulfoniopropionate (DMSP). DMS and DMSP play important roles in driving the global sulfur cycle and may affect climate. DMSP is proposed to serve as an osmolyte, a grazing deterrent, a signaling molecule, an antioxidant, a cryoprotectant and/or as a sink for excess sulfur. It was long believed that only marine eukaryotes such as phytoplankton produce DMSP. However, we recently discovered that marine heterotrophic bacteria can also produce DMSP, making them a potentially important source of DMSP. At present, one prokaryotic and two eukaryotic DMSP synthesis enzymes have been identified. Marine heterotrophic bacteria are likely the major degraders of DMSP, using two known pathways: demethylation and cleavage. Many phytoplankton and some fungi can also cleave DMSP. So far seven different prokaryotic and one eukaryotic DMSP lyases have been identified. This review describes the global distribution pattern of DMSP and DMS, the known genes for biosynthesis and cleavage of DMSP, and the physiological and ecological functions of these important organosulfur molecules, which will improve understanding of the mechanisms of DMSP and DMS production and their roles in the environment

Predictive model of positive surgical margins after radical prostatectomy based on Bayesian network analysis

ObjectiveThis study aimed to analyze the independent risk factors for marginal positivity after radical prostatectomy and to evaluate the clinical value of the predictive model based on Bayesian network analysis.MethodsWe retrospectively analyzed the clinical data from 238 patients who had undergone radical prostatectomy, between June 2018 and May 2022. The general clinical data, prostate specific antigen (PSA)–derived indicators, puncture factors, and magnetic resonance imaging (MRI) characteristics were included as predictive variables, and univariate and multivariate analyses were conducted. We established a nomogram model based on the independent predictors and adopted BayesiaLab software to generate tree-augmented naive (TAN) and naive Bayesian models based on 15 predictor variables.ResultsOf the 238 patients included in the study, 103 exhibited positive surgical margins. Univariate analysis revealed that PSA density (PSAD) (P = 0.02), Gleason scores for biopsied tissue (P = 0.002) and the ratio of positive biopsy cores (P < 0.001), preoperative T staging (P < 0.001), and location of abnormal signals (P = 0.002) and the side of the abnormal signal (P = 0.009) were all statistically significant. The area under curve (AUC) of the established nomogram model based on independent predictors was 73.80%, the AUC of the naive Bayesian model based on 15 predictors was 82.71%, and the AUC of the TAN Bayesian model was 80.80%.ConclusionThe predictive model of positive resection margin after radical prostatectomy based on Bayesian network demonstrated high accuracy and usefulness

Use of facile mechanochemical method to functionalize carbon nanofibers with nanostructured polyaniline and their electrochemical capacitance

A facile approach to functionalize carbon nanofibers [CNFs] with nanostructured polyaniline was developed via in situ mechanochemical polymerization of polyaniline in the presence of chemically treated CNFs. The nanostructured polyaniline grafting on the CNF was mainly in a form of branched nanofibers as well as rough nanolayers. The good dispersibility and processability of the hybrid nanocomposite could be attributed to its overall nanostructure which enhanced its accessibility to the electrolyte. The mechanochemical oxidation polymerization was believed to be related to the strong Lewis acid characteristic of FeCl3 and the Lewis base characteristic of aniline. The growth mechanism of the hierarchical structured nanofibers was also discussed. After functionalization with the nanostructured polyaniline, the hybrid polyaniline/CNF composite showed an enhanced specific capacitance, which might be related to its hierarchical nanostructure and the interaction between the aromatic polyaniline molecules and the CNFs

p-n junction theory in view of excess majority carriers

The classical $p\text{-}n$ junction theory is reconstructed in view of “excess majority carriers”. The effects of excess majority carriers, in addition to the excess minority carriers, are described analytically and integrated into the theory. The quantity and distribution of excess majority carriers are presented, which give rise to an “accompanying electric field” and guarantee the space-charge neutrality of each side of the junction. The accompanying electric field is figured out analytically, and the contributions of majority carriers are clarified quantitatively, which enables the current continuity in either side of the junction. Furthermore, at any position in the quasi-neutral region, the various current components are solved in closed form and the net current is obtained in a straightforward way. The reconstructed theory provides a more thorough understanding of $p\text{-}n$ junction operation with physical conciseness

Springtime spatial distributions of biogenic sulfur compounds in the Yangtze River Estuary and their responses to seawater acidification and dust

The spatial distributions of dimethylsulfide (DMS), dimethylsulfoniopropionate (DMSP), and dimethylsulfoxide (DMSO) were investigated in the Yangtze River Estuary from 9 to 23 March, 2018. Besides, we analyzed the vertical distributions of DMS, DMSP, and DMSO in early spring. An onboard incubation experiment was also carried out to study how the production and release of biogenic sulfur compounds responded to simulated seawater acidification and dust deposition