Low‐Voltage‐Ride‐Through Performance of an HVDC Transmission System Using Two Modular Multilevel Double‐Star Chopper‐Cells Converters

This paper presents an intensive discussion on a long‐distance high‐voltage direct‐current (HVDC) transmission system that combines two modular multilevel cascade converters based on double‐star chopper cells (MMCC‐DSCC) with DC power cables. Hereinafter, a single MMCC‐DSCC is referred to as a DSCC converter or just as a DSCC for the sake of simplicity. The HVDC transmission system is required to provide low‐voltage‐ride‐through (LVRT) capability to enhance transmission system availability. This paper proposes a new LVRT method without any direct information exchange between the two DSCC converters. The validity of the method is verified, using simulated waveforms from the software package of “PSCAD/EMTDC” and experimental waveforms from a three‐phase 200‐V, 400‐Vdc, 10‐kW, 50‐Hz downscaled HVDC system with a set of 300‐meter‐long DC power cables.     

Computed tomographic evaluation of gas hole formation and structural quality in Gouda‐type cheese

Computed tomography (CT) was performed on Gouda‐type cheese during ripening to evaluate gas hole formation and structural quality. The cheese was exposed to different ripening conditions, including variations in ripening temperature and concentration of butyric acid bacteria. Computed tomography images were obtained every 2 weeks for 16 weeks to assess the volume, shape and location of gas holes. The results demonstrate that CT makes the nondestructive monitoring of cheese gas hole formation and evaluation of the structural features of cheese possible throughout the ripening period.     

洛神花纤维增强通用树脂复合物的力学性能及其化学镀镍金属化

洛神花纤维采用5％的氢氧化钠溶液处理后用于制备纤维增强型通用树脂复合物.对含不同纤维体积分数的复合物的拉伸行为进行研究后发现,其力学性能与传统复合物类似.复合物的抗拉强度随着纤维含量的增大而提高.采用化学镀镍工艺对复合物进行金属化后,其显微硬度是原来的7倍.     

Experimental Verification of a Front‐to‐Front (FTF) System Consisting of Two Modular Multilevel Cascade Converters Based on Double‐Star Chopper Cells

This paper presents an experimental discussion on modular multilevel cascade converters based on double‐star chopper cells (MMCC‐DSCC). Hereinafter, a single MMCC‐DSCC is referred to simply as a “DSCC”. A couple of DSCCs are used to form a front‐to‐front (FTF) system capable of dc voltage matching and galvanic isolation between two dc grids. The FTF system can be considered as a dc–ac–dc power conversion system including an ac‐link high‐power transformer. The higher the ac‐link frequency, the smaller and lighter are the ac‐link transformer and dc capacitors. When the so‐called “phase‐shifted‐carrier PWM” is applied to the DSCC, theoretical analysis and computer simulation have confirmed that a ratio of the carrier frequency with respect to the ac‐link frequency can be reduced to 5/2. This paper designs, constructs, and tests a 400‐Vdc 10‐kW downscaled FTF system with a carrier frequency of 450 Hz and an ac‐link frequency of 180 Hz, where their ratio is 5/2. Experimental waveforms obtained from the downscaled system are compared with simulated ones obtained from a software package, PSCAD/EMTDC, under the same operating and circuit conditions. They agree well each other not only under steady states but also under transient states.     

Electrical Conductivity of TiO2-V2O5-P205 Glasses

The dc conductivities (σ) of V₂O₅-P₂O₅ glasses containing up to 30 mol% TiO₂ were measured at T=100° to ∼10°C below the glass-transition temperature. Dielectric constants from 30 to 10⁶ Hz, densities, and the fraction of reduced V ion were measured at room temperature. The conduction mechanism was considered to be small polaron hopping between V ions, as previously reported for V₂O₅-P₂O₅ glass. The temperature dependence of σ was exponential with σ = σ₀ exp(-W/kT ) in the high-temperature range. When part of the P₂O₅ was replaced by TiO_2,σ increased and W decreased. The hopping energy depended on the reciprocal dielectric constant which, in this case, increased with increasing TiO₂ content.     

Effects of docosahexaenoic acid or arachidonic acid supplementation on the behavior of cardiomyocytes derived from human pluripotent stem cells

Background: Human heart changes its energetic substrates from lactate and glucose to fatty acids during the neonatal period. Noticing the lack of fatty acids in media for the culture of cardiomyocytes derived from human pluripotent stem cells (hiPS-CM), researchers have supplemented mixtures of fatty acids to hiPS-CM and reported the enhancement in the maturation of hiPS-CM. In our previous studies, we separately supplemented two polyunsaturated fatty acids (PUFAs), docosahexaenoic acid (DHA) or arachidonic acid (AA), to rat fetal cardiomyocytes and found that the supplementations upregulated the expressions of mRNAs for cardiomyocyte differentiation, fatty acid metabolism, and cellular adhesion. The enhancement in cellular contractility was attributed to the improvement in intercellular connection rather than a direct enhancement of the contractile force. Methods: This study reports the successive results of the effects of DHA or AA supplementation on hiPS-CM. In addition to the contractile force and mRNA measurements used in the previous study, we further investigated the effect of different cellular aggregations on the contractile force output by means of finite element analysis, measured glucose and fatty acids metabolites, and assessed cTNT and MLC2v expressions through immunofluorecsence evaluation. Results: It showed that the sole supplementation of albumin-conjugated DHA or AA can be taken up by hiPS-CM without other uptake-enhancing factors, and the supplementations may activate the CD36_­ERRγ metabolic pathway. DHA or AA supplementation increased the cellular contractile ratio on collagen gels and AA supplementation stimulated hiPS-CM aggregation to form cellular clusters. The enhancement effect on the hiPS-CM contractile force was modest since the increase in contractile force was not significant. AA supplementation was more effective than DHA supplementation because it significantly upregulated mRNA expressions of P300 and CD36. However, finite element analysis showed that the formation of clusters on a collagen gel attenuated the contractile force exerted by the gel on its surroundings. Conclusion: DHA and AA, as having been supplemented in infant formulas, have no direct and significant enhancement effect on the performance of the hiPS-CM when they were supplemented individually, although they were able to enter the cellular metabolic system. The AA supplementation showed some auxiliary effect on the maturation of hiPS-CM, which is worthy of further investigation under the consideration of membrane composition alteration and remodeling of membrane molecules.