Iron Loss Calculation of AC Filter Inductor for Three‐Phase PWM Inverters

In recent years, remarkable advancement of new power semiconductor devices, such as SiC and GaN, enables the increase of switching frequency of power converters, and hence the volume of passive components, such as ac filters and transformers, can be reduced. However, temperature rise caused by the inductor loss is increasing, and hence iron loss evaluation of the inductor is one of the most important issues to realize high power density converters. Conventionally, an improved generalized Steinmetz equation (iGSE) has proposed in order to calculate the iron loss under a pulse voltage magnetizing condition. However, accurate iron loss calculation of the ac filter inductor used in a PWM inverter cannot be realized. The authors have proposed two methods of iron loss evaluation of ac filter inductors. The first one is a loss map method which can calculate the iron loss without using a real PWM inverter. Another one is an ILA (Inductor Loss Analyzer) which can measure the iron loss in every switching period in a real PWM inverter. In this paper, comparisons of the iron loss between the ILA and the loss map method on both the single‐phase and three‐phase inverters are studied. It is found that iron loss of the ac filter inductor in the three‐phase PWM inverter which is calculated by the loss map method cause a large error on a specific condition. In order to prevent the calculation error, the authors proposed a revised loss map method and proved the effectiveness of the method.     

A Method for Systematic Assessment of Intrinsically Disordered Protein Regions by NMR

Intrinsically disordered proteins (IDPs) that lack stable conformations and are highly flexible have attracted the attention of biologists. Therefore, the development of a systematic method to identify polypeptide regions that are unstructured in solution is important. We have designed an “indirect/reflected” detection system for evaluating the physicochemical properties of IDPs using nuclear magnetic resonance (NMR). This approach employs a “chimeric membrane protein”-based method using the thermostable membrane protein PH0471. This protein contains two domains, a transmembrane helical region and a C-terminal OB (oligonucleotide/oligosaccharide binding)-fold domain (named NfeDC domain), connected by a flexible linker. NMR signals of the OB-fold domain of detergent-solubilized PH0471 are observed because of the flexibility of the linker region. In this study, the linker region was substituted with target IDPs. Fifty-three candidates were selected using the prediction tool POODLE and 35 expression vectors were constructed. Subsequently, we obtained ¹⁵N-labeled chimeric PH0471 proteins with 25 IDPs as linkers. The NMR spectra allowed us to classify IDPs into three categories: flexible, moderately flexible, and inflexible. The inflexible IDPs contain membrane-associating or aggregation-prone sequences. This is the first attempt to use an indirect/reflected NMR method to evaluate IDPs and can verify the predictions derived from our computational tools.     

Verification of Iron Loss Calculation Method Using a High‐Precision Iron Loss Analyzer

Because of the improved performance of power devices, the volume of the ac filter inductors used in high‐frequency PWM inverters has been reduced. However, the temperature rise in the filter inductor due to this miniaturization has become more pronounced. Therefore, we have proposed an iron loss calculation method for the ac filter inductor. However, the accuracy of the value calculated via the loss map method cannot be verified, because the iron loss arising during each switching period cannot be measured with conventional power measuring instruments. In order to resolve this problem, we developed an inductor loss analyzer (ILA), which allows precise measurement of the iron loss in the inductor during each switching period. The accuracy of the calculation of iron loss in the filter inductor by the loss map method was verified with the ILA. We found that the value calculated by the loss map method differed slightly from the value measured with the ILA. However, these differences can be reduced if we take into account the accurate flux density calculation and the effect of the duty ratio of PWM pulses on the loss. Finally, we verified that the loss map method can provide accurate iron loss calculations.     

Comparison of isolation methods using commercially available kits for obtaining extracellular vesicles from cow milk

Extracellular vesicles (EV) are important for delivering biologically active substances to facilitate cell-to-cell communication. Milk-derived EV are widely known because of their potential for immune enhancement. However, procedures for isolating milk-derived EV have not been fully established. To obtain pure milk-derived EV and accurately reveal their function, such procedures must be established. The aim of the present study was to compare methods using commercially available kits for isolating milk-derived EV. Initially, we investigated procedures to remove casein, which is the major obstacle in determining milk-derived EV purity. We separated whey using centrifugation only, acetic acid precipitation, and EDTA precipitation. Then, we isolated milk-derived EV by ultracentrifugation, membrane affinity column, size exclusion chromatography (SEC), polymer-based isolation, or phosphatidylserine-affinity isolation. Using EV count per milligram of protein, which is a good indicator of purity, we determined that acetic acid precipitation was the best method for removing casein. Using nanoparticle tracking analysis, protein quantity analysis, and RNA quantity analysis, we comprehensively compared each isolation method for its purity and yield. We found that SEC-based qEV column (Izon Science) could collect purer milk-derived EV at higher quantities. Thus, a combination of acetic acid precipitation and qEV can effectively isolate high amounts of pure extracellular vesicles from bovine milk.     

Two Triterpene Synthases from Imperata cylindrica Catalyzing the Formation of a Pair of Diastereoisomers through Boat or Chair Cyclization

Imperata cylindrica is known to produce a pair of triterpenes, isoarborinol and fernenol, that exhibit identical planar structures but possess opposite stereochemistry at six of the nine chiral centers. These differences arise from a boat or a chair cyclization of the B-ring of the substrate. Herein, we report the characterization of three OSC genes from I. cylindrica. IcOSC1 and IcOSC5 were identified as isoarborinol and fernenol synthases, respectively, while IcOSC3 was characterized as a multifunctional enzyme that produces glutinol and friedelin as its major products. Mutational studies of isoarborinol and fernenol synthases revealed that the residues surrounding the DCTAE motif partially affected the conformation of the B-ring during cyclization. Additionally, the IcOSC1-W255H mutant produced the rare triterpene boehmerol. The introduced histidine residue presumably abstracted a proton from the intermediary carbocation at C18 during the 1,2-rearrangement. Expression analysis indicated that all OSC genes were highly expressed in stems.