Development of a five-stage solid-state linear transformer driver.

In this paper, the development of a five-stage solid-state linear transformer driver (LTD) is described. Each stage consists of eight compact pulse generating modules and a magnetic core. The pulse generating modules contain a multilayer-ceramic-capacitor-based pulse-forming network (PFN) and an insulated-gate bipolar transistor (IGBT) switch array, as well as magnetic switches, which are used to speed up the pulse front. To prevent damage from the reverse voltage to the IGBT switch, a reverse voltage absorption circuit was added to the PFN. For this study, a larger cross-sectional core with improved output characteristics was adopted. The developed five-stage LTD has the advantages of long life, low jitter, fast rising edge, and so on. The device can provide a 35 kV, 119 ns, 4.3 kA square pulse train with a maximum frequency of 50 Hz. On this basis, a 50-stage LTD of output 500 kV, which would serve as a high-power microwave driver source, is under development.

A solid-state pulse generator based on multilayer ceramic capacitors and insulated gate bipolar transistors.

A solid-state pulse-forming network (PFN) module was designed using multilayer ceramic capacitors (MLCCs). In addition, an all-solid-state pulse generator was fabricated with a Blumlein line that consisted of two PFN single lines and an insulated gate bipolar transistor (IGBT) switch array. This generator was integrated on printed circuit boards (PCBs). The stage capacitors of the PFN were composed of MLCCs connected in series and parallel. To obtain a compact structure, folded, copper-clad wires were used as interstage inductors. The copper-clad wires were structurally optimized to reduce coupling between adjacent interstage inductors. A relatively fast rising waveform edge was obtained using an IGBT gate-boosting circuit and magnetic switch technology. A square-wave pulse with a rise time of 27 ns, a voltage of 5 kV, a width of 120 ns, a maximum repetition rate of 100 Hz, and an evaluated lifetime of 109 pulses was obtained on a load of 6.6 Ω. With its compact size, fast rise time, and long lifetime, the fabricated pulse generator can be used as a component in linear transformer drivers or Marx generators.

Efficient Semisynthesis of (-)-Pseudoirroratin A from (-)-Flexicaulin A and Assessment of Their Antitumor Activities.

Accumulating evidence indicates that natural ent-kaurane diterpenoids show great potential for medical treatment of different pathological conditions including cytotoxicity, antibacterial, and anti-inflammatory activity. Among a variety of diterpenoids tested, (-)-pseudoirroratin A displayed a promising antitumor property in vitro and in vivo. However, this diterpenoid could merely be isolated in a limited amount from a rare source of Isodon pseudoirrorata. To overcome such scanty source, we developed a novel, facile, and efficient semisynthetic strategy to prepare (-)-pseudoirroratin A from natural (-)-flexicaulin A, which can be expediently obtained from I. flexicaulis in a great quantity. The three-dimensional structure and the absolute configuration of our synthetic diterpenoid have been determined and confirmed with the X-ray crystallographic analysis. More importantly, we demonstrated for the first time that pseudoirroratin A exerted significant cytotoxicity against human colorectal carcinoma cells via an induction of apoptosis, as well as a remarkable suppression on tumor growth in a colon cancer xenograft mouse model.

The integrative taxonomic approach reveals host specific species in an encyrtid parasitoid species complex.

Integrated taxonomy uses evidence from a number of different character types to delimit species and other natural groupings. While this approach has been advocated recently, and should be of particular utility in the case of diminutive insect parasitoids, there are relatively few examples of its application in these taxa. Here, we use an integrated framework to delimit independent lineages in Encyrtus sasakii (Hymenoptera: Chalcidoidea: Encyrtidae), a parasitoid morphospecies previously considered a host generalist. Sequence variation at the DNA barcode (cytochrome c oxidase I, COI) and nuclear 28S rDNA loci were compared to morphometric recordings and mating compatibility tests, among samples of this species complex collected from its four scale insect hosts, covering a broad geographic range of northern and central China. Our results reveal that Encyrtus sasakii comprises three lineages that, while sharing a similar morphology, are highly divergent at the molecular level. At the barcode locus, the median K2P molecular distance between individuals from three primary populations was found to be 11.3%, well outside the divergence usually observed between Chalcidoidea conspecifics (0.5%). Corroborative evidence that the genetic lineages represent independent species was found from mating tests, where compatibility was observed only within populations, and morphometric analysis, which found that despite apparent morphological homogeneity, populations clustered according to forewing shape. The independent lineages defined by the integrated analysis correspond to the three scale insect hosts, suggesting the presence of host specific cryptic species. The finding of hidden host specificity in this species complex demonstrates the critical role that DNA barcoding will increasingly play in revealing hidden biodiversity in taxa that present difficulties for traditional taxonomic approaches.

Effects of female diet and age on offspring sex ratio of the solitary parasitoid Pachycrepoideus vindemmiae (Rondani) (Hymenoptera, Pteromalidae) / Efeitos da dieta e idade da fêmea em relação à prole e à razão sexual do parasitoide solitário Pachycrepoideus vindemmiae (Rondani) (Hymenoptera, Pteromalidae)

Effects of female diet and age on offspring sex ratio of the solitary parasitoid Pachycrepoideus vindemmiae (Rondani) (Hymenoptera, Pteromalidae). Theories predict that females of parasitoid wasps would adjust the offspring sex ratio to environmental conditions in the oviposition patch, but the diet and age of females would also affect the sex ratio adjustment. Our focus was to test the effects of female diet and age on offspring sex ratio of the solitary parasitoid wasp, Pachycrepoideus vindemmiae (Rondani, 1875). Our results showed that females fed with honey had significantly less female biased offspring sex ratio than those fed only with water. Offspring sex ratio (male percentage) decreased with female age or female longevity at the beginning of oviposition but increased at the end. There should be a sperm limitation in P. vindemmiae females at the end of oviposition, and a higher frequency of unfertilized eggs were laid then. Females also laid more unfertilized eggs at the beginning of oviposition, which would be necessary to insure the mating among offspring. Male offspring developed faster and emerged earlier, which would also reduce the risk of virginity in offspring with female-biased sex ratio.

Efeitos da dieta e idade da fêmea em relação à prole e à razão sexual do parasitoide solitário Pachycrepoideus vindemmiae (Rondani) (Hymenoptera, Pteromalidae). As teorias predizem que as fêmeas parasitoides de vespas ajustam a relação razão sexual dos descendentes, de acordo com condições ambientais, em cada oviposição. Entretanto, a dieta e idade das fêmeas também podem afetar o ajuste da razão sexual. Nosso foco foi testar os efeitos da dieta e idade da fêmeas em relação a razão sexual da prole da vespa parasitoide Pachycrepoideus vindemmiae (Rondani, 1875). Nossos resultados mostraram que as fêmeas alimentadas com mel apresentaram uma razão sexual significativa menor de fêmeas, do que aquelas alimentadas apenas com água. A razão sexual (percentagem dos machos) diminuiu com a idade ou longevidade das fêmeas no início da oviposição, mas com aumento no final. Deve haver uma limitação de esperma nas fêmeas de P. vindemmiae no final da oviposição e uma maior frequência de posturas de ovos infertilizados. As fêmeas também fazem posturas de um número maior de ovos infertilizados no início da oviposição, que seria necessário para assegurar o acasalamento entre os descendentes. A prole masculina desenvolverá mais rapidamente e emergirá mais cedo, o que também reduziria o risco de virgindade da prole, com a tendenciosa proporção de razão sexual maior das fêmeas.

DNA barcoding of six Ceroplastes species (Hemiptera: Coccoidea: Coccidae) from China.

Ceroplastes Gray (wax scales) is one of the genera of Coccidae, most species of which are considered to be serious economic pests. However, identification of Ceroplastes species is always difficult owing to the shortage of easily distinguishable morphological characters. Mitochondrial cytochrome c oxidase I (COI) sequences (or DNA barcodes) and the D2 expansion segments of the large subunit ribosomal RNA gene 28S were used for accurate identification of six Ceroplastes species (C. floridensis Comstock, C. japonicus Green, C. ceriferus (Fabricius), C. pseudoceriferus Green, C. rubens Maskell and C. kunmingensis Tang et Xie) from 20 different locations in China. For COI data, low G·C content was found in all species, averaging about 20.4%. Sequence divergences (K2P) between congeneric species averaged 12.19%, while intra-specific divergences averaged 0.42%. All 112 samples fell into six reciprocally monophyletic clades in the COI neighbour-joining (NJ) tree. The NJ tree inferred from 28S showed almost same results, but samples of two closely related species, C. ceriferus and C. pseudoceriferus, were clustered together. This research indicates that the standard barcode region of COI can efficiently identify similar Ceroplastes species. This study provides an example of the usefulness of barcoding for Ceroplastes identification.