The Future Potential of Nuclear Power: Fission and Fusion

A comparison is made between fission and fusion as potential future power sources for mankind. Fission is seen to be less complex, but fusion is seen to be environmentally more benign.     

Fusion-fission hybrids: Environmental aspects and their role in hybrid rationale

The rationale for developing hybrids depends on real or perceived liabilities of relying on pure fission to do the same job. Quite possibly the main constraint on expanded use of fission will be neither lack of fuel nor high costs, but perceived environmental liabilities—radioactive wastes, reactor safety, and links to nuclear weaponry. The environmental characteristics of hybrid systems and pure-fission systems are compared here in detail. The findings are that significant environmental advantages for hybrids cannot now be demonstrated and may not exist. Therefore, if environmental drawbacks constrain the application of pure fission, hybrids probably also will be thus constrained.     

用MCNP程序计算确定桶装α废物测定装置最佳设计安排

本文介绍了用Ｍｏｎｔｅ Ｃａｒｌｏ方法计算桶装α废物测定装置最佳设计安排的两步过程，第一步，计算出外中子源在废物中生成的缓发裂变中子，第二步计算这个缓发裂变中子源在控制中所形成的熟中子通量密度，为利用现有的ＭＣＮＰ程序进行计算，我们编制了有关的外源和缓发裂变中子源生成及抽样子程序，文中附有各方案各步骤的计算结果。     

Mutations in deoxyribonucleotide biosynthesis pathway cause spreading of silencing across heterochromatic barriers at the mating-type region of the fission yeast

The mat2,3-region of Schizosaccharomyces pombe is flanked by two inverted repeat elements, IRL and IRR, which define the boundaries of the silent domain resulting from heterochromatin assembly in the region. We employed a genetic screen to isolate factors whose mutations allowed spreading of heterochromatin across boundary elements. Surprisingly, this screen revealed that mutations in the genes required for deoxyribonucleotide biosynthesis, cdc22 (encoding the large subunit of ribonucleotide reductase) and tds1 (putative thymidylate synthase), cause silencing of marker genes inserted outside of the silent domain. Chromatin-immunoprecipitation analysis showed that histone H3 lysine 9 methylation modification, an epigenetic mark associated with gene silencing, is enriched by two- to three-fold in the cdc22 mutant as compared to the level found in the wild-type strain in regions outside the silent domain. The spreading of heterochromatin across barriers required functional Atf1/Pcr1, ATF-CREB family proteins, but not the RNA-interference Dcr1, Ago1, or Rdp1 factors, previously implicated in silencing. These results implicate the deoxyribonucleotide biosynthesis pathway in limiting epigenetic controls at barrier elements at the mating-type region, but the mechanism remains unknown.     

An in vitro study on the dental caries preventing effect of oligomeric procyanidins in sorghum episperm

Procyanidins are abundant in sorghum episperm. In this study, the effects of procyanidins from Sorghum bicolor (L.) moench episperm (sorghum procyanidins, SPC) in preventing dental caries were investigated through analysis on SPCs’ effects on cariogenic bacteria and ability in scavenging superoxide anion free radicals. In addition, the SPC with activity in preventing dental caries were identified. The ESI-MS/MS analysis results revealed that the compositions of SPC purified by macroporous resin were dimmers, trimers, tetramers, pentamers and hexamers of procyanidins and catechin/epicatechin monomers. The minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) of SPC on Streptococcus mutans (Ingbritt C) and Streptococcus sobrinus 6715 were 8 and 16 mg/ml, respectively. The SPC had a remarkable inhibition effect (P < 0.05) on acid production of S. sobrinus (Ingbritt C) and S. mutans 6715 compared with the control group, and a dose-dependent relationship was observed. By increasing the concentration of SPC in the experimental condition (200–600 mg/L), the scavenging ratio of superoxide anion radicals increased significantly, indicating that SPC could be used as a potential dental-caries-preventative medicine with its antibacterial and antioxidant ability.     

偏心套筒夹具的设计

介绍了一种大型偏心套筒的磨削工艺装备 ,该装备的设计改变了传统的整体设计方法 ,利用工件本身的条件 ,采用分体的结构形式 ,变难为易 ,圆满解决了高精度要求的制造问题     

The study of fission track and other crystalline defects using confocal scanning laser microscopy

Confocal scanning laser microscopy (SLM) is a technique that offers geologists a new way of studying structures in minerals at the submicrometre level. As an example we show how the non-destructive nature of confocal SLM can be used to measure and count fission tracks (line defects formed by the spontaneous fission of²³⁸U) in the uranium-bearing mineral apatite, and to provide information about the geometry and crystallographic orientation of fluid inclusions trapped inside apatite grains during crystallization. The technique also provides a means of studying the internal geometry of chemical zonation in minerals. The digitized nature of the SLM images makes them amenable to a variety of image analysis techniques, and we show how image analysis can be used to measure fission tracks in mica sheets and provide crude estimates of track dip. Finally, using a chemically etched mica sheet we show how confocal SLM can be used to provide a detailed near-surface (1–5 μm) analysis of geological materials.     

Kinetics of oxidative cracking of n‐hexane to olefins over VOx/Ce‐Al2O3 under gas phase oxygen‐free environment

The kinetics of oxidative cracking of n‐hexane to olefins using lattice oxygen of VO_x/Ce‐Al₂O₃ is investigated. The TPR/TPO analysis shows a consistent reducibility (79%) of VO_x/Ce‐Al₂O₃ in repeated redox cycles. The total acidity of the sample is found to be 0.54 mmol/g with 22% are strong acid sites that favors olefin selectivity. The oxidative cracking of n‐hexane in a fluidized CREC Riser simulator gives approximately 60% olefin selectivity at 30% n‐hexane conversion. A kinetic model is developed considering (1) cracking, (2) oxidative dehydrogenation (ODH), and (3) catalyst deactivations. The proposed cracking mechanism considers adsorption, C–H and C–C bond fission and desorption as elementary steps and implemented by pseudo steady state hypothesis. A Langmuir‐Hinshelwood mechanism is found to represent the ODH reactions. The developed model fits the experimental data with favorable statistical indicators. The estimated specific reaction rate constants are also found to be consistent with the product selectivity data. © 2016 American Institute of Chemical Engineers AIChE J, 63: 130–138, 2017