Spark decomposition of SF6: chemical and biologicalstudies

Because electric arcs, sparks or corona can decompose SF₆ insulators into byproducts having chemical properties different from SF₆, environmental concerns arise regarding inadvertent human exposures to electrically decomposed SF₆. Biological assays using mammalian cell culture systems have revealed that SF₆ , spark-decomposed under specific experimental conditions, can produce cell death. Chemical analysis of spark-decomposed SF₆ has identified the major decomposition pathways and byproducts. Biological testing of individual byproduct mixtures has indicated that these major decomposition products may not account for the majority of the cell-killing effects seen in the assays. Further experiments have suggested that S₂F₁₀ may be produced and accumulate under the specific decomposition conditions and that this compound may be a major contributor to the observed cell lethality. It is concluded that testing of samples from commercial facilities and assays of decomposed gas after ameliorative treatments would both be appropriate investigations     

电池与数字负载

随着通讯器件从模拟信号转向数字信号,对电池也提出了新的要求。同模拟收发机采用稳定的电流不同,数字收发机要求电池承受短促的尖峰电流;对于具有双向电波信号功能的通讯设备来说,要求电池内阻低;过冷或过热对于电池的工作性能也有较大影响。适合数字式双向电波应用的电池当今电池的研究主要集中在锂离子电池系统,在图1中,对镍镉、镍氢锂离子电池的能量密度和内阻的关系进行了比较。为了达到镍基电池的预期寿命,要求对其进行周期性放电以进行维护。镍镉电池和镍氢电池为了避免记忆性,需要周期性的进行放电维护。而且对于NiCd电池使用记忆…     

On Freedom and Determinism.

Comment in response to Ludwig Immergluck, who, in "Determinism-Freedom in Contemporary Psychology" (American Psychologist, 1964, 19, 270-281), claims that the experience of freedom is a distorted percept, perhaps even an inescapable illusion as it applies to oneself, but that it implies a view of the nature of man that is incompatible with the advancement of science. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Comparison of marginal fit and microleakage of ceramic and composite inlays: an in vitro study

The purpose of this in vitro study was to evaluate the marginal fit and microleakage of four types of ceramic or resin composite inlays. Sixty extracted human third molar teeth were randomly assigned into four groups. MOD cavities without bevels were prepared. The mesiogingival margin was cut in enamel, whereas the distogingival margin was placed below the amelocemental junction. The preparations and inlays were made according to the manufacturers' instructions. After acid-etching and treatment with a dentine bonding agent the inlays were cemented with dual curing CEREC resin composite luting material. After placement and polishing 10 teeth of each group were thermocycled 2500 times between 14 degrees C and 62 degrees C. Each tooth was bisectioned and from each part, one occlusal and three proximal sections of 75-100 microns thickness were cut and ground (EXAKT Cutting and Grinding system). The marginal discrepancy and the thickness of the luting cement were measured microscopically at each section and an average for each tooth was calculated. Considerable variation of marginal fit was seen, within inlays, and among different types of inlays. In general, the Vita Dur N inlays showed the best fit, e.g. the thickness of the luting cement for Vita Dur N was 114 microns occlusally and 119 microns mesiogingivally compared to 199 microns occlusally for CEREC and 219 microns mesiogingivally for Estilux. At enamel margins, a tendency of less microleakage was seen for ceramic inlays compared to composite inlays.     

Minor groove-directed and intercalative ligand-DNA interactions in the poisoning of human DNA topoisomerase I by protoberberine analogs

Spectroscopic, calorimetric, DNA cleavage, electrophoretic, and computer modeling techniques have been employed to characterize the DNA binding and topoisomerase poisoning properties of three protoberberine analogs, 8-desmethylcoralyne (DMC), 5,6-dihydro-8-desmethylcoralyne (DHDMC), and palmatine, which differ in the chemical structures of their B- and/or D-rings. DNA topoisomerase-mediated cleavage assays revealed that these compounds were unable to poison mammalian type II topoisomerase. By contrast, the three protoberberine analogs poisoned human topoisomerase I according to the following hierarchy: DHDMC > DMC > palmatine. DNA binding by all three protoberberine analogs induced negative flow linear dichroism signals as well as unwinding of the host duplex. These two observations are consistent with an intercalative mode of protoberberine binding to duplex DNA. However, a comparison of the DNA binding properties for DMC and DHDMC, which differ only by the state of saturation at the 5,6 positions of the B-ring, revealed that the protoberberine analogs do not "behave" like classic DNA intercalators. Specifically, saturation of the 5-6 double bond in the B-ring of DMC, thereby converting it to the DHDMC molecule, was associated with enhanced DNA unwinding as well as a reversal of DNA binding preference from a DNA duplex with an inaccessible or occluded minor groove {poly[d(G-C)]2} to DNA duplexes with accessible or unobstructed minor grooves {poly[d(A-T)]2 and poly[d(I-C)]2}. In addition, a comparison of the DNA binding properties for DHDMC and palmatine revealed that transferring the 11-methoxy moiety on the D-ring of DHDMC to the 9 position, thereby converting it to palmatine, was associated with a reduction in binding affinity for both duplexes with unobstructed minor grooves as well as for duplexes with occluded minor grooves. These DNA binding properties are consistent with a "mixed-mode" DNA binding model for protoberberines in which a portion of the ligand molecule intercalates into the double helix, while the nonintercalated portion of the ligand molecule protrudes into the minor groove of the host duplex, where it is thereby available for interactions with atoms lining the floor and/or walls of the minor groove. Furthermore, saturation at the 5,6 positions of the B-ring, which causes the A-ring to be tilted relative to the plane formed by rings C and D, appears to stabilize the interaction between the host duplex and the minor groove-directed portion of the protoberberine ligand. Computer modeling studies on the DHDMC-poly[d(A-T)]2 complex suggest that this interaction may involve van der Waals contacts between the ligand A-ring and backbone sugar atoms lining the minor groove of the host duplex. The hierarchy of topoisomerase I poisoning noted above suggests that this minor groove-directed interaction may play an important role in topoisomerase I poisoning by protoberberine analogs. In the aggregate, our results presented here, coupled with the recent demonstration of topoisomerase I poisoning by minor groove-binding terbenzimidazoles [Sun, Q., Gatto, B., Yu, C., Liu, A. , Liu, L. F., & LaVoie, E. J. (1995) J. Med. Chem. 38, 3638-3644], suggest that minor groove-directed ligand-DNA interactions may be of general importance in the poisoning of topoisomerase I.     

High voltage studies of dielectric materials for HTS power equipment

The discovery of high temperature superconductors (HTS) has triggered renewed interest in the study of dielectric materials at cryogenic temperatures. While considerable work was done in the 1970s and 1980s on dielectrics immersed in liquid helium for low temperature superconducting applications, there remains a need for dielectric research at liquid nitrogen temperature for HTS applications, requiring experimental data oriented toward practical situations. We report on AC breakdown (puncture and/or flashover), and impulse breakdown of solid materials in either vacuum or in liquid nitrogen. Solid materials which we examined, include fiberglass reinforced plastics, epoxies with and without filler, and polymeric tape. Combinations of some of these materials have also been studied at low temperatures. Additionally we have measured permittivity and dissipation factor for materials for which these parameters are not available at 77 K. Finally, we also discuss specific applications for HTS cables including breakdown and aging studies on model cables, with lapped tape electrical insulation, immersed in liquid nitrogen.