5,773 research outputs found

    Nuclear fragmentation studies for microelectronic application

    Get PDF
    A formalism for target fragment transport is presented with application to energy loss spectra in thin silicon devices. Predicted results are compared to experiments with the surface barrier detectors of McNulty et al. The intranuclear cascade nuclear reaction model does not predict the McNulty experimental data for the highest energy events. A semiempirical nuclear cross section gives an adequate explanation of McNulty's experiments. Application of the formalism to specific electronic devices is discussed

    H.E. Warren and Thomas M. Noble, articles of agreement, 1858

    Get PDF

    Shock-induced color changes in nontronite: Implications for the Martian fines

    Get PDF
    Riverside nontronite, a candidate for the major mineral in the Martian fines, becomes both redder and darker upon shock loading between 180 and 300 kbar. The change from olive-yellow (2.5 Y 6/6) to strong brown (7.5 YR 4/6) in the 300-kbar sample brackets the range of color observed at the Viking lander sites. Optical microscopy, X-ray diffraction, optical, infrared, and ^(57)Fe Mössbauer spectroscopy were applied to understand the physical basis of the color change. The Riverside nontronite experienced partial dehydroxylation, probably due to shock-induced heating, that changed the coordination of the Fe3+ in the octahedral layer of the clay to a mixture of 4- and 6-fold or a distorted 5-fold coordination. These changes in the clay cause the O^(2−)-Fe^(3+) charge transfer absorption edge to shift from the near ultraviolet into the visible, producing a redder and darker phase. The absorption spectra of both impacted and nonimpacted Riverside nontronite contains the basic features of the reflectance spectra of the bright regions of Mars: a steep drop in absorption from the near UV into the visible and a featureless near IR region. Calculations indicate that significant impact induced color changes (and dehydration) can occur on Mars, though it seems likely that the mechanism would be more effective, volumetrically, at producing variations in color rather than affecting the absolute color

    Evidence for deuterium astration in the planetary nebula Sh2-216?

    Get PDF
    We present FUSE observations of the line of sight to WD0439+466 (LS V +46 21), the central star of the old planetary nebula Sh2-216. The FUSE data shows absorption by many interstellar and stellar lines, in particular D I, H2 (J = 0 - 9), HD (J = 0 - 1), and CO. Many other stellar and ISM lines are detected in the STIS E140M HST spectra of this sightline, which we use to determine N(HI). We derive, for the neutral gas, D/H=(0.76 +0.12 -0.11)E-5, O/H = (0.89 +0.15 -0.11)E-4 and N/H = (3.24 +0.61-0.55)E-5. We argue that most of the gas along this sightline is associated with the planetary nebula. The low D/H ratio is likely the result of this gas being processed through the star (astrated) but not mixed with the ISM. This would be the first time that the D/H ratio has been measured in predominantly astrated gas. The O/H and N/H ratios derived here are lower than typical values measured in other planetary nebulae likely due to unaccounted for ionization corrections.Comment: Accepted for publication is ApJ

    Flight areas of British butterflies: assessing species status and decline

    Get PDF
    Geographical range size is a key ecological variable, but the consequences of measuring range size in different ways are poorly understood. We use high-resolution population data from British butterflies to demonstrate that conventional distribution maps, widely used by conservation biologists, grossly overestimate the areas occupied by species and grossly underestimate decline. The approximate flight areas occupied by 20 out of 45 colonial British species were estimated to cover a median of only 1.44% of the land surface within occupied regions. Common species were found to be declining faster than conventional distribution maps suggest: common and rare species had no significant difference in their population-level rates of extinction. This, combined with the log-normal form of the range-size frequency distribution, implies that species-level extinction rates may accelerate in the medium to long term. Population-level conservation is a matter of great urgency for all species, not just for the rarest

    Disruption of PCNA-lamins A/C interactions by prelamin A induces DNA replication fork stalling

    Get PDF
    The accumulation of prelamin A is linked to disruption of cellular homeostasis, tissue degeneration and aging. Its expression is implicated in compromised genome stability and increased levels of DNA damage, but to date there is no complete explanation for how prelamin A exerts its toxic effects. As the nuclear lamina is important for DNA replication we wanted to investigate the relationship between prelamin A expression and DNA replication fork stability. In this study we report that the expression of prelamin A in U2OS cells induced both mono-ubiquitination of proliferating cell nuclear antigen (PCNA) and subsequent induction of Pol η, two hallmarks of DNA replication fork stalling. Immunofluorescence microscopy revealed that cells expressing prelamin A presented with high levels of colocalisation between PCNA and γH2AX, indicating collapse of stalled DNA replication forks into DNA double-strand breaks. Subsequent protein-protein interaction assays showed prelamin A interacted with PCNA and that its presence mitigated interactions between PCNA and the mature nuclear lamina. Thus, we propose that the cytotoxicity of prelamin A arises in part, from it actively competing against mature lamin A to bind PCNA and that this destabilises DNA replication to induce fork stalling which in turn contributes to genomic instability
    corecore