Radial oscillations of neutron stars in strong magnetic fields

The eigen frequencies of radial pulsations of neutron stars are calculated in a strong magnetic field. At low densities we use the magnetic BPS equation of state (EOS) similar to that obtained by Lai and Shapiro while at high densities the EOS obtained from the relativistic nuclear mean field theory is taken and extended to include strong magnetic field. It is found that magnetized neutron stars support higher maximum mass whereas the effect of magnetic field on radial stability for observed neutron star masses is minimal.     

The whole is more than the sum of its parts: Modeling community-level effects of UVR in marine ecosystems

The effect of UVB radiation (UVBR, 290-320 nm) on the dynamics of the lower levels of the marine plankton community was modeled. The model was built using differential equations and shows a good fit to experimental data collected in mesocosms (defined as large enclosures of 1500 L filled with natural marine waters). Some unexpected results appear to be possible by indirect effects in prey (bacteria, phytoplankton and heterotrophic flagellates). In particular, apparent competition appears between small phytoplankton and bacteria. This effect is caused by a shared predator (ciliates). Another remarkable effect is an increase in bacteria and flagellates populations due to enhanced UVBR. This effect is similar to that observed under mesocosm experimental conditions and is related to the decrease of predation due to the direct damage to predators (ciliates) by UVBR. The effect of UVBR changing interaction coefficients may be dramatic on the community structure, producing big changes in equilibrium populations, as demonstrated by sensitivity analysis of the model. In order to generalize these results to field conditions it will be necessary to increase model complexity and include extra organic mater sources, mixing and sinking effects and predation by large zooplankton. This work shows that UVBR may produce community global responses that are consequence of both direct and indirect effects among populations.     

Photoacclimation to long-term ultraviolet radiation exposure of natural sub-Antarctic phytoplankton communities: Fixed surface incubations versus mixed mesocosms

Solar UVB radiation (280-320 nm) is known to have detrimental effects on marine phytoplankton. Associated with the seasonal ozone hole in Antarctica, stratospheric ozone depletion occasionally influences the sub-Antarctic (Beagle Channel, Argentina) region, enhancing levels of UVB. The primary objective of this work was to study the effects of several (i.e. 6-10) days of exposure to UVB on the taxonomic composition and photosynthetic inhibition of local phytoplankton communities. For different light treatments, fixed-depth incubations placed in an outdoors water tank were compared with incubations in 1900 L mesocosms, where vertical mixing was present. Phytoplankton growth was inhibited by UV radiation (UVR) in fixed-depth experiments but not in the mixed mesocosms. Under fixed and mixed conditions alike, photosynthesis was significantly inhibited by UVB at the beginning of the experiment but no longer after several days of exposure, suggesting that cells had acclimated to radiation conditions. There was a change in species composition in response to UVR exposure in both experiments, which likely explained acclimation. In the community exposed to fixed conditions this change was from a phytoflagellate-dominated assemblage to a community with high relative abundance of diatoms after 6 days of exposure. UVA was responsible for most of the observed growth inhibition; however, the reduction in photosynthesis was produced by UVB. The reasons behind this variability in responses to UVR are associated with species-specific sensitivity and acclimation, and the previous light history of cells. In the community exposed in mesocosms, an assemblage codominated by phytoflagellates and diatoms was observed at the beginning of the experiments. After 10 days of exposure, green algae (Eutreptiella sp.) had increased, and phytoflagellates were the dominant group. The synthesis of mycosporine-like amino acids (MAAs), antioxidant enzymes and photosynthetic antenna pigments, in relation to repair and protection processes, may explain the reduced inhibition of both growth and photosynthesis that was observed in the phytoplankton community after several days of exposure. For environments such as the Beagle Channel seasonally exposed to the ozone hole, the results obtained from the fixed-depth experiments show that species can cope with UVR by means of MAA synthesis, while mixing would primarily promote a change in species composition and defense strategies.     

A Convenient One-Flask Procedure for the Direct Conversion of Alkenes to Homoallylic Alcohols

Homoallylic alcohols have been prepared from alkenes by direct reaction of the ozonide with an allylic bromide in the presence of zinc.     

高T_c超导体YBCO磁通钉扎的计算机模拟研究

临界电流密度Jc是影响高温超导体在强电领域应用的一个重要参数,在实际应用中,特别在外加磁场下,临界电流密度与超导材料的磁通钉扎性质密切相关.因此,磁通钉扎一直是高温超导体研究中的一个重要领域.由于高温超导体磁通钉扎力密度Fp的标度律存在,本文根据D.Dew-Hughes总结的钉扎力函数,主要存在两种主要作用类型(正常相和△K).我们将D.Dew-HugBes给出的钉扎力密度Fp标度函数改进为一个简化的具有物理意义的函数表达式.结合文献中已有的实验数据,我们对YBcO进行了计算机模拟,确定了它的磁通钉扎类型,模拟的研究结果与实际情况比较吻合.     

Harnuntersuchung

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