Light echoes from ancient supernovae in the Large Magellanic Cloud

The light from historical supernovae could in principle still be visible as scattered-light echoes centuries after the explosion. The detection of light echoes could allow us to pinpoint the supernova event both in position and age and, most importantly, permit the acquisition of spectra to determine the 'type' of the supernova centuries after the direct light from the explosion first reached Earth. Although echoes have been discovered around some nearby extragalactic supernovae, targeted searches have not found any echoes in the regions of historical Galactic supernovae. Here we report three faint variable-surface-brightness complexes with high apparent proper motions pointing back to three of the six smallest (and probably youngest) previously catalogued supernova remnants in the Large Magellanic Cloud, which are believed to have been thermonuclear (type Ia) supernovae. Using the distance and apparent proper motions of these echo arcs, we estimate ages of 610 and 410 years for two of them.     

Cyclin-dependent kinase 2 is essential for meiosis but not for mitotic cell division in mice

We targeted the locus encoding the cyclin-dependent kinase 2 (CDK2) by homologous recombination in mouse embryonic stem (ES) cells. Embryonic fibroblasts lacking CDK2 proliferate normally and become immortal after continuous passage in culture. Elimination of a conditional Cdk2 allele in immortal cells does not have a significant effect on proliferation. Cdk2-/- mice are viable and survive for up to two years, indicating that CDK2 is also dispensable for proliferation and survival of most cell types. But CDK2 is essential for completion of prophase I during meiotic cell division in male and female germ cells, an unforeseen role for this cell cycle kinase.     

Neural substrates of awakening probed with optogenetic control of hypocretin neurons

The neural underpinnings of sleep involve interactions between sleep-promoting areas such as the anterior hypothalamus, and arousal systems located in the posterior hypothalamus, the basal forebrain and the brainstem. Hypocretin (Hcrt, also known as orexin)-producing neurons in the lateral hypothalamus are important for arousal stability, and loss of Hcrt function has been linked to narcolepsy. However, it is unknown whether electrical activity arising from Hcrt neurons is sufficient to drive awakening from sleep states or is simply correlated with it. Here we directly probed the impact of Hcrt neuron activity on sleep state transitions with in vivo neural photostimulation, genetically targeting channelrhodopsin-2 to Hcrt cells and using an optical fibre to deliver light deep in the brain, directly into the lateral hypothalamus, of freely moving mice. We found that direct, selective, optogenetic photostimulation of Hcrt neurons increased the probability of transition to wakefulness from either slow wave sleep or rapid eye movement sleep. Notably, photostimulation using 5-30 Hz light pulse trains reduced latency to wakefulness, whereas 1 Hz trains did not. This study establishes a causal relationship between frequency-dependent activity of a genetically defined neural cell type and a specific mammalian behaviour central to clinical conditions and neurobehavioural physiology.     

Zinc bioleaching from an iron concentrate using <Emphasis Type=Italic>Acidithiobacillus ferrooxidans</Emphasis> strain from Hercules Mine of Coahuila,Mexico

The iron concentrate from Hercules Mine of Coahuila, Mexico, which mainly contained pyrite and pyrrhotite, was treated by the bioleaching process using native strain Acidithiobacillus ferrooxidans (A. ferrooxidans) to determine the ability of these bacteria on the leaching of zinc. The native bacteria were isolated from the iron concentrate of the mine. The bioleaching experiments were carried out in shake flasks to analyze the effects of pH values, pulp density, and the ferrous sulfate concentration on the bioleaching process. The results obtained by microbial kinetic analyses for the evaluation of some aspects of zinc leaching show that the native bacteria A. ferrooxidans, which is enriched with a 9K Silverman medium under the optimum conditions of pH 2.0, 20 g/L pulp density, and 40 g/L FeSO₄, increases the zinc extraction considerably observed by monitoring during15 d, i.e., the zinc concentration has a decrease of about 95% in the iron concentrate.