Strained silicon as a new electro-optic material

For decades, silicon has been the material of choice for mass fabrication of electronics. This is in contrast to photonics, where passive optical components in silicon have only recently been realized. The slow progress within silicon optoelectronics, where electronic and optical functionalities can be integrated into monolithic components based on the versatile silicon platform, is due to the limited active optical properties of silicon. Recently, however, a continuous-wave Raman silicon laser was demonstrated; if an effective modulator could also be realized in silicon, data processing and transmission could potentially be performed by all-silicon electronic and optical components. Here we have discovered that a significant linear electro-optic effect is induced in silicon by breaking the crystal symmetry. The symmetry is broken by depositing a straining layer on top of a silicon waveguide, and the induced nonlinear coefficient, chi(2) approximately 15 pm V(-1), makes it possible to realize a silicon electro-optic modulator. The strain-induced linear electro-optic effect may be used to remove a bottleneck in modern computers by replacing the electronic bus with a much faster optical alternative.     

Measurement of stellar age from uranium decay

The ages of the oldest stars in the Galaxy indicate when star formation began, and provide a minimum age for the Universe. Radioactive dating of meteoritic material and stars relies on comparing the present abundance ratios of radioactive and stable nuclear species to the theoretically predicted ratios of their production. The radioisotope 232Th (half-life 14 Gyr) has been used to date Galactic stars, but it decays by only a factor of two over the lifetime of the Universe. 238U (half-life 4.5 Gyr) is in principle a more precise age indicator, but even its strongest spectral line, from singly ionized uranium at a wavelength of 385.957 nm, has previously not been detected in stars. Here we report a measurement of this line in the very metal-poor star CS31082-001, a star which is strongly overabundant in its heavy elements. The derived uranium abundance, log(U/H) = -13.7 +/- 0.14 +/- 0.12 yields an age of 12.5 +/- 3 Gyr, though this is still model dependent. The observation of this cosmochronometer gives the most direct age determination of the Galaxy. Also, with improved theoretical and laboratory data, it will provide a highly precise lower limit to the age of the Universe.     

Ether soluble pigments in interglacial gyttja

Zusammenfassung Etwa 100 000 Jahre alte, interglaziale Gyttja aus Rodebäk im westlichen Dänemark (Riss-Würm-Interglazialzeit) wurde mit Äther extrahiert und die Extrakte mittels Papierchromatographie getrennt und untersucht. Es wurden grüne, gelbe und rote Pigmente gefunden. Aus den Absorptionsspektren und der Fluoreszenz dieser Stoffe ergibt sich, dass die grünen Pigmente Chlorophyllderivate, die gelben (sowie wenigstens eines der roten) Karotinoide sind. Die Gyttja enthielt schr wenige bestimmbare Pflanzenreste, hauptsächlich nur Pollen und Diatomeen. Die Farbstoffe müssen von lebenden Pflanzen im interglazialen See, in erster Linie Algen, herrühren, und haben infolge Lichtabschluss und niedrigem Redoxpotential sowie niedriger Temperatur ausserordentlich gute Aufbewahrungsbedingungen gefunden; normalerweise werden solche Stoffe schnell abgebaut.     

Bilayer-dependent inhibition of mechanosensitive channels by neuroactive peptide enantiomers

The peptide GsMTx4, isolated from the venom of the tarantula Grammostola spatulata, is a selective inhibitor of stretch-activated cation channels (SACs). The mechanism of inhibition remains unknown; but both GsMTx4 and its enantiomer, enGsMTx4, modify the gating of SACs, thus violating a trademark of the traditional lock-and-key model of ligand-protein interactions. Suspecting a bilayer-dependent mechanism, we examined the effect of GsMTx4 and enGsMTx4 on gramicidin A (gA) channel gating. Both peptides are active, and the effect increases with the degree of hydrophobic mismatch between bilayer thickness and channel length, meaning that GsMTx4 decreases the energy required to deform the boundary lipids adjacent to the channel. GsMTx4 decreases inward SAC single-channel currents but has no effect on outward currents, suggesting it is located within a Debye length of the outer vestibule of the SACs, but significantly farther from the inner vestibule. Likewise, GsMTx4 decreases gA single-channel currents. Our results suggest that modulation of membrane proteins by amphipathic peptides--mechanopharmacology--involves not only the protein itself but also the surrounding lipids. The surprising efficacy of the d form of GsMTx4 peptide has important therapeutic implications, because d peptides are not hydrolysed by endogenous proteases and may be administered orally.     

Nucleolar proteome dynamics

The nucleolus is a key organelle that coordinates the synthesis and assembly of ribosomal subunits and forms in the nucleus around the repeated ribosomal gene clusters. Because the production of ribosomes is a major metabolic activity, the function of the nucleolus is tightly linked to cell growth and proliferation, and recent data suggest that the nucleolus also plays an important role in cell-cycle regulation, senescence and stress responses. Here, using mass-spectrometry-based organellar proteomics and stable isotope labelling, we perform a quantitative analysis of the proteome of human nucleoli. In vivo fluorescent imaging techniques are directly compared to endogenous protein changes measured by proteomics. We characterize the flux of 489 endogenous nucleolar proteins in response to three different metabolic inhibitors that each affect nucleolar morphology. Proteins that are stably associated, such as RNA polymerase I subunits and small nuclear ribonucleoprotein particle complexes, exit from or accumulate in the nucleolus with similar kinetics, whereas protein components of the large and small ribosomal subunits leave the nucleolus with markedly different kinetics. The data establish a quantitative proteomic approach for the temporal characterization of protein flux through cellular organelles and demonstrate that the nucleolar proteome changes significantly over time in response to changes in cellular growth conditions.     

Physiology: postprandial cardiac hypertrophy in pythons

Oxygen consumption by carnivorous reptiles increases enormously after they have eaten a large meal in order to meet metabolic demands, and this places an extra load on the cardiovascular system. Here we show that there is an extraordinarily rapid 40% increase in ventricular muscle mass in Burmese pythons (Python molurus) a mere 48 hours after feeding, which results from increased gene expression of muscle-contractile proteins. As this fully reversible hypertrophy occurs naturally, it could provide a useful model for investigating the mechanisms that lead to cardiac growth in other animals.     

Complexity and Change: Two "Semantic Tricks" in the Triumphant Oscillating Organization

This article is about the effects of the semantics "complexity and change" used for intraorganizational communication about the relation between organization and environment. Our hypothesis is that communications along this semantic will have profound effects on the organization as to steering as it undermines the idea of organizational unity and establishes the future or utopia as the frame of reference for communication around steering. Our empirical findings from the development in the Danish central administration points in that direction. This is not necessarily implying organizational breakdown, however it might provide the basis for "oscillocracy" that is steering through acceleration of communicative flexibility and ambiguity. As theoretical frame we have chosen the German sociologist Niklas Luhmann and his communicative systems theory, which is introduced at the beginning of the article. In the central part, we present our empirical findings and at the end of the article we reflect upon oscillation.     

Direct visuomotor transformations for reaching

The posterior parietal cortex (PPC) is thought to have a function in the sensorimotor transformations that underlie visually guided reaching, as damage to the PPC can result in difficulty reaching to visual targets in the absence of specific visual or motor deficits. This function is supported by findings that PPC neurons in monkeys are modulated by the direction of hand movement, as well as by visual, eye position and limb position signals. The PPC could transform visual target locations from retinal coordinates to hand-centred coordinates by combining sensory signals in a serial manner to yield a body-centred representation of target location, and then subtracting the body-centred location of the hand. We report here that in dorsal area 5 of the PPC, remembered target locations are coded with respect to both the eye and hand. This suggests that the PPC transforms target locations directly between these two reference frames. Data obtained in the adjacent parietal reach region (PRR) indicate that this transformation may be achieved by vectorially subtracting hand location from target location, with both locations represented in eye-centred coordinates.