A rapid mechanism to remobilize and homogenize highly crystalline magma bodies

The largest products of magmatic activity on Earth, the great bodies of granite and their corresponding large eruptions, have a dual nature: homogeneity at the large scale and spatial and temporal heterogeneity at the small scale. This duality calls for a mechanism that selectively removes the large-scale heterogeneities associated with the incremental assembly of these magmatic systems and yet occurs rapidly despite crystal-rich, viscous conditions seemingly resistant to mixing. Here we show that a simple dynamic template can unify a wide range of apparently contradictory observations from both large plutonic bodies and volcanic systems by a mechanism of rapid remobilization (unzipping) of highly viscous crystal-rich mushes. We demonstrate that this remobilization can lead to rapid overturn and produce the observed juxtaposition of magmatic materials with very disparate ages and complex chemical zoning. What distinguishes our model is the recognition that the process has two stages. Initially, a stiff mushy magma is reheated from below, producing a reduction in crystallinity that leads to the growth of a subjacent buoyant mobile layer. When the thickening mobile layer becomes sufficiently buoyant, it penetrates the overlying viscous mushy magma. This second stage rapidly exports homogenized material from the lower mobile layer to the top of the system, and leads to partial overturn within the viscous mush itself as an additional mechanism of mixing. Model outputs illustrate that unzipping can rapidly produce large amounts of mobile magma available for eruption. The agreement between calculated and observed unzipping rates for historical eruptions at Pinatubo and at Montserrat demonstrates the general applicability of the model. This mechanism furthers our understanding of both the formation of periodically homogenized plutons (crust building) and of ignimbrites by large eruptions.     

Broadband waveguide quantum memory for entangled photons

The reversible transfer of quantum states of light into and out of matter constitutes an important building block for future applications of quantum communication: it will allow the synchronization of quantum information, and the construction of quantum repeaters and quantum networks. Much effort has been devoted to the development of such quantum memories, the key property of which is the preservation of entanglement during storage. Here we report the reversible transfer of photon-photon entanglement into entanglement between a photon and a collective atomic excitation in a solid-state device. Towards this end, we employ a thulium-doped lithium niobate waveguide in conjunction with a photon-echo quantum memory protocol, and increase the spectral acceptance from the current maximum of 100?megahertz to 5?gigahertz. We assess the entanglement-preserving nature of our storage device through Bell inequality violations and by comparing the amount of entanglement contained in the detected photon pairs before and after the reversible transfer. These measurements show, within statistical error, a perfect mapping process. Our broadband quantum memory complements the family of robust, integrated lithium niobate devices. It simplifies frequency-matching of light with matter interfaces in advanced applications of quantum communication, bringing fully quantum-enabled networks a step closer.     

A cellular oncogene (c-Ki-ras) is amplified, overexpressed, and located within karyotypic abnormalities in mouse adrenocortical tumour cells

The cellular oncogene c-Ki-ras is amplified 30- to 60-fold in cells of the mouse adrenocortical tumour Y1. The amplified oncogene is located in double minute chromosomes and in a homogeneously staining chromosomal region, common karyotypical anomalies of tumour cells. The amounts of c-Ki-ras specific mRNA and of the protein (p21) encoded by the amplified gene are correspondingly elevated. Amplification and enhanced expression of cellular oncogenes may contribute to the genesis and/or maintenance of at least some naturally occurring tumours.     

Molecular orbital studies on the conformations of bicuculline and β-hydroxy GABA

Zusammenfassung Mit Hilfe der MO-Theorie wurden bevorzugte Konformationen für den GABA Agonisten -Hydroxy-GABA und den Antagonisten Bicucullin berechnet. In beiden Fällen ergeben sich fast gleiche Abstände zwischen der Ammoniumgruppe und dem Sauerstoffatom wie in der entsprechenden Struktur von GABA selbst.

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Supported by National Institutes of Health (US) Grant No. 19709.     

Selection overrides gene flow to break down maladaptive mimicry

Predators typically avoid dangerous species, and batesian mimicry evolves when a palatable species (the 'mimic') co-opts a warning signal from a dangerous species (the 'model') and thereby deceives its potential predators. Because predators would not be under selection to avoid the model and any of its look-alikes in areas where the model is absent (that is, allopatry), batesian mimics should occur only in sympatry with their model. However, contrary to this expectation, batesian mimics often occur in allopatry. Here we focus on one such example--a coral snake mimic. Using indirect DNA-based methods, we provide evidence suggesting that mimics migrate from sympatry, where mimicry is favoured, to allopatry, where it is disfavoured. Such gene flow is much stronger in nuclear genes than in maternally inherited mitochondrial genes, indicating that dispersal by males may explain the presence of mimetic phenotypes in allopatry. Despite this gene flow, however, individuals from allopatry resemble the model less than do individuals from sympatry. We show that this breakdown of mimicry probably reflects predator-mediated selection acting against individuals expressing the more conspicuous mimetic phenotype in allopatry. Thus, although gene flow may explain why batesian mimics occur in allopatry, natural selection may often override such gene flow and promote the evolution of non-mimetic phenotypes in such areas.     

Amygdala intercalated neurons are required for expression of fear extinction

Congruent findings from studies of fear learning in animals and humans indicate that research on the circuits mediating fear constitutes our best hope of understanding human anxiety disorders. In mammals, repeated presentations of a conditioned stimulus that was previously paired to a noxious stimulus leads to the gradual disappearance of conditioned fear responses. Although much evidence suggests that this extinction process depends on plastic events in the amygdala, the underlying mechanisms remain unclear. Intercalated (ITC) amygdala neurons constitute probable mediators of extinction because they receive information about the conditioned stimulus from the basolateral amygdala (BLA), and contribute inhibitory projections to the central nucleus (CEA), the main output station of the amygdala for conditioned fear responses. Thus, after extinction training, ITC cells could reduce the impact of conditioned-stimulus-related BLA inputs to the CEA by means of feed-forward inhibition. Here we test the hypothesis that ITC neurons mediate extinction by lesioning them with a toxin that selectively targets cells expressing micro-opioid receptors (microORs). Electron microscopic observations revealed that the incidence of microOR-immunoreactive synapses is much higher in ITC cell clusters than in the BLA or CEA and that microORs typically have a post-synaptic location in ITC cells. In keeping with this, bilateral infusions of the microOR agonist dermorphin conjugated to the toxin saporin in the vicinity of ITC neurons caused a 34% reduction in the number of ITC cells but no significant cell loss in surrounding nuclei. Moreover, ITC lesions caused a marked deficit in the expression of extinction that correlated negatively with the number of surviving ITC neurons but not CEA cells. Because ITC cells exhibit an unusual pattern of receptor expression, these findings open new avenues for the treatment of anxiety disorders.     

DNA-programmable nanoparticle crystallization

It was first shown more than ten years ago that DNA oligonucleotides can be attached to gold nanoparticles rationally to direct the formation of larger assemblies. Since then, oligonucleotide-functionalized nanoparticles have been developed into powerful diagnostic tools for nucleic acids and proteins, and into intracellular probes and gene regulators. In contrast, the conceptually simple yet powerful idea that functionalized nanoparticles might serve as basic building blocks that can be rationally assembled through programmable base-pairing interactions into highly ordered macroscopic materials remains poorly developed. So far, the approach has mainly resulted in polymerization, with modest control over the placement of, the periodicity in, and the distance between particles within the assembled material. That is, most of the materials obtained thus far are best classified as amorphous polymers, although a few examples of colloidal crystal formation exist. Here, we demonstrate that DNA can be used to control the crystallization of nanoparticle-oligonucleotide conjugates to the extent that different DNA sequences guide the assembly of the same type of inorganic nanoparticle into different crystalline states. We show that the choice of DNA sequences attached to the nanoparticle building blocks, the DNA linking molecules and the absence or presence of a non-bonding single-base flexor can be adjusted so that gold nanoparticles assemble into micrometre-sized face-centred-cubic or body-centred-cubic crystal structures. Our findings thus clearly demonstrate that synthetically programmable colloidal crystallization is possible, and that a single-component system can be directed to form different structures.     

Carbon nanotube and conducting polymer composites for supercapacitors

Composites of carbon nanotubes and conducting polymers can be prepared via chemical synthesis, electrochemical deposition on preformed carbon nanotube electrodes, or by electrochemical co-deposition. The composites combine the large pseudocapacitance of the conducting polymers with the fast charging/discharging double-layer capacitance and excellent mechanical properties of the carbon nanotubes. The electrochemically co-deposited composites are the most homogeneous and show an unusual interaction between the polymer and nanotubes, giving rise to a strengthened electron delocalisation and conjugation along the polymer chains. As a result they exhibit excellent electrochemical charge storage properties and fast charge/discharge switching, making them promising electrode materials for high Dower suDercapacitors.