Frozen magma lenses below the oceanic crust

The Earth's oceanic crust crystallizes from magmatic systems generated at mid-ocean ridges. Whereas a single magma body residing within the mid-crust is thought to be responsible for the generation of the upper oceanic crust, it remains unclear if the lower crust is formed from the same magma body, or if it mainly crystallizes from magma lenses located at the base of the crust. Thermal modelling, tomography, compliance and wide-angle seismic studies, supported by geological evidence, suggest the presence of gabbroic-melt accumulations within the Moho transition zone in the vicinity of fast- to intermediate-spreading centres. Until now, however, no reflection images have been obtained of such a structure within the Moho transition zone. Here we show images of groups of Moho transition zone reflection events that resulted from the analysis of approximately 1,500 km of multichannel seismic data collected across the intermediate-spreading-rate Juan de Fuca ridge. From our observations we suggest that gabbro lenses and melt accumulations embedded within dunite or residual mantle peridotite are the most probable cause for the observed reflectivity, thus providing support for the hypothesis that the crust is generated from multiple magma bodies.     

Storage and retrieval of single photons transmitted between remote quantum memories

An elementary quantum network operation involves storing a qubit state in an atomic quantum memory node, and then retrieving and transporting the information through a single photon excitation to a remote quantum memory node for further storage or analysis. Implementations of quantum network operations are thus conditioned on the ability to realize matter-to-light and/or light-to-matter quantum state mappings. Here we report the generation, transmission, storage and retrieval of single quanta using two remote atomic ensembles. A single photon is generated from a cold atomic ensemble at one site , and is directed to another site through 100 metres of optical fibre. The photon is then converted into a single collective atomic excitation using a dark-state polariton approach. After a programmable storage time, the atomic excitation is converted back into a single photon. This is demonstrated experimentally, for a storage time of 0.5 microseconds, by measurement of an anti-correlation parameter. Storage times exceeding ten microseconds are observed by intensity cross-correlation measurements. This storage period is two orders of magnitude longer than the time required to achieve conversion between photonic and atomic quanta. The controlled transfer of single quanta between remote quantum memories constitutes an important step towards distributed quantum networks.     

Mechanism of genetic exchange in American trypanosomes

The kinetoplastid Protozoa are responsible for devastating diseases. In the Americas, Trypanosoma cruzi is the agent of Chagas' disease--a widespread disease transmissible from animals to humans (zoonosis)--which is transmitted by exposure to infected faeces of blood-sucking triatomine bugs. The presence of genetic exchange in T. cruzi and in Leishmania is much debated. Here, by producing hybrid clones, we show that T. cruzi has an extant capacity for genetic exchange. The mechanism is unusual and distinct from that proposed for the African trypanosome, Trypanosoma brucei. Two biological clones of T. cruzi were transfected to carry different drug-resistance markers, and were passaged together through the entire life cycle. Six double-drug-resistant progeny clones, recovered from the mammalian stage of the life cycle, show fusion of parental genotypes, loss of alleles, homologous recombination, and uniparental inheritance of kinetoplast maxicircle DNA. There are strong genetic parallels between these experimental hybrids and the genotypes among natural isolates of T. cruzi. In this instance, aneuploidy through nuclear hybridization results in recombination across far greater genetic distances than mendelian genetic exchange. This mechanism also parallels genome duplication.     

A Systemic Action Learning Cycle as the Key Element of an Ongoing Spiral of Analyses

The Systems movement in the United Kingdom, in addressing the task of enquiry, has created a surfeit of methodologies. Each, like some closely guarded religious sect, demands adherence to its own presentational rules and procedures, its own epistemological and ontological position. Much of the secondary literature of the U.K. Systems movement focuses on examining the strengths and weaknesses of these separate approaches, devises complex decision rules for when to use which methodology, and attempts to map particular methodologies onto "appropriate" scenarios. This paper attempts to present a generalized form of the cyclic activity of investigation and action which is encompassed by many of the methodologies. It is shown that this does not require the presentation of a "lowest common denominator" activity set, which is of no value, but rather draws on the underlying power of the approaches to present a robust and defensible cycle of activities which are continuously reenacted over time. The implications of this spiral model of Action Learning are examined, both in relation to the development of existing methodologies and in relation to the issues related to managing a complex analysis project. The paper concludes by showing how individual analysis cycles merge into a never-ending learning spiral in a complex, dynamic, real-world environment.     

Ultrastructural changes in the stratum corneum after profuse swabbing of the skin with dimethyl sulfoxide

Résumé Une abondante aspersion de la peau du cobaye avec du dimetil sulfoxide produit de notables changements dans les cellules basales de la couche cornée. Elles s'agrandissent, l'aspect fibrillaire de la kératine disparaît et la couche cornée (barrière cutanée) se décolle de la couche granuleuse.

---

---

Supported by Research Career Development Award No. 1-K3-AI-31-210-01 (Dr.Montes) and by National Aeronautics and Space Administration Contracts Nos. 9-2468 and NGR 44-003-018.