We report the design and performance of 300-mK composite bolometers that use micromesh absorbers and support structures patterned from thin films of low-stress silicon nitride. The small geometrical filling factor of the micromesh absorber provides 20ϫ reduction in heat capacity and cosmic ray cross section relative to a solid absorber with no loss in IR-absorption efficiency. The support structure is mechanically robust and has a thermal conductance, G Ͻ 2 ϫ 10 Ϫ11 W͞K, which is four times smaller than previously achieved at 300 mK. The temperature rise of the bolometer is measured with a neutron transmutation doped germanium thermistor attached to the absorbing mesh. The dispersion in electrical and thermal parameters of a sample of 12 bolometers optimized for the Sunyaev-Zel'dovich Infrared Experiment is Ϯ7% in R͑T͒, Ϯ5% in optical efficiency, and Ϯ4% in G.

This study deals with the construction of identity in institutional contexts, taking as a starting point a Bakhtinian approach. We focus on the idea of author and hero and consider it as a metaphor allowing us to look for new models through which to understand human learning. We consider in particular the ethical and aesthetic dimension of human activity, which relate to the concepts of ‘I’ and ‘other’, respectively, and pay special attention to personal and interpersonal dimensions of consciousness. After exploring some of Bakhtin’s earliest texts, we focus on classroom conversations in which children worked together with their teacher and the researchers on the production of a web page which was to include their own comments and reflections following a discussion of violence on TV programs. Our examples are drawn from a wider investigation carried out in a Spanish elementary school, where we have been working from within an ethnographical and action research perspective. The analyses show that when mass media are present in the classroom, and children and adults talk about violence on television, specific situations are created that favor the construction of identity from an ethical-aesthetic perspective: that is, children are capable of assuming responsibilities and, furthermore, they create heroes who are also responsible for their own actions.

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The MeOH extract of the aerial parts of Croton ruizianus afforded two new pregnane glycosides 1 and 2, together with the morphinandienone alkaloids flavinantine (3) and O-methylflavinantine (4). Their structures were elucidated by NMR experiments including 1H-1H (1D TOCSY and 2D DQF-COSY) and 1H-13C (HSQC, HMBC) spectroscopy. The proaggregating activity of the MeOH extract and the isolates were evaluated. Although the MeOH extract and pregnane glycosides (at different doses) were found to promote platelet aggregation, flavinantine (3) and O-methylflavinantine (4) showed only slight activity. The ability of the MeOH extract and the four compounds to act synergistically with thrombin was also evaluated. All the tested compounds were successful in augmenting the aggregating effect of thrombin, although to different degrees.

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