Equivalent dose measurements on board an Armenian Airline flight and Concorde (correction of Concord) (9-17 km)

The results of investigations of the neutron component (E=1–10 MeV) of cosmic radiation on board the “Armenian Airlines” aircrafts using nuclear photoemulsion are presented. The emulsions were exposed on the flights from Yerevan to Moscow, St.-Petersburg, Beirut, Athens, Frankfurt, Amsterdam, Paris and Sofia, and on Concord supersonic flights from Paris to New York.

The dependence of the neutron fluxes, and on absorbed and equivalent doses on the flight parameters were investigated. On the flights of the supersonic Concord, with an altitude of 17 km, the neutron fluxes were essentially higher in comparison to those measured on Armenian airliners. It is interesting to note, that the neutron flux and equivalent dose rate decrease with altitude up to 470 km in space, for example, on board the STS-57.

The shape of the differential energy spectrum for fast neutrons is the same on all Armenian airlines flights, but significantly different at 17 km altitude, where the flux in the energy region above 3 MeV is increasing.     

α - Benzenesulfonyl free radicals

Allylic α-halosulfones give, on reduction with tri n-butyl tin hydride, sizeable amounts of dimers. It so appears that free radicals can indeed be formed α to an arenesulfonyl group and coupling can occur during tin hydride reduction of halides.     

Electrocarboxylation of benzyl halides through redox catalysis on the preparative scale

The electrocarboxylation of benzyl halides to the corresponding carboxylic acids through homogeneous charge-transfer catalysis was investigated both theoretically and experimentally to determine the influence of the operative parameters on the yield of the process and on the catalyst consumption. Theoretical considerations, based on fast kinetics of redox catalysis, were confirmed by the electrocarboxylation of 1-phenyl-1-chloroethane catalyzed by 1,3-benzenedicarboxylic acid dimethyl ester performed at a carbon cathode under different operative conditions. We obtained high yields of the target carboxylic acid and experienced a low catalyst consumption by operating with optimized [RX]bulk/[CO2]bulk and [RX]bulk/[catalyst] ratios.     

Head and backbone of the Early Cambrian vertebrate Haikouichthys

Agnathan fish hold a key position in vertebrate evolution, especially regarding the origin of the head and neural-crest-derived tissue. In contrast to amphioxus, lampreys and other vertebrates possess a complex brain and placodes that contribute to well-developed eyes, as well as auditory and olfactory systems. These sensory sytems were arguably a trigger to subsequent vertebrate diversifications. However, although they are known from skeletal impressions in younger Palaeozoic agnathans, information about the earliest records of these systems has been largely wanting. Here we report numerous specimens of the Lower Cambrian vertebrate Haikouichthys ercaicunensis, until now only known from the holotype. Haikouichthys shows significant differences from other fossil agnathans: key features include a small lobate extension to the head, with eyes and possible nasal sacs, as well as what may be otic capsules. A notochord with separate vertebral elements is also identifiable. Phylogenetic analysis indicates that this fish lies within the stem-group craniates. Although Haikouichthys somewhat resembles the ammocoete larva of modern lampreys, this is because of shared general craniate characters; adult lampreys and hagfishes (the cyclostomes if monophyletic) are probably derived in many respects.     

Couplage mixte entre sulfones vinyliques et réactifs de grignard en présence de sels de métal de transition: synthèse stéréosélective d'oléfines trisubstituées.

A new cross coupling reaction of vinylic sulphones with Grignard reagents catalyzed by nickel and iron complexes is described. This reaction is stereospecific: tri-substituted olefins of defined stereochemistry are obtained in good yield.     

Synthèse stéréosélective des sulfones vinyliques Z et E.

The condensation of α-sulphonyl carbanions with esters or with aldehydes (followed in this case by oxidation) gives β-ketosulphones. These were reduced stereoselectively into threo β-hydroxysulphones.Basic conditions have been found where the corresponding tosylates are converted into Z vinylic sulphones whereas the erythro tosylates lead to the E isomer. The corresponding acetoxy-sulphones erythro or threo, under different alkaline conditions are converted into the same E vinylic sulphone in a “convergent” manner.     

Synthèse d'oléfines et de polyènes par doublement d'anions α-sulfonylés en présence de sels de nickel (XXII).

The lithium or magnesium derivatives of allyl, benzyl and alkyl sulphones are converted efficiently by a catalytic amount of nickel(II) acetylacetonate into symmetrical olefins in THF at 60°C. Thus, phytoene was obtained in a 74% yield from geranylgeranylsulphone.     

Couplage des sulfones allyliques avec des reactifs de grignard en presence de cuivre synthese d'olefines

A convenient synthesis of di- and trisubstituted olefins using the coupling of Grignard reagents with allylic sulphones in the presence of copper II acetylacetonate is reported. The influence of sulphone, Grignard reagent and solvent on the regio- and stereoselectivity is discussed.     

Ancestral echinoderms from the Chengjiang deposits of China

Deuterostomes are a remarkably diverse super-phylum, including not only the chordates (to which we belong) but groups as disparate as the echinoderms and the hemichordates. The phylogeny of deuterostomes is now achieving some degree of stability, especially on account of new molecular data, but this leaves as conjectural the appearance of extinct intermediate forms that would throw light on the sequence of evolutionary events leading to the extant groups. Such data can be supplied from the fossil record, notably those deposits with exceptional soft-part preservation. Excavations near Kunming in southwestern China have revealed a variety of remarkable early deuterostomes, including the vetulicolians and yunnanozoans. Here we describe a new group, the vetulocystids. They appear to have similarities not only to the vetulicolians but also to the homalozoans, a bizarre group of primitive echinoderms whose phylogenetic position has been highly controversial.