Observation of Events with an Energetic Forward Neutron in Deep Inelastic Scattering at HERA

In deep inelastic neutral current scattering of positrons and protons at the center of mass energy of 300 GeV, we observe, with the ZEUS detector, events with a high energy neutron produced at very small scattering angles with respect to the proton direction. The events constitute a fixed fraction of the deep inelastic, neutral current event sample independent of Bjorken x and Q2 in the range 3 · 10-4 \u3c xBJ \u3c 6 · 10-3 and 10 \u3c Q2 \u3c 100 GeV2

Karyological studies in Asteraceae. VIII

Meiotic and/or mitotic chromosome numbers were determined and observations on meiotic behavior were made in 14 accessions belonging to 14 especies concerning 8 genera distributed in 4 tribes of the Asteraceae. Five species are investigated chromosomally for the first time. These are as follows, tribe Mutisieae: Brachyclados cespitosus(Phil.) Speg. (n = 23), Nassauvia pygmaea (Cass.) Hooker (n = 22); tribe Cichorieae: Hypochoeris acaulis (Remy) Britton (n = 4, 2n = 8), Hieracium glaucifolium Poepp. ex Froelich in DC. (2n = 18) and Hieracium aff. palezieuxii Zahn (2n = 18). Different chromosome number to those previously reported in the literature were found for Hypochoeris chondrilloides (A. Gray) Cabrera (n = 8), Baccharis ulicina Hook. Arn. (2n = 18+3B), Conyza aff. bonariensis (L.) Cronquist (2n = 18). The karyotypes of Brachyclados lycioides Don, Hypochoeris acaulis (Remy) Britton, Hieracium aff. palezieuxii Zahn and Senecio chilensis Less. are described for the first time. Meanwhile, the karyotypes of Hypochoeris microcephala (Sch. Bip.) Cabrera var. albiflora (Kuntze) Cabrera, H. chillensis (Kunth) Hieron. and H. megapotamica Cabrera showed to be slightly different with those described in previous publications. The significance of some of the results in relation to taxonomical and evolutionary problems is discussed.Fil:Wulff, A.F. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

Permanent translocation heterozygosity in dioecious Baccharis coridifolia DC. (Asteraceae)

The karyotype of Baccharis coridifolia DC., a dioecious diploid species consists of 16 chromosomes with median (m) and 2 with submedian centromeric positions (sm) (2n = 18). Meiotic analyses of 219 male plants belonging to 12 populations showed across a wide geographical range one quadrivalent and seven bivalents in all of them. The quadrivalent involves the four biggest m chromosomes and probably constitutes a sex multivalent carrying in tight linkage the sex genes and provides a mechanism whereby permanent translocation heterozygosity is maintained. In metaphase I alternate orientation of the quadrivalent was predominant (85.71 %). Fourteen megaspore mother cells were analyzed and did not show the quadrivalent. A model for the origin and maintenance of the sexual translocation system is presented. It is assumed that there are two non-allelic factors M and n; M would be a dominant female suppresor and n a recessive male-suppresor. The excess of male plants observed in several populations at different localities might result from heterotic effects of some gene complexes carried by the translocation. This excess probably ensures a good supply of pollen for the vagaries of insect pollination at flowering time.Fil:Wulff, A.F. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

Phase-field theory of edges in an anisotropic crystal

In the presence of sufficiently strong surface energy anisotropy the equilibrium shape of an isothermal crystal may include corners or edges. Models of edges have, to date, involved the regularisation of the corresponding free boundary problem resulting in equilibrium shapes with smoothed out edges. In this paper we take a new approach and consider how a phase-field model, which provides a diffuse description of an interface, can be extended to the consideration of edges by an appropriate regularisation of the underlying mathematical model. Using the method of matched asymptotic expansions we develop an approximate solution which corresponds to a smoothed out edge from which we are able to determine the associated edge energy

Potential for re-emergence of wheat stem rust in the United Kingdom.

Wheat stem rust, a devastating disease of wheat and barley caused by the fungal pathogenPuccinia graminis f. sp. tritici, was largely eradicated in Western Europe during the mid-to-latetwentieth century. However, isolated outbreaks have occurred in recent years. Here weinvestigate whether a lack of resistance in modern European varieties, increased presence of itsalternate host barberry and changes in climatic conditions could be facilitating its resurgence.We report the first wheat stem rust occurrence in the United Kingdom in nearly 60 years,with only 20% of UK wheat varieties resistant to this strain. Climate changes over the past 25years also suggest increasingly conducive conditions for infection. Furthermore, we documentthe first occurrence in decades of P. graminis on barberry in the UK . Our data illustrate thatwheat stem rust does occur in the UK and, when climatic conditions are conducive, couldseverely harm wheat and barley production