62,204 research outputs found


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    Callose (β-1,3 glucan) is essential for Arabidopsis pollen wall patterning, but not tube growth

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    Background: Callose (β-1,3 glucan) separates developing pollen grains, preventing their underlying walls (exine) from fusing. The pollen tubes that transport sperm to female gametes also contain callose, both in their walls as well as in the plugs that segment growing tubes. Mutations in CalS5, one of several Arabidopsis β-1,3 glucan synthases, were previously shown to disrupt callose formation around developing microspores, causing aberrations in exine patterning, degeneration of developing microspores, and pollen sterility. Results: Here, we describe three additional cals5 alleles that similarly alter exine patterns, but instead produce fertile pollen. Moreover, one of these alleles (cals5-3) resulted in the formation of pollen tubes that lacked callose walls and plugs. In self-pollinated plants, these tubes led to successful fertilization, but they were at a slight disadvantage when competing with wild type. Conclusion: Contrary to a previous report, these results demonstrate that a structured exine layer is not required for pollen development, viability or fertility. In addition, despite the presence of callose-enriched walls and callose plugs in pollen tubes, the results presented here indicate that callose is not required for pollen tube functions

    Review of Heavy Hadron Spectroscopy

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    The status of some of the recently discovered heavy hadrons is presented.Comment: 6 pages, plenary talk at International Conference on QCD and Hadronic Physics, Beijing, June 200

    Quantum string integrability and AdS/CFT

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    Recent explorations of the AdS/CFT correspondence have unveiled integrable structures underlying both planar N = 4 super-Yang-Mills theory and type IIB string theory on AdS_5 x S^5. Integrability in the gauge theory emerges from the fact that the dilatation generator can be identified with the Hamiltonian of an integrable quantum spin chain, and the classical string theory has been shown to contain infinite towers of hidden currents, a typical signature of integrability. Efforts to match the integrable structures of various classical string configurations to those of corresponding gauge theory quantum spin chains have been largely successful. By studying a semiclassical expansion about a class of point-like solitonic solutions to the classical string equations of motion on AdS_5 x S^5, we take a step toward demonstrating that integrability in the string theory survives quantum corrections beyond tree level. Quantum fluctuations are chosen to align with background curvature corrections to the pp-wave limit of AdS_5 x S^5, and we present evidence for an infinite tower of local bosonic charges that are conserved by the quantum theory to quartic order in the expansion. We explicitly compute several higher charges based on a Lax representation of the worldsheet sigma model and provide a prescription for matching the eigenvalue spectra of these charges with corresponding quantities descending from the integrable structure of the gauge theory.Comment: v2: references and typos corrected; v3: minor corrections and comments, 23 page

    Designing educational tasks for success in industry: a reflection on the evolution of business communication studies in tertiary education

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    This paper is the result of a &quot;Rip Van Winkle&quot; experience I had concerning the teaching of Business Communication. The paper focuses on the remarkable expansion in the curriculum of the traditional &quot;Business Communication&quot; or &quot;Business Writing&quot; course offered by many tertiary institutions around the world. Based on 25 years of personal observation and experience in a number of educational settings, the paper will trace the increasing sophistication and complexity of the study of business communication from one that covered little more than lessons in the design of hardcopy memos, letters, and reports to one that now covers a broad spectrum of topics such as &quot;emotional intelligence,&quot; &quot;intercultural communication,&quot; &quot;effective public speaking,&quot; as well as the effects of purpose and audience on the design of a wide variety of business communications.An example of an effective task that involves a number of on the job activities is provided in the form of a ready to use assignment that is applicable in a number of contexts.<br /

    The minimal components of the Mayr-Meyer ideals

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    Mayr and Meyer found ideals J(n,d)J(n,d) (in a polynomial ring in 10n+210n+2 variables over a field kk and generators of degree at most d+2d+2) with ideal membership property which is doubly exponential in nn. This paper is a first step in understanding the primary decomposition of these ideals: it is proved here that J(n,d)J(n,d) has nd2+20nd^2 + 20 minimal prime ideals. Also, all the minimal components are computed, and the intersection of the minimal components as well
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