Towards a combinatorial Intersection Cohomology for Fans

The real intersection cohomology of a toric variety is described in a purely combinatorial way using methods of elementary commutative algebra only. We define, for arbitrary fans, the notion of a ``minimal extension sheaf'' on the fan as an axiomatic characterization of the equivariant intersection cohomology sheaf. This provides a purely algebraic interpretation of Stanley's generalized f- and g-vector of an arbitrary polytope or complete fan under a natural vanishing condition. -- The results presented in this note originate from joint work with G.Barthel, J.-P.Brasselet and L.Kaup, continuing earlier research (see math.AG/9904159). A detailed exposition will appear elsewhere (see math.AG/0002181).Comment: 8 pages, TeX, special macros are included, To appear in CRAS, Acad. Sci. Pari

Diversity and function of phage encoded depolymerases

Bacteriophages of the Podoviridae family often exhibit so-called depolymerases as structural components of the virion. These enzymes appear as tail spike proteins (TSPs). After specific binding to capsular polysaccharides (CPS), exopolysaccharides (EPS) or lipopolysaccharide (LPS) of the host bacteria, polysaccharide-repeating units are specifically cleaved. Finally, the phage reaches the last barrier, the cell wall, injects its DNA, and infects the cell. Recently, similar enzymes from bacteriophages of the Ackermannviridae, Myoviridae, and Siphoviridae families were also described. In this mini-review the diversity and function of phage encoded CPS-, EPS-, and LPSdegrading depolymerases is summarized. The function of the enzymes is described in terms of substrate specificity and applications in biotechnology

Partnerships, Lemons and Efficient Trade

We analyze the possibility of efficient trade with informationally interdependent valuations and with a dispersed ownership. A crucial role is played by the sign of the derivatives that measure how valuation functions depend on others’ signals. If valuations are increasing functions of other agents’ signals, it is more difficult to achieve efficient trade with interdependent values than with private values (where the respective derivatives are zero.) In contrast, if valuations are decreasing functions of other agents’ signals, it is easier to achieve efficient trade with interdependent values. Our results unify and generalize the insights of Cramton et al. [1987], Myerson and Satterthwaite [1983], and Akerlof [1970].

The Soviet Union’s “Great Patriotic War” Invalids:: The Poverty of a New Status Group

Die Sowjetunion ging aus dem „Großen Vaterländischen Krieg“ als Sieger und zweite Supermacht neben den USA hervor. Doch der Preis für diesen Triumph war schrecklich hoch. Der Krieg kostete schätzungsweise 27 Mio. Menschen das Leben, Millionen Soldaten kehrten verstümmelt, blind oder chronisch krank von der Front zurück. Aufgrund rigider Anerkennungsverfahren wurden aber nicht alle dieser Kriegsopfer in die Statusgruppe der staatlich anerkannten Kriegsinvaliden aufgenommen, die Anspruch auf Rentenzahlung und andere Privilegien geltend machen konnten. Aus staatlicher Sicht war vor allem die schnelle Wiedereingliederung ins Arbeitsleben die beste Therapie gegen kriegsbedingte körperliche Leiden und wurde deshalb zum Hauptinstrument sowjetischer Sozialpolitik. Es fehlte allerdings an begleitenden Umschulungs- oder Ausbildungsprogrammen, medizinischen Rehabilitationsmaßnahmen und einer ausreichenden Zahl funktionstüchtiger Prothesen. Während die staatliche Propaganda „umfassende Fürsorge“ für die Kriegsversehrten in Aussicht stellte, erlebten sich diese selbst als „arme Sieger“

Equivariant Intersection Cohomology of Toric Varieties

We investigate the equivariant intersection cohomology of a toric variety. Considering the defining fan of the variety as a finite topological space with the subfans being the open sets (that corresponds to the "toric" topology given by the invariant open subsets), equivariant intersection cohomology provides a sheaf (of graded modules over a sheaf of graded rings) on that "fan space". We prove that this sheaf is a "minimal extension sheaf", i.e., that it satisfies three relatively simple axioms which are known to characterize such a sheaf up to isomorphism. In the verification of the second of these axioms, a key role is played by "equivariantly formal" toric varieties, where equivariant and "usual" (non-equivariant) intersection cohomology determine each other by Kunneth type formulae. Minimal extension sheaves can be constructed in a purely formal way and thus also exist for non-rational fans. As a consequence, we can extend the notion of an equivariantly formal fan even to this general setup. In this way, it will be possible to introduce "virtual" intersection cohomology for equivariantly formal non-rational fans.Comment: 31 pages, AMS-Latex (all "private" macros included), to be published in "Algebraic Geometry - Hirzebruch 70" (Proceedings of the conference at the Banach Centre, Warszawa, May 1998), Contemporary Mathematics, AM

Complete genome sequences of escherichia coli phages vB_EcoM-EP75 and vB_EcoP-EP335

Phages vB_EcoM-EP75 (EP75) and vB_EcoP-EP335 (EP335) specifically infect Shiga toxin (Stx)-producing Escherichia coli (STEC) O157 strains. EP75 has a genome size of 158,143 bp and belongs to the genus Vi1virus The genome size of EP335 is 76,622 bp, and it belongs to the genus Phieco32virus

Corporate Social Responsibilityin the Blogosphere

This paper uses social network analysis to examine the interaction between corporate blogs devoted to sustainability issues and the blogosphere, a clustered online network of collaborative actors. By analyzing the structural embeddedness of a prototypical blog in a virtual community, we show the potential of online platforms to document corporate social responsibility (CSR) activities and to engage with an increasingly socially and ecologically aware stakeholder base. The results of this study show that stakeholder involvement via sustainability blogs is a valuable new practice for CSR communications and stakeholder engagement. It also opens new horizons for communicating CSR issues to key constituencies onlin