213 research outputs found
Conocimiento desde una perspectiva disciplinaria y holistica
Versión en inglés disponible en la Biblioteca Digital del IDRC: Disciplinary and holistic approaches to knowledgePublicado también en: Conocimiento sin barreras : propuestas, discusión y síntesi
Disciplinary and holistic approaches to knowledge
Spanish version available in IDRC Digital Library: Conocimiento desde una perspectiva disciplinaria y holistic
Interacting Open Wilson Lines in Noncommutative Field Theories
In noncommutative field theories, it was known that one-loop effective action
describes propagation of non-interacting open Wilson lines, obeying the flying
dipole's relation. We show that two-loop effective action describes cubic
interaction among `closed string' states created by open Wilson lines. Taking
d-dimensional noncommutative [\Phi^3] theory as the simplest setup, we compute
nonplanar contribution at low-energy and large noncommutativity limit. We find
that the contribution is expressible in a remarkably simple cubic interaction
involving scalar open Wilson lines only and nothing else. We show that the
interaction is purely geometrical and noncommutative in nature, depending only
on sizes of each open Wilson line.Comment: v1: 27 pages, Latex, 7 .eps figures v2: minor wording change +
reference adde
GEN1 from a thermophilic fungus is functionally closely similar to non-eukaryotic junction-resolving enzymes
AbstractProcessing of Holliday junctions is essential in recombination. We have identified the gene for the junction-resolving enzyme GEN1 from the thermophilic fungus Chaetomium thermophilum and expressed the N-terminal 487-amino-acid section. The protein is a nuclease that is highly selective for four-way DNA junctions, cleaving 1nt 3′ to the point of strand exchange on two strands symmetrically disposed about a diagonal axis. CtGEN1 binds to DNA junctions as a discrete homodimer with nanomolar affinity. Analysis of the kinetics of cruciform cleavage shows that cleavage of the second strand occurs an order of magnitude faster than the first cleavage so as to generate a productive resolution event. All these properties are closely similar to those described for bacterial, phage and mitochondrial junction-resolving enzymes. CtGEN1 is also similar in properties to the human enzyme but lacks the problems with aggregation that currently prevent detailed analysis of the latter protein. CtGEN1 is thus an excellent enzyme with which to engage in biophysical and structural analysis of eukaryotic GEN1
Irreducible holonomy algebras of Riemannian supermanifolds
Possible irreducible holonomy algebras \g\subset\osp(p,q|2m) of Riemannian
supermanifolds under the assumption that \g is a direct sum of simple Lie
superalgebras of classical type and possibly of a one-dimensional center are
classified. This generalizes the classical result of Marcel Berger about the
classification of irreducible holonomy algebras of pseudo-Riemannian manifolds.Comment: 27 pages, the final versio
The novel transcriptional regulator SczA mediates protection against Zn2+ stress by activation of the Zn2+-resistance gene czcD in Streptococcus pneumoniae
Maintenance of the intracellular homeostasis of metal ions is important for the virulence of many bacterial pathogens. Here, we demonstrate that the czcD gene of the human pathogen Streptococcus pneumoniae is involved in resistance against Zn2+, and that its transcription is induced by the transition-metal ions Zn2+, Co2+ and Ni2+. Upstream of czcD a gene was identified, encoding a novel TetR family regulator, SczA, that is responsible for the metal ion-dependent activation of czcD expression. Transcriptome analyses revealed that in a sczA mutant expression of czcD, a gene encoding a MerR-family transcriptional regulator and a gene encoding a zinc-containing alcohol dehydrogenase (adhB) were downregulated. Activation of the czcD promoter by SczA is shown to proceed by Zn2+-dependent binding of SczA to a conserved DNA motif. In the absence of Zn2+, SczA binds to a second site in the czcD promoter, thereby fully blocking czcD expression. This is the first example of a metalloregulatory protein belonging to the TetR family that has been described. The presence in S. pneumoniae of the Zn2+-resistance system characterized in this study might reflect the need for adjustment to a fluctuating Zn2+ pool encountered by this pathogen during infection of the human body
Thermodynamics of Large-N_f QCD at Finite Chemical Potential
We extend the previously obtained results for the thermodynamic potential of
hot QCD in the limit of large number of fermions to non-vanishing chemical
potential. We give exact results for the thermal pressure in the entire range
of temperature and chemical potential for which the presence of a Landau pole
is negligible numerically. In addition we compute linear and non-linear quark
susceptibilities at zero chemical potential, and the entropy at small
temperatures. We compare with the available perturbative results and determine
their range of applicability. Our numerical accuracy is sufficiently high to
check and verify existing results, including the recent perturbative results by
Vuorinen on quark number susceptibilities and the older results by Freedman and
McLerran on the pressure at zero temperature and high chemical potential. We
also obtain a number of perturbative coefficients at sixth order in the
coupling that have not yet been calculated analytically. In the case of both
non-zero temperature and non-zero chemical potential, we investigate the range
of validity of a scaling behaviour noticed recently in lattice calculations by
Fodor, Katz, and Szabo at moderately large chemical potential and find that it
breaks down rather abruptly at , which points to a
presumably generic obstruction for extrapolating data from small to large
chemical potential. At sufficiently small temperatures , we find
dominating non-Fermi-liquid contributions to the interaction part of the
entropy, which exhibits strong nonlinearity in the temperature and an excess
over the free-theory value.Comment: 18 pages, 7 figures, JHEP style; v2: several updates, rewritten and
extended sect. 3.4 covering now "Entropy at small temperatures and
non-Fermi-liquid behaviour"; v3: additional remarks at the end of sect. 3.4;
v4: minor corrections and additions (version to appear in JHEP
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