953 research outputs found
The O(2) model in polar coordinates at nonzero temperature
We study the restoration of spontaneously broken symmetry at nonzero
temperature in the framework of the O(2) model using polar coordinates. We
apply the CJT formalism to calculate the masses and the condensate in the
double-bubble approximation, both with and without a term that explicitly
breaks the O(2) symmetry. We find that, in the case with explicitly broken
symmetry, the mass of the angular degree of freedom becomes tachyonic above a
temperature of about 300 MeV. Taking the term that explicitly breaks the
symmetry to be infinitesimally small, we find that the Goldstone theorem is
respected below the critical temperature. However, this limit cannot be
performed for temperatures above the phase transition. We find that, no matter
whether we break the symmetry explicitly or not, there is no region of
temperature in which the radial and the angular degree of freedom become
degenerate in mass. These results hold also when the mass of the radial mode is
sent to infinity.Comment: 23 pages, 10 figure
Structure-Function insights of Jaburetox and Soyuretox: Novel intrinsically disordered polypeptides derived from plant ureases
Intrinsically disordered proteins (IDPs) and intrinsically disordered regions (IDRs) do not have a stable 3D structure but still have important biological activities. Jaburetox is a recombinant peptide derived from the jack bean (Canavalia ensiformis) urease and presents entomotoxic and antimicrobial actions. The structure of Jaburetox was elucidated using nuclear magnetic resonance which reveals it is an IDP with small amounts of secondary structure. Different approaches have demonstrated that Jaburetox acquires certain folding upon interaction with lipid membranes, a characteristic commonly found in other IDPs and usually important for their biological functions. Soyuretox, a recombinant peptide derived from the soybean (Glycine max) ubiquitous urease and homologous to Jaburetox, was also characterized for its biological activities and structural properties. Soyuretox is also an IDP, presenting more secondary structure in comparison with Jaburetox and similar entomotoxic and fungitoxic effects. Moreover, Soyuretox was found to be nontoxic to zebra fish, while Jaburetox was innocuous to mice and rats. This profile of toxicity affecting detrimental species without damaging mammals or the environment qualified them to be used in biotechnological applications. Both peptides were employed to develop transgenic crops and these plants were active against insects and nematodes, unveiling their immense potentiality for field applications.Fil: Grahl, Matheus V. Coste. Pontificia Universidade Católica do Rio Grande do Sul; BrasilFil: Lopes, Fernanda Cortez. Universidade Federal do Rio Grande do Sul; BrasilFil: Martinelli, Anne H. Souza. Universidade Federal do Rio Grande do Sul; BrasilFil: Carlini, Célia Regina R. S.. Pontificia Universidade Católica do Rio Grande do Sul; BrasilFil: Fruttero, Leonardo Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Córdoba. Centro de Investigaciones en Bioquímica Clínica e Inmunología; Argentin
Folksonomies and clustering in the collaborative system CiteULike
We analyze CiteULike, an online collaborative tagging system where users
bookmark and annotate scientific papers. Such a system can be naturally
represented as a tripartite graph whose nodes represent papers, users and tags
connected by individual tag assignments. The semantics of tags is studied here,
in order to uncover the hidden relationships between tags. We find that the
clustering coefficient reflects the semantical patterns among tags, providing
useful ideas for the designing of more efficient methods of data classification
and spam detection.Comment: 9 pages, 5 figures, iop style; corrected typo
Bloch-Wall Phase Transition in the Spherical Model
The temperature-induced second-order phase transition from Bloch to linear
(Ising-like) domain walls in uniaxial ferromagnets is investigated for the
model of D-component classical spin vectors in the limit D \to \infty. This
exactly soluble model is equivalent to the standard spherical model in the
homogeneous case, but deviates from it and is free from unphysical behavior in
a general inhomogeneous situation. It is shown that the thermal fluctuations of
the transverse magnetization in the wall (the Bloch-wall order parameter)
result in the diminishing of the wall transition temperature T_B in comparison
to its mean-field value, thus favouring the existence of linear walls. For
finite values of T_B an additional anisotropy in the basis plane x,y is
required; in purely uniaxial ferromagnets a domain wall behaves like a
2-dimensional system with a continuous spin symmetry and does not order into
the Bloch one.Comment: 16 pages, 2 figure
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