556 research outputs found
Frustrated magnets in three dimensions: a nonperturbative approach
Frustrated magnets exhibit unusual critical behaviors: they display scaling
laws accompanied by nonuniversal critical exponents. This suggests that these
systems generically undergo very weak first order phase transitions. Moreover,
the different perturbative approaches used to investigate them are in conflict
and fail to correctly reproduce their behavior. Using a nonperturbative
approach we explain the mismatch between the different perturbative approaches
and account for the nonuniversal scaling observed.Comment: 7 pages, 1 figure. IOP style files included. To appear in Journal of
Physics: Condensed Matter. Proceedings of the conference HFM 2003, Grenoble,
Franc
Two-loop Functional Renormalization Group of the Random Field and Random Anisotropy O(N) Models
We study by the perturbative Functional Renormalization Group (FRG) the
Random Field and Random Anisotropy O(N) models near , the lower critical
dimension of ferromagnetism. The long-distance physics is controlled by
zero-temperature fixed points at which the renormalized effective action is
nonanalytic. We obtain the beta functions at 2-loop order, showing that despite
the nonanalytic character of the renormalized effective action, the theory is
perturbatively renormalizable at this order. The physical results obtained at
2-loop level, most notably concerning the breakdown of dimensional reduction at
the critical point and the stability of quasi-long range order in , are
shown to fit into the picture predicted by our recent non-perturbative FRG
approach.Comment: 19 pages, 20 figures. Minor correction
A 'cyanoacrylate case' for developing fingerprints in cars
A portable case has been developed by which cyanoacrylate (super glue) fuming can be used inside a vehicle suspected of being involved in serious crime. The car itself serves as a fumigation chamber and the cyanoacrylate vapours are fed into the car via a hose. Connected to the hose and suspended inside the car is a vapour diffuser. The cyanoacrylate originates from a portable case where there is a sealed heater and also a command panel with hygrometer and thermometer for a technician to control the process. There is also space inside the case for other necessary equipment
Chiral phase transitions: focus driven critical behavior in systems with planar and vector ordering
The fixed point that governs the critical behavior of magnets described by
the -vector chiral model under the physical values of () is
shown to be a stable focus both in two and three dimensions. Robust evidence in
favor of this conclusion is obtained within the five-loop and six-loop
renormalization-group analysis in fixed dimension. The spiral-like approach of
the chiral fixed point results in unusual crossover and near-critical regimes
that may imitate varying critical exponents seen in physical and computer
experiments.Comment: 4 pages, 5 figures. Discussion enlarge
Critical thermodynamics of three-dimensional chiral model for N > 3
The critical behavior of the three-dimensional -vector chiral model is
studied for arbitrary . The known six-loop renormalization-group (RG)
expansions are resummed using the Borel transformation combined with the
conformal mapping and Pad\'e approximant techniques. Analyzing the fixed point
location and the structure of RG flows, it is found that two marginal values of
exist which separate domains of continuous chiral phase transitions and where such
transitions are first-order. Our calculations yield and
. For the structure of RG flows is identical to
that given by the and 1/N expansions with the chiral fixed point
being a stable node. For the chiral fixed point turns out to be a
focus having no generic relation to the stable fixed point seen at small
and large . In this domain, containing the physical values and , phase trajectories approach the fixed point in a spiral-like
manner giving rise to unusual crossover regimes which may imitate varying
(scattered) critical exponents seen in numerous physical and computer
experiments.Comment: 12 pages, 3 figure
Методические особенности управления туристскими потоками в регионе (на примере Автономной Республики Крым)
Экономическая жизнь, начиная от простых жителей сел и городов, до экономики полуострова в целом зависит от количества туристов, приехавших в Крым на отдых и лечениеЕкономічне життя, починаючи від простих мешканців сіл і міст, до економіки півострова в цілому залежить від кількості туристів, що приїхали до Криму на відпочинок і лікуванн
On the leading OPE corrections to the ghost-gluon vertex and the Taylor theorem
This brief note is devoted to a study of genuine non-perturbative corrections
to the Landau gauge ghost-gluon vertex in terms of the non-vanishing
dimension-two gluon condensate. We pay special attention to the kinematical
limit which the bare vertex takes for its tree-level expression at any
perturbative order, according to the well-known Taylor theorem. Based on our
OPE analysis, we also present a simple model for the vertex, in acceptable
agreement with lattice data.Comment: Final version published in JHE
A single cytochrome P450 oxidase from <i>Solanum habrochaites</i> sequentially oxidizes 7-<i>epi</i>-zingiberene to derivatives toxic to whiteflies and various microorganisms
Spin-stiffness and topological defects in two-dimensional frustrated spin systems
Using a {\it collective} Monte Carlo algorithm we study the low-temperature
and long-distance properties of two systems of two-dimensional classical tops.
Both systems have the same spin-wave dynamics (low-temperature behavior) as a
large class of Heisenberg frustrated spin systems. They are constructed so that
to differ only by their topological properties. The spin-stiffnesses for the
two systems of tops are calculated for different temperatures and different
sizes of the sample. This allows to investigate the role of topological defects
in frustrated spin systems. Comparisons with Renormalization Group results
based on a Non Linear Sigma model approach and with the predictions of some
simple phenomenological model taking into account the topological excitations
are done.Comment: RevTex, 25 pages, 14 figures, Minor changes, final version. To appear
in Phys.Rev.
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