170 research outputs found
Seiberg--Witten maps for gauge invariance and deformations of gravity
A family of diffeomorphism-invariant Seiberg--Witten deformations of gravity
is constructed. In a first step Seiberg--Witten maps for an SO(1,3) gauge
symmetry are obtained for constant deformation parameters. This includes maps
for the vierbein, the spin connection and the Einstein--Hilbert Lagrangian. In
a second step the vierbein postulate is imposed in normal coordinates and the
deformation parameters are identified with the components
of a covariantly constant bivector. This procedure gives for the classical
action a power series in the bivector components which by construction is
diffeomorphism-invariant. Explicit contributions up to second order are
obtained. For completeness a cosmological constant term is included in the
analysis. Covariant constancy of , together with the
field equations, imply that, up to second order, only four-dimensional metrics
which are direct sums of two two-dimensional metrics are admissible, the
two-dimensional curvatures being expressed in terms of . These
four-dimensional metrics can be viewed as a family of deformed emergent
gravities.Comment: 1 encapsulated figur
The short-time critical behaviour of the Ginzburg-Landau model with long-range interaction
The renormalisation group approach is applied to the study of the short-time
critical behaviour of the -dimensional Ginzburg-Landau model with long-range
interaction of the form in momentum space. Firstly the
system is quenched from a high temperature to the critical temperature and then
relaxes to equilibrium within the model A dynamics. The asymptotic scaling laws
and the initial slip exponents and of the order
parameter and the response function respectively, are calculated to the second
order in .Comment: 18 pages, 4 figures, 1 tabl
Noncommutative Einstein-Maxwell pp-waves
The field equations coupling a Seiberg-Witten electromagnetic field to
noncommutative gravity, as described by a formal power series in the
noncommutativity parameters , is investigated. A large
family of solutions, up to order one in , describing
Einstein-Maxwell null pp-waves is obtained. The order-one contributions can be
viewed as providing noncommutative corrections to pp-waves. In our solutions,
noncommutativity enters the spacetime metric through a conformal factor and is
responsible for dilating/contracting the separation between points in the same
null surface. The noncommutative corrections to the electromagnetic waves,
while preserving the wave null character, include constant polarization, higher
harmonic generation and inhomogeneous susceptibility. As compared to pure
noncommutative gravity, the novelty is that nonzero corrections to the metric
already occur at order one in .Comment: 19 revtex pages. One refrence suppressed, two references added. Minor
wording changes in the abstract, introduction and conclusio
Driven Heisenberg Magnets: Nonequilibrium Criticality, Spatiotemporal Chaos and Control
We drive a -dimensional Heisenberg magnet using an anisotropic current.
The continuum Langevin equation is analysed using a dynamical renormalization
group and numerical simulations. We discover a rich steady-state phase diagram,
including a critical point in a new nonequilibrium universality class, and a
spatiotemporally chaotic phase. The latter may be `controlled' in a robust
manner to target spatially periodic steady states with helical order.Comment: 7 pages, 2 figures. Published in Euro. Phys. Let
Addenda and corrections to work done on the path-integral approach to classical mechanics
In this paper we continue the study of the path-integral formulation of
classical mechanics and in particular we better clarify, with respect to
previous papers, the geometrical meaning of the variables entering this
formulation. With respect to the first paper with the same title, we {\it
correct} here the set of transformations for the auxiliary variables
. We prove that under this new set of transformations the
Hamiltonian , appearing in our path-integral, is an exact
scalar and the same for the Lagrangian. Despite this different transformation,
the variables maintain the same operatorial meaning as before but
on a different functional space. Cleared up this point we then show that the
space spanned by the whole set of variables () of our
path-integral is the cotangent bundle to the {\it reversed-parity} tangent
bundle of the phase space of our system and it is indicated as
. In case the reader feel uneasy with this strange
{\it Grassmannian} double bundle, we show in this paper that it is possible to
build a different path-integral made only of {\it bosonic} variables. These
turn out to be the coordinates of which is the
double cotangent bundle of phase-space.Comment: Title changed, appendix expanded, few misprints fixe
Drived diffusion of vector fields
A model for the diffusion of vector fields driven by external forces is
proposed. Using the renormalization group and the -expansion, the
dynamical critical properties of the model with gaussian noise for dimensions
below the critical dimension are investigated and new transport universality
classes are obtained.Comment: 11 pages, title changed, anisotropic diffusion further discussed and
emphasize
Topological Yang-Mills Theory with Two Fermionic Charges. A Superfield Approach on K\"ahler Manifolds
The four-dimensional topological Yang-Mills theory with two anticommuting
charges is naturally formulated on K\"ahler manifolds. By using a superspace
approach we clarify the structure of the Faddeev-Popov sector and determine the
total action. This enables us to perform perturbation theory around any given
instanton configuration by manifestly maintaining all the symmetries of the
topological theory. The superspace formulation is very useful for recognizing a
trivial observable (i.e. having vanishing correlation functions only) as the
highest component of a gauge invariant superfield. As an example of non-trivial
observables we construct the complete solution to the simultaneous cohomology
problem of both fermionic charges. We also show how this solution has to be
used in order to make Donaldson's interpretation possible.Comment: 41 pages, LaTeX. Section about Donaldson cohomology revised and
completed. To be published in Nucl. Phys.
Toward a new hybrid proton conductor: lanthanum niobate layered perovskites as a source of tailorable surfaces
The modification of metal oxide surfaces with organic moieties has been widely studied as a method of preparing organic-inorganic hybrid materials for various applications. Among inorganic oxides, the ion-exchangeable layered perovskites [1], materials composed by perovskite-like slabs and intercalated cations, stimulated authors\u2019 interest in reason of some encouraging electronic and reactive properties. In particular it is well known that the interlayer surface of such materials in their protonated form can be easily functionalized with organic groups (such as alcohols [2-3] or organophosphonic acids [4]) thus allowing the production of stable hybrid materials with new electronic and reactive features.
As a first step to design a new inorganic-organic hybrid proton conductor, a comprehensive theoretical investigation of the MLaNb2O7 (M=H, Li, Na, K, Rb and Cs) series of ion-exchangeable layered perovskite is presented. In particular, their structural and electronic properties have been investigated by periodic calculations in the framework of DFT. A general very good agreement with the available experimental data has been found. The protonated compound (HLaNb2O7) has been then functionalized with imidazole trying two different settings: in the first arrangement the molecule is adsorbed on the layered oxide exposing the interlayer surface, in the second the organic moiety is just put between two perovskites slabs. This latter model, including the effect of the confinement, allowed to better reproduce the experimental structural XRD data and 13C-NMR measurements of the hybrid system.
[1] Schaak, R. E. and Mallouk T. E., Chem. Mat. 2002, 14, 1455-1471.
[2] Takahashi S. et al., Inorg. Chem. 1995, 34, 5065-5069.
[3] Suzuki H. et al., Chem. Mater. 2003, 15, 636-641.
[4] Shimada, A. et al., Chem. Mat. 2009, 21, 4155-4162
Soft capacitor fibers using conductive polymers for electronic textiles
A novel, highly flexible, conductive polymer-based fiber with high electric
capacitance is reported. In its crossection the fiber features a periodic
sequence of hundreds of conductive and isolating plastic layers positioned
around metallic electrodes. The fiber is fabricated using fiber drawing method,
where a multi-material macroscopic preform is drawn into a sub-millimeter
capacitor fiber in a single fabrication step. Several kilometres of fibers can
be obtained from a single preform with fiber diameters ranging between 500um
-1000um. A typical measured capacitance of our fibers is 60-100 nF/m and it is
independent of the fiber diameter. For comparison, a coaxial cable of the
comparable dimensions would have only ~0.06nF/m capacitance. Analysis of the
fiber frequency response shows that in its simplest interrogation mode the
capacitor fiber has a transverse resistance of 5 kOhm/L, which is inversely
proportional to the fiber length L and is independent of the fiber diameter.
Softness of the fiber materials, absence of liquid electrolyte in the fiber
structure, ease of scalability to large production volumes, and high
capacitance of our fibers make them interesting for various smart textile
applications ranging from distributed sensing to energy storage
Diagnostic performance and reference values of novel biomarkers of paediatric heart failure
Objective: Biomarkers play a pivotal role in heart failure (HF) management. Reference values and insights from studies in adults cannot be extrapolated to the paediatric population due to important differences in pathophysiology and compensatory reserve. We assessed the diagnostic utility of four novel biomarkers in paediatric HF.
Methods: Midregional (MR) pro-atrial natriuretic peptide (proANP), soluble ST2 (sST2), growth differentiation factor-15 (GDF-15), MR-pro-adrenomedullin (proADM) and N-terminal pro-B natriuretic peptide (NT-proBNP) were measured in 114 patients and 89 controls. HF was defined as the presence of HF symptoms and/or abnormal systolic ventricular function. Receiver-operating characteristics were plotted, and the area under the curve (AUC) was measured. This was repeated for subgroups with cardiomyopathy and congenital heart disease (CHD). Ventricular systolic function was measured by magnetic resonance or echocardiography. Reference values were calculated according to the current guidelines.
Results: The AUC for diagnosing HF was 0.76 for MR-proANP (CI 0.70 to 0.84) and 0.82 for NT-proBNP (CI 0.75 to 0.88). These parameters performed similarly in the subgroups with CHD and cardiomyopathy. By contrast, MR-proADM, GDF-15 and sST2 performed poorly. When used in conjunction with NT-proBNP, no parameter added significantly to its diagnostic accuracy. NT-proBNP, MR-proANP, GDF-15 and sST2 could accurately discriminate between patients with preserved and patients with poor functional status. In a subset of patients with dilated cardiomyopathy, NT-proBNP, MR-proANP, MR-proADM and GDF-15 were associated with poor LV function.
Conclusions: MR-proANP could accurately detect HF in children and adolescents. Its diagnostic performance was comparable with that of NT-proBNP, regardless of the underlying condition. Reference values are presented
- …