515 research outputs found
Action for IIB Supergravity in 10 dimensions
We review the construction of a manifestly covariant, supersymmetric and
SL(2R) invariant action for IIB supergravity in D=10.Comment: 9 pages, LaTeX, Talk given at "Quantum Aspects of Gauge Theories,
Supersymmetry and Unification", Greece, September 199
On Lorentz Invariant Actions for Chiral P-Forms
We demonstrate how a Lorentz covariant formulation of the chiral p-form model
in D=2(p+1) containing infinitely many auxiliary fields is related to a Lorentz
covariant formulation with only one auxiliary scalar field entering a chiral
p-form action in a nonpolynomial way. The latter can be regarded as a
consistent Lorentz-covariant truncation of the former. We make the Hamiltonian
analysis of the model based on the nonpolynomial action and show that the Dirac
constraints have a simple form and are all of the first class. In contrast to
the Siegel model the constraints are not the square of second-class
constraints. The canonical Hamiltonian is quadratic and determines energy of a
single chiral p-form. In the case of d=2 chiral scalars the constraint can be
improved by use of `twisting' procedure (without the loss of the property to be
of the first class) in such a way that the central charge of the quantum
constraint algebra is zero. This points to possible absence of anomaly in an
appropriate quantum version of the model.Comment: RevTeX file, 7 page
Normal Bundles, Pfaffians and Anomalies
We deal with the problem of diffeomorphism anomaly in theories with branes.
In particular we thoroughly analyze the problem of the residual chiral anomaly
of a five-brane immersed in M-theory, paying attention to its global
formulation in the five-brane world-volume. We conclude that the anomaly can be
canceled by a {\it local} counterterm in the five-brane world-volume.Comment: 17 pages, Latex, sign convention changed, typos correcte
Dual Projection and Selfduality in Three Dimensions
We discuss the notion of duality and selfduality in the context of the dual
projection operation that creates an internal space of potentials. Contrary to
the prevailing algebraic or group theoretical methods, this technique is
applicable to both even and odd dimensions. The role of parity in the kernel of
the Gauss law to determine the dimensional dependence is clarified. We derive
the appropriate invariant actions, discuss the symmetry groups and their proper
generators. In particular, the novel concept of duality symmetry and
selfduality in Maxwell theory in (2+1) dimensions is analysed in details. The
corresponding action is a 3D version of the familiar duality symmetric
electromagnetic theory in 4D. Finally, the duality symmetric actions in the
different dimensions constructed here manifest both the SO(2) and
symmetries, contrary to conventional results.Comment: 20 pages, late
Multi-Omics and Genome Editing Studies on Plant Cell Walls to Improve Biomass Quality
Biomass is one of the most important sources of renewable energy and plays an important role in reducing our reliance on fossil fuels. Efficient biomass production is essential to obtain large amounts of sustainable energy with minimal environmental cost. However, the biochemical and molecular processes behind the synthesis of the main components of biomass are still not fully understood. This review provides a comprehensive summary of the most relevant studies on cell wall biosynthesis and degradation mechanisms, focusing on the lignocellulosic component, in which the conversion process to fermentable sugars is expensive, due to its recalcitrant nature. A focus is placed on multi-omics research involving genomics, transcriptomics, proteomics, metabolomics, and phenomics, since multi-omics approaches offer a unique opportunity to investigate the biological pathways underlying the genotype traits characterizing cell wall energy crops. Furthermore, our study highlights the advances in genome editing approaches and proposes the modification of the genes that are involved in the complex cell wall structure as a feasible solution to an efficient biomass production. Several key points for future research activities based on these emerging technologies are also discussed, focusing on the combination of multi-omics and gene editing approaches, which offer potential for improved biomass valorization and the development of tangible bioproducts
Accumulation of trace metals in crayfish tissues: is Procambarus clarkii a vector of pollutants in Po Delta inland waters?
Concentrations of trace elements (Cd, Pb, As, Cu and Zn) were determined in superficial sediments and in hepatopancreas, exoskeleton, and abdominal muscle of the red swamp crayfish Procambarus clarkii from several canals of the Po River Delta area. Sediments of the studied canals exhibited some metal pollution. The hepatopancreas of the crayfish showed a higher concentration of trace metals in comparison to the other tissues at all sites under scrutiny. Concentrations of As and Pb, either in sediment and P. clarkii tissues, were probably related to the use of fertilizers and pesticides. Moreover, the levels of certain metals accumulated in the abdominal muscle (Pb, Cu and Zn) exceeded the threshold values considered harmful to human health. The Toxic Contamination Index, depending on the bioaccumulation data of hepatopancreas and abdominal muscle, allowed us to assess the toxicity by heavy metals of sediments measuring the stress level of the detoxification organ, and resulted in >1 only at two sampling canals. We hypothesize that P. clarkii in the Po River Delta aquatic communities can act as a vector of pollutants, as crayfish can transfer their relatively high amount of heavy metals to higher trophic levels
New Formulations of D=10 Supersymmetry and D8-O8 Domain Walls
We discuss a generalized form of IIA/IIB supergravity depending on all R-R
potentials C^(p) (p=0,1,...,9) as the effective field theory of Type IIA/IIB
superstring theory. For the IIA case we explicitly break this R-R democracy to
either p=5 which allows us to write a new bulk action that can be
coupled to N=1 supersymmetric brane actions.
The case of 8-branes is studied in detail using the new bulk & brane action.
The supersymmetric negative tension branes without matter excitations can be
viewed as orientifolds in the effective action. These D8-branes and O8-planes
are fundamental in Type I' string theory. A BPS 8-brane solution is given which
satisfies the jump conditions on the wall. It implies a quantization of the
mass parameter in string units. Also we find a maximal distance between the two
walls, depending on the string coupling and the mass parameter. We derive the
same results via supersymmetric flow equations.Comment: 30 pages, 2nd version: reference adde
Duality in a fermion-like formulation for the electromagnetic field
We employ the Dirac-like equation for the gauge field proposed by Majorana to
obtain an action that is symmetric under duality transformation. We also use
the equivalence between duality and chiral symmetry in this fermion-like
formulation to show how the Maxwell action can be seen as a mass term.Comment: 4 pages. Revtex. Final version to be published in Phys. Rev.
Coexistence of amplitude and frequency modulations in intracellular calcium dynamics
The complex dynamics of intracellular calcium regulates cellular responses to
information encoded in extracellular signals. Here, we study the encoding of
these external signals in the context of the Li-Rinzel model. We show that by
control of biophysical parameters the information can be encoded in amplitude
modulation, frequency modulation or mixed (AM and FM) modulation. We briefly
discuss the possible implications of this new role of information encoding for
astrocytes.Comment: 4 pages, 4 figure
The anomaly line bundle of the self-dual field theory
In this work, we determine explicitly the anomaly line bundle of the abelian
self-dual field theory over the space of metrics modulo diffeomorphisms,
including its torsion part. Inspired by the work of Belov and Moore, we propose
a non-covariant action principle for a pair of Euclidean self-dual fields on a
generic oriented Riemannian manifold. The corresponding path integral allows to
study the global properties of the partition function over the space of metrics
modulo diffeomorphisms. We show that the anomaly bundle for a pair of self-dual
fields differs from the determinant bundle of the Dirac operator coupled to
chiral spinors by a flat bundle that is not trivial if the underlying manifold
has middle-degree cohomology, and whose holonomies are determined explicitly.
We briefly sketch the relevance of this result for the computation of the
global gravitational anomaly of the self-dual field theory, that will appear in
another paper.Comment: 41 pages. v2: A few typos corrected. Version accepted for publication
in CM
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