1,568 research outputs found
Evidence for directed percolation universality at the onset of spatiotemporal intermittency in coupled circle maps
We consider a lattice of coupled circle maps, a model arising naturally in
descriptions of solid state phenomena such as Josephson junction arrays. We
find that the onset of spatiotemporal intermittency (STI) in this system is
analogous to directed percolation (DP), with the transition being to an unique
absorbing state for low nonlinearities, and to weakly chaotic absorbing states
for high nonlinearities. We find that the complete set of static exponents and
spreading exponents at all critical points match those of DP very convincingly.
Further, hyperscaling relations are fulfilled, leading to independent controls
and consistency checks of the values of all the critical exponents. These
results lend strong support to the conjecture that the onset of STI in
deterministic models belongs to the DP universality class.Comment: Submitted to Physical Review
Search for solar axions using Li-7
We describe a novel approach to the search for solar, near-monochromatic
hadronic axions, the latter being suggested to be created in the solar core
during M1 transitions between the first excited level of Li-7, at 478 keV, and
the ground state. As a result of Doppler broadening, in principle these axions
can be detected via resonant absorption by the same nuclide on the Earth.
Excited nuclei of Li-7 are produced in the solar interior by Be-7 electron
capture and thus the axions are accompanied by emission of Be-7 solar neutrinos
of energy 384 keV. An experiment was made which has yielded an upper limit on
hadronic axion mass of 32 keV at the 95% confidence level.Comment: revtex, 4 pages with 2 figures, title revised, minor changes, matches
version to appear in Phys. Rev.
On Symmetry Enhancement in the psu(1,1|2) Sector of N=4 SYM
Strong evidence indicates that the spectrum of planar anomalous dimensions of
N=4 super Yang-Mills theory is given asymptotically by Bethe equations. A
curious observation is that the Bethe equations for the psu(1,1|2) subsector
lead to very large degeneracies of 2^M multiplets, which apparently do not
follow from conventional integrable structures. In this article, we explain
such degeneracies by constructing suitable conserved nonlocal generators acting
on the spin chain. We propose that they generate a subalgebra of the loop
algebra for the su(2) automorphism of psu(1,1|2). Then the degenerate
multiplets of size 2^M transform in irreducible tensor products of M
two-dimensional evaluation representations of the loop algebra.Comment: 35 pages, v2: references added, sign inconsistency resolved in
(5.5,5.6), v3: Section 3.4 on Hamiltonian added, minor improvements, to
appear in JHE
Site-specific biotinylation of RNA molecules by transcription using unnatural base pairs
Direct site-specific biotinylation of RNA molecules was achieved by specific transcription mediated by unnatural base pairs. Unnatural base pairs between 2-amino-6-(2-thienyl)purine (denoted by s) and 2-oxo(1H)pyridine (denoted by y), or 2-amino-6-(2-thiazolyl)purine (denoted as v) and y specifically function in T7 transcription. Using these unnatural base pairs, the substrate of biotinylated-y (Bio-yTP) was selectively incorporated into RNA, opposite s or v in the DNA templates, by T7 RNA polymerase. This method was applied to the immobilization of an RNA aptamer on sensor chips, and the aptamer accurately recognized its target protein. This direct site-specific biotinylation will provide a tool for RNA-based biotechnologies
Serre Relation and Higher Grade Generators of the AdS/CFT Yangian Symmetry
It was shown that the spin chain model coming from AdS/CFT correspondence
satisfies the Yangian symmetry if we assume evaluation representation, though
so far there is no explicit proof that the evaluation representation satisfies
the Serre relation, which is one of the defining equations of the Yangian
algebra imposing constraints on the whole algebraic structure. We prove
completely that the evaluation representation adopted in the model satisfies
the Serre relation by introducing a three-dimensional gamma matrix. After
studying the Serre relation, we proceed to the whole Yangian algebraic
structure, where we find that the conventional construction of higher grade
generators is singular and we propose an alternative construction. In the
discussion of the higher grade generators, a great simplification for the proof
of the Serre relation is found. Using this expression, we further show that the
proof is lifted to the exceptional superalgebra, which is a non-degenerate
deformation of the original superalgebra.Comment: 24 pages, 1 figure, v2: on exceptional superalgebra, previous
incorrect comments removed and new sections added, v3: clarifications adde
Search for solar Kaluza-Klein axions in theories of low-scale quantum gravity
We explore the physics potential of a terrestrial detector for observing
axionic Kaluza-Klein excitations coming from the Sun within the context of
higher-dimensional theories of low-scale quantum gravity. In these theories,
the heavier Kaluza-Klein axions are relatively short-lived and may be detected
by a coincidental triggering of their two-photon decay mode. Because of the
expected high multiplicity of the solar axionic excitations, we find
experimental sensitivity to a fundamental Peccei-Quinn axion mass up to
eV (corresponding to an effective axion-photon coupling GeV) in theories with 2 extra
dimensions and a fundamental quantum-gravity scale of order 100
TeV, and up to eV (corresponding to GeV) in theories with 3 extra dimensions and
TeV. For comparison, based on recent data obtained from lowest
level underground experiments, we derive the experimental limits: GeV and GeV in the
aforementioned theories with 2 and 3 large compact dimensions, respectively.Comment: 19 pages, extended version, as to appear in Physical Review
Grain Dynamics in a Two-dimensional Granular Flow
We have used particle tracking methods to study the dynamics of individual
balls comprising a granular flow in a small-angle two-dimensional funnel. We
statistically analyze many ball trajectories to examine the mechanisms of shock
propagation. In particular, we study the creation of, and interactions between,
shock waves. We also investigate the role of granular temperature and draw
parallels to traffic flow dynamics.Comment: 17 pages, 24 figures. To appear in Phys.Rev.E. High res./color
figures etc. on http://www.nbi.dk/CATS/Granular/GrainDyn.htm
Evolutionary algorithms for optimal control in fed-batch fermentation processes
In this work, Evolutionary Algorithms (EAs) are used to achieve optimal feedforward control in a recombinant bacterial fed-batch
fermentation process, that aims at producing a bio-pharmaceutical product.
Three diferent aspects are the target of the optimization procedure: the feeding trajectory (the amount of substrate introduced in a bioreactor per time unit), the duration of the fermentation and the initial conditions
of the process. A novel EA with variable size chromosomes and using real-valued representations is proposed that is capable of simultaneously optimizing the aforementioned aspects. Outstanding productivity levels
were achieved and the results are validated by practice
Secret Symmetries in AdS/CFT
We discuss special quantum group (secret) symmetries of the integrable system
associated to the AdS/CFT correspondence. These symmetries have by now been
observed in a variety of forms, including the spectral problem, the boundary
scattering problem, n-point amplitudes, the pure-spinor formulation and quantum
affine deformations.Comment: 20 pages, pdfLaTeX; Submitted to the Proceedings of the Nordita
program `Exact Results in Gauge-String Dualities'; Based on the talk
presented by A.T., Nordita, 15 February 201
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