617 research outputs found
Reduction and approximation in gyrokinetics
The gyrokinetics formulation of plasmas in strong magnetic fields aims at the
elimination of the angle associated with the Larmor rotation of charged
particles around the magnetic field lines. In a perturbative treatment or as a
time-averaging procedure, gyrokinetics is in general an approximation to the
true dynamics. Here we discuss the conditions under which gyrokinetics is
either an approximation or an exact operation in the framework of reduction of
dynamical systems with symmetryComment: 15 pages late
On a Watson-like Uniqueness Theorem and Gevrey Expansions
We present a maximal class of analytic functions, elements of which are in
one-to-one correspondence with their asymptotic expansions. In recent decades
it has been realized (B. Malgrange, J. Ecalle, J.-P. Ramis, Y. Sibuya et al.),
that the formal power series solutions of a wide range of systems of ordinary
(even non-linear) analytic differential equations are in fact the Gevrey
expansions for the regular solutions. Watson's uniqueness theorem belongs to
the foundations of this new theory. This paper contains a discussion of an
extension of Watson's uniqueness theorem for classes of functions which admit a
Gevrey expansion in angular regions of the complex plane with opening less than
or equal to (\frac \pi k,) where (k) is the order of the Gevrey expansion. We
present conditions which ensure uniqueness and which suggest an extension of
Watson's representation theorem. These results may be applied for solutions of
certain classes of differential equations to obtain the best accuracy estimate
for the deviation of a solution from a finite sum of the corresponding Gevrey
expansion.Comment: 18 pages, 4 figure
Criticality without frustration for quantum spin-1 chains
Frustration-free (FF) spin chains have a property that their ground state
minimizes all individual terms in the chain Hamiltonian. We ask how entangled
the ground state of a FF quantum spin-s chain with nearest-neighbor
interactions can be for small values of s. While FF spin-1/2 chains are known
to have unentangled ground states, the case s=1 remains less explored. We
propose the first example of a FF translation-invariant spin-1 chain that has a
unique highly entangled ground state and exhibits some signatures of a critical
behavior. The ground state can be viewed as the uniform superposition of
balanced strings of left and right parentheses separated by empty spaces.
Entanglement entropy of one half of the chain scales as log(n)/2 + O(1), where
n is the number of spins. We prove that the energy gap above the ground state
is polynomial in 1/n. The proof relies on a new result concerning statistics of
Dyck paths which might be of independent interest.Comment: 11 pages, 2 figures. Version 2: minor changes in the proof of Lemma
Fauna coralina de las plataformas mixtas del Paleógeno de las Baleares
Abstract not availabl
Evaluation of two alternative procedures for measuring airflow resistance of sound absorbing materials
[EN] It is well known that sound absorption and sound transmission properties of open porous materials
are highly dependent on their airflow resistance values. Low values of airflow resistance indicate little
resistance for air streaming through the porous material and high values are a sign that most of the pores
inside the material are closed. The laboratory procedures for measuring airflow resistance have been stan-
dardized by several organizations, including ISO and ASTM for both alternate flow and continuous flow.
However, practical implementation of these standardized methods could be both complex and expensive.
In this work, two indirect alternative measurement procedures were compared against the alternate flow
standardized technique. The techniques were tested using three families of eco-friendly sound absorbent
materials: recycled polyurethane foams, coconut natural fibres, and recycled polyester fibres. It is found
that the values of airflow resistance measured using both alternative methods are very similar. There is
also a good correlation between the values obtained through alternative and standardized methods.This project has been made possible thanks to the FONDECYT Project 1110605 and the grant GV/2012/066 Projects I+D for emerging research groups. The authors would like to thank Dr. Luis Godinho from the Department of Civil Engineering of University of Coimbra (Portugal) for his help with the experimental work and the ISO data reported in Table 1
of this paper.Rey Tormos, RMD.; Alba Fernández, J.; Arenas, JP.; Ramis Soriano, J. (2013). Evaluation of two alternative procedures for measuring airflow resistance of sound absorbing materials. Archives of Acoustics. 38(4):547-554. https://doi.org/10.2478/aoa:2013-0064S54755438
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