21 research outputs found
On the integrability of a system describing the stationary solutions in Bose--Fermi mixtures
We study the integrability of a Hamiltonian system describing the stationary
solutions in Bose--Fermi mixtures in one dimensional optical lattices. We prove
that the system is integrable only when it is separable. The proof is based on
the Differential Galois approach and Ziglin-Morales-Ramis method.Comment: 21 page
Non-Integrability of Some Higher-Order Painlev\'e Equations in the Sense of Liouville
In this paper we study the equation which is one of the higher-order
Painlev\'e equations (i.e., equations in the polynomial class having the
Painlev\'e property). Like the classical Painlev\'e equations, this equation
admits a Hamiltonian formulation, B\"acklund transformations and families of
rational and special functions. We prove that this equation considered as a
Hamiltonian system with parameters , , , is not integrable in Liouville sense by means of
rational first integrals. To do that we use the Ziglin-Morales-Ruiz-Ramis
approach. Then we study the integrability of the second and third members of
the -hierarchy. Again as in the previous case it
turns out that the normal variational equations are particular cases of the
generalized confluent hypergeometric equations whose differential Galois groups
are non-commutative and hence, they are obstructions to integrability
Public access defibrillation: Suppression of 16.7 Hz interference generated by the power supply of the railway systems
BACKGROUND: A specific problem using the public access defibrillators (PADs) arises at the railway stations. Some countries as Germany, Austria, Switzerland, Norway and Sweden are using AC railroad net power-supply system with rated 16.7 Hz frequency modulated from 15.69 Hz to 17.36 Hz. The power supply frequency contaminates the electrocardiogram (ECG). It is difficult to be suppressed or eliminated due to the fact that it considerably overlaps the frequency spectra of the ECG. The interference impedes the automated decision of the PADs whether a patient should be (or should not be) shocked. The aim of this study is the suppression of the 16.7 Hz interference generated by the power supply of the railway systems. METHODS: Software solution using adaptive filtering method was proposed for 16.7 Hz interference suppression. The optimal performance of the filter is achieved, embedding a reference channel in the PADs to record the interference. The method was tested with ECGs from AHA database. RESULTS: The method was tested with patients of normal sinus rhythms, symptoms of tachycardia and ventricular fibrillation. Simulated interference with frequency modulation from 15.69 Hz to 17.36 Hz changing at a rate of 2% per second was added to the ECGs, and then processed by the suggested adaptive filtering. The method totally suppresses the noise with no visible distortions of the original signals. CONCLUSION: The proposed adaptive filter for noise suppression generated by the power supply of the railway systems has a simple structure requiring a low level of computational resources, but a good reference signal as well
Can the nucleon axial charge be O(Nc^0)?
The nucleon self-energy and its relation to the nucleon axial charge gA are
discussed at large Nc. The energy is compared for the hedgehog, conventional,
and recently proposed dichotomous nucleon wavefunctions which give different
values for gA. We consider their energies at both perturbative and
non-perturbative levels. In perturbative estimates, we take into account the
pion exchanges among quarks up to the third orders of axial charge vertices,
including the many-body forces such as the Wess-Zumino terms. It turns out that
the perturbative pion exchanges among valence quarks give the same leading Nc
contributions for three wavefunctions, while their mass differences are
O(Lamba_qcd). The signs of splittings flip for different orders of the axial
charge vertices, so it is hard to conclude which one is the most energetically
favored. For non-perturbative estimates involving the modification of quark
bases, we use the chiral quark soliton model as an illustration. With the
hedgehog quark wavefunctions with gA of O(Nc), we investigate whether solutions
with coherent pions are energetically favored. Again it is hard to give
decisive conclusions, but it is likely that adding the confining effects
disfavors the solution with the coherent pions, making a pion cloud around a
nucleon quantum rather than coherent. The nuclear matter at large Nc is also
discussed in light of the value of gA.Comment: 40 pages, 7 figures. Published version in Nuclear Physics
Baryon Tri-local Interpolating Fields
We systematically investigate tri-local (non-local) three-quark baryon fields
with U_L(2)*U_R(2) chiral symmetry, according to their Lorentz and isospin
(flavor) group representations. We note that they can also be called as
"nucleon wave functions" due to this full non-locality. We study their chiral
transformation properties and find all the possible chiral multiplets
consisting J=1/2 and J=3/2 baryon fields. We find that the axial coupling
constant |g_A| = 5/3 is only for nucleon fields belonging to the chiral
representation (1/2,1)+(1,1/2) which contains both nucleon fields and Delta
fields. Moreover, all the nucleon fields belonging to this representation have
|g_A| = 5/3.Comment: 8 pages, 3 tables, accepted by EPJ
Hyperfine Splitting of Low-Lying Heavy Baryons
We calculate the next-to-leading order contribution to the masses of the
heavy baryons in the bound state approach for baryons containing a heavy quark.
These corrections arise when states of good spin and isospin are
generated from the background soliton of the light meson fields. Our study is
motivated by the previously established result that light vector meson fields
are required for this soliton in order to reasonably describe the spectrum of
both the light and the heavy baryons. We note that the inclusion of light
vector mesons significantly improves the agreement of the predicted hyperfine
splitting with experiment. A number of aspects of this somewhat complicated
calculation are discussed in detail.Comment: Modification of the discussion on the numerical results, version to
be published in Nucl. Phys.
Transverse Polarisation of Quarks in Hadrons
We review the present state of knowledge regarding the transverse
polarisation (or transversity) distributions of quarks. After some generalities
on transverse polarisation, we formally define the transversity distributions
within the framework of a classification of all leading-twist distribution
functions. We describe the QCD evolution of transversity at leading and
next-to-leading order. A comprehensive treatment of non-perturbative
calculations of transversity distributions (within the framework of quark
models, lattice QCD and QCD sum rules) is presented. The phenomenology of
transversity (in particular, in Drell-Yan processes and semi-inclusive
leptoproduction) is discussed in some detail. Finally, the prospects for future
measurements are outlined.Comment: small changes, references added, as finally published in Physics
Report