4,532 research outputs found
Nonparametric regression penalizing deviations from additivity
Due to the curse of dimensionality, estimation in a multidimensional
nonparametric regression model is in general not feasible. Hence, additional
restrictions are introduced, and the additive model takes a prominent place.
The restrictions imposed can lead to serious bias. Here, a new estimator is
proposed which allows penalizing the nonadditive part of a regression function.
This offers a smooth choice between the full and the additive model. As a
byproduct, this penalty leads to a regularization in sparse regions. If the
additive model does not hold, a small penalty introduces an additional bias
compared to the full model which is compensated by the reduced bias due to
using smaller bandwidths. For increasing penalties, this estimator converges to
the additive smooth backfitting estimator of Mammen, Linton and Nielsen [Ann.
Statist. 27 (1999) 1443-1490]. The structure of the estimator is investigated
and two algorithms are provided. A proposal for selection of tuning parameters
is made and the respective properties are studied. Finally, a finite sample
evaluation is performed for simulated and ozone data.Comment: Published at http://dx.doi.org/10.1214/009053604000001246 in the
Annals of Statistics (http://www.imstat.org/aos/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Solitons and kinks in a general car-following model
We study a car-following model of traffic flow which assumes only that a
car's acceleration depends on its own speed, the headway ahead of it, and the
rate of change of headway, with only minimal assumptions about the functional
form of that dependence. The velocity of uniform steady flow is found
implicitly from the acceleration function, and its linear stability criterion
can be expressed simply in terms of it. Crucially, unlike in previously
analyzed car-following models, the threshold of absolute stability does not
generally coincide with an inflection point in the steady velocity function.
The Burgers and KdV equations can be derived under the usual assumptions, but
the mKdV equation arises only when absolute stability does coincide with an
inflection point. Otherwise, the KdV equation applies near absolute stability,
while near the inflection point one obtains the mKdV equation plus an extra,
quadratic term. Corrections to the KdV equation "select" a single member of the
one-parameter set of soliton solutions. In previous models this has always
marked the threshold of a finite- amplitude instability of steady flow, but
here it can alternatively be a stable, small-amplitude jam. That is, there can
be a forward bifurcation from steady flow. The new, augmented mKdV equation
which holds near an inflection point admits a continuous family of kink
solutions, like the mKdV equation, and we derive the selection criterion
arising from the corrections to this equation.Comment: 25 page
Chiral Corrections to Lattice Calculations of Charge Radii
Logarithmic divergences in pion and proton charge radii associated with
chiral loops are investigated to assess systematic uncertainties in current
lattice determinations of charge radii. The chiral corrections offer a possible
solution to the long standing problem of why present lattice calculations yield
proton and pion radii which are similar in size.Comment: PostScript file only. Ten pages. Figures included. U. of MD Preprint
#92-19
Hadronic eta and eta-prime decays
The hadronic decays eta, eta-prime -> 3 pi and eta-prime -> eta pi pi are
investigated within the framework of U(3) chiral effective field theory in
combination with a relativistic coupled-channels approach. Final state
interactions are included by deriving s- and p-wave interaction kernels for
meson-meson scattering from the chiral effective Lagrangian and iterating them
in a Bethe-Salpeter equation. Very good overall agreement with currently
available data on decay widths and spectral shapes is achieved.Comment: 28 pages, 5 figures, 8 table
The eta' in baryon chiral perturbation theory
We include in a systematic way the eta' in baryon chiral perturbation theory.
The most general relativistic effective Lagrangian describing the interaction
of the lowest lying baryon octet with the Goldstone boson octet and the eta' is
presented up to linear order in the derivative expansion and its heavy baryon
limit is obtained. As explicit examples, we calculate the baryon masses and the
pi N sigma-term up to one-loop order in the heavy baryon formulation. A
systematic expansion in the meson masses is possible, and appearing divergences
are renormalized.Comment: 16 pages, 2 figure
The size of flavor changing effects induced by the symmetry breaking sector
It has recently been shown that strong interactions underlying electroweak
symmetry breaking will induce four-fermion amplitudes proportional to m_t^2,
which in turn will influence a variety of flavor changing processes. We argue
that the size of these effects are likely to be far below the current
experimental bounds.Comment: 5 pages, LaTeX, 1 figur
Integrating out the heaviest quark in N--flavour ChPT
We extend a known method to integrate out the strange quark in three flavour
chiral perturbation theory to the context of an arbitrary number of flavours.
As an application, we present the explicit formulae to one--loop accuracy for
the heavy quark mass dependency of the low energy constants after decreasing
the number of flavours by one while integrating out the heaviest quark in
N--flavour chiral perturbation theory.Comment: 18 pages, 1 figure. Text and references added. To appear in EPJ
Cusps in K_L --> 3 pi decays
The pion mass difference generates a pronounced cusp in K --> 3 pi decays,
the strength of which is related to the pi pi S-wave scattering lengths. We
apply an effective field theory framework developed earlier to evaluate the
amplitudes for K_L --> 3 pi decays in a systematic manner, where the strictures
imposed by analyticity and unitarity are respected automatically. The
amplitudes for the decay eta --> 3 pi are also given.Comment: 15 pages, 3 figures, uses Elsevier styl
Tv-RIO1 – an atypical protein kinase from the parasitic nematode Trichostrongylus vitrinus
Background: Protein kinases are key enzymes that regulate a wide range of cellular processes, including cell-cycle progression, transcription, DNA replication and metabolic functions. These enzymes catalyse the transfer of phosphates to serine, threonine and tyrosine residues, thus playing functional roles in reversible protein phosphorylation. There are two main groups, namely eukaryotic protein kinases (ePKs) and atypical protein kinases (aPKs); RIO kinases belong to the latter group. While there is some information about RIO kinases and their roles in animals, nothing is known about them in parasites. This is the first study to characterise a RIO1 kinase from any parasite.
Results: A full-length cDNA (Tv-rio-1) encoding a RIO1 protein kinase (Tv-RIO1) was isolated from the economically important parasitic nematode Trichostrongylus vitrinus (Order Strongylida). The uninterrupted open reading frame (ORF) of 1476 nucleotides encoded a protein of 491 amino acids, containing the characteristic RIO1 motif LVHADLSEYNTL. Tv-rio-1 was transcribed at the highest level in the third-stage larva (L3), and a higher level in adult females than in males. Comparison with homologues from other organisms showed that protein Tv-RIO1 had significant homology to related proteins from a range of metazoans and plants. Amino acid sequence identity was most pronounced in the ATP-binding motif, active site and metal binding loop. Phylogenetic analyses of selected amino acid sequence data revealed Tv-RIO1 to be most closely related to the proteins in the species of Caenorhabditis. A structural model of Tv-RIO1 was constructed and compared with the published crystal structure of RIO1 of Archaeoglobus fulgidus (Af-Rio1).
Conclusion: This study provides the first insights into the RIO1 protein kinases of nematodes, and a foundation for further investigations into the biochemical and functional roles of this molecule in biological processes in parasitic nematodes
Can one see the number of colors in eta, eta-prime --> pi^+ pi^- gamma?
We investigate the decays eta, eta-prime --> pi^+ pi^- gamma up to
next-to-leading order in the framework of the combined 1/N_c and chiral
expansions. Counter terms of unnatural parity at next-to-leading order with
unknown couplings are important to acommodate the results both to the
experimental decay width and the photon spectrum. The presence of these
coefficients does not allow for a determination of the number of colors from
these decays.Comment: 8 pages, 2 figure
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