1,357 research outputs found
Pseudoscalar pole contribution to the hadronic light-by-light piece of
We have studied the form factor in Resonance
Chiral Theory, with , to compute the contribution of the
pseudoscalar pole to the hadronic light-by-light piece of the anomalous
magnetic moment of the muon. In this work we allow the leading chiral
symmetry breaking terms, obtaining the most general expression for the form
factor of order . The parameters of the Effective Field
Theory are obtained by means of short distance constraints on the form factor
and matching with the expected behavior from QCD. Those parameters that cannot
be fixed in this way are fitted to experimental determinations of the form
factor within the spacelike momentum region of the virtual photon. Chiral
symmetry relations among the transition form factors for and
allow for a simultaneous fit to experimental data for the three mesons.
This shows an inconsistency between the BaBar data and the rest of the
experimental inputs. Thus, we find a total pseudoscalar pole contribution of
for our best fit (neglecting the
BaBar data). Also, a preliminary rough estimate of the impact of NLO in
corrections and higher vector multiplets (asym) enlarges the
uncertainty up to Comment: 7 pages, 3 figures, Proceedings for the workshop QCD@Wor
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Long distance chiral corrections in beta meson amplitudes
We discuss the chiral corrections to fB and BB with particular emphasis on determining the portion of the correction that arises from long distance physics. For very small pion and kaon masses all of the usual corrections are truly long distance, while for larger masses the long distance portion decreases. These chiral corrections have been used to extrapolate lattice calculations towards the physical region of lighter masses. We show in particular that the chiral extrapolation is better behaved if only the long distance portion of the correction is used. We also display the long distance portions of the infrared enhanced chiral logarithms that appear in partially quenched chiral perturbation theory
Refining the scalar and tensor contributions in decays
In this article we analyze the contribution from intermediate spin-0 and
spin-2 resonances to the decay by means of a chiral
invariant Lagrangian incorporating these mesons. In particular, we study the
corresponding axial-vector form-factors. The advantage of this procedure with
respect to previous analyses is that it incorporates chiral (and isospin)
invariance and, hence, the partial conservation of the axial-vector current.
This ensures the recovery of the right low-energy limit, described by chiral
perturbation theory, and the transversality of the current in the chiral limit
at all energies. Furthermore, the meson form-factors are further improved by
requiring appropriate QCD high-energy conditions. We end up with a brief
discussion on its implementation in the Tauola Monte Carlo and the prospects
for future analyses of Belle's data.Comment: 32 pages, 13 figures. Extended discussion on the numerical importance
of the tensor and scalar resonances and the parametrization of the scalar
propagator. Version published in JHE
Real-time experimental implementation of predictive control schemes in a small-scale pasteurization plant
Model predictive control (MPC) is one of the most used optimization-based control strategies for large-scale systems, since this strategy allows to consider a large number of states and multi-objective cost functions in a straightforward way. One of the main issues in the design of multi-objective MPC controllers, which is the tuning of the weights associated to each objective in the cost function, is treated in this work. All the possible combinations of weights within the cost function affect the optimal result in a given Pareto front. Furthermore, when the system has time-varying parameters, e.g., periodic disturbances, the appropriate weight tuning might also vary over time. Moreover, taking into account the computational burden and the selected sampling time in the MPC controller design, the computation time to find a suitable tuning is limited. In this regard, the development of strategies to perform a dynamical tuning in function of the system conditions potentially improves the closed-loop performance. In order to adapt in a dynamical way the weights in the MPC multi-objective cost function, an evolutionary-game approach is proposed. This approach allows to vary the prioritization weights in the proper direction taking as a reference a desired region within the Pareto front. The proper direction for the prioritization is computed by only using the current system values, i.e., the current optimal control action and the measurement of the current states, which establish the system cost function over a certain point in the Pareto front. Finally, some simulations of a multi-objective MPC for a real multi-variable case study show a comparison between the system performance obtained with static and dynamical tuning.Peer ReviewedPostprint (author's final draft
Regulation of pancreatic cancer aggressiveness by stromal stiffening
No abstract available
The "Solar Model Problem" Solved by the Abundance of Neon in Stars of the Local Cosmos
The interior structure of the Sun can be studied with great accuracy using
observations of its oscillations, similar to seismology of the Earth. Precise
agreement between helioseismological measurements and predictions of
theoretical solar models has been a triumph of modern astrophysics (Bahcall et
al. 2005). However, a recent downward revision by 25-35% of the solar
abundances of light elements such as C, N, O and Ne (Asplund et al. 2004) has
broken this accordance: models adopting the new abundances incorrectly predict
the depth of the convection zone, the depth profiles of sound speed and
density, and the helium abundance (Basu Antia 2004, Bahcall et al. 2005). The
discrepancies are far beyond the uncertainties in either the data or the model
predictions (Bahcall et al. 2005b). Here we report on neon abundances relative
to oxygen measured in a sample of nearby solar-like stars from their X-ray
spectra. They are all very similar and substantially larger than the recently
revised solar value. The neon abundance in the Sun is quite poorly determined.
If the Ne/O abundance in these stars is adopted for the Sun the models are
brought back into agreement with helioseismology measurements (Antia Basu 2005,
Bahcall et al. 2005c).Comment: 13 pages, 3 Figure
Increased circulating microRNAs miR-342-3p and miR-21-5p in natural sheep prion disease
Scrapie is a transmissible spongiform encephalopathy (TSE), or prion disease, of sheep and goats. As no simple diagnostic tests are yet available to detect TSEs in vivo, easily accessible biomarkers could facilitate the eradication of scrapie agents from the food chain. To this end, we analysed by quantitative reverse transcription PCR a selected set of candidate microRNAs (miRNAs) from circulating blood plasma of naturally infected, classical scrapie sheep that demonstrated clear scrapie symptoms and pathology. Significant scrapie-associated increase was repeatedly found for miR-342-3p and miR-21-5p. This is the first demonstration, to our knowledge, of circulating miRNA alterations in any animal suffering from TSE. Genome-wide expression studies are warranted to investigate the true depth of miRNA alterations in naturally occurring TSEs, especially in presymptomatic animals, as the presented study demonstrates the potential feasibility of miRNAs as circulating TSE biomarkers
Transanal total mesorectal excision: a pure NOTES approach for selected patients
Background: The concept of natural orifice transluminal endoscopic surgery (NOTES) has stimulated the development of various âincisionlessâ procedures. One of the most popular is the transanal approach for rectal lesions. The aims of this study were to report how we standardized NOTES technique for transanal mesorectal excision without abdominal assistance, discuss the difficulties and surgical outcomes of this technique and report its feasibility in a small group of selected patients. Methods: Three consecutive female patients underwent transanal NOTES rectal resection without transabdominal laparoscopic assistance for rectal lesions. Functional results were assessed with the Fecal Incontinence Quality of Life scale and the Wexner score. Results: The technical steps are described in details and complemented with a video. All procedures were completed without transabdominal laparoscopic help. The mesorectal plane was entirely dissected without any disruption, and distal and circumferential margins were tumor-free. No major complications were observed. Functional results show a significant impairment after surgery with improvement at 6 months to levels near those of the preoperative period. Conclusions: The performance and publication of NOTES procedures are subject to much discussion. Despite the small number of patients, this procedure appears feasible and can be accomplished maintaining fecal continence and respecting oncologic principles
Weinberg like sum rules revisited
The generalized Weinberg sum rules containing the difference of isovector
vector and axial-vector spectral functions saturated by both finite and
infinite number of narrow resonances are considered. We summarize the status of
these sum rules and analyze their overall agreement with phenomenological
Lagrangians, low-energy relations, parity doubling, hadron string models, and
experimental data.Comment: 31 pages, noticed misprints are corrected, references are added, and
other minor corrections are mad
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