6,818 research outputs found
Evidence for the two pole structure of the Lambda(1405) resonance
The K^- p --> pi^0 pi^0 Sigma^0 reaction is studied within a chiral unitary
model. The distribution of pi^0 Sigma^0 states forming the Lambda(1405) shows,
in agreement with a recent experiment, a peak at 1420 MeV and a relatively
narrow width of Gamma = 38 MeV. The mechanism for the reaction is largely
dominated by the emission of a pi^0 prior to the K^- p interaction leading to
the Lambda(1405). This ensures the coupling of the Lambda(1405) to the K^- p
channel, thus maximizing the contribution of the second state found in chiral
unitary theories, which is narrow and of higher energy than the nominal
Lambda(1405). This is unlike the pi^- p --> K^0 \pi Sigma reaction, which gives
more weight to the pole at lower energy and with a larger width. The data of
these two experiments, together with the present theoretical analysis, provides
a firm evidence of the two pole structure of the Lambda(1405).Comment: 4 pages, 6 figure
K*-couplings for the antidecuplet excitation
We estimate the coupling of the K* vector meson to the N-->Theta+ transition
employing unitary symmetry, vector meson dominance, and results from the GRAAL
Collaboration for eta photoproduction off the neutron. Our small numerical
value for the coupling constant is consistent with the non-observation of the
Theta+ in recent CLAS searches for its photoproduction. We also estimate the
K*-coupling for the N-->Sigma* excitation, with Sigma* being the Sigma-like
antidecuplet partner of the Theta+-baryon.Comment: 9 pages, 1 figure. Minor changes in text and abstract, references
added; version to appear in Phys. Rev.
Leading-twist pion and kaon distribution amplitudes in the gauge-invariant nonlocal chiral quark model from the instanton vacuum
We investigate the leading-twist light-cone distribution amplitudes for the
pion and kaon based on the gauge-invariant nonlocal chiral quark model from the
instanton vacuum in the presence of external axial-vector currents. We find
that the nonlocal contribution from the gauge invariance has much effects on
the pion distribution amplitudes, while it changes mildly the kaon ones. We
also study the Gegenbauer moments of the distribution amplitudes and compare
them with the empirical analysis of the CLEO data.Comment: 14 pages, 10 figure
Micropropagation of rose cultivar ‘Pareo’
A protocol was developed for micropropagation of rose cv. ‘Pareo’. Nodal segments were surface sterilized with 0.1% solution of mercuric chloride for 10 min and these disinfected explants were inoculated aseptically on culture medium. The, axillary shoots were regenerated from nodal explants on agar-gelled Murashige and Skoog medium supplemented with 1.5 mg/l BAP. In vitro rooting was obtained when shoot clusters were cultured on half strength Murashige and Skoog medium supplemented with 1.0 mg/l IBA. The rooted plantlets were acclimatized successfully in the field.Key words: Micropropagation, nodal segments, rose
Selective dilution and magnetic properties of La_{0.7}Sr_{0.3}Mn_{1-x}M'_xO_3 (M' = Al, Ti)
The magnetic lattice of mixed-valence Mn ions in LaSrMnO
is selectively diluted by partial substitution of Mn by Al or Ti. The
ferromagnetic transition temperature and the saturation moment decreases with
substitution in both series. The volume fraction of the non-ferromagnetic
phases evolves non-linearly with the substitution concentration and faster than
theoretically expected. By presenting the data in terms of selective dilutions,
the reduction of is found to be scaled by the relative ionic
concentrations and is consistent with a prediction derived from molecular-field
theory.Comment: 6 pages, 5 figures, REVTex4.0. Submitted to PR
Spin-dependent twist-4 matrix elements from the instanton vacuum: Flavor-singlet and nonsinglet
We estimate the twist-4 spin-1 nucleon matrix element f_2 in an
instanton-based description of the QCD vacuum. In addition to the
flavor-nonsinglet we compute also the flavor-singlet matrix element, which
appears in next-to-leading order of the (1/N_c)-expansion. The corresponding
twist-3 spin-2 matrix elements d_2 are suppressed in the packing fraction of
the instanton medium, (\bar \rho)/(\bar R) << 1. We use our results to estimate
the leading (1/Q^2) power corrections to the first moment of the proton and
neutron spin structure functions G_1, as well as the intrinsic charm
contribution to the nucleon spin.Comment: 17 pages, 4 eps figures include
Kinematic modelling of a 3-axis NC machine tool in linear and circular interpolation
Machining time is a major performance criterion when it comes to high-speed
machining. CAM software can help in estimating that time for a given strategy.
But in practice, CAM-programmed feed rates are rarely achieved, especially
where complex surface finishing is concerned. This means that machining time
forecasts are often more than one step removed from reality. The reason behind
this is that CAM routines do not take either the dynamic performances of the
machines or their specific machining tolerances into account. The present
article seeks to improve simulation of high-speed NC machine dynamic behaviour
and machining time prediction, offering two models. The first contributes
through enhanced simulation of three-axis paths in linear and circular
interpolation, taking high-speed machine accelerations and jerks into account.
The second model allows transition passages between blocks to be integrated in
the simulation by adding in a polynomial transition path that caters for the
true machining environment tolerances. Models are based on respect for path
monitoring. Experimental validation shows the contribution of polynomial
modelling of the transition passage due to the absence of a leap in
acceleration. Simulation error on the machining time prediction remains below
1%
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