4,828 research outputs found
A case in favor of the
Using an interaction extracted from the local hidden gauge Lagrangians, which
brings together vector and pseudoscalar mesons, and the coupled channels (s-wave), (d-wave), (s-wave) and (d-wave),
we look in the region of MeV and we find two resonances
dynamically generated by the interaction of these channels, which are naturally
associated to the and . The appears neatly as a pole in the complex plane. The free parameters of
the theory are chosen to fit the (d-wave) data. Both the real and
imaginary parts of the amplitude vanish in our approach in the vicinity
of this resonance, similarly to what happens in experimental determinations,
what makes this signal very weak in this channel. This feature could explain
why this resonance does not show up in some experimental analyses, but the
situation is analogous to that of the resonance, the second scalar
meson after the in the (d-wave) amplitude. The
unitary coupled channel approach followed here, in connection with the
experimental data, leads automatically to a pole in the 1700 MeV region and
makes this second resonance unavoidable
Space-Time diversity for NLOS mitigation in TDOA-based positioning systems
This paper studies the potential impact of using space-Time information in the mitigation of the Non-LineOf-Sight condition in mobile subscriber's positioning systems. First of all, this work discusses the positioning problem based on measures of Time Differences Of Arrival departing from a more exact characterization of the signal statistics and including some geometrical restrictions to achieve an improved accurate. Furthermore, a novel approach that integrates signal propagation characteristics to information provided by a suitable timing estimation model based on Cramer Rao Bound for a Rayleigh-fading channel, when antenna arrays are used at the receiver and when a set ofchannel vector estimates are available, has been introduced to study the positive benefits of space-Time diversity. These approaches are evaluated within a realistic simulation scenario.Peer ReviewedPostprint (published version
Circular dichroism simulated spectra of chiral gold nanoclusters: A dipole approximation
Circular dichroism (CD) spectra of chiral bare and thiol-passivated gold
nanoclusters have been calculated within the dipole approximation. The
calculated CD spectra show features that allow us to distinguish between
clusters with different indexes of chirality. The main factor responsible of
the differences in the CD lineshapes is the distribution of interatomic
distances that characterize the chiral cluster geometry. These results provide
theoretical support for the quantification of chirality and its measurement,
using the CD lineshapes of chiral metal nanoclusters.Comment: 3 pages + 4 figure
A Photovoice Evaluation of Coping Mechanisms Among Children of Immigrants
In this community based participatory research, photovoice was used to shine a light on the coping mechanisms of children of immigrants. Photovoice was chosen to give the children a platform to explore and identify how they cope with difficult circumstances and situations. Eight children were chosen by convenience sampling. Children were recruited from the after-school program offered by Puentes de Salud, a non-profit organization in South Philadelphia. Participants varied in ages from 7 to 12 years old or, 3rd through 5th grade. The primary purpose of the study was to (a) provide a deeper understanding of the coping mechanisms of vulnerable children whom experience adversity and (b) provide insight to Puentes de Salud, for them to implement and/or evaluate their activities to suit those coping mechanisms of the children. The study occurred over 5 sessions with parents and children. The children were given a disposable camera with 27 frames and were given the probing question: âWhat or who do you turn to when things go and get tough?â The three major themes that emerged from the pictures were: Culture, Friends and Family, and Puentes (the after-school program). This research shed light on the adversity faced by these children and how they try to cope with it. There was both personal buy-in and skepticism from this vulnerable populations, given the scope of the research project. Puentes de Salud can implement strategies and activities into their education program to teach effective coping mechanisms and styles
Inversion of stellar statistics equation for the Galactic Bulge
A method based on Lucy (1974, AJ 79, 745) iterative algorithm is developed to
invert the equation of stellar statistics for the Galactic bulge and is then
applied to the K-band star counts from the Two-Micron Galactic Survey in a
number of off-plane regions (10 deg.>|b|>2 deg., |l|<15 deg.).
The top end of the K-band luminosity function is derived and the morphology
of the stellar density function is fitted to triaxial ellipsoids, assuming a
non-variable luminosity function within the bulge. The results, which have
already been outlined by Lopez-Corredoira et al.(1997, MNRAS 292, L15), are
shown in this paper with a full explanation of the steps of the inversion: the
luminosity function shows a sharp decrease brighter than M_K=-8.0 mag when
compared with the disc population; the bulge fits triaxial ellipsoids with the
major axis in the Galactic plane at an angle with the line of sight to the
Galactic centre of 12 deg. in the first quadrant; the axial ratios are
1:0.54:0.33, and the distance of the Sun from the centre of the triaxial
ellipsoid is 7860 pc. The major-minor axial ratio of the ellipsoids is found
not to be constant. However, the interpretation of this is controversial. An
eccentricity of the true density-ellipsoid gradient and a population gradient
are two possible explanations.
The best fit for the stellar density, for 1300 pc<t<3000 pc, are calculated
for both cases, assuming an ellipsoidal distribution with constant axial
ratios, and when K_z is allowed to vary. From these, the total number of bulge
stars is ~ 3 10^{10} or ~ 4 10^{10}, respectively.Comment: 19 pages, 23 figures, accepted in MNRA
Mixing of pseudoscalar-baryon and vector-baryon in the J(P)=1/2(-) sector and the N* (1535) and N* (1650) resonances
We study the meson-baryon interaction with J(P) = 1/2 using the hidden-gauge Lagrangians and mixing pseudoscalar meson-baryon with the vector meson-baryon states in a coupled channels scheme with pi N, eta N, K Lambda, K Sigma, rho N, and pi Delta (d wave). We fit the subtraction constants of each channel to the S-11 partial wave amplitude of the pi N scattering data extracted from the partial wave analysis of the George Washington group. We find two poles that we associate to the N*(1535) and the N*(1650) resonances, with negative subtraction constants of natural size, and compare the results with empirical determinations of these pole positions. We calculate the branching ratios for the different channels of each resonance and we find a good agreement with the experimental data. The cross section for the pi(-)p -> eta n scattering is also evaluated and compared with experiment
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