42,029 research outputs found
Atmospheric refraction correction for Ka-band blind pointing on the DSS-13 beam waveguide antenna
An analysis of the atmospheric refraction corrections at the DSS-13 34-m diameter beam waveguide (BWG) antenna for the period Jul. - Dec. 1990 is presented. The current Deep Space Network (DSN) atmospheric refraction model and its sensitivity with respect to sensor accuracy are reviewed. Refraction corrections based on actual atmospheric parameters are compared with the DSS-13 station default corrections for the six-month period. Average blind-pointing improvement during the worst month would have amounted to 5 mdeg at 10 deg elevation using actual surface weather values. This would have resulted in an average gain improvement of 1.1 dB
Charged current neutrino induced coherent pion production
We analyze the neutrino induced charged current coherent pion production at
the energies of interest for recent experiments like K2K and MiniBooNE. Medium
effects in the production mechanism and the distortion of the pion wave
function, obtained solving the Klein Gordon equation with a microscopic optical
potential, are included in the calculation. We find a strong reduction of the
cross section due to these effects and also substantial modifications of the
energy distributions of the final lepton and pion.Comment: 11 pages, 6 figures. Some details and new references added; results
unchanged. Accepted in PR
Educational Activities to Help Transferring Knowledge in Nuclear: The Seminars of Spanish Young Generation in Nuclear (Jóvenes Nucleares)
From its creation, Spanish Young Generation in Nuclear (Jóvenes Nucleares, JJNN), a non-profit organization that depends on the Spanish Nuclear Society (SNE), has as an important scope to help transferring the knowledge between those generations in the way that it can be possible
From Secondary School To University: Attracting Young Students Towards A Career In Nuclear
From its creation, Spanish Young Generation in Nuclear (Jóvenes Nucleares, JJNN), a non-profit organization that depends on the Spanish Nuclear Society (SNE), has as an important scope to help spread knowledge about nuclear energy, not only pointing out its advantages and its role in our society, but also trying to correct some of the ideas that are due to the biased information and to the lack of knowledge. To try to have success in that goal, some high school lectures were taught and it has been organized regularly a Basic Course on Nuclear Science and Technolog
Masses and magnetic moments of ground-state baryons in covariant baryon chiral perturbation theory
We report on some recent developments in our understanding of the light-quark
mass dependence and the SU(3) flavor symmetry breaking corrections to the
magnetic moments of the ground-state baryons in a covariant formulation of
baryon chiral perturbation theory, the so-called EOMS formulation. We show that
this covariant ChPT exhibits some promising features compared to its
heavy-baryon and infrared counterparts.Comment: 8 pages, 3 figures; plenary talk delivered by LSG at the 14th
national conference on nuclear structure, April 12nd - 16th, 2012, Huzhou,
Chin
Can We Detect the Anisotropic Shapes of Quasar HII Regions During Reionization Through The Small-Scale Redshifted 21cm Power Spectrum?
Light travel time delays distort the apparent shapes of HII regions
surrounding bright quasars during early stages of cosmic reionization.
Individual HII regions may remain undetectable in forthcoming redshifted 21 cm
experiments. However, the systematic deformation along the line of sight may be
detectable statistically, either by stacking tomographic 21cm images of quasars
identified, for example, by JWST, or as small-scale anisotropy in the
three-dimensional 21cm power spectrum. Here we consider the detectability of
this effect. The anisotropy is largest when HII regions are large and expand
rapidly, and we find that if bright quasars contributed to the early stages of
reionization, then they can produce significant anisotropy, on scales
comparable to the typical sizes of HII regions of the bright quasars (approx.
30 Mpc and below). The effect therefore cannot be ignored when analyzing future
21cm power spectra on small scales. If 10 percent of the volume of the IGM at
redshift z=10 is ionized by quasars with typical ionizing luminosity of S= 5 x
10^{56} photons/second, the distortions can enhance by more than 10 percent the
21cm power spectrum in the radial (redshift) direction, relative to the
transverse directions. The level of this anisotropy exceeds that due to
redshift-space distortion, and has the opposite sign. We show that on-going
experiments such as MWA should be able to detect this effect. A detection would
reveal the presence of bright quasars, and shed light on the ionizing yield and
age of the ionizing sources, and the distribution and small-scale clumping of
neutral intergalactic gas in their vicinity.Comment: Version accepted by ApJ, with new fiducial model and improved
discussio
Neutral current coherent pion production
We investigate the neutrino induced coherent pion production reaction at low
and intermediate energies. The model includes pion, nucleon and Delta(1232)
resonance as the relevant hadronic degrees of freedom. Nuclear medium effects
on the production mechanisms and pion distortion are taken into account. We
obtain that the dominance of the Delta excitation holds due to large
cancellations among the background contributions. We consider two sets of
vector and axial-vector N-Delta transition form-factors, evidencing the strong
sensitivity of the results to the axial coupling C5A(0). The differences
between neutrino and antineutrino cross sections, emerging from interference
terms, are also discussed.Comment: 4 pages, 3 figures, minor corrections, a few references adde
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