46,121 research outputs found
Minimally Allowed Neutrinoless Double Beta Decay Rates From Approximate Flavor Symmetries
Neutrinoless double beta decay () is among the only realistic
probes of Majorana neutrinos. In the standard scenario, dominated by light
neutrino exchange, the process amplitude is proportional to , the
element of the Majorana mass matrix. Naively, current data allows for vanishing
, but this should be protected by an appropriate flavor symmetry. All
such symmetries lead to mass matrices inconsistent with oscillation
phenomenology. I perform a spurion analysis to break all possible Abelian
symmetries that guarantee vanishing rates and search for
minimally allowed values. I survey 230 broken structures to yield
values and current phenomenological constraints under a variety of scenarios.
This analysis also extracts predictions for both neutrino oscillation
parameters and kinematic quantities. Assuming reasonable tuning levels, I find
that eV at 99% confidence. Bounds below this value
might indicate the Dirac neutrino nature or the existence of new light (eV-MeV
scale) degrees of freedom that can potentially be probed elsewhere.Comment: 19 Pages, 4 .eps Figures, 3 Table
Effect of creep in titanium alloy Ti-6Al-4V at elevated temperature on aircraft design and flight test
Short-term compressive creep tests were conducted on three titanium alloy Ti-6Al-4V coupons at three different stress levels at a temperature of 714 K (825 F). The test data were compared to several creep laws developed from tensile creep tests of available literature. The short-term creep test data did not correlate well with any of the creep laws obtained from available literature. The creep laws themselves did not correlate well with each other. Short-term creep does not appear to be very predictable for titanium alloy Ti-6Al-4V. Aircraft events that result in extreme, but short-term temperature and stress excursions for this alloy should be approached cautiously. Extrapolations of test data and creep laws suggest a convergence toward predictability in the longer-term situation
SPECIES I: Spectroscopic Parameters and atmosphEric ChemIstriEs of Stars
The detection and subsequent characterisation of exoplanets are intimately
linked to the characteristics of their host star. Therefore, it is necessary to
study the star in detail in order to understand the formation history and
characteristics of their companion(s). Our aims were to develop a community
tool that allows the automated calculation of stellar parameters for a large
number of stars, using high resolution echelle spectra and minimal photometric
magnitudes, and introduce the first results in this work. We measured the
equivalent widths of several iron lines and used them to solve the radiative
transfer equation assuming local thermodynamic equilibrium to obtain the
atmospheric parameters (, [Fe/H], logg and ). We used
these values to derive the abundance of 11 chemical elements in the stellar
photosphere (Na, Mg, Al, Si, Ca, Ti, Cr, Mn, Ni, Cu and Zn). Rotation and
macroturbulent velocity were obtained using temperature calibrators and
synthetic line profiles to match the observed spectra of five absorption lines.
Finally, by interpolating in a grid of MIST isochrones, we derived the mass,
radius and age using a Bayesian approach. SPECIES obtains bulk parameters that
are in good agreement with measured values from different existing catalogues,
including when different methods are used to derive them. We find excellent
agreement with previous works that used similar methodologies. We find
discrepancies in the chemical abundances for some elements with respect to
other works, which could be produced by differences in , or in
the line list or the atomic line data used to derive them. We also obtained
analytic relations to describe the correlations between different parameters,
and we implemented new methods to better handle these correlations, which
provides a better description of the uncertainties associated with the
measurements.Comment: 28 pages, 26 figures, resubmitted to A&
Dendritic cells activated with products released by schistosome larvae drive Th2-type immune responses, which can be inhibited by manipulation of CD40 costimulation
The early immune events in response to infective larvae of the parasitic helminth Schistosoma mansoni are poorly understood, but here for the first time we report on the potential of products released by schistosome larvae (material released in the first 3 It after transformation [0-3hRP]) to stimulate the maturation of dendritic cells (DC) and alter their T-cell-polarizing function. This was performed in comparison with lipopolysaccharide (LPS) and zymosan A, which classically activate DC to prime for Th1- and Th2-type responses, respectively. In our study, immature bone marrow-derived DC stimulated in vitro with 0-3hRP exhibited up-regulated expression of major histocompatibility complex class II, CD40, and CD86 and increased production of interleukin 12p40 (IL-12p40) and IL-6, albeit at lower levels than in response to LPS or zymosan A. Using an in vitro ovalbumin peptide-restricted priming assay, DC matured with 0-3hRP exhibited a potent capacity to drive Th2 polarization of CD4(+) cells from DO11.10 transgenic mice. This was characterized by increased IL-4 production (but not gamma interferon) of a magnitude similar to that primed by DC matured with zymosan A. Inoculation of DO11.10 mice with 0-3hRP-activated DC pulsed with ovalbumin peptide also led to the development of a Th2-type polarized response in the skin-draining lymph nodes and spleen. However, ligation of CD40 on DC by anti-CD40 antibody treatment reversed the ability of 0-3hRP-activated DC to prime for Th2-type responses and instead caused the induction of a more Th1-type response
Critical Analysis of Baryon Masses and Sigma-Terms in Heavy Baryon Chiral Perturbation Theory
We present an analysis of the octet baryon masses and the and
--terms in the framework of heavy baryon chiral perturbation theory. At
next-to-leading order, , knowledge of the baryon masses and
allows to determine the three corresponding finite
low--energy constants and to predict the the two --terms
. We also include the spin-3/2 decuplet in the
effective theory. The presence of the non--vanishing energy scale due to the
octet--decuplet splitting shifts the average octet baryon mass by an infinite
amount and leads to infinite renormalizations of the low--energy constants. The
first observable effect of the decuplet intermediate states to the baryon
masses starts out at order . We argue that it is not sufficient to retain
only these but no other higher order terms to achieve a consistent description
of the three--flavor scalar sector of baryon CHPT. In addition, we critically
discuss an SU(2) result which allows to explain the large shift of via intermediate states.Comment: 18 pp, TeX, BUTP-93/05 and CRN-93-0
Decuplet baryon magnetic moments in a QCD-based quark model beyond quenched approximation
We study the decuplet baryon magnetic moments in a QCD-based quark model
beyond quenched approximation. Our approach for unquenching the theory is based
on the heavy baryon perturbation theory in which the axial couplings for baryon
- meson and the meson-meson-photon couplings from the chiral perturbation
theory are used together with the QM moment couplings. It also involves the
introduction of a form factor characterizing the structure of baryons
considered as composite particles. Using the parameters obtained from fitting
the octet baryon magnetic moments, we predict the decuplet baryon magnetic
moments. The magnetic moment is found to be in good agreement with
experiment: is predicted to be compared to the
experimental result of (2.02 0.05) .Comment: 19 pages, 2 figure
Wall-Enhanced Convection in Vibrofluidized Granular Systems
An event-driven molecular dynamics simulation of inelastic hard spheres
contained in a cylinder and subject to strong vibration reproduces accurately
experimental results[1] for a system of vibrofluidized glass beads. In
particular, we are able to obtain the velocity field and the density and
temperature profiles observed experimentally. In addition, we show that the
appearance of convection rolls is strongly influenced by the value of the
sidewall-particle restitution coefficient. Suggestions for observing more
complex convection patterns are proposed.Comment: 4 pages, 6 figure
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