933 research outputs found
Synthesis and Characterization of LnAg(WO4)(MoO4)
Polycrystalline LnAg(WO4)(MoO4) powders, with Ln = La to Lu and Y, have been obtained by ceramic method. Rietveld refinement for all compounds reveals that they present tetragonal symmetry, space group I41/a (No. 88), where the Ln3+/Ag+ ions are located in the 4a atomic positions, since the W/Mo are randomly distributed into 4b crystal sites.
In these compounds, a and b lattice parameters take values between those corresponding to tungstate and molybdate compounds. A progressive decrease in the lattice parameters is observed in going from La to Lu derivatives as a consequence of the well-known lanthanide contraction
Semileptonic decays, magnetic moments and spin distributions of spin-1/2 baryons with sea contribution
Spin-1/2 baryons are considered as a composite system made out of a "core" of
three quarks surrounded by a "sea" (of gluons and -pairs) which is
specified by its total quantum numbers. Specifically, we assume this sea to be
a flavor octet with spin-0 or 1 but no color. We show our model can provide
very goods fits to magnetic moments and semileptonic decay data using
experimental errors. The predictions for spin distributions are in reasonable
agreement with experiment.Comment: To be published in Int. J. of Mod. Phys.
Narrow Band Halpha Photometry of the Super-Earth GJ 1214b with GTC/OSIRIS Tunable Filters
The super-earth planet GJ 1214b has recently been the focus of several
studies, using the transit spectroscopy technique, trying to determine the
nature of its atmosphere. Here we focus on the Halpha line as a tool to further
restrict the nature of GJ1214's atmosphere. We used the Gran Telescopio
Canarias (GTC) OSIRIS instrument to acquire narrow band photometry with tunable
filters. With our observations, we were able to observe the primary transit of
the super-Earth GJ 1214b in three bandpasses: two centered in the continuum
around Halpha (653.5 nm and 662.0 nm) and one centered at the line core (656.3
nm). We measure the depth of the planetary transit at each wavelength
interval.By fitting analytic models to the measured light curves we were able
to compute the depth of the transit at the three bandpasses. Taking the
difference in the computed planet to star radius ratio between the line and the
comparison continuum filters, we find Delta (Rp/Rstar)_{Halpha-653.5} = (6.60
+/- 3.54) 10^-3 and Delta (Rp/Rstar)_{Halpha-662.0} = (3.30 +/- 3.61) 10^-3.
Although the planet radius is found to be larger in the Halpha line than in the
surrounding continuum, the quality of our observations and the sigma level of
the differences (1.8 and 1.0, respectively) does not allow us to claim an
Halpha excess in GJ1214's atmosphere. Further observations will be needed to
resolve this issue.Comment: Accepted for publication in A&A, language and typos correcte
Mirror matter admixtures in K_L \to \gamma\gamma
Based on possible albeit tiny, admixtures of mirror matter in ordinary mesons
we study the K_L \to \gamma\gamma transition. We find that this process can be
described with a small SU(3) symmetry breaking of only 3%. We also determine
the eta-eta' mixing angle and the pseudoscalar decay constants. The results for
these parameters are consistent with some obtained in the literature. They
favor two recent determinations; one based on two analytical constraints, and
another one based on next-to-leading order power corrections
Synthesis for Polynomial Lasso Programs
We present a method for the synthesis of polynomial lasso programs. These
programs consist of a program stem, a set of transitions, and an exit
condition, all in the form of algebraic assertions (conjunctions of polynomial
equalities). Central to this approach is the discovery of non-linear
(algebraic) loop invariants. We extend Sankaranarayanan, Sipma, and Manna's
template-based approach and prove a completeness criterion. We perform program
synthesis by generating a constraint whose solution is a synthesized program
together with a loop invariant that proves the program's correctness. This
constraint is non-linear and is passed to an SMT solver. Moreover, we can
enforce the termination of the synthesized program with the support of test
cases.Comment: Paper at VMCAI'14, including appendi
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