On the symplectic phase space of KdV

We prove that the Birkhoff map \Om for KdV constructed on H^{-1}_0(\T) can be interpolated between H^{-1}_0(\T) and L^2_0(\T). In particular, the symplectic phase space H^{1/2}_0(\T) can be described in terms of Birkhoff coordinates. As an application, we characterize the regularity of a potential q\in H^{-1}(\T) in terms of the decay of the gap lengths of the periodic spectrum of Hill's operator on the interval $[0,2]$

The impact of metallic contacts on propagation losses of an underlying photonic crystal waveguide

In view of an electrically pumped photonic crystal-based semiconductor optical amplifier (SOA), we investigate optical mode propagation in 2D PhC waveguides in the presence of metal contacts for carrier injection. Our photonic crystal (PhC) devices are manufactured in the InP/InGaAsP material system. For the loss measurements, we have fabricated contact strips as narrow as 300nm with a sub-50nm placing accuracy on top of W3 waveguides. We study the influence of their position and width on optical power transmission through passive waveguides with respect to viability for future active devices. Our experimental results are complemented by numerical studies (FDTD, plane-wave expansion method)

Are Neutron-Rich Elements Produced in the Collapse of Strange Dwarfs ?

The structure of strange dwarfs and that of hybrid stars with same baryonic number is compared. There is a critical mass (M~0.24M_sun) in the strange dwarf branch, below which configurations with the same baryonic number in the hybrid star branch are more stable. If a transition occurs between both branches, the collapse releases an energy of about of 3x10^{50} erg, mostly under the form of neutrinos resulting from the conversion of hadronic matter onto strange quark matter. Only a fraction (~4%) is required to expel the outer neutron-rich layers. These events may contribute significantly to the chemical yield of nuclides with A>80 in the Galaxy, if their frequency is of about one per 1500 years.Comment: Accepted for publication in IJMP

128Xe and 130Xe: Testing He-shell burning in AGB stars

The s-process branching at 128I has been investigated on the basis of new, precise experimental (n,g) cross sections for the s-only isotopes 128Xe and 130Xe. This branching is unique, since it is essentially determined by the temperature- and density-sensitive stellar decay rates of 128I and only marginally affected by the specific stellar neutron flux. For this reason it represents an important test for He-shell burning in AGB stars. The description of the branching by means of the complex stellar scenario reveals a significant sensitivity to the time scales for convection during He shell flashes, thus providing constraints for this phenomenon. The s-process ratio 128Xe/130Xe deduced from stellar models allows for a (9+-3)% p-process contribution to solar 128Xe, in agreement with the Xe-S component found in meteoritic presolar SiC grains.Comment: 24 pages, 9 figures, accepted for publication in Astophysical Journa

Asymptotic Giant Branch models at very low metallicity

In this paper we present the evolution of a low mass model (initial mass M=1.5 Msun) with a very low metal content (Z=5x10^{-5}, equivalent to [Fe/H]=-2.44). We find that, at the beginning of the AGB phase, protons are ingested from the envelope in the underlying convective shell generated by the first fully developed thermal pulse. This peculiar phase is followed by a deep third dredge up episode, which carries to the surface the freshly synthesized 13C, 14N and 7Li. A standard TP-AGB evolution, then, follows. During the proton ingestion phase, a very high neutron density is attained and the s-process is efficiently activated. We therefore adopt a nuclear network of about 700 isotopes, linked by more than 1200 reactions, and we couple it with the physical evolution of the model. We discuss in detail the evolution of the surface chemical composition, starting from the proton ingestion up to the end of the TP-AGB phase.Comment: Accepted for Publication on PAS

The effect of 12C + 12C rate uncertainties on s-process yields

The slow neutron capture process in massive stars (the weak s-process) produces most of the s-only isotopes in the mass region 60 < A < 90. The nuclear reaction rates used in simulations of this process have a profound effect on the final s-process yields. We generated 1D stellar models of a 25 solar mass star varying the 12C + 12C rate by a factor of 10 and calculated full nucleosynthesis using the post-processing code PPN. Increasing or decreasing the rate by a factor of 10 affects the convective history and nucleosynthesis, and consequently the final yields.Comment: Conference proceedings for the Nuclear Physics in Astrophysics IV conference, 8-12 June 2009. 4 pages, 3 figures. Accepted for publication to the Journal of Physics: Conference Serie

The s-process branching at 185W

The neutron capture cross section of the unstable nucleus 185W has been derived from experimental photoactivation data of the inverse reaction 186W(gamma,n)185W. The new result of sigma = (687 +- 110) mbarn confirms the theoretically predicted neutron capture cross section of 185W of sigma = 700 mbarn at kT = 30 keV. A neutron density in the classical s-process of n_n = (3.8 +0.9 -0.8} * 1e8 cm-3 is derived from the new data for the 185W branching. In a stellar s-process model one finds a significant overproduction of the residual s-only nucleus 186Os.Comment: ApJ, in pres

Species delimitation in lemurs: multiple genetic loci reveal low levels of species diversity in the genus Cheirogaleus

<p>Abstract</p> <p>Background</p> <p>Species are viewed as the fundamental unit in most subdisciplines of biology. To conservationists this unit represents the currency for global biodiversity assessments. Even though Madagascar belongs to one of the top eight biodiversity hotspots of the world, the taxonomy of its charismatic lemuriform primates is not stable. Within the last 25 years, the number of described lemur species has more than doubled, with many newly described species identified among the nocturnal and small-bodied cheirogaleids. Here, we characterize the diversity of the dwarf lemurs (genus <it>Cheirogaleus</it>) and assess the status of the seven described species, based on phylogenetic and population genetic analysis of mtDNA (<it>cytb </it>+ <it>cox2</it>) and three nuclear markers (<it>adora3</it>, <it>fiba </it>and <it>vWF</it>).</p> <p>Results</p> <p>This study identified three distinct evolutionary lineages within the genus <it>Cheirogaleus</it>. Population genetic cluster analyses revealed a further layer of population divergence with six distinct genotypic clusters.</p> <p>Conclusion</p> <p>Based on the general metapopulation lineage concept and multiple concordant data sets, we identify three exclusive groups of dwarf lemur populations that correspond to three of the seven named species: <it>C. major</it>, <it>C. medius </it>and <it>C. crossleyi</it>. These three species were found to be genealogically exclusive in both mtDNA and nDNA loci and are morphologically distinguishable. The molecular and morphometric data indicate that <it>C. adipicaudatus </it>and <it>C. ravus </it>are synonymous with <it>C. medius </it>and <it>C. major</it>, respectively. <it>Cheirogaleus sibreei </it>falls into the <it>C. medius </it>mtDNA clade, but in morphological analyses the membership is not clearly resolved. We do not have sufficient data to assess the status of <it>C. minusculus</it>. Although additional patterns of population differentiation are evident, there are no clear subdivisions that would warrant additional specific status. We propose that ecological and more geographic data should be collected to confirm these results.</p

Novel method to study neutron capture of U 235 and U 238 simultaneously at keV energies

The neutron capture cross sections of the main uranium isotopes, U235 and U238, were measured simultaneously for keV energies, for the first time by combining activation technique and atom counting of the reaction products using accelerator mass spectrometry. New data, with a precision of 3%-5%, were obtained from mg-sized natural uranium samples for neutron energies with an equivalent Maxwell-Boltzmann distribution of kT∼25keV and for a broad energy distribution peaking at 426 keV. The cross-section ratio of U235(n,γ)/U238(n,γ) can be deduced in accelerator mass spectrometry directly from the atom ratio of the reaction products U236/U239, independent of any fluence normalization. Our results confirm the values at the lower band of existing data. They serve as important anchor points to resolve present discrepancies in nuclear data libraries as well as for the normalization of cross-section data used in the nuclear astrophysics community for s-process studies

Constraints on the Variations of the Fundamental Couplings

We reconsider several current bounds on the variation of the fine-structure constant in models where all gauge and Yukawa couplings vary in an interdependent manner, as would be expected in unified theories. In particular, we re-examine the bounds established by the Oklo reactor from the resonant neutron capture cross-section of 149Sm. By imposing variations in \Lambda_{QCD} and the quark masses, as dictated by unified theories, the corresponding bound on the variation of the fine-structure constant can be improved by about 2 orders of magnitude in such theories. In addition, we consider possible bounds on variations due to their effect on long lived \alpha- and \beta-decay isotopes, particularly 147Sm and 187Re. We obtain a strong constraint on \Delta \alpha / \alpha, comparable to that of Oklo but extending to a higher redshift corresponding to the age of the solar system, from the radioactive life-time of 187Re derived from meteoritic studies. We also analyze the astrophysical consequences of perturbing the decay Q values on bound state \beta-decays operating in the s-process.Comment: 25 pages, latex, 5 eps figure