PopII 1/2 stars: very high N14 and low O16 yields

Nine 20 Mo models were computed with metallicities ranging from solar, through $Z=10^{-5}$ ([Fe/H]=~-3.1) down to $Z=10^{-8}$ ([Fe/H]=~-6.1) and with initial rotational velocities between 0 and 600 km/s to study the impact of initial metallicity and rotational velocity. The very large amounts of N14 observed (~0.03 Mo) are only produced at $Z=10^{-8}$ (PopII 1/2). The strong dependence of the N14 yields on rotation and other parameters like the initial mass and metallicity may explain the large scatter in the observations of N14 abundance. The metallicity trends are best reproduced by the models with Omega_ini/Omega_c=~0.75, which is slightly above the mean observed value for OB solar metallicity stars. Indeed, in the model with Vini=600 km/s at $Z=10^{-8}$, the O16 yield is reduced due to strong mixing. This allows in particular to reproduce the upturn for C/O and a slightly decreasing [C/Fe], which are observed below [Fe/H]=~-3.Comment: 2 pages, Conf. Proceedings: From Lithium to Uranium: Elemental Tracers of Early Cosmic Evolution, June 2005, Eds.:V. Hill, P. Fran\c{c}ois and F. Prima

Symbolic Abstractions for Quantum Protocol Verification

Quantum protocols such as the BB84 Quantum Key Distribution protocol exchange qubits to achieve information-theoretic security guarantees. Many variants thereof were proposed, some of them being already deployed. Existing security proofs in that field are mostly tedious, error-prone pen-and-paper proofs of the core protocol only that rarely account for other crucial components such as authentication. This calls for formal and automated verification techniques that exhaustively explore all possible intruder behaviors and that scale well. The symbolic approach offers rigorous, mathematical frameworks and automated tools to analyze security protocols. Based on well-designed abstractions, it has allowed for large-scale formal analyses of real-life protocols such as TLS 1.3 and mobile telephony protocols. Hence a natural question is: Can we use this successful line of work to analyze quantum protocols? This paper proposes a first positive answer and motivates further research on this unexplored path

The GSF Instability and Turbulence do not Account for the Relatively Low Rotation Rate of Pulsars

The aim of this paper is to examine the effects of the horizontal turbulence in differentially rotating stars on the GSF instability and apply our results to pre-supernova models. For this purpose we derive the expression for the GSF instability with account of the thermal transport and smoothing of the mu-gradient by the horizontal turbulence. We apply the new expressions in numerical models of a 20 solar mass star. We show that if N^2_{Omega} < 0 the Rayleigh-Taylor instability cannot be killed by the stabilizing thermal and mu-gradients, so that the GSF instability is always there and we derive the corresponding diffusion coefficient. The GSF instability grows towards the very latest stages of stellar evolution. Close to the deep convective zones in pre-supernova stages, the transport coefficient of elements and angular momentum by the GSF instability can very locally be larger than the shear instability and even as large as the thermal diffusivity. However the zones over which the GSF instability is acting are extremely narrow and there is not enough time left before the supernova explosion for a significant mixing to occur. Thus, even when the inhibiting effects of the mu-gradient are reduced by the horizontal turbulence, the GSF instability remains insignificant for the evolution. We conclude that the GSF instability in pre-supernova stages cannot be held responsible for the relatively low rotation rate of pulsars compared to the predictions of rotating star models.Comment: 6 pages, 4 figures, accepted for publication in A&

ORGANIC ROW CROPS IN A DIVERSIFIED FARM PORTFOLIO

This paper estimates and compares the net returns of an organic row crop rotation to the returns of a conventional row crop rotation in the Midwest, and explores some of the sources of risk associated with organic row crop production. The study concludes modeling the optimal land use of a risk-averse producer assuming a producer is able to grow both organic and conventional row crops. The results indicate that the expected net returns of organic row crop production can be competitive with traditional corn and soybean production, however, the variation in returns can be nearly twice those of conventional production. The land use model indicates that organics is part of an optimal portfolio for producers with low levels of risk aversion. Land use changes to conventional corn and soybean production as risk aversion and farm size increase.Farm Management,

Revision of Star-Formation Measures

Rotation plays a major role in the evolution of massive stars. A revised grid of stellar evolutionary tracks accounting for rotation has recently been released by the Geneva group and implemented into the Starburst99 evolutionary synthesis code. Massive stars are predicted to be hotter and more luminous than previously thought, and the spectral energy distributions of young populations mirror this trend. The hydrogen ionizing continuum in particular increases by a factor of up to 3 in the presence of rotating massive stars. The effects of rotation generally increase towards shorter wavelengths and with decreasing metallicity. Revised relations between star-formation rates and monochromatic luminosities for the new stellar models are presented.Comment: 5 pages, 3 figures, to appear in IAU Symp. 255, Low-Metallicity Star Formation, ed. L. Hunt, S. Madden, & R. Schneider (Cambridge: CUP

A Reduced Semantics for Deciding Trace Equivalence

Many privacy-type properties of security protocols can be modelled using trace equivalence properties in suitable process algebras. It has been shown that such properties can be decided for interesting classes of finite processes (i.e., without replication) by means of symbolic execution and constraint solving. However, this does not suffice to obtain practical tools. Current prototypes suffer from a classical combinatorial explosion problem caused by the exploration of many interleavings in the behaviour of processes. M\"odersheim et al. have tackled this problem for reachability properties using partial order reduction techniques. We revisit their work, generalize it and adapt it for equivalence checking. We obtain an optimisation in the form of a reduced symbolic semantics that eliminates redundant interleavings on the fly. The obtained partial order reduction technique has been integrated in a tool called APTE. We conducted complete benchmarks showing dramatic improvements.Comment: Accepted for publication in LMC