Galactic chemical evolution of heavy elements: from Barium to Europium

We follow the chemical evolution of the Galaxy for elements from Ba to Eu, using an evolutionary model suitable to reproduce a large set of Galactic (local and non local) and extragalactic constraints. Input stellar yields for neutron-rich nuclei have been separated into their s-process and r-process components. The production of s-process elements in thermally pulsing asymptotic giant branch stars of low mass proceeds from the combined operation of two neutron sources: the dominant reaction 13C(alpha,n)16O, which releases neutrons in radiative conditions during the interpulse phase, and the reaction 22Ne(alpha,n)25Mg, marginally activated during thermal instabilities. The resulting s-process distribution is strongly dependent on the stellar metallicity. For the standard model discussed in this paper, it shows a sharp production of the Ba-peak elements around Z = Z_sun/4. Concerning the r-process yields, we assume that the production of r-nuclei is a primary process occurring in stars near the lowest mass limit for Type II supernova progenitors. The r-contribution to each nucleus is computed as the difference between its solar abundance and its s-contribution given by the Galactic chemical evolution model at the epoch of the solar system formation. We compare our results with spectroscopic abundances of elements from Ba to Eu at various metallicities (mainly from F and G stars) showing that the observed trends can be understood in the light of the present knowledge of neutron capture nucleosynthesis. Finally, we discuss a number of emerging features that deserve further scrutiny.Comment: 34 pages, 13 figures. accepted by Ap

Horizontal Branch Stars: The Interplay between Observations and Theory, and Insights into the Formation of the Galaxy

We review HB stars in a broad astrophysical context, including both variable and non-variable stars. A reassessment of the Oosterhoff dichotomy is presented, which provides unprecedented detail regarding its origin and systematics. We show that the Oosterhoff dichotomy and the distribution of globular clusters (GCs) in the HB morphology-metallicity plane both exclude, with high statistical significance, the possibility that the Galactic halo may have formed from the accretion of dwarf galaxies resembling present-day Milky Way satellites such as Fornax, Sagittarius, and the LMC. A rediscussion of the second-parameter problem is presented. A technique is proposed to estimate the HB types of extragalactic GCs on the basis of integrated far-UV photometry. The relationship between the absolute V magnitude of the HB at the RR Lyrae level and metallicity, as obtained on the basis of trigonometric parallax measurements for the star RR Lyrae, is also revisited, giving a distance modulus to the LMC of (m-M)_0 = 18.44+/-0.11. RR Lyrae period change rates are studied. Finally, the conductive opacities used in evolutionary calculations of low-mass stars are investigated. [ABRIDGED]Comment: 56 pages, 22 figures. Invited review, to appear in Astrophysics and Space Scienc

POWER ESTIMATION METHODS FOR SEQUENTIAL LOGIC-CIRCUITS

Recently developed methods for power estimation have primarily focused on combinational logic, We present a framework for the efficient and accurate estimation of average power dissipation in sequential circuits. Switching activity is the primary cause of power dissipation in CMOS circuits, Accurate switching activity estimation for sequential circuits is considerably more difficult than that for combinational circuits, because the probability of the circuit being in each of its possible states has to be calculated, The Chapman-Kolmogorov equations can be used to compute the exact state probabilities in steady state, However, this method requires the solution of a linear system of equations of size 2(N) where N is the number of flip-flops in the machine. We describe a comprehensive framework for exact and approximate switching activity estimation in a sequential circuit. The basic computation step is the solution of a nonlinear system of equations which is derived directly from a logic realization of the sequential machine. Increasing the number of variables or the number of equations in the system results in increased accuracy, For a aide variety of examples, we show that the approximation scheme is within 1-3\% of the exact method, but is orders of magnitude faster for large circuits. Previous sequential switching activity estimation methods can have significantly greater inaccuracies

Some Methods for Monitoring Rangelands and Other Natural Area Vegetation

Arizona Cooperative Extension Publication 190043 / Originally published 1990, Revised 1995.Introduction / Considerations when monitoring rangeland vegetation / E.L. Smith and G.B. Ruyle -- Plant frequency sampling for monitoring rangelands / D.W. Despain, P.R. Ogden, and E.L. Smith -- The dry-weight rank method of estimating plant species composition / E.L. Smith and D.W. Despain -- The comparative yield method for estimating range productivity / D.W. Despain and E.L. Smith / Appendices

Some Methods For Monitoring Rangelands and Other Natural Area Vegetation

Arizona Cooperative Extension Publication 190043 / Originally published 1990, revised 1995, revised 1997.Introduction / Considerations when monitoring rangeland vegetation / E.L. Smith and G.B. Ruyle -- Plant frequency sampling for monitoring rangelands / D.W. Despain, P.R. Ogden, and E.L. Smith -- The dry-weight rank method of estimating plant species composition / E.L. Smith and D.W. Despain -- The comparative yield method for estimating range productivity / D.W. Despain and E.L. Smith / Appendices