Heterogeneity and vulnerability of livestock in forest plantations of Uruguay

In this paper we study the situation of livestock farmers related to the afforestation of the northwest region of Uruguay and suggest that their vulnerability has characteristics that vary according to characteristics of the modified ecosystem in which they operate and develop their resource endowments. We present an overview of mixed farming that includes trees and especially those that include cattle grazing. It is shown that the development of these systems has been associated with incentives from public policies, the demand for primary goods and the emergence of forms of agricultural organization that had not been present in the country. It presents various aspects of developments in the areas where forestry has shown great progress, justifying the need to elaborate on knowledge of the consequences of these changes. In particular, it proposes an approach that emphasizes the identification of interactions that we consider to be beneficial for both items. Briefly reviews some consequences that are manifested in changes in ecosystem services and the changes are associated with the original holding in the region: livestock. To analyze differences in vulnerability among farmers and in particular how this feature is affected by its connection with afforestation present a typology and the results of a series of interviews conducted archetypal representatives of the types we offer. Our study shows that differences exist between farmers associated with the afforestation that allow us to propose that will be affected differentially by changes that occur and the desirability of developing differential offers training and include consideration of public policy proposals that improve their situation. In particular, the valuation of environmental services throughout the silvopastoral systems can result in improved income from these new players in our national agriculture. (Résumé d'auteur

Combining symmetry collective states with coupled cluster theory: Lessons from the Agassi model Hamiltonian

The failures of single-reference coupled cluster for strongly correlated many-body systems is flagged at the mean-field level by the spontaneous breaking of one or more physical symmetries of the Hamiltonian. Restoring the symmetry of the mean-field determinant by projection reveals that coupled cluster fails because it factorizes high-order excitation amplitudes incorrectly. However, symmetry-projected mean-field wave functions do not account sufficiently for dynamic (or weak) correlation. Here we pursue a merger of symmetry projection and coupled cluster theory, following previous work along these lines that utilized the simple Lipkin model system as a testbed [J. Chem. Phys. 146, 054110 (2017)]. We generalize the concept of a symmetry-projected mean-field wave function to the concept of a symmetry projected state, in which the factorization of high-order excitation amplitudes in terms of low-order ones is guided by symmetry projection and is not exponential, and combine them with coupled cluster theory in order to model the ground state of the Agassi Hamiltonian. This model has two separate channels of correlation and two separate physical symmetries which are broken under strong correlation. We show how the combination of symmetry collective states and coupled cluster is effective in obtaining correlation energies and order parameters of the Agassi model throughout its phase diagram

Review of recent results in spin physics

Recent results in polarized DIS are reviewed. Particular emphasis is placed on new measurements of transverse and longitudinal asymmetries, on the tests of the spin sum rules and on the analysis of the spin structure function $g_1$ in perturbative QCD at NLO.Comment: 15 pages, LaTex, 15 eps figures included, to be published in Proceedings of 7th Int. Workshop on Deep Inelastic Scattering and QCD (DIS99

A New Gravitational Wave Verification Source

We report the discovery of a detached 20 min orbital period binary white dwarf. WD0931+444 (SDSS J093506.93+441106.9) was previously classified as a WD + M dwarf system based on its optical spectrum. Our time-resolved optical spectroscopy observations obtained at the 8m Gemini and 6.5m MMT reveal peak-to-peak radial velocity variations of 400 km/s every 20 min for the WD, but no velocity variations for the M dwarf. In addition, high-speed photometry from the McDonald 2.1m telescope shows no evidence of variability nor evidence of a reflection effect. An M dwarf companion is physically too large to fit into a 20 min orbit. Thus, the orbital motion of the WD is almost certainly due to an invisible WD companion. The M dwarf must be either an unrelated background object or the tertiary component of a hiearchical triple system. WD0931+444 contains a pair of WDs, a 0.32 Msol primary and a >0.14 Msol secondary, at a separation of >0.19 Rsol. After J0651+2844, WD0931+444 becomes the second-shortest period detached binary WD currently known. The two WDs will lose angular momentum through gravitational wave radiation and merge in <9 Myr. The log h ~ -22 gravitational wave strain from WD0931+444 is strong enough to make it a verification source for gravitational wave missions in the milli-Hertz frequency range, e.g. the evolved Laser Interferometer Space Antenna (eLISA), bringing the total number of known eLISA verification sources to nine.Comment: MNRAS Letters, in pres