Farmer preferences for milpa diversity and genetically modified maize in Mexico: a latent class approach

Maize, the second most globally important staple crop after wheat, originated in Mexico, where it is typically grown as part of a set of associated crops and practices called the milpa system. This ancient mode of production is practiced today in ways that vary by cultural context and agro-environment. Milpas generate private economic value, in terms of food security, diet quality and livelihoods, for the twomillion farm households who manage them. Furthermore, milpas generate public economic value by conserving agrobiodiversity, especially that of maize landraces, which have the potential to contribute unique traits needed by plant breeders for future crop improvement. In this way, milpas contribute to global food security in maize. However, the sustainability of the milpa system has been threatened by offfarm employment opportunities, long-distance migration, the increasing commercialization and intensification of maize production. Most recently, the milpa system has been negatively impacted by the contamination of maize landraces by genetically modified (GM) maize, cultivation of which is currently prohibited in Mexico. Here, we employ a choice experiment to estimate Mexican farmers’ valuation of three components of agrobiodiversity (crop species richness, maize variety richness and maize landraces), and examine their interest in cultivating GM maize. Choice experiment data, household level social, economic and demographic data, community level economic development data, and information on milpa production characteristics, and farmers’ attitudes and perceptions with regards to GM food and crops were collected from 420 farm households across 17 communities in three states of Mexico. Using these data, we analyzed the heterogeneity of farmer preferences using a latent class model, which can be used to simultaneously identify sample segments having homogenous preferences for milpa attributes, as well as farmer characteristics affecting preferences. We further identified the characteristics of farmers who are most likely to continue growing maize landraces and managing milpa systems, as well as those least likely to accept GM maize. Specifically, we identified three distinct segments of farmers: (i) Landrace Conservationists derive the highest private economic value from continued management of landraces and the highest economic loss from the possible adoption of GM maize. These farmers are young, dislike GM foods and crops, and are mainly located at the Oaxaca site, where transgenic constructs have been found in maize landraces. (ii) Milpa Diversity Managers derive the highest economic value from managing all of the agrobiodiversity components of the milpa, and suffer fewer losses from management of GM maize. These are older farmers, who are curious and like to experiment with maize varieties. (iii) Marginalized Maize Producers derive little value from crop species and maize variety richness, receive minimal value from maize landraces, and also experience the smallest negative impact from the adoption of GM maize. These farmers are located in the most isolated communities, have the lowest level of productivity, and oversee the largest milpa areas. They are also the most tightly integrated into the maize output markets. These novel findings have implications for debates concerning the adoption of GM maize in Mexico and its associated costs and benefits, as well as for the design of targeted, cost-effective conservation programs on farms

Assessment of the conservation status of natural and semi-natural patches associated with urban areas through habitat suitability indices

Urban environments rely on the surrounding natural ecosystems remnants as providers of ecosystem functions, therefore these areas not only support a unique biodiversity but also have a social value for maintaining public health and wellbeing. For this reason, urbanization is considered to be one the biggest threats to ecosystems, leading to native biodiversity simplification and, thus, to a detriment of the provided ecosystem services. Moreover, this change in land use results in high levels of landscape fragmentation and modification in areas surrounding the habitat remnants which, in consequence, become inadequate for many native species. In this context, it is important that urban planners have the information to assess the possible consequences of future changes in land use in order to increase the landscape chances of supporting both, native biodiversity and the needs of a growing human population. The objective of the present work is to evaluate the ecological integrity of natural and semi-natural vegetation patches immersed in an urban area in order to generate a conceptual framework for landscape assessment that allows urban planners to envision the best choice for city development at a given place. To do so, we developed a quantitative integral environmental evaluation index that includes ecological characterization, geological characterization, and environmental characterization (presence of anthropic disturbance) of the assessed area. We conclude that the index we have generated in this work is suitable to be used as a management tool to allow an unbiased valuation and to identify managing situations that require a short term response.Fil: Natale, Evangelina Sandra. Fundación Conservación y Desarrollo; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Villalba, G.. Fundación Conservación y Desarrollo; ArgentinaFil: Junquera, J. E.. Fundación Conservación y Desarrollo; ArgentinaFil: Zalba, Sergio Martín. Universidad Nacional del Sur. Departamento de Biología, Bioquímica y Farmacia. Grupo de Estudios en Conservación y Manejo; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Calculation of the energy spectrum of a two-electron spherical quantum dot

We study the energy spectrum of the two-electron spherical parabolic quantum dot using the exact Schroedinger, the Hartree-Fock, and the Kohn-Sham equations. The results obtained by applying the shifted-1/N method are compared with those obtained by using an accurate numerical technique, showing that the relative error is reasonably small, although the first method consistently underestimates the correct values. The approximate ground-state Hartree-Fock and local-density Kohn-Sham energies, estimated using the shifted-1/N method, are compared with accurate numerical self-consistent solutions. We make some perturbative analyses of the exact energy in terms of the confinement strength, and we propose some interpolation formulae. Similar analysis is made for both mean-field approximations and interpolation formulae are also proposed for these exchange-only ground-state cases.Comment: 18 pages, LaTeX, 2 figures-ep

QED with external field: Hamiltonian treatment for anisotropic medium formed by the Lorentz-non-invariant vacuum

Nonlinear electrodynamics, QED included, is considered against the Lorentz-noninvariant external field background, treated as an anisotropic medium. Hamiltonian formalism is applied to electromagnetic excitations over the background, and entities of electrodynamics of media, such as field inductions and intensities, are made sense of in terms of canonical variables. Both conserved and nonconserved generators of space-time translations and rotations are defined on the phase space, and their Hamiltonian equations of motion and Dirac bracket relations, different from the Poincar\'e algebra, are established. Nonsymmetric, but--in return--gauge-invariant, energy-momentum tensor suggests a canonical momentum density other than the Poynting vector. A photon magnetic moment is found to govern the evolution of the photon angular momentum. It is determined by the antisymmetric part of the energy-momentum tensor.Comment: 28 page

Tropical–North Pacific Climate Linkages over the Past Four Centuries

Analyses of instrumental data demonstrate robust linkages between decadal-scale North Pacific and tropical Indo-Pacific climatic variability. These linkages encompass common regime shifts, including the noteworthy 1976 transition in Pacific climate. However, information on Pacific decadal variability and the tropical high-latitude climate connection is limited prior to the twentieth century. Herein tree-ring analysis is employed to extend the understanding of North Pacific climatic variability and related tropical linkages over the past four centuries. To this end, a tree-ring reconstruction of the December-May North Pacific index (NPI)-an index of the atmospheric circulation related to the Aleutian low pressure cell-is presented (1600-1983). The NPI reconstruction shows evidence for the three regime shifts seen in the instrumental NPI data, and for seven events in prior centuries. It correlates significantly with both instrumental tropical climate indices and a coral-based reconstruction of an optimal tropical Indo-Pacific climate index, supporting evidence for a tropical-North Pacific link extending as far west as the western Indian Ocean. The coral-based reconstruction (1781-1993) shows the twentieth-century regime shifts evident in the instrumental NPI and instrumental tropical Indo-Pacific climate index, and three previous shifts. Changes in the strength of correlation between the reconstructions over time, and the different identified shifts in both series prior to the twentieth century, suggest a varying tropical influence on North Pacific climate, with greater influence in the twentieth century. One likely mechanism is the low-frequency variability of the El Nino-Southern Oscillation (ENSO) and its varying impact on Indo-Pacific climate.</p

Influence of Gravity on noncommutative Dirac equation

In this paper, we investigate the influence of gravity and noncommutativity on Dirac equation. By adopting the tetrad formalism, we show that the modified Dirac equation keeps the same form. The only modification is in the expression of the covariant derivative. The new form of this derivative is the product of its counterpart given in curved space-time with an operator which depends on the noncommutative $\theta$-parameter. As an application, we have computed the density number of the created particles in presence of constant strong electric field in an anisotropic Bianchi universe.Comment: 9 pages, correct some miprints, Accepted for publication in journal of Mod. Phys. Letters

Self-heating Effect in Silicon-Photomultipliers

The main effect of radiation damage in a Silicon-Photolumtiplier (SiPM) is a dramatic increase in the dark current. The power dissipated, if not properly cooled, heats the SiPM, whose performance parameters depend on temperature. Heating studies were performed with a KETEK SiPM, glued on an Al$_2$O$_3$ substrate, which is either directly connected to the temperature-controlled chuck of a probe station, or through layers of material with well-known thermal resistance. The SiPM is illuminated by a LED operated in DC-mode. The SiPM current is measured and used to determine the steady-state temperature as a function of power dissipated in the multiplication region of the SiPM and thermal resistance, as well as the time dependencies for heating and cooling. This information can be used to correct the parameters determined for radiation-damaged SiPM for the effects of self-heating. The method can also be employed for packaged SiPMs with unknown thermal contact to a heat sink. The results presented in this paper are preliminary

Atypical plug formation in internal elastoviscoplastic fluid flows over a non-smooth topology

An experimental and computational investigation of the internal flow of elastoviscoplastic fluids over non-smooth topologies is presented in two complimentary studies. In the first study, we visualize the creeping flow of a Carbopol gel over a cavity embedded in a thin slot using Optical Coherence Tomography (OCT) and confocal microscopy. We measure the size and shape of the plug as a function of Bingham and Weissenberg numbers. An asymmetry in the plug shape is observed which is also evident in our second study -- numerical simulations using adaptive finite element method based upon an augmented Lagrangian scheme. We quantify the asymmetry and present the results as a function of the product of the Weissenberg and Bingham numbers which collapse onto a single curve for each of these geometries. These findings underscore the theoretical underpinnings of the synergy between elasticity and plasticity of these complex fluids