Construction of a specification from its singleton part

We state a construction theorem for specifications starting from single-site conditional probabilities (singleton part). We consider general single-site spaces and kernels that are absolutely continuous with respect to a chosen product measure (free measure). Under a natural order-consistency assumption and weak non-nullness requirements we show existence and uniqueness of the specification extending the given singleton part. We determine conditions granting the continuity of the specification. In addition, we show that, within a class of measures with suitable support properties, consistency with singletons implies consistency with the full specification.Comment: 19 pages. Version to appear in ALEA. We added Proposition 4.3 and made small corrections with respect to version

Missing Links: Referrer Behavior and Job Segregation

The importance of networks in labor markets is well-known, and their job segregating effects in organizations taken as granted. Conventional wisdom attributes this segregation to the homophilous nature of contact networks, and leaves little role for organizational influences. But employee referrals are necessarily initiated within a firm by employee referrers subject to organizational policies. We build theory regarding the role of referrers in the segregating effects of network recruitment. Using mathematical and computational models, we investigate how empirically-documented referrer behaviors affect job segregation. We show that referrer behaviors can segregate jobs beyond the effects of homophilous network recruitment. Further, and contrary to past understandings, we show that referrer behaviors can also mitigate most if not all of the segregating effects of network recruitment. Although largely neglected in previous labor market network scholarship, referrers are the missing links revealing opportunities for organizations to influence the effects of network recruitment

Marshallian Agglomeration Economies and Entrepreneurship: The Spanish Case

This paper analyzes to what extent marshallian agglomeration economies affect the creation of new entrepreneurial ventures at the metropolitan level. The measuring of agglomeration economies is based on the construction of indexes using the methodology of Glaeser and Kerr (2009). The indexes attempt to capture the effects of resource sharing, labor matching and knowledge spillovers according to the taxonomy proposed by Marshall (1920). Also an index to measure the influence of small suppliers to attract new business ventures, following Chinitz (1961), is constructed. Data on new firms and employment generated is accounted for the period 2000-2008. The analysis is based on the activity of the 15 largest metropolitan areas in Spain. Sixty two-digit industries (CNAE-93) are considered. The results show that jobs created by entrepreneurs are highly influenced by the ability to share suppliers and customers. Firm creation is influenced by those factors as well as the presence of small suppliers and the proximity to innovative activity. Agglomeration indexes with sector and city fixed effects explain more than 90% of new entry and employment generated. The potential multicollinearity among indexes is tested using principal component analysis. This analysis shows some complementarities among the indexes. New regressions using the factorized terms show that traditional measures of localization economies hide specific information about the process of agglomeration.

Crop intensification, land use, and on-farm energy-use efficiency during the worldwide spread of the green revolution

We analyzed crop production, physical inputs, and land use at the country level to assess technological changes behind the threefold increase in global crop production from 1961 to 2014. We translated machinery, fuel, and fertilizer to embedded energy units that, when summed up, provided a measure of agricultural intensification (human subsidy per hectare) for crops in the 58 countries responsible for 95% of global production. Worldwide,there was a 137% increase in input use per hectare, reaching 13 EJ, or 2.6% of the world´s primary energy supply, versus only a 10% increase in land use. Intensification was marked in Asia and Latin America, where input-use levels reached those that North America and Europe had in the earlier years of the period; the increase was more accentuated, irrespective of continent, for the 12 countries with mostly irrigated production. Half of the countries (28/58), mainly developed ones, had an average subsidy >5 GJ/ha/y (with fertilizers accounting for 27% in 1961 and 45% in 2014), with most of them (23/28) using about the same area or less than in 1961 (net land sparing of 31 Mha). Most of the remaining countries (24/30 with inputs <5 GJ/ha/y), mainly developing ones, increased their cropped area (net land extensification of 135 Mha). Overall, energy-use efficiency (cropoutput/inputs) followed a U-shaped trajectory starting at about 3 and finishing close to 4. The prospects of a more sustainable intensification are discussed, and the inadequacy of the land-sparing model expectation of protecting wilderness via intensified agriculture is highlighted.Fil: PELLEGRINI, PEDRO. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; ArgentinaFil: FERNANDEZ, Roberto J.. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentin

Perfect simulation for interacting point processes, loss networks and Ising models

We present a perfect simulation algorithm for measures that are absolutely continuous with respect to some Poisson process and can be obtained as invariant measures of birth-and-death processes. Examples include area- and perimeter-interacting point processes (with stochastic grains), invariant measures of loss networks, and the Ising contour and random cluster models. The algorithm does not involve couplings of the process with different initial conditions and it is not tied up to monotonicity requirements. Furthermore, it directly provides perfect samples of finite windows of the infinite-volume measure, subjected to time and space ``user-impatience bias''. The algorithm is based on a two-step procedure: (i) a perfect-simulation scheme for a (finite and random) relevant portion of a (space-time) marked Poisson processes (free birth-and-death process, free loss networks), and (ii) a ``cleaning'' algorithm that trims out this process according to the interaction rules of the target process. The first step involves the perfect generation of ``ancestors'' of a given object, that is of predecessors that may have an influence on the birth-rate under the target process. The second step, and hence the whole procedure, is feasible if these ``ancestors'' form a finite set with probability one. We present a sufficiency criteria for this condition, based on the absence of infinite clusters for an associated (backwards) oriented percolation model.Comment: Revised version after referee of SPA: 39 page

Infinitesimal moduli for the Strominger system and Killing spinors in generalized geometry

We construct the space of infinitesimal variations for the Strominger system and an obstruction space to integrability, using elliptic operator theory. We initiate the study of the geometry of the moduli space, describing the infinitesimal structure of a natural foliation on this space. The associated leaves are related to generalized geometry and correspond to moduli spaces of solutions of suitable Killing spinor equations on a Courant algebroid. As an application, we propose a unifying framework for metrics with holonomy \SU(3) and solutions of the Strominger system.Comment: 48 pages. Section 5 and Appendix A from previous version have been suppressed and will appear elsewhere. Title slightly changed, references added, presentation improved. To appear in Math. Anna