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Structural Modelling of Female Labour Participation and Occupation Decisions
The objective of this paper is to estimate the parameters defining female labour participation and occupation decisions. Departing from a theoretical framework, we use micro data to estimate the wage-participation elasticity in Mexico. Consistency between the selectivity-adjusted wages and the multinomial participation equations is achieved via a two-step estimation procedure following Lee (1984). We use the results of our model to test and quantify three hypotheses explaining recent increases in female labour participation in Mexico. Our results show that the observed 12 per cent increase in female labour participation in Mexico between 1994 and 2000 is explained by the combination of a negative income shock caused by the 1994-95 Peso crisis, the increase in expected wages taking place in the manufacturing sector during the post-NAFTA period and a reduction in the female reservation wage
Phase diagrams and universality classes of random antiferromagnetic spin ladders
The random antiferromagnetic two-leg and zigzag spin-1/2 ladders are
investigated using the real space renormalization group scheme and their
complete phase diagrams are determined. We demonstrate that the first system
belongs to the same universality class of the dimerized random spin-1/2 chain.
The zigzag ladder, on the other hand, is in a random singlet phase at weak
frustration and disorder. Otherwise, we give additional evidence that it
belongs to the universality class of the random antiferromagnetic and
ferromagnetic quantum spin chains, although the universal fixed point found in
the latter system is never realized. We find, however, a new universal fixed
point at intermediate disorder.Comment: 10 pages, 10 figure
Computational modelling of the behaviour of biomarker particles of colorectal cancer in fecal matter
Colorectal adenocarcinoma is one of the carcinogenic diseases that is increasing the morbidity and mortality rates worldwide. The disease initially occurs through the segregation of biomarker substances in the human system without manifesting symptoms that affect the health of the carrier. Early detection would allow the application of more effective treatments, less invasive procedures and reduce the development of cancer. The purpose of this investigation was the elaboration of a mathematical model and the development of computational simulations to visualize the behavior of biomarker particles in transit through the colon. The flow conditions, properties of the viscous medium and biological regions of interest were established. Constitutive models, numerical conditions and solution strategies were determined. A numerical grid was used to represent the model of the colon and the human feces that carry the bioparticles (biomarkers). The results indicated the trajectories of the bioparticles in the fecal mass and the interactive movement with the natural contractions of the colon. The analysis of the movement of the biomarker particles can provide future less invasive alternatives for the detection in real time of the cancer by means of the implantation of biosensors in the walls of the colon
A cluster-based mean-field and perturbative description of strongly correlated fermion systems. Application to the 1D and 2D Hubbard model
We introduce a mean-field and perturbative approach, based on clusters, to
describe the ground state of fermionic strongly-correlated systems. In cluster
mean-field, the ground state wavefunction is written as a simple tensor product
over optimized cluster states. The optimization of the single-particle basis
where the cluster mean-field is expressed is crucial in order to obtain
high-quality results. The mean-field nature of the ansatz allows us to
formulate a perturbative approach to account for inter-cluster correlations;
other traditional many-body strategies can be easily devised in terms of the
cluster states. We present benchmark calculations on the half-filled 1D and
(square) 2D Hubbard model, as well as the lightly-doped regime in 2D, using
cluster mean-field and second-order perturbation theory. Our results indicate
that, with sufficiently large clusters or to second-order in perturbation
theory, a cluster-based approach can provide an accurate description of the
Hubbard model in the considered regimes. Several avenues to improve upon the
results presented in this work are discussed.Comment: 22 pages, 21 figure
Poverty effects of higher food prices : a global perspective
The spike in food prices between 2005 and the first half of 2008 has highlighted the vulnerabilities of poor consumers to higher prices of agricultural goods and generated calls for massive policy action. This paper provides a formal assessment of the direct and indirect impacts of higher prices on global poverty using a representative sample of 63 to 93 percent of the population of the developing world. To assess the direct effects, the paper uses domestic food consumer price data between January 2005 and December 2007--when the relative price of food rose by an average of 5.6 percent --to find that the implied increase in the extreme poverty headcount at the global level is 1.7 percentage points, with significant regional variation. To take the second-order effects into account, the paper links household survey data with a global general equilibrium model, finding that a 5.5 percent increase in agricultural prices (due to rising demand for first-generation biofuels) could raise global poverty in 2010 by 0.6 percentage points at the extreme poverty line and 0.9 percentage points at the moderate poverty line. Poverty increases at the regional level vary substantially, with nearly all of the increase in extreme poverty occurring in South Asia and Sub-Saharan Africa.Rural Poverty Reduction,Food&Beverage Industry,Poverty Lines,Emerging Markets
Emergent SU(3) symmetry in random spin-1 chains
We show that generic SU(2)-invariant random spin-1 chains have phases with an
emergent SU(3) symmetry. We map out the full zero-temperature phase diagram and
identify two different phases: (i) a conventional random singlet phase (RSP) of
strongly bound spin pairs (SU(3) "mesons") and (ii) an unconventional RSP of
bound SU(3) "baryons", which are formed, in the great majority, by spin trios
located at random positions. The emergent SU(3) symmetry dictates that
susceptibilities and correlation functions of both dipolar and quadrupolar spin
operators have the same asymptotic behavior.Comment: 5 pages plus 3-page Supplemental Material, 5 figures; published
versio
Economic performance under NAFTA : a firm-level analysis of the trade-productivity linkages
Did the North American Free Trade Agreement make Mexican firms more productive? If so, through which channels? This paper addresses these questions by deploying an innovative microeconometric approach that disentangles the various channels through which integration with the global markets (via international trade) can affect firm-level productivity. The results show that the North American Free Trade Agreement stimulated the productivity of Mexican plants via: (1) an increase in import competition and (2) a positive effect on access to imported intermediate inputs. However, the impact of trade reforms was not identical for all integrated firms, with fully integrated firms (i.e. firms simultaneously exporting and importing) benefiting more than other integrated firms. Contrary to previous results, once self-selection problems are solved, the analysis finds a rather weak relationship between exports and productivity growth.Economic Theory&Research,Free Trade,Labor Policies,Knowledge for Development,Microfinance
Polyradical character and spin frustration in fullerene molecules: An ab initio non-collinear Hartree--Fock study
Most {\em ab initio} calculations on fullerene molecules have been carried
out based on the paradigm of the H\"uckel model. This is consistent with the
restricted nature of the independent-particle model underlying such
calculations, even in single-reference-based correlated approaches. On the
other hand, previous works on some of these molecules using model Hamiltonians
have clearly indicated the importance of short-range inter-atomic spin-spin
correlations. In this work, we consider {\em ab initio} non-collinear
Hartree--Fock (HF) solutions for representative fullerene systems: the bowl,
cage, ring, and pentagon isomers of C, and the larger C,
C, C, C, and C fullerene cages. In all cases but
the ring we find that the HF minimum corresponds to a truly non-collinear
solution with a torsional spin density wave. Optimized geometries at the
generalized HF (GHF) level lead to fully symmetric structures, even in those
cases where Jahn-Teller distortions have been previously considered. The nature
of the GHF solutions is consistent with the -electron space becoming
polyradical in nature: each -orbital remains effectively singly occupied.
The spin frustration, induced by the pentagon rings in an otherwise
anti-ferromagnetic background, is minimized at the HF level by aligning the
spins in non-collinear arrangements. The long-range magnetic ordering observed
is reminiscent of the character of broken symmetry HF solutions in polyacene
systems.Comment: 16 figure
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