649 research outputs found
Quantum criticality and first-order transitions in the extended periodic Anderson model
We investigate the behavior of the periodic Anderson model in the presence of
- Coulomb interaction () using mean-field theory, variational
calculation, and exact diagonalization of finite chains. The variational
approach based on the Gutzwiller trial wave function gives a critical value of
and two quantum critical points (QCPs), where the valence
susceptibility diverges. We derive the critical exponent for the valence
susceptibility and investigate how the position of the QCP depends on the other
parameters of the Hamiltonian. For larger values of , the Kondo regime
is bounded by two first-order transitions. These first-order transitions merge
into a triple point at a certain value of . For even larger
valence skipping occurs. Although the other methods do not give a critical
point, they support this scenario.Comment: 8 pages, 7 figure
Hubbard physics in the symmetric half-filled periodic Anderson-Hubbard model
Two very different methods -- exact diagonalization on finite chains and a
variational method -- are used to study the possibility of a metal-insulator
transition in the symmetric half-filled periodic Anderson-Hubbard model. With
this aim we calculate the density of doubly occupied sites as a function of
various parameters. In the absence of on-site Coulomb interaction ()
between electrons, the two methods yield similar results. The double
occupancy of levels remains always finite just as in the one-dimensional
Hubbard model. Exact diagonalization on finite chains gives the same result for
finite , while the Gutzwiller method leads to a Brinkman-Rice transition
at a critical value (), which depends on and .Comment: 10 pages, 5 figure
Space-time correlation and momentum exchanges in compound open-channel flow by simultaneous measurements of two-sets of ADVs
River hydrodynamicsOverbank flows and vegetatio
Periodic Anderson model with correlated conduction electrons: Variational and exact diagonalization study
We investigate an extended version of the periodic Anderson model (the so-called periodic Anderson-Hubbard model) with the aim to understand the role of interaction between conduction electrons in the formation of the heavy-fermion and mixed-valence states. Two methods are used: (i) variational calculation with the Gutzwiller wave function optimizing numerically the ground-state energy and (ii) exact diagonalization of the Hamiltonian for short chains. The f-level occupancy and the renormalization factor of the quasiparticles are calculated as a function of the energy of the f orbital for a wide range of the interaction parameters. The results obtained by the two methods are in reasonably good agreement for the periodic Anderson model. The agreement is maintained even when the interaction between band electrons, U d, is taken into account, except for the half-filled case. This discrepancy can be explained by the difference between the physics of the one- and higher-dimensional models. We find that this interaction shifts and widens the energy range of the bare f level, where heavy-fermion behavior can be observed. For large-enough U d this range may lie even above the bare conduction band. The Gutzwiller method indicates a robust transition from Kondo insulator to Mott insulator in the half-filled model, while U d enhances the quasiparticle mass when the filling is close to half filling. © 2012 American Physical Society
Periodic anderson model with d-f interaction
We investigate an extended version of the periodic Anderson model where an interaction is switched on between the doubly occupied d- and f-sites. We perform variational calculations using the Gutzwiller trial wave function. We calculate the f-level occupancy as a function of the f-level energy with different interaction strengths. It is shown that the region of valence transition is sharpened due to the new interaction
Health examination of aluminum refinery workers exposed to fluoride. Serum and urinary level of fluoride and its effect on the ventilatory lung function
Eff ect of increased concentrations of atmospheric carbon dioxide on the global threat of zinc defi ciency: a modelling study
Background Increasing concentrations of atmospheric carbon dioxide (CO2) lower the content of zinc and other
nutrients in important food crops. Zinc defi ciency is currently responsible for large burdens of disease globally, and
the populations who are at highest risk of zinc defi ciency also receive most of their dietary zinc from crops. By
modelling dietary intake of bioavailable zinc for the populations of 188 countries under both an ambient CO2 and
elevated CO2 scenario, we sought to estimate the eff ect of anthropogenic CO2 emissions on the global risk of zinc
defi ciency.
Methods We estimated per capita per day bioavailable intake of zinc for the populations of 188 countries at ambient
CO2 concentrations (375â384 ppm) using food balance sheet data for 2003â07 from the Food and Agriculture
Organization. We then used previously published data from free air CO2 enrichment and open-top chamber
experiments to model zinc intake at elevated CO2 concentrations (550 ppm, which is the concentration expected by
2050). Estimates developed by the International Zinc Nutrition Consultative Group were used for country-specifi c
theoretical mean daily per-capita physiological requirements for zinc. Finally, we used these data on zinc bioavailability
and population-weighted estimated average zinc requirements to estimate the risk of inadequate zinc intake among
the populations of the diff erent nations under the two scenarios (ambient and elevated CO2). The diff erence between
the population at risk at elevated and ambient CO2 concentrations (ie, population at new risk of zinc defi ciency) was
our measure of impact.
Findings The total number of people estimated to be placed at new risk of zinc defi ciency by 2050 was 138 million
(95% CI 120â156). The people likely to be most aff ected live in Africa and South Asia, with nearly 48 million (32â63)
residing in India alone. Global maps of increased risk show signifi cant heterogeneity.
Interpretation Our results indicate that one heretofore unquantifi ed human health eff ect associated with anthropogenic
CO2 emissions will be a signifi cant increase in the human population at risk of zinc defi ciency. Our country-specifi c
fi ndings can be used to help guide interventions aimed at reducing this vulnerability
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