205 research outputs found
Quantum Ratchets at High Temperatures
Using the continued-fraction method we solve the Caldeira-Leggett master
equation in the phase-space (Wigner) representation to study Quantum ratchets.
Broken spatial symmetry, irreversibility and periodic forcing allows for a net
current in these systems. We calculate this current as a function of the force
under adiabatic conditions. Starting from the classical limit we make the
system quantal. In the quantum regime tunnel events and over-barrier wave
reflection phenomena modify the classical result. Finally, using the
phase-space formalism we give some insights about the decoherence in these
systems.Comment: submitted to Physia E (proceedings of conference "Frontiers of
Quantum and Mesoscopic Thermodynamics", Prague 26-29 July 2004
Exergoecology assessment of mineral exports from Latin America: Beyond a tonnage perspective
Latin America has traditionally been a raw material supplier since colonial times. In this paper, we analyze mineral exports from an exergoecology perspective from twenty countries in Latin American (LA-20). We apply material flow analysis (MFA) principles along with the concept of the exergy replacement cost (ERC), which considers both quantity and thermodynamic quality of minerals, reflecting their scarcity in the crust. ERC determines the energy that would be required to recover minerals to their original conditions in the mines once they have been totally dispersed into the Earth''s crust, with prevailing technology. Using ERC has helped us identify the importance of certain traded minerals that could be overlooked in a traditional MFA based on a mass basis only. Our method has enabled us to determine mineral balance, both in mass (tonnes) and in ERC terms (Mtoe). Using indicators, both in mass and ERC, we have assessed the self-sufficiency and dependency of the region. We have also analyzed the mineral exports flows from Latin America for 2013. Results show that half of the mineral production from LA-20 was mainly exported. High-quality minerals, such as, gold, silver, and aluminum were largely exported to China and the United States. Extraction of high-quality minerals also implies higher losses of natural stock and environmental overburdens in the region
Thermodynamic perturbation theory for dipolar superparamagnets
Thermodynamic perturbation theory is employed to derive analytical
expressions for the equilibrium linear susceptibility and specific heat of
lattices of anisotropic classical spins weakly coupled by the dipole-dipole
interaction. The calculation is carried out to the second order in the coupling
constant over the temperature, while the single-spin anisotropy is treated
exactly. The temperature range of applicability of the results is, for weak
anisotropy (A/kT << 1), similar to that of ordinary high-temperature
expansions, but for moderately and strongly anisotropic spins (A/kT > 1) it can
extend down to the temperatures where the superparamagnetic blocking takes
place (A/kT \sim 25), provided only the interaction strength is weak enough.
Besides, taking exactly the anisotropy into account, the results describe as
particular cases the effects of the interactions on isotropic (A = 0) as well
as strongly anisotropic (A \to \infty) systems (discrete orientation model and
plane rotators).Comment: 15 pages, 3 figure
Avoided energy cost of producing minerals: The case of iron ore
There is growing concern about the decline of the ore grade in mines and the increased energy usage for processing and refining metals. In the limit, where no concentrated deposits exist, minerals must be obtained from bare rock. A method for quantitatively assessing the “free bonus” granted by nature in providing concentrated minerals in mines and thus assessing the quality of the different resources is estimating how much energy is needed to concentrate the minerals, as they are already in mines, from bare rock. This bonus granted by nature reduces the costs of human mining and metallurgical processes, as well as the mining effort required of future generations. In this study, the concentration of high-iron-content minerals in common rocks was investigated via a computational model developed using the HSC software. As expected, the range of results for the specific energy for the concentration of iron from common rocks was considerably higher than the energy required by modern processes. This reveals the need to value current iron deposits and the challenge of developing sustainable methods of metal production to satisfy the needs of the present and future generations
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