914 research outputs found
Far-from-equilibrium growth of thin films in a temperature gradient
The irreversible growth of thin films under far-from-equilibrium conditions
is studied in dimensional strip geometries. Across one of the
transverse directions, a temperature gradient is applied by thermal baths at
fixed temperatures between and , where and
is the critical temperature of the system in contact with
an homogeneous thermal bath. By using standard finite-size scaling methods, we
characterized a continuous order-disorder phase transition driven by the
thermal bath gradient with critical temperature and critical
exponents , , and , which belong
to a different universality class from that of films grown in an homogeneous
bath. Furthermore, the effects of the temperature gradient are analyzed by
means of a bond model that captures the growth dynamics. The interplay of
geometry and thermal bath asymmetries leads to growth bond flux asymmetries and
the onset of transverse ordering effects that explain qualitatively the shift
in the critical temperature.Comment: 4 pages, 4 figures. arXiv admin note: substantial text overlap with
arXiv:1207.253
Features of spin-charge separation in the equilibrium conductance through finite rings
We calculate the conductance through rings with few sites described by
the model, threaded by a magnetic flux and weakly coupled to
conducting leads at two arbitrary sites. The model can describe a circular
array of quantum dots with large charging energy in comparison with the
nearest-neighbor hopping . We determine analytically the particular values
of for which a depression of the transmittance is expected as a
consequence of spin-charge separation. We show numerically that the equilibrium
conductance at zero temperature is depressed at those particular values of
for most systems, in particular at half filling, which might be easier
to realize experimentally.Comment: 8 pages, 7 figure
Spin-charge separation in strongly interacting finite ladder rings
We study the conductance through Aharonov-Bohm finite ladder rings with
strongly interacting electrons, modelled by the prototypical t-J model. For a
wide range of parameters we observe characteristic dips in the conductance as a
function of magnetic flux, predicted so far only in chains which are a
signature of spin and charge separation. These results open the possibility of
observing this peculiar many-body phenomenon in anisotropic ladder systems and
in real nanoscopic devices.Comment: 4 pages, 6 figure
A Review of Soil-Improving Cropping Systems for Soil Salinization
A major challenge of the Sustainable Development Goals linked to Agriculture, Food Security, and Nutrition, under the current global crop production paradigm, is that increasing crop yields often have negative environmental impacts. It is therefore urgent to develop and adopt optimal soil-improving cropping systems (SICS) that can allow us to decouple these system parameters. Soil salinization is a major environmental hazard that limits agricultural potential and is closely linked to agricultural mismanagement and water resources overexploitation, especially in arid climates. Here we review literature seeking to ameliorate the negative effect of soil salinization on crop productivity and conduct a global meta-analysis of 128 paired soil quality and yield observations from 30 studies. In this regard, we compared the effectivity of different SICS that aim to cope with soil salinization across 11 countries, in order to reveal those that are the most promising. The analysis shows that besides case-specific optimization of irrigation and drainage management, combinations of soil amendments, conditioners, and residue management can contribute to significant reductions of soil salinity while significantly increasing crop yields. These results highlight that conservation agriculture can also achieve the higher yields required for upscaling and sustaining crop production
Climate change impacts on African crop production
According to the most recent IPCC report, changes in climates over the last 30 years
have already reduced global agricultural production in the range 1-5 % per decade
globally, with particularly negative effects for tropical cereal crops such as maize and
rice (Porter et al., 2014). In addition, there is now mounting evidence suggesting that
even at low (+2 ºC) levels of warming, agricultural productivity is likely to decline
across the globe, but particularly across tropical areas (Challinor et al., 2014). This
Working Paper provides an overview of projected climate change impacts on crop
production and suitability across Africa, using a combination of literature review,
models and new data analysis
Irreversible growth of binary mixtures on small-world networks
Binary mixtures growing on small-world networks under far-from-equilibrium
conditions are studied by means of extensive Monte Carlo simulations. For any
positive value of the shortcut fraction of the network (), the system
undergoes a continuous order-disorder phase transition, while it is noncritical
in the regular lattice limit (). Using finite-size scaling relations, the
phase diagram is obtained in the thermodynamic limit and the critical exponents
are evaluated. The small-world networks are thus shown to trigger criticality,
a remarkable phenomenon which is analogous to similar observations reported
recently in the investigation of equilibrium systems.Comment: 7 pages, 7 figures; added/removed references and modified
presentation. To appear in PR
Improved parallelization techniques for the density matrix renormalization group
A distributed-memory parallelization strategy for the density matrix
renormalization group is proposed for cases where correlation functions are
required. This new strategy has substantial improvements with respect to
previous works. A scalability analysis shows an overall serial fraction of 9.4%
and an efficiency of around 60% considering up to eight nodes. Sources of
possible parallel slowdown are pointed out and solutions to circumvent these
issues are brought forward in order to achieve a better performance.Comment: 8 pages, 4 figures; version published in Computer Physics
Communication
Residual Strength of Liquefied Sand: Laboratory vs. Field Measurements
Determining the residual strength of liquefied sand is essential for estimating post-earthquake stability of vulnerable earth structures, or calculating runout of liquefaction flow slides. Current practice is to select values from a database of back-calculated residual strengths from failure case histories, which have been related to representative penetration test resistance numbers in the failed materials. Given the uncertainties involved, it is desirable to compare the field data with laboratory tests under controlled conditions. This paper describes residual strength measurements for a uniform fine sand using two recently-developed tests designed to impose large strains and strain rates: a modified triaxial test in which a metal coupon is dragged through the liquefied sample by an external dead weight, and a ring shear device which can impose constant rates of strain on the liquefied sand. In all cases, a stress-thinning behavior is observed; however, coupon movement through the liquefied sand is basically laminar, representing conditions in the interior of a flowing mass, while the rotating ring creates a well-defined contact shear band and higher resistance, which might be considered more representative of flow at the base of a sliding mass. Comparison with back-calculated field values shows that coupon residual strengths plot at the lower bound, and ring shear results at the upper bound, of backcalculated field values
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