215 research outputs found
Numerical simulation of a binary communication channel: Comparison between a replica calculation and an exact solution
The mutual information of a single-layer perceptron with Gaussian inputs
and deterministic binary outputs is studied by numerical simulations. The
relevant parameters of the problem are the ratio between the number of output
and input units, , and those describing the two-point
correlations between inputs. The main motivation of this work refers to the
comparison between the replica computation of the mutual information and an
analytical solution valid up to . The most relevant results
are: (1) the simulation supports the validity of the analytical prediction, and
(2) it also verifies a previously proposed conjecture that the replica solution
interpolates well between large and small values of .Comment: 6 pages, 8 figures, LaTeX fil
Social considerations for the cultivation of industrial crops on marginal agricultural land as feedstock for bioeconomy
Marginal agricultural land (MAL) has received much attention in research and policy formation as a potential resource for cultivating biomass for energy and biobased products. However, it is still unclear whether biomass from MAL meets the requirements of social sustainability. This study develops a conceptual linkage between value-chain analysis and social life-cycle analysis (S-LCA), and assesses both positive impacts (handprints) and negative impacts (footprints). A participatory approach including interviews and surveys was used to understand views and perceptions of the relevant stakeholders. A systemic strategy was applied to analyze value-chain activities, understand challenges, and identify competitive advantages and disadvantages. For S-LCA, the variety of impacts and indicators was met through a literature review and a consistent scoring system. The cultivation of perennial crops on MAL tends to cause skepticism among stakeholders, who are concerned about long-term commitment and biodiversity risks. Annual crops, on the other hand, are perceived by all stakeholder categories as very promising opportunities across all impact categories and indicators. They can facilitate income diversification and offer smart sustainable cropping options through crop rotation, agroforestry, etc. Most of the technological pathways examined are highly innovative, have a low technological readiness level, and are still at the early market development stage. As such they are ranked by stakeholders as medium opportunities for short-term implementation. In contrast, pyrolysis to industrial heat, ethanol from switchgrass, insulation material from hemp, and biogas/biomethane from sorghum are considered opportunities with good chances of being implemented in the short term. © 2022 The Authors. Biofuels, Bioproducts and Biorefining published by Society of Industrial Chemistry and John Wiley & Sons, Ltd
On the Tail of the Overlap Probability Distribution in the Sherrington--Kirkpatrick Model
We investigate the large deviation behavior of the overlap probability
density in the Sherrington--Kirkpatrick model from several analytical
perspectives. First we analyze the spin glass phase using the coupled replica
scheme. Here generically
, and we compute the first correction to the expansion of \A
in powers of . We study also the case, where is know
exactly. Finally we study the paramagnetic phase, where exact results valid for
all 's are obtained. The overall agreement between the various points of
view is very satisfactory. Data from large scale numerical simulations show
that the predicted behavior can be detected already on moderate lattice sizes.Comment: 18 pages including ps figure
Equilibrium properties of a Josephson junction ladder with screening effects
In this paper we calculate the ground state phase diagram of a Josephson
Junction ladder when screening field effects are taken into account. We study
the ground state configuration as a function of the external field, the
penetration depth and the anisotropy of the ladder, using different
approximations to the calculation of the induced fields. A series of tongues,
characterized by the vortex density , is obtained. The vortex density
of the ground state, as a function of the external field, is a Devil's
staircase, with a plateau for every rational value of . The width of
each of these steps depends strongly on the approximation made when calculating
the inductance effect: if the self-inductance matrix is considered, the
phase tends to occupy all the diagram as the penetration depth
decreases. If, instead, the whole inductance matrix is considered, the width of
any step tends to a non-zero value in the limit of very low penetration depth.
We have also analyzed the stability of some simple metastable phases: screening
fields are shown to enlarge their stability range.Comment: 16 pp, RevTex. Figures available upon request at
[email protected] To be published in Physical Review B (01-Dec-96
Renormalization Group Study of the soliton mass on the (lambda Phi^4)_{1+1} lattice model
We compute, on the model on the lattice, the soliton
mass by means of two very different numerical methods. First, we make use of a
``creation operator'' formalism, measuring the decay of a certain correlation
function. On the other hand we measure the shift of the vacuum energy between
the symmetric and the antiperiodic systems. The obtained results are fully
compatible.
We compute the continuum limit of the mass from the perturbative
Renormalization Group equations. Special attention is paid to ensure that we
are working on the scaling region, where physical quantities remain unchanged
along any Renormalization Group Trajectory. We compare the continuum value of
the soliton mass with its perturbative value up to one loop calculation. Both
quantities show a quite satisfactory agreement. The first is slightly bigger
than the perturbative one; this may be due to the contributions of higher order
corrections.Comment: 19 pages, preprint DFTUZ/93/0
Static chaos and scaling behaviour in the spin-glass phase
We discuss the problem of static chaos in spin glasses. In the case of
magnetic field perturbations, we propose a scaling theory for the spin-glass
phase. Using the mean-field approach we argue that some pure states are
suppressed by the magnetic field and their free energy cost is determined by
the finite-temperature fixed point exponents. In this framework, numerical
results suggest that mean-field chaos exponents are probably exact in finite
dimensions. If we use the droplet approach, numerical results suggest that the
zero-temperature fixed point exponent is very close to
. In both approaches is the lower critical dimension in
agreement with recent numerical simulations.Comment: 28 pages + 6 figures, LateX, figures uuencoded at the end of fil
The influence of critical behavior on the spin glass phase
We have argued in recent papers that Monte Carlo results for the equilibrium
properties of the Edwards-Anderson spin glass in three dimensions, which had
been interpreted earlier as providing evidence for replica symmetry breaking,
can be explained quite simply within the droplet model once finite size effects
and proximity to the critical point are taken into account. In this paper, we
show that similar considerations are sufficient to explain the Monte Carlo data
in four dimensions. In particular, we study the Parisi overlap and the link
overlap for the four-dimensional Ising spin glass in the Migdal-Kadanoff
approximation. Similar to what is seen in three dimensions, we find that
temperatures well below those studied in Monte Carlo simulations have to be
reached before the droplet model predictions become apparent. We also show that
the double-peak structure of the link overlap distribution function is related
to the difference between domain-wall excitations that cross the entire system
and droplet excitations that are confined to a smaller region.Comment: 8 pages, 8 figure
A Numerical Study of Ultrametricity in Finite Dimensional Spin Glasses
We use a constrained Monte Carlo technique to analyze ultrametric features of
a 4 dimensional Edwards-Anderson spin glass with quenched couplings J=\pm 1. We
find that in the large volume limit an ultrametric structure emerges quite
clearly in the overlap of typical equilibrium configurations.Comment: 8 one column pages, latex, 4 figures with epsfig.st
4D Spin Glasses in Magnetic Field Have a Mean Field like Phase
By using numerical simulations we show that the 4D Edwards Anderson
spin glass in magnetic field undergoes a mean field like phase transition. We
use a dynamical approach: we simulate large lattices (of volume ) and work
out the behavior of the system in limit where both and go to infinity,
but where the limit is taken first. By showing that the dynamic
overlap converges to a value smaller than the static one we exhibit replica
symmetry breaking. The critical exponents are compatible with the ones obtained
by mean field computations.Comment: Physrev format, 5 ps figures include
Numerical study of a short-range p-spin glass model in three dimensions
In this work we study numerically a short range p-spin glass model in three
dimensions. The behaviour of the model appears to be remarkably different from
mean field predictions. In fact it shares some features typical of models with
full replica-symmetry breaking (FRSB). Nevertheless, we believe that the
transition that we study is intrinsically different from the FRSB and basically
due to non-perturbative contributions. We study both the statics and the
dynamics of the system which seem to confirm our conjectures.Comment: 20 pages, 15 figure
- …