743 research outputs found
Sustainability, stakeholders and business. Editorial
Over the past 20 years, there has been an increasing attention on the drivers of value in organizations. Both the strategic management literature and practice have remarked the importance for managers to be aware of the impact of firm activities, products and services on either the external and internal environment and, more generally, on all firm stakeholders. The emergence of the notions of “sustainable development” and “sustainability” reflects a profound change in global thinking, which forces firms to move beyond trade-offs between business and society
Exactly solvable model with two conductor-insulator transitions driven by impurities
We present an exact analysis of two conductor-insulator transitions in the
random graph model. The average connectivity is related to the concentration of
impurities. The adjacency matrix of a large random graph is used as a hopping
Hamiltonian. Its spectrum has a delta peak at zero energy. Our analysis is
based on an explicit expression for the height of this peak, and a detailed
description of the localized eigenvectors and of their contribution to the
peak. Starting from the low connectivity (high impurity density) regime, one
encounters an insulator-conductor transition for average connectivity
1.421529... and a conductor-insulator transition for average connectivity
3.154985.... We explain the spectral singularity at average connectivity
e=2.718281... and relate it to another enumerative problem in random graph
theory, the minimal vertex cover problem.Comment: 4 pages revtex, 2 fig.eps [v2: new title, changed intro, reorganized
text
Uso da RMN-DT no desenvolvimento e validação de método para detecção de adulteração em azeites de oliva comerciais lacrados.
The asymmetric simple exclusion process: an integrable model for non-equilibrium statistical mechanics
The asymmetric simple exclusion process (ASEP) plays the role of a paradigm
in non-equilibrium statistical mechanics. We review exact results for the ASEP
obtained by Bethe ansatz and put emphasis on the algebraic properties of this
model. The Bethe equations for the eigenvalues of the Markov matrix of the ASEP
are derived from the algebraic Bethe ansatz. Using these equations we explain
how to calculate the spectral gap of the model and how global spectral
properties such as the existence of multiplets can be predicted. An extension
of the Bethe ansatz leads to an analytic expression for the large deviation
function of the current in the ASEP that satisfies the Gallavotti-Cohen
relation. Finally, we describe some variants of the ASEP that are also solvable
by Bethe ansatz.
Keywords: ASEP, integrable models, Bethe ansatz, large deviations.Comment: 24 pages, 5 figures, published in the "special issue on recent
advances in low-dimensional quantum field theories", P. Dorey, G. Dunne and
J. Feinberg editor
Power Spectra of a Constrained Totally Asymmetric Simple Exclusion Process
To synthesize proteins in a cell, an mRNA has to work with a finite pool of
ribosomes. When this constraint is included in the modeling by a totally
asymmetric simple exclusion process (TASEP), non-trivial consequences emerge.
Here, we consider its effects on the power spectrum of the total occupancy,
through Monte Carlo simulations and analytical methods. New features, such as
dramatic suppressions at low frequencies, are discovered. We formulate a theory
based on a linearized Langevin equation with discrete space and time. The good
agreement between its predictions and simulation results provides some insight
into the effects of finite resoures on a TASEP.Comment: 4 pages, 2 figures v2: formatting change
Asymmetric exclusion model with several kinds of impurities
We formulate a new integrable asymmetric exclusion process with
kinds of impurities and with hierarchically ordered dynamics.
The model we proposed displays the full spectrum of the simple asymmetric
exclusion model plus new levels. The first excited state belongs to these new
levels and displays unusual scaling exponents. We conjecture that, while the
simple asymmetric exclusion process without impurities belongs to the KPZ
universality class with dynamical exponent 3/2, our model has a scaling
exponent . In order to check the conjecture, we solve numerically the
Bethe equation with N=3 and N=4 for the totally asymmetric diffusion and found
the dynamical exponents 7/2 and 9/2 in these cases.Comment: to appear in JSTA
Distribution of exchange energy in a bond-alternating S=1 quantum spin chain
The quasi-one-dimensional bond-alternating S=1 quantum antiferromagnet NTENP
is studied by single crystal inelastic neutron scattering. Parameters of the
measured dispersion relation for magnetic excitations are compared to existing
numerical results and used to determine the magnitude of bond-strength
alternation. The measured neutron scattering intensities are also analyzed
using the 1st-moment sum rules for the magnetic dynamic structure factor, to
directly determine the modulation of ground state exchange energies. These
independently determined modulation parameters characterize the level of spin
dimerization in NTENP. First-principle DMRG calculations are used to study the
relation between these two quantities.Comment: 10 pages, 10 figure
Magnetic Field Behaviour of a Haldane Gap Antiferromagnet
We investigate the magnetic field behaviour of an antiferromagnetic
Heisenberg spin-1 chain with the most general single-ion anisotropy. We discuss
the regime in which the magnetic field is below the transition value. The
splitting of the Haldane triplet is obtained as a function of a field applied
in an arbitrary orientation by means of a Lancz\H os exact diagonalization of
chains of up to 16 spins. Our results are nicely summarized in terms of a
first-order perturbation theory. We explain various level crossings that occur
by the existence of discrete symmetries. A discussion is given of the electron
spin resonance and neutron scattering experiments on the compound
Ni(CHN)NOClO (NENP).Comment: 18 pages and 6 figs not included available by ftp, plain TeX,
SPhT/93-04
Feedback and Fluctuations in a Totally Asymmetric Simple Exclusion Process with Finite Resources
We revisit a totally asymmetric simple exclusion process (TASEP) with open
boundaries and a global constraint on the total number of particles [Adams, et.
al. 2008 J. Stat. Mech. P06009]. In this model, the entry rate of particles
into the lattice depends on the number available in the reservoir. Thus, the
total occupation on the lattice feeds back into its filling process. Although a
simple domain wall theory provided reasonably good predictions for Monte Carlo
simulation results for certain quantities, it did not account for the
fluctuations of this feedback. We generalize the previous study and find
dramatically improved predictions for, e.g., the density profile on the lattice
and provide a better understanding of the phenomenon of "shock localization."Comment: 11 pages, 3 figures, v2: Minor change
Time-Dependent Density Functional Theory for Driven Lattice Gas Systems with Interactions
We present a new method to describe the kinetics of driven lattice gases with
particle-particle interactions beyond hard-core exclusions. The method is based
on the time-dependent density functional theory for lattice systems and allows
one to set up closed evolution equations for mean site occupation numbers in a
systematic manner. Application of the method to a totally asymmetric site
exclusion process with nearest-neighbor interactions yields predictions for the
current-density relation in the bulk, the phase diagram of non-equilibrium
steady states and the time evolution of density profiles that are in good
agreement with results from kinetic Monte Carlo simulations.Comment: 11 pages, 3 figure
- …