139 research outputs found
Purpose in corporate governance: the path towards a more sustainable world
In order to give a more realistic view of how ESG and sustainability are developed in organisations, this paper explores the development of purpose in corporate governance and the challenges faced. The theme is analysed at the intersection between stakeholder theory and business models in two dimensions: the capability of the market to align stakeholders’ interests (invisible hand) and the trade-offs between purpose and profit. The analysis conducted gave rise to four scenarios with a range of theoretical and practical implications focused on corporate governance
A Mathematical Model to Study the Meningococcal Meningitis
AbstractThe main goal of this work is to introduce a novel mathematical model to study the spreading of meningococcal meningitis. Specifically, it is a discrete mathematical model based on cellular automata where the population is divided in five classes: sus- ceptible, asymptomatic infected, infected with symptoms, carriers, recovered and died. It catches the individual characteristics of people in order to give a prediction of both the individual behavior, and whole evolution of population
Coarse-Grained Finite-Temperature Theory for the Condensate in Optical Lattices
In this work, we derive a coarse-grained finite-temperature theory for a Bose
condensate in a one-dimensional optical lattice, in addition to a confining
harmonic trap potential. We start from a two-particle irreducible (2PI)
effective action on the Schwinger-Keldysh closed-time contour path. In
principle, this action involves all information of equilibrium and
non-equilibrium properties of the condensate and noncondensate atoms. By
assuming an ansatz for the variational function, i.e., the condensate order
parameter in an effective action, we derive a coarse-grained effective action,
which describes the dynamics on the length scale much longer than a lattice
constant. Using the variational principle, coarse-grained equations of motion
for the condensate variables are obtained. These equations include a
dissipative term due to collisions between condensate and noncondensate atoms,
as well as noncondensate mean-field. To illustrate the usefulness of our
formalism, we discuss a Landau instability of the condensate in optical
lattices by using the coarse-grained generalized Gross-Pitaevskii
hydrodynamics. We found that the collisional damping rate due to collisions
between the condensate and noncondensate atoms changes sign when the condensate
velocity exceeds a renormalized sound velocity, leading to a Landau instability
consistent with the Landau criterion. Our results in this work give an insight
into the microscopic origin of the Landau instability.Comment: 38 pages, 2 figures. Submitted to Journal of Low Temperature Physic
Quantum charges and spacetime topology: The emergence of new superselection sectors
In which is developed a new form of superselection sectors of topological
origin. By that it is meant a new investigation that includes several
extensions of the traditional framework of Doplicher, Haag and Roberts in local
quantum theories. At first we generalize the notion of representations of nets
of C*-algebras, then we provide a brand new view on selection criteria by
adopting one with a strong topological flavour. We prove that it is coherent
with the older point of view, hence a clue to a genuine extension. In this
light, we extend Roberts' cohomological analysis to the case where 1--cocycles
bear non trivial unitary representations of the fundamental group of the
spacetime, equivalently of its Cauchy surface in case of global hyperbolicity.
A crucial tool is a notion of group von Neumann algebras generated by the
1-cocycles evaluated on loops over fixed regions. One proves that these group
von Neumann algebras are localized at the bounded region where loops start and
end and to be factorial of finite type I. All that amounts to a new invariant,
in a topological sense, which can be defined as the dimension of the factor. We
prove that any 1-cocycle can be factorized into a part that contains only the
charge content and another where only the topological information is stored.
This second part resembles much what in literature are known as geometric
phases. Indeed, by the very geometrical origin of the 1-cocycles that we
discuss in the paper, they are essential tools in the theory of net bundles,
and the topological part is related to their holonomy content. At the end we
prove the existence of net representations
A Model of Graceful Exit in String Cosmology
We construct, for the first time, a model of graceful exit transition from a
dilaton-driven inflationary phase to a decelerated Friedman-Robertson-Walker
era. Exploiting a demonstration that classical corrections can stabilize a high
curvature string phase while the evolution is still in the weakly coupled
regime, we show that if additional terms of the type that may result from
quantum corrections to the string effective action exist, and induce violation
of the null energy condition, then evolution towards a decelerated
Friedman-Robertson-Walker phase is possible. We also observe that stabilizing
the dilaton at a fixed value, either by capture in a potential minimum or by
radiation production, may require that these quantum corrections are turned
off, perhaps by non-perturbative effects or higher order contributions which
overturn the null energy condition violation.Comment: 17 pages including 9 figures, RevTeX. Uses epsfi
Euler-Poincar\'e approaches to nematodynamics
Nematodynamics is the orientation dynamics of flowless liquid-crystals. We
show how Euler-Poincar\'e reduction produces a unifying framework for various
theories, including Ericksen-Leslie, Luhiller-Rey, and Eringen's micropolar
theory. In particular, we show that these theories are all compatible with each
other and some of them allow for more general configurations involving a non
vanishing discination density. All results are also extended to flowing liquid
crystals.Comment: 26 pages, no figure
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Influence of 4f filling on electronic and magnetic properties of rare earth-Au surface compounds
One-atom-thick rare-earth/noble metal (RE-NM) compounds are attractive materials to investigate two-dimensional magnetism, since they are easy to synthesize into a common RE-NM2 structure with high crystal perfection. Here we perform a comparative study of the GdAu2, HoAu2, and YbAu2 monolayer compounds grown on Au(111). We find the same atomic lattice quality and moiré superlattice periodicity in the three cases, but different electronic properties and magnetism. The YbAu2 monolayer reveals the characteristic electronic signatures of a mixed-valence configuration in the Yb atom. In contrast, GdAu2 and HoAu2 show the trivalent character of the rare-earth and ferromagnetic transitions below 22 K. Yet, the GdAu2 monolayer has an in-plane magnetic easy-axis, versus the out-of-plane one in HoAu2. The electronic bands of the two trivalent compounds are very similar, while the divalent YbAu2 monolayer exhibits different band features. In the latter, a strong 4f-5d hybridization is manifested in neatly resolved avoided crossings near the Fermi level. First principles theory points to a residual presence of empty 4f states, explaining the fluctuating valence of Yb in the YbAu2 monolayer. © The Royal Society of Chemistry
Time Evolution via S-branes
Using S(pacelike)-branes defined through rolling tachyon solutions, we show
how the dynamical formation of D(irichlet)-branes and strings in tachyon
condensation can be understood. Specifically we present solutions of S-brane
actions illustrating the classical confinement of electric and magnetic flux
into fundamental strings and D-branes. The role of S-branes in string theory is
further clarified and their RR charges are discussed. In addition, by examining
``boosted'' S-branes, we find what appears to be a surprising dual S-brane
description of strings and D-branes, which also indicates that the critical
electric field can be considered as a self-dual point in string theory. We also
introduce new tachyonic S-branes as Euclidean counterparts to non-BPS branes.Comment: 62 pages, 10 figures. v2 references adde
Singularity free dilaton-driven cosmologies and pre-little-bang
There are no reasons why the singularity in the growth of the dilaton
coupling should not be regularised, in a string cosmological context, by the
presence of classical inhomogeneities. We discuss a class of inhomogeneous
dilaton-driven models whose curvature invariants are all bounded and regular in
time and space. We prove that the non-space-like geodesics of these models are
all complete in the sense that none of them reaches infinity for a finite value
of the affine parameter. We conclude that our examples represent truly
singularity-free solutions of the low energy beta functions. We discuss some
symmetries of the obtained solutions and we clarify their physical
interpretation. We also give examples of solutions with spherical symmetry. In
our scenario each physical quantity is everywhere defined in time and space,
the big-bang singularity is replaced by a maximal curvature phase where the
dilaton kinetic energy reaches its maximum. The maximal curvature is always
smaller than one (in string units) and the coupling constant is also smaller
than one and it grows between two regimes of constant dilaton, implying,
together with the symmetries of the solutions, that higher genus and higher
curvature corrections are negligible. We argue that our examples describe, in a
string cosmological context, the occurrence of ``little bangs''(i.e. high
curvature phases which never develop physical singularities). They also suggest
the possibility of an unexplored ``pre-little-bang'' phase.Comment: 25 pages in LaTex style, 3 encapsulated figure
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