2,297 research outputs found
Phases dynamics in VCSELs with delayed optical feedback and cross re-injection
We study theoretically the non linear polarization dynamics of
Vertical-Cavity Surface-Emitting Lasers in the presence of an external cavity
providing delayed optical feedback and cross polarization re-injection. We show
that far from the laser threshold, the dynamics remains confined close to the
equatorial plane of a Stokes sphere of a given radius and we reduce the
dynamics to a dynamical system composed of two phases: the orientation phase of
the quasi-linear polarization and the optical phase of the field. We explore
the complex modal structure given by the double feedback configuration and
recovers as particular cases the Lang-Kobayashi modes and the modes founds by
Giudici et al. [1]. We also re-interpret the square waves switching dynamics as
phase kinks.Comment: 10 pages, 7 figures, pre-submission to Phys. Rev.
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Entrepreneurial workaround practices in severe institutional voids: Evidence from Kenya
Entrepreneurs in developing economies try to cope with weak or absent formal institutions – often referred to as ‘institutional voids’ – by relying extensively on intermediary organizations such as business incubators and development organizations or informal institutions such as political, kinship, or family relationships. However, in many African countries, intermediary support is limited and informal institutions are also unreliable, adding risks and costs to doing business and increasing the severity of institutional voids in the surrounding ecosystem. We investigate the practices followed by 47 commercial entrepreneurs in Kenya to ‘work around’ these severe institutional voids to achieve their goals of business creation and growth. We find that severe institutional voids stimulate the hybridization of goals to include social value creation, create a need for a more strategic orchestration of business relationships, and motivate entrepreneurs to proactively cross-brace the institutional infrastructure around them. We contribute by unveiling the important role of entrepreneurs as microinstitutional agents in developing economies and by detailing how commercial and social goals become intertwined in the context of African entrepreneurship
Entanglement guided search for parent Hamiltonians
We introduce a method for the search of parent Hamiltonians of input
wave-functions based on the structure of their reduced density matrix. The two
key elements of our recipe are an ansatz on the relation between reduced
density matrix and parent Hamiltonian that is exact at the field theory level,
and a minimization procedure on the space of relative entropies, which is
particularly convenient due to its convexity. As examples, we show how our
method correctly reconstructs the parent Hamiltonian correspondent to several
non-trivial ground state wave functions, including conformal and
symmetry-protected-topological phases, and quantum critical points of
two-dimensional antiferromagnets described by strongly coupled field theories.
Our results show the entanglement structure of ground state wave-functions
considerably simplifies the search for parent Hamiltonians.Comment: 5 pages, 5 figures, supplementary materia
Measuring von Neumann entanglement entropies without wave functions
We present a method to measure the von Neumann entanglement entropy of ground
states of quantum many-body systems which does not require access to the system
wave function. The technique is based on a direct thermodynamic study of
entanglement Hamiltonians, whose functional form is available from field
theoretical insights. The method is applicable to classical simulations such as
quantum Monte Carlo methods, and to experiments that allow for thermodynamic
measurements such as the density of states, accessible via quantum quenches. We
benchmark our technique on critical quantum spin chains, and apply it to
several two-dimensional quantum magnets, where we are able to unambiguously
determine the onset of area law in the entanglement entropy, the number of
Goldstone bosons, and to check a recent conjecture on geometric entanglement
contribution at critical points described by strongly coupled field theories
Intrinsic gap and exciton condensation in the nu_T=1 bilayer system
We investigate the quasiparticle excitation of the bilayer quantum Hall (QH)
system at total filling factor in the limit of
negligible interlayer tunneling under tilted magnetic field. We show that the
intrinsic quasiparticle excitation is of purely pseudospin origin and solely
governed by the inter- and intra-layer electron interactions. A model based on
exciton formation successfully explains the quantitative behavior of the
quasiparticle excitation gap, demonstrating the existence of a link between the
excitonic QH state and the composite fermion liquid. Our results provide a new
insight into the nature of the phase transition between the two states.Comment: 4 pages, 3 figure
An integrated approach project for the revaluation of a traditional sourdough bread production chain
The influence of organic and conventional farming systems on the performance of a panel of old and modern Italian bread wheat varieties has been evaluated, with the aim to individuate an agronomic protocol suitable for the production of a sourdough bread traditionally prepared in a hill zone of Emilia-Romagna. The agronomic and technological characterisation of the wheat samples obtained in organic and conventional farming conditions has been done and the sensorial qualities of the sourdough bread obtained have been evaluated
The use of hydrological and geoelectrical data to fix the boundary conditions of a ground water flow model: a case study
International audienceTo assess whether the hydrometric level of an artificial lake in a quarry near Milan (Italy) could be assigned as a Dirichlet boundary condition for the phreatic aquifer in a fine scale groundwater flow model, hydrological measurements of piezometric head and rainfall rate time series have been analysed by spectral and statistical methods. The piezometric head close to the quarry lake proved to be well correlated with seasonal variations in the rainfall. Furthermore, geoelectrical tomography detected no semi-permeable layer between the phreatic aquifer and the lake, so the contact between surface and ground water is good. Finally, a time-varying prescribed head condition can be applied for ground water flow modelling
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