883 research outputs found
Occurrence and fate of heavy metals in large wastewater treatment plants treating municipal and industrial wastewaters.
This paper deals with a detailed study on the occurrence and fate of heavy metals (plus As, Fe and Al) in five Italian large wastewater treatment plants treating municipal and industrial wastewaters. The study showed that some of the compounds (As, Hg and Cd) were present at trace levels, while others were dispersed in a broad range of concentrations and were sometimes under the detection limit. The occurrence followed the order Hg = As < Hg < Pb < Ni < Cu < Cr < Fe < Zn < Al. Metals were mainly present bound to particulate organic matter in municipal wastewaters while they were often present in soluble phase in industrial wastewaters. Some heavy metals, like Hg and Pb, showed clear correlations with Al and Fe, therefore the last could be used as control parameters. Metals were removed with good efficiency in the treatment works, with the order As < Cd = Cr = Zn < Pb < Hg < Ni = Al < Cu < Fe. Metals then concentrated in waste activated sludge and accumulated after sludge stabilisation because of volatile solids degradation, therefore some problems may arise with limit for agricultural application, in particular for Hg, Cd and Ni
Statistical theory of quasi stationary states beyond the single water-bag case study
An analytical solution for the out-of-equilibrium quasi-stationary states of
the paradigmatic Hamiltonian Mean Field (HMF) model can be obtained from a
maximum entropy principle. The theory has been so far tested with reference to
a specific class of initial condition, the so called (single-level) water-bag
type. In this paper a step forward is taken by considering an arbitrary number
of overlapping water bags. The theory is benchmarked to direct microcanonical
simulations performed for the case of a two-levels water-bag. The comparison is
shown to return an excellent agreement
Desenvolvimento e Aplicação de um Gerador Síncrono Virtual para o Controle de Inversores na Geração Distribuída
O crescimento exponencial da parcela de Fontes de Energia Renováveis (FER),
juntamente com o aumento no número de unidades de Geração Distribuída (GD) instaladas
como, por exemplo, painéis fotovoltaicos modulares, célula a combustível, entre outras, pode
levar a um sistema elétrico instável e inseguro no futuro devido à redução da inércia
rotacional total do sistema. Para resolver este problema, uma solução utilizando o controle dos
inversores de potência que fazem a interface entre essas FER e a rede está se tornando
popular. Uma maneira de melhorar a estabilização do sistema seria introduzir de alguma
forma uma inércia rotacional virtual às GDs. Para isto, é necessário que se combine uma
forma de armazenamento rápido de energia, com um mecanismo de controle adequado ao
conversor de potência da GD. Desta forma, a GD pode se comportar como um Gerador
Síncrono Virtual e contribuir para a estabilização do sistema.
Neste trabalho, todo o equacionamento necessário para o controle de uma máquina
síncrona virtual é apresentado. Um sistema será proposto para simulação de forma que seja
comprovada a equivalência entre o controle proposto e uma máquina síncrona real frente a
várias situações de operação. Os resultados de simulação serão analisados de forma a validar a
equivalência entre o modelo proposto e os geradores síncronos. Por fim, uma aplicação do
VSG será estudada em uma planta real. Será feita a simulação de um painel fotovoltaico
conectado ao sistema através de um conversor trabalhando como um gerador virtual
Digital humanities and crowdsourcing: an exploration
publication-status: Published‘Crowdsourcing’ is a recent and evolving phenomenon, and the term has been broadly adopted to define different shades of public participation and contribution. Cultural institutions are progressively exploring crowdsourcing, and projects’ related research is increasing. Nonetheless, few studies in the digital humanities have investigated crowdsourcing as a whole. The aim of this paper is to shed light on crowdsourcing practices in the digital humanities, thus providing insights to design new paths of collaboration between cultural organisations and their audiences. A web survey was carried out on 36 crowdsourcing projects promoted by galleries, libraries, archives, museums, and education institutions. A variety of practices emerged from the research. Even though, it seems that there is no ‘one-solution-fits-all’ for crowdsourcing in the cultural domain, few reflections are presented to support the development of crowdsourcing initiatives.Horizon Digital Economy Research Hu
Resonant, broadband and highly efficient optical frequency conversion in semiconductor nanowire gratings at visible and UV wavelengths
Using a hydrodynamic approach we examine bulk- and surface-induced second and
third harmonic generation from semiconductor nanowire gratings having a
resonant nonlinearity in the absorption region. We demonstrate resonant,
broadband and highly efficient optical frequency conversion: contrary to
conventional wisdom, we show that harmonic generation can take full advantage
of resonant nonlinearities in a spectral range where nonlinear optical
coefficients are boosted well beyond what is achievable in the transparent,
long-wavelength, non-resonant regime. Using femtosecond pulses with
approximately 500 MW/cm2 peak power density, we predict third harmonic
conversion efficiencies of approximately 1% in a silicon nanowire array, at
nearly any desired UV or visible wavelength, including the range of negative
dielectric constant. We also predict surface second harmonic conversion
efficiencies of order 0.01%, depending on the electronic effective mass,
bistable behavior of the signals as a result of a reshaped resonance, and the
onset fifth order nonlinear effects. These remarkable findings, arising from
the combined effects of nonlinear resonance dispersion, field localization, and
phase-locking, could significantly extend the operational spectral bandwidth of
silicon photonics, and strongly suggest that neither linear absorption nor skin
depth should be motivating factors to exclude either semiconductors or metals
from the list of useful or practical nonlinear materials in any spectral range.Comment: 12 pages, 4 figure
Persistence of chimera states and the challenge for synchronization in real-world networks
The emergence of order in nature manifests in different phenomena, with
synchronization being one of the most representative examples. Understanding
the role played by the interactions between the constituting parts of a complex
system in synchronization has become a pivotal research question bridging
network science and dynamical systems. Particular attention has been paid to
the emergence of chimera states, where subsets of synchronized oscillations
coexist with asynchronous ones. Such coexistence of coherence and incoherence
is a perfect example where order and disorder can persist in a long-lasting
regime. Although considerable progress has been made in recent years to
understand such coherent and (coexisting) incoherent states, how they manifest
in real-world networks remains to be addressed. Based on a symmetry-breaking
mechanism, in this paper, we shed light on the role that non-normality, a
ubiquitous structural property of real networks, has in the emergence of
several diverse dynamical phenomena, e.g., amplitude chimeras or oscillon
patterns. Specifically, we demonstrate that the prevalence of source or leader
nodes in networks leads to the manifestation of phase chimera states.
Throughout the paper, we emphasize that non-normality poses ongoing challenges
to global synchronization and is instrumental in the emergence of chimera
states
Noisy continuous--opinion dynamics
We study the Deffuant et al. model for continuous--opinion dynamics under the
influence of noise. In the original version of this model, individuals meet in
random pairwise encounters after which they compromise or not depending of a
confidence parameter. Free will is introduced in the form of noisy
perturbations: individuals are given the opportunity to change their opinion,
with a given probability, to a randomly selected opinion inside the whole
opinion space. We derive the master equation of this process. One of the main
effects of noise is to induce an order-disorder transition. In the disordered
state the opinion distribution tends to be uniform, while for the ordered state
a set of well defined opinion groups are formed, although with some opinion
spread inside them. Using a linear stability analysis we can derive approximate
conditions for the transition between opinion groups and the disordered state.
The master equation analysis is compared with direct Monte-Carlo simulations.
We find that the master equation and the Monte-Carlo simulations do not always
agree due to finite-size induced fluctuations that we analyze in some detail
Sustainable water resources management to combat desertification in the Nurra region, northwestern Sardinia, Italy
Sustainable water management plays an important role in the frame of the multidisciplinary research activities aiming to combat or to mitigate the desertification processes. The study activities have been carried out by RIADE Research Project (Integrated Research for Applying new technologies and processes for combating Desertification, www.riade.net. RIADE was co-financed by MIUR within the National Operative Programme 2000-2006. The primary objective was to explore and to develop models and strategies for innovative and sustainable solutions of water resources management, adopting a multidisciplinary approach, at the catchment and hydrogeological basin scale in a Mediterranean context, using a case history of a pilot area in NW Sardinia (Italy). The high concentration of population in this coastal zone and the intense agricultural activity have determined a relevant increase of water demand. This demand is generally satisfied by surface water, but, in some peculiar dry periods, it exceeds the available quantities. In these critical periods, groundwater are the only alternative source constituting a strategic water resource. The groundwater chemical properties are then correlated with the effects of the anthropogenic pressures. The used approach shows the application of groundwater protection criteria, in accordance with EU policies, and it was aimed to develop a methodological tool which can be applied to different scenarios
Indoor Air Quality in the Uffizi Gallery of Florence: sampling methodology and preliminary results
THz Generation via Optical Rectification in Nanomaterials: Universal Modeling Approach and Effective Description
Optical rectification (OR) at the nanoscale has attracted an increasing interest in the prospect of providing efficient ultracompact terahertz (THz) sources. Here, a universal modeling approach capable of addressing both isotropic and anisotropic all-dielectric nonlinear nanomaterials on an ultra-broad spectral range, covering the highly dispersive phonon-polariton window, and different orientations of the crystallographic axes with respect to the geometry of the structure is reported. This analysis is exemplified by considering two study cases, that is, nanopillars of AlGaAs and of LiNbO3. A close comparison between the two cases is established in terms of THz generation efficiency from 4 to 14 THz. Phonon-polariton contributions to the OR process are disentangled from the electronic one, and a model order reduction based on the reciprocity theorem is applied and validated on both the considered configurations. These results, combined with the inspection of the THz near-field features, pave the way to the design and optimization of nonlinear metasurfaces for THz generation and detection at the nanoscale
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