339 research outputs found
Driven lattice gas of dimers coupled to a bulk reservoir
We investigate the non-equilibrium steady state of a one-dimensional (1D)
lattice gas of dimers. The dynamics is described by a totally asymmetric
exclusion process (TASEP) supplemented by attachment and detachment processes,
mimicking chemical equilibrium of the 1D driven transport with the bulk
reservoir. The steady-state phase diagram, current and density profiles are
calculated using both a refined mean-field theory and extensive stochastic
simulations. As a consequence of the on-off kinetics, a new phase coexistence
region arises intervening between low and high density phases such that the
discontinuous transition line of the TASEP splits into two continuous ones. The
results of the mean-field theory and simulations are found to coincide. We show
that the physical picture obtained in the corresponding lattice gas model with
monomers is robust, in the sense that the phase diagram changes quantitatively,
but the topology remains unaltered. The mechanism for phase separation is
identified as generic for a wide class of driven 1D lattice gases.Comment: 15 pages, 10 figures, 1tabl
“Fra questi sí e no son di parer contrario”: Affermazione di sé e nome d’arte nella Marchesa Colombi
By choosing her nom de plume, taken from the homonymous characterin the play La satira e Parini (1856) by Paolo Ferrari, Marchesa Colombiexplicitly takes up a stance of ambiguity which aims to avoid limiting social expectations. Whereas this ambiguity endorses her use of irony, her presentation of herself as an ultra-centenarian gives her writing authority and wisdom. The latter allows the author to assert the authentic values of the feminine as well as her own individual personality both as a woman and a writer. This is perceived as a prerequisite leading to the emergence of the so-called “donna nuova”
Waste heat recovery technologies for offshore platforms
none5siThis article aims at finding the most suitable waste heat recovery technology for existing and future offshore facilities. The technologies considered in this work are the steam Rankine cycle, the air bottoming cycle and the organic Rankine cycle.
A multi-objective optimization approach is employed to attain optimal designs for each bottoming unit by selecting specific functions tailored to the oil and gas sector, i.e. yearly CO2 emissions, weight and economic revenue. The test case is the gas turbine-based power system serving an offshore platform in the North Sea.
Results indicate that the organic Rankine cycle technology presents larger performances compared to steam Rankine cycle units, whereas the implementation of air bottoming cycle modules is not attractive from an economic and environmental perspective compared to the other two technologies.
Despite the relatively high cost of the expander and of the primary heat exchanger, organic Rankine cycle turbogenerators appear thus to be the preferred solution to abate CO2 emissions and pollutants on oil and gas facilities.
As a practical consequence, this paper provides guidelines for the design of high-efficiency, cost-competitive and low-weight power systems for offshore installationsrestrictedL. Pierobon;A. Benato;E. Scolari;F. Haglind;A. StoppatoL., Pierobon; Benato, Alberto; E., Scolari; F., Haglind; Stoppato, Ann
Bottleneck-induced transitions in a minimal model for intracellular transport
We consider the influence of disorder on the non-equilibrium steady state of
a minimal model for intracellular transport. In this model particles move
unidirectionally according to the \emph{totally asymmetric exclusion process}
(TASEP) and are coupled to a bulk reservoir by \emph{Langmuir kinetics}. Our
discussion focuses on localized point defects acting as a bottleneck for the
particle transport. Combining analytic methods and numerical simulations, we
identify a rich phase behavior as a function of the defect strength. Our
analytical approach relies on an effective mean-field theory obtained by
splitting the lattice into two subsystems, which are effectively connected
exploiting the local current conservation. Introducing the key concept of a
carrying capacity, the maximal current which can flow through the bulk of the
system (including the defect), we discriminate between the cases where the
defect is irrelevant and those where it acts as a bottleneck and induces
various novel phases (called {\it bottleneck phases}). Contrary to the simple
TASEP in the presence of inhomogeneities, many scenarios emerge and translate
into rich underlying phase-diagrams, the topological properties of which are
discussed.Comment: 14 pages, 15 figures, 1 tabl
May car washing represent a risk for Legionella infection?
Background. Legionella is a ubiquitous Gram-negative bacterium naturally found in aquatic environments. It can pose a health problem when it grows and spreads in man-made water systems. Legionella pneumophila is the most common cause of Legionnaires\u2019 disease nowadays, a community-acquired pneumonia with pulmonary symptoms and chest radiography no different from any other form of infectious pneumonia. Legionella monitoring is important for public health reasons, including the identification of unusual environmental sources of Legionella.
Methods. We report two cases of Legionnaires\u2019 disease associated with two different car wash installations in the province of Vicenza, in the Veneto region, northeastern Italy. Patients were not employees of the car wash installations, but users of the service. In both cases, Legionella antigen was detected in urine using the Alere BinaxNOW\uae Legionella Urinary Antigen, and Legionella antibodies were detected in serum using SERION ELISA classic Legionella pneumophila 1-7 IgG and IgM. Water samples were also analyzed as part of the surveillance program for Legionella prevention and control in compliance with the Italian guidelines.
Results. Both patients had clinical symptoms and chest radiography compatible with pneumonia, and only one of them had diabetes as a risk factor. Legionella urinary antigen and serological test on serum samples were positive for Legionella in both patients, even if much slighter in the case A due to the retrospective serological investigation performed a year later the episode and after the second clinical case occurred in the same district. The environmental investigations highlighted two different car wash plants as potential source of infection. A certified company using shock hyperchlorination was asked to disinfect the two plants and, subsequently, control samples resulted negative for Legionella pneumophila.
Conclusions. Any water source producing aerosols should be considered at risk for the transmission of Legionella bacteria, including car wash installations frequently used by a large number of customers and where poor maintenance probably creates favorable conditions for Legionella overgrowth and spreading. Additional research is needed to ascertain optimal strategies for Legionella monitoring and control, but environmental surveillance, paying careful attention to possible unconventional sources, should remain an important component of any Legionnaires\u2019 disease prevention program. Additionally, all available diagnostic methods would be recommended for the confirmation of all cases even in the event of non-serogroup 1 Legionella pneumophila infection, probably underestimated at this time
Second-harmonic generation in silicon waveguides strained by silicon nitride
Silicon photonics meets the electronics requirement of increased speed and bandwidth with on-chip optical networks.
All-optical data management requires nonlinear silicon photonics. In silicon only third-order optical nonlinearities are present
owing to its crystalline inversion symmetry. Introducing a second-order nonlinearity into silicon photonics by proper material
engineering would be highly desirable. It would enable devices for wideband wavelength conversion operating at relatively low
optical powers. Here we show that a sizeable second-order nonlinearity at optical wavelengths is induced in a silicon waveguide
by using a stressing silicon nitride overlayer. We carried out second-harmonic-generation experiments and first-principle
calculations, which both yield large values of strain-induced bulk second-order nonlinear susceptibility, up to 40pm/V at
2.300 nm. We envisage that nonlinear strained silicon could provide a competing platform for a new class of integrated light
sources spanning the near- to mid-infrared spectrum from 1.2 to 10 micron
Transport by molecular motors in the presence of static defects
The transport by molecular motors along cytoskeletal filaments is studied
theoretically in the presence of static defects. The movements of single motors
are described as biased random walks along the filament as well as binding to
and unbinding from the filament. Three basic types of defects are
distinguished, which differ from normal filament sites only in one of the
motors' transition probabilities. Both stepping defects with a reduced
probability for forward steps and unbinding defects with an increased
probability for motor unbinding strongly reduce the velocities and the run
lengths of the motors with increasing defect density. For transport by single
motors, binding defects with a reduced probability for motor binding have a
relatively small effect on the transport properties. For cargo transport by
motors teams, binding defects also change the effective unbinding rate of the
cargo particles and are expected to have a stronger effect.Comment: 20 pages, latex, 7 figures, 1 tabl
Testing the theory of immune selection in cancers that break the rules of transplantation
Modification of cancer cells likely to reduce their immunogenicity, including loss or down-regulation of MHC molecules, is now well documented and has become the main support for the concept of immune surveillance. The evidence that these modifications, in fact, result from selection by the immune system is less clear, since the possibility that they may result from reorganized metabolism associated with proliferation or from cell de-differentiation remains. Here, we (a) survey old and new transplantation experiments that test the possibility of selection and (b) survey how transmissible tumours of dogs and Tasmanian devils provide naturally evolved tests of immune surveillance
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