318 research outputs found
Anomalies, absence of local equilibrium and universality in 1-d particles systems
One dimensional systems are under intense investigation, both from
theoretical and experimental points of view, since they have rather peculiar
characteristics which are of both conceptual and technological interest. We
analyze the dependence of the behaviour of one dimensional, time reversal
invariant, nonequilibrium systems on the parameters defining their microscopic
dynamics. In particular, we consider chains of identical oscillators
interacting via hard core elastic collisions and harmonic potentials, driven by
boundary Nos\'e-Hoover thermostats. Their behaviour mirrors qualitatively that
of stochastically driven systems, showing that anomalous properties are typical
of physics in one dimension. Chaos, by itslef, does not lead to standard
behaviour, since it does not guarantee local thermodynamic equilibrium. A
linear relation is found between density fluctuations and temperature profiles.
This link and the temporal asymmetry of fluctuations of the main observables
are robust against modifications of thermostat parameters and against
perturbations of the dynamics.Comment: 26 pages, 16 figures, revised text, two appendices adde
Dissipation function: Nonequilibrium physics and dynamical systems
An exact response theory has recently been developed within the field of Nonequilibrium Molecular Dynamics. Its main ingredient is known as the Dissipation Function, W. This quantity determines nonequilbrium properties like thermodynamic potentials do with equilibrium states. In particular, Ω can be used to determine the exact response of particle systems obeying classical mechanical laws, subjected to perturbations of arbitrary size. Under certain conditions, it can also be used to express the response of a single system, in contrast to the standard response theory, which concerns ensembles of identical systems. The dimensions of Ω are those of a rate, hence Ω can be associated with the entropy production rate, provided local thermodynamic equilibrium holds. When this is not the case for a particle system, or generic dynamical systems are considered, Ω can equally be defined, and it yields formal, thermodynamic-like, relations. While such relations may have no physical content, they may still constitute interesting characterizations of the relevant dynamics. Moreover, such a formal approach turns physically relevant, because it allows a deeper analysis of Ω and of response theory than possible in case of fully fledged physical models. Here, we investigate the relation between linear and exact response, pointing out conditions for the validity of the response theory, as well as difficulties and opportunities for the physical interpretation of certain formal results
The Levels of DAHP Synthase, the First Enzyme of the Shikimate Pathway, Are Related to Free Aromatic Amino Acids and Glutamine Content in Nicotiana plumbaginifolia Cell Cultures
Aromatic amino acid homeostasis was investigated in cell suspension cultures of Nicotiana plumbaginifolia and was related to the activity of the first enzyme in aromatic biosynthesis, 3-deoxy-D-arabino-heptulosonate-7-phosphate (DAHP) synthase. An inverse relationship was found between the intracellular content of free phenylalanine, tyrosine and tryptophan and enzyme specific activity levels, suggesting the occurrence of end-product control mechanisms. Two DAHP synthase isogenes are present in wild tobacco that showed a different expression pattern during the culture growth cycle. Intracellular levels of aromatic amino acids were increased or decreased by adding the culture medium with phenylalanine, tyrosine and tryptophan, or with sublethal doses of the shikimate pathway inhibitor glyphosate, respectively. As a consequence, enzyme levels varied in the opposite direction. The concomitant exogenous supply of glutamine further reduced enzyme activity in mid-log cells, suggesting induction by both aromatic amino acid depletion and nitrogen starvation
Sensing of gaseous malodors characteristic of landfills and waste treatment plants
Abstract. We approached the problem of sensing gaseous pollutants and malodors originating as a result of decomposition of organic compounds via chemoresistive sensors. A set of four screen-printed films based on two types of mixed tin and titanium oxides, mixed tungsten and tin oxides, and zinc oxide has been tested vs. the main gaseous components of malodors. N-butanol was also considered because of its importance as a reference gas in the odorimetric intensity scale. We found that, under proper working conditions, the films can sensitively detect such gases either in dry or in wet environments, within the range of concentrations of interest for their monitoring. We also demonstrated that the array is robust under solicitation by harmful interference gases such as CO, C6H6, NO2 and NO
Order Picking Systems: A Queue Model for Dimensioning the Storage Capacity, the Crew of Pickers, and the AGV Fleet
Designing an order picking system can be very complex, as several interrelated control variables are involved. We address the sizing of the storage capacity of the picking bay, the crew of pickers, and the AGV fleet, which are the most important variables from a tactical viewpoint in a parts-to-pickers system. Although order picking is a widely explored topic in the literature, no analytical model that can simultaneously deal with these variables is currently available. To bridge this gap, we introduce a queue model for Markovian processes, which enables us to jointly optimise the aforementioned control variables. A discrete-event simulation is then used to validate our model, and we then test our proposal with real data under different operative scenarios, with the aim of assessing the usefulness of the proposal in real settings
A non-contact optical technique for vehicle tracking along bounded trajectories
This paper presents a method for measuring the non-controlled trajectory of a cart along a bounded rectilinear path. The method uses non-contact measurement devices to identify the position of a movable laser scanner working in helical mode in order to reconstruct the 3D model of bridges. The main idea of the proposed method is to use vision systems in order to identify the coordinates of the laser scanner placed on the cart with respect to the global reference system. A fit-to-purpose vision system has been implemented: the system uses three CCD's cameras mounted on the cart to identify the relative rotations with respect to the environment. Two lasers pointers and a laser distance meter are fixed at the starting point of the trajectory and pointing in the direction of motion of the cart, creating three dots on a plane placed on the cart. One of the camera detects the cart displacements and rotations in the plane using a blob analysis procedure. The method described in this paper has a constant uncertainty and the measurement range only depends on the lasers power. The theoretical accuracy of the measurement system is close to 1 mm for the translation along the motion direction and around 0.5 mm along the other two directions. Orientations measurement have a theoretical accuracy of less than 0.1 °. The solution has been implemented for the 3D reconstruction of concrete bridge; preliminary experimental results are presented and discussed
On the transient behavior of frictional melt during seismic slip
In a recent work on the problem of sliding surfaces under the presence
of frictional melt (applying in particular to earthquake fault dynamics),
we derived from first principles an expression for the steady state
friction compatible with experimental observations. Building on the
expressions of heat and mass balance obtained in the above study for
this particular case of Stefan problem (phase transition with a migrating
boundary) we propose here an extension providing the full time-dependent
solution (including the weakening transient after pervasive melting
has started, the effect of eventual steps in velocity and the final
decelerating phase). A system of coupled equations is derived and
solved numerically. The resulting transient friction and wear evolution
yield a satisfactory fit (1) with experiments performed under variable
sliding velocities (0.9-2 m/s) and different normal stresses (0.5-20
MPa) for various rock types and (2) with estimates of slip weakening
obtained from observations on ancient seismogenic faults that host
pseudotachylite (solidified melt). The model allows to extrapolate
the experimentally observed frictional behavior to large normal stresses
representative of the seismogenic Earth crust (up to 200 MPa), high
slip rates (up to 9 m/s) and cases where melt extrusion is negligible.
Though weakening distance and peak stress vary widely, the net breakdown
energy appears to be essentially independent of either slip velocity
and normal stress. In addition, the response to earthquake-like slip
can be simulated, showing a rapid friction recovery when slip rate
drops. We discuss the properties of energy dissipation, transient
duration, velocity weakening, restrengthening in the decelerating
final slip phase and the implications for earthquake source dynamics
Clinical validation results of an innovative non-invasive device for colorectal cancer preventive screening through fecal exhalation analysis
Screening is recommended to reduce both incidence and mortality of colorectal cancer.
Currently, many countries employ fecal occult blood test (FOBT). In Emilia-Romagna (Italy), since
2005, FOBT immunochemical version (FIT) is performed every two years on people aged between 50
and 69 years. A colonoscopy is then carried out on those who are FIT positive. However, FIT shows
approximately 65% false positives (non-tumoral bleedings), leading to many negative colonoscopies.
The use of an economic and easy-to-use method to check FOBT-positives will improve screening
effectiveness, reducing costs to the national health service. This work illustrates the results of a
three-year clinical validation protocol (started in 2016) of a patented device composed of a core of
nanostructured gas sensors. This device was designed to identify CRC presence by fecal volatile
compounds, with a non-invasive, in vitro and low-cost analysis. Feces are, in fact, affected by
tumor-volatile biomarkers, produced by cellular peroxidation and metabolic alterations. The protocol
consisted in the analysis of fecal samples of FIT-positive subjects, using colonoscopy as a gold standard.
A total of 398 samples were analyzed with machine learning techniques, leading to a sensitivity and
specificity of 84.1% and 82.4%, respectively, and a positive predictive value of 72% (25–35% for FIT)
Devices for Screening and Monitoring of Tumors Based on Chemoresistive Sensors
Abstract In this work two devices are presented, named SCENT A1 (A1) and SCENT B1 (B1), composed of chemoresistive sensors. Such devices are capable of discriminating the different compositions of gas mixtures emitted by stools, for colorectal cancer screening (A1), and by blood, for tumors monitoring (B1), according to defined sampling protocols. Results have been acquired by a LabView® software and statistically treated (e.g. quadratic discriminant analysis, QDA) and show to be encouraging with an error of 5% for SCENT A1. Preliminary results of SCENT B1 proved to be promising. Further studies will be carried out for clinically validating the two devices
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