1,721,063 research outputs found
Presence and clinical significance of bacterial DNA and other bacterial markers in culture-negative clinical samples from patients with severe liver pathologies
No full textDurante il processo infettivo , agenti patogeni possono raggiungere siti anatomici in cui sono esposti a sostanze che ostacolano la loro crescita . Queste sostanze , ossia
molecole immunologhe e antibiotici , provocano l'inibizione della crescita batterica e l'infezione è solitamente fermata. Tuttavia, come osservato nell'ambiente, anche in un ospite infetto concentrazioni di molecole inibenti e condizioni di stress potrebbero
indurre l'attivazione di meccanismi di sopravvivenza che bloccano la capacità divisione dei batteri, ma permettono loro di rimanere in vita . I batteri "dormienti " possono essere riattivati in particolari circostanze e possono determinare infezioni ricorrenti. Alcuni ricercatori hanno considerato la possibilità che le forme microbiche "non recuperabili" (batteri - privi di parete o microrganismi feriti o ( VBNC ) forme vitali ma non coltivabili ) possono causare la malattia .
I batteri non in divisione o feriti non possono essere identificati attraverso le procedure
microbiologiche diagnostiche standard, basate su metodi di coltura . Per questo motivo, negli ultimi tempi l'applicazione di metodi molecolari per la diagnosi microbiologica è in aumento nonostante ci sia la mancanza di un chiaro significato clinico dei risultati ottenuti.During the infectious process, pathogens may reach anatomical sites where they are
exposed to substances hindering their growth. These substances, i.e. immunological
molecules and antibiotics, cause the inhibition of bacterial growth and the infection is
usually stopped. However, as observed in the environment, also in infected host suboptimal
concentrations of inhibitory molecules and a number of stress conditions might
induce the activation of survival mechanisms blocking the division capability of bacteria
but allowing them to stay alive. The “dormant” bacteria can be re-activated in particular
circumstances and might determine recurrent infections and some researchers have
considered the possibility that “non-recoverable” microbial forms (wall-deprived bacteria,
injured microorganisms, viable but nonculturable (VBNC) forms, dormant bacteria) may
cause disease.
The non-dividing or injured bacteria cannot be identified by standard diagnostic
microbiological procedures based on culture methods. For this reason, in recent times the
application of molecular methods to the microbiological diagnosis is increasing despite of
the lack of a clear clinical significance of the obtained results
Wakes Calculation in a Offshore Wind Farm
No full textThis paper is focusing on the wake modeling in large offshore wind farms. Over the sea the ambient turbulence is much lower than onshore, wakes persist for long distances, mixing in a complex pattern. Hence an accurate evaluation of the wakes become crucial in the estimation both of the production and loads. Regarding loads the main effect of the turbines wakes is an increase of turbulence compared to the ambient one. A careful assessment of the wakes is therefore required when analyzing offshore wind farms.
The approaches in estimating the wake losses go from simple theoretical or empirical laws to full rotor aerodynamic calculations; in between there is a range of intermediate calculations.
Two approaches will be presented: the use of relative simple equations (also called analytical models) which are the standards in the wind resource assessment and a more accurate, but computationally more demanding, the actuator disc technique
Validation of the Actuator Disk Model for wind turbine wakes calculations.
No full textNumerical simulation of wind turbine wakes is a fundamental tool for the optimization of the exploitation of the wind renewable energy potential especially in off-shore conditions or in coastal areas. Usually analytical models are used for on-shore wind farm with success and poor calculation load; anyway for off-shore cases CFD (Computational Fluid Dynamics) models are recently discovered to be able to reproduce the wakes interactions in a more reliable way.
In present work an actuator disc model was implemented in order to simulate the wakes for a small coastal wind farm. CFD numerical simulations were performed using WindSim 5.0 to reproduce the interaction between the main wind flow and the wakes induced by the actuator discs for the prevailing direction sectors.
A particular attention was addressed to the boundary conditions: since generally the domain is rectangular the inlet and outlet conditions must be different for orthogonal and non-orthogonal cases.
The CFD code PHOENICS works using an orthogonal structured cartesian grid so that only for orthogonal sectors the disc can be aligned face to the wind.
This problem can be overcome rotating the model: for coastal areas where a small influence of the terrain is also to be considered such technique can give an improvement of the results.
In the present work the numerical model was validated using real production data from a small wind farm in the western coastal region of Finland; the numerical wind speed profiles were verified using anemometer data from a mast placed near the turbines.
Results demonstrate that, despite its simplicity, the actuator disc model can give very useful information when developing a wind farm in off-shore or coastal areas.
This work was developed within a cooperation between the Department of Industrial Engineering of the University of Perugia and VTT, the technical research centre of Finland
On the way to harness high-altitude wind power: Defining the operational asset for an airship wind generator
No full textThe utilization of high-altitude wind energy potential is a very attractive challenge. This is mainly due to the perspective of producing a large amount of electricity from a renewable source without using land, and having a very low visibility impact. The wind flow on the upper levels of the surface boundary layer is characterized by good power with low variability of wind conditions.Many innovative wind energy conversion flying devices are currently under development for this purpose. The technological solutions can be grouped in:. •land installed generators (such as kite systems);•airship flying generators that can produce electricity far from the ground and are tethered by control wires, also used for the power transmission.Flying generators could prove more problematic in maintaining flying conditions due to their heavier weight, but they have the advantage that they can be moved to different locations with less intervention on the ground.Another important characteristic that the airship wind generator has, is the possibility of changing its height of operation very quickly and simply by using control cables.In this study, the operational scenario of the possible application of an innovative airship wind generator is studied and discussed. The possibility of adjusting the height of operation was analysed, and a methodology for choosing the optimal operating level was developed and applied to real test cases. Numerical and experimental techniques used to assess the characteristics of high-altitude winds, were also considered.Remotely sensed wind data obtained from a monostatic phased-array Doppler Sonic Detection and Ranging (SODAR) system were used to validate and tune the CFD model in one of the real-test cases investigate
An application of the actuator disc model for wind turbine wakes calculations
No full textNumerical simulation of wake losses is a fundamental step towards the optimization of the exploitation of the renewable wind energy potential especially in off-shore conditions or in coastal areas.
The scientific community is quickly developing new advanced modelling techniques in order to improve the reliability of power losses calculation in many different kinds of environment; analytical models are going to be replaced by new Computational Fluid Dynamics (CFD) codes that seem to be more useful, especially for large offshore wind farms.
In the present work an actuator disc model was implemented in order to simulate the wakes of a wind farm; this model was used within the CFD code PHOENICS (the numerical core of the Windsim package) working with an orthogonal Cartesian grid.
The model was validated using real production data from a small wind farm operating in the western coastal region of Finland; the numerical wind speed profiles were verified using anemometer data from a mast placed near the turbines.
The results demonstrate that, despite its simplicity, the actuator disc model can give very useful information when developing a wind farm in off-shore or coastal areas.
This work was carried out within a cooperation between the Department of Industrial Engineering of the University of Perugia and VTT, the technical research centre of Finland
CONFRONTO FRA DIFFERENTI TECNICHE DI MODELLAZIONE DELLA DISPERSIONE DI INQUINANTI IN ATMOSFERA GENERATA DA UNA PICCOLA CENTRALE A BIOMASSE.
No full textNonostante i notevoli pregi, lo sfruttamento dell’energia da biomassa implica in ogni caso emissioni di fumi in atmosfera
che spesso, specialmente in caso di cogenerazione, avviene in prossimità di abitazioni o di attività lavorative. La pericolosità
delle emissioni è fortemente correlata alle caratteristiche di ventosità locali; per questo motivo la dispersione degli inquinanti è
usualmente studiata attraverso modelli di calcolo che, oltre alle caratteristiche della sorgente, utilizzano come input dati storici
sul vento.
La famiglia di modelli più diffusamente utilizzata per questo tipo di indagini è quella dei codici gaussiani (Gaussian Plume
Model - GPM); tale tipologia di modelli tuttavia non è in grado di interpretare gli effetti di singolarità del campo di moto del
vento indotte da complessità orografiche.
Nel presente lavoro viene proposta una nuova tecnica di modellazione della dispersione di inquinanti quali particolato ed
emissioni gassose che utilizza il modello CFD (Computational Fluid Dynamics) Phoenics; le potenzialità del codice e
l’accuratezza dei risultati sono stati verificati attraverso il confronto dei risultati ottenuti con il modello gaussiano Windimula
sullo stesso dominio di calcolo. Il confronto è stato dunque effettuato considerando le emissioni prodotte da una piccola
centrale a biomassa inserita in una località caratterizzata da orografia fortemente complessa
Cap. I “ATMOSFERA” – Cap. 9 “Energia”
No full textprogetto Agenda 21 locale co-finanziato dal Ministero dell’Ambient
Mathematical methods for SCADA data mining of onshore wind farms: Performance evaluation and wake analysis
No full textSupervisory control and data acquisition (SCADA) systems have become widely diffuse in modern wind energy technology. The slowdown of new installations and the increasing percentage of energy entering the grid from renewable stochastic sources has diverted attention to the careful optimization of operating farms. Elaborating the complex data stream from SCADA systems into knowledge poses technological and scientific challenges. SCADA data analysis therefore lies at the crossroads of mechanical engineering, applied mathematics, statistics and physics. In the present work, mathematical methods are proposed for tackling the complexity of SCADA data. This idea is to elaborate simplified and more powerful data sets through one action: discretization of continuous quantities. The approach is employed for two very different issues: performance evaluation and wake effects analysis, which is investigated from the point of view of power losses, due to the difficulties associated with optimal turbine alignment with the wind. Two indexes for performance evaluation are formulated. Recurrent non-trivial orientation patterns of clusters of turbines are individuated, and the efficiency associated to them is analyzed. The methods are tested on two wind farms situated in southern Italy
Actuator disc wind turbine wakes simulation: about the dependences on the wind shear conditions
No full textModelling wind turbine wakes is going to be a fundamental issue in wind energy assessment studies (especially for offshore wind farms) in order to minimize the losses and to maximize the overall energy production. Analytical wake models were successfully used for on-shore wind farm but for off-shore cases CFD (Computational Fluid Dynamics) models seem to give more reliable results.
In present work CFD and the actuator disc concept have been applied to simulate the wakes of a group of wind turbines; the force on the rotor was defined according to the thrust coefficient curve supplied by the turbine manufacturer. The numerical model was validated using operational data available from the Horns Rev offshore wind farm.
Results demonstrate that the actuator disc model can give useful information on the wakes evolution and that the wind shear conditions can change modestly the energy conversion efficiency but can have a great impact on the wakes propagation
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