Classical limit of the Nelson model

Since the development of quantum mechanics it has been natural to analyze the connection between classical and quantum mechanical descriptions of physical systems. In particular one should expect that in some sense when quantum mechanical effects becomes negligible the system will behave like it is dictated by classical mechanics. One famous relation between classical and quantum theory is due to Ehrenfest. This result was later developed and put on firm mathematical foundations by Hepp. He proved that matrix elements of bounded functions of quantum observables between suitable coherents states (that depend on Planck's constant h) converge to classical values evolving according to the expected classical equations when h goes to zero. His results were later generalized by Ginibre and Velo to bosonic systems with infinite degrees of freedom and scattering theory. In this thesis we study the classical limit of Nelson model, that describes non relativistic particles, whose evolution is dictated by Schrödinger equation, interacting with a scalar relativistic field, whose evolution is dictated by Klein-Gordon equation, by means of a Yukawa-type potential. The classical limit is a mean field and weak coupling limit. We proved that the transition amplitude of a creation or annihilation operator, between suitable coherent states, converges in the classical limit to the solution of the system of differential equations that describes the classical evolution of the theory. The quantum evolution operator converges to the evolution operator of fluctuations around the classical solution. Transition amplitudes of normal ordered products of creation and annihilation operators between coherent states converge to suitable products of the classical solutions. Transition amplitudes of normal ordered products of creation and annihilation operators between fixed particle states converge to an average of products of classical solutions, corresponding to different initial conditions.

Advanced Waste-To-Energy Cycles

The increase in environmental and healthy concerns, combined with the possibility to exploit waste as a valuable energy resource, has led to explore alternative methods for waste final disposal. In this context, the energy conversion of Municipal Solid Waste (MSW) in Waste-To-Energy (WTE) power plant is increasing throughout Europe, both in terms of plants number and capacity, furthered by legislative directives. Due to the heterogeneous nature of waste, some differences with respect to a conventional fossil fuel power plant have to be considered in the energy conversion process. In fact, as a consequence of the well-known corrosion problems, the thermodynamic efficiency of WTE power plants typically ranging in the interval 25% ÷ 30%. The new Waste Framework Directive 2008/98/EC promotes production of energy from waste introducing an energy efficiency criteria (the so-called “R1 formula”) to evaluate plant recovery status. The aim of the Directive is to drive WTE facilities to maximize energy recovery and utilization of waste heat, in order to substitute energy produced with conventional fossil fuels fired power plants. This calls for novel approaches and possibilities to maximize the conversion of MSW into energy. In particular, the idea of an integrated configuration made up of a WTE and a Gas Turbine (GT) originates, driven by the desire to eliminate or, at least, mitigate limitations affecting the WTE conversion process bounding the thermodynamic efficiency of the cycle. The aim of this Ph.D thesis is to investigate, from a thermodynamic point of view, the integrated WTE-GT system sharing the steam cycle, sharing the flue gas paths or combining both ways. The carried out analysis investigates and defines the logic governing plants match in terms of steam production and steam turbine power output as function of the thermal powers introduced.

High resolution study of local stress inside alumina - micro mechanical analysis using laser scanning confocal microscope

The aim of this work is to measure the stress inside a hard micro object under extreme compression. To measure the internal stress, we compressed ruby spheres (a-Al2O3: Cr3+, 150 µm diameter) between two sapphire plates. Ruby fluorescence spectrum shifts to longer wavelengths under compression and can be related to the internal stress by a conversion coefficient. A confocal laser scanning microscope was used to excite and collect fluorescence at desired local spots inside the ruby sphere with spatial resolution of about 1 µm3. Under static external loads, the stress distribution within the center plane of the ruby sphere was measured directly for the first time. The result agreed to Hertz’s law. The stress across the contact area showed a hemispherical profile. The measured contact radius was in accord with the calculation by Hertz’s equation. Stress-load curves showed spike-like decrease after entering non-elastic phase, indicating the formation and coalescence of microcracks, which led to relaxing of stress. In the vicinity of the contact area luminescence spectra with multiple peaks were observed. This indicated the presence of domains of different stress, which were mechanically decoupled. Repeated loading cycles were applied to study the fatigue of ruby at the contact region. Progressive fatigue was observed when the load exceeded 1 N. As long as the load did not exceed 2 N stress-load curves were still continuous and could be described by Hertz’s law with a reduced Young’s modulus. Once the load exceeded 2 N, periodical spike-like decreases of the stress could be observed, implying a “memory effect” under repeated loading cycles. Vibration loading with higher frequencies was applied by a piezo. Redistributions of intensity on the fluorescence spectra were observed and it was attributed to the repopulation of the micro domains of different elasticity. Two stages of under vibration loading were suggested. In the first stage continuous damage carried on until certain limit, by which the second stage, e.g. breakage, followed in a discontinuous manner.

External drivers of biogeochemical cycles in a tropical montane forest in Ecuador

Successful conservation of tropical montane forest, one of the most threatened ecosystems on earth, requires detailed knowledge of its biogeochemistry. Of particular interest is the response of the biogeochemical element cycles to external influences such as element deposition or climate change. Therefore the overall objective of my study was to contribute to improved understanding of role and functioning of the Andean tropical montane forest. In detail, my objectives were to determine (1) the role of long-range transported aerosols and their transport mechanisms, and (2) the role of short-term extreme climatic events for the element budget of Andean tropical forest. In a whole-catchment approach including three 8-13 ha microcatchments under tropical montane forest on the east-exposed slope of the eastern cordillera in the south Ecuadorian Andes at 1850-2200 m above sea level I monitored at least in weekly resolution the concentrations and fluxes of Ca, Mg, Na, K, NO3-N, NH4-N, DON, P, S, TOC, Mn, and Al in bulk deposition, throughfall, litter leachate, soil solution at the 0.15 and 0.3 m depths, and runoff between May 1998 and April 2003. I also used meteorological data from my study area collected by cooperating researchers and the Brazilian meteorological service (INPE), as well as remote sensing products of the North American and European space agencies NASA and ESA. My results show that (1) there was a strong interannual variation in deposition of Ca [4.4-29 kg ha-1 a-1], Mg [1.6-12], and K [9.8-30]) between 1998 and 2003. High deposition changed the Ca and Mg budgets of the catchments from loss to retention, suggesting that the additionally available Ca and Mg was used by the ecosystem. Increased base metal deposition was related to dust outbursts of the Sahara and an Amazonian precipitation pattern with trans-regional dry spells allowing for dust transport to the Andes. The increased base metal deposition coincided with a strong La Niña event in 1999/2000. There were also significantly elevated H+, N, and Mn depositions during the annual biomass burning period in the Amazon basin. Elevated H+ deposition during the biomass burning period caused elevated base metal loss from the canopy and the organic horizon and deteriorated already low base metal supply of the vegetation. Nitrogen was only retained during biomass burning but not during non-fire conditions when deposition was much smaller. Therefore biomass burning-related aerosol emissions in Amazonia seem large enough to substantially increase element deposition at the western rim of Amazonia. Particularly the related increase of acid deposition impoverishes already base-metal scarce ecosystems. As biomass burning is most intense during El Niño situations, a shortened ENSO cycle because of global warming likely enhances the acid deposition at my study forest. (2) Storm events causing near-surface water flow through C- and nutrient-rich topsoil during rainstorms were the major export pathway for C, N, Al, and Mn (contributing >50% to the total export of these elements). Near-surface flow also accounted for one third of total base metal export. This demonstrates that storm-event related near-surface flow markedly affects the cycling of many nutrients in steep tropical montane forests. Changes in the rainfall regime possibly associated with global climate change will therefore also change element export from the study forest. Element budgets of Andean tropical montane rain forest proved to be markedly affected by long-range transport of Saharan dust, biomass burning-related aerosols, or strong rainfalls during storm events. Thus, increased acid and nutrient deposition and the global climate change probably drive the tropical montane forest to another state with unknown consequences for its functions and biological diversity.

Generating vegetation-spectra as a basis for global monitoring of annual vegetation cycles using DOAS satellite observations

Vegetation-cycles are of general interest for many applications. Be it for harvest-predictions, global monitoring of climate-change or as input to atmospheric models.rnrnCommon Vegetation Indices use the fact that for vegetation the difference between Red and Near Infrared reflection is higher than in any other material on Earth’s surface. This gives a very high degree of confidence for vegetation-detection.rnrnThe spectrally resolving data from the GOME and SCIAMACHY satellite-instrumentsrnprovide the chance to analyse finer spectral features throughout the Red and Near Infrared spectrum using Differential Optical Absorption Spectroscopy (DOAS). Although originally developed to retrieve information on atmospheric trace gases, we use it to gain information on vegetation. Another advantage is that this method automatically corrects for changes in the atmosphere. This renders the vegetation-information easily comparable over long time-spans.rnThe first results using previously available reference spectra were encouraging, but also indicated substantial limitations of the available reflectance spectra of vegetation. This was the motivation to create new and more suitable vegetation reference spectra within this thesis.rnThe set of reference spectra obtained is unique in its extent and also with respect to its spectral resolution and the quality of the spectral calibration. For the first time, this allowed a comprehensive investigation of the high-frequency spectral structures of vegetation reflectance and of their dependence on the viewing geometry.rnrnThe results indicate that high-frequency reflectance from vegetation is very complex and highly variable. While this is an interesting finding in itself, it also complicates the application of the obtained reference spectra to the spectral analysis of satellite observations.rnrnThe new set of vegetation reference spectra created in this thesis opens new perspectives for research. Besides refined satellite analyses, these spectra might also be used for applications on other platforms such as aircraft. First promising studies have been presented in this thesis, but the full potential for the remote sensing of vegetation from satellite (or aircraft) could bernfurther exploited in future studies.

Design and optimization of turbo-expanders for organic rankine cycles

In a world focused on the need to produce energy for a growing population, while reducing atmospheric emissions of carbon dioxide, organic Rankine cycles represent a solution to fulfil this goal. This study focuses on the design and optimization of axial-flow turbines for organic Rankine cycles. From the turbine designer point of view, most of this fluids exhibit some peculiar characteristics, such as small enthalpy drop, low speed of sound, large expansion ratio. A computational model for the prediction of axial-flow turbine performance is developed and validated against experimental data. The model allows to calculate turbine performance within a range of accuracy of ±3%. The design procedure is coupled with an optimization process, performed using a genetic algorithm where the turbine total-to-static efficiency represents the objective function. The computational model is integrated in a wider analysis of thermodynamic cycle units, by providing the turbine optimal design. First, the calculation routine is applied in the context of the Draugen offshore platform, where three heat recovery systems are compared. The turbine performance is investigated for three competing bottoming cycles: organic Rankine cycle (operating cyclopentane), steam Rankine cycle and air bottoming cycle. Findings indicate the air turbine as the most efficient solution (total-to-static efficiency = 0.89), while the cyclopentane turbine results as the most flexible and compact technology (2.45 ton/MW and 0.63 m3/MW). Furthermore, the study shows that, for organic and steam Rankine cycles, the optimal design configurations for the expanders do not coincide with those of the thermodynamic cycles. This suggests the possibility to obtain a more accurate analysis by including the computational model in the simulations of the thermodynamic cycles. Afterwards, the performance analysis is carried out by comparing three organic fluids: cyclopentane, MDM and R245fa. Results suggest MDM as the most effective fluid from the turbine performance viewpoint (total-to-total efficiency = 0.89). On the other hand, cyclopentane guarantees a greater net power output of the organic Rankine cycle (P = 5.35 MW), while R245fa represents the most compact solution (1.63 ton/MW and 0.20 m3/MW). Finally, the influence of the composition of an isopentane/isobutane mixture on both the thermodynamic cycle performance and the expander isentropic efficiency is investigated. Findings show how the mixture composition affects the turbine efficiency and so the cycle performance. Moreover, the analysis demonstrates that the use of binary mixtures leads to an enhancement of the thermodynamic cycle performance.

Absolute Hodge cycles and Deligne's principle b

I cicli di Hodge assoluti sono stati utilizzati da Deligne per dividere la congettura di Hodge in due sotto-congetture. La prima dice che tutte le classi di Hodge su una varietà complessa proiettiva liscia sono assolute, la seconda che le classi assolute sono algebriche. Deligne ha dato risposta affermativa alla prima sottocongettura nel caso delle varietà abeliane. La dimostrazione si basa su due teoremi, conosciuti rispettivamente come Principio A e Principio B. In questo lavoro vengono presentate la teoria delle classi di Hodge assolute e la dimostrazione del Principio B.

Einzelpartikel- und Ensemblemessungen mit dem Aerosolmassenspektrometer (AMS): Untersuchungen zu Quellen und chemischer Prozessierung von Aerosolpartikeln im Submikrometerbereich

Atmosphärische Aerosolpartikel haben einen Einfluss sowohl auf das Klima als auch auf die menschliche Gesundheit, wobei sowohl die Größe, als auch die chemische Zusammensetzung der Partikel maßgeblich sind. Um insbesondere die chemische Zusammensetzung der Partikel in Abhängigkeit ihrer Quellen besser zu verstehen, wurden im Rahmen dieser Arbeit massenspektrometrische Untersuchungen thermisch verdampfbarer Partikel im Submikrometerbereich durchgeführt. Hierzu wurden sowohl die Massenspektren einzelner Partikel, als auch die von Ensembles von Partikeln mit dem Aerodyne Aerosolmassenspektrometer (AMS) in mehreren Feldmesskampagnen untersucht. Für die Messung von Einzelpartikelmassenspektren wurde das AMS zunächst durch den Einbau eines optischen Partikeldetektors (light scattering probe) modifiziert und anschließend eingehend charakterisiert. Dabei wurde festgestellt, dass mit dem Gerät im Partikelgrößenbereich von etwa 400-750 nm (untere Grenze bedingt durch die Detektionseffizienz des optischen Detektors, obere Grenze durch die Transmissionseffizienz des Aerosoleinlasssystems) quantitative Einzelpartikelmessungen möglich sind. Zudem wurde die Analyse der erhaltenen Messdaten systematisiert, und durch Einsatz von Standardspektren ein Sortieralgorithmus für die Einzelpartikelmassenspektren entwickelt, der erfolgreich auf Daten von Feldmesskampagnen angewandt werden konnte. Mit diesem Sortieralgorithmus sind zudem quantitative Aussagen über die verschiedenen Partikelbestandteile möglich. Im Sommer 2009 und im Winter 2010 fanden im Großraum Paris zwei einmonatige Feldmesskampagnen statt, bei denen unter anderem der Einfluss der Abluftfahne der Megastadt auf seine Vororte untersucht wurde. Erhöhte Konzentrationen sekundär gebildeter Aerosolkomponenten (Nitrat, Sulfat, oxidiertes organisches Aerosol (OOA)) waren insbesondere beim Herantransport kontinentaler Luftmassen zu beobachten. Im Gegensatz dazu waren die beobachteten Konzentrationen der Tracer primärer Emissionen NOx, BC (black carbon) und HOA (hydrocarbonlike organic aerosol) neben der lokalen Quellstärke insbesondere durch die herrschende Windgeschwindigkeit beeinflusst. Aus dem Vergleich der Messungen an drei Stationen konnte der Einfluss der Megastadt Paris auf seine Vororte (unter Annahme gleicher lokaler Emissionen an den zwei Vorort-Stationen) zu 0,1-0,7 µg m-3 BC, 0,3-1,1 µg m-3 HOA, und 3-5 ppb NOx abgeschätzt werden. Zudem konnten für zwei Stationen aus den Ensemble- bzw. den Einzelpartikelmessungen unabhängig voneinander zwei verschiedene HOA-Typen unterschieden werden, die den Quellen „Kochen“ und „Autoabgase“ zugeordnet wurden. Der Anteil der Partikel aus den Quellen „Kochen“ bzw. „Autoabgase“ am Gesamt-HOA betrug 65,5 % und 34,5 % für die Ensemblemessungen in der Innenstadt (nahe vieler Restaurants), und für die Einzelpartikelmessungen in einem Vorort 59 % bzw. 41 % (bezogen auf die Partikelanzahl, welche hier der Masse etwa proportional ist). Die Analyse der Einzelpartikelmassenspektren erbrachte zudem neue Erkenntnisse über den Mischungszustand der Einzelpartikel. So konnte belegt werden, dass Nitrat, Sulfat und OOA intern gemischt sind, HOA-Partikel aber als externe Mischung mit diesen vorliegen. Zudem konnte anhand der Tagesgänge der Masse pro Partikel von OOA, Nitrat und Sulfat und der Anzahl der diese Substanzen enthaltenden Partikel gezeigt werden, dass der im Ensemblemodus beobachtete fehlende Tagesgang der Sulfat-Massenkonzentration wahrscheinlich durch die gegensätzlichen Effekte der Modulation der Partikelanzahlkonzentration durch die sich verändernde Mischungsschichthöhe und der variierenden Masse an Sulfat pro Partikel (mittägliche photochemische Neuproduktion und Kondensation auf existierende Partikel) erklärt werden kann. Für OOA ist eine ähnliche Erklärung des Ensemblemodus-Tagesganges jedoch nur teilweise möglich; weitere Arbeit ist daher nötig, um auch für diese Substanzklasse belastbare Aussagen aus dem Vergleich der Ensemble- und Einzelpartikelmessungen zu erhalten. Im Rahmen einer Labormesskampagne an der AIDA-Kammer in Karlsruhe wurden Ensemble- und Einzelpartikelmassenspektren von Bakterien aufgenommen. Es konnte gezeigt werden, dass es prinzipiell möglich ist, Bakterien in Außenluft mittels Einzelpartikelmessungen nachzuweisen, jedoch wahrscheinlich nur bei sehr hohen Anzahlkonzentrationen. Der Nachweis von Bakterien und anderen primären biologischen Aerosolpartikeln mit dem AMS sollte daher in weiterführenden Experimenten noch optimiert werden.

Modelling biogeochemical cycles in forest ecosystems: a Bayesian approach

Forest models are tools for explaining and predicting the dynamics of forest ecosystems. They simulate forest behavior by integrating information on the underlying processes in trees, soil and atmosphere. Bayesian calibration is the application of probability theory to parameter estimation. It is a method, applicable to all models, that quantifies output uncertainty and identifies key parameters and variables. This study aims at testing the Bayesian procedure for calibration to different types of forest models, to evaluate their performances and the uncertainties associated with them. In particular,we aimed at 1) applying a Bayesian framework to calibrate forest models and test their performances in different biomes and different environmental conditions, 2) identifying and solve structure-related issues in simple models, and 3) identifying the advantages of additional information made available when calibrating forest models with a Bayesian approach. We applied the Bayesian framework to calibrate the Prelued model on eight Italian eddy-covariance sites in Chapter 2. The ability of Prelued to reproduce the estimated Gross Primary Productivity (GPP) was tested over contrasting natural vegetation types that represented a wide range of climatic and environmental conditions. The issues related to Prelued's multiplicative structure were the main topic of Chapter 3: several different MCMC-based procedures were applied within a Bayesian framework to calibrate the model, and their performances were compared. A more complex model was applied in Chapter 4, focusing on the application of the physiology-based model HYDRALL to the forest ecosystem of Lavarone (IT) to evaluate the importance of additional information in the calibration procedure and their impact on model performances, model uncertainties, and parameter estimation. Overall, the Bayesian technique proved to be an excellent and versatile tool to successfully calibrate forest models of different structure and complexity, on different kind and number of variables and with a different number of parameters involved.

Process-based modelling of lichens and bryophytes and their role in global biogeochemical cycles

This thesis presents a process-based modelling approach to quantify carbon uptake by lichens and bryophytes at the global scale. Based on the modelled carbon uptake, potential global rates of nitrogen fixation, phosphorus uptake and chemical weathering by the organisms are estimated. In this way, the significance of lichens and bryophytes for global biogeochemical cycles can be assessed. The model uses gridded climate data and key properties of the habitat (e.g. disturbance intervals) to predict processes which control net carbon uptake, namely photosynthesis, respiration, water uptake and evaporation. It relies on equations used in many dynamical vegetation models, which are combined with concepts specific to lichens and bryophytes, such as poikilohydry or the effect of water content on CO2 diffusivity. To incorporate the great functional variation of lichens and bryophytes at the global scale, the model parameters are characterised by broad ranges of possible values instead of a single, globally uniform value. The predicted terrestrial net uptake of 0.34 to 3.3 Gt / yr of carbon and global patterns of productivity are in accordance with empirically-derived estimates. Based on the simulated estimates of net carbon uptake, further impacts of lichens and bryophytes on biogeochemical cycles are quantified at the global scale. Thereby the focus is on three processes, namely nitrogen fixation, phosphorus uptake and chemical weathering. The presented estimates have the form of potential rates, which means that the amount of nitrogen and phosphorus is quantified which is needed by the organisms to build up biomass, also accounting for resorption and leaching of nutrients. Subsequently, the potential phosphorus uptake on bare ground is used to estimate chemical weathering by the organisms, assuming that they release weathering agents to obtain phosphorus. The predicted requirement for nitrogen ranges from 3.5 to 34 Tg / yr and for phosphorus it ranges from 0.46 to 4.6 Tg / yr. Estimates of chemical weathering are between 0.058 and 1.1 km³ / yr of rock. These values seem to have a realistic order of magnitude and they support the notion that lichens and bryophytes have the potential to play an important role for global biogeochemical cycles.

Coca cola hbc italia: Modello per il calcolo di inventory stock target e production cycles ottimali

Approccio unificato alla gestione e alla valutazione del planning in stabilimenti e magazzini, presso Coca Cola HBC Italia

Velocity recovery cycles of human muscle action potentials in chronic renal failure

To test the hypothesis that muscle fibers are depolarized in patients with chronic renal failure, by measuring velocity recovery cycles of muscle action potentials as indicators of muscle membrane potential.

Muscle membrane dysfunction in critical illness myopathy assessed by velocity recovery cycles

To test the hypothesis that muscle fibers are depolarized in patients with critical illness myopathy by measuring velocity recovery cycles (VRCs) of muscle action potentials.