Acqua: solvente elettivo in Organocatalisi e Biocatalisi

Water is a safe, harmless, and environmentally benign solvent. From an eco-sustainable chemistry perspective, the use of water instead of organic solvent is preferred to decrease environmental contamination. Moreover, water has unique physical and chemical properties, such as high dielectric constant and high cohesive energy density compared to most organic solvents. The different interactions between water and substrates, make water an interesting candidate as a solvent or co-solvent from an industrial and laboratory perspective. In this regard, organic reactions in aqueous media are of current interest. In addition, from practical and synthetic standpoints, a great advantage of using water is immediately evident, since it does not require any preliminary drying process. This thesis was found on this aspect of chemical research, with particular attention to the mechanisms which control organo and bio-catalysis outcome. The first part of the study was focused on the aldol reaction. In particular, for the first time it has been analyzed for the first time the stereoselectivity of the condensation reaction between 3-pyridincarbaldehyde and the cyclohexanone, catalyzed by morpholine and 4-tertbutyldimethylsiloxyproline, using water as sole solvent. This interest has resulted in countless works appeared in the literature concerning the use of proline derivatives as effective catalysts in organic aqueous environment. These studies showed good enantio and diastereoselectivities but they did not present an in depth study of the reaction mechanism. The analysis of the products diastereomeric ratios through the Eyring equation allowed to compare the activation parameters (ΔΔH≠ and ΔΔS≠) of the diastereomeric reaction paths, and to compare the different type of catalysis. While morpholine showed constant diasteromeric ratio at all temperatures, the O(TBS)-L-proline, showed a non-linear Eyring diagram, with two linear trends and the presence of an inversion temperature (Tinv) at 53 ° C, which denotes the presence of solvation effects by water. A pH-dependent study allowed to identify two different reaction mechanisms, and in the case of O(TBS)-L-proline, to ensure the formation of an enaminic species, as a keyelement in the stereoselective process. Moreover, it has been studied the possibility of using the 6- aminopenicillanic acid (6-APA) as amino acid-type catalyst for aldol condensation between cyclohexanone and aromatic aldehydes. A detailed analysis of the catalyst regarding its behavior in different organic solvents and pH, allowed to prove its potential as a candidate for green catalysis. Best results were obtained in neat conditions, where 6-APA proved to be an effective catalyst in terms of yields. The catalyst performance in terms of enantio- and diastereo-selectivity, was impaired by the competition between two different catalytic mechanisms: one via imine-enamine mechanism and one via a Bronsted-acid catalysis. The last part of the thesis was dedicated to the enzymatic catalysis, with particular attention to the use of an enzyme belonging to the class of alcohol dehydrogenase, the Horse Liver Alcohol Dehydrogenase (HLADH) which was selected and used in the enantioselective reduction of aldehydes to enantiopure arylpropylic alcohols. This enzyme has showed an excellent responsiveness to this type of aldehydes and a good tolerance toward organic solvents. Moreover, the fast keto-enolic equilibrium of this class of aldehydes that induce the stereocentre racemization, allows the dynamic-kinetic resolution (DKR) to give the enantiopure alcohol. By analyzing the different reaction parameters, especially the pH and the amount of enzyme, and adding a small percentage of organic solvent, it was possible to control all the parameters involved in the reaction. The excellent enatioselectivity of HLADH along with the DKR of arylpropionic aldehydes, allowed to obtain the corresponding alcohols in quantitative yields and with an optical purity ranging from 64% to >99%.

Lineare und nichtlineare dielektrische Spektroskopie am Relaxor-Ferroelektrikum Bleimagnesiumniobat

Relaxor-Ferroelektrika sind wegen ihrer möglichen technischen Anwendungen und vom Standpunkt der Grundlagenforschung als Beispiel für ungeordnete Systeme von wissenschaftlichem Interesse. Trotz zahlreicher experimenteller Untersuchungen sind die mikroskopischen Ursachen ihrer Eigenschaften aber nach wie vor ungeklärt. Im Rahmen dieser Arbeit wurde das Relaxor-Ferroelektrikum Bleimagnesiumniobat-Bleititanat (PMN-10PT) mittels linearer und nichtlinearer dielektrischer Spektroskopie untersucht. Durch Anregung mit starken elektrischen Wechselfeldern konnten mit der Methode des nichtresonanten dielektrischen Lochbrennens frequenzselektiv einzelne spektrale Bereiche aus dem verbreiterten Relaxationsspektrum herausgegriffen und deren Rückrelaxation separat verfolgt werden. Die experimentellen Ergebnisse zeigten, daß eine langlebige dynamische Heterogenität der dipolaren Reorientierung existiert. Durch ihr ausgeprägt nichtergodisches Verhalten zeigen Relaxor-Ferroelektrika starke Alterungseffekte. Die Untersuchung des Alterungsverhaltens der dielektrischen Suszeptibilität zeigte, daß ein Gedächtnis für die bei einer Alterungstemperatur eingenommene Konfiguration bestehen bleibt, sofern die Temperatur nach einer unvollständigen isothermen Alterung nur um einige Grad abgesenkt oder erhöht wurde.Außerdem wurde die induzierte Polarisation bei stochastischen dielektrischen Anregungen mit elektrischen Feldern, die in sehr guter Näherung ein weißes Rauschen darstellten, untersucht. Über die Bildung der Kreuzkorrelationsfunktion zwischen Feld und Polarisation konnte die Impulsantwortfunktion des Systems berechnet werden.Die experimentellen Ergebnisse am Relaxor-Ferroelektrikum PMN-10PT können sehr gut mit einem Modell eines ungeordneten Ferroelektrikums erklärt werden, dessen Domänenwände unordnungsbedingt an sogenannten Pinning-Zentren festhaften.

Shear behavior of reinforced concrete slabs under concentrated load: an investigation through Sequentially Linear Analysis

ABSTRACT (italiano) Con crescente attenzione riguardo al problema della sicurezza di ponti e viadotti esistenti nei Paesi Bassi, lo scopo della presente tesi è quello di studiare, mediante la modellazione con Elementi Finiti ed il continuo confronto con risultati sperimentali, la risposta in esercizio di elementi che compongono infrastrutture del genere, ovvero lastre in calcestruzzo armato sollecitate da carichi concentrati. Tali elementi sono caratterizzati da un comportamento ed una crisi per taglio, la cui modellazione è, da un punto di vista computazionale, una sfida piuttosto ardua, a causa del loro comportamento fragile combinato a vari effetti tridimensionali. La tesi è incentrata sull'utilizzo della Sequentially Linear Analysis (SLA), un metodo di soluzione agli Elementi Finiti alternativo rispetto ai classici approcci incrementali e iterativi. Il vantaggio della SLA è quello di evitare i ben noti problemi di convergenza tipici delle analisi non lineari, specificando direttamente l'incremento di danno sull'elemento finito, attraverso la riduzione di rigidezze e resistenze nel particolare elemento finito, invece dell'incremento di carico o di spostamento. Il confronto tra i risultati di due prove di laboratorio su lastre in calcestruzzo armato e quelli della SLA ha dimostrato in entrambi i casi la robustezza del metodo, in termini di accuratezza dei diagrammi carico-spostamento, di distribuzione di tensioni e deformazioni e di rappresentazione del quadro fessurativo e dei meccanismi di crisi per taglio. Diverse variazioni dei più importanti parametri del modello sono state eseguite, evidenziando la forte incidenza sulle soluzioni dell'energia di frattura e del modello scelto per la riduzione del modulo elastico trasversale. Infine è stato effettuato un paragone tra la SLA ed il metodo non lineare di Newton-Raphson, il quale mostra la maggiore affidabilità della SLA nella valutazione di carichi e spostamenti ultimi insieme ad una significativa riduzione dei tempi computazionali. ABSTRACT (english) With increasing attention to the assessment of safety in existing dutch bridges and viaducts, the aim of the present thesis is to study, through the Finite Element modeling method and the continuous comparison with experimental results, the real response of elements that compose these infrastructures, i.e. reinforced concrete slabs subjected to concentrated loads. These elements are characterized by shear behavior and crisis, whose modeling is, from a computational point of view, a hard challenge, due to their brittle behavior combined with various 3D effects. The thesis is focused on the use of Sequentially Linear Analysis (SLA), an alternative solution technique to classical non linear Finite Element analyses that are based on incremental and iterative approaches. The advantage of SLA is to avoid the well-known convergence problems of non linear analyses by directly specifying a damage increment, in terms of a reduction of stiffness and strength in the particular finite element, instead of a load or displacement increment. The comparison between the results of two laboratory tests on reinforced concrete slabs and those obtained by SLA has shown in both the cases the robustness of the method, in terms of accuracy of load-displacements diagrams, of the distribution of stress and strain and of the representation of the cracking pattern and of the shear failure mechanisms. Different variations of the most important parameters have been performed, pointing out the strong incidence on the solutions of the fracture energy and of the chosen shear retention model. At last a confrontation between SLA and the non linear Newton-Raphson method has been executed, showing the better reliability of the SLA in the evaluation of the ultimate loads and displacements, together with a significant reduction of computational times.

Seismic mitigation of existing masonry structures by means of added damping and stiffness

In this work seismic upgrading of existing masonry structures by means of hysteretic ADAS dampers is treated. ADAS are installed on external concrete walls, which are built parallel to the building, and then linked to the building's slab by means of steel rod connection system. In order to assess the effectiveness of the intervention, a parametric study considering variation of damper main features has been conducted. To this aim, the concepts of equivalent linear system (ELS) or equivalent viscous damping are deepen. Simplified equivalent linear model results are then checked respect results of the yielding structures. Two alternative displacement based methods for damper design are herein proposed. Both methods have been validated through non linear time history analyses with spectrum compatible accelerograms. Finally ADAS arrangement for the non conventional implementation is proposed.

Valutazione dell'efficacia delle procedure di Pushover convenzionali, modali ed adattive applicate a telai piani in c.a. regolari ed irregolari in elevazione.

The research performed during the PhD and presented in this thesis, allowed to make judgments on pushover analysis method about its application in evaluating the correct structural seismic response. In this sense, the extensive critical review of existing pushover procedures (illustrated in chapter 1) outlined their major issues related to assumptions and to hypothesis made in the application of the method. Therefore, with the purpose of evaluate the effectiveness of pushover procedures, a wide numerical investigation have been performed. In particular the attention has been focused on the structural irregularity on elevation, on the choice of the load vector and on its updating criteria. In the study eight pushover procedures have been considered, of which four are conventional type, one is multi-modal, and three are adaptive. The evaluation of their effectiveness in the identification of the correct dynamic structural response, has been done by performing several dynamic and static non-linear analysis on eight RC frames, characterized by different proprieties in terms of regularity in elevation. The comparisons of static and dynamic results have then permitted to evaluate the examined pushover procedures and to identify the expected margin of error by using each of them. Both on base shear-top displacement curves and on considered storey parameters, the best agreement with the dynamic response has been noticed on Multi-Modal Pushover procedure. Therefore the attention has been focused on Displacement-based Adative Pushover, coming to define for it an improvement strategy, and on modal combination rules, advancing an innovative method based on a quadratic combination of the modal shapes (QMC). This latter has been implemented in a conventional pushover procedure, whose results have been compared with those obtained by other multi-modal procedures. The development of research on pushover analysis is very important because the objective is to come to the definition of a simple, effective and reliable analysis method, indispensable tool in the seismic evaluation of new or existing structures.

Collective effects for the LHC injectors: non-ultrarelativistic approaches

The upgrade of the CERN accelerator complex has been planned in order to further increase the LHC performances in exploring new physics frontiers. One of the main limitations to the upgrade is represented by the collective instabilities. These are intensity dependent phenomena triggered by electromagnetic fields excited by the interaction of the beam with its surrounding. These fields are represented via wake fields in time domain or impedances in frequency domain. Impedances are usually studied assuming ultrarelativistic bunches while we mainly explored low and medium energy regimes in the LHC injector chain. In a non-ultrarelativistic framework we carried out a complete study of the impedance structure of the PSB which accelerates proton bunches up to 1.4 GeV. We measured the imaginary part of the impedance which creates betatron tune shift. We introduced a parabolic bunch model which together with dedicated measurements allowed us to point to the resistive wall impedance as the source of one of the main PSB instability. These results are particularly useful for the design of efficient transverse instability dampers. We developed a macroparticle code to study the effect of the space charge on intensity dependent instabilities. Carrying out the analysis of the bunch modes we proved that the damping effects caused by the space charge, which has been modelled with semi-analytical method and using symplectic high order schemes, can increase the bunch intensity threshold. Numerical libraries have been also developed in order to study, via numerical simulations of the bunches, the impedance of the whole CERN accelerator complex. On a different note, the experiment CNGS at CERN, requires high-intensity beams. We calculated the interpolating Hamiltonian of the beam for highly non-linear lattices. These calculations provide the ground for theoretical and numerical studies aiming to improve the CNGS beam extraction from the PS to the SPS.

Application of reactive fluid transport modeling to hydrothermal systems

A one-dimensional multi-component reactive fluid transport algorithm, 1DREACT (Steefel, 1993) was used to investigate different fluid-rock interaction systems. A major short coming of mass transport calculations which include mineral reactions is that solid solutions occurring in many minerals are not treated adequately. Since many thermodynamic models of solid solutions are highly non-linear, this can seriously impact on the stability and efficiency of the solution algorithms used. Phase petrology community saw itself faced with a similar predicament 10 years ago. To improve performance and reliability, phase equilibrium calculations have been using pseudo compounds. The same approach is used here in the first, using the complex plagioclase solid solution as an example. Thermodynamic properties of a varying number of intermediate plagioclase phases were calculated using ideal molecular, Al-avoidance, and non-ideal mixing models. These different mixing models can easily be incorporated into the simulations without modification of the transport code. Simulation results show that as few as nine intermediate compositions are sufficient to characterize the diffusional profile between albite and anorthite. Hence this approach is very efficient, and can be used with little effort. A subsequent chapter reports the results of reactive fluid transport modeling designed to constrain the hydrothermal alteration of Paleoproterozoic sediments of the Southern Lake Superior region. Field observations reveal that quartz-pyrophyllite (or kaolinite) bearing assemblages have been transformed into muscovite-pyrophyllite-diaspore bearing assemblages due to action of fluids migrating along permeable flow channels. Fluid-rock interaction modeling with an initial qtz-prl assemblage and a K-rich fluid simulates the formation of observed mineralogical transformation. The bulk composition of the system evolves from an SiO2-rich one to an Al2O3+K2O-rich one. Simulations show that the fluid flow was up-temperature (e.g. recharge) and that fluid was K-rich. Pseudo compound approach to include solid solutions in reactive transport models was tested in modeling hydrothermal alteration of Icelandic basalts. Solid solutions of chlorites, amphiboles and plagioclase were included as the secondary mineral phases. Saline and fresh water compositions of geothermal fluids were used to investigate the effect of salinity on alteration. Fluid-rock interaction simulations produce the observed mineral transformations. They show that roughly the same alteration minerals are formed due to reactions with both types of fluid which is in agreement with the field observations. A final application is directed towards the remediation of nitrate rich groundwaters. Removal of excess nitrate from groundwater by pyrite oxidation was modeled using the reactive fluid transport algorithm. Model results show that, when a pyrite-bearing, permeable zone is placed in the flow path, nitrate concentration in infiltrating water can be significantly lowered, in agreement with proposals from the literature. This is due to nitrogen reduction. Several simulations investigate the efficiency of systems with different mineral reactive surface areas, reactive barrier zone widths, and flow rates to identify the optimum setup.

Rheology and Fourier-transform rheology on water-based systems

The influence of shear fields on water-based systems was investigated within this thesis. The non-linear rheological behaviour of spherical and rod-like particles was examined with Fourier-Transform rheology under LAOS conditions. As a model system for spherical particles two different kinds of polystyrene dispersions, with a solid content higher than 0.3 each, were synthesised within this work. Due to the differences in polydispersity and Debye-length, differences were also found in the rheology. In the FT-rheology both kinds of dispersions showed a similar rise in the intensities of the magnitudes of the odd higher harmonics, which were predicted by a model. The in some cases additionally appearing second harmonics were not predicted. A novel method to analyse the time domain signal was developed, that splits the time domain signal up in four characteristic functions. Those characteristic functions correspond to rheological phenomena. In some cases the intensities of the Fourier components can interfere negatively. FD-virus particles were used as a rod-like model system, which already shows a highly non-linear behaviour at concentrations below 1. % wt. Predictions for the dependence of the higher harmonics from the strain amplitude described the non-linear behaviour well at large, but no so good at small strain amplitudes. Additionally the trends of the rheological behaviour could be described by a theory for rod-like particles. An existing rheo-optical set-up was enhanced by reducing the background birefringence by a factor of 20 and by increasing the time resolution by a factor of 24. Additionally a combination of FT-rheology and rheo-optics was achieved. The influence of a constant shear field on the crystallisation process of zinc oxide in the presence of a polymer was examined. The crystallites showed a reduction in length by a factor of 2. The directed addition of polymers in combination with a defined shear field can be an easy way for a defined change of the form of crystallites.

Electrothermal characterization and nonlinear modelling of GaN transistors for telecommunication circuit design

This thesis starts showing the main characteristics and application fields of the AlGaN/GaN HEMT technology, focusing on reliability aspects essentially due to the presence of low frequency dispersive phenomena which limit in several ways the microwave performance of this kind of devices. Based on an equivalent voltage approach, a new low frequency device model is presented where the dynamic nonlinearity of the trapping effect is taken into account for the first time allowing considerable improvements in the prediction of very important quantities for the design of power amplifier such as power added efficiency, dissipated power and internal device temperature. An innovative and low-cost measurement setup for the characterization of the device under low-frequency large-amplitude sinusoidal excitation is also presented. This setup allows the identification of the new low frequency model through suitable procedures explained in detail. In this thesis a new non-invasive empirical method for compact electrothermal modeling and thermal resistance extraction is also described. The new contribution of the proposed approach concerns the non linear dependence of the channel temperature on the dissipated power. This is very important for GaN devices since they are capable of operating at relatively high temperatures with high power densities and the dependence of the thermal resistance on the temperature is quite relevant. Finally a novel method for the device thermal simulation is investigated: based on the analytical solution of the tree-dimensional heat equation, a Visual Basic program has been developed to estimate, in real time, the temperature distribution on the hottest surface of planar multilayer structures. The developed solver is particularly useful for peak temperature estimation at the design stage when critical decisions about circuit design and packaging have to be made. It facilitates the layout optimization and reliability improvement, allowing the correct choice of the device geometry and configuration to achieve the best possible thermal performance.

Advanced signal and receiver design for next generation OFDM systems

This thesis deal with the design of advanced OFDM systems. Both waveform and receiver design have been treated. The main scope of the Thesis is to study, create, and propose, ideas and novel design solutions able to cope with the weaknesses and crucial aspects of modern OFDM systems. Starting from the the transmitter side, the problem represented by low resilience to non-linear distortion has been assessed. A novel technique that considerably reduces the Peak-to-Average Power Ratio (PAPR) yielding a quasi constant signal envelope in the time domain (PAPR close to 1 dB) has been proposed.The proposed technique, named Rotation Invariant Subcarrier Mapping (RISM),is a novel scheme for subcarriers data mapping,where the symbols belonging to the modulation alphabet are not anchored, but maintain some degrees of freedom. In other words, a bit tuple is not mapped on a single point, rather it is mapped onto a geometrical locus, which is totally or partially rotation invariant. The final positions of the transmitted complex symbols are chosen by an iterative optimization process in order to minimize the PAPR of the resulting OFDM symbol. Numerical results confirm that RISM makes OFDM usable even in severe non-linear channels. Another well known problem which has been tackled is the vulnerability to synchronization errors. Indeed in OFDM system an accurate recovery of carrier frequency and symbol timing is crucial for the proper demodulation of the received packets. In general, timing and frequency synchronization is performed in two separate phases called PRE-FFT and POST-FFT synchronization. Regarding the PRE-FFT phase, a novel joint symbol timing and carrier frequency synchronization algorithm has been presented. The proposed algorithm is characterized by a very low hardware complexity, and, at the same time, it guarantees very good performance in in both AWGN and multipath channels. Regarding the POST-FFT phase, a novel approach for both pilot structure and receiver design has been presented. In particular, a novel pilot pattern has been introduced in order to minimize the occurrence of overlaps between two pattern shifted replicas. This allows to replace conventional pilots with nulls in the frequency domain, introducing the so called Silent Pilots. As a result, the optimal receiver turns out to be very robust against severe Rayleigh fading multipath and characterized by low complexity. Performance of this approach has been analytically and numerically evaluated. Comparing the proposed approach with state of the art alternatives, in both AWGN and multipath fading channels, considerable performance improvements have been obtained. The crucial problem of channel estimation has been thoroughly investigated, with particular emphasis on the decimation of the Channel Impulse Response (CIR) through the selection of the Most Significant Samples (MSSs). In this contest our contribution is twofold, from the theoretical side, we derived lower bounds on the estimation mean-square error (MSE) performance for any MSS selection strategy,from the receiver design we proposed novel MSS selection strategies which have been shown to approach these MSE lower bounds, and outperformed the state-of-the-art alternatives. Finally, the possibility of using of Single Carrier Frequency Division Multiple Access (SC-FDMA) in the Broadband Satellite Return Channel has been assessed. Notably, SC-FDMA is able to improve the physical layer spectral efficiency with respect to single carrier systems, which have been used so far in the Return Channel Satellite (RCS) standards. However, it requires a strict synchronization and it is also sensitive to phase noise of local radio frequency oscillators. For this reason, an effective pilot tone arrangement within the SC-FDMA frame, and a novel Joint Multi-User (JMU) estimation method for the SC-FDMA, has been proposed. As shown by numerical results, the proposed scheme manages to satisfy strict synchronization requirements and to guarantee a proper demodulation of the received signal.

Refined Estimation of Earthquake Source Parameters: Methods, Applications and Scaling Relationships

The objective of this work of thesis is the refined estimations of source parameters. To such a purpose we used two different approaches, one in the frequency domain and the other in the time domain. In frequency domain, we analyzed the P- and S-wave displacement spectra to estimate spectral parameters, that is corner frequencies and low frequency spectral amplitudes. We used a parametric modeling approach which is combined with a multi-step, non-linear inversion strategy and includes the correction for attenuation and site effects. The iterative multi-step procedure was applied to about 700 microearthquakes in the moment range 1011-1014 N•m and recorded at the dense, wide-dynamic range, seismic networks operating in Southern Apennines (Italy). The analysis of the source parameters is often complicated when we are not able to model the propagation accurately. In this case the empirical Green function approach is a very useful tool to study the seismic source properties. In fact the Empirical Green Functions (EGFs) consent to represent the contribution of propagation and site effects to signal without using approximate velocity models. An EGF is a recorded three-component set of time-histories of a small earthquake whose source mechanism and propagation path are similar to those of the master event. Thus, in time domain, the deconvolution method of Vallée (2004) was applied to calculate the source time functions (RSTFs) and to accurately estimate source size and rupture velocity. This technique was applied to 1) large event, that is Mw=6.3 2009 L’Aquila mainshock (Central Italy), 2) moderate events, that is cluster of earthquakes of 2009 L’Aquila sequence with moment magnitude ranging between 3 and 5.6, 3) small event, i.e. Mw=2.9 Laviano mainshock (Southern Italy).

Fiber-Optic Technologies for Wireline and Wireless In-building Networks

This doctoral dissertation aims to establish fiber-optic technologies overcoming the limiting issues of data communications in indoor environments. Specific applications are broadband mobile distribution in different in-building scenarios and high-speed digital transmission over short-range wired optical systems. Two key enabling technologies are considered: Radio over Fiber (RoF) techniques over standard silica fibers for distributed antenna systems (DAS) and plastic optical fibers (POFs) for short-range communications. Hence, the objectives and achievements of this thesis are related to the application of RoF and POF technologies in different in-building scenarios. On one hand, a theoretical and experimental analysis combined with demonstration activities has been performed on cost-effective RoF systems. An extensive modeling on modal noise impact both on linear and non-linear characteristics of RoF link over silica multimode fiber has been performed to achieve link design rules for an optimum choice of the transmitter, receiver and launching technique. A successful transmission of Long Term Evolution (LTE) mobile signals on the resulting optimized RoF system over silica multimode fiber employing a Fabry-Perot LD, central launch technique and a photodiode with a built-in ball lens was demonstrated up to 525m with performances well compliant with standard requirements. On the other hand, digital signal processing techniques to overcome the bandwidth limitation of POF have been investigated. An uncoded net bit-rate of 5.15Gbit/s was obtained on a 50m long POF link employing an eye-safe transmitter, a silicon photodiode, and DMT modulation with bit and power loading algorithm. With the insertion of 3x2N quadrature amplitude modulation constellation formats, an uncoded net-bit-rate of 5.4Gbit/s was obtained on a 50 m long POF link employing an eye-safe transmitter and a silicon avalanche photodiode. Moreover, simultaneous transmission of baseband 2Gbit/s with DMT and 200Mbit/s with an ultra-wideband radio signal has been validated over a 50m long POF link.

Comportamento dinamico fuori del piano di pareti murarie: influenza della deformabilità degli impalcati

The aim of this study was to investigate the influence of the diaphragm flexibility on the behavior of out-of-plane walls in masonry buildings. Simplified models have been developed to perform kinematic and dynamic analyses in order to compare the response of walls with different restraint conditions. Kinematic non linear analyses of assemblages of rigid blocks have been performed to obtain the acceleration-displacement curves for walls with different restraint conditions at the top. A simplified 2DOF model has been developed to analyse the dynamic response of the wall with an elastic spring at the top, following the Housner rigid behaviour hypothesis. The dissipation of energy is concentrated at every impact at the base of the wall and is modelled through the introduction of the coefficient of restitution. The sets of equations of the possible configurations of the wall, depending on the different positions of the centre of rotation at the base and at the intermediate hinge have been obtained. An algorithm for the numerical integration of the sets of the equations of motion in the time domain has been developed. Dynamic analyses of a set of walls with Gaussian impulses and recorded accelerograms inputs have been performed in order to compare the response of the simply supported wall with the one of the wall with elastic spring at the top. The influence of diaphragm stiffness Kd has been investigated determining the variation of maximum displacement demand with the value of Kd. A more regular trend has been obtained for the Gaussian input than for the recorded accelerograms.

Nicht-wässrige Emulsionspolymerisationen

Die vorliegende Arbeit beschäftigt sich mit der Darstellung von Latexpartikeln in nicht-wässrigen Emulsionssystemen. Hintergrund der Untersuchungen war die Frage, ob es durch die Anwendung von nicht-wässrigen Emulsionen ermöglicht werden kann, sowohl wassersensitive Monomere als auch feuchtigkeitsempfindliche Polymerisationen zur Darstellung von Polymer-Latexpartikeln und deren Primärdispersionen einzusetzen. Das Basiskonzept der Arbeit bestand darin, nicht-wässrige Emulsionen auf der Basis zweier nicht mischbarer organischer Lösungsmittel unterschiedlicher Polarität auszubilden und anschließend die dispergierte Phase der Emulsion zur Synthese der Latexpartikel auszunutzen. Hierzu wurden verschiedene nicht-wässrige Emulsionssysteme erarbeitet, welche als dispergierte Phase ein polares und als kontinuierliche Phase ein unpolares Lösungsmittel enthielten. Auf Basis dieser Ergebnisse wurde in den nachfolgenden Untersuchungen zunächst die Anwendbarkeit solcher Emulsionen zur Darstellung verschiedener Acrylat- und Methacrylatpolymerdispersionen mittels radikalischer Polymerisation studiert. Um zu zeigen, dass die hier entwickelten nicht-wässrigen Emulsionen auch zur Durchführung von Stufenwachstumsreaktionen geeignet sind, wurden ebenfalls Polyester-, Polyamid- und Polyurethan-Latexpartikel dargestellt. Die Molekulargewichte der erhaltenen Polymere lagen bei bis zu 40 000 g/mol, im Vergleich zu wässrigen Emulsions- und Miniemulsions¬polymerisationssystemen sind diese um den Faktor fünf bis 30 höher. Es kann davon ausgegangen werden, dass hauptsächlich zwei Faktoren für die hohen Molekulargewichte verantwortlich sind: Zum einen die wasserfreien Bedingungen, welche die Hydrolyse der reaktiven Gruppen verhindern, und zum anderen die teilweise erfüllten Schotten-Baumann-Bedingungen, welche an der Grenzfläche zwischen dispergierter und kontinuierlicher Phase eine durch Diffusion kontrollierte ausgeglichene Stöchiometrie der Reaktionspartner gewährleisten. Somit ist es erstmals möglich, hochmolekulare Polyester, -amide und -urethane in nur einem Syntheseschritt als Primär¬dispersion darzustellen. Die Variabilität der nicht-wässrigen Emulsionen wurde zudem in weiteren Beispielen durch die Synthese von verschiedenen elektrisch leitfähigen Latices, wie z.B. Polyacetylen-Latexpartikeln, aufgezeigt. In dieser Arbeit konnte gezeigt werden, dass die entwickelten nicht-wässrigen Emulsionen eine äußerst breite Anwendbarkeit zur Darstellung von Polymer-Latexpartikeln aufweisen. Durch die wasserfreien Bedingungen erlauben die beschriebenen Emulsionsprozesse, Latexpartikel und entsprechende nicht-wässrige Dispersionen nicht nur traditionell radikalisch, sondern auch mittels weiterer Polymerisationsmechanismen (katalytisch, oxidativ oder mittels Polykondensation bzw. -addition) darzustellen.

Constraint based methods for allocation and scheduling of periodic applications

This work presents exact algorithms for the Resource Allocation and Cyclic Scheduling Problems (RA&CSPs). Cyclic Scheduling Problems arise in a number of application areas, such as in hoist scheduling, mass production, compiler design (implementing scheduling loops on parallel architectures), software pipelining, and in embedded system design. The RA&CS problem concerns time and resource assignment to a set of activities, to be indefinitely repeated, subject to precedence and resource capacity constraints. In this work we present two constraint programming frameworks facing two different types of cyclic problems. In first instance, we consider the disjunctive RA&CSP, where the allocation problem considers unary resources. Instances are described through the Synchronous Data-flow (SDF) Model of Computation. The key problem of finding a maximum-throughput allocation and scheduling of Synchronous Data-Flow graphs onto a multi-core architecture is NP-hard and has been traditionally solved by means of heuristic (incomplete) algorithms. We propose an exact (complete) algorithm for the computation of a maximum-throughput mapping of applications specified as SDFG onto multi-core architectures. Results show that the approach can handle realistic instances in terms of size and complexity. Next, we tackle the Cyclic Resource-Constrained Scheduling Problem (i.e. CRCSP). We propose a Constraint Programming approach based on modular arithmetic: in particular, we introduce a modular precedence constraint and a global cumulative constraint along with their filtering algorithms. Many traditional approaches to cyclic scheduling operate by fixing the period value and then solving a linear problem in a generate-and-test fashion. Conversely, our technique is based on a non-linear model and tackles the problem as a whole: the period value is inferred from the scheduling decisions. The proposed approaches have been tested on a number of non-trivial synthetic instances and on a set of realistic industrial instances achieving good results on practical size problem.