Max Bill in Italia . Lo spazio logico dell'architettura

I Max Bill is an intense giornata of a big fresco. An analysis of the main social, artistic and cultural events throughout the twentieth century is needed in order to trace his career through his masterpieces and architectures. Some of the faces of this hypothetical mural painting are, among others, Le Corbusier, Walter Gropius, Ernesto Nathan Rogers, Kandinskij, Klee, Mondrian, Vatongerloo, Ignazio Silone, while the backcloth is given by artistic avant-gardes, Bauhaus, International Exhibitions, CIAM, war events, reconstruction, Milan Triennali, Venice Biennali, the School of Ulm. Architect, even though more known as painter, sculptor, designer and graphic artist, Max Bill attends the Bauhaus as a student in the years 1927-1929, and from this experience derives the main features of a rational, objective, constructive and non figurative art. His research is devoted to give his art a scientific methodology: each work proceeds from the analysis of a problem to the logical and always verifiable solution of the same problem. By means of composition elements (such as rhythm, seriality, theme and its variation, harmony and dissonance), he faces, with consistent results, themes apparently very distant from each other as the project for the H.f.G. or the design for a font. Mathematics are a constant reference frame as field of certainties, order, objectivity: ���for Bill mathematics are never confined to a simple function: they represent a climate of spiritual certainties, and also the theme of non attempted in its purest state, objectivity of the sign and of the geometrical place, and at the same time restlessness of the infinity: Limited and Unlimited ���. In almost sixty years of activity, experiencing all artistic fields, Max Bill works, projects, designs, holds conferences and exhibitions in Europe, Asia and Americas, confronting himself with the most influencing personalities of the twentieth century. In such a vast scenery, the need to limit the investigation field combined with the necessity to address and analyse the unpublished and original aspect of Bill���s relations with Italy. The original contribution of the present research regards this particular ���geographic delimitation���; in particular, beyond the deep cultural exchanges between Bill and a series of Milanese architects, most of all with Rogers, two main projects have been addressed: the realt�� nuova at Milan Triennale in 1947, and the Contemporary Art Museum in Florence in 1980. It is important to note that these projects have not been previously investigated, and the former never appears in the sources either. These works, together with the most well-known ones, such as the projects for the VI and IX Triennale, and the Swiss pavilion for the Biennale, add important details to the reference frame of the relations which took place between Zurich and Milan. Most of the occasions for exchanges took part in between the Thirties and the Fifties, years during which Bill underwent a significant period of artistic growth. He meets the Swiss progressive architects and the Paris artists from the Abstraction-Cr��ation movement, enters the CIAM, collaborates with Le Corbusier to the third volume of his Complete Works, and in Milan he works and gets confronted with the events related to post-war reconstruction. In these years Bill defines his own working methodology, attaining an artistic maturity in his work. The present research investigates the mentioned time period, despite some necessary exceptions. II The official Max Bill bibliography is naturally wide, including spreading works along with ones more devoted to analytical investigation, mainly written in German and often translated into French and English (Max Bill himself published his works in three languages). Few works have been published in Italian and, excluding the catalogue of the Parma exhibition from 1977, they cannot be considered comprehensive. Many publications are exhibition catalogues, some of which include essays written by Max Bill himself, some others bring Bill���s comments in a educational-pedagogical approach, to accompany the observer towards a full understanding of the composition processes of his art works. Bill also left a great amount of theoretical speculations to encourage a critical reading of his works in the form of books edited or written by him, and essays published in ���Werk���, magazine of the Swiss Werkbund, and other international reviews, among which Domus and Casabella. These three reviews have been important tools of analysis, since they include tracks of some of Max Bill���s architectural works. The architectural aspect is less investigated than the plastic and pictorial ones in all the main reference manuals on the subject: Benevolo, Tafuri and Dal Co, Frampton, Allenspach consider Max Bill as an artist proceeding in his work from Bauhaus in the Ulm experience . A first filing of his works was published in 2004 in the monographic issue of the Spanish magazine 2G, together with critical essays by Karin Gimmi, Stanislaus von Moos, Arthur R��egg and Hans Frei, and in ���Konkrete Architektur?���, again by Hans Frei. Moreover, the monographic essay on the Atelier Haus building by Arthur R��egg from 1997, and the DPA 17 issue of the Catalonia Polytechnic with contributions of Carlos Mart��, Bruno Reichlin and Ton Salvad��, the latter publication concentrating on a few Bill���s themes and architectures. An urge to studying and going in depth in Max Bill���s works was marked in 2008 by the centenary of his birth and by a recent rediscovery of Bill as initiator of the ���minimalist��� tradition in Swiss architecture. Bill���s heirs are both very active in promoting exhibitions, researching and publishing. Jakob Bill, Max Bill���s son and painter himself, recently published a work on Bill���s experience in Bauhaus, and earlier on he had published an in-depth study on ���Endless Ribbons��� sculptures. Angela Thomas Schmid, Bill���s wife and art historian, published in end 2008 the first volume of a biography on Max Bill and, together with the film maker Eric Schmid, produced a documentary film which was also presented at the last Locarno Film Festival. Both biography and documentary concentrate on Max Bill���s political involvement, from antifascism and 1968 protest movements to Bill experiences as Zurich Municipality councilman and member of the Swiss Confederation Parliament. In the present research, the bibliography includes also direct sources, such as interviews and original materials in the form of letters correspondence and graphic works together with related essays, kept in the max+binia+jakob bill stiftung archive in Zurich. III The results of the present research are organized into four main chapters, each of them subdivided into four parts. The first chapter concentrates on the research field, reasons, tools and methodologies employed, whereas the second one consists of a short biographical note organized by topics, introducing the subject of the research. The third chapter, which includes unpublished events, traces the historical and cultural frame with particular reference to the relations between Max Bill and the Italian scene, especially Milan and the architects Rogers and Baldessari around the Fifties, searching the themes and the keys for interpretation of Bill���s architectures and investigating the critical debate on the reviews and the plastic survey through sculpture. The fourth and last chapter examines four main architectures chosen on a geographical basis, all devoted to exhibition spaces, investigating Max Bill���s composition process related to the pictorial field. Paintings has surely been easier and faster to investigate and verify than the building field. A doctoral thesis discussed in Lausanne in 1977 investigating Max Bill���s plastic and pictorial works, provided a series of devices which were corrected and adapted for the definition of the interpretation grid for the composition structures of Bill���s main architectures. Four different tools are employed in the investigation of each work: a context analysis related to chapter three results; a specific theoretical essay by Max Bill briefly explaining his main theses, even though not directly linked to the very same work of art considered; the interpretation grid for the composition themes derived from a related pictorial work; the architecture drawing and digital three-dimensional model. The double analysis of the architectural and pictorial fields is functional to underlining the relation among the different elements of the composition process; the two fields, however, cannot be compared and they stay, in Max Bill���s works as in the present research, interdependent though self-sufficient. IV An important aspect of Max Bill production is self-referentiality: talking of Max Bill, also through Max Bill, as a need for coherence instead of a method limitation. Ernesto Nathan Rogers describes Bill as the last humanist, and his horizon is the known world but, as the ���Concrete Art��� of which he is one of the main representatives, his production justifies itself: Max Bill not only found a method, but he autonomously re-wrote the ���rules of the game���, derived timeless theoretical principles and verified them through a rich and interdisciplinary artistic production. The most recurrent words in the present research work are synthesis, unity, space and logic. These terms are part of Max Bill���s vocabulary and can be referred to his works. Similarly, graphic settings or analytical schemes in this research text referring to or commenting Bill���s architectural projects were drawn up keeping in mind the concise precision of his architectural design. As for Mies van der Rohe, it has been written that Max Bill took art to ���zero degree��� reaching in this way a high complexity. His works are a synthesis of art: they conceptually encompass all previous and ���considered their developments- most of contemporary pictures. Contents and message are generally explicitly declared in the title or in Bill���s essays on his artistic works and architectural projects: the beneficiary is invited to go through and re-build the process of synthesis generating the shape. In the course of the interview with the Milan artist Getulio Alviani, he tells how he would not write more than a page for an essay on Josef Albers: everything was already evident ���on the surface��� and any additional sentence would be redundant. Two years after that interview, these pages attempt to decompose and single out the elements and processes connected with some of Max Bill���s works which, for their own origin, already contain all possible explanations and interpretations. The formal reduction in favour of contents maximization is, perhaps, Max Bill���s main lesson.

Physiology and Biotechnology of the Hydrogen Production with the Green Microalga Chlamydomonas reinhardtii

The hydrogen production in the green microalga Chlamydomonas reinhardtii was evaluated by means of a detailed physiological and biotechnological study. First, a wide screening of the hydrogen productivity was done on 22 strains of C. reinhardtii, most of which mutated at the level of the D1 protein. The screening revealed for the first time that mutations upon the D1 protein may result on an increased hydrogen production. Indeed, productions ranged between 0 and more than 500 mL hydrogen per liter of culture (Torzillo, Scoma et al., 2007a), the highest producer (L159I-N230Y) being up to 5 times more performant than the strain cc124 widely adopted in literature (Torzillo, Scoma, et al., 2007b). Improved productivities by D1 protein mutants were generally a result of high photosynthetic capabilities counteracted by high respiration rates. Optimization of culture conditions were addressed according to the results of the physiological study of selected strains. In a first step, the photobioreactor (PBR) was provided with a multiple-impeller stirring system designed, developed and tested by us, using the strain cc124. It was found that the impeller system was effectively able to induce regular and turbulent mixing, which led to improved photosynthetic yields by means of light/dark cycles. Moreover, improved mixing regime sustained higher respiration rates, compared to what obtained with the commonly used stir bar mixing system. As far as the results of the initial screening phase are considered, both these factors are relevant to the hydrogen production. Indeed, very high energy conversion efficiencies (light to hydrogen) were obtained with the impeller device, prooving that our PBR was a good tool to both improve and study photosynthetic processes (Giannelli, Scoma et al., 2009). In the second part of the optimization, an accurate analysis of all the positive features of the high performance strain L159I-N230Y pointed out, respect to the WT, it has: (1) a larger chlorophyll optical cross-section; (2) a higher electron transfer rate by PSII; (3) a higher respiration rate; (4) a higher efficiency of utilization of the hydrogenase; (5) a higher starch synthesis capability; (6) a higher per cell D1 protein amount; (7) a higher zeaxanthin synthesis capability (Torzillo, Scoma et al., 2009). These information were gathered with those obtained with the impeller mixing device to find out the best culture conditions to optimize productivity with strain L159I-N230Y. The main aim was to sustain as long as possible the direct PSII contribution, which leads to hydrogen production without net CO2 release. Finally, an outstanding maximum rate of 11.1 �� 1.0 mL/L/h was reached and maintained for 21.8 �� 7.7 hours, when the effective photochemical efficiency of PSII (��F/F'm) underwent a last drop to zero. If expressed in terms of chl (24.0 �� 2.2 ��moles/mg chl/h), these rates of production are 4 times higher than what reported in literature to date (Scoma et al., 2010a submitted). DCMU addition experiments confirmed the key role played by PSII in sustaining such rates. On the other hand, experiments carried out in similar conditions with the control strain cc124 showed an improved final productivity, but no constant PSII direct contribution. These results showed that, aside from fermentation processes, if proper conditions are supplied to selected strains, hydrogen production can be substantially enhanced by means of biophotolysis. A last study on the physiology of the process was carried out with the mutant IL. Although able to express and very efficiently utilize the hydrogenase enzyme, this strain was unable to produce hydrogen when sulfur deprived. However, in a specific set of experiments this goal was finally reached, pointing out that other than (1) a state 1-2 transition of the photosynthetic apparatus, (2) starch storage and (3) anaerobiosis establishment, a timely transition to the hydrogen production is also needed in sulfur deprivation to induce the process before energy reserves are driven towards other processes necessary for the survival of the cell. This information turned out to be crucial when moving outdoor for the hydrogen production in a tubular horizontal 50-liter PBR under sunlight radiation. First attempts with laboratory grown cultures showed that no hydrogen production under sulfur starvation can be induced if a previous adaptation of the culture is not pursued outdoor. Indeed, in these conditions the hydrogen production under direct sunlight radiation with C. reinhardtii was finally achieved for the first time in literature (Scoma et al., 2010b submitted). Experiments were also made to optimize productivity in outdoor conditions, with respect to the light dilution within the culture layers. Finally, a brief study of the anaerobic metabolism of C. reinhardtii during hydrogen oxidation has been carried out. This study represents a good integration to the understanding of the complex interplay of pathways that operate concomitantly in this microalga.

Bestimmung der Ionisationsenergie von Actinium und Ultraspurenanalyse von Plutonium mit resonanter Ionisationsmassenspektrometrie (RIMS)

ZusammenfassungDie Resonanzionisationsmassenspektrometrie (RIMS) verbindet hohe Elementselektivit��t mit guter Nachweiseffizienz. Aufgrund dieser Eigenschaften ist die Methode f��r Ultraspurenanalyse und Untersuchungen an seltenen oder schwer handhabbaren Elementen gut geeignet. F��r RIMS werden neutrale Atome mit monochromatischem Laserlicht ein- oder mehrfach resonant auf energetisch hoch liegende Niveaus angeregt und anschlie��end durch einen weiteren Laserstrahl oder durch ein elektrisches Feld ionisiert. Die Photoionen werden in einem Massenspektrometer massenselektiv registriert.Ein Beispiel f��r die Anwendung von RIMS ist die pr��zise Bestimmung der Ionisationsenergie als fundamentale physikalisch-chemische Eigenschaft eines bestimmten Elements; insbesondere bei den Actinoiden ist die Kenntnis der Ionisationsenergie von Interesse, da es dort bis zur Anwendung der laser-massenspektroskopischer Methode nur wenige experimentelle Daten gab. Die Bestimmung der Ionisationsenergie erfolgt durch die Methode der Photoionisation im elektrischen Feld gem���� dem klassischen Sattelpunktsmodell. Im Experiment werden neutrale Atome in einem Atomstrahl mittels Laserlicht zun��chst resonant angeregt. Die angeregten Atome befinden sich in einem ��u��eren, statischen elektrischen Feld und werden durch einen weiteren Laserstrahl, dessen Wellenl��nge durchgestimmt wird, ionisiert. Das ��berschreiten der Laserschwelle macht sich durch einen starken Anstieg im Ionensignal bemerkbar. Man f��hrt diese Messung bei verschiedenen elektrischen Feldst��rken durch und erh��lt bei Auftragen der Ionisationsschwellen gegen die Wurzel der elektrischen Feldst��rke durch Extrapolation auf die Feldst��rke Null die Ionisationsenergie.Im Rahmen dieser Arbeit wurde die Ionisationsenergie von Actinium erstmalig zu 43398(3) cm-1 �� 5,3807(4) eV experimentell bestimmt. Dazu wurden Actiniumatome zun��chst einstufig resonant mit einem Laser mit einer Wellenl��nge von 388,67 nm auf einen Zustand bei 25729,03 cm-1 angeregt und anschlie��end mit Laserlicht mit einer Wellenl��nge von ca. 568 nm ionisiert. Damit sind die Ionisationsenergien aller Actinoiden bis einschlie��lich Einsteinium mit Ausnahme von Protactinium bekannt. Als Atomstrahlquelle wird ein spezielles 'Sandwichfilament' benutzt, bei dem das Actinoid als Hydroxid auf eine Tantalfolie aufgebracht und mit einer reduzierenden Deckschicht ��berzogen wird. Das Actinoid dampft bei Heizen dieser Anordnung atomar ab. Bei den schwereren Actinoiden wurde Titan als Deckschicht verwendet. Um einen Actiniumatomstrahl zu erzeugen, wurde aufgrund der hohen Abdampftemperaturen statt Titan erstmals Zirkonium eingesetzt. Bei Protactinium wurde Thorium, welches noch st��rkere Reduktionseigenschaften aufweist, als Deckmaterial eingesetzt. Trotzdem gelang es mit der 'Sandwichtechnik' nicht, einen Protactiniumatomstrahl zu erzeugen. In der Flugzeitapparatur wurde lediglich ein Protactinium-monoxidionensignal detektiert. Um ein erst seit kurzem verf��gbares Fest-k��rperlasersystem zu explorieren, wurden zus��tzlich noch die bekannten Ionisations-ener-gien von Gadolinium und Plutonium erneut bestimmt. Die gemessenen Werte stimmen mit Literaturdaten gut ��berein.Ferner wurde noch ein bestehender Trennungsgang f��r Plutonium aus Umweltproben auf die Matrices Meerwasser und Hausstaub angepasst und f��r die Bestimmung von Plutonium und dessen Isotopenzusammensetzung in verschiedenen Probenreihen mittels RIMS eingesetzt. Der modifizierte Trennungsgang erm��glicht das schnelle Aufarbeiten von gro��en Probenmengen f��r Reihenuntersuchungen von Plutoniumkontaminationen. Die ermittelten Gehalten an 239Pu lagen zwischen 8,2*107 Atome pro 10 l Meerwasserprobe und 1,7*109Atome pro Gramm Staubprobe.

Influence of particle size, density and concentration on bend erosive wear in pneumatic conveyors

Particle concentration is a principal factor that affects erosion rate of solid surfaces under particle impact, such as pipe bends in pneumatic conveyors; it is well known that a reduction in the specific erosion rate occurs under high particle concentrations, a phenomenon referred to as the ���shielding effect���. The cause of shielding is believed to be increased likelihood of inter-particulate collisions, the high collision probability between incoming and rebounding particles reducing the frequency and the severity of particle impacts on the target surface. In this study, the effects of particle concentration on erosion of a mild steel bend surface have been investigated in detail using three different particulate materials on an industrial scale pneumatic conveying test rig. The materials were studied so that two had the same particle density but very different particle size, whereas two had very similar particle size but very different particle density. Experimental results confirm the shielding effect due to high particle concentration and show that the particle density has a far more significant influence than the particle size, on the magnitude of the shielding effect. A new method of correcting for change in erosivity of the particles in repeated handling, to take this factor out of the data, has been established, and appears to be successful. Moreover, a novel empirical model of the shielding effects has been used, in term of erosion resistance which appears to decrease linearly when the particle concentration decreases. With the model it is possible to find the specific erosion rate when the particle concentration tends to zero, and conversely predict how the specific erosion rate changes at finite values of particle concentration; this is critical to enable component life to be predicted from erosion tester results, as the variation of the shielding effect with concentration is different in these two scenarios. In addition a previously unreported phenomenon has been recorded, of a particulate material whose erosivity has steadily increased during repeated impacts.

Changes in the microbial community based on seawater pH variations

Ocean acidification is an effect of the rise in atmospheric CO2, which causes a reduction in the pH of the ocean and generates a number of changes in seawater chemistry and consequently potentially impacts seawater life. The effect of ocean acidification on metabolic processes (such as net community production and community respiration and on particulate organic carbon (POC) concentrations was investigated in summer 2012 at Cap de la Revellata in Corsica (Calvi, France). Coastal surface water was enclosed in 9 mesocosms and subjected to 6 pCO2 levels (3 replicated controls and 6 perturbations) for approximately one month. No trend was found in response to increasing pCO2 in any of the biological and particulate analyses. Community respiration was relatively stable throughout the experiment in all mesocosms, and net community production was most of the time close to zero. Similarly, POC concentrations were not affected by acidification during the whole experimental period. Such as the global ocean, the Mediterranean Sea has an oligotrophic nature. Based on present results, it seems likely that seawater acidification will not have significant effects on photosynthetic rates, microbial metabolism and carbon transport.

Existence of solutions and asymtptotic limits of the Euler-Poisson and the quantum drift-diffusion systems

My work concerns two different systems of equations used in the mathematical modeling of semiconductors and plasmas: the Euler-Poisson system and the quantum drift-diffusion system. The first is given by the Euler equations for the conservation of mass and momentum, with a Poisson equation for the electrostatic potential. The second one takes into account the physical effects due to the smallness of the devices (quantum effects). It is a simple extension of the classical drift-diffusion model which consists of two continuity equations for the charge densities, with a Poisson equation for the electrostatic potential. Using an asymptotic expansion method, we study (in the steady-state case for a potential flow) the limit to zero of the three physical parameters which arise in the Euler-Poisson system: the electron mass, the relaxation time and the Debye length. For each limit, we prove the existence and uniqueness of profiles to the asymptotic expansion and some error estimates. For a vanishing electron mass or a vanishing relaxation time, this method gives us a new approach in the convergence of the Euler-Poisson system to the incompressible Euler equations. For a vanishing Debye length (also called quasineutral limit), we obtain a new approach in the existence of solutions when boundary layers can appear (i.e. when no compatibility condition is assumed). Moreover, using an iterative method, and a finite volume scheme or a penalized mixed finite volume scheme, we numerically show the smallness condition on the electron mass needed in the existence of solutions to the system, condition which has already been shown in the literature. In the quantum drift-diffusion model for the transient bipolar case in one-space dimension, we show, by using a time discretization and energy estimates, the existence of solutions (for a general doping profile). We also prove rigorously the quasineutral limit (for a vanishing doping profile). Finally, using a new time discretization and an algorithmic construction of entropies, we prove some regularity properties for the solutions of the equation obtained in the quasineutral limit (for a vanishing pressure). This new regularity permits us to prove the positivity of solutions to this equation for at least times large enough.

Surface layer formation in polymer melts and in solutions

In this work the surface layer formation in polymer melts and in polymer solutions have been investigated with the atomic force microscope (AFM). In polymer melts, the formation of an immobile surface layer results in a steric repulsion, which can be measured by the AFM. From former work it is know, that polydimethyl siloxane (PDMS) forms a stable surface layer for molecular weights above 12 kDa. In the present thesis, polyisoprene (PI) was investigated apart from PDMS, by a)measuring the steric surface interactions and b)measuring the surface slip in hydrodynamic experiments. If a polymer flows over a surface, the flow velocity at the surface is larger then zero. If case of a surface layer formation the flow plane changes to the top of the adsorbed layer and the surface slip is reduced to zero. By measuring the surface slip in hydrodynamic experiments, it is therefore possible to determine the presence of a stable surface layer. The results show no stable repulsion for PI and only a small decrease of the surface slip. This indicates that PI does not form a stable surface layer, but is only adsorbed weakly to the surface. Furthermore for 8 kDa PDMS the timescale of the formation of a surface layer was investigated by changing themaximal force the tip applied to the surface. With a repulsive force present, applying a higher force than 15 nN resulted in a destruction of the surface layer, indicated by attractive forces. Reducing the applied force below 15 nN then resulted in an increase of the repulsion to the former state during one minute, thus indicating that a surface layer can be formed within one minute even under the influence of continuous measurements. As a next step, mixtures of two PDMS homopolymers with different chain lengths have been investigated. The aim was to verify theoretical predictions that shorter chains should predominate at the surface due to their smaller loss in conformational entropy. The measurements where done in dependence of the volume fractions of short and long chain PMDS. The results confirmed the short chain dominance for all mixtures with less then 90 vol.% long chain PDMS. Surface layer formation in solution was investigated for superplasticizers which are industrially used as an additive to cement. They change the surface interaction between the cement grains from attractive to repulsive and the freshlymixed cement paste therefore becomes liquid. The aimin this part of the thesis was, to investigate cement particle interactions in a close to real environment. Therefore calcium silicate hydrate phases have been precipitated onto an AFM tip and onto a calcite crystal and the interaction between these surfaces have beenmeasured with and without addition of superplasticizers. The measurements confirmed the change from attraction to repulsion upon addition of superplasticizers. The repulsive steric interaction increased with the length of the sidechain of the superplasticizer, and the dependence of the range of the steric interactions on the sidechain length indicated that the sidechains are in a coiled conformation.

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 Schr��dinger 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.

Detection of small buried objects: asymptotic factorization and MUSIC

In this work, we consider a simple model problem for the electromagnetic exploration of small perfectly conducting objects buried within the lower halfspace of an unbounded two���layered background medium. In possible applications, such as, e.g., humanitarian demining, the two layers would correspond to air and soil. Moving a set of electric devices parallel to the surface of ground to generate a time���harmonic ���eld, the induced ���eld is measured within the same devices. The goal is to retrieve information about buried scatterers from these data. In mathematical terms, we are concerned with the analysis and numerical solution of the inverse scattering problem to reconstruct the number and the positions of a collection of ���nitely many small perfectly conducting scatterers buried within the lower halfspace of an unbounded two���layered background medium from near ���eld measurements of time���harmonic electromagnetic waves. For this purpose, we ���rst study the corresponding direct scattering problem in detail and derive an asymptotic expansion of the scattered ���eld as the size of the scatterers tends to zero. Then, we use this expansion to justify a noniterative MUSIC���type reconstruction method for the solution of the inverse scattering problem. We propose a numerical implementation of this reconstruction method and provide a series of numerical experiments.

Sensitivity analysis of a parabolic-elliptic problem

We consider the heat flux through a domain with subregions in which the thermal capacity approaches zero. In these subregions the parabolic heat equation degenerates to an elliptic one. We show the well-posedness of such parabolic-elliptic differential equations for general non-negative L-infinity-capacities and study the continuity of the solutions with respect to the capacity, thus giving a rigorous justification for modeling a small thermal capacity by setting it to zero. We also characterize weak directional derivatives of the temperature with respect to capacity as solutions of related parabolic-elliptic problems.

Dynamics, rheology and critical properties of colloidal fluid mixtures

Liquids under the influence of external fields exhibit a wide range of intriguing phenomena that can be markedly different from the behaviour of a quiescent system. This work considers two different systems ��� a glassforming Yukawa system and a colloid-polymer mixture ��� by Molecular Dynamics (MD) computer simulations coupled to dissipative particle dynamics. The former consists of a 50-50 binary mixture of differently-sized, like-charged colloids interacting via a screened Coulomb (Yukawa) potential. Near the glass transition the influence of an external shear field is studied. In particular, the transition from elastic response to plastic flow is of interest. At first, this model is characterised in equilibrium. Upon decreasing temperature it exhibits the typical dynamics of glassforming liquids, i.e. the structural relaxation time ���� grows strongly in a rather small temperature range. This is discussed with respect to the mode-coupling theory of the glass transition (MCT). For the simulation of bulk systems under shear, Lees-Edwards boundary conditions are applied. At constant shear rates ���� ��� 1/���� the relevant time scale is given by 1/���� and the system shows shear thinning behaviour. In order to understand the pronounced differences between a quiescent system and a system under shear, the response to a suddenly commencing or terminating shear flow is studied. After the switch-on of the shear field the shear stress shows an overshoot, marking the transition from elastic to plastic deformation, which is connected to a super-diffusive increase of the mean squared displacement. Since the average static structure only depends on the value of the shear stress, it does not discriminate between those two regimes. The distribution of local stresses, in contrast, becomes broader as soon as the system starts flowing. After a switch-off of the shear field, these additional fluctuations are responsible for the fast decay of stresses, which occurs on a time scale 1/���� . The stress decay after a switch-off in the elastic regime, on the other hand, happens on the much larger time scale of structural relaxation ����. While stresses decrease to zero after a switch-off for temperatures above the glass transition, they decay to a finite value for lower temperatures. The obtained results are important for advancing new theoretical approaches in the framework of mode-coupling theory. Furthermore, they suggest new experimental investigations on colloidal systems. The colloid-polymer mixture is studied in the context of the behaviour near the critical point of phase separation. For the MD simulations a new effective model with soft interaction potentials is introduced and its phase diagram is presented. Here, mainly the equilibrium properties of this model are characterised. While the self-diffusion constants of colloids and polymers do not change strongly when the critical point is approached, critical slowing down of interdiffusion is observed. The order parameter fluctuations can be determined through the long-wavelength limit of static structure factors. For this strongly asymmetric mixture it is shown how the relevant structure factor can be extracted by a diagonalisation of a matrix that contains the partial static structure factors. By presenting first results of this model under shear it is demonstrated that it is suitable for non-equilibrium simulations as well.

Teoria e pratica dell'architettura solare - Morfologia, rendimento, strategia progettuale

La recente Direttiva 31/2010 dell���Unione Europea impone agli stati membri di riorganizzare il quadro legislativo nazionale in materia di prestazione energetica degli edifici, affinch�� tutte le nuove costruzioni presentino dal 1�� gennaio 2021 un bilancio energetico tendente allo zero; termine peraltro anticipato al 1�� gennaio 2019 per gli edifici pubblici. La concezione di edifici a energia ���quasi��� zero (nZEB) parte dal presupposto di un involucro energeticamente di standard passivo per arrivare a compensare, attraverso la produzione preferibilmente in sito di energia da fonti rinnovabili, gli esigui consumi richiesti su base annuale. In quest���ottica la riconsiderazione delle potenzialit�� dell���architettura solare individua degli strumenti concreti e delle valide metodologie per supportare la progettazione di involucri sempre pi�� performanti che sfruttino pienamente una risorsa inesauribile, diffusa e alla portata di tutti come quella solare. Tutto ci�� in considerazione anche della non pi�� procrastinabile necessit�� di ridurre il carico energetico imputabile agli edifici, responsabili come noto di oltre il 40% dei consumi mondiali e del 24% delle emissioni di gas climalteranti. Secondo queste premesse la ricerca pone come centrale il tema dell���integrazione dei sistemi di guadagno termico, cosiddetti passivi, e di produzione energetica, cosiddetti attivi, da fonte solare nell���involucro architettonico. Il percorso sia analitico che operativo effettuato si �� posto la finalit�� di fornire degli strumenti metodologici e pratici al progetto dell���architettura, bisognoso di un nuovo approccio integrato mirato al raggiungimento degli obiettivi di risparmio energetico. Attraverso una ricognizione generale del concetto di architettura solare e dei presupposti teorici e terminologici che stanno alla base della stessa, la ricerca ha prefigurato tre tipologie di esito finale: una codificazione delle morfologie ricorrenti nelle realizzazioni solari, un���analisi comparata del rendimento solare nelle principali aggregazioni tipologiche edilizie e una parte importante di verifica progettuale dove sono stati applicati gli assunti delle categorie precedenti

Zweikernige 3d-��bergangsmetall-Komplexe mit Derivaten des para-Phenylendiamins als redoxaktive Br��ckenliganden

Die vorliegende Arbeit besch��ftigt sich mit der Darstellung zweikerniger Koordinationsverbindungen, bei denen zweiwertige Ionen der 3d-��bergangsmetalle ��ber einen bestimmten Liganden verbr��ckt sind. Dieser Br��ckenligand, das N,N,N���,N���-Tetrakis-(2-methylpyridyl)-benzol-1,4-diamin (TPBD), besteht aus einem p-Phenylendiamin-Ger��st, an dessen Stickstoffe je zwei Methylpyridin-Gruppen gebunden sind. In diesen zwei jeweils dreiz��hnigen Bindungstaschen wurden 3d-��bergangsmetallionen komplexiert, wobei deren Koordinationssph��re mit einem zweiz��hnigen capping-Liganden vom Typ des 1,10-Phenanthrolins und einem einz��hnigen dritten Liganden abges��ttigt wird. Die strukturellen, magnetischen und elektronischen Eigenschaften der so erhaltenen homometallischen Komplexe mit Mn(II), Fe(II), Co(II), Ni(II), Cu(II) und Zn(II) wurden untersucht. Dabei wurde besonderes Augenmerk auf die Ver��nderung dieser Eigenschaften bei dem Einsatz unterschiedlicher capping- und dritter Liganden gerichtet. Die schwach antiferromagnetische Wechselwirkung der metallzentrierten Spins ��ber den Br��ckenliganden f��hrt dabei stets zu einem diamagnetischen Grundzustand, was diese als m��gliche Einzelmolek��lmagnete ausschlie��t. Mit der Oxidierbarkeit des Liganden zu seiner radikalischen Spezies besteht die M��glichkeit, einen zus��tzlichen Spin in dem System zu erzeugen, woraus ein Spingrundzustand von ungleich null resultiert. Es zeigte sich, dass die Lebensdauer der radikalischen Spezies eine starke Abh��ngigkeit sowohl von den eingesetzten Metallionen als auch den weiteren Liganden besitzt. Auch vier Derivate des urspr��nglichen Br��ckenliganden konnten synthetisiert und deren Oxidierbarkeit zu den entsprechenden Radikalformen gezeigt werden. Neben der Darstellung homometallischer Komplexe gelang zudem die Synthese und Strukturaufkl��rung dreier heterometallischer zweikerniger Komplexe mit Mn(II), Co(II) und Ni(II) als Metallionen. Es konnte gezeigt werden, dass diese auch ohne die Oxidation des Br��ckenliganden bei schwacher antiferromagnetischer Wechselwirkung der Spins einen paramagnetischen Spingrundzustand besitzen.

Energy-efficient Communication and Estimation in Wireless Sensor Networks

This thesis focuses on the energy efficiency in wireless networks under the transmission and information diffusion points of view. In particular, on one hand, the communication efficiency is investigated, attempting to reduce the consumption during transmissions, while on the other hand the energy efficiency of the procedures required to distribute the information among wireless nodes in complex networks is taken into account. For what concerns energy efficient communications, an innovative transmission scheme reusing source of opportunity signals is introduced. This kind of signals has never been previously studied in literature for communication purposes. The scope is to provide a way for transmitting information with energy consumption close to zero. On the theoretical side, starting from a general communication channel model subject to a limited input amplitude, the theme of low power transmission signals is tackled under the perspective of stating sufficient conditions for the capacity achieving input distribution to be discrete. Finally, the focus is shifted towards the design of energy efficient algorithms for the diffusion of information. In particular, the endeavours are aimed at solving an estimation problem distributed over a wireless sensor network. The proposed solutions are deeply analyzed both to ensure their energy efficiency and to guarantee their robustness against losses during the diffusion of information (against information diffusion truncation more in general).

Raum-zeitliche Analyse der Klimavariabilit��t anhand von hochaufgel��sten interpolierten Klimakarten am Beispiel von Europa (Region VI der Weltorganisation f��r Meteorologie)

Klimamontoring ben��tigt eine operative, raum-zeitliche Analyse der Klimavariabilit��t. Mit dieser Zielsetzung, funktionsbereite Karten regelm����ig zu erstellen, ist es hilfreich auf einen Blick, die r��umliche Variabilit��t der Klimaelemente in der zeitlichen Ver��nderungen darzustellen. F��r aktuelle und k��rzlich vergangene Jahre entwickelte der Deutsche Wetterdienst ein Standardverfahren zur Erstellung solcher Karten. Die Methode zur Erstellung solcher Karten variiert f��r die verschiedenen Klimaelemente bedingt durch die Datengrundlage, die nat��rliche Variabilit��t und der Verf��gbarkeit der in-situ Daten.rnIm Rahmen der Analyse der raum-zeitlichen Variabilit��t innerhalb dieser Dissertation werden verschiedene Interpolationsverfahren auf die Mitteltemperatur der f��nf Dekaden der Jahre 1951-2000 f��r ein relativ gro��es Gebiet, der Region VI der Weltorganisation f��r Meteorologie (Europa und Naher Osten) angewendet. Die Region deckt ein relativ heterogenes Arbeitsgebiet von Gr��nland im Nordwesten bis Syrien im S��dosten hinsichtlich der Klimatologie ab.rnDas zentrale Ziel der Dissertation ist eine Methode zur r��umlichen Interpolation der mittleren Dekadentemperaturwerte f��r die Region VI zu entwickeln. Diese Methode soll in Zukunft f��r die operative monatliche Klimakartenerstellung geeignet sein. Diese einheitliche Methode soll auf andere Klimaelemente ��bertragbar und mit der entsprechenden Software ��berall anwendbar sein. Zwei zentrale Datenbanken werden im Rahmen dieser Dissertation verwendet: So genannte CLIMAT-Daten ��ber dem Land und Schiffsdaten ��ber dem Meer.rnIm Grunde wird die ��bertragung der Punktwerte der Temperatur per r��umlicher Interpolation auf die Fl��che in drei Schritten vollzogen. Der erste Schritt beinhaltet eine multiple Regression zur Reduktion der Stationswerte mit den vier Einflussgr����en der Geographischen Breite, der H��he ��ber Normalnull, der Jahrestemperaturamplitude und der thermischen Kontinentalit��t auf ein einheitliches Niveau. Im zweiten Schritt werden die reduzierten Temperaturwerte, so genannte Residuen, mit der Interpolationsmethode der Radialen Basis Funktionen aus der Gruppe der Neuronalen Netzwerk Modelle (NNM) interpoliert. Im letzten Schritt werden die interpolierten Temperaturraster mit der Umkehrung der multiplen Regression aus Schritt eins mit Hilfe der vier Einflussgr����en auf ihr urspr��ngliches Niveau hochgerechnet.rnF��r alle Stationswerte wird die Differenz zwischen gesch��tzten Wert aus der Interpolation und dem wahren gemessenen Wert berechnet und durch die geostatistische Kenngr����e des Root Mean Square Errors (RMSE) wiedergegeben. Der zentrale Vorteil ist die wertegetreue Wiedergabe, die fehlende Generalisierung und die Vermeidung von Interpolationsinseln. Das entwickelte Verfahren ist auf andere Klimaelemente wie Niederschlag, Schneedeckenh��he oder Sonnenscheindauer ��bertragbar.