Etnofaulismos e os dicionários monolíngues brasileiros

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Comparative study on structure and magnetic properties of polycrystalline PrxY1-xBa2Cu3O7-delta prepared in oxygen and argon atmosphere

We report a systematic study on the influence of the synthesis routes on the structural and magnetic properties of polycrystalline PrxY1-xBa2Cu3O7-delta. We have prepared high-quality samples of this material by following a sol-gel method based on heat treatment in both inert argon and oxygen atmospheres in order to compare their effect on the formation of the superconducting phase using X-ray powder diffraction. Magnetic measurements (DC and AC susceptibility) clearly demonstrate that, for the same concentration of Pr, the superconducting transition temperature markedly increases in all samples prepared in argon atmosphere, including pure Pr-123. (C) 2012 Elsevier B.V. All rights reserved.

Dynamics of doublon-holon pairs in Hubbard two-leg ladders

The dynamics of holon-doublon pairs is studied in Hubbard two-leg ladders using the time-dependent density matrix renormalization group method. We find that the geometry of the two-leg ladder, which is qualitatively different from a one-dimensional chain due to the presence of a spin gap, strongly affects the propagation of a doublon-holon pair. Two distinct regimes are identified. For weak interleg coupling, the results are qualitatively similar to the case of the propagation previously reported in Hubbard chains, with only a renormalization of parameters. More interesting is the case of strong interleg coupling where substantial differences arise, particularly regarding the double occupancy and properties of the excitations such as the doublon speed. Our results suggest a connection between the presence of a spin gap and qualitative changes in the doublon speed, indicating a weak coupling between the doublon and the magnetic excitations.

Inhomogeneous Fermi and quantum spin systems on lattices

We study the thermodynamic properties of a certain type of space-inhomogeneous Fermi and quantum spin systems on lattices. We are particularly interested in the case where the space scale of the inhomogeneities stays macroscopic, but very small as compared to the side-length of the box containing fermions or spins. The present study is however not restricted to "macroscopic inhomogeneities" and also includes the (periodic) microscopic and mesoscopic cases. We prove that - as in the homogeneous case - the pressure is, up to a minus sign, the conservative value of a two-person zero-sum game, named here thermodynamic game. Because of the absence of space symmetries in such inhomogeneous systems, it is not clear from the beginning what kind of object equilibrium states should be in the thermodynamic limit. However, we give rigorous statements on correlations functions for large boxes. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4763465]

Molecular organization and doping in poly(2-methoxyaniline)/Ni(dmit)(2) films obtained with the Langmuir-Blodgett technique

The control of the properties of materials at the molecular level is pursued for many applications, especially those associated with nanostructures. In this paper, we show that the coordination compound [Ni(dmit)(2)], where (dmit) is the 1,3-dithiole-2-thione-4,5-dithiolate ligand, can induce doping of poly(2-methoxyaniline) (POMA) in molecularly ordered Langmuir and Langmuir-Blodgett (LB) films. Doping was associated with interactions between the components and the compression of the Langmuir film at the air-water interface, according to polarization-modulated infrared reflection-absorption spectroscopy (PM-IRRAS) data. Taking these results together with in situ UV-Vis absorption measurements, we could identify the molecular groups involved in the interaction, including the way they were reoriented upon film compression. The Langmuir films were sufficiently stable to be transferred as Y-type LB films, while the hybrid POMA/[Ni(dmit)(2)] films remain doped in the solid state. As expected, the molecular charges affected the film morphology, as observed from combined atomic and electric force microscopy measurements. In summary, with adequate spectroscopy and microscopy tools we characterized molecular-level interactions, which may allow one to design molecular electronic devices with controlled electrical properties.

Flux-Line-Lattice Melting and Upper Critical Field of Bi1.65Pb0.35Sr2Ca2Cu3O10+delta Ceramic Samples

We have conducted magnetoresistance measurements rho(T,H) in applied magnetic fields up to 18 T in Bi1.65Pb0.35Sr2Ca2Cu3O10+delta ceramic samples which were subjected to different uniaxial compacting pressures. The anisotropic upper critical fields H (c2)(T) were extracted from the rho(T,H) data, yielding and the out-of-plane superconducting coherence length xi (c) (0)similar to 3 . We have also estimated and xi (ab) (0) similar to 90 . In addition to this, a flux-line-lattice (FLL) melting temperature T (m) has been identified as a second peak in the derivative of the magnetoresistance d rho/dT data close to the superconducting transition temperature. An H (m) vs. T phase diagram was constructed and the FLL boundary lines were found to obey a temperature dependence H (m) ae(T (c) /T-1) (alpha) , where alpha similar to 2 for the sample subjected to the higher compacting pressure. A reasonable value of the Lindemann parameter c (L) similar to 0.29 has been found for all samples studied.

Enzyme Microheterogeneous Hydration and Stabilization in Supercritical Carbon Dioxide

Supercritical carbon dioxide is a promising green-chemistry solvent for many enzyme-catalyzed chemical reactions, yet the striking stability of some enzymes in such unconventional environments is not well understood. Here, we investigate the stabilization of the Candida antarctica Lipase B (CALB) in supercritical carbon dioxide-water biphasic systems using molecular dynamics simulations. The preservation of the enzyme structure and optimal activity depend on the presence of small amounts of water in the supercritical dispersing medium. When the protein is at least partially hydrated, water molecules bind to specific sites on the enzyme surface and prevent carbon dioxide from penetrating its catalytic core. Strikingly, water and supercritical carbon dioxide cover the protein surface quite heterogeneously. In the first solvation layer, the hydrophilic residues at the surface of the protein are able to pin down patches of water, whereas carbon dioxide solvates preferentially hydrophobic surface residues. In the outer solvation shells, water molecules tend to cluster predominantly on top of the larger water patches of the first solvation layer instead of spreading evenly around the remainder of the protein surface. For CALB, this exposes the substrate-binding region of the enzyme to carbon dioxide, possibly facilitating diffusion of nonpolar substrates into the catalytic funnel. Therefore, by means of microheterogeneous solvation, enhanced accessibility of hydrophobic substrates to the active site can be achieved, while preserving the functional structure of the enzyme. Our results provide a molecular picture on the nature of the stability of proteins in nonaqueous media.

Multiscale fractal descriptors applied to nanoscale images

This work proposes the application of fractal descriptors to the analysis of nanoscale materials under different experimental conditions. We obtain descriptors for images from the sample applying a multiscale transform to the calculation of fractal dimension of a surface map of such image. Particularly, we have used the Bouligand-Minkowski fractal dimension. We applied these descriptors to discriminate between two titanium oxide films prepared under different experimental conditions. Results demonstrate the discrimination power of proposed descriptors in such kind of application.

Analisi e valutazione delle performance acustiche degli aeromobili nella fase di atterraggio

Nella tesi si analizzano le principali fonti del rumore aeronautico, lo stato dell'arte dal punto di vista normativo, tecnologico e procedurale. Si analizza lo stato dell'arte anche riguardo alla classificazione degli aeromobili, proponendo un nuovo indice prestazionale in alternativa a quello indicato dalla metodologia di certificazione (AC36-ICAO) Allo scopo di diminuire l'impatto acustico degli aeromobili in fase di atterraggio, si analizzano col programma INM i benefici di procedure CDA a 3° rispetto alle procedure tradizionali e, di seguito di procedure CDA ad angoli maggiori in termini di riduzione di lunghezza e di area delle isofoniche SEL85, SEL80 e SEL75.

L'a(rche)tipico Brian O'Nolan. Comico e riso dalla tradizione al post-

This study aims at analysing Brian O'Nolans literary production in the light of a reconsideration of the role played by his two most famous pseudonyms ,Flann Brien and Myles na Gopaleen, behind which he was active both as a novelist and as a journalist. We tried to establish a new kind of relationship between them and their empirical author following recent cultural and scientific surveys in the field of Humour Studies, Psychology, and Sociology: taking as a starting point the appreciation of the comic attitude in nature and in cultural history, we progressed through a short history of laughter and derision, followed by an overview on humour theories. After having established such a frame, we considered an integration of scientific studies in the field of laughter and humour as a base for our study scheme, in order to come to a definition of the comic author as a recognised, powerful and authoritative social figure who acts as a critic of conventions. The history of laughter and comic we briefly summarized, based on the one related by the French scholar Georges Minois in his work (Minois 2004), has been taken into account in the view that humorous attitude is one of man’s characteristic traits always present and witnessed throughout the ages, though subject in most cases to repression by cultural and political conservative power. This sort of Super-Ego notwithstanding, or perhaps because of that, comic impulse proved irreducible exactly in its influence on the current cultural debates. Basing mainly on Robert R. Provine’s (Provine 2001), Fabio Ceccarelli’s (Ceccarelli 1988), Arthur Koestler’s (Koestler 1975) and Peter L. Berger’s (Berger 1995) scientific essays on the actual occurrence of laughter and smile in complex social situations, we underlined the many evidences for how the use of comic, humour and wit (in a Freudian sense) could be best comprehended if seen as a common mind process designed for the improvement of knowledge, in which we traced a strict relation with the play-element the Dutch historian Huizinga highlighted in his famous essay, Homo Ludens (Huizinga 1955). We considered comic and humour/wit as different sides of the same coin, and showed how the demonstrations scientists provided on this particular subject are not conclusive, given that the mental processes could not still be irrefutably shown to be separated as regards graduations in comic expression and reception: in fact, different outputs in expressions might lead back to one and the same production process, following the general ‘Economy Rule’ of evolution; man is the only animal who lies, meaning with this that one feeling is not necessarily biuniquely associated with one and the same outward display, so human expressions are not validation proofs for feelings. Considering societies, we found that in nature they are all organized in more or less the same way, that is, in élites who govern over a community who, in turn, recognizes them as legitimate delegates for that task; we inferred from this the epistemological possibility for the existence of an added ruling figure alongside those political and religious: this figure being the comic, who is the person in charge of expressing true feelings towards given subjects of contention. Any community owns one, and his very peculiar status is validated by the fact that his place is within the community, living in it and speaking to it, but at the same time is outside it in the sense that his action focuses mainly on shedding light on ideas and objects placed out-side the boundaries of social convention: taboos, fears, sacred objects and finally culture are the favourite targets of the comic person’s arrow. This is the reason for the word a(rche)typical as applied to the comic figure in society: atypical in a sense, because unconventional and disrespectful of traditions, critical and never at ease with unblinkered respect of canons; archetypical, because the “village fool”, buffoon, jester or anyone in any kind of society who plays such roles, is an archetype in the Jungian sense, i.e. a personification of an irreducible side of human nature that everybody instinctively knows: a beginner of a tradition, the perfect type, what is most conventional of all and therefore the exact opposite of an atypical. There is an intrinsic necessity, we think, of such figures in societies, just like politicians and priests, who should play an elitist role in order to guide and rule not for their own benefit but for the good of the community. We are not naïve and do know that actual owners of power always tend to keep it indefinitely: the ‘social comic’ as a role of power has nonetheless the distinctive feature of being the only job whose tension is not towards stability. It has got in itself the rewarding permission of contradiction, for the very reason we exposed before that the comic must cast an eye both inside and outside society and his vision may be perforce not consistent, then it is satisfactory for the popularity that gives amongst readers and audience. Finally, the difference between governors, priests and comic figures is the seriousness of the first two (fundamentally monologic) and the merry contradiction of the third (essentially dialogic). MPs, mayors, bishops and pastors should always console, comfort and soothe popular mood in respect of the public convention; the comic has the opposite task of provoking, urging and irritating, accomplishing at the same time a sort of control of the soothing powers of society, keepers of the righteousness. In this view, the comic person assumes a paramount importance in the counterbalancing of power administration, whether in form of acting in public places or in written pieces which could circulate for private reading. At this point comes into question our Irish writer Brian O'Nolan(1911-1966), real name that stood behind the more famous masks of Flann O'Brien, novelist, author of At Swim-Two-Birds (1939), The Hard Life (1961), The Dalkey Archive (1964) and, posthumously, The Third Policeman (1967); and of Myles na Gopaleen, journalist, keeper for more than 25 years of the Cruiskeen Lawn column on The Irish Times (1940-1966), and author of the famous book-parody in Irish An Béal Bocht (1941), later translated in English as The Poor Mouth (1973). Brian O'Nolan, professional senior civil servant of the Republic, has never seen recognized his authorship in literary studies, since all of them concentrated on his alter egos Flann, Myles and some others he used for minor contributions. So far as we are concerned, we think this is the first study which places the real name in the title, this way acknowledging him an unity of intents that no-one before did. And this choice in titling is not a mere mark of distinction for the sake of it, but also a wilful sign of how his opus should now be reconsidered. In effect, the aim of this study is exactly that of demonstrating how the empirical author Brian O'Nolan was the real Deus in machina, the master of puppets who skilfully directed all of his identities in planned directions, so as to completely fulfil the role of the comic figure we explained before. Flann O'Brien and Myles na Gopaleen were personae and not persons, but the impression one gets from the critical studies on them is the exact opposite. Literary consideration, that came only after O'Nolans death, began with Anne Clissmann’s work, Flann O'Brien: A Critical Introduction to His Writings (Clissmann 1975), while the most recent book is Keith Donohue’s The Irish Anatomist: A Study of Flann O'Brien (Donohue 2002); passing through M.Keith Booker’s Flann O'Brien, Bakhtin and Menippean Satire (Booker 1995), Keith Hopper’s Flann O'Brien: A Portrait of the Artist as a Young Post-Modernist (Hopper 1995) and Monique Gallagher’s Flann O'Brien, Myles et les autres (Gallagher 1998). There have also been a couple of biographies, which incidentally somehow try to explain critical points his literary production, while many critical studies do the same on the opposite side, trying to found critical points of view on the author’s restless life and habits. At this stage, we attempted to merge into O'Nolan's corpus the journalistic articles he wrote, more than 4,200, for roughly two million words in the 26-year-old running of the column. To justify this, we appealed to several considerations about the figure O'Nolan used as writer: Myles na Gopaleen (later simplified in na Gopaleen), who was the equivalent of the street artist or storyteller, speaking to his imaginary public and trying to involve it in his stories, quarrels and debates of all kinds. First of all, he relied much on language for the reactions he would obtain, playing on, and with, words so as to ironically unmask untrue relationships between words and things. Secondly, he pushed to the limit the convention of addressing to spectators and listeners usually employed in live performing, stretching its role in the written discourse to come to a greater effect of involvement of readers. Lastly, he profited much from what we labelled his “specific weight”, i.e. the potential influence in society given by his recognised authority in determined matters, a position from which he could launch deeper attacks on conventional beliefs, so complying with the duty of a comic we hypothesised before: that of criticising society even in threat of losing the benefits the post guarantees. That seemingly masochistic tendency has its rationale. Every representative has many privileges on the assumption that he, or she, has great responsibilities in administrating. The higher those responsibilities are, the higher is the reward but also the severer is the punishment for the misfits done while in charge. But we all know that not everybody accepts the rules and many try to use their power for their personal benefit and do not want to undergo law’s penalties. The comic, showing in this case more civic sense than others, helped very much in this by the non-accessibility to the use of public force, finds in the role of the scapegoat the right accomplishment of his task, accepting the punishment when his breaking of the conventions is too stark to be forgiven. As Ceccarelli demonstrated, the role of the object of laughter (comic, ridicule) has its very own positive side: there is freedom of expression for the person, and at the same time integration in the society, even though at low levels. Then the banishment of a ‘social’ comic can never get to total extirpation from society, revealing how the scope of the comic lies on an entirely fictional layer, bearing no relation with facts, nor real consequences in terms of physical health. Myles na Gopaleen, mastering these three characteristics we postulated in the highest way, can be considered an author worth noting; and the oeuvre he wrote, the whole collection of Cruiskeen Lawn articles, is rightfully a novel because respects the canons of it especially regarding the authorial figure and his relationship with the readers. In addition, his work can be studied even if we cannot conduct our research on the whole of it, this proceeding being justified exactly because of the resemblances to the real figure of the storyteller: its ‘chapters’ —the daily articles— had a format that even the distracted reader could follow, even one who did not read each and every article before. So we can critically consider also a good part of them, as collected in the seven volumes published so far, with the addition of some others outside the collections, because completeness in this case is not at all a guarantee of a better precision in the assessment; on the contrary: examination of the totality of articles might let us consider him as a person and not a persona. Once cleared these points, we proceeded further in considering tout court the works of Brian O'Nolan as the works of a unique author, rather than complicating the references with many names which are none other than well-wrought sides of the same personality. By putting O'Nolan as the correct object of our research, empirical author of the works of the personae Flann O'Brien and Myles na Gopaleen, there comes out a clearer literary landscape: the comic author Brian O'Nolan, self-conscious of his paramount role in society as both a guide and a scourge, in a word as an a(rche)typical, intentionally chose to differentiate his personalities so as to create different perspectives in different fields of knowledge by using, in addition, different means of communication: novels and journalism. We finally compared the newly assessed author Brian O'Nolan with other great Irish comic writers in English, such as James Joyce (the one everybody named as the master in the field), Samuel Beckett, and Jonathan Swift. This comparison showed once more how O'Nolan is in no way inferior to these authors who, greatly celebrated by critics, have nonetheless failed to achieve that great public recognition O’Nolan received alias Myles, awarded by the daily audience he reached and influenced with his Cruiskeen Lawn column. For this reason, we believe him to be representative of the comic figure’s function as a social regulator and as a builder of solidarity, such as that Raymond Williams spoke of in his work (Williams 1982), with in mind the aim of building a ‘culture in common’. There is no way for a ‘culture in common’ to be acquired if we do not accept the fact that even the most functional society rests on conventions, and in a world more and more ‘connected’ we need someone to help everybody negotiate with different cultures and persons. The comic gives us a worldly perspective which is at the same time comfortable and distressing but in the end not harmful as the one furnished by politicians could be: he lets us peep into parallel worlds without moving too far from our armchair and, as a consequence, is the one who does his best for the improvement of our understanding of things.

Electronic transport properties of YBa 2 Cu 3 O 7-x

documentstyle[12pt,german]{article} pagestyle{empty} topmargin-1.5cm textheight24.5cm footskip-1.5cm % % begin{document} % begin{center} {Large {it Hern'{a}n Rodr'{i}guez}}\ vspace{24pt} {Large {bf Elektronische Transporteigenschaften von YBa$_{2}$Cu$_{3}$O$_{7-x}$/PrBa$_{2}$Cu$_{2.9}$Ga$_{0.1}$O$_{7-y}$ Dreifachschichten und "Ubergittern senkrecht zur Lagenstruktur}} end{center} vspace{24pt} noindent In der vorliegenden Arbeit wurden die Transporteigenschaften senkrecht zu den CuO$_{2}$--Ebenen von Hochtemperatur Supraleitern an YBa$_{2}$Cu$_{3}$O$_{7-x}$/\ PrBa$_{2}$Cu$_{2.9}$Ga$_{0.1}$O$_{7-y}$/ YBa$_{2}$Cu$_{3}$O$_{7-x}$ Dreifachschichten und [(YBa$_{2}$Cu$_{3}$O$_{7-x}$)$_{n}$\/(PrBa$_{2}$Cu$_{2.9}$Ga$_{0.1}$O$_{7-y}$)$_{m}$]$_{times M}$ "Ubergittern untersucht. Um die Transporteigenschaften senkrecht zu den Grenzfl"achen in Mehrlagenstrukturen messen zu k"onnen, ist ein Verfahren zur Herstellung von planaren Bauelemente verwendet worden. Die Untersuchungen an YBa$_{2}$Cu$_{3}$O$_{7-x}$/PrBa$_{2}$Cu$_{2.9}$Ga$_{0.1}$O$_{7-y}$ Dreifachschichten und "Ubergittern zeigen, da"s die Substrattemperatur w"ahrend des Wachstums die elektronischen Eigenschaften entlang der $c$--Achse stark beeinflusst. Bei Senkung der Abscheidetemperatur ergibt sich eine "Anderung von normalmetallischem zu tunnelkontaktartigem Verhalten. Die bei 840$^circ$C hergestellten Vielfachschichten weisen sowohl eine konstante Hintergrundleitf"ahigkeit als auch eine "Uberschu"sleitf"ahigkeit bei niedrigen Spannungen auf. Dies deutet darauf hin, da"s es sich um einen Supraleiter--Normalleiter--Supraleiter (S--N--S) Kontakt handelt. Dagegen zeigen Vielfachschichten, die bei 760$^circ$C deponiert wurden, deutlich unterschiedliches Verhalten verglichen mit den bei 840$^circ$C pr"aparierte Proben. Die Leitf"ahigkeit nimmt mit der Spannung zu, wobei der Leitf"ahigkeithintergrund eine ``V''--Form darstellt. Dar"uber hinaus zeigen die Leitf"ahigkeitskennlinien bei niedrigen Spannungen eine starke Abh"angigkeit sowohl von der Bias Spannung als auch von der Temperatur. Bei Dreifachschichten mit 20 nm PrBa$_{2}$Cu$_{2.9}$Ga$_{0.1}$O$_{7-y}$ tritt ein Leitf"ahigkeitmaximun bei Null--Spannung auf. Die Wechselwirkung zwischen tunnelnden Quasiteilchen und magnetischen Momenten in der Barriere ruft dieses Maximun hervor. Das "Ubergitter mit ($n/m$) = (4/5) Modulation zeigt Supraleiter--Isolator--Supraleiter (S--I--S) Tunnelkontakt--Verhalten mit Strukturen, die von der Energiel"ucke des Supraleiters hervorgerufen werden. Das S--N-- bzw., S--I--Kontaktverhalten der Heterostrukturen wurden ebenfalls mit Messungen der Leitf"ahigkeit bei tiefern Temperaturen weit au"serhalb der supraleitenden Energiel"ucke best"atigt. Diese Ergebnisse weisen auf die M"oglichkeit hin, durch Einstellen der Substrattemperaturen bei der Deposition das Auftreten von S--N--S und S--I--S Verhalten der Kontakte zu steuern. vspace{24pt} noindent Datum: 05.07.2004\ Betreuer: Prof. Dr. Hermann Adrian %Name des Betreuers, daneben dessen Unterschrift end{document}

Nanotechnology control of self organized biomolecules and biomaterials for medical research

Nanotechnology entails the manufacturing and manipulation of matter at length scales ranging from single atoms to micron-sized objects. The ability to address properties on the biologically-relevant nanometer scale has made nanotechnology attractive for Nanomedicine. This is perceived as a great opportunity in healthcare especially in diagnostics, therapeutics and more in general to develop personalized medicine. Nanomedicine has the potential to enable early detection and prevention, and to improve diagnosis, mass screening, treatment and follow-up of many diseases. From the biological standpoint, nanomaterials match the typical size of naturally occurring functional units or components of living organisms and, for this reason, enable more effective interaction with biological systems. Nanomaterials have the potential to influence the functionality and cell fate in the regeneration of organs and tissues. To this aim, nanotechnology provides an arsenal of techniques for intervening, fabricate, and modulate the environment where cells live and function. Unconventional micro- and nano-fabrication techniques allow patterning biomolecules and biocompatible materials down to the level of a few nanometer feature size. Patterning is not simply a deterministic placement of a material; in a more extended acception it allows a controlled fabrication of structures and gradients of different nature. Gradients are emerging as one of the key factors guiding cell adhesion, proliferation, migration and even differentiation in the case of stem cells. The main goal of this thesis has been to devise a nanotechnology-based strategy and tools to spatially and temporally control biologically-relevant phenomena in-vitro which are important in some fields of medical research.

Electronic transport in the heavy fermion superconductors UPd 2 Al 3 and UNi 2 Al 3

This work addresses the electronical properties of the superconductors UPd2Al3 and UNi2Al3 on the basis of thin film experiments. These isotructural compounds are ideal candiates to study the interplay of magnetism and superconductivity due to the differences of their magnetically ordered states, as well as the experimental evidence for a magnetic pairing mechanism in UPd2Al3. Epitaxial thin film samples of UPd2Al3 and UNi2Al3 were prepared using UHV Molecular Beam Epitaxy (MBE). For UPd2Al3, the change of the growth direction from the intrinsic (001) to epitaxial (100) was predicted and sucessfully demonstrated using LaAlO3 substrates cut in (110) direction. With optimized deposition process parameters for UPd2Al3 (100) on LaAlO3 (110) superconducting samples with critical temperatures up to Tc = 1.75K were obtained. UPd2Al3-AlOx-Ag mesa junctions with superconducting base electrode were prepared and shown to be in the tunneling regime. However, no signatures of a superconducting density of states were observed in the tunneling spectra. The resistive superconducting transition was probed for a possible dependence on the current direction. In contrast to UNi2Al3, the existence of such feature was excluded in UPd2Al3 (100) thin films. The second focus of this work is the dependence of the resisitive transition in UNi2Al3 (100) thin films on the current direction. The experimental fact that the resisitive transition occurs at slightly higher temperatures for I║a than for I║c can be explained within a model of two weakly coupled superconducting bands. Evidence is presented for the key assumption of the two-band model, namely that transport in and out of the ab-plane is generated on different, weakly coupled parts of the Fermi surface. Main indications are the angle dependence of the superconducting transition and the dependence of the upper critical field Bc2 on current and field orientation. Additionally, several possible alternative explanations for the directional splitting of the transition are excluded in this work. An origin due to scattering on crystal defects or impurities is ruled out, likewise a relation to ohmic heating or vortex dynamics. The shift of the transition temperature as function of the current density was found to behave as predicted by the Ginzburg-Landau theory for critical current depairing, which plays a significant role in the two-band model. In conclusion, the directional splitting of the resisitive transition has to be regarded an intrinsic and unique property of UNi2Al3 up to now. Therefore, UNi2Al3 is proposed as a role model for weakly coupled multiband superconductivity. Magnetoresistance in the normalconducting state was measured for UPd2Al3 and UNi2Al3. For UNi2Al3, a negative contribution was observed close to the antiferromagnetic ordering temperature TN only for I║a, which can be associated to reduced spin-disorder scattering. In agreement with previous results it is concluded that the magnetic moments have to be attributed to the same part of the Fermi surface which generates transport in the ab-plane.

Essays in Macroeconomics

The dissertation consists of four papers that aim at providing new contributions in the field of macroeconomics, monetary policy and financial stability. The first paper proposes a new Dynamic Stochastic General Equilibrium (DSGE) model with credit frictions and a banking sector to study the pro-cyclicality of credit and the role of different prudential regulatory frameworks in affecting business cycle fluctuations and in restoring macroeconomic and financial stability. The second paper develops a simple DSGE model capable of evaluating the effects of large purchases of treasuries by central banks. This theoretical framework is employed to evaluate the impact on yields and the macroeconomy of large purchases of medium- and long-term government bonds recently implemented in the US and UK. The third paper studies the effects of ECB communications about unconventional monetary policy operations on the perceived sovereign risk of Italy over the last five years. The empirical results are derived from both an event-study analysis and a GARCH model, which uses Italian long-term bond futures to disentangle expected from unexpected policy actions. The fourth paper proposes a DSGE model with an endogenous term structure of interest rates, which is able to replicate the stylized facts regarding the yield curve and the term premium in the US over the period 1987:3-2011:3, without compromising its ability to match macro dynamics.

Transport properties of YBa 2 Cu 3 O 7, PrBa 2 Cu 3 O 7-superlattices

The understanding of the coupling between superconducting YBa2Cu3O7 (YBCO) layers decoupled by non superconducting PrBa2Cu3O7 (PBCO) layers in c-axis oriented superlattices was the aim of this thesis. For this purpose two conceptually different kind of transport experiments have been performed. rnrnIn the first type of transport experiments the current is flowing parallel to the layers. Here the coupling is probed indirectly using magnetic vortex lines, which are penetrating the superlattice. Movement of the vortex segments in neighbouring YBCO layers is more or less coherent depending on the thickness of both the superconducting and non superconducting layers. This in-plane transport was measured either by sending an external current through bridges patterned in the superlattice or by an induced internal current. rnThe vortex-creep activation energy U was determined by analysis of the in-plane resistive transition in an external magnetic field B oriented along the c-axis. The activation energies for two series of superlattices were investigated. In one series the thickness of the YBCO layers was constant (nY=4 unit cells) and the number of the PBCO unit cells was varied, while in the other the number of PBCO layers was constant (nP=4) and nY varied. The correlation length of the vortex system was determined to be 80 nm along the c-axis direction. It was found that even a single PBCO unit cell in a superlattice effectively cuts the flux lines into shorter weakly coupled segments, and the coupling of the vortex systems in neighbouring layers is negligible already for a thickness of four unit cells of the PBCO layers. A characteristic variation of the activation energy for the two series of superlattices was found, where U0 is proportional to the YBCO thickness. A change in the variation of U0 with the current I in the specimen was observed, which can be explained in terms of a crossover in the vortex creep process, generated by the transport current. At low I values the dislocations mediated (plastic) vortex creep leads to thermally assisted flux-flow behaviour, whereas at high current the dc transport measurements are dominated by elastic (collective) creep.rnThe analysis of standard dc magnetization relaxation data obtained for a series superlattices revealed the occurrence of a crossover from elastic (collective) vortex creep at low temperature to plastic vortex creep at high T. The crossover is generated by the T dependent macroscopic currents induced in the sample. The existence of this creep crossover suggests that, compared with the well known Maley technique, the use of the normalized vortex creep activation energy is a better solution for the determination of vortex creep parameters.rnrnThe second type of transport experiments was to measure directly a possible Josephson coupling between superconducting CuO2 double planes in the superlattices by investigation of the transport properties perpendicular to the superconducting planes. Here three different experiments have been performed. The first one was to pattern mesa structures photolithographically as in previous works. The second used three-dimensional nanostructures cut by a focused ion beam. For the these two experiments insufficient patterning capabilities prevented an observation of the Josephson effect in the current voltage curves. rnA third experiment used a-axis and (110) oriented YBCO films, where in-plane patterning can in principle be sufficient to measure transport perpendicular to the superconducting planes. Therefore the deposition of films with this unusual growth orientation was optimized and investigated. The structural and microstructural evolution of c-axis to a-axis orientation was monitored using x-ray diffraction, scanning electron microscopy and magnetization measurements. Films with full a-axis alignment parallel to the substrate normal could be achieved on (100)SrTiO3. Due to the symmetry of the substrate the c-axis direction in-plane is twofold. Transferring the deposition conditions to films grown on (110)SrTiO3 allowed the growth of (110) oriented YBCO films with a unique in-plane c-axis orientation. While these films were of high quality by crystallographic and macroscopic visual inspection, electron microscopy revealed a coherent crack pattern on a nanoscale. Therefore the actual current path in the sample was not determined by the macroscopic patterning which prohibited investigations of the in-plane anisotropy in this case.rn