O (alpha 4 s) loop-by-loop contributions to heavy quark pair production in hadronic collisions

The present state of the theoretical predictions for the hadronic heavy hadron production is not quite satisfactory. The full next-to-leading order (NLO) ${cal O} (alpha_s^3)$ corrections to the hadroproduction of heavy quarks have raised the leading order (LO) ${cal O} (alpha_s^2)$ estimates but the NLO predictions are still slightly below the experimental numbers. Moreover, the theoretical NLO predictions suffer from the usual large uncertainty resulting from the freedom in the choice of renormalization and factorization scales of perturbative QCD.In this light there are hopes that a next-to-next-to-leading order (NNLO) ${cal O} (alpha_s^4)$ calculation will bring theoretical predictions even closer to the experimental data. Also, the dependence on the factorization and renormalization scales of the physical process is expected to be greatly reduced at NNLO. This would reduce the theoretical uncertainty and therefore make the comparison between theory and experiment much more significant. In this thesis I have concentrated on that part of NNLO corrections for hadronic heavy quark production where one-loop integrals contribute in the form of a loop-by-loop product. In the first part of the thesis I use dimensional regularization to calculate the ${cal O}(ep^2)$ expansion of scalar one-loop one-, two-, three- and four-point integrals. The Laurent series of the scalar integrals is needed as an input for the calculation of the one-loop matrix elements for the loop-by-loop contributions. Since each factor of the loop-by-loop product has negative powers of the dimensional regularization parameter $ep$ up to ${cal O}(ep^{-2})$, the Laurent series of the scalar integrals has to be calculated up to ${cal O}(ep^2)$. The negative powers of $ep$ are a consequence of ultraviolet and infrared/collinear (or mass ) divergences. Among the scalar integrals the four-point integrals are the most complicated. The ${cal O}(ep^2)$ expansion of the three- and four-point integrals contains in general classical polylogarithms up to ${rm Li}_4$ and $L$-functions related to multiple polylogarithms of maximal weight and depth four. All results for the scalar integrals are also available in electronic form. In the second part of the thesis I discuss the properties of the classical polylogarithms. I present the algorithms which allow one to reduce the number of the polylogarithms in an expression. I derive identities for the $L$-functions which have been intensively used in order to reduce the length of the final results for the scalar integrals. I also discuss the properties of multiple polylogarithms. I derive identities to express the $L$-functions in terms of multiple polylogarithms. In the third part I investigate the numerical efficiency of the results for the scalar integrals. The dependence of the evaluation time on the relative error is discussed. In the forth part of the thesis I present the larger part of the ${cal O}(ep^2)$ results on one-loop matrix elements in heavy flavor hadroproduction containing the full spin information. The ${cal O}(ep^2)$ terms arise as a combination of the ${cal O}(ep^2)$ results for the scalar integrals, the spin algebra and the Passarino-Veltman decomposition. The one-loop matrix elements will be needed as input in the determination of the loop-by-loop part of NNLO for the hadronic heavy flavor production.

A chemical loop approach for methanol reforming

Over the past few years, the switch towards renewable sources for energy production is considered as necessary for the future sustainability of the world environment. Hydrogen is one of the most promising energy vectors for the stocking of low density renewable sources such as wind, biomasses and sun. The production of hydrogen by the steam-iron process could be one of the most versatile approaches useful for the employment of different reducing bio-based fuels. The steam iron process is a two-step chemical looping reaction based (i) on the reduction of an iron-based oxide with an organic compound followed by (ii) a reoxidation of the reduced solid material by water, which lead to the production of hydrogen. The overall reaction is the water oxidation of the organic fuel (gasification or reforming processes) but the inherent separation of the two semireactions allows the production of carbon-free hydrogen. In this thesis, steam-iron cycle with methanol is proposed and three different oxides with the generic formula AFe2O4 (A=Co,Ni,Fe) are compared in order to understand how the chemical properties and the structural differences can affect the productivity of the overall process. The modifications occurred in used samples are deeply investigated by the analysis of used materials. A specific study on CoFe2O4-based process using both classical and in-situ/ex-situ analysis is reported employing many characterization techniques such as FTIR spectroscopy, TEM, XRD, XPS, BET, TPR and Mössbauer spectroscopy.

Simulazioni Software-In-the-Loop per la verifica funzionale di un sistema di tracking satellitare (ALMATracker)

L'ALMATracker è un sistema di puntamento per la stazione di terra di ALMASat-1. La sua configurazione non segue la classica Azimuth-Elevazione, bensì utilizza gli assi α-β per evitare punti di singolarità nelle posizioni vicino allo zenit. Ancora in fase di progettazione, utilizzando in congiunta SolidWorks e LabVIEW si è creato un Software-in-the-loop per la sua verifica funzionale, grazie all'utilizzo del relativamente nuovo pacchetto NI Softmotion. Data la scarsa esperienza e documentazione che si hanno su questo recente tool, si è prima creato un Case Study che simulasse un sistema di coordinate cilindriche in modo da acquisire competenza. I risultati conseguiti sono poi stati sfruttati per la creazione di un SIL per la simulazione del movimento dell'ALMATracker. L'utilizzo di questa metodologia di progettazione non solo ha confermato la validità del design proposto, ma anche evidenziato i problemi e le potenzialità che caratterizzano questo pacchetto software dandone un analisi approfondita.

A chemical-loop approach for the generation of hydrogen by means of ethanol reforming

The work investigates the feasibility of a new process aimed at the production of hydrogen with inherent separation of carbon oxides. The process consists in a cycle in which, in the first step, a mixed metal oxide is reduced by ethanol (obtained from biomasses). The reduced metal is then contacted with steam in order to split the water and sequestrating the oxygen into the looping material’s structure. The oxides used to run this thermochemical cycle, also called “steam-iron process” are mixed ferrites in the spinel structure MeFe2O4 (Me = Fe, Co, Ni or Cu). To understand the reactions involved in the anaerobic reforming of ethanol, diffuse reflectance spectroscopy (DRIFTS) was used, coupled with the mass analysis of the effluent, to study the surface composition of the ferrites during the adsorption of ethanol and its transformations during the temperature program. This study was paired with the tests on a laboratory scale plant and the characterization through various techniques such as XRD, Mössbauer spectroscopy, elemental analysis... on the materials as synthesized and at different reduction degrees In the first step it was found that besides the generation of the expected CO, CO2 and H2O, the products of ethanol anaerobic oxidation, also a large amount of H2 and coke were produced. The latter is highly undesired, since it affects the second step, during which water is fed over the pre-reduced spinel at high temperature. The behavior of the different spinels was affected by the nature of the divalent metal cation; magnetite was the oxide showing the slower rate of reduction by ethanol, but on the other hand it was that one which could perform the entire cycle of the process more efficiently. Still the problem of coke formation remains the greater challenge to solve.

Numerical loop calculations with contour deformation

Gegenstand dieser Arbeit ist die nummerische Berechnung von Schleifenintegralen welche in höheren Ordnungen der Störungstheorie auftreten.rnAnalog zur reellen Emission kann man auch in den virtuellen Beiträgen Subtraktionsterme einführen, welche die kollinearen und soften Divergenzen des Schleifenintegrals entfernen. Die Phasenraumintegration und die Schleifenintegration können dann in einer einzigen Monte Carlo Integration durchgeführt werden. In dieser Arbeit zeigen wir wie eine solche numerische Integration unter zu Hilfenahme einer Kontourdeformation durchgeführt werden kann. Ausserdem zeigen wir wie man die benötigeten Integranden mit Rekursionsformeln berechnen kann.

Closed-loop investigation of the dynamical properties of cardiomyocyte electrophysiology by means of Dynamic clamp and Mathematical modelling

The research field of my PhD concerns mathematical modeling and numerical simulation, applied to the cardiac electrophysiology analysis at a single cell level. This is possible thanks to the development of mathematical descriptions of single cellular components, ionic channels, pumps, exchangers and subcellular compartments. Due to the difficulties of vivo experiments on human cells, most of the measurements are acquired in vitro using animal models (e.g. guinea pig, dog, rabbit). Moreover, to study the cardiac action potential and all its features, it is necessary to acquire more specific knowledge about single ionic currents that contribute to the cardiac activity. Electrophysiological models of the heart have become very accurate in recent years giving rise to extremely complicated systems of differential equations. Although describing the behavior of cardiac cells quite well, the models are computationally demanding for numerical simulations and are very difficult to analyze from a mathematical (dynamical-systems) viewpoint. Simplified mathematical models that capture the underlying dynamics to a certain extent are therefore frequently used. The results presented in this thesis have confirmed that a close integration of computational modeling and experimental recordings in real myocytes, as performed by dynamic clamp, is a useful tool in enhancing our understanding of various components of normal cardiac electrophysiology, but also arrhythmogenic mechanisms in a pathological condition, especially when fully integrated with experimental data.

Il ruolo delle architetture di controllo nella progettazione e sviluppo di applicazioni web: Un confronto fra event-loop e control-loop utilizzando il linguaggio dart e linguaggi agent-oriented

Quando si parla di architetture di controllo in ambito Web, il Modello ad Eventi è indubbiamente quello più diffuso e adottato. L’asincronicità e l’elevata interazione con l’utente sono caratteristiche tipiche delle Web Applications, ed un architettura ad eventi, grazie all’adozione del suo tipico ciclo di controllo chiamato Event Loop, fornisce un'astrazione semplice ma sufficientemente espressiva per soddisfare tali requisiti. La crescita di Internet e delle tecnologie ad esso associate, assieme alle recenti conquiste in ambito di CPU multi-core, ha fornito terreno fertile per lo sviluppo di Web Applications sempre più complesse. Questo aumento di complessità ha portato però alla luce alcuni limiti del modello ad eventi, ancora oggi non del tutto risolti. Con questo lavoro si intende proporre un differente approccio a questa tipologia di problemi, che superi i limiti riscontrati nel modello ad eventi proponendo un architettura diversa, nata in ambito di IA ma che sta guadagno popolarità anche nel general-purpose: il Modello ad Agenti. Le architetture ad agenti adottano un ciclo di controllo simile all’Event Loop del modello ad eventi, ma con alcune profonde differenze: il Control Loop. Lo scopo di questa tesi sarà dunque approfondire le due tipologie di architetture evidenziandone le differenze, mostrando cosa significa affrontare un progetto e lo sviluppo di una Web Applications avendo tecnologie diverse con differenti cicli di controllo, mettendo in luce pregi e difetti dei due approcci.

Hunting for warped extra dimensions via loop-induced processes

This thesis is on loop-induced processes in theories with warped extra dimensions where the fermions and gauge bosons are allowed to propagate in the bulk, while the Higgs sector is localized on or near the infra-red brane. These so-called Randall-Sundrum (RS) models have the potential to simultaneously explain the hierarchy problem and address the question of what causes the large hierarchies in the fermion sector of the Standard Model (SM). The Kaluza-Klein (KK) excitations of the bulk fields can significantly affect the loop-level processes considered in this thesis and, hence, could indirectly indicate the existence of warped extra dimensions. The analytical part of this thesis deals with the detailed calculation of three loop-induced processes in the RS models in question: the Higgs production process via gluon fusion, the Higgs decay into two photons, and the flavor-changing neutral current b → sγ. A comprehensive, five-dimensional (5D) analysis will show that the amplitudes of the Higgs processes can be expressed in terms of integrals over 5D propagators with the Higgs-boson profile along the extra dimension, which can be used for arbitrary models with a compact extra dimension. To this end, both the boson and fermion propagators in a warped 5D background are derived. It will be shown that the seemingly contradictory results for the gluon fusion amplitude in the literature can be traced back to two distinguishable, not smoothly-connected incarnations of the RS model. The investigation of the b → sγ transition is performed in the KK decomposed theory. It will be argued that summing up the entire KK tower leads to a finite result, which can be well approximated by a closed, analytical expression.rnIn the phenomenological part of this thesis, the analytic results of all relevant Higgs couplings in the RS models in question are compared with current and in particular future sensitivities of the Large Hadron Collider (LHC) and the planned International Linear Collider. The latest LHC Higgs data is then used to exclude significant portions of the parameter space of each RS scenario. The analysis will demonstrate that especially the loop-induced Higgs couplings are sensitive to KK particles of the custodial RS model with masses in the multi tera-electronvolt range. Finally, the effect of the RS model on three flavor observables associated with the b → sγ transition are examined. In particular, we study the branching ratio of the inclusive decay B → X_s γ

Simulazione numerica di un sistema geotermico a bassa entalpia open-loop in presenza di un gradiente geotermico anomalo

Il lavoro svolto nella presente tesi di laurea magistrale consiste nella modellazione e simulazione numerica, tramite il software commericale COMSOL MULTIPHYSICS, di un reservoir geotermico a bassa entalpia sfruttato mediante un impianto di teleriscaldamento a pompa di calore accoppiato ad un sistema open-loop.

Fast frontend electronics for high rate particle detectors

Future experiments in nuclear and particle physics are moving towards the high luminosity regime in order to access rare processes. In this framework, particle detectors require high rate capability together with excellent timing resolution for precise event reconstruction. In order to achieve this, the development of dedicated FrontEnd Electronics (FEE) for detectors has become increasingly challenging and expensive. Thus, a current trend in R&D is towards flexible FEE that can be easily adapted to a great variety of detectors, without impairing the required high performance. This thesis reports on a novel FEE for two different detector types: imaging Cherenkov counters and plastic scintillator arrays. The former requires high sensitivity and precision for detection of single photon signals, while the latter is characterized by slower and larger signals typical of scintillation processes. The FEE design was developed using high-bandwidth preamplifiers and fast discriminators which provide Time-over-Threshold (ToT). The use of discriminators allowed for low power consumption, minimal dead-times and self-triggering capabilities, all fundamental aspects for high rate applications. The output signals of the FEE are readout by a high precision TDC system based on FPGA. The performed full characterization of the analogue signals under realistic conditions proved that the ToT information can be used in a novel way for charge measurements or walk corrections, thus improving the obtainable timing resolution. Detailed laboratory investigations proved the feasibility of the ToT method. The full readout chain was investigated in test experiments at the Mainz Microtron: high counting rates per channel of several MHz were achieved, and a timing resolution of better than 100 ps after walk correction based on ToT was obtained. Ongoing applications to fast Time-of-Flight counters and future developments of FEE have been also recently investigated.

Bouncing black holes in loop quantum gravity

In questo lavoro viene presentato un recente modello di buco nero che implementa le proprietà quantistiche di quelle regioni dello spaziotempo dove non possono essere ignorate, pena l'implicazione di paradossi concettuali e fenomenologici. In suddetto modello, la regione di spaziotempo dominata da comportamenti quantistici si estende oltre l'orizzonte del buco nero e suscita un'inversione, o più precisamente un effetto tunnel, della traiettoria di collasso della stella in una traiettoria di espansione simmetrica nel tempo. L'inversione impiega un tempo molto lungo per chi assiste al fenomeno a grandi distanze, ma inferiore al tempo di evaporazione del buco nero tramite radiazione di Hawking, trascurata e considerata come un effetto dissipativo da studiarsi in un secondo tempo. Il resto dello spaziotempo, fuori dalla regione quantistica, soddisfa le equazioni di Einstein. Successivamente viene presentata la teoria della Gravità Quantistica a Loop (LQG) che permetterebbe di studiare la dinamica della regione quantistica senza far riferimento a una metrica classica, ma facendo leva sul contenuto relazionale del tessuto spaziotemporale. Il campo gravitazionale viene riformulato in termini di variabili hamiltoniane in uno spazio delle fasi vincolato e con simmetria di gauge, successivamente promosse a operatori su uno spazio di Hilbert legato a una vantaggiosa discretizzazione dello spaziotempo. La teoria permette la definizione di un'ampiezza di transizione fra stati quantistici di geometria spaziotemporale, applicabile allo studio della regione quantistica nel modello di buco nero proposto. Infine vengono poste le basi per un calcolo in LQG dell'ampiezza di transizione del fenomeno di rimbalzo quantistico all'interno del buco nero, e di conseguenza per un calcolo quantistico del tempo di rimbalzo nel riferimento di osservatori statici a grande distanza da esso, utile per trattare a posteriori un modello che tenga conto della radiazione di Hawking e, auspicatamente, fornisca una possibile risoluzione dei problemi legati alla sua esistenza.

Characterization of X-ray detectors based on organic semiconducting single crystals

Negli anni recenti, lo sviluppo dell’elettronica organica ha condotto all’impiego di materiali organici alla base di numerosi dispositivi elettronici, quali i diodi ad emissione di luce, i transistor ad effetto di campo, le celle solari e i rivelatori di radiazione. Riguardo quest’ultimi, gli studi riportati in letteratura si riferiscono per la maggiore a dispositivi basati su materiali organici a film sottile, che tuttavia presentano problemi relativi ad instabilità e degradazione. Come verrà illustrato, l’impiego di singoli cristalli organici come materiali alla base di questi dispositivi permette il superamento delle principali limitazioni che caratterizzano i rivelatori basati su film sottili. In questa attività sperimentale, dispositivi basati su cristalli organici semiconduttori verranno caratterizzati in base alle principali figure di merito dei rivelatori. Tra i campioni testati, alcuni dispositivi basati su singoli cristalli di 6,13-bis (triisopropylsilylethynyl)-pentacene (TIPS-Pentacene) e 5,6,11,12-tetraphenyltetracene (Rubrene) hanno mostrato interessanti proprietà e sono stati quindi maggiormente studiati.

Novel materials for direct X-ray detectors based on semiconducting organic polymers

Conventional inorganic materials for x-ray radiation sensors suffer from several drawbacks, including their inability to cover large curved areas, me- chanical sti ffness, lack of tissue-equivalence and toxicity. Semiconducting organic polymers represent an alternative and have been employed as di- rect photoconversion material in organic diodes. In contrast to inorganic detector materials, polymers allow low-cost and large area fabrication by sol- vent based methods. In addition their processing is compliant with fexible low-temperature substrates. Flexible and large-area detectors are needed for dosimetry in medical radiotherapy and security applications. The objective of my thesis is to achieve optimized organic polymer diodes for fexible, di- rect x-ray detectors. To this end polymer diodes based on two different semi- conducting polymers, polyvinylcarbazole (PVK) and poly(9,9-dioctyluorene) (PFO) have been fabricated. The diodes show state-of-the-art rectifying be- haviour and hole transport mobilities comparable to reference materials. In order to improve the X-ray stopping power, high-Z nanoparticle Bi2O3 or WO3 where added to realize a polymer-nanoparticle composite with opti- mized properities. X-ray detector characterization resulted in sensitivties of up to 14 uC/Gy/cm2 for PVK when diodes were operated in reverse. Addition of nanoparticles could further improve the performance and a maximum sensitivy of 19 uC/Gy/cm2 was obtained for the PFO diodes. Compared to the pure PFO diode this corresponds to a five-fold increase and thus highlights the potentiality of nanoparticles for polymer detector design. In- terestingly the pure polymer diodes showed an order of magnitude increase in sensitivity when operated in forward regime. The increase was attributed to a different detection mechanism based on the modulation of the diodes conductivity.

Loop ileostomy closure: comparison of cost effectiveness between suture and stapler

Closure of loop ileostomy can be safely performed using sutures or staplers. The aim of the present study was to compare the cost effectiveness of three different techniques.

Innate-like control of human iNKT cell autoreactivity via the hypervariable CDR3beta loop

Invariant Natural Killer T cells (iNKT) are a versatile lymphocyte subset with important roles in both host defense and immunological tolerance. They express a highly conserved TCR which mediates recognition of the non-polymorphic, lipid-binding molecule CD1d. The structure of human iNKT TCRs is unique in that only one of the six complementarity determining region (CDR) loops, CDR3beta, is hypervariable. The role of this loop for iNKT biology has been controversial, and it is unresolved whether it contributes to iNKT TCR:CD1d binding or antigen selectivity. On the one hand, the CDR3beta loop is dispensable for iNKT TCR binding to CD1d molecules presenting the xenobiotic alpha-galactosylceramide ligand KRN7000, which elicits a strong functional response from mouse and human iNKT cells. However, a role for CDR3beta in the recognition of CD1d molecules presenting less potent ligands, such as self-lipids, is suggested by the clonal distribution of iNKT autoreactivity. We demonstrate that the human iNKT repertoire comprises subsets of greatly differing TCR affinity to CD1d, and that these differences relate to their autoreactive functions. These functionally different iNKT subsets segregate in their ability to bind CD1d-tetramers loaded with the partial agonist alpha-linked glycolipid antigen OCH and structurally different endogenous beta-glycosylceramides. Using surface plasmon resonance with recombinant iNKT TCRs and different ligand-CD1d complexes, we demonstrate that the CDR3beta sequence strongly impacts on the iNKT TCR affinity to CD1d, independent of the loaded CD1d ligand. Collectively our data reveal a crucial role for CDR3beta for the function of human iNKT cells by tuning the overall affinity of the iNKT TCR to CD1d. This mechanism is relatively independent of the bound CD1d ligand and thus forms the basis of an inherent, CDR3beta dependent functional hierarchy of human iNKT cells.