Near-Optimum Coding for q-ary Symmetric Channel with Application to Space Communications

Questa Tesi aspira a mostrare un codice a livello di pacchetto, che abbia performance molto vicine a quello ottimo, per progetti di comunicazioni Satellitari. L’altro scopo di questa Tesi è quello di capire se rimane ancora molto più difficile maneggiare direttamente gli errori piuttosto che le erasures. Le applicazioni per comunicazioni satellitari ora come ora usano tutte packet erasure coding per codificare e decodificare l’informazione. La struttura dell’erasure decoding è molto semplice, perché abbiamo solamente bisogno di un Cyclic Redundancy Check (CRC) per realizzarla. Il problema nasce quando abbiamo pacchetti di dimensioni medie o piccole (per esempio più piccole di 100 bits) perché in queste situazioni il costo del CRC risulta essere troppo dispendioso. La soluzione la possiamo trovare utilizzando il Vector Symbol Decoding (VSD) per raggiungere le stesse performance degli erasure codes, ma senza la necessità di usare il CRC. Per prima cosa viene fatta una breve introduzione su come è nata e su come si è evoluta la codifica a livello di pacchetto. In seguito è stato introdotto il canale q-ary Symmetric Channel (qSC), con sia la derivazione della sua capacità che quella del suo Random Coding Bound (RCB). VSD è stato poi proposto con la speranza di superare in prestazioni il Verification Based Decoding (VBD) su il canale qSC. Infine, le effettive performance del VSD sono state stimate via simulazioni numeriche. I possibili miglioramenti delle performance, per quanto riguarda il VBD sono state discusse, come anche le possibili applicazioni future. Inoltre abbiamo anche risposto alla domande se è ancora così tanto più difficile maneggiare gli errori piuttosto che le erasure.

On the identification of bridge decks aeroelastic coefficients: the covariance block hankel matrix method

Il seguente elaborato si concentra sull'identifi�cazione strutturale di sistemi soggetti a sollecitazioni aeroelastiche e nello speci�fico l'attenzione viene rivolta ad impalcati da ponte. Si analizzano i concetti principali caratterizzanti il campo dell'aeroelasticità indagando i fattori dominanti che entrano in gioco sul piano teorico. In seguito, si considera il metodo di identifi�cazione strutturale chiamato Covariance Block Hankel Matrix (CBHM) utilizzato come strumento di derivazione dei coeffi�cienti aeroelastici propri della struttura. Infi�ne, si indaga il comportamento di questo metodo di identi�ficazione al variare di una serie di parametri chiave e all'interno di diversi scenari, visionando risultati ottenuti tramite una serie di test eff�ettuati per provare l'a�dattabilità del metodo stesso al variare delle condizioni che caratterizzano il sistema.

Coded slotted aloha with multipacket reception over block fading channels (for satellite networks)

Random access (RA) protocols are normally used in a satellite networks for initial terminal access and are particularly effective since no coordination is required. On the other hand, contention resolution diversity slotted Aloha (CRDSA), irregular repetition slotted Aloha (IRSA) and coded slotted Aloha (CSA) has shown to be more efficient than classic RA schemes as slotted Aloha, and can be exploited also when short packets transmissions are done over a shared medium. In particular, they relies on burst repetition and on successive interference cancellation (SIC) applied at the receiver. The SIC process can be well described using a bipartite graph representation and exploiting tools used for analyze iterative decoding. The scope of my Master Thesis has been to described the performance of such RA protocols when the Rayleigh fading is taken into account. In this context, each user has the ability to correctly decode a packet also in presence of collision and when SIC is considered this may result in multi-packet reception. Analysis of the SIC procedure under Rayleigh fading has been analytically derived for the asymptotic case (infinite frame length), helping the analysis of both throughput and packet loss rates. An upper bound of the achievable performance has been analytically obtained. It can be show that in particular channel conditions the throughput of the system can be greater than one packets per slot which is the theoretical limit of the Collision Channel case.

Chargaff symmetric stochastic processes

Scopo della modellizzazione delle stringhe di DNA è la formulazione di modelli matematici che generano sequenze di basi azotate compatibili con il genoma esistente. In questa tesi si prendono in esame quei modelli matematici che conservano un'importante proprietà, scoperta nel 1952 dal biochimico Erwin Chargaff, chiamata oggi "seconda regola di Chargaff". I modelli matematici che tengono conto delle simmetrie di Chargaff si dividono principalmente in due filoni: uno la ritiene un risultato dell'evoluzione sul genoma, mentre l'altro la ipotizza peculiare di un genoma primitivo e non intaccata dalle modifiche apportate dall'evoluzione. Questa tesi si propone di analizzare un modello del secondo tipo. In particolare ci siamo ispirati al modello definito da da Sobottka e Hart. Dopo un'analisi critica e lo studio del lavoro degli autori, abbiamo esteso il modello ad un più ampio insieme di casi. Abbiamo utilizzato processi stocastici come Bernoulli-scheme e catene di Markov per costruire una possibile generalizzazione della struttura proposta nell'articolo, analizzando le condizioni che implicano la validità della regola di Chargaff. I modelli esaminati sono costituiti da semplici processi stazionari o concatenazioni di processi stazionari. Nel primo capitolo vengono introdotte alcune nozioni di biologia. Nel secondo si fa una descrizione critica e prospettica del modello proposto da Sobottka e Hart, introducendo le definizioni formali per il caso generale presentato nel terzo capitolo, dove si sviluppa l'apparato teorico del modello generale.

Multifrequency VLBA observations of two compact symmetric objects

In this thesis the results of the multifrequency VLBA observations of the GPS 1944+5448 and the HFP J0111+3906 are presented. They are compact objects smaller than about 100 pc, completely embedded in the host galaxy. The availability of multi-epoch VLBI observations spanning more than 10 years, allowed us to compute the hot spot advance speed in order to obtain the kinematic age of both sources. Both radio sources are young, in agreement with the idea that they are in an early evolutionary stage. The spectral analysis of each source component, such as the lobes, the hot spots, the core and the jets, making a comparison with the theoretical ones is described. In addition the physical parameters derived from VLBA images as the magnetic field, the luminosity, the energy and the ambient medium density of both sources are discussed.

Synthesis and metal complexes of C2 symmetric ligands obtained from (R)-(+)-Betti and dialdehydes for asymmetric induction reactions

The aim of this master’s research thesis was the employment of an enantiopure 1,3-aminoalcohol, the 1-(α-aminobenzyl)-2-naphthol, known as Betti base, for the synthesis of some novel compounds which show a C2 symmetry. Some of these compounds, after derivatization, were used as ligands in association with transition metals to prepare some catalysts for enantioselective catalytic reactions. Some aminoalcohol (Salan-type) derivatives of these compounds were obtained upon reduction and in some cases it was possible to obtain complexes with transition metals such as Mn, Ni, Co and Cu. Furthermore a novel 6-membered analogue bisoxazoline ligand, 2,6-bis((R)-1-Phenyl-1H-naphtho[1,2-e][1,3]oxazin-3-yl)pyridine, was obtained and from it two Cu-complexes were prepared. The metal complexes were employed in some reactions to test the asymmetric induction, which was in some cases up to discrete values.

The effect of poly(lactide)-poly(carbonate) based block copolymers on the morphology and crystallization of double crystalline poly(lactide)/poly(ε-caprolactone) blends

Block copolymers of poly(lactide) and poly(carbonate) were synthetized in three different compositions and characterized by 1H-NMR and ATR analyses. The compatibilization effect of this copolymers on 80/20 (w/w%) PLA/PCL blend was evaluated. SEM micrographs show that all the blends exhibit the typical sea-island morphology characteristic of immiscible blends with PCL finely dispersed in droplets on a PLA matrix. Upon the addiction of the copolymers a reduction on PCL droplets size is observable. At the same time, a Tg depression of the PLA phase is detected when the copolymers are added in the blend. These results indicate that these copolymers are effective as compatibilizers. The copolymer that acts as the best compatibilizer is the one characterized by the same amount of PLA and PC as repeating units. As result, in the blend containing this copolymer PLA phase exhibits the highest spherulitic growth rate. An analyses on PLA phase crystallization behaviour from the glassy state within the blends was evaluated by DSC experiments. Isothermal cold crystallization of the PLA phase is enhanced up an order of magnitude upon the blending with PCL. Annealing experiments demonstrated that the crystallization of the PCL phase induces the formation of active nuclei in PLA when cooled above cooled below Tg. When the crystallization rate of PCL is retarded, a reduction on PLA nucleation is observed.

Economic and Environmental Optimization of Ornamental Stone Block Cutting with a 3D Algorithm

This thesis focuses on finding the optimum block cutting dimensions in terms of the environmental and economic factors by using a 3D algorithm for a limestone quarry in Foggia, Italy. The environmental concerns of quarrying operations are mainly: energy consumption, material waste, and pollution. The main economic concerns are the block recovery, the selling prices, and the production costs. Fractures adversely affect the block recovery ratio. With a fracture model, block production can be optimized. In this research, the waste volume produced by quarrying was minimised to increase the recovery ratio and ensure economic benefits. SlabCutOpt is a software developed at DICAM–University of Bologna for block cutting optimization which tests different cutting angles on the x-y-z planes to offer up alternative cutting methods. The program tests several block sizes and outputs the optimal result for each entry. By using SlabCutOpt, ten different block dimensions were analysed, the results indicated the maximum number of non-intersecting blocks for each dimension. After analysing the outputs, the block named number 1 with the dimensions ‘1mx1mx1m’ had the highest recovery ratio as 43% and the total Relative Money Value (RMV) with a value of 22829. Dimension number 1, also had the lowest waste volume, with a value of 3953.25 m3, for the total bench. For cutting the total bench volume of 6932.25m3, the diamond wire cutter had the lowest dust emission values for the block with the dimension ‘2mx2mx2m’, with a value of 24m3. When compared with the Eco-Label standards, block dimensions having surface area values lower than 15m2, were found to fit the natural resource waste criteria of the label, as the threshold required 25% of minimum recovery [1]. Due to the relativity of production costs, together with the Eco-Label threshold, the research recommends the selection of the blocks with a surface area value between 6m2 and 14m2.

Quantum computing and post-quantum cryptography

One of the main practical implications of quantum mechanical theory is quantum computing, and therefore the quantum computer. Quantum computing (for example, with Shor’s algorithm) challenges the computational hardness assumptions, such as the factoring problem and the discrete logarithm problem, that anchor the safety of cryptosystems. So the scientific community is studying how to defend cryptography; there are two defense strategies: the quantum cryptography (which involves the use of quantum cryptographic algorithms on quantum computers) and the post-quantum cryptography (based on classical cryptographic algorithms, but resistant to quantum computers). For example, National Institute of Standards and Technology (NIST) is collecting and standardizing the post-quantum ciphers, as it established DES and AES as symmetric cipher standards, in the past. In this thesis an introduction on quantum mechanics was given, in order to be able to talk about quantum computing and to analyze Shor’s algorithm. The differences between quantum and post-quantum cryptography were then analyzed. Subsequently the focus was given to the mathematical problems assumed to be resistant to quantum computers. To conclude, post-quantum digital signature cryptographic algorithms selected by NIST were studied and compared in order to apply them in today’s life.

Structural steel design with BIM technology - interventions on a three buildings block in Deruta (PG)

The aim of this thesis is to use the developments, advantages and applications of "Building Information Modelling" (BIM) with emphasis on the discipline of structural design for steel building located in Perugia. BIM was mainly considered as a new way of planning, constructing and operating buildings or infrastructures. It has been found to offer greater opportunities for increased efficiency, optimization of resources and generally better management throughout the life cycle of a facility. BIM increases the digitalization of processes and offers integrated and collaborative technologies for design, construction and operation. To understand BIM and its benefits, one must consider all phases of a project. Higher initial design costs often lead to lower construction and operation costs. Creating data-rich digital models helps to better predict and coordinate the construction phases and operation of a building. One of the main limitations identified in the implementation of BIM is the lack of knowledge and qualified professionals. Certain disciplines such as structural and mechanical design depend on whether the main contractor, owner, general contractor or architect need to use or apply BIM to their projects. The existence of a supporting or mandatory BIM guideline may then eventually lead to its adoption. To test the potential of the BIM adoption in the steel design process, some models were developed taking advantage of a largely diffuse authoring software (Autodesk Revit), to produce construction drawings and also material schedule that were needed in order to estimate quantities and features of a real steel building. Once the model has been built the whole process has been analyzed and then compared with the traditional design process of steel structure. Many relevant aspect in term of clearness and also in time spent were shown and lead to final conclusions about the benefits from BIM methodology.

Diagnosing criticality in symmetric and chiral clock models

Quantum clock models are statistical mechanical spin models which may be regarded as a sort of bridge between the one-dimensional quantum Ising model and the one-dimensional quantum XY model. This thesis aims to provide an exhaustive review of these models using both analytical and numerical techniques. We present some important duality transformations which allow us to recast clock models into different forms, involving for example parafermions and lattice gauge theories. Thus, the notion of topological order enters into the game opening new scenarios for possible applications, like topological quantum computing. The second part of this thesis is devoted to the numerical analysis of clock models. We explore their phase diagram under different setups, with and without chirality, starting with a transverse field and then adding a longitudinal field as well. The most important observables we take into account for diagnosing criticality are the energy gap, the magnetisation, the entanglement entropy and the correlation functions.