Màster Oficial - Física Avançada

URI permanent per a aquesta col·leccióhttps://hdl.handle.net/2445/59959

Treballs finals del Màster Oficial en Física Avançada de la Facultat de Física de la Universitat de Barcelona.

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Study of quantum scattering T-matrix
(2016-06) Sánchez Baena, Juan; Mazzanti Castrillejo, Ferran; Polls Martí, Artur
We present an off-shell calculation of T-matrix elements for different kinds of potentials. In this report we review the basic concepts about this quantity, as well as its relation with the general quantum scattering problem, remmarking its relevance when dealing with anisotropic and/or long ranged interactions. We emphasize the calculation of the generalized scattering lengths for the combination of a dipolar and a hard core potential (DHC), since it is of special interest in the field of ultra-cold quantum dipolar gases
Autocatalytic colloid suspensions in the presence of a liquid-liquid interface
(2016-06) Palacios Ruiz, Lucas Santiago; Pagonabarraga Mora, Ignacio; Ordóñez Sánchez, Samuel
Self-propelled diffusiophoretic colloids are currently being studied because of its revolutionary way to solve real applications on fields such as water cleaning or medicine. One of the most considered prototypes is the Pt-silica Janus because of its simplicity and easy construction. Although today Janus can be built within hours, still it lacks some physical knowledge of their behaviour. In an attempt to understand better Janus, in this project I have performed not only an experimental but also a computational approach to Janus. In particular, I have focus on what happens for Pt-silica Janus in a dilute regime near a liquid-liquid interface. Experimental results have shown how the velocity is decreased compared to its usual velocity on bulk up to 45%. Moreover, interface modifications with surfactants has also shown how on the one hand, surfactants interfere in Janus velocity but also, how Janus are further to the interface. Computational results, could not approximate as much as experimental, but at least they show how Janus can be modelled and how this model could explain real behaviour of Janus at the bulk by selecting a small region for chemorepellant mobility parameters related to each of the parts of the Janus particle
Flow in elastic networks subject to pulsatile forcing
(2016-06) González, Laia (González Mena); Pagonabarraga Mora, Ignacio; Corvera Poiré, Eugenia
The hemodynamics of a vascular vessel network can be affected by the presence of obstructions. We present a theoretical analysis of the effect that obstructions have on a vessel network under pulsatile inlet pressure, and analyze the importance of the level in which obstructions occur. The elasticity of the vessels is implemented following a recently developed model. Flow and pressure along the network are calculated for a network of equal vessels and for a network that follows Murray's law for radii. The effect of obstructions is evaluated in terms of an effective response, which relates the pressure difference, between the inlet and the outlet of the network, with the blood flow. Our calculations reveal that results obtained for a rigid network and those obtained by taking into account the elasticity of the vessel walls, are qualitatively different. The response of the network when a certain degree of obstruction is present is highly dependent on the level at which the obstructions occur
Viscoelastic properties of Red Blood Cells in a flow
(2016-06) Gironella Torrent, Marta; Ritort Farran, Fèlix
Red Blood Cells (RBC) are transported through blood stream and are responsible of oxygen delivery to the body tissues in vertebrates animals. This is achieved by squeezing RBC through body's capillaries, with mechanical properties being essential to achieve this function. Shape and composition of RBC are tightly related to their mechanical properties and their variation could induce several diseases and disorders. For that reason, the quantification of the mechanical properties of RBC could acts as an important biomarker. In this project we have performed flow experiments with RBC attached to a micron-sized bead using Optical Tweezers. The obtained results show two different populations of RBC characterized by the formation of a membrane microtube observed at high flow velocities values (800 [mu]m/s or 50 pN of drag force). Analysing the force-velocity curves, we are able to differentiate these two populations and extract drag coefficient of RBC
A 3D computational model for understanding tuberculosis lesions dynamics in lungs
(2016-06) Català Sabaté, Martí; Pagonabarraga Mora, Ignacio; Prats, Clara
Tuberculosis (TB) is an infectious bacterial disease caused by Mycobacterium tuberculosis (Mtb), which most commonly affects the lungs. In healthy people, an infection with Mtb often causes no symptoms, remaining controlled as a non-contagious latent tuberculosis infection. World Health Organization estimates that one third of the world population is already infected by this bacillus. From those, a 10% will probably develop an active disease the next decade. Nowadays, over 1 million people die annually because of an active TB. The mechanisms that maintain a latent infection for a few years or that make it evolving towards an active disease are not fully understood, yet. In a previous work, the dynamics of TB lesions during an active disease in mice was described by an Agent-Based Model (ABM). This model accounted for the growth, coalescence and proliferation of lesions, showing that the most important mechanism for lesions growth during the active disease was coalescence. In a later work, the dynamics of lesions during a latent infection in minipigs was tackled by implementing a revised version of the previous ABM into a computational model of the bronchial tree. The model was fed with Computed Tomography scan data from latent infection in minipigs. In this case, the model showed that the proliferation of lesions through the bronchial tree was essential for maintaining the latent infection. In this Master thesis we propose a first approach on the evolution of a latent tuberculosis infection into an active disease. The parameter space will be explored trying to elucidate which is the role of each mechanism on the trigger for the disease
Tuning Synchronization through mobility and limited vision
(2016-06) Beardo Ricol, Albert; Sagarra Pascual, Oleguer Josep; Prignano, Luce; Díaz Guilera, Albert
In this work we analyse the emergence of synchronization in a population of mobile Integrate-and-Fire oscillators with limited vision. By proposing novel interaction rules among oscillators we bridge phenomenology detected in a variety of previous models. In particular, we explore the effect that the effective asymmetry of interactions have on the non monotonic behaviour observed in the synchronization time of the population as a function of their velocities. We recover non linear features with the same origin as [1] but considering only geometrical interactions, and we study the scaling properties of the model as well as predict the values of the parameters where the different dynamical regimes take place.
Conductive inks printing through laser-induced forward transfer
(2015-06) Sopeña i Martínez, Pol; Serra Coromina, Pere
The laser-induced forward transfer of silver nanoparticle ink with long laser pulse duration (120 ns) was investigated in this work. The feasibility of the technique for printing patterns was proven. The study focuses on the analysis of the deposition of droplets and transfer dynamics. Several droplets were printed at different laser pulse energies, showing a radius-energy linear dependence. However, the volume-energy dependence was non-monotonous, increasing at low energies and staying fairly constant at high ones. A time-resolved study of the transfer dynamics showed four stages during the transfer process: bubble expansion, bubble burst, jet formation and deposition, which always occur independently of the energy. A feasibility test was also carried out to prove the functionality of printed lines as interconnects in electronic circuits
Mechanical folding and unfolding of the redox protein Flavodoxin
(2015-06) Sanmartí, Enric; Ritort Farran, Fèlix; Alemany i Arias, Anna
We investigate the unfolding and folding processes of redox protein Flavodoxin under the action of mechanical forces at the single molecule level using force spectroscopy methods with optical tweezers. Previous bulk studies have provided valuable information about the structure of the folded and unfolded states, and pointed out the existence intermediate states along the unfolding and folding pathways. However direct evidence about the existence of such kinetic intermediates and their lifetimes is still missing. Here we pull molecular constructs of the protein Flavodoxin flanked by double stranded DNA linkers tethered to micron-sized beads with optical tweezers to mechanically unfold the protein. The distributions of rupture forces have been characterized and intermediate states have been found along the unfolding and folding pathways. Moreover, the molecular free energy landscape of the protein has been characterized from the unfolding kinetics using the Bell-Evans model and an estimate of the free energy of formation of the protein has been extracted using the Crooks fluctuation theorem
Bose-Fermi mixtures in 1D few-sites optical lattices
(2015-06) Pelegrí Andrés, Gerard; Juliá-Díaz, Bruno; Polls Martí, Artur
We use exact diagonalization techniques to study the ground state properties of few-site optical lattices where bosons and fermions are mixed and interact. First, we consider a two-site system with 50 bosons and one single fermionic impurity. The interaction of the impurity with the bosonic background is shown to modify its properties. Then, we consider a three-site system in order to see effects of the fermionic nature of the impurities. In this system, the modifcation of the properties of the bosons by the interaction with the fermions is even more dramatic, and is different when the system hosts one fermion than two
Avalanches in the athermal 2d Random-Field Ising model: front propagation versus nucleation and growth dynamics
(2015-06) Navas Portella, Víctor; Vives i Santa-Eulàlia, Eduard
The two-dimensional zero-temperature Random Field Ising Model with local adiabatic relaxation dynamics is studied. When externally driven, this model allows to analyse the properties of an advancing front for different amounts of disorder. By imposing special forced boundary conditions and allowing for systems with rectangular geometry, we favour the existence of a unique interface which is the boundary of a 1d spanning avalanche. We show that the description of an advancing front in terms of a univalued function x(y) lacks of a relevant contribution in the thermodynamic limit: the existence of overhangs and islands which are characteristic of the nucleation and growth dynamics
Quantum properties of two-component two-sites Bose-Hubbard model
(2015-06) Mujal Torreblanca, Pere; Juliá-Díaz, Bruno; Polls Martí, Artur
This work contains a detailed analysis of the properties of the ground state of a two-component two-sites Bose-Hubbard model, which captures the physics of a binary mixture of Bose-Einstein condensates trapped in a double-well potential. The atom-atom interactions within each species and among the two species are taken as variable parameters while the hopping terms are kept fixed. To characterize the ground state we use observables such as the imbalance of population and its quantum uncertainty. The quantum many-body correlations present in the system are further quantified by studying the degree of condensation of each species, and the entanglement between the two species. The latter is measured by means of the Schmidt gap, the von Neumann entropy or the purity obtained after tracing out a part of the system. A number of relevant states are identified, e.g. Schrödinger catlike many-body states, in which the outcome of the population imbalance of both components is completely correlated, and other states with even larger von Neumann entropy which have a large spread in Fock space
The complex architecture of primes and natural numbers
(2014-12) García Pérez, Guillermo; Serrano Moral, Ma. Ángeles (María Ángeles); Boguñá, Marián
Natural numbers can be divided in two non-overlapping infinite sets, primes and composites, with composites factorizing into primes. Despite their apparent simplicity, the elucidation of the architecture of natural numbers with primes as building blocks remains elusive. Here, we propose a new approach to decoding the architecture of natural numbers based on complex networks and stochastic processes theory. We introduce a parameter-free non-Markovian dynamical model that naturally generates random primes and their relation with composite numbers with remarkable accuracy. Our model satisfies the prime number theorem as an emerging property and a refined version of Cramér's conjecture about the statistics of gaps between consecutive primes that seems closer to reality than the original Cramér's version. Regarding composites, the model helps us to derive the prime factors counting function, giving the probability of distinct prime factors for any integer. Probabilistic models like ours can help to get deeper insights about primes and the complex architecture of natural numbers
Study of the magnetic properties of nanoparticles interacting with surface acoustic
(2015-06) Checa Nualart, Martí; Tejada Palacios, Javier; Hernández Mínguez, Alberto
In this work we design and build from zero, a device with the aim of studying the spin-phonon interaction in magnetic nanoparticles. New techniques to manipulate the magnetic moments of nanostructures are demanding to be studied. Surface acoustic waves (SAWs) are an excellent candidate as they offer a dynamic and tunable mechanism for the control of low energy excitations. The final goal of the project is to get closer towards acousto-magnetic devices as well as the better understanding of the fundamentals of the interaction. Both the design and building of the samples have been made by us at Paul-Drude-Institut für Festkörperelektronik in Berlin, with the idea of having an exhaustive control of all the parameters. Fe2O3 magnetic nanoparticles were embedded in a SiO2 matrix, and deposited in a piezoelectric substrate (LiNbO3) between two interdigital transducers (IDTs) that generate SAWs when they are connected to a source of microwaves. Magnetic measurements are taking place in a SQUID magnetometer at University of Barcelona, consisting in studying the magnetization dynamics when applying SAWs of different frequencies and powers to the sample. The effects of the temperature and the external applied field are also studied.
Tonks-Girardeau gas in different potential traps by exact diagonalization
(2014-07) Yuste Roca, Abel Vicenç; Polls Martí, Artur
We computed the second-quantized many-mode Hamiltonian for spinless ultracold bosons trapped in di erent one-dimensional potentials and diagonalized it for a small number of atoms. We observed the transition from the non-interacting gas to the Tonks-Girardeau gas, i.e. the fermionization process, as we increase the strength of the interactions between the atoms. We computed the energy spectrum, the one-body density matrix, the two-body correlations, the momentum distribution, the natural orbitals and the occupations for di erent interaction strengths. We compared the fermionization in di erent potentials with special attention to the largest occupation of the natural orbits, the build up of quantum many-body correlations between di erent parts of the system, and the energy of the ground and excited states.
Cold bosons in optical lattices: an exact diagonalization study
(2014-07) Raventós i Ribera, David; Juliá-Díaz, Bruno
Experimental setups of cold atoms in optical lattices reproduce several quantum many-particle models, including the Bose-Hubbard model. We study this model by means of exact diagonalization. This model carries a super uid to Mott insulator quantum phase transition. In order to characterize the phase transition, we have computed the ground state of the system and its overlap with the analytic expressions for the Mott insulator and super uid states, its one-body density matrix, and its Von Neumann entropy. We have also studied the e ect of setting an attractive bias potential in one site of the lattice at di erent strengths and also the strongly biased case in the repulsive regime. Finally, we have also explored the case with attractive on-site interactions, nding correlated states in the weakly attractive regime.
Inkjet printing of flexible MOS structures based on graphene and high-k dielectrics
(2014-07) Olmedo Ferrer, Omar; Cirera Hernández, Albert
MOS structures have been inkjet printed using silver, hafnium oxide (HfO2) and reduced graphene oxide (rGO). Main drawbacks with inkjet printing and electrospray deposition have been overcome. C-V characteristics of these devices have been measured and common phenomenology has been established. Deviations from known theory as well as technical improvement have been proposed.
An experimental study of the temperature-dependent DNA elasticity using optical tweezers
(2014-07) Martínez Monge, Álvaro; Ritort Farran, Fèlix
Temperature plays a key role in all biological processes. Slight changes of temperature may lead to completely di erent behaviors of biological systems. In fact, living matter carry out its function in a small range of temperature. Therefore, it is interesting to study and understand what is the effect of temperature in biological systems. Single-stranded DNA (ssDNA) is one of the most relevant molecules in biological processes, providing us an excellent scenario to understand how the temperature a ect its properties. In this project we aim to understand and characterize the elastic response of ssDNA at di erent temperatures. We have used the Laser Optical Tweezers (LOT) technique in order to measure the Force-Distance Curves (FDC) of ssDNA under the e ect of a mechanical force at di erent temperatures. By tting the stretching response of ssDNA to two semi exible polymer models we have obtained the temperature dependence of the elastic parameters. We have found that persistence length and Kuhn length increase with temperature while the stretching modulus seems to be insensitive to temperature changes. Finally, we have found that the persistence length is proportional to the Debye screening length and that it varies with temperature according to a power law with exponent < 1.

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