Hole dynamics in one-dimensional optical lattices

Màster Oficial de Ciència i Tecnologia Quàntiques / Quantum Science and Technology, Facultat de Física, Universitat de Barcelona. Curs: 2022-2023. Tutors: Ivan Morera, Grigory AstrakharchikWe study the dynamical properties of a single hole on top of a Mott insulator described by the Bose-Hubbard Hamiltonian in the strongly interacting regime. The full Hamiltonian can be mapped to an effective one by means of the perturbation theory approach, which allows us to obtain the hole effective mass and study the long-time dynamics of a hole, initially localized with a Gaussian distribution or a delta function. The hole effective mass becomes infinite at a critical value of the onsite interaction, which is reflected in its time evolution described by a dispersionless Gaussian distribution. Moreover, a hole, initially localized in a single site, exhibits an oscillatory behavior in its time evolution. We also perform exact diagonalization simulations of the full Bose-Hubbard model and compare the results with the predictions obtained with perturbation theory. The hole effective mass shows a similar trend in the strong coupling regime as in our perturbation theory, however, it does not diverge at a critical on-site interaction. Nevertheless, we also obtain an oscillatory behavior of the hole density in time when starting the time evolution with a hole localized in a site

Study of neutron background at n_TOF facility

Treballs Finals de Grau de Física, Facultat de Física, Universitat de Barcelona, Curs: 2022, Tutors: Guillem Cortés, Assumpta ParreñoTo have accurate results when measuring neutron capture cross sections is important a good characterization of neutrons involved in these reactions. In this project, the first steps to compute the neutron background in the two experimental areas at the n_TOF facility at CERN have been performed via Monte Carlo simulations using the FLUKA code. Specifically, the energy spectrum and space distribution for background neutrons within energies between meV and GeV have been compute

Flexibility Relative to What? Change to Research Infrastructure

It is often said that, in the face of an ever-changing world, infrastructure must remain flexible. Yet, what is meant by change remains glib and, consequently, so too do our studies on flexibility. In this paper, we develop three sensitizing concepts to investigate change to research infrastructure: 1) technoscientific: changes in research objects, scientific methods, and instruments; 2) sociotechnical: changes in social organization, coordination and, collaboration tools; and data sharing techniques; and 3) institutional: changes in funding and regulatory regimes. The majority of studies of “information infrastructure” have focused on the sociotechnical facet, and so we offer the two additional facets of change to help sensitize researchers to empirical instances of these encountered in the field, and to broaden the research agenda. To elaborate these concepts, we focus on a long-term research infrastructure that has been investigating HIV disease for nearly thirty years: The Multicenter AIDS Cohort Study (MACS). Over time, the MACS has faced tremendous changes in its science, collaboration and communication tools, its data and specimen repositories, its institutional environment, and the disease itself. Before we can begin to characterize flexibility, we must understand the nature of change research infrastructures face. We conclude by outlining a research agenda that will match forms of flexibility to the heterogeneity of changes an infrastructure may encounter

An energy-efficient distributed dynamic bandwidth allocation algorithm for Passive Optical Access Networks

The rapid deployment of passive optical access networks (PONs) increases the global energy consumption of networking infrastructure. This paper focuses on the minimization of energy consumption in Ethernet PONs (EPONs). We present an energy-efficient, distributed dynamic bandwidth allocation (DBA) algorithm able to power off the transmitter and receiver of an optical network unit (ONU) when there is no upstream or downstream traffic. Our main contribution is combining the advantages of a distributed DBA (namely, a smaller packet delay compared to centralized DBAs, due to less time being needed to allocate the transmission slot) with energy saving features (that come at a price of longer delays due to the longer queue waiting times when transmitters are switched off). The proposed algorithm analyzes the queue size of the ONUs in order to switch them to doze/sleep mode when there is no upstream/downstream traffic in the network, respectively. Our results show that we minimized the ONU energy consumption across a wide range of network loads while keeping delay bounded.Postprint (published version

Ladrillo cerámico con huecos hexagonales

Ladrillo cerámico con huecos hexagonales. La invención consiste en un ladrillo cerámico con huecos hexagonales a lo largo de su dirección longitudinal. Resuelve el problema de la transmisión de ruido aéreo que presentan los ladrillos cerámicos con hueco cuadrado o rectangular. La intensidad del sonido transmitido en sólidos decrece con el aumento de camino recorrido. Por ello, la sustitución de las paredes perpendiculares que definen los huecos cuadrados o rectangulares, por las que definen los huecos hexagonales representa un mayor recorrido y una absorción mayor de ruido. El espesor del ladrillo puede variar según contenga una o más filas de hexágonos compartiendo caras o vértices. No hay limitación en las dimensiones del largo y ancho del mismo. Exteriormente los cantos de las piezas pueden ser machihembrados y las caras planas pueden o no presentar estriado. La colocación de la pieza se realiza con los huecos paralelos a la horizontal. Utilización en construcción de paramentos verticales en edificio