Imatge de diagramació Imatge de diagramació Imatge de diagramació Imatge de diagramació
Logo Universitat de Barcelona

Facultat de Física

Imatge de diagramaci�
Inici Facultat Inici UB   
Imatge de diagramació
Agenda/Conferències i seminaris Imatge de diagramació
Imatge de diagramació Imatge de diagramació
Imatge de diagramació Imatge de diagramació Imatge de diagramació
Imatge de diagramació

 
 
   

El límit per poder anunciar en paper seminaris i conferències en els ascensors és el divendres a les 12 hores de la setmana anterior. Amb posterioritat a aquesta data el seminari o conferència quedarà només recollit al web de la Facultat. Aleshores la publicitació en paper serà responsabilitat dels organitzadors.



Facultat de Física, de Dilluns 29 de Abril de 2019 a Dilluns 01 de Juliol de 2019, a les 11 - h

Curs de la Facultat de Física

Títol: Stochastic Modelling of Transport in Heterogeneous Media
Conferenciant: Marco Dentz / Juan Hidalgo (IDAEA-CSIC)
Abstract:

Postgraduate course for physicists, chemists and engineers.
Organized in five 2-hour sessions, on Monday:
- April 29: Introduction to transport in heterogeneous media.
- May 13: Langevin and Fokker-Planck equations
- May 20: Dispersion
- June 3: Continuous time random walks
- July 1: Trapping models

Lloc: Aula 3.20 (planta 3 Fisica UB part nova)
Contacte: jordi.ortin@ub.edu
Web:

Facultat de Física, Dimecres 19 de Juny de 2019, a les 12:00h

Seminari de l'Institut de Ciències del Cosmos

Títol: Binary black hole populations with LIGO/Virgo
Conferenciant: Javier Roulet (Princeton University)
Abstract:

The LIGO and Virgo detectors have observed several gravitational waves from mergers of compact binary objects, mostly binary black holes. These discoveries have allowed to start characterizing the astrophysical population of binary black holes, e.g. the distribution of masses and spins, which carry information about
their origin. Still, these efforts are currently limited by the relatively small number of detections.
Recently, we developed an independent pipeline to analyze public LIGO data and identified seven new binary black hole mergers, roughly doubling the sample of these systems. In this talk I will outline the main stages of the pipeline and describe the constraints we obtain on the properties of binary black holes.

Lloc: Seminari DAM
Contacte: secretariacientifica@icc.ub.edu
Web: http://icc.ub.edu/activity/1357

Facultat de Física, Dimecres 19 de Juny de 2019, a les 12:00h

Seminari del Dep. de Física de la Matèria Condensada

Títol: Phase transitions in fatty acids Langmuir monolayers at the air/water interface: An interfacial shear rheology
Conferenciant: Miguel Angel Rubio (UNED)
Abstract:

Insoluble surfactants on fluid-fluid interfaces form single molecule deep films that are called Langmuir monolayers. Such systems have been studied extensively on air-water interfaces because of their intrinsic interest as biological membrane models, their applications in many industrial processes, or as adequate models to study the physics of two-dimensional systems.

Experiments on the thermodynamic properties and the microstructure of Langmuir monolayers have revealed an extraordinarily rich phase behavior. Particular emphasis has been made on fatty acid and fatty alcohol monolayers [1]. The mechanical properties of these systems have also been studied to some extent [2], but detailed knowledge about the rheological properties of the different thermodynamic phases appearing is still lacking. Technical limitations affecting both instrument resolution and long term measurement stability have precluded such studies.
The magnetic needle Interfacial Shear Rheometer [3] has recently been the object of interesting developments [4] that, by using magnetic tweezers to impose the probe motion, allow for a span of eight orders of magnitude in interfacial dynamic moduli just by opting between two types of probe (a commercial one and a magnetic micro-wire [5]). Interfacial dynamic moduli as low as $10^{-9}$ N/m can be measured with this new type of interfacial rheometer.
We will, first, describe the new rheometer design, and its working principles and performance. Second, we will show that interfacial shear rheology is a useful tool in the study of phase transitions of fatty acids (and alcohols) Langmuir monolayers. We will report on a thorough study of the phase diagram of such monolayers through rheological measurements made with the new interfacial rheometer. Particular emphasis will be made in the study of the rheology of the untilted S and LS phases, where, by cross-checking the results of isothermal interfacial pressure sweeps and isobaric temperature sweeps, we will show a striking temperature dependence of the loss modulus of the viscosity dominated response in the LS phase that increases upon increasing the temperature [6].

References
[1] V.M. Kaganer et al., Rev. Mod. Phys., 71 (1999) 779-819.
[2] C. Alonso et al., J. Phys. Chem. B, 110 (2006) 22185-22191.
[3] C.F. Brooks et al., Langmuir, 5 (1999) 2450-2459.
[4] J. Tajuelo et al., J. of Rheology, 60 (2016) 1095-1113.
[5] J. Tajuelo et al., Langmuir, 31 (2015) 1410-1420.
[6] L.E. Copeland et al., J. Chem. Phys., 10 (1942) 357-365.


Lloc: Aula Pere Pascual, Planta 5. Facultat de Fisica. UB
Contacte: a.hernandezmachado@gmail.com
Web: www.nanobarna.fluidics.com

Facultat de Física, Dimecres 19 de Juny de 2019, a les 15:00h

Seminari de l'Institut de Ciències del Cosmos

Títol: Late bursts of star formation in normal elliptical galaxies
Conferenciant: Jeremiah Ostriker (University of Columbia)
Abstract:

We normally think of elliptical galaxies as massive, stellar systems which are quasi-spherical, filled with old stars and hot gas and essentially quiescent objects. Successful simulations find them made at high redshift, as relatively small objects which grow at early times from gas infall and at late times from accreting satellites. They are known to contain massive black holes of unknown origin. I will show cosmological simulations that are in accord with this and will also show new, very high resolution sims which indicate quite different phenomena. Matter ejected via normal stellar evolution (AGB stars and SN I) provides enough gas to cause cooling flows which lead to episodic formation of dense cold gas disks at the centers of normal ellipticals. These, in turn host formation of massive stars and also feed the central black hole. The disks are dramatic sources of IR and molecular emission. This leads to the commonly observed “E + A” phenomenon and many other dramatic observational events hosted by otherwise passive old galaxies.

Lloc: Aula 507 (Pere Pascual)
Contacte: secretariacientifica@icc.ub.edu
Web: http://icc.ub.edu/activity/1380

Facultat de Física, Dijous 20 de Juny de 2019, a les 15:00h

Seminari de l'Institut de Ciències del Cosmos

Títol: Quantum-assisted Machine Learning in Near-Term Quantum Devices
Conferenciant: Alejandro Perdomo-Ortiz
Abstract:

With quantum computing technologies nearing the era of commercialization and quantum advantage, machine learning (ML) has been proposed as one of the promising killer applications. Despite significant effort, there has been a disconnect between most quantum ML proposals, the needs of ML practitioners, and the capabilities of near-term quantum devices towards a conclusive demonstration of a meaningful quantum advantage in the near future. In this talk, we provide concrete examples of intractable ML tasks that could be enhanced with near-term devices. We argue that to reach this target, the focus should be on areas where ML researchers are struggling, such as generative models in unsupervised and semi-supervised learning, instead of the popular and more tractable supervised learning tasks. We focus on hybrid quantum-classical approaches and illustrate some of the key challenges we foresee for near-term implementations. We will present as well recent experimental implementations of these quantum ML models in both, superconducting-qubit and ion-trap quantum computers

Lloc: Aula 507 (Pere Pascual)
Contacte: secretariacientifica@icc.ub.edu
Web: http://icc.ub.edu/activity/1369

Facultat de Física, Dijous 20 de Juny de 2019, a les 11:45h

Seminari de l'Institut de Ciències del Cosmos

Títol: Constraints on the hadron-quark phase transition and the properties of twin stars with GW170817
Conferenciant: Glòria Montaña
Abstract:

Hybrid stars are compact stars that consist of a core of pure quark or mixed hadron-quark matter and outer layers of hadronic (or nuclear) matter. Depending on its features, the hadron-quark phase transition can lead to a separate mass-radius stable branch of hybrid stars and therefore to "twin-star" solutions, i.e. stars with similar masses and different radii. Therefore, a proof of the existence of twin stars by experimental measurements of masses radii and tidal deformabilities may provide a signature for a phase transition inside neutron stars.

In this talk I will show that the data from the gravitational-wave event GW170817 is compatible with the existence of twin stars and could also be interpreted as the merger of a binary system of hybrid stars or of a hybrid star with a neutron star [1]. In addition, combining the 2Msun observations and the information from GW170817 I will set constraints on the parameters that characterise the phase transition, the maximum masses, and the radii of 1.4Msun stars described by equations of state supporting twin-star configurations

Lloc: Aula 507 (Pere Pascual)
Contacte: secretariacientifica@icc.ub.edu
Web: http://icc.ub.edu/activity/1371

Facultat de Física, Dijous 20 de Juny de 2019, a les 11:00h

Seminari del Dep. de Física de la Matèria Condensada

Títol: Computer simulations of skyrmionic textures in magnetic materials with Dzyaloshinskii-Moriya interactions
Conferenciant: David Cortés Ortuño (Computational Modeling group, University of Southampton, UK)
Abstract:

Research on magnetic systems with broken inversion symmetry has been stimulated by the experimental proof of particle-like configurations
known as skyrmions, whose non-trivial topological properties make them ideal candidates for spintronic technology. In this class of materials,
Dzyaloshinskii-Moriya interactions (DMI) are present, which favor the stabilisation of chiral magnetic configurations. With the help of computer
simulations, it has been possible to analyse and predict multiple properties of skyrmions and more complex magnetic states[1]. At the University
of Southampton, we develop two computer software for the simulation of magnetic materials, the finite element micromagnetic code Finmag,
and the finite difference micromagnetic and atomistic code Fidimag [1]. Using these tools, it has been possible to analyse the ground states of
confined skyrmionic states in bulk cylinder [2] or thin interfacial structures [3], the thermal stability of skyrmions in racetrack systems by means
of energy barrier calculations [4] or understanding the observation of so called bi-skyrmion states [5]. In this talk I will present an overview of
these investigations and the methods we apply for simulating magnetic systems with DMI.
[1] D. Cortés-Ortuño, et al., New Journal of Physics, 20, 113015 (2018)
[2] M. Beg, et al., Scientific Reports 5, 17137 (2015)
[3] D. Cortés-Ortuño, et al., Preprint at: arXiv:1901.06999 (2019)
[4] D. Cortés-Ortuño, et al., Scientific Reports 7, 4060 (2017)
[5] J. C. Loudon et al., Advanced Materials 31, 1806598 (2019)

Lloc: Room 320 (Dpt. Fís. Mater. Cond.)
Contacte: oscariglesias@ub.edu
Web:

Facultat de Física, Dijous 20 de Juny de 2019, a les 12:00h

Seminari de l'Institut de Ciències del Cosmos

Títol: Particle acceleration in protostellar jets: an observational approach
Conferenciant: Adriana R. Rodríguez Kamenetzky (Instituto de Astronomía Teórica y Experimental, Córdoba, Argentina)
Abstract:

Deeply embedded protostellar jets are well known to be dominated by the emission of thermal electrons. Interestingly, in the last decades, negative spectral indices have been detected at centimeter wavelengths in some protostellar jets, indicating the presence of a non-thermal component. Detecting non-thermal emission implies the existence of relativistic particles interacting with magnetic fields, and therefore, the action of a mechanism able to efficiently accelerate them. In this talk I will discuss the conditions that need to be met in order to produce efficient particle acceleration in these low energy systems, based on the analysis of radio continuum images of two representative young stellar objects, obtained with the Karl G. Jansky Very Large Array.

Lloc: Seminari DAM (724)
Contacte: secretariacientifica@icc.ub.edu
Web: http://icc.ub.edu/activity/1377