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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, Dijous 30 de Juny de 2016, a les 12:00h

Seminari del Dep. de Física de la Matèria Condensada

Títol: Local structural and dipolar fluctuations in liquid water: Insights from ab initio molecular dynamics simulati
Conferenciant: Ioannis Skarmoutsos (University of Athens)
Abstract:

A Car-Parrinello molecular dynamics simulation was performed to investigate the local tetrahedral order, molecular dipole fluctuations and their interrelation with hydrogen bonding in liquid water. Water molecules were classified in three types, exhibiting low, intermediate and high tetrahedral order. Transitions from low to high tetrahedrally ordered structures take place only through transitions to the intermediate state. The molecular dipole moments depend strongly on the tetrahedral order and hydrogen bonding. The average dipole moment of water molecules with a strong tetrahedral order around them comes in excellent agreement with previous estimations of the dipole moment of ice Ih molecules. The dependence of the water vibrational spectrum on the number of hydrogen bonds formed revealed that the increase of the number of hydrogen bonds causes a red-shift in the bond-stretching peak positions, whereas the libration peak positions are blue-shifted. The calculated low frequency peaks and the effect of the HB state of the water molecules upon them comes also in agreement with previously reported interpretations of the experimental low frequency Raman spectrum of liquid water.



[1] I. Skarmoutsos, M. Masia, E. Guardia “Structural and dipolar fluctuations in liquid water: A Car-Parrinello molecular dynamics study “, Chemical Physics Letters 648, 102-108 (2016)
[2] E. Guardia, I. Skarmoutsos, M. Masia “Hydrogen Bonding and Related Properties in Liquid Water: A Car-Parrinello Molecular Dynamics Study”, Journal of Physical Chemistry B 119, 8926-8938 (2015)

Lloc: A320, Planta 4, Dep. Fis. Mat. Cond.
Contacte: gfranzese@ub.edu
Web: http://www.ffn.ub.es/gfranzese

Facultat de Física, Divendres 01 de Juliol de 2016, a les 11:30h

Seminari del Dep. de Física de la Matèria Condensada

Títol: QUANTUM EINSTEIN - DE HAAS EFFECT
Conferenciant: EUGENE CHUDNOVSKY (University of New York)
Abstract:

Research on spin-based quantum information processing and the emergence of nanoelectromechanical systems rejuvenated interest to microscopic mechanisms of the Einstein – de Haas effect [1-9]. The concept of a phonon spin, similar to a photon spin, has been recently introduced and applied to achieve a better understanding of the conservation of angular momentum in magnetic relaxation [7]. It has been shown that spin-rotation coupling dictated by the conservation of the total angular momentum limits the quality factor of a nanocantilever [4]. Experimental discovery of quantum Einstein – de Haas effect predicted more than 20 years ago [10] has been reported this year [11] in experiments with a magnetic molecule grafted on a carbon nanotube. Related problems of practical interest include switching of the magnetic moment in a nanoresonator by the combined effect of the spin-polarized current and mechanical kick [6], possibility of the electromechanical magnetization switching in multiferroics [8], and switching of the magnetization by surface acoustic waves [9]. This research has been supported by grants from the U.S. National Science Foundation.

1. M. F. O’Keeffe, E. M. Chudnovsky, and D. A. Garanin, Landau-Zener Dynamics of a Nanoresonator Containing a Tunneling Spin, Physical Review B 87, 174418 (2013).
2. S-H. Lim, A. Imtiaz, T. M. Wallis, S. Russek, P. Kabos, L. Cai, and E. M. Chudnovsky, Magneto-Mechanical Investigation of Spin Dynamics in Magnetic Multilayers, Europhysics Letters 105, 37009 (2014).
3. E. M. Chudnovsky and D. A. Garanin, Damping of a Nanocantilever by Paramagnetic Spins, Physical Review B 89, 174420 (2014).
4. E. M. Chudnovsky, Spin Tunneling in Magnetic Molecules That Have Full or Partial Mechanical Freedom (Ch. 3 in “Molecular Magnets: Physics and Applications”, Springer 2014).
5. L. Cai, R. Jaafar, and E. M. Chudnovsky, Mechanically-Assisted Current-Induced Switching of the Magnetic Moment in a Torsional Oscillator, Physical Review Applied 1, 054001 (2014).
6. D. A. Garanin and E. M. Chudnovsky, Angular Momentum in Spin-Phonon Processes, Physical Review B 92, 024421 (2015).
7. E. M. Chudnovsky and R. Jaafar, Electromechanical Magnetization Switching, Journal of Applied Physics 117, 103910 (2015).
8. E. M. Chudnovsky and R. Jaafar, Manipulating the Magnetization of a Nanomagnet with Surface Acoustic Waves: Spin-Rotation Mechanism, Physical Review Applied 5, 031002 (2016).
9. M. Ganzhorn, S. Klyatskaya, M. Ruben, and W. Wernsdorfer, Quantum Einstein – de Haas Effect, Nature Communications 7, 11443 (2016).
10. E. M. Chudnovsky, Conservation of Angular Momentum in the Problem of Tunneling of the Magnetic Moment, Physical Review Letters 72, 3433 (1994).

Lloc: Seminari 3.20 FÍSICA MATÈRIA CONDENSADA
Contacte: jtejada@ubxlab.com
Web:

Facultat de Física, Dilluns 04 de Juliol de 2016, a les 12:00h

Seminari del Dep. de Física Quàntica i Astrofísica

Títol: The importance of the wind structure in the gamma-ray emission from high-mass microquasars
Conferenciant: Santiago del Palacio (Instituto Argentino de Radioastronomía)
Abstract:

Microquasars are astronomical sources of great interest for
the extreme physical conditions they present. These objects are a subclass of the X-ray binaries with the peculiarity that they present relativistic jets. High-mass microquasars, in particular, consist of a (stellar-mass) compact object and an early-type star. Moreover, massive stars present powerful winds that are not completely smooth, but inhomogeneous (\"clumpy\" instead. In this talk we will show how the wind clumps can lead to complex interactions with the relativistic jets,
giving rise to the emission of gamma-rays. Under this jet-clump interaction scenario we can explain the high-energy observations of systems like Cygnus X-1 and Cygnus X-3, and we also provide an alternative method for exploring the properties of the poorly-known stellar wind structure.

Lloc: Seminari Departament d
Contacte: vbosch@am.ub.es
Web: www.am.ub.edu

Facultat de Física, Dilluns 11 de Juliol de 2016, a les 11:30h

Seminari del Dep. de Física de la Matèria Condensada

Títol: TOPOLOGY AND GLASSY STATES OF MATTER
Conferenciant: EUGENE CHUDNOVSKY (University of New York)
Abstract:

Quenched randomness is common in physics. It is relevant to properties of disordered magnets, pinned vortex lattices in superconductors, charge density waves in solids with impurities, and Josephson junction arrays. Analytical and large-scale numerical studies of these systems [1-8] reveal the important role of topology: The behavior of the n-component order parameter in d dimensions is governed by the presence and structure of topological defects. These findings have theoretical explanation and have been confirmed numerically on lattices of up to one billion sites. They have been extended to the investigation of glassy properties and memory effects in disordered, to models with dilute random fields in applications to systems with impurities, and to random-anisotropy systems. Mapping of quantum models of Josephson-junction arrays onto classical XY spin models allow one to perform comprehensive studies of persistent currents and quantum phase transitions in 1d Josephson junction rings and 2d Josephson junction arrays with randomness. This research has been supported by grants from the U.S. Department of Energy.

1. D. A. Garanin, E. M. Chudnovsky, and T. Proctor, Random Field XY Model in Three Dimensions, Physical Review B 88, 224418 (2013).
2. D. A. Garanin, E. M. Chudnovsky, and T. Proctor, The Role of Vortices in the Three-Dimensional Random-Field XY Model, Europhysics Letters 103, 67009 (2013).
3. T. C. Proctor, D. A. Garanin, and E. M. Chudnovsky, Random Fields, Topology, and Glassy States of Matter, Physical Review Letters 112, 097201 (2014).
4. D. A. Garanin and E. M. Chudnovsky, Ordered vs Disordered States of the Random-Field Model in Three Dimensions, European Physics Journal B 88, 81 (2015).
5. T. C. Proctor and E. M. Chudnovsky, Effect of Dilute Random Field on Continuous-Symmetry Order Parameter, Physical Review B 91, 140201(R) (2015).
6. T. C. Proctor, E. M. Chudnovsky, and D. A. Garanin, Scaling of Coercivity in a 3d Random Anisotropy Model, Journal of Magnetism and Magnetic Materials 384, 181 (2015).
7. D. A. Garanin and E. M. Chudnovsky, Quantum Decay of the Persistent Current in a Josephson Junction Ring, Physical Review B 93, 094506 (2016).
8. D. A. Garanin and E. M. Chudnovsky, Persistent Current in a 2D Josephson Junction Array Wrapped Around a Cylinder, arXiv:1605.08451 [cond-mat.supr-con] 26 May 2016

Lloc: Seminari 3.20 FÍSICA MATÈRIA CONDENSADA
Contacte: jtejada@ubxlab.com
Web:

Facultat de Física, Divendres 15 de Juliol de 2016, a les 15:00h

Seminari del Dep. de Física de la Matèria Condensada

Títol: The mean field solution for Hard Sphere Jamming and a new scenario for the low temperature landscape of glasse
Conferenciant: Giorgio Parisi (Sapienza Università di Roma)
Abstract:

In a hard spheres systems particles cannot overlap. Increasing the density
we reach a point where most of the particles are blocked and the density
cannot be increased any more: this is the jamming point. The jamming point
separates the phase, where all the constraint can be satisfied, from an
unsatifiable phase, where spheres do have to overlap.
A scaling theory of the behavior around the jamming critical point has been
formulated and a few critical exponents have been introduced. The exponents
are apparently super-universal, as far as they do seem to be independent
from the space dimensions.
The mean field version of the model (i.e. the infinite dimensions limit) has
been solved analytically using broken replica symmetry techniques and the
computed critical exponents have been found in a remarkable agreement with
three-dimensional and two-dimensional numerical results and experiments.
The theory predicts in hard spheres (in glasses) a new transition (the
Gardener transition) from the replica symmetric phase to the replica broken
phase at high density (at low temperature), in agreement with simulations on
hard sphere systems.
I will briefly discuss the possible consequences of this new picture on the
very low temperature behavior of glasses in the quantum regime.

Lloc: Aula Seminari 3.20, facultat de física, planta 3
Contacte: ritort@ub.edu
Web: http://ffn.ub.es/ritort/

Facultat de Física, Dilluns 18 de Juliol de 2016, a les 12:00h

Seminari del Dep. de Física de la Matèria Condensada

Títol: CASIMIR FORCES AND STABILITY OF SUSPENDED GRAPHENE
Conferenciant: EUGENE CHUDNOVSKY (University of New York)
Abstract:

Micro-electromechanical systems that involve suspended graphene must take into account interaction of graphene with surrounding elements.
Graphene sheet suspended above a conducting surface is subject to the Casimir force. This poses the problem of stability of the graphene sheet against attaching to the underlying conductor [1]. The stability threshold can be obtained rather accurately within a model of a 2D conducting elastic membrane. It depends on temperature, elastic stress, and separation of the graphene sheet from the conductor at the edges. Nontrivial mathematics of the problem contains solutions for the exfoliation of graphene, which is the primary method of its mass production.

1. 1. E. M. Chudnovsky and R. Zarzuela, Stability of Suspended Graphene under Casimir Force, arXiv:1605.08644 [cond-mat.mes-hall] 27 May 2016.


Lloc: Seminari 3.20 FÍSICA MATÈRIA CONDENSADA
Contacte: jtejada@ubxlab.com
Web:

Facultat de Física, de Dilluns 25 de Juliol de 2016 a Divendres 29 de Juliol de 2016, a les 08:00h

Seminari de Altre

Títol: Congrés d´Impacte Social de la Ciència a Barcelona (25 a 29 de juliol, 2016)
Conferenciant:
Abstract:

Per si és d´interès: Els i les estudiants de la facultat tenen l´oportunitat de participar (prèvia inscripció, amb pagament) en el primer congrés d´Impacte Social de la Ciència a Barcelona en el que hi haurà ponències de tres premis Nobel: François Englert en Física, Ada Yonah en Química, i Harald zur Haussen en Medicina.
Així com representants de revistes científiques com Nature i PLOS o de les agències més destacades del món com National Science Foundation i la Comissió Europea, en totes les ciències i altres camps del coneixement.
En aquesta conferència internacional podran aprendre i gaudir de les aportacions de figures rellevants de la ciència en un context de debat científic internacional, iniciant-se en els fòrums acadèmics de caire científic.
De dilluns a divendres de la darrera setmana de juliol, podran escoltar i conversar amb persones i agències científiques de primer nivell mundial vingudes de més de 40 països diferents. Aquest aprenentatge serà de gran utilitat pels seus estudis i també per la seva pràctica futura professional. La quota per estudiants és de 60 euros.

Lloc: Barcelona
Contacte: info@socialimpactscience.org
Web: http://socialimpactscience.org/sis2016/