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Exploring exotic nuclei within the MCAS framework Imprimir
Steven Karataglidis
Department of Physics
University of Johannesburg
South Africa

Martes 7 de abril, 16:15
Sala de seminarios, 3er piso
Departamento de Física (DFI)
Av Blanco Encalada 2008

The study of exotic nuclei, especially near and beyond the drip lines, is becoming increasingly important, as the nuclear landscape is explored well beyond the valley of stability, with the advent of new facilities. There is direct application also to nuclear astrophysics, which requires specific information on the structure of exotic nuclei for the modeling of the reactions involved in nucleosynthesis. The talk will present the Multi-Channel Algebraic Scattering (MCAS) theory, a theory of low-energy scattering, currently based on a collective model description of the target nucleus, allowing for the determination of the structures of the compound systems formed in the scattering. This has had great success in the descriptions of exotic nuclei. Comparisons to shell model are made where possible. Future prospects will also be discussed.

Seminarios Anteriores

Fundamental physics and astrophysics with Gravitational Waves from coalescing binaries Imprimir
Riccardo Sturani

Miércoles 1 de abril, 16:15
Sala de seminarios, 3er piso
Departamento de Física (DFI)
Av Blanco Encalada 2008

The large interferometric detectors of gravitational waves LIGO and Virgo will resume data taking later this year after having taken data at lower sensitivity for few years until 2010. After giving an overview of the observational results obtained in past science runs, I will discuss coalescing binaries as the most likely sources for the first direct detection of gravitational waves. Beside opening the new field of gravitational astrophysics, waves emitted by compact stars and black holes in binary systems are an ideal probes of the fundamental gravity dynamics and their eventual repeated detection will allow to test General Relativity (or any other gravity theory) to unprecedented precision. It will be shown how accurate knowledge of the waveform is actually crucial in both enhancing detection probability and maximizing the (astro)physics outcome of a detection.
B-mode polarization with the BICEP / Keck Array series Imprimir
Walter Ogburn
Department of Physics
Stanford University

Miércoles 25 de marzo, 16:30
Departamento de Física - Sala F12
Av Blanco Encalada 2008

The BICEP/Keck Array program is a series of telescopes at South Pole designed to measure cosmic microwave background (CMB) polarization on degree angular scales. If detected, cosmological B-modes on degree angular scales could represent an imprint of gravitational waves produced during cosmic inflation. We will describe the instruments and latest results of the program. Using data collected during 2010-2013 at 150 GHz, the BICEP2+Keck Array polarization maps achieve noise levels of 57 nK-deg (3.4 uK-arcmin) over an effective area of 400 square degrees, for a survey weight of 250,000 uK^-2.  A strong excess B-mode signal is observed above the lensing B-mode signal predicted by LCDM. A joint analysis with data from the Planck satellite finds the excess to be at a similar level to the Galactic dust foreground. After accounting for dust, BICEP2+Keck Array continues to detect lensing B-modes at 7.0 sigma. Keck Array and the newly installed BICEP3 are actively taking data of the same field at 95 and 220 GHz to further separate the Galactic dust foreground from the primordial CMB signal.
What is the strength of gravity? A guided tour from cosmological to laboratory scales Imprimir
Subodh Patil
Department of Theoretical Physics
Geneva University

Viernes 20 de marzo, 16:15
Departamento de Física - F12
Av Blanco Encalada 2008

Gravity, like all forces must ultimately be quantized. However, in spite of our continued ignorance as to how this really happens, we have a very useful tool through which we can incorporate weak quantum effects systematically in a self consistent approximation-- that of effective field theory. In this talk, we will review several well known results in this context about how the strength of gravity depends on the scale of the process we are interested in and review various examples from laboratory to cosmological scales. We present the consequences of this scale dependence of the strength of gravity for inferring various quantities in the early universe (i.e. during inflation) through late time observations.

Floating on Air Imprimir
Detlef Lohse
Physics of Fluids Group
Department of Science and Technology
University of Twente

Miércoles 18 de marzo, 16:15
Sala de seminarios, 3er piso
Departamento de Física (DFI)
Av Blanco Encalada 2008 
A drop impacting on a solid surface deforms before the liquid makes contact with the surface. We directly measure the time evolution of the air layer profile under the droplet using high-speed color interferometry, obtaining the air layer thickness before and during the wetting process and the volume of the entrained droplet. This volume shows a maximum as function of the impact velocity. We physically explain this maximum as a balance between capillary and inertial effects. The experiments are complemented by numerical simulations, based on potential flow for the impacting droplet and a lubrication theory for the gas layer in between the droplet and the surface, and by scaling laws which we derived analytically. 

The work is then extended in various directions: For the drop impact on a hot surface heated above the liquid’s boiling point, the droplet either immediately boils when it contacts the surface (‘‘contact boiling’’), or without any surface contact forms a Leidenfrost vapor layer towards the hot surface and bounces back (‘‘gentle film boiling’’), or both forms the Leidenfrost layer and ejects tiny droplets upward (‘‘spraying film boiling’’). We also look at the maximum spreading  of impacting droplets on such heated surfaces, which is much further than for the impact on non-heated surfaces and shows universal scaling behavior. We also explain under what conditions splashing is achieved and connect it to the vapor and gas flow under the droplet.

In the lecture we will not only show the (beautiful!) phenomena with high-speed visualisations and account for them theoretically, but we will also address various applications of our research in the industrial context.

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