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Active systems: from bacterial suspensions to granular Imprimir
Anton Peshkov
Departamento de Física
FCFM, Univ. de Chile

Viernes 24 de abril, 16:15
Sala de seminarios, 3er piso
Departamento de Física (DFI)
Av Blanco Encalada 2008

We call active systems any collection of self-propelled individuals, which can be natural like a bacterial suspension or a flock of birds, or artificial like colloids or shaken granular. The self-propelled nature of these particles put the whole system out of equilibrium, which give rise to a plethora of interesting phenomena. In the first part of my talk, I will present an experimental work on mechanical energy extraction from a suspension of bacteria. I will show that using smartly designed carriers it is possible to extract mechanical energy from these out of equilibrium suspensions. In the second part, I will present another work, this time numerical simulations, on the rheology of active granular particles. I will show that activity can drastically reduce the friction of granular particles.
 

Seminarios Anteriores

Structure Formation in the Universe: Small Scale Issues Imprimir
Andrés Escala
Departamento de Astronomía
FCFM, Universidad de Chile

Viernes 17 de abril, 16:15
Departamento de Física (DFI), F12
Av Blanco Encalada 2008

When the cosmic microwave background came into 400.000 years after the big bang, the universe was almost perfectly uniform, with tiny density fluctuations  that were the seeds  of the galaxies and other structures we see today. I will review the standard theory  of structure formation in the universe, based on Lambda-CDM cosmological paradigm, with  special focus on the  open issues on the smallest scales. I will discuss in detail problems currently studied by the theory group  at Calan, such as cosmological massive black hole formation and star formation laws in galaxies.
 
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.
 
Fundamental physics and astrophysics with Gravitational Waves from coalescing binaries Imprimir
Riccardo Sturani
ICTP-SAIFR, Sao Paulo
Brasil

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
and KIPAC

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.
 
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