JUNE 17 - 21, 2013
MONDAY, JUNE 17
11:00 am: Atomic and Molecular Physics Division Informal Seminar. "Patterned Deposition and Spontaneous Formation of Density Waves in the Non-Equilibrium Dynamics of Spatio-Temporally Driven Lattices," Prof. Peter Schmelcher, Zentrum für Optische Quantumtechnologien, Universität Hamburg. Phillips Auditorium.
Abstract: We investigate the non-equilibrium classical dynamics and directed transport in lattices with a spatially-dependent driving. Prototype examples are phase, frequency or amplitude-modulated lattices which, via a tuning of the parameters of the driven unit cell, allow for an engineering of the classical phase space and therefore of the magnitude and direction of the directed currents. Several mechanisms for transient localization and trapping of particles in different wells of the driven unit cell are presented and analyzed. As a major first application we derive a mechanism for the patterned deposition of particles in a spatio-temporally driven lattice. The working principle is based on the breaking of the spatio-temporal translation symmetry, which is responsible for the equivalence of all lattice sites. The patterned trapping of the particles occurs in confined chaotic seas, created via the ramping of the height of the lattice potential. Complex density profiles on the length scale of the complete lattice can be obtained by a quasi-continuous, spatial deformation of the chaotic sea in a frequency modulated lattice. In a second step we explore spatio-temporal upper-lattices consisting of domains of differently time-driven spatial lattices. Here we demonstrate a novel mechanism for the conversion of ballistic to diffusive motion and vice versa. This process takes place at the interfaces of domains subjected to different time-dependent forces. As a consequence a complex short-time depletion dynamics at the interfaces followed by long-time transient oscillations of the particle density are observed. The latter can be converted to permanent density waves by an appropriate tuning of the driving forces. The proposed mechanism opens the perspective of an engineering of the non-equilibrium dynamics of particles in inhomogeneously driven lattices.
WEDNESDAY, JUNE 19
12:30 pm: High Energy Astrophysics Division Lunch Talk. "The Shape of the Cutoff in the Synchrotron Emission of SN 1006 Observed with XMM-Newton," Marco Miceli, INAF/OAPA. Pratt Conference Room.
Abstract: Synchrotron X-ray emission from the rims of young supernova remnants allows us to study the high-energy tail of the electrons accelerated at the shock front. The analysis of X-ray spectra can provide information on the physical mechanisms that limit the energy achieved by the electrons in the acceleration process. We analyzed the deep observations of the XMM-Newton SN 1006 Large Program. We performed spatially resolved spectral analysis of a set of small regions in the nonthermal limbs and we modelled the X-ray spectra by adopting models that assume different shapes of the cutoff in the electron spectra. We found that radiative losses play a fundamental role in shaping the electron spectrum in SN 1006. In fact, a loss-limited model provides the best fit to all the spectra and this indicates that the shape of the cutoff in the electron momentum (p) distribution has the form exp[-(p/p_cut)^2].
THURSDAY, JUNE 20
4:00 pm: CfA Summer Colloquium. "X-ray and Multiwavelength Extragalactic Surveys," Dr. Francesca Civano, Dartmouth College and SAO. Preceded by refreshments at 3:30 pm. Phillips Auditorium.
Abstract: Two currently active X-ray missions, NASA's Chandra X-Ray Observatory and ESA's XMM Newton, are performing some of the deepest and widest serendipitous X-ray surveys ever undertaken. Multiwavelength photometric and spectroscopic follow-up of serendipitously detected X-ray sources is crucial to understand the properties of the objects observed, resulting in large imaging campaigns from radio to UV. I will present a broad overview of these surveys, focusing on the COSMOS survey and on the results achieved by sampling a large sample of Active Galactic Nuclei at high redshift with uniform observed properties.
FRIDAY, JUNE 21
11:00 am: Solar, Stellar, and Planetary Sciences Division Special Seminar. "Magnetic Fields in T Tauri Stars," Gaitee Hussain, European Southern Observatory. Pratt Conference Room.
Abstract: Strong, kilogauss, magnetic fields are required to explain a range of observational properties in young, accreting pre-main sequence systems. I will review the results from our five-year campaign aimed at characterizing the magnetic field properties of young T Tauri stars. As a rule we find that magnetic fields are ubiquitous in low mass pre-main sequence stars (< 1.3 Msun) though they do cover a range of magnetic field properties. A complementary large study of magnetic fields in higher mass stars finds that the incidence of significant magnetic fields in main sequence and pre-main sequence higher mass stars (2-5 Msun) is much lower, typically between 5-10%. Pre-main sequence Herbig Ae/Be stars show similar characteristics to their main sequence A and B star counterparts. We have launched a new study to catalogue the incidence and characteristics of magnetic fields in intermediate mass T Tauri stars (1.5-5 Msun) at different stages of PMS evolutionary tracks. I will present the first results from our study aimed at exploring the incidence of magnetic fields in the precursors to Herbig Ae/Be stars: the intermediate mass T Tauri stars.
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