FEBRUARY 11 - 15, 2008
MONDAY, FEBRUARY 11
12 noon: Solar, Stellar, and Planetary Sciences Division Seminar. "Structure, Complexity and Relaxation in Turbulence and the Solar Wind," Prof. William H. Matthaeus, Bartol Research Institute and Department of Physics and Astronomy, University of Delaware. Pratt Conference Room.
Abstract: MHD turbulence is often associated with randomness and global processes such as relaxation and cascade, concepts that can meaningfully be explored in the context of solar wind turbulence. Alfvenic turbulence and anisotropy are two familiar examples. However turbulence can also give rise to structure and spatial complexity, which have implications in the behavior of field line random walk and charged particle diffusion. Notable among these are the appearance of "flux tubes" in turbulence and the temporary trapping of charged particles that might explain observed interplanetary dropouts of solar energetic particles. Recent numerical studies of MHD turbulence reveal that structure formation, and therefore spatial intermittency, can be related to local relaxation processes that act rapidly to reduce nonlinear stresses in turbulence. This gives rise to patches of correlations of several types -- force free magnetic field, Beltrami velocity fields, Alfvenic directional alignment and anti-correlations between magnetic and fluid accelerations. These ideas can be applied to a reexamination of MHD discontinuities in the solar wind, and to refinements in our perspective on solar energetic particles transport.
3:00 pm: Joint CfA/MIT Supernova Remnants and Neutron Stars Seminar. "Complementary X-ray and VHE Gamma-ray Study of Pulsar Wind Nebulae," Dr. Anne Lemiere, CfA. Pratt Conference Room.
Abstract: Studies of PWNe, particularly the spectacular images obtained these last years who allow us to resolve details of their morphology, provide a powerful testing ground for studying shocks and particles acceleration via interaction of relativistic flows with their surrounding. X-ray observations have revealed an amount of new information on the composition of the winds, the presence of jets and equatorial outflows and the structure around the termination shocks. At the same time, the last few years have seen the birth of a genuine astronomy at TeV energies which allowed to mark a breakthrough in the field of PWN study : many of these objects were observed and their morphological and spectral structure were resolved for the first time in the gamma-ray band, opening a new window on PWN physics. The coordinated X-ray and gamma-ray observations of many objects as well as detailed studies of particular cases appears to be the key to understand the mechanisms involved in PWNe. In this talk, I will present the results of our recent study of three particular cases (HESS J1640-465 / G338.3-0.0, MSH15-52 and 3C58) and discuss the implications of our results on the nature of underlying emission process.
WEDNESDAY, FEBRUARY 13
12:30 pm: High Energy Astrophysics Division Lunch Talk. "Evolutionary Pathways Leading to SN Ia Progenitors, and the Impact of White Dwarf Binary Populations on LISA," Dr. Ashley Ruiter, New Mexico State University. Pratt Conference Room.
Abstract: I will discuss the results of two different projects carried out using population synthesis methods: i) white dwarf binaries as sources of gravitational waves for the Laser Interferometer Space Antenna (LISA) and ii) delay times of Type Ia Supernovae and the nature of their progenitors. Discussion related to the first topic will focus on the characteristics of the Galactic double white dwarf populations (Milky Way disc, bulge and halo) and how they contribute to the LISA gravitational wave signal. For the second topic, I will show expected SN Ia delay times for our standard model calculations for three SN Ia formation channels: Single Degenerate Scenario, Double Degenerate Scenario and the AM CVn channel, and discuss these (preliminary) results in context of recent observationally-derived delay times of SN Ia.
4:00 pm: Initiative in Innovative Computing (IIC) Seminar. "From Biopolymer Translocation to Hemodynamics: New Challenges in Multiscale Computing," Simone Melchionna, Visiting Scholar, Multiscale Numerical Experimentation & Simulation Group (Applied Physics), SEAS CyberInfrastructure Labs Information Technology, Harvard School of Engineering & Applied Sciences, & NFM CNR, Physics Department, University of Rome. Preceded by refreshments at 3:45 pm. Room 330, 60 Oxford Street, Cambridge. Event parking is available at the 52 Oxford Street Garage [map]. Please inform the parking attendant you are attending the IIC seminar. (The IIC seminar series schedule is updated often with additional information and seminars.)
Abstract: Multiscale modelling is the capability of representing different levels of physical phenomena, occurring at diverse spatial and temporal scales, within a unified conceptual framework. A typical example is the behavior of long molecules or nanosuspensions under the action of complex hydrodynamic flows. Our computational work tackles different phenomena such as biopolymer translocation through nanopores and hemodynamics in arteries with a novel computational scheme. The solution of such large scale problems calls for the exploitation of powerful parallel architectures, such as the Blue Gene supercomputer, and sophisticated visualization tools to gain insight into the realm of multi-scale phenomena.
4:30 pm: Joint CfA/Harvard University Atomic Physics Colloquium. "A Quantum-Entangled View of Quantum Critical Phenomena," Prof. Lorenza Viola, Dartmouth College. Preceded by tea at 4:00 pm. Room 356, Jefferson Laboratory, Harvard University.
Abstract: Developing a qualitative and quantitative understanding of quantum critical phenomena is a key challenge for both fundamental condensed matter theories and device technology applications. In recent years, entanglement theory has provided a bridging testbed for revisiting zero-temperature quantum phase transitions from a quantum information physics perspective. What is the nature and role of entanglement across a quantum phase transition? Can appropriate entanglement measures detect quantum critical points and characterize their universality class? To what extent can non-equilibrium behavior be predicted from knowledge of the equilibrium phase diagram? These are some of the broad motivating questions I plan to survey and address by example. In the process, I will argue how seeking satisfactory answers may challenge the traditional definition of entanglement in terms of distinguishable quantum subsystems, and suggest an alternative approach based on so-called "generalized entanglement."
THURSDAY, FEBRUARY 14
11:00 am: Institute for Theory and Computation (ITC) Colloquium. "Gas Giants and Rocky Planets Around G and M Dwarfs," Dr. Doug Lin, University of California, Santa Cruz. Pratt Conference Room.
Abstract: Outstanding issues in the sequential accretion scenario for gas giant planet formation include, 1) the retention of dust grains in the presence of gas drag and that of cores despite type I migration, 2) time scale for gas giant formation, 3) halting migration at stellar proximity, and 4) the structural and dynamical diversities. In these context, we investigate the influence of the snow line and other transition regions in MRI induced turbulent protostellar disks and show that they naturally provide retention barriers for planetary building blocks. We also examine the role of protoplanetary disks in speeding up the gas giant formation process and the dynamical consequences of rapidly emerging gas giant planets. We present planetary population synthesis which reproduce the observed distribution of extra solar gas giants. Radial velocity and transit surveys will soon be able to detect Earth-mass rocky planets close to G and M main-sequence dwarf stars. There are many several avenues through which such planets may be formed. Although rocky planets may be formed in situ from the grains which migrated to the stellar proximity, their mass is likely to be severely limited by dynamical isolation. More massive rocky planets can form near the snow line barrier and migrate to their proximity of their stars with or without the presence of gas giant planets. Their statistical properties will provide a caliberation on the efficiency of migration and the frequency of rocky planets in the habital zone.
12:30 pm: Optical and Infrared Astronomy Division Lunch Talk. "Infrared Astronomy: What Next?" Dr. Dimitra Rigopoulou, Oxford. Pratt Conference Room.
Abstract: I will present the scientific case for the new JAXA/ESA mission SPICA. The mission was recently approved by ESA Cosmic Vision 2015-2020 with Europe contributing one of the three focal plane instruments the far-infrared camera/spectrometer SAFARI. I will review the scientifc case for SAFARI and discuss its specific advatnages for the exploration of the high-redshift Universe.
4:00 pm: Colloquium. "Active Galactic Nuclei: The Weather Report," Prof. Bozena Czerny, Copernicus Astronomical Center, Warsaw. (Anyone wishing to meet with the speaker should contact the host, Dr. Aneta Siemiginowska, ext. 5-7243. Preceded by tea at 3:30 pm. Phillips Auditorium.
Abstract: Accretion onto massive black holes in active galactic nuclei provides insights into a behavior of the material in the strong gravity field. However, active nuclei are enshrouded by the host galaxy material obscuring the direct view. In addition the same accretion process powers also an outflow, and inflow/outflow phenomena are strongly coupled. Both the outflowing material and the accreting one contribute to the observed variability, particularly in the X-ray band. These "weather-type" phenomena complicate analysis of the flow close to a black hole. They may as well provide a strong impact onto the host galaxy environment. I will summarize the current understanding of the galactic nuclear activity concentrating on radio-quiet sources, which generally allow for a better view of the most central regions, and stress the trends with the Eddington luminosity ratio that vary over several orders of magnitude between highly active quasars and weakly active low luminosity AGN.
FRIDAY, FEBRUARY 15
2:00 pm: Institute for Theory and Computation (ITC) Colloquium. Speaker: Prof. Tsvi Piran, Hebrew University. Topic: To be announced. Pratt Conference Room.
SAO HUMAN RESOURCES NOTES
Leave Donations Requested
Due to a medical emergency, Joyce Janjigian of the Solar, Stellar and Planetary Science Division has been approved as a leave donor recipient in the Leave Transfer Program. Any SAO Trust Fund employee who wishes to donate annual leave to Joyce should complete a Leave Donor Form and send it to MS 17.
Under the Leave Transfer Program, Trust Fund employees may only donate annual leave to other Trust Fund employees and Federal employees may donate annual leave only to other Federal employees. If you should have any questions or are not able to access the form, please contact Anne LeBlanc, ext. 5-7371.
Job Vacancies
An online listing of all current SAO job openings is available. For more information, please call Human Resources, ext. 5-7371, or view your nearest bulletin board.