Physics Colloquia Fall 2011

(Fridays 2:00 PM in GS 101)

Note: Colloquia meet in a new location this semester, 101 General Classroom South ( map).

Titles link to the abstracts.

Date Speaker Title
16 Sep Chris Beetle (FAU)
23 Sep Jim McGuire (FAU)
4:00 Wed
28 Sep
PS 111
Roberto Sussman (UNAM) Recent developments and new outlooks in the study of inhomogeneous cosmological models
30 Sep Ruslan Vaulin (MIT)
7 Oct Silvia Pella (FAU)
14 Oct Matt Wood (FIT)
4:00 Wed
19 Oct
PS 111
Grant Mathews (Notre Dame)
28 Oct Cancelled  
4 Nov Wolfgang Tichy (FAU)
18 Nov
BS 303
Armin Fuchs (FAU)
2 Dec Jonathan Tan (UF)

Colloquium Abstracts

The future of spacetime: The uncertain role of Einstein’s deepest insight in 21st century Physics
Chris Beetle (Florida Atlantic University), 16 September
This talk examines the fundamental tension between the relativity principle and quantum theory, which is responsible for the "problem of time" in theories of quantum gravity. This difficulty raises significant obstacles to developing a definitive theory of the quantum gravitational field at both the technical and conceptual levels. We will examine the origins of this tension in classical theory and discuss possible ways to resolve the tension at the quantum level.
The Axiom of Choice, Algebraic Geometry and Quantum Complexity
Jim McGuire(Florida Atlantic University), 23 September
A flagrant attempt to draw an audience (through a catchy title) to a talk that is really about Quantum Mechanics and the Symmetric Group.
Recent developments and new outlooks in the study of inhomogeneous
cosmological models
Roberto Sussman (Universidad Nacional Autónoma de México), 28 September
( Note: special time and place, Wednesday, 28 September, 4:00–5:00, 111 Physical Science)
Spherically symmetric inhomogeneous void models have been successful in explaining cosmic observations without assuming the existence of dark energy, but their overall description of cosmic dynamics is too idealized. In this talk I examine the Szekeres dust solutions, which are a class of cosmological models that do not admit Killing vectors, and thus, allow for a more realistic depiction of the inhomogeneities of observed cosmic structures. A new set of coordinate independent variables are introduced in which the models can be conceived as a superposition of a monopole plus a "dipole-like" exact perturbations on an abstract homogeneous background. Under this description, the dynamical equations of the models reduce to a system of constrained autonomous ordinary differential equations that can be analyzed, numerically and qualitatively, as a standard dynamical system. Besides its utility in the construction of more realistic void models to fit observations, our approach to these non-spherical models provides important clues on various relevant theoretical issues, such as
averaging of inhomogeneities and non-locality, as well as a qualitative and numerically tractable treatment of specetimes admitting more general forms of inhomogeneity.
Searching for gravitational waves from compact binary coalescence
Ruslan Vaulin (Massachusetts Institute of Technology), 30 September

General theory of relativity predicts that binary systems consisting of massive, compact objects (e.g. neutron stars and/or black holes) radiate their energy in the form of gravitational waves. In the last stage of this process, when the compact objects inspiral in close orbits and eventually coalesce, the gravitational-wave signal is the strongest and is detectable by the ground based detectors such as LIGO and Virgo. If detected, it will not only serve as a direct confirmation of the general theory of relativity, but also provide invaluable information on the gravity in the strong field regime and the physics of neutron stars and black holes. In anticipation of the start of the advanced LIGO and Virgo detectors around 2015, I will review the methods and strategies that are used to search for gravitation waves from coalescing binaries illustrating them with some of the results from the recent scientific runs of the initial LIGO and Virgo detectors. When discussing prospects of observing coalescing binaries with advanced detector network I will focus primarily on new and rapidly developing multi-messenger program in which central role is given to the low-latency searches with followup observations of interesting candidates by optical, X-ray and radio telescopes. While presenting new challenges for data analysis, this approach offers exciting possibility of observing binary coalescence in multi-wavelengths thus providing a complete picture of the process.

High Dose Radiation Brachytherapy Commissioning and Quality Assurance
Sylvia Pella (Florida Atlantic University), 7 October

Brachytherapy is the first conformal radiation therapy. A sealed source is placed in or in contact with the tumor providing dose to the tumor with small volumes of normal tissue irradiated. It became more sophisticated with the usage of remote afterloader. With this, our responsibility as physicists increased and became critical in ensuring an accurate and precise treatment planning and delivery. The ability to deliver a correct treatment is conditioned by the precision of the source placement at the dwell point/points predicted by the treatment planning system (TPS). The introducing of the CT based planning gave the possibility of reconstructing not only the correct shape of a treated volume but the correct reconstruction of the applicators, the catheters, and localizing the first dwell position (the stopping point) of the radioactive source that will deliver the treatment.

This colloquium will provide an introduction into the understanding of High Dose Radiation (HDR) Therapy and into organizing a safe HDR program in a cancer center.

V344 Lyr: A Touchstone Cataclysmic Variable in the Kepler Field
Matt Wood (Florida Institute of Technology), 14 October

Cataclysmic variable (CV) systems are mass transfer binary star systems with white dwarf primaries, low-mass main sequence secondaries, and an accretion disk that typically provides most of the system luminosity.

The previously little-studied cataclysmic variable system V344 Lyr has been observed by the Kepler instrument at a 1-min cadence since 2009 June 20, and as a result it is now the CV with the best time-series data set in history. The system is rich in its behavior and promises to be a touchstone for CV studies for the foreseeable future. The Kepler data reveal that two physical sources yield positive superhumps: viscous dissipation within the periodically flexing disk, and the signal generated as the accretion stream bright spot sweeps around the rim of the non-axisymmetric disk. The V344 Lyr data also reveal negative superhumps arising from accretion onto a tilted disk precessing in the retrograde direction. The changing negative superhump period results from a changing precession rate, which in turn results from a changing mass distribution within the disk.

At present, the source of accretion disk tilt in cataclysmic variables is unknown, however the Kepler data show that in one of the DN outbursts, negative superhumps are excited. Further study of this system may conclusively reveal the physical source of accretion disk tilt as well as severely constrain the microphysics and macroscopic effects of viscosity in differentially-rotating astrophysical plasmas.

Formation and Evolution of Galactic Streaming Flows in Local-Group
Like Systems
Grant Mathews (University of Notre Dame), 19 October

The Milky way did not form in isolation, but is the product of a complex evolution of generations of merges, collapse, star formation, supernova and collisional heating, radiative and collisional cooling, and ejected nucleosynthesis. Moreover, all of this occurs in the context of the cosmic expansion, the formation of cosmic filaments, dark-matter haloes, spiral density waves, and emerging dark energy. In this talk I will summarize recent calculations of the formation and evolution of Local-Group like systems derived from simulations of large scale structure. We begin with a variety of simulations on the scale of (400-800 Mpc)$^3$. We then scan for poor clusters which contain two large spirals presently separated by $\sim 800$ kpc. We compare simulated properties with various observed properties of the Local Group. Among the generic features of these systems is the tendency for galactic halos to form within the dark matter filaments that define a super-galactic plane. Gravitational interaction along this structure leads to a streaming flow toward the two dominant galaxies in the cluster. We analyze this alignment and streaming flow and compare with observed properties of Local-Group galaxies. Our comparison with Local Group properties suggests that some dwarf galaxies in the Local Group are part of a local streaming flow. These simulations also suggest that a significant fraction of the Galactic halo formed as at large distances and then arrived later along these streaming flows.

Binary neutron stars with spin
Wolfgang Tichy (Florida Atlantic University), 4 November
In general neutron stars in binaries are spinning. Due to the existence of millisecond pulsars we know that these spins can be substantial. We argue that spins with periods on the order a few dozen milliseconds could influence the late inspiral and merger dynamics. Thus numerical simulations of the last few orbits and the merger should start from initial conditions that allow for arbitrary spins. We discuss quasi-equilibrium approximations one can make in the construction of binary neutron star initial data with spins. The spin of each star is described by a rotational velocity that can be chosen freely so that one can create stars in arbitrary rotation states. We show a that our initial data can be evolved with our evolution code.
Pumpkin Drop and Turkey Dinner

Armin Fuchs (Florida Atlantic University), 18 November
( Note: special place, 303 Behavioral Science)

Inspired by seasonal events (Halloween and Thanksgiving), I apply scaling laws and dimensional analysis to everyday physics, such as the dropping of pumpkins and the cooking time for turkeys. The results show that, first, in principle, the pumpkin drop cannot show the intended phenomenon, i.e. all pumpkins fall equally. Second, as it turns out, from the view point of physics, cook books and their peers on the internet are close to useless.
Massive Star Formation Through The Universe — A Physics Playground
Jonathan Tan (University of Florida), 2 December
Massive stars have sculpted our universe since its earliest times — churning space with their winds, radiation and supernovae; forging the elements of life; and seeding the formation of black holes, perhaps including the supermassive variety of galactic centers. Despite this importance, there is little consensus on even basic questions of their birth: How do massive stars form? What sets their maximum mass? Do they always form as binaries and in the centers of star clusters? I describe some of our recent progress in trying to answer these questions, focusing on two extremes of massive protostars: the nearest and best-observed, including those of the Orion Nebula; and the farthest and earliest, so far purely theorized to form from the primordial gas. I highlight the wide variety of physical processes we must summon to build a complete theory of massive star formation.